Walking ability and its relationship to lower-extremity muscle strength in children with idiopathic inflammatory myopathies.

Objective: To describe gait deficits and their association with lower-extremity muscle strength in children with juvenile idiopathic inflammatory myopathies (IIM).

Design: Cross-sectional, descriptive study.

Setting: Clinical research center.

Participants: Consecutive sample of 25 ambulatory children diagnosed with juvenile IIM.

Interventions: Not applicable.

Main Outcome Measures: Manual muscle test (MMT) of bilateral hip flexor, extensor, and abductor; knee extensor; and ankle plantarflexor strength, all measured on a 0- to 10-point scale and summary strength measures. Video-based movement analysis to determine walking speed; gait cycle time; right and left step time; stride length; right and left step length; and stance, swing, and double-limb support phase durations.

Results: Walking speed (1.03+/-0.27 m/s) was reduced because of shortened stride lengths (1.03+/-0.21 m) more than prolonged gait cycle times (1.05+/-0.22s). Walking speed highly correlated with the number of muscle groups weaker than grade 7 out of 10 (r=-.89) and the strength of the hip flexors (r=.85).

Conclusions: Lower-extremity strength measures, including MMT scores of individual muscle groups and the number of weak muscle groups, were predictive of gait limitations in children with juvenile IIM.