In vitro analysis of periprosthetic strains following total knee arthroplasty

Clinical case studies have disclosed certain risk factors associated with periprosthetic fracture in elderly patients. How the mechanical strength of the distal femur is changed by total knee arthroplasty (TKA) has not been elucidated. Using elderly cadaveric femora, this study evaluated both periprosthetic strains and associated fracture patterns arising from an in vitro simulation of a fall onto the distal femur. The data showed a significant increase in anterior and posterior mechanical strain following TKA. Neither stemless nor stemmed versions of two cemented Howmedica prostheses (Rutherford, NJ) reduced distal femur strains to baseline values. However, neither produced a disproportionate frequency of periprosthetic fractures. Although not formally evaluated herein, bone geometry/density may contribute more profoundly to the occurrence of periprosthetic fracture than the implants tested.