Torsional stability of uncemented femoral stems in oncologic reconstructions

Modular oncology implants using uncemented fixation represent a popular reconstruction technique for limb salvage patients. Initial stability is critical to facilitate bony ingrowth of host bone into the stem of a press-fit oncologic modular rotating-hinge total knee arthroplasty (TKA). The impact of stem design on initial stability has not been defined. The goal of this study was to evaluate the initial stability of 3 different stem designs as defined by torsional load to failure. An analysis of imaging was also performed. The pilot study consisted of 5 femora in each of 3 groups based on stem design. The specimen was mounted on a multi-axis biomechanical test frame equipped with a Vicon 3D motion analysis 4-camera system (Vicon Motion Systems, Lake Forest, California) to track the relative motion between the implant and the femur. Torsional force was applied until failure. The straight-fluted stem design had the highest average torsional stiffness (18.3±8.2 Nm/deg) and average torque at 150 μm of implant micromotion (23.2±10.6 Nm) of the 3 stem types tested.The results of this study will help to guide surgical decision making in limb salvage cases. Further investigation is warranted.