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Terms in this set (79)

The deltoid atrophies when the axillary nerve (C5 and C6) is severely damaged. Because it passes inferior to the humeral head and winds around the surgical neck of the humerus, the axillary nerve is usually injured during fracture of this part of the humerus. It may also be damaged during dislocation of the glenohumeral
joint, and by compression from the incorrect use of crutches. As the deltoid atrophies, the rounded contour of the shoulder is flattened compared to the uninjured side. This gives the shoulder a flattened appearance and produces a slight hollow inferior to the acromion. In addition to atrophy of the deltoid, a loss of sensation may occur over the lateral side of the proximal part of the arm, the area supplied by the superior lateral cutaneous nerve of the arm, the cutaneous branch of the axillary nerve.

The deltoid is a common site for the intramuscular injection of drugs. The axillary nerve runs transversely under cover of the deltoid at the level of the surgical neck of the humerus. Awareness of its location also avoids injury to it during surgical approaches to the shoulder.

The axillary nerve has two main branches: the anterior branch and the posterior branch. The anterior branch of the axillary nerve innervates the anterior and middle portions of the deltoid before becoming cutaneous and supplying the skin over the anterior and lateral portions of the shoulder. The posterior branch of the axillary nerve innervates the posterior portion of the deltoid and also becomes cutaneous, supplying the skin over the posterior portion of the shoulder. A small articular branch supplies the glenohumeral joint.
Radial nerve injury at axilla (e.g. crutch palsy - radial nerve continuously compressed against humerus) Because these types of injuries are "upstream" from all of the muscles that the radial nerve innervates, this lesion causes motor loss in the extension of the elbow (triceps), extension of the wrist (extensor carpi radialis longus), supination of the forearm (supinator), extension of the metacarpophalangeal joints of digits two through five (extensor digitorium) and the extension (extensor pollicis longus) and abduction (abductor pollicis longus) of the thumb. The denervation of the forearm extensor compartment causes wrist drop, a condition where a patient's hand hangs flaccidly because they cannot extend at the wrist. Wrist drop is a characteristic distal sign of proximal radial nerve palsy. Sensory loss on the posterior arm, forearm, and dorsum of the thumb also occur in axilla lesions of the radial nerve.

Radial nerve injury at radial groove (e.g. Saturday night palsy) Lesions on the shaft of the humerus are usually due to humeral fractures or compression lesions such as Saturday night palsy. Saturday night palsy is an acute retrohumeral compression palsy that occurs when a patient falls asleep curled over their arm. Upon waking up, the patient notices that they cannot extend their wrist, a hallmark of wrist drop. In addition to wrist drop, a radial nerve lesion in the spiral groove of the humerus shares all of the characteristics of lesions in the axilla, EXCEPT for loss of extension at the elbow and posterior arm cutaneous sensation. In other words, extension in the elbow and posterior arm cutaneous sensation is spared in spiral groove lesions, as the lesion is "downstream" from where the radial nerve innervates the tricep and posterior arm skin. Sensation on the posterior aspect of the forearm may or may not be spared.
Injury of the median nerve where the size of the carpal tunnel is decreased, causing impingement of the median nerve. The borders of the carpal tunnel include the carpal bones and the flexor retinaculum, a transverse ligament that wraps around the carpal bones. In addition to containing the median nerve, the carpal tunnel contains the tendons of the antebrachial flexor muscles. Fluid retention, infection, or overuse injuries can cause swelling of these tendonous structures or their synovial sheaths; thereby impinging the median nerve. Symptoms of Carpal Tunnel Syndrome include paresthesia, hypoesthesia, or anesthesia. If not treated, Carpal Tunnel Syndrome cause progressive loss or coordination and strength of the thumb and sensory changes may radiate up into the forearm and axilla. An examiner can test for Carpal Tunnel Syndrome by compressing or tapping on median nerve; reproduction of neurologic symptoms is a positive sign. Treatment includes carpal tunnel release, a surgical procedure where the flexor retinaculum is partially or fully divided to release pressure on the median nerve.

Damage involving the ulnar nerve at the level of the elbow (cubital tunnel syndrome) or above will produce a weakness in medial (ulnar) flexion of the wrist and an inability to flex the metacarpophalangeal (MCP) and proximal interphanageal (PIP) joints of the fourth and fifth digits. The resulting unbalanced extensor tone pulls the fourth and fifth digit into extension at the MCP and PIP joints with flexion still present at the distal interphalanegeal joint. The resulting posture is termed "claw hand" and occurs in the relaxed position.