Design and application of combined hip-knee intramedullary joint replacements

Cases in which there is a total hip arthroplasty and a stemmed total knee arthroplasty 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 combined hip and stemmed knee, designed so that they could be rigidly connected during the surgical procedure. The advantages of this implant design are that the entire femur with its muscle attachments is preserved, and the inherent stability allows for immediate weight bearing. To determine the viability of the connection between the hip and the knee, a stress analysis was carried out using finite element analysis. Guidelines were thus provided for the required metal and cement thicknesses. Three case examples are presented with an average follow-up of 3 years. It was shown that the combined hip-knee implant could provide successful results for these difficult reconstructive problems in appropriately selected cases.