Effects of transection of the cranial arm of the medial glenohumeral ligament on shoulder stability in adult Beagles.

Objective: To assess the effects of arthroscopic transection of the cranial arm of the medial glenohumeral ligament on shoulder stability. Animals: Six adult Beagles. Procedures: After transection, the effects were compared with baseline values by orthopaedic and radiographic examinations, by synovial fluid analysis at two, four, and six weeks, and by arthroscopic evaluation at six weeks. The articular surfaces of the glenoid cavity and humeral head were evaluated radiographically and arthroscopically for evidence of arthritis, and five intra-articular regions were examined arthroscopically for villus reactions and vascularisation. Results: According to orthopaedic examinations (including measurement of the abduction angle), radiography, and synovial fluid analyses, there were no abnormal findings. Arthroscopically, the articular surfaces of the glenoid cavity and humeral head showed no signs of degeneration, but the craniomedial and caudal joint capsules had significant villus reactions and the subscapularis tendon and medial glenohumeral ligament had significant vascularisation. The biceps tendon was unchanged. Conclusions: Transection of the cranial arm of the medial glenohumeral ligament in normal Beagles did not appear to affect shoulder stability. However, villus reactions and vascularisation in the medial compartment suggest that damage to the medial glenohumeral ligament may trigger a process in which inflammation can lead to enzymatic breakdown of cartilage. Exacerbated by weight bearing and repetitive motion, this may result in shoulder instability over time.