Meralgia Paresthetica (M.P.): was first described by Bernhardt (1) in
1895 and named
the same year by Roth. This entity consists of numbness, tingling, pain and/or burning
sensation in the distribution of the lateral femoral cutaneous nerve(LFCN).Figure 1.
Figure 1: Schematic representation of the sensory distribution of the lateral femoral cutaneous nerve (LFCN)
The male to female ratio is 2.8:1 and the involved side is split evenly between the right - 36% and the left 38%. The remaining 22% of cases present with bilateral symptoms. The majority of patients experience decrease of touch, pain and temperature but preserved pressure sensation in the LFCN distribution.There are multiple etiologies for this condition but obesity is an important factor with 90.7% of patients being overweight(>79.5 kg) . A recent weight gain of 6.8 to 9 kg has been reported in upto 8% of patients with this condition (2).The differential diagnosis for this condition includes upper lumbar - intervertebral foraminal pathology, intraabdominal conditions such as pregnancy and cirrhosis(3). Abdominal compression by trusses, belts and corsets,(4) and wallets(5) have also been described. About half the cases are idiopathic in nature.(6)The remaining etiologies are iatrogenic in nature and include nephrectomy,appendectomy, cholecystectomy, inguinal herniorrhaphy(7),diaphragmatic hernia repair, hip surgery and iliac crest bone graft harvesting(ICBG)(8) for varied fusion.(2).
We present here the clinical features and surgical results of MP following ICBG harvesting.
This 52 year old man presented with a disc herniation at the C6-7 level. An anterior cervical
discectomy was performed, followed by a right ICBG harvesting.(Figure 2).
Figure 2: Magnified plain x-ray view of the iliac crest bone harvesting area (arrow).
A right skin incision was made over the anterior superior iliac crest (Figure 3).
Figure 3: Skin incision performed for iliac crest bone graft harvesting (arrow). The same incision was modified (black marker) for lateral femoral cutaneous nerve exploration.
His cervical radiculopathy resolved but five weeks later, he presented with
numbness, pain and
paresthesia in the right lateral aspect of the thigh.
He was treated conservatively first with a right LFCN local injection of 10 cc of 25% Marcaine® and 40 mg of Aristocort® , and he was started on Elavil® 25 mg po qhs. His pain was refractory to medical treatment and he refused to pursue medical treatment secondary to the side effects of Elavil. He was refered to us at LSUMC for surgical evaluation. He subsequently underwent a LFCN exploration and the nerve was found to be partially transected. Figure 4 .
Figure 4: Intraoperative view showing lateral femoral cutaneous nerve partially transected (arrow). Download a larger JPEG image of the above figure.
Neurolysis and then resection of the LFCN was performed proximally to the anteior superior iliac spine to allow retraction of the severed nerve into the abdominal wall.Figure 5.
Figure 5: Intraoperative picture showing neurolysis and resection of the lateral femoral cutaneous nerve (arrow). Download a larger JPEG image of the above figure.
The patient experienced relief of symptoms immediately.
As mentioned earlier, many factors must be taken into consideration in the evaluation of MP. Electrophysiological parameters such as sensory conduction velocity(9-10) and somatosensory evoked potentials(11) may help to support the diagnosis of MP. Conservative treatment is initially favored for idiopathic MP because spontaneous recovery is frequent, especially with the removal of provocative agents. Analgesics and local injection may also be successful (12,13,14). In this case, MP was iatrogenic and surgical option was indicated, especially with an iatrogenic mechanism. MP is a rare complication following ICBG . Habal in 1977 reported one case of MP following 160 ICBG that he treated succesfully with conservative measures.(8) Among surgical treatment , transposition of the LFCN and section of the inguinal ligament, neurolysis and transection of the nerve have all been advocated.(2,12,13,15,16). Optimal surgical treatment after conservative treatment remains somewhat controversial. Dellon in 1995 reported 6 cases of MP following ICBG that they treated with neurolysis alone. (6) The follow-up in his series was four month .Van Eerten in 1995 reported a prospective study showing that transection of the LFCN was superior to neurolysis.(16) Kline in 1995 reported good results with nerve
transection.(15) MP is a rare but a distressing complication following ICBG harvesting.
Avoidance of this entity is possible if due consideration is given to the nerve location, understanding of the LFCN's anatomic variation (17,18)- see Figure 6, and bone graft size.
Figure 6: A. Normal course of the lateral femoral cutaneous nerve (LFCN) under the inguinal ligament; B. LFCN passing through a split in the inguinal ligament; C. LFCN astride lateral to the anterior superior iliac spine. (From Edelson JG, Nathan H: Meralgia Paresthetica: An anatomical interpretation. Clinical Orthopedics and Related Research. 122:255-262, 1977 and Keegan JJ, Holyoke EA: Meralgia Paresthetica: An anatomical and surgical study. J Neurosurgery. 19:341-345, 1962).
A well planned incision ( Figure 7) will reduce if not eliminate this complication.(19).
Figure 7: Schematic representation of the suggested incision (red dashed line) to avoid meralgia paresthetica secondary to manipulation of the lateral femoral cutaneous nerve. (From Banwart JC, Asher MA, Hassanein RS: Iliac crest bone graft harvest donor site morbidity: A statistical evaluation. Spine 20:9 1055-1060, 1995). Download a larger JPEG image of the above figure.
MP is a rare complication following ICBG harvesting but is extremely distressing for the patient and the surgeon.There are a variety of surgical options available when non-operative measures have failed. Avoidance of the complication is still the optimal strategy and a well planned incision will avoid this complication. At LSUMC, we prefer LFCN nerve section, excision of a length of damaged nerve, and retraction of the proximal stump into the protection of the abdominal wall as the most successful therapeutic option when we encounter this complication. In our experience, numbness of the thigh is preferable to most patients rather than the possibility of continued neuropathic pain.