MEDIAN NERVE COMPRESSION - DNB Orthopaedics MS Orthopedics MRCS Exam GUIDE - Orthodnb.com

DNB Orthopaedics  MS Orthopedics  MRCS Exam GUIDE - Orthodnb.com

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Tuesday 5 June 2018

MEDIAN NERVE COMPRESSION

MEDIAN NERVE COMPRESSION ABOUT ELBOW



Anatomy
  • lateral cord of brachial plexus – fibers from C6, C7, C8, T1
  • lateral cord – provides sensory axons form C6, C7
  • medial cord – contribute to bulk of motor output through C8, T1
  • median nerve courses lateral and superficial to brachial artery – middle of arm – crosses over the artery to lie medial of artery – pass under bicipital aponeurosis together – enter antecubital region medial to biceps tendon and anterior to brachialis – passes beneath the superficial head and above the deep head of pronator teres – passes between humero ulnar and radial portions of FDS – further down the forearm under the belly of FDS – lie over the FDP at its lateral side
  • last branch of median nerve in forearm – AIN – departs from median at 4cm distal to medial epicondyle – passes under the fibrous tissue originating from FDS or PT – along the interosseous membrane between FDP and FPL along with ant interosseous artery– terminates in distal part of forearm – deep to PQ – innervates FDP to index, FPL, PQ
  • autonomous zone of median nerve – palmar surface of index and middle finger and dorsal distal to DIP
  • median nerve compression at elbow
    • Anterior Interosseous Nerve syndrome (motor palsy)
    • Pronator syndrome ( pain and paraesthesia)
ANTERIOR INTEROSSEOUS NERVE SYNDROME ( KILOH NEVIN SYNDROME)

Pathophysiology and Anatomy
  • br of median – entirely motor
  • give br to FPL and FDP at 4cm distal to its origin
  • compression cause by
    • deep head of PT, FDS
    • acc. Muscles eg. Gantzer's muscle, acc. FPL
    • aberrant vessels eg. Anomalous radial artery
    • tendinous bands
Clinical evaluation
  • Symptoms
    • vague pain proximal forearm, wrist – in rest and increased by activities
    • no sensory deficit
    • difficulty in writing, weakness in tip pinch
  • Signs
    • weakness or paralysis of muscles innervated by AIN
    • FPL and radial half FDP – can not pinch thumb and index finger – compensate with key pinch ( thumb adductor and I dorsal interosseous by ulnar N)– OK sign of Kiloh Nevin
    • hyperextension attitude of DIP of thumb and index – Fist sign
    • elbow flexed (stronger PT neutralized) – cant pronate against resistance – PQ weakness
  • Martin Gruber connection – median to ulnar motor nerve connection in the forearm – in 15% - of these 50% arise from AIN- AIN syndrome in this cause intrinsic muscle weakness of hand
Diagnosis
  • confirmed by EMG of FDP, FHL, PQ
  • NCV no value
Differential diagnosis
  • avulsion/ injury/ rupture of muscles
    • tenodesis test – wrist maximal extension, MCP, PIP also extension – slight flexion of DIP occurs – absent in rupture of tendon
  • Parsonage turner syndrome (brachial neuritis)
    • acute pain forearm with muscle weakness days to weeks later – shoulder pain – shoulder muscle involvement – no h/o injury
    • deltoid show EMG abnormalities
Conservative treatment
  • avoidance of exacerbating activities
  • immobilization – elbow flex and forearm pronation
  • NSAIDS
Surgical Indications
  • spontaneous recovery in most cases maximum to 2 years – surgical exploration in cases of slow or not apparent recovery – motor symptoms without a sign of recovery for 8-12 wks indicates exploration
  • recovery complete in 6 months after surgery
  • surgical exploration is the treatment of choice
  • Surgical decompression
    • exploration with fibrous bands, tendon release, removal of anomalous vessels, neurolysis
    • tendon transfer in cases of failure
PRONATOR SYNDROME


  • initially coined to describe the compression of median N in proximal forearm beneath PT – now used as a common term denotes compression of Median Na t proximal forearm and elbow
Pathophysiology and anatomy
  • supracondylar process – anomalous spur arising in anteromedial aspect of distal humerus, 5cm proximal to medial epicondyle – in 3% individuals
  • ligament of Struthers – fibrous band form supracondylar process of humerus and attaches to medial epicondyle forming fibro osseous tunnel – median N and brachial A pass through it
Sites of compression
  • supracondylar process and ligament of struthers
  • bicipital aponeurosis
  • arch of origin of PT
  • arch of origin of FDS


Symptoms
  • numbness and tingling of radial digits
  • numbness of thenar eminence palm
  • pain proximal forearm
  • fatigue and cramping in forearm with use
Sensory examination
  • decreased sensation in radial digits, thenar eminence
  • Threshold tests of Weinstein, vibrometry – most sensitive
Motor examination
  • thenar weakness and atrophy uncommon
  • Provocative tests
    • resisted elbow flexion and forearm supination – entrapment at bicipital aponeurosis
    • resisted pronation with elbow in extension – entrapment at pronator
    • resisted flexion of PIP – entrapment at FDS arch
    • Pronator compression test – entrapment at PT
    • Tinel's sign
Diagnostic studies
  • NCV positive in only 30% - r/o CTS, radiculopathy
  • supra condylar process evaluated by X ray
Differential diagnosis
  • CTS, cervical radiculopathy
    • CTS – pain more prominent – Phalens test negative -
Conservative Treatment
  • NSAIDS, splinting
  • modification of activities
  • physiotherapy – massage, stretching, iontophoresis
  • local steroid injection
Surgery
  • indications
    • symptoms persisting longer than 6wks to 3months of conservative treatment
    • decompression
      • release of ligament of struthers
      • excision of supracondylar process
      • division of bicipital aponeurosis
      • detaching superficial head of PT, radial origin of FDS
      • done proximal to distal
      • explore acc. Muscles as Gantzer's muscle – is acc muscle of FPL from medial epicondyle or coranoid

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