Articular surface defects in the third metatarsal and third cuneiform: nonosseous tarsal coalition

Frequencies of articular surface defects on the third metatarsal and third cuneiform, seen as pits of varying sizes on the plantar one third of the tarsometatarsal articular face, were investigated in skeletal populations from North America and Japan, as well as in gibbon, orangutan, chimpanzee, and gorilla skeletons. The apes did not exhibit the defects, although the number of observed specimens of each type was small. The newly presented human frequencies corresponded well with those from other published sources. The defects appeared both unilaterally and bilaterally, with no apparent sex or side biases. Statistical tests between the various populations found that, in general, geographically close populations had more similar frequencies of the defect. Possible etiologies for the defect were investigated, including biomechanical influences, degenerative arthritis, infection, trauma, and a developmental condition known as tarsal coalition, which proved to be the best explanation. Tarsal coalition results from the failure of a joint space to form properly during fetal growth. It can occur between any two adjacent bones of the foot. Several clinically important coalitions, whose presence interferes with normal walking, are known. However, coalition between the third metatarsal and third cuneiform has not been reported in the clinical literature, suggesting that the defect causes little or no foot dysfunction. Tarsal coalition is thought to have a strong genetic component, suggesting that the pit defect may be useful as a skeletal nonmetric trait, as others have stated.