A 32-year-old patient with multiple fractures of the pelvis has no cutaneous sensation in the urogenital triangle. The function of which of the following nerves is most likely to be spared?
**Core Concept**
The urogenital triangle of the perineum receives its sensory innervation from the pudendal nerve, which is responsible for transmitting sensations of touch, pressure, and temperature from the external genitalia and surrounding skin. The pudendal nerve is derived from the S2-S4 nerve roots.
**Why the Correct Answer is Right**
The pudendal nerve is primarily responsible for the sensory innervation of the urogenital triangle. It also plays a crucial role in the motor innervation of the external anal sphincter and the bulbospongiosus muscle. However, the motor function of the pudendal nerve is not the primary concern in this scenario. The patient has no cutaneous sensation in the urogenital triangle, indicating a problem with the sensory function of the pudendal nerve. The nerve responsible for motor function in the perineum is the perineal nerve, which is derived from the S2-S4 nerve roots and is a branch of the pudendal nerve. However, the perineal nerve is primarily involved in the motor innervation of the muscles of the perineum.
**Why Each Wrong Option is Incorrect**
**Option A:** The ilioinguinal nerve is responsible for the sensory innervation of the medial aspect of the thigh, the root of the penis, and the upper part of the scrotum in males, and the mons pubis and labia majora in females. It is not responsible for the sensory innervation of the urogenital triangle.
**Option B:** The obturator nerve is primarily involved in the motor innervation of the adductor muscles of the thigh. It does not provide sensory innervation to the urogenital triangle.
**Option C:** The femoral nerve is responsible for the sensory innervation of the anterior aspect of the thigh and the medial aspect of the leg. It does not provide sensory innervation to the urogenital triangle.
**Clinical Pearl / High-Yield Fact**
The pudendal nerve is at risk during pelvic fractures, which can result in sensory deficits in the urogenital triangle.
**Correct Answer:** D.