## **Core Concept**
Kohler's disease is a rare bone disorder that affects the navicular bone in the foot. It is characterized by the collapse of the navicular bone's architecture due to **avascular necrosis**, leading to pain and limited mobility in the foot. This condition primarily affects children and adolescents.

## **Why the Correct Answer is Right**
The correct answer involves the navicular bone because Kohler's disease specifically affects this bone. The navicular bone is a small, boat-shaped bone in the foot that plays a crucial role in supporting the medial (inner) arch. Avascular necrosis of the navicular bone disrupts its blood supply, leading to bone collapse and the characteristic symptoms of Kohler's disease.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because Kohler's disease does not involve the lunate bone; it involves the navicular bone of the foot. The lunate bone is actually associated with Kienbock's disease, which is a similar condition but affects the wrist.
- **Option B:** This option is incorrect as it does not accurately represent the bone involved in Kohler's disease.
- **Option D:** This option is incorrect because the bone involved in Kohler's disease is not listed here; the correct bone is the navicular.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Kohler's disease presents with **pain and swelling** in the midfoot area, particularly in children and adolescents. It is often diagnosed with the help of X-rays, which show a characteristic increase in density and fragmentation of the navicular bone.

## **Correct Answer:** . Navicular bone.