Differentiating subluxation from developmental dislocation of the hip.

The radiological and clinical picture of a developmental hip dislocation and a severe subluxation are identical. According to Leveuf and Wiberg the diagnosis can only be made by arthrography. The differential diagnosis is critical, as treatment differs dependent on the diagnosis. In this study, the diagnosis of subluxation was based on a plain radiograph of the pelvis. A radiograph of the pelvis with the hips abducted at least 45° and internally rotated (AIR view) was used to differentiate these two entities. In subluxations, the femoral head will relocate into the acetabulum with perfect or near perfect reconstitution of the Shenton's line. It will fail to do so in true dislocations. Five patients, mean age 14.6 months (range 9 to 20 months), presented with delayed diagnosis of hip dysplasia. The examination revealed minimal or no limitation of hip abduction, a leg length discrepancy, and a Trendelenburg gait in the three walking age girls. The radiograph suggested a hip dislocation. The diagnosis of hip subluxation was based on the relocation of the femoral head with the abduction/internal rotation radiograph. All were successfully treated with an Ilfeld abduction splint. None had examination with general anesthesia, arthrograms, traction or immobilization in spica cast. Avoiding over diagnosis of hip dislocation in cases of subluxation is important. This is necessary to prevent overtreatment and to accurately assess the results of treatment. The abduction/internal rotation view may achieve this goal while avoiding diagnostic and therapeutic procedures, such as arthrograms, cast immobilization and surgery.