Ch 70 - Muscle and Tendon Disorders

Question 1

What is the most common general location for a muscle strain?
What are the three stages of muscle strain?

Answer 1

Most common at musculotendinous junction, muscles which cross two or more joints appear predisposed

Three stages:
- Stage I: Myositis and brusing, architecture intact
- Stage II: Myositis and some tearing of the fascial sheath
- Stage III: Tearing of the fascial sheath, muscle fiber disruption and haematoma formation

Question 2

What are the two processes of muscle healing?

Answer 2

• Direct regeneration of myofibrils
• Production of fibrous scar tissue

Question 3

What are the general principles of muscle treatment?

Answer 3

• Maximise direct myofibril repair while minimising scar formation (excessive scar can reduce a muscles ability to produce tension by 50%)
• Early mobilisation essential for proper myofibril orientation and can be considered after day 5-10

Question 4

What are some common muscle injuries of the thoracic limb?

Answer 4

• Rupture of long head of triceps brachii (racing Greyhounds). Causes depression caudal and distal to scapula. Reattachment recommended
• Avulsion of triceps brachii tendon of insertion. Primary reattachment to olecranon with immobilisation with transarticular ESF or transarticular screw
• Rupture of serratus ventralis causing dramatic dorsal replacement of scapula

Question 5

What are some common muscle injuries of the pelvic limb?

Answer 5

• Rupture of gracilis (Greyhounds, GSD, Foxhounds). Surgical repair or reattachment
• Iliopsoas and pectineus muscle strain. Most common! Conservative management usually successful

Question 6

What are the most common forms of muscle contracture in dogs?

Answer 6

• Infraspinatus contracture (circumbuction and carpal flip with abduction of shoulder, adduction of elbow, lower limb abducted and externally rotated. Tendonectomy with release of surrounding fibrous tissue
• Quadriceps contracture
• Gracilis and semitendinosus contracture (limb rises in jerk-like fashion with hyperflexion of the tarsocrural joint and internal rotation of metatarsus)
• Flexor carpi ulnaris muscle of puppies
• Myositis ossificans (heterotrophic bone formation in muscles after trauma, most common at hip)

Question 7

What cells do tendon healing rely on?

Answer 7

Influx of fibroblasts to produce new collagen

Question 8

How does tendon healing differ between paratenon-lined tendons and sheathed tendons?

Answer 8

Paratenon-lined:
- Can recieve vascular buds and an influx of undifferentiated cells from the paratenon and surrounding soft tissues.
- Better capacity for rapid healing
- Tendons of insertion of gastroc and triceps

Sheathed:
- Depend much more on intrinsic blood supply
- Digital flexor tendons

Question 9

How long must the suture material primarily maintain strength and resist gap formation during tendon healing?
What are the three main forms of suture patterns for tendon apposition?

Answer 9

Initial three weeks

Suture patterns:
- Locking loop
- Krakow
- Three-loop pulley

Question 10

What percentage strength does a tendon have at 6 weeks and 1 year after repair?
What percentage of normal capacity strain in placed on a tendon during normal muscle contraction?

Answer 10

• 6 weeks: 56%
• 1 year: 79%

Normal contraction places 25-33% of normal full capacity of strain. Thus, strength at 6 weeks should be sufficient to withstand limited exercise

Question 11

What is the general principle of tendon repair?

Answer 11

Produce healing without gap formation and allow early loading to ensure correct collagen formation and alignment

Question 12

What are some common tendon injuries in small animals?

Answer 12

• Superficial digital flexor tendon laceration
• Common calcaneal tendon injury (most common)
• Injuries to tendon of origin of biceps brachii (second most common)
• Injuries to long digital extensor tendon (avulsion or displacement)