At the root of the neck, the nerves form acomplicated plexus called the brachial plexus. This allows the nerve fibers derived from differentsegments of the spinal cord to be arranged anddistributed efficiently in different nerve trunks to thevarious parts of the upper limb. The brachial plexus is formed in the posteriortriangle of the neck by the union of the anteriorrami of the fifth, sixth, seventh, and eighth cervicaland the first thoracic spinal nerves
The nerves entering the upper limb providethe following important functions: sensory innervation to the skin and deepstructures, such as the joints; motor innervation to the muscles; influence over the diameters of the bloodvessels by the sympathetic vasomotornerves; sympathetic secretomotor supply to thesweat glands.
Lesions in continuity:more than half of the lesions are of thistype and most are caused by tractionThe nerve roots are affected between theintervetebral foramina and theclavipectoral fascia(postganglionic).The lesions may be transient(neuropraxia)or if the axons degerates(axonotemesis)
In more severe cases the nerves aredisrupted at the same level.
Rarely, the posterior roots are spared,sothat there may be the paradox of muscleparalysis with preservation of sansation.
The nerve is avulsed from the cord andsurgical repair is impossible.
The upper trunk of the plexus isaffected(C5,C6)Result:Wrist is flexed and pronated, and thefingers flexedThe elbow is extended and the shoulderinternally rotated giving a waiter’s tipdeformity
The small muscles of the hand,includingthe hypothenar and thenar groups arewaisted giving a claw hand deformity.There is sensory loss on the medial side ofthe forearm and wristThere is association with Horner’ssyndrome
The t1 root may be solely affected and givethe following signs: Wasting of the small muscles of the handincuding the thenar Sensory loss on the medial side of the handonly Lesions of this type are found in theincomplete lower obsterical palsy, cervicalspondylosis, cervical ribsyndrome,neurofibromatosis,and apical andmetastatic carcinoma.
Clinical anatomy by regions(Richard.S.Snell)Clinical orthopaedic examination(RonaldMcRae)