Page 272 - Canine Lameness

244 15 Shoulder Region

Video 15.2

Infraspinatus contracture – gait and surgery.

Because of its location within the infraspinous fossa, osteofascial compartment syndrome has
been hypothesized to be a component of the disease process. This condition occurs when muscles
that are confined to a tight osteofascial space are injured. The hemorrhage and inflammation
result in a substantial increase in pressure within the compartment. This pressure is hypothesized
to cause decreased blood supply, necrosis, and ultimately contracture of the muscle (Devor and
Sorby 2006).
Early diagnosis is key since treatment options differ greatly if animals are diagnosed during the
acute phase. The contracted infraspinatus can be treated with tenectomy of the insertion of the
infraspinatus tendon. A good-to-excellent outcome is anticipated for infraspinatus contracture
release, making this condition the only fibrotic myopathy with a favorable prognosis. However,
surgical treatment may potentially be avoided if therapy is initiated during the acute phase.
Therapy for this phase is not well studied but may include a fascial release to decrease the pressure
and avoid progression of the disease (Devor and Sorby 2006).

15.8.1 Signalment and History
Hunting dogs are most commonly afflicted with infraspinatus contracture. Frequently, they are
reported to have an acute lameness that resolves with rest and medical therapy, followed by a
recurrent, persistent, static, and non-painful lameness occurring several weeks later. The first stage
is thought to be related to the original pain when the muscle is acutely injured. The inflammation
and associated pain then subside, and the abnormal gait is appreciated when fibrotic changes have
SHOULDER REGION occurred. Patients typically have a unilateral lameness; bilateral infraspinatus disease is reported
but extremely rare (Franch et al. 2009).

15.8.2 Physical Exam

Physical exam findings vary depending on the phase of infraspinatus injury. During the acute
phase, mild swelling and varying degrees of pain may be identified on direct palpation and
stretching of the infraspinatus muscle. The infraspinatus originates in the infraspinous fossa of
the scapula (i.e. caudal to the scapular spine), crosses the shoulder joint, and inserts on the proxi-
molateral surface of the humerus (i.e. on the cranial aspect of the proximal humerus). Given this
location, the concentric action of the muscle varies depending on the shoulder joint position. For
instance, when the shoulder joint is flexed, the muscle extends the joint. But when extended, the
muscle flexes the joint. It is also an abductor and lateral rotator of the joint. Stretching of the
muscle, therefore, can be performed by either extending or flexing the shoulder joint, while
adducting and internally rotating the shoulder. This can be accomplished by examining the
“down” leg in recumbent position (Figure 15.14). If performed during extension and examining
the “up” leg, the entire muscle can be palpated. The emphasis of this palpation should be placed
on the myotendinous portion, which is located approximately at the level of the acromion.
However, this area may not be palpable because of the overlying deltoid muscle, particularly in
well-muscled dogs.