A portable, pneumatically driven device for measuring passive metatarsophalangeal joint quasi-stiffness

The assessment of passive metatarsophalangeal joint (MPJ) quasi-stiffness is of growing importance for both athletic performance optimization and clinical monitoring in patient populations. To deepen our understanding and facilitate broader data collection, there is a need to develop a portable device for measuring passive MPJ quasi-stiffness that can be employed in training facilities and clinical settings. Therefore, we designed a portable, pneumatically driven test device to determine the passive quasi-stiffness of the MPJ. The aim of the present study was to investigate the within-day and between-day test-retest reliability of the device. A total of 19 healthy subjects participated in the study. Passive MPJ quasi-stiffness was assessed at three time points: two measurements were conducted on the same day (within-day reliability), and a third measurement was performed on a different day within the same week (between-day reliability). A standardized protocol ensured identical conditions across all three test sessions. The results of the intra-rater intraclass correlation coefficient (ICC (3,1)) comparing passive MPJ quasi-stiffness indicated excellent test-retest reliability for both within-day measurements (ICC = 0.999, 95% CI: 0.99-0.99, p < 0.001) and between-day measurements (ICC = 0.993, 95% CI: 0.98-0.99, p < 0.001). Bland-Altman analysis revealed minimal systematic bias. These findings demonstrate that the standardized protocol and the custom-made device used in this study provide highly reliable results. Its portability, combined with its ease of use and reliability, makes it highly practical for sports and in clinical settings.