Non-traumatic Shoulder Dislocation

A 42-year-old female with a past medical history significant for intravenous drug abuse presented to the emergency department complaining of a two-week history of worsening left shoulder pain. She denied any trauma to the shoulder but noted it had become increasingly difficult to move secondary to pain. On physical exam she was afebrile and the rest of her vital signs were within normal limits. Asymmetry was noted between the right and left shoulders and the left shoulder was warm, erythematous and tender to palpation. Her left arm was held in adduction and internal rotation, with extremely limited range of motion secondary to pain. We obtained a radiograph of the shoulder and laboratory tests that revealed an elevated white blood cell count of 12.9, erythrocyte sedimentation rate of 66 mm/hr and a C-reactive protein level of 5.4 mg/dl. Orthopedic surgery was then consulted. A needle tap of the left shoulder yielded 30 ml of purulent fluid. Lab cultures grew methicillin-resistant Staphylococcus aureus, and the patient was started on empiric intravenous vancomycin. In the operating room orthopedic surgery found that the patient had an extracapsular subdeltoid abscess. A review of the literature indicates this is a rare case of an extracapsular abscess causing marked radiographic evidence of dislocation in the shoulder. There are case reports of septic arthritis in the shoulder represented with radiographic evidence of dislocation.1 Atlanto-axial subluxation secondary to retropharyngeal abscess is described; however, there are no reports of similar dislocations outside of the axial skeleton.2 This case reinforces the point that every dislocation is not secondary to trauma. It also emphasizes the importance of a detailed history and physical examination to discern the causes of pain, with corroboration of radiographic findings.