UPSC-CMS 2023 — Orthopaedics

Question 1: The following hallmarks characterise Diaphyseal aclasis except

• A. Pseudoarthrosis is common
• B. Chondrosarcoma may occur in less than 1% cases (Correct Answer)
• C. It is inherited as an autosomal dominant dysplasia
• D. Genu valgum can be found

Explanation: ***Chondrosarcoma may occur in less than 1% cases*** - This statement is incorrect as the risk of malignant transformation to **chondrosarcoma** in Diaphyseal aclasis (hereditary multiple exostoses) is commonly reported to be significantly higher, ranging from **5-25%**. - Therefore, stating it occurs in "less than 1% cases" is factually inaccurate, making this the correct answer as to what does *not* characterize the condition. *Pseudoarthrosis is common* - **Pseudoarthrosis** (false joint formation) can occur as a complication of **bony deformities** and the presence of osteochondromas, particularly in regions where they interfere with bone growth or cause fractures. - The abnormal growth of osteochondromas can predispose to fractures, which may heal poorly and result in pseudoarthrosis. *It is inherited as an autosomal dominant dysplasia* - Diaphyseal aclasis, also known as **hereditary multiple exostoses (HME)**, is indeed an **autosomal dominant** skeletal dysplasia. - It is caused by mutations in the **EXT1 or EXT2 genes**, which are involved in heparan sulfate proteoglycan synthesis, leading to abnormal bone growth. *Genu valgum can be found* - **Genu valgum** (knock-knees) is a common **skeletal deformity** observed in individuals with Diaphyseal aclasis. - The multiple osteochondromas can disturb the normal growth and alignment of long bones, frequently affecting the distal femur and proximal tibia leading to this angular deformity.