Do short-stemmed-prostheses induce periprosthetic fractures earlier than standard hip stems? A biomechanical ex-vivo study of two different stem designs.

INTRODUCTION: The causes of periprosthetic fractures of the femur due to the design of the prosthesis and the individual parameters of the patient are unexplored. By different anchorage techniques in cementless total hip arthroplasties, it is assumed that there are various load limits of the implant's bearing femur.
MATERIALS AND METHODS: In the present study, we compared a standard hip stem (cementless Spotorno) and a short-stemmed design (Mayo) by an artificial reproduction of periprosthetic fractures in 20 femur specimens.
RESULTS: The measured fracture loads showed an extensive range, with higher maximum loads in the standard stem group. The bone mineral density and the subsiding pattern of the standard stems showed a significant correlation to the incidence of the periprosthetic fractures. In the experimental setup, a slightly lower fracture resistance was shown for the short-stemmed prosthesis. Additionally, it was shown that donors with a higher body mass index had a significantly increased fracture risk.
CONCLUSIONS: Short-stemmed prostheses, especially the Mayo hip, do not constitute a higher fracture risk. In general, an increased body mass index among patients with a cementless hip stem is associated with an increased fracture risk, particularly at high load values, i.e., resulting from a step during stumbling. Taking into account the ascertained results, the danger of provoking a femoral periprosthetic fracture can be reduced.