Development and Validation of a Myometric Test of Strength in Lower Extremities for Multiple Sclerosis Patients Using Hand-Held Dynamometer

Background: Reliable, quantitative measures of strength are needed for clinical purposes and research in multiple sclerosis (MS). 

Objectives: We developed a myometric test of strength in lower extremities using a commercially-available hand-held dynamometer (HHD) and measured reliability characteristics across a range of disability levels in a cross-sectional MS study.

Methods: Twenty-one participants with MS were recruited with 7 participants in each of three disability levels Group 1) EDSS = 0-3.5, Group 2) EDSS = 4.0-5.5, Group 3 (EDSS = 6.0-7.5. Participants were strength tested by two physical therapists on two occasions (4 examinations total).  The assessment used a standardized protocol for muscle testing with HHD (three trials recording maximum voluntary force [kg]) and included 10 muscle groups: bilateral hip abductors (HA), hip flexors (HF), knee extensors (KE), knee flexors (KF) and ankle dorsiflexors (DF). The Lower Extremities Strength sum score (LES sum score) was calculated by summing the peak HHD recording from 10 muscle groups.  An intra-class correlation coefficient (ICC) of ≥ 0.85 was used as a reliability benchmark. Manual muscle testing (MMT) was also done for comparison.

Results: Strength testing with HHD took 10 minutes on average and was well-tolerated.  Group 1 had the highest strength recordings for all muscle groups (HHD and MMT) and highest LES sum score.  Within each EDSS category, HHD strength records were highest for KE and lowest for KF. For inter-rater reliability, only HF and KF had consistent ICC >0.85 across both visits and all EDSS subgroups. For inter-session reliability, most muscle groups and LES sum scores had ICC >0.85 across both examiners and all EDSS groups.  There was no difference in reliability statistics across EDSS subgroups, except for LES sum score for which reliability was lower at the highest disability level. 

Conclusions: This was a study of a myometric test of Strength in Lower Extremities for Multiple Sclerosis Patients using a HHD.  The test yielded a combined quantitative measure of lower limb strength (LES sum score) as a global measure. Single-rater reliability was high across a range of disability levels, but inter-rater reliability was lower.  Work is in progress to revise the test and perform a multi-center validation study.  Similar research is recommended in upper extremity strength testing.