Objectives

Despite distinct aetiologies, the end-stages of primary osteoarthritis (OA) and secondary OA are described by common radiological features. However, the morphology of the bone–cartilage unit may differ depending on the pathogenesis. In this cross-sectional study, we aimed to investigate the histological differences in the bone–cartilage unit of the femoral head between patients with primary OA and secondary OA due to rheumatoid arthritis (RA).

Method

Femoral heads were obtained from 12 patients with primary OA, six patients with secondary OA due to RA, and 12 control subjects. The femoral heads were investigated using stereological methods to ensure unbiased quantification.

Results

The volume (mean difference [95% confidence interval]) (2.1 [0.5;3.8] cm³, p = 0.016) and thickness (413 [78.9;747] µm, p = 0.029) of the articular cartilage and the thickness of the calcified cartilage (56.4 [0.4;113] µm, p = 0.017) were larger in patients with primary OA than in patients with secondary OA due to RA. Femoral head volume (1.2 [−3.6;6.1] cm³, p = 0.598), bone volume fraction (−1.1 [−2.8;5.1] cm³, p = 0.553), subchondral bone thickness (−2.5 [−212;207] µm, p = 0.980), and osteophyte area (25.3 [−53.6;104] cm², p = 0.506) did not differ between patients.

Conclusion

The thicker calcified cartilage in primary OA preceding the loss of articular cartilage can be attributed to endochondral ossification. Patients with secondary OA due to RA had severely thinner calcified cartilage as the pathogenesis is driven by inflammation and is characterized by a generalized and more severe loss of articular cartilage.

中文翻译：

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髋关节类风湿性关节炎终末期原发性骨关节炎和继发性骨关节炎患者的钙化软骨不同

目标

尽管病因不同，但原发性骨关节炎 (OA) 和继发性 OA 的终末期具有共同的放射学特征。然而，骨软骨单位的形态可能因发病机制而异。在这项横断面研究中，我们旨在研究原发性 OA 和类风湿性关节炎 (RA) 引起的继发性 OA 患者股骨头骨软骨单位的组织学差异。

方法

股骨头取自 12 名原发性 OA 患者、6 名因 RA 导致的继发性 OA 患者和 12 名对照受试者。使用体视学方法研究股骨头以确保无偏量化。

结果

关节软骨的体积（平均差 [95% 置信区间]）（2.1 [0.5;3.8] cm ³，p = 0.016）和厚度（413 [78.9;747] µm，p = 0.029）和关节软骨的厚度原发性 OA 患者的钙化软骨 (56.4 [0.4;113] µm，p = 0.017) 大于因 RA 导致的继发性 OA 患者。股骨头体积 (1.2 [−3.6;6.1] cm ³ , p = 0.598)，骨体积分数 (−1.1 [−2.8;5.1] cm ³ , p = 0.553)，软骨下骨厚度 (−2.5 [−212;207 ] µm，p = 0.980）和骨赘面积（25.3 [−53.6;104] cm ²，p = 0.506）在患者之间没有差异。

结论

在关节软骨丢失之前，原发性 OA 中较厚的钙化软骨可归因于软骨内骨化。由于 RA 导致的继发性 OA 患者的钙化软骨严重变薄，因为发病机制是由炎症驱动的，其特征是关节软骨的普遍和更严重的损失。