Etiology of peroneal spastic flat foot.

A type of rigid flat foot which is accompanied by contraction of the peroneal muscles has long been recognised. The etiology is obscure. Correction of the deformity seems to be prevented by tension of the peroneal muscles, and there has been wide acceptance of the thesis that the deformity is caused by peroneal muscle spasm induced by painful stimuli arising from the tarsal joints. It has been assumed that these stimuli result from abnormal stresses thrown upon the tarsal joints by severe degrees of weak flat foot. The concept, therefore, has been that of a weak flat foot which originally was flexible but which was transformed later into a rigid flat foot by the development of peroneal spasm. This theory does not explain all the features of peroneal spastic flat foot. In many cases it can be demonstrated by electromyographic studies that there is no spasm of the peroneal muscles ; the peronei react in every way as do normal muscles. The apparent spasm, in reality, is an organic shortening of the muscles adaptive to long-continued deformity. If all possibility of peroneal spasm is eliminated by novocaine block of the peroneal nerve, by section of the peroneal nerve, by section of the peroneal tendons, or by anaesthesia supplemented with curare, the deformity still persists in many cases. It is difficult to believe that peroneal spastic flat foot develops from flexible flat foot by reason of the stresses which fall upon the tarsal joints. Flexible flat foot is comparatively