Effect of Femoral Head Necrosis Lesion Size on the Stress Distribution of Proximal Femur Following Hip Resurfacing

• Main Authors: Youg Chou Chen, 陳勇舟
• Other Authors: C. L. Tai
• Format: Others
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/25194029437140898272

碩士 === 長庚大學 === 醫療機電工程研究所 === 101 === Background: Hip resurface arthroplasty (HRA) has been widely accepted in treatment of osteoarthritis and femoral head avascular necrosis. With the advantages of the mitigation of necrotic lesion expansion, bone-conserving nature and delay of total hip arthroplasty, HRA has gained the interest for orthopedic surgeon in recent year. However, the long-term follow-up studies have reported that the narrowing of femoral neck leading to neck fracture was often found following HRA. This phenomenon has been recognized to be attributed to the stress alteration (stress shielding). Literatures addressing the effects of necrotic lesion size and malalignment of femoral component on alteration of the stress distribution are lacking. Methods: Computed tomography images of a standard composite femur were used to create the three-dimensional finite-element (FE) intact femur model. Based on the intact model, FE models simulating four different levels of necrotic region (0°, 60°, 100° and 115°) together with three different insertion angles (varus 10°, neutral and valgus 10°) of femoral component were created. The von Mises stress distributions and the displacement of stem tip of each model were analyzed and compared for a loading condition simulating single-legged stance. Results: 1). The effect of necrotic lesion size on stress distribution: For neutral insertion, the von Mises stress on the most superior point of femoral neck were 32.162 MPa, 30.323 MPa, 29.55 MPa, 28.445 MPa and 27.293 MPa, respectively, for intact and femora with 0°, 60°, 100° and 115° lesion size. The intact femur exhibited the highest stress. Following HRA, the stress decreased with increasing lesion size. This implied more severe stress shield was found for femur with larger lesion size. 2). The effect of malalignment of femoral component on the displacement of stem tip: For femur with 60° lesion size, the displacement of stem tip for femoral components with varus, neutral and valgus insertion were 8.631 µm, 8.328 µm and 7.837 µm, respectively. For femur with 100° lesion size, 8.768 µm, 8.35 µm and 7.867 µm, respectively. Whereas for femur with 115° lesion size, 8.825 µm, 8.405 µm and 8.303 µm, respectively. 3). For femur with identical lesion size, femoral components with varus insertion exhibited the highest stem tip displacement. However, regardless of lesion size, no obvious displacement of stem tip was found for femoral components inserted with identical angle. Conclusion: Stress shielding occurred at proximal femur after hip resurfacing. More severe stress shielding was found for femur with larger lesion size. From view point of biomechanics, the results were in consistence with the clinical outcome of neck narrowing. Besides, varus insertion of femoral component resulted in a larger displacement of the stem tip, which might lead to an increasing risk of loosening of femoral component.