Conversion of grip strength scores between Jamar dynamometer and a modified sphygmomanometer in patients with rheumatoid arthritis

BACKGROUND: Jamar dynamometer and modified sphygmomanometer (SphM) are used to evaluate grip strength (GS) in patients with rheumatoid arthritis (RA). However, their scores are not interchangeable. OBJECTIVES: The aim of this study was to describe the intertrial reliability of grip strength measures obtained with Jamar dynamometer and an SphM, and delineate the relationship of the measures obtained with these two instruments when they were used in patients with RA. METHODS: Patients were eligible volunteers among 74 consecutive patients with definite diagnosis of RA. The data from 61 patients were analyzed. Student's t test was used to compare GS means of the male and female patients. Intertrial reliability was examined using one-way repeated measures ANOVA and intraclass correlation coefficients. The relationship between the measures was established using Pearson correlation coefficients and inverse regression analysis. The latter allowed the generation of conversion tables. RESULTS: GS means were not significantly different between the genders. Both instruments demonstrated excellent intertrial reliabilities. No significant difference was observed among the trials with each instrument. There was a strong relationship between the instruments' scores. This relationship was proven to be linear. Conversion equations were calculated based on the instruments' scores. CONCLUSION: Clinicians now have a table to convert hand strength scores between Jamar dynamometer and an SphM, and can determine the deviation from the normal in patients with RA.