PARTIAL CUBO-NAVICULAR COALITION AS A CAUSE OF PERONEAL SPASTIC FLAT FOOT

Abstract

It is now recognised that congenital fusion between the talus and the calcaneum or between the calcaneum and the navicular bone is found in a high proportion ofpatients who have peroneal spastic flat foot. This paper presents an example of partial coalition between the cuboid and navicular bones. In the normal foot there may or may not be a synovial joint between these two bones. Oblique radiographs show well defined articular facets in approximately one quarter of the feet examined. In the remainder there is a space between the adjacent angles of the cuboid and navicular, the edges of the bones being irregular. It is important to appreciate that slight alterations in the obliquity of the x-rays can produce an overlapping of shadows which may suggest bony fusion. Further films, at varying angles, will demonstrate the true situation. Harris and Beath (1948) suggested that the typical congenital tarsal fusions occur in relation to accessory bones. The os cuboidum secundarium is found on the plantar surface of the foot at the point of contact between cuboid, navicular, calcaneum and talus (Trolle 1948). It may be fused to the navicular or cuboid, but more commonly to the former (O’Rahilly 1953). Jack (1954) suggested that coalition was due to an error in differentiation (possibly hereditary) which may lead to a large complete bony fusion at one extreme or to a small accessory bone at the other. Since an accessory bone may be present between the navicular and the cuboid, it is reasonable to suppose that coalition may occur between the two bones. Dwight (1907) illustrated by radiograph and photograph of the plantar surface of the bones of the foot what he described as synchondrosis of the navicular and cuboid, but it has not been possible to find any account of this particular abnormality as a cause of spastic flat foot.