A New Model of Bone-Conserving Cementless Hip Prosthesis Made of High-Tech Materials: Kobelco H-5

Abstract

A new model of bone-conserving cementless hip prosthesis was developed aiming at reducing the wear rate of the ultrahigh-molecular-weight polyethylene (UHMWPE) socket, minimizing the stress-shielding effect on the femur, accelerating the initial bonding between the bone and prosthesis components, and preventing third body wear. The stem and the socket back are made of vanadium-free titanium alloy (Ti-6A1-2Nb-lTa); a zirconia femoral head with a diameter of 22 mm is articulated against a UHMWPE socket, and the titanium plasma spray coating in combination with a bottom coating of apatite-wollastonite containing glass-ceramic (AW-GC) is applied over the whole surface of the socket back and a small area of the proximal part of the stem. Animal experiments using canine hip joints revealed that the AW-GC bottom-coated socket and stem developed significantly earlier bone-bonding than those with titanium plasma spray coating alone. Ninety-six osteoarthritic hip joints of 76 female and 12 male patients aged between 37 and 79 years underwent total hip replacement by the use of this cementless hip prosthesis during the period between 1992 and 1995. There were 4 cases of early postoperative dislocation and 1 case of thigh pain, but no cases of loosening of the prosthesis. Radiologically, bone ingrowth into the bottom-coated surface was satisfactory in 95% of cases at the latest follow-up at an average of 4 years postoperatively.