Infraspinatus contracture
Fibrosis and shortening of the infraspinatus muscle after a strain, typically in active hunting and working dogs. The shoulder becomes fixed in external rotation and the limb swings outward when the dog walks.
Draft, not yet reviewed by a veterinarian. Content may contain errors. It is published so the community can review it.
What it is
Infraspinatus contracture is a fibrotic shortening of the infraspinatus muscle. It is believed to start with an acute strain or partial tear of the muscle during strenuous exercise. The injured muscle fibres are replaced by fibrous tissue that contracts over the following weeks, so the muscle can no longer lengthen. As a result the shoulder stays in external rotation and abduction, and its range of motion is restricted.
Who it affects
Medium and large, active dogs, especially hunting and working breeds. It is usually unilateral.
Anatomy involved
The infraspinatus (m. infraspinatus) fills the infraspinous fossa of the scapula, caudal to the spine, and inserts by a strong tendon on the lateral surface of the greater tubercle of the humerus, distal to the insertion of the supraspinatus. A synovial bursa lies under its tendon. It acts as a lateral collateral ligament of the shoulder and rotates the arm outward; it also flexes or extends the shoulder depending on the position of the joint. It is innervated by the suprascapular nerve.
Clinical signs
- Initial phase: sudden lameness and pain over the shoulder after exercise, which improves within about two weeks.
- Chronic phase (weeks later): non-painful lameness with a typical posture. At rest the elbow is held adducted and the paw is turned outward (abducted and externally rotated). When walking, the lower limb swings outward in an arc (circumduction) during the swing phase. Atrophy of the muscle over the scapula is visible, and full flexion and internal rotation of the shoulder are restricted.
Diagnosis
- Typical history, posture and gait, and restricted internal rotation of the shoulder on manipulation. Flexing the shoulder and elbow makes the distal limb rotate outward.
- Ultrasound or MRI to show the fibrotic muscle. Radiographs are usually normal and serve to rule out other shoulder diseases.
Treatment
Tenotomy of the infraspinatus tendon at its insertion on the greater tubercle releases the shoulder; the range of motion and the gait usually improve immediately on the operating table. Removal of part of the fibrotic tendon is sometimes added. Prognosis after surgery is excellent, and most dogs return to full function.
References
- Fossum TW. Small Animal Surgery, 5th ed. Elsevier (2018)
- Piermattei DL, Flo GL, DeCamp CE. Brinker, Piermattei and Flo's Handbook of Small Animal Orthopedics and Fracture Repair, 4th ed. Saunders (2006)