Idiopathic hip instability. An unrecognized cause of coxa saltans in the adult.

The painful, snapping hip often presents a diagnostic dilemma having many potential etiologies. An understanding of the precise cause increases the potential for successful treatment. Five patients with no prior history of significant trauma were evaluated, all of whom had longstanding painful snapping in the groin and consistent symptoms of gait disturbance and increased pain in the provocative position of hip flexion, adduction, and internal rotation. Multiple prior tests and procedures had been nondiagnostic. Simple manual longitudinal traction under fluoroscopy showed subluxation with appearance of a vacuum sign in the symptomatic hip, whereas no such finding was observed on the asymptomatic side. This strongly suggests atraumatic hip instability as a previously unrecognized cause of the painful, snapping hip. The easily obtainable diagnostic traction radiograph is described.