Q&A: Diagnosis of Nerve Damage in Mid-Shaft Humeral Fracture

Fractures of the humerus can occur proximally, in the shaft (diaphysis), or distally. The majority of both proximal and midshaft humeral fractures are nondisplaced and can be treated conservatively (ie, nonsurgically). Complex fracture patterns pose greater challenges for treatment.

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In this article:
Fracture of the humerus
MCQ exam: clinical scenario
MCQ exam: answer
MCQ exam: explanation

Fracture of the humerus

Proximal humeral fractures occur most commonly in older adults, and their incidence is increasing.

Midshaft humeral fractures account for about 2 percent of all fractures. They occur in all age groups, but show a bimodal distribution: The first peak is seen in the third decade in males and is often associated with high velocity trauma; the second peak is noted in females in the seventh decade and is associated with low velocity falls. An observational study of 401 humeral shaft fractures noted that 68 percent resulted from a simple fall and 90 percent overall were due to trauma. Trauma, increasing age, and osteoporosis are known risk factors.

In children, fractures of the humeral shaft are uncommon, representing less than 10 percent of all fractures in children. One of the most important features of humeral fractures in children is their ability to remodel and heal with minimal to no deformity despite displacement and angulation. The majority of these fractures can be treated by immobilization alone.

MCQ exam: clinical scenario

A man came to the emergency room after a road traffic accident. He had swelling, pain and shortening of the left arm. On examination the man was found to have a fracture of the mid shaft of the humerus. On further examination the man was found to have a wrist drop, finger drop and thumb drop on the left side.

The cause for this is:

a) injury to the radial nerve
b) injury to the ulnar nerve
c) injury to the median nerve
d) injury to the axillary nerve
e) none of the above

MCQ exam: answer

The correct answer is A.

MCQ exam: explanation

Radial nerve during its course along the arm passes through the radial groove present in the mid shaft area of the humerus. The nerve is commonly damaged due to a mid shaft fracture of the humerus. The radial nerve is responsible for supplying the extensor muscles of the wrist, fingers and the thumb. The damage to the nerve causes paralysis of the extensor muscles in the forearm. This results in unopposed action of the flexor muscles causing a wrist, finger and thumb drop.

The ulnar nerve is never injured in a fracture of the mid- shaft of the humerus. Injury to the ulnar nerve results in the paralysis of the flexor carpii ulnaris and medial half of the flexor digitorum profundus. The paralysis of these muscles causes flattening of the medial border of the forearm and claw hand deformity of the hand. It does not cause a wrist, thumb or finger drop.

Median nerve injury does not occur with the fracture of mid shaft of the humerus. Also the median nerve supplies the flexors of the wrist therefore injury to the nerve causes flexion weakness at the wrist and not a 'drop' deformity.

Axillary nerve is a short nerve which does not reach up to the level of mid shaft of humerus, thus cannot be injured in its fracture. Also it does not supply any muscles in the forearm therefore its injury does not cause a wrist, finger or thumb drop.

Reference(s)
1). UpToDate: Midshaft humerus fractures in adults. Available online: https://www.uptodate.com/contents/midshaft-humerus-fractures-in-adults
2). UpToDate: Midshaft humeral fractures in children. Available online: https://www.uptodate.com/contents/midshaft-humeral-fractures-in-children