MRI-detected inflammation around the extensor tendons of metacarpophalangeal (MCP-) joints is prevalent in RA and poses a markedly increased risk of RA development when present in arthralgia patients. Such inflammation is called ‘peritendinitis’ since anatomy literature reports no presence of a tenosynovial sheath at these tendons. However, the presence or absence of tenosynovium at these extensor tendons has never been studied. Therefore, an anatomical and histological study of extensor tendons at the MCP-joints of three embalmed human hands was performed. Immunohistochemical staining showed the presence of markers for synovial macrophages and fibroblast-like synoviocytes bordering a natural dorsal space next to the extensor tendon, suggesting the presence of a synovial lining. This implies that contrast-enhancement on MRI around extensor tendons at MCP-joints observed in early RA and pre-RA likely represents tenosynovitis and that inflammation of this synovial tissue is an early feature of RA.

中文翻译：

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掌指关节伸肌腱周围存在滑膜鞘的证据：显微镜研究

MRI 检测到掌指关节 (MCP-) 伸肌腱周围的炎症在 RA 中很普遍，当关节痛患者出现 RA 时，其发生 RA 的风险显着增加。这种炎症被称为“腱鞘炎”，因为解剖学文献报道在这些肌腱处不存在腱鞘。然而，从未研究过这些伸肌腱处是否存在腱鞘膜。因此，对三只经过防腐处理的人手的 MCP 关节处的伸肌腱进行了解剖学和组织学研究。免疫组织化学染色显示滑膜巨噬细胞和成纤维细胞样滑膜细胞的标记物与伸肌腱旁边的自然背侧空间接壤，表明存在滑膜衬里。