Overview
The brachial plexus is the neural network supplying the entire upper limb. It is formed by the ventral rami of spinal nerves C5–T1 and extends from the cervical spine to the axilla. The plexus provides both motor and sensory innervation to the shoulder, arm, forearm and hand.
Understanding the brachial plexus is extremely important for orthopaedic surgeons because injuries to the plexus frequently occur in trauma, shoulder dislocations, clavicle fractures and obstetric injuries. Accurate anatomical knowledge helps localize nerve injuries based on clinical examination.
Formation
The brachial plexus is formed by the anterior rami of five spinal nerves.
- C5
- C6
- C7
- C8
- T1
These roots emerge from the intervertebral foramina and pass between the anterior and middle scalene muscles in the neck.
Anatomical Variations
- Prefixed plexus: contribution from C4
- Postfixed plexus: contribution from T2
These variations are clinically important because injury patterns may differ depending on the dominant roots.
Roots
The roots represent the first component of the brachial plexus.
Branches from Roots
| Nerve | Root Value | Function |
|---|---|---|
| Dorsal scapular nerve | C5 | Rhomboid muscles |
| Long thoracic nerve | C5–C7 | Serratus anterior |
Trunks
The roots combine to form three trunks.
| Trunk | Roots |
|---|---|
| Upper trunk | C5–C6 |
| Middle trunk | C7 |
| Lower trunk | C8–T1 |
Trunks lie in the posterior triangle of the neck and are susceptible to traction injuries.
Divisions
Each trunk divides into anterior and posterior divisions.
- Anterior divisions supply flexor compartments
- Posterior divisions supply extensor compartments
Although divisions do not give off branches, they reorganize to form the cords of the plexus.
Cords
The cords are named according to their relationship with the axillary artery.
| Cord | Origin |
|---|---|
| Lateral cord | Anterior divisions of upper and middle trunks |
| Medial cord | Anterior division of lower trunk |
| Posterior cord | Posterior divisions of all trunks |
Terminal Branches
| Nerve | Root Value | Key Function |
|---|---|---|
| Musculocutaneous | C5–C7 | Elbow flexion |
| Axillary | C5–C6 | Shoulder abduction |
| Radial | C5–T1 | Wrist extension |
| Median | C6–T1 | Forearm flexors |
| Ulnar | C8–T1 | Intrinsic hand muscles |
Clinical Correlations
Erb Palsy
- Upper trunk injury (C5–C6)
- Common in obstetric traction injuries
- Produces waiters tip deformity
Klumpke Palsy
- Lower trunk injury (C8–T1)
- Intrinsic hand muscle paralysis
- May cause Horner syndrome
Key Exam Points
- Roots lie between anterior and middle scalene muscles
- Upper trunk injury causes Erb palsy
- Lower trunk injury causes Klumpke palsy
- Long thoracic nerve injury causes scapular winging
- Cords are named relative to axillary artery