Blount disease

Blount disease (also known as tibia vara) refers to a local disturbance of growth of the medial proximal tibial epiphysis. The condition is commonly bilateral. 

Epidemiology

There is no recognised inheritance pattern. 

Clinical presentation

Clinically, the child often presents with leg bowing with little or no associated pain.

Pathology

A relative lack of growth of the medial proximal tibial physis occurs, likely secondary to an increase in compressive forces on the proximal tibial physis

Sub types

There are infantile, juvenile and adolescent forms.

The infantile type is 5 times more frequent than the others, and is seen particularly in early walkers. It appears to be the result of abnormal compressive forces inhibiting growth at the medial growth plate - and not from avascular necrosis. 

Grading

The condition can be graded into six stages according the system proposed by Langenskiöld et al ².

Associations

Childhood obesity : especially for the adolescent type ⁴

Radiographic features

The tibial shaft is in varus position and the epiphysis is wedge-shaped, fragmented or can appear absent. The adjacent metaphysis is also depressed and has a beak-like protuberance of rarified bone oriented medially. This causes the metaphyseal diaphyseal angle (MDA) of Drennan to increase (typically more than 11 degrees). The lateral cortical wall of the upper tibial metaphysis remains notably straight.

Pre-operative MRI can be used to detect physeal bone bars.

Treatment and prognosis

Treatment depends on the sub type and stage. As a general rule:

• infantile / early stage : often conservatively managed
• adolescent / late stage : a proximal tibial osteotomy is often considered

Etymology

First described by Blount in 1932

Differential diagnosis

For leg bowing consider : differential for leg bowing in children