Bilateral hypoplasia of the minor tubercle of the humerus with medial luxation of the biceps tendon in two Quarter Horses

Two Quarter Horses were examined at the Washington State University Veterinary Teaching Hospital with forelimb lameness. Case 1 was a 4-year-old female with a 4 month history of intermittent forelimb lameness that had partially responded to oral anti-inflammatories. The horse was in full training and actively competing in cutting. Case 2 was a one-year-old filly bred for cutting that presented with a right forelimb lameness of 3 weeks’ duration, which was not responsive to oral anti-inflammatories. The horse was not in training. On lameness examination, Case 1 was grade 1/5 (American Association of Equine Practitioners scale) lame in the left forelimb in a straight line on a hard surface, extension and flexion of the shoulder was resented and exacerbated the lameness. Case 2 was grade 3/5 lame in the right forelimb in a straight line on a hard surface, flexion and extension of the shoulder was resented and exacerbated the lameness. Both horses had a characteristic dished appearance to the dorsal aspect of the shoulder, with prominence of the proximal aspect of the humerus. Ultrasound and proximodistal oblique (skyline) radiographic views of the scapulohumeral joints demonstrated bilateral hypoplasia of the minor tubercle of the humerus with bilateral medial luxation of the proximal biceps tendon in both cases. To the authors' knowledge this is the first report of 2 cases of bilaterally affected horses, as well as the first report of the condition in the Quarter Horse breed.