Anatomy

Front 1

Sacroiliac Joint

Back 1

Sacroiliac Joint

The sacroiliac articulations are strong synovial joint between the articular surfaces of the sacrum and ilium.
These surfaces have irregular elevations and depressions, which result in a partial interlocking of the bones. The strong articular capsule is attached close to the articulating surfaces of the sacrum and ilium.
The sacrum is suspended between the iliac bones, and the bones are firmly held together by the interosseous and posterior sacroiliac ligaments. These are the strongest ligaments in the body.
Hyaline cartilage on the sacrum.
Fibrocartilage on the ilium.


The Interosseous Sacroiliac Ligaments

These massive, very strong ligaments unite the iliac and sacral tuberosities. They consist of short, strong bundles of fibres that blend with and are supported by the thick firm posterior sacroiliac ligaments.


The Posterior (Dorsal) Sacroiliac Ligaments

These ligaments are composed of:

Strong, short transverse fibres joining the ilium and the first and second tubercles of the lateral crest and the sacrum.
Long vertical fibres uniting the third and fourth transverse tubercles of the sacrum to the posterior iliac spines. These ligaments blend with the sacrotuberous ligaments.


The Anterior (Ventral) Sacroiliac Ligaments

This thin wide sheet of transverse fibres is located on the anterior and inferior aspects of the sacroiliac joint. It covers the abdominopelvic surface of this articulation. Replacement of most or all of these ligaments by bone often begins after 50 years of age.
The iliolumbar, sacrotuberous, and sacrospinous ligaments are accessory ligaments of the sacroiliac joints. These articulations are covered posteriorly by the massive erectory spine and gluteus maximus muscles. The skin dimples indicating the posterior superior iliac spines are located at the middle of the sacroiliac joints.


Functions and Movements of the Sacroiliac Joints

These joints are strong weight bearing synovial joints of an irregular plane type.
They differ from other synovial joints in that they possess very little mobility.
This provides for stability and is related to their responsibility for transmitting the weight of most of the body to the hip bones.
Because the articular surfaces of the sacrum and ilium are irregular, they fit together securely and are not easily dislocated. This arrangement lessens the strain on the supporting ligaments of the joints.
Movement of the sacroiliac joints is limited to a slight gliding and rotary movement, except when a considerable force is applied as occurs during a jump from a height. In this case the force is transmitted via the vertebral column to the superior end of the sacrum, which tends to rotate anteriorly. This rotation is counterbalanced by the interlocking articular surfaces and the strong supporting ligaments, especially the strong sacrotuberous and sacrospinous ligaments. This allows the force to be transmitted to each ilium and lower limb.

Front 2

Pubic Symphysis

Back 2

The pubic symphysis (symphysis pubis) is a median, secondary cartilaginous joint between the bodies of the two pubic bones.
Each articular surface is covered by a thin layer of hyaline cartilage, which is connected to the cartilage of the other side by a thick fibrocartilaginous interpubic disc. This disc is generally thicker in women than in men; it also contains a small cavity that is also larger in women and increases in size during pregnancy.
These sex differences in the interpubic disc permit more mobility of the bones and increase the diameter of the pelvic cavity for passage of the foetus during childbirth.
The articular surface of each pubic bone is irregularly ridged and grooved but the irregularities of the two sides fit tightly together to form a strong joint.


The ligaments of the pubic symphysis

The ligaments joining the pubic bones are thickened superiorly and inferiorly to form the superior pubic ligament and the arcuate pubic ligament, respectively.
The superior pubic ligament connects the superior pubic rami along their superior surfaces. It extends as far laterally as the pubic tubercles.
The arcuate pubic ligament is a thick arch of fibres that (1) connects the inferior borders of the joint, (2) rounds off the subpubic angle, and (3) forms the superior border of the pubic arch.
The decussating tendinous fibres of the rectus abdominis and external oblique muscles also strengthen the joint anteriorly.

Front 3

Hip Joint

Back 3

This is a multilaxial ball and socket type of synovial joint between the head of the femur and the acetabulum of the hip bone.


Articular Surfaces of the Hip Joint

The globular head of the femur articulates with the cup-like acetabulum of the hip bone.
The wider superior part of the articular surface is the weight bearing area. Thus it is the ilium that bears the weight.
The rim of the acetabulum is defective inferiorly at the acetabular notch, which is bridged by the transverse acetabular ligament. The head of the femur forms about two-thirds of a sphere and is covered with hyaline cartilage, except over the roughened fovea or pit, to which the ligaments of the head of the femur is attached.
More than half of the femoral surface is contained within the acetabulum.
The articular or lunate surface of the acetabulum is horseshoe-shaped.
The acetabulum has a centrally located nonarticular fossa, which is occupied by a fatpad that is covered with synovial membrane.
This nonarticular bone is paper thin and translucent.


The Acetabular Labrum

The depth of the acetabulum is increased by this fibrocartilaginous labrum (L. lip). It is attached to the bony rim of the acetabulum and to the transverse acetabular ligament.
The labrum deepens the socket for the femoral head and its free thin edge clasps the head beyond the widest diameter. This helps to hold it firmly in the acetabulum (i.e., preventing dislocation)


The Articular Capsule of the Hip Joint

The fibrous capsule is strong and dense. Proximally, it is attached to the edge of the acetabulum, just distal to the acetabular labrum, and to the transverse acetabular ligament.
Distally, the fibrous capsule is attached to the neck of the femur as follow: anteriorly to the intertrochanteric line and the root of the greater trochanter and posteriorly to the neck proximal to the greater trochanter and posterior to the neck proximal to the intertrochanteric crest.
The fibrous capsule forms a cylindrical sleeve that encloses the hip joint and most of the neck of the femur.
Most of its fibre take a spiral course from the hip bone to the lateral potion of the intertrochanteric line of the femur, but some deep fibres from an orbicular zone (zona orbicularis) and pass circularly around the neck of the femur. These fibres form a collar around the neck of the femur, which constricts the capsule and helps to hold the femoral head in the acetabulum.
Some deep longitudinal fibres of the fibrous capsule form retinacula, which are reflected superiorly along the neck of the femur as longitudinal bands that blend with the periosteum.
The retinacula contain blood vessels that supply the head and neck of the femur.
Four main groups of longitudinal capsular fibres or intrinsic ligaments are given names according to the region of the hip bone which they attach to the femur.
These intrinsic ligaments are thickened parts of the fibrous capsule that strengthen the hip joint.


Ligaments of the Hip Joint

The Iliofemoral Ligament is a very strong band that covers the anterior aspect of the hip joint. It is Y-shaped and attached proximally to the anterior inferior iliac spine and the acetabular rim.
The iliofemoral ligament is attached distally to the intertrochanteric line of the femur.
The capsule of the hip joint is taut and the iliofemoral ligament is tense in full extension of the joint. This strong ligament has an important role in preventing overextension of the hip joint during standing (i.e., it helps to maintain the erect posture.
It screws the head of the femur into the acetabulum and thereby maintains the integrity of the joint.
The Pubofemoral Ligament arises from the pubic part of the acetabular rim and the iliopubic eminence and blends with the medial part of the iliofemoral ligament.
It strengthens the inferior and anterior parts of the fibrous capsule of the hip joint.
The pubofemoral ligament tightens during extension of the hip joint and becomes tense during abduction. Although it is relatively weak, this ligament tends to prevent overabduction of the thigh at the hip joint.
The Ishiofemoral Ligament reinforces the fibrous capsule to the hip joint posteriorly. It arises from the ischial portion of the acetabular rim and spiral superolaterally to the neck of the femur, medial to the base of the greater trochanter. Its anatomical construction tends to screw the femoral head medially into the acetabulum during extension of the thigh at the hip joint, thereby preventing hyperextension of it.
The Ligament of the Head of the Femur is an intracapsular ligament about 3.5 centimetres long, is weak and appears to be of little importance in strengthening the hip joint.
Its wide end is attached to the margins of the acetabular notch and to the transverse acetabular ligament, and its narrow end is attached to the fovea or pit in the femur.
Usually it contains a small artery to the head of the femur, which is a branch of the obturator artery. The ligament of the head of the femur (LHF) is stretched when the flexed thigh is adducted or laterally rotated. It is located inside the fibrous capsule of the hip joint and is surrounded by a sleeve of synovial membrane.


Stability of the Hip Joint

The hip joint is very strong and stable articulation. It is surrounded by powerful muscles and a dense fibrous capsule, which is strengthened by strong intrinsic ligaments, particularly the iliofemoral ligament, unites the articulating bones.
Its stability is largely the result of the adaptation of the articulating surfaces of the acetabulum and the femoral head to each other.
Anterior aspect-fewer muscles, strong ligaments.
Posterior aspect-stronger muscles, fewer ligaments.
Position of weakness is when the hip joint is flexed, adducted and medially rotated.

Front 4

Anterior Thigh Muscles

Back 4

This group of muscles consists of the iliopsoas, tensor fasciae latae, sartorius, and quadriceps femoris muscles.


The Iliopsoas Muscles

This powerful muscle is composed of the psoas major and iliacus muscles.

The Psoas Major Muscles (pp. 229, 385-7)

Long, thick, powerful muscle passes from the abdomen to the thigh deep to the inguinal ligament.
The lumbar plexus is imbedded in this muscle.
Proximal attachments are: sides of T12 to L5 vertebrae and intervertebral discs between them.
Distal attachment is: lesser trochanter of femur
Innervation: ventral rami of lumbar nerves (L1, L2, and L3)


The Iliacus Muscle (pp. 386-7)

Large triangular or fan-shaped muscle lies along the lateral side of the psoas major in the pelvis.
Proximal attachments are: iliac crest, iliac fossa, ala of sacrum, and anterior sacroiliac ligaments.
Distal attachments are: tendon of psoas major and body of femur, inferior to lesser trochanter.
Innervation: femoral nerve (L2 and L3)


Action of Iliopsoas Muscle

This composite muscle is the strongest flexor of the thigh at the hip joint.
The iliopsoas muscles are also important antigravity postural muscles, which help to maintain erect posture at the hip joints.
Acting inferiorly, the iliopsoas muscles flex the trunk, as in raising the trunk from the supine position to the sitting position.


Anterior Compartment

Comprises of the quadriceps femoris, sartorius and tensor fasciae latae mm.


The Tensor Fasciae Latae Muscle (p. 386-7)

The Deep Fascia of the Thigh-Fascia lata (p. 385)

Strong, dense, broad (lata: L. broad) layer that invests the muscles of the thigh like an elastic stocking.
It provides a dense tubular sheath for the thigh muscles, which prevents them from bulging excessively when they contract.
Improves the effectiveness of these muscles.
Proximal attachments are: the inguinal ligament, the external lip of the iliac crest, the posterior surface of the sacrum and coccyx, the sacrotuberous ligament, the ischial tuberosity, the margin of the pubic arch, the body of the pubis, and the pubic tubercle.
It is extremely laterally where it runs from the iliac crest to the tibia. This part is known as the iliotibial tract.
The sides don't form a complete stocking. The fascia dives under and connects on the pecten pubis. There is a "loop".
The cribiform fascia is a loose covering of fascia over this loop.
It receives tendinous reinforcements from the tensor fasciae latae and gluteus maximus mm.
Distal end of the iliotibial tract is attached to the lateral condyle of the tibia.


The Muscle

Fusiform muscle, lies on the lateral side of the thigh, enclosed between two layers of the fascia lata, which form its sheath.
Proximal attachments are: anterior superior iliac spine and anterior part of external lip of iliac crest.
Distal attachments are: iliotibial tract that attaches to lateral condyle of tibia.
Innervation: superior gluteal (L4 and L5)
It tightens the fascia lata, thereby enabling the thigh muscles to act with increased power.
It also tightens the iliotibial tract enabling the gluteus maximus muscle to keep the knee joint in the extended position.
In addition, when in the standing position, it steadies the trunk on the thigh and counteracts the posterior pull of the gluteus maximus on the iliotibial tract.


The Sartorius Muscle (p. 386-7)

This narrow, elongated, strap-like muscle is the longest one in the body and is the most superficial muscle in the anterior part of the thigh.
It acts across two joints.
It was given its name because it is used to cross the legs in the tailor's squatting position (L. sartor, a tailor).
Throughout much of its course, this muscle covers the femoral artery as it runs in the adductor canal (subartorial).
Proximal attachments are: ASIS and superior part of notch inferior to it.
Distal attachments are: superior part of medial surface of tibia.
Innervation: femoral nerve (L2 and L3)
During squatting, it flexes, abducts, and laterally rotates the thigh at the hip joint, and it flexes the leg at the knee joint.
Acting inferiorly, it also flexes the trunk on the thigh and rotates the trunk to the opposite side.


The Quadriceps Femoris Muscle (pp. 386-7)

The great extensor muscle of the leg, the biggest muscle in the body.
It covers almost all of the anterior surface and sides of the femur.
It is divided into 4 parts: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. (L. vastus, large) and (L. rectus, straight)
The names of the parts of the quadriceps m. indicate their form or location.
The rectus femoris has deep fibres that run straight down the thigh.
Proximal attachments are: AIIS and groove superior to acetabulum.
The vastus lateralis lies on the lateral side of the thigh.
Proximal attachments are: greater trochanter and lateral lip of linea aspera of femur.
The vastus medialis covers the medial aspect of the thigh.
Proximal attachments are: intertrochanteric line and medial lip of linea aspera of femur.
The vastus intermedius is located between the above two mm.
Proximal attachments are: anterior and lateral surfaces of the body of the femur.
The tendons of all of this large muscle unite to form the quadriceps tendon. This broad tendon attaches to and surrounds the patella and then continues as the patellar ligament (ligamentum patellae), which is attached to the tuberosity of the tibia.
Expansions of the aponeuroses of the vasti muscles, called the medial and lateral retinaculum of the patella, insert into the condyles of the tibia.
All parts of the quadriceps, acting through the patella ligament, extend the leg at the knee joint, and through the actions of the rectus femoris, they flex the hip joint. All four parts of this muscle is used during climbing, running, jumping, and rising from a chair.

Front 5

Gluteal Muscles

Back 5

The gluteal muscles consist of three glutei mm., gluteus maximus, g. medius, and g. minimus.


The Gluteus Maximus Muscle (pp. 407,411-2,417)

This is the largest, heaviest, and most coarsely fibred muscle in the gluteal region and is one of the largest muscles in the body.
It forms a thick quadrilateral pad over the ischial tuberosity when the thigh is extended.
When the thigh is flexed, the distal border of this muscle moves superiorly, leaving the ischial tuberosity subcutaneous.
Proximal attachments are: external surface of ala of ilium, including iliac crest, dorsal surface of sacrum and coccyx, and sacrotuberous ligament.
Distal attachments are: most fibres end in iliotibial tract; some fibres insert on gluteal tuberosity of femur.
Innervation: inferior gluteal nerve.
A thick flat sheet of muscle, the gluteus maximus slopes inferolaterally from the pelvis across the buttock at a 45 degree angle. Its inferior edge lies just superior to the gluteal fold produced by bulging fat.
The gluteus maximus m., extends the thigh and steadies it. It is the chief extensor of the thigh. When acting with its distal attachment fixed, it is a strong extensor of the pelvis (e.g., when rising from a seated or stooped position).
It also assists with lateral rotation of the thigh.
It is used very little during ordinary walking and is relaxed when one stands still. It acts when force is required, e.g., in running, climbing and similar activities.
As the thigh is being flexed, e.g. during sitting, the gluteus maximus steadies the movement by relaxing gradually.
When acting from its distal attachment, it tilts the superior part of the pelvis posteriorly (when one stands to attention).


Gluteus Medius Muscle (pp. 412, 417)

Most of this thick, fan-shaped or triangular muscle lies deep to the gluteus maximus on the external surface of the ilium.
Proximal attachments are: external surface of ilium between anterior and posterior gluteal lines.
Distal attachments are: lateral surface of greater trochanter of femur.
Innervation: superior gluteal nerve (L5 and S1)
This muscle is an abductor of the hip joint and plays an essential role during locomotion; it is largely responsible for the tilt of the pelvis. When the left muscle pulls the left side of the pelvis down, the right side is prevented from sagging as the right limb is raised during walking. Conversely, the right gluteus muscle permits the left foot to clear the ground during walking.
It also helps to rotate the thigh medially.
Summary: abduct and medially rotate thigh; steady pelvis.


The Gluteus Minimus Muscle (pp. 412, 417)

The fan-shaped or triangular muscle, the smallest of the gluteal muscles, lies deep to the gluteus medius.
Proximal attachments are: external surface of ilium between anterior and inferior gluteal lines.
Distal attachments are: anterior surface of greater trochanter of femur.
Innervation: superior gluteal nerve (L5 and S1)
During locomotion its actions are similar to those of the gluteus medius.
Its anterior fibres help to rotate the thigh medially, more strongly that do those of the gluteus medius.

Front 6

Lateral Rotator Muscles of Thigh

Back 6

The Piriformis Muscle (pp. 412, 417)

This muscle is located partly on the posterior wall of the pelvis minor and partly posterior to the hip joint.
It leaves the pelvis though the greater sciatic foramen to reach its distal attachment to the greater trochanter of the femur.
Because of its position, this narrow, pear-shaped (L. piriform) muscle is landmark of the gluteal region. It is the key to understanding relationships in this area because it determines the names of the blood vessels and nerves; e.g., the superior gluteal vessels and nerve emerge superior to it.
The surface marking of the superior border of the piriformis muscle is indicated by a line joining the skin dimple formed by the posterior superior iliac spine, to the superior border of the greater trochanter of the femur.
Proximal attachments are: anterior surface of sacrum and sacrotuberous ligament.
Distal attachments are: superior border of greater trochanter of femur.
Innervation: branches from ventral rami of S1 and S2
It laterally rotates extended thigh and abducts the flexed thigh; steadies femoral head in acetabulum.


The Obturator Internus Muscle (pp. 412-3, 417)

This thick fan-shaped muscle, like the piriformis, is located partly in the pelvis where it covers most of the lateral wall of the pelvis minor.
It leaves the pelvis through the lesser sciatic foramen to reach its attachment to the greater trochanter of the femur.
Proximal attachments are: pelvic surface of obturator membrane and surrounding bones.
Distal attachments are: medial surface of greater trochanter of femur.
Innervation: nerve to obturator internus (L5 and S1). Note: same as superior gemellus.


The Gamelli Muscles (Superior and Inferior) (pp. 412-413, 417)

The two gemelli muscles are narrow, triangular extrapelvic parts of the obturator internus.
The superior and inferior gemelli arise from the ischial spine and ischial tuberosity, respectively.
The obturator internus and gemelli muscles laterally rotate the extended thigh, abduct it when it is flexed and also help to hold the head of the femur in the acetabulum.
Note: the innervation of inferior gemellus is the nerve to quadratus femoris (L5 and S1)


The Quadratus Femoris Muscle (pp. 413, 417)

This is a short, flat, rectangular muscle.
Proximal attachments are: lateral border of ischial tuberosity.
Distal attachments are: quadrate tubercle on intertrochanteric crest of femur and inferior to it

Front 7

Medial Thigh Muscles

Back 7

This group of muscles include the pectineus, gracilis and adductor magnus, brevis, and longus muscles.
The obturator nerve (L2, L3, and L4) supplies all adductors of the thigh, except the pectineus.
The femoral nerve (L2 and L3) supplies the pectineus. The "hamstring" part of the adductor magnus is supplied by the sciatic nerve (L4).


The Pectineus Muscle (pp. 393, 399)

This is a short, flat quadrangular muscle.
It forms part of the floor of the femoral triangle.
Proximal attachments are: pecten pubis (pectineal line of pubis).
Distal attachments are: pectineal line of femur.
Innervation: femoral nerve (L2 and L3); may receive a branch from obturator nerve.
It adducts and flexes the thigh.


The Adductor Longus Muscle (pp. 393, 399)

This long adductor is a triangular muscle and is the most anterior muscle in the adductor group.
Proximal attachments are: body of pubis, inferior to pubic crest.
Distal attachments are: middle third of linea aspera of femur.
Innervation: obturator nerve, anterior branch (L2, L3, L4)
It adducts the thigh.


Adductor Brevis Muscle (pp. 393, 399)

This short adductor lies deep to the pectineus and adductor longus mm. and anterior to the adductor magnus.
Proximal attachments are: body and inferior ramus of pubis.
Distal attachments are: pectineal line and proximal part of linea aspera of femur.
Innervation: Obturator (L2, L3, and L4).
It adducts the thigh and to some extent flexes it.


The Adductor Magnus Muscle (pp. 393, 399)

This large adductor is the largest in the muscle adductor group.
It is a composite, triangular muscle and comprises adductor and hamstring parts.
The two portions differ in their attachments, nerve supply, and main actions.
There is a hiatus in the aponeurotic attachment of the adductor magnus to the supracondylar line, called the adductor hiatus. It is located at the junction of the adductor canal and the popliteal fossa, a bout a handbreadth superior to the adductor tubercle of the femur. This opening enables the femoral vessels to pass into the popliteal fossa.
Proximal attachments are: inferior ramus of pubis, ramus of ischium (adductor part), and ischial tuberosity (hamstring part).
Distal attachments are: gluteal tuberosity, linea aspera, medial supracondylar line (adductor part), and adductor tubercle of femur (hamstring part).
Innervation: adductor part, obturator nerve (L2, L3, and L4). Hamstring part, tibial portion of sciatic nerve (L4).
It adducts the thigh; its adductor part also flexes thigh, and its hamstring part extends it.


The Gracilis Muscle (pp. 393, 399)

It is a long, strap-like fusiform muscle that lies along the medial side of the thigh and knee.
The gracilis (L. slender) is the most superficial of the adductor group of muscles and is the weakest member.
It is the only one that crosses the knee joint.
Proximal attachments are: body and inferior ramus of pubis.
Distal attachments are: superior part of medial surface of tibia.
Innervation: obturator nerve (L2, L3).
It laterally rotates the thigh and steadies the head of the femur in the acetabulum.


The Obturator Externus Muscle (pp. 393, 399)

This is a flat, relatively small, fan-shaped muscle is deeply placed in the superomedial part of the thigh.
Its tendon crosses the posterior aspect of the neck of the femur.
Proximal attachments are: margins of obturator foramen and obturator membrane.
Distal attachments are: trochanteric fossa of femur.
Innervation: Obturator nerve (L3 and L4)
It laterally rotates thigh and steadies the head of femur in acetabulum.

Front 8

Posterior Thigh Muscles (Hamstrings)

Back 8

Three large (semitendinosus, semimembranosus, and biceps femoris) in the posterior aspect of the thigh are commonly called the hamstring muscles.
They can be made to stand out by flexing the leg against resistance.
The hamstrings have a common proximal attachment to the ischial tuberosity deep to the gluteus maximus, but one of them, the biceps femoris, has an additional attachment to the body of the femur. They also have a common nerve supply from the sciatic nerve.
The hamstring muscles span the hip and knee joints; hence, they are extensors of the thigh and flexors of the leg. Both actions cannot be performed fully at the same time.
The hamstrings descend in the posterior aspect of the thigh and their tendons are visible posterior to the knee.


The Semitendinosus Muscle (pp. 422-3)

As its name indicates, this muscle is half-tendinous. It is fusiform with a long, rounded, cord-like tendon, which begins about two-thirds of the way down the thigh.
Proximal attachments are: ischial tuberosity (common attachment with the semimembranosus and long head of the biceps femoris).
Distal attachments are: medial surface of superior part of tibia.
Innervation: tibial division of sciatic nerve (L5, S1, and S2).
It extends the thigh, flexes the leg and medially rotates when the thigh and leg are flexed. It can extend the trunk.


The Semimembranosus Muscle (pp. 422-3)

This broad muscle is half-membranous.
It is located deep to the semitendinosus muscle.
Proximal attachments are: ischial tuberosity.
Distal attachments are: posterior part of medial condyle of tibia.
Innervation: tibial division of sciatic nerve (L5, S1, and S2)-same as the above.
Its actions are the same as the semitendinosus muscle.


The Biceps Femoris Muscle (pp. 422-3)

A fusiform muscle with two heads, a long and a short.
The rounded tendon of the biceps femoris can easily be seen and felt as it passes the knee to insert into the head of the fibula, especially when the knee is flexed against resistance.
Like the other hamstrings, the long head of the biceps femoris extends the thigh at the hip joint.
Both heads flex the leg at the knee joint and laterally rotate the leg when it is flexed.
Proximal attachments are: long head; ischial tuberosity, short head; lateral lip of linea aspera and lateral supracondylar line.
Distal attachments are: lateral side of head of fibula; tendon is split at this site by fibular collateral ligament of knee joint.
Innervation: long head; tibial division of sciatic nerve (L5, S1, and S2), short head; common fibular (peroneal) division of sciatic nerve (L5, S1, S2).

Front 9

Anterior Compartment of Leg

Back 9

This extensor compartment, located anterior to the interosseous membrane, is located between the lateral surface of the tibia and the anterior crural intermuscular septum.
The four muscles of the anterior compartment are extensor (dorsiflexor) muscles: tibialis anterior, extensor hallucis longus, extensor digitorum longus, and the fibularis (peroneus) tertius muscles.
These muscles are mainly concerned with dorsiflexion of the ankle joint and extension of the toes.
They are supplied by the deep fibular (peroneal) nerve, which is derived from the sciatic via the common fibular (peroneal), and by the anterior tibial artery. The muscles of this group are true extensors of the foot, although their action is usually referred to as dorsiflexion.


The Tibialis Anterior Muscle (p. 444-5)

This long, thick muscle lies against the lateral surface of the tibia, where it is easy to palpate.
Proximal attachments are: lateral condyle and superior half of lateral surface of tibia.
Distal attachments are: medial and inferior surfaces of medial cuneiform bond and base of first metatarsal bone.
Innervation: deep fibular (peroneal) nerve (L4 and L5)
It dorsiflexes and inverts the foot.


Paralysis of the tibialis anterior muscle

It is paralysed when there is injury to the common fibular (peroneal) nerve or to its branch, the deep fibular (peroneal) nerve, resulting in the condition known as foot-drop.


Shin Splits

This is the common name for the painful condition of the anterior compartment of the leg that follows vigorous and/or lengthy exercise. Often people who lead sedentary lives develop pains in the anterior part of their legs when they take long walks.
Their anterior tibial muscles swell from sudden overuse and the swollen muscles in the anterior compartment reduce the blood flow to the muscles. Cramps may develop if use of the muscles is continued.


The Extensor Hallucis Longus Muscle (p. 444-5)

This thin muscle lies between and partly deep to the tibialis anterior and extensor digitorum longus muscles.
Proximal attachments are: middle part of anterior surface of fibula and interosseous membrane.
Distal attachments are: dorsal aspect of base of distal phalanx of the great toe (hallux).
Innervation: deep fibular (peroneal) nerve (L5 and S1)
It extends the great toe and dorsiflexes the foot.


The Extensor Digitorum Longus Muscle (p. 445-6)

This pennate (feather-like) muscle lies laterally to the tibialis anterior and can be easily palpated.
Its tendons may be seen and felt when the toes are dorsiflexed.
A common synovial sheath surrounds its four tendons, which diverge on the dorsum of the foot as they pass to their distal attachments.
Each tendon forms a membranous extensor expansion over the dorsum of the proximal phalanx, which divides into two lateral slips and one central slip.
The central slip inserts into the base of the middle phalanx and the lateral slips converge to insert into the base of the distal phalanx.
Proximal attachments are: lateral condyle of tibia, superior three-fourths of anterior surface of fibula, and interosseous membrane.
Distal attachments are: middle and distal phalanges of lateral four digits.
Innervation: deep fibular (peroneal) nerve (L5 and S1)
It extends the lateral four digits and dorsiflexes foot.


The Fibularis (Peroneus) Tertius Muscle (p. 445-6)

This is a small variable muscle and a partially separated part of the extensor digitorum longus muscle.
The two muscles are fused at their proximal attachments, but distally the tendon of the fibularis tertius does not attach to a digit.
Proximal attachments are: inferior third of anterior surface of fibula and interosseous membrane.
Distal attachments are: dorsum of base of fifth metatarsal bone.
Innervation: deep fibular (peroneal) nerve (L5 and S1)
It dorsiflexes the foot and aids in eversion.

Front 10

Lateral Compartment of Leg

Back 10

This compartment is bounded by the lateral surface of the fibula, the anterior and posterior crural fascia.
The lateral (fibular or peroneal) compartment contains the fibularis (peroneus) longus and brevis muscles, which plantarflex and everts the foot.
The superficial fibular (peroneal) nerve, a branch of the common fibular (peroneal) nerve, supplies them.


The Fibularis (Peroneus) Longus Muscle (p. 448)

This is the longer and more superficial of the two fibularis (peroneal) mm. and it arises much more superiorly on the body of the fibula.
The fibularis longus is a narrow muscle that extends from the head of the fibula to the sole of the foot.
Its tendon can be palpated and observed proximal and posterior to the lateral malleolus.
When standing on one foot, the fibularis longus also helps to stead the leg on the foot.
The fibularis longus is enclosed in a common synovial sheath with the fibularis (peroneus) brevis muscle.
It passes inferior to the fibular (peroneal) trochlea on the calcaneus to enter a groove on the anteroinferior aspect of the cuboid bone.
It then crosses the sole of the foot, running obliquely and distally to reach its distal attachment to the first metatarsal and medial cuneiform bones.
Proximal attachments are: head and superior two-thirds of lateral surface of fibula.
Distal attachments are: base of first metatarsal bone and medial cuneiform bone.
Innervation: superficial fibular (peroneal) nerve (L5, S1, and S2).
It everts foot and weakly plantarflexes it.


The Fibularis (Peroneus) Brevis Muscle (p. 448)

This is a fusiform muscle and it lies deep to the fibularis longus.
As its name indicates, it is shorter than its partner in the lateral compartment of the leg is.
Its tendon grooves the posterior aspect of the lateral malleolus, where it lies in a common tendon sheath with the fibularis (peroneus) longus.
The tendon of the fibularis brevis can be easily traced to its distal attachment to the base of the fifth metatarsal bone.
Proximal attachments are: interior two-thirds of lateral surface of fibula.
Distal attachments are: dorsal surface of tuberosity on lateral side of base of fifth metatarsal bone.
Innervation: superficial fibular (peroneal) nerve (L5, S1, S2)

Front 11

Posterior Compartment of Leg

Back 11

From medial to lateral, this compartment lies posterior to the tibia, interosseous membrane, fibula, and the posterior crural intermuscular septum.
The calf muscles in this compartment are divided into superficial and deep groups by the transverse crural intermuscular septum formed by the deep transverse fascia of the leg.
The superficial group of muscles forms a powerful mass in the calf of the leg, which plantarflexes the foot.
The large size of these muscles is a human characteristic, which is directly related to our upright stance.
They are strong and heavy because they support and move the weight of the body.
The tibial nerve and posterior tibial vessels supply both divisions of the posterior compartment.


The Superficial Group

The gastrocnemius, soleus, and plantaris comprise the superficial group. The gastrocnemius and soleus form a tripartite muscle that is referred to as the triceps surae, which forms the prominence of the calf.
These muscles act together in plantarflexing the foot at the ankle joint. They raise the heel against the weight of the body.
It is the gastrocnemius that produces the rapid movements occurring during running and jumping. "One strolls along with the soleus, but one wins the long jump with the gastrocnemius."


The Gastrocnemius Muscle (pp. 449, 451)

This is the most superficial of the muscles in the posterior compartment; it forms most of the prominence of the calf.
It is a fusiform, two-headed, two-joint muscle.
Its medial head is slightly larger and extends a little more distally than does its lateral head.
The heads come together at the inferior margin of the popliteal fossa where they form the inferolateral and inferomedial boundaries of this fossa.
As its fibres are mainly vertical, contraction of this muscle produces rapid movements during running and jumping.
These muscles help to steady the legs; consequently they are active during standing, even when at ease.
When standing on toes or when high heels are worn, these muscles are especially active.
Although the gastrocnemius acts on both the knee and ankle joints, it is unable to exert its full power on both joints at the same time.
The lateral head of the gastrocnemius often contains a sesamoid bone called a fabella (L. bean), which is close to its proximal attachment.
The distal attachment of the gastrocnemius to the calcaneus via the tendo calcaneus or calcaneal tendon (Achilles tendon) is shared with the soleus muscle. The inferior expanded end of the tendo calcaneus attaches to the middle of the posterior surface of the calcaneus.
A tendo calcaneus bursa separates the tendo calcaneus from the superior part of this bony surface.
Proximal attachments are: lateral head: lateral aspect of lateral condyle of femur; medial head: popliteal surface of femur, superior to medial condyle.
Distal attachments are: posterior surface of calcaneus via tendo calcaneus.
Innervation: tibial nerve (S1 and S2)
Its main actions are plantarflexion of the foot, raising of heel during walking, and flexion of the knee joint.


The Soleus Muscle (pp. 449, 451)

This broad, flat, fleshy, multipennate muscle was named because of its resemblance to sole, a flat fish.
It lies deep to the gastrocnemius and can be palpated on each side of it, inferior to the midcalf, when a person is standing on tiptoes.
The soleus has a horseshoe-shaped proximal attachment to the tibial and fibula.
It acts with the gastrocnemius in plantarflexing the ankle, but it does not act on the knee joint. It is also concerned with the maintenance of posture by steadying the leg on the foot, e.g., it prevents the body from falling anteriorly when standing.
Because it is broad and multipennate, it is a very powerful muscle, but its contractions are slower than those of the gastrocnemius.
Proximal attachments are: posterior aspect of head of fibular, superior fourth of posterior surface of fibula, soleal line, and medial border of tibia.
Distal attachments are: posterior surface of calcaneus via tendo calcaneus.
Innervation: tibial nerve (S1 and S2)
It plantarflexes the foot and steadies the leg on the foot.


The Plantaris Muscle (pp. 449, 451)

This small muscle is variable in size and extent. It may be absent; sometimes it is double.
It has a small, fusiform fleshy belly and a long slender tendon, which runs obliquely between the gastrocnemius and soleus muscles.
This feeble muscle, the rudiment of a large muscle, is of no practical importance, but is clinically significant.
Proximal attachments are: inferior end of lateral supracondylar line of femur and oblique popliteal ligament.
It weakly assists gastrocnemius in plantarflexing the foot and the knee joint.
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The Deep Group of Muscles in the Posterior Compartment of the Leg

Four muscles comprise in this group. These muscles are the popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior.
The popliteus acts on the knee joint, whereas the other muscles act on the ankle and foot joint.


The Popliteus Muscle (pp. 452, 455)

This is a flat triangular muscle that forms the floor of the inferior part of the popliteal fossa.
The proximal attachment of the popliteus is inside the fibrous capsule of the knee joint, deep to the fibular collateral ligament; thus its deep surface is covered by synovial membrane.
Proximal attachments are: lateral surface of lateral condyle of femur and lateral meniscus.
Distal attachments are: posterior surface of tibia, superior to soleal line
Innervation: tibial nerve (L4, L5, and S1)
The popliteus weakly flexes the knee, but its important action is in unlocking the knee.
It unlocks the extended leg by rotating the femur laterally on the fixed tibia (e.g., when the foot is set on the ground).
As the lateral condyle of the femur moves posteriorly, the lateral meniscus of the knee joint is also drawn posteriorly so it will not be injured.
When the femur is fixed, the popliteus muscle unlocks the locked knee by rotating the tibia medially on the femur.


Flexor Retinaculum of the Ankle

The tendons of the three deep muscles (flexor hallucis longus, flexor digitorum longus, and tibialis posterior) pass deep to the flexor retinaculum of the ankle.
The flexor retinaculum is a thickening of the deep fascia of the leg, which passes from the medial side of the calcaneus to the medial malleolus.


The Flexor Hallucis Longus Muscle (pp. 452-457)

This is the long, powerful flexor of the great toe is the largest of the four deep muscles.
It lies laterally and is closely attached to the fibula.
Its tendon passes posterior to the distal end of the tibial and deep to the flexor retinaculum.
The tendon occupies a shallow groove on the posterior surface of the sustentaculum tali.
This tendon then crosses deep to the tendon of the flexor digitorum longus in the sole of the foot, giving a tendinous slip to its tendon.
As it passes the great toe, the tendon runs between two sesamoid bones in the tendons of the flexor hallucis brevis.
These bones protect the tendon from the pressure of the head of the first metatarsal bone.
The flexor hallucis longus is the powerful "push-off" muscle during walking, running, and jumping.
It provides much of the spring to the step.
The flexor hallucis longus is also important in holding the leg in the normal position on the foot.
Proximal attachments are: inferior two-thirds of posterior surface of fibula and inferior part of interosseous membrane.
Distal attachments are: base of distal phalanx of great toe (hallux).
Innervation: tibial nerve (S2 and S3)
It flexes the great toe at all joints and plantarflexes foot; and supports the longitudinal arch of foot.


The Flexor Digitorum Longus Muscle (pp. 455, 457)

This is the long flexor of the lateral four toes and it lies medially and closely attached to the tibia.
It is smaller than the flexor hallucis longus, even though it moves four digits.
Its tendon runs inferiorly, passing posterior to the tibialis posterior tendon and the medial malleolus.
It then passes diagonally in the sole of the foot, superficial to the tendon of the flexor hallucis longus.
As the tendon reaches the middle of the foot, it divides into four tendons, which pass to the distal phalanges of the four lateral digits.
Proximal attachments are: medial part of posterior surface of tibia, inferior to soleal line, and by a broad aponeurosis to the fibula.
Distal attachments are: bases of distal phalanges of lateral four digits.
Innervation: tibial nerve (S2 and S3)
It flexes the lateral four digits and plantarflexes foot and also supports the longitudinal arch of the foot.


The Tibialis Posterior Muscle (pp. 455, 457)

This is a large, fusiform muscle and is the deepest one in the posterior crural compartment.
It lies between the flexor digitorum longus and the flexor hallucis longus in the same plane as the tibia and fibula.
Its tendon can be seen and felt posterior to the medial malleolus, especially when the foot is inverted against resistance.
Proximal attachments are: interosseous membrane, posterior surface of tibia inferior to the soleal line, and posterior surface of fibula.
Distal attachments are: tuberosity of navicular, cuneiform, and cuboid bones, and bases of second, third, and fourth metatarsal bones.
Innervation: tibial nerve (L4 and L5)
It plantarflexes and inverts the foot.

Front 12

Ankle Joint

Back 12

This is a hinge type of synovial joint.
It is located between the inferior ends of the tibia and fibula and the superior part of the talus.
The talocrural joint can be felt between the tendons on the anterior surface of the ankle as a slight depression, about 1 cm proximal to the tip of the medial malleolus.


Articular Surfaces of the Talocrural Joint (p. 488)

The inferior ends of the tibia and fibula form a deep socket or box-like mortise into which the pulley-shaped trochlea of the talus fits.
The two malleoli and the inferior end of the tibia form the three-sided mortise.
The fibula has an articular facet on its lateral malleolus, which faces medially and articulates with the facet on the lateral surface of the talus.
The tibia articulates with the talus in two places: (1) its inferior surface forms the roof of the mortise, which is wider anteriorly than posteriorly; and (2) the lateral surface of its medial malleolus articulates with the talus.
The talus has three articular facets, which articulate with the inferior surface of the tibia and malleoli.
The trochlea of the talus is wider anteriorly than posteriorly and slightly concave side to side.


Movements of the Talocrural Joint (p. 488)

The talocrural joint is uniaxial; its main movements are dorsiflexion and plantarflexion.
When the foot is plantarflexed, some rotation, abduction, and adduction of the ankle joint is possible.
This occurs as in plantarflexion, the trochlea of the talus rocks anteriorly in the three-side mortise. Since the anteriorly it is not as wide, there is considerable room for the ankle to move.
During dorsiflexion the trochlea of the talus rocks posteriorly in the three-sided mortise, and the malleoli are forced apart because the superior articular surface of the talus is wider anteriorly than posteriorly.
The separation of the malleoli requires some movement of the proximal tibiofibular joint. Thus, the range of plantarflexion is greater than that of dorsiflexion, but there is considerable variation in these movements.


Articular Capsule of the Talocrural Joint (p. 488)

The fibrous capsule is thin anteriorly and posteriorly, but it is supported one each side by strong collateral ligaments (medial or deltoid and lateral ligaments).
It is attached superiorly to the borders of the articular surfaces of the tibia and malleoli.
It is attached inferiorly to the talus close to the superior articular surface, except anteroinferiorly, where it is attached to the dorsum of the neck of the talus.


The Medial or Deltoid Ligament (p. 488)

This strong ligament attaches the medial malleolus to the tarsus (tarsal bones).
The apex of the ligament is attached to the margins and tip of the medial malleolus.
Its broad base fans out and attaches to three tarsal bones (talus, navicular, and calcaneus).
The deltoid ligament consists of four parts, which are named according to their bony attachments: (1) tibionavicular, (2) and (3) anterior and posterior tibiotalar, and (4) tibiocalcanean ligaments.
They strengthen the joint and hold the calcaneus and navicular bones against the talus. In addition, they help to maintain the medial side of the foot against the longitudinal arch.


The Lateral Ligament of the Ankle (pp. 488-9)

On the lateral side of the ankle there are three ligaments that attach the lateral malleolus to the talus and calcaneus.
These are not as strong as the medial ligament.
The three distinct parts of the lateral ligament are the anterior and posterior talofibular ligaments and the calcaneofibular ligaments.
The anterior talofibular ligament is a flat band that extends anteromedially from the lateral malleolus to the neck of the talus. It is not very strong.
The posterior talofibular ligament is thick and fairly strong. It runs horizontally medially and slightly posteriorly from the malleolar fossa to the lateral tubercle of the posterior process of the talus.
The calcaneofibular ligament is a round cord that passes posteroinferiorly from the tip of the lateral malleolus to the lateral surface of the calcaneus. It is crossed superficially by the tendons of the fibularis (peroneus) longus and brevis muscles.


The Synovial Capsule of the Talocrural Joint (p. 489)

The synovial capsule of the ankle joint lines the fibrous capsule and occasionally projects superiorly for a short distance into the inferior tibiofibular ligament between the tibia and fibula.
The synovial cavity of the ankle joint is somewhat superficial on each side of the tendo calcaneus. Hence, when the ankle joint is inflamed, the synovial fluid may increase, causing swelling in these locations.


Stability of the Talocrural Joint (pp. 489-90)

This joint is very strong during dorsiflexion because it is supported by powerful ligaments and it is crossed by several tendons that are tightly bound down by thickenings of the deep fascia called retinacula.
The stability is also greatest in dorsiflexion because in this position the trochlea of the talus fills the mortise formed by the malleoli. Furthermore, the anterior part of the trochlea forces the malleoli of the leg bones apart slightly.


Blood Supply of the Talocrural Joint (p. 490)

The articular arteries are derived from the malleolar branches of the fibular (peroneal) and anterior and posterior tibial arteries.


Nerve Supply of the Ankle Joint (p. 490)

The articular nerves are derived from the tibial nerve and the deep fibular (peroneal) nerve, a division of the common fibular (peroneal nerve).

Front 13

Joints of Foot

Back 13

The Subtalar (talocalcanean) Joint (p. 490-1)

The subtalar (talocalcanean) joint is distal to the ankle joint where the talus rests on and articulates with the calcaneus.
The subtalar joint is a synovial joint between the inferior surface of the body of the talus and the superior surface of the calcaneus.
It is surrounded by an articular capsule, which is attached near the margins of the articular facets.
The fibrous capsule is weak but it is supported by medial, lateral and posterior talocalcanean ligaments.
In addition, it is supported anteriorly by the interosseous talocalcanean ligament.


Movements of the Subtalar (talocalcanean) Joint (p. 491)

Inversion and eversion are the main movements that occur at this joint.
The joint also permits slight gliding and rotation that assist with inversion and eversion of the posterior part of the foot.
Movements of the subtalar (talocalcanean) joint are closely associated with those at the talocalcaneonavicular and calcaneocuboid joints (parts of the transverse tarsal joint).
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The Talocalcaneonavicular Joint (p. 491)

This joint is located where the head of the talus articulates with the socket formed by the posterior surface of the navicular bone, the superior surface of the plantar calcaneonavicular ligament ("spring ligament"), the sustentaculum tali, and the articular surface of the calcaneus.
The talocalcaneonavicular articulation is a synovial joint of the ball and socket type.
The ball is the head of the talus and the socket comprises two bones and two ligaments.
The head of the talus has three facets, one for the navicular and two for the calcaneus.
All these articular surfaces are surrounded by a single articular capsule that blends with the interosseous talocalcanean ligament posteriorly.
The talocalcaneonavicular joint is reinforced dorsally by the dorsal talonavicular ligament, a broad band connecting the neck of the talus and the dorsal surface of the navicular bone.
The plantar calcaneonavicular ligament ("spring ligament") is a triangular band that extends from the sustentaculum tali to the posteroinferior surface of the navicular bone.
This ligament blends with the deltoid ligament medially and forms part of the socket for the head of the talus.
It also plays an important role in maintaining the longitudinal arch of the foot.
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The Calcaneocuboid Joint (p. 491)

This is a synovial joint between the anterior surface of the calcaneus and the posterior surface of the cuboid.
It is part of the transverse tarsal joint.
The dorsal calcaneocuboid ligament and plantar calcaneocuboid ligament (short plantar ligament) strengthen the capsule of the calcaneocuboid joint.
The long plantar ligament covers the plantar surface of the calcaneus. It passes from the plantar surface of the calcaneus, including its anterior and posterior tubercles, to both lips of the groove on the cuboid bone.
Some of its fibres extend to the bases of the second, third, and fourth metatarsal bones, thereby forming a tunnel for the tendon of the fibularis (peroneus) longus muscle.
This muscle passes though the groove in the cuboid bone to insert into the bases of the first metatarsal and the adjoining part of the medial cuneiform bone.
The long plantar ligament is important in maintaining the arches of the foot.
The plantar calcaneocuboid ligament (short plantar ligament) is deep to the long plantar ligament. It extends from the anterior aspect of the inferior surface of the calcaneus to the inferior surface of the cuboid.
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The Transverse Tarsal Joint (p. 491-2)

This joint is the talonavicular joint and the calcaneocuboid joint.
These are separate joints but together they constitute the transverse tarsal joint or mid-tarsal joint.
They extend across the tarsus in almost the same transverse plane.


Movements of the Transverse Tarsal Joint

Movements occurring at this joint produce inversion and eversion of the foot.
During inversion, the foot is adducted and directed so that its medial border is raised and its lateral border is depressed, i.e., the sole of the foot is directed towards the medial plane.
In eversion, the foot is abducted and directed so that the lateral border is raised and the medial border is depressed, i.e., the sole of the foot is directed away from the median plane.
The strong medial (deltoid) ligament tends to prevent overeversion of the foot; the weaker lateral ligaments (with the assistance of the fibularis (peroneus) longus and brevis muscles) tend to prevent overinversion of the foot.

Front 14

Femoral Triangle

Back 14

This is a clinically important triangular subfascial space in the superomedial one-third part of the thigh.
It appears as a depression inferior to the inguinal ligament when the thigh is actively flexed at the hip joint. Its main contents are the femoral vessels and the femoral nerve.


Boundaries of the Femoral Triangle (pp. 393, 396)

It is bounded superiorly by the inguinal ligament.
It is bounded medially by the medial border of the adductor longus muscle.
It is bounded laterally by the medial border of the sartorius muscle.
The muscular floor of the femoral triangle is not flat but gutter-shaped.
It is formed from medial to lateral by the adductor longus, pectineus, and the iliopsoas. It is the juxtaposition of the iliopsoas and pectineus muscles that forms the deep gutter in the muscular floor.
The roof of the femoral triangle is formed by the fascia lata, which includes the cribiform fascia.


Surface Anatomy of the Femoral Triangle (p. 396)

When the thigh is actively flexed at the hip joint, the femoral triangle appears as a triangular depression in its proximal third.
You can easily palpate and usually observe its base, the inguinal ligament.
Its lateral boundary, the medial border of the sartorius muscle is obvious in most people but the medial boundary (the medial border of the adductor longus muscle) is not usually so easy to identify.
The femoral pulse can easily be palpated in the femoral triangle, 2 to 3 cm inferior to the midpoint of the inguinal ligament. The head of the femur lies posterior to the femoral artery at this site, making compression of the vessel easy.


Contents of the Femoral Triangle

This triangular space in the anterior aspect of the thigh contains the femoral artery (femoral artery in femoral triangle) and its branches, the femoral vein and its tributaries, the femoral nerve and its branches, the lateral cutaneous nerve, the femoral branch of the genitofemoral nerve, lymphatic vessels, and some inguinal lymph nodes.

Front 15

Popliteal Fossa

Back 15

This diamond-shaped region is posterior to the knee, between the semitendinosus and biceps femoris tendons. It lies posterior to the distal third of the femur, the knee joint and the proximal part of the tibia.
This fossa appears as a hollow when the knee is flexed.
Skin and fasciae form the roof of the popliteal fossa (its posterior wall).
The superficial popliteal fascia contains fat, the small saphenous vein, and three cutaneous nerves.
The roof is pierced proximally by the posterior femoral cutaneous nerve and distally by the small saphenous vein.
This vein perforates the deep popliteal fascia and ends in the popliteal vein.
The deep popliteal fascia forms a strong, dense sheet of deep fascia, which affords a protective covering for the neurovascular structures passing from the thigh to the leg.
The deep fascia of the thigh is strengthened posterior to the knee by transverse fibres. When the leg is extended, the semimembranosus muscle moves laterally, offering further protection for these structures.
The popliteal surface of the femur, the oblique popliteal ligament, an expansion of the semimembranosus tendon, and the popliteus fascia form the floor of the popliteal fossa (its anterior wall).
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Boundaries of the Popliteal Fossa (p. 423)

Superolaterally: biceps femoris muscle.
Superomedially: semimembranosus and semitendinosus muscles.
Inferolaterally and inferomedially: lateral and medial heads of the gastrocnemius muscle.
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Contents of the Popliteal Fossa (p. 423)

When the muscles forming the boundaries of the fossa are pulled apart, especially the heads of the gastrocnemius, the popliteal fossa and its contents can be observed.
Although the fossa appears large when this is done, normally the muscles are packed closely together and the fossa is relatively small.
The contents of the fossa are: fat; the popliteal vessels (artery, vein, and lymphatics); the tibial and common peroneal nerves; the small saphenous vein; the end branch of the posterior femoral cutaneous nerve; and articular branch of the obturator nerve; four to six popliteus lymph nodes; and the popliteus bursa.

Front 16

Knee Joint

Back 16

This is a hinge type of synovial joint that permits some rotation.
Its structure is complicated because it consists of three articulations: an intermediate one between the patella and femur and lateral and medial ones between the femoral and tibial condyles.


Articular Surfaces of the Knee Joint

The bones involved are the femur, tibia, and patella.
The articular surfaces are the large curved condyles of the femur, the flattened condyles of the tibia, and the facets of the patella.
The knee joint is relatively weak mechanically because of the configurations of its articular surfaces. It relies on the ligaments that bind the femur to the tibia for strength.
On the superior surface of each tibial condyle, there is an articular area for the corresponding femoral condyle.
These areas, commonly referred to as the medial and lateral tibial plateaux, are separated from each other by a narrow, nonarticular area, which widens anteriorly and posteriorly into anterior and posterior intercondylar areas, respectively.


Surface Anatomy of the Knee Joint

This joint may be felt as a slight gap on each side between the corresponding femoral and tibial condyles. When the leg is flexed or extended, a depression appears on each side of the patellar ligament.
The articular capsule is very superficial in these depressions. The knee joint lies deep to the apex of the patella.


Movements of the Knee Joint

The principal movements occurring at this joint are flexion and extension of the leg, but some rotation also occurs in the flexed position.
Flexion and extension of the knee joint are very free movements.
Flexion normally stops when the calf contacts the thigh. The ligaments of the knee stop extension of the leg.
When the knee is fully extended, the skin anterior to the patella is loose and can easily be picked up. This laxity of the skin helps flexion to occur.
The knee "locks" owing to medial rotation of the femur on the tibia. This makes the lower limb a solid column and more adapted for weight bearing. To "unlock" the knee the popliteus muscle contracts, thereby rotating the femur laterally so that flexion of the knee can occur.
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The Articular Capsule of the Knee

The fibrous capsule is strong, especially where local thickenings of it form ligaments.
Superiorly, the fibrous capsule is attached to the femur, just proximal to the articular margins of the condyles and to the intercondylar line posteriorly.
It is deficient on the lateral condyle, which allows the tendon of the popliteus muscle to pass out of the joint and insert into the tibia.
Inferiorly the fibrous capsule is attached to the articular margin of the tibia, except where the tendon of the popliteus muscle crosses the bone.
Here the fibrous capsule is prolonged inferolaterally over the popliteus to the head of the fibula, forming the arcuate popliteal ligament.
The fibrous capsule is supplemented and strengthened by five intrinsic ligaments; patellar ligament, fibular collateral ligament, tibial collateral ligament, oblique popliteal ligament, and arcuate popliteal ligament.
These are often called the external ligaments to differentiate them from the internal ligaments (e.g., the cruciate ligaments, which are internal to the fibrous capsule).


The Patellar Ligament or Ligamentum Patellae (pp. 478-9)

This very strong, thick band is the continuation of the tendon of the quadriceps femoris muscle.
The patella is a sesamoid bone in this tendon.
The patella is continuous with the fibrous capsule of the knee joint and is most easily felt when the leg is extended.
The superior part of its deep surface is separated from the synovial membrane of the knee joint by a mass of loose fatty tissue called the infrapatellar fatpad. The inferior part of the patellar ligament is separated from the anterior surface of the tibia by the deep infrapatellar bursa.


Patellar Reflex

With the leg flexed, the patellar ligament is struck to elicit a knee jerk. This patellar reflex or knee reflex results in the extension of the leg. This reflex is blocked by damage to the femoral nerve, which supplies the quadriceps muscle. Similarly, damage to the reflex centres in the spinal cord (L2, L3, and L4) will affect the patellar reflex.



The Fibular Collateral Ligament (p. 479)

The fibular collateral ligament (lateral ligament) is a round pencil-like cord about 5 cm long.
It extends inferiorly from the lateral epicondyle of the femur to the lateral surface of the head of the fibula.
The tendon of the popliteus muscle passes deep to the fibular collateral ligament, separating it from the lateral meniscus.
The biceps femoris muscle is also split into two parts by this ligament.
The fibular collateral ligament is fused with the fibrous capsule of the knee joint superiorly; hence, this part of it is an intrinsic ligament.
Inferiorly the fibular collateral ligament is separated from the fibrous capsule by fatty tissue; hence this part of it is an extrinsic ligament.


The Tibial Collateral Ligament (p.479-50)

This ligament (also known as the medial ligament) is a strong, flat band, 8 to 9 cm long, which extends from the medial epicondyle of the femur to the medial condyle and superior part of the medial surface of the tibia.
It is a thickening of the fibrous capsule of the knee joint and is partly continuous with the tendon of the adductor magnus muscle.
The medial inferior genicular vessels and nerve separate the inferior end of the ligament from the tibia.
The deep fibres of the tibial collateral ligament are firmly attached to the medial meniscus and the fibrous capsule of the knee.


Injuries, the collateral ligaments and the knee joint

The tibial and fibular collateral ligaments normally prevent disruption of the sides of the knee joint.
They are tightly stretched when the leg is extended and prevent the rotation of the tibia laterally or the femur medially.
As the collateral ligaments are slack during flexion of the leg, they permit some rotation of the tibia on the femur in this position.
The fibular collateral ligament is not commonly torn because it is very strong. However, lesions (e.g., strains or tears) or the fibular collateral ligament can have serious consequences.
Usually, it is the distal end of the ligament that tears, and sometimes the head of the fibular is pulled off because the ligament is stronger than the bone. Complete tears are associated with stretching of the common fibular (peroneal) nerve. This affects the muscles of the anterior and lateral compartments of the leg and may produce foot-drop owing to paralysis of the dorsiflexor and eversion muscles of the foot.
The firm attachment of the tibial collateral ligament to the medial meniscus is of considerable clinical significance because injury to the tibial collateral ligament frequent results in concomitant injury to the medial meniscus.
Rupture of the tibial collateral ligament, often associated with tearing of the medial meniscus and anterior cruciate ligament, is a common type of football injury. The damage is frequently caused by a blow to the lateral side of the knee.
When considering soft tissue injuries of the knee, always think of the three Cs which indicate those structures that may be damaged: Collateral ligaments, Cruciate ligaments, and Cartilage (menisci).


The Oblique Popliteal Ligament (p. 482)

The broad band is an expansion of the tendon of the semimembranosus muscle. The oblique popliteal ligament strengthens the fibrous capsule of the knee joint posteriorly.
It arises posterior to the medial epicondyle of the tibia and passes superolaterally to attach to the central part of the posterior aspect of the fibrous capsule of the knee joint.


The Arcuate Popliteal Ligament (p. 482)

This Y-shaped band of fibres also strengthens the fibrous capsule posteriorly. The stem of the ligament arises from the posterior aspect of the head of the fibula. As it passes superomedially over the tendon of the popliteus muscle, the arcuate popliteal ligament spreads out over the posterior surface of the knee joint.
It inserts into the intercondylar area of the tibia and the posterior aspect of the lateral epicondyle of the femur.


Cruciate Ligaments of the Knee Joint (pp. 483-5)

These are very strong ligaments within the capsule of the joint but are outside the synovial cavity.
Joining the femur and tibia, they are located between they are located between the medial and lateral condyles and are separated from the joint cavity by the synovial membrane. The synovial capsule lines the fibrous capsule, except posteriorly where it is reflected anteriorly around the cruciate ligaments.
The cruciate (L. resembling a cross) ligaments are strong, rounded bands that cross each other obliquely in a manner similar to an X. They are named anterior and posterior according to their site of attachment to the tibia, i.e., the anterior cruciate ligament attaches to the tibia anteriorly and the posterior cruciate ligament attaches to it posteriorly. These ligaments are essential to the anteroposterior stability of the knee joint, especially when it is flexed.


The Anterior Cruciate Ligament (p. 483)

The weaker of the two ligaments, the anterior cruciate ligament arises from the anterior part of the intercondylar area of the tibia, just posterior to the attachment of the medial meniscus.
It extends superiorly, posteriorly, and laterally to attach to the posterior part of the medial side of the lateral condyle of the femur.
The anterior cruciate ligament, which is slack when the knee is flexed and taut when it is fully extended, prevents posterior displacement of the femur on the tibia hyperextension of the knee joint. When the joint is flexed at a right angle, the tibia cannot be pulled anteriorly because it is held by the anterior cruciate ligament.


The Posterior Cruciate Ligament (p. 483-5)

This is the stronger of the two ligaments. It arises from the posterior part of the intercondylar area of the tibia and passes superiorly and anteriorly on the medial side of the anterior cruciate ligament to attach to the anterior part of the lateral surface of the medial condyle of the femur.
The posterior cruciate ligament is the first structure observed when the knee joint is surgically opened posteriorly.
The posterior cruciate ligament, which tightens during flexion of the knee joint, prevents anterior displacement of the femur on the tibia or posterior displacement of the tibia.
It also helps to prevent hyperflexion of the knee joint. In the weight bearing flexed knee, it is the main stabilising factor for the femur, e.g., when walking downhill or downstairs.

Front 17

Muscles of Foot

Back 17

Muscles on the Dorsum of the Foot (p. 464)

There are two closely connected muscles on the dorsum of the foot, the extensor digitorum brevis and extensor hallucis brevis. The latter muscle is part of the extensor digitorum brevis.


The Extensor Digitorum Brevis and Extensor Hallucis Brevis Muscles (p. 464)

These broad thin muscles form a fleshy mass on the lateral part of the dorsum of the foot, anterior to the lateral malleolus, which can be seen in most feet and felt in all of them.
Actions: the extensor digitorum brevis extends the second to fourth digits at the metatarsophalangeal joints, and the extensor hallucis brevis extends the first digit or great toe at the metatarsophalangeal joint.
These muscles help the long extensor muscles extend the toes.
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Muscles in the Sole of the Foot

There are four muscular layers in the sole of the foot.
They are specialised to maintain the arches of the foot and to enable one to stand on uneven ground.
These muscles have gross functions rather than delicate individual functions like those in the hand.
There are two neurovascular planes in the foot: a superficial one between the first and second layer and a deep one between the third and fourth muscular layers.


First Layer of Plantar Muscles (p. 464)

This superficial layer contains 3 short muscles.
They all extend from the posterior part of the calcaneus to the phalanges.
It contains the abductor of the great and small digits and the short flexors of the lateral four digits.
These muscles act as a functional group that acts as an elastic spring for supporting the arches of the foot and maintaining the concavity of the foot.
It contains abductor hallucis, flexor digitorum brevis, and abductor digiti minimi.

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Second layer of Plantar Muscles (pp. 464-5)

This layer, located deep to the first layer consists of the quadratus plantae and lumbrical muscles.
The long tendons of flexor hallucis longus and flexor digitorum longus are also located on this layer.
The tendon of the flexor hallucis longus crosses deep to the flexor digitorum longus as it passes to the first digit or the great toe.
Quadratus plantae is from the calcaneus --> tendon of flexor digitorum longus.
The lumbrical muscles are from tendons of flexor digitorum longus --> dorsal digital expansion.

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Third Layer of Plantar Muscles (p. 465, 467)

This layer has 3 short muscles of the great and small digits, which lie in the anterior half of the sole of the foot.
Two act on the great digit and one on the small digit.
Includes: flexor hallucis brevis, adductor hallucis and flexor digiti minimi.
A sesamoid bone adheres to each of the tendons of the two heads of flexor hallucis brevis.

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Fourth Layer of Plantar Muscles (p. 467)

This layer consists of the interosseous muscles and the tendons of the fibularis (peroneus) longus and tibialis posterior muscles, which cross the foot to reach their distal attachments.

Front 18

Deep Fascia of Foot

Back 18

This fascia is continuous with that of the ankle.
It is thin on the dorsum of the foot, where it is continuous with the inferior extensor retinaculum.
Over the lateral and posterior aspects of the foot, the deep fascia is continuous with the plantar fascia or deep fascia of the sole.


The Plantar Aponeurosis (pp. 463-3)

This is the greatly thickened central part of the plantar fascia.
It consists of a strong, thick central part and weaker and thinner medial and lateral portions.
This plantar aponeurosis covers the entire length of the sole and consists of longitudinally arranged bands of dense fibrous connective tissue.
It helps to support the longitudinal arches of the foot and hold the parts of the foot together.
It arises posteriorly from the tuber calcanei and fans out over the sole, where it becomes broader and somewhat thinner.
The plantar aponeurosis divides into five bands that split to enclose the digital tendons.
They are attached to the margins of the fibrous digital sheaths and to the sesamoids of the great toe.
From the margins of the central part of the plantar aponeurosis, vertical septa extend deeply to form three compartments of the sole of the foot: a medial compartment, a lateral compartment and a central compartment.
The muscles, nerves and vessels may be described according to these compartments, but the muscles are usually described by layers.

Front 19

Femoral Artery

Back 19

The Femoral Sheath (p. 405)

This oval, funnel-shaped fascial tube encloses the proximal parts of the femoral vessels, which lie inferior to the inguinal ligament. It also surrounds the femoral canal but it does not enclose the nerve.
The femoral sheath is a diverticulum or inferior prolongation of the fasciae lining of the abdomen (trasversalis fascia anteriorly and iliac fascia posteriorly).
It is covered by the fascia lata.
The femoral sheath ends about 4 cm inferior to the inguinal ligament by becoming continuous with the adventitia or external loose connective tissue covering of the femoral vessels.
The great saphenous nerve and lymphatic vessels piece the medial wall of the femoral sheath.
The presence of the femoral sheath allows the femoral artery and vein to glide in and out, deep to the inguinal ligament, during movements of the hip joint.
The sheath does not project into the thigh when the thigh is fully flexed, but is drawn further into the femoral triangle when the thigh is extended.


Compartments of the Femoral Sheath (p. 405)

This sheath is subdivided by two vertical septa into three compartments: (1) a lateral compartment for the femoral artery; (2) an intermediate compartment for the femoral vein; and (3) a medial compartment or space called the femoral canal.


The Femoral Artery in the Femoral Triangle (p. 396)

This large vessel is the continuation of the external iliac artery.
It provides the chief arterial supply to the lower limb.
It enters the femoral triangle deep to the midpoint of the inguinal ligament and lateral to the femoral vein.
The femoral artery is located posterior to the deep fascia, whereas the great saphenous vein is in the superficial fascia.
The artery descends on the psoas major, pectineus, and adductor longus muscles in the floor of the femoral triangle.
It bisects the femoral triangle and at its apex the femoral artery runs deep to the sartorius muscle within the adductor canal.


The Femoral Artery in the Adductor Canal (p. 407)

Click here to go to the Adductor Canal

The femoral vessels enter the adductor canal where the sartorius muscle crosses over the adductor longus muscle, the vein lying posterior to the artery.
The femoral artery and vein leave the adductor canal through the tendinous opening in the adductor magnus muscle, known as the adductor hiatus.
As soon as the femoral vessels enter the popliteal fossa, they are called the popliteal vessels.
The saphenous nerve, a cutaneous branch of the femoral nerve, accompanies the femoral artery through the adductor canal.
It enters the adductor canal lateral to the artery, crosses it anteriorly, and lies medial to it at the distal end of the canal.
The nerve to the vastus medialis muscle accompanies the femoral artery through the proximal part of the adductor canal and then divides into the branches that supply this muscle and the knee joint.

Front 20

Popliteal Artery

Back 20

This vessel begins as soon as the femoral artery passes through the adductor hiatus in the tendon of the adductor magnus muscle.
The popliteal artery is a continuation of the femoral artery.
From its origin in the adductor hiatus, it passes inferolaterally through the fat of the popliteus fossa.
It ends by dividing into the anterior and posterior tibial arteries at the inferior border of the popliteus muscle.
The popliteal artery is located deeply throughout its course.
Anteriorly, from proximal to distal, it lies against the fat on the posterior surface of the femur, the fibrous capsule of the knee joint, and the popliteus fascia.
Posteriorly, from proximal to distal, it lies deep to the semimembranosus muscle, popliteal vein, tibial nerve, and gastrocnemius muscle.
There are numerous branches of the popliteal artery. These supply the skin on the posterior aspect of the leg and the muscles of the thigh and leg.


Genicular Branches of the Popliteal Artery (p. 426)

There are five of these branches that supply the articular capsule and the ligaments of the knee joint.
The genicular arteries are named as follows: lateral superior and inferior, medial superior and inferior, and middle genicular arteries.


Muscular Branches of the Popliteal Artery (p. 426)

These vessels supply the hamstrings, gastrocnemius, soleus and plantaris muscles.
The arteries supplying the two heads of the gastrocnemius muscles, called sural arteries, may arise from a common trunk.
The superior muscular branches of the popliteal artery have clinically important anastomoses with the terminal part of the profunda femoris and gluteal arteries.
A cutaneous branch of the popliteal artery, the superficial sural artery, accompanies the small saphenous vein.


The Genicular Anastomoses (p. 426)

This is an important network of arterial vessels around the knee involving ten vessels.
The anastomoses are around the patella and the proximal ends of the tibia and fibula.
There is a superficial network of arterial vessels between the fascia and skin, superior and inferior to the patella, and in the fat posterior to the patella.
A deep network of arterial vessels also lies on the articular capsule of the knee joint and on the condyles of the femur and tibia.
In addition to supplying the capsule of the knee joint, these arteries supply the adjacent bones.

Front 21

Anterior Tibial Artery

Back 21

This artery and its branches supply the structures in the anterior crural compartment.
It is the smaller of the two terminal branches of the popliteal artery.
It begins opposite the inferior border of the popliteus muscle and ends at the ankle joint, midway between the malleoli where it becomes the dorsalis pedis artery.
From its origin, the anterior tibial artery passes anteriorly though the interosseous membrane.
It then descends on the anterior surface of this membrane between the extensor hallucis longus and tibialis anterior with the deep fibular nerve.
In the distal part of the leg, the anterior tibial artery lies on the tibia.
In addition to supplying the muscles in the anterior crural compartment, the anterior tibial artery has several named branches.
The anterior and posterior tibial recurrent arteries join the anastomoses around the knee.
The medial and lateral anterior malleolar arteries ramify over the medial and lateral malleoli, contributing to the arterial network over the ankle.

Front 22

Posterior Tibial Artery

Back 22

This vessel is the larger terminal branch of the popliteal artery, and it also begins at the distal border of the popliteus muscle.
The posterior tibial artery passes deep to the origin of the soleus muscle, and after giving off the fibular (peroneal) artery, its largest branch, it passes inferomedially on the posterior surface of the tibialis posterior muscle.
During its descent, it is accompanied by the tibial nerve and two venae comitantes, deep to the transverse crural intermuscular septum.
At the ankle, the posterior tibial artery runs posterior to the medial malleolus, from which it is separated by the tendons of the tibialis posterior and flexor digitorum longus muscles.
Inferior to the medial malleolus, it runs between the tendons of the flexor hallucis longus and flexor digitorum longus muscles.
Deep to the flexor retinaculum and the origin of the abductor hallucis muscle, the posterior tibial artery divides into medial and lateral plantar arteries.

Front 23

Plantar Arteries

Back 23

The posterior tibial artery divides into the medial and lateral plantar arteries deep to the flexor retinaculum and the origin of the abductor hallucis muscle.


The Medial Plantar Artery

It is on the medial side of the foot.


The Lateral Plantar Artery

This passes between the first and second layer to the lateral side of the foot, and it forms the plantar arch.

Front 24

Adductor Canal

Back 24

The adductor canal (subsartorial canal or Hunter's canal) is about 15 cm in length and is a narrow, fascial tunnel in the thigh.
It is located deep to the middle third of the sartorius muscle, it provides an intermuscular passage through which the femoral vessels pass to reach the popliteal fossa, where they become popliteal vessels.
The adductor canal begins about 15 cm inferior to the inguinal ligament, where the sartorius muscle crosses over the adductor longus muscle.
It ends at the adductor hiatus in the tendon of the adductor magnus muscle.
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Boundaries of the Adductor Canal

Laterally: vastus medialis muscle
Posteromedially: adductor longus and adductor magnus muscles
Anteriorly: sartorius muscle
The sartorius and the subsartorial fascia form the roof of the adductor canal.
About the middle third of the thigh, a subsartorial plexus of nerves lies on this fascia. It supplies the overlying skin.
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Contents of the Adductor Canal

The femoral vessels enter the adductor canal where the sartorius muscle crosses over the adductor longus muscle, the vein lying posterior to the artery.
The femoral artery and femoral vein leave the adductor canal through the tendinous opening in the adductor magnus muscle, known as the adductor hiatus.
As soon as the femoral vessels enter the popliteal fossa, they are called the popliteal vessels.
The profunda femoris artery and vein do not enter the adductor canal.
The perforating branches of these deep vessels pierce the fibres of the adductor muscles to reach the posterior aspect of the thigh.
The saphenous nerve, a cutaneous branch of the femoral nerve, accompanies the femoral artery through the adductor canal.
It enters the adductor canal lateral to the artery, crosses it anteriorly, and lies medial to it at the distal end of the canal.
The saphenous nerve does not leave the adductor canal via the adductor hiatus.
It passes between the sartorius and gracilis muscles, pierces the deep fascia on the medial aspect of the knee, and passes down the medial side of the leg with the great saphenous vein.
The nerve to the vastus medialis muscle accompanies the femoral artery through the proximal part of the adductor canal and then divides into the branches that supply this muscle and the knee joint.

Front 25

Femoral Nerve

Back 25

This is the largest branch of the lumbar plexus.
It forms in the abdomen within the substance of the psoas major muscle and descends posterolaterally through the pelvis to the midpoint of the inguinal ligament.
It pierces the psoas major muscle and runs inferolaterally within it to emerge between the psoas major and iliacus muscles, just superior to the inguinal ligament
It then passes lateral to the femoral vessels, outside the femoral sheath enclosing them.
The femoral nerve is not contained in the femoral sheath.
After passing distally in the femoral triangle, the femoral nerve divides into several terminal branches, which supply the anterior thigh muscles.
It also sends articular branches to the hip and knee joints and gives several branches to the skin on the anteromedial side of the lower limb.


The Muscular Branches of the Femoral Nerve

The muscular branches are the nerves to: iliacus, pectineus, sartorius and the 4 heads of quadriceps.


The Cutaneous Branches from the Femoral Nerve (p. 385)

The intermediate and medial femoral cutaneous nerves supply the skin on the anterior and lateral aspect of skin.
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The Saphenous Nerve (pp. 403, 405)

This cutaneous branch of the femoral nerve descends through the femoral triangle, lateral to the femoral sheath containing the femoral vessels.
The saphenous nerve accompanies the femoral artery in the adductor canal and becomes superficial by passing between the sartorius and gracilis muscles.
It passes anteroinferiorly to supply the skin and fascia of the anterior and medial aspects of the knee, leg and foot.

Front 26

Obturator Nerve

Back 26

It arises from the lumbar plexus in the abdomen.
This nerve descends though the psoas major muscle, leaving its medial border at the brim of the pelvis.
It pierces the psoas fascia, crosses the sacroiliac joint, passes lateral to the internal iliac vessels and ureter, and enters the pelvis minor.
The obturator nerve leaves the pelvis through the obturator foramen and enters the thigh.
The obturator is the nerve to the adductor muscles of the thigh.


The Muscular Branches of the Obturator Nerve

This nerve sends branches to: obturator externus, pectineus, adductor longus, adductor brevis, gracilis and the adductor part of adductor magnus.


The Cutaneous Branches of the Obturator Nerve

This cutaneous branch of this nerve supplies the medial side of the thigh

Front 27

Sciatic Nerve

Back 27

This is the main branch of the sacral plexus.
This is the largest nerve in the body and is formed by the ventral rami of L4-S3, which converge at the inferior border of the piriformis muscle.
The sciatic nerve leaves the pelvis as a thick, flattened band (about 2 cm wide) and travels through the inferior part of the greater sciatic foramen.
It enters the gluteal region inferior to the piriformis muscle and is the most lateral of all the structures emerging inferior to the piriformis.
It runs inferolaterally deep to the gluteus maximus muscle, midway between the greater trochanter of the femur and the ischial tuberosity.
The sciatic nerve rests on the ischium and then passes posterior to the obturator internus, quadratus femoris, and adductor magnus mm.
The sciatic nerve usually supplies no structures in the gluteal region.
The sciatic nerve is really two nerves, the tibial and common peroneal, which are bound together by the same connective tissue sheath.
The nerves usually separate from each other about halfway or more down the thigh, but occasionally they are separate when they leave the pelvis. In this case, the tibial nerve passes inferior to the piriformis and the common peroneal passes through or superior to it.
Usually, the sciatic nerve divides to its two terminal branches near the apex of the popliteal fossa.


The Muscular Branches of the Sciatic Nerve

The sciatic nerve supplies the hamstring muscles as well as the ischial head (hamstring part) of the adductor magnus.

Front 28

Tibial Nerve

Back 28

This is the medial terminal branch of the sciatic nerve.
It is the most superficial of the three main central components of the popliteal fossa (i.e., nerve, vein and artery).
It lies immediately deep to the popliteal fascia.
At first, the semimembranosus muscle covers the tibial nerve. It then passes obliquely, superficial to the popliteal vessels, and comes to lie medial to them, where it is covered by the converging heads of the gastrocnemius muscle.
This nerve supplies all the muscles in the posterior compartment of the leg.
The tibial nerve descends though the middle of the popliteal fossa, posterior to the popliteal vein and artery.
At the distal border of the popliteus muscle, the tibial nerve passes with the posterior tibial vessels deep to the tendinous arch of the soleus muscle.
It then descends straight down the medial plane of the calf, deep to the soleus.
It runs inferiorly on the tibialis posterior muscle, in company with the posterior tibial vessels.
The tibial nerve leaves the posterior compartment of the leg by passing deep to the flexor retinaculum in the interval between the medial malleolus and calcaneus.
The tibial nerve lies between the posterior tibial vessels and the tendon of the flexor hallucis longus.
Posteroinferior to the medial malleolus, the tibial nerve divides into the medial and lateral plantar nerves.
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The Sural Nerve (p. 458)

This is formed from a cutaneous branch of the tibial, the medial sural cutaneous nerve and the communicating branch from the common peroneal nerve.
This nerve supplies the skin of the lateral and posterior part of the inferior third of the leg and the lateral side of the foot.

Front 29

Common and Deep peroneal Nerve

Back 29

This is the lateral and smaller of the two terminal branches of the sciatic nerve.
The common peroneal nerve usually begins at the superior angle of the popliteal fossa and follows the medial border of the biceps femoris muscle and its tendon along the superolateral boundary of the popliteal fossa.
It leaves the fossa by passing superficial to the lateral head of the gastrocnemius muscle.
The common fibular nerve then passes over the posterior aspect of the head of the fibula before winding around the lateral surface of the neck of this bone.
It then runs deep to the superior part of the fibularis longus muscle.
It is palpable where it winds around the neck of the bone.
In this region the nerve ends by dividing into the superficial and deep peroneal nerves.
Within the popliteal fossa (before dividing), this nerve gives off the lateral sural cutaneous nerve to the skin of the calf and the peroneal communicating branch.
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The Deep Peroneal Nerve (pp. 446-7)

This is the nerve of the anterior crural compartment.
It begins between the fibula and the superior part of the fibularis longus muscle.
It then runs inferomedially on the fibula, deep to the extensor digitorum longus.
After piercing the anterior crural intermuscular septum and the extensor digitorum longus, the deep peroneal nerve descends anterior to the interosseous membrane in the anterior crural compartment.
It accompanies the anterior tibial artery between the extensor hallucis longus and tibialis anterior muscles.
It supplies the muscles in the anterior compartment.
It also supplies the skin between the first and second toes