Periprosthetic fractures may be more likely in cementless femoral stems with sharp edges

Many contour designs have been developed to improve the femoral stem in cementless total hip arthroplasty.

To assess the initial interfacial micromotion and stress distribution.

The prosthesis-bone interfacial micromotions and stress distributions of four commonly used femoral stems were assessed by finite element simulation: Alloclassic, Ribbed Anatomic, VerSys, and Secur-Fit. The proximal interfacial micromotions and stress distributions were calculated under the loading conditions of stair climbing. Three-dimensional micromotions were calculated in three proximal sections distal to the osteotomy level with 400 mm between each section. Medial, anterior, lateral and posterior points in each section were selected for calculations.

The micromotions were <100 microm at all the selected points. Significant stress was detected along the sharp corners and ribs of the Alloclassic and Ribbed Anatomic stems, respectively.

Significant stresses are associated with the stems with sharp edges.