Referred pain from ureteric colic is felt in the groin due to involvement of the following nerve:
**Core Concept**
The phenomenon of referred pain from ureteric colic is related to the convergence of visceral and somatic afferent fibers in the spinal cord. This results in the perception of pain in a region other than the actual site of the lesion.
**Why the Correct Answer is Right**
The correct answer is due to the involvement of the ilioinguinal nerve, which provides sensory innervation to the medial thigh and the inguinal region. The ureter's pain fibers converge with the ilioinguinal nerve fibers in the lumbar spinal cord, resulting in referred pain in the groin area. The ilioinguinal nerve is a mixed nerve that carries both sensory and motor fibers from the L1 spinal nerve.
**Why Each Wrong Option is Incorrect**
**Option A:** The genitofemoral nerve is primarily involved in the innervation of the cremaster muscle and the skin of the anterior superior iliac spine, but it is not primarily responsible for referred pain from ureteric colic.
**Option B:** The obturator nerve is primarily involved in the innervation of the adductor muscles of the thigh, but it is not primarily responsible for referred pain from ureteric colic.
**Option C:** The femoral nerve is primarily involved in the innervation of the anterior thigh muscles and the skin of the anterior thigh, but it is not primarily responsible for referred pain from ureteric colic.
**Clinical Pearl / High-Yield Fact**
Referred pain from ureteric colic can also involve the psoas muscle, resulting in pain that radiates to the back and is often associated with muscle spasm. This is due to the shared innervation of the psoas muscle by the lumbar nerves that also carry visceral afferent fibers from the ureter.
**Correct Answer: C. The ilioinguinal nerve.**