A 2-year-old child with a history of old knee injury now has varus deformity of the left knee. Deformity persists on flexion; blood report is normal. X-ray shows unilateral genu varum and angulated tibia. What is the diagnosis?

1. A

   A. Malunion of tibial fracture

2. B

   B. Osteofibrous dysplasia

3. C

   C. Rickets

4. D

   D. Focal fibrocartilaginous dysplasia

Appeared in: INI-CET EXAM -2026

Explanation

• The diagnosis is based on the clear history of a previous knee injury in a 2-year-old child.
• A fracture of the tibia, especially a subtle 'toddler's fracture,' can heal in an improper position (malunion), leading to an angular deformity like genu varum.
• The presentation is unilateral (affecting only one leg), which is characteristic of a post-traumatic condition.
• Normal blood reports exclude systemic metabolic causes, such as rickets, which would affect both legs and show biochemical abnormalities.
• The X-ray finding of an 'angulated tibia' is the definitive sign of a malunited fracture.

Why Other Options Were Wrong

• Option B: Osteofibrous dysplasia is a rare, benign bone tumor that causes tibial bowing. However, it is a developmental condition and is not caused by a specific traumatic event.
• Option C: Rickets is a metabolic bone disease caused by vitamin D deficiency. It typically causes bilateral, symmetrical bowing of the legs and would be accompanied by abnormal blood tests (e.g., low vitamin D, changes in calcium and phosphate levels).
• Option D: Focal fibrocartilaginous dysplasia is a rare, benign condition that can cause unilateral tibial bowing in young children. However, it is a developmental anomaly, not a result of trauma. The history of injury is the key feature that points away from this diagnosis.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Differential diagnosis of unilateral genu varum in a toddler to guide bedside assessment, documentation, and the next nursing action.
• This case highlights the importance of considering a missed or occult fracture in a toddler who presents with a limp or deformity, even after what seems like a minor injury.
• A malunion can affect the child's gait and place abnormal stress on the knee and ankle joints, potentially leading to early arthritis if not addressed.
• What if the deformity was bilateral and the blood reports showed low phosphate? In that case, the diagnosis would shift towards a metabolic cause like hypophosphatemic rickets, and the management would involve medical treatment rather than just orthopedic correction.

How to Approach the Question

• First, analyze the patient's age and chief complaint: a 2-year-old with a varus deformity (bowleg). Note that while some bowing is normal in toddlers, this case has specific concerning features.
• Next, identify the key positive finding in the history: a previous knee injury. This immediately raises suspicion for a post-traumatic cause.
• Evaluate the physical exam and lab findings: the deformity is unilateral, and blood work is normal. Use this information to rule out systemic or metabolic diseases like nutritional rickets.
• Interpret the imaging report: 'unilateral genu varum and angulated tibia.' An angulated bone strongly suggests a healed fracture.
• Synthesize the clues: History of trauma + unilateral deformity + normal labs + angulated bone on X-ray. This combination points directly to a malunion of a previous fracture.
• Review the options and select the one that best fits this synthesis. Malunion of a tibial fracture is the only option that accounts for all the provided information.

Concept Tested & Keywords

• Concept Tested: Differential diagnosis of unilateral genu varum in a toddler.
• Stem keywords: 2-year-old child, old knee injury, varus deformity, unilateral genu varum, angulated tibia, normal blood report
• Lead-in keywords: What is the diagnosis?
• Clinical cues: History of old knee injury: Points towards a traumatic etiology.
• Clinical cues: Unilateral deformity: Suggests a local cause rather than a systemic disease.

Question ID

Q806cZM5tQ_2R0mR7JsDla

Copy ID

Reference Book

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 2026-2028