Pes valgus is common in cerebral palsy with spastic diplegia with severe peroneal spasticity. Pes valgus consists of eversion and equinus inclination of the calcaneus and abduction of midfoot, resulting in prominence of the head of the talus medially. Pronation of the foot or flat foot is one of the cause of the entrapment of the tibial nerve in or below the tarsal tunnel and causes burning or sharp shooting pain from the medial side of the ankle into the foot. But the children with cerebral palsy could hardly express pain.

The medial and lateral mixed plantar nerve conduction study was performed in order to look for the possibility of tarsal tunnel syndrome according to Saeed and Gatens in cerebral palsy with spastic diplegia. Twenty-one control subjects aged from 2 to 13 and 31 patients from 3 to 13 years of age were studied. Mean conduction velocity of medial plantar nerve showed significant delay in patients as 39.8±10.6m/sec compared with the control subjects as 45.3±3.9m/sec and that of lateral plantar nerve was also delayed significantly in patients as 40.3±11.2m/sec compared with the control subjects as 45.8±4.3m/sec.

But the mean amplitude of medial plantar nerve was not significantly different between patients as 24.4±12.5uV and the control as 27.6±14.3uV and that of lateral plantar nerve also was not significantly different, either. There was no compound nerve action potentials that was not evoked in controls but in 2 cases of patients those were not evoked. The longer the years of walking, the more decreased amplitude of medial and lateral plantar nerves in cerebral palsy with spastic diplegia.

In conclusion, pes valgus in cerebral palsy may cause stretch or local compression of medial and lateral plantar nerves, resulting in decreased conduction velocity and amplitude of compound nerve action potentials.