Brachial Plexus Test

The Brachial Plexus Compression Test, also called Morley’s Compression Test is employed for the assessment of thoracic outlet syndrome which produces tenderness at the basis of the neck when pressure is placed over the neurovascular (the plexus brachialis and therefore the subclavian vessels) structures within the area of the brachial plexus can be palpated in the lower portion of the posterior triangle, between the clavicle and the trapezius muscle. The 5 terminal branches of the brachial plexus are the musculocutaneous, median, ulnar, axillary, and radial nerves.

Exam of the adult plexus brachialis is vital within the localization of the extent of the injury also as determining if the nerve injury is spontaneously recovering. Conventions of manual muscle grading, measurement of range of motion, evaluation of the patient by observation, and methods of examination

Structure

The plexus brachialis is made by the anterior primary rami of C5 through T1 and provides sensory and motor innervation of the upper extremity. The plexus brachialis is split, proximally to distally into rami/roots, trunks, divisions, cords, and terminal branches. The trunks are often found within the posterior triangle of the neck, between the anterior and middle scalene muscles. The plexus brachialis, alongside the arteria axillaris, is often considered as an outsized neurovascular bundle that travels within the axilla to provide the upper extremity.

The plexus brachialis provides somatic motor and sensory innervation to the upper extremity, including the scapular region. because the plexus brachialis travels through the posterior triangle of the neck into the axilla, arm, forearm, and hand, it contains various named regions that supported how the plexus is made. Ventral rami from spinal nerves C5 through T1, often mentioned as roots of the plexus brachialis, close to permit their fibers to intermingle forming superior, inferior, and middle trunks.

The 3 trunks continue from the posterior triangle into the axilla with C5 and C6 roots forming the superior trunk, C8 and T1 roots forming the inferior trunk, and therefore the C7 root continuing because of the middle trunk.

Continuing from the trunks are bundles that are called divisions. Each of the trunks of the plexus brachialis continues as an anterior and posterior division to make lateral, posterior, and medial cords.

The 3 cords (posterior, medial, and lateral) are formed from the anterior and posterior divisions, and they are named to support their relationship to the two parts of the arteria axillaris. the three posterior divisions converge to make the posterior cord while the anterior division from the superior trunk and therefore the anterior division from the center trunk join to make the lateral cord. The medial cord is made as a continuation of the anterior division from the inferior trunk. The results of this “mixing” of nerve fibers are that the lateral cord contains components of C5, C6, and C7, the medial cord with contribution from C8 and T1, and therefore the posterior cord carrying fibers from all levels of the plexus brachialis (C5 to T1).

The final subdivision of the plexus brachialis consists of 5 terminal branches containing different contributions from the C5-T1 spinal levels.

The branches, terminal and otherwise, of the plexus brachialis are expanded on below within the section Nerves and Muscles.

Clinical Examination of the Brachial Plexus by

BRACHIAL PLEXUS ANATOMY:

SEQUENCE (MNEMONIC): Robert Taylor Drinks Cold Beer = Rami, Trunks, Divisions, Cords & Branches

POSITIONS:

  • The roots and trunks lie in the posterior triangle of the neck
  • The divisions are deep to the clavicle
  • The cords are posterior to the pectoralis minor
  • Terminal branches begin in the axilla.

ROOTS (5)

  • Are formed by the ventral rami of spinal nerves C5-C8 and T1.

TRUNKS (3)

  • The 5th and 6th cervical roots join to form the upper trunk.
  • The 7th cervical root forms the middle trunk.
  • The 8th cervical and 1st thoracic roots join to form the lower trunk.

DIVISIONS (6)
Each trunk divides into an anterior and a posterior division.

CORDS (3)

  • The three posterior divisions join to form the posterior cord.
  • The anterior divisions of the upper and middle trunk unite to form the lateral cord.
  • The anterior division of the lower trunk continues alone as the medial cord.

BRANCHES

  • Branches come from the rami, the trunks, and the cords; usually, no branches originate from the divisions.
  • The upper trunk is formed by the fusion of ventral rami C5 and C6, therefore it carries nerve fibers from C5 and C6. The middle trunk carries only C7 fibers. The lower trunk carries both C8 and T1 fibers as a result of the fusion of ventral rami of C8 and T1.
  • Since the posterior divisions of all the trunks (upper, middle, and lower) join to form the posterior cord, it carries fibers from C5, 6, 7, 8, and T1. The lateral cord is formed from anterior divisions of the upper (C5, 6) and middle (C7) trunks. Therefore, it carries fibers from C5, 6, and 7. The medial cord is formed from the anterior division of only the lower trunk, thus it carries fibers from C8 and T1.
  • The fibers carried in any named branch will be determined by which part of the plexus they originate from and what fibers that particular part is carrying. Any combination of fibers carried in a part can be carried by a branch from that region. (Example: the posterior cord carries C5, 6, 7, 8 and T1 but the axillary nerve carries only C5 and C6 fibers.)

Branches from Roots of the plexus

  • Branch to the phrenic nerve (C5)
  • The dorsal scapular nerve (C5) innervates rhomboideus major and minor and gives a branch to levator scapulae.
  • The long thoracic nerve (nerve to the serratus anterior) (C5,6,7) may be involved in supraclavicular and axillary wounds, neck blows or compression resulting from carrying excess weight on the shoulder. Paralysis of the serratus anterior causes “winging” of the scapula when the arm is flexed and pressed against a fixed object. There is also difficulty in abducting the shoulder above the horizontal position due to a decreased ability to rotate the glenoid fossa upward.

Branches from Trunks

  • Nerve to the subclavius (C5,6) from the upper trunk
  • Suprascapular nerve (C5,6) from the upper trunk innervates supraspinatus and infraspinatus.

Branches from Divisions

  • Usually none

Branches from Cords

  • Lateral Cord
    • The lateral pectoral nerve (C5,6,7) innervates the pectoralis major (clavicular or upper head) and pectoralis minor.
    • The lateral root of the median nerve (C6,7) contributes to the median nerve.
  • Posterior Cord
    • The upper subscapular nerve (C5,6) innervates the upper part of the subscapularis.
    • Thoracodorsal nerve or nerve to the Latissimus dorsi (C5,6,7) innervates the latissimus dorsi.
    • The lower subscapular nerve (C5,6) innervates the lower part of the subscapularis and the teres major.
  • Medial Cord
    • The medial pectoral nerve (C8, T1) innervates the pectoralis major and pectoralis minor.
    • The medial cutaneous nerve to the arm (medial brachial cutaneous) (C8, T1) innervates the medial portion of the arm.
    • The medial cutaneous nerve to the forearm (medial antebrachial cutaneous) (C8, T1) innervates the medial half of the forearm.
    • The medial root of the median nerve (C8, T1) contributes to the median nerve.

Terminal Branches (5)

  • Musculocutaneous nerve (C5,6,7)
  • Median nerve (C6,7,8, T1)
  • Ulnar nerve (C8, T1)
  • Radial nerve (C5,6,7,8,T1)
  • Axillary nerve (C5,6)

 Note that all branches from the medial cord carry C8, T1 fibers and that the higher spinal segments in the brachial plexus (C5-C6) tend to innervate muscles more proximal on the upper extremity whereas the lower segments (C8, T1) tend to innervate more distal muscles such as those in the hand. (T1).

Top Tips

  • Have a quick glance at the hand which would give you clues as to whether this is partial palsy (good hand) or total palsy (poor hand).
  • A totally flail arm and hand represent total palsy.

An examiner’s favourite – Is it a pre-ganglionic or post-ganglionic lesion?

The following are clues to a pre-ganglionic injury that you may identify and mention to the examiners in order to demonstrate your higher order thinking:

  • Horner’s syndrome
    • Partial ptosis of the upper eyelid
    • Miosis (constricted pupil)
    • Anhidrosis (loss of sweating on one half of the face)
    • Enophthalmos (eye appears sunken)
  • The T1 root lies close to the T1 sympathetic ganglion. Evidence of injury to the T1 sympathetic chain as evidenced by a Horner’s syndrome would infer that the T1 root has probably been injured.
  • If rhomboids or serratus anterior are weak then a pre-ganglionic injury should be suspected.
  • If chest X-ray is shown, look for elevated (paralysed) hemi-diaphragm (phrenic nerve palsy C3,4,5).
  • Fractures of the transverse processes of the cervical vertebrae or a fractured first rib indicate a high-energy injury with likely intradural injury of the lower two roots.
  • Scapulothoracic dissociation is often associated with root avulsion and major vascular injury.

Suggested Sequence of Clinical Examination

(You may be requested to demonstrate part of the whole sequence only)

  • Inspection
    • Best to start with the patient stood with both arms and torso exposed.
    • Look at the face for Horner’s syndrome
    • Look for surgical scars
    • Comment on muscle wasting – shoulder girdle, arm, forearm or hand
    • Comment on the resting posture of the limb
  • Exclude fixed contractures by gentle passive movements.
  • Motor testing
    • Requires knowledge of the Medical Research Council (MRC) grading
      • 0 – No Contraction
      • 1 – Flicker
      • 2 – Active motion (gravity eliminated)
      • 3 – Active motion (against gravity only)
      • 4 – Acitve motion (against resistance)
      • 5 – Normal power
    • If a muscle is weak, repeat testing in the horizontal plane in order to eliminate gravity eg abducting the shoulder to test elbow flexion/extension power.
    • Muscle testing is an active process involving
      • Look (for contraction and movement of the limb)
      • Feel (for contracted muscle/tendon)
      • Move (to test resistance)
    • Be systematic. Start proximally and work distally

      Standing from the back

      • Trapezius (spinal accessory – XI, C3,4)
        • Can you shrug your shoulders
      • Rhomboids (dorsal scapular nerve – C4,5)
        • Push your shoulder blades together
      • Serratus anterior (long thoracic nerve – C5,6,7)
        • The classic test is wall-press test.
        • In BPI, the patient may be unable to lift the arm.
        • The arm should be supported by the examiner with one hand and the patient asked to push forward as if trying to open a door. At the same time the examiner should hold the lower pole of the scapula with another hand.
      • Latissimus dorsi (thoracodorsal nerve – C6,7,8)
        • While the arm is supported in a flexed position, ask the patient to push down (while the examiner palpates for musle contraction).
      • Deltoids (axillary nerve – C5,6)
        • Extend, abduct and flex the shoulder to test the posterior, middle and anterior parts respectively (unless the muscle is clearly wasted).
        • Demonstrate specific signs (if isolated nerve palsy suspected):
          • Swallow-tail sign
            • The patient is asked to extend the shoulder while bending the trunk forward. A result of 20˚ or greater of extension lag relative to the normal side indicates a positive sign.
          • Abduction internal rotation
            • Actively and maximally abduct the shoulder in internal rotation with the elbow flexed. Abduction lag relative to the normal side indicates a positive sign.

      Standing from the front

      • Pectoralis major (lateral and medial pectoral nerves)
        • Clavicular head (C5,6)
          • Atrophy would imply lateral cord injury.
          • Ask the patient to touch their contralateral shoulder (and the examiner palpates for evidence of contraction).
        • Sternocostal head (C7,8,T1)
          • Atrophy would imply medial cord injury.
          • Ask the patient to push against the hip (and the examiner palpates the axillary fold).
      • Rotator cuffs
        • Supraspinatus (suprascapular nerve – C5,6)
          • Test shoulder abduction in the scapular plane with the thumb pointing downwards.
        • Infraspinatus (suprascapular nerve – C5,6)
          • Test external rotation with the shoulder in adduction and the elbow flexed.
        • Teres minor (axillary nerve – C5,6)
          • Test external rotation with the shoulder in abduction and the elbow flexed.
        • Subscapularis (upper and lower subscapular nerves – C5,6,7)
          • Belly-press sign. Ask the patient to bring the elbows forward while pressing the belly. A flexed wrist relative to the normal side indicates a positive sign.

        Next, proceed with the following composite testings to demonstrate the myotomes (levels) involved (accept some degree of variability):

      • Elbow flexion (C5,6)
      • Elbow extension (C7,8)
      • Forearm supination (C6)
      • Forearm pronation (C7,8)
      • Wrist flexion/extension (C6,7)
      • MCPJ flexion/extension (C7,8)
      • Grip (C8)
      • Fingers abduction (T1)
  • Sensory testing
    • Establish normal sensation in an uninjured area (such as the forehead or sternum).
    • First, assess the dermatomes (C5-lateral elbow; C6-thumb tip; C7-middle fingertip; C8-little fingertip; T1-medial elbow) and then if necessary such as in infraclavicular BPI, examine according to the terminal branch distribution.
  • Check for Tinel’s signs (and take note of the dermatomal distribution).
  • Palpate for the radial pulse and check the reflexes.

References