Blount Disease

What is Blount disease?

Blount disease is a growth disorder of the shin bone (tibia) that causes one or both legs to bow outward below the knee. Doctors also call it tibia vara, which simply means that the tibia angles inward at the knee so that the lower leg curves away from the body. The problem starts in the growth plate, the area of soft cartilage near the end of a child’s bone where new bone forms. In Blount disease, the inner (medial) part of the growth plate at the top of the tibia grows more slowly than the outer part. Over time this uneven growth produces a bowed, twisted leg that does not straighten on its own.

Blount disease is a condition of childhood and adolescence, because it depends on bones that are still growing. Doctors generally describe two forms. The infantile form appears in toddlers, usually between about 1 and 4 years of age, and often affects both legs. The late-onset form appears in older children and teenagers, is more often seen in only one leg, and is strongly linked with excess body weight. Both forms are uncommon, but they are among the more important causes of persistent bowed legs in children because, unlike normal bowing, they tend to worsen without care.

Many toddlers have mildly bowed legs that are a normal part of development and straighten by about age 2 or 3. Blount disease is different. The bowing is usually more pronounced, may involve only one side, and typically gets worse rather than better as the child grows. In a hospital setting this condition is generally managed by pediatric orthopedic specialists, such as those working in an Orthopedics & Joint Center.

Blount disease symptoms

The main sign of Blount disease is bowing of the leg just below the knee. Many families first notice it when a toddler begins to walk, or when an older child’s legs seem to look different from one another. Pain is often absent in young children, which is one reason the condition can be overlooked at first.

• Bowing of one or both legs below the knee that does not improve with age
• A visible difference between the two legs, especially in the late-onset form
• A sharp bend or angle just under the knee rather than a gentle curve of the whole leg
• Inward turning of the foot or lower leg (in-toeing)
• An awkward, waddling, or limping walk
• Knee pain or a sense of instability, more common in older children and teenagers
• One leg that appears slightly shorter than the other
• A knee that seems to shift or thrust outward during walking

Symptoms tend to differ by age and stage. In Blount disease in toddlers, the child usually has no pain and appears healthy, but the bowing is noticeable and both legs are often involved. The deformity may become more obvious when the child stands with the ankles together. In the late-onset form, older children and adolescents more often report aching in the knee, especially after activity, along with visible bowing that is frequently limited to one leg. As the condition progresses in any age group, the growth plate can become increasingly damaged, and the deformity may combine bowing with twisting of the shin bone, making walking more difficult.

Causes and risk factors

The exact cause of Blount disease is not fully understood. The leading explanation is that abnormal mechanical stress on the inner part of the upper tibial growth plate slows bone growth there. When a young child’s legs are naturally bowed and the child places heavy loads on them, the inner part of the knee carries more force. This pressure may suppress growth on the inner side while the outer side keeps growing, creating a cycle in which the bowing causes more uneven pressure and the pressure causes more bowing.

Several factors appear to raise the risk, although having one or more of them does not mean a child will develop the condition:

• Excess body weight: children who are overweight or obese place greater force on the growing knee, and this is the strongest recognized risk factor, particularly for the late-onset form.
• Early walking: children who begin walking independently at a young age, often before about 1 year, may load their still-bowed legs earlier.
• Family history: Blount disease sometimes runs in families, suggesting that inherited factors may play a part.
• Ancestry: the condition has been reported more often in children of African descent, although it occurs in all populations.
• Female sex in the infantile form: some reports suggest the infantile type is slightly more common in girls, while the late-onset type is seen more often in boys.
• Persistent physiological bowing: a child whose normal toddler bowing does not improve as expected may be more likely to develop growth plate changes.

Blount disease is not caused by rickets, which is a vitamin D or mineral deficiency that softens bones, but rickets can also cause bowed legs. Because the two problems can look similar, doctors usually check for rickets and other bone disorders before confirming a diagnosis.

Diagnosis

Doctors confirm Blount disease through a combination of physical examination and imaging. There is no blood test that identifies the condition itself, but blood tests may be used to rule out other causes of bowing.

The evaluation typically begins with a detailed history. Your doctor may ask when the bowing was first noticed, whether it is getting better or worse, when the child began walking, and whether relatives have had similar leg shapes. During the physical exam, the clinician looks at the child standing and walking, measures the distance between the knees when the ankles are together, checks for a sharp angle just below the knee, and assesses rotation of the lower leg and any difference in leg length.

X-rays are the key test. Standing X-rays of both legs from hip to ankle allow the doctor to measure the alignment of the whole limb and to look at the shape of the upper tibia. In Blount disease the inner part of the tibia just below the growth plate often looks beaked, sloped, or fragmented, and the growth plate itself may appear irregular. Doctors often measure specific angles on the X-ray, such as the metaphyseal-diaphyseal angle, which compares the angle of the upper end of the tibia with the shaft of the bone. Larger angles make Blount disease more likely and help separate it from normal developmental bowing, especially in children under 3, where the two can be difficult to tell apart.

Orthopedic surgeons frequently classify infantile Blount disease using the Langenskiöld staging system, which grades the X-ray appearance from stage I (mild changes) to stage VI (a bony bridge across the growth plate). This helps guide treatment decisions and predict how the condition may behave.

Additional tests may include:

• MRI (magnetic resonance imaging): a scan using magnets and radio waves that shows cartilage and the growth plate in detail, useful for planning surgery or checking for a bony bridge across the growth plate.
• CT (computed tomography): a detailed X-ray-based scan sometimes used to assess bone shape or twisting before surgery.
• Blood tests: to check vitamin D, calcium, and phosphate levels and exclude rickets or other metabolic bone conditions.
• Repeat X-rays over time: in very young children, doctors may recheck alignment after several months to see whether the bowing is improving, as normal bowing would, or worsening.

Blount disease treatment options

Blount disease treatment depends on the child’s age, the stage of the condition, how severe the bowing is, and whether one or both legs are affected. The overall goal is to restore straighter alignment of the leg, protect the knee joint, and allow the remaining growth to proceed as normally as possible. Treatment is planned individually, and your doctor may recommend a different approach as the child grows.

Observation

In toddlers under about 2 years, it can be hard to distinguish early Blount disease from normal bowing. When X-ray findings are mild and the diagnosis is uncertain, doctors often recommend careful monitoring with repeat examinations and X-rays every few months. If the legs straighten, no further treatment is needed. If the bowing worsens or X-ray features become clearer, active treatment is considered.

Bracing

For young children, usually under age 3, with early-stage infantile Blount disease, a brace may be recommended. The most common type is a knee-ankle-foot orthosis (KAFO), a long leg brace designed to shift force away from the inner knee and encourage the growth plate to recover. Bracing is typically worn for most of the day or during walking hours, and it requires consistent use and regular adjustment as the child grows. Bracing is less likely to work in older children, in advanced stages, or in children with significant excess weight, and it is generally not used for the late-onset form.

Medication

There is no medication that treats Blount disease itself. Over-the-counter pain relievers may be used for knee discomfort in older children, and vitamin D or other supplements may be prescribed only if a deficiency is found on blood tests. Medication does not correct the bowing.

Surgery

Surgery is generally recommended when bracing has not worked, when the child is older than about 3 or 4 at diagnosis, when the deformity is severe, or for most cases of late-onset Blount disease. Several surgical approaches exist, and the surgeon chooses based on age, remaining growth, and severity:

• Guided growth (hemiepiphysiodesis): a small plate or staple is placed on the outer side of the growth plate to slow growth there temporarily, allowing the inner side to catch up and the leg to straighten gradually. This is a relatively minor operation used in children who still have significant growth remaining and moderate deformity.
• Tibial osteotomy: the surgeon cuts the tibia below the growth plate, realigns the bone into a straighter position, and holds it with plates, screws, or an external frame while it heals. This is often used for more severe bowing or in children who are nearly done growing.
• Gradual correction with an external fixator: a frame attached to the bone through pins is adjusted over weeks to slowly straighten and, if necessary, lengthen the leg. This is used for large or complex deformities.
• Growth plate procedures for advanced disease: in later stages, a bony bridge across the inner growth plate may need to be removed, or the inner part of the knee joint surface may need to be raised (plateau elevation) to restore a level joint.

Each procedure carries risks, including infection, nerve or blood vessel injury, incomplete correction, recurrence of the bowing with further growth, and, in the case of osteotomy, delayed healing. Recurrence is more common in younger children and in those with higher body weight, so several procedures over the years are sometimes needed.

Rehabilitation and follow-up

After surgery, children usually need a period of restricted weight-bearing, sometimes with a cast, crutches, or a walker. Physical therapy helps restore knee and ankle motion, strength, and a normal walking pattern. Regular follow-up visits with X-rays continue until the child stops growing, because alignment can change as the bones lengthen. Where excess weight is a factor, doctors typically recommend a supportive, family-based approach to nutrition and activity, since weight management may reduce stress on the knee and lower the chance of recurrence.

Living with Blount disease and outlook

The outlook for Blount disease depends largely on how early it is recognized and how advanced it is when treatment starts. In many cases, young children with early-stage disease who are treated promptly, whether with bracing or guided growth, achieve straight, functional legs and go on to normal activity. Children treated at later stages, or with significant damage to the growth plate, are more likely to need one or more operations and to have some lasting difference in leg length or shape.

Without treatment, the bowing tends to progress. Over years this can lead to a marked deformity, an abnormal walking pattern, chronic knee pain, and uneven wear of the knee joint, which may raise the risk of arthritis of the knee in adulthood. Even after successful correction, some people have a mild remaining difference between their legs or occasional knee discomfort, and long-term follow-up into adulthood is often advised.

Day to day, most children with Blount disease can attend school and take part in age-appropriate play. Your doctor may suggest temporary limits on high-impact activity during bracing or after surgery. Families often find that consistent brace wear, attending scheduled X-ray checks, and addressing weight concerns in a supportive way make the biggest difference to results. Because the condition is uncommon, care is usually coordinated by a pediatric orthopedic team.

Frequently asked questions

What is the difference between Blount disease and normal bowed legs in toddlers?

Most toddlers have some bowing that is part of normal growth and improves by about age 2 to 3. Blount disease in toddlers usually shows a sharper bend just below the knee, is often more severe or one-sided, and worsens rather than improves over time. Only a doctor, usually with standing X-rays, can reliably tell the two apart, and in very young children this may take more than one visit.

What are the first Blount disease symptoms parents notice?

The first sign is usually bowing of one or both legs below the knee that becomes more obvious once the child is walking. Some parents also notice in-toeing, a waddling gait, or that one leg looks different from the other. Pain is uncommon in toddlers but is more often reported by older children and teenagers with the late-onset form.

Is tibia vara the same as Blount disease?

Tibia vara is the medical term for an inward angling of the shin bone at the knee that produces bowed legs. Blount disease is the most widely recognized cause of pathological tibia vara in children, so the two terms are often used interchangeably. However, tibia vara can occasionally result from other conditions, such as rickets or a previous injury to the growth plate, which doctors consider before confirming Blount disease.

Can Blount disease go away on its own?

True Blount disease generally does not resolve without treatment, because the affected growth plate continues to grow unevenly. Very early cases in young toddlers can be difficult to distinguish from normal bowing, and some of these children do straighten with time, which is why doctors may observe first. Once X-ray changes are clear, treatment is usually needed.

What does Blount disease treatment involve for older children?

For children older than about 4 and for adolescents, bracing is rarely effective, so Blount disease treatment is usually surgical. Options include guided growth with a small plate if enough growth remains, or an osteotomy, in which the bone is cut and realigned. The surgeon selects the approach based on age, severity, and remaining growth, followed by rehabilitation and regular X-ray follow-up.

Does Blount disease cause problems in adulthood?

When corrected early and well, many people have good long-term leg alignment and function. If the deformity is severe, treated late, or recurs, there may be a lasting leg length difference, knee pain, and a higher chance of early knee arthritis. Long-term follow-up is often recommended so that any late problems can be identified.

Can Blount disease be prevented?

There is no proven way to prevent Blount disease, and it is not caused by anything a parent did. Maintaining a healthy weight during childhood may reduce stress on the growing knee and is thought to lower the risk, particularly of the late-onset form, but it cannot guarantee that the condition will not develop.

When to see a doctor

Any child whose legs remain clearly bowed after about age 2, whose bowing is getting worse, or whose two legs look noticeably different should be evaluated by a pediatrician or pediatric orthopedic specialist. Early assessment gives the widest range of treatment options. Seek prompt medical attention if you notice any of the following:

• Bowing that appears to worsen over a few months instead of improving
• Bowing that affects only one leg or is markedly uneven between the two legs
• A sharp angle or bend just below the knee
• Knee pain, swelling, or the knee giving way during walking
• A limp, frequent falls, or a walking pattern that is getting worse
• One leg that looks shorter than the other
• Bowed legs together with signs that could suggest rickets, such as widened wrists, delayed growth, or bone pain
• After surgery or during bracing: fever, redness, drainage, or severe pain at the site, or new numbness or color change in the foot

These signs do not mean a child definitely has Blount disease, but they indicate that a proper examination and, in most cases, X-rays are needed to find the cause and plan any care.