Tarsal coalitions can be acquired secondary to infection, trauma, surgery, arthritis or neoplasia but these are rare. Congenital coalitions have been reported to be the most prevalent in adolescents [7]. It has been found that an inherited defect in genetic coding can result in tarsal coalition. Leonard [6] described an autosomal dominant pattern of inheritance with almost full penetrance. Thirty-nine percent of first degree relatives may have tarsal coalitions [6]. Mosca has described tarsal coalition as a developmental malformation instead of congenital deformity, as it is not present at birth but it is genetically programmed to develop. Tarsal coalitions may be present with other congenital disorders such as fibular hemimelia, clubfoot, Apert syndrome, and Nievergelt-Pearlman syndrome, involving multiple bony connections [3].

Most patients are asymptomatic. Only 25 % will go on to develop symptoms and this usually happens between 8 and 12 years for children with calcaneonavicular coalitions [5] and between 12 and 16 years for children with talocalcaneal coalitions [7]. Progressive flattening of longitudinal arch and later onset of aching pain, are the main clinical features of tarsal coalition. Symptoms are activity related and are improving with rest. Tip toeing and Jack’s test will not reconstitute the medial arch due to rigidity of subtalar joint (Fig. 20.1). The term “peroneal spastic flat foot” has been misused in the past as a synonym to tarsal coalition, but it describes a rigid flat foot with involuntary contracture of peroneal tendons that may exist without tarsal coalition [3]. Mubarak et al. [8] also noticed that plantar flexion may be decreased in calcaneonavicular coalitions apart from subtalar joint movements.

Weight bearing radiographs of the foot anteroposterior, lateral and oblique 45° can diagnose a calcaneonavicular coalition with the oblique being the most helpful view [9]. On oblique and lateral radiographs “anteater’s sign” is diagnostic for calcaneonavicular coalition [10]. In addition to previous radiographs, the Harris axial view can help in identifying talocalcaneal coalitions [11]. An anteroposterior ankle view could show a ball-and-socket type joint in a longstanding tarsal coalition. A C-sign on the lateral view can be indicative of talocalcaneal coalition, but since it has also been found to be positive in flexible flat foot, it is considered neither sensitive nor specific for the diagnosis of talocalcaneal coalition [12]. Dorsal talar beaking is another obvious sign on the lateral view. This is considered a traction spur rather than degenerative disease [13]. The gold standard imaging modality to diagnose tarsal coalition is Computed Tomography which can offer also information regarding the size and location, as well as other concurrent coalitions (Figs. 20.2 and 20.3) [14]. Upasani et al. [15] suggested that a CT scan should be performed in order to assess if there is any concurrent osteoarthritis of adjacent joints as well as for preoperative planning as persistent postoperative symptoms may relate to inadequate resection. MRI scanning has comparable results with CT scan and may be useful for early identification of fibrous coalitions [16, 17].