Blount's disease or 'tibia vara,' is a growth disorder in the shin bone that affects the bones of the lower leg causing the lower leg to angle inward. This resembles a bow leg.
Named after the American orthopedic surgeon, Putnam Blount (1900 - 1992), Blount's disease is characterized by progressive lower limb deformity. Though Blount can affect people at any time during the growing process, it is more common in kids younger than four and in teens. A lot of pressure is put on the growth plate on the top of the tibia. This portion is called the physis - made out of cartilage, weaker than bone. The function of the physis is to allow the bone to lengthen and grow.
Due to excess pressure, the bone does not grow normally and instead the lateral outer side of the tibia keeps growing whereas the medial or inner side of the bone does not. Because of uneven bone growth, the tibia tends to bend outward instead of growing straight. Blount is not the same as naturally bowed legs that babies and toddlers have which usually straighten out when they start walking.
Blount is described as two distinct forms, early or infantile and late or adolescent Blount disease.
Infantile Blount disease is diagnosed between age one and three years. The disease presents when a child begins to ambulate. This disease is often bilateral and is less commonly associated with obesity.
Quite unlike the infantile Blount, late onset of Blount disease occurs in older children and is commonly associated with obesity and is often unilateral.
A combination of mechanical and biological factors influences Blount's disease to varying degrees. The mechanical forces contributing to the disease are weight of the child, age at walking, and varus deformity. The compressive forces across the medial femoral physis lead to growth retardation. Adolescent Blount does not appear to be progressive, or as common as the infantile form.
The cause of Blount disease remains controversial but it is mostly due to a combination of hereditary and developmental factors. There is increased incidence of the disease in overweight children who walk at an early age. Certain theories that mechanical overload of the proximal tibia contribute to Blount disease has been found. This mechanical overload is attributed to obesity and varus deformity. But this alone cannot be a cause as the disease is also noticed in children with normal weight.
Increasingly it is more common in people of African heritage, where kids start walking at an early age and whose family member might have had it. There is a genetic component to the disease as well, though a direct pattern of inheritance has not been clearly revealed. Hence, Blount is multifactorial and may differ in the early or late onset forms of the disease.
It is imperative to understand that Blount disease starts in early childhood or late teen years, the curve can get worse if not treated. Hence early diagnosis is important. The most obvious sign of Blount is bowing of the leg below the knee. While in young kids it is usually not painful, it teens it can be. It can feel like a growing pain in the knee area. The pain may come and go and many teens resort to over-the-counter pain relievers. As the lower leg bears the weight of the body, other problems such as rotation of the tibia are noticed. This causes a condition called in-toeing, wherein the feet point inward instead of straight out. Blount disease, over several years, can lead to arthritis of the knee joint and trouble walking. One leg may become slightly shorter than the other.
If there is knee pain that seems to be getting worse and cannot be traced to an injury, then the doctor might possibly consider Blount. A complete physical examination will be done, and X-rays of legs taken. The doctor will look for any abnormal growth pattern at the top of the tibia - a tell tale sign of Blount. This will help the doctor measure how severe the bowing is.
Treatment for Blount depends on the age of the patient and how far the disease has progressed. Young kids are advised braces, which are long-legged and lock the knee and need to be worn whilst weight bearing. But bracing is usually unsuccessful in girls and those with obesity. Older kids and teens will need surgery. There are different types of surgeries to correct Blount disease. These involve cutting the tibia, realigning it and holding it in place with plate and screws. This procedure is called Osteotomy. Sometimes, the damaged growth plate is removed and a device called external fixator is used to hold bones in place from the outside. In case of a twisted toe, surgeons correct the cause of it. Surgery is done under general anesthesia, and the patient might wear a cast and use crutches for a while. Physical therapy will be needed after surgery.
Bow legs or Genu varum is a pediatric medical condition if the developing child's legs do not straighten up during the stages of walking. At birth children usually have bow legged appearance which gradually disappears. It is necessary to differentiate between rickets, Blount's disease and bow legs as the former is caused because of vitamin D deficiency. In a developing child, the bow legged condition slowly disappears. Orthopedic opinion is necessary if the child complains of pain or limping as it may indicate some other associated condition. Bow legs usually last for first two or three years and gradually a right posture is noticed.
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Collection of Pages - Last revised Date: December 5, 2023