The effect of shear fatigue on bovine articular cartilage

The objective of this study was to investigate the effects of mechanical fatigue in the form of cyclic shear strain on articular cartilage. Three millimeter diameter full-thickness plugs were cored from the lateral aspect of bovine tibial plateaus. Sinusoidal shear strains of +/- 5, +/- 10, and +/- 15% were applied to the specimens at 100 Hz for 3 h (a total of 108 x 10(4) cycles). The mechanical shear properties of the tissue (loss and storage moduli) were determined as a function of the number of applied strain cycles. A rapid, irreversible decrease of approximately 35% of initial modulus was found to occur in both loss and storage modulus during application of the first 90,000 cycles. Further decay in the moduli was found to occur from 90 x 10(3) to 108 x 10(4) cycles, but was of considerably smaller magnitude than the initial decrease. The moduli remained relatively constant beyond application of 108 x 10(4) cycles. No consistent change in proteoglycan content was found to be associated with the fatigue process when comparing tested specimens with fresh, untested tissue, and with experimental controls. In addition, no structural defects in the mechanically altered tissue were revealed by scanning electron microscopy.     

The initial repair response of articular cartilage after mechanically induced damage

The regenerative potential of articular cartilage (AC) defects is limited and depends on defect size, biomechanical conditions, and age. Early events after overloading might be predictive for cartilage degeneration in the long term. Therefore, the present aim is to investigate the temporal response of cartilage to overloading at cell, matrix, and tissue level during the first period after mechanical overloading. In the present study, the effect of high loading (∼8 MPa) at a high rate (∼14 MPa/s) at day 0 during a 9 day period on collagen damage, gene expression, cell death, and biochemical composition in AC was investigated. A model system was developed which enabled culturing osteochondral explants after loading. Proteoglycan content was repeatedly monitored over time using μCT, whereas other evaluations required destructive measurements. Changes in matrix related gene expressions indicated a degenerative response during the first 6 h after loading. After 24 h, this was restored and data suggested an initial repair response. Cell death and microscopic damage increased after 24 h following loading. These degradative changes were not restored within the 9 day culture period, and were accompanied by a slight loss of proteoglycans at the articular surface that extended into the middle zones. The combined findings indicate that high magnitude loading of articular cartilage at a high rate induces an initial damage that later initiates a healing response that can probably not be retained due to loss of cell viability. Consequently, the matrix cannot be restored in the short term. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1265–1273, 2017.

     

The effect of cryopreservation on the biomechanical behavior of bovine articular cartilage

The short-term effect of cryopreservation on specific mechanical behaviors of bovine articular cartilage has been investigated. A flat-ended nonporous indentor was used in a nondestructive, repetitive, axisymmetric unconstrained testing system. Cyclical indentation from a fixed position to a fixed load was applied until a steady-state load-deformation relationship (limit cycle) was achieved. Indentation behaviors measured from the limit cycles of each articular cartilage specimen before and after treatment were compared. Testing was done in vitro using fresh, mature bovine radiocarpal joints. Twenty pairs of cartilage-subchondral bone cores from anatomically similar sites on contralateral joints were separated into three groups; thickness controls, dimethylsulfoxide (DMSO) controls, and cryopreserved experimental samples. Thickness controls and DMSO controls were used to examine the isolated effects of the thickness measurement and DMSO incubation techniques on articular cartilage indentation characteristics. Experimental samples were cryopreserved using DMSO, their thicknesses similarly measured and indentation behaviors examined. Following testing, histological and histochemical assessment of the specimens confirmed the nondestructive nature of the tests. Intra- and intergroup comparisons of controls and experimentals revealed no statistical differences in the mechanical behaviors measured from the limit cycle or in cartilage thickness. These results indicate that the cryopreservation protocol used did not have an effect that we could measure on these specific mechanical behaviors of articular cartilage.     

The effect of a passive muscle stretching protocol on the articular cartilage

OBJECTIVE: The aim of this study is to evaluate the articular cartilage alterations of rat ankles, after applying unilateral cyclic passive muscle stretching protocol in previously immobilized rats. METHODS: Twenty-two male albino rats divided into four groups, I--immobilized; IS--immobilized and stretched; S--stretched and C--control, were used in this experiment. The I and IS groups were immobilized for 4 weeks. In the muscle stretching protocol the treated ankle joint (groups IS and S) was manually full dorsal flexed 10 times for 60s with a 30s interval between each 60s period, 7 days a week for 3 weeks, to stretch the ankle plantar flexors muscle group. The right hind limb was free to move. At the end of the experiment, the ankles were removed, processed in paraffin and stained with hematoxylin-eosin and Safranin-O. Two blinded observers evaluated cellularity, chondrocyte cloning and Safranin-O staining through light microscopy. And a morphometric study was carried out using a hand count of chondrocyte cells and cartilage thickness measurement. RESULTS: No significant effect of solely muscle stretching concerning cellularity, chondrocyte cloning and Safranin-O staining parameters was detected. However, IS group presented a significantly higher reduction of proteoglycans content than the solely stretched and solely immobilized groups and the morphometric analysis showed significant cellularity increase without thickness alteration compared to control. CONCLUSIONS: These findings suggest that the stretching protocol used was harmful to the previously immobilized articular cartilage. However, the same stretching protocol did not harm the cartilage of non-immobilized groups.     

The effects of exercise on articular cartilage

The effect of exercise on articular cartilage has been assessed on animal models and on humans using various imaging techniques. Joint cartilage, whose water content decreases itself thanks to its unique permeable medium, maintains load distribution and joint function together with the synovial fluid under physiologic conditions and sports activities. The adaptive capacity of joint cartilage is limited under various conditions such as excessive load bearing or prolonged immobilization; however, when these factors are reversed deformed cartilage returns to its former state under normal conditions. Due to its adverse effect on joint cartilage, immobilization period following cartilage damage or operation should be as short as possible for wound healing. It is reported that exercise contributes to cartilage healing and reduces risk for injury, and that moderate exercise can even decrease the number of cases requiring arthroplasty. Conversely, excessive (harsh) exercise may be associated with increased cartilage damage or degenerative changes. Despite the presence of osteophytic changes in joint cartilage of athletes performing mild sports activities, these may not result in osteoarthritis due to the adaptive feature of joint cartilage. In contrast, the risk for osteoarthritis is increased in professional sportsmen exposed to acute repetitive impact and torsional loading. This article reviews the influence of controlled, passive-active exercise on healing, and on the development of osteoarthritis and the short- and long-term changes in articular cartilage associated with exercise and participation in sports of different duration and intensity.     

福善美调控软骨下骨骨重塑保护关节软骨的机制研究

目的 探讨福善美调控软骨下骨骨重塑保护关节软骨的机制.方法 以清洁级健康雌性SD大鼠为动物模型,分为Sham组、模型组和福善美组.通过切除双侧卵巢并切断右侧膝交叉韧带建立骨关节炎动物模型,术后第4周开始灌服福善美,模型组、Sham组灌服等量的生理盐水,分别于术后8、12、16周取材,采用骨关节炎软骨病理变化评价系统(OARSI)评价关节软骨的病变,对软骨下骨进行骨形态计量学分析.结果 术后8、12、16周,模型组较Sham组OARSI评分差异有显著意义(P＜0.01),福善美组较模型组OARSI评分差异有显著意义(P＜0.05).软骨下骨组织形态计量学参数测量显示模型组较Sham组骨小梁面积百分数(%Tb.Ar)、骨小梁宽度(Tb.Th)、骨小梁数量(Tb.N)、骨小梁分离度(Tb.Sp)、每毫米破骨细胞数(Oc.N/mm)差异有显著性(P＜0.01);模型组荧光周长百分率(%L.Pm)、矿化沉积率(MAR)、骨形成率(BFR/BV)、骨形成率(BFR/BS)低于Sham组,差异有显著性(P＜0.05).结论 软骨下骨在骨关节炎发生发展中起重要作用,骨吸收抑制剂福善美可作为治疗骨关节炎有潜力的药物.     

The effect of monopolar radiofrequency energy on partial-thickness defects of articular cartilage.

PURPOSE: To evaluate the effect of monopolar radiofrequency (RF) energy on partial-thickness defects of articular cartilage, comparing the outcome of partial-thickness defects treated with monopolar RF energy with that of treatment by conversion of partial-thickness defects to full-thickness defects by curettage and microfracture. TYPE OF STUDY: Randomized trial using adult female sheep. MATERIALS AND METHODS: Thirty-six sheep were used in this study. Both stifles in each animal were randomly assigned to 1 of the following 3 procedures: (1) partial-thickness defect without any treatment to serve as a sham-operated control, (2) partial-thickness defect with RF energy treatment, and (3) partial-thickness defect treated by conversion of the defect to a full-thickness defect by curettage and microfracture. Nine sheep were euthanized at 0, 2, 12, and 24 weeks after surgery (n = 6 per group). After euthanasia, cartilage samples were harvested from the defect sites, and chondrocyte viability was analyzed by confocal laser microscopy using a triple-labeling technique. Cartilage samples also were decalcified and stained with hematoxylin and eosin and safranin-O for histologic analysis. Surface properties of cartilage samples were analyzed using scanning electron microscopy. RESULTS: The analysis of chondrocyte viability showed that RF treatment caused death of almost all chondrocytes in the defect. Histologic analysis showed that RF treatment caused detrimental effects to chondrocytes and proteoglycan concentration that progressed over time, and that full-thickness defects were repaired by fibrocartilage by 24 weeks after surgery. Scanning electron microscopy analysis indicated that RF-treated groups were significantly smoother and less irregular than control groups at 2, 12, and 24 weeks after surgery. CONCLUSIONS: This study showed that monopolar RF energy caused long-term damage to cartilage in this sheep model and did not appear to have the beneficial effects reported in a previous study that evaluated application of this technique using a bipolar RF probe.     

The effect of tibial lengthening on immature articular cartilage of the knee joint

OBJECTIVE: To investigate the acute response of immature articular cartilage, in the distraction and consolidation phases, to 30% tibial lengthening. DESIGN: Sixteen immature New Zealand white rabbits underwent diaphyseal lengthening of the left tibia by callotasis at a distraction rate of 0.4mm twice daily. A sham control group of 12 rabbits underwent fixation and osteotomy without lengthening. In each group, half of the rabbits were killed at the end of the distraction phase or at an equivalent time period and the rest were killed after an additional 5 weeks (consolidation phase). The tibial condyles and synovial fluid in the knee joint cavity were taken for laboratory examination. Sulfated glycosaminoglycan in synovial fluid was estimated using a colorimetric method. Sections along the mid-coronal plane of the whole of the tibial condyles were examined histologically and by scanning electron microscopy. A grading system was used to make a semiquantitative assessment of the histopathological changes in articular cartilage. RESULTS: Damage to the immature articular cartilage had occurred by the end of the distraction period and the cartilage continued to deteriorate in the consolidation phase of 5 weeks. However, when compared with a similar study in a mature rabbit model, damage to immature cartilage appeared less severe. CONCLUSION: This model of 30% lengthening caused acute cartilage damage which did not recover in the short term. The result may have implications for longer lengthening in children; the effects may be disadvantageous and lead to degenerative diseases later in life.     

The microhardness of articular cartilage.

The standard metallurgical technique of microhardness testing was useful for investigations on the physical properties of articular cartilage. The problem of visco-elasticity of the cartilage was overcome by using a brittle lacquer coating as a memory device. The surface layer was the hardest plane when the superficial layer was intact. Removal of the superficial layer however, made this plane the softest. There was no variation in hardness with depth. The plane at right angles to the vector of movement of the joint was harder than the plane parallel to the vector of movement. This indicates the presence of a secondary fiber system in the middle layer of articular cartilage. The fibers in this system run predominantly at right angles to the direction of motion of the joint.     

The glycosaminoglycans of bovine articular cartilage

Calcified Tissue International - The glycosaminoglycans in different layers of bovine articular cartilage from calves, heifers and cows were studied quantitatively and qualitatively using CPC...     

The synthetic processes of articular cartilage

The cells of cartilage are constantly remodeling the matrix in which they are suspended. The stimulus to initiate remodeling is probably the chondrocyte's response to physical and or chemical changes in the environment. Heat, pressure, friction, load, pH, and growth are examples of such factors, which, if altered, would have a dramatic effect on the cell's state of health. The mode of response by the chondrocyte is specific for a given stimulus. Elevated temperature, for example, switches on a set of genes, the heat shock genes, in chondrocytes. This results in the synthesis of a series of cellular protein that presumably in turn protects the cell from the injurious effects of heat. Load and pressure affect both the synthetic rate of matrix protein and the degradation rates of preexisting matrix. A number of low-molecular-weight proteins appear to be involved in anabolic and catabolic processes of cartilage. A protein recently isolated from synovium stimulates the synthesis of degradative enzymes in cartilage. This factor is probably involved in the remodeling process under normal physiologic conditions. More recently, it has been found in elevated levels under pathologic conditions such as in the synovial fluid of patients with rheumatoid and osteoarthritis. The mechanism by which this factor turns on the degradative pathway appears complex and is under investigation.     

The deleterious effects of drying on articular cartilage

Knee joints of mature rabbits were exposed to room air for periods of time ranging from thirty minutes to one hour in an attempt to mimic the human situation in the operating room. The animals were killed after the joint had been closed and activity in a cage had been allowed for twenty-four hours. When the animal was killed, cartilage was removed and was incubated with radioactive proline for four hours before light microscopy autoradiographs were made. Other samples were prepared for study by electron microscopy. The results in the animals that were killed immediately after the cartilage was exposed to room air and in those that were killed twenty-four hours after closure of the joint were identical. Both the ultrastructural and the autoradiographic findings indicated that the entire thickness of the articular cartilage was necrotic after sixty minutes of drying. Forty-five minutes of drying produced complete necrosis of the cartilage in half of the animals. In the other half, some cells survived, although many areas of the cartilage had complete necrosis, top to bottom. Thirty minutes of drying produced patchy necrosis that extended only to the middle zone of the cartilage. In joints that were exposed to room air for one hour, necrosis of the chondrocytes was completely prevented by irrigating the joint every five minutes with Ringer lactate solution.