STRESS SHIELDING AS IT RELATES TO PROXIMALLY POROUS-COATED FEMORAL STEMS OF VARYING CONFIGURATIONS - A 10-YEAR CEMENTLESS TOTAL HIP-REPLACEMENT STUDY

A cementless, straight-stemmed, proximally porous coated, femoral comp onent was developed to over-come the problems of proximal femoral stre ss shielding and calcar resorption seen with fully porous coated total hip devices. Proportional stem sizes and a horizontally angled collar were designed to improve proximal femoral loading mechanics and minim ize thigh pain. Four specific implant types were studied; each having a slight variation of collar geometry, porous coating or material used . Type I, II, and III stems were made of Co-Cr-Mo alloy, while Type IV stems were made of TiAl6V4 alloy. Type I stems had a calcar collar an gled at 45-degrees from the straight stemmed body, while Type II, III, and IV stems had 32-degrees angled collars. Type I and II stems had c omplete, proximal one third porous coating; while Type III and IV stem s had laterally-tapered, proximal one third porous coating, with no co ating on the medial side of the component. The results of 49 primary t otal hip replacements using these varying geometries from 1983 to 1989 demonstrate that removing proximal porous coating from the medial sid e of the implant in conjunction with a 32-degrees collar angle and a s traight-stemmed, TiAl6V4 alloy component improves bone loading, minimi zes stress shielding of the calcar and reduces the incidence of thigh pain over other design configurations.