BRACHIAL PLEXUS

Anatomy of Brachial Plexus (MSLV)

1. Define nerve plexus
   A nerve plexus is a complex network of intersecting nerves formed by the anterior (ventral) rami of spinal nerves, where nerve fibers reorganize and redistribute to form peripheral nerves supplying specific regions of the body.

2. Enumerate the root value of Brachial plexus
   The brachial plexus is formed by the anterior rami of the spinal nerves C5, C6, C7, C8, and T1 (cervical 5–8 and thoracic 1). In some variations, it may include minor contributions from C4 or T2.

3. Mention the stages of formation of Brachial plexus
   The brachial plexus forms through sequential stages:

   • Roots: Anterior rami of C5–T1 emerge from the intervertebral foramina.
   • Trunks: Roots unite to form three trunks – Upper (C5–C6), Middle (C7), Lower (C8–T1).
   • Divisions: Each trunk splits into anterior and posterior divisions.
   • Cords: Divisions regroup into three cords – Lateral (anterior divisions of upper + middle trunks), Posterior (posterior divisions of all trunks), Medial (anterior division of lower trunk).
   • Terminal branches: Cords give rise to the major peripheral nerves.

4. Name the branches of Brachial plexus
   The branches are categorized by their origin:

   • From roots: Dorsal scapular nerve (C5; to rhomboids), Long thoracic nerve (C5–C7; to serratus anterior).
   • From trunks: Suprascapular nerve (upper trunk, C5–C6; to supraspinatus and infraspinatus), Nerve to subclavius (upper trunk, C5–C6).
   • From lateral cord: Lateral pectoral nerve (C5–C7; to pectoralis major), Musculocutaneous nerve (C5–C7; to anterior arm muscles and lateral forearm skin), Lateral root of median nerve (joins medial root to form median nerve).
   • From medial cord: Medial pectoral nerve (C8–T1; to pectoralis minor and major), Medial cutaneous nerve of arm (C8–T1), Medial cutaneous nerve of forearm (C8–T1), Ulnar nerve (C7–T1; to medial forearm and hand), Medial root of median nerve.
   • From posterior cord: Upper subscapular nerve (C5–C6; to subscapularis), Thoracodorsal nerve (C6–C8; to latissimus dorsi), Lower subscapular nerve (C5–C6; to subscapularis and teres major), Axillary nerve (C5–C6; to deltoid and teres minor, plus shoulder skin), Radial nerve (C5–T1; to posterior arm and forearm).

5. Enlist the deformities due to injuries to Brachial plexus
   Injuries to the brachial plexus can cause various deformities depending on the level affected:

   • Erb's palsy (upper trunk injury, C5–C6): "Waiter's tip" deformity – arm adducted and internally rotated, elbow extended, forearm pronated, wrist flexed (due to paralysis of shoulder abductors, external rotators, and elbow flexors).
   • Klumpke's palsy (lower trunk injury, C8–T1): "Claw hand" deformity – intrinsic hand muscle paralysis leading to hyperextended metacarpophalangeal joints and flexed interphalangeal joints, often with Horner's syndrome if T1 is involved.
   • Total brachial plexus injury: Flail arm – complete paralysis and sensory loss in the entire upper limb.
   • Winged scapula: From long thoracic nerve injury (C5–C7), causing serratus anterior paralysis and medial scapular winging.
   • Ape hand: From median nerve injury, with thenar atrophy and inability to oppose thumb.
   • Wrist drop: From radial nerve injury, with inability to extend wrist and fingers.