Among individuals without painful osteoarthritis (OA) of the knee, ultrasound effusion and synovial hypertrophy, but not power Doppler signal, are commonly observed but differ by gender, according to the results of a cross-sectional cohort study published in Osteoarthritis and Cartilage.

The investigators sought to determine “normal” ranges of synovial thickness and effusion, as detected by ultrasound, and to establish cutoffs associated with knee pain and radiographic knee OA in a community-derived cohort of patients. A total of 147 women and 152 men aged ≥40 years were randomly selected from the Nottingham Knee Pain and Related Health in the Community cohort. The normal range was set using the percentile method in 163 participants with no knee pain or radiographic knee OA. Receiver operating characteristic curve analysis was used to establish optimal (ie, maximum sensitivity and specificity) and high-specificity (90%) cutoffs when individuals with both knee pain and radiographic knee OA were compared with normal control patients.

Because effusion and synovial hypertrophy differed according to gender but not according to age or laterality, gender-specific reference limits had to be estimated. The normal ranges among men and women were similar with respect to effusion (0-10.3 mm vs 0-9.8 mm, respectively), but differed with respect to synovial hypertrophy (0-6.8 mm vs 0-5.4 mm, respectively). Moreover, the prevalence of power Doppler signal differed significantly among healthy control patients (0.65%; 1.2% in men and 0.0% in women) vs those with symptomatic radiographic knee OA (7%; 14.3% in men and 3.6% in women; P =.0083).

The optimal cutoff was 7.4 mm for men vs 5.3 mm for women with regard to effusion, and 3.7 mm for men vs 1.6 mm for women with regard to hypertrophy. The high-specificity cutoff was 8.9 mm for men and 7.8 mm for women for effusion compared with cutoffs of 5.8 mm for men and 4.2 for women for hypertrophy. Regarding power Doppler signal, as the frequency of the signals was near zero among the healthy control patients, there was no reason to establish a normal range and cutoff.

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The results of this study suggest that different thresholds for both effusion and synovial hypertrophy should be applied for among men and women. The data derived from this analysis are beneficial for the classification of synovial abnormalities among individuals with symptomatic radiographic knee OA and for the development/revision of evidence-based guidelines for ultrasound abnormalities in patients with knee OA.

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Reference

Sarmanova A, Hall M, Fernandes GS, et al. Thresholds of ultrasound synovial abnormalities for knee osteoarthritis – a cross sectional study in the general population [published online November 15, 2018]. Osteoarthritis Cartilage. doi: 10.1016/j.joca.2018.09.018.