Diagnosis of shoulder instability in dogs and cats: a retrospective study.

The glenohumeral joint is a remarkable articulation providing the greatest range of motion of any joint in the body. Glenohumeral stability results from several mechanisms, including those that do not require expenditure of energy by muscle ("passive mechanisms") and those that do ("active mechanisms"). Glenohumeral instability has been recognized in 47 shoulders of 45 dogs and one cat. Cases are presented because of chronic foreleg lameness. Shoulder joint pain is obviated by the orthopedic examination. Only 57% of the involved shoulders presented with degenerative joint disease. Signs of instability are recognized under anesthesia using a craniocaudal or mediolateral drawer sign or both. This report describes the radiographic and arthroscopic findings of shoulder instability. Arthroscopy of the shoulder joint allows identification of all intra-articular pathologies. Shoulder instability, not fully recognized in the past, appears to be the most common cause of shoulder lameness in the dog.