**Core Concept**
Z plasty is a surgical technique used to lengthen a scar or a narrow area of skin by transposing triangular flaps of skin. The length gained in Z plasty is dependent on the angle at which it is performed, with steeper angles resulting in greater length gain.

**Why the Correct Answer is Right**
When a Z plasty is performed at a 60-degree angle, the length gain is calculated by the formula: length gain = (2 * (180 - angle) / π) * original length. Substituting the given angle, we get length gain = (2 * (180 - 60) / π) * original length. This simplifies to length gain = (2 * 120 / π) * original length, which is approximately 76.4% of the original length. This is a significant increase in length, making 60-degree Z plasty a useful technique for lengthening scars.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the effect of the angle on the length gain. Without considering the angle, it is impossible to accurately calculate the length gain.

**Option B:** This option is incorrect because it suggests a flat angle, which is not possible in a Z plasty procedure. The angle in a Z plasty is always greater than 0 degrees.

**Option C:** This option is incorrect because it does not provide a numerical value for the length gain, making it impossible to determine its accuracy.

**Clinical Pearl / High-Yield Fact**
When performing Z plasty, it is essential to consider the angle at which the procedure is done, as it significantly affects the length gain. A 60-degree angle is a good compromise between length gain and cosmetic outcome.

**Correct Answer:** C. 76.4%