IN SEARCH OF TARSAL COALITIONS: A DISSECTION AND CT STUDY OF 114 FEET

Abstract

The incidence of tarsal coalitions (TC) is not known. Most of the clinical studies report it as less then 1% but they disregard the asymptomatic coalitions. Two main theories have been elaborated regarding their etiology: 1) they result by incorporation of accessory bones into the nearby tarsals; 2) they occur as a result of the failure of differentiation and segmentation of the foetalmes-enchyme. Tarsal coalitions have been associated with degenerative arthritic changes. Computer tomography is the most commonly used diagnostic test in the detection of TC. The aims of our study were to establish the incidence of TC; the association between TC and accessory tarsal bones and between TC and tarsal arthritis; and to assess the sensitivity of CT as a diagnostic tool in TC. For this purpose we have undertaken coronal and sagittal CTs of 114 cadaveric feet which were subsequently dissected. The dissections identified 10 non-osseous tarsal coalitions, two talocalcaneal and eight calcaneonavicular. In nine cases we identified a synovial joint between the calcaneus and the navicular. We identified eight os trigonum, one accessory lateral malleolus bone, 38 sesamoid bones in the tendon of tibialis posterior and 19 sesamoid bones in the tendon of fibularis longus. Tarsal arthritis was identified in 37 cases. Both talocalcaneal coalitions were associated with talocal-caneal arthritis while none of the calcaneonavicular coalitions were associated with tarsal arthritis. The CT examination of five of the cases of calcaneonavicular coalitions showed one coalition and was suspicious of a coalition in another two instances. In conclusion our study demonstrated that the incidence of tarsal coalition is higher than previously thought (8.8%). The calcaneonavicular coalitions are more common (7%) but they do not seem to be associated with arthritic changes in the tarsal bones. The 7.9% of the calcaneonavicular synovial joint demonstrate that the “abnormality” of the calcaneonavicular space can take any form. Our preliminary CT results demonstrate a low sensitivity in the detection of nonosseous coalitions.