The tridimensional geometry of the proximal femur should determine the design of cementless femoral stem in total hip arthroplasty

Purpose Using a cementless femoral stem in total hip arthroplasty (THA), optimal filling of the proximal femoral metaphyseal volume (PFMV) and restoration of the extramedullary proximal femoral (PF) parameters (i.e., femoral offset (FO), neck length (FNL), and head height (FHH)) constitute key goals for optimal hip biomechanics, functional outcome, and THA survivorship. However, almost 30% of mismatch between the PF anatomy and implant geometry of the most widely implanted non-modular cementless femoral stem has been demonstrated in a computed tomography scan (CTscan) study. Therefore, this anatomic study aimed to evaluate the relationship between the intra-and extramedullary PF parameters using tridimensional CT scan reconstructions. Methods One hundred fifty-one CTscans of adult healthy hips were obtained from 151 male Caucasian patients (mean age = 66 +/- 11 years) undergoing lower limb CTscan arteriography. Tridimensional PF reconstructions and parameter measurements were performed using a corrected PF coronal plane-defined by the femoral neck and diaphyseal canal longitudinal axes-to avoid influence of PF helitorsion and femoral neck version on extramedullary PF parameters. Results Independently of the femoral neck-shaft angle, the PFMV was significantly and positively correlated with the FO, FNL, and FHH (r = 0.407 to 0.420; p < 0.0001). Conclusion This study emphasized that the tridimensional PF geometry measurement in the corrected coronal plane of the femoral neck can be useful to determine and optimize the design of a non-modular cementless femoral stem. Particularly, continuous homothetic size progression of the intra-and extramedullary PF parameters should be achieved to assure stem fixation and restore anatomic hip biomechanics.