Smooth uncemented femoral stems do not provide torsional stability of femurs with cortical defects

Revision total hip arthroplasty (THA) can be complicated by fracture secondary to operative penetration of the cortex or by thinning of the cortex from eccentric reaming which create stress risers in the femoral shaft and significantly weaken the bone. In the presence of such known defects in the femur, the use of a long-stemmed prosthesis is indicated. The effect of various stem lengths in bypassing cortical defects is studied. Results indicate that the introduction of a 50% defect reduces the torsional strength of test bones to only 46% as compared to intact bone. The introduction of a cemented prosthesis improved strength ratios to a range of 60% to 80% of intact bone for different bypass lengths.