Meralgia Paresthetica: Chẩn đoán và điều trị ppt

Journal of the American Academy of Orthopaedic Surgeons 336 The symptom complex of pain, numbness, tingling, and paresthe- sias in the anterolateral thigh not associated with a surgical procedure was first described by Bernhardt in 1878. In 1885, Hager was the first to postulate that compression of the lateral femoral cutaneous nerve (LFCN) was the cause of the pain. In 1895, Roth reported on five pa- tients with similar presentations and initially coined the term “meral- gia paresthetica” from the Greek words meros (“thigh”) and algos (“pain”). Perhaps the most famous case is that of Sigmund Freud, who described symptoms in himself as well as in one of his sons. 1 Anatomic Considerations Familiarity with the underlying neuroanatomy of the affected region is key to understanding the patho- logic changes that occur in meralgia paresthetica. In particular, the ori- gin of the LFCN and its relation to the other structures about the ilium are characteristics that must be con- sidered. The LFCN is an entirely sensory nerve that is usually derived from one of several different combina- tions of the lumbar nerve roots, including L1 and L2, L2 and L3, and L3 alone. 2 Piersol reported that the LFCN can also be partially or entirely derived from adjacent peripheral nerves, such as the genitofemoral and femoral nerves. 3 Keegan and Holyoke 4 reported LFCN variation in 30% of 50 cadaveric dissections. The nerve emerges from the lat- eral aspect of the psoas muscle. It runs beneath the iliac fascia as it crosses the anterior surface of the ili- acus muscle and travels along this retroperitoneal route across the ilium toward the anterior superior Dr. Grossman is Orthopedic Sports Medicine Fellow, Kerlan-Jobe Orthopedic Clinic, Los Angeles, Calif. Dr. Ducey is in private prac- tice in Bellville, NJ. Dr. Nadler is Attending Physician, Department of Physical Medicine and Rehabilitation, New Jersey Medical School, Newark. Dr. Levy is in private practice in Summit, NJ. Reprint requests: Dr. Grossman, Kerlan-Jobe Orthopedic Institute, Suite 125, 6801 Park Terrace, Los Angeles, CA 90045. Copyright 2001 by the American Academy of Orthopaedic Surgeons. Abstract Meralgia paresthetica is a symptom complex that includes numbness, paresthe- sias, and pain in the anterolateral thigh, which may result from either an entrapment neuropathy or a neuroma of the lateral femoral cutaneous nerve (LFCN). The condition can be differentiated from other neurologic disorders by the typical exacerbating factors and the characteristic distribution of symptoms. The disease process can be either spontaneous or iatrogenic. The spontaneous form is usually mechanical in origin. The LFCN is subject to compression throughout its entire course. Injuries most commonly occur as the nerve exits the pelvis. The regional anatomy of the LFCN is highly varied and may account for its susceptibility to local trauma. Relief of pain and paresthesias after injec- tion of a local anesthetic agent is helpful in establishing the diagnosis. If no improvement is found, proximal LFCN irritation should be sought. Idiopathic meralgia paresthetica usually improves with nonoperative modalities, such as removal of compressive agents, nonsteroidal anti-inflammatory drugs, and, if necessary, local corticosteroid injections. If intractable pain persists despite such measures, surgery can be considered, although whether neurolysis or tran- section is the procedure of choice is still controversial. Iatrogenic meralgia paresthetica has been found to occur after a number of orthopaedic procedures, such as anterior iliac-crest bone-graft harvesting and anterior pelvic procedures. Prone positioning for spine surgery has also been implicated. Variations in the anatomy of the LFCN about the anterior superior iliac spine may place the nerve at higher risk for damage. Although nonoperative management usually results in satisfactory results, efforts should be made to avoid injury at the time of surgery. J Am Acad Orthop Surg 2001;9:336-344 Meralgia Paresthetica: Diagnosis and Treatment Mark G. Grossman, MD, Stephen A. Ducey, MD, Scott S. Nadler, DO, and Andrew S. Levy, MD Mark G. Grossman, MD, et al Vol 9, No 5, September/October 2001 337 iliac spine (ASIS). Distally, it enters the anterior region of the thigh by passing under, through, or above the inguinal ligament. It is in this re- gion that the nerve most commonly becomes trapped or injured during surgery (Fig. 1). Most commonly, the LFCN passes 1 cm medial to the ASIS at the level of the inguinal ligament, although there is considerable anatomic varia- tion. 5,6 It is important to understand the regional anatomy and have a working knowledge of the most common variations that can precipi- tate entrapment and increase sus- ceptibility to injury during surgery. Aszmann et al 7 delineated the fre- quency of five variant locations of the LFCN in 52 cadavers (Fig. 2). In type A, the nerve overlies the iliac crest (which occurred in 4% of the cadavers in that study). In type B, it is ensheathed by the inguinal liga- ment (27%). In type C, the LFCN is ensheathed by the tendinous origin of the sartorius (23%). In type D, it is deep to the inguinal ligament and medial to the sartorius (26%). In type E, it is positioned medially on top of the iliopsoas (20%). Of note, 34 (65%) of the cadavers had symmetrical dis- tribution of nerves. Other authors have noted multi- ple branches of the LFCN crossing the inguinal ligament. The intersec- tion with the inguinal ligament can be up to 2 cm lateral to, adjacent to, or as much as 6 cm medial to the ASIS. 6 Murata et al 8 characterized the degree of risk of injury to por- tions of the LFCN in relation to bone-graft harvesting from the ante- rior iliac crest. In their anatomic study, 9.9% of the dissected nerves lay in peril on top of or near the iliac crest. The LFCN lies at a marked angle to the inguinal ligament. This angle can become more acute with extension of the hip; therefore, ex- treme positions should be avoided intraoperatively. Distal to the inguinal ligament, the LFCN splits into anterior and posterior divisions. Each penetrates the fascia lata several centimeters below the ASIS. The anterior branch innervates the area from the anterior thigh to the knee. The posterior branch supplies the lateral thigh up to the level of the greater trochanter. Epidemiology Although spontaneous meralgia paresthetica occurs in all age groups, 9 it is most frequently noted in middle- aged individuals. It may be more prevalent in children than has been reported in the literature. 10 The spontaneous condition is generally regarded as uncommon. Ecker and Woltman 11 showed an incidence of 3 cases in 10,000 general clinic patients. Jones 12 reported the diagnosis in 6.7% to 35% of patients referred for leg discomfort. There is no consen- sus in the literature about whether there is a sex predominance. Etiology The etiology of this mononeuropa- thy is highly variable. The disease process may be categorized as either spontaneous or iatrogenic. The spon- taneous form occurs in the absence of any prior surgical procedure that may have injured the LFCN at some point along its pathway, and can be further categorized as either idio- pathic or metabolic. The iatrogenic form is a well-known complication of many common orthopaedic proce- dures. Both mechanical and meta- bolic factors may be involved. Mechanical Factors The LFCN is subject to injury at several sites along its course. Irri- tation most often occurs at or near the site where the LFCN pierces or crosses the inguinal ligament. The nerve is superficial at this point and lies at an acute angle in hip exten- sion. Stookey 13 noted that standing aggravates symptoms and sitting helps to relieve them. Predisposing anatomic variations, such as types A, B, and C in the classification of Aszmann et al, 7 increase the likeli- hood of compression. External causes, such as the wearing of seat belts, 11 girdles, 11 and tight trousers, 14 can result in direct pressure on the LFCN. Obe- sity, pregnancy, and other condi- tions associated with increased ab- dominal pressure may predispose to entrapment. 6 Pelvic disease, such as an intra-abdominal tumor, has reportedly presented as meralgia paresthetica. 15 The nerve may also become trapped in a retroperitoneal location or at the point where it pene- trates the fascia lata. In rare in- stances, a bone tumor in the iliac crest near the ASIS can present as meralgia paresthetica. 16 Metabolic Factors Metabolic disorders such as dia- betes mellitus, alcoholism, and lead poisoning can cause an isolated Figure 1 The anatomic course of the LFCN. (Adapted with permission from Mirovsky Y, Neuwirth M: Injuries to the lateral femoral cutaneous nerve during spine surgery. Spine 2000;25:1266-1269.) LFCN Likely point of compression Meralgia Paresthetica Journal of the American Academy of Orthopaedic Surgeons 338 neuropathy of the LFCN. However, the cause of metabolic neuropathy has not been well defined. In diabetes, there are two current theories. One hypothesis involves abnormalities in the metabolism of pyruvate, sorbitol, and lipids. Spe- cifically, the slowing of nerve con- duction has been experimentally linked to activation of the polyol (sorbitol) pathway by glucose. 17 Sec- ondary alterations in myo-inositol and phosphoinositide metabolism result in impairment of sodium- potassium adenosine triphosphatase activity, which leads to nerve dys- function. The second hypothesis is that in diabetes the nerve swells due to decreased axoplasmic transport, rendering it more susceptible to compression. 18 Optimization of blood glucose levels has not provided relief for affected patients. The treatment goal and therapeu- tic approach for metabolic meralgia paresthetica remain the same as those for the mechanical form of the disease. Similar treatment is also employed for meralgia paresthetica associated with inflammatory disor- ders, such as lupus neuropathy. 18 Evaluation The clinical presentation of meralgia paresthetica includes pain, numb- ness, and/or dysesthesia in the region of the anterolateral thigh. There is often a delay in diagnosis in patients with these symptoms and even failure to recognize the entity. It is important for the clini- cian to be familiar with the presen- tation and treatment of this condi- tion, because if undetected it may lead to significant patient distress and disability. Figure 3 is an algo- rithm for the evaluation and treat- ment of meralgia paresthetica. History and Physical Examination Patients typically describe numb- ness, tingling, pain, burning, and decreased sensitivity to pain, touch, and temperature in the distribution of the LFCN. Hypersensitivity to touch and dysesthesias may also be reported. Palpating the area in question usually aggravates symp- toms. Many patients have tender- ness over the lateral inguinal liga- ment at the point where the nerve crosses the ligament. The condition is often exacerbated by hip exten- sion during walking or getting into and out of an automobile. An area Figure 2 Five common variant locations of the LFCN as it exits the abdomen. In type A, the LFCN overlies the iliac crest (frequency in the study by Aszmann et al 7 of 52 cadavers, 4%). In type B, the nerve is ensheathed by the inguinal ligament (27%). In type C, it is ensheathed by the tendinous origin of the sartorius (23%). In type D, the nerve is deep to the inguinal ligament and medial to the sartorius (26%). In type E, it is positioned medial- ly on top of the iliopsoas (20%). (Adapted with permission from Aszmann OC, Dellon ES, Dellon AL: Anatomical course of the lateral femoral cutaneous nerve and its susceptibility to compression and injury. Plast Reconstr Surg 1997;100:600-604.) Type A Type B Type C Type D Type E Mark G. Grossman, MD, et al Vol 9, No 5, September/October 2001 339 of hair loss may be present on the thigh secondary to repetitive rub- bing of the region by the patient. This massaging is a common at- tempt to relieve symptoms and is an important diagnostic clue. The clinical presentation is usu- ally unilateral; however, 20% of patients present with bilateral com- plaints. 11 Other neurologic, gastro- intestinal, and urogenital symptoms are not part of the process; their presence should suggest that the leg symptoms are due to a condition other than meralgia paresthetica. The constellation of signs and symptoms that has been described usually enables the physician to make a diagnosis based on the histo- ry and physical examination find- ings. A Tinel’s sign is frequently pres- ent 1 cm medial and inferior to the ASIS, but is dependent on anatomic variation. The nerve may be palpa- ble in thin patients, which may cause irritation. Rapid relief of symptoms with a local anesthetic nerve block can confirm the diagnosis. Electrodiagnostic Testing When the history and physical examination are nonconfirmatory, electrodiagnostic testing may be effective in establishing the diagno- sis. Two techniques for evaluating nerve conduction can be used. The first method involves stimulating the LFCN as it exits the pelvis near the ASIS and recording potentials distally. The second technique in- volves stimulating distally along the course of the nerve and recording proximally in the region of the ASIS. Measurements on the unaffected side should always be recorded, as these responses are typically of small amplitude. 19 Somatosensory evoked potentials (SSEPs) can also be utilized with segmental or dermatomal tech- niques. An abnormal latency or a side-to-side decrement greater than 50% is considered abnormal. 20,21 Wiezer et al 22 found that SSEPs were useful in determining whether meralgia paresthetica was caused by an injury in a region proximal to the ASIS. However, on comparing the results of nerve conduction studies with the SSEP findings in 30 patients with clinical evidence of unilateral meralgia paresthetica, Seror 23 found that nerve conduction studies were more accurate. Differential Diagnosis Any patient with a motor deficit, reflex changes, or sensory deficits not specific to the LFCN should be completely evaluated. Other causes of anterolateral thigh pain must be considered. A plain radiograph should be obtained to assess the pel- vic architecture as well as to elimi- nate pelvic tumors and osteoarthritis Positive Negative Condition resolved No further treatment Condition unresolved Condition resolved Condition unresolved No further treatment Surgical exploration Evaluate further for underlying condition (e.g., neuropathy, radiculopathy, proximal entrapment) Initial treatment with NSAIDs, protection, avoidance of compression Pharmacologic intervention Local steroid injection History that suggests idiopathic meralgia paresthetica: • Location of sensory alteration in anterolateral thigh • Pain, numbness, dull ache, itching, tingling • History of trauma to region • History of diabetes, alcoholism, or lead poisoning • No previous surgery that might have affected the LFCN Diagnostic regimen: • Diagnostic nerve block • Electrodiagnostic testing • Somatosensory evoked potentials Physical examination findings that suggest idiopathic meralgia paresthetica: • Sensory changes (hypesthesia, hyperesthesia, dysesthesia present over anterolateral thigh) • Signs/symptoms exacerbated by hip extension Figure 3 Algorithm for the evaluation and treatment of idiopathic meralgia paresthetica. Meralgia Paresthetica Journal of the American Academy of Orthopaedic Surgeons 340 of the hip as potential etiologic factors. Differentiation of inguinal re- gional entrapment of the LFCN due to upper lumbar nerve compression or intra-abdominal compression is more challenging. In such cases, local block would not be expected to relieve the symptoms. Any con- comitant gastrointestinal or urogen- ital symptoms should immediately raise suspicion of a pelvic mass. Ultrasound, computed tomogra- phy, or magnetic resonance imaging can be used to assess the retroperi- toneal region. The entity most com- monly confused with meralgia paresthetica is lumbar disk disease. Meralgia paresthetica is purely sen- sory in nature and does not follow distinct dermatomal distributions, in contrast to disk disease, in which there may be motor or reflex def- icits. In the patient with meralgia paresthetica, there should be no sci- atic notch tenderness or a positive response to the straight-leg-raising test. Symptoms are usually relieved with hip flexion. Both clinical exam- ination and electromyography can usually differentiate the entities. However, magnetic resonance imag- ing may be necessary to establish the diagnosis. Somatosensory evoked potentials have been used success- fully by several authors to support a diagnosis of meralgia paresthetica if further clarification is needed. 24 Nonoperative Management Nonoperative treatment of patients with focal compression of the LFCN should be directed at correcting the underlying disorder. A history of recent weight gain, tightness when wearing trousers, or recent trauma should be sought. The patient should be warned to avoid compression, and application of protective padding over the region should be considered. Nonsteroidal anti-inflammatory drugs are the mainstay of treatment to alleviate inflammation, which may cause intrinsic compression. The use of tricyclic antidepressants, anticon- vulsants, and antiarrhythmic agents may be initiated to treat the effects of neuropathic pain. 25 Topical agents, such as capsaicin and lidocaine- prilocaine cream, can also be tried to decrease surface hypersensitivity. 26 Meralgia paresthetica in pregnancy usually resolves after delivery. 5 Local injection of xylocaine with a corticosteroid may be beneficial to decrease local inflammation. This should be performed 1 cm medial to the ASIS or in the region of maximal tenderness. Repeat injections may be required, as determined by the clini- cal course. Local infiltration resulted in complete relief for 32 (74%) of 43 patients in one study with a follow- up interval of 1 year. 27 Edelson and Stevens, 10 however, found a lack of response to steroids in children. Overall, nonoperative treatment has yielded excellent results. How- ever, most clinical series have em- ployed numerous treatment methods; therefore, the efficacy of individual modalities is unclear. In a review of 29 patients, Ecker and Woltman 11 reported that approximately two thirds showed improvement with nonoperative treatment at the 2- year follow-up evaluation. How- ever, no details were offered regard- ing the condition of those for whom nonoperative therapy was a failure. Williams and Trzil 6 demonstrated relief of symptoms with nonopera- tive care in more than 91% of 277 patients with meralgia paresthetica. Bollinger 28 reported a 25% recovery rate in his series of 158 patients. Surgical Intervention Nonoperative treatment alone will reduce the severity of most patients’ symptoms to an acceptable level. Only when the complaints become intractable and disabling should surgery become an option. Surgical procedures for meralgia paresthetica date back to 1885. Three basic sur- gical techniques have evolved for this disorder: neurolysis of only the constricting tissue, neurolysis and transposition of the LFCN, and tran- section with excision of a portion of the LFCN. Neurolysis Macnicol and Thompson 29 re- ported on 25 patients with refractory meralgia paresthetica. Exploration and decompression of the LFCN 18 months after the onset of pain was successful in 11 (44%) of these pa- tients at an average follow-up inter- val of 5.5 years. On the basis of their results, the authors recommended surgery for patients with symptoms with a duration of less than 1 year as well as clearly defined sensory loss. Nahabedian and Dellon 18 noted complete relief of symptoms in 18 of 23 patients and partial relief in 4 others after surgical decompression of the nerve. Edelson and Stevens 10 reported the results of treatment of 21 lesions in 13 children. After oper- ative decompression, there was com- plete relief of pain from 14 lesions, occasional pain but no disability from 5 lesions, and persistent pain only with sports activities with 2 lesions. Neurolysis and Transposition Keegan and Holyoke 4 described two cases in which LFCN release and medial transposition provided good results. Aldrich and van den Heever 30 described a suprainguinal ligament approach for release and transposition. In both studies, per- formance of this procedure was con- tingent on the nerve appearing as a single trunk at the ASIS. No larger series in which this particular tech- nique was used have been reported. Transection Williams and Trzil 6 reported the data on 24 patients with meralgia paresthetica that was unrelieved by Mark G. Grossman, MD, et al Vol 9, No 5, September/October 2001 341 nonoperative measures. Sectioning of the LFCN successfully relieved symptoms in 23 of the 24 patients. Although sectioning of the nerve results in permanent anesthesia in the anterolateral thigh, there were no other serious sequelae. Transection Versus Neurolysis In 1995, van Eerten et al 31 com- pared the results of transection and neurolysis in 21 patients after failure of nonoperative treatment. Transec- tion was performed in 11 patients and neurolysis in 10 patients. The average follow-up interval was 74 months. Complete relief of symp- toms occurred in 9 patients who underwent transection, compared with 3 patients in whom neurolysis was used. Therefore, the authors recommended transection as the procedure of choice. Ivins 32 performed neurolysis in four of eight operative cases of me- ralgia paresthetica. All four patients had consistent immediate relief, but the symptoms recurred 2 to 24 months later. All four subsequently underwent resection of the LFCN and had no recurrence. The other four underwent initial transection and had persistent relief at long- term follow-up (3 to 6 years). Whether the preferred surgical management is neurolysis or tran- section remains controversial. Pro- ponents of neurolysis assert that the nerve should be decompressed from just proximal to the pelvic brim to as far distally as possible. They believe this will provide ade- quate decompression and successful surgery without the disadvantage of creating permanent anterolateral anesthesia. Some surgeons have reported unpleasant hyperesthesias with resection, whereas others have reported dysesthesias after neu- rolysis but not after transection. 31 Symptoms in an intact nerve may be due to an LFCN neuroma, which neurolysis cannot ameliorate. Re- section should, therefore, be cura- tive, providing more predictable relief but at the expense of the sen- sory innervation. The initial step should be to per- form neurolysis with decompres- sion. Resection is contemplated only after failure of neurolysis. In certain situations, transection may be the treatment of choice if neurol- ysis and/or transposition is not feasible. Transection may be ap- propriate if the LFCN has been irreparably damaged by pressure, if there are multiple branches of the LFCN exiting the pelvis, if the LFCN crosses the iliac crest, or if an adult patient has had symptoms for more than 1 year. Surgical Technique As the entire nerve should be ex- plored, an adequate incision must be made to allow for the anatomic variations that have been reported. With the patient under general anesthesia, a 3- to 5-cm oblique or S- shaped incision is made 2 cm distal to the area of tenderness at the pre- sumed pelvic brim exit of the LFCN. Exposure is carried down to the level of the LFCN. Once identified, the nerve is examined for pathologic changes (Fig. 4). The nerve is then released toward the thigh and into the retroperitoneum, with excision of all overlying and underlying fas- cia, including the compressive por- tion of the inguinal ligament. The nerve must be properly ex- posed for transection. The nerve is then pulled distally and sectioned so that the released proximal end falls back in the pelvis, thereby avoiding neuroma formation. A nerve segment of at least 4 cm must be resected, including any portion with obvious pathologic changes. Iatrogenic Meralgia Paresthetica Meralgia paresthetica has been re- ported after several types of surgical procedures in the region of the ASIS. The surgical approaches may either directly injure the nerve or endanger the nerve with local scarring. 33 These procedures include acetabular fracture surgery, 34,35 pelvic osteoto- mies, 36 and bone-graft harvesting from the iliac crest. 33,37-39 It has also been reported after several nonor- thopaedic interventions, such as bariatric surgery 40 and laparoscopic hernia repair. 41 Symptoms of antero- lateral dysesthesia after surgery in the region of the hip or pelvis should suggest the presence of meralgia paresthetica. Nonoperative modalities, in- cluding the use of nonsteroidal anti- inflammatory drugs, looser clothing, and steroid injections, are impor- tant initial measures. Resolution of symptoms generally occurs within 3 months. However, persistent symp- toms may necessitate surgical inter- vention. There has not yet been a well- controlled study comparing the use of neurolysis and transection in the treatment of postsurgical meralgia paresthetica. However, most authors of larger series recommend transec- tion because of the potential for neu- roma formation. Figure 4 Exploration of the LFCN reveals entrapment of the nerve. White arrow indicates inguinal ligament; arrowhead, LFCN; black arrow, point of entrapment between two slips of inguinal ligament. Meralgia Paresthetica Journal of the American Academy of Orthopaedic Surgeons 342 Bone-Graft Harvesting From the Anterior Iliac Crest Injury to the LFCN has been re- ported in as many as 10% of cases in series in which bone was harvested from the anterior iliac crest. 33,37-39 Kurz et al 39 described three mecha- nisms for nerve injury in this setting: neurotmesis as the nerve crosses the anterior iliac crest, neurapraxia due to retraction of the iliacus during exposure of the ilium, and crush injury to the outer table of the iliac crest secondary to excessive strip- ping. One recommendation is to keep incisions 2 cm lateral to the ASIS. 39 The LFCN is lateral to the ASIS when it crosses the iliac crest in as many as 10% of cases. 5-8 When taking a graft from the outer table of the iliac crest, it is important to avoid penetration of the inner table, so as to prevent in- jury as the LFCN crosses the iliacus muscle. Careful retraction and dis- section of the inner table will also limit injury to the LFCN. If the LFCN is found to be injured, the nerve should be severed and allowed to retract into the pelvic region. This will decrease the incidence of neu- roma formation. Overall, meticu- lous hemostasis and dissection will minimize hematoma and scar for- mation. Use of a drain may be ben- eficial in preventing postoperative hematoma formation. Newer coring techniques for bone-graft harvesting from the iliac crest have also been implicated in LFCN damage. 42 Although there are many potential advantages to the coring technique for graft har- vesting, one must understand that with certain anatomic variants the LFCN is still in danger. Recom- mendations to avoid injury include making a 1-cm incision at least 5 cm but no more than 8 cm posterior to the ASIS. Retractors should be placed after careful blunt dissection to the crest and should remain fixed during coring to minimize the risk of neurotmesis. Spine Procedures Spine surgery carries the risk of LFCN injury during bone-graft har- vesting from the anterior iliac crest, prone positioning, and retroperito- neal approaches. Mirovsky and Neuwirth 43 found a 20% complica- tion rate in 105 patients who under- went a spine procedure. Each subset of spine procedures or approaches was examined separately. Compres- sion was implicated as the cause of LFCN damage when a Hall-Relton frame was used for posterior spinal fusions. All the bilateral injuries were found in this group. Bone- graft harvesting from the anterior iliac crest was also implicated in the anterior cervical fusion group. Two patients who did not recover func- tion after 1 year were in this group. It may be assumed that the nerve was transected during the surgical approach. Retraction of the psoas during retroperitoneal dissection was also found to be a cause of LFCN neurapraxia, as the LFCN travels just lateral to the muscle in the pelvic region. Because of the small numbers of patients in the subgroups in that study, it was not possible to mea- sure the prevalence of LFCN injury in each. However, 89% of all injured nerves had recovered by 3 months. Avoiding excessive retraction about the LFCN and using adequate pad- ding during prone positioning may decrease the incidence of postopera- tive meralgia paresthetica. It is im- portant that patients be informed about the potential occurrence of this complication. Use of Ilioinguinal and Iliofemoral Approaches The ilioinguinal approach to the acetabulum risks injury to the LFCN. The nerve may be injured due to excessive retraction, postoperative scar or hematoma formation, or di- rect injury. Hospodar et al 35 per- formed cadaver dissections utilizing the ilioinguinal approach to deter- mine its relationship to the LFCN. At some points, the nerve was as much as 40 mm away from the ASIS. Therefore, if the LFCN is not found near the ASIS, careful medial dissec- tion may be necessary to locate the nerve. De Ridder et al 34 performed a two-part study: an anatomic study and a clinical correlation. An ilioin- guinal approach was used on 200 cadavers. The LFCN was found to be normal in position in 149 (74%) and abnormal in 51 (26%). A clini- cal retrospective analysis found 82 patients with postoperative LFCN sensory changes after use of an ilioinguinal approach. Eleven had persistent symptoms after 1 year, and 5 went on to require surgical in- tervention. In a second group of 40 patients treated after the first group, a perioperative protocol was insti- tuted to diminish the risk of meral- gia paresthetica. The LFCN was identified and neurolysis was per- formed in 33 patients. The remain- ing 7 patients underwent transection of the nerve because of an intraoper- ative lesion. No complaints were noted at 1 year. The transection group had a decrease in the area of insensate distribution. Overall, the incidence of decreased sensation in their series was 35%, and painful dysesthesias occurred in 5% of their patients. Recommendations regarding acetabular approaches include flexing the hip to minimize LFCN tension and trimming the anterior iliac crest before wound closure to avoid excessive retraction of the nerve. Knowledge of the anatomic variations should lessen direct injury. If intraoperative injury is discovered, transection may be necessary to avoid neuroma for- mation. Most symptoms subside by 3 to 6 months after surgery. The patient should always be informed of the risk of potential LFCN injury when discussing these acetabular approaches. Mark G. Grossman, MD, et al Vol 9, No 5, September/October 2001 343 Summary Meralgia paresthetica is a mono- neuropathy of the LFCN. The con- dition may be categorized as either spontaneous or iatrogenic. The spontaneous form may be further categorized as either mechanical or metabolic in origin. A thorough clinical history and physical exami- nation will often be sufficient for accurate diagnosis of the disorder. Nonoperative treatment is usually successful. However, a small num- ber of patients will need operative intervention. Most iatrogenic cases of meralgia paresthetica abate with time. It is essential to clearly in- form patients about the risk of LFCN injury before surgery about the ASIS. Meticulous intraopera- tive technique may decrease the incidence of the disorder after pelvic surgery. References 1. Schneck JM: Sigmund Freud, Josef Breuer, and Freud’s self-observations on meralgia paresthetica. N Y State J Med 1983;83:968-969. 2. Sunderland S: Nerves and Nerve Injuries. Edinburgh: E & S Livingstone, 1968. 3. Huber GC (ed): Human Anatomy: Includ- ing Structure and Development and Prac- tical Considerations, 9th ed. Philadel- phia: JB Lippincott, 1930, pp 2104-2106. 4. Keegan JJ, Holyoke EA: Meralgia paresthetica: An anatomical and surgi- cal study. J Neurosurg 1962;19:341-345. 5. Ghent WR: Further studies on meral- gia paresthetica. Can Med Assoc J 1961; 85:871-872. 6. Williams PH, Trzil KP: Management of meralgia paresthetica. J Neurosurg 1991;74:76-80. 7. 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