#The Common Peroneal (external popliteal) nerve# is exposed to injury where it winds round the neck of the fibula, because it is superficial and lies against the unyielding bone.  It may be compressed by a tourniquet, or it may be bruised or torn in fractures of the upper end of the bone.  It has been divided in accidental wounds,—­by a scythe, for example,—­in incising for cellulitis, and in performing subcutaneous tenotomy of the biceps tendon.  Cases have been observed of paralysis of the nerve as a result of prolonged acute flexion of the knee in certain occupations.

When the nerve is divided, the most obvious result is “drop-foot”; the patient is unable to dorsiflex the foot and cannot lift his toes off the ground, so that in walking he is obliged to jerk the foot forwards and laterally.  The loss of sensibility depends upon whether the nerve is divided above or below the origin of the large cutaneous branch which comes off just before it passes round the neck of the fibula.  In course of time the foot becomes inverted and the toes are pointed—­pes equino-varus—­and trophic sores are liable to form.

#The Tibial (internal popliteal) nerve# is rarely injured.

#The Cranial nerves# are considered with affections of the head and neck (Vol.  II.).

NEURALGIA

The term neuralgia is applied clinically to any pain which follows the course of a nerve, and is not referable to any discoverable cause.  It should not be applied to pain which results from pressure on a nerve by a tumour, a mass of callus, an aneurysm, or by any similar gross lesion.  We shall only consider here those forms of neuralgia which are amenable to surgical treatment.

#Brachial Neuralgia.#—­The pain is definitely located in the distribution of one of the branches or nerve roots, is often intermittent, and is usually associated with tingling and disturbance of tactile sensation.  The root of the neck should be examined to exclude pressure as the cause of the pain by a cervical rib, a tumour, or an aneurysm.  When medical treatment fails, the nerve-trunks may be injected with saline solution or recourse may be had to operative measures, the affected cords being exposed and stretched through an incision in the posterior triangle of the neck.  If this fails to give relief, the more serious operation of resecting the posterior roots of the affected nerves within the vertebral canal may be considered.

Neuralgia of the sciatic nerve—­#sciatica#—­is the most common form of neuralgia met with in surgical practice.

It is chiefly met with in adults of gouty or rheumatic tendencies who suffer from indigestion, constipation, and oxaluria—­in fact, the same type of patients who are liable to lumbago, and the two affections are frequently associated.  In hospital practice it is commonly met with in coal-miners and others who assume a squatting position at work.  The onset of the pain may follow over-exertion and exposure to cold and wet, especially in those who do not take regular exercise.  Any error of diet or indulgence in beer or wine may contribute to its development.