Endoscopy of the femoral canal in revision arthroplasty of the hip - A newmethod for improving the operative technique and analysis of implant failure

Femoral endoscopy using a special endoscope was performed in 28 revision ar throplasties with the aim of improving the operative technique and to analy ze implant failure. Before clinical application, the method was used to ana lyze the implant bed in clinically and radiographically well-fixed prosthes es in autopsy cases without implant failure. Initially, it was performed on 4 experimental implantations of newly designed revision devices into cadav er femurs to obtain additional information concerning the design rationale of implants and instruments for revision surgery. During revision surgery, the new endoscope showed that controlled removal of the cement and granulom atous tissue was possible while avoiding cortical windows or transfemoral a pproaches. Under visual control, preparation of the new implant bed was les s hazardous and more efficient, resulting in good preservation of bone stoc k and reduced exposure to X-rays. Analysis of the implant bed in failed hip endoprostheses revealed cracks or fractures of the cement mantle in 21 of 23 cemented components. There were two different types of cracks: longitudi nal and transverse, which were mostly connected and invisible to X-ray anal ysis. Cement defects, thin cement mantles, or the proximal border of the ce ment mantle were found to be places where cracks originated. Granulomatous tissue was noted to protrude into the cement fissures and cracks. In autops y cases, cement cracks were also found in clinically asymptomatic and radio graphically well-fixed prostheses. These cracks were observed to be mainly oriented in the longitudinal direction, similar to those seen in the revisi on cases. Early signs of debonding became obvious even without lesions in t he cement mantle. In experimental implantations of newly designed stems, th e efficacy of the different instruments and the fit of the implant could be evaluated by endoscopic control inside the intramedullary canal. Further, it was possible to directly visualize the shape and condition of the primar y implant bed after removal of the implant. Femoral endoscopy improved the surgical technique in revision arthroplasty. In addition, it is a very usef ul tool for the analysis of the implant bed in clinical and autopsy cases a s well as in experimental implantations.