Handheld dynamometer reliability to measure knee extension strength in rehabilitation patients—A cross-sectional study

Introduction The Handheld Dynamometer (HHD) has the potential to overcome some of the logistic and economic limitations of isokinetic dynamometers for measuring knee extension muscle strength. However, its reliability has not been fully assessed. The purpose of this study is to measure intra and inter-rater reliability of HHD for knee extension strength in patients receiving rehabilitation treatment, as well as to understand in which conditions is the reliability higher. Methods Twenty-nine patients admitted in an inpatient Physical Medicine and Rehabilitation unit were consecutively included in this cross-sectional study. Two experienced and two inexperienced physicians made two assessments of knee extension strength with HHD, separated by three hours. Intraclass Correlation Coefficients (ICC), absolute differences between assessments, and correlations between strength and functional variables were calculated. Results Intra and inter-rater ICC were overall high (≥ 0.950 and 0.927, respectively). Higher values were found when average of two measurements were made for estimating intra-rater ICC (ICC = 0.978; 95%CI = 0.969–0.985) but not for inter-rater ICC. ICC were not statistically significantly different when calculated based on measurements performed by inexperienced physicians and experienced ones. There was a moderate correlation between strength and functional variables. Conclusion Handheld Dynamometer seems to be a reliable option to measure knee extension muscle strength, particularly when two measurements are performed and their average is reported.