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 microm 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.

Relevance: The data set for initial stability justifies the clinical use of a custom-made femoral stem in primary hip replacement. An individualized stem fit into the endosteal cortical bone decrease micromotion.