The Divided Navicular of the Foot

The divided or extra navicular, the true tibiale externum of the foot , a well-recognized anatomical entity as early as 1907 (1), has received relatively little attention in recent x-ray literature and is omitted from most charts indicating extra ossicles or anomalies of the foot. Although it is a rare condition, a brief report would seem in order to call attention to this regular anomaly which is most prone to have a mistaken interpretation on roentgenograms when seen for the first time. The following case seems typical. Case Report M. J., female, 25 years of age, a nurse , received an injury to the foot while riding in a taxicab when the car stopped suddenly and the patient slid forward, forcibly flexing her right foot against the back of the front seat. She was taken to the hospital, where it was noticed that the region of the right navicular was prominent. A diagnosis of a sprained ankle was made. Six weeks later a second physician examined the patient and after having roentgenograms made of the foot from different angles, made a diagnosis of a fractured navicular and had a cast applied. The patient suffered little and the cast was removed at the end of two weeks. A few days later the patient reported to one of us (E. B. W.) for a check-up examination. The other (W. E. A.) was requested to make a roentgenographic examination to note progress. Films of the right foot made at different angles showed the navicular divided into two apparently isolated portions (Fig. 2). Each had normal appearing borders, but at the point of contact with each other the surfaces were slightly flattened. The texture of each segment appeared normal and while there did not seem to be a well-formed joint space between them, they presented the appearance of two distinct bones. An anomalous divided navicular was thought to exist, and an examination of the normal left foot showed identical changes (Fig. 1). Through the kindness of the patient and the courtesy of the physician making the earlier examination, we were able to compare roentgenograms made at different periods and found that in all, the texture and contour of the bones were similar. Comment While the divided navicular of the foot has been occasionally mentioned in the literature, and this condition was beautifully illustrated by Dwight in 1907 (Fig. 3), it has been given little attention since, and demonstrations on roentgenograms have been rare. Although this condition is infrequently met with, its similarity to a fracture should cause it to be included on working charts. It is the largest regular anomaly of the tarsals and because of having a closer relationship to the regular bones it is more prone to have a mistaken interpretation than the more common extra ossicle, also called the tibiale externum, which is located in the tendon and is usually at some distance from the regular navicular.