Infraspinatus 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, which 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 infraspinatus tendon of the rotator cuff is particularly prone to developing tendinitis ( Fig. 34.1 ). The onset of infraspinatus tendinitis is usually acute, occurring after overuse or misuse of the shoulder joint. Inciting factors may include activities that require repeated abduction and lateral rotation of the humerus, such as installing brake pads during assembly-line work. The vigorous use of exercise equipment also has been implicated. The pain of infraspinatus tendinitis is constant, severe, and localized in the deltoid area. Significant sleep disturbance is often reported. The patient may attempt to splint the inflamed infraspinatus tendon by rotating the scapula anteriorly to remove tension from the tendon. Patients with infraspinatus tendinitis exhibit pain with lateral rotation of the humerus and on active abduction ( Fig. 34.2 ).

In addition to the previously described pain, patients with infraspinatus 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 and/or ultrasound imaging of the shoulder is indicated if a rotator cuff tear is suspected. The injection technique presented later serves as both a diagnostic and a therapeutic maneuver.

Clinically Relevant Anatomy

The infraspinatus muscle is part of the rotator cuff. It provides shoulder joint stability and, along with the teres minor muscle, externally rotates the arm at the shoulder. It is innervated by the suprascapular nerve, has its origin in the infraspinatus fossa of the scapula, and inserts into the middle facet of the greater tuberosity of the humerus. It is at this insertion that infraspinatus tendinitis most commonly occurs ( Fig. 34.3 ). The infraspinatus muscle and tendons are susceptible to trauma and to wear and tear from overuse and misuse, as mentioned previously.