Zusammenfassung
Studienziel: Das neue Load Shift-Fixationskonzept, das durch die adaptive Veränderung geometrischer Eigenschaften der in situ befindlichen Hüftendoprothese charakterisiert ist, wurde präklinisch sowie klinisch evaluiert. Methode: Durch dreidimensionale, dynamische Finite Elemente-Modellierung wurden die biomechanischen Eigenschaften der Prothese in der postoperativen Früh- sowie Langzeitkonfiguration analysiert. Durch klinisches und radiologisches Follow-up einer ersten Implantatserie (n = 20) nach 20 ± 10 bzw. 18 ± 10 Monaten wurde die primäre Funktionsfähigkeit der Prothese in vivo überprüft. Ergebnisse: Im präklinischen Studienteil zeigte sich, dass die metaphysären Mikrobewegungen postoperativ bei diaphysärem Fit der Stielkomponente signifikant reduziert werden. Durch Resorption eines in die Stielspitze integrierten bioresorbierbaren Elements (Spreizer) und die daraus resultierende Änderung der Stielgeometrie kommt es im Verlauf zur Aufhebung des diaphysären Fits und damit zur vollständigen Verlagerung der Lasteinleitung (Load Shift) in den metaphysären Bereich. Im klinischen Studienteil erreichte der postoperative Harris Hip Score 92,9 ± 10,5 Punkte. Lediglich bei zwei Patienten traten vollständig reversible Episoden von Oberschenkelschmerzen auf. Die radiologische Analyse der Bone Remodeling-Phänomene ließ auf eine physiologische Lasteinleitung schließen. Es ergaben sich keine Zeichen der Lockerung oder osteolytischer Knochenresorption. Radiologisch konnte die eingetretene Stielverjüngung nachgewiesen werden. Schlussfolgerung: Die innovative Load Shift-Hüftendoprothese sollte aufgrund vielversprechender präklinischer und früher klinischer Ergebnisse in größeren prospektiven Langzeitstudien weiter evaluiert werden.
Abstract
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.
Schlüsselwörter
Zementfreie Hüftendoprothese - modulare Implantate - Stress Shielding - Finite Elemente - Bone Remodeling
Key words
Cementless total hip replacement - modular implants - stress shielding - finite elements - bone remodeling
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Dr. med. Frank Lampe
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