Orthonotes
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Brachial plexus consists of Roots (C5–T1), Trunks (upper, middle, lower), Divisions (each trunk splits into anterior/posterior), Cords (lateral, posterior, medial), and terminal Branches (musculocutaneous, axillary, radial, median, ulnar). Anatomical course: roots emerge between scalene muscles; trunks in posterior triangle; divisions under clavicle; cords encircle axillary artery and give off named nerves (e.g. lateral cord → musculocutaneous). Key relationships: the long thoracic nerve (C5-7) arises from roots (winged scapula if injured); axillary nerve from posterior cord (risk in shoulder dislocation); radial nerve from posterior cord (mid-shaft humerus fracture → wrist drop). Injury patterns: Upper plexus (Erb’s palsy, C5-6) causes arm adducted/internally rotated ('waiter’s tip'); Lower plexus (Klumpke’s, C8-T1) causes hand paralysis and Horner syndrome if sympathetic chain involved. Examination: look for motor deficits by peripheral nerve distribution (e.g. loss of shoulder abduction suggests axillary nerve/C5 injury) and sensory deficits (e.g. lateral forearm numbness indicates musculocutaneous nerve). Imaging: MRI or nerve conduction studies help localize root avulsions vs stretch injuries. Management ranges from physical therapy for neuropraxia to nerve grafts/transfers for severe root avulsions.
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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.
The brachial plexus is formed by the anterior rami of five spinal nerves.
These roots emerge from the intervertebral foramina and pass between the anterior and middle scalene muscles in the neck.
These variations are clinically important because injury patterns may differ depending on the dominant roots.
The roots represent the first component of the brachial plexus.
| Nerve | Root Value | Function |
|---|---|---|
| Dorsal scapular nerve | C5 | Rhomboid muscles |
| Long thoracic nerve | C5–C7 | Serratus anterior |
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.
Each trunk divides into anterior and posterior divisions.
Although divisions do not give off branches, they reorganize to form the cords of the plexus.
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 |
| 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 |
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