Knee Effusion Volume Predicts Osteoarthritis Progression and Knee Replacement

In patients diagnosed with or at risk for knee osteoarthritis (OA), baseline effusion volume and change in volume over 1 year were positively correlated with loss of cartilage volume and radiographic OA (ROA) progression over 4 years and the risk of having total knee replacement (TKR) surgery across 6 years, according to a report published in Rheumatology.

Knee OA may be partially driven by synovial inflammation, which manifests as membrane thickening and fluid effusion, or effusion-synovitis. However, only a few studies available regarding the effect of effusion-synovitis on knee OA disease progression have been described. Investigators sought to employ a novel technique for quantifying effusion volume via magnetic resonance imaging (MRI) to evaluate these relationships, with a goal of targeting at-risk patients and tailoring interventions accordingly.

The Osteoarthritis Initiative was a multicenter, observational cohort study that enrolled 4796 patients with knee OA who were between the ages of 45 and 79. This analysis included 4115 participants (mean age, 61.2 years; 57.9% women; mean body mass index [BMI], 28.6 kg/m²; median effusion volume at baseline, 5.0 ml) whose OA was Kellgren-Lawrence (KL) graded, with effusion volume assessed at baseline.

Effusion volume was automatically quantified using MRI at baseline and after 1 year, as was cartilage volume after 4 years. The progression of ROA was assessed by radiographs at 4-year follow-up, whereas the rate of TKR surgery was evaluated after 6 years. Regression analyses were conducted with adjustments for age, gender, BMI, and KL grade (when applicable), and regression coefficients (RC) and odds ratios (OR) were calculated.

At baseline, effusion volume increased with KL grade (P <.001), with a mean change in volume after 1 year of 0.1 mL. Signs of ROA progression at 4 years were seen in 14.5% of participants, and 186 individuals reported having TKR performed by 6 years.

There was a positive association between baseline effusion volume and cartilage volume reduction in the medial (RC, 0.13%/y; 95% CI, 0.10-0.17; P <.001) and lateral (RC, 0.13%/y; 95% CI, 0.10-0.16; P <.001) compartments, as well as ROA progression (OR 1.28; 95% CI, 1.20-1.37; P <.001) and risk of TKR (OR 1.12; 95% CI, 1.05-1.20; P =.001). In addition, over 1 year, an effusion volume increase of 5 mL predicted cartilage volume loss in the medial compartment (RC, 0.09%/y; 95% CI, 0.04-0.15; P =.001) only, along with ROA progression (OR 1.21; 95% CI, 1.11-1.33; P <.001) and increased TKR risk (OR 1.24; 95% CI, 1.12-1.37; P <.001).

Study strengths included automated assessment of volume changes via MRI that improved reliability and investigation of effusion volume change over time.

Study limitations included lack of adjustment for all possible confounders, adjustment for knee injury and steroid injection that might affect effusion volume, and potential bias introduced by loss to follow-up, with 4- and 6-year retention rates of 78.8% and 66.5%, respectively.

“Knee joint effusion volume assessed from MRI was associated with structural progression of knee OA,” summarized the authors. Regarding clinical implications, the authors noted, “Knee effusion volume may provide a method to identify individuals who have a higher risk of knee OA progression.”

Disclosure: JP Pelletier and J Martell-Pelletier are shareholders in ArthroLab, and F Abram is an employee of ArthroLab.

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Reference

Wang Y, Teichtahl AJ, Pelletier J-P, et al. Knee effusion volume assessed by magnetic resonance imaging and progression of knee osteoarthritis: data from the Osteoarthritis Initiative [published online September 10, 2018]. Rheumatology (Oxford). doi: 10.1093/rheumatology/key274.