Introduction

Tarsal coalition is an uncommon congenital foot problem in which two or more of the tarsal bones fuse instead of forming separate joints. It affects approximately one person in every hundred, although figures vary depending on the imaging method used and may be higher when computed tomography (CT) is routinely employed.¹ Symptoms usually start in late childhood, when the fused segment stops the subtalar and midtarsal joints from moving freely, and the child reports aching after sport or repeated ankle sprains.³ If pain is ignored, the joint surfaces can degenerate, leading to lifelong difficulty.

The purpose of this article is to explain how genetic factors influence tarsal coalition, why the condition often runs in families, and how this information guides diagnosis, treatment, and counselling. Three messages matter most for patients and parents. First, most familial cases follow an autosomal dominant inheritance pattern, so each child of an affected parent has a fifty-percent chance of inheriting the trait.⁴ Second, mutations in the NOG gene, responsible for regulating early joint formation, are linked to several well-described families.^5,6 Third, knowing the inheritance pattern allows prompt imaging in at-risk children and, where needed, early treatment that can prevent years of avoidable pain.

Epidemiology

Early cadaver studies suggested a prevalence of about one per cent in the general population.¹ Modern cross-sectional imaging has pushed that estimate higher: a population study in Minnesota found that up to thirteen per cent of children undergoing CT scans of the foot had some form of coalition.² The calcaneonavicular coalition is the most common type. Talocalcaneal coalitions come next and are more likely to cause a rigid flatfoot. Prevalence does not differ markedly by sex or ethnic background, but detection rates rise in centres that use magnetic resonance imaging (MRI) for unexplained hind-foot pain.⁷

Genetic mechanisms

Bone and joint segmentation in the embryo relies on a delicate balance of growth signals and their inhibitors. NOG encodes noggin, a protein that restrains bone morphogenetic proteins. When NOG is disrupted, excessive bone forms between adjacent tarsal primordia, creating the permanent bridge seen at birth. Three separate families with tarsal-carpal coalition syndrome have been shown to carry different missense mutations in NOG.⁵ A later report from India described a novel NOG variant in a mother and two children, confirming autosomal dominant inheritance with variable severity.⁶

Although NOG is the best studied, it is unlikely to be the only gene involved. The existence of families whose linkage studies do not point to chromosome 17 (where NOG sits) suggests further loci remain to be found. Variable penetrance also implies the influence of modifier genes and environmental factors. Population-wide screening is not offered because the condition is rare and the genotype–phenotype link is still incomplete.

Clinical presentation

Children usually become symptomatic as their coalitions ossify, most often between eight and sixteen years of age.³ Pain is felt deep in the ankle or just below it after running or prolonged standing. Recurrent ankle sprains are common. On examination, the subtalar joint feels stiff, and the heel may be fixed in valgus with a flattened arch. Attempted inversion or eversion triggers discomfort. Some children present acutely with a spasm of the peroneal muscles, making the foot point outwards.

Adults who were never diagnosed in childhood attend with chronic hind-foot ache or early degenerative arthritis. Large talocalcaneal coalitions can restrict rotation between the leg and foot, transferring stress to the knee and hip.

Diagnostic approach

Plain radiographs remain the first imaging step. Oblique views often reveal a calcaneonavicular bar, while a “C-sign” on the lateral film hints at talocalcaneal fusion.⁸ Radiographs, however, miss up to half of non-osseous coalitions. CT gives a three-dimensional view of the coalition and outlines its length and depth, information essential for surgical planning.⁷ MRI equals CT at detecting both fibrous and cartilaginous coalitions and spares the child from ionising radiation.⁹

Clinical suspicion should rise in any child with rigid flatfoot and a family history of similar problems. In such cases, earlier MRI is justified even if radiographs look normal. Where a known NOG mutation exists in a family, targeted genetic testing can confirm carrier status, although it is still largely confined to research laboratories due to cost and rarity.

Treatment approaches

Initial management is non-operative. Most children benefit from activity modification, physiotherapy to strengthen the calf and foot muscles, and custom orthoses that support the arch and reduce joint strain.¹⁰ Short periods in a walking cast or removable boot can quieten acute pain. Non-steroidal anti-inflammatory drugs reduce discomfort. These measures succeed in up to eighty-five per cent of mild coalitions.^4,10

Surgery is indicated when pain persists despite six months of conservative care or when the coalition is large enough to block the subtalar joint completely. The standard operation in growing children is resection of the bar with insertion of fat or muscle to prevent re-ossification.¹¹ Meta-analysis shows that three-quarters of patients achieve meaningful pain relief and return to sport after resection.¹² Outcomes depend on coalition size, joint alignment, and absence of arthritis.

When degeneration is advanced or foot alignment is poor, subtalar or triple fusion provides long-term stability at the cost of permanently stiffening the hindfoot. A long-term series of ninety-seven resections found an average return to full activity in eighteen weeks and sustained good function after three years.¹³ Although fusion sacrifices movement, many adults report better quality of life once pain stops.

Living with the condition

Most children who receive timely treatment, whether conservative or surgical, live active lives. Footwear choice is important; shoes with a firm heel counter and arch support reduce symptoms. Physiotherapy focuses on calf stretching and proprioceptive training to lessen the risk of ankle sprain. Long-distance running may remain uncomfortable for some, but swimming and cycling are usually pain-free. Psychological support is sometimes needed when sport-minded adolescents have to cut back on competition.

Familial screening and genetic counselling

Counsellors explain inheritance, advise on the value and limits of genetic testing, and discuss imaging for asymptomatic relatives. Because penetrance is incomplete, a child who inherits a NOG variant might never have symptoms; reassurance rather than intervention may be all that is required. Conversely, parents of a symptomatic child with no known family history often feel relief when told that sporadic cases occur through new (de novo) mutations and that the chance of a second affected child is low. In families with several affected members, early MRI at around age eight can catch a coalition before pain begins, allowing footwear modifications or timely surgery to minimise joint damage.¹⁴

Future directions

Research is moving in three directions. Gene-editing models are exploring how different NOG mutations produce variable severity. Advanced weight-bearing CT is improving three-dimensional assessment of foot alignment before and after surgery. Finally, scientists are mapping modifier genes that may explain why some carriers escape symptoms altogether. These studies aim to refine prognosis and open the door to preventive therapies that limit inappropriate bone formation in utero or early infancy.

Summary

Tarsal coalition arises when rear-foot bones fail to separate during embryo development. Around one per cent of people carry a coalition, but only a minority become symptomatic. Most familial cases follow autosomal dominant inheritance with incomplete penetrance, frequently linked to mutations in the NOG gene. Diagnosis combines a careful history, examination, and imaging; plain radiographs first, then CT or MRI for detail. Non-operative management relieves many mild cases, while persistent pain calls for resection or, in advanced arthritis, fusion. Genetic counselling helps families understand risk, plan early imaging, and cope with the emotional impact of a congenital disorder. With prompt recognition and appropriate care, the outlook for children and adults with tarsal coalition is good.

FAQs

Is tarsal coalition always inherited?

No. Most cases are genetic, but some arise from new mutations or are linked to conditions such as clubfoot.

Does every child who inherits the gene develop symptoms?

No. Incomplete penetrance means some carriers stay pain-free for life.

At what age should at-risk children be screened?

Around eight to ten years before heavy sport begins and while coalitions are still partly cartilaginous.

Can physiotherapy cure the problem?

It cannot remove the fusion, but can reduce pain and improve function.

Is surgery safe?

Resection in children has a high success rate and low complication risk when performed by experienced foot surgeons.