Fracture of the neck of the femur after surface arthroplasty of the hip.

BACKGROUND:
There are two main modes of failure of the femur following surface arthroplasty of the hip: femoral neck fracture and aseptic loosening. The purpose of the present study was to present our experience with femoral neck fractures that occurred after metal-on-metal hybrid surface arthroplasty and to assess their cause.

METHODS:
A series of 600 metal-on-metal surface arthroplasties was performed between late 1996 and early 2003. Failures that occurred during this period were assessed radiographically and with implant retrieval analysis to determine their cause.

RESULTS:
Five femoral neck fractures occurred in this series (prevalence, 0.83%). Four of the five fractures occurred at the component-neck junction within the first five months (average, three months) after surgery. All five fractures were associated with a traumatic episode, but all five also were associated with structural and/or technical risk factors, which we believe weakened the femoral neck. The most important technical deficiency that contributed to three of the five fractures was the failure to cover all of the reamed bone with the component.

CONCLUSIONS:
It is important to avoid or at least minimize notching of the femoral neck by performing the cylindrical reaming at the recommended angle of 140 degrees and to stop reaming before the reamer touches the lateral cortex. Osteophytes should be removed judiciously only if there is notable impingement when the hip is flexed to 90 degrees and internally rotated. We believe that understanding the factors that contribute to femoral neck fracture after surface arthroplasty may reduce the prevalence of this mode of failure.