Tatjana Paternostro-Sluga, Martina Grim-Stieger, Martin Posch, Othmar Schuhfried, Gerda Vacariu, Christian Mittermaier, Christian Bittner, Veronika Fialka-Moser
DOI: 10.2340/16501977-0235

Objective: To assess the inter-rater and intra-rater reliability and validity of the original and a modified Medical Research Council scale for testing muscle strength in radial palsy.
Design: Prospective, randomized validation study

Patients: Thirty-one patients with peripheral paresis of radial innervated forearm muscles were included.
Methods: Wrist extension, finger extension and grip strength were evaluated by manual muscle testing. Dynamometric measurement of grip strength was performed. Pair-wise weighted kappa coefficients were calculated to determine inter-rater and intra-rater reliability. The 2 scores were compared using the signed-rank test. Spearman's correlation coefficients of the maximal relative force measurements with the median (over-raters) Medical Research Council and modified Medical Research Council scores were calculated to determine validity.
Results: Inter-rater agreement of the Medical Research Council scale (finger extension: 0. 77; wrist extension: 0. 78; grip strength: 0. 78) and the modified Medical Research Council scale (finger extension: 0. 81; wrist extension: 0. 78; grip strength: 0. 81) as well as intra-rater agreement of the Medical Research Council scale (finger extension: 0. 86; wrist extension: 0. 82; grip strength: 0. 84) and the modified Medical Research Council scale (finger extension: 0. 84, wrist extension: 0. 81; grip strength: 0. 88) showed almost perfect agreement. Spearman's correlation coefficients of the maximal relative force measurements with the median Medical Research Council and modified Medical Research Council score were both 0. 78.
Conclusion: Medical Research Council and modified Medical Research Council scales are measurements with substantial inter-rater and intra-rater reliability in evaluating forearm muscles.