summary Tarsal Coalition is a common congenital condition caused by failure of embryonic segmentation leading to abnormal coalition 2 or more of the tarsal bones. The condition is usually asymptomatic, but may present with a flatfoot deformity or recurrent ankle sprains. Diagnosis is made with plain radiographs of the foot and ankle showing a coalition, most commonly a calcaneonavicular or talocalcaneous coalition. Treatment is usually a course of casting and NSAIDs for symptomatic patients. Surgical coalition resection or joint arthrodesis is indicated for patients with persistent symptoms who fail conservative management. Epidemiology Prevalence varies from 1%-2% Demographics age of onset calcaneonavicular usually 8-12 years old talocalcaneal usually 12-15 years old Anatomic location calcaneonavicular (most common) talocalcaneus Etiology Two types congenital most common acquired less common and caused by trauma degenerative infections Pathophysiology embryology failure of mesenchymal segmentation leading to coalition between two or three tarsal bones develops into a fibrous coalition, or undergoes metaplasia to cartilage +/- bone pathoanatomy gait mechanics subtalar joint will normally rotate 10 degrees internally during stance phase in presence of coalition, internal rotation does not occur deformity flattening of longitudinal arch abduction of forefoot valgus hindfoot peroneal spasticity (also known as peroneal spastic flatfoot) pain generator theories ossification of previously fibrous or cartilaginous coalition microfracture at coalition bone interface secondary chondral damage or degenerative changes increased stress on other hindfoot joints Associated conditions nonsyndromic autosomal dominant syndromic fibular hemimelia carpal coalition FGFR-associated craniosynostosis (FGFR-1, FGFR-2, FGFR-3) Apert syndrome, Pfeiffer, Crouzon, Jackson-Weiss and Muenke Classification Anatomic classification calcaneonavicular between calcaneus and navicular bones (most common) talocalcaneal middle facet of talocalcaneal joint Pathoanatomic classification 3 types fibrous coalition (syndesmosis) cartilagenous coalition (synchondrosis) osseous coalition (synostosis) Presentation History history of prior recurrent ankle sprains Symptoms asymptomatic most coalitions are found incidentally 75% of people are asymptomatic pain location of pain sinus tarsi and inferior fibula suggests calcaneonavicular distal to medial malleolus or medial foot suggests talocalcaneal pain worsened by activity onset of symptoms correlates with age of ossification of coalition calf pain secondary to peroneal spasticity Physical exam inspection hindfoot valgus forefoot abduction pes planus range of motion limited subtalar motion heel cord contractures arch of foot does not reconstitute upon toe-standing hindfoot remains in valgus (does not swing into varus) upon toe-standing special tests reverse Coleman block test evaluate for subtalar rigidity Imaging Radiographs recommended views required anteroposterior view standing lateral foot view 45-degree internal oblique view most useful for calcaneonavicular coalition Harris view of heel findings calcaneonavicular coalition "anteater" sign elongated anterior process of calcaneus talocalcaneal coalition talar beaking on lateral radiograph occurs as a result of limited motion of the subtalar joint irregular middle facet joint on Harris axial view c-sign c-shaped arc formed by the medial outline of the talar dome and posteroinferior aspect of the sustentaculum tali dysmorphic sustentaculum appears enlarged and rounded CT scan Has been suggested as part of the preoperative workup to rule-out additional coalitions incidence approx. 5% determine size, location and extent of coalition size of talocalcaneal coalition based on size of posterior facet using coronal slices MRI may be helpful to visualize a fibrous or cartilaginous coalition STIR sequences help to differentiate inflammatory changes (e.g. tendinitis) in local structures Treatment Nonoperative observation, shoe inserts indications unclear. techniques medial arch support and preserved hindfoot alignment outcomes In rigid flat feet shoe inserts may be the cause of discomfort. immobilization with casting, analgesics indications initial treatment for symptomatic cases techniques below-knee walking cast for six-weeks outcomes up to 30% of symptomatic patients will become pain-free with a short period of immobilization Operative coalition resection with interposition graft, +/- correction of associated foot deformity indications persistent symptoms despite nonoperative management coalition involves <50% of joint surface area techniques open vs arthroscopic coalition resection interposition material extensor digitorum brevis (calcaneonavicular coalition) split flexor hallucis longus tendon (talocalcaneal coalition) interposed fat graft bone wax correction of associated hindfoot, midfoot or forefoot deformities calcaneal osteotomy for hindfoot valgus calcaneal lengthening to create arch after resection heel cord lengthening if intraoperative ankle dorsiflexion is not past neutral outcomes 80-85% will experience pain relief poor outcomes coalition resection >50% size of joint surface area uncorrected hindfoot valgus associated degenerative changes subtalar arthrodesis indications role has not been well established consider if coalition involves >50 % of the joint surface of a talocalcaneal coalition technique open vs. arthroscopic consider an associated calcaneal osteotomy with severe hindfoot malalignment triple arthrodesis (subtalar, calcaneocuboid, and talonavicular) indications advanced coalitions that fail resection diffuse associated degenerative changes affecting calcaneocuboid and talonavicular joints technique open vs. arthroscopic Techniques Calcaneonavicular coalition resection approach lateral or sloppy lateral position anterolateral approach over coalition incision oblique incision just distal to subtalar joint between extensor tendons and peroneal tendons technique protect branches of superficial peroneal and sural nerves reflect fibrofatty tissues in sinus tarsi anterior and extensor digitorum brevis distally identify coalition between anterior process of calcaneus and navicular bones and confirm with fluorscopy excise bar with saw or osteotomes, which leaves defect ~1cm in size interpose fat, bone wax or portion of extensor digitorum brevis muscle into defect post-operative short-leg, non-weight bearing cast for 3-4 weeks Talocalcaneal coalition resection approach positioned supine medial approach to hindfoot incision horizontal or curved incision centered over sustentaculum tali between flexor digitorum longus and neurovascular bundle technique sustentaculum tali usually just plantar to the talocalcaneal coalition identify normal subtalar joint cartilage by dissecting out the anterior and posterior facets this will help determine location and size of coalition resection confirm with two needles immediately anterior and posterior to coalition clinically and confirm with fluorscopy resect coalition with high speed-burr, ronguers and curettes invert and evert subtalar joint to demonstrate improvement in subtalar motion interpose fat, bone wax or portion of flexor hallucis longus tendon into defect post-operative short-leg non-weight bearing cast for three weeks Complications Incomplete resection Recurrence of the coalition Residual pain or stiffness due to malalignment or associated arthritis due to unrecognized 2nd coalition - this should be identified by a preoperative CT scan