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AN10.1-13 | Axilla, Shoulder and Scapular region — Part 3

Klumpke's Paralysis — The Claw Hand (AN10.6)

When the lower trunk of the brachial plexus (C8, T1) is injured, it's called Klumpke's paralysis. This is less common than Erb's palsy.

How does it happen?
• Grabbing a tree branch or railing during a fall (the arm is forcibly abducted and the lower trunk is stretched)
• In newborns: a breech delivery where the arm is pulled upward
• Cervical rib compressing the lower trunk

The injury damages nerves that supply the small muscles of the hand (intrinsic hand muscles via T1) and the long flexors of the fingers (via C8).

The result — the "claw hand":
• The hand has a clawed appearance — hyperextension at the metacarpophalangeal joints with flexion at the interphalangeal joints (because the lumbricals and interossei are paralysed)
• Loss of grip strength
• Sensory loss over the medial side of the hand and forearm
• If T1 is involved: Horner's syndrome may occur (because T1 carries sympathetic fibres to the eye) — ptosis (drooping eyelid), miosis (constricted pupil), and anhidrosis (loss of sweating on that side of the face)

Compare and contrast:
• Erb's palsy = upper trunk (C5,C6) = shoulder/elbow affected, hand spared
• Klumpke's paralysis = lower trunk (C8,T1) = hand affected, shoulder spared

Brachial plexus diagram with lower trunk (C8-T1) highlighted showing nerve root anatomy — click to enlarge

SELF-CHECK

A newborn delivered after shoulder dystocia presents with the right arm adducted, medially rotated, elbow extended, and forearm pronated. The hand grip is preserved. Which part of the brachial plexus is most likely injured?

A. Lower trunk (C8, T1)

B. Upper trunk (C5, C6)

C. Posterior cord

D. All five roots

Reveal Answer

Answer: B. Upper trunk (C5, C6)

This is the classic 'waiter's tip' position of Erb's palsy — injury to the upper trunk (C5, C6). The shoulder and elbow are affected but the hand is spared. Key clue: hand grip is preserved (C8, T1 intact). Shoulder dystocia causes traction on the upper trunk as the head is pulled away from the trapped shoulder.

CLINICAL PEARL

Birth injuries to the brachial plexus occur in approximately 1–2 per 1000 births. Risk factors include macrosomia (large baby, >4 kg), shoulder dystocia, prolonged labour, and instrumental delivery. In India, where home deliveries and delayed referrals still occur in rural areas, brachial plexus injuries are an important cause of disability. Most neonatal Erb's palsy (80–90%) recovers spontaneously within 3–6 months. If there's no recovery by 3 months, nerve surgery (nerve grafting or nerve transfer) should be considered. Klumpke's paralysis has a poorer prognosis because the small hand muscles, once denervated, don't recover as well.

The Big Movers — Trapezius and Latissimus Dorsi (AN10.8)

Two large, flat muscles dominate the back and contribute to shoulder movements. You can feel both on your own body right now.

Trapezius — the diamond-shaped muscle covering the upper back. Place your hand on your opposite shoulder and shrug — you're feeling trapezius contract.

Origin: skull (superior nuchal line), ligamentum nuchae, spinous processes of C7–T12
Insertion: clavicle (lateral third), acromion, spine of scapula
Action: Upper fibres = elevate scapula (shrugging), middle fibres = retract scapula (squeezing shoulder blades together), lower fibres = depress scapula
Nerve supply: Spinal accessory nerve (CN XI) + C3, C4 (proprioception)

Latissimus dorsi — the broadest muscle of the back ('latissimus' = widest). It wraps from the lower back to the arm.

Origin: spinous processes of T6–T12, thoracolumbar fascia, iliac crest, lower 3–4 ribs
Insertion: floor of intertubercular sulcus (bicipital groove) of humerus
Action: extension, adduction, and medial rotation of the arm. The climbing muscle — pull your body up with your arms and latissimus dorsi does most of the work
Nerve supply: Thoracodorsal nerve (C6, 7, 8 — from the posterior cord)

Both muscles are superficial — you can see them clearly on a muscular person. They move the scapula and arm respectively in powerful, gross movements.

IMAGE PLACEHOLDER

Posterior view showing trapezius (diamond shape, skull to T12) and latissimus dorsi (broad triangle, T6 to humerus), with origins, insertions, and nerve supply labels

The Rotator Cuff — SITS Muscles (AN10.9, AN10.10)

The shoulder joint is the most mobile joint in the body — but this mobility comes at a cost: stability. Unlike the hip (where the ball sits deep in a socket), the shoulder's humeral head sits on a shallow glenoid cavity, like a golf ball on a tee.

What keeps the ball on the tee? The answer is the rotator cuff — four muscles whose tendons blend with the shoulder joint capsule, forming a 'cuff' that holds the humeral head firmly against the glenoid.

Remember them with the mnemonic SITS (from top to bottom around the scapula):

Supraspinatus — sits above the spine of the scapula
Action: initiates abduction (first 0–15°), then deltoid takes over
Nerve: suprascapular nerve (C5, C6)
This is the most commonly torn rotator cuff muscle

Infraspinatus — sits below the spine of the scapula
Action: lateral (external) rotation of the arm
Nerve: suprascapular nerve (C5, C6)

Teres minor — small muscle below infraspinatus
Action: lateral rotation (assists infraspinatus)
Nerve: axillary nerve (C5, C6)

Subscapularis — fills the subscapular fossa (front of the scapula)
Action: medial (internal) rotation of the arm
Nerve: upper and lower subscapular nerves (C5, C6)

Key concept: three of the four SITS muscles rotate the arm laterally (supraspinatus helps, infraspinatus and teres minor are the main lateral rotators), while only subscapularis rotates medially. This imbalance matters: when the rotator cuff is torn (usually supraspinatus), the arm can't initiate abduction properly — the painful arc of a rotator cuff tear.

Cross-sectional comparison of shoulder joint (shallow glenoid) versus hip joint (deep socket), illustrating structural stability differences — click to enlarge