**Core Concept**
The sciatic notch index is a metric used in forensic anthropology to estimate the sex of an individual from skeletal remains. It is based on the observation that the sciatic notch, a bony structure in the pelvis, tends to be wider in females due to the presence of the round ligament of the uterus, which passes through the notch.

**Why the Correct Answer is Right**
The sciatic notch index is calculated by measuring the width of the notch at its widest point and comparing it to the width of the ilium (the largest bone of the pelvis). In females, the notch is typically wider and more shallow, while in males, it is narrower and more V-shaped. This difference is due to the presence of the round ligament of the uterus in females, which causes the notch to widen over time. The sciatic notch index is a useful tool for sex estimation in forensic anthropology because it can help to determine the sex of an individual when other methods are inconclusive.

**Why Each Wrong Option is Incorrect**
**Option A:** The sciatic notch index is not related to the estimation of age at death from skeletal remains.
**Option B:** The sciatic notch index is not a measure of the size of the pelvis, but rather a specific metric used to estimate sex.
**Option C:** The sciatic notch index is not a measure of the presence of pelvic fractures, but rather a metric used to estimate sex.

**Clinical Pearl / High-Yield Fact**
In forensic anthropology, the sciatic notch index is often used in conjunction with other metrics, such as the subpubic angle and the ischial tuberosity, to estimate the sex of an individual from skeletal remains. This can be useful in cases where the identity of a deceased individual is unknown.

**Correct Answer:** C.