The crucial therapeutic objective in rheumatoid arthritis (RA) management is reinstating the normal physical functioning. Whether the extent of synovial inflammation quantified by musculoskeletal ultrasound (US) can predict current or future capacity for physical functioning is still undisclosed. Hence, this study was performed to estimate the  longitudinal relationship between physical function assessed by the health assessment questionnaire (HAQ) and the German 7-joint ultrasound score (US7S) in a prospective cohort of RA patients.

For 30.9 ± 9.1 months, the patients suffering from RA (n = 185 (46 with incident and 139 with prevalent disease) were followed. The disease activity score inculcated baseline and annual assessments in 28 joints (DAS28), HAQ and US7S. The semiquantitative measurements of synovitis estimated by greyscale (GS) and power Doppler (PD) in seven joints of the clinically dominant hand and foot were a part of the US7S. These are then accumulated in PD and GS synovitis sum-scores (PDsynSS and GssynSS). To estimate the longitudinal relationship between GSsynSS, PDsynSS and HAQ, a linear mixed-effect model was used. The standard and time-lag models were used to find the association between HAQ, and GSsynSS, PDsynSS and DAS28 calculated at the same time or at the previous visit 12 months ago, respectively.

In univariate analysis HAQ score was positively related with GSsynSS and PDsynSS with β coefficients significantly higher in incident than in prevalent disease, when the standard model was used. Both synSSs were individually no longe important predictors of HAQ score in multivariate analysis. Both  PDsynSS and GSsynSS were significantly and negatively related with the current HAQ when the time-lag model was used.

It was revealed that the US7 PD and GS synovitis sum-scores alone were positively related with current functional status reflected by the HAQ in RA patients, and this association was stronger in patients with early disease. Over a period of one year, US7 PD and GS synovitis sum-scores were predictive of the change in HAQ score when merged with the DAS28 or HAQ.