COMPARATIVE ANALYSIS OF BONE STRAIN DISTRIBUTION IN HIP SURFACING – NUMERICAL STUDY

António Ramos, Carlos Relvas, António Completo, José A. Simões

Mechanical Engineering Department, TEMA, University of Aveiro, Portugal

Introduction

A resurfaced femur presents a considerable interest

for application in young patients. The main cause of

premature failure of resurfaced hip has been

associated with femur fracture neck (Amstutz et al,

2004). There is an interest in the load transfer

mechanism and influence of mechanical factors

associated with potential failure for this application.

Other studies have observed micro motions in this

application associated with the effect of strain

shielding in proximal region (Bidytut, et al 2010).

Other studies have associated the failure to wrong,

valgus or varus positions to adverse mechanical

effects (Sakagoshi, et al, 2010).

The main goal of this study was to analyse

comparatively the strain distribution in intact and

resurfacing implanted femur using finite element

models.

Methods

A synthetic left femur (Sawbones®) was implanted

with a hip surfacing prosthesis (Birmingham Hip

Resurfacing) and press-fit stem, with 48 mm head.

The model was built based on a ScanIP geometry

from CT scan images and meshed with a

hexahedral elements (Figure 1).

Figure 1: Intact femur model, hip surfacing

prosthesis and in vitro model.

Material Young

Modulos (GPa)

Poison ratio

Cortical bone Exx=Eyy= 7,

Ezz=11.5

0.4

Cancel bone 0.480 0.28

Stem 210 0.3

Table 1: Material properties used in the finite

element models.

The materials were considered linear elastic, and

properties presented in table 1. For the contact

condition we assumed contact between the implant

and cancellous bone with a 0.3 friction coefficient.

The boundary conditions were similar to those

applied elsewhere [Ramos, et. al. 2006] composed

by the hip contact reaction and the abductor, psoas-

iliac and vastus lateralis muscles.

Results

The maximum principal strains in the medial and

posterior aspect in both models (natural and

implanted) are presented in Fig. 2. In the anterior

aspect the maximum principal stress increased

30%.

Figure 2: Cortical bone strain distribution in the

posterior aspect for intact and implanted femur.

Discussion

The numerical results presented a small reduction

of the principal strains in all aspects of the proximal

region. In the posterior aspect we observed some

strain shielding and an increase of strain in the

anterior aspect.

Acknowledgement

The authors gratefully acknowledge the funding

PTDC/EME-PME/112977/209

References

Amstutz, et al, J Bone & Joint Surgery, 86A:1874-

1877, 2004.

Bidyut, et al, J Biomechanics, 43:1923-1930, 2010.

Ramos, et al, J Biomech Eng, 138:579–587, 2006.

Sakagoshi, et al, J Arthoplasty, 25-8:1282-1289,

2010.

S288 Presentation 1736 − Topic 23. Hip biomechanics

Journal of Biomechanics 45(S1) ESB2012: 18th Congress of the European Society of Biomechanics