Background Osteoarthritis (OA) is a common joint disease, but the pathology is not fully understood. It has been suggested that bone changes are important for the pathogenesis of OA. However, only few histological studies have examined bone remodelling, and results are conflicting.
Objectives The aim of this study was to quantify bone remodelling and bone volume in human hip OA in relation to overlying cartilage lesions using design-based stereological estimators.
Methods Femoral heads, from 25 OA patients (64.0±7.3 yrs) and 24 controls (CTRL) (61.5±7.9 yrs), were cut systematic uniform randomly in accordance with the principles of Cavalieri and vertical sectioning. The bone slaps was then cut into two halves, and embedded in methylmethacrylate. Each section was stained with Masson-Goldner trichrome. Design-based quantitative histology were used to estimate absolute values of the femoral head's tissue volume (TV), bone volume (BV), bone surfaces (BS), osteoid surfaces (OS), and eroded surfaces (ES). The fractional bone volume (BV/TV), osteoid surface (OS/BS), and eroded surface (ES/BS) were calculated for the subchondral bone and the central region of the femoral head. Subchondral bone was further subdivided according to the histological osteoarthritis score (OARSI-grade) into three groups OARSI-grade 0-2 (normal-mild), 3-4 (moderate), and 5-6 (severe). The OA patients and the CTRL group were compared with Mann-Whitney U-test, and correlation between bone changes, and cartilage lesions was calculated for OA patients using spearman's rank correlation coefficient (ρ).
Results In the subchondral bone, BV/TV was higher in OA (30.4±6.1%) than in CTRL (25.9±4.2%) (p<0.01) as were ES/BS (4.6±2.0% vs. 3.0±1.3%, p<0.001) and OS/BS (8.8±5.4% vs. 2.6±3.7%, p<0.001). In the centre of the femoral head, ES/BS (7.8±3.1% vs. 4.3±1.6%, p<0.001) and OS/BS (8.8±5.4% vs. 4.4±6.3%, p<0.001) were also higher in OA than in CTRL, whereas BV/TV did not differ between OA and CTRL (21.4±4.1% vs. 20.5±3.0%, p=0.87). The subchondral regions with normal-mild cartilage lesions, showed higher ES/BS (9.8±3.9% vs. 4.3±1.6%, p<0.001) and higher OS/BS (15.9±6.7% vs. 4.3±6.2%, p<0.001) in OA compared to CTRL, but no difference in BV/TV (25.3±5.5% vs. 25.9±4.2%, p=0.44). In OA patients, subchondral BV/TV was correlated to the severity of the overlying cartilage lesions (ρ=0.686, p<0.001). The same was seen for ES/BS and OS/BS which showed a correlation of ρ=0.524, p<0.001, and ρ=0.637, p<0.001, respectively.
Conclusions In this cross-sectional study of human hip OA using design-based stereological estimators on entire femoral heads, OA was associated with increased bone mass and increased bone remodelling in the subchondral region. Furthermore, in OA patients, changes in bone volume and remodelling were correlated with the degree of the osteoarthritic lesions. In the subchondral region with normal or mildly affected cartilage and in the centre of the femoral head, bone remodelling was higher in OA patients than in controls, although the bone mass did not differ. Therefore, we suggest, that subchondral bone remodelling is affected already at an early stage of OA, where changes in bone mass are not present.
Acknowledgements This work was supported by the Danish Rheumatism Association
Disclosure of Interest None declared
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