Accessory Cuboid Facet Associated with Calcaneonavicular Coalitions

Background: Calcaneonavicular (CN) coalitions are the most commonly encountered tarsal coalition. No study has assessed anatomic variations of the adjacent joints in the presence of a CN coalition. This study sought to identify differences in the anatomy of the calcaneocuboid (CC) articulation in feet with and without CN coalitions. Methods: An institutional review board approved retrospective analysis of patients with symptomatic CN coalitions presenting to a single tertiary care pediatric orthopaedic hospital was performed. Patients without computed tomographic or magnetic resonance imaging were excluded. The morphology and dimensions of the cuboid portion of the CC joint were documented. When contralateral imaging was available in patients with a unilateral coalition, the morphology of the uninvolved side was evaluated to provide a cohort of controls for comparison. Results: Imaging was available for 55 patients who had a mean age of 11.7 years. There were 80 CN coalitions and 18 normal feet. An accessory cuboid facet was identified articulating with the calcaneal portion of the coalition in 60/80 (75%) feet in the coalition group. In feet with a coalition and an accessory facet, the mean total length of the cuboid articular surface measured 25.3 mm (range, 17.7 to 33.3 mm). The average length of the accessory facet was 10.7 mm (range, 5.4 to 15.5 mm), while the length of the primary vertical cuboid articulation with the calcaneus was 14.6 mm (range, 6.4 to 21 mm). The accessory facet comprised 42.3% of the cuboid articular surface in these patients. Feet without a coalition as well as feet with a coalition and no accessory facet had primary vertical cuboid articulations that were significantly larger than feet with a coalition and an accessory facet (P<0.0001). An accessory cuboid facet was identified in only a single control foot (5.6%). Conclusions: This study reports the frequent presence of an accessory cuboid facet in patients with CN coalitions. This facet was present in 75% of patients with CN coalitions and comprised just over 40% of the cuboid articular length. This anatomic variation represents a significant difference in CC joint morphology between feet with and without CN coalitions. This information may be useful when planning surgical resections. Level of Evidence: Level III - retrospective cohort study.