AAMT Fellowship Osteopractor

Lateral Femoral Cutaneous Neuralgia: an Under Reported Complication of Anterior Hip Arthroplasty

The Lateral Femoral Cutaneous Nerve (LFCN) is a sensory nerve that originates from the lumbar plexus at L2-3, courses laterally along the psoas, across the iliacus obliquely, and then dives under the inguinal ligament 1-3 cm medially to the anterior superior iliac spine.1,2 Cutaneous branches of the LFCN typically arise between the sartorius and tensor fascia latae muscles, providing sensory information to the anterolateral and lateral thigh.3

The LFCN can also provide sensory information medially and distally to the patella, a pseudo mirroring of the femoral nerve.4 The inherent anatomical variability of the LCFN, which can derive from 7 different distinct pelvic exits and 4 different branching patterns poses challenges with locating, diagnosing, and treating LFCN injuries.2

LCFN injuries are idiopathically or iatrogenically derived. Meralgia Paresthetica is an idiopathic injury to the LCFN caused by mechanical compression at the inguinal ligament.  In contrast, iatrogenic LFCN injuries are typically distal to the inguinal ligament and are most commonly caused by surgical procedures including total hip arthroplasty, iliac bone harvesting, or laparoscopic inguinal herniorrhapy.1,5 

The incidence of iatrogenic LFCN injuries from anterior total hip arthroplasties is reported to be between 73% and 81% and is often misdiagnosed as “typical post-surgical pain/paresthesia”.6,7 The inherent risk of LFCN injury during total hip arthroplasty depends in part on the incision type. Bikini type and longitudinal extensions of direct anterior hip arthroplasties have been shown to frequently jeopardize the LFCN.8 

The classic Smith-Peterson anterior hip approach has been modified in an attempt to spare the LFCN, but this does not eliminate the risk due to the anatomic variability of the LFCN.8 Since anterior approach arthroplasties are becoming more common than the posterior approach, the incidence of iatrogenic LFCN injuries is becoming more common. However, improper or under-reporting surgically induced LCFN injuries appears commonplace.7

PHYSICAL EXAMINATION & DIAGNOSIS

Patients with an injury to the LFCN typically present with numbness, paresthesia (burning, tingling, pins/needles), and/or pain along the anterior and lateral aspect of the thigh.1,9 Hyperalgesia or mechanical allodynia (i.e., pain to a non-painful stimulus) of the nerve distribution can be triggered by clothing and bed sheets.1 Tinel’s sign at the inguinal ligament, just medial to the ASIS, or at the border of the sartorius and tensor fascia latae may reproduce pain.10 Femoral Nerve Tension Tests or hip hyperextension can also elicit positive symptoms.1,5 A diagnostic nerve block may also be considered to implicate the LFCN.3

To differentially diagnose a LFCN injury, femoral nerve injury, L2-4 lumbar radiculopathy, lumbar plexopathies, hip joint referral, thoraco-lumbar junction referral, and trigger point referral, need to be ruled out.1,11,12,13,14 Motor deficits concurrent with positive LFCN distribution findings would implicate femoral nerve, lumbar radiculopathy, and lumbar plexopathy while excluding a LFCN injury.

FABER/FADIR testing should be utilized to determine if lateral thigh pain is referred from the acetabulofemoral joint.11 Thoraco-lumbar pain syndrome is often misdiagnosed and can also refer pain to the lateral thigh. Differential testing would include careful manual assessment of the thoraco-lumbar junction, including deep pressure over the facets and rotational stress to the spinous processes.13

A pelvic compression test can be used to help determine if the source of LFCN entrapment is at the inguinal ligament or more distal. Administration of this test is performed with the patient in a side lying position, with the painful side up, while a medially sustained pressure is applied at the ASIS in an attempt to slack the inguinal ligament. A reduction of paresthesia/pain within 45 seconds indicates a positive test for LFCN entrapment at the inguinal ligament.14 Notably, a high sensitivity (95%) and high specificity (91%) for this test has been reported in meralgia paresthetica. To diagnose a more peripheral entrapment or neuroma, diagnostic ultrasound is effective.2,15,16 A diagnostic nerve block under ultrasound guidance may also be considered.17

TREATMENT of LFCN INJURIES

There is no consensus on best conservative treatment for LFCN injuries. A few case studies recommend manual therapy18,19, acupuncture20, and/or electroacupuncture.21 Notably, there is weak evidence for surgical decompression or neurectomy for patients who are unresponsive to conservative treatment.23 Therefore, in the absence of a preponderance of direct outcome studies, theoretical evidence and expert opinion should be implemented until best practice can be established. 

Acupuncture has a growing body of evidence in the management of peripheral neuropathies, including carpal tunnel syndrome and Bell’s palsy.23 Dry needling with electrical stimulation may decrease pain by stimulating A-delta fibers.23 In addition, dry needling likely promotes opioid and non-opioid responses both peripherally and centrally, helping to further drive down pain.24 

There is evidence to suggest that invasive stimulation may enhance nerve regeneration after injury vs superficial application of TENS, via a more direct stimulation aiding in faster regeneration of myelin sheaths.25 However, due to the anatomic variance of the LFCN, ensuring proximity to the nerve is difficult. Moreover, there is a 5% efficacy in contacting the LFCT without ultrasound guidance compared with 84% efficacy with ultrasound guidance.26 Therefore, ultrasound-guided dry needling for the LFCN should be utilized in order to properly stimulate the LFCN.

If ultrasound guidance is unavailable, the anatomic variability of the LFCN warrants starting with dry needling to the sartorius, tensor fascia latae, ITB, and cutaneous distribution of the nerve.  Interestingly, a common trigger point at GB31 (midpoint of the ITB) has been reported across subjects with meralgia paresthetica.21 Dry needling to these areas will allow the most complete stimulation of the LFCN and its receptive field. 

Due to the origination of the LFCN at L2-3, spinal manipulation should also be considered. Spinal manipulation has been shown to have a centrally mediated effect on pain and improve neuropathic pain and function.27,28,29,30 Manipulation to those targeted segments could be indicated in an attempt to create a downstream effect on the nerve similar to changes seen with lumbar radiculopathy.31,32

CONCLUSION

Lateral Femoral Cutaneous Neuralgia can be a debilitating and frustrating condition for patients. Due to its variable course, it is frequently misdiagnosed, under-reported, and managed incorrectly. Dry needling along the course of the LFCN, particularly with ultrasound guidance, and spinal manipulation targeting the upper lumbar spine should be considered as first line treatment for these patients. 

AUTHORS

Ty Zimmerman, DPT, OCS, Dip. Osteopractic
Physical Therapist, Mercyhealth, Lake Geneva, WI
Fellow-in-Training, AAMT Fellowship in Orthopaedic Manual Physical Therapy

Casey Charlebois, PhD(c), DPT, MSc, FAAOMPT, Dip. Osteopractic
Director of Clinical Research, AAMT Fellowship in Orthopaedic Manual Physical Therapy
PhD Candidate, Nova Southeastern University, Fort Lauderdale, FL

James Dunning, PhD, DPT, MSc, FAAOMPT, Dip. Osteopractic
Director, AAMT Fellowship in Orthopaedic Manual Physical Therapy
Montgomery Osteopractic Physical Therapy & Acupuncture, Montgomery, AL

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