University of Connecticut, Department of Mechanical Engineering, Storrs, CT, USA.
Hartford Healthcare, Bone & Joint Institute, Hartford, CT, USA.
Osteoarthritis Cartilage. 2019 May;27(5):810-822. doi: 10.1016/j.joca.2018.12.025. Epub 2019 Jan 18.
The composition and structure of articular cartilage evolves during the development and progression of osteoarthritis (OA) resulting in changing mechanical responses. We aimed to assess the evolution of the intrinsic, large-strain mechanics of human articular cartilage-governed by collagen and proteoglycan and their interactions-during the progression of OA.
We completed quasi-static, large-strain shear tests on 64 specimens from ten donors undergoing total knee arthroplasty (TKA), and quantified the corresponding state of OA (OARSI grade), structural integrity (PLM score), and composition (glycosaminoglycan and collagen content).
We observed nonlinear stress-strain relationships with distinct hystereses for all magnitudes of applied strain where stiffnesses, nonlinearities, and hystereses all reduced as OA advanced. We found a reduction in energy dissipation density up to 80% in severely degenerated (OARSI grade 4, OA-4) vs normal (OA-1) cartilage, and more importantly, we found that even cartilage with a normal appearance in structure and composition (OA-1) dissipated 50% less energy than healthy (control) load-bearing cartilage (HL). Changes in stresses and stiffnesses were in general less pronounced and did not allow us to distinguish between healthy load-bearing controls and very early-stage OA (OA-1), or to distinguish consistently among different levels of degeneration, i.e., OARSI grades.
Our results suggest that reductions in energy dissipation density can be detected by bulk-tissue testing, and that these reductions precede visible signs of degeneration. We highlight the potential of energy dissipation, as opposed to stress- or stiffness-based measures, as a marker to diagnose early-stage OA.
骨关节炎（OA）发展过程中关节软骨的组成和结构发生变化，导致力学响应发生变化。我们旨在评估人类关节软骨固有大应变力学的演变，该力学受胶原蛋白和蛋白聚糖及其相互作用控制，并在 OA 进展过程中发生变化。
我们对接受全膝关节置换术（TKA）的 10 名供体的 64 个标本进行了准静态大应变剪切测试，并量化了相应的 OA 状态（OARSI 分级）、结构完整性（PLM 评分）和组成（糖胺聚糖和胶原含量）。
我们观察到所有施加应变幅度的非线性应力-应变关系，具有明显的滞后，其中刚度、非线性和滞后都随着 OA 的进展而降低。我们发现，在严重退化（OARSI 分级 4，OA-4）与正常（OA-1）软骨中，能量耗散密度降低了高达 80%，更重要的是，我们发现即使结构和组成正常（OA-1）的软骨也比健康（对照）承重软骨（HL）的能量耗散少 50%。一般来说，应力和刚度的变化不太明显，无法区分健康承重对照和早期 OA（OA-1），也无法始终如一地区分不同退化水平，即 OARSI 分级。
我们的结果表明，通过整体组织测试可以检测到能量耗散密度的降低，并且这些降低先于可见的退化迹象。我们强调能量耗散的潜力，与基于应力或刚度的测量相比，作为诊断早期 OA 的标志物。
