Introduction: The objective of this study was to evaluate the biomechanical proprieties of a hip resurfacing system in terms of failure of the implant with different positioning of the prosthesis in cadaveric femurs.

Materials and Methods: The study has been divided in 3 phases. First phase: Six-teen cadaveric femurs were tested to failure using a standard MTS device once the Conserve Plus (Wright Medical) system was implanted: 8 femurs after a 4mm notching of the neck and 8 contralateral without notching. Second phase: Six-teen cadaveric femurs were tested using a 210 Kg axial load: 8 with the Conserve Plus system implanted at 140° and 8 contralateral with 10° of varus. Third phase: Eight femurs were tested with the implant having 10 ° of excessive antiversion of the component and 8 with the implant having 10 ° of excessive retroversion. The control group was represented by 16 femurs having the system implanted following the natural version of the femoral neck.

Results: An average of 4865 Newtons(N) was necessary for the failure of the implant after notching, compared to 7043 N without notching. The varus alignment of the implant showed a statistical different increase of the stress on the femoral neck: 15% postero-superiorly and 21% antero-superiorly. The neutral alignment at 140° showed a decrease of the overall stress on the femoral neck. Adding 10 ° of excessive anteversion or retroversion did not show any statistical difference in terms of failure of the implant when compared to the anatomical alignment.

Conclusions: This biomechanical study showed that the correct positioning of the implant represents a fundamental requirement for the success of the hip resurfacing procedure. The notching of the neck decreases significantly the biomechanical proprieties of the implant, while the varus alignment increases the stress on the superior neck cortex.