Sustained superiority in KOOS subscores after matrix-associated chondrocyte implantation using spheroids compared to microfracture.

PURPOSE: To evaluate the safety and efficacy of matrix-associated autologous chondrocyte implantation (ACI) using spheroids in comparison to arthroscopic microfracture for the treatment of symptomatic cartilage defects of the knee. METHODS: In a prospective multicenter-controlled trial, patients aged between 18 and 50 years, with single symptomatic focal cartilage defects between 1 and 4 cm2 (mean 2.6 ± 0.8, median 2.75, range 1.44-5.00) in the knee were randomized to treatment with ACI with spheroids (n = 52) or microfracture (n = 50). Primary clinical outcome was assessed by the Knee Injury and Osteoarthritis Outcome Score (KOOS). Analyses were performed in a defined hierarchical manner where outcomes of ACI were first compared to baseline values followed by a comparison to the microfracture group with repeated-measures ANCOVA with a non-inferiority approach. Subgroup analyses were performed to investigate the influence of age and defect size on the overall KOOS. Secondary clinical outcomes were the magnetic resonance observation of cartilage repair tissue (MOCART), modified Lysholm score and International Knee Documentation Committee (IKDC) examination form. Safety data focused on adverse events. Here the 5 years results are presented at which there were 33 observed cases in the ACI group and 30 in the microfracture group. RESULTS: The overall KOOS and its five subscores were significantly improved compared to baseline for both the ACI and microfracture group. Non-inferiority of ACI to microfracture was confirmed for the overall KOOS and the subscores, while for the subscores activities of daily living, quality of life and sports and recreation of the threshold for superiority was passed. In the ACI group, a notably more rapid initial improvement of the KOOS was found at three months for the older age group compared to the younger age group and the microfracture group. No other differences were found based on age or defect size. In addition, clinical improvement was found for the MOCART, modified Lysholm and IKDC examination form both the ACI and microfracture group. No safety concern related to either treatment was observed. CONCLUSION: This study confirms the safety and efficacy of matrix-associated ACI with spheroids at a mid to long-term follow-up. Non-inferiority of ACI to microfracture was confirmed for the overall KOOS and all subscores, while superiority was reached for the subscores activities of daily living, quality of life and sports and recreation in the ACI group. This underlines the importance of ACI for the young and active patients. LEVEL OF EVIDENCE: I.

Safety and Efficacy of Matrix-Associated Autologous Chondrocyte Implantation With Spheroids for Patellofemoral or Tibiofemoral Defects: A 5-Year Follow-up of a Phase 2, Dose-Confirmation Trial.

BACKGROUND: Matrix-associated autologous chondrocyte implantation (ACI) is a well-established treatment for cartilage defects. High-level evidence at midterm follow-up is limited, especially for ACI using spheroids (spherical aggregates of ex vivo expanded human autologous chondrocytes and self-synthesized extracellular matrix). PURPOSE: To assess the safety and efficacy of 3-dimensional matrix-associated ACI using spheroids to treat medium to large cartilage defects on different locations in the knee joint (patella, trochlea, and femoral condyle) at 5-year follow-up. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: A total of 75 patients aged 18 to 50 years with medium to large (4-10 cm2), isolated, single cartilage defects, International Cartilage Repair Society grade 3 or 4, were randomized on a single-blind basis to treatment with ACI at 1 of 3 dose levels: 3 to 7, 10 to 30, or 40 to 70 spheroids/cm2 of defect size. Outcomes were assessed via changes from baseline Knee injury and Osteoarthritis Outcome Score (KOOS), International Knee Documentation Committee score, and modified Lysholm assessments at 1- and 5-year follow-up. Structural repair was evaluated using MOCART (magnetic resonance observation of cartilage repair tissue) score. Treatment-related adverse events were assessed up to 5 years for all patients. The overall KOOS at 12 months was assessed for superiority versus baseline in a 1-sample, 2-sided t test. RESULTS: A total of 73 patients were treated: 24 in the low-dose group, 25 in the medium-dose group, and 24 in the high-dose group. The overall KOOS improved from 57.0 ± 15.2 at baseline to 73.4 ± 17.3 at 1-year follow-up (P < .0001) and 76.9 ± 19.3 at 5-year follow-up (P < .0001), independent of the applied dose. The different defect locations (patella, trochlea, and weightbearing part of the femoral condyles; P = .2216) and defect sizes (P = .8706) showed comparable clinical improvement. No differences between the various doses were observed. The overall treatment failure rate until 5 years was 4%. Most treatment-related adverse events occurred within the first 12 months after implantation, with the most frequent adverse reactions being joint effusion (n = 71), arthralgia (n = 14), and joint swelling (n = 9). CONCLUSION: ACI using spheroids was safe and effective for defect sizes up to 10 cm2 and showed maintenance of efficacy up to 5 years for all 3 doses that were investigated. REGISTRATION: NCT01225575 (ClinicalTrials.gov identifier); 2009-016816-20 (EudraCT number).

Matrix-Associated Autologous Chondrocyte Implantation with Spheroid Technology Is Superior to Arthroscopic Microfracture at 36 Months Regarding Activities of Daily Living and Sporting Activities after Treatment.

OBJECTIVE: Matrix-associated autologous chondrocyte implantation (ACI) and microfracture (MF) are well-established treatments for cartilage defects of the knee. However, high-level evidence comparing microfracture and spheroid technology ACI is limited. DESIGN: Prospective, phase III clinical trial with patients randomized to ACI (N = 52) or MF (N = 50). Level of evidence: 1, randomized controlled trial. Both procedures followed standard protocols. For ACI 10 to 70 spheroids/cm2 were administered. Primary outcome measure was the Knee Injury and Osteoarthritis Outcome Score (KOOS). This report presents results for 36 months after treatment. RESULTS: Both ACI and MF showed significant improvement over the entire 3-year observation period. For the overall KOOS, noninferiority of ACI (the intended primary goal of the study) was formally confirmed; additionally, for the subscores "Activities of Daily Living" and "Sport and Recreation," superiority of ACI over MF was shown at descriptive level. Occurrence of adverse events were not different between both treatments (ACI 77%; MF 74%). Four patients in the MF group required reoperation which was defined as treatment failure. No treatment failure was reported for the ACI group. CONCLUSIONS: Patients treated with matrix-associated ACI with spheroid technology showed substantial improvement in various clinical outcomes after 36 months. The advantages of ACI compared with microfracture was underlined by demonstrating noninferiority, in overall KOOS and superiority in the KOOS subscores "Activities of Daily Living" and "Sport and Recreation." In the present study, subgroups comparing different age groups and defect sizes showed comparable clinical outcomes.

Safety and efficacy of matrix-associated autologous chondrocyte implantation with spheroid technology is independent of spheroid dose after 4 years.

PURPOSE: The aim of this study was to investigate the effect of product dose in autologous chondrocyte implantation (ACI) for the treatment of full-thickness cartilage defects of the knee and to assess its influence on clinical and morphological mid-term outcome. METHODS: Seventy-five patients were included in this single-blind, randomised, prospective, controlled clinical trial. Patients were assigned randomly to three different dose groups [low (3-7 spheroids/cm2), medium (10-30 spheroids/cm2), or high (40-70 spheroids/cm2)] and assessed using standardised clinical and morphological scoring systems (KOOS, IKDC, MOCART) for 4 years following the intervention. RESULTS: The analysis population comprised 75 patients (22 women, 53 men) aged 34 ± 9 years. Defect sizes ranged from 2 to 10 cm2 following intraoperative debridement. The assessment of the primary variable 'overall KOOS' showed a statistically significant improvement, compared with baseline, for each dose group, i.e., at baseline the mean 'overall KOOS' scores were 60.4 ± 13.6, 59.6 ± 15.4, and 51.1 ± 15.4 for the low-, medium-, and high-dose groups, respectively, and 57.0 ± 15.2 for 'all patients'. After 48 months those values improved to 80.0 ± 14.7, 84.0 ± 14.9, and 66.9 ± 21.5 in the respective dose groups and 77.1 ± 18.6 for 'all patients'. Pairwise comparisons of these dose groups did not reveal any statistically significant differences. Likewise, assessment of the subjective IKDC score revealed no statistically significant differences between the three dose groups up to the 48-month visit. However, between 12 and 48 months there was a low, but steady, improvement in the low-dose group and a substantial amelioration in the medium-dose group. The mean MOCART total scores 3 months after treatment were 59.8 ± 10.9, 64.5 ± 10.3, and 64.7 ± 9.4 for the low-, medium-, and high-dose groups, and 62.9 ± 10.3 for 'all patients'; 48 months after treatment these were 73.9 ± 13.1, 78.0 ± 12.4, and 74.3 ± 14.0 for the respective dose groups and 75.5 ± 13.1 for 'all patients'. CONCLUSIONS: Results of this study confirm the efficacy and safety of the applied "advanced therapy medicinal product"; no dose dependence was found either for the incidence or for the severity of any adverse reactions. All doses applied in the present study led to significant clinical improvement over time and can therefore be regarded as effective doses. The influence of product doses in the range investigated seems to be low and can be neglected. Thus, the authorised dose range of 10-70 spheroids/cm2 confirmed by this clinical trial offers a broad therapeutic window for the surgeon applying the product, thereby reducing the risk of over- or underdosing. LEVEL OF EVIDENCE: I.

Clinical outcome and success rates of ACI for cartilage defects of the patella: a subgroup analysis from a controlled randomized clinical phase II trial (CODIS study).

AIM: Cartilage defects of the patella are considered as a problematic entity. Purpose of the present study was to evaluate the outcome of patients treated with autologous chondrocyte implantation (ACI) for cartilage defects of the patella in comparison to patient with defects of the femoral condyles. PATIENTS AND METHODS: 73 patients with a follow-up of 5 years have been included in this subgroup analysis of the randomized controlled clinical trial (RCT). In dependence of defect location, patients were divided into two groups [patella defects (n = 45) and femoral condyle defects (n = 28)]. Clinical outcome was evaluated by the means of the KOOS score at baseline and 6 weeks, 3, 6, 12, 18, 24, 36, 48 and 60 months following ACI. RESULTS: "Responder rate" at 60 months (improvement from baseline of > 7 points in the KOOS score) in patients with patella defects was 86.2%. All scores showed a significant improvement from baseline. While overall KOOS score at 60 months was 81.9 (SD 18.6) points in femoral condyle defects, a mean of 82.6 (SD 14.0) was observed in patella defects (p = 0.2483). CONCLUSION: ACI seems an appropriate surgical treatment for cartilage defects of the patella leading to a high success rate. In this study, the clinical outcome in patients with patellar defects was even better than the already excellent results in patients with defects of the femoral condyle even though the study included relatively large defect sizes for both groups (mean defect size 6.0 ± 1.7 and 5.4 ± 1.6 for femur and patella, respectively).

A Prospective, Randomized, Open-Label, Multicenter, Phase III Noninferiority Trial to Compare the Clinical Efficacy of Matrix-Associated Autologous Chondrocyte Implantation With Spheroid Technology Versus Arthroscopic Microfracture for Cartilage Defects of the Knee.

BACKGROUND: Autologous chondrocyte implantation (ACI) and microfracture are established treatments for large, full-thickness cartilage defects, but there is still a need to expand the clinical and health economic knowledge of these procedures. PURPOSE: To confirm the noninferiority of ACI compared with microfracture. STUDY DESIGN: Randomized controlled trial; Level of evidence, 2. METHODS: Patients were randomized to be treated with matrix-associated ACI using spheroid technology (n = 52) or microfracture (n = 50). Both procedures followed standard methods. Patients were assessed by the Knee injury and Osteoarthritis Outcome Score (KOOS), MOCART (magnetic resonance observation of cartilage repair tissue) scoring system, Bern score, modified Lysholm score, International Cartilage Repair Society (ICRS) rating (histological and immunochemical scoring after rebiopsy 24 months after implantation), and International Knee Documentation Committee (IKDC) examination form. The main assessments were conducted 24 months after study treatment. RESULTS: In the primary intention-to-treat analysis, the overall KOOS score for both ACI and microfracture yielded a statistically significant improvement relative to baseline. According to the between-group analysis, ACI passed the test of noninferiority compared with microfracture; thus, the primary goal of the study was achieved. The KOOS subscores yielded the same qualitative results as the overall KOOS score (ie, for each of these, noninferiority was demonstrated), and in 1 case (Activities of Daily Living subscore), the threshold for superiority was passed. The subgroup analyses did not yield any clear evidence of an association between treatment effect and any of the categories investigated (age, diagnosis, defect localization, sex). A histological analysis of biopsies from 16 patients (ACI: n = 9; microfracture: n = 7) suggested a better quality of repair in the patients treated with ACI. CONCLUSION: The efficacy of both ACI and microfracture was demonstrated with respect to both functional outcomes and morphological repair. The primary analysis confirmed the statistical hypothesis of the noninferiority of ACI, even for relatively small cartilage defects (1-4 cm2) treated in this study, the indication for which microfracture is generally accepted as the standard of care. ACI showed significant superiority in the KOOS subscores of Activities of Daily Living at 24 months and Knee-related Quality of Life at 12 months. REGISTRATION: NCT01222559 (ClinicalTrials.gov identifier).

[Debridement in Focal Cartilage Damage of the knee. Systematical review of the literature and recommendations of the working group "clinical tissue regeneration" of the German Society of Orthopaedics and Trauma (DGOU)]. / Stellenwert des Débridements bei der Behandlung fokaler (Grad II ­â€ŠIII) Knorpelschäden des Kniegelenks. Systematische Literaturübersicht und Empfehlungen der AG Geweberegeneration (DGOU).

BACKGROUND: In clinical practice, there is still no definite treatment algorithm for focal, partial thickness cartilage lesions (grade II - III). It is well-established that debridement (shaving/lavage) of large degenerative cartilage lesions is not recommended, but there is no such recommendation in the case of focal, partial thickness cartilage defects. MATERIALS AND METHODS: The scientific rationale of cartilage shaving and joint lavage was investigated and a systematic analysis was performed of the literature on the clinical effect of cartilage debridement. Furthermore, a consensus statement on this issue was developed by the working group on Clinical Tissue Regeneration of the German Society of Orthopaedics and Trauma (DGOU). RESULTS: The therapeutic approach is different for asymptomatic lesions with biomechanical stable residual cartilage tissue and clinically symptomatic defects with unstable fragments. The benefit of a joint lavage or surface smoothening of focal partial thickness has not been proved. Even more importantly, the mechanical or thermal resection of cartilage tissue even induces a zone of necrosis in adjacent cartilage, and thus leads to additional injury. Therefore, large scale smoothening (shaving) of clinically asymptomatic, fibrillated or irregular cartilage defects should not be performed. However, if there are clinical symptoms, resection of unstable and delaminated cartilage fragments may be reasonable, as it can reduce harmful shear tension in residual tissue. This can help to brake the progression of the damage and avoid formation of free bodies. CONCLUSION: The decision criteria for debridement of partial thickness focal cartilage lesions are multifactorial and include the clinical symptoms, the size and the degree of the defect, the stability of remaining cartilage, localisation of the defect, and individual patient-specific parameters. Debridement is not recommended for asymptomatic lesions, but may be reasonable for symptomatic cases with unstable tissue.

Safety of three different product doses in autologous chondrocyte implantation: results of a prospective, randomised, controlled trial.

BACKGROUND: This study was conducted to assess the efficacy and safety of the three dose levels of the three-dimensional autologous chondrocyte implantation product chondrosphere® in the treatment of cartilage defects (4-10 cm2) of knee joints. We hereby report the safety results for a 36-month post-treatment observation period. METHODS: This was a prospective phase II trial with a clinical intervention comprising biopsy for culturing spheroids and their subsequent administration (level of evidence: I). Patients' knee defects were investigated by arthroscopy, and a cartilage biopsy was taken for culturing. Patients were randomised, on a single-blind basis, to treatment at the dose levels 3-7 (low), 10-30 (medium) or 40-70 (high) spheroids per square centimetre. Assessment (adverse events, vital signs, electrocardiography, physical examination, concomitant medication and laboratory values) took place 1.5, 3, 6, 12, 24 and 36 months after chondrocyte implantation. RESULTS: Seventy-five patients were included and 73 treated. The incidence of adverse events, of patients with adverse events and of patients with treatment-related adverse events showed no relevant difference between the treatment groups. There were no fatal adverse events, no adverse events led to premature withdrawal from the trial and none led to permanent sequelae. Two patients experienced serious adverse events considered related to the study treatment: arthralgia 2-3 years after implantation and chondropathy 1 and 2 years after implantation. CONCLUSIONS: The treatment with chondrosphere® was generally well tolerated. No relationship was detected between any safety criteria and the dose level: Differences between the dose groups in the incidence of any adverse events, and in numbers of patients with treatment-related adverse events, were insubstantial. TRIAL REGISTRATION: clinicaltrials.gov, NCT01225575 .

The Effect of Cell Dose on the Early Magnetic Resonance Morphological Outcomes of Autologous Cell Implantation for Articular Cartilage Defects in the Knee: A Randomized Clinical Trial.

BACKGROUND: Although autologous chondrocyte implantation (ACI) has been established as a standard treatment for large full-thickness cartilage defects, the effect of different doses of autologous chondrocyte products on structural outcomes has never been examined. HYPOTHESIS: In ACI, the dose level may have an influence on medium-term magnetic resonance morphological findings after treatment. STUDY DESIGN: Randomized controlled trial; Level of evidence, 1. METHODS: A total of 75 patients who underwent ACI using a pure, autologous, third-generation matrix-associated ACI product were divided into 3 groups representing different doses: 3 to 7 spheroids/cm(2), 10 to 30 spheroids/cm(2), and 40 to 70 spheroids/cm(2). Magnetic resonance imaging was performed at 1.5, 3, 6, and 12 months after ACI and was evaluated by the magnetic resonance observation of cartilage repair tissue (MOCART) score and the Knee injury and Osteoarthritis Outcome Score (KOOS). RESULTS: MOCART scores showed improvements after 3 months, with slight dose dependence, and further improvement after 12 months, although without significant dose dependence. The mean MOCART scores after 3 months (0 = worst, 100 = best) were 59.8, 64.5, and 64.7 for the low-, medium-, and high-dose groups, respectively, and 62.9 for all patients; at 12 months, these were 74.1, 74.5, and 68.8 for the respective dose groups and 72.4 for all patients. Several MOCART items (surface of repair tissue, structure of repair tissue, signal intensity of repair tissue, subchondral bone, and synovitis) showed a more rapid response with the medium and high doses than with the low dose, suggesting a potential dose relationship. No significant correlation between the MOCART (overall and subscores) with clinical outcomes as assessed by the overall KOOS was detected at 3- and 12-month assessments. CONCLUSION: This study reveals a trend toward earlier recovery after treatment with higher spheroid doses in terms of better defect filling for full-thickness cartilage defects of the knee, while outcomes after 12 months were similar in all dose groups. However, a correlation with clinical outcomes or the failure rate at 1 year after ACI was not found. A longer follow-up will be required for more definite conclusions on the clinical relevance of ACI cell density to be drawn. REGISTRATION: NCT01225575 (ClinicalTrials.gov identifier); 2009-016816-20 (EudraCT number).

Interleukin-1alpha treatment of meniscal explants stimulates the production and release of aggrecanase-generated, GAG-substituted aggrecan products and also the release of pre-formed, aggrecanase-generated G1 and m-calpain-generated G1-G2.

Pro-inflammatory cytokines induce meniscal matrix degradation and inhibition of endogenous repair mechanisms, but the pathogenic mechanisms behind this are mostly unknown. Therefore, we investigated details of interleukin-1 (IL-1alpha)-induced aggrecan turnover in mature meniscal tissue explants. Fibro-cartilagenous disks (3 mm diameter x 1 mm thickness) were isolated from the central, weight-bearing region of menisci from 2-year-old cattle. After 3 or 6 days of IL-1alpha-treatment, GAG loss (DMMB assay), biosynthetic activity ([(35)SO(4)]-sulfate and [(3)H]-proline incorporation), gene expression (quantitative RT-PCR) and the abundance (zymography, Western blot) of matrix-degrading enzymes and specific aggrecan products were determined. Meniscal fibrocartilage had a 4-fold lower GAG content (per wet weight) than adjacent articular cartilage, and expressed MMPs-1, -2, -3 and ADAMTS4 constitutively, whereas ADAMTS5 m-RNA was essentially undetectable. Significant IL-1 effects were a decrease in biosynthetic activity, an increase in GAG release and in the expression/abundance of MMP-2, MMP-3 and ADAMTS4. Fresh tissue contained aggrecan core protein products similar to those previously described for bovine articular cartilage of this age. IL-1 induced the release of aggrecanase-generated CS-substituted products including both high (>250 kDa) and low molecular weight (about 75 kDa) species. TIMP-3 (but not TIMP-1 and -2 or a broad spectrum MMP inhibitor) inhibited IL-1-dependent GAG loss. In addition, IL-1 induced the release of preformed pools of three known G1-bearing products. We conclude that aggrecanases are responsible for IL-1-stimulated GAG release from meniscal explants, and that IL-1 also stimulates release of G1-bearing products, by a process possibly involving hyaluronan fragmentation.

A new symptomatic intra-articular cord-like structure associated with discoid meniscus.

We introduce a new, not yet described cord-like structure of the knee of children associated with discoid or enlarged menisci. This structure was responsible for knee pathology (loss of extension) in 3 cases. The patients (5 to 8 years of age) complained of knee pain without skeletal abnormality or trauma. Magnetic resonance imaging revealed enlarged or discoid lateral menisci. The patients showed increasing limp with limited range of motion. Lack of extension was between 10 degrees and 45 degrees and continued under anesthesia. During arthroscopy, the menisci and the anterior and posterior cruciate ligaments (ACL, PCL) showed no abnormality other than the variant of the lateral meniscus described above. A tight cord-like structure was imposed, running laterally along the ACL. This cord-like structure was attached to the lateral femoral intercondylar area and the posterior horn region of the lateral meniscus in a sail-like shape. Two knees showed abnormal mobility of the lateral meniscus, tending to luxate. The ligamentous structure was cut stepwise lateral to the ACL, leaving the entire lateral meniscus undisturbed. Finally, full extension was achieved. Examination 7 to 27 months after surgery showed asymptomatic knees. This ligamentous structure is an important differential diagnosis to symptoms usually referred to as meniscus pathology. The appropriate treatment involves dissection. A loss of meniscal tissue followed by development of osteoarthritis can be prevented.

Reactive oxygen species induce expression of vascular endothelial growth factor in chondrocytes and human articular cartilage explants.

Vascular endothelial growth factor (VEGF) promotes cartilage-degrading pathways, and there is evidence for the involvement of reactive oxygen species (ROS) in cartilage degeneration. However, a relationship between ROS and VEGF has not been reported. Here, we investigate whether the expression of VEGF is modulated by ROS. Aspirates of synovial fluid from patients with osteoarthritis (OA) were examined for intra-articular VEGF using ELISA. Immortalized C28/I2 chondrocytes and human knee cartilage explants were exposed to phorbol myristate acetate (PMA; 0-20 microg/ml), which is a ROS inducer, or 3-morpholino-sydnonimine hydrochloride (SIN-1; 0-20 microM), which is a ROS donor. The levels of VEGF protein and nitric oxide (NO) production were determined in the medium supernatant, using ELISA and Griess reagent, respectively. Gene expression of VEGF-121 and VEGF-165 was determined by splice variant RT-PCR. Expression of VEGF and VEGF receptors (VEGFR-1 and VEGFR-2) was quantified by real-time RT-PCR. Synovial fluid from OA patients revealed markedly elevated levels of VEGF. Common RT-PCR revealed that the splice variants were present in both immortalized chondrocytes and cartilage discs. In immortalized chondrocytes, stimulation with PMA or SIN-1 caused increases in the levels of VEGF, VEGFR-1 and VEGFR-2 mRNA expression. Cartilage explants produced similar results, but VEGFR-1 was only detectable after stimulation with SIN-1. Stimulation with PMA or SIN-1 resulted in a dose-dependent upregulation of the VEGF protein (as determined using ELISA) and an increase in the level of NO in the medium. Our findings indicate ROS-mediated induction of VEGF and VEGF receptors in chondrocytes and cartilage explants. These results demonstrate a relationship between ROS and VEGF as multiplex mediators in articular cartilage degeneration.

Pathomechanisms of cartilage destruction by mechanical injury.

Mechanical injury is considered to be a major inductor of articular cartilage destruction and therefore a risk factor for the development of secondary osteoarthritis. Mechanical injury induces damage to the tissue matrix directly or mediated by chondrocytes via expression of matrix-degrading enzymes and reduction of biosynthetic activity. As a consequence the mechanical properties of cartilage change. Some of the pathomechanisms of mechanical injury have already been uncovered by the use of a broad range of in vitro-models. They demonstrate that mechanical injury induces tissue swelling and decrease in both the compressive and shear stiffness of articular cartilage, probably due to disruption of the collagen network. Injurious compression induces chondrocyte death by necrosis and apoptosis and the remaining cells decrease their biosynthetic activity. The tissue content of proteoglycans also decreases with time in injured cartilage, and the tissue loses its ability to respond to physiological levels of mechanical stimulation with an increase in biosynthesis. Immature cartilage seems to be more vulnerable to injurious compression than more mature tissue. The expression of several matrix-degrading enzymes like ADAM-TS5 and matrix-metalloproteinases (MMP-1, MMP-2, MMP-3, MMP-9, MMP-13) is increased after injury and may in part be regulated by an autocrine vascular endothelial growth factor (VEGF)-dependent signalling pathway. Apoptosis seems to be mediated by caspase activity and reactive oxygen species. For that reason activation of antioxidative defense mechanisms as well as the inhibition of angiogenetic factors and MMPs might be key regulators in the mechanically induced destruction of cartilage and might be suggested as potential therapeutic interventions. This review summarizes some of the most important data from in vitro injury studies dealing with the pathomechanisms of cartilage destruction.