**Question:** Absent radius is seen in all except

A. Salter-Harris type II fracture
B. Congenital absence of radius
C. Metaphyseal chondrodystrophy
D. Salter-Harris type I fracture

**Core Concept:**
The absence or malformation of the radius is a significant issue in forearm skeletal development. The radius is one of the two long bones in the forearm, alongside the ulna. A normal forearm consists of two bones: the radius and the ulna. These bones are connected by the radioulnar joint, which allows for forearm rotation and pronation-supination movements.

**Why the Correct Answer is Right:**
Congenital absence of radius (option B) is a rare condition where the radius fails to form during development, leading to a complete absence of the radius bone in the forearm. This can result in limited mobility and deformity of the forearm.

**Why Each Wrong Option is Incorrect:**

A. Salter-Harris type II fracture (option A) is a type of fracture that occurs in growing bones, typically in adolescents. It is characterized by a fracture in the growth plate, which typically heals well and often does not cause long-term issues.

B. Salter-Harris type I fracture (option D) is another type of fracture in growing bones, usually seen in children. It occurs in the epiphysis or growth plate, and also tends to heal well, with minimal long-term consequences.

C. Metaphyseal chondrodysplasia (option C) is a group of genetic disorders affecting bone growth and development. While these conditions often involve multiple skeletal issues, they typically do not result in the complete absence of the radius bone.

**Clinical Pearl:**
The correct answer, congenital absence of the radius, is a rare condition that should be suspected in patients with a fixed flexion deformity of the forearm, limited range of motion, or a palpable gap in the forearm. In contrast, the wrong options are conditions that affect the forearm bones but do not result in their complete absence.

Understanding these conditions can help guide clinical assessments and differential diagnosis of forearm abnormalities.