MSK L5.1 Brachial Plexus

Question 1

Axilla

Answer 1

Question 2

Boundaries of the axilla

Answer 2

Borders (Key Muscular Boundaries)

Anterior Border: Pectoralis major and minor

Posterior Border: Subscapularis, Teres major, Latissimus dorsi

Medial Border: Serratus anterior and thoracic wall

Lateral Border: Intertubercular sulcus of humerus

💡 What runs through the intertubercular sulcus?
→ Tendon of the long head of biceps brachii

Question 3

Upper limb blood supply
Which artery perfuses the upper limb?
Which artery runs with axillary nerve?
Which artery runs with median and ulnar nerves?
Which artery runs with radial nerve?
Which artery is at risk of mid-shaft humerlal fractures?

Answer 3

Subclavian artery perfuses upper limb.

1. Subclavian ArteryPasses behind the medial 1/3 of the clavicleBecomes the axillary artery after crossing rib 1
2. Axillary ArteryContinuation of subclavian arteryRuns from 1st rib to teres majorBecomes the brachial artery after passing below teres majorLies posterior to the medial clavicle (palpable)Rich anastomoses with subclavian artery via scapular arteriesDivided into 3 parts (not detailed in slides but useful for exams)
3. Brachial ArteryContinuation of axillary arteryRuns medial to humerus and biceps tendonPulse palpable in medial arm and cubital fossaCan be auscultated & catheterisedGives off profunda brachii artery

Question 4

What is lymphatic drainage?

Answer 4

• Immune sysem
• Infection protection
• Cleans up waste
• Finds + destroys abnormal cells (cancer cells)

Question 5

Lymph nodes
Lymphadenopathy

Answer 5

Lymphadenopathy:
* swollen or enlarged lymph nodes

Question 6

Axilla
What do the axillary nodes drain?

Answer 6

Question 7

1) How is the upper limb innervated?

2) Spinal cord orignins of brachical plexus

Answer 7

Question 8

Scalenus Medius Muscle
Scalenus Anterior Muscle

Answer 8

Brachial plexus comes out between these two muscles

Question 9

Brachical Plexus

Answer 9

C5 and C6 join
C7 on its own
C8 and T1 join

Long thoracic nerve - supplies seratus anterior muscle, which rotates scapula.

ALL POSTERIOR BRANCHES FROM ALL TRUNKS JOIN TOGETHER

Anterior brancghes from superior and middle trunks join together

Anterior branch from inferior trunk stays on its own

Cords are important, can get damaged, they are found around the axillary artery. “Lateral, posterior, medial” - that is where they are in relation to the axillary artery.

Watch L5.1 31.40]

2 branches, lateral and medial cords come together to form median terminal nerve

Question 10

BRACHIAL PLEXUS M

Answer 10

Middle of M = medial nerve.
Use this as guide
Most lateral nerve of M = musculocutaneous. Most medial = ulnar
Radial nerve, behind median, closer to medial side of body, goes down back of the arm as its from posterior cords.

Question 11

1) Cords are named in relation to which artery?
2) Radial nerve is derived from which cord?
3) Ulnar nerve is derived from which cord?
4) Median nerve is derived from which cords?

Answer 11

Question 12

What happens when damage to:
1) Musculocutaneous nerve?
2) Median nerve?
3) Radial nerve?
4) Ulnar nerve?
5) Axillary nerve?

Answer 12

Question 14

Cadaver image of brachial plexus

Answer 14

Question 15

Extra branches coming off brachial plexus

Answer 15

KNOW THE RED
Inferior part of brachial plexus can get damaged by things in chets, pancoast tumour, lung cancer high in Apex of lungs.

Question 16

Brachial Plexus Nerve Root Values

Answer 16

Question 17

How can a penetrating neck injury affect the brachial plexus?

Answer 17

Brachial Plexus Roots originate in the neck C5-T1

Question 18

Dermatome and Peripheral Nerve Sensory Areas

Answer 18

Question 19

Brachial Plexus Injuries

Answer 19

⚙️ What’s Affected?

Motor (muscle) and sensory (feeling) functions.

Injury → imbalance → abnormal limb resting position (due to unopposed working muscles).

📍 Location of Injury:

Can affect either:

    Upper brachial plexus (C5-C6)

    Lower brachial plexus (C8-T1)

❗ Common Causes (Mnemonic: D-S-W-T):

Disease

Stretching (e.g. during birth or sudden arm traction)

Wounds (e.g. penetrating injuries)

Trauma (e.g. road traffic accidents, falls)

🩻 Key Concept:

Injury may not paralyze all muscles — remaining ones pull the limb into a different resting posture.

Question 20

Injury to upper part of brachial plexus

Answer 20

C5-C6
Excessive increase in angle between neck and shoulder (excessive lateral stretching)
Biking injury
Newborn - excessive stretching during delivery

Question 21

Injury to lower part of brachial plexus

Answer 21

🩺 Klumpke’s Palsy – Key Revision Notes
📍 Cause:

Injury to lower brachial plexus (C8 & T1 roots)
Much less common than upper plexus injury.
❗ Mechanisms (How it happens):

Upward traction of arm (e.g. falling while grabbing a ledge)

Pancoast tumor (apical lung cancer compressing lower plexus)

Cervical rib compressing nerves

Birth injury with arm pulled upward

🧠 Motor Deficit:

Paralysis of intrinsic hand muscles

Weak grip

Finger abduction/adduction lost

✋ Classic Sign:

Claw hand deformity

Hyperextended MCP joints

Flexed IP joints (especially 4th & 5th fingers)

🧪 Sensory Deficit:

Loss along medial arm & hand (C8–T1 dermatomes)

🔑 Mnemonic:

"Klumpke = Claw"

Question 22

Thoracic Outlet Syndrome

Answer 22

🧠 Definition:

Neurovascular compression of the brachial plexus and/or subclavian vessels as they pass through the thoracic outlet (between neck and shoulder).

⚠️ Causes:

Cervical rib (extra rib compressing nerves/vessels)

Hyperabduction of shoulder
→ e.g. sleeping with arm over chair: “Saturday night palsy”

Poor posture or heavy backpacks

📍 Structures at risk:

Lower trunk of brachial plexus (C8–T1)

Subclavian artery or vein

❗ Clinical Signs (for deeper study):

Numbness or tingling in the hand

Weak grip

Swelling or discoloration of the arm (if vascular)

🧠 Mnemonic:

"TOS = Tight Outlet Space"