Ossification of the infraspinatus tendon-bursa in 13 dogs.

Ossification of the infraspinatus tendon-bursa was diagnosed in 13 labrador retrievers, 12 of which were lame in one thoracic limb and the other in both. They ranged in age from 28 to 121 months (mean 69.4 months). The lameness developed gradually and was progressive in 11 of the 14 affected joints. Scapular muscle atrophy and signs of pain on direct pressure over the infraspinatus tendon of insertion were key clinical signs. Caudocranial radiographs revealed multiple mineralised masses lateral to the proximal humerus or glenohumeral joint in 11 of the 26 joints and single masses in 12. An arthroscopic examination revealed concomitant ligament or tendon abnormalities in six of seven shoulders. The dogs were followed up from one to 55 months (mean 20 months). Of five shoulders treated with non-steroidal anti-inflammatory drugs (nsaids), one resolved, two improved and two were managed surgically. Of six shoulders treated by the injection of long-acting intra-articular corticosteroid (five before and one after surgery), three resolved, two improved and one was unchanged. Of six shoulders treated by the surgical resection of the infraspinatus tendon and bursa (three before and two after treatment with nsaids, and one after treatment with a long-acting intra-articular corticosteroid), four improved, one was unchanged and one was managed with an intra-articular long-acting corticosteroid. One shoulder was managed by restricted exercise and the lameness resolved. Histological examination of the excised tissues revealed heterotopic bone within the infraspinatus tendon and/or bursa.