[Load shift-total hip replacement--numerical and clinical evaluation of a new concept of adaptive stem fixation]. / Die Load Shift-Hüftendoprothese--numerische und klinische Evaluation eines neuen Konzepts der adaptiven Stielverankerung.

AIM: The new load-shift fixation concept pursues the goal of an adaptive change of geometrical characteristics of the in-situ hip replacement. In this study a preclinical and clinical evaluation was performed. METHODS: By three-dimensional, dynamic finite element calculation the biomechanical properties of the prosthesis were analyzed in the early postoperative and long-term configuration. By clinical (20 +/- 10 months) and radiological (18 +/- 10 months) follow-up of a first series of implants (n = 20) the primary functional status of the prosthesis was examined in vivo. RESULTS: The preclinical results revealed that the metaphyseal micromotions are reduced significantly with the diaphyseal fit of the stem postoperatively. By absorption of a biodegradable element (spreader) integrated into the tip of the stem a change of stem geometry associated with loss of the diaphyseal fit occurs. This results in a complete shifting of load transmission into the metaphyseal area. In the clinical situation the postoperative Harris hip score averaged 92.9 +/- 10.5 points. Only in two patients did reversible episodes of thigh pain occur. The radiological analysis of bone remodeling phenomena pointed to a physiological load transmission. There was no evidence of loosening or osteolysis. On radiology, stem tapering could be demonstrated. CONCLUSION: On the basis of these promising preclinical and early clinical results the innovative load-shift prosthesis should now be further evaluated in prospective long-term studies.