The Ability of Bone Mineral Density and Microstructural Indices to Reflect Mechanical Properties of Trabecular Bone

Abstract

PURPOSE: The goals of this experimental study were to (1) apply high-resolution imaging techniques (micro-CT imaging) in combination with new computer modeling techniques (FEA) to quantify 3D microstructural and biomechanical properties of trabecular bone in the intertrochanteric region (2) investigate contribution of bone mineral density (BMD) and microstructure of trabecular bone to predicting its mechanical property, i.e., elastic modulus, and (3) determine if the prediction of bone elastic constant can be improved when BMD is combined with any one structural index, or the structural indices are associated each other as independent variable. MATERIALS AND METHODS: Total 15 trabecular bone core specimens were obtained from the proximal femurs with patients undergoing to total hip arthroplasty. BMD of all bone cores was measured using PIXImus2 densitometer. A high-resolution microcomputed tomography (micro-CT) was used to scan each specimen to obtain histomorphology. Microstructural parameters such as bone volume fraction (BV/TV), trabecular number (Tb.Th), trabecular separation (Tb.Sp) were directly calculated from the 2-D and 3-D datasets, and then the hexahedron mesh models were created. Micro-finite element analysis was performed to derive indices of mechanical properties of trabecular bone. The multiple relationships among BMD, structural parameters and mechanical indices were assessed using linear regression analyses. A p value<0.05 was considered to be significant. RESULTS: Linear regression analysis showed that the BV/TV was the best predictor for Young’s modulus (R²=0.758, p<0.001), as well as BMD (R²=0.752, p<0.001). The structure model index (SMI), Tb.Sp and Tb.N could well explain the variance of Young’s modulus by 51%, 42% and 39%, respectively. If BMD is supplemented with any of the examined structural indices there is a clear improvement for predicting Young’s moduli. Likewise, the ability to explain variance of Young’s modulus is improved by combining the structural indices each other. CONCLUSION: A combination of microstructural parameters each other or with bone mineral measurements could provide the best prediction of mechanical property of cancellous bone. Therefore, as regards detection of osteoporosis and evaluation of the efficacy of drug treatments for osteoporosis, BMD measurement should be supplemented with assessment of bone microarchitecture in vivo.

목적: 본 연구의 목적은 골밀도와 미세 골구조의 성질이 전자부 골소주의 기계적 특성(예, 탄성계수)에 미치는 영향을 연구하는 것이다. 대상 및 방법: 인공관절 전치환술을 시행 받은 15명의 환자로부터 대퇴골 전자부에서 총 15개의 고관절 골소주 시편을 채취하여, 이들을 대상으로 PIXImus2 골밀도 측정기, 고해상도 미세 컴퓨터 단층촬영기, 유한요소법을 이용하여 골밀도와 2차 및 3차원 미세구조 지수, 그리고 기계적 특성을 분석하였다. 골밀도, 구조 지수, 탄성계수 간의 상관관계를 선형회귀분석을 이용하여 통계처리 하였다. 결과: 본 연구에서 골밀도 및 골 체적비는 기계적 특성을 예측하는데 가장 중요한 인자였으며, 3 차원 미세구조지수(예를 들어 구조 모델 지수) 또한 51%정도 통계적으로 의미 있게 기계적 특성을 예측하였다. 골밀도와 미세구조지수를 조합한 경우에 탄성계수의 변화량을 예측하는데 잘 반영하였다. 결론: 골밀도와 미세구조지수를 이용한 분석은 전자부에서 탄성계수를 예측하는데 가장 좋은 방법이다.