OTA 1997 Posters - Hip Fractures

The Anatomical Variations of the Lateral Femoral Cutaneous Nerve and its Consequences for Surgery

V.A. De Ridder, S. De Lange

Westeinde Hospital, Den Haag, Holland

Purpose: to determine the localization and its variations of the lateral femoral cutaneous nerve, and to diminish the incidence of meralgia paraesthetica.

Methods: Anatomical studies were at random performed on 200 recently deceased patients. The lateral femoral cutaneous nerve was explored from its origin to the inguinal region. The following "normal and abnormal" variations were found: "normal" 149, lateral end inguinal ligament 18, over or behind ASIS 9, through the M. Sartorius 7, superior to ASIS 6, absent or other 11 (other: branch from femoral nerve, from ilio-inguinal nerve or multiple).

Meralgia paraesthetica as a complication of pelvic surgery was assessed in 82 patients (24 women, 58 men) following an ilio-inguinal approach between 1989-1994. No special perioperative procedure was performed to lessen a future problem with the LFCN. Thirty-seven reported altered sensation in the distribution of the lateral femoral cutaneous nerve for several years operatively within 3 months postoperatively (minimal follow up 1 year). Most patients improved with time, indicating that the nerve had suffered a traction lesion at time of surgery. However, in 11 patients (11/37) the complaints progressed. Another 5 patients (5/82) had total loss of sensation without apparent laceration of the nerve during operation. Entrapment of the nerve was confirmed in 5 patients (5/11) whose symptoms had prompted an eventual exploration of the nerve between 8 and 26 months following surgery. The outcome following these explorations was unpredictable, 2 patients being relieved of their pain, one experiencing partial relief and 2 claiming no benefit from the release. In all 5 instances, the nerve had appeared both entrapped by scar and firmer than normal, and in 2 instances the exploration had proved difficult as the nerve was distant from its classical site.

In the following 40 patients (17 women, 23 men) following an ilio-inguinal approach to the pelvis between 1994-1996, special perioperative care was taken to lessen a future problem with the LFCN: either a neurolysis of the LFCN was performed with covering of the proximal end in the musculus iliopsoas. Neurolysis of the LFCN was done in 33 patients, 5 developed a loss of sensation, but none a meralgia paraesthetica. In 7 patients, a nerve transection was undertaken. All had loss of sensation, 2 developed meralgia paraesthetica like complaints and in both cases a neuroma of the proximal end was found during exploration. After resection of the neuroma, the proximal end was again covered by musculus iliopsoas. The complaints did not recur within 6 months.

Discussion: The lateral femoral cutaneous nerve (lateral or external cutaneous nerve of the thigh) is of particular importance to the trauma surgeons as its variable course in the inguinal region can present a hazard at surgery whether during approaches to the iliac crest as in ilio-inguinal acetabular approaches, pelvic osteotomies or surgical exploration of the nerve itself running towards the anterolateral brim of the pelvis. The intra-abdominal and intra-pelvic course is relatively consistent (Aldritch & van den Heever, 1989).

Several variations in the course of the lateral femoral cutaneous nerve in the groin have been described (Ghent, 1961). In the commonest abnormality, the nerve passes between the fibers of the lateral end of the inguinal ligament (Edelson & Nathan, 1977); tension on the ligament closes the slit-like opening and compresses the nerve. Alternatively, the nerve may pass over or just behind the ASIS, or deep to, or through, the sartorius. Alternatively, the nerve may be absent, being replaced by a branch from the femoral nerve arising below the inguinal ligament, or from the ilio-inguinal nerve (Sunderland, 1978).

The practical importance of these various aberrant courses of the nerve ties in alerting the surgeon to a possible anatomical variation during surgery. The variations have been described but a frequency has never been mentioned in a patient or cadaver study.

The complication meralgia paraesthetica after an ilio-inguinal approach can be avoided if tension or kinking of the nerve is lessened by flexion of the hip joint during operation or by trimming down the anterior iliac wing prior to wound closure (Hogh & Macnicol, 1987). It relaxes the attachment of the inguinal ligament and the sartorius muscle, both potent structures in producing a compression of the nerve where it enters the thigh.

Recently two articles compared two operative methods of treatment, neurolysis and transection. Antoniades reports of 29 patients, operated after failure of conservative treatment of meralgia paraesthetica. Eighteen underwent neurolysis and 11 nerve transection. Complete or partial pain relief was found in 72% after decompression and in 82% after transection of the nerve.

Van Eerten reports of 21 patients, referred for operation. Neurolysis in 10 patients and transaction in 11. Statistical analysis confirmed the superiority of transection as a treatment compared to neurolysis. In their series neurolysis was a nonsignificant improvement in comparison to previous conservative treatment. Due to our own experience and these two articles, the perioperative approach of the LFCN was changed.

Conclusion: The practical importance of these various aberrant courses of the nerve lies in alerting the surgeon to a possible anatomical variation in about 25% when approaching the iliac crest during surgery. The incidence of meralgia paraesthetica was lowered by the new perioperative approach of the LFCN.