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Duke Orthopaedics
presents
Wheeless' Textbook of Orthopaedics

Median Nerve

 


   - Carpal Tunnel Syndrome
    - Combined Lesions of the Median and Ulnar Nerves:
    - High Median Nerve Lesions
    - Low Median Nerve Lesions
    - Median Nerve Block
    - Median Nerve Injuries at the Wrist
    - Martin Gruber Anastomosis

- Anatomy:
    - roots: C6, C7, C8, and T1 (? C5)
    - brachial plexus
          - cords:
                - lateral cord: contributes mainly sensory axons from C6 and C7
                - medial cord: provides main bulk of motor input through C8 and T1 
    - position in the arm:
          - has no branches in arm;
          - crosses brachial artery from lateral to medial in the arm, then passes over brachialis
          - median nerve is parallel and anterior to the medial intermuscular septum;
    - entrapment of median nerve at the elbow and forearm:
          - supracondylar process:
                  - small hook of bone 5 cm above medial epicondyle;
                  - may form accessory origin for pronator teres, thru ligament of Struthers;
                  - median nerve may be displaced medially and compressed by these structures;
                  - compression is worsened w/ extension and supination; 
                  - present in approximately 1% of individuals of European descent
                  - references:
                         - Entrapment neuropathy of the median nerve at the ligament of Struthers.  
                         - Median nerve compression by the supracondylar process: A case report.  
          - lacertus fibrosis: 
                  - this is a site of potential compression; 
                  - is tightened w/ pronation of forearm as bicipital tuberosity of the radius passes posteriorly; 
                  - ref: Acute compression of the median nerve at the elbow by the lacertus fibrosus. 
          - pronator teres compression syndrome:
                  - nerve enters forearm between 2 heads of pronator teres (beneath the superficial-humeral) which is a site of potential compression; 
          - passing superficial to the FDP and beneath FDS, it supplies all muscles on front of forearm except FCU & ulnar half of FDP;
                  - nerve may be compressed by the fibrous arch of FDS; 
          - anterior interosseous branch 
    - position in distal forearm and in the carpal tunnel:
          - see: carpal tunnel syndrome and surgical decompression and median nerve injuries at the wrist
          - palmar cutaneous branch:
          - runs between & deep to FCR & palmaris longus into carpal tunnel;
          - nerve lies superficial to the tendons of the FDP and FPL;
          - FDS tendons lie lateral to the nerve;
          - motor branch:
    - variations:
          - martin gruber anastomosis
          - bifid (high division) of median nerve: associated w/ a median artery;
          - references:
                - Variations of the median nerve in the carpal canal.
                - Anatomical variations of the median nerve in the carpal tunnel.

- Exam:
    - signs of a median nerve lesion include weak pronation of the forearm, weak flexion &  radial deviation of wrist, with thenar atrophy & inability to oppose or flex the thumb;
    - sensory distribution includes thumb, radial 2 1/2 fingers, and corresponding portion of palm.
    - w/ intact nerve, thumb can be pronated, lining up nails at or near 180 deg;
          - w/ median nerve palsy, thumb can't be pronated & nail is < 100 deg

 

  


  Clinical features of paralytic claw fingers.

  Lipofibroma of the median nerve in the palm and digits of the hand.

  Congenital anomaly of the thumb: absent intrinsics and flexor pollicis longus.

  Restoration of strong opposition after median-nerve or brachial plexus paralysis.

  Abductor digiti quinti opponensplasty.

  Intraoperative assessment of median nerve blood flow during carpal tunnel release with laser Doppler flowmetry.

  Variations of the median nerve in the carpal canal.

  An analysis of the results of late reconstruction of 132 median nerves.

  Successful reeducation of functional sensibility after median nerve repair at the wrist.

  Experimental sensory reinnervation of the median nerve by nerve transfer in monkeys.

  Repair of median and ulnar nerves. Primary suture is best.

  Injection injuries to the median and ulnar nerves at the wrist.

  Palmar lipomas associated with compression of the median nerve.



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Wednesday, April 11, 2012 11:02 am