Supraspinatus tendon calcification is thought to be due to the deposition of calcium hydroxyapatite crystals inside the supraspinatus tendon near the greater tuberosity of the humerus insertion point, and the calcium deposits in the supraspinatus tendon may be due to fibrosis, necrosis, tendon degeneration, or systemic non-degenerative causes [1, 8]. Supraspinatus tendon calcification may lead to tendon thickening which could lead to impingement under the acromion of the scapula, causing an impingement syndrome and severe pain upon humerus abduction .
Dr. Charles Neer in 1972 was the first person to describe subacromial impingement syndrome as a distinct clinical problem [2, 3, 7]. Neer described three stages of subacromial impingement: stage I impingement involves edema and hemorrhage of the subacromial-subdeltoid bursa and rotator cuff, and typically occurs in patients less than 25 years old; stage II impingement involves tendinopathy, such as fibrosis or tendinosis and calcific tendonitis, usually occurring in patients 25 to 40 years old; and stage III impingement typically involves surgical problems such as a rotator cuff tear and usually manifests in patients older than 40 years old [3, 7]. Bigliani and Levine have classified the causes of subacromial impingement syndrome as either intrinsic/intratendinous or extrinsic/extratendinous, and each group can be either a primary etiology that directly causes the impingement or a secondary etiology which is the result of another process such as instability or neurologic injury . Examples of intrinsic primary impingement are degenerative tendinopathy and calcification of the supraspinatus tendon that can lead to tendon thickening and impingement, the most likely etiology of our patient's supraspinatus tendon subacromial impingement and shoulder pain. Examples of extrinsic primary impingement include thickening of the coracoacromial ligament and a hook-shaped acromial scapular bone because a hook-shaped acromial bone is more likely to be present in patients with subacromial impingement syndrome and with patients with rotator cuff tears compared to patients who have a flat- or curve-shaped acromial bone . Emergency physicians should consider the diagnosis of supraspinatus tendon calcification with subacromial impingement syndrome in patients with shoulder pain to expedite urgent musculoskeletal specialist referral.
Radiologists have developed a full five-step ultrasonographic shoulder protocol that includes evaluation of the following structures: the long head of the biceps brachii tendon, the subscapularis tendon, the supraspinatus tendon and rotator interval with both static and dynamic evaluation for subacromial impingement, the acromioclavicular joint, and the infraspinatus and teres minor tendons with the posterior glenoid labrum . The performed ultrasonography is 79% sensitive and 88% specific for diagnosing supraspinatus tendon calcification and impingement syndrome using dynamic maneuvers such as humerus abduction . One of the key pitfalls for all musculoskeletal ultrasound examinations is anisotropy artifact that requires perpendicular insonation of tendons, ligaments, muscle, and nerves to observe the correct echotexture of the structures . Another pitfall is the improper positioning of the shoulder in visualizing the supraspinatus tendon. Radiologists have also developed specific sonographic signs of shoulder subacromial impingement such as pooling of fluid laterally to the subdeltoid portion of the subacromial-subdeltoid bursa while the humerus is abducted . Our patient had excellent internal and external rotation motor strength of her shoulder, and she stated no tenderness over her long head of the biceps tendon. A focused point-of-care emergency department bedside ultrasound examination was performed over her supraspinatus tendon, and this revealed calcification near the attachment to the greater tuberosity of the humerus; a dynamic bedside ultrasound long-axis evaluation of the patient's supraspinatus tendon showed elevation of the greater tuberosity cranially to the level of the acromion and impingement of the supraspinatus tendon underneath the acromion of the scapula when the patient actively abducted her left humerus. A complete evaluation of our patient's supraspinatus tendon was obstructed by the calcifications in her supraspinatus tendon, and which may have hidden a partial rotator cuff tear.
Musculoskeletal ultrasonography is an operator-dependent imaging modality, yet the inter-rater reliability of shoulder ultrasonography performed in the radiology department to detect supraspinatus tendon calcification among inexperienced radiologists (6 months of experience) versus experienced radiologists (6 years of experience) has been reported as kappa of 0.70 to 0.83, substantial agreement . No reliability data are currently available for emergency physicians in performing shoulder ultrasonographic examinations.
The initial treatment for supraspinatus tendon calcification with subacromial impingement syndrome is pain control and rest, as some patients will improve with conservative therapy . Many additional treatment modalities for supraspinatus tendon calcification with subacromial impingement syndrome are available including extracorporeal shock wave therapy, diathermy hyperthermia therapy, ultrasound-guided percutaneous needle aspiration and lavage, and more invasive arthroscopic and open orthopedic surgical procedures [13–20]. Patients with supraspinatus tendon calcification with subacromial impingement syndrome, who undergo ultrasound-guided percutaneous needle aspiration and lavage with corticosteroid injections into the subdeltoid-subacromial bursa have been found to have prompt shoulder function recovery after the procedure and better outcomes at 1-year follow-up; however, at five and ten years, the non-needle aspirated and lavage group reported outcomes similar to the needle aspirated and lavage group . Emergency department primary therapy will include oral pain medication, rest, provision of an arm sling, and urgent musculoskeletal specialist referral. Emergency department ultrasonography can help in preventing missed or delayed diagnosis of supraspinatus tendon calcification with subacromial impingement syndrome when the diagnosis is not always clear clinically, and bedside point-of-care ultrasound is of great utility in cases where physical examination maneuvers can be limited by pain and soft tissue swelling.