A Parents guide to Blount’s disease
This guide is written for those parents whose child may have bow-legs, and for those who have been told that their child has Blount’s disease.
Children normally start walking with some element of bowing (varus) which tends to straightens out over the second year to become slightly valgus ( knocked kneed) by 3 to 4. If your child continues to have bow-legs after the age of 3, specialist opinion should be sought. Apart from normal developmental bow-legs( physiological varus) there are many conditions that must be considered at this age. Infantile tibia vara (Blount’s disease), growth disturbance from infection or trauma, metabolic causes, generalized skeletal dysplasia and focal fibro- cartilaginous dysplasia are some.
Blount’s disease (early-onset)
This is a developmental disorder where inhibition of medial tibial growth occurs just below the knee and often occurs as a continuation of normal physiological bow-legs. The deformity can be bilateral or unilateral. The cause is not clear but may include hereditary factors (common in children of African descent), early walking, obesity with weight above the 90th percentile for age as well as poor mineralization of bone (even obese children may have under-mineralized bone).
Once a critical point is reached in a bow-leg situation, reversal is unlikely. In the early stages bracing is recommended by some but this requires an expensive tailor-made item and constant attention to detail and insistence by the parents on its use. It is probably not justified over the age of 3.
Once the age of 3 is reached and a definite diagnosis of Blount’s disease has been made, surgery in the form of an osteotomy of both tibia and fibula is advised. At this age a single operation should solve the condition if no obesity exists. Failure to do this timeously (before 4) results in a high recurrence rate. This is because a permanent impairment of medial tibial growth occurs at a younger age than previously thought, and continued lateral growth results in a recurrence of the deformity.
This may necessitate operations on the lateral growth plates or even joint elevation. In unilateral cases this has limb length implications which may require more complex surgery.
It is thus critical that expert opinion be sought early, and to realize that obesity can have serious implications in this condition.
Key Factors in early-onset Blount’s
Bow-legs after the age of 3 requires specialist assessment.
Internal tibial torsion (rotation) is an important element of the deformity.
Clinical and radiological deterioration over months is important in making a diagnosis.
Surgical correction before the age of 4 in true Blount’s disease gives the best results.
Obesity is a major risk factor for the disease and for recurrence after osteotomy.
Blount’s disease (late-onset)
This is a bowleg deformity starting in later childhood. The cause is also not clearly understood but the deformity is usually not as complex as that in early-onset disease.
Management is by tibial osteotomy with acute correction and fixation, or with slow correction using external fixation.
Obesity is also an important risk factor in the occurrence and in management of this condition.
D M Thompson