POS0557 THE RELATION BETWEEN INVOLVEMENT OF INDIVIDUAL JOINTS OF THE UPPER EXTREMITY AND GRIP FORCE IN EARLY RHEUMATOID ARTHRITIS

Abstract

Background:Rheumatoid arthritis (RA) has a major impact on hand function in many patients.Objectives:The objective of this study was to investigate the relation between swelling and tenderness of individual joints in the upper extremities and grip force in patients with early RA.Methods:An inception cohort of patients with early RA (symptom duration ≤12 months), recruited in 1995-2005, was investigated and followed in a structured program. All patients were examined by the same rheumatologist according to a structured protocol, and swelling and tenderness of individual joints was recorded. Grip force (Newton, N) was measured using the electronic instrument Grippit (AB Detektor, Gothenburg, Sweden). Average grip force values of each hand were evaluated and compared to the expected, based on age- and sex-specific reference values from the literature (1). Grip force was expressed as % of expected values. Linear regression analyses were used to assess the relation between upper extremity joint involvement in individual joints and grip force, using the presence/absence of synovitis/tenderness in each joint as covariates. For the multivariate analysis, covariates with p<0.10 in the univariate analyses were selected. In cases with major collinearity (Spearman’s r>0.3), the covariate with the stronger association in the univariate analysis was included.Results:A total of 215 patients with early RA (71 % women; mean age 60 years) were investigated. The median symptom duration at inclusion was 7 months; interquartile range 5-10. The median 28 joint counts for swollen joints was 7 (interquartile range, IQR 5-11) and for tender joints 4 (IQR 1-9). In univariate analyses, swelling of the wrist, each metacarpophalangeal (MCP) joint and proximal interphalangeal (PIP) joints III and V, as well as tenderness of the elbow, wrist and each MCP and PIP joint were associated with significantly reduced grip force in the right hand. In the left extremity, corresponding associations were observed for swelling of the wrist, each MCP joint and PIP joints I and V, and for tenderness of the wrist and each MCP and PIP joint. In multivariate analysis, wrist synovitis was associated with reduced grip force (β -11.0 and -14.3 % of expected, respectively). There were also independent significant associations for tenderness of MCP IV and the elbow with reduced grip force in the right hand, and for swelling of MCP I and MCP V with reduced grip force in the left hand (Table 1).Table 1.Joint involvement associated with average grip force (% of expected value), multivariate linear regressionUnstandardized β95 % CIRight handSwollen Wrist-11.0-17.5 to -4.5Tender MCP IV-15.6-25.2 to -6.0Tender PIP V-2.3-12.0 to 7.3Tender Elbow-11.7-22.1 to -1.3Left handSwollen Wrist-14.3-20.4 to -7.6Swollen MCP I-7.6-14.6 to -0.6Swollen MCP V-11.7-21.9 to -1.5Swollen PIP I-0.8-9.2 to 7.5MCP: Metacarpo phalangeal jointPIP: Proximal interphalangeal jointConclusion:Involvement of several different joints in the upper extremity contributes to impaired hand function. Clinical synovitis of the wrist was associated with reduced grip force in both hands. In the left hand, arthritis of the thumb had a major impact on grip force. In general, MCP involvement was found to be more important for the grip than PIP involvement.