Median Nerve and Median Nerve Neuropathy (Benediction, AIN S, CTS) Flashcards
What are the possible 3 sites of median nerve neuropathy?
- At or below elbow - Cubital fossa syndrome with Hand of Benediction
- Supracondylar humerus fracture
- Ligament of Struthers compression
- Iatrogenic surgery
- Pronator teres compression - Forearm - AIN syndrome
- Forearm laceration, inflammation, compressive disease - Wrist - Carpal tunnel syndrome
- Increased risk in pregnancy, DM, acromegaly
Median nerve and branches
- Roots: C6 to T1 (+/- C5)
- Enters anterior compartment of forearm via cubital fossa
- Pronator teres
- Palmaris longus
- Flexor digitorum superficialis (FDS)
- Flexor carpi radialis (FCR) - Branches into anterior interosseous nerve (AIN)
- Flexor digitorum profundus (FDP) lateral half
- Flexor pollicis longus (FPL)
- Pronator quadratus
3A. Palmar cutaneous branch branches off before enter carpal tunnel
- Enters hand beneath flexor retinaculum via carpal tunnel
- Recurrent branch - thenar muscle (abductor pollicis brevis (APB), opponens pollicis (OP), flexor pollicis brevis (FPB)
- Palmar digital branch - lateral 2 lumbricals, sensation over palmar surface and fingertips of lateral 3 and 1/2 digits
Motor function of median nerve
Anterior forearm
1. Pronator teres - forearm pronation
2. FCR - wrist flexion
3. Palmaris longus - minor wrist flexion
4. FDB - all PIPJ flexion
5. AIN
5A. FDP lateral half - index and middle finger DIPJ flexion
5B. FPL - Thumb IPJ flexion
5C. PQ - minor forearm pronation
Hand (mnemonic: LOAF)
1. Lateral 2 lumbricals - index and middle finger MCPJ flexion, extension of IPJs
2. OP - thumb opposition
3. APB - thumb abduction
4. FPB - thumb MCPJ flexion
Sensory function of median nerve
Sensation over the hands
1. Palmar cutaneous branch before carpal tunnel
- Lateral palmar region (thenar eminence)
–> Spared in CTS
- Palmar digital branch
- Lateral palm (excluding thenar eminence)
- Ventral surface of lateral 3 and 1/2 fingers
- Palmar surface and tips of lateral 3 and 1/2 fingers
(Thumb, index, middle and lateral half of ring finger)
No contribution of arm and forearm sensation
Examination of median nerve
A. Inspection
Muscle wasting of thenar eminence only
(Concomitant hypothenar eminence wasting unlikely pure median nerve neuropathy! (innervated by ulnar nerve)
B. Screening
1. Clench a fist - Hand of Benediction (cubital tunnel syndrome)
- OK sign (tests AIN)
- Positive: volar surface of distal phalanges come into contact instead of fingertip - Carpal tunnel syndrome
- Phalen: flex wrist for 30-60s for numbness/tingling
- Tinel: tap wrist over flexor retinaculum
C. Motor function
1. Pronator teres - Elbow flexed at 90 degree, pronate forearm against resistance
2. FDS - Flex fingers at PIPJ against resistance
3. FDP lateral half - Index and middle finger DIPJ against resistance
4. APB - Abduct thumb against resistance
5. Thumb opposition with little finger
D. Sensation over specific sites
- Test in between ring fingers
- Test thenar eminence (spared in CTS, affected in AIN)
High median nerve neuropathy (elbow) / Cubital fossa syndrome
- Cause: supracondylar humeral fracture, trauma
- Sign: Hand of Benediction
Attempts at making a fist results in Hand of Benediction
- Impaired all finger PIPJ flexion (FDS), with profound index and middle finger flexion defect (lateral FDP)
Motor weakness
1. Forearm pronator weakness
2. Wrist flexion weakness (FCR)
3. All PIPJ flexion weakness (FDS)
4. Index and middle finger DIPJ flexion weakness (lateral FDP)
Sensory deficit
1. Lateral palm and thenar eminence numbness (AIN + digital branch)
2. Ventral, palmar and fingertip of lateral 3 1/2 fingers numbness
What is pronator syndrome?
Compression of median nerve when it passes through 2 heads of pronator teres just distal to elbow
Presents with pain over volar surface of forearm after sustained pronation
AIN syndrome
- Cause: forearm laceration, inflammation, compressive disease
- Sign: OK sign defect, pure motor weakness
OK sign defect, or positive pinch sign
- Unable to oppose thumb and index finger tip
Straight thumb sign
- Thumb IP joint fail to flex on grasping object
Pure motor weakness
1. +/- sparing of pronators (pronator quadratus)
2. Index and middle finger DIPJ flexion weakness (lateral FDP)
3. Thumb IPJ flexion weakness (FPL)
No sensory deficit
- Unless injury to palmar cutaneous branch (that branches before flexor retinaculum), which results in thenar eminence numbness
Carpal tunnel syndrome
- Increased risk in pregnancy, DM, acromegaly
Thenar eminence wasting with SPARING of hypothenar eminence
Motor weakness
1. Thenar muscle weakness - thumb flexion, abduction and opposition
2. Lateral 2 lumbricals weakness - index and middle finger MCPJ flexion
Sensory deficit
3. Ventral, palmar and fingertip of lateral 3 1/2 fingers numbness
4. Sparing of thenar eminence - sensation intact
Specific signs
5. Tinel’s sign
6. Phalen’s sign
Very relevant negatives
7. Wrist flexion is NORMAL
8. Distal thumb flexion, arm pronation is NORMAL
How common is carpal tunnel syndrome?
9% in females
0.6% in males
Consolidating the causes of median nerve palsy (not location specific)
- Acromegaly - look for prominent supraorbital ridges, enlarged nose, prognathism, macroglossia, bitemporal hemianopia
- RA - arthropathy, nodules, eye signs
- Trauma - old fractures, surgical scars over elbow
- Hypothyroidism - goitre, thyroidectomy scars, hypothyroidism features
- Amyloidosis - macroglossia, thickened/palpable nerve
- Gout - tophi over hands, feet, ears
- CKD/ESRF - RRT evidence
- Diabetes - finger prick tests, retinopathy
- Paget’s disease - skull enlargement, hearing aid, anterior bowing of tibia
- Idiopathic - middle aged, obese female (check occupational history)
Pathophysiology of carpal tunnel syndromw
- Local and systemic cause of raised pressure in carpal tunnel
- Normal: 2mmHg
- At 20mmHg, impedes epineural blood flow in median nerve
- At 30mmHg, impairs axonal conduction
- At 40mmHg, evident sensory and motor symptoms
- At 50mmHg, epineural oedema, inflammation and injury -> protein leak and further vicious cycle
- At 60mmHg, complete stop of blood flow - Segmental demyelination, axonal loss and irreversible nerve dysfunction in prolonged elevated pressures
Investigations for Carpal Tunnel Syndrome
- Nerve conduction study
- Reduced conduction velocity of both motor and sensory
- Sensory latency > 3.5ms; motor latency > 4.5ms
(Unilateral - compare discrepancy, sensory > 0.5ms; motor latency > 1ms) - Electromyography of abductor pollicis
- Positive sharp waves and fibrillation potentials in CTS
Management of Carpal Tunnel Syndrome
- Multidisciplinary team involvement
- Physiotherapy and hand occupational therapy
- Hand and microsurgery - Wrist splint 30 degree extension - temporary relief
- Local steroid injection
- Diuretics (temporary relief)
- Carpal tunnel decompression
