Are tarsal coalitions a common anatomical variant?

Tarsal coalitions are defined as fibrous, cartilaginous or osseous union of two or more tarsal bones (Kulik & Clanton 1996, Mosier & Asher 1984). Most clinical studies report the incidence of tarsal coalitions (TC) as less then 1% (Drenna 1996, Sakellariou & Claridge 1999) but they disregard the asymptomatic coalitions (Leonard 1974). Since TC have been associated with several pathologic conditions, including degenerative arthritic changes, the knowledge of its incidence has a clinical impact. The aims of our study were to establish the incidence of TC and the association between TC and tarsal arthritis in a sample of cadaver feet. 114 feet of 62 individuals (mean age at death 78y) without any obvious foot pathologies were dissected at the Department of Anatomical Sciences, University of Adelaide. The dissections identified ten non-osseous TC in eight subjects: two talocalcaneal and eight calcaneonavicular. Tarsal arthritis was identified in 37 cases. Both talocalcaneal coalitions were associated with talcalcaneal arthritis while none of the calcaneonavicular coalitions were associated with tarsal arthritis. Our study demonstrated that the overall incidence of TC is higher (12.9%; 8/62) than previously thought, making them a rather frequent normal anatomical variant. The calcaneovicular coalitions are the most common (9.7%; 6/62) but they do not seem to be associated with arthritic changes in the tarsal bones. The found increased incidence of TC might reflect a microevolutionary trend