**Question:** Medial arch of foot is made up of

A. Navicular bone
B. Cuboid bone
C. Talus bone
D. Os calcis (calcaneus)

**Correct Answer:** D. Os calcis (calcaneus)

**Core Concept:**
The medial arch of the foot is a crucial structural component for maintaining proper foot biomechanics and preventing foot deformities. It is formed by the fusion of several bones during development.

**Why the Correct Answer is Right:**
The medial arch of the foot is primarily composed of the Os calcis (calcaneus), which is a tarsal bone located at the hindfoot region. The calcaneus contributes to the arch formation by articulating with other tarsal bones and connecting to the navicular and cuboid bones via syndesmosis joints. This alignment helps distribute body weight evenly and provides stability to the foot.

**Why Each Wrong Option is Incorrect:**
A. Navicular bone (Navicularia bone): While the navicular bone is also a tarsal bone, it does not contribute significantly to the medial arch formation. It primarily supports the arch from the lateral side.
B. Cuboid bone: The cuboid bone is part of the transverse tarsal arch and supports the medial arch from the lateral side.
C. Talus bone: The talus bone is a tibiotalar joint component and does not directly contribute to the medial arch construction.

**Clinical Pearl:**
Understanding the anatomy of the medial arch and its constituent bones is essential for recognizing and treating foot conditions like fallen arches (pes planus) and high arches (pes cavus). Proper knowledge of these structures helps in formulating an accurate diagnosis and selecting the most effective treatment plan for patients with foot problems.