Nerve supply of obturator internus is by
**Core Concept**
The obturator internus muscle is a deep gluteal muscle that plays a crucial role in hip rotation and stabilization. Its nerve supply is derived from the sacral plexus, which is a complex network of nerves originating from the L4-S3 nerve roots.
**Why the Correct Answer is Right**
The obturator internus muscle receives its nerve supply from the nerve to obturator internus, which is a branch of the sacral plexus. This nerve arises from the L5, S1, and S2 nerve roots and provides motor innervation to the obturator internus and the adjacent superior gemellus muscle. The nerve to obturator internus is a mixed nerve that also provides sensory innervation to the obturator internus muscle.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the nerve supply of the obturator internus muscle.
**Option B:** This option refers to the nerve supply of the obturator externus muscle, which is a different muscle.
**Option D:** This option is incorrect as it refers to the nerve supply of the gluteus medius muscle, which is a different muscle.
**Clinical Pearl / High-Yield Fact**
The obturator internus muscle is an important landmark for the sacroiliac joint, and its nerve supply is closely related to the sciatic nerve, which is a common site of compression in patients with sciatica.
**Correct Answer: C. The nerve to obturator internus.**