Common DisordersBlount's Disease (Tibia Vara)
Blount's disease is a rare growth disorder that affects children, causing the legs to bow outwards just below the knees. A small amount of bowing is actually quite normal in young infants, and is referred to as physiologic bowing of the knees. However, as most children begin to walk, between the ages of 1 and 2 years old, their legs gradually straighten out. In children with Blount's disease the lower legs remain bowed or bow further outwards, which can lead to future problems with walking. In addition, the inner surface of the legs just below the knee may bulge outward slightly, the toes may point inwards excessively (a condition known as in-toeing), and one leg may undergo very mild shortening compared to the other leg. Occasionally, children may experience some discomfort in the legs near the knees and may have some instability when walking. In general, however, children with Blount's disease have few significant symptoms and do not experience pain from their condition. Moreover, nearly all children who receive early treatment respond very well and suffer no long-term consequences to their health as a result of the condition.
Abnormal bowing of the legs, which has the formal, clinical name tibia vara, most frequently affects children at ages younger than 4 years old, and is referred to as infantile tibia vara. However, children may also be diagnosed with adolescent tibia vara or late-onset tibia vara, in which the condition emerges or begins to affect a child at ages older than 4 or in the adolescent years. Our pediatric orthopaedic group sees and manages the treatment of a large number of patients in both infantile and adolescent age groups.
The lower portionof the leg consists of two bones, the tibia and the fibula. The tibia is the shin bone, the larger of the two bones, which bears most of the weight placed on the lower leg. It is located to the inside of the fibula, closer to the other leg. The other leg bone is the fibula, which is a thinner bone located to the outside of the tibia and runs parallel to it. (Blount's disease is a condition that affects the tibia, which explains the clinical name tibia vara, which literally means, in Latin, 'the shin is bent inward.')
Like all long bones in the human body, the tibia does most of its growing not in the middle, but at the end of the bone during childhood, in a region known as the epiphysis. The epiphysis is responsible for the rapid production of bone and cartilage cells and the gradual lengthening of the leg.
As mentioned above, the exact cause of Blount's disease remains unknown. However, scientists believe that it is the interplay of several contributing factors -- genetic, environmental, and mechanical -- that most likely represents the collective cause of the condition.
A number of research studies have shown that the incidence of the condition is higher within certain families, which suggests that inherited, genetic factors play a part in its development. However, because no single gene has been identified as being responsible for the condition, a combination of genes is most likely involved. Because most children who develop Blount's disease began walking at an early age, early walking is believed to be another major contributing factor. While the lower legs of most children begin to become less varus and more straight by the time they begin walking, if the mechanical force of the body weight is applied to the leg earlier than normal, the upper epiphysis of the tibia will begin to undergo abnormal changes in the critical growth period. Specifically, the area just below the inside of the knee experiences abnormal compression, which reduces its ability to produce bone cells and expand. At the same time, the area just below the outside of the knee expands normally in length, gradually causing the tibia to bend inwards from the top down. This pushes the feet inward relative to the knees and causes the knees to bow outward. Because this new positioning places even greater weight on the inner portion of the epiphysis, the process is self-perpetuating, which will progress and become more severe without early treatment. Epidemiological evidence supports this theory as well, given that African-Americans tend to walk at an earlier age than children of other races, and girls walk at an earlier age than boys, on average. Because Blount's disease is also more common in obese or overweight children, it is felt that the extra weight placed on the tibia in these children leads to the abnormal process in bone growth described above. The abnormal growth of the epiphyseal region can also contribute to the rotational deformity called in-toeing, which is commonly seen along with the bowing in Blount's disease. In these cases, the tibia is actually rotated on its axis slightly, so that the upper bone points approximately forward (though bowed outward), while the lower portion of the tibia points inward toward the other leg.
The cause of adolescent tibia vara also remains somewhat unclear, but is believed to be related to rapid weight gain or obesity. This hypothesis is supported by the fact that most adoelscents with the condition are significantly overweight. However, most researchers contend that older children who develop tibia vara already had a mild degree of bowing during childhood, which is exacerbated when they undergo significant weight gain later in childhood or adolescents. A disproportionate number of these children also have a positive family history of Blount's disease, further supporting the possible genetic contribtuion in this age group as well.
Blount's disease is often first suspected when bowing of the legs is noticed in a child during a normal visit to a pediatrician, who will generally refer the case to an orthopaedic surgeon. Diagnosis of Blount's disease is made through a careful physical examination, followed by x-rays of the legs. These x-rays will show the abnormal shape of the tibia and possibly the changes in the epiphysis of the bone just under the knee. The older a child is when the condition is detected, the more apparent these changes will be on x-ray. Orthopaedic surgeons will take measurements of the angles of different segments of the leg, in order to distinguish between physiologic bowing and Blount's disease, which shows more severe bowing. If the diagnosis of Blount's disease is made, these measurements will allow the surgeon to ascertain how far the condition may have progressed, to formulate the appropriate treatment plan, and to track the correction of the deformity as a result of treatment in the future.
The treatment of Blount's disease ranges from simple observation to the wearing of orthotic braces to surgery. Decisions about the appropriate treatment for each child depend mostly upon the age of the child at the time of diagnosis and the severity of bowing of the legs. If mild bowing is detected in a child under 2 years old, the best treatment is most often observation, in which the progression of the condition is monitored by an orthopaedic surgeon. In many cases, the bowing will prove to have been physiologic, or just a harmless, mild deviation from the normal, and will correct itself over the course of about 1 year without any further treatment by a doctor.
However, if the bowing worsens, or is detected in a child 2-4 years old, Blount's disease is usually best treated with the use of orthotic braces that are fitted by an orthopaedic surgeon and worn on the child's legs. These braces, referred to as KAFP braces, which stands for Knee-Ankle-Foot Prosthetic, extend from top of the thigh to the tips of the toes, following underneath the feet. Several different models of braces exist, but the goal is the same with each?to gradually guide the growth of the legs towards a straighter position of the legs, so that the knees and feet are aligned properly, without bowing. Each child's brace is designed specifically for them, which requires the creation of casts of the legs. The ongoing development of the legs with the use of bracing is then monitored by an orthopaedic surgeon, through follow-up exams and x-rays.
In some instances, the best treatment for Blount's disease is a surgical operation, which is performed under general anesthesia, which means that the child is put to sleep throughout the operation and experiences no pain throughout the procedure. These are generally cases in which a child's bracing treatment has not been effective in correcting the bowing of the legs, or in which the condition is identified in children older than ages 3 or 4, with more severe bowing. Thus, when Blount's disease is diagnosed in adolescents, surgical treatment is almost always the most appropriate treatment. The operation most commonly used is called an osteotomy , in which a very small wedge of the tibia (shinbone), and sometimes the fibula as well, is removed in an effort to realign the lower leg in a straighter position. Small pins are inserted in order to maintain this realignment, and a cast extending from above the knee to the foot is applied. About 1 month following the operation, the pins are removed and a new cast is applied, which is generally worn for another 2 to 3 months. Other operative treatments include performing an epiphysiodesis, in which the epiphysis is removed in order to halt the abnormal growth of the tibia and correct its alignment, or an osteotomy followed by external fixation, in which a device on the outside of the leg is attached to the leg for a number of months with small metal bars, which facilitates the proper healing of the newly aligned tibia.
Blount's disease may require some difficult adjustments for parents and their child with the condition. Frequent visits to the doctor, the wearing of braces or casts, and a surgical operation at a young age can represent emotional and physical challenges for children and parents alike. However, early treatment of the condition has proven to be extremely effective, and almost all children that receive treatment for Blount's disease grow into late childhood or adulthood without any deformities or restrictions on their activities and abilities, from everyday walking to demanding, competitive sports.
Naturally, you may have other questions about Blount's disease that are not answered in the above summary. As your orthopaedic surgeons, we welcome any and all questions you may have, which we urge you to pose during your next office visit. We have listed several additional websites below that further explain Blount's disease and some of the services and support groups available to children with the disease and their parents: