Iliohypogastric Nerve
Anatomy
The iliohypogastric nerve arises primarily from the ventral primary rami of L1 and occasionally with a twig from T12. This nerve has a pathway similar to that of the intercostal nerves in the thoracic region. The iliohypogastric nerve traverses the psoas major muscle, piercing the lateral border of the muscle anterior to the quadratus lumborum muscle and posterior to the kidney to traverse the lateral abdominal wall. The nerve penetrates the transverse abdominal muscle near the iliac crest, coming between it and the internal oblique musculature. The nerve supplies the lower fibers of the transverse abdominal muscle and the internal oblique, and divides into the lateral and anterior cutaneous branches.
The anterior cutaneous branch continues anteriorly between the internal oblique and transverse abdominal muscle, then pierces the internal oblique and becomes cutaneous through an opening in the fascial aponeurosis of the external oblique muscle, approximately 2-3 cm cephalad to the superficial inguinal ring. The distribution of the cutaneous sensation is a small region just superior to the pubis.
Etiology
The iliohypogastric nerve is rarely injured in isolation. The most common causes of injury are surgical procedures. These include transverse lower abdominal incisions, as in hysterectomies, or injuries from procedures such as inguinal herniorrhaphy and appendectomies. The injuries mainly occur if the incision extends beyond the lateral margin of the inferior rectus abdominis fibers. The damage can result from direct surgical trauma, such as passing a suture around the nerve and incorporating it into the fascial repair, or postoperative entrapment in scar tissue or neuroma formation. Sports injuries, such as trauma or muscle tears of the lower abdominal muscles, may also result in injury to the nerve. Injury may also occur during pregnancy, owing to the rapidly expanding abdomen in the third trimester. This is called the idiopathic iliohypogastric syndrome and is rare.
Clinical
Symptoms include burning or lancinating pain immediately following the abdominal operation. The pain extends from the surgical incision laterally into the inguinal region and suprapubic region. Discomfort may occur immediately or up to several years after the procedure, and may last for months to years. This discomfort is possibly because of the formation of scar tissue in the region. Occasionally, the pain may extend into the genitalia because of significant overlap with other cutaneous nerves. Loss of sensation is usually minimal and not problematic. Iliohypogastric nerve entrapment causing symptoms similar to trochanteric bursitis refractory to conventional therapy has been reported.
On examination, pain and tenderness are usually present in the area of scarring or entrapment. Hyperesthesia or hypoesthesia may occur in the area supplied by this nerve. Diagnosis is difficult, owing to the small area of cutaneous supply that this nerve provides. There may be overlap in sensory supply with the genitofemoral and ilioinguinal nerves.
Three major criteria are used to diagnose this nerve injury. The first is a history of a surgical procedure in the lower abdominal area, although spontaneous entrapment can occur. Pain can usually be elicited by palpating laterally about the scar margin, and the pain usually radiates inferomedially toward the inguinal region and into the suprapubic and proximal genital area. Second, a definite area of hypoesthesia or hyperesthesia should be identified in the region of supply of the iliohypogastric nerve. Third, infiltration of a local anesthetic into the region where the iliohypogastric and ilioinguinal nerves depart the internal oblique muscle and where symptoms can be reproduced on physical examination by palpation should provide symptomatic relief.
If no relief is obtained with injection, a different etiology should be sought for the discomfort. Alternate diagnoses include upper lumbar or lower thoracic nerve root pathology, or discogenic etiology of the pain. If the iliohypogastric nerve is identified clearly as the source of pain, and a favorable response is not obtained with local anesthetic injection, then surgical exploration and resection of the nerve should be considered. No reliable electrodiagnostic techniques are available to define the integrity of this nerve, although needle electromyography of the lower abdominal musculature may serve as an adjunct in the diagnosis.
Treatment
Treatment includes local injection of an anesthetic (as noted above), oral medications, or physical therapy. The oral medications may include antiseizure medications, such as gabapentin (Neurontin), carbamazepine (Tegretol), or lamotrigine (Lamictal), as well as nonsteroidal anti-inflammatory drugs (NSAIDs), tricyclic antidepressant medications (amitriptyline [Elavil], doxepin), capsaicin cream, topical lidocaine (Lidoderm patches), or tramadol (Ultram). With physical therapy, cryotherapy or a transcutaneous electrical nerve stimulation (TENS) unit may be tried. When conservative measures are not successful, surgical excision may result in relief of pain with few potential complications. Potential complications include possible neurolysis of the nerve in refractory cases. Surgical excision is more invasive but has had good outcomes in several reports. Krahenbuhl and colleagues reported an endoscopic approach.
[1]Ilioinguinal Nerve
Anatomy
The ilioinguinal nerve arises from the fusion of T12 and L1 nerve roots and emerges from the lateral border of the psoas muscle; it traverses the anterior abdominal wall to the iliac crest just inferior to the hypogastric nerve. Adjacent to the anterior margin of the iliac crest, the nerve pierces the transversus abdominis and internal oblique muscles (providing neural branches to these) and sending neural branches to the iliohypogastric nerve. The nerve then supplies sensory branches to supply the pubic symphysis, the superior and medial aspect of the femoral triangle, and either the root of the penis and anterior scrotum in the male or the mons pubis and labia majora in the female.
Etiology
Causes of injury include lower abdominal incisions (Pfannenstiel), pregnancy, iliac bone harvesting, appendectomy, inguinal herniorrhaphy, inguinal lymph node dissection, femoral catheter placement, orchiectomy, total abdominal hysterectomy, and abdominoplasty. Nerve injury can also occur idiopathically. The prevalence of injury with surgery has declined, owing to the use of laparoscopic procedures. Tearing of the lower external oblique aponeurosis may also cause injury to this nerve. This injury has been reported in hockey players.
Clinical
Symptoms may include hyperesthesia or hypoesthesia of the skin along the inguinal ligament. The sensation may radiate to the lower abdomen. Pain may be localized to the medial groin, the labia majora or scrotum, and the inner thigh. The characteristics of the pain may vary considerably. Patients may be able to associate their pain clearly with a traumatic event or with the surgical procedure.
Pain and tenderness may be present with application of pressure where the nerve exits the inguinal canal in up to 75% of patients. Sensory impairment is common in the above-noted distribution of the nerve supply. Symptoms usually increase with hip extension (patients walk with the trunk in a forward-flexed posture). Pain may also be reproduced with palpation medial to the anterosuperior iliac spine (ASIS).
The diagnosis can be made on the basis of local infiltration of anesthetic with or without steroid, which should result in relief within 10 minutes. Unfortunately, no electrodiagnostic techniques are readily available to test this nerve. Abdominal needle electromyography may be helpful in determining the severity of nerve injury, but electromyography is not sensitive or specific.
Treatment
Treatment includes local injection of an anesthetic, physical therapy, or oral medications. Types of medications may include antiseizure medications, such as gabapentin (Neurontin), carbamazepine (Tegretol), or lamotrigine (Lamictal), as well as NSAIDs, tricyclic antidepressant medications (amitriptyline [Elavil], doxepin), capsaicin cream, topical lidocaine (Lidoderm patches), or tramadol (Ultram). Ice or possibly a TENS unit may be used with physical therapy. When conservative measures are not successful, surgical excision may result in relief of pain with few potential complications.
Genitofemoral Nerve
The genitofemoral nerve or its branches (genital or femoral branches) can be entrapped throughout its course. Nerve injury occurs most commonly as a complication of lower abdominal surgeries.
Anatomy
The genitofemoral nerve arises from the L1 and L2 ventral primary rami, which fuse in the psoas muscle. The nerve then pierces the anterior surface of the psoas major muscle at the level of L3-4 and descends on the fascial surface of the psoas major muscle past the ureter. It then splits into the genital and femoral branches near the inguinal ligament.
The genital branch continues along the psoas major to the deep inguinal ring and enters the inguinal canal. It supplies the cremaster muscle, spermatic cord, scrotum, and adjacent thigh in males. In females, it travels with the round ligament of the uterus and provides cutaneous sensation to the labia majora and adjacent thigh. The femoral branch lies lateral to the genital on the psoas major and travels lateral to the femoral artery and posterior to the inguinal ligament to enter the proximal thigh. There, it pierces the sartorius muscle distal to the inguinal ligament and supplies the proximal portion of the thigh about the femoral triangle just lateral to the skin that is innervated by the ilioinguinal nerve.
Etiology
Nerve injury may result from hernia repair, appendectomy, biopsies, and cesarean delivery. Injury may also result from intrapelvic trauma to the posterior abdominal wall, retroperitoneal hematoma, pregnancy, or trauma to the inguinal ligament. Fortunately, injury to this nerve is rare, even with open herniorrhaphy.
A prospective study was performed to evaluate the genitofemoral nerve electrophysiologically in children with inguinal hernia repair. Latency of the genitofemoral nerve was found to be prolonged after inguinal hernia repair possibly because of surgical-related injury.
[2]Clinical
Injury to the femoral branch causes hypoesthesia over the anterior thigh below the inguinal ligament, which is how it is distinguished from the iliohypogastric and ilioinguinal nerve. Groin pain is a common presentation of neuralgia from nerve injury or entrapment. The pain may be worse with internal or external rotation of the hip, prolonged walking, or even with light touch. Differential diagnoses include injury to the ilioinguinal and genitofemoral nerves as well as L1-2 radiculopathies. Some anatomic overlap may exist with the supply of the ilioinguinal and genitofemoral nerves, which makes the diagnosis somewhat difficult to establish.
Unfortunately, no reliable electrodiagnostic test exists that can be used for diagnosis of injury to this nerve. Oh has discussed a side-to-side sensory comparison study, but this test is technically difficult to perform.
[3] Diagnosis typically is made using anesthetic nerve blocks. Injection of the ilioinguinal and iliohypogastric nerves anteriorly should leave the pain or abnormal sensation unchanged. A block of the L1 and L2 roots should then result in relief. This should help to determine the diagnosis and to prevent unnecessary surgical exploration of an uninjured nerve.
Treatment
The above-mentioned blocks are diagnostic and therapeutic. Avoidance of aggravating activities should be emphasized. Treatment may also consist of antiseizure medications, such as gabapentin (Neurontin), carbamazepine (Tegretol), or lamotrigine (Lamictal), as well as tricyclic antidepressant medications (amitriptyline [Elavil], doxepin). Other medications include capsaicin cream, topical lidocaine (Lidoderm patches), NSAIDs, or, possibly, tramadol (Ultram). A trial with a TENS unit may also be beneficial.
If conservative treatment fails, surgical excision of the nerve is the treatment of choice. Some authors describe a transabdominal approach to the nerve (Magee and Lyon) with satisfactory results.
[4, 5] The complications of this procedure include hypoesthesia of the scrotum or labium majus and of the skin over the femoral triangle, as well as loss of the cremasteric reflex. This usually will not result in notable morbidity. According to Harms and colleagues, an extraperitoneal approach should result in fewer operative complications.
[6]Lateral Femoral Cutaneous Nerve
Injury or entrapment of the lateral femoral cutaneous nerve is also known as meralgia paresthetica. It is derived from the Greek word meros, meaning thigh, and algo, meaning pain. It is a syndrome of paresthesia and pain in the lateral and anterolateral thigh. This syndrome is seen most commonly in individuals aged 20-60 years, but it can occur in people of all ages.
Anatomy
This nerve arises from the ventral primary rami of L2-4 where they divide into anterior and posterior branches. The dorsal portions fuse to form the lateral femoral cutaneous nerve in the midpelvic region of the psoas major. The nerve then courses over the iliacus toward the ASIS. The nerve travels posterior to the inguinal ligament and superior to the sartorius muscle at the iliac crest region and divides into anterior and posterior branches. The anterior branch comes off 10 cm distal to the inguinal ligament in line with the ASIS, and supplies cutaneous sensation to the lateral thigh, including just proximal to the patella. It then communicates with cutaneous branches of the femoral nerve and saphenous nerve to form the patellar plexus. The posterior branch pierces the fascia lata posteriorly and laterally, and divides into multiple, small branches that supply the skin from the greater trochanter to the midthigh.
[7]Etiology
Entrapment usually occurs at the inguinal ligament. The peak incidence for this condition is in middle age. Differential diagnoses include lumbar radiculopathies and discogenic or nerve root problems at L2 and L3. The entrapment may be from intrapelvic causes, extrapelvic causes, or mechanical causes. Intrapelvic causes include pregnancy, abdominal tumors, uterine fibroids, diverticulitis, or appendicitis. Injury has been described in cases of abdominal aortic aneurysm. Examples of extrapelvic causes include trauma to the region of the ASIS (eg, from a seatbelt in a motor vehicle accident), tight garments, belts, girdles, or stretch from obesity and ascites. Mechanical factors include prolonged sitting or standing and pelvic tilt from leg-length discrepancy. Diabetes can also cause this neuropathy in isolation or in the clinical setting of a polyneuropathy.
Clinical
Symptoms include anterior and lateral thigh burning, tingling, and/or numbness, that increase with standing, walking, or hip extension. Symptoms may also increase with lying prone. Symptoms usually are unilateral but may be bilateral in rare cases. The symptoms usually improve with sitting unless compressive forces, such as tight belts or garments, remain.
Physical examination findings may be completely normal. Findings may include hyperesthesia over the lateral thigh (usually in a smaller area than the symptoms). Pain can be produced by pressure medial to the ASIS. A positive Tinel sign may be present over the ASIS or inguinal ligament.
Diagnosis of this entrapment may again be based on an injection of local anesthetic near the inguinal ligament or ASIS. Spontaneous recovery usually is expected. Electrodiagnostic testing may be performed for diagnosis. With nerve conduction studies, the technique includes using a bar electrode for recording and reference. This can be performed with either antidromic (conduction against the direction of sensory fiber conduction) or orthodromic (conduction in the direction of nerve conduction) methods. The antidromic study is usually easier to perform, although response may be absent bilaterally on occasion. The response is small and difficult to obtain in obese patients.
A needle stimulation electrode may needed. The sensory response is absent in 71% of patients with meralgia paresthetica and is prolonged in 24% of patients with this condition. Electromyographic test results with needle are normal in patients with this diagnosis, which may help to differentiate it from an upper lumbar radiculopathy. Technically, the sensory test is a difficult study and a response must be present on the opposite side to determine entrapment. It may be nearly impossible to obtain a response in an obese patient or a patient with a large abdomen without using a needle for stimulation. Unfortunately, the test may be difficult for the patient to tolerate because of the large amount of current (with respect to more peripheral nerves) that is required to stimulate a nerve that lies under adipose tissue.
Treatment
Treatment may include the injection of local anesthetic agents, as previously noted. A steroid can also be used to prolong the effects of the local anesthetic and reduce inflammation. Oral medications, such as NSAIDs, antiseizure medications (gabapentin [Neurontin]), tricyclic antidepressants, and tramadol may be used, as may capsaicin cream and topical lidocaine. One must also instruct patients on ways to prevent further irritation of the nerve. These may include avoidance of hip extension, prolonged standing, and compressive garments. The use of ice and a TENS unit may also be helpful. Surgical exploration may be required if the above treatment options are not helpful. This includes transection of the nerve, or decompression with or without neurolysis. Anatomical variations of the nerve and neuromas can occur and lead to recurrence.
[8]Femoral Nerve
Anatomy
The femoral nerve arises from the posterior divisions of the ventral primary rami of L2, L3, and L4 within the psoas major muscle. These nerves join to form the largest branch of the lumbar plexus. The nerve emerges from the lateral border of the psoas muscle and courses inferiorly in the intermuscular groove between this muscle and the iliacus muscle. It then passes under the inguinal ligament lateral to the femoral artery and vein. It then divides into multiple branches within the femoral triangle. In the proximal thigh it divides into sensory branches that innervate the upper and anterior thigh, and muscular branches that innervate the quadriceps muscle. One of the major branches is the lateral femoral cutaneous nerve, as discussed previously.
[9]Another branch is the medial femoral cutaneous nerve, which originates just distal to the inguinal ligament, descends on the sartorius muscle, and penetrates the deep fascia about the distal third of the thigh to split into 2 terminal nerve branches. One branch innervates the skin covering the medial aspect of the distal thigh and knee joint region. The second branch supplies the skin superior to the patella and shares several communicating branches with the saphenous nerve. The posterior branch of the medial cutaneous nerve travels along the medial border of the sartorius muscle and pierces the deep fascia about the knee to also communicate with the saphenous nerve in providing cutaneous sensation to the patellar region. The best-known cutaneous nerve arising from the femoral nerve is the saphenous nerve (discussed below).
Etiology
The femoral nerve can have several entrapment locations or causes of injury, including intrapelvic injury or injury in the inguinal region. Diabetic amyotrophy is the most common cause of femoral nerve neuropathy. Open injuries can occur from gunshots, knife wounds, glass shards, or needle puncture in some medical procedures. The most worrisome complication of major trauma to the femoral triangle region is an associated femoral artery injury. The nerve can be injured at the time of the trauma or inadvertently sutured during repair of this injury. Large-blade, self-retaining retractors used during pelvic operations can cause injury to the nerve due to compression.
[10]Conduction of the femoral nerve was measured in diabetic patients without clinical signs of femoral nerve involvement, and there was a statistically significant difference between diabetics and healthy individuals in terms of both femoral nerve motor latency and amplitude. The authors observed that these abnormalities became more evident as the polyneuropathy of the patients became more serious.
[11]Most entrapment neuropathies occur below the inguinal ligament. After passing beneath the inguinal ligament, the femoral nerve is in close proximity to the femoral head, the tendon insertion of the vastus intermedius, the psoas tendon, the hip, and the joint capsule. The femoral nerve does not have significant protection in this area.
Heat developed by methylmethacrylate during a total hip arthroplasty can injure the femoral nerve. Pelvic procedures that require the lower extremity to be positioned in an acutely flexed, abducted, and externally rotated position for long periods can cause compression by angling the femoral nerve beneath the inguinal ligament. The nerve may be compromised by pressure from a fetus in a difficult birth. Pelvic fractures and acute hyperextension of the thigh may also cause an isolated femoral nerve injury. Pelvic radiation, appendiceal or renal abscesses, and tumors can cause femoral nerve injuries as well. The nerve can also be injured by a compartment-like compression from a hemorrhage (caused by a hemorrhagic disorder or by anticoagulant use).
Clinical
The symptoms of a femoral neuropathy may include pain in the inguinal region that is partially relieved by flexion and external rotation of the hip, and dysesthesia over the anterior thigh and anteromedial leg. Patients complain of difficulty in walking and of knee buckling, depending on the severity of the injury. The nerve gives rise to the saphenous nerve in the thigh; therefore, numbness in this distribution can be present. Anterior knee pain may also be present because the saphenous nerve supplies the patella.
On examination, patients may present with weak hip flexion, weak knee extension, and impaired quadriceps tendon reflex, as well as sensory deficit in the anteromedial aspect of the thigh. Pain may be increased with hip extension and relieved with external rotation of the hip. If compression occurs at the inguinal region, no hip flexion weakness is present. Sensory loss may occur along the medial aspect of the leg below the knee (saphenous distribution).
Electrodiagnostic testing typically is performed for diagnosis, but is also important to determine the extent of the injury and the prognosis for recovery. With electrodiagnostic testing, either surface or needle electrodes lateral to the femoral artery in the inguinal region are used for stimulation. The stimulation can be performed above and below the inguinal ligament. Disk electrodes from the vastus medialis are used to record stimulation.
A saphenous nerve sensory study may also be performed (continuation of the sensory portion of the femoral nerve over the medial aspect of the leg and ankle). Needle examination should be completed for the paraspinal muscles as well as for the iliopsoas (also L2-3) and hip adductors supplied by the obturator nerve, to determine the presence of root or plexus injury versus peripheral nerve injury. Needle electromyography is usually the most revealing portion of the electrodiagnostic test. The examiner must look not only for denervation potentials but also for any active motor units.
Treatment
Treatment may be based on symptoms only, or it may be more invasive and include surgical intervention, depending upon the severity of the injury. Quadriceps weakness may be treated with a locking knee brace to prevent instability, and the patient may require an assistive device for walking. Good recovery has been reported in up to 70% of patients with a femoral neuropathy and may take up to a year. The recovery may even occur in the setting of a fairly severe injury, as determined through electrodiagnostic testing and by physical examination. Patients with severe axonal loss have some recovery of function, although it is usually incomplete.
Saphenous Nerve
Anatomy
The saphenous nerve, the terminal branch of the femoral nerve, is the femoral nerve's longest branch. It is a pure sensory nerve that is made up of fibers from the L3 and L4 spinal segments. Because of its long course, it can become entrapped in multiple locations, from the thigh to the leg. It branches from the femoral nerve just distal to the inguinal ligament and courses with the superficial femoral artery to enter the adductor (Hunter's) canal in the distal third of the thigh. This canal extends proximally from the apex of the femoral triangle to the inferomedial aspect of the thigh in the adductor magnus tendon, just proximal to the femoral condyle. The canal is somewhat triangular and lies between the vastus medialis laterally and the adductor magnus and longus muscles medially.
The roof of the canal is a dense bridge of connective tissue extending between these muscle groups. The saphenous nerve exits the canal by piercing the roof, and becomes subcutaneous about 10 cm proximal to the medial epicondyle of the femur. The nerve may also pierce the sartorius muscle. Once it becomes subcutaneous, the nerve branches to form the infrapatellar plexus, while the main branch continues along the medial leg and foot.
Etiology
The saphenous nerve can become entrapped where it pierces the roof of the adductor canal. Inflammation results from a sharp angulation of the nerve at its exit and from the dynamic forces of the muscles in this region, which cause contraction and relaxation of the fibrous tissue that impinges on the nerve. The nerve can also be injured as a result of an improperly protected knee or leg support during surgery. It may be injured by a neurilemoma, entrapment by femoral vessels, direct trauma, pes anserine bursitis, varicose vein operations, and medial knee arthrotomies and meniscus repairs.
[12]Clinical
Symptoms of entrapment may include a deep aching sensation in the thigh, knee pain, and paresthesias in the cutaneous distribution of the nerve in the leg and foot. The infrapatellar branch may also become entrapped on its own. This is because it passes through a separate foramen in the sartorius muscle tendon. It may also be exposed to trauma where courses horizontally across the prominence of the medial femoral epicondyle. Patients report paresthesias and numbness about the infrapatellar region that is worse with flexion of the knee or compression from garments and braces.
Saphenous nerve entrapment is a frequently overlooked cause of persistent medial knee pain in patients who experience trauma or direct blows to the medial aspect of the knee. As this is a purely sensory nerve, weakness should not be noted with an isolated injury of this nerve. If weakness is present, look for an injury of the femoral nerve or possibly an upper lumbar radiculopathy, particularly if thigh adduction is present (obturator nerve).
Deep palpation proximal to the medial epicondyle of the femur may reproduce the pain and complaints. Some weakness may be present because of guarding or disuse atrophy from pain, but no direct weakness will result from the nerve impingement. Sensory loss in the saphenous distribution may be present on examination. No weakness should be present in the quadriceps muscles or in the hip adductors.
The diagnosis may be made on the basis of injection of local anesthetic along the course of the nerve and proximal to the proposed site of entrapment. Nerve conduction techniques are available to assess neural conduction in the main branch of the saphenous nerve or in the terminal branches. The routine tests may be disappointing in persons with subcutaneous adipose tissue or swelling. A side-to-side comparison of the nerve should be made, and must demonstrate a lesion consistent with the patient's complaints. A somatosensory evoked potential (SSEP) test can also be performed and the results compared with those of the contralateral side for diagnosis, although this test may be cumbersome and time-consuming.
No findings should be present on needle examination of the muscle during electromyography. Needle examination should include the quadriceps muscle and the adductor longus to assess for femoral and obturator nerve injury. If findings are present in both of these muscles, then paraspinal muscles definitely should be examined to rule out radiculopathy.
Treatment
Entrapment in the adductor canal usually is treated conservatively with an injection of anesthetic (with or without corticosteroid) at the point of maximal tenderness (usually 10 cm proximal to the medial femoral condyle). The injection may need to be repeated periodically. Avoiding aggravating activities and using proper body mechanics will also be helpful. If this approach fails, surgical decompression may be needed. In patients who have had a direct blow to the medial knee who have persistent medial knee pain despite conservative trials for treatment, a neurectomy or neurolysis of the infrapatellar branch may be helpful.
Anterior Leg & Dorsum of Foot
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