## Core Concept
Cobb's angle is a measurement used in orthopedics and radiology to quantify the degree of deformity in spinal conditions, particularly **scoliosis**. It is measured from a posteroanterior (PA) radiograph of the spine. The angle helps in assessing the severity of the curvature and in planning treatment.

## Why the Correct Answer is Right
The correct answer, **scoliosis**, is the condition for which Cobb's angle is specifically used. Scoliosis is a medical condition in which a person's spine has a sideways curve. The Cobb's angle is calculated by drawing lines parallel to the superior endplate of the uppermost vertebra and the inferior endplate of the lowermost vertebra involved in the curve. Perpendicular lines are then drawn from these, and the angle where they intersect is measured. This method provides a standardized way to assess the severity of the spinal curvature.

## Why Each Wrong Option is Incorrect
- **Option A:** While kyphosis involves an abnormal curvature of the spine, it is specifically an anteroposterior curvature, not the lateral curvature that Cobb's angle measures.
- **Option B:** Lordosis refers to an excessive inward curvature of the spine. Although it's a type of spinal deformity, Cobb's angle is not used to measure lordosis.
- **Option C:** This option seems to be missing but based on the context, any option not related to scoliosis would be incorrect.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that a Cobb's angle of **10-20 degrees** is generally considered mild scoliosis, **20-40 degrees** is moderate, and **>40 degrees** is severe. This classification helps guide treatment decisions, which can range from observation to bracing or surgical intervention.

## Correct Answer: D. Scoliosis