Factors influencing postoperative movement in displaced femoral neck fractures: evaluation by conventional radiography and stereoradiography.

Postoperative movement in 46 displaced femoral neck fractures was studied using roentgen stereophotogrammetric analysis (RSA). Thirty-four fractures became stable, all within 1 year. Measurements on pre- and postreduction radiographs and scintimetry were performed to evaluate factors of importance in healing, redisplacement, and nonunion. Thirty-three fractures were treated with two hook-pins with (7 cases) or without (26 cases) a plate, and 13 were treated with two cancellous screws. Presence of intermediate fracture fragments and fixation with two screws implied increased movement of the femoral head center during the postoperative period. Remaining ad latus displacement on the anteroposterior or lateral view after reduction of more than 1 mm and low scintimetric uptake implied increased risk of redisplacement or pseudarthrosis. Increased displacement of the femoral head center during the first postoperative month was recorded in fractures that did not heal. The magnitude of the femoral head rotations did not differ between the implants, but smaller screw axis rotations were noted in fractures that subsequently healed. In most hips fixated with screws, the instant center of femoral head rotation went through the femoral head or neck, whereas hook-pin fixation more commonly was associated with screw axis position within or close to the trochanteric region, suggesting a more durable fixation in the femoral head of this device.