Nerve Injuries

Question 1

How are nerve injuries classified?

Answer 1

4 Axonal reactions to injury

Transient ischaemic nerve blocks

No structural nerve damage, last only minutes

Neurapraxia

Damaged myelin with intact axon. Impulse conduction across the affected segment fails. Mild and reversible nerve injury. Recovery usually occurs in weeks to months and prognosis is good.

Axonotmesis

Complete disruption of the axon within an intact nerve sheath. Recovery and prognosis is variable (because complete recovery requires regeneration of the distal nerve, this is unlikely to happen)

Neurotmesis

Nerve is completely severed. There is complete destruction of all supporting connective tissue structures. Surgery may be required and prognosis is poor.

Question 2

What are the clinical tests associated with Carpel Tunnel Syndrome?

Answer 2

• Phalen’s test
  
  • Flexed elbows on table and wrists flexed and pushed together for 30-60 seconds.
  • This increases pressure on the median nerve in the carpel tunnel and so symptoms are exacerbated
• Tinel’s sign
  
  • Provocative tapping on the site of the median nerve in the tunnel to reproduce symptoms
• Carpel Tunnel Compression Test
  
  • Direct pressure over nerve in tunnel; symptoms within 30 seconds results in positive test. Better sensitivity than above tests.

Question 3

What peripheral nerve injuries may occur as a result of poor positioning on the operating table and how do you prevent these?

Answer 3

• ulnar nerve as it passes behind the medial epicondyle of the humerus
  
  • injury: paraesthesia and numbness of ring and little finger and medial border of hand
  • prevention: padding under arm and forearm, forearm in supination, avoid positioning of elbow in flexion for prolonged periods
• superficial peroneal nerve or common peroneal nerve (compressed against head of fibula)
  
  • injury: foot drop
  • prevention: padding at lateral aspect of fibula in lithotomy; avoid >2hrs in lithotomy; flexion of hip and knees results in stretching of sciatic nerve and minor degrees of external pressure are therefore likely to cause damage; if supine without heel supports leading to external rotation of lower leg
• sciatic nerve injury
  
  • prevention: avoid lithotomy positions that stretch hamstrings beyond comfortable range
• supraorbital nerve in prone position or by position of ET tube
  
  • injury:
  • prevention: pillow with ‘hole’ for face to minimise pressure
• posterior tibial nerve in lithotomy position
  
  • • prevention: ensure knee is well padded posteriorly and that yellowfins don’t press into popliteal fossa
• brachial plexus (traction injury)
  
  • prevention: abduction to 90 degrees is permitted provided the hand is pronated and the head turned towards the abducted arm - minimises tension on nerve roots
• femoral nerve
  
  • if pt slips cranially on bed whilst in lithotomy
  • fiex retractor in pelvis
  • excessive flexion in lithotomy
• median nerve if pt’s prone wrist hangs over end of operating bed/arm board, or excessive elbow extension from same
• radial nerve if arm abducted and externally rotated - avoid prolonged pressure on radial nerve in spiral groove

Question 4

Lithotomy position

Answer 4

Legs should be put up together, hips minimally flexed, knees in comfortable flexion to permit access, slight ext rotation with knees in mid ax line, padding on fibula heads

Arms should be on arm boards rather than at patient’s side to reduce risk of hand injury, make sure not squished under bottom or risk compartment syndrome

Question 5

Prone position

Answer 5

Pre-formed facial padding and arm gutters

avoid direct pressure on eyes to prevent retinal injuries

pillows/padding between hips and torso but allow free diaphragmatic movement

protect genitalia and breasts

arms carefully brought round and forward, placed with elbows comfortably flexed & hands pronated

careful padding for prevention of pressure areas on knees and toes

Question 6

What contributes to peripheral nerve injuries during surgery?

Answer 6

5 in vivo mechanisms: stretch, compression, generalised ischaemia, metabolic derangement, surgical section

• avoid hypotension (vasa nervorum sensitive)
• avoid prolonged tourniquet use
• metabolic disease common eg diabetes, nutritional problems, drugs, smoking, atherosclerosis
• increased risk with old age - reduced muscule bulk and subcut fat stores, and impaired tissue perfusion

Question 7

Supine

Answer 7

avoid pressure on ulnar groove, judivious use of elbow padding. Arm abduction should be limited to 90 degrees or less and forearm and hand supinated or kept neutral. Care with tucking arms - upper limb compartment syndromes have been described from excessive pressure to forearms and hands. Pad pressure areas like occiput, heels and sacrum.

Question 8

Dupuytren’s

Answer 8

• epidemiology
  
  • men>women
  • usu in 5th-7th decades
  • high incidence in northern Europeans
• aetiology
  
  • unknown
  • is an AD hereditary form
  • associated with but not caused by alcohol use and diabetes
  • other associations: DEAFEST PAIL - diabetes, epilepsy, age, family history, epileptic medication, smoking, trauma and heavy manual labour, Peyronie’s disease (fibrosis of corpus cavernosum), AIDs, Idiopathic, Liver disease
• clinical presentation
  
  • benign, slowly progressive thickening/contraction of longitudinal palmar fascia, forming nodules (usu painless), fibrous cords and eventually flexion contractures at the MCPJs & IPJs
  • flexor tendons not involved
  • order of digit involvement (most common to least common): ring > little > middle > thumb > index
  • may also involve feet (Lederhosen’s) and pensi (Peyronie’s)
  • stages of disease process:
    
    • palmar pit or nodule
    • palpable band/cord with no limitation of extension of eitehr MCP or PIP
    • lack of extension at MCP or PIP
    • irreversible periarticular joint changes/scarring
• pathogenesis
  
  • involves proliferation of fibroblasts (typically myofibroblasts) which have contractile properties) and disordered deposition of collagen causing thickening of the palmar fascia, which progresses to cause contractures of the MCP and PIPJs of affected fingers
  • nodules contain fibroblasts and type III collagen and are typical of teh early proliferative phase of the disease
  • increased fibrosis of overlying skin cause it to become attached, puckered and tethered to tendons below
• ddx: skin contracture, tendon contracture, trigger finger, ulnar nerve palsy, palmar fibromatosis
• management
  
  • non-operative
    
    • physio, stretching
    • local injections of triamcinolone acetonide into fibrous nodules may slow progression, and injection into synovial sheahts treat episodes of tenodynovitis; main complication is tendon rupture
  • operative
    
    • fasciotomy - transection of fibrous bands
    • partial fasciectomy (with Z-plasty to lengthen wound)
    • Dermofasciectomy (with full-thickness skin grafting)
    • arthrodesis/amputation - for late presentations and repeated recurrences

Question 9

Median nerve anatomy

Answer 9

• terminal branch of brachial plexus; takes divisions from lateral and medial cords to derive supply from C5-T1
• axillary artery clasped between the 2 roots of the median nere, the medial root crossing in front of the vessel
• nerve starts lateral to the artery, passes through arm in front of it and at elbow is medial to it
• descends between the two heads of pronator teres and passes deep to the fibrous arch of FDS
• emerges between FCR and PL before entering the carpal tunnel
• gives vascular (sympathetic) branches to the brachial artery & may give a branch to pronator teres above the elbow joint
• around the elbow joint gives branches to FCR, PL and FDS (however nerve to index finger part of this arises in middle of forearm)
• supplies elbow and prox radioulnar joints
• deep to FDS, gives off anterior interosseous branch which supplies FDP (bellies that move index and middle fingers), FPL, PQ and the inferior radioulnar, wrist and carpal joints
• in distal forearm, above flexor retinaculum, gives off palmar branch to skin over thenar muscles; pierces deep fascia just above flexor retinaculum
• in the hand
  
  • muscular recurrent branch supplies radial two lumbricals and the thenar muscles - LOAF (lumbricals, opponens pollicis brevis, abductor pollicis brevis, flexor pollicis brevis
  • palmar digital branches - supply flexor skin of radial 3.5 digits and nail beds and dorsal skin over distal and middle phalanges of these digits

Question 10

What does the median nerve supply

Answer 10

• most of the flexor muscles of the forearm but only the three thenar muscles and two lumbricals in the hand
• cutaneous to the flexor surfaces and nail beds of the 3.5 radial digits and a corresponding area of palm (but only autonomous area of median nerve supply are over the pulp pads of 2nd and 3rd digits)

Question 11

What is carpel tunnel syndrome?

Answer 11

• in the tightly crowded flexor tunnel the median nerve can be compressed by arthritic changes in the wrist joint, synovial sheath thickening or oedema
• direct pressure against the nerve assoc w ischaemia; initially temporary causing paraesthesia but w chronic compression can cause demyelination, Wallerian degeneration and permanent loss of function of nerve segment
• impaired sensation/aching/burning over 3.5 digits on thumb side of hand (worse at night)
• in late cases, wasting and weakness of thenar muscles
• no sensory loss over tehnar eminence itself - this area of skin is supplied by palmar branch of median nerve, which enters palm superfiical to retinaculum so escapes compression
• ddx: median nerve damage at a higher level, in which case palmar cutaneous branch will be affected + weakness of relevant flexor muscles in forearm (eg FPL); in carpal tunnel syndrome the terminal phalanx of thumb can be flexed w normal power but w higher lesions this power is lost
• surgical division of retinaculum relieves pressure and symptoms
• risks:
  
  • median nerve injury
  • injury to cutaneous branch of median nerve (sensory to thenar eminence)
  • injury to recurrent branch of median nerve (Motor supply to thenar muscles)
  • damage to superficial palmar arch (blood supply to hand)
  • injury to ulnar nerve as it passes through flexor retinaculum in Guyon’s canal - if incision too far towards ulnar side

Question 12

Consequences of median nerve injury

Answer 12

• at wrist:
  
  • loss of sensation over pulp pads of index and middle fingers
  • can’t abduct thumb –> in longstanding cases thenar eminence wasting
• proximal to midforearm
  
  • wasting of front of forearm bc long flexors (except FCU and half of FDP)
  • pronators paralysed
  • hand held with index finger straight in ‘pointing finger’ position, often w all other fingers flexed incl middle finger (though part of FDP to middle finger tendon usu has a median supply, its close connection w the part supplied by the ulnar nerve can lead to middle finger flexion)
    
    • branch to index finger part of FDS arises near mid-forearm rather than in cubital fossa

Question 13

Ulnar nerve injuries

Answer 13

• most commonly injured behind elbow or at wrist
  
  • can be compressed in cubital tunnel formed by tendinous arch connecting humeral and ulnar heads of FCU - may require division of aponeurotic ulnar origin of muscle & ant submuscular transposition of nerve
• low lesion
  
  • CLAW hand - hyperextension of MCPJs of ring & little fingers and flexion of IPJs bc their interossei and lumbricals are paralysed so can’t flex MCPJs or extend IPJs
    
    • claw produced by unopposed action of finger extensors and FDP
• injury at elbow
  
  • straighter fingers (‘ulnar paradox’) bc ulnar half of FDP gone so can’t flex DIPJs of ring and little fingers
• guttering between metacarpals
• variable sensory loss on ulnar side of hand and on little and ring fingers but often less than expected

Question 14

Radial nerve injuries

Answer 14

• most commonly high from fractures of shaft of humerus
  
  • also transient paralysis from improper use of crutch pressing on nerve in axilla or Saturday night palsy
• WRIST DROP - unable to exted wrist and MCPJs (but IPJs can still be straighted by action of interossei adn lumbricals)
• minimal sensory loss usually just over first dorsal interosseous
• with high injuries in axilla - triceps paralysis so weak elbow etension (this doesn’t occur after humeral shaft fracture)