**Question:** All are branches of lumbar plexus except-

A. Sacral Plexus
B. Thoracic Plexus
C. Cervical Plexus
D. Truncus Brachialis

**Core Concept:**
The lumbar plexus is a network of nerves formed by the union of the ventral rami of the spinal nerves L1 to L5. It plays a crucial role in supplying sensory and motor innervation to the lower abdomen, thigh, and lower limb. The lumbar plexus consists of three main divisions:

1. L1-L2: L1-L2 roots form the anterior division, which supplies the abdominal wall, genitals, and skin of the lower abdomen.
2. L2-L3: L2-L3 roots form the posterior division, which supplies the skin and subcutaneous tissue of the thigh and knee.
3. L3-L4: L3-L4 roots form the lateral division, which supplies the skin, muscles, and joint capsules of the thigh.

**Why the Correct Answer is Right:**

The correct answer is **D. Truncus Brachialis**, because it is a branch of the brachial plexus, which is formed by the union of the ventral rami of cervical spinal nerves C5 to C8 and T1. The brachial plexus supplies motor and sensory innervation to the upper limb, while the lumbar plexus supplies the lower limb.

**Why Each Wrong Option is Incorrect:**

A. **Sacral Plexus**: The sacral plexus is a separate plexus composed of ventral rami of spinal nerves S2-S4, which supplies the lower limb and pelvic region.

B. **Thoracic Plexus**: The thoracic plexus is formed by the ventral rami of the spinal nerves T1-T12 and supplies the anterior chest wall, neck, and upper limb.

C. **Cervical Plexus**: Although the cervical plexus is mentioned in the question, it is incorrect to exclude it from the lumbar plexus. The cervical plexus is formed by the ventral rami of spinal nerves C5-C8 and supplies the upper limb.

In summary, the correct answer (D) is right because it belongs to the brachial plexus, while the incorrect options (A, B, and C) are wrong due to their involvement in other regions and plexuses.

**Clinical Pearls:**

1. Understanding the anatomy and distribution of peripheral nerves is essential for accurate diagnosis and management of neuropathies, entrapment neuropathies, and other peripheral nerve disorders.
2. In clinical practice, it is crucial to know the distribution of nerves for proper management of patients with pain, sensory, or motor deficits in specific regions of the body.
3. A thorough knowledge of the lumbar plexus and its divisions can help identify the cause of lower limb symptoms and guide appropriate management strategies.