Stookey12 was the first to advance the idea of a mechanical cause of meralgia paresthetica in an excellent clinical and anatomical study in 1928. He was impressed by the constant accentuation of the symptoms by standing or walking, with relief when sitting or lying down, and by the sharp angulation of the nerve where it crosses the ridge of the ilium. He compared this angulation with that of the ulnar nerve at the elbow, where neuritis develops commonly, and interpreted that meralgia paresthetica is caused by repeated stretching of the lateral femoral cutaneous nerve over this angle of the ilium. Later observers have tended to emphasize other trauma, as pressure on the nerve in its superficial position by bed, belts or braces, and the repeated tensing of the inguinal ligament over the restricted nerve.6 These observations have given increasing evidence that meralgia paresthetica is caused in major degree by mechanical factors and is a traumatic neuritis, comparable to ulnar neuritis and similar syndromes elsewhere in the body.
Trauma to nerves is of varying types, dependent on the manner and severity of the force applied. Sustained pressure or stretching of a nerve is not significantly painful, giving rise chiefly to loss of function of the nerve, which recovers promptly when the physical force is released unless axonal death has occurred. Examples of this are the leg “asleep” after sitting with pressure or stretch on the sciatic nerve and numbness of the arm after sleeping with the arm above the head. Severe injury to a nerve, with associated swelling, hemorrhage or infection, may heal slowly and develop inflammatory interstitial fibrosis with accompanying loss of function and severe “causalgic” pain, interpreted as caused in part by the sympathetic component of peripheral nerves. Intermittent compression of a peripheral nerve is a common cause of painful traumatic neuritis, as ulnar neuritis in a shallow ulnar groove and nerve-root pain related to a compressible herniation of an intervertebral disc. Simple stretching of a nerve over a smooth surface does not cause pain, otherwise ulnar neuritis would be much more common than it is. These observations apply equally to lateral femoral cutaneous neuritis, tensing of the inguinal ligament being the chief factor in continuation of symptoms. Since transposition or release of intermittently compressed nerves elsewhere has given satisfactory relief from this type of traumatic neuritis, this should be the best procedure for relief of meralgia paresthetica, and both Lee7 and Mack8 have reported good results from transposition of the lateral femoral cutaneous nerve to an osteoplastic slot in the crest of the ilium. This operation necessitates section of the inguinal ligament, removal of bone and lateral stretching of the nerve for its transposed position.
Other methods for surgical relief of meralgia paresthetica have been tried with varying results. Simple section of the nerve above or below the inguinal ligament leaves the nerve with its sympathetic components at the site of irritation and disturbing paresthesia usually has returned or persisted. Resection of the portion of the nerve passing beneath the inguinal ligament should be more effective if done extensively enough, but this necessitates section of the inguinal ligament and results in complete loss of function of the nerve. In view of the difficulties involved in the several surgical procedures for meralgia paresthetica and the interpretation that the best procedure is transposition of the nerve from its intermittently compressed position, an anatomical study was done of the relation of the nerve to the inguinal ligament and attached fascias and muscles to determine if a simpler method of transposition could be found.
This anatomical study is based on dissection of 50 cadavers in the laboratory of gross anatomy at the University of Nebraska College of Medicine (Fig. 1). The lateral femoral cutaneous nerve has its origin in the lumbar plexus, usually from the 2nd and 3rd lumbar nerves, and appears at the lateral border of the psoas major muscle just above the crest of the ilium. It is directed somewhat laterally across the anterior surface of the iliacus muscle, from which it is separated by the muscle sheath. This sheath is very thin and the adjacent tissue is loose, permitting the nerve to be moved easily. Both the muscle sheath and the nerve are covered by a much denser layer of fascia which is termed the iliac fascia. As the nerve approaches the lateral portion of the inguinal ligament to enter the thigh, it passes posterior to the deep circumflex iliac artery which courses parallel to the inguinal ligament beneath the iliac fascia.
The most common site of passage of the nerve from the iliac fossa to the thigh beneath the inguinal ligament is just medial and inferior to the anterior superior iliac spine but this is quite variable. The nerve often is found a half inch or more medial to the spine and not infrequently is derived in part or entirely from the adjacent genitofemoral or femoral nerve. Piersol9 has mentioned these variations but did not suggest the frequency with which we found them, about 30 per cent. In the more common position of the nerve near the anterior superior iliac spine it lies in contact with a smooth ridge of the iliac bone around which it turns in a moderate curve. As the nerve crosses the bone it is confined in a narrow tunnel between two slips of attachment of the inguinal ligament, which arise from the anterior superior spine and the bone immediately inferior to that point. This anatomy was noted by Soulié11 and by Learmonth.5
Several muscle and fascial attachments to the inguinal ligament have an effect on its tension. The sartorius muscle has a medial aponeurotic expansion from its tendinous attachment to the anterior superior spine, which attaches to the inferior border of the inguinal ligament and would depress this ligament intermittently when contracting. This medial origin of the sartorius muscle has been mentioned as a variation in Gray's Anatomy of the Human Body,4 and by Grant3 in Morris' Human Anatomy, but otherwise has not been noted. We have found it in the majority of the specimens examined. Medial to the tendinous origin of the sartorius muscle there is a heavy aponeurotic band which attaches to the inguinal ligament for a distance of about an inch and passes beneath the sartorius and rectus femoris muscles to fuse with the deep surface of the iliotibial band. This in reality is a continuation of the iliac fascia into the thigh, with attachment to the lateral portion of the inguinal ligament. Occasionally some iliacus muscle fibers take origin from this fascial attachment and their action would depress the inguinal ligament. The fascia lata attaches to the inguinal ligament throughout its length and covers the upper part of the sartorius muscle. It covers the opening in the inguinal ligament transmitting the lateral femoral cutaneous nerve which runs deep to it a distance of about 2 inches before piercing the fascia in several branches to enter the lateral part of the thigh.
The inguinal ligament provides an insertion for the external oblique and an origin for the lowest fibers of the internal oblique and transversus abdominis muscles, hence is tensed by contraction of these muscles. One additional fascial attachment which may be of significance in its influence on the inguinal ligament in obese persons is the deep layer of the superficial abdominal fascia, called Scarpa's fascia. This attaches to fascia lata about a half inch below the inguinal ligament so that dependent abdominal fat might exert some downward pull and compression of this ligament.
The lateral femoral cutaneous nerve, after emerging from its narrow canal between the two slips of lateral attachment of the inguinal ligament, passes anterior or ventral to the tendinous origin and upper fibers of the sartorius muscle, separated from it by the muscle sheath and covered by fascia lata. In some texts, Cunningham's2 Text-Book of Anatomy, Piersol's9 Human Anatomy, and in Stookey's12 anatomical study, it is stated that the nerve may pass over, under or through the origin of the sartorius muscle. There were no specimens with the nerve passing under or through the muscle in our series of 50 cadavers, although this variation has been seen in the laboratory in previous years. Our findings indicate that the nerve does not often pass through the sartorius muscle but passes between the two slips of lateral attachment of the inguinal ligament, the lower one of which gives origin to some sartorius fibers.
From this anatomical study and physiological analysis of the relations of the lateral femoral cutaneous nerve in its location beneath the lateral portion of the inguinal ligament, with intermittent compression by the ligament considered the probable cause for continuation of the syndrome of meralgia paresthetica, it seemed possible and more logical to transpose the nerve medially rather than laterally as Lee7 had done for relief. Several postmortem dissections were done to develop this technique into an easy surgical procedure through a 2- to 3-inch incision parallel to and slightly below the lateral portion of the inguinal ligament. In this dissection it first is necessary to expose the lateral femoral cutaneous nerve as it emerges from beneath the inguinal ligament. This is done by opening the fascia lata over the upper portion of the sartorius muscle, being careful not to cut aberrant branches of the nerve crossing the muscle. Then dissection with blunt curved clamp is extended upward toward the anterior superior iliac spine, interrupting the medial light attachment of the sartorius muscle to the inguinal ligament. The nerve is best identified by inserting the curved clamp into its narrow canal between the two slips of lateral attachment of the inguinal ligament as fat may obscure the nerve at a lower level. Interestingly, no observation in the literature of operation for meralgia paresthetica has been found in which the nerve was not located in this common restricted lateral position. Sharp dissection then is carried medially and posteriorly to cut the lower slip of attachment of the inguinal ligament. This frees the nerve in some degree, as was done by Lear-month5 with reported satisfactory relief, but it is still restricted by the lower lateral attachment of the iliac fascia to the inguinal ligament. For better release and transposition this attachment is cut a distance of about 1 inch medially, directing the incision somewhat posteriorly to avoid entering the ligament or interrupting the deep circumflex iliac artery. After this is done the iliacus muscle is exposed and it is very easy to mobilize the nerve and transpose it a half inch or more medially by blunt dissection upward beneath the inguinal ligament and intact pelvic iliac fascia. This upward dissection and mobilization is facilitated by use of a small curved blunt ligature carrier and by the outwardly curved course of the nerve from its origin to the thigh (Fig. 2). The nerve then lies on the soft portion of the iliacus and sartorius muscles. Closure of the wound requires only a few sutures in the fascia lata, subcutaneous tissue and skin. There is no need to suture deeper layers to prevent abdominal herniation as the pelvic iliac fascia remains intact, attached laterally to the inguinal ligament. This operation has been done in 2 cases with satisfactory relief, reported below.
Case 1. F.G., a 35-year-old man, height 6 ft., weight 225 lbs., and youth weight 180 lbs., was referred by Dr. M. P. Margules, neurosurgeon of Council Bluffs, Iowa. He was a city mail carrier, walking 9 to 10 miles daily, carrying a 15-to 25-lb. mail sack with strap always over his left shoulder. With no associated local injury or soreness, mild pain and tingling numb sensation developed in the anterolateral region of the right thigh, gradually becoming more disturbing and requiring that he discontinue work at increasing intervals. His symptoms were initiated and made worse by walking, relieved by sitting or lying down. A characteristic oval area of analgesia to light pin scratch was outlined in the right anterolateral area of the thigh; touch was felt there. Two injections of novocain into the right lateral femoral cutaneous nerve were done by Dr. Margules with relief of symptoms lasting only 6 to 8 hours.
Surgical relief seemed indicated and the operation of medial transposition of the involved nerve, as described above, was done July 17, 1961, with Dr. Margules, at Mercy Hospital, Council Bluffs, Iowa.
Postoperatively there was prompt complete relief of his meralgia paresthetica. He was allowed up on the 1st day and dismissed on the 3rd day. Six months later he reported that he has been working regularly with no recurrence of symptoms. Sensation has largely returned in the analgesic area of his thigh.
Case 2. M.S., a 55-year-old woman, height 5 ft. 1 in., weight 170 lbs., youth weight 125 lbs., was referred by Dr. A. R. Pantano of Omaha, Nebraska. Onset of symptoms 1 year previously, possibly related to wearing of a tight girdle which caused tenderness over the region of the left anterior superior iliac spine, developed with characteristic burning, numb, tingling sensations in the anterolateral part of the left thigh. This was made worse by standing and walking, and required her to lie down frequently for relief while doing her housework. Injections of novocain were done without satisfactory relief. She discontinued wearing a girdle and reduced her weight over several months without significant relief.
Operation of medial transposition of the left lateral femoral cutaneous nerve, as described above, was done Dec. 1, 1961 at St. Catherine's Hospital, Omaha, Nebraska.
She was dismissed on the 3rd day. Postoperatively, now 2 months, there has been satisfactory relief of her disturbing paresthesia. She is able to do her housework. There is some remaining complaint of the “dead” feeling in her thigh, which is expected to disappear as axonal regeneration develops.