Manual muscle testing and hand-held dynamometry in people with inflammatory myopathy: An intra- and interrater reliability and validity study

Abstract

Manual muscle testing (MMT) and hand-held dynamometry (HHD) are commonly used in people with inflammatory myopathy (IM), but their clinimetric properties have not yet been sufficiently studied. To evaluate the reliability and validity of MMT and HHD, maximum isometric strength was measured in eight muscle groups across three measurement events. To evaluate reliability of HHD, intra-class correlation coefficients (ICC), the standard error of measurements (SEM) and smallest detectable changes (SDC) were calculated. To measure reliability of MMT linear Cohen`s Kappa was computed for single muscle groups and ICC for total score. Additionally, correlations between MMT8 and HHD were evaluated with Spearman Correlation Coefficients. Fifty people with myositis (56±14 years, 76% female) were included in the study. Intra-and interrater reliability of HHD yielded excellent ICCs (0.75-0.97) for all muscle groups, except for interrater reliability of ankle extension (0.61). The corresponding SEMs% ranged from 8 to 28% and the SDCs% from 23 to 65%. MMT8 total score revealed excellent intra-and interrater reliability (ICC>0.9). Intrarater reliability of single muscle groups was substantial for shoulder and hip abduction, elbow and neck flexion, and hip extension (0.64-0.69); moderate for wrist (0.53) and knee extension (0.49) and fair for ankle extension (0.35). Interrater reliability was moderate for neck flexion (0.54) and hip abduction (0.44); fair for shoulder abduction, elbow flexion, wrist and ankle extension (0.20-0.33); and slight for knee extension (0.08). Correlations between the two tests were low for wrist, knee, ankle, and hip extension; moderate for elbow flexion, neck flexion and hip abduction; and good for shoulder abduction. In conclusion, the MMT8 total score is a reliable assessment to consider general muscle weakness in people with myositis but not for single muscle groups. In contrast, our results confirm that HHD can be recommended to evaluate strength of single muscle groups.

Fig 1. Sample selection.

From 76 people with myositis fulfilling all inclusion criteria 50 agreed to participate. After the first measurement four participants dropped out.

Fig 2. Procedure of the intra- and interrater reliability.

Each patient was measured three times. For intrarater reliability MMT8 and HHD were performed by the same tester (Measurement 1 and 2) and for interrater reliability MMT8 and HHD were performed by two different testers (Measurement 2 and 3). Abbreviations: MMT8: Manual muscle test 8, HHD: Hand-held dynamometry.

Fig 3. Bland and Altman plots of hand-held dynamometry (peak force).

The blue continuous horizontal line shows the mean difference between tests. The dashed orange horizontal lines show the upper and lower 95% limits of agreement (bias ± 1.96 × standard deviation). Abbreviations: M: measurement, S_ABD: shoulder abduction, E_FLEX: elbow flexion, A_EXT: ankle extension, H_ABD: hip abduction, H_EXT: hip extension, K_EXT: knee extension, W_EXT: wrist extension, N_FLEX: neck flexion.

Fig 4. Bland and Altman plots of hand-held dynamometry (peak force).

The blue continuous horizontal line shows the mean difference between tests. The dashed orange horizontal lines show the upper and lower 95% limits of agreement (bias ± 1.96 × standard deviation).Abbreviations: M: measurement, S_ABD: shoulder abduction, E_FLEX: elbow flexion, A_EXT: ankle extension, H_ABD: hip abduction, H_EXT: hip extension, K_EXT: knee extension, W_EXT: wrist extension, N_FLEX: neck flexion.

Fig 5. Ceiling effects of MMT8.

All but one muscle group (hip extension) showed ceiling effects of 22 to 82%. Abbreviations: A_EXT: ankle extension, E_FLEX: elbow flexion, W_EXT: wrist extension, K_EXT: knee extension, N_FLEX: neck flexion, S_ABD: shoulder abduction, H_ABD: hip abduction, H_EXT: hip extension.

Fig 6. Muscle strength measured by hand-held dynamometry (in Newton) and MMT8 (MMT-Scale).

The association between results from MMT8 and HHD are not consistent.

Fig 7. Measuring knee extension using a belt to stabilize the dynamometer.

Standard body position of the patient and the device are shown with knees and hips flexed to 90°.

Fig 8. Measuring hip extension using a belt to stabilize the examiner.

Standard body position of the patient and the device are shown with stretched hip and knees.