The reaction of articular cartilage to injury and osteoarthritis (first of two parts)

Human urinary trypsin inhibitor inhibits the activation of pro-matrix metalloproteinases and proteoglycans release in rabbit articular cartilage

Treatment of primary cultured chondrocytes from rabbit articular cartilage with interleukin-1 (IL-1)alpha and plasminogen induced the production of pro-matrix metalloproteinase 1 (proMMP-1/interstitial collagenase), proMMP-3 (stromelysin 1) and proMMP-9 (gelatinase B), as well as their active forms. Human urinary trypsin inhibitor (UTI), a multipotent inhibitor of serine proteases, including plasmin inhibited the activation of proMMP-1, proMMP-3 and proMMP-9 when added to the culture medium together with IL-1alpha and plasminogen, in a dose-dependent manner. Moreover, UTI inhibited the release of proteoglycans induced by IL-1alpha and plasminogen from rabbit articular cartilage explants. These findings strongly suggest that UTI inhibits the destruction of articular cartilage induced by plasmin and/or MMPs. Thus, UTI probably exert an anti-osteoarthritic action via inactivation of proMMPs.

Expression of decorin and biglycan by rabbit articular chondrocytes. Effects of cytokines and phenotypic modulation

In this study, the levels of mRNAs coding for aggrecan, decorin and biglycan in rabbit articular chondrocytes were investigated, using both monolayer and 3D-alginate cultures treated with TGF-beta 1 and IL-1 beta. The cells were shown to express higher amounts of proteoglycan messages, specially the aggrecan, in gels than in monolayers. TGF-beta 1 increased aggrecan mRNA in both systems, whereas biglycan message was elevated only in alginate. It markedly decreased decorin expression in monolayer, either in primary or passaged cultures. In contrast, IL-1 beta had a weak inhibitory effect on both decorin and biglycan expression. Subculturing induced a dramatic decrease of aggrecan mRNA, while that of decorin augmented. Biglycan expression transiently increased after two passages, whereas it declined in further subcultures. Passaged chondrocytes transferred to alginate re-expressed high levels of aggrecan, decorin and biglycan. The data point to the influence of morphology, proliferative state and environment of the articular chondrocytes on their biosynthetic responses to cytokines. Although these immature cells do not fully reflect the adult chondrocytes present in the cartilage, this study may help in understanding the behaviour of these cells in osteoarticular diseases, where the surrounding extracellular matrix is profoundly altered.

Articular cartilage repair

Articular cartilage can tolerate a tremendous amount of intensive and repetitive physical stress. However, it manifests a striking inability to heal even the most minor injury. Both the remarkable functional characteristics and the healing limitations reflect the intricacies of its structure and biology. Cartilage is composed of chondrocytes embedded within an extracellular matrix of collagens, proteoglycans, and noncollagenous proteins. Together, these substances maintain the proper amount of water within the matrix, which confers its unique mechanical properties. The structure and composition of articular cartilage varies three-dimensionally, according to its distance from the surface and in relation to the distance from the cells. The stringent structural and biological requirements imply that any tissue capable of successful repair or replacement of damaged articular cartilage should be similarly constituted. The response of cartilage to injury differs from that of other tissues because of its avascularity, the immobility of chondrocytes, and the limited ability of mature chondrocytes to proliferate and alter their synthetic patterns. Therapeutic efforts have focused on bringing in new cells capable of chondrogenesis, and facilitating access to the vascular system. This review presents the basic science background and clinical experience with many of these methods and information on synthetic implants and biological adhesives. Although there are many exciting avenues of study that warrant enthusiasm, many questions remain. These issues need to be addressed by careful basic science investigations and both short- and long-term clinical trials using controlled, prospective, randomized study design.

Spontaneous repair of superficial defects in articular cartilage in a fetal lamb model

A fetal lamb model was developed to investigate the capacity of fetal articular cartilage for repair after the creation of a superficial defect. Superficial defects, 100 micrometers deep, were made in the articular cartilage of the trochlear groove in the distal aspect of the femur in eighteen fetal lambs that were halfway through the 145-day gestational period; the contralateral limb was used as a sham control. The wounds were allowed to heal in utero for three, seven, fourteen, twenty-one, or twenty-eight days. Seven days after the injury, the defects were filled with a hypocellular matrix, which stained lightly with safranin O. At twenty-eight days, the staining of the matrix was similar to that of the sham controls and the chondrocyte density and the architectural arrangement of the cell layers had been restored. An inflammatory response was not elicited, and no fibrous scar tissue was observed.

The effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the healing of full-thickness defects of articular cartilage

Articular cartilage has a limited capacity for repair. We investigated the effect of rhBMP-2 (recombinant human bone morphogenetic protein-2) on the healing of full-thickness osteochondral defects in adult New Zealand White rabbits. A single defect, three millimeters wide by three millimeters deep, was created in the trochlear groove of the right femur in eighty-nine rabbits. The defect was either left empty, filled with a plain collagen sponge, or filled with a collagen sponge impregnated with five micrograms of rhBMP-2. The animals were killed at four, eight, or twenty-four weeks, and the repair tissue was examined histologically and evaluated with use of a grading scale. The defects also were examined immunohistochemically for the presence of type-II collagen at four and eight weeks. The rate of bone repair was evaluated with fluorescent labeling of bone at two and four weeks and with use of fluorescence microscopy at eight weeks. Treatment with rhBMP-2 greatly accelerated the formation of new subchondral bone and improved the histological appearance of the overlying articular surface. At twenty-four weeks, the thickness of the repair cartilage was 70 per cent that of the normal adjacent cartilage and a new tidemark usually had formed between the repair cartilage and the underlying subchondral bone. The average total scores on the histological grading scale were significantly better (p < 0.01) for the defects treated with rhBMP-2 than for the untreated defects (those left empty or filled with a plain collagen sponge) at all time-points. Immunostaining with an antibody against type-II collagen showed the diffuse presence of this cartilage-specific collagen throughout the repair cartilage in the treated defects. The untreated defects demonstrated minimum staining with this antibody.

Effects of triamcinolone acetonide on an in vivo equine osteochondral fragment exercise model

The objective of this study was to determine the effects of intra-articularly administered triamcinolone acetonide (TA) in exercised equine athletes with carpal osteochondral fragmentation. Eighteen horses were randomly assigned to each of 3 groups. An osteochondral chip fragment was created in one randomly chosen intercarpal joint of each horse. Both intercarpal joints in the placebo control group (CNT) horses were injected with intra-articular administration (IA) of polyionic fluid. Both joints in the TA control group (TA CNT) horses were treated with 12 mg of TA in the intercarpal joint without an osteochondral fragment, and the opposite intercarpal joint was injected with a similar volume of polyionic fluid. The TA treated group (TA TX) horses were treated with 12 mg of TA in the joint that contained the osteochondral fragment and the opposite intercarpal joint was injected with a similar volume of polyionic fluid. All horses were treated IA on days 13 and 27 after surgery and exercised on a high speed treadmill for 6 weeks starting on Day 14. Horses in the TA TX group were significantly less lame than horses in the CNT and TA CNT groups. Horses in either TA CNT or TA TX groups had lower total protein, and higher hyaluronan, and glycosaminoglycan concentrations in synovial fluid than did those in the CNT group. Synovial membrane collected from subjects in TA CNT and TA TX groups had significantly less inflammatory cell infiltration, subintimal hyperplasia and subintimal fibrosis compared to the CNT group. Articular cartilage histomorphological parameters were significantly better from the TA CNT and TA TX groups compared to the CNT group. In conclusions, results from this study support favourable effects of TA on degree of clinically detectable lameness, and on synovial fluid, synovial membrane, and articular cartilage morphological parameters, both with direct intra-articular administration and remote site administration as compared to placebo treatment. The clinical use of IA administered TA in horses may be therapeutically beneficial in selected cases of osteochondral fragmentation and osteoarthritis.

The involvement of subchondral mineralized tissues in osteoarthrosis: quantitative microscopic evidence

This paper reviews evidence for the role of subchondral bone and calcified cartilage in the initiation and progression of osteoarthrosis (OA). There is consensus that OA is characterized by subchondral sclerosis, but disagreement about whether bone changes are concurrent with, primary to, or secondary to cartilage deterioration. Clinical observation suggests that bone density and cartilage fibrillation are inversely related. Evidence from the rabbit impulsive loading model is consistent with early bone changes, but evidence from other models of subchondral stiffening, such as the sheep metallic implant model, do not strongly support this idea. However, evidence from tibial angulation models and from the Pond-Nuki (anterior cruciate ligament resection) model show evidence that bone changes precede cartilage fibrillation temporally, and are associated spatially within a single joint. Evidence is also presented for the importance of calcified cartilage changes in pre-disposing the joint towards progression to OA. Microdamage accumulation and repair by vascular invasion may be a component of the pathogenesis of OA in some cases, but more work is needed to demonstrate this conclusively. We conclude that changes in the subchondral mineralized tissues are not required for initiation of cartilage fibrillation, but may be necessary for progression, and that only changes in bone and calcified cartilage close to the joint are significant to the disease process.

Evaluation of matrix scaffolds for tissue engineering of articular cartilage grafts

Injury to articular cartilage predisposes that joint to further degeneration and eventually osteoarthritis. Recent studies have demonstrated the feasibility of using chondrocytes together with different biomaterial carriers as grafts for the repair of cartilage defects. The following study was undertaken to determine the effect of a variety of these materials on chondrocyte growth and extracellular matrix synthesis. We cultured chondrocytes on several commonly used materials and compared their rates of synthesis of proteoglycan and collagen. Additionally, we evaluated them in a closed culture recirculating system on these materials and compared them with standard culture techniques. This was done to see whether such a bioreactor-type system can be used to enhance the quality of in vitro reconstructed tissues. Our results demonstrated marked variability with respect to how chondrocytes responded to culture on the various materials. Bioabsorbable polymers such as polyglycolic acid (PGA)--enhanced proteoglycan synthesis, whereas collagen matrices stimulated synthesis of collagen. The use of the closed culture system, in general, improved the rates of synthesis of collagen and proteoglycan on the different material scaffolds. Exceptions were collagen synthesis on collagen matrices: use of the closed culture system did not enhance the rate of synthesis. Rates of proteoglycan synthesis on PGA scaffold initially was higher in the closed culture system but did not sustain a difference over the entire course of the 3-week culture period. This study demonstrates the importance of carrier material for the purpose of cartilage tissue reconstruction in vitro.

Prostaglandin E2 up-regulates insulin-like growth factor binding protein-3 expression and synthesis in human articular chondrocytes by a c-AMP-independent pathway: role of calcium and protein kinase A and C

Insulin-like growth factor-1, IGF-1, is believed to be an important anabolic modulator of cartilage metabolism and its bioactivity and bioavailability is regulated, in part, by IGF-1 binding protein 3 (IGFBP-3). Prostaglandin E2 (PGE2) stimulates IGF-1 production by articular chondrocytes and we determined whether the eicosanoid could regulate IGFBP-3 and, as such, act as a modifier of IGF-1 action at a different level. Using human articular chondrocytes in high density primary culture, Western and Western ligand blotting to measure secreted IGFBP-3 protein, and Northern analysis to monitor IGFBP-3 mRNA levels, we demonstrated that PGE2 provoked a 3.9 +/- 1.1 (n = 3) fold increase in IGFBP-3 mRNA and protein. This effect was reversed by the Ca++ channel blockers, verapamil and nifedipine, and the Ca++/calmodulin inhibitor, W-7. The Ca+2 ionophore, ionomycin, mimicked the effects of PGE2 as did the phorbol ester PMA, which activates Ca++/-phospholipid-dependent protein kinase C (PKC). Cyclic AMP mimetics, such as forskolin, IBMX, Ro-20-1724, and Sp-cAMP, inhibited the expression and synthesis of the binding protein. PGE2 did not increase the levels of cAMP or protein kinase A (PKA) activity in chondrocytes. The PGE2 secretagogue, IL-1 beta, down-regulated control levels of IGFBP-3 which could be completely abrogated by pre-incubation with the tyrosine kinase inhibitor, erbstatin, and partially reversed (50 +/- 8%) by KT-5720, a PKA inhibitor. These observations suggested that PGE2 does not mediate the effect of its secretagogue and that IL-1 beta signalling in chondrocytes may involve multiple kinases of diverse substrate specificities. Dexamethasone down-regulated control, constitutive levels of IGFBP-3 mRNA and protein eliminating the previously demonstrated possibility of cross-talk between glucocorticoid receptor (GR) and PGE2 receptor signalling pathways. Taken together, our results suggest that PGE2 modulates IGFBP-3 expression, protein synthesis, and secretion, and that such regulation may modify human chondrocyte responsiveness to IGF-1 and influence cartilage metabolism.

Prostaglandin E2 stimulates incorporation of proline into collagenase digestible proteins in human articular chondrocytes: identification of an effector autocrine loop involving insulin-like growth factor I

Prostaglandin E2 (PGE2) stimulates collagen gene promoter activity in transfected human chondrocytes though no canonical cyclic AMP (cAMP) response element has been yet identified. Human insulin-like growth factor-1 (IGF-1) induces an increase in collagen type II expression and synthesis in chondrocytes. Since our preliminary data suggested that PGE2 can stimulate IGF-1 release from human articular chondrocytes, we examined whether the eicosanoid could influence collagen synthesis and whether the effect was mediated by IGF-1. Incubation of primary cultures of human articular chondrocytes with increasing concentrations of PGE2 resulted in a dose-dependent (ANOVA, F= 51.62, P < 0.0001, n = 5) and saturable increase in the synthesis and release of IGF-1 and expression of IGF-1 mRNA. At relatively low concentrations (30 pmol/1 to 30 nmol/l), PGE2 stimulated an increase in the incorporation of [3H]proline into collagenase digestible protein (CDP) (P < 0.01, n = 5) whereas at high levels (300 nmol/l to 3 micromol/l) of the eicosanoid, incorporation diminished precipitously. Human IGF-1 mimicked the effects of low PGE2 concentrations by stimulating in a dose-dependent (ANOVA, F= 31.65, P < 0.001, n = 3) and saturable fashion the incorporation of [3H]proline into CDP although the magnitude of the response induced by IGF-1 was far greater (3.5-fold). An IGF-1 receptor blocking antibody completely abrogated the IGF-1 induced response suggesting that the effect was specifically IGF-1 receptor mediated. Furthermore, the PGE2-induced increase in [3H]proline incorporation into CDP was inhibited (63%, P < 0.001, n = 7) by the addition to the culture medium of an anti-IGF-1 antibody. We conclude that PGE2 may act as a secretagogue of IGF-1 and that the latter growth factor may mediate, via an autocrine loop and the IGF-1 receptor, at least some of the anabolic effects of the eicosanoid on cartilage metabolism.

Histologic comparison of posterior cruciate ligaments from arthritic and age-matched knee specimens

Twenty-four posterior cruciate ligaments (PCLs) harvested at the time of total knee arthroplasty (TKA) were histologically compared with an age-matched group of 36 PCLs harvested from above-knee amputations, cadavers, and bone bank donors. Ligaments were considered histologically abnormal and degenerative if either loose, mucoid, myxoid, or cystic changes were noted. The magnitude of degeneration was defined as normal, slight, mild, moderate, or marked, based on the amount of tissue demonstrating change. Examination of the PCLs from the TKA group demonstrated 17% normal ligaments, 20% with mild focal changes, and 63% with marked degenerative changes. The control group demonstrated 45% normal cruciate ligaments and 33% with slight, 11% with mild, and 11% with moderate focal changes. No PCL from the control group showed marked changes. The overall degenerative changes between these two groups were found to be statistically significant (P < .001). This study demonstrated that the PCL obtained at the time of TKA is characterized by distinct histologic degenerative changes that are different from age-related changes (P < .001) and that the PCL is not spared degenerative changes in involved osteoarthritic knees. This may help explain the finding that the PCL in osteoarthritic knees is biomechanically abnormal. Many studies have reported excellent results with TKA systems that retain the PCL, implying that a completely normal PCL is not required or that neural input is sufficient for proper kinematic knee function in knees that have undergone total joint arthroplasty.

A comparison of abrasion burr arthroplasty and subchondral drilling in the treatment of full-thickness cartilage lesions in the rabbit

The purpose of this study was to observe the difference in healing of full-thickness articular cartilage defects treated with burr arthroplasty versus subchondral drilling. Cartilage was shaved off the medial femoral condyles of 39 rabbits without penetrating the subchondral plate. In left knees, two 2.0-mm holes were drilled into the condyle until bleeding was obtained. Right knees underwent a burr arthroplasty until punctate bleeding was observed. Animals were sacrificed at 6, 12, and 24 weeks postoperatively. Joint resurfacing and degenerative changes were evaluated grossly and histologically. Degenerative changes in the cartilage surface were observed with both treatments. Rabbits undergoing subchondral drilling had increased fibrocartilaginous healing with time, with a slight increase in degenerative changes. With burr arthroplasty, there was significant decrease in cartilaginous coverage of the exposed surface as well as progressive increase in degenerative changes. Although both techniques were suboptimal, histological evidence at 6 months suggests that subchondral drilling may result in a longer-lived repair than abrasion arthroplasty in the treatment of full-thickness lesions.

Techniques of cartilage growth enhancement: a review of the literature

This review attempts to present an overview of the literature pertaining to the techniques of cartilage growth enhancement. Only cartilage has an incomplete capacity for self-repair, especially of superficial defects. Full-thickness defects involving the subchondral bone can be repaired with the use of pluripotent progenitor cells from bone marrow or from transplanted perichondreum or periosteum. Bone-cartilage autografts and allografts transplanted into the cartilage defect heal primarily, but they loose their long-term biomechanical qualities because of transformation into fibrous cartilage. Cultivated human chondrocyte autografts may make cartilage healing possible in the future.

Human chondrocytes proliferate and produce matrix components in microcarrier suspension culture

Chondrocytes propagated in monolayer culture proliferate and change into 'fibroblastoid'-like cells. This change is characterized by a shift in production of collagen type II to I and from high- to low-molecular-weight proteoglycans. When propagated in three-dimensional culture, chondrocytes have limited ability to divide but re-express their original characteristics. The goal of the present study was to determine whether a microcarrier suspension culture system would support chondrocyte proliferation and phenotype expression. Our experiments indicate that a collagen type I microcarrier (cellagen) best supported chondrocyte proliferation and phenotype expression. Cells in cellagen microcarriers multiplied at least twentyfold within 2 weeks and had doubling times of 2 to 3 d. Viable and metabolically active cells were retrieved with ease. The harvested chondrocytes had no detectable staining for collagen type I and stained intensely for collagen type II. Our studies demonstrate that the microcarrier suspension culture system supports growth and enhances expression of the 'chondrocytic' phenotype. Attachment to a constrained surface and the fluid shear forces on the microcarriers during suspension culture may have helped chondrocytes to reacquire their rounded shape and produce cartilage matrix components.

Repair of partial-thickness defects in articular cartilage: cell recruitment from the synovial membrane

Partial-thickness defects evolving in mature articular cartilage do not heal spontaneously. This type of defect was created in the articular cartilage of adult rabbits and Yucatan minipigs, and the effects of chondroitinase ABC or trypsin, fibrin clots, and mitogenic growth factors on the healing process were examined histologically at intervals ranging from one to forty-eight weeks. The effect of chondroitinase ABC or trypsin was examined initially. Articular cartilage contains macromolecules, including proteoglycans, which render the surfaces of this tissue, and of partial-thickness defects within it, antiadhesive. Chondroitinase ABC digests the glycosaminoglycan chains of cartilage proteoglycans, and trypsin degrades their core proteins. To test the hypothesis that mesenchymal cells may be prevented from adhering to and migrating over the surfaces of partial-thickness defects by proteoglycans, we removed a superficial layer of these macromolecules from the surface of the defect with use of one of these enzymes. The treatment evoked an increase in the coverage of the defect surface with mesenchymal cells; when combined with the local application of a mitogenic growth factor (basic fibroblast growth factor, transforming growth factor-beta 1, epidermal growth factor, insulin-like growth factor-1, or growth hormone), the coverage was more extensive but mesenchymal cells did not extend into and completely fill the volume of the defect. When the surface of the defect was treated with chondroitinase ABC and the cavity of the defect was filled with a fibrin clot to furnish a matrix or scaffolding for the migration of cells therein, there was migration and proliferation of cells throughout the volume of the defect but at a low population density. Mesenchymal cells remodeled the deposited fibrin matrix, which was replaced by a loose fibrous connective tissue. When defects that had been treated with chondroitinase ABC were filled with a fibrin clot containing a mitogenic growth factor, mesenchymal cells filled the entire cavity of the defect, and the density of the cells was greatly increased, particularly when transforming growth factor-beta 1 was used. Histological studies revealed a continuous layer of mesenchymal cells extending from the synovial membrane across the superficial tangential zone of normal articular cartilage into the defect, indicating that the cells that were recruited for the repair process were of synovial origin. At forty-eight weeks, the entire cavity of the defect remained filled with a fibrous connective tissue.

Healing of chondral and osteochondral defects in a canine model: the role of cultured chondrocytes in regeneration of articular cartilage

In this study a canine model was developed to investigate the nature of early healing responses to both chondral and osteochondral defects and to evaluate the tissue regenerative capacity of cultured autologous chondrocytes in chondral defects. The healing response to surgically created chondral defects was minor, with little cellular infiltration. In contrast, osteochondral defects exhibited a rapid cellular response, resulting ultimately in the formation of fibrous tissue. The lack of significant cellular activity in chondral defects suggests that an evaluation of the capacity of cultured autologous chondrocytes to regenerate articular cartilage is best studied in chondral defects using the canine model. When dedifferentiated cultured articular chondrocytes were implanted into chondral defects, islands of type II collagen staining were demonstrated in the regenerative tissue within 6 weeks. The relatively early expression of cartilage specific markers by the implanted chondrocytes, coupled with the inability of untreated chondral defects to repair or regenerate, demonstrates the utility of the canine model in evaluating novel materials for cartilage repair and regeneration.

The dose-related effects of phenylbutazone and a methylprednisolone acetate formulation (Depo-Medrol) on cultured explants of equine carpal articular cartilage

The dose-related effects of phenylbutazone and Depo-Medrol on chondrocyte viability and chondrocyte-mediated synthesis and depletion of proteoglycans were investigated using cultured explants of equine middle carpal joint articular cartilage. Explants from 12 horses (941 x 3 mm diameter) were cultured for a total of 5 days, which included 3 days' exposure to either phenylbutazone (0, 2, 20, 200 or 2000 micrograms/mL) or Depo-Medrol (0, 20, 200 or 2000 micrograms/mL). For each explant, amino sugar content was used as a measure of proteoglycan content, 35S incorporation as a measure of the rate of proteoglycan synthesis and the number of pyknotic nuclei as a measure of cell death. During culture, control explants remained metabolically active and viable but suffered a net loss of proteoglycans. Proteoglycan loss was reduced by the presence of either phenylbutazone or Depo-Medrol. This effect was significant at clinically relevant concentrations of phenylbutazone (2-20 micrograms/mL), but not Depo-Medrol (20-200 micrograms/mL). Depo-Medrol caused a dose-dependent suppression of proteoglycan synthesis at all concentrations, but chondrocyte viability was affected only at the 2000 micrograms/mL dose. Phenylbutazone affected proteoglycan synthesis and cell viability only at the 2000 micrograms/mL concentration. At all concentrations, the anticatabolic effects of each drug influenced the proteoglycan content of the explants far more than did any antianabolic or cytotoxic drug effect. The results suggest that the therapeutic potential of both phenylbutazone and Depo-Medrol may not be restricted to their anti-inflammatory effects on the soft tissues of the joint.

Effects of function and weight-bearing on the healing of full-thickness cartilage defects in rats

The effects of different degrees of active motion were studied in 30 male Wistar rats. In all rats a full-thickness cartilage defect of 1.0 mm in diameter was made in the medial condyle of both femurs. The rats were then allocated to the following three groups; i) exercising group which followed a 4-week training program of moderate intensity, ii) a non-weight-bearing group in which unilateral achilles tenotomy was made to reduce weight-bearing and iii) control rats which were allowed normal cage activity. Healing of the defect was evaluated by planimetric analysis and histologic evaluation. Effects of the training program was confirmed by a lesser weight increase in the exercise group. Planimetric analysis revealed no differences between the groups in the area of the original defect at the end of the experiment. There were no differences in healing ratio (area of healing/area of original defect) between the exercise and control groups, whereas the healing ratio was increased in the non-weight-bearing limbs compared with control and exercised rats. The favorable effect of non-weight-bearing was further indicated by differences in healing ratio between the two limbs in the non-weight-bearing group. Histological evaluation showed that the defect was repaired by a fibrocartilage substance along the periphery of the original defect and fibrovascular granulation tissue centrally. Evaluated by microscopic appearance, there were no qualitative differences between the three groups. We conclude that in the initial repair process by fibrocartilage non-weight-bearing is conductive to healing of full-thickness cartilage defects. The short-term effects revealed no differences on qualitative healing. Increased activity does not seem to prolong the initial fibrocartilage healing compared with normal activity with full weight-bearing.

Modulation of interleukin-1 receptor expression by transforming growth factor-beta in cultured rabbit articular chondrocytes: analysis by reverse transcription-polymerase chain reaction

Interleukin-1 receptor type I (IL-1RI) expression in cultured rabbit articular chondrocytes (RAC) was studied by reverse transcription-polymerase chain reaction (RT-PCR). A cDNA probe specific for the rabbit IL-1RI gene was constructed using primers derived from the sequence data of the human, murine and chick receptors. Transforming growth factor-beta 1 (TGF beta-1) was shown to transiently increase the level of expected 900-bp PCR product at 1 h of incubation and decrease the expression at 48 and 72 h with no effect at 24 h. In receptor binding assays using [125I]-IL-1 alpha, TGF beta decreased IL-1R bioactivity at all time points. These results suggest that TGF beta-induced down-regulation of IL-1 RI could be responsible for its ability to antagonize the effect of IL-1 and that TGF beta may have a role in the repair of articular cartilage.

Exercise and the musculoskeletal system

1. Normal joints in individuals of all ages may tolerate prolonged and vigorous exercise without adverse consequences or accelerated development of OA. 2. Individuals who have underlying muscle weakness or imbalance, neurological abnormalities, anatomical variances, and who engage in significant amounts of exercise that stress the lower extremities, may accelerate the development of OA. 3. Individuals who have suffered injuries to supporting structures may also be susceptible to accelerated development of OA in weight-bearing joints, even without increased stress to the joint from exercise. 4. Certain individuals with established degenerative or inflammatory arthritis may benefit from supervised exercise programmes. 5. Still more information is needed so that physicians can identify subjects at risk for the development of OA, advise the millions of participants about the beneficial and deleterious effects of regular exercise and sports participation, and develop successful rehabilitation programmes for injured joints.

Effects of exercise and polysulfated glycosaminoglycan on repair of articular cartilage defects in the equine carpus

Our aim was to determine if mild to moderate postoperative exercise and intra-articular polysulfated glycosaminoglycan result in improved repair of large, experimentally induced osteochondral defects in a weight-bearing surface of equine joints. Arthroscopic debridement was used to produce full-thickness defects in a weight-bearing area of the radial carpal bones in 18 ponies. The ponies were randomly assigned to two groups balanced for age: nine animals in the exercise and nine in the no exercise group. Six ponies in each group were medicated weekly for 5 weeks with an intra-articular injection of polysulfated glycosaminoglycan in one middle carpal joint beginning at the time of operation. Walking (twice daily) was begun 6 days postoperatively, and by the twelfth week postoperatively the ponies were trotting for 25 min and walking for 15 min twice daily. At the time of the ponies' death, 17 weeks postoperatively, each defect had an average of 50-75% coverage with repair tissue. Exercised, medicated joints had a significantly smaller area of coverage with repair tissue than exercised, nonmedicated joints. Cartilaginous repair tissue from exercised ponies contained significantly more glycosaminoglycan and type-II collagen (r = 0.53, p < 0.05). The ratio of hydroxylysine to hydroxyproline was significantly lower and the ratio of collagen content to total protein was significantly higher in the repair tissue of medicated joints than in the repair tissue of nonmedicated joints; this is consistent with the presence of less type-II collagen in the repair tissue in medicated joints. We concluded that postoperative exercise was beneficial and that the immediate postoperative use of intra-articular polysulfated glycosaminoglycan was detrimental to the development of cartilaginous repair tissue in large osteochondral defects of equine joints.

Healing and remodeling of articular incongruities in a rabbit fracture model

Healing of 0.5 or 1.0-millimeter step-off defects associated with displaced intra-articular fractures of the medial femoral condyle was examined in fifty-four adult New Zealand White rabbits. The rabbits were treated with either immobilization for three weeks, intermittent active motion, or continuous passive motion for seven days. At twelve weeks, the healing and remodeling of the step-off defects were examined with use of contact-pressure maps on pressure-sensitive film, light microscopy (with hematoxylin and eosin or safranin-O staining), and scanning electron microscopy. Macroscopically, the sharp profile that had been present initially with both sizes of step-off defect had rounded off; however, there was less residual incongruity with the 0.5-millimeter step-offs than with the 1.0-millimeter step-offs. Among step-off defects of the same size, the method of treatment had no discernible effect on the macroscopic appearance of the surface of the joint. With fresh step-offs (the control group), the contact pressure of the cartilage on the elevated side was approximately three times greater than that at a distance from the step-off. On the depressed side, an unloaded zone extended approximately three times the height of the step-off, with an average width of 3.4 millimeters for the 1.0-millimeter step-offs and 1.6 millimeters for the 0.5-millimeter step-offs. After healing and remodeling, the unloaded zone still averaged 2.5 millimeters in width for the 1.0-millimeter step-offs but had decreased to only 0.35 millimeter in width for the 0.5-millimeter step-offs. For seven of the nine 0.5-millimeter step-offs, the contact pressure in the previously unloaded zone ranged from 0.5 to 1.5 megapascals, with a mean of 0.8 megapascal (40 per cent of the normal mean contact pressure at this location). Under light microscopy, the cartilage on the elevated side of the healed step-offs had decreased in thickness, was displaced toward the defect and tapered toward the depressed side, and ended in a hypocellular tissue flap. In contrast, the cartilage on the depressed side had thickened as a result of hyperplasia of the chondrocytes and hypertrophy of the cartilage and had failed to establish continuity between the sides of the defect. There was a marked increase in the subchondral vascular bed and re-establishment of the subchondral plate. With the exception of the aforementioned hypocellular tissue flap, safranin O stained the cartilage on both levels of the step-off uniformly, which indicated the absence of glycosaminoglycan depletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell origin and differentiation in the repair of full-thickness defects of articular cartilage

The origin and differentiation of cells in the repair of three-millimeter-diameter, cylindrical, full-thickness drilled defects of articular cartilage were studied histologically in New Zealand White rabbits. The animals were allowed to move freely after the operation. Three hundred and sixty-four individual defects from 122 animals were examined as long as forty-eight weeks postoperatively. In the first few days, fibrinous arcades were established across the defect, from surface edge to surface edge, and this served to orient mesenchymal cell ingrowth along the long axes. The first evidence of synthesis of a cartilage extracellular matrix, as defined by safranin-O staining, appeared at ten days. At two weeks, cartilage was present immediately beneath the surface of collagenous tissue that was rich in flattened fibrocartilaginous cells in virtually all specimens. At three weeks, the sites of almost all of the defects had a well demarcated layer of cartilage containing chondrocytes. An essentially complete repopulation of the defects occurred at six, eight, ten, and twelve weeks, with progressive differentiation of cells to chondroblasts, chondrocytes, and osteoblasts and synthesis of cartilage and bone matrices in their appropriate locations. At twenty-four weeks, both the tidemark and the compact lamellar subchondral bone plate had been re-established. The cancellous woven bone that had formed initially in the depths of the defect was replaced by lamellar, coarse cancellous bone. Autoradiography after labeling with 3H-thymidine and 3H-cytidine demonstrated that chondrocytes from the residual adjacent articular cartilage did not participate in the repopulation of the defect. The repair was mediated wholly by the proliferation and differentiation of mesenchymal cells of the marrow. Intra-articular injections of 3H-thymidine seven days after the operation clearly labeled this mesenchymal cell pool. The label, initially taken up by undifferentiated mesenchymal cells, progressively appeared in fibroblasts, osteoblasts, articular chondroblasts, and chondrocytes, indicating their origin from the primitive mesenchymal cells of the marrow. Early traces of degeneration of the cartilage matrix were seen in many defects at twelve to twenty weeks, with the prevalence and intensity of the degeneration increasing at twenty-four, thirty-six, and forty-eight weeks. Polarized light microscopy demonstrated failure of the newly synthesized repair matrix to become adherent to, and integrated with, the cartilage immediately adjacent to the drill-hole, even when light microscopy had shown apparent continuity of the tissue. In many instances, a clear gap was seen between repair and residual cartilage.(ABSTRACT TRUNCATED AT 400 WORDS)

Cellular aspects on treatment of cartilage injuries

Cellular aspects on articular cartilage growth and development are discussed. Cells with chondrogenic potential are described and current treatment models for cartilage injuries are considered. A rabbit model for treatment of articular cartilage defects with autologous cultured and transplanted chondrocytes for treatment of knee cartilage defects in humans are discussed.

The repair of osteochondral defects using an exogenous fibrin clot. An experimental study in dogs

To evaluate the ability of an exogenous fibrin clot to hasten or optimize the repair of full-thickness articular cartilage defects, 4-mm diameter, full-thickness articular cartilage defects in 20 adult mongrel dogs were packed with an exogenous fibrin clot that had been prepared from each animal. The defects were created in a loaded and unloaded portion of the femoral trochlea. The healing response was then examined using routine histology at various intervals from 2 weeks to 6 months. Both the experimental (clot-filled) and control (empty) defects healed through a proliferation of fibrous connective tissue that eventually modulated into fibrocartilage. However, in the 2-, 4-, and 8-week animals, the experimental defects (both loaded and unloaded) demonstrated a more organized and advanced healing response than did the control defects. This difference was less pronounced in the 12- and 24-week animals. In all specimens, the clot-filled defects healed more uniformly than controls with less surface depression. In general, the unloaded sites were more uniform in healing than the corresponding loaded sites.

Preliminary observations of chondral abrasion in a canine model

Articular cartilage repair was followed for one year in skeletally mature dogs after destabilisation by anterior cruciate ligament transection of the stifle joint (CT), abrasion of the inferior medial condyle (ABR) to bleeding bone, or anterior cruciate transection followed by chondral abrasion (CT/ABR). ABR animals formed repair cartilage at the abrasion site (ABR and CT/ABR) at six months as determined by arthroscopy and at necropsy. CT and CT/ABR animals had an additional cartilage ulcer on the superior aspect of the medial condyle. The abraded site extended in CT/ABR condyles. Repair cartilage (ABR and CT/ABR) contained reduced amounts of proteoglycan as seen by histological loss of safranin O staining and reduced uronic acid content. Fibrocartilage was suggested by histological appearance, hypocellularity, and a higher hydroxyproline content. In contrast with ABR animals, the repair cartilage in the CT/ABR animals contained near normal amounts of hydroxyproline. Collagen profiles of abrasion site repair cartilage in ABR animals had more types I and V collagens, similar amounts of type VI collagen, and decreased amounts of types II, IX, and XI collagens than CT/ABR animals. The results of this study are consistent with abrasion chondroplasty leading to a repair cartilage. Despite extended ulcers, repair cartilage from the destabilised joint (CT/ABR) animals was more hyaline-like in its hydroxyproline content and collagen composition than repair cartilage from the stable joint (ABR animals). In these models additional measures appear to be needed as the defects induced by abrasion chondroplasty did not form a functional hyaline cartilage.

Cushioning properties of footwear during walking: accelerometer and force platform measurements

Repetitive impact loadings of the musculoskeletal system have been linked to the development of osteoarthritis and low back pain. An important function of footwear is to attenuate foot-ground impacts. The purpose of this study was to measure the effects of footwear types upon the impact ground reaction forces and the transient stress waves transmitted up the lower limb. The results have shown that both transient stress waves and ground reaction forces are affected by footwear during walking. Furthermore, with harder midsoles footwear, higher shock was transmitted to the lower extremities. This paper confirms the importance of using footwear to cushion the impact generated at heelstrike during walking. It also reveals that both shock and force measurements are required to evaluate and prescribe footwear to patients suffering from impact-related chronic diseases.

Histological examination of surface repair tissue after successful osteotomy for osteoarthritis of the hip joint

In this study biopsy specimens of the surface repair tissue from the weightbearing area of the hip joint were collected from 15 patients who had undergone successful valgus osteotomy, and these were examined histologically. In 6 of the 15 patients the specimens stained strongly with safranin-O in all three layers of the matrix. However, the repair tissue from another 6 patients showed strong staining only in the intermediate and deep layers, while that from 2 patients stained only in the deep layer. Specimens from 5 patients were stained for S-100 protein and positive cells were detected in all cases, demonstrating that the cells in the repair tissue were chondrocytes. However, there was no tide mark in the repair tissue and the arrangement of the cells differed from that in normal cartilage. Discontinuity of the subchondral bone was also noted. These findings make it likely that the repair tissue was of bone marrow origin.

The pathology of canine hip dysplasia

Although the complete pathogenesis of cartilage damage in canine hip dysplasia has not been completely worked out, it appears that joint laxity with resultant excessive stresses upon articular cartilage is the initiating factor. Grossly, this damage is characterized by cartilage thinning with potential exposure of subchondral bone, osteophyte formation, and pannus formation. Microscopically, there is a marked variation in chondrocyte cellularity, with focal regions of hypocellularity and chondrocyte clusters and synovial lining cell hyperplasia and hypertrophy as well as a decrease in proteoglycan content. This latter change has been substantiated biomechanically. Ultrastructural studies indicate that there is extensive alteration of collagen organization within the cartilage.

Rabbit knee immobilization: bone remodeling precedes cartilage degradation

This study analyzed processes underlying osteoporosis and osteoarthrosis after short-term immobilization of the right hind limb of postadolescent (2.8 kg) and mature (4.0 kg) rabbits. After 3 weeks, the lateral posterior aspect of the lateral tibial plateau and the lateral femoral condyle of the immobilized limb exhibited prominent subchondral vascular eruptions. Femoral metaphyseal bone density decreased 27 and 18% in the immobilized limbs of postadolescent and mature rabbits, respectively. Calcein green fluorescence increased 1.9-fold (p less than 0.001) in the metaphyseal trabeculae of immobilized femurs. With immobilization, sulfate incorporation into femoral cartilage glycosaminoglycan increased, although total cartilage glycosaminoglycan and hydroxyproline levels were unchanged. Thymidine incorporation into DNA increased four- to fivefold in tibial and femoral cartilage of the immobilized limb. In this study, bone loss and remodeling preceded erosive cartilage degradation.

Effects of osteochondral defect size on cartilage contact stress

Contact stress distributions were studied in vitro for 13 dog knees, with full-thickness osteochondral defects drilled in the weight-bearing area of both femoral condyles. Diameters of the circular defects were concentrically enlarged from 1 to 7 mm. Digitally-imaged Fuji film was used to record cartilage contact stress distribution on femoral condyles for each increment of defect diameter. All specimens showed at least some tendency for contact stress concentration at the rim of the defects. However, detailed distributions had large interspecimen variability and, within a given specimen, contact stress distributions became progressively more nonuniform around the defect rim as the diameter was enlarged. Averaged over the full series of 26 condyles, circumferential mean cartilage contact stress around the defect rim was only moderately higher (by 10-30%) than intact surface's peak local contact stress [series average = 6.2 mega pascals (MPa)]. Maximal rim stress concentration occurred for 2 mm defects, there being a consistent trend toward mild rim stress decrease with further defect enlargement. Such modest contact stress elevations, per se, are probably insufficient to inhibit defect repair or to cause degeneration of surrounding cartilage. However, near the defect rim (for all diameters), the radial component of the gradient of contact stress (i.e., radial-direction variation of contact stress) was consistently elevated by an order of magnitude above that for intact, condyle articular cartilage.

Are cytokines involved in osteoarthritic pathophysiology?

The putative role and mechanism of action of cytokines in the progression of arthritic diseases such as osteoarthritis (OA) has received particular attention because of the important interaction between articular cartilage and synovium in the pathophysiology of the diseased state. Maintaining matrix homeostasis in the normal adult cartilage phenotype requires normal turnover of matrix components, principally collagen and proteoglycan. Chondrocytes and synovial fibroblasts are targeted, via specific cell-surface receptors, by cytokines like interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) to produce matrix proteases and to suppress the synthesis of collagen and proteoglycan. Thus, cytokines not only favor tissue destruction, but also inhibit tissue repair. A structurally heterogeneous group of factors capable of directly antagonizing cytokine action is described, which acts either by blocking cytokine-receptor binding, inhibiting local cytokine synthesis, or complexing the cytokine into an inactive form. Furthermore, many growth factors, such as transforming growth factor-beta (TGF-beta), can counteract the net effect of cytokines by stimulating the synthesis of matrix components or natural inhibitors of cartilage degrading enzymes.

Characteristics of the immediate postarthroscopic blood clot formation in the knee joint

The immediate postoperative bleeding and blood clot formation was observed in 26 human knee joints following a variety of arthroscopic surgical procedures. Observations were made following lavage with lactated Ringer's and normal saline solutions. Bleeding occurred from all incised vascular tissue. Blood clot accumulated after each solution within 5 min following tourniquet release and decompression of the joint. Most of the blood clot remained unattached within the joint cavity. Blood clot did attach to all surgically incised or excised surfaces. The clinical relevance of these observations is related to the potential role of the blood clot in intraarticular tissue repair following arthroscopic surgery.

Experimental haemarthrosis in rhesus monkeys: morphometric, biochemical and metabolic analyses

The effects of a single episode of massive haemarthrosis in rhesus monkeys were studied. Autologous whole blood was injected into a femorotibial joint of 16 anaesthetized monkeys, equally divided into four groups and killed 7 days, 2, 3 and 6 months post-injection (PI). Synovial membrane and femoral articular cartilage were analysed morphometrically and articular cartilage was further analysed biochemically and metabolically. At 7 days PI, morphometric evaluation revealed a significant increase (P less than 0.05) in synovial membrane cellularity and synovial intimal thickness of injected joints versus control joints. This change was no longer evident 2 months PI. There was also an overall (n = 16) significant increase (P less than 0.05) in femoral articular cartilage cellularity in injected joints. The average chondrocyte lacuna area of injected joints was not statistically different from the control joints. Biochemical analyses of femoral articular cartilage revealed a significant decrease in hexosamine concentration (P less than 0.05) of injected joints. There was no significant difference between the injected and control joints in hydroxyproline or total protein concentration. Metabolic analyses revealed a significant increase (P less than 0.05) in cartilage collagenous protein production by injected joints compared with control joints. There were no significant differences in cartilage or secreted total protein production between injected and control joints. There were also no significant differences in cartilage or secreted proteoglycan production between joints. Morphometric evaluation of articular tissues following massive haemarthrosis has quantified a temporary hyperplastic reaction. A significant decrease in cartilage hexosamine concentration in haemarthrotic joints suggests this is a crucial biochemical event in the pathogenesis of blood-induced cartilage destruction.

The effect of exercise on the healing of articular cartilage defects in the equine carpus

Arthroscopic surgery was performed on 12 horses (2-4 years of age) to create a 7 x 14 mm full-thickness cartilage defect in one radial carpal bone and in the contralateral third carpal bone. Six horses remained confined to a small paddock and six horses underwent a program of increasing exercise consisting of walking, trotting, and cantering for 13 weeks. All lesions showed evidence of healing at week 6 that progressed to more complete healing at week 13. There was no difference in the amount of repair tissue covering the defect. Histologically, the lesions healed with a combination of fibrous tissue and fibrocartilage. The repair tissue was significantly thicker in the exercised horses but there was no difference in repair quality. It was concluded that radial carpal and third carpal lesions have an equal ability to heal and that early postoperative exercise is not detrimental to the repair tissue within these carpal cartilage defects.

Effect of ofloxacin on the uptake of [3H]thymidine by articular cartilage cells in the rat

Ofloxacin (900 mg/kg) was orally administered to Sprague-Dawley rats aged 4 weeks. A single dosage induced chondrocyte degeneration in the middle zone of the articular cartilage 5 h later and cavity formation 12 and 24 h later. The number of cells labeled with [3H]thymidine was decreased in histologically normal and abnormal cartilage at 5 h. Incorporation rate of [3H]thymidine into the articular cartilage was gradually decreased until 12 h later, but increased above the control level at 24 h. Another experiment showed that labeled cells were retained for a longer period than in control rats in the middle zone at the predilection site of osteochondrosis.

Effect of osteochondral defects on articular cartilage. Contact pressures studied in dog knees

Full thickness osteochondral defects 6 mm in diameter were created in the weight-bearing regions of the femoral condyles in 5 adult mongrel dogs to study the contact pressure changes accompanying healing. A digital imaging technique employing Fuji Prescale film mapped contact pressures following 11 months of healing for comparison with contralateral normal knees, and knees with freshly made defects. Although all defects healed uneventfully with subchondral plate reconstitution and with growth restoration of the articular surface, the repair soft tissue appeared histologically to be primarily fibrous tissue, with varying degrees of a fibrocartilaginous component. The mean and peak stresses about fresh defects were not appreciably different from those about healed defects. Neither were there substantial differences in the total cartilage area making contact, except when very low loads were applied. The results suggest that the repair tissue is of poor mechanical quality, and does not contribute appreciably to weight bearing. The cartilage adjacent to the defect did not experience high stresses; neither gross nor light microscopic evidence of degeneration appeared at 11 months. If degeneration does occur following such defects, our data suggest that it is not because of elevated contact stresses.

Arthroscopic treatment of sports-related anterior osteophytes in the ankle

Osteophytes on the anterior aspect of the tibia and anterior talus are common in athletes such as dancers, runners, and high jumpers who impact with quick and forceful dorsiflexion to this area. This pathology is often confirmed easily on lateral x-ray films. Excision, debridement, and/or abrasion arthroplasty can be performed arthroscopically to remove osteophytic bone. The joint space is easily approached and managed using small joint or even regular-sized arthroscopic instruments. Care is taken to reshape the anterior tibia and/or talus to its original contour, thus avoiding impingement of the joint space and scuffing of adjacent articular cartilage. Proper abrasion depths and punch lesions may be needed to expose bleeding capillary bone. This allows a regeneration of a fibrocartilage covering that not only decreases pain but also permits a return to functional and athletic activities. Postoperative treatment, including physical therapy, is described. Three case studies are presented that adequately demonstrate this problem, along with the corrective measures taken. Each case concludes with a brief summary of follow-up.