Total hip joint replacement using a CoCrMo metal-metal sliding pairing.

Late loosening in total hip replacement is explained by a foreign body reaction of the connective tissue along the bone-implant interface due to polyethylene debris. In contrast, metal-metal prostheses of the McKee type implanted in the sixties, may still work perfectly today without any signs of osteolysis along the bone-cement interface, proving that metal-metal pairing is superior to prostheses with polyethylene cups and proving also that cement anchorage may be adequate for fixation. A new metal-metal total hip joint is presented, that has been implanted 90 times between 1988 and 1991.

Joint replacement components made of hot-forged and surface-treated Ti-6Al-7Nb alloy.

We have developed a titanium-aluminium alloy with the inert alloying element niobium. The optimal composition was found to be Ti-6Al-7Nb (Protasul-100). This custom-made alloy designed for implants shows the same alpha/beta structure as Ti-6Al-4V and exhibits equally good mechanical properties. The corrosion resistance of Ti-6Al-7Nb in sodium chloride solution is equivalent to that of pure titanium and Ti-6Al-4V. This is due to a very dense and stable passive layer. Highly stressed anchorage stems of different hip prosthesis designs have been made from hot-forged Ti-6Al-7Nb. The polished surfaces of hip, knee and wrist joints made of Ti-6Al-7Nb and articulating against polyethylene are surface-treated by means of a very hard and 3-5 microns thick titanium nitride coating (Tribosul-TiN) or by oxygen diffusion hardening (Tribosul-ODH) to a depth of 30 microns.

Total Hip Joint Replacement Using a CoCrMo Metal-Metal-Sliding Pairing.

Late loosening in total-hip replacement is explained by a foreign body reaction of the connective tissue along the bone-implant interface due to polyethylene debris. In contrast, metal-metal prostheses of the McKee type implanted in the sixties, may still work perfectly today without any signs of osteolysis along the bone-cement interface, providing that metal-metal pairing is superior to prostheses with polyethylene cups and providing also that cement anchorage may be adequate for fixation. A new metal-metal total hip joint is presented, that has been implanted 62 times between 1988 and 1990. Key words: total hip replacement, metal-metal pairing.

Biologic fixation of a press-fit titanium hip joint endoprosthesis.

The rectangular cross section of a straight-stem prosthesis makes a primary stable, rotation-safe fixation possible that is independent of the individual form of the femur. Due to the curvature of the femur, a three-dimensional large-area anchorage is achieved along the entire prosthesis length in the corticalis as well as in the spongiosa. The titanium-aluminum-niobium alloy is extremely biocompatible and enables the fast ongrowth of newly formed osseous tissue to act as secondary stabilization. Pathohistologic examinations on the prostheses of deceased patients show that this osseointegration leads to a complete osseous ingrowth of the implant. The average surface roughness of 3-5 microns, with which the entire prosthesis length is structured, supports this osseointegration. This microroughness is, therefore, totally sufficient for the primary and secondary stabilization of the implant. The osseous fixation of the prosthesis over the entire stem length guarantees a physiologic and functional load transmission to the surrounding femoral bone, thus avoiding stress shielding. The combination of a ceramic ball head with a polyethylene cup results in less wear than is the case with the customary metal-polyethylene combination and, thus, prolongs the life span of artificial hip joints. Good results in the future can only be expected in osseointegrated implants with minimal wear of the synthetic material.