Knee bobbing in Charcot-Marie-Tooth disease.

Patients with Charcot-Marie-Tooth (CMT) disease most commonly have a slowly progressive neuropathy where ankle dorsiflexion weakness is much more prominent than ankle plantar flexion weakness. The eventual involvement of the ankle plantar flexors has major functional consequences for patients as they lose the ability to stand still. We have found the knee bob sign whereby both knees bob up and down when standing still to be a reliable marker of ankle plantar flexion weakness in CMT.