Quantification of muscle strength and imbalance in neurogenic pes cavus, compared to health controls, using hand-held dynamometry

Background. Pes cavus foot deformity in neuromuscular disease is thought to be related to an imbalance of musculature around the foot and ankle. The most common cause of neurogenic pes cavus is Charcot-Marie-Tooth (CMT) disease. The aim of this investigation was to objectively quantify muscle strength and imbalance using hand-held dynamometry in patients diagnosed with CMT and pes cavus, compared to healthy controls. Methods: Muscles responsible for inversion, eversion, plantarflexion, and dorsiflexion of the foot and ankle were measured in 55 subjects (11 CMT patients with a frank pes cavus, and 44 healthy controls with normal feet) using the Nicholas hand-held dynamometer (HHD). Test-retest reliability of the HHD procedure also was determined for each of the four muscle groups in the healthy controls. Results: Test-retest reliability of the HHD procedure was excellent (ICC3,1 = 0.88 to 0.95) and the measurement error was low (SEM = 0.3 to 0.7 kg). Patients with CMT were significantly weaker than normal for all foot and ankle muscle groups tested (p < 0.001). Strength ratios of inversion-to-eversion and plantarflexion-to-dorsiflexion were significantly higher in the patients with CMT and pes cavus compared to individuals with normal foot types (p > 0.01). Conclusions: Hand-held dynamometry is an objective and reliable instrument to measure muscle strength and imbalance in patients with CMT and a pes cavus foot deformity.