Design and validation of a machine for reproducible precision insertion offemoral hip prostheses for preclinical testing

Preclinical testing of orthopaedic implants is becoming increasingly import ant to eliminate inferior designs before animal experiments or clinical tri als are begun. Preclinical tests call include both laboratory bench tests a nd computational modeling. One problem with bench tests is that variability in prosthesis insertion can significantly influence the failure rate; this makes comparison of prostheses more difficult. To solve this problem an in sertion method is required that is both accurate and reproducible. In this work, a general approach to the insertion of hip prostheses into femoral bo nes is proposed based on physically replicating an insertion path determine d using computer animation. As a first step, the seared prosthesis position is determined from templates and femur radiographs. Three-dimensional imag es of the prosthesis and bone are then imported into computer animation sof tware and an insertion path in the coronal plane is determine. The insertio n path is used to determine the profile of a cam. By attaching the prosthes is to a carriage, which is pneumatically moved along this cam, the required insertion motion of the prosthesis in the coronal plane can be achieved. T his paper describes the design and validation of the insertion machine. For the validation study, a nonsymmetric hip prosthesis design (Lubinus SPII; Waldemar Link, Germany) is used. It is shown that the insertion machine has sufficient accuracy and reproducibility for preclinical mechanical testing . [S0148-0731(00)00602-6].