Subcapital fractures complicating pertrochanteric fractures treated by internal fixation

Abstract

Three female patients over 70 years of age were treated surgically for a pertrochanteric fracture of the hip. In 2 of them internal fixation was achieved by way of a dynamic screw-plate assembly while intramedullary Ender nails were used in the 3rd patient. All 3 patients were readmitted a couple of months after discharge from hospital due to a new subcapital fracture that occurred ipsilaterally through the tip of the fixation device after the primary pertrochanteric fracture had already reached a solid union. None of these cases resulted from inadequate placement of the fixation device: 1. The neck-shaft angle had been correctly restored. 2. The metals were centrally positioned in the femoral head and neck as documented in both the AP and axial views. 3. The distance between the subchondral bone and the tip of the device was consistently less than 10 mm. Neither X-rays nor histology showed any evidence of AVN or other pathologic processes (other than osteoporosis).

This rare complication which requires immediate reoperation with removal of the metals and some form of arthroplasty of the hip joint has been reported 27 times following different types of internal fixation methods. The etiology of these interesting cases is still unclear and multiple theories have been proposed to explain this phenomenon. Among these the most popular is that of a technical error consisting of inserting the nail not deeply enough into the subchondral bone thus exposing the cancellous femoral neck to strong forces that tend to deform the femoral head into a varus position, with the metallic tip acting as a stress riser. Our own observations hereby presented challenge this theory as we have found no evidence to support it. The fact that perfect positioning of the device is not enough to guarantee a successful outcome raises the issue of whether it is justified to consider a second operative intervention for early removal of the metals as a preventive measure.