Multilead electromyographic studies and clinical evaluations were carried out on the leg muscles of nine children on whom anterior transposition of the peroneus longus had been done eight and one-half months to ten years previously. In one patient, one preoperative and three postoperative electromyographic studies were performed. The action-potential patterns of the leg muscles of seven normal young adults were used as controls to aid in the interpretation of the pathological findings. The muscles studied were the tibialis anterior, extensor digitorum longus, tibialis posterior, peroneus longus, peroneus brevis, gastrocnemius, and flexor digitorum longus. The activities performed were simple range of motion and barefoot walking. The clinical evaluations of the end results were tabulated and correlated with the electromyographic analyses of the gait patterns.

The data presented support the following conclusions:

Normal automatic walking is made possible by the activity of the leg muscles which function with split-second timing in relation to the swing and stance phases and the double-weight-bearing portion of the stance phase.

In the normal walking patterns, the timing and phasic activity of these muscles generally have similar characteristics. There are certain variations among individuals, especially in the anterior tibial and toe extensors. The pattern of activity of the gastroenemius shows the least individual variation in normal subjects.

The normal phasic activity of the muscles of the leg is frequently lost when there are various degrees of paralysis due to poliomyelitis.

After anterior transposition of the peroneus longus, transfer of activity of this muscle from the usual stance phase to the swing phase may occur. In one patient, a progressive and complete transition of activity to the swing phase was demonstrated by a series of electromyograms over a period of eight and one-half months.

In the small series studied good clinical results were obtained in all patients whose electromyograms demonstrated partial or complete shift of the activity of the transposed muscle to the swing phase of walking, but good clinical results were also obtained when electromyographic evidence of dorsiflexion activity was not present during the swing phase.

All patients with poor clinical results also had poor electromyographic evidence of transplant activity in the swing phase of walking.

Further studies simould be carried out concerning the mechanism by which the transfer of phase occurs in the peroneus longus muscle.