Relationship between two measures of upper extremity strength: manual muscle test compared to hand-held myometry

One hundred and twenty-two individuals with spinal cord injuries at levels C4-6, Frankel classifications A through D, were evaluated to determine the relationship between the manual muscle test (MMT) and hand-held myometry as accurate methods for measuring muscular strength. More specifically, this study attempted to define a range of myometry scores that could be correlated with discrete MMT grades. It also investigated which of the two modalities (MMT or hand-held myometry) is the best reflection of improvement in muscle strength over time. Sequential motor strength examinations using both modalities were performed at 72 hours, one week, and two weeks post SCI and then one, two, three, four, six, 12, 18, and 24 months post injury. The data analyses included calculations of Spearman ranked correlations, analyses of variance, and linear regressions. Results showed that 22 of 24 correlations between MMT and myometry were significant at p values less than .001. The range of myometry measurements for a particular MMT grade appears to be most specific for MMT scores less than 4 (ie, poor-plus to good), and less specific for MMT scores greater than or equal to 4. The results of this study also indicate that myometry measurements detect increases in strength over time, which are not reflected by changes in MMT scores.