Precision, comfort and mechanical performance of the Quadriso-tester, a quadriceps force measuring device

The mechanical performance, repeatability and comfort of the Quadriso-tester, which assesses isometric knee extensor muscle strength, were examined. Twenty healthy subjects and 20 patients treated for unilateral anterior ligamenta cruciata insufficiency were tested. Intra-rater repeatability was determined by the testing and retesting of subjects and calculation of the intra-class correlation coefficient and the mean difference between test and retest values. The comfort level was determined a questionnaire. Measuring time was recorded, and the relationship between knee angle and extension moment was plotted. Strength and stiffness were determined using the finite element method. Intra-rater repeatability was high; the intra-class correlation coefficient of the right and left leg was 0.90 and 0.91, respectively; the coefficient of variation was 6.4 and 6.0%, respectively. The median comfort score of the healthy subjects was 7, and that of the patients was 9. Measuring time remained within 30min. Misalignment of the knee and sidebar axis disturbed the relationship between knee angle and extension moment. Strength and stiffness were higher than required. In conclusion, the Quadriso-tester is a comfortable and fast device to determine quadriceps force with a high repeatability. The knee and sidebar axis should be well aligned.