BACKGROUND: It is of great significance to study the resilience of articular cartilage for human daily routine and their match quality. OBJECTIVE: To analyze the micromechanical properties of articular cartilage resilience under different loads and at time points. METHODS: The swine cartilage samples coated with tracers were compressed using the MTF-100 tensile machine, and the cartilage compression and resilience were recorded by CCD. Images were processed using digital image correlation technology.RESULTS AND CONCLUSION: During resilience, the strain value on the superficial surface of the cartilage was decreased most, successively followed by the middle layer and the deep layer, while the time of a decrease from 20%, 10% and 6% to 3% was similar. The longer the resilience time was, the more slowly the strain changed in different layers of the cartilage, but the ultimate strain was less than 1%. On the same layer under different compressive stress, the larger load caused faster strain change firstly, and then the smaller load brought about faster strain change. The effect of different continuous compressive time on the same layer of cartilage was similar with the load. These results showed that 90% resilience of the articular cartilage occurred within the first 15 minutes. The mechanical resilience of different layers of the articular cartilage has a close relationship with the loading and the loading time, and both compressive time and loading do harm to the resilience of articular cartilage. Besides, the cartilage will rebound to the state before compression.

Objective To study the biomechanical influence of posterior laminectomy with varying extent on adjacent segment after lumbar interbody fusion. Methods Three finite element models of lumbar posterior fusion were developed based on the validated intact lumbar model. These models were: posterior fusion with bi-lateral incision of facet joint (Bi-TLIF），inferior partly incision of laminar (PLIF)，total laminectomy (LAM-PLIF). The range of motion (ROM), intradiscal pressure (IDP), facet joint contact force (FJF) of adjacent segment of fusion models under various loading were compared with the intact model. The follower load of 400 N under 7.5 N·m torque was exerted on superior endplate of L1 segment. The 6-DOF (degree of freedom) of sacroiliac joint surface was constrained during loading. ResultsDuring flexion, obvious biomechanical changes of superior adjacent segment (L3-4) were found in Bi-TLIF, PLIF, LAM-PLIF surgery groups. Compared with the intact model, the ROM in Bi-TLIF, PLIF, LAM-PLIF group increased by 1.0%, 9.3%, 24.5%, respectively, while IDP in the above fusion groups increased by 1.4%, 4.3%, 10.0%，respectively. These changes were not obvious in other postures. For FJF, the Bi-TLIF and PLIF group showed obvious increasing effect on L3-4 segment, while almost had no effect on L5-S1 segment. Conclusions Laminectomy increased ROM, IDP and FJF of adjacent segment (especially superior adjacent segment) after posterior lumbar fusion, which might increase the risk of adjacent segment degeneration. This biomechanical effect was more obvious with the increase in incision range of laminar. Therefore, preserving more posterior complex during decompression has a positive effect on preventing adjacent segment degeneration (ASD) following lumbar fusion surgeries.

Objective To investigate the distribution of streaming potential generated by interstitial fluid flow in articular cartilage and obtain electrical characteristics of articular cartilage. Methods The governing equation of fluid and electrostatic theory were combined to establish a two-dimensional (2D) micro-element model of cartilage, and the steady streaming potential generated in microelement under certain pressure was calculated by finite element method. Results The streaming potential in micro-pore model of articular cartilage with the length of 5 μm was about 38.4 μV. The effect of external pressure and Zeta potential on streaming potential of articular cartilage model was significant and showed a linear increase relationship. The streaming potential decreased with the increase of ion number concentration, but the concentration had different effects on streaming potential of articular cartilage. When the ion number concentration was low, streaming potential was more dependent on ion number concentration. When ion number concentration was high, the effect of ion number concentration on streaming potential was very small. Conclusions The results of this study provide important theoretical basis for differentiation and proliferation of chondrocytes, prevention and treatment of articular cartilage diseases, development of tissue-engineered cartilage and repair of articular cartilage injury by means of electric current, electric field and electromagnetic field stimulation.

Objective To study the effects of collagen fiber bundle on mechanical properties of articular cartilage, so as to provide references for clinicians to guide the rehabilitation of patients with early cartilage injury. Methods The two-dimensional (2D) numerical model of fiber-reinforced porous viscoelasticity was established, with consideration of the relationship of fiber distribution, elastic modulus, porosity and permeability with cartilage depth. The influences from local fracture of the fiber bundle, the progressive fracture from the surface and the fiber bundle size on mechanical properties of the cartilage were studied, and the maximum principle strain of cartilage matrix was obtained. Results The maximum principal strain of the matrix occurred at a position in middle layer of the cartilage, about upper 1/3 of the cartilage, which was not affected by fiber breakage mode and fiber bundle size. The strain of the cartilage with thicker fiber bundles decreased. Conclusions The middle layer of the cartilage was prone to mechanical damage. The thicker fiber bundle could reduce the maximum principal strain of the matrix. Once the fiber bundle broke, the maximum principal strain of the cartilage matrix with thicker fiber bundle became larger, leading to an easier evolution of the cartilage damage.

Objective To study the ratcheting behavior of defective cartilage under cyclic compressive loading, so as to explore the pattern of damage evolution for defective articular cartilage. Methods Fresh articular cartilage was obtained from the distal femur of adult porcine, and the cartilage samples with different depth of defect were applied under triangular wave cyclic loading with different parameters. Combined with non-contact digital image technology, the ratcheting strain at different layers of cartilage was obtained. Results With the increase of loading cycles numbers, the ratcheting strain at each layer of cartilage increased sharply at first, then increased slowly and tended to be stable, and the ratcheting strain decreased gradually from shallow layer to deep layer. The response of each layer to cycle number was different. The strain in shallow layer increased rapidly within 50 cycles, while the strain in middle layer increased rapidly within 100 cycles and the strain in deep layer increased rapidly within 75 cycles. The ratcheting strain in shallow and deep layers was positively correlated with the stress amplitude and defect depth, and negatively correlated with the loading rate, while hysteresis response occurreds in middle layer. Conclusions The ratcheting behavior of cartilage was affected by special structure of the cartilage. The defect caused the strain increasing in each layer of cartilage, which could easily result in the aggravation of damage. The experiment results provide references for the construction of tissue-engineered cartilage.

Cartilage surface fibrosis is an early sign of osteoarthritis and cartilage surface damage is closely related to load. The purpose of this study was to study the relationship between cartilage surface roughness and load. By applying impact, compression and fatigue loads on fresh porcine articular cartilage, the rough value of cartilage surface was measured at an interval of 10 min each time and the change rule of roughness before and after loading was obtained. It was found that the load increased the roughness of cartilage surface and the increased value was related to the load size. The time of roughness returning to the initial condition was related to the load type and the load size. The impact load had the greatest influence on the roughness of cartilage surface, followed by the severe fatigue load, compression load and mild fatigue load. This article provides reference data for revealing the pathogenesis of early osteoarthritis and preventing and treating articular cartilage diseases.
Animals ; Cartilage, Articular ; Fatigue ; Osteoarthritis/pathology* ; Pressure ; Swine