Response Of Articular Cartilage Research Articles

Propagation of surface fissures in articular cartilage in response to cyclic loading in vitro

Background. Mechanical overloading of synovial joints can damage the articular cartilage surface and may lead to osteoarthritis. However, causal links between mechanical and biological events in cartilage are poorly understood. Objectives. To test the hypothesis that surface fissures in cartilage can propagate mechanically if the joint surface is subjected to vigorous cyclic loading. Methods. Thirty-five cartilage-on-bone specimens, 15-mm square, were removed from mature bovine knee and shoulder joints. Specimens were loaded by means of a 9-mm-diameter flat indenter with a beveled edge, and their compressive strength determined. Failure occurred in the cartilage surface at an average stress of 36 MPa. Cartilage fissures were marked with Indian ink, photographed, and their length and width measured using image analysis software. Each damaged specimen was subjected to cyclic loading at 40% of its compressive strength, at 0.5 Hz, for up to 5 h. Fissure length and width were measured at regular intervals. After testing, fissure depth was measured from histological sections, and compared with measurements from damaged cartilage which was not cyclically loaded. Results. Cyclic loading caused cartilage fissures to increase in length (mean 353%, P<0.01) and width (360%, P<0.01) but not depth. Propagation was rapid at first, but approached equilibrium after several hundred cycles. Rehydration in saline had no effect on fissure length, but width returned to pre-cyclic loading values. Conclusion. Cartilage fissures can propagate mechanically when a joint surface is subjected to cyclic compressive loading in vitro. The transient opening-up of fissures to form wide surface “wounds” during cyclic loading could be of biological significance if it occurred in living people. Relevance In living joints, wide open fissures in the cartilage surface could promote degenerative changes in the tissue.

Induction of apoptosis of articular chondrocytes and suppression ofarticular cartilage proteoglycan synthesis by heat shock

We investigated cellular and matrix responses ofarticular cartilage to heat shock. Rat articular cartilage waspretreated at 37°C for 24 h before being exposed to 48°C for10min and subsequently incubated at 37°C for 1, 2, 4, 7, 10,and 14 days. Following heat shock, a terminal deoxynucleotidyltransferase nick end labeling assay showed that articularchondrocyte apoptosis appeared at day 1, peaked at day 7,and declined by day 14. Analysis by transmission electronmicroscopy confirmed that the chondrocytes had characteristicmorphological features of apoptosis; immunohistochemicalstaining revealed that caspase-3 activity inchondrocytes increased, 3-B-3-positive articular chondrocytesdecreased in number, and the expression of 3-B-3 nativeepitope in articular chondrocytes was reduced. Safranin-Ostaining revealed that depletion of proteoglycans in the matrixwas not found in any group. Morphological and biochemicalevidence from this study suggested that heat shock at 48°Cinduced articular chondrocyte apoptosis and suppressedproteoglycan synthesis of articular cartilage in vitro. Thisstudy thus provides evidence of the onset of osteoarthritisinduced by heat shock and a basis for choosing a temperatureat which malignant bone tumor cells can be killed with minimaldamage to articular cartilage.

Topographical analysis of the structural, biochemical and dynamic biomechanical properties of cartilage in an ovine model of osteoarthritis

Objective The relationship between the topographical variations in the structural, biochemical and dynamic biomechanical properties of articular cartilage (AC) before and 6 months after meniscectomy has not been previously reported but is clearly relevant to our understanding of the role of mechanical factors on the pathogenesis of osteoarthritis (OA). The objective of this study was to address this deficiency using an ovine model of OA induced by bilateral lateral meniscectomy.Design The dynamic effective shear modulus (G*) and phase lag were determined ex vivo at 26 individual locations over the medial and lateral tibial plateaux of non-operated and meniscectomized ovine joints 6 months after surgery using a novel hand-held dynamic indentation probe. AC thickness was measured with a needle penetration probe. The AC from the same topographical locations as indented was then analysed for sulfated glycosaminoglycans (S-GAG) as a measure of proteoglycan (PG) levels, collagen and water content. Histological evaluation of the collagen organization using quantitative analysis of birefringence intensity was performed on stained tissue sections from the same topographical locations of each animal.Results It was demonstrated that the AC of the entire lateral tibial compartment of the meniscectomized joints underwent significant local degenerative and compensatory changes as indicated by a decreased G* and an increase in phase lag and water content. This was accompanied by a decrease in PG content of the AC of the middle and inner regions. While the AC of the outer region of the lateral meniscectomized compartment showed a marked increase in PG content and a more than two-fold increase in thickness, these tissues were also found to be structurally inferior, as indicated by a decreased G* and abnormal collagen birefringence intensity. The AC thickness was elevated at all locations of the lateral and medial tibial plateau of the meniscectomized joints. Strong and significant correlations between the biomechanical and biochemical data were established for a number of the parameters examined, especially between collagen content and G*, collagen content and AC thickness, and G* and AC thickness. An inverse correlation between S-GAG content and G* was only apparent in non-operated control tissues, whereas correlations between collagen and water content, water content and G*, and water content and thickness were evident for AC of the meniscectomized tibial plateaux. Less striking changes were noted in the medial compartment where the intact meniscus remained in place. However, elevated PG content, thicker AC together with slight changes in G* suggested an early hypertrophic response in these tissues.Conclusions This study has highlighted the variable response of AC in different topographical regions of meniscectomized joints to the altered mechanical stresses introduced by this surgical procedure. The AC at the joint margins, while thicker and richer in PG, was found to be biomechanically softer (lower shear modulus) than normal AC, and because of this, would be expected to undergo degenerative changes with time leading to the onset of OA. Copyright 2003 OsteoArthritis Research Society International. Published by Elsevier Science Ltd. All rights reserved.

Biomechanical, histological and immunohistological studies of patellar cartilage in an ovine model of osteoarthritis induced by lateral meniscectomy

Objective: To evaluate the biomechanical, histological and immunohistochemical changes induced in patellar articular cartilage (AC) in ovine stifle joints 3 months after bilateral lateral meniscectomy, a procedure known to induce experimental osteoarthritis (OA) in the femoro-tibial joint (FTJ).Methodology: Fifteen mature adult Merino female sheep were used in this study. Ten were subjected to bilateral-lateral meniscectomy, while the remaining five were used as ‘non-operated controls’ (NOC). All animals were killed 3 months post-surgery. Topographical biomechanical indentation tests were performed on each patellae using a UMIS-2000 micro-indentation system. Initial load, relaxed and unload shear moduli were determined using an elastic analytical model, while the permeability was assessed by comparing the indentation response to a simulated indentation test conducted using a poroelastic finite element model. Immunohistochemical, normal and polarized histological studies were performed on each specimen after biomechanical testing.Results: Patellar AC from meniscectomized joints exhibited an overall decrease in initial (−34%), relaxed (−32%) and unload shear modulus (−22%), and an increase in the permeability (+72%) relative to NOC cartilage (P<0.01). The most significant differences in mechanical properties occurred on the lateral and central aspects of the patellae. There were no significant histological difference in staining between sections from NOC and meniscectomized joint AC using Toluidine Blue, a dye which binds to proteoglycans. However immunohistochemical staining with monoclonal antibody MAb 3B3(−), a putative marker of early OA change in PGs, demonstrated increased binding in the lateral and central regions of patellar sections from meniscectomized joints relative to the same regions of NOC AC. Moreover polarized light microscopy of Picro Sirius red stained sections revealed a significant decrease in birefringence intensity in the superficial-middle zones of the lateral and central regions of the patellar cartilage derived from the meniscectomized joints.Conclusion: This study has demonstrated that lateral meniscectomy is a procedure which was known to induce classical OA like changes in AC and subchondral bone of the FTJ also produced an early pathological response in the patellar AC.

Hypertrophic repair of articular cartilage in experimental osteoarthrosis.

Section of the anterior cruciate ligament has been performed in the knee of 11 mature dogs. The macroscopically normal cartilage from patella and femoral trochlea of animals killed from 2 to 32 weeks after operation was used for histological, histomorphometrical, and biochemical analysis. Previously undescribed degenerative lesions of the superficial matrix were observed, and there was evidence for secondary healing of these lesions. An early and progressive decrease in superficial cell density and a later progressive increase in cartilage thickness without any change in the cell density of the middle and deep cartilage layers was found. A slight increase in water content with no reduction in glycosaminoglycan content was observed. The results suggest that joint laxity results initially in superficial degenerative changes and later in hypertrophic regenerative changes due to cell proliferation and increased matrix synthesis. Hypertrophic remodeling of articular cartilage in response to abnormal mechanical stresses is postulated.

Changes in the metabolism of the proteoglycans from sheep articular cartilage in response to mechanical stress

The effect of altered mechanical stress on the metabolism of sheep articular cartilage has been investigated. A simple experimental model involving the immobilisation of a single sheep foreleg was used to study the effect of increased or decreased functional demand on the chemical composition of, and the incorporation of labelled acetate into, the proteoglycans of sheep articular cartilage. By immobilisation of one of the sheep forelegs, mechanical stress is removed from that particular joint, while increased stress is placed on the other foreleg. The load distribution about the two hind legs remains essentially the same. After a 4-week immobilisation period there was a significant increase in the hexuronic acid content of the cartilage from the loadbearing ankle joint, and a corresponding decrease in the hexuronic acid content of the non-loadbearing joint cartilage. Hexosamine analyses of the cartilage from each joint showed that the major chemical occurred in the chondroitin sulphate fraction. From analyses of the extracted and isolated proteoglycans from each experimental joint it was evident that there was a significant decrease in the molecular weight of the proteoglycan from the non-loadbearing joint. In vitro studies showed increased incorporation of labelled acetate into the chondroitin sulphate fraction from the loadbearing joint but a corresponding decreased incorporation into the non-loadbearing immobilised joint cartilage. These results suggest that the changes observed in the chemical composition of the cartilage from the loadbearing and non-loadbearing joints may be accounted for in part by changes in the biosynthesis of the cartilage proteoglycan in response to altered functional demand.