The latter point holds good in the forearm also; here, individual injuries often occurred.
While at work in the Field hospital alone I gained the impression that the musculo-spiral nerve would not retain the unenviable character of being the most vulnerable nerve of the upper extremity, since the chances of each individual nerve seemed about equal, putting the question of the long course of the musculo-spiral nerve against the humerus out of question. This expectation was, however, not confirmed, since the musculo-spiral itself, if not primarily affected, was so often the seat of secondary mischief in fractures of the humerus. The posterior interosseous branch seemed to exhibit a similar vulnerability to slight injuries, to be referred to later under the external popliteal of the lower extremity. Again, in complex injuries of the brachial plexus, or nerve trunks, the musculo-spiral branch rarely escaped being a member, if not individually singled out.
Of the thoracic nerves I have little to say. They must have been often injured in the thoracic wounds, yet, as far as my experience went, intercostal neuralgia was uncommon, or at any rate not a special feature. One observation of interest, however, does exist; in the cases in which the ribs were fractured by bullets travelling across them within the thorax, pain was distinctly a prominent feature. This was no doubt referable to the facts that in such instances the intercostal nerves were especially liable to direct injury, and that this was often multiple. On one occasion a crop of herpetic vesicles developed along the course of a dorsal nerve in an injury implicating a single intercostal space posteriorly.
Lumbar plexus.—Although not quite so well arranged to escape bullet wounds as the thoracic nerves, the lumbar, by reason of their deep position and the comparatively wide area they cover, together with the rarity of wounds taking a sufficiently longitudinal direction to cross the course of more than one or two branches, were also comparatively rarely damaged. I never saw an uncomplicated case of anterior crural paralysis, and rarely cruralgia. I think this is to be explained in two ways: first, that the trunk course of the nerve is short; secondly, that it lies in the inguinal fossa. The second fact is of importance, since wounds in this region were in my experience responsible for a considerable percentage of the deaths on the field or shortly afterwards. Such deaths probably occurred from internal hæmorrhage from the iliac arteries, and it was in such cases that the anterior crural nerve stood in greatest danger of injury. I also never saw a case of localised obturator paralysis. On the other hand, anæsthesia or hyperæsthesia in the area of distribution of the lumbar nerves in the groin, the external cutaneous and the long saphenous in the thigh, were not uncommon. Hyperæsthesia developed in more than one case in which injury to the psoas had led to hæmorrhage into the muscle sheath.
Sacral plexus.—The sacral plexus is far more liable to extensive direct injury than either of the two preceding. Its cords are larger, gathered up into a much smaller space, and more liable to injury, from the fact that the slope in which they lie is more readily followed by a bullet track. Again, the cords rest for a considerable portion of their course on a bony bed, a particularly dangerous position in gunshot wounds, since the nerves are not only exposed to the danger of direct wound, or pressure from bony spicules, but also readily receive transmitted vibrations secondary to impact of the bullet with the bone.
None the less I had few occasions to observe extensive injuries of the plexus. In one instance damage particularly affecting the lumbo-sacral cord occurred, but this was complicated by signs of irritation of the anterior crural and obturator nerves, as the result of retro-peritoneal hæmorrhage and injury to the psoas muscle. Two cases in which the sacro-coccygeal plexus suffered isolated injury on account of their characteristic nature as gunshot injuries will be shortly quoted:
(116) Sacro-coccygeal plexus.—Entry, at the junction of the middle and posterior thirds of the left iliac crest; the bullet passed obliquely downwards through the pelvis to lodge 3 inches below the right trochanter major. Incontinence of soft fæces persisted for five weeks, and retention of urine during three weeks.
This patient subsequently died on the homeward voyage, but I am unable to say from what cause.
(117) Entry, over third sacral vertebra; exit, 2 inches from the median line, and 1½ inch above Poupart's ligament on the anterior abdominal wall. Incontinence, with involuntary passage of fæces, persisted during the first twenty-four hours, and for two days the urine had to be withdrawn with a catheter. No further signs of nerve injury were noted.
The same explanation of the comparative rarity of injuries to the sacral plexus that has been already given in the case of the anterior crural nerve holds good—viz. that in a great many of the pelvic wounds involving the plexus early death followed from the severity of the concurrent injuries.