The increasing incidence of periprosthetic femoral fractures (PFF) after total hip arthroplasty presents growing concerns due to challenges in treatment and increased mortality. PFF are often observed when the prosthesis is implanted in varus, especially with blade-type stems. To help elucidate its impact on the PFF risk, the specific research question is: What is the effect of misalignment of a blade-type stem (resulting in down-sized prosthesis) on 1)the distribution and magnitude of cortical stresses and 2)implant-bone micromotion. We developed two finite element models consisting of an average female femur implanted within a generic blade-type stem prosthesis, (i)in neutral alignment, and (ii)oriented in 5° of varus, coupled with corresponding down-sizing of the prosthesis. Each model consisted of 1.1million elements, while the average mesh length at the implant-bone interface was 0.4mm. Elastic moduli of 15GPa(cortex), 150MPa(trabecular bone), and 121GPa(implant), and Poisson's ratio of 0.3 were assumed. The distal end was fixed and the interface was defined as a surface-to-surface contact with friction coefficients (dynamic 0.3; static 0.4). Walking and stair-climbing were simulated by loading the joint contact and muscle forces after scaling to the subjects’ body weight. The peak von Mises stress and the average stress within the surface having 1cm diameter and the center at where the peak stress occurred at each contacting area, the interfacial micromotion along medial, lateral side were analyzed. For statistical analysis, two-tailed t-test was performed between the neutral and varus cases over four loading cycles with significance level of p<0.05.INTRODUCTION
METHOD
