Clubfoot is caused by a combination of genetic, environmental, and physical factors, though in most cases no single cause can be pinpointed. About 80% of clubfoot cases are classified as “idiopathic,” meaning they occur as isolated birth defects without a clear underlying condition. The remaining 20% are linked to known genetic syndromes, chromosomal abnormalities, or conditions like spina bifida and arthrogryposis. Clubfoot affects roughly 1.2 out of every 1,000 births worldwide, with boys more likely to be affected than girls.
Genetic Factors
The strongest genetic link to clubfoot involves two genes, PITX1 and TBX4, that work together during early development to build the lower limbs. PITX1 helps establish hindlimb identity, essentially telling cells “you’re building a leg, not an arm.” TBX4 is a gene active specifically in the lower limbs that helps pattern muscles and tendons. When either gene carries mutations or has sections duplicated or deleted, the foot can develop in the characteristic inward, downward-turned position.
These mutations typically follow a dominant inheritance pattern with incomplete penetrance. That means a parent can carry the mutation and pass it to a child, but not everyone who inherits it will actually develop clubfoot. This explains why the condition sometimes appears to skip generations or affects one sibling but not another. Researchers have found both small point mutations and larger structural changes (duplications or deletions of DNA segments) in both genes among affected families.
Family history is one of the clearest risk factors. If one parent had clubfoot, or if an older sibling was born with it, the chances increase significantly. But many babies with clubfoot have no family history at all, which is why genetics alone doesn’t explain the full picture.
What Happens Inside the Affected Foot
Clubfoot isn’t just a matter of bones being in the wrong position. The soft tissue on the inner side of the foot undergoes real structural changes at the cellular level. The tissue between the ankle bone, heel, and the small bone at the top of the arch accumulates far more collagen (the protein that gives connective tissue its strength) than normal. Specifically, there’s an overproduction of type I collagen, the same tough variety found in tendons and ligaments.
That extra collagen also develops more chemical crosslinks between its fibers than tissue on the outer side of the foot. These crosslinks act like molecular staples, making the tissue stiffer, tighter, and more resistant to stretching. In lab tests, this heavily crosslinked tissue takes significantly longer to break down than normal tissue. The result is a dense band of contracted tissue that actively holds the foot in its deformed position. Cells resembling myofibroblasts, which are specialized cells that can contract and remodel tissue, have been found throughout this area, further tightening the structures on the inner foot.
This is why clubfoot can’t simply be “stretched out” with a single manipulation. The tissue itself has a fundamentally different composition that requires gradual, sustained correction.
Maternal and Pregnancy Risk Factors
Several factors during pregnancy increase the odds of a baby being born with clubfoot. A large meta-analysis of observational and randomized trials found three that stand out:
- Smoking during pregnancy raises the odds by about 65%.
- Maternal obesity (BMI over 30) increases the odds by roughly 46%.
- Gestational diabetes raises the odds by about 40%.
Of these, smoking carries the highest individual risk. The mechanism likely involves reduced blood flow and oxygen delivery to the developing fetus during the critical weeks when limbs are forming. These are population-level risk factors, not guarantees. Most mothers who smoke or have a higher BMI will not have a baby with clubfoot, but the statistical association is consistent across studies.
Physical Crowding in the Womb
The uterine environment itself can physically mold a developing baby’s soft, pliable tissues. One of the key functions of amniotic fluid is to distend the uterus and give the fetus room to move freely, with pressure distributed evenly across all parts of the body. When that fluid is abnormally low, a condition called oligohydramnios, the fetus becomes compressed. The magnitude of the deforming force and the resulting damage depend on when the compression happens and how pliable the affected tissue is at that stage.
Oligohydramnios during late gestation is associated with positional limb abnormalities, including clubfoot. Even in normal pregnancies, the fetus begins to outgrow the uterine cavity after about 35 to 38 weeks, and the relative proportion of amniotic fluid drops during this period of rapid growth. For most babies this brief period of tighter quarters causes no lasting effects, but when fluid levels are already low or when constriction begins earlier, the feet can be held in abnormal positions long enough to affect development.
Early rupture of the amniotic membrane (the sac surrounding the baby) can also lead to compressive effects including clubfoot, scoliosis, and joint contractures. In these cases the clubfoot is considered a “deformation” rather than a malformation, meaning the foot was forming normally but was physically pushed into the wrong shape by external forces.
Syndromic Causes
About one in five cases of clubfoot occurs alongside other medical conditions. Two of the most common are distal arthrogryposis, a group of disorders that cause joint stiffness throughout the body, and myelomeningocele, the most severe form of spina bifida. In these cases, the clubfoot is typically a consequence of abnormal nerve signaling to the muscles and tendons of the lower leg. When the nerves that control foot positioning don’t function correctly, the muscles develop unevenly, pulling the foot into a fixed position.
Chromosomal abnormalities, including certain trisomies and microdeletions, can also include clubfoot as one feature among many. When clubfoot is detected alongside other structural differences on a prenatal ultrasound, doctors are more likely to recommend genetic testing to look for an underlying syndrome. Isolated clubfoot, detected on its own, carries a much lower chance of being linked to a broader condition.
Prenatal Detection
Clubfoot can be spotted on ultrasound, sometimes as early as the first trimester, though early detection isn’t always reliable. Foot positioning that looks like clubfoot in the first trimester can be a normal, temporary stage of lower limb development. A systematic review and meta-analysis found that ultrasound diagnosis of clubfoot has an average accuracy of about 81% when based on imaging alone. That number rises to roughly 91% when genetic information is combined with imaging findings.
Most reliable diagnoses happen during the second-trimester anatomy scan, typically around 18 to 22 weeks. The latest reported diagnostic window in the research was 28 weeks. If clubfoot is the only finding on ultrasound, the prognosis is generally very good. The standard treatment, a method of gentle serial casting, has a success rate above 90% in correcting the deformity without major reconstructive surgery, with visible improvement often appearing within the first one to two weeks of treatment.
Why No Single Cause Explains Most Cases
The reason 80% of clubfoot cases remain “idiopathic” is that the condition most likely results from multiple small genetic susceptibilities interacting with environmental exposures and physical conditions in the womb. A baby might carry a minor variant in PITX1 that alone wouldn’t cause problems, but combined with reduced amniotic fluid or maternal smoking, the threshold tips toward clubfoot developing. This “multifactorial” model explains why clubfoot runs in families without following a simple inheritance pattern, and why it’s more common in firstborn children (who may experience a tighter uterine environment).
The good news is that regardless of the cause, the vast majority of clubfoot cases respond well to early treatment. Understanding the cause matters most when there’s a family history and parents want to assess recurrence risk, or when clubfoot appears alongside other findings that suggest a broader genetic condition.