Sofie Vertriest, Pascal Coorevits, Kerstin Hagberg, Rickard Brånemark, Eva Elisabet Häggström, Guy Vanderstraeten, Laurent Alain Frossard

Load-bearing exercises are performed by transfemoral amputees fitted with an osseointegrated implant to facilitate bone remodelling. This study presents the loading compliance comparing loads prescribed and applied on the three axes of the implant during static load-bearing exercises with a specific emphasis on axial and vectorial comparisons. Cohort study. A total of 11 fully rehabilitated unilateral transfemoral amputees fitted with an osseointegrated implant performed five trials in four loading conditions using a static standing frame. The load prescribed was monitored using a vertical single-axis strain gauge connected to an electronic display. The tri-axial forces applied on the implant were measured directly with an instrumented pylon including a six-channel transducer. The analysis included 'axial' and 'vectorial' comparisons corresponding to the difference between the force applied on the long axis of the implant and the load prescribed as well as the resultant of the three components of the load applied and the load prescribed, respectively. The results demonstrated that axial and vectorial differences were significant in all conditions (p < 0.05), except for the vectorial difference for the 40 kg condition (p = 0.182). The significant lack of axial compliance led to systematic underloading of the long axis of the implant. This study contributes to a better understanding of the load applied on an osseointegrated implant during the static load-bearing exercises that could contribute to improve the design of apparatus to monitor loading exercises as well as clinical guidelines for the loading progression during rehabilitation.