Expert Pearls For Treating Charcot-Marie-Tooth Disease
The classic patterns of neuromuscular weakness in CMT involve the peroneus brevis with sparing of the peroneus longus. This leads to a varus position of the rearfoot driven unopposed by the normal strength of the tibialis posterior. The tibialis anterior is also affected early and this allows the peroneus longus to drive the first metatarsal into plantarflexion. This also produces instability of the first metatarsophalangeal joint, producing a hallux malleus. The intrinsic muscles are also involved in such a way that the intrinsic stability of the toes is lost, leading to claw toe deformity (see Figure 2).
The result is a medial peritalar subluxation due to neuromuscular imbalance. The tibialis posterior unopposed by the paralyzed peroneus brevis drives the subtalar joint into varus and accentuates external rotation of the tibio-fibular complex. Due to its plantarflexed position on the first metatarsal and a loss of tibial anterior strength, the unopposed peroneus longus forces the heel into varus and accentuates arch height. Intrinsic weakness activates the windless mechanism as the toes drive the metatarsals into plantarflexion by the flexor digitorum longus overpowering the extensor digitorum longus, which also contributes to elevation of arch height.
When A Patient With ‘High Arches’ Presents With Pain and Instability
Our review is of a 35-year-old Caucasian male who presented with chronic foot and ankle pain with instability. He noted that he had very “high arches” as long as he can remember but they were much worse the past five years. The patient stated that he was very unstable and that his ankles “gave way” very easily. He also noted that his mother, who was in a wheelchair, had very high arches as well. The patient also had a son whose feet looked very similar to his feet.
Upon the clinical exam, we noted adequate vascular perfusion with normal peripheral pulses. The patient had pes cavus and when the patient had a resting calcaneal stance position (RCSP), his heels were in varus with the presence of a “peek-a-boo” heel sign (see Figure 3).
During the neuromuscular exam, we noted a lack of ankle joint dorsiflexion to -5 degrees with the knee extended. With the knee flexed, the foot was brought to 90 degrees to the leg. There was complete loss of peroneal brevis function but the peroneus longus was of normal strength. We determined this when noting no eversion strength with the ankle in a plantarflexed position. When bringing the ankle to 90 degrees, we noticed significant plantarflexion of the first metatarsal, indicating normal strength of the peroneus longus.