Multiscale Correlations between Joint and Tissue-Specific Biomechanics and Anatomy in Postmortem Ovine Stifles
The stability of the knee joint is an important indicator of its overall health and function. Joint stability depends on multiple structural and functional properties that include the anatomy of the underlying bones, the geometry and stiffness of the joint capsule and the soft tissues within like tendon, ligaments, cartilage and meniscus. The multiscale biomechanical relationships between the form and function of the whole joint and individual tissues can provide useful insights on the physiological condition of the knee and require further exploration. To better understand these relationships, in this study we compare multiple structural and mechanical parameters in healthy ovine stifles (n = 6). Specifically, we have evaluated joint laxity, joint morphology, individual tissue T2* relaxation and mechanical properties of the anterior and posterior cruciate ligaments (ACL, PCL), medial and lateral collateral ligaments (MCL, LCL), the patellar tendon, menisci, and cartilage from the femoral condyles. Using mechanical testing at two length scales along with anatomical and quantitative magnetic resonance imaging (MRI) scans, we investigate the correlation between individual tissue and whole joint mechanical properties. We also performed statistical tests to measure the strength of correlation coefficients between the measured metrics at multiple levels among whole joint mechanics, joint size, and individual tissue properties. We observe positive correlations between the joint laxity forces and the epicondyle-to-epicondyle distance measured as an anatomical marker. We also find that the viscoelastic properties of the tendons and ligaments correlate positively with joint laxity forces. No such correlations were observed between the cartilage and meniscus properties and the joint laxity forces. Further, we found a weak inverse correlation between the tissue viscoelastic properties and T2* for MCL; strong and moderately positive correlations for cartilage samples from both femoral condyles and the menisci, LCL and PCL respectively. These results provide useful insights into the differential role of individual tissue properties that can be used to predict the whole joint responses that are key indicators of knee health and performance.