Articular responses to purified cartilage proteoglycans

Evaluation of cartilage injury in horses with osteochondral fragments in the metacarpo-/metatarsophalangeal joint: A study on 823 arthroscopies

BACKGROUND

Osteochondral fragment removal is commonly performed but there are little scientific data supporting this procedure in the absence of clinical signs. More information is needed to facilitate clinical decision-making regarding fragment removal of the metacarpo-/metatarsophalangeal joint.

OBJECTIVES

To assess prevalence of cartilage injury in the equine metacarpo-/metatarsophalangeal joint and its association to fragment size, location, age and lameness.

STUDY DESIGN

Retrospective observational study.

METHODS

Clinical records, including radiographs of 823 metacarpo-/metatarsophalangeal joints (640 horses) that underwent arthroscopic fragment removal, were reviewed. Fragment size, intra-articular fragment location and cartilage injury score were recorded. Presence of synovitis was retrospectively evaluated in 157 joints. Kruskal-Wallis and Mann-Whitney tests were used for group comparisons, and Dunn's post hoc test was applied for multiple comparisons. Linear regression analysis was used to assess strength of association between age and mean cartilage score. Univariable regression analysis was performed and variables with p < 0.2 were used in the final mixed-effects multivariable model to which backwards stepwise selection was applied. Significance level was p < 0.05.

RESULTS

Cartilage injury was present in 28.8% (95% CI = 25.8-32.0) of joints. Lameness was not associated with fragment location or fragment size. Fragment size was not associated with cartilage injury. Age (OR = 1.35, 95% CI = 1.22-1.48, p < 0.001) and lameness (OR = 5.03, 95% CI = 2.27-11.68, p < 0.001) were associated with cartilage injury as well as fragment location (palmar/plantar, OR = 0.22, 95% CI = 0.13-0.38, p < 0.001), with dorsal fragments being more likely to be associated with cartilage lesions than palmar/plantar fragments. There was a significant association between age and mean cartilage score (b = 0.18, 95% CI = 0.14-0.22, p < 0.001).

MAIN LIMITATIONS

The series included a heterogenous group of horses of different breed, sex, age and use. Data were collected retrospectively and could, in parts, not be fully evaluated.

CONCLUSIONS

Early fragment removal, especially in joints with dorsal fragmentation, can be beneficial to avoid future cartilage injuries in equine athletes.

The emerging role of fibroblast-like synoviocytes-mediated synovitis in osteoarthritis: An update

Osteoarthritis (OA), the most ubiquitous degenerative disease affecting the entire joint, is characterized by cartilage degradation and synovial inflammation. Although the pathogenesis of OA remains poorly understood, synovial inflammation is known to play an important role in OA development. However, studies on OA pathophysiology have focused more on cartilage degeneration and osteophytes, rather than on the inflamed and thickened synovium. Fibroblast-like synoviocytes (FLS) produce a series of pro-inflammatory regulators, such as inflammatory cytokines, nitric oxide (NO) and prostaglandin E₂ (PGE₂ ). These regulators are positively associated with the clinical symptoms of OA, such as inflammatory pain, joint swelling and disease development. A better understanding of the inflammatory immune response in OA-FLS could provide a novel approach to comprehensive treatment strategies for OA. Here, we have summarized recently published literatures referring to epigenetic modifications, activated signalling pathways and inflammation-associated factors that are involved in OA-FLS-mediated inflammation. In addition, the current related clinical trials and future perspectives were also summarized.

Synovitis in knee osteoarthritis: a precursor of disease?

OBJECTIVES

It is unknown whether joint inflammation precedes other articular tissue damage in osteoarthritis. Therefore, this study aims to determine if synovitis precedes the development of radiographic knee osteoarthritis (ROA).

METHODS

The participants in this nested case-control study were selected from persons in the Osteoarthritis Initiative with knees that had a Kellgren Lawrence grading (KLG)=0 at baseline (BL). These knees were evaluated annually with radiography and non-contrast-enhanced MRI over 4 years. MRIs were assessed for effusion-synovitis and Hoffa-synovitis. Case knees were defined by ROA (KLG≥2) on the postero-anterior knee radiographs at any assessment after BL. Radiographs were assessed at P0 (time of onset of ROA), 1 year prior to P0 (P-1) and at BL. Controls were participants who did not develop incident ROA (iROA) from BL to 48 months).

RESULTS

133 knees of 120 persons with ROA (83 women) were matched to 133 control knees (83 women). ORs for occurrence of iROA associated with the presence of effusion-synovitis at BL, P-1 and P0 were 1.56 (95% CI 0.86 to 2.81), 3.23 (1.72 to 6.06) and 4.7 (1.10 to 2.95), respectively. The ORs for the occurrence of iROA associated with the presence of Hoffa-synovitis at BL, P-1 and P0 were 1.80 (1.1 to 2.95), 2.47 (1.45 to 4.23) and 2.40 (1.43 to 4.04), respectively.

CONCLUSIONS

Effusion-synovitis and Hoffa-synovitis strongly predicted the development of iROA.

Arthritis gene therapy and its tortuous path into the clinic

Arthritis is a disease of joints. The biology of joints makes them very difficult targets for drug delivery in a manner that is specific and selective. This is especially true for proteinaceous drugs ("biologics"). Gene transfer is the only technology that can solve the delivery problem in a clinically reasonable fashion. There is an abundance of preclinical data confirming that genes can be efficiently transferred to tissues within joints by intra-articular injection using a variety of different vectors in conjunction with ex vivo and in vivo strategies. Using the appropriate gene transfer technologies, long-term, intra-articular expression of anti-arthritic transgenes at therapeutic concentrations can be achieved. Numerous studies confirm that gene therapy is effective in treating experimental models of rheumatoid arthritis (RA) and osteoarthritis (OA) in the laboratory. A limited number of clinical trials have been completed, which confirm safety and feasibility but only 3 protocols have reached phase II; as yet, there is no unambiguous evidence of efficacy in human disease. Only 2 clinical trials are presently underway, both phase II studies using allogeneic chondrocytes expressing transforming growth factor-β1 for the treatment of OA. Phase I studies using adeno-associated virus to deliver interleukin-1Ra in OA and interferon-β in RA are going through the regulatory process. It is to be hoped that the recent successes in treating rare, Mendelian diseases by gene therapy will lead to accelerated development of genetic treatments for common, non-Mendelian diseases, such as arthritis.

Presence of MRI-detected joint effusion and synovitis increases the risk of cartilage loss in knees without osteoarthritis at 30-month follow-up: the MOST study

OBJECTIVE

To evaluate if two different measures of synovial activation, baseline Hoffa synovitis and effusion synovitis, assessed by MRI, predict cartilage loss in the tibiofemoral joint at 30 months follow-up in subjects with neither cartilage damage nor tibiofemoral radiographic osteoarthritis of the knee.

METHODS

Non-contrast-enhanced MRI was performed using proton density-weighted fat-suppressed sequences in the axial and sagittal planes and a short tau inversion recovery sequence in the coronal plane. Hoffa synovitis, effusion synovitis and cartilage status were assessed semiquantitatively according to the WORMS scoring system. Included were knees that had neither radiographic osteoarthritis nor MRI-detected tibiofemoral cartilage damage at the baseline visit. The presence of Hoffa synovitis was defined as any grade ≥ 2 (range 0-3) and effusion synovitis as any grade ≥ 2 (range 0-3). Logistic regression was performed to examine the relation of the presence of either measure to the risk of cartilage loss at 30 months adjusting for other potential confounders.

RESULTS

Of 514 knees included in the analysis, the prevalence of Hoffa synovitis and effusion synovitis at the baseline visit was 8.4% and 10.3%, respectively. In the multivariable analysis, baseline effusion synovitis was associated with an increased risk of cartilage loss. No such association was observed for baseline Hoffa synovitis.

CONCLUSIONS

Baseline effusion synovitis, but not Hoffa synovitis, predicted cartilage loss. The findings suggest that effusion synovitis, a reflection of inflammatory activity including joint effusion and synovitic thickening, may play a role in the future development of cartilage lesions in knees without osteoarthritis.

Imaging of synovitis in osteoarthritis: current status and outlook

OBJECTIVES

This review article provides an overview of the current state of imaging of synovitis in osteoarthritis (OA), looking at recent advances and controversies and focusing particularly on the application of ultrasound and magnetic resonance imaging (MRI) in the assessment of the hand and knee joint. Computed tomography and nuclear medicine including positron emission tomography are also briefly discussed.

METHODS

PubMed and MEDLINE search for articles published up to 2010, using the keywords synovitis, osteoarthritis, rheumatoid arthritis, pathogenesis, imaging, radiography, computed tomography, nuclear medicine, magnetic resonance imaging, ultrasound, and pain.

RESULTS

Synovitis is defined as inflammation of the synovial membrane. Modern imaging techniques have demonstrated that synovial pathology is common in the early and late stages of OA and may be associated with pain. The current standard for OA imaging in clinical practice is conventional radiography but it does not allow direct visualization of synovitis. MRI without contrast administration, although widely used in clinical studies, cannot assess synovitis directly. Contrast-enhanced MRI and ultrasound, however, both allow direct visualization of synovitis including early inflammatory changes. They are regularly used to image synovitis in rheumatoid arthritis and increasingly in OA.

CONCLUSIONS

Synovitis is increasingly recognized as an important feature of the pathophysiology of OA, although there is conflicting evidence with respect to its association with disease severity and clinical parameters. Contrast-enhanced MRI and ultrasound are the most important methods for assessing synovitis associated with OA.

Etiopathogenesis of osteoarthritis

Because of the implications for prevention and treatment, how a clinician views osteoarthritis (OA) matters. We view OA as an attempt to contain a mechanical problem in the joint and as failed repair of damage caused by excessive mechanical stress on the joint. OA is organ failure of the synovial joint. Because of insufficient focus on reduction of the habitually loaded contact area of the joint and on aberrant loading, we believe that therapeutic efforts aimed at pathogenetic mechanisms in OA have been misdirected: neither the large role that a reduction of excessive levels of mechanical stress plays in promoting the healing response in OA nor the evidence that relief of joint pain and improvement in function, rather than the appearance of the articular surface, are the most important outcomes of the healing process have been sufficiently emphasized. Various mechanical abnormalities can trigger the processes involved in repair and attempts by the joint to contain the mechanical insult, but without a return to mechanical normality, attempts at healing will fail. In our view, drugs may be helpful symptomatically, but cannot accomplish this. In our view, as long as the joint remains in the same adverse mechanical environment that got it into trouble in the first place, it is unlikely that a drug that inhibits a specific enzyme or cytokine in the pathways of cartilage breakdown, or further stimulates the already increased synthesis of cartilage matrix molecules will solve the problem of OA. Also, because the subchondral bone is critically important in containing the mechanical abnormalities that damage the cartilage, emphasis on cartilage repair alone is likely to be futile. On the other hand, if the abnormal stresses on the joint are corrected, intervention with a structure-modifying drug may be superfluous.

Pathophysiology and Management of Arthritis

This article primarily reviews the pathophysiology, diagnosis, and therapy of osteoarthritis but also briefly discusses immune-mediated arthritides. Given the frequency of occurrence of arthritis in veterinary patients, it is crucial that clinicians be aware of the mechanisms of the disease and be comfortable with diagnosis and treatment. Unfortunately,there is a great deal of information still to be learned in regards to management of these cases. Because of the rapid and continuing research gains, it behooves clinicians to maintain a current awareness of the related literature.

Joint irrigation as treatment for osteoarthritis

Irrigation is necessary to achieve distension and visualization of the joint during arthroscopy. Clinical improvement observed after diagnostic arthroscopy has been attributed to irrigation, and this is supported by sound pathophysiologic rationales. Studies have been performed using various irrigation techniques with and without concomitant arthroscopy. Unblinded studies have generally yielded favorable results, although recent blinded studies have demonstrated a substantial and durable placebo effect, but little support for the benefit of the irrigation procedure.

The role of cytokines as inflammatory mediators in osteoarthritis: lessons from animal models

Studies in animal models of osteoarthritis (OA) have been used extensively to gain insight into the pathogenesis of OA, but early studies largely ignored inflammation except as a secondary phenomenon. Synovitis has often been noted as a feature in experimental OA, and more recent work has established a central role for inflammatory cytokines as biochemical signals which stimulate chondrocytes to release cartilage-degrading proteinases. Thus, proteinase inhibitors, cytokine antagonists and receptor blocking antibodies, and growth/differentiation factors have been considered as potential therapeutic agents and targets for gene therapy. Although there is some disagreement, it is generally accepted that IL-1 is the pivotal cytokine at early and late stages, while TNF-alpha is involved primarily in the onset of arthritis. Other cytokines released during the inflammatory process in the OA joint may be regulatory (IL-6, IL-8) or inhibitory (IL-4, IL-10, IL-13, IFN-gamma). Furthermore, studies in animal models have illustrated the potentially beneficial effects of anticytokine therapy with monoclonal antibodies or receptor antagonists, although local rather than systemic delivery would be necessary for the largely localized OA in humans. Transgenic or knockout mice have also provided insights into general mechanisms of cytokine-induced cartilage degradation but have not directly addressed OA pathogenesis. Similarly, animals with spontaneous or transgenic modifications in cartilage matrix components, growth/differentiation factors, or developmentally regulated transcription factors have provided information about potential gene defects that predispose to OA without addressing the role of inflammatory mediators in cartilage destruction. Although the multiple etiologies of human OA indicate that it is more complex than any animal model, the use of appropriate, well-defined animal models will establish the feasibility of novel forms of therapy.

Intra-articular pressure, elastance and range of motion in healthy and injured racehorse metacarpophalangeal joints

The objective of this study was to determine if intraarticular pressure, elastance of the soft tissue forming the dorsal pouch, and range of motion in flexion measurements are significantly different in Thoroughbred metacarpophalangeal joints with clinical evidence of idiopathic synovitis, primary synovitis, synovitis/capsulitis, or osteoarthritis relative to clinically normal joints. Forty-two metacarpophalangeal joints, in 25 active or retired Thoroughbred racehorses, were categorised by palpation and visual inspection of the palmar pouch into one of 4 increasing grades of distention. Intra-articular pressures were then measured using 2 pressure transducers attached to 22-gauge needles from both the dorsal and palmar pouches simultaneously while the horses stood squarely under mild sedation. After obtaining baseline pressure measurements, a third needle was inserted into the dorsal pouch, and 0.5 ml increments of saline solution were added every 10 s to perform a pressure/volume (elastance) study of the dorsal pouch. The elastance study for each joint ended when leakage into the palmar pouch was detected by the pressure transducer placed in that region. A lateral radiographic view was taken of each metacarpophalangeal joint in maximal flexion. The maximum angle of flexion was measured from the radiograph, and this angle was subtracted from 180 degrees to acquire the range of motion in flexion. In this study, all Thoroughbreds with clinical evidence of lameness and/or sensitivity to flexion, referable to the metacarpophalangeal joint region, had fluid distention of the palmar pouch (grade 2 or 3 distention). The 16 metacarpophalangeal joints with no clinical abnormalities had a mean palmar pouch pressure of -1.25 mmHg. Joints afflicted with synovitis/capsulitis had the highest intraarticular pressures (mean +51.00 mmHg); however, joints with idiopathic synovitis (mean +15.71 mmHg), primary synovitis (mean +28.33 mmHg) and osteoarthritis (mean +26.20 mmHg) also had significantly elevated intraarticular pressures relative to the clinically normal group. Thoroughbred metacarpophalangeal joints diagnosed with synovitis/capsulitis, or osteoarthritis, had significantly increased elastance (stiffness) of the soft tissue forming the dorsal pouch relative to the normal group and, probably, as a result significantly decreased range of motion in flexion. The presence of primary synovitis alone did not have a significant immediate effect on elastance of the dorsal pouch and range of motion in flexion. The 16 Thoroughbred metacarpophalangeal joints assessed as having no clinical abnormalities had a mean range of motion in flexion of 60.81 degrees. The mean range of motion in flexion of Thoroughbred metacarpophalangeal joints with a clinical diagnosis of primary synovitis was 53.67 degrees; idiopathic synovitis 52.14 degrees; synovitis/capsulitis 44.20 degrees; and those with radiographic evidence of moderate to marked osteoarthritis 30.80 degrees. This study demonstrated that, as the severity of the clinical evidence of metacarpophalangeal joint injury/disease increased, the range of motion in flexion decreased.

Osteoarthritis. Joint anatomy, physiology, and pathobiology

Normal cartilage is a complex material consisting of a solid matrix composed primarily of collagen and proteoglycan, which is saturated with water. It is not a homogenous material. The interaction of the physical and biochemical structures of cartilage is necessary to allow the normal function of providing nearly frictionless motion, wear resistance, joint congruence, and transmission of load to subchondral bone. Chondrocytes are responsible for synthesizing and maintaining this material. Osteoarthritis occurs when there is disruption of normal cartilage structure and homeostasis. Osteoarthritis results from a complex interaction of biochemical and biomechanical factors that occur concurrently and serve to perpetuate degradative change. The progressive pathologic change that occurs in osteoarthritis has been characterized, not only for articular cartilage but also for periarticular tissues. The occurrence of mechanical and biochemical changes is well established, but the role of each in the etiopathogenesis of osteoarthritis is not rigidly defined. It is likely that there are multiple etiologies sharing common pathways of physical and chemical disruption. (see Fig. 1). The changes associated with osteoarthritis ultimately have an impact on the patient through decreased ability to use the joint or the production of pain, or both. Unfortunately, once these changes are severe enough to be recognized clinically, they are likely to be irreversible with current treatments. Nevertheless, understanding the basic mechanisms involved in the development and progression of osteoarthritis provides a basis for establishing a reasonable expectation for the patient and a rational plan for medical and surgical treatment of this condition.

Even low-grade synovitis significantly accelerates the clearance of protein from the canine knee. Implications for measurement of synovial fluid "markers" of osteoarthritis

OBJECTIVE

In recent studies, the synovial fluid concentration of molecules derived from the extracellular matrix of articular cartilage has been used to deduce the magnitude of cartilage destruction or repair in osteoarthritic (OA) joints. Because low-grade synovitis is often present in such joints, we assessed the effect of synovial inflammation on the clearance of a prototypical protein, albumin, from synovial fluid.

METHODS

131I-labeled albumin (RISA) was injected into 1 (control) knee of each of 14 dogs. The concentration of RISA in synovial fluid aspirated 7 hours after the injection and serial measurements of surface radioactivity were used to calculate the volume of distribution (Vd) and clearance of RISA. One week later, synovitis was induced in the contralateral knee by intraarticular injection of various quantities of calcium pyrophosphate dihydrate (CPPD) crystals, after which RISA was injected into that joint and these measurements were repeated.

RESULTS

Intraarticular injection of 500 micrograms of CPPD crystals produced intense synovitis, with a mean synovial fluid white blood cell (WBC) count of 43,200 cells/mm3, and values for RISA Vd and RISA clearance (36.5 ml and 33.7 microliters/minute) were much higher than those for saline-injected control knees (2.7 ml and 1.5 microliters/minute, respectively). Injection of 0.5 microgram of CPPD also produced marked synovitis and values for Vd and RISA clearance that were 2-3-fold greater than those in the contralateral knee. The low-grade synovitis produced by only 0.05 microgram of CPPD, which resulted in synovial fluid WBC counts as low as 1,000-2,000 cells/mm3, was accompanied by increases in the clearance and Vd of RISA to levels approximately 40% and approximately 80% higher, respectively, than those for the contralateral knee.

CONCLUSION

Even mild synovitis, as seen in OA, may significantly increase the clearance of a protein from the joint. Synovitis is a significant variable which must be considered in studies of putative chondroprotective drugs if conclusions about the effects of drugs on cartilage metabolism are to be drawn from changes in the synovial fluid concentration of a "marker" protein.

Theories of wear and loosening in hip prostheses. Wear-induced loosening vs loosening-induced wear--a review

The observation of perioprosthetic granulomas containing wear debris around apparently well-fixed as well as around loose-fitting prosthetic components has led to the development of the hypothesis of wear-induced loosening. However, the hypothesis of wear-induced loosening can neither explain the rapid early prosthetic migration detected by roentgen stereophotogrammetry nor the epidemiology of clinical failure without supplementary ad hoc-assumptions. By contrast, apart from explaining the rapid early prosthetic migration detected by roentgen stereophotogrammetry, the theory of early loosening can explain the development of wear granulomas as well as to a great extent the epidemiology of clinical failure.

The role of cartilage-derived antigens, pro-coagulant activity and fibrinolysis in the pathogenesis of osteoarthritis

Superficial fraying, splitting and fibrillation of articular cartilage as a consequence of ageing or mechanical injury is not always associated with joint pain. However, similar cartilage lesions accompanied by synovitis and engorgement of the subchondral vasculature generally is; the disorder being known as osteoarthritis (OA). In this hypothesis it is contended that the progression of early cartilage fibrillation to symptomatic OA arises as a consequence of the antigenic nature of cartilage components which when released into synovial fluid and the circulation can stimulate leukocytes (to a varying degree) to produce a number of factors some of which promote blood coagulation. While it is known that with ageing hyper-coagulation and plaque deposition is increased, the augmentation of this process by factors released by activated leukocytes is considered to exacerbate the problem. These haematological events may be particularly relevant in individuals whose leukocytes are hypersensitive to the cartilage-derived antigens, and whose fibrinolytic system is less capable of mobilizing the thrombi deposited in synovial tissues and the subchondral vascular tree.

Cellular immunity to cartilage proteoglycans: relevance to the pathogenesis of ankylosing spondylitis

Cellular immunity to cartilage proteoglycans may be responsible for sustaining chronic inflammation in ankylosing spondylitis. This hypothesis was examined by measuring peripheral blood and synovial fluid mononuclear cell proliferation in five preparations of human cartilage proteoglycan monomer in vitro. Peripheral blood mononuclear cells from 25 patients and synovial fluid mononuclear cells from five patients were compared with those from normal and disease control subjects matched for age. No significant differences were found between the three groups. This suggests that autoimmune responses to cartilage proteoglycans are unlikely to play a significant part in the pathogenesis of ankylosing spondylitis.

The role of proteinases in cartilage destruction

Most of the organic, extracellular matrix of articular cartilage consists of collagens and proteoglycans. Their degradation is initiated extra- or peri-cellularly by proteinases produced locally by cells in and around the joint. Although enzymes from all four classes of proteinases can degrade the cartilagenous matrix, serine proteinases, particularly plasmin, and various neutral metalloproteinases (NMPs) are likely to be the key enzymes in this process. Much attention has been paid to members of the latter group, which are synthesised both by the resident, mesenchymal cells of the joint and by various types of white blood cells which colonise it during inflammation. NMPs can be conveniently grouped into three classes, the collagenases, the stromelysins and the gelatinases. Two members are known for each class, with the recently identified "pump" (Putative Metalloproteinase) probably constituting a third member of the stromelysin group. Regulation of these enzymes is complex. Cells normally synthesise NMPs at low rates, but their production increases markedly following cellular activation by cytokines or certain other stimuli. Major control points for enzyme synthesis occur at the levels of transcription and the conversion of proenzyme to active enzyme; enzyme activity is further regulated through the action of inhibitors. Alpha-2 macroglobulin is the major systemic inhibitor, while a number of tissue inhibitors act as local regulators. These include at least two TIMPs and several IMPs. Pharmacologic manipulation of NMP activity holds promise as an approach to anti-erosive therapy in arthritis.

Changes of immunoregulatory properties and induction of autoimmune reactivity to cartilage in rabbits with antigen-induced arthritis

The chronicity of the antigen-induced arthritis is characterized as dependent on the development of cell-mediated immunity to the antigen, but the exact mechanisms underlying are unclear. We have evidenced decreased suppressor and increased helper cell potential in the early phase of arthritis as result of the immunization procedure. In the late phase of arthritis proliferative responses of spleen lymphocytes to cartilage proteoglycans were revealed which were neither present in immunized animals without arthritis induction nor in the early phase of arthritis. The changes of the regulatory properties on the T-cell level are probably responsible for the transition of acute arthritis into the chronic stage. The deficiency of an effective suppression and/or the increased helper cell potential results in the activation of B- and T-lymphocytes with increased cell-mediated and humoral immune responsiveness to the antigen maintaining the inflammatory process for a long time. In this situation the release of cartilage proteoglycans during the acute joint reaction induces autoimmune responses against cartilage which could contribute to the chronification of inflammation and to cartilage degradation.

Increased levels of proteoglycan fragments in knee joint fluid after injury

We measured levels of cartilage proteoglycan (PG) fragments in knee joint synovial fluid obtained from patients with previous trauma of the knee, early gonarthrosis, or pyrophosphate synovitis, and in age-matched control subjects. During the initial 3-4 weeks after rupture of the anterior cruciate ligament or the meniscus (confirmed by arthroscopy), markedly increased PG fragment levels were found. At later times after trauma (up to 4 years), many of these patients still had significantly elevated levels of cartilage PG fragments in the joint fluid. In a group of older patients with gonarthrosis, these levels were only moderately elevated, while in patients with acute pseudogout, greatly increased levels were observed. Although longitudinal studies are needed to validate the significance, PG fragments in joint fluid may be a marker for early posttraumatic arthrosis.

HIG-82: an established cell line from rabbit periarticular soft tissue, which retains the "activatable" phenotype

We have isolated a continuous cell line from soft tissue lining the knee joints of rabbits. Designated HIG-82, this line was produced by spontaneous establishment of an aging, late-passage culture of primary cells. Like unpassaged, primary cells, HIG-82 cells can be activated by a number of stimuli, including phorbol myristate acetate (PMA), interleukin-1 (IL-1), and the endocytosis of latex beads. Activated cells secrete collagenase, gelatinase, caseinase (stromelysin), and prostaglandin E2 (PGE2) into their culture medium. Pseudodiploid, HIG-82 cells combine a high plating efficiency with a doubling time of approximately 24 h. As primary tissue of this origin is difficult to obtain in large quantities and shows cellular heterogeneity, the HIG-82 cell line should facilitate research into the biology and biochemistry of the fibroblastic cells that line the diarthrodial joints of mammals. Such cells are likely to be important in the pathophysiology of various arthritides.