Radiological study to evaluate suspected scapulohumeral joint dysplasia inShetland ponies

A radiological study was performed to test the hypothesis that osteoarthrit is of the scapulohumeral joint in Shetland ponies is secondary to shoulder dysplasia. Animals were selected into 3 groups: Group I: Shetland ponies wi th a radiological and clinical diagnosis of scapulohumeral osteoarthritis ( n = 8); Group 2: Shetland ponies without forelimb lameness (n = 12); Group 3: Horses/ponies without a history or clinical signs of forelimb lameness ( n = 22). Anatomical indices were measured from mediolateral radiographs of a scapulohumeral joint from each animal. There was a significant difference in the mean radius of curvature of the g lenoid cavity of the scapula (RCG) between the 3 groups (MANOVA test, P = 0 .003). The mean RCG of both Group I (P = 0.001) and Group 2 (P = 0.022) was significantly greater than that of Group 3. There was no significant effec t of group on the radius of curvature of the humeral head or on the Conform ity Index. There was a significant effect of group on the Glenoid Ratio (MA NOVA test, P = 3 x 10(-6)). The mean Glenoid Ratio was significantly lower in both Group I (P = 2 x 10(-6)) and in Group 2 (P = 0.006) than in Group 3 . These results indicate that the glenoid cavity of the scapula is 'flatter ' and 'shallower' in Shetland ponies which we postulate to be a primary dys plasia in this breed.