Partial Cubo-Navicular Coalition as a Cause of Peroneal Spastic Flat Foot

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