Relevance

A flatfoot deformity due to tarsal coalition is characterized by a flat medial arch that will not improve on toe standing, and rigid hindfoot valgus with restricted subtalar motion.¹,² Concomitant flatfoot deformity is commonly seen with talocalcaneal (TC) coalitions and can cause pain and disability.³ TC coalitions typically involve the middle facet, but can occur at any location in the subtalar joint. Symptomatic TC coalitions are commonly treated with resection and interposition of fat or bone wax. Poor results have been reported for TC coalition resection when hindfoot valgus is >16°.⁴ There are no reported predictors of outcome or consensus guidelines for treatment of rigid flatfeet with tarsal coalitions.

Clinical comment

Based on the commonly used criteria established by Wilde et al., TC coalitions are deemed resectable with good outcomes if the surface area of the coalition is <50% of the surface area of the calcaneal posterior facet on coronal computed tomography (CT) images, hindfoot valgus is <16°, and there is no narrowing of the posterior facet of the subtalar joint or impingement of the lateral talar process on the calcaneus.⁴

Is this patient a candidate for coalition resection? Should her flatfoot deformity be reconstructed? If so, should it be performed simultaneously with coalition resection or staged in a second surgery?

Available literature and quality of the evidence

• Level III: 1 case control.⁵
  
• Level IV: 6 retrospective case series.⁶–¹¹

Findings

Excellent functional outcomes have been reported following coalition excision in both mid‐ and long‐term follow‐up with minimal functional limitations.⁶,⁷ In some studies, these results were independent of coalition type and size.⁶,⁷ Postoperative subtalar range of motion was significantly decreased for TC coalitions,⁶ but this restricted motion did not affect functional outcome.⁷ Increased medial midfoot pressure during running has been demonstrated after TC coalition resection from the resulting altered subtalar mechanics.⁵ Patient‐reported functional outcomes were not obtained in this biomechanical study.

Several small series have evaluated coalition resection with simultaneous or staged flatfoot reconstruction. Reconstruction techniques and indications vary. Kernbach et al. included six adolescent feet with TC coalitions that underwent resection with naviculocuneiform fusion, Evans calcaneal lengthening osteotomy, and medializing calcaneal osteotomies.⁸ They demonstrated significant improvement in radiographic alignment as measured by calcaneal inclination, Meary’s, and anteroposterior talar‐first metatarsal angles. All had excellent postoperative American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot scores.

Mosca and Bevan found similar radiographic and clinical improvement with calcaneal lengthening osteotomy combined with plication of the posterior tibialis tendon and talonavicular joint capsule, and Achilles lengthening or gastrocnemius recession in eight adolescent patients with flatfeet and tarsal coalitions with an average follow‐up of 3.7 years.⁹ Five of these patients underwent osteotomy alone as the coalitions were deemed unresectable by the Wilde criteria, one patient underwent simultaneous resection and osteotomy, and two patients underwent osteotomy following prior resection. Their suggested algorithm is to resect the coalition if the posterior subtalar joint is healthy and to correct flatfoot deformity if present. In the case of a large osseous coalition, they recommend leaving the coalition in situ. Their postoperative protocol consists of a short leg cast for eight weeks, with pin removal and change to weight bearing cast at six weeks. Postoperative AOFAS scores improved in all patients and did not correlate to timing of reconstruction (staged versus simultaneous).

Gantsoudes et al. prefer to first resect the coalition, regain mobility of the joint, and realign the foot in a second surgery.¹⁰ In their series of adolescents with coalitions treated with resection and fat interposition, 8 of 49 feet that had flatfoot deformities underwent staged resection with subsequent deformity correction with calcaneal, cuboid, and medial cuneiform osteotomies. The decision to include flatfoot reconstruction was based on preoperative hindfoot valgus. Radiographic and clinical improvement after resection was similar regardless of concomitant flatfoot deformity (average AOFAS score 88 with versus 90 without flatfoot correction).

Masquijo et al. reported similar outcomes to Mosca and Bevan in 14 feet.⁹,¹¹ Eight were treated with flatfoot reconstruction and coalition resection and six were by reconstruction alone. The coalitions were resected if the coalition surface area was <50% of the calcaneus posterior facet. Hindfoot valgus was >16° in all patients. Reconstruction techniques included sliding posterior calcaneal osteotomy, calcaneal lengthening osteotomy, medial cuneiform osteotomy, and Achilles tendon lengthening. Both groups showed restoration of radiographic parameters to normal range and improvement in AOFAS scores with a minimum 12‐month follow‐up.

To date, no studies have been published directly comparing results of resection alone to resection and reconstruction, or outcomes of coalitions treated in childhood to those treated in adulthood.

Resolution of clinical scenario

• There is level III and IV evidence that this girl’s coalition can be resected successfully; studies report good results with resection and reconstruction in flatfeet with tarsal coalitions whether staged or simultaneous. There is, however, no evidence directly comparing staged versus simultaneous resection and reconstruction to establish superiority of either approach.
  
• Based on the available literature, she would benefit from both resection and reconstruction. To minimize the number of surgeries, she could have the procedures simultaneously.

Relevance

CN is the most common type of tarsal coalition, representing 54% of all coalitions.¹² Although deformity is more common in TC coalitions, CN coalitions can also present with flatfoot deformity causing pain and disability. Unlike TC coalitions, CN coalitions do not involve a joint. They act as an extra‐articular tether, limiting movement through otherwise healthy cartilage.

Clinical comment

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