Quantitative Computed Tomography Based Finite Element Modeling of Normal and Osteoarthritic Knees: In vivo Precision and Preliminary Comparisons

Osteoarthritis (OA) is a debilitating joint disease which affects nearly 85% of the Canadian population over 75 years of age. OA not only affects cartilage, but it also alters subchondral bone (bone underlying cartilage). Altered subchondral bone could be related to OA initiation, progression, and OA-related pain. To help clarify the role of subchondral bone in OA, accurate in vivo methods are needed to monitor subchondral bone mechanical property variations in people living with OA. Subject-specific finite element (FE) modeling has potential to investigate the role of mechanical properties of subchondral bone in OA. However, associated precision errors of FE-derived mechanical properties are not known. The objectives of this study were to 1) develop a subject-specific FE modeling methodology for OA and normal knees, 2) determine the in vivo precision of FE-derived stress/strain distributions and stiffness of the proximal tibia, and 3) determine whether FE-derived metrics discriminate normal and OA knees. Subject-specific FE models were developed for 14 participants (7 OA, 7 normal) with three repeated CT images of knee joint. Von-Mises stress and strain, minimum principal stress and strain, plus structural stiffness outcomes were acquired for each proximal tibia image. Root mean square coefficient of variations (CV%) were used to assess in vivo precision of the FE-based outcomes. Comparisons between OA and normal groups were performed using unpaired t-tests for normally distributed outcomes, and Mann-Whitney U-tests for not normally distributed outcomes. For all the outcomes the average CV% was less than 6.1%. On average, von-Mises stress and minimum principal stress were respectively 65% and 70% higher in OA versus normal knees whereas strain values did not differ. No difference was observed in stiffness values. Thesis results indicate that FE modeling could be used to precisely quantify and differentiate mechanical property variations in normal and OA knees, in vivo. Results suggest that OA and normal bone exhibit dissimilar stress levels but similar strain levels, likely indicating adaptation of bone in response to altered joint mechanics with OA