Knee ligaments in osteoarthritis: structural and functional analyses

Osteoarthritis (OA) is a painful, chronic degenerative joint disease affecting more than 500 million people worldwide. Once regarded as simple “wear and tear” of cartilage, OA is now recognized as a whole-joint disease affecting all joint tissues. However, its impact on knee ligaments remains poorly understood. Using an animal model of osteoarthritis and cadaver tissue, this thesis aimed to investigate the viscoelastic properties, composition, and microstructural characteristics of knee ligaments in OA.

For Study 1, medial collateral ligaments (MCLs) and lateral collateral ligaments (LCLs) were harvested from both limbs of six New Zealand White rabbits that underwent unilateral ACL transection eight weeks earlier. At the same time point, collateral ligaments were also collected from both knees of four age-matched New Zealand White rabbits serving as a healthy control group. Tensile stress-relaxation and sinusoidal testing revealed that the LCLs of ACL-transected knees became less stiff and viscous than intact contralateral knees. To understand these changes, Study 2 investigated the biocomposition of these same samples using Fourier transform infrared imaging and quantitative polarized light microscopy. The collateral ligaments of operated knees exhibited an overall lower collagen content and less organized fiber alignment than those of the contralateral and control groups. Together, these differences in mechanical properties, composition, and microstructural characteristics among the ACL-transected, contralateral, and control groups suggest that collateral ligaments adapt in this OA model.

Study 3 developed a new protocol for imaging the microstructure of the knee ligaments. The cruciate and collateral ligaments from eight fresh-frozen cadaveric knees were dissected, fixed in formalin, subjected to gradual dehydration and critical point drying, and then imaged using micro-computed tomography (micro-CT). The pretreatment imaging protocol enabled imaging of microstructures using micro-CT, allowing three-dimensional (3D) visualization and quantitative analysis of the fascicular structure of knee ligaments. Future studies may use this approach to assess ligament microstructure at the fascicle level.

Overall, the function, composition, and structure of knee ligaments adapt to the altered loading environment resulting from OA development, and micro-CT can serve as an effective technique for assessing the microstructure of knee ligaments.