Articular cartilage mineralization in osteoarthritis of the hip

Abstract

BackgroundThe aim of this study was to examine the frequency of articular cartilage calcification in patients with end-stage hip OA. Further, its impact on the clinical situation and the OA severity are analyzed.MethodsEighty patients with OA of the hip who consecutively underwent total hip replacement were prospectively evaluated, and 10 controls were included. The patients' X-rays were analyzed for the presence of articular cartilage mineralization. A Harris Hip Score (HHS) was preoperatively calculated for every patient.Slab specimens from the femoral head of bone and cartilage and an additional square centimeter of articular cartilage from the main chondral defect were obtained from each patient for analysis of mineralization by digital contact radiography (DCR). Histological grading was also performed. In a subset of 20 patients, minerals were characterized with an electron microscope (FE-SEM).ResultsCalcifications were seen in all OA cartilage and slab specimens using DCR, while preoperative X-rays revealed calcification in only 17.5%. None of the control cartilage specimens showed mineralization. There was a highly significant inverse correlation between articular cartilage calcification and preoperative HHS. Histological OA grade correlated positively with the amount of matrix calcification. FE-SEM analysis revealed basic calcium phosphate (BCP) as the predominant mineral; CPPD crystals were found in only two patients.ConclusionsArticular cartilage calcification is a common event in osteoarthritis of the hip. The amount of calcification correlates with clinical symptoms and histological OA grade.

Basic Calcium Phosphate Crystals Induce Monocyte/Macrophage IL-1β Secretion through the NLRP3 Inflammasome In Vitro

“…Articular cartilage calcification is associated with severe osteoarthritis (OA) and destructive arthropathies, such as Milwaukee shoulder syndrome. Interestingly, BCP crystals are detected in 100% of knee and hip osteoarthritic cartilages harvested at the time of total joint arthroplasty (1,2). BCP crystal deposition in knee articular cartilage is correlated with cartilage destruction and more severe lesions (1).…”

Osteoarthritis, a basic calcium phosphate crystal–associated arthropathy? Comment on the article by Fuerst et al

“…A similar study by the same group showed that BCP deposits also occurred in hip OA cartilage, further emphasizing the generalization of the cartilage mineralization process during OA (14). However, the exact role of BCPs in OA cartilage destruction has yet to be investigated.…”

Cartilage biology, pathology, and repair

“…These include the perichondrocytic degradation of the cartilage matrix by aforementioned proteases but also cartilage mineralization. Cartilage mineralization is of interest because recent data suggest that in human osteoarthritis (OA), mineralization of cartilage is re-initiated as part of the pathogenic changes associated with the terminal, hypertrophic differentiation of diseased chondrocytes [80,81]. While in healthy articular cartilage most chondrocytes maintain a stable resting phenotype and resist proliferation and differentiation, articular chondrocytes from osteoarthritic joints form clusters by proliferating more strongly and eventually develop hypertrophy, typically close to areas of mineralized cartilage matrix and near sites of surface lesions [40,82].…”

“…While in healthy articular cartilage most chondrocytes maintain a stable resting phenotype and resist proliferation and differentiation, articular chondrocytes from osteoarthritic joints form clusters by proliferating more strongly and eventually develop hypertrophy, typically close to areas of mineralized cartilage matrix and near sites of surface lesions [40,82]. Recent evidence suggests that hypertrophic chondrocytes in the growth plate and in osteoarthritic cartilage share certain similarities, and that the calcification of hyaline cartilage is a regular event in human OA [81,83]. One key finding linking chondrocyte hypertrophy to similar mechanisms involved in endochondral ossification is the expression of HIF-2 alpha during both processes.…”

“…The mineralization of the matrix during OA surrounding late hypertrophic chondrocytes is due to the deposition of basic calcium phosphate (BCP) [82,87]. Hypertrophic chondrocytes release membrane-bound matrix vesicles containing a specific combination of proteins, annexins, phosphate transporters, and phosphatases which provide the nucleation site for mineralization [81,88]. Matrix mineralization of cartilage and vesicles is dependent on alkaline phosphatase activity, which hydrolyses organic phospho compounds.…”