Nonlinear Three‐Dimensional Finite Element Analysis of Newly Designed Cementless Total Hip Stems

Abstract

We designed 2 new types of proximally coated stems (the FMS and FMS-anatomic) based on the endosteal geometry of femora with congenital dislocation or dysplastic hip. The FMS was symmetric while the FMS-anatomic was asymmetric. We compared the proximal fit and fill to the femoral canal, contact stress, relative motion, and load transfer to the femur of 5 stems (FMS, FMS-anatomic, Omnifit, Omniflex, and individual stem) using three-dimensional computer simulation and finite element analysis. The FMS and FMS-anatomic showed a significantly greater fit and fill than conventional stems. The dispersion of the contact stresses and reduction of relative motions in the proximal area were the best in the FMS-anatomic compared to other stems with the exception of the individual stem. In addition, the FMS-anatomic stem transferred most of the load to the proximal femur. Our results suggest that the FMS-anatomic should provide better biomechanical stability at least in the early postoperative period.

Design process of cementless femoral stem using a nonlinear three dimensional finite element analysis

“…The implant fills the endosteal canal to a high percentage; 83.10% at anteroposterior view and 71.70% at mediolateral view. The comparison between different cementless stems [13,20] is illustrated in Figure 7. This newly designed stem was among the highest percentage of fit and fill compared to others except the Fukui Medical School (FMS and FMS-A), and IDS stem.…”

“…The intact femora consisted of 5000 nodes and 34 000 elements, and the ‘virtual surgery femora’ consisted of 7900 nodes and 41 900 elements. The material properties of the cementless femoral stem were assigned as titanium alloy (Ti 6 Al 4 V) with Young’s Modulus of 110 GPa and a Poisson’s ratio of 0.3 [13]. In addition, the femora were assumed as isotropic and linear elastic, with bone properties determined according to the CT datasets grey level values.…”

“…In addition, Pettersen et al [11,12] supported the excellent correlation between an actual human cadaver and finite element study while investigating the feasibility of subjects specific to stress shielding and micromotion using cementless Summit stem. Ando et al [13] also performed a finite element analysis to compare their stems for Japanese dysplastic hip (FMS and FMS-anatomic) with other commercial stems such as Omnifit, Omniflex and IDS focusing on contact stress, relative motion and load transfer prior clinical use. The results showed the load was transferred mostly in proximal region with low micromotion value, which supported the excellent success rate of this implant [14,15].…”

Morphological Study of the Newly Designed Cementless Femoral Stem

“…Our study showed a femoral flare of 3.71 at 10 mm above the zero level that gradually stabilized at the diaphyseal region as illustrated in Figure 7. Several studies in Japan considered these differences when they designed implants and focused on the metaphyseal region anterolaterally flared for loading purposes [17–20, 46]. Laine et al emphasized the selection of the cementless stem from the metaphyseal region (MCFI) rather than the CFI [10].…”

“…Biological fixation can be achieved by comprehending the morphology of the proximal femur prior design to achieve an optimum fit, fill implant, and promote bone ingrowth. Several studies in Japan emphasized obtaining precise information about the endosteal canal in a proximal femur, which is essential for metaphyseal support for cementless hip stems [17–21]. These researchers developed the cementless femoral stem that was specifically designed for dysplastic hips with proximal fitting anterolaterally flared stems, which has showed promising results.…”