Measuring intrinsic hand strength in healthy adults: The accuracy intrarater and inter-rater reliability of the Rotterdam Intrinsic Hand Myometer

Abstract

Study Design: Clinical measurement study. Introduction: Measuring the isometric strength generated during isolated hand joint motions is a challenging feat. The Rotterdam Intrinsic Hand Myometer (RIHM; med.engineers, Rotterdam, Netherlands) permits measurement of isolated movements of the hand. To date, there is limited evidence on the inter-rater reliability and limited adult normative data of RIHM. Given that multiple raters, often with varying degrees of experience, are needed to collect normative data, inter-rater reliability testing and a comparison of novice and experienced raters are needed. Purposes of the Study: The purposes of this study were to test the accuracy, intrarater reliability, and inter-rater reliability of the RIHM in healthy-handed adults. Methods: RIHM accuracy was tested through use of precision class F weights. Adults 18 years or older without upper limb dysfunction were recruited. Each participant was tested by 4 raters, 3 occupational therapy graduate students, and an experienced certified hand therapist, through use of a calibrated RIHM. Five strength measures were tested bilaterally (ie, thumb carpometacarpal palmar abduction, index finger metacarpophalangeal [MP] abduction, index finger MP flexion, thumb MP flexion, and small finger MP abduction) 3 times per a standardized protocol. Statistical methods were used to test accuracy, inter-rater reliability, and intrarater/response stability. Results: The accuracy of RIHM device error was 5% or less. Reliability testing included the participation of 19 women and 10 men (n = 29). All raters were in excellent agreement across all muscles (intraclass correlation coefficient, ≥0.81). Low standard error of measurement values of ≤8.3 N (1.9 lb) across raters were found. The response stability and/or intrarater reliability of the novice and certified hand therapist raters were not statistically different. Discussion: The RIHM has an acceptable instrument error; the RIHM and its standardized procedure have excellent inter-rater reliability and response stability when testing those without hand limitations; and the response stability and/or intrarater reliability of expert and novice raters were consistent. Conclusions: The use of the RIHM is justified when multiple raters of varying expertise collect normative data or conduct cohort studies on persons with healthy hands. Future research is warranted. Level of Evidence: Not applicable.