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Findings: There is narrowing of the medial left tibial epiphysis with beaking of the medial left tibial metaphysis. There is also associated tibia varus deformity. The right lower extremity is unaffected.

Diagnosis: Blount deformity

Discussion: Blount deformity is a disorder of unknown etiology characterized by disturbed growth of the medial aspect of the proximal tibial epiphysis causing bowing of the lower extremity. Two forms of Blount deformity are recognized, infantile tibia vara and late onset tibia vara. It is thought that infantile tibia vara is the sequela of developmental bowing that fails to straighten as the child puts weight on the leg and becomes heavier. Histologically, there is disturbed enchondral ossification with disorganized and malaligned physeal zones. Clinically, there is angulation of the upper tibia although the diaphysis below this point is straight. This form of Blount deformity is in most cases bilateral. Obesity, ligamentous laxity, and prominence of the fibular head are often associated. Late onset tibia vara is thought to be due to segmental arrest of growth plate function. It has been seen after trauma and osteomyelitis although some cases develop without identifiable previous insult. This form is much less common than infantile tibia vara and affects children between eight and fifteen years of age.

Radiologic Findings for Blount deformity includes angulation in the proximal tibial metaphysis with abduction of the tibial shaft without intrinsic curvature of the diaphyseal portion of the tibia. The cortical outline of the medial tibial metaphysis is angled down giving the appearance of a prominent beak or a hypertrophic depressed spur. Lateral subluxation of the proximal tibia may also be seen. The posteromedial cortex of the tibia is often thickened, and the lateral growth plate is often widened. The medial portion of the tibial epiphysis is underdeveloped and wedge-shaped. Given these findings, the differential diagnosis of vitamin D resistant rickets must also be considered. The treatment for severe cases of this disorder may include tibial osteotomy.

References:
Ozonoff MB: Pediatric Orthopaedic Radiology, 1992, WB Saunders,
Philadelphia.

Behrman R, Vauchan V: Nelson Textbook of Pediatrics, 1983, WB
Saunders, Philadelphia.

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