Tarsal Coalition is Not Necessarily Associated with a Flatfoot Deformity: A Cohort of Clinically Misdiagnosed Cases and Alignment Features in 41 Feet

CATEGORY: Hindfoot; Ankle; Midfoot/Forefoot INTRODUCTION/PURPOSE: Tarsal coalition has been historically reported to be associated with a flatfoot deformity. There are however case reports demonstrating that it can be found in cavovarus and clubfoot deformities. The goal of this study was to retrospectively review all weightbearing CT (WBCT) scans that were taken in one medical center, to investigate the clinically diagnosed as well as missed cases of tarsal coalition, and to determine the hindfoot alignment and arch height features of each case. METHODS: 800 WBCT scans were reviewed separately by two senior fellowship trained foot and ankle surgeons. The structure of the hindfoot and midfoot was carefully examined in all three views to screen for different types of tarsal coalition. For cases that were diagnosed with tarsal coalition on WBCT, the medical charts were then reviewed to determine the original clinical diagnoses. Hindfoot alignment and arch height features of the midfoot were subsequently evaluated on WBCT scans. RESULTS: There were 41 feet that were diagnosed with tarsal coalition on WBCT (Figure 1). The clinical diagnosis of coalition was only made in 15 feet and 26 symptomatic feet were clinically missed. Among the 26 symptomatic feet diagnosed on WBCT but clinically missed, 16 had a clinical diagnosis of congenital or acquired flatfoot, 3 with subtalar arthritis, 1 with talonavicular arthritis, 1 with peroneal tendinopathy and a cavovarus foot deformity, 2 with cavovarus deformity and midfoot arthritis, 2 with posttraumatic ankle arthritis, and 1 with subtalar impingement. A valgus hindfoot was found in 19 feet, a neutral hindfoot in 18, and a varus hindfoot in 4 feet. In the midfoot, 38 feet had a positive (>=1) distal medial cuneiform/fifth metatarsal arch height index, and 3 feet had a negative index (<1); all 41 feet had a positive proximal cuneiform/cuboid height index (>=1). CONCLUSION: One should be aware that patients with tarsal coalition do not always present with a flatfoot and hindfoot valgus, since many can have a variety of hindfoot and midfoot alignment features. In cases presenting with history of trauma, degenerative arthritis, as well as a cavovarus or clubfoot deformity, tarsal coalition can easily be clinically overlooked. References: - Lemley F, Berlet G, Hill K, Philbin T, Isaac B, Lee T. Current concepts review: Tarsal coalition. Foot Ankle Int. 2006 Dec;27(12):1163-9. - Van Rysselberghe NL, Souder CD, Mubarak SJ. Unsuspected tarsal coalitions in equinus and varus foot deformities. J Pediatr Orthop B. 2020 Jul;29(4):370-374.