Effect of Cement Mantle Thickness on Stress-Strain Distribution Around Acetabular Region

Introduction Improper positioning of the acetabular component can change the thickness of thecement mantle and may lead to alter the stress-strain distribution around acetabularregion. Excessive stress or strain shielding causes bone density loss due to boneremodelling and potentially leading to loosening of the implant.The aim of the study is toinvestigate the effect of variation of cement mantle thickness on acetabular stress-straindue to Total Hip Replacement (THR).Material and MethodThe finite element (FE) models of intact and implant pelvic bone were developed usingcomputed tomography (CT) scan data of a 35 year old female patient. The cortical bonewas considered as linear, elastic, isotropic having Young’s modulus 17GPa andPoisson’s ratio of 0.3, respectively. The cancellous bone was assumed asheterogeneous, linearly elastic and isotropic. The Young’s modulus for cancellous bonewas derived from CT grey value [1]. For cement mantle, acetabulum and sphericalfemoral head, the Young’s modulus were considered as 2GPa, 1.174GPa and 210GPa,respectively and Poisson’s ratio were 0.33, 0.4 and 0.3, respectively. In the FE modelspubic symphysis and sacroiliac joint were fully constrained. Eight load cases of normalwalking cycle were considered as applied loading conditions, which included 21 muscleforces and hip joint reaction forces. Thickness of the cement mantle was varied from1mm to 5mm in superior to inferior direction and anterior to posterior direction,respectively. Bonded condition was assumed between bone-cement and cement-acetabulum.Results and DiscussionResults of the present study indicates thickness variation in particular to anterior-posterior direction have influences on stress and strain distribution around theacetabular region. However, the effect of cement mantle thickness in the superior toinferior direction was found to be less as compared to anterior-posterior direction. Thisis caused due to hip joint reaction force is directed towards superior region duringnormal walking. Decreases in stress and strain were observed at the posterior direction,when cement mantle thickness increases and indicating stress and strain shieldingaround this region. Conclusion: The present study concluded that variation of cement mantle thickness in anterior-posterior region have impact on stress and strain distribution around the acetabularregion than that of superior-inferior region and it is preferred to have uniform cementthickness for long term success.