The subdeltoid bursa is the largest of the ˜160 bursae in the human body (Fig. 48.1). Because it is usually contiguous and communicates with the subacromial bursa, the names are often used interchangeably, although each bursa can exist as a separate anatomic structure on ultrasound and magnetic resonance images. As its name implies, the subdeltoid bursa lies beneath the deltoid muscle and serves to cushion and facilitate sliding of the supraspinatus muscle as it passes under the acromion process. The bursa is subject to inflammation from a variety of causes with acute shoulder trauma and repetitive microtrauma being the most common (Table 48.1). If the inflammation of the bursa is not treated and the condition becomes chronic, calcification of the bursa with further functional disability may occur. The patient suffering from subdeltoid bursitis most frequently presents with the complaint of severe pain with any movement of the shoulder. Activities requiring abduction of the affected upper extremity are particularly painful, and the patient may complain bitterly of a knife-like catching sensation when using the shoulder upon first awakening. The patient will often be unable to sleep on the affected shoulder. The pain of subdeltoid bursitis is localized to the subdeltoid region and is often referred to the points of insertion of the deltoid muscle along the proximal one-third of the humerus.

Physical examination of the patient suffering from subdeltoid bursitis will reveal point tenderness at the acromion process as well as over the deltoid muscle. If there is significant inflammation, rubor and color may be present and the entire area may feel boggy or edematous to palpation. Passive elevation and rotation of the shoulder may exacerbate the pain of subdeltoid bursitis, and the patient will often exhibit a positive drop-arm test when the affected upper extremity is passively elevated with the elbow flexed and supported by the examiner and then suddenly released. The sudden release of the elevated extremity will cause the patient to cry out in pain. Active resisted abduction and lateral rotation of the affected extremity will also reproduce the patient’s pain, and a sudden release in resistance to active abduction will also markedly exacerbate the pain. If calcification has occurred, the examiner may appreciate crepitus with active range of motion of the affected shoulder.

Plain radiographs are indicated in all patients who present with shoulder pain to rule out occult bony pathology. 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 imaging of the affected area may also help confirm the diagnosis as well as delineate the presence of bursitis, calcific tendonitis, rotator cuff tendinopathy, or other shoulder pathology (Figs. 48.2 and 48.3).

Rarely, the inflamed bursa may become infected, and failure to diagnose and treat the acute infection can lead to dire consequences (Fig. 48.4).

The subdeltoid bursa lies primarily under the acromion, extending laterally between the deltoid muscle and supraspinatus muscle (see Fig. 48.1). The acromial arch covers the superior aspect of the shoulder joint and articulates with the clavicle at the acromioclavicular joint. The acromioclavicular joint is formed by the distal end of the clavicle and the anterior and medial aspect of the acromion. The strength of the joint is due to the dense coracoclavicular ligament, which attaches the bottom of the distal end of the clavicle to the coracoid process. The superior portion of the joint is covered by the superior acromioclavicular ligament, which attaches the distal clavicle to the upper surface of the acromion. The inferior portion of the joint is covered by the inferior acromioclavicular ligament, which attaches the inferior portion of the distal clavicle to the acromion.