RESUMO
BACKGROUND: Acromioclavicular joint (ACJ) cysts are uncommon causes of shoulder pain. Type 1 ACJ cysts are limited to the ACJ and form in the presence of intact rotator cuff musculature, while type 2 cysts form secondary to biomechanical instability following rotator cuff tear or rupture. CASE PRESENTATION: A 36-year-old overweight male with history of chronic left grade 2 (Rockwood classification) ACJ separation presented with intermittent pain at the distal superoanterior left clavicle. Physical examination revealed small step off at the ACJ and multiple subcutaneous cysts surrounding the ACJ. Ultrasound examination revealed a mild separation of the left ACJ, mild distension of the joint capsule, and a small, well-circumscribed, compressible hypo-echoic cyst overlying the clavicle. Palpation of the cyst against the clavicle reproduced the patient's symptoms of intermittent pain. He opted for ultrasound-guided aspiration and subsequently had full resolution of his symptoms. DISCUSSION: Musculoskeletal ultrasound is useful for diagnosis and management of refractory musculoskeletal conditions that are commonly misdiagnosed on physical examination and translucent to radiographic imaging. Musculoskeletal ultrasound allowed us to exclude rotator cuff pathology, identify ACJ cyst as the pain generator, classify it as a type 1 ACJ cyst, and aid in needle guidance for successful aspiration leading to full resolution of our patient's pain.