Hyaluronic acid injection less effective in knee OA patients with suprapatellar effusion

Among patients with knee osteoarthritis (OA), ultrasound-detected suprapatellar synovial fluid (SF) predicts weakened response to hyaluronic acid (HA) injection, a study has found.

“The current results demonstrate significant associations between both synovitis and the Kellgren–Lawrence (KL) grade with clinical outcomes of HA injection. The regression model used to predict pain and knee function according to SF depth indicates that the increased accumulation of SF is a crucial factor for determining the therapeutic efficacy of HA injection,” according to the investigators.

“Moreover, the long-term outcome measurement afforded more significant results than the short-term measurement did, [showing] that increased effusion is associated with symptom recurrence. Ultrasound-detected SF fluid, but not other synovial markers, seems to play an essential role in predicting the efficacy of HA injection in knee OA treatment,” they said.

The analysis included 137 patients with symptomatic knee OA (median age, 67.5 years; 60.6 percent male; median body mass index, 25.1). They received HA injection two times at 2-week intervals. Mean grade of Power Doppler signal was 1.5 at baseline, while the mean synovial effusion depth was 0.53 cm in diameters. Two patients who presented with >1 cm SF depth in diameters were found to have high KL grade, 3 and 4, respectively.

At 1 and 6 months after treatment, all patients showed improvement in visual analogue scale (VAS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC; p<0.001). Regression model-based analysis revealed SF depth to be significantly associated with the VAS and WOMAC scores. [Rheumatology 2021;doi:10.1093/rheumatology/keab020]

Specifically, each centimetre increase in the effusion diameter correlated with a decline in the 1-month post-treatment VAS improvement percentage (15.26, 95 percent confidence interval [CI], 0.05–29.5; p=0.042) and 6-month post-treatment WOMAC improvement (37.43, 95 percent CI, 37.68–50.69; p<0.01).

Meanwhile, synovial hypertrophy and vascularity showed no significant association with VAS or WOMAC scores.

“[R]egardless of KL or synovitis grade, HA injection improves both WOMAC and VAS scores, with the therapeutic effect lasting up to 6 months,” the investigators noted. They also emphasized that the degree of clinical symptom improvement with HA may be predicted by effusion size.

The present data are in line with other studies reporting that effusion-related synovitis, but not synovitis of the perisynovial tissue, contributes to progressive cartilage loss. As such, effusion-related synovitis is a better surrogate marker for structural damage in knees affected by OA. [Osteoarthritis Cartilage 2015;23:1499-1505; Osteoarthritis Cartilage 2010 Oct;18:1269-1274]

However, the investigators pointed out, “although SF depth is independently associated with outcome, it must be cautiously used in combination with KL grade for more accurate prediction. Ultrasound-detected SF depth appears to be a feasible and potentially accurate marker for outcome measurement in OA; but further trials on synovitis are warranted.”