Stability of femoral neck fracture. Roentgen stereophotogrammetry of 29 hook-pinned fractures.

The stability of hook-pin fixation during weight bearing was studied in 29 femoral neck fractures using roentgen stereophotogrammetric analysis. Twenty-three fractures became stable within 1 to 9 months, whereas redisplacement or continuing movement of the fracture occurred in 6 cases. Displaced fractures shortened about 7 mm more than undisplaced ones before healing. The rotations of the femoral heads were greatest in the forward/backward direction, followed by varus-valgus tilting in both fracture groups. Rotation about the longitudinal axis was recorded in the displaced fractures, mainly as a retroversion, whereas no rotation occurred about this axis in the undisplaced fractures. Healing after 6 months, intermediate fracture fragments, and a decreased Pauwels' angle seemed to imply increased fracture compression or rotatory instability. Fractures that subsequently developed healing complications displayed an increased distal displacement of the femoral head during the first postoperative month.