Acute atraumatic hip dislocation in an adult with rheumatoid arthritis.

There are no reports of atraumatic hip subluxation and dislocation in the adult patient with rheumatoid arthritis (RA). This rare phenomenon is most prevalent in patients with congenital hip dislocation, von Recklinghausen disease, tumor infiltration, connective tissue disorders, and juvenile rheumatoid arthritis. We report an acute atraumatic dislocation of the hip in an adult patient with RA. We believe that two factors contributed to the patient's atraumatic dislocation: a shallow but appropriately positioned acetabulum and erosive RA with substantiate panus formation. Similar to previous reports, there was a rent or capsular defect that may have contributed to the mechanism of dislocation. Physicians should be aware that, although rare, a de novo atraumatic hip dislocation is a possibility in a patient with a long-standing history of RA and hip pain. Distinguishing features of this case include the acuteness of the dislocation, the absence of previous symptoms, and adult-onset RA.