[Biomechanical aspects of load-bearing capacity after total endoprosthesis replacement of the hip joint. An evaluation of current knowledge and review of the literature].

PURPOSE: Purpose of the study was to summarize the current scientific knowledge of the interaction between rehabilitative procedures and the periprosthetic bone remodeling processes in the early postoperative phase of total hip arthroplasties.
METHOD: In a comprehensive review of the international literature we analysed the interdependence between osseointegration, primary implant stability, relative micromotion of implant versus bone, and joint loading forces during mobilisation or physiotherapy. Accordingly, guidelines for the rehabilitation of cemented as well as cementless hip arthroplasties were established in order to eliminate factors disturbing prosthetic integration and hence provide for the best long-term stability of the implanted prosthesis possible.
RESULTS: Osseointegration of cementless implants is impossible if relative micromotions exceed > 150 microns. Furthermore, torsional stresses (i.e. alternate climbing of stairs, rising from seated position without arm support) will destabilize uncemented femoral shaft implants. Cemented prostheses may be loaded with full body weight. Uncemented implants should be loaded only partially for at least 6 weeks. Loadings of the hip joint with more than twice the body-weight (i.e. walking without crutches, physical exercise against high resistances or long levers) are to be avoided for 3 months. The transition from the three-points walking to the two-points walking technique depends particularly on the conditions of the muscles stabilizing the hip joint.
CONCLUSION: The rehabilitation of patients after total hip arthroplasty has to be brought into line with the changed biomechanical situation, the particulars of the implants and the individual requirements of the patients.