Tarsal Coalition: Clinical Significance and Roentgenographic Demonstration
Coalition of the tarsal bones has been known for several centuries (15). Only within the last fifty years has it been associated with certain clinical situations. In 1921, Slomann (79) first related the calcaneonavicular bar to the clinical entity of peroneal spastic flat foot. It was soon evident that this relationship did not explain the etiology of all examples of peroneal spastic flat foot. Harris and Beath (36), in 1948, recognized that talocalcaneal bridge was also a cause of peroneal spastic flat foot. However, there still remain many cases which demonstrate the typical clinical findings but which have “normal” roentgenograms when examined by the usual technics. This problem stimulated our interest in the diagnosis and treatment of the various forms of tarsal coalition. It was apparent from a review of the world literature, that each advance in the understanding of tarsal coalition has been through the development of roentgenographic technics designed to illustrate the specific abnormalities. The use of tomography in examining the tarsal region has led us to recognize the significance of characteristic secondary roentgenographic signs. These signs, one of which has not been previously described, are produced by abnormal subtalar motion which is usually secondary to the coalition. A previously undescribed variant of talocalcaneal coalition involving the anterior facet of the calcaneus and talus will be presented. This occult coalition, hidden on routine views of the foot, explains some of the perplexing cases that present clinically as coalitions but have normal roentgenographic findings on routine studies.
It is the purpose of this paper to review the causes and variations of tarsal coalition, to discuss the logical approach to the diagnosis of this condition, and to outline the treatment of the various types of coalition.
Tarsal coalition is the union of two or more tarsal bones into a single structure. The union may be fibrous (syndesmosis), cartilagenous (synchondrosis), or osseous (synostosis). It may be either congenital or acquired. The most common varieties of single coalition include the calcaneonavicular bar, talocalcaneal bridge, talonavicular, and calcaneocuboid coalitions. We would prefer, for scientific standardization, to term all these unions as coalitions, rather than by their popular synonyms, bars, or bridges. For brevity we shall abbreviate the four common coalitions noted above as CN, TC, TN, and CC respectively.
Coalition has been demonstrated in the fetus (37, 61, 62, 81). The coalition is usually fibrous or cartilagenous at birth and no radiographic abnormalities may be noted. Good tarsal motion is feasible in the presence of a fibrous lesion. Some limitation of motion will occur with a cartilaginous lesion, and there is complete loss of joint motion in the presence of an osseous coalition. Therefore, the clinical abnormality is rarely detected at birth.