Meralgia paresthetica, known as Bernhardt-Roth syndrome or NCFL neuralgia, is a condition characterized by tingling and burning pain on the anterolateral surface of the thigh.

The Main Causes Are

Compression of (NCFL), damage to the same, due to diabetes, alcoholism or lead poisoning, trauma or iatrogenic after surgery. Compression is most common below the inguinal ligament. Tight clothing or a belt, excess weight, pregnancy and ascites lead to compression of the nerve. The most common NCFL injury is seat belt injury. The characteristic iatrogenic injury is in hip arthroplasty using anterior access and spinal surgery.

Direct anterior approach was first described by Carl Hueter in 1881 in his work – “Grundriss der Chirurgie” (The Compendium of Surgery). DAA is populated later in 1917 from Smith-Peterson. In the beginning this approach is used for DDH, fractures of the proximal femur and FAI. The anterior-based incision utilizes the interval to the hip joint between the tensor fascia lata and the sartorius muscles. DAA is intramuscular and intranervous- femoral nerve and superior gluteal nerve. Light and Keggi published their experience using this approach for hip arthroplasty in 1980, and Judet described the procedure with the use of a fracture table in 1985. Later in 1996 Dr. Laude modified fracture table to leg positioner. Originally approach uses longitudinal skin incision, later it was modified to oblique (vertical), parallel to the inguinal ligament and it is called “bikini” incision. This approach is characterized by less pain, faster recovery with minimal blood loss, with no damage to the muscle and nerves. Anterior access is preferred because the risk of luxation is lower, with no change in gait post-operatively, with a shorter hospital stay.

LFCN is a purely sensory (cutaneous) nerve, part of the lumbar plexus. It does not affect the muscles of the lower limbs. It is formed by the dorsal branches of the second and third lumbar nerves of (L2-L3). It runs from the lateral to the middle part of m. Psoas major and crosses m. Iliacus oblique to anterior superior iliac spine (ASIS). It then passes under the inguinal ligament and along the course of and over the m. Sartorius descends to the thigh, where it divides into two branches - anterior and posterior

The anterior branch becomes superficial about 10 cm from the inguinal ligament, where it divides into two branches that innervate the anterior and lateral parts of the thigh, including the knee. The terminal branches of the nerve often communicate with the anterior cutaneous coons of the n. Femoralis and with infrapatellar branches of n. Saphenus, together forming the "patellar plexus" (Figure 1).

Figure 1: Femoralis and with infrapatellar branches of n. Saphenus, together forming the "patellar plexus".

The posterior branch crosses the Fascia lata and divides into small branches that pass to the posterior and lateral surface of the thigh, innervating the skin from the level of the greater trochanter to the middle of the thigh (Figure 2).

Figure 2: Innervating the skin from the level of the greater trochanter to the middle of the thigh.

Anatomical variations are observed in 25% of people. The main ones are: early bifurcation, epifascial position of the nerve, inferior-medial direction and exit from the pelvis through the iliac canal.

In 5%, NCFL is not detected. Anatomical variations of the nerve must be taken into account during surgery in order to protect it during surgical dissection of the area.

Purpose of the study is to show our experience and results with one of the most common complication in THA using DAA. This study show neurological complication rate in low experienced surgeon with unfinished learning curve. This finding should not discourage young surgeon to perform THA using DAA, as we will see later in the study, all the LFCN complication resolved in 2 years. THA using DAA is difficult procedure and needs to be done precisely. There are complications, which can be avoided.

This is a retrospective single-cohort observational single centre and single surgeon study in the beginning of his learning curve. Only longitudinal skin incision is used by this surgeon and the wound was sutured with non-resolvable 0 threads in continuous locking manner. In Positioning and manipulating the leg intraoperativle, AMIS leg positioner was used. Study gathers information between 2020 and 2024 and it contains 16 patients undergone THA via DAA. Lesion of the LFCN was confirmed by a neurological examination. Clinical complaints of pain, burning sensation, tingling, numbness, or a feeling of discomfort were included. All patients with these symptoms at the earliest follow-up were referred to neurological clinical examination to confirm the diagnosis of meralgia paresthetica as per their standard clinical practice. Peri-incisional events, such as wound inflammation or other complication that could mask as meralgia paresthetica, were differentiated, and excluded. One case with damage to the femoral nerve was observed and excluded of the study.

Surgeon had used different surgical technique – In 3 patient’s standard Smith-Peterson approach with patient in supine position and leg in the figure of four. In the rest 13 patient was used AMIS modification with leg positioner.

The skin incision is positioned 2 cm lateral and 2 distal to the anterior-superior border of the iliac bone (ASIS) 8-10 cm vertically. Sometimes, in order to improve the cosmetic defect, the skin incision can be placed obliquely - "bikini" access.

For convenience, the main structural landmarks for the front access are noted. ASIS, greater trochanter, head of fibula. A straight line is drawn from the ASIS to the head of the fibula and medial to this line is considered the danger zone. From the greater trochanter it is cut perpendicular to this line and divided into 4 equal quadrants. The skin access is positioned at the border between the first and second quadrants as a continuation of the ASIS (Figure 3).

Figure 3: The skin access is positioned at the border between the first and second quadrants as a continuation of the ASIS.

Superficially, the access passes between M. tensor fascia lata (innervated by n. gluteus superior) and M. Sartorius (n. femoralis), in depth between m. rectus femoris (n. femoralis) I gluteus medius (n. gluteus superior). Most often, the NCFL is traumatized at the superficial level between the M. tensor fascia lata and M. Sartorius. In order to avoid the nerve, the skin incision is positioned over the M. tensor fascia lata. After transection of the fascia, the latter is pushed laterally and the fascia with subcutaneous tissue and M. Sartorius are carefully dissected medially. Targeted haemostasis is achieved continuously during dissection- subcutanues vessels and lateral circumflex artery (LCA). LCA can be ligated of coagulated. In literature ligated LCA led to less complications like haematoma. Care must be taken when placing and using excessive force with retractors to the femoral neck and acetabulum. Damage may occur secondary to compression from the post-operative cicatrix (Figure 4 and Figure 5).

Figure 4: In literature ligated LCA led to less complications like haematoma.

Figure 5: Damage may occur secondary to compression from the post-operative cicatrix.

Patients were examined on follow-up visits at 2 weeks, 6 weeks, 6 months, 1 and 2 years after surgery. In 8 patients damage to the LFCN was observed. Symptoms had different velocity from mild hypoesthesia to severe burning pain in the anterolateral thigh. One patient had pain in anetrolateral thigh and in 7 hypoesthesia. All cases of clinically presenting LFCN injury clinically improved at the 1-year follow-up, with 5 patients fully recovered. 2 patients had still mild symptoms of nerve damage at the 1year follow up. By the 2 year follow up, all the symptoms resolved. Possible explanations for iatrogenic nerve injury are direct cut, extreme traction, hyperextension or external rotation, postoperative haematoma, excessive force with retractors.

All symptomatic patients were treated conservatively – using medication like -Gabapentin, Pregabalin, Phenytoin, Milgamma N, Nivalin and physiotherapy.

Limitations of our study are using subjective signs of lateral femoral cutaneous nerve lesion, and a clinical diagnosis as opposed to radiological (e.g., ultrasound) or electrophysiological, as this was normal clinical practice during the study period. This can lead to underreporting of the complication rate of meralgia paresthetica. This is explained by the fact that lateral femoral cutaneous nerve injury has no effect on the functional outcome of total hip replacement, and only the subjectively significant lesions causing the patient discomfort or decrease of function would warrant investing further resources in the clinical practice. On the other hand, peri-incisional pain and discomfort could confound the results in the way of overestimating the complication rate. In this study, it was assumed the confounding risk of this kind was limited by examining the patient by both an orthopod and neurologist.

Meralgia paresthetica is serious and most common complication in DAA after THA. However this approach to the THA is most preferred among others, due to its advantages. Exploring LCFN and protecting it during the surgery lead to fewer nerve damage complication. If it managed carefully with experienced surgeon after its learning curve, it can be safe. This complication in most cases is temporary with fully recover with or without treatment.

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2. Almasi J, Ambrus R, Steno B. Meralgia Paresthetica-An Approach Specific Neurological Complication in Patients Undergoing DAA Total Hip Replacement: Anatomical and Clinical Considerations Life. 2024; 14: 151.
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