•biomechanics of a Stemless, Metaphyseal Fixation Femoral Design: Effects of Screw Fixation and Interface Conditions

INTRODUCTION: Bone conserving designs, such as hip resurfacings, are an alternative treatment option to conventional total hip arthroplasty (THA) in young, active patients. Previous studies have shown that medullary fixation can result in significant proximal bone resorption through stress shielding [1,2], while it has been suggested that hip resurfacing arthroplasty will load the proximal femoral bone in a more physiological manner [2,3]. Metaphyseal fixation has been proposed as a solution for preserving proximal bone stock, while minimizing bone resorption induced by medullary fixation [4]. The stemless Munting hip is an example of a design that relies on proximal metaphyseal fixation (Fig. 1) [4,5]. The hydroxyapatite-coated implant has no intramedullary stem and fits into an angular resection of the femoral neck. The component has five lamellae that fit into the metaphyseal cancellous bone, while two trans-trochanteric screws and a distal screw provide initial fixation in place of bone cement. Although in vitro experiments of the Munting hip have been performed previously [4], the effects of screw fixation and interface conditions have not been fully described. The goal of our study was to develop a three dimensional FE model of the implanted femur to examine the effects of screw fixation and boneimplant interface conditions on femoral stresses, strains, and remodeling and to determine if these data support the concept of metaphyseal fixation.