What is Blount's disease?

Overview

Tibia vara, genu varum, and bow-leggedness are different names for Blount’s disease. Blount’s disease is a pediatric condition where a child’s legs turn inward to resemble the curve of the letter C. There are two types of this disease, based on the clinical presentation: an infantile and an adolescent variant. The infantile type is observed in children under the age of four and affects both limbs. The adolescent variant, on the other hand, affects children later in life, predominantly those over the age of ten. It is important to understand that infants and toddlers have naturally bent legs and they get straightened when the child begins to walk. However, in children with Blount’s disease, there is a recognizable curvature of the legs that is hard to resolve as the child ages and worsens as the bones grow. This article will provide you with more information about Blount's disease: outlining its causes, signs and symptoms, management and treatments, and discussing the process of reaching a  diagnosis.¹

Causes of Blount's disease

The cause of Blount's disease is still unknown. The aetiology of this disease is considered to be multi-factorial. Genetic susceptibility and mechanical overload are considered risk factors. Some studies show that children who walk before 12 months are at risk of acquiring Blount’ disease. Also, overweight children, as well as Hispanic and Black children, are at a higherrisk of developing this condition.^1,2

There is a significant association between high body weight and Blount’s disease. It is linked with the effect of the increased compressive forces  around the knee, which inhibits growth. Also, children with a higher body mass index (BMI) were more likely to be diagnosed with this disease than children with a lower BMI.³Children who were scheduled for surgical correction had greater BMIs and more severe deformities than children treated with observation treatment.

Metabolic abnormalities have an association with Blount’s disease. Studies have found that children diagnosed with vitamin D deficiency have a higher risk of being diagnosed with Blount’s disease. Another study found that children with Blount’s disease had higher levels of alkaline phosphatase and lower levels of zinc compared to a control group of the same sex assigned at birth and age.⁴

Signs and symptoms of Blount's disease

The first and principlesign of Blount’s disease is the bowing of the legs at the level of the knee. Characteristic signs of the disease include the presence of a curvature in the leg which resembles the letter C, toes and feet pointing inward instead of pointing straight, and the bowing of the knee in one or both legs. This disease is not painful in toddlers, however, adolescents may experience knee pain and  joint instability. The pain  usually escalateswduring physical activity. The severe symptoms of this disease include arthritis of the knee, nerve and joint damage, and difficulty walking.

Management and treatment for Blount's disease

The type of treatment for Blount’s disease depends on the patient's age and the severity of the deformity.

• Braces

Bracing is generally applied from the top of the leg to the foot, applying a valgus force to the knee to reposition the knee inwards. The use of a knee-ankle-foot orthosis (KAFO) is common. For children with mild Blount’s disease,  who wear a brace  at night, orthostatic therapy may be useful if it is started before the age of three. It is necessary to continue treatment for a period of one year. However, even with orthotic treatment, a surgical procedure known as osteotomy must be performed before four years of age to reshape the bonesd.Braces are complicated to installin obese children who are younger than three years of age and this is considered an important limitation of the treatment. In 80% of patients with progressive early-onset Blount’s disease, surgical alignment prior to four years of age ensures complete recovery. A distinguishing sign that the motor control of the knee is impaired is a change in how a person walks (gait) , known as a lateral thrust.

• Surgery

Hemiepiphysiodesis is a procedure performed on the lateral epiphysis (the growth plate) ,involving the use of staples, pins and band tension plates. In order to make this process a success, there must be at at least four years of growth prior to the surgery. The insertion of compression plates inhibits the longitudinal growth of bones in accordance with the Hueter Volkmann principle, which states that mechanical compression reduces growth. This is the basis of for thistype of therapy.

Osteotomy- which is known as bone cutting- is a procedure done in patientsyounger than four years of age who exhibit risk factors. There are two techniques used: high tibial osteotomy with rigid internal fixation, and osteotomy with external fixation and gradual correction. The advantage of the latter approach is that it allows for gradual correction and limits the risk of neurovascular injury, such as compartment syndrome. In addition, it can correct deformities on all sides on the bone. Limitations of this method include the risk of developing post-surgical infection at the pin-site and prolonged treatment duration.⁵

After surgery for Blount's disease, it is important to monitor the site of pin insertion (if an external fixation procedure was done) for infectionIt is also crucial to make sure your child does not apply too much pressureon the affected legs for six to eight weeks to keep the bones from moving and allow them to heal.This approach is very effective as it results in an immediate correction of the deformities, however, it has drawbacks. Nerve damage l and compartment syndrome are examples of the issues which can arise after osteotomy is performed.¹

Diagnosis of Blount's disease

This disease is diagnosed through physical examination and the evaluationof X-rays of your child’s legs,from the ankles to the hip. The X-rays help your doctor to identify the positionof the bend and the inward curve. Also, it will help the doctor to monitor your child’s leg growth. The diagnosis of this disease starts after the age of two years old as your child's natural bowing of the legs gets straightened by this time. If the curve persists after the age of two, the doctor will order imaging tests to confirm the diagnosis of Blount’s disease.

FAQs

Can Blount's disease be prevented?

There is no one way of preventing this disease, but there are multiple steps that can help your child to have strong and healthyof bones. A healthy diet, regular exercise, calcium and vitamin C supplements, and maintaining a healthy weight for your age can all be beneficial for the health of your bones. You should keep in mind that you must consult your health provider before giving vitamin supplements to your child. 

How common is Blount's disease?

Blount disease is uncommon and it affects less than 1% of the population. 

Is Blount's disease hereditary?

Blount’s disease is inherited from parents and runs in families, in some cases. The area at the end of bones which is responsible for bone growth is called the growth plate. The growth plate of the tibia- the inner part of the shin bone- does not develop normally for people diagnosed with Blount’s disease. This condition is linked to a gene that you might inherit from your parents whichcauses the underdevelopment of the growth plates. 

Who isat risk of Blount's disease?

Children with infantile Blount's disease are usually able to walk early (under 12 months of age) and are often overweight. Adolescent Blount's disease may be associated with rapid weight gain or obesity. It is believed that there is also a genetic component. Blount's disease usually runs in families.

When should I see a doctor?

You should see a doctor when your child starts walking and you notice that their legs do not correct themselves by the age of two years old. Also, you should see a doctor when your child suffers from  pain associated with the bow in their legs, and cannot walk or put pressure on their legs. 

Summary

Blount’s disease is a rare condition that affects children and adolescents. The exact cause of this disease is not known. Genetics, BMI level, and obesity are contributing factors to the disease. A bend in the legs is the first sign of Blount’s disease.Treatment involves observation, wearing leg braces or undergoing bone surgeries. The type of treatment depends on the age of the child and the severity of the disease. It is important to monitor your child's health and avoid high pressure on their knees and legs. Blount’s disease can be diagnosed through physical examination and X-rays. You should seek medical help if your child’s legsdo not straigthen by the age of two years.