Question

What is the most likely cause of unilateral genu varum (bow-leg deformity of one leg) in a patient with a history of a previous injury to that limb?

(Figure: AP X-ray of both lower limbs showing bowing of one leg.)

• A. Malunion of a previous fracture
• B. Rickets
• C. Non-ossifying fibroma
• D. Osteofibrous dysplasia

Hint:

Unilateral + prior injury = malunion; rickets is bilateral and symmetric.

Answer 1

The Correct Option is A

Step 1: Focus on the two key clues - UNILATERAL deformity and PREVIOUS INJURY.
The deformity is confined to one leg and there is a history of trauma to that limb. This combination points strongly to a post-traumatic structural cause rather than a systemic or developmental one.

Step 2: Reason from the cause of unilateral bowing.
A fracture that heals in an angulated position - malunion - or growth-plate injury producing asymmetric growth, will result in a localised, unilateral angular deformity such as genu varum. The history of previous injury makes malunion the natural explanation.

Step 3: Eliminate the distractors.
• Rickets - a metabolic (vitamin-D deficiency) disorder that classically causes bilateral, symmetrical bowing of the legs; it does not fit a unilateral, trauma-related deformity.
• Non-ossifying fibroma - usually an incidental, asymptomatic benign cortical lesion; it can occasionally cause pathological fracture, but it is not the typical cause of a unilateral varus deformity following injury.
• Osteofibrous dysplasia - a rare benign fibro-osseous lesion of the tibia in young children causing anterior/anterolateral tibial bowing, not a varus deformity linked to prior trauma.

Step 4: Key fact.
Unilateral genu varum with a history of injury is most consistent with malunion of a previous fracture (or post-traumatic growth disturbance); systemic rickets produces bilateral symmetric bowing.