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.