Rheumatoid Arthritis and Tenosynovitis at the Metatarsophalangeal Joints: An Anatomic and MRI Study of the Forefoot Tendon Sheaths.

Background Although tenosynovitis in the hands is associated with rheumatoid arthritis (RA), it is unknown whether tenosynovitis of the forefoot is associated with RA. Purpose To determine the anatomy of tendon sheaths of the forefoot and the relationship between MRI-detected tenosynovitis at metatarsophalangeal (MTP) joints and RA. Materials and Methods Fourteen forefeet of donated bodies were examined at flexor tendons and extensor tendons for the presence and course of tendon sheaths. In the prospective study between June 2013 and March 2016, newly presenting patients with RA, patients with other early arthritides, and healthy control participants all underwent MRI of unilateral MTP joints 1-5. MRI studies were scored by two independent readers for tenosynovitis, synovitis, and bone marrow edema. The association between the presence of these features and RA was examined by using logistic regression. Results Macroscopically, all extensor and flexor tendons crossing MTP joints demonstrated sheaths surrounding tendons. Microscopically, a synovial sheath was present. MRI evaluation was performed in 634 participants: 157 newly presenting patients with RA (109 women; mean age, 59 years ± 11 [standard deviation]), 284 patients with other early arthritides (158 women; mean age, 56 years ± 17), and 193 healthy control participants (136 women; mean age, 50 years ± 16). MRI-detected tenosynovitis was associated with RA, both when compared with patients with other arthritides (odds ratio [OR], 2.5; 95% confidence interval [CI]: 1.7, 3.9; P < .001) and healthy control participants (OR, 46; 95% CI: 14, 151; P < .001). The association was OR of 2.4 (95% CI: 1.5, 3.8; P < .001) for flexor tendons and OR of 3.1 (95% CI: 1.9, 5.2; P < .001) for extensor tendons. The sensitivity of tenosynovitis in RA was 65 of 157 (41%; 95% CI: 35%, 50%). The specificity for RA was 63 of 284 (78%; 95% CI: 72%, 82%) compared with other arthritides, and three of 193 (98%; 95% CI: 96%, 99%) compared with healthy control participants. Conclusion Tendons at metatarsophalangeal joints are surrounded by tenosynovium. MRI-detected tenosynovitis at metatarsophalangeal joints was specific for rheumatoid arthritis when compared with findings in patients with other arthritides and findings in healthy control participants. © RSNA, 2020 Online supplemental material is available for this article.

Evidence for the presence of synovial sheaths surrounding the extensor tendons at the metacarpophalangeal joints: a microscopy study.

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.