Preoperative Tracing of Lateral Femoral Cutaneous Nerve with Sonography for Sensory Anterolateral Thigh Free Flap Reconstruction

The anterolateral thigh free flap (ALTF) is one of the more commonly used microvascular flaps. This results from its high versatility and relatively low donor site morbidity. The ALTF is often used as a flap with sensory innervation, especially in reconstruction of the area of the head and neck and of the foot. Studies have shown that the combination of sensory nerves during reconstruction positively affects the qualities and speeds with which functions are regained.[1]

The dominant sensory nerve for the ALTF is the lateral femoral cutaneous nerve (LFCN) originating from the lumbar plexus. It is composed of the anterior branches of the spinal nerves at L2 and L3. After emerging from under the edge of the lateral lumbar muscle, it runs under the iliac fascia, on the front surface of the iliacus muscle. After perforating the hip fascia, the nerve passes under or through the inguinal ligament, and then runs along the anterolateral surface of the sartorius muscle, where it divides into the anterior and posterior branches.[2]

Blocking of the LFCN in the groin using ultrasonography (USG) is an applied technique of regional anesthesiology. There are several protocols for identifying the nerve. In our practice, we use the method according to Zhu et al.[3] The probe is placed across, 1 to 2 cm below the inguinal ligament at the height of the anterior superior iliac spine. Next, the sartorius muscle and the tensor fasciae latae are identified. The lateral cutaneous nerve of the thigh is located in the space between these two muscles as a hypoechogenic structure with hyperechogenic dots inside. After identifying the nerve in the groin, the course of the anterior branch is then traced and marked on the thigh. To our knowledge, USG has not thus far been used for preoperative mapping of the course of the LFCN on the thigh before harvesting the ALTF.

We use two USG devices to identify the nerve: the Konica Minolta SONIMAGE HS1 and the Mindray M7. The first is equipped with a linear probe of 18 MHz, and the second with one of 15 MHz. The preset configuration for surface tissues is used. This is a simple study and people with basic experience performing USG studies are able to identify the nerve in under 20 seconds. In the study conducted by Ng et al, the mean time needed to establish the position of the nerve was 22 seconds.[4]

So far, we have performed preoperative identification in five patients qualified for reconstruction using the ALTF. In all the patients, the nerve was successfully specified to at least half the length of the thigh ([Fig. 1]). What is more, in all cases, the preoperative tracing matched intraoperative localization ([Fig. 2]).

Fig. 1 ( (A) Ultrasonography (USG) image of the nerve in the area of the inguinal ligament, with the anterior and posterior branches (outlined in red) and sartorius muscle visible (outlined in green). (B) The anterior branch of the LFCN, visible in a USG 1/4 of the way down the thigh. (C) The anterior branch of the LFCN, visible in a USG halfway down the thigh, just above the deep fascia. D) The lateral femoral cutaneous nerve (LFCN) marked on the thigh. The green arrow marks the perforator.

Fig. 2 Prepared anterolateral thigh flap. The lateral femoral cutaneous nerve is marked with a green arrow.

In our opinion, mapping of the course of the lateral cutaneous nerve of the thigh should be performed in all patients for whom reconstruction using the ALTF is planned. First in those in whom a sensory flap will be used, because the course of the LFCN is anatomically variable. Therefore, establishing the position of the neve and perforators will allow the best orientation of the flap, especially if the planned skin island is to be small.[5] From the opposite direction, lateral thigh paresthesia is the most common complication after harvesting of the ALTF (occurring in 24% of patients)[2] thus, preoperative identification of the course of the nerve will allow this area to be preserved and limited.

Publikationsverlauf

Eingereicht: 20. Januar 2020

Angenommen: 25. August 2020

Artikel online veröffentlicht:
14. Oktober 2020

• References

• 1 Santanelli F, Tenna S, Pace A, Scuderi N. Free flap reconstruction of the sole of the foot with or without sensory nerve coaptation. Plast Reconstr Surg 2002; 109 (07) 2314-2322 , discussion 2323–2324
• 2 Luenam S, Prugsawan K, Kosiyatrakul A, Chotanaphuti T, Sriya P. Neural anatomy of the anterolateral thigh flap. J Hand Microsurg 2015; 7 (01) 49-54
• 3 Zhu J, Zhao Y, Liu F, Huang Y, Shao J, Hu B. Ultrasound of the lateral femoral cutaneous nerve in asymptomatic adults. BMC Musculoskelet Disord 2012; 13: 227-231
• 4 Ng I, Vaghadia H, Choi PT, Helmy N. Ultrasound imaging accurately identifies the lateral femoral cutaneous nerve. Anesth Analg 2008; 107 (03) 1070-1074
• 5 Doklamyai P, Agthong S, Chentanez V. et al. Anatomy of the lateral femoral cutaneous nerve related to inguinal ligament, adjacent bony landmarks, and femoral artery. Clin Anat 2008; 21 (08) 769-774