J R Britton1, L A Walsh, P J Prendergast. 1. Centre for Bioengineering, Department of Mechanical Engineering, Trinity College, Dublin 2, Ireland.
Abstract
OBJECTIVE: This study examines the effect of including muscle forces in fatigue tests of cemented total hip arthroplasty reconstructions. DESIGN: An experimental device capable of applying the joint reaction force, the abductor force, the vastus lateralis force, and the tensor fasciae latae force to the implanted femur is described. BACKGROUND: Current in vitro fatigue tests of cemented total hip arthroplasty reconstructions do not apply physiological muscle loads. Experimental and numerical studies report significant differences in stresses obtained in the cement mantle depending on the loads applied. The differing stresses may alter the outcome of an in vitro test. METHODS: Ten femoral components were reproducibly implanted into proximal composite femurs. Five of these femoral components were tested using a loadprofile which included muscle loading, five were tested without muscle loading. The migration of each femoral component was monitored continuously during dynamic fatigue tests. RESULTS: Clinically comparable migration amounts were found for both sets of femoral components, with the femoral components tested with muscle loading experiencing lower mean migration, lower mean inducible displacement, and less experimental scatter. CONCLUSIONS: The inclusion of muscle forces seems to stabilise the femoral component during the test. In vitro fatigue tests of cemented total hip arthroplasty reconstructions should include muscle loading to provide increased confidence in the results obtained. RELEVANCE: This study examines how the migration of cemented femoral hip prostheses is influenced by muscle forces. Hip prostheses are one of the few medical devices for which pre-clinical testing protocols have emerged, and this study ascertains whether or not the inclusion of muscle forces is necessary for pre-clinical tests. The conclusion that muscle loading should be included, and that it is important for the development of a new generation of standardised tests to provide enhanced patient protection against functionally poor prostheses.
OBJECTIVE: This study examines the effect of including muscle forces in fatigue tests of cemented total hip arthroplasty reconstructions. DESIGN: An experimental device capable of applying the joint reaction force, the abductor force, the vastus lateralis force, and the tensor fasciae latae force to the implanted femur is described. BACKGROUND: Current in vitro fatigue tests of cemented total hip arthroplasty reconstructions do not apply physiological muscle loads. Experimental and numerical studies report significant differences in stresses obtained in the cement mantle depending on the loads applied. The differing stresses may alter the outcome of an in vitro test. METHODS: Ten femoral components were reproducibly implanted into proximal composite femurs. Five of these femoral components were tested using a loadprofile which included muscle loading, five were tested without muscle loading. The migration of each femoral component was monitored continuously during dynamic fatigue tests. RESULTS: Clinically comparable migration amounts were found for both sets of femoral components, with the femoral components tested with muscle loading experiencing lower mean migration, lower mean inducible displacement, and less experimental scatter. CONCLUSIONS: The inclusion of muscle forces seems to stabilise the femoral component during the test. In vitro fatigue tests of cemented total hip arthroplasty reconstructions should include muscle loading to provide increased confidence in the results obtained. RELEVANCE: This study examines how the migration of cemented femoral hip prostheses is influenced by muscle forces. Hip prostheses are one of the few medical devices for which pre-clinical testing protocols have emerged, and this study ascertains whether or not the inclusion of muscle forces is necessary for pre-clinical tests. The conclusion that muscle loading should be included, and that it is important for the development of a new generation of standardised tests to provide enhanced patient protection against functionally poor prostheses.