Stability of the canine shoulder joint: an in vitro analysis

The stability of the canine shoulder joint was assessed with and without the restraining effects of selected supporting structures. Shoulder joints from medium-sized (15 to 30 kg) canine cadavers were dissected, and all soft tissues were removed except for the 4 cuff muscles (supraspinous, infraspinous, teres minor, subscapular), the biceps muscle (m biceps brachii) and the joint capsule with its associated glenohumeral ligaments. The humerus was fixed in position, and with the shoulder extended, the joint was stressed into abduction, adduction, internal rotation, and external rotation. The range of motion was measured from transverse pins placed above and below the joint. Measurements were made before and after severance of the cuff tendons and joint capsule. In selected joints, medial and lateral luxations were created. The biceps tendon was then transposed medially or laterally, respectively, to aid joint stability. Selected medial luxations were stabilized by transferring a portion of the insertion of the supraspinous tendon to a medial location. All joints were stressed as just described, and the range of motion was measured before and after tendon transfer. The joint capsule with its associated glenohumeral ligaments was an important restraint of joint motion. Lateral transfer of the biceps tendon partially corrected lateral joint instability by imposed marked rotational constraints on the joint. Medial transfer of the biceps tendon or the supraspinous tendon partially corrected medial joint instability, but did not resolve rotational abnormalities.