Radial nerve injury

Anatomical background and mechanism of injury

The radial nerve (n. radialis) originates from the posterior cord of the brachial plexus (plexus brachialis). Topographically, the plexus itself is located in the supraclavicular region, whereas its cords pass through the infraclavicular zone.

Damage to the nervous structures of the upper extremity most frequently occurs via an indirect mechanism of injury. The anatomical proximity to bone and vascular structures determines the high frequency of combined injuries. Trauma to the brachial plexus and its branches is often accompanied by:

• Clavicle fracture;
• Shoulder joint dislocation;
• Injury to the subclavian and axillary arteries and veins;
• Trauma to the pleura and lungs.

Severe concomitant injuries, especially vascular ones, present particular diagnostic challenges. Massive hemorrhages distract the surgeon's attention and obscure the true symptomatology of nerve trunk lesions. Neurological deficits in such cases may not appear immediately, but rather develop gradually as the hematomas resolve.

Clinical presentation of the lesion

Isolated or combined damage to the posterior cord predictably leads to radial nerve dysfunction.

Motor disorders:

1. Complete impairment of triceps brachii muscle function (m. triceps brachii).
2. Loss of function of all wrist extensors.
3. Inability to extend the fingers.

Sensory disturbances: Loss of sensitivity corresponding to the specific pattern of radial nerve involvement is observed.

Since the axillary nerve (n. axillaris) also branches off from the posterior cord, trauma at this level is accompanied by the loss of its function as well. In some cases, paresis of the latissimus dorsi muscle joins the clinical picture, which is associated with impairment of the thoracodorsal nerve.

Differential diagnosis of paralyses

For precise topical diagnosis, radial nerve injury must be differentiated from other syndromes of traumatic brachial plexus injury:

• Total plexus injury: Manifests as flaccid paralysis of the entire arm, absence of reflexes, complete anesthesia (except for the upper areas of the deltoid region), and loss of joint-position sense.
• Erb–Duchenne syndrome (upper paralysis): Involvement of the C5 and C6 nerve roots. Abduction and rotation of the shoulder and flexion of the forearm are affected, but the grasping function of the hand is preserved.
• Dejerine–Klumpke syndrome (lower paralysis): Involvement of the lower roots (C8 and T1). Characterized by paralysis of the intrinsic muscles of the hand and flexors, often accompanied by Horner's syndrome.

Class and exam questions

What else to study on this topic

• Topographic anatomy of the primary and secondary trunks of the brachial plexus
• Erb–Duchenne paralysis: clinical manifestations and functional tests
• Dejerine–Klumpke paralysis and concomitant Horner's syndrome
• Obstetric palsy as a consequence of birth trauma
• Differences between flaccid paralyses of the upper extremity and total plexus injury

Other topics in the section "General Questions of Traumatology and Orthopedics"

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