Primary stability in cementless femoral stems:: custom-made versus conventional femoral prosthesis

Objective. To compare a custom-made femoral stem with a conventional cementless stem for initial stability in human femurs. Design. The bone-femoral prosthesis interface motion was measured in vitro using displacement transducers. Combined axial and torsional loads simulating single-leg stance, loading were applied. Background. The custom-made prosthesis is a cementless femoral stem fabricated from the patient's CT- reconstruction. To justify its clinical use its design has to be tested regarding his primary stability. Methods. Seven pairs of human cadaveric femurs were used for testing the custom-made prosthesis versus a conventional cementless stem. Subsidence, rotation and interface motion were measured with load cycles up to 2000 N. Results. The critical interface motion of 150 pm for the cementless prosthesis was not exceed for both types of prosthesis. The custom-made prosthesis enlarged in its metaphyseal part showed a decrease of dynamic micromotions and rotation behavior in the proximal region compared to the Alloclassic prosthesis stem. Conclusions. The initial stability of the custom-made femoral stem was comparable to that of a conventional femoral stem.