Subscapularis Tendon Injection

Indications and Clinical Considerations

The musculotendinous unit of the shoulder joint is susceptible to developing tendinitis for several reasons. First, the joint is subjected to a wide range of motions that are often repetitive. Second, the space in which the musculotendinous unit functions is restricted by the coracoacromial arch, making impingement a likely possibility with extreme movements of the joint. Third, the blood supply to the musculotendinous unit is poor, making healing of microtrauma more difficult. All of these factors can contribute to tendinitis of 1 or more of the tendons of the shoulder joint. Calcium deposition around the tendon may occur if the inflammation continues, making subsequent treatment more difficult. Tendinitis of the musculotendinous unit of the shoulder frequently coexists with bursitis of the associated bursae of the shoulder joint, creating additional pain and functional disability.

The subscapularis tendon of the rotator cuff is particularly prone to developing tendinitis and associated bursitis. The onset of subscapularis tendinitis is usually acute, occurring after overuse or misuse of the shoulder joint. Inciting factors may include activities that require repeated adduction and medial rotation of the humerus, such as repetitive motions during assembly-line work. The pain of subscapularis tendinitis is constant, severe, and localized in the anterior deltoid and shoulder. Significant sleep disturbance is often reported. The patient may attempt to splint the inflamed subscapularis tendon by limiting medial rotation of the humerus. Patients with subscapularis tendinitis experience pain on resisted medial rotation and in active rotation and adduction. As mentioned earlier, bursitis often accompanies subscapularis tendinitis.

In addition to the previously described pain, patients with subscapularis tendinitis often experience a gradual decrease in functional ability with decreasing shoulder range of motion, making simple everyday tasks, such as hair combing, fastening a bra, or reaching overhead, difficult. With continued disuse, muscle wasting may occur and a frozen shoulder may develop.

Plain radiographs are indicated for all patients with shoulder pain. On the basis of 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 shoulder is indicated if a rotator cuff tear is suspected ( Fig. 35.1 ). The common sign seen on magnetic resonance imaging is believed to be suggestive of detachment of the subscapularis superficial fascia. The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

Clinically Relevant Anatomy

The subscapularis muscle is part of the rotator cuff. It provides shoulder joint stability along with the supraspinatus, infraspinatus, and teres minor muscle ( Fig. 35.2 ). The subscapularis muscle medially rotates the arm at the shoulder and is innervated by branches of the posterior cord of the brachial plexus and the upper and lower subscapular nerves. It has its origin in the subscapular fossa of the anterior scapula and inserts into the lesser tuberosity of the humerus. It is at this insertion that subscapularis tendinitis most commonly occurs ( Fig. 35.3 ). The subscapularis muscle and tendons are susceptible to trauma and to wear and tear from overuse and misuse, as mentioned previously.