Doppler in small joints was rare in healthy people at any age; grey-scale findings were common

Design

International multicentre cross-sectional observational study

Population

802 healthy adults aged 18–80 from 13 countries

Primary outcome

Age- and joint-specific ultrasound thresholds for synovitis features

Effect

13% of 28,735 joints had a finding >0; MTP1 45%, MTP2 39%; Doppler minimal at all ages

The OMERACT Ultrasound Working Group scanned both hands, wrists and feet in 802 healthy adults aged 18 to 80 at 20 centres in 13 countries, excluding anyone with inflammatory arthritis, joint pain, hand osteoarthritis or recent steroid or NSAID use. Findings were graded with the EULAR–OMERACT synovitis score and normal thresholds set at the 95th percentile.

Of 28,735 joints, 13% had at least one finding above grade 0. The first and second metatarsophalangeal joints were most often affected (45% and 39%). Doppler signal was minimal in every joint and age group, as was grey-scale hypertrophy in the PIP 2–5, MCP 5 and MTP 5 joints. Normal levels of effusion varied mainly by joint, and of hypertrophy by joint and age.

This matters most in early arthritis clinics and in older patients, where low-grade grey-scale findings are easily over-called as synovitis. The practical rule is that Doppler in these joints is likely to be abnormal whatever the patient's age, while grey-scale hypertrophy or effusion alone, particularly at MTP 1 and 2, should be read against joint- and age-specific norms.

• Treat Doppler signal in MCP, PIP, wrist or MTP joints as likely abnormal at any age.
• Interpret grey-scale effusion or hypertrophy alone with caution, especially at MTP 1 and 2.
• Expect more low-grade grey-scale findings in older adults without disease.
• Do not diagnose inflammatory arthritis on low-grade grey-scale findings without clinical or Doppler support.
• Use joint-specific normal ranges when reporting small-joint ultrasound.

Why it matters

It reduces the risk of labelling normal findings as synovitis, particularly in older patients and at the forefoot.

Don't overread it

A healthy-volunteer reference study; it defines normal ranges but has not been tested for diagnostic accuracy in patients.

The statistics, in plain English

The 95% prevalence rule sets 'normal' as the grade that covers 95% of healthy people for that joint and age group. So a finding above that threshold is unusual in health, but not proof of disease. Participants were mostly White and recruited from staff and volunteers, which may limit how widely the thresholds apply.

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