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Unlike synovitis, the presence of joint effusions on MRI among patients with hand osteoarthritis (OA) was not associated with pain or progression, Dutch researchers reported.

Pain in a specific joint was not associated with effusion in the same joint, with an odds ratio of 0.8 (95% CI 0.5-1.4), according to Wendy Damman, MD, and colleagues from Leiden University Medical Center in the Netherlands.

Radiographic progression also showed no association with effusions in hand joints, with an odds ratio of 0.5 (95% CI 0.2-1.1). But the presence of synovitis, as shown on MRI as enhanced synovial thickening, was significantly linked with both pain (OR 1.8, 95% CI 1.2-2.8) and progression (OR 3.2, 95% CI 1.9-5.4), the researchers reported online in .

Previous imaging studies have implicated synovitis and bone marrow lesions in the pathogenesis of hand OA, and while these inflammatory characteristics typically have been associated with pain and progression, the nature of their precise contribution to the disease process remains uncertain.

Also unclear is the potential role of effusion, which represents an additional feature associated with joint inflammation that frequently has been reported along with synovitis.

Effusion detected on imaging is poorly understood. This excess fluid in the joint may represent changes in osmotic pressure, inadequate drainage, or pressure from local tissues, and can be seen in erosive OA, but also in healthy joints. Triggers may include mechanical and inflammatory factors.

Damman and colleagues sought to investigate whether effusion contributed to the pain and progression associated with synovitis, hypothesizing that "the presence of effusion reflects inflammation and therefore reinforces the known association between synovitis and joint pain and progression."

They included 87 patients with hand OA. For each patient, eight joints (the distal and proximal interphalangeal joints of the right hand) were examined, evaluating for pain with palpation and swelling around the joint. Radiographs and MRIs were obtained at baseline and after 2 years. Enhanced synovial thickening on MRI served as a proxy for synovitis, which requires histology and was not considered feasible for this study.

Patients' mean age was 59, and more than 80% were women. Pain on palpation was detected in 17% of joints in 39 patients, swelling in 7% of joints in 21 patients, and radiographic progression was observed in 11% of joints in 45 patients.

On MRI, 17% of joints in 52 patients showed effusion, and in 44% of joints in 74 patients, enhanced synovial thickening was present. Synovitis and effusions were both visible in 52.5% of joints in 35 patients, but "remarkably," the investigators noted, 47.5% of joints in 32 patients had effusions present without any synovitis.

Soft tissue swelling was present with synovitis in 63% of joints and with effusions in 31%.

When the researchers then considered the influence of effusions on the pain and progression associated with synovitis, they found that enhanced synovial thickening both with and without effusion was associated with pain in the same joint. Synovitis without effusion was significantly associated with progression, but effusion without synovitis was not associated with either pain or progression.

The observation that effusion was not associated with either pain or progression suggested a slight protective effect. "Contrary to our hypothesis, the known association between synovitis ... and progression was attenuated by the presence of effusion," the researchers stated.

Explanations for why effusion -- extra fluid in the joint -- could be protective include a decrease in mechanical stress that can enhance radiographic progression, and the possibility that the fluid itself contains anti-inflammatory factors.

Currently, the presence of effusion is not included in MRI scoring for hand OA. "It would be interesting to investigate whether a change in effusion would be associated with a change in pain or a lower chance of radiographic progression over time and how this is related to the effect of synovitis," Damman and colleagues wrote.

If future studies do confirm those possibilities, it could be helpful to include effusion in MRI scoring for prognostic purposes, they suggested.

"Our results warrant further study into the presence and role of effusion apart from synovitis in hand OA, to further elucidate the role of inflammation, and in particular, effusion, in hand OA pathology and its treatment," they concluded.

A limitation of the study was reliance on the proxy of enhanced synovial thickening for synovitis.

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