Docstoc

Dermatomes

Document Sample
Dermatomes Powered By Docstoc
					                                     Dermatomes                                                  MAIN NERVES OUT OF BRACHIAL PLEXUS:

•   Brachial plexus: nerve roots going into plexus are C5, 6, 7, 8 and T1 and the 5 main
    nerves coming out are radial, median, ulnar, musculocutaneous and axillary     ie 5 in and   Radial Nerve:
    5 out                                                                                        • Motor:
•   Most imp sensory nerve is median as gives sensation for most fingers                                 o   Is the extensor nerve of the arm
•   Ulnar nerve is most imp motor nerve since supplies intrinsic muscles so allows opposition            o   Extends wrist and metacarpals (since it supplies
                                                                                                             extensors of forearm) and also extends elbow (IP
                                                                                                             extension is by ulnar)
                                                                                                 • Sensory:
                                                                                                         o   Dorsum of hand on radial side to ½ way along 3rd digit
                                                                                                             – extends up fingers but not all way to top (top
                                                                                                             supplied by median)
                                                                                                 • Testing:
                                                                                                         o   Check wrist extension and check for sensation of skin in area over cleft between
                                                                                                             thumb and index finger (NB: despite above saying that some of dorusm of hand is
                                                                                                             supplied by radial, there is overlap so best place to assess for sensory component
                                                                                                             is in this area as this is innervated by radial nerve alone)
                                                                                                 • Palsy:
                                                                                                         o   Aka ‘Saturday night palsy’
                                                                                                         o   Wrist drop with inability to extend wrist due to compression of the nerve:
                                                                                                                      Where it wraps round the humerus (upper arm)
                                                                                                                      In the extensor muscle compartment of the forearm
                                                                                                         o   Severity depends on the site of the lesion


                                                                                                 Ulnar Nerve:
                                                                                                 • Motor:
                                                                                                        o    Intrinsic muscles of hand: medial lumbricals, interossei
                                                                                                        o    Ulnar nerve supplies most (14 out of 19) intrinsic muscles
                                                                                                             (rest are by median)
                                                                                                 • Sensory:
                                                                                                        o    5th & ½ of 4th finger palmar and dorsal
                                                                                                 • Testing:
                                                                                                        o    Test interossei by assessing power of abduction and adduction of fingers and
                                                                                                             check sensation on fingertips of 4th and 5th finger
                                                                                                        o    Froment's sign is a test for ulnar nerve palsy, which specifically tests the action of
                                                                                                             adductor pollicis (also moves thumb but not part of thenar eminence)
                                                                                                        o    Pt is asked to hold paper between thumb and a flat palm as paper is pulled away
                                                                                                                   Ulnar nerve palsy pt will flex thumb to try to maintain a hold on the paper
                                                                                                                   (since use long flexors of forearm instead)
                                                                                                        o    Test sensation along ulnar side of palm and fingers
                                                                                                 • Palsy:
                                                                                                        o    Clawing of the 2 medial fingers due to weakness of lumbricals
                                                                                                             III & IV (other 2 fingers still have intact median supply to their
                                                                                                             lumbricals)
Median Nerve:                                                                                  •   T1: intrinsic muscles of hand
•  Motor:
        o   Supplies LOAF: lateral two lumbricals, opponens pollicis, abductor pollicis        Intrinsic Muscles of Hand:
            brevis and flexor pollicis brevis (the last three are the                          •    Modify action of the long muscles of forearm that do most of finer flexion/ extension so as to
            3 muscles of thenar eminence)                                                           allow skilled movements
        o   Also flexes thumb and index finger and flexor                                      •    Includes the 4 lumbricals and 8 interossei (4 dorsal and 4 palmar)
            muscles of the forearm                                                             •    Lumbricals are unusual in that they are attached on one side to tendon (flexor tendon) and
 • Sensory:                                                                                         same on other (extensor tendon) ie not to bone
        o   Sensory to palmar surface of thumb, 2nd, 3rd & ½ of                                •    Ulnar nerve supplies most 14 out of the 19 intrinsic muscles (rest are median)
            4th finger and to dorsal surface for peripheral 1st, 2nd,                          •    In terms of nerve roots then intrinsic muscles are supplied by T1 so T1 problems also gives
            3rd and 4th                                                                             rise to claw hand but can distinguish from ulnar nerve problems viz:
•  Testing:                                                                                               o    With former get numbness in hand
        o   Test motor by testing abductor pollicus by feeling for muscle contract under                  o    In later get numbness in T1 dermatome (around armpit)
            thumb when abducting thumb against pressure) and sensory over pulp of index        •    Testing of intrinsic muscles:
            finger                                                                                        o    Opposition of fingers (though this uses other muscles too)
• Palsy:                                                                                                  o    Grip strength – not really testing intrinsics but forearm muscles
        o   Eg. Carpal Tunnel Syndrome – compression of median nerve as it passes                         o    Paper test between fingers (make sure fingers are straight) – if pt can keep paper
            through carpal tune (space formed by flexor retinaculum above (dense band of                       then shows that ulnar nerve and T1 nerve root are working
            fibrous tissue) and carpal bones below)        seen in RA due to synovitis of                 o    Test palmar interossei but trying to push in against pts spread fingers (PAD:
            tendon membranes                                                                                   palmar adducts)
                  Thumb externally rotated, thenar eminence wasted                                        o    Test dorsal (DAB: dorsal abducts) by reverse (or in kids by crossing fingers)
                  Paraesthesia in digits supplied by the nerve                                 •    Grip strength: 70% is C8 from median and ulnar nerves and 30% intrinsics (T1) aided by
                                                                                                    radial nerve which stabilises wrist

                                                                                               How to distinguish a nerve root sensory problem from a nerve sensory problem:
                                                                                               •  One eg is if median nerve problem and trying to distinguish from nerve root – area of
                                                                                                  sensory impairment if median problem extends only as far as wrist whereas the nerve root
                                                                                                  problem (in this case C6) will extend further
                                                                                               •  Also, test upper limb jerks if jerk lost then likely to be nerve root problem

                                                                                               Testing upper limb movement/ power:
                                                                                               •   Test interossei (paper test)
Normal hand               Median nerve lesions
                                                                                               •   Finger flexion, finger extension
Thumb is perpendicular to Thumb is externally rotated into plane of palm
plane of palm             Thenar eminence is wasted                                            •   Make fist – check wrist flexion and extension
                                                                                               •   Elbow flexion and extension
Musculocutaneous Nerve:                                                                        •   Shoulder – hand behind head (abd + ext rot) and behind back (add + int rot)
•  Motor: Supplies biceps and brachialis (bends elbow)                                                  o    Deltoids abduct shoulder, pecs adduct
•  Sensory: Skin of lateral side of forearm
                                                                                               Lower Limb Dermatomes:
Axillary Nerve:                                                                                •  Stand on S1, lie on S2, sit on S3, wipe S4, poke S5 (PR)
•    Motor: Supplies deltoids (abducts shoulder)                                               •  Myotomes: L3 hip flexion, L4 knee extension, L5 lift toes (rock back on heel), S1 stand on
                                                                                                  toes
•    Sensory: Skin of badge-patch area (lat side of shoulder)
                                                                                               •  Largest branches of lumbar plexus: femoral nerve and obturator nerve
•    Testing: Test sensation over badge patch area and abduction of shoulder (though later
     wont be possible if eg have shoulder dislocation and are trying to work out if axillary   •  Largest branches of sacral plexus: sciatic nerve that divides into tibial nerve and common
     nerve ok)                                                                                    peroneal nerve

Myotomes:                                                                                          Cord lesion eg C5/6 (LMNL) will cause hyporeflexic supinator/ biceps jerk but will get brisk
                                                                                                   triceps (loss of inhibition below lesion)
•  C5: shoulders incl deltoids (abductors)
                                                                                                   Bilateral brisk reflexes UL/ LL seen in lesions high in cord/ brain eg bilat stroke
•  C6: elbow flexion
•  C7: elbow extension
•  C8: finger flexors

				
DOCUMENT INFO
Shared By:
Categories:
Stats:
views:561
posted:2/11/2011
language:English
pages:2