An in vitro comparison of surface strain patterns in cementless femoral arthroplasty

A hypothesis associated with applications of contemporary cementless pressfit femoral stem designs is that stems which uniformly fit the proximal medullary canal of the femur will result in load transmission patterns which approximate those of a normal femur. The objective of this study was to examine biomechanical variables such as implant/bone fit and the associated load transmission patterns of the proximal femur before and after cementless femoral arthroplasty utilizing the technique of reflection photoelasticity. Harris-Galante (Zimmer), S-ROM (Joint Medical Products), and INFINITY prostheses were implanted in cadaveric femora and subjected to conditions simulating single-limb stance loading. The bone/implant constructs were later transversely sectioned and fit was analyzed. Insertion and subsequent loading of both prothesis types resulted in a large decrease in strain in the medial calcar of each intact control. Visual examination of the Harris-Galante prosthesis under polarized light revealed patchy, localized areas of high strain along the proximal region. In contrast, the modular prostheses displayed more uniform and diffuse strain profiles with minimal regions of localized strain. In all cases, the surface strain patterns produced by cementless femoral arthroplasty correlated with the pattern and degree of implant/bone fit.