Validity and reliability of hand-held dynamometry for proximal strength assessment in systemic sclerosis-associated...

To evaluate the validity and reliability of hand-held dynamometry (HHD) for quantifying proximal muscle strength in patients with systemic sclerosis-associated myopathy (SSc-AM), and to compare HHD with the validated manual muscle testing-8 (MMT-8) and modified three-muscle proximal MMT (MMT-3).

In this prospective, cross-sectional study, 36 patients with SSc-AM underwent strength testing using MMT-8, a proximal MMT-3 (neck flexors, shoulder abductors, hip abductors) and a quantitative hand-held dynamometry (MicroFET-2). For each muscle group, three HHD trials were averaged, and composite HHD scores were calculated. Eight participants underwent repeat testing by a second examiner to assess inter-rater reliability. Pearson correlation coefficients were calculated to assess the association between HHD and MMT scores. Intra-rater and inter-rater reliability were evaluated using intraclass correlation coefficients (ICCs) derived from two-way mixed effects model with absolute agreement.

Composite HHD scores showed strong correlations with MMT-8 total scores (r = 0.695, p < 0.0001) and with the proximal MMT-3 (r = 0.736, p < 0.0001). Intra-rater reliability was excellent across all proximal muscle groups (ICC range 0.885-0.985). Inter-rater reliability was acceptable for neck flexors and shoulder abductors (ICC 0.60-0.75) but lower for hip abductors (ICC 0.06-0.13), reflecting higher stabilization requirements and small sample size (n = 8).

Hand-held dynamometry provides a quantitative assessment of proximal isometric strength in SSc-AM and demonstrated excellent intra-rater reproducibility in this study. Correlation with MMT-8 and MMT-3 demonstrates alignment with commonly used strength measures. Given known limitations of MMT-based assessment and variable inter-rater reproducibility, further longitudinal studies are needed to evaluate responsiveness and define its clinical utility.