Objective. To investigate whether the abnormal expression of matrix metalloproteinases (MMPs) 3, 9, and 13 and ADAMTS-4 by human osteoarthritic (OA) chondrocytes is associated with epigenetic "unsilencing."Methods. Cartilage was obtained from the femoral heads of 16 patients with OA and 10 control patients with femoral neck fracture. Chondrocytes with abnormal enzyme expression were immunolocalized. DNA was extracted, and the methylation status of the promoter regions of MMPs 3, 9, and 13 and ADAMTS-4 was analyzed with methylation-sensitive restriction enzymes, followed by polymerase chain reaction amplification.Results. Very few chondrocytes from control cartilage expressed the degrading enzymes, whereas all clonal chondrocytes from late-stage OA cartilage were immunopositive. The overall percentage of nonmethylated sites was increased in OA patients (48.6%) compared with controls (20.1%): 20% versus 4% for MMP-13, 81% versus 47% for MMP-9, 57% versus 30% for MMP-3, and 48% versus 0% for ADAMTS-4. Not all CpG sites were equally susceptible to loss of methylation. Some sites were uniformly methylated, whereas in others, methylation was generally absent. For each enzyme, there was 1 specific CpG site where the demethylation in OA patients was significantly higher than that in controls: at -110 for MMP-13, -36 for MMP-9, -635 for MMP-3, and -753 for ADAMTS-4.Conclusion. This study provides the first evidence that altered synthesis of cartilage-degrading enzymes by late-stage OA chondrocytes may have resulted from epigenetic changes in the methylation status of CpG sites in the promoter regions of these enzymes. These changes, which are clonally transmitted to daughter cells, may contribute to the development of OA.Osteoarthritis (OA) is characterized by the progressive failure of the extracellular cartilage matrix, which leads to the destruction of articular cartilage (1,2). Primary OA is a late-onset complex disease with genetic, mechanical, and environmental components. Concordance of the disease in monozygotic twins is 40-60%, and the overall contribution of genetic factors is estimated to be ϳ50% (3). Given that more than 60% of unrelated adults over the age of 60 years are affected, other factors must also play a role in the development of this disease. Age, obesity, abnormal joint loading, and sports injuries are all risk factors, but OA is more than just the result of "wear and tear" (4,5). Articular chondrocytes are increasingly being suspected of playing major roles in the initiation and progression of the disease (1). This warrants closer examination of the cellular changes that occur in OA.The main extracellular matrix components of articular cartilage are collagens (principally, types II, IX, and XI) and proteoglycans (mainly, aggrecan). The major enzymes that mediate the destructive processes are aggrecanases 1 and 2 (ADAMTS-4 and ADAMTS-5) and matrix metalloproteinases (MMPs) 2 (gelatinase A),

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Background:Existing radiographic classification schemes (eg, Tönnis criteria) for DDH quantify the severity of disease based on the position of the ossific nucleus relative to Hilgenreiner’s and Perkin’s lines. By definition, this method requires the presence of an ossification centre, which can be delayed in appearance and eccentric in location within the femoral head. A new radiographic classification system has been developed by the International Hip Dysplasia Institute (IHDI), which uses the mid-point of the proximal femoral metaphysis as a reference landmark, and can therefore be applied to children of all ages. The purpose of this study was to compare the reliability of this new method with that of Tönnis, as the first step in establishing its validity and clinical utility.Methods:Twenty standardized anteroposterior pelvic radiographs of children with untreated DDH were selected purposefully to capture the spectrum of age (range, 3 to 32 mo) at presentation and disease severity. Each of the hips was classified separately by the IHDI and Tönnis methods by 6 experienced pediatric orthopaedists from the United States, Canada, Mexico, United Kingdom, and by 2 orthopaedic senior residents. The inter-rater reliability was tested using the Intra Class Correlation coefficient (ICC) to measure concordance between raters.Results:All 40 hips were classifiable by the IHDI method by all raters. Ten of the 40 hips could not be classified by the Tönnis method because of the absence of the ossific nucleus on one or both sides. The ICC (95% confidence interval) for the IHDI method for all raters was 0.90 (0.83-0.95) and 0.95 (0.91-0.98) for the right and left hips, respectively. The corresponding ICCs for the Tönnis method were 0.63 (0.46-0.80) and 0.60 (0.43-0.78), respectively. There was no significant difference between the ICCs of the 6 experts and 2 trainees.Conclusions:The IHDI method of classification has excellent inter-rater reliability, both among experts and novices, and is more widely applicable than the Tönnis method as it can be applied even when the ossification centre is absent.Level of Evidence:Level II (diagnostic).

Despite the continued presence of growth plates in aged rats, longitudinal growth no longer occurs. The aims of this study were to understand the reasons for the cessation of growth. We studied the growth plates of femurs and tibiae in Wistar rats aged 62-80 weeks and compared these with the corresponding growth plates from rats aged 2-16 weeks. During skeletal growth, the heights of the plates, especially that of the hypertrophic zone, reflected the rate of bone growth. During the period of decelerating growth, it was the loss of large hydrated chondrocytes that contributed most to the overall decrease in the heights of the growth plates. In the old rats we identified four categories of growth plate morphology that were not present in the growth plates of younger rats: (a). formation of a bone band parallel to the metaphyseal edge of the growth plate, which effectively sealed that edge; (b). extensive areas of acellularity, which were resistant to resorption and/or remodeling; (c). extensive remodeling and bone formation within cellular regions of the growth plate; and (d). direct bone formation by former growth plate chondrocytes. These processes, together with a loss of synchrony across the plate, would prevent further longitudinal expansion of the growth plate despite continued sporadic proliferation of chondrocytes.