Upper Extremity Anatomy Quiz 2 - Biomechanics

Front 1

What is biomechanics?

Back 1

The study of the mechanics of a living body, especially of the forces exerted by muscles and gravity on the skeletal structure”

Front 2

Sternoclavicular joint

Back 2

SC jt
Synovial (diathrodal) Joint

Double-Saddle Shaped - not super stable
Contains a Fibrocartilage Disc - attaches to cartilage of 1st rib and provides stability against superior and medial displacement

Front 3

Ligaments of the SC joint

Back 3

Interclavicular- between sternal ends, superior stability

Anterior Sternoclavicular - anterior stability

Posterior Sternoclavicular

Costoclavicular - superior stability

Front 4

Motions of the SC joint

Back 4

Elevation / Depression

Protraction / Retraction

Rotation

Front 5

Elevation/depression of the SC joint

Back 5

Refers to movement of lateral end of clavicle

Jt movment around Anterior-Posterior axis
~45o of elevation
<15o of depression

Arthrokinematics:
Superior / inferior translation

Front 6

Protraction/retraction of the SC joint

Back 6

Refers to movement of lateral end of clavicle
~15o in each direction
Accompanies pro/retraction of scapula

Joint movement around vertical axis

concave clavicle on convex manubrium

Arthrokinematics:
Anterior/ posterior translation

Front 7

Anterior/posterior rotation of the SC joint

Back 7

Spins around its long axis
50o posterior rotation
<10o anterior rotation

Front 8

SC joint movement during shoulder movements

Back 8

Elevation of arm and scapula
1st 30 ° upward rotation of scapula
Elevation of clavicle at SC jt
Further upward rotation of scapula (30 - 60°)
Requires rotation of clavicle at SC jt

Protraction / Retraction of scapula
Associated with protraction and retraction at SC jt

Front 9

Acromioclavicular joint

Back 9

AC
Synovial Joint

Convex Clavicle and Concave Acromion
May have an intra-articular disc

Purpose:
Maintain relationship between clavicle and scapula during arm movements

Allow scapula free motion during arm movement

Front 10

Reinforcement and Stability of AC joint

Back 10

Acromioclavicular ligament
Coracoclavicular
-Conoid (medial)
-Trapezoid (lateral)


Joint is also reinforced superiorly by Upper Trapezius and Deltoid

Front 11

AC joint ligaments

Back 11

Acromioclavicular ligament

Coracoclavicular ligament
-Trapezoid (lateral)
Vertical orientation
-Conoid (medial)
More horizontal orientation

Front 12

Acromioclavicular Joint Sprain

Back 12

(“Separated Shoulder”)
looks gnarly, tear ligaments

grade 1: partial tear of 1 or 2 ligaments

2: complete rupture of 1 (usually AC) and no or a partial tear of other lig (coracoclavicular), most common

3: complete rupture of both ligs, physical deformation

4,5,etc. refers to how much separation

Front 13

Motions of the AC joint

Back 13

Upward / Downward Rotation

Anterior / Posterior tilting (tipping)

Internal / External rotation

Front 14

Upward/downward rotation of the AC joint

Back 14

Upward / Downward Rotation

Causes glenoid fossa to face upward or downward

Closely tied with rotation of clavicle
Posterior rotation of clavicle puts coracoclavicular ligament on slack and allows upward rotation

Front 15

Anterior / Posterior Tilting (tipping) of the AC joint

Back 15

Anterior / Posterior Tilting (tipping)

Forward / Backward tilt of glenoid fossa
Purpose:
Keeps scapula in contact with thorax
Allows the glenoid fossa to follow the humeral head

Front 16

Internal / External Rotation of the AC joint

Back 16

Internal / External Rotation
Causes glenoid to face anteromedially / posterolaterally

Purpose:
Keeps the scapula in contact with the thorax
Allows the glenoid fossa to follow the humeral head

Front 17

Scapulothoracic articulation motions

Back 17

Not a “True” Joint

Motion is actually the result of the combination of S-C and A-C joint motion

Motions:
Upward / Downward rotation
Elevation / Depression
Protraction / Retraction

Front 18

upward/downward rotation of the scapula

Back 18

Occurs as a result of combined:

SC elevation/depression
SC posterior/anterior rotation
AC upward/downward rotation

Total of ~ 60° of upward rotation

First 30°of motion:
Axis is at base of spine

Last 30 degrees of motion:
Axis is at A-C joint

Front 19

Muscles causing scapular rotation

Back 19

Upward Rotation:
Serratus Anterior
Upper Trapezius
Lower Trapezius
Downward Rotation:
Rhomboids
Pectoralis Minor
Levator Scapulae

Front 20

Elevation/depression of the scapula

Back 20

Occurs as a result of combined:

SC elevation/depression
AC anterior / posterior tilt
AC internal / external rotation

Front 21

Muscles causing Elevation/depression of the scapula

Back 21

Elevation
Upper Trapezius
Levator Scapulae
Rhomboids
Depression
Lower Trapezius
Pectoralis Minor
Serratus Anterior

Front 22

Protraction/retraction of the scapula

Back 22

Occurs as a result of combined:
?

Front 23

Muscles causing Protraction/retraction of the scapula

Back 23

Protraction
Serratus Anterior
Pectoralis Minor
Pectoralis Major (clavicular portion)

Retraction
Rhomboids
Middle Trapezius

Front 24

Abnormal movements of the scapula

Back 24

Winging - Prominence of the Vertebral Border
Tipping - Prominence of the inferior angle, postural fault or muscle weakness

Front 25

Glenohumeral joint

Back 25

“Ball and Socket”
3 degrees of freedom
Flexion / Extension
Abduction / Adduction
Internal / External Rot.

Articulation of:
Concave Glenoid fossa with Convex Humeral head

Front 26

Humeral orientation

Back 26

130-150 degrees in the frontal plane

30 degrees posterior in the transverse plane
“Retroverted”
Proposed reason why external rotation typically > internal rotation

Implications of excess retroversion?

Front 27

Glenoid labrum
Function

Back 27

Ring shaped fibrocartilage structure which surrounds glenoid fossa

Blends with the joint capsule superiorly

GH ligaments and Long Head of Biceps attach here

Increases stability of GH joint:
Serves to deepen the glenoid fossa
Controls mild to moderate translation forces
50% increase in depth

Acts as “suction cup” to hold humeral head in place
Surface tension created by synovial fluid
Negative osmotic pressure

Front 28

Glenohumeral joint capsule

Back 28

Large and Loose
Allows for much free movement
Taut superiorly
Lax inferiorly & anteriorly
Reinforced:
STATICALLY:
By ligaments
DYNAMICALLY:
By muscle & tendons of rotator cuff
except inferiorly – weakest here
Synovial fluid produces adhesion / cohesion
Disrupted if the capsule is compromised

Front 29

Ligaments of GH joint

Back 29

Glenohumeral ligaments
Superior
Middle
Inferior
Form a “Z” on anterior portion of GH capsule

Coracohumeral ligament
Coracoacromial ligament

Front 30

Superior Glenohumeral Ligament

Back 30

Superior Glenohumeral Ligament

Purpose:
Anterior and Inferior stabilizer with arm by side
Taut in external rotation

Front 31

Middle Glenohumeral ligament

Back 31

Middle Glenohumeral
Absent in 30% of individuals

Purpose:
Anterior stabilizer with arm in 0-60o of abduction
Inferior stabilizer with arm in adduction
Taut in external rotation

Front 32

Inferior Glenohumeral ligament

Back 32

Inferior Glenohumeral
Resembles a Hammock
Anterior Band
Posterior Band
Axillary Pouch

Strong stabilizer beyond 45o of abduction

Anterior stabilizer with arm in abduction and external rotation (position of dislocation)
Anterior Band
Axillary Pouch (fans out)

Posterior stabilizer with arm in flexion and internal rotation
Posterior Band

Front 33

Coracohumeral ligament

Back 33

Coracohumeral
Taut in:
External Rotation
Extension
Anterior fibers
Flexion
Posterior fibers

Provides passive support against gravity, especially with adduction and external rotation

Front 34

anterior shoulder dislocation

Back 34

Most common dislocation
Abduction and ER is most vulnerable position
Potential to secondary injury
Hill Sacs injury - chunk of humerus gets knocked out
Axillary nerve damage - cutaneous innervation around deltoid tuberosity
maybe suprascapular nerve, but less common

Front 35

Coracoacromial arch

Back 35

Formed by the Acromion and Coracoacromial ligament

Functions to:
Protect the humeral head
Protect muscle and tendons crossing over the humeral head
Prevent superior dislocation

But … plays a major Role in causing Shoulder Impingement

Front 36

Bursae about the shoulder

Back 36

Subacromial

Subdeltoid

Subcoracoid - not everyone has

Subscapular

Front 37

Rotator cuff tear

Back 37

Most commonly affects the supraspinatus

FOOSH - fall on outstretched hand

or can be from overuse over time

Front 38

Scapulohumeral rhythm during shoulder elevation

Back 38

ROM of the Shoulder complex is comprised of movement at the:
Scapulothoracic articulation (~60 degrees)
S-C Joint
A-C Joint
G-H joint (~120 degrees)

Ratio of GH: ST
movement is ~2:1

Front 39

Scapulo-Humeral Rhythm Breakdown (from 0-180o of shoulder elevation)

Back 39

0o – 30o (Setting Phase)
Scapular motion is minimal and inconsistent
Primarily humeral contribution
Stress or resistance to arm ↑s scapular contribution
30o – 90o
Significant increase is scapular contribution
Ratio of 2 to 2.75:1
90o – 160o
Relatively equal contributions
Ratio of 1:1

Front 40

Scapulo-Humeral Rhythm
Function and Purpose:

Back 40

Allows larger ROM with maximum stability

Allow the glenoid fossa to be in an optimal position to receive the humeral head

Permits SITS muscles maintain optimal length-tension relationship

Front 41

Osteokinematics (aka: physologic motion)
of the Glenohumeral Joint

Back 41

Flexion / Extension

Internal / External Rotation
Greater range is available when the humerus is abducted

Abduction
Limited if humerus is internally rotated
Greater Tubercle contacts the Acromion

Front 42

Arthrokinematics (accessory motions)
of the Glenohumeral Joint

Back 42

Accessory Motions
The Humeral Head Undergoes:
Rotation or spin
Roll
Glide or Translation

From 30o – 60o of arm elevation (scapular plane), the Humeral head rolls superiorly ~3mm
This centers the head since it was already inferior
Once centered, the humeral head undergoes pure inferior glide and follows the convex/concave rule.

Front 43

What happens if GH capsule is “tight”?

Back 43

Law of Capsular Restraint
The direction of humeral head translation is influenced by the relative tightness of the capsule
Glide is “pushed” opposite of capsular tightness

Tight posterior capsule during flexion
Pushes humeral head anteriorly

Front 44

Static Stability of the Shoulder

Back 44

With the arm by the side, no muscle activity is required to resist gravity’s pull
Superior Joint Capsule
Coracohumeral Ligament
Inclination of glenoid

The Supraspinatus and Posterior Deltoid are only recruited with added load

Front 45

Role of Muscles About the Shoulder

Back 45

Role of Muscles About the Shoulder
Move the Humerus

Produce Intra-articular gliding *

Maintain opposition of joint surfaces *

* Required for Dynamic Stability

Front 46

DYNAMIC Stability of the Shoulder

Back 46

During movement:
Ligaments provide some support but …
shoulder muscles provide DYNAMIC STABILITY !!!

Participants:
Force of Prime Mover
Force of Gravity
Force of Steerers
Force of Friction
Joint Reaction Forces

Front 47

Prime mover of shoulder

Back 47

Prime Mover (Mainly Deltoid)
Rotatory Component
Upward Translation Component
Acts as a de-stabilizing force !!!

If unopposed, the humerus will impact the acromion

Front 48

Dynamic stability of supraspinatus

Back 48

Supraspinatus
Upward translation
Joint compression

Resultant force is abduction
Its large moment arm makes it a significant abductor

Front 49

Dynamic Stability: steering muscles of shoulder

Back 49

Infraspinatus, Teres, Minor, Subscapularis (ITS)

Downward translation component

Joint compression

Front 50

Subacromial Impingement Anatomy

Back 50

What does the impinging?
Under surface of acromion
Tip of coracoid
Greater tubercle

What can be impinged?
Supraspinatus tendon
Infraspinatus tendon
Biceps tendon
Subacromial bursa
Subscapularis

Front 51

Causes of Subacromial Impingement

Back 51

Dynamic stability
Rotator cuff musculature
Scapular musculature
Structural factors
Acromion type
Degenerative changes at coracoacromial arch
Postural factors
Hypermobility
Hypo-mobility

Front 52

What is the open packed position of the humerus?

Back 52

50 degrees abduction and slight horizontal adduction and ER