Supporting layers of the glenohumeral joint. An anatomic study.

Based on anatomic and surgical dissections, the anatomy of the shoulder region is described in terms of four layers that overlie and support the glenohumeral joint. Each layer envelops the glenohumeral joint on its anterior, lateral, and posterior aspects, and between each layer there is a plane for safe and easy dissection. Layer 1 is composed of the deltoid and pectoralis major muscle bellies with their overlying fascia and enveloping epimysium. Anteriorly, Layer 2 consists of the clavipectoral fascia, the conjoined tendon of the short head of the biceps and coracobrachialis, and the coracoacromial ligament. Posteriorly, Layer 2 is the dense posterior scapular fascia that overlies the infraspinatus and teres minor muscle bellies. It is continuous with the clavipectoral fascia around the lateral aspect of the proximal humerus. Deep to Layer 2, the subdeltoid bursa yields a dissection plane that encompasses the anterior, lateral, superior, and variably the posterior aspects of the glenohumeral joint. Layer 3 consists of the deep layer of the subdeltoid bursa and the underlying musculotendinous units of the rotator cuff, including subscapularis, supraspinatus, infraspinatus, and teres minor. Layer 4 is the capsule of the glenohumeral joint. This includes the glenohumeral ligaments and coracohumeral ligament. These four layers were present and consistent in each shoulder dissected. Significant variations were present only within the deepest layer (shoulder joint capsule). This system can serve as a learning tool and will provide a more organized approach to facilitate surgical dissection in the region.