It is known that stress shielding frequently occurs after total hip arthroplasty (THA). However, the status of bone metabolism in stress shielding region is not still clear. 18F-fluoride positron emission tomography (PET) is a useful tool for the quantitative evaluation of bone metabolism, which uptake relates with the activity of bone formation by osteoblast. In this study, we evaluated the status of bone turnover in stress shielding region using 18F -fluoride PET. A total of 88 hip joints from 70 cases after THA were analyzed using X-ray and 18F-fluoride PET. We classified these hips into 2 groups, stress shielding or non-stress shielding group. Each femur was divided into 7 regions by Gruen's zone classification. We measured SUV of 18F-fluoride PET in these regions and compared SUV to evaluate the difference of bone metabolism between 2 groups.Objective
Design
Implantation of total hip arthroplasty (THA) components caused a significant alteration in stress environment. Several studies have reported that bone mineral density (BMD) decreases after THA, especially in the proximal femur. This phenomenon is explained as an adaptive remodeling response of bone tissue to a significant alteration in its stress environment. SL-PLUS MIA stem (Smith & Nephew Orthopaedics AG) is a modified implant of Zweymuller type SL-PLUS standard stem (Smith & Nephew Orthopaedics AG). The major change is an omission of the trochanteric wing, which enables a bone-sparing and may lead to changes of femoral stress distribution and rotational stability. The change of stress distribution in the femur could affect BMD after THA. In the present study, we constructed finite element (FE) models of femurs and stems before and at 1week after THA and analyzed equivalent stresses in the femur. In addition, we measured BMD in the femur by dual-energy X-ray absorptiometry (DEXA) after THA. The purpose of this study was to investigate the equivalent stress in the femur and to compare the results of the FE analyses with changes in BMD after THA. Twenty-one patients (18 women and 3 men) who underwent primary cementless THA with SL-PLUS MIA stem or SL-PLUS standard stem formed the basis of this study. Eleven patients received SL-PLUS MIA stem and ten patients received SL-PLUS standard stem. The mean age of the patients at THA was 67 years (range: 48∼82). BMD was measured with DEXA at 1 week and 3, and 6 months after THA. Zones were defined according to Gruen's system (zones 1∼7). Computed-tomography (CT) images of the femur of all patients were taken before and at 1 week after THA. FE models of the femur and prosthesis were obtained from CT data by Mechanical Finder (Research Center of Computational Mechanics Inc., Tokyo, Japan), software that creates FE models showing individual bone shape and density distribution. Equivalent stresses were analyzed in zones 1 to 7 and compared to the DEXA data.INTRODUCTION
METHODS
