Reliability of a portable device for measuring lower-limb muscle strength in patients who underwent total knee arthroplasty.

[Purpose] This study aimed to analyze the reliability of using the Locomo Scan to measure quadriceps muscle strength in patients who underwent total knee arthroplasty. [Participants and Methods] Two testers (A and B) used the Locomo Scan to perform three measurements of quadriceps muscle strength on the operated side of 64 patients who underwent total knee arthroplasty and recorded the mean and maximum values. We then assessed intra- and inter-rater reliability using intraclass correlation coefficients and obtained systematic errors via Bland-Altman analysis. We calculated the 95% confidence interval and percentage error for the minimum detectable change. [Results] The intraclass correlation coefficients for case 1 were 0.903 and 0.889 for testers A and B, respectively, and those of case 2 were 0.783 and 0.818 for the mean and maximum values, respectively. Bland-Altman analysis revealed no systematic errors. The 95% confidence interval and percentage error for the minimum detectable change were 0.138 kgf/kg and 39.6% for the mean value and 0.132 kgf/kg and 35.1% for the maximum value, respectively. [Conclusion] The Locomo Scan can reliably measure quadriceps strength in patients who underwent total knee arthroplasty and may be useful in clinical settings.