[Noncemented total hip arthroplasty: influence of extramedullary parameters on initial implant stability and on bone-implant interface stresses].

Abstract

The extra-medullary stem design has been shown to affect the primary stability of implant and the stress transfer after THR. Most interfacial regions present small micro-slipping which normally allows the occurrence of bone ingrowth. The anatomical design presents the lowest micromotions and the lowest interfacial stresses. The worst cases correspond to the anteverted and lateralized cases. Probably, the anteverted situation involves higher torsion torque, which in turn may induce high torsion shear micromotions and higher stress at the interface. Moreover, the lever arm of the weight bearing force on the femoral head is augmented for the augmented neck length situation. This increases the bending moment, and therefore may increase the stresses as well as the stem shear micromotions. In summary, the present results could be taken as biomechanical arguments for the requirement of anatomical reconstruction of not only the intra-medullary shape but also the extra-medullary parameters (reconstruction of the normal hip biomechanics).