Tarsal Coalition

Tarsal coalition is an abnormal connection between two or more tarsal bones, which may be fibrous (syndesmosis), cartilaginous (synchondrosis) or bony (synostosis), and restricts subtalar and midtarsal motion. It is a common cause of a painful, rigid flatfoot in children and adolescents.

Its prevalence is about 1 to 2% of the population (probably higher), and about 50 to 60% are bilateral, although only a minority are symptomatic. The commonest types are calcaneonavicular (about 45%) and talocalcaneal (about 45 to 50%, mostly at the middle facet at the sustentaculum tali); talonavicular and calcaneocuboid coalitions are rare. A family history is found in many, and autosomal dominant inheritance with variable penetrance is described (SLC44A2 is one candidate gene). The sexes are equally affected or males slightly more so.

Symptoms appear as the coalition ossifies: age 8 to 12 years for calcaneonavicular and 12 to 16 years for talocalcaneal. Complications are chronic pain, recurrent ankle sprains, a peroneal spastic flatfoot, subtalar and ankle arthritis (talar beaking, ball-and-socket ankle), and reduced sport participation.

Pathophysiology.

Failure of mesenchymal segmentation in the embryonic tarsus leaves a continuous bridge. As cartilage turns to bone with growth, the bridge becomes rigid and stops subtalar motion, so the ankle and the transverse tarsal joints are overloaded. Peroneal muscle spasm is a reflex response to painful subtalar movement and keeps the foot in valgus.

Pain in the hindfoot and sinus tarsi region, worsened by activity and uneven ground, relieved by rest, with repeated ankle sprains, a limp, and stiffness. Many are asymptomatic and found by chance. Symptoms may follow a minor injury.

Examination: a rigid flatfoot (the arch does not form on tiptoe), heel valgus, loss of subtalar inversion and eversion, peroneal spasm (with limited inversion), tenderness over the sinus tarsi, calcaneonavicular joint or the sustentaculum tali, and sometimes shortened peroneal and Achilles tendons. Examine the other foot, the ankle and the neurological state.

• Weight bearing radiographs of the foot and ankle (anteroposterior, lateral, oblique, and Harris axial view). The oblique view shows calcaneonavicular coalition best. Findings:
  • The "anteater" sign: elongated anterior process of the calcaneus in a calcaneonavicular coalition, on the lateral view.
  • Absent or irregular middle facet of the subtalar joint.
  • The "C" sign: a continuous C-shaped line from the talar dome to the sustentaculum tali.
  • Talar beaking.
  • A dysmorphic talar head ("ball-and-socket" ankle) in some.
• CT (with 3D reconstruction) is the reference investigation to define the type, size and orientation of the coalition, hindfoot valgus and degenerative change; it is needed for any coalition planned for surgery.
• MRI shows fibrous or cartilaginous coalitions, bone marrow oedema and associated tendon or joint change.
• Blood tests are not needed, and the diagnosis is made by imaging.

Differential diagnosis.

• Flexible flatfoot and peroneal tendon pathology.
• Ankle sprain and osteochondral lesion of the talus.
• Juvenile idiopathic arthritis and infection.
• Stress fracture, osteoid osteoma and accessory navicular.

Asymptomatic coalitions need no treatment. Symptomatic coalitions are treated non-operatively first.

Non-operative treatment (first line for 3 to 6 months).

• Activity modification, rest from high impact sport, and a medial arch support or a custom orthosis with heel cup.
• Immobilisation in a short leg walking cast or boot for 3 to 6 weeks to settle acute pain (relief in about 30%), followed by physiotherapy and an orthosis.
• Corticosteroid injection into the sinus tarsi or the calcaneonavicular joint (methylprednisolone acetate 20 to 40 mg with lidocaine 1% 2 to 3 mL, once only; avoid with infection, and watch for fat atrophy and skin depigmentation) may relieve pain for a time.

Surgery (persistent pain after 3 to 6 months of non-operative treatment).

• Calcaneonavicular coalition: resection of the bar with interposition of extensor digitorum brevis muscle or fat, which gives good results in about 80 to 90% when there is no arthritis.
• Talocalcaneal coalition: resection (the coalition involves less than 50% of the posterior facet area, with hindfoot valgus under 16 degrees and no arthritis), with interposition of fat or a tendon graft; add a calcaneal osteotomy for hindfoot valgus.
• Subtalar arthrodesis, triple arthrodesis or talonavicular fusion for large coalitions (over 50% of the facet), marked valgus, degenerative change, failure of resection or older patients.
• Peroneal lengthening or Achilles lengthening for contracture.
• Postoperative short leg cast or boot for 2 to 6 weeks, early motion after resection, and non-weight bearing for 6 to 12 weeks after fusion.

Medical treatment.

• Ibuprofen 400 mg orally every 8 hours with food for short courses of up to 5 to 7 days during flare ups (maximum 1200 mg daily); avoid with eGFR under 30 mL/min/1.73 m2, peptic ulcer, heart failure or anticoagulant use.
• Children: ibuprofen 10 mg/kg orally every 6 to 8 hours with food (maximum 40 mg/kg daily and not exceeding 2400 mg daily), with paracetamol 15 mg/kg orally every 4 to 6 hours (maximum 75 mg/kg daily and not exceeding 4 g daily), for up to 5 days.
• Avoid ibuprofen with kidney impairment, dehydration or active bleeding.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over; 30 mg/kg to a maximum of 2 g in children) within 60 minutes before incision as a single dose.

With severe penicillin allergy, give clindamycin 10 mg/kg (maximum 900 mg) intravenously or vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose.

Thromboprophylaxis (adolescents and adults after surgery with a cast and restricted weight bearing). Enoxaparin 40 mg subcutaneously once daily, started 6 to 12 hours after surgery and continued while weight bearing is restricted, usually 4 to 6 weeks.

Use 20 mg once daily at creatinine clearance under 30 mL/min. Adjust by anti-Xa level in obesity and renal impairment. Check the platelet count on days 5 to 14 for heparin induced thrombocytopenia. Not routinely used in children under 14 years.

Analgesia after surgery.

• Paracetamol 1 g orally every 6 hours as needed for up to 5 to 7 days (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Children: paracetamol 15 mg/kg orally every 4 to 6 hours (maximum 75 mg/kg daily and not exceeding 4 g daily).
• Adults: oral morphine 5 to 10 mg every 4 hours as needed for severe pain for up to 3 days (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2; avoid exceeding 60 mg in 24 hours without senior review).
• Children: oral morphine 0.1 to 0.2 mg/kg every 4 hours as needed for up to 2 to 3 days (maximum 10 mg a dose).
• Monitor sedation and respiration and prescribe a laxative.

Monitoring. Review at 6 weeks and 3 months after starting non-operative treatment, and the need for surgery at 6 months. After surgery, review at 2 weeks, 6 weeks, 3 months, 6 months and 12 months, with weight bearing radiographs after fusion and CT if resection fails or pain recurs. Hindfoot alignment, subtalar motion and activity level at each visit.

Referral and escalation. Refer every child or adolescent with a painful rigid flatfoot or recurrent sprains to paediatric orthopaedics or foot and ankle surgery. Urgent referral for fever, a hot joint, a night pain pattern or a suspected tumour or infection.

Special groups.

• Adolescents: talocalcaneal coalitions present later; consider early resection in active patients.
• Athletes: resection allows return to sport at 3 to 6 months after surgery.
• Adults with arthritis: fusion is usually needed.
• Kidney impairment: avoid NSAIDs and reduce morphine doses.