The glenohumeral joint is the most mobile joint in the human body. The joint’s articular cartilage is susceptible to damage, which if left untreated will result in arthritis with its associated pain and functional disability. Osteoarthritis of the joint is the most common form of arthritis that results in shoulder joint pain and functional disability, with rheumatoid arthritis, posttraumatic arthritis, and rotator cuff tear arthropathy also causing arthritis of the glenohumeral joint (Fig. 35.1). Less common causes of arthritis-induced shoulder joint pain include the collagen vascular diseases, infection, villonodular synovitis, and Lyme disease. Acute infectious arthritis of the glenohumeral joint is best treated with early diagnosis, with culture and sensitivity of the synovial fluid and prompt initiation of antibiotic therapy. The collagen vascular diseases generally manifest as a polyarthropathy rather than a monoarthropathy limited to the glenohumeral joint, although shoulder pain secondary to the collagen vascular diseases responds exceedingly well to ultrasound-guided intra-articular injection of steroid into the glenohumeral joint.

Patients with glenohumeral joint pain secondary to arthritis, rotator cuff tendinopathy, and collagen vascular disease-related joint pain complain of pain that is localized to the shoulder and upper arm. Activity makes the pain worse, with rest and heat providing some relief. The pain is constant and characterized as aching. Sleep disturbance is common with awakening when patients roll over onto the affected shoulder. Some patients complain of a grating, catching, or popping sensation with range of motion of the joint, and crepitus may be appreciated on physical examination.

Functional disability often accompanies the pain associated with many pathologic conditions of the glenohumeral joint. Patients will often notice increasing difficulty in performing their activities of daily living and tasks that require reaching overhead or behind are particularly problematic. If the pathologic process responsible for the patient’s pain symptomatology is not adequately treated, the patient’s functional disability may worsen and muscle wasting and ultimately a frozen shoulder may occur.

Plain radiographs are indicated in all patients who present with shoulder pain (see Fig. 35.1). Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging or ultrasound of the shoulder is indicated if a rotator cuff tendinopathy, tear, or other joint pathology is suspected.

The glenohumeral joint is a multiaxial synovial ball and socket joint. The rounded head of the humerus articulates with the pear-shaped glenoid fossa of the scapula (Fig. 35.2). The joint’s articular surface is covered with hyaline cartilage, which is susceptible to arthritis and degeneration. The rim of the glenoid fossa is composed of a fibrocartilaginous layer called the glenoid labrum (Fig. 35.3). The labrum is susceptible to damage should the humerus be subluxed or dislocated. The most mobile joint in the human body, the glenohumeral joint, is surrounded by a relatively lax capsule that allows the wide range of motion of the shoulder joint, albeit at the expense of decreased joint stability. The joint capsule is lined with a synovial membrane, which attaches to the articular cartilage. This membrane gives rise to synovial tendon sheaths and bursae that are subject to inflammation. The shoulder joint is innervated by the axillary and suprascapular nerves.

The major ligaments of the shoulder joint are the glenohumeral ligaments in front of the capsule, the transverse humeral ligament between the humeral tuberosities, and the coracohumeral ligament, which stretches from the coracoid process to the greater tuberosity of the humerus (Fig. 35.4). Along with the accessory ligaments of the shoulder, these major ligaments provide strength to the shoulder joint. The strength of the shoulder joint also is dependent on short muscles that surround the joint: the subscapularis, the supraspinatus, the infraspinatus, and the teres minor. These muscles and their attaching tendons are susceptible to trauma and to wear and tear from overuse and misuse.