Bow Leg Deformity (Blount's Disease)

Pediatric Orthopedic Surgery, Hospital for Special Surgery


Causes of Blount's Disease

Causes of Blountís disease include metabolic disorders such as rickets, renal failure, infection, skeletal dysplasias (developmental abnormalities), and achondroplasia (a form of dwarfism). Most commonly, the deformity is found at the top of the tibia, the larger of the two bones in the lower leg; the deformity occurs when the lateral (outer) side of the tibia continues growing while the medial (or inner) side of the bone does not. Blountís disease may affect one or both legs.

Diagnosis

A diagnosis of Blountís disease is based on physical examination and a standing alignment x-ray, in which an image of the leg - from hip to ankle - is obtained [Figures 1 & 2]. The pediatric orthopedist uses this image to determine the mechanical axis of the deformity as well as its location.

 
Figures 1 & 2: Front and back of a child with bow legs due to Blount's Disease, prior to guided growth treatment

Treatment Bracing

The initial treatment for infantile Blountís disease is bracing , usually for a period of up to one year to determine effectiveness [Figures 3 & 4]. Standard bracing protocol involves use of a brace during waking hours with the knee in full extension during weight bearing. If gradual correction does not occur, surgery may be recommended. Results of surgery are much better before age four than after, when the recurrence rate of bowing goes up.

 
Figures 3 & 4: Photos of a child with Blount's Disease in a brace.

Surgical Correction

In surgical correction of Blountís disease, the pediatric orthopedist performs an osteotomy, cutting the tibia and fibula as close to the growth plate as possible and realigning the bones. Following the procedure, the surgeon places a fixator on the leg to maintain proper alignment during healing.

 
Figures 5 & 6: X-ray images of the same child before (left) and after (right) a guided growth surgical procedure.
Note the plates used to fully correct the lower extremities in the knee area, outlined in white.

 
Figures 7 & 8: Child after surgery

External Fixators

In an acute (severe) correction, a monolateral or single-lane fixator is used. If the correction is gradual, a circular fixator (also called the Ilazarov) is used. This fixator is also used when additional procedures are done simultaneously to correct other deformities such as a limb length discrepancy. The latter can develop when Blountís disease affects only one leg. In most cases, the correction is gradual with frames that allow for fine-tuning. If the deformity correction is not absolutely perfect on an x-ray, correction can continue it until it is.Ē The fixator is worn for between 8 and 12 weeks as the leg heals.


Figure 9: External Fixator

For additional information on External Fixation, see the Guide to Pediatric External Fixators (pdf).

Rehabilitation

Physical therapy is an important part of treatment and most patients continue to see their therapists three times a week after leaving the hospital. Physical therapy helps ensure that the surrounding soft tissues remain flexible as the bone heals, and that muscle strength is maintained.

Treatment for Adolescent Blountís Disease

The initial approach for patients with adolescent Blountís disease is usually guided growth. This treatment involves the pediatric orthopedic surgeon placing a small plate and two screws against the lateral side of the tibia, where bone growth has occurred. This limits growth on the growth side while allowing growth on the medial side. As the patientís natural growth occurs, the deformity is progressively corrected.

If guided growth fails to correct the deformity, or if the patient doesnít have enough growth left to achieve the desired correction, osteotomy may be recommended. Patients with adolescent Blountís disease are likely to have some limb length discrepancy as described above and can have both deformities corrected during surgery.

If Left Untreated

Blountís disease that is left untreated not only results in progression of the deformity, but also an increased risk of joint arthritis of the knee and other early degenerative changes.


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