A radiologic classification of talocalcaneal coalitions based on 3D reconstruction

Talocalcaneal coalitions can be difficult to detect on plain radiographs, despite obvious clinical findings. The purpose of this study is two-fold: (1) to delineate the benefits of thin-cut computed tomography (CT) and 3D reconstructions and (2) to develop a classification scheme for talocalcaneal coalitions that will provide valuable information for surgical planning.

From 2005 to 2009, 54 feet (35 patients) with a talocalcaneal coalition were evaluated with thin-cut (1 mm) CT, using multi-planar 2D and 3D reconstructions. The talocalcaneal coalitions were classified into five types based on the cartilaginous or bony nature, location, and facet joint orientation.

Bilateral coalitions were found in 22/35 patients. Types I and II were fibrocartilaginous coalitions, which was the most common type, comprising 40.7 and 16.7% of the coalitions, respectively. Of the patients, 14.8% had a shingled Type III coalition, while 11.1% of the feet examined had a complete bony coalition (Type IV). Small peripheral posterior bony coalitions (Type V), which are heretofore not described, were found in 16.7% of feet.

CT scans can provide valuable information regarding the bony or cartilaginous nature of coalitions, as well as the facet orientation, which is helpful in diagnosis and treatment. In this study, the 2D and 3D reconstructions revealed previously unreported peripheral posterior bony coalitions (Type V), as well as coalitions that are in the same plane as the standard CT cuts or Harris view radiographs (Type I). The CT scan also improved the crucial pre-operative planning of the resection in the more complex vertical and combined horizontal and vertical fibrocartilaginous coalitions (Type I and II). Additionally, the complete bony coalitions (Type IV) can be sized accurately, which is helpful in decision-making on the resectability of the coalition.