Evaluation of the patient with the painful shoulder can be difficult in the emergency department. The septic glenohumeral joint, while less common than infections of the knee and hip (fewer than 10 percent of cases of septic arthritis), can be often difficult to diagnose.1 Among the myriad musculoskeletal pathologies that can present with a painful shoulder, detection of a septic glenohumeral joint is critical because delay to diagnosis has been shown to allow for irreversible cartilage damage leading to functional impairment. An infected glenohumeral joint can be easily missed because classic signs and symptoms are often not present, plain film imaging does not detect a joint effusion, and classic laboratory tests are insensitive and nonspecific for septic joints.2 Also, even when a septic glenohumeral joint is suspected clinically, landmark-based aspirations can be unsuccessful. Even in the hands of experienced orthopedic surgeons, the failure rates are up to 30 percent.3 Point-of-care ultrasound allows for both an accurate method to detect the presence of a glenohumeral joint effusion and also a simplified method for reliable joint aspiration.4
1. Evaluate the nonaffected glenohumeral joint.
To determine the patient’s normal anatomy, obtain clear ultrasound views of the patient’s nonaffected/contralateral glenohumeral joint. For simplicity, I recommend evaluation of the posterior glenohumeral joint space (the anterior approach can be more challenging). Place the ultrasound system in front of the patient and palpate the patient’s scapular spine to identify basic surface anatomy (see Figure 1). The low-frequency (5 to 1 MHz) curvilinear transducer should be placed parallel to the bed, probe marker pointing to the patient’s left and positioned just below the scapular spine. Slowly slide the transducer toward the humeral head. A clear image of the humeral head, glenoid, infraspinatus tendon, and glenohumeral joint space will be obtained on the ultrasound screen (see Figure 2). Gentle passive or active internal and external rotation of the patient’s forearm can help novice sonographers recognize the relevant anatomy.
2. Evaluate the affected glenohumeral joint.
Using the same technique as detailed above, examine the affected glenohumeral joint (see Figure 3). A joint effusion will be an anechoic effusion just above the humeral head and under the synovial membrane. Exact measurements of the effusion are not useful, and the patient’s clinical evaluation, in conjunction with the ultrasound examination, should help determine the need for synovial fluid analysis.