[3D-based production of hip joints: the Aldinger system]

Total hip replacement is regarded as one of the most successful surgical procedures. However, aseptic loosening of the foreign material still remains a great problem with endoprostheses. Bone cement, a material for filling and fitting, allows a solution to the problem in old people, but for younger people surgeons have looked for alternatives without cement. In fixation hip stems without form-filling cement, the greatest difficulty with standardized stems was the lack of adequate fit into the individual bone cavity. The new approach, the Aldinger custom-made hip stem, is based on a series of computer tomographical X-rays. This free-styled prosthesis stem is derived directly from the 3D-reconstruction of the inner contour of the femur without any parametrization of the cross-sections. A simulation of the implantation procedure is performed to ensure the implantability of the prosthesis and to give the surgeon some useful hints for the individual operation. In addition to the excellent form-fit to the individual bone, this prosthesis has further advantages such as the special disk-like surface structure, allowing good stress transfer to the bone, and the possibility of positioning the artificial head freely in three dimensions according to the requirements of therapy. Seven years of experience with this new system demonstrate that "computer-fit" can be a successful alternative to "cement-fit," especially in younger patients with a life expectancy of more than 10-15 years.