Auer Ch 84 Muscle Disorders

Front 1

What is a muscle fiber composed of?

Back 1

many myofibrils that are a series of repeating sarcomeres

Front 2

What is a sarcomere?

Back 2

basic contractile unit of the muscle fiber

Front 3

What are thick filaments composed of?

Back 3

protein myosin

Front 4

What are thin filaments composed of?

Back 4

proteins acting, tropomysin, and troponin

Front 5

How does muscle contraction occur?

Back 5

Action potential propagation through the tubular system causes release of calcium ions stored in the sarcoplasmic reticulum. These calcium ions bind troponin, altering the actin filament and allowing interaction of the actin and myosin filament. With energy from ATP, the sliding of the actin filament relative to the myosin filament causes shortening of the sarcomere. After propagation of the action potential, calcium returns to the sarcoplasmic reticulum and the sarcomere relaxes.

Front 6

What replenishes ATP?

Back 6

from ADP with the enzyme creatine phosphokinase

Front 7

How does enlargement or growth of muscle occur?

Back 7

enlargement of muscle fibers

Front 8

How damaged muscle repaired?

Back 8

replacement with connective tissue

Front 9

What is fibrotic myopathy?

Back 9

adhesion and fibrous tissue formation after trauma to the semitendinosus, semimembranosus, biceps femoris, or gracilis

Front 10

Surgical treatment of fibrotic myopathy:

Back 10

ST myotomy, ST myotenectomy, or ST tenectomy

Front 11

Disavantages of ST myotomy and myotenotomy?

Back 11

associated with high post-operative complication rate from hemorrhage, wound dehiscence, recurrence, and poor cosmesis

Front 12

Advantage of ST tenectomy?

Back 12

few complications and less risk of recurrence

Front 13

Disadvantage of ST tenectomy?

Back 13

may not result in complete resolution of gait abnormality

Front 14

Describe ST tenectomy:

Back 14

8 cm incision over the tibial insertion of the ST just distal to the medial femorotibial joint and caudal to the saphenous vein. The tendon is identified and forceps are used to isolate it before a 3 cm segment is transected. The limb is then pulled forward and the limb is palpated for a taut band at the tendon of insertion of the ST on the calcaneus. This tendon is isolated and transected slightly caudal and distal to the first tenectomy

Front 15

Term for stringhalt:

Back 15

equine reflex hypertonia

Front 16

Forms of stringhalt:

Back 16

idiopathic, acquired

Front 17

Conditions of idiopathic stringhalt?

Back 17

unilateral and progresses over years

Front 18

Proposed etiology of idiopathic stringhalt?

Back 18

may be caused by injury to the limb or foot or spinal cord disease. There is histologic evidence of neuropathy and degenerative myopathy.

Front 19

Treatment of idiopathic stringhalt:

Back 19

lateral digital extensor tenectomy and partial myectomy

Front 20

Describe lateral digital extensor tenectomy and partial myectomy?

Back 20

2-10 cm segment of tendon and muscle is removed through a proximal and distal incision. The distal incision is made just proximal to the junction of the lateral digital extensor tendon with the long digital extensor tendon. The proximal incision is made over the lateral digital extensor tendon muscle belly 2 cm proximal to the lateral malleolus of the tibia. The tendon is pulled from the distal incision through the proximal incision before myectomy is performed.

Front 21

Complications of lateral digital tenectomy and partial myectomy:

Back 21

dehiscence, infection, and failure to improve the condition

Front 22

Conditions of acquired stringhalt:

Back 22

epidemically in horses grazing pastures with the Australian or European dandelion or mallow. It usually is bilateral and associated with RLN in 60% of horses. Histologically there is evidence of distal axonopathy.

Front 23

Treatment of acquired stringhalt?

Back 23

removing the horse from the pasture but is not always curative +/- lateral digital tenectomy and partial myectomy

Front 24

Origin of peroneus tertius:

Back 24

with the long digital extensor tendon on the proximal craniolateral aspect of the distal femur in the extensor fossa

Front 25

Relation of PT to cranialis tibialis?

Back 25

PT forms a sleeve near the proximal lateral aspect of the trochlear ridge of the talus through which the cranialis tibialis muscles passes

Front 26

Insertion of PT:

Back 26

dorsal branch inserts with the dorsal cranialis tibialis branch on the central tarsal bone, the 3rd tarsal bone, and the proximal MT3. The medial branch inserts on the medial aspect of the central and 3rd tarsal bones. The superficial lateral branch inserts on the calcaneous and the 4th tarsal bone. The deep lateral branch inserts on the middle extensor retinaculum

Front 27

Where does PT rupture occur?

Back 27

origin, midbody, or near the insertion just proximal to formation of the sleeve

Front 28

When does origin ruptures PT occur?

Back 28

more commonly in foals, often with an avulsion fracture of the distal femur, and can communicate with the lateral femorotibial joint

Front 29

Treatment of PT rupture:

Back 29

removal of small fragments arthroscopically for origin ruptures. Large fragments should not be removed. Stall rest and controlled exercise are advocated for other ruptures.

Front 30

What is assicated with a poorer prognosis for PT rupture?

Back 30

if the rupture occurred during racing or if an additional structure was injured at the same time as rupture

Front 31

Treatment of ECR rupture:

Back 31

repair with a 3 loop pulley or interlocking loop if there is an open wound and the ends of the tendon are accessible, with splint placement for 6 weeks. If there is no wound associated with ECR, treatment is splint placement for at least 6 weeks

Front 32

Complications of ECR rupture:

Back 32

infection of the tendon sheath, dehiscence of the tendon suture, or dehiscence of the laceration repair

Front 33

Surgical approaches to eliminate cribbing behavior:

Back 33

forssell procedure, modified forssell procedure, or neurectomy of the ventral branch of the spinal accessory nerve

Front 34

What is the forssell procedure?

Back 34

myectomy of the omohyoideus, sternomandibularis, and sternothyrohyoideus muscles

Front 35

Disadvantage of forssell procedure?

Back 35

Complications of seroma formation and wound healing

Front 36

Describe modified forssell procedure?

Back 36

30 cm incision is made on ventral midline of the neck. The ventral surface of the sternothyroideous and omohyoideus are exposed. On the medial aspect of the sternomandibularis, about 5 cm from its musculotendinous junction, it is rolled lateraly to identify the ventral branch of the accessory spinal nerve. A 6-12 cm segement of the nerve is removed. The combined belly of the omohyoideus and sternothyrohyoideus muscle is separated and an approximately 30 cm segement is removed. A drain is placed through separate incisions. The SQ and skin are closed and a stent bandage is placed over the incision

Front 37

Post-op care for modified forssell procedure?

Back 37

stent is maintained for 2-3 days and the drain is maintained for 4-6 days. Sutures are removed in 2 weeks and exercise resumes in 3 weeks

Front 38

Prognosis for modified forssell procedure?

Back 38

57% remission rate and in 12% the surgery is unsuccessful

Front 39

What is calcinosus circumscripta?

Back 39

mass of mineralized fibrous tissue

Front 40

Most common location for calcinosus circumscripta:

Back 40

lateral aspect of the stifle near the fibula

Front 41

Treatment of calcinosus circumscripta?

Back 41

If not causing any lameness, no treatment is required. If lameness is associated or the owner is unhappy with the cosmetic appearance of the horse, the mass can be removed