Okay, let's tackle this question about Saturday Night Palsy. The user wants a detailed explanation for an MCQ where the correct answer is the radial nerve. First, I need to recall what Saturday Night Palsy is. From what I remember, it's a type of radial nerve palsy caused by compression, usually from prolonged pressure on the arm, like when someone falls asleep with their arm draped over a hard surface.

The core concept here is the radial nerve's anatomical course and where it's vulnerable. The radial nerve runs along the spiral groove of the humerus and then continues down the arm, innervating the extensor muscles of the forearm. When compressed, especially at the elbow or in the spiral groove, it can lead to weakness in wrist and finger extension.

Now, the correct answer is the radial nerve. I need to explain why. The radial nerve is responsible for extending the wrist and fingers. When it's compressed, the person can't extend their wrist (like the "waiter's tip" position) and might have sensory loss over the dorsal forearm and hand. The mechanism here is usually compression, not trauma, which differentiates it from other causes of radial nerve injury.

For the wrong options, let's consider other nerves. The ulnar nerve is often involved in cubital tunnel syndrome, causing claw hand. The median nerve is affected in carpal tunnel, leading to thenar atrophy. The musculocutaneous nerve affects biceps function but isn't related to this condition. Each of these has different clinical presentations and anatomical locations, so they don't fit the Saturday Night Palsy scenario.

The clinical pearl should highlight the key features: radial nerve compression from prolonged pressure, typical presentation, and the importance of history in diagnosis. Also, noting that it's a mononeuropathy, not a polyneuropathy, which helps in differential diagnosis.

I need to make sure the explanation is concise, covers all sections, and uses proper medical terms. Let me check the character count to stay within the limit. Also, avoid markdown except for bold labels. Alright, putting it all together now.

**Core Concept**
Saturday Night Palsy is a mononeuropathy caused by **radial nerve compression**, typically from prolonged pressure on the posterior arm (e.g., sleeping with the arm bent at the elbow against a hard surface). The radial nerve is vulnerable at the **spiral groove of the humerus** and near the **lateral epicondyle**.

**Why the Correct Answer is Right**
The **radial nerve** innervates wrist/finger extensors and the extensor carpi radialis longus. Compression leads to **inability to extend the wrist and fingers** (characteristic "waiter’s tip" posture) and sensory loss over the dorsal forearm/hand. The injury is usually **atraumatic** and self-limiting due to localized compression, not trauma.

**Why Each Wrong Option is Incorrect**
**Option A:** The *median nerve* is involved in carpal tunnel syndrome (thenar atrophy, "猿手" [ape hand]), not wrist/finger extension loss.
**Option B:** The *ulnar nerve* causes claw hand (intrinsic hand muscle weakness) from cubital tunnel syndrome, not radial nerve symptoms.
**Option C:** The *musculocutaneous nerve* innervates

✓ Correct Answer: A. Radial nerve