Implant-related fractures of the femur following hip fracture surgery

Background: Most hip fractures are treated surgically, with use of either internal fixation or prosthetic replacement of the femoral head. The presence of these implants increases the risk of a later femoral fracture in susceptible osteoporotic patients. The purpose of this study was to analyze the incidence of and risk factors for implant-related fractures of the femur after previous hip fracture surgery. Methods: Over a ten-year period from January 1988 to December 1997, 6230 patients (median age, eighty-two years; male:female ratio, 1247:4983) who sustained a total of 6696 hip fractures were admitted to the Edinburgh Orthopaedic Trauma Unit. Demographic information on the patients and details of the original treatment of the hip fracture were prospectively coded and entered into a trauma database. All subsequent readmissions due to a femoral fracture related to the implant were prospectively audited and extracted for the purposes of this study. Results: One hundred and forty-one patients sustained an ipsilateral fracture of the femur at a median of twenty-four weeks following the original hip fracture surgery. Survivorship analysis of the hip fracture population revealed an overall rate of subsequent femoral fracture of 2.9% at five years, which increased to 5.1% at ten years. The median age and gender distribution of the patients who sustained a subsequent femoral fracture were similar to those of the hip fracture population as a whole. Two-thirds of the fractures propagated from the tip of the implant. Analysis of the subsequent fractures according to the type of implant used to treat the original fracture revealed considerable differences in incidence. The incidence was relatively high in the patients initially treated with a Gamma nail (18.74 fractures per 1000 person-years) or a cementless hemiarthroplasty (11.72 per 1000 person-years) and was relatively low in those treated with a compression hip screw (4.46 per 1.000 person-years), cannulated screws (4.50 per 1000 person-years), or a primary arthroplasty with cement (6.2 per 1000 person-years). The highest incidence of fracture was seen in the patients who had required an arthroplasty with cement as a revision procedure following failure of a primary implant (22.39 per 1000 person-years). Conclusions: Implant-related fractures following hip fracture surgery are more common than has previously been appreciated. The risk of later ipsilateral femoral fracture is increased by the use of a Gamma nail or a cementless hemiarthroplasty to treat the original hip fracture.