Tarsal Coalition

The topic names the C-sign, the talar beak and "middle-facet angulation on the Harris view" piecemeal, but the reason these matter deserves to be assembled. Unlike the calcaneonavicular bar — where the anteater nose is a direct bony sign — the talocalcaneal coalition sits at the middle facet and is frequently fibrous or cartilaginous (non-osseous), so there is often no directly visible bony bridge on plain film. Diagnosis therefore rests on indirect signs that betray the abnormal subtalar mechanics, and any one of them should trigger the confirmatory CT.

Putting it together: in a rigid adolescent flatfoot, the absent middle-facet sign and the C-sign are the two that most reliably point to a TC coalition; the talar beak and posterior-facet changes are supportive but less specific. None of these replaces cross-sectional imaging — they are the prompt for it. CT remains the reference standard for confirming the bar, quantifying the percentage of facet involvement and heel valgus (the resectability question), and excluding a second (double) coalition; MRI is reserved for the purely fibrous/cartilaginous bar that CT cannot show as bone.

The cardinal task is separating a rigid painful flatfoot (coalition) from the far more common flexible flatfoot and from other causes of a stiff adolescent hindfoot.

The resection criteria ("no severe valgus, more than 16 to 20 degrees") and the controversies section both invoke the hindfoot valgus deformity, but the management body never develops the key point: bar resection restores motion and relieves pain, but it does not by itself correct a fixed hindfoot valgus. The flatter and more valgus the heel, the worse resection alone performs — Wilde's poor-outcome group all had heel valgus more than 16 degrees. So the decision is not simply "resect vs fuse" but a three-way choice driven by the deformity as much as by the coalition size.

Assess the deformity before choosing: standing heel valgus, forefoot abduction ("too many toes" sign), and how much of it is flexible (correctable on tiptoe / Coleman block) versus fixed, supported by weight-bearing imaging. A correctable valgus accompanying a resectable bar is the classic indication for adding a realigning osteotomy (for example a lateral column lengthening or a medialising calcaneal osteotomy) at the time of resection. The general technique and indications for these flatfoot-reconstruction osteotomies are developed in the flatfoot topics; here the coalition-specific point is simply that significant valgus must be addressed, not ignored. Whether to perform the osteotomy at the index resection or stage it remains debated.

Complications of Surgery

Complications of Non-Treatment

• Progressive Valgus deformity.
• Peroneal tendon contracture/shortening.
• Subtalar and TN joint arthritis.

Protocol:

• Immobilization: Initial splinting/casting to protect the repair/fracture.
• Rehabilitation: Gradual Range of Motion (ROM) and strengthening as healing progresses.
• Weight Bearing: Progression depends on stability of fixation and healing.

• CN Resection: Usually very successful. Pain relief and improved motion.
• TC Resection: success depends on size (less than 50%). If greater than 50%, consider primary fusion.
• Recurrence: Bone can regrow. Interposition material helps prevent this.

Global epidemiology

• Population prevalence is classically quoted as under 1%, but cadaveric and CT studies suggest the true figure may approach 1-13%, with many coalitions remaining asymptomatic. CN and TC together account for over 90% of cases; bilateral in roughly 50%.
• Slight male predominance; autosomal-dominant inheritance with variable penetrance.

Society guidance — practical points (no dedicated coalition guideline exists)

Registry note: There is no national registry specific to tarsal coalition; outcome data come from single-centre series and the Garg 2023 systematic review rather than arthroplasty-style registries.

High- vs limited-resource practice

• Where CT/MRI is freely available, the resect-vs-fuse decision is CT-driven. In limited-resource settings the diagnosis often rests on plain radiographs (oblique for CN, Harris axial and lateral C-sign for TC) plus clinical examination, and management leans on prolonged casting/orthoses with surgery reserved for refractory cases.
• Terminology: Historically "peroneal spastic flatfoot"; "rigid (painful) flatfoot" is preferred, as the peroneal tightness is contracture, not spasticity.

• Resection thresholds for TC: The classic 50% facet / 16-degree valgus cut-offs (Wilde) are widely taught, but Luhmann & Schoenecker reported good outcomes in some feet exceeding these limits and argued the CT criteria should guide counselling, not absolute operative choice. There is no level-I evidence defining a hard cut-off.
• Best interposition material: EDB, fat graft, bone wax and vascularised adipofascial flaps have all been used. Fat-graft and EDB give comparable results; any interposition appears better than none for reducing reossification, but no randomised comparison exists.
• Arthroscopic / endoscopic resection: Posterior arthroscopic TC resection (Knörr) and endoscopic CN resection are emerging, with good early series and complete resection without recurrence — but follow-up is short and the technique demanding.
• Concomitant deformity correction: Whether to add a calcaneal lengthening / medialising osteotomy for marked hindfoot valgus at the time of resection (rather than relying on resection alone) is debated.
• Fusion vs joint-preservation in large/arthritic TC: When resection is unsuitable, subtalar versus triple arthrodesis (and timing in the growing foot) remains individualised.