Page 679 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 645

The primary cartilage lesion is located in the glenoid,
humeral head, or both (most common), and the disease
VetBooks.ir of the site of the lesion, secondary degenerative changes
often affects a major part of the joint surface. Regardless
74
in the joint are prominent features of this disease. An
exception is the solitary subchondral cystic lesions that
are occasionally seen in the glenoid cavity. 38,54

Etiology
Overnutrition, imbalanced nutrition, and a genetic
predisposition to rapid growth at some stage of the
development still appear to be reasonable hypotheses
for most young affected horses. The secondary degener-
ative changes within the joint are exacerbated by the
resultant instability. 74
Occasionally, subchondral bone cysts are seen in the
glenoid without cartilage changes in the humeral head,
alterations of the contour of the articulations of the
shoulder, or signs of secondary osteoarthritis. 38,54 Thus,
it has been suggested that subchondral bone cysts may
not be a manifestation of OC in the scapulohumeral
(SH) joint. A traumatic etiology is often suspected in
40
such cases of subchondral bone cysts. 54

Clinical Signs
Figure 5.51. Thumb pressure applied just cranial to the
Most horses present with a history of mild to moder- infraspinatus tendon may elicit a painful response in horses with
ate intermittent forelimb lameness with insidious onset. shoulder osteochondrosis.
Atrophy of the muscles associated with the shoulder
region is a common finding in chronic cases. A smaller
foot with a higher heel and excessive toe wear is also 5. Remodeling of the humeral head and glenoid cavity
commonly observed in the foot of the affected limb. (Figure 5.52) 67
Direct firm pressure with the thumb just cranial to the
tendon of the infraspinatus muscle over the cranial lat- Less common findings include osteophytes and sub-
74
eral aspect of the shoulder joint may elicit a painful chondral bone cysts associated with the humeral head.
response, particularly in younger horses (Figure 5.51). Intra‐articular free bodies are uncommon, but when
Exercise usually results in a moderate to severe lame- present they settle in the cranial and caudal cul‐de‐sacs
72
ness that is characterized by a shortened cranial (exten- of the joint. Centrally located glenoid sclerosis and
32
sion) phase of the stride and a delay in limb protraction. small glenoid cysts can easily be overlooked.
Stumbling may occur in some cases due to inadequate The normal ultrasonographic anatomy of the SH
foot clearance. A prominent shoulder lift, reduced car- joint has been described, and humeral head OC has been
pal flexion, and limb circumduction are often seen in the diagnosed using ultrasonography; however, the evalua-
92
most severely affected horses. Manipulation of the tion of the glenoid is difficult. Nuclear scintigraphy
affected limb in extension and flexion and abduction may be used to identify subtle lesions. 32,54
may cause pain and often increases the signs of lame- Arthroscopy may be useful to make a definitive diag-
ness. Intrasynovial anesthesia is used to localize the nosis in cases in which the lameness is localized to the
lameness to the shoulder region; 10–15 mL of a local SH joint with intrasynovial anesthesia but a lesion is not
anesthetic should improve or eliminate the lameness in identified on radiography or scintigraphy. The conclu-
most cases. 38 sions drawn in one retrospective study of 15 horses with
subtle osteochondral lesions in the SH joint suggested
that a combination of the physical examination, radiol-
Diagnosis ogy, scintigraphy, and arthroscopy may be necessary to
Radiographs are necessary to definitively diagnose diagnose subtle osteochondral lesions of the SH joint. 32
the OC lesion. The most common radiographic findings
include: Treatment
1. Flattening and indentation of the caudal aspect of the Rest and confinement may be considered for horses
humeral head with mild to moderate radiographic changes that are
2. Alterations in the contour of the glenoid cavity with not intended for athletic performance. 52,67,74 Of the 17
a subchondral cystic radiolucency horses treated with rest, the treatment was considered
3. Osteophytes at the caudal and cranial aspect of the moderately successful in 7 cases. In another case
74
glenoid cavity (Figure 5.52) series of 3 horses with isolated subchondral cysts in the
4. Subchondral bone sclerosis glenoid, HA was injected into the affected joint with