Ultrasound of the Lateral Femoral Cutaneous Nerve in Asymptomatic Adults

Jiaan Zhu; Yiwen Zhao; Fang liu; Yunxia Huang; Junjie Shao; Bing Hu

Disclosures

BMC Musculoskelet Disord. 2012;13(227) 

In This Article

Methods

This study met the guidelines set by the ethics committee of the Shanghai Sixth People's Hospital (Shanghai, China). All subjects were selected randomly and gave informed written consent for their inclusion in this study.

Subjects

A total of 120 subjects were prospectively included in the study. All study subjects were asymptomatic volunteers without any symptoms of pre-existing pain or dysesthesia in the distribution of the LFCN. Subjects with diabetes mellitus, pregnancy, peripheral neuritis, and a history of injury or surgery on the spinal column, pelvis, or the groin were excluded from the study.

Ultrasound

Each subject was positioned supine and was scanned bilaterally by an investigator (J.A., 10 years of neuromuscular ultrasound experience) using the Mylab 90 (Esaote, Genoa, Italy) with an 18 MHz linear array transducer.

The ultrasound transducer was placed in the transverse position and was first placed 1–2 cm distal to the lateral IL. Initially, the tensor fasciae latae muscle and the sartorius were imaged (Figure 1). To verify the tensor fasciae latae muscle, the transducer was sometimes moved distally. As the distal tensor fasciae latae muscle inserts into the iliotibial band, the echo of the muscle of the tensor fasciae latae muscle should sonographically disappear. The LFCN was then identified in the intermuscular space between the tensor fasciae latae muscle and the sartorius. Because there was substantial contrast between the echo characteristics of the LFCN and that of the surrounding tissue, the LFCN could be easily identified and usually showed an ovoid hypoechoic structure with hyperechoic dots within it (Figure 2). which was similar to the other of the peripheral nerve. The nerve cross-sectional area (CSA) at this site was measured bilaterally in all 120 participants. When the LFCN was identified using ultrasound and then the angle of incidence of the probe was adjusted until it was perpendicular to the nerve, the smallest cross-sectional image was obtained. Because the CSA of the LFCN is so small that the trace function on the ultrasound device is unable to trace the nerve, the CSA was calculated from an area formula for ovals (CSA= Pi * A * B *1/4, Pi=3.14, A=the longest side of the oval, B=the shortest side of the oval). If the LFCN had several branches, the CSA of the anterior branch was measured. The CSA was measured three times, and the mean value was recorded. Then, the transducer was slowly moved proximally along the LFCN to the IL. The IL is noted as a linear hyperechoic structure running from the pubic tubercle to the ASIS.[12,18] The number of nerve branches at the level of the IL and the relationship between the LFCN and IL were assessed. The distance between the LFCN and the ASIS was also measured. By observing the course of the nerve, the nervous structure assed was identified LFCN and not another nerve structure.

Figure 1.

Schematic diagram showing the course of the LFCN and the initial location of the probe. ASIS: anterior superior iliac spine; LFCN: lateral femoral cutaneous nerve; TEL: tensor fasciae latae muscle; IL: inguinal ligament; S: Sartorius.

Figure 2.

Transverse ultrasound image of the LFCN lying within the intermuscular space between the tensor fasciae latae muscle and the sartorius. LFCN: lateral femoral cutaneous nerve; TEL: tensor fasciae latae muscle; S: Sartorius; R: rectus femoris.

To test the difficulty or ease of using our protocol to detect the LFCN, the other two radiologists (Y.X. and F., who both had 2 years of neuromuscular ultrasound experience) were trained by J.A to perform the ultrasound examination procedure for inspecting the LFCN, and the time taken to identify the nerve was recorded. Intraobserver reliability was evaluated in 30 cases that were selected by the radiologist (Y.X.).

Statistical Analyses

All parameters were compared bilaterally. Numerical and categorical variables were compared by independent unpaired t-tests and by the Chi-squared test, respectively. A regression analysis of the data that compared age, sex, height, weight, and the distance between the ASIS and LFCN was performed. The intraobserver reliability was assessed according to the kappa coefficient. A p value of less than 0.05 was considered significant.

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