Design and application of combined hip-knee intramedullary joint replacements

Cases in which there is a total hip arthroplasty and a stemmed total knee a rthroplasty in the same femur, with loosening of 1 or both components, with serious endosteal bone loss or even a fracture between the stems present a difficult reconstruction problem. We describe a reconstruction using a com bined hip and stemmed knee, designed so that they could be rigidly connecte d during the surgical procedure. The advantages of this implant design are that the entire femur with its muscle attachments is preserved, and the inh erent stability allows for immediate weight bearing. To determine the viabi lity of the connection between the hip and the knee, a stress analysis was carried out using finite element analysis. Guidelines were thus provided fo r the required metal and cement thicknesses. Three case examples are presen ted with an average follow-up of 3 years. It was shown that the combined hi p-knee implant could provide successful results for these difficult reconst ructive problems in appropriately selected cases.