Imaging description

Accessory anterolateral facet of the talus is a normal variation involving the anterolateral aspect of the lateral process of the talus, which articulates with an extended facet of the anterior process of the calcaneus (Figure 62.1). Combined with the extended facet of the calcaneus, this opposing structure looks like an anterior extension of the posterior subtalar joint. Detection on the lateral radiographs may be difficult particularly in the presence of a valgus hindfoot deformity. Cross-sectional studies especially MRI can detect articular cartilage in the interface (Figure 62.2). This variation was seen in 34% of the 79 pediatric cadaveric specimens.

Importance

Painful talocalcaneal impingement associated with this variation has been reported in a small number of pediatric patients with rigid flatfoot. Although tarsal coalitions are the most common etiology of the rigid flatfoot in adolescents and young adults, lateral talocalcaneal impingement associated with accessory anterolateral facet of the talus can be a cause of painful rigid foot. Interestingly the accessory anterolateral facet is commonly associated with dorsal talar beaking (29%).

Typical clinical scenario

Pediatric to young adult patients may present with painful rigid flatfoot deformity. Subtalar motion is restricted with the pain localized to the sinus tarsi. Lateral radiographs may show flatfoot deformity with dorsal talar beaking. CT or MRI may be requested for possible tarsal coalition. Accessory anterolateral facet can be detected on these cross-sectional studies. MRI demonstrates bone marrow edema on both talar and calcaneal sides along the accessory articulation. Surgical resection of accessory anterolateral facet provides improvement in symptoms.