Poster AA11 - Anatomical Variation of Depth-dependent Shear Mechanics of Human Knee Cartilage

Introduction: Cartilage has a depth-dependent architecture with specific organization of its components that appear as distinct zones: surface, middle, and deep. Each possesses unique mechanical properties and biochemical composition that give cartilage its overall function. Within the knee joint cartilage varies anatomically, each region having different compressive loads (1), shear modulus (2), thickness, and permeability (1). Although it is known that tissues from low weight-bearing regions (patellofemoral groove) are stiffer in tension than those from the high weight-bearing region (3) (femoral condyle). It has been found very complaint shear mechanics within the first 500 µm of the tissue surface in bovine patella, patellofemoral groove, tibial plateau, and femoral condyle (2). However, there’s little knowledge of the depth-dependent shear mechanics between the patella, patellofemoral groove, tibial plateau, and femoral condyle within the human knee joint. The objective of this study was to compare depth-dependent mechanical properties of the patella, patellofemoral groove, tibial plateau, and femoral condyle inside human knee cartilage.

Materials and

Methods: Human knee joints were obtained from the Hospital for Special Surgery as operation room discards from patients undergoing osteochondral allograft (OCA). OCA tissues were provided by JRF Ortho (Englewood, CO) from cadaveric donors aged 14 to 28 after consent for research use. Articular cartilage plugs (6mm diameter and 2mm height) were obtained from the femoral condyle (n=6), tibial plateau (n=4), patella femoral groove (n=3), and patella (n=8). The tested samples were six male and four female. Depth-dependent shear mechanics of the samples were tested flowing by an established protocol and custom MATLAB code (4). The samples were compressed with 15% tissue thickness and 1% peak shear. The strain data were fitted into a sinusoidal function and stress was calculated from the force applied by the stationary plate to the cross-section of the tissue. The final shear modulus (G*) was calculated by dividing the depth-dependent shear strain with constant shear stress. The G* min is the minimum the modulus reached and the G* plateau was calculated once the tissue modulus no longer increased at a depth greater than 1000 µm.

Results, Conclusions, and Discussions: Results and

Discussion: The shear strain data showed the anatomical variations in which the patella has the highest shear strain for the first 200 µm, followed by PFG, tibial plateau, and femoral condyle (Fig 1A). The patella showed a shear modulus that is an order of magnitude lower than the patellofemoral, tibial plateau, and femoral condyle (Fig 1B). The patella showed to have very low G* min (p < 0.05) compared to the rest of the groups (Fig 1C). The G* plateau showed the shear modulus of the sample doesn’t increase after 1000 µm and there is no significant between the patellofemoral groove, tibial plateau, and femoral condyle (Fig 1D). The only significance was observed between the patella and the other three locations, thus showing that the patella doesn’t experience high compressive and shear forces compared to the femoral condyle and tibial plateau. It is notable that tissues that experience low weight bearing (patella and patellofemoral groove) have low shear modulus while tissue that experiences high weight bearing is shown to have a higher shear modulus.

Conclusion: The goal of this study was to investigate depth-dependent shear mechanics in different anatomical locations of human knee cartilage. The study showed that low-weight-bearing locations of the knee have the lowest shear mechanics (patella) while high-weight-bearing parts of the knee showed to have high shear mechanics. This study will provide important information about the relationship of mechanics and anatomical variations of human knee cartilage; thus, benefiting future OA therapeutics and tissue-engineered cartilage.

Acknowledgements (Optional): NSF (DGE – 2139899), NSF Recode (2225559), NSF Recode (2225528). Thanks to Haniff Prissila for her support on the paperwork.

References: (1) Treppo, S et al. Orthopaedic Research Society 2000. (2) Silverberg, J + et al. JOR 2013. (3) Akizuki, S et al. Orthopaedic Research Society 1986. (4)Buckley, Mark R et al. Journal of biomechanics 2008.