The sciatic nerve block by the posterior approaches represents one of the more difficult ultrasound-guided nerve blocks. Our clinical experiences with these blocks indicated a point slightly distal to the subgluteal fold as an advantageous position to allow good ultrasonic visibility. In this study, we systematically scanned the sciatic nerve from the subgluteal fold to the popliteal crease, to determine an optimal point for ultrasonographic visualization.
After institutional approval and written informed consent, we recruited 15 volunteers to visualize the sciatic nerve from the subgluteal fold to the popliteal crease using a linear ultrasound probe in the range of 7-13 MHz. The ultrasonographic visibility of the sciatic nerve, nerve diameter (width and thickness), and skin-to-nerve distance at 20 equidistant points between the subgluteal fold and the popliteal crease were recorded.
The sciatic nerve could be successfully visualized in cross-section as a hyperechoic structure on ultrasound in all volunteers. In the course from subgluteal to the popliteal area, the shape of the sciatic nerve changed from flat to round, while the skin-nerve distance varied with the smallest skin-nerve distances at the popliteal crease and at 5.4 cm (on average) distal to the subgluteal fold. The best ultrasonographic visibility scores were found between 7.2 and 10.8 cm (on average) distal to the gluteal fold.
Between 5.4 and 10.8 cm from the subgluteal fold seems to be the best area to scan the sciatic nerve in terms of superficial nerve position and good ultrasonic visibility.
"The ultrasound transducer was placed on the mid-posterior thigh (see Fig. 1) and a transverse ultrasound image of the sciatic nerve was acquired. The nerve was located on a line between the ischial tuberosity and the greater trochanter (Karmakar et al., 2007) and 10 cm distal to the gluteal fold (Bruhn et al., 2008). The knee was extended in 2 stages; 90 to approximately 45 of knee extension, and 45 to approximately 0 . "
[Show abstract][Hide abstract] ABSTRACT: Minimal data exists on how much sciatic nerve motion occurs during straight leg raise (SLR). The purpose of this study was to report preliminary normative ranges of sciatic nerve excursion using real time ultrasound during a modified SLR. The sciatic nerve was scanned in the posterior thigh in sixteen asymptomatic participants (age range 19-68 years). Nerve excursion was measured in transverse and longitudinal planes during knee extension from 90° to 0°, with the hip flexed to 30° and 60°. The ultrasound data was analysed off-line using cross correlation software. Results demonstrated that most nerves moved superficially during knee extension, a large proportion (10/16) moved laterally. Longitudinal excursion ranged from 6.4 to 14.7 mm (mean (SD) 9.92 mm (2.2)) in 30° hip flexion, and 5.1-20.2 mm (mean (SD) 12.4 mm (4.4)) in 60° hip flexion. Mean nerve excursion was significantly greater in 60° hip flexion (p = 0.02). There is a large between-subject variation in sciatic nerve excursion during this modified SLR in asymptomatic subjects. Mean nerve excursion was found to be higher with the hip pre-positioned in greater flexion, suggesting that pre-loading may not consistently reduce excursion.
"An image of the sciatic nerve was then acquired in the posterior thigh in transverse view with the ultrasound. The nerve was found in the upper thigh on a line between the ischial tuberosity and the greater trochanter (Karmakar et al., 2007) and 7e10 cm distal to the gluteal fold (Bruhn et al., 2008). The transducer was then rotated to acquire the sciatic nerve in longitudinal view. "
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to establish the reliability of a frame-by-frame cross correlation method of assessing longitudinal sciatic nerve excursion motion using real time ultrasound imaging during a modified passive straight leg raise (SLR) test. Eighteen asymptomatic participants (age range 19-68 years) lay on their sides on a purpose made jig and the sciatic nerve in the posterior thigh was imaged during knee extension at 30° and then 60° of hip flexion (HF). Participants were re-tested ≥48 h later. The ultrasound images were analysed off-line using cross correlation software. Results demonstrated excellent repeatability of in vivo sciatic nerve excursion during a modified SLR (HF30° ICC 0.92, CI 0.79-0.97, SEM 0.69; HF60° ICC 0.96, CI 0.89-0.99, SEM 0.87). The authors also identify points of good practise to ensure an accurate as possible measurement of nerve excursion using this method. These include breaking down larger movements into sub-components, visually tracking the moving nerve during the tracking procedure, and ensuring the optimal image is captured prior to analysis. The use of ultrasound imaging in lower limb nerve dysfunction will enhance the understanding of how nerves move in vivo during neurodynamic testing, as well as being able to identify possible alteration to nerve movements in patients with neuropathic pain states.
"In the morbidly obese patients, it may be difficult to recognize even the bony structures. Previous investigators, who have attempted to identify easy and reliable internal ultrasound landmarks for the localization of the sciatic nerve, suggested that locations as much as 7–10 cm distal to the subgluteal fold may be advantageous for sciatic nerve visualization with ultrasound [12, 14]. Negotiating the sciatic nerve at a level above the subgluteal fold may be difficult with the use of just ultrasound in certain patient populations such as the morbidly obese or patients with positioning issues. "
[Show abstract][Hide abstract] ABSTRACT: Nerve stimulation and ultrasound have been introduced to the practice of regional anesthesia mostly in the last two decades.
Ultrasound did not gain as much popularity as the nerve stimulation until a decade ago because of the simplicity, accuracy and portability of the nerve stimulator.
Ultrasound is now available in most academic centers practicing regional anesthesia and is a popular tool amongst trainees for performance of nerve blocks.
This review article specifically discusses the role of ultrasonography for deeply situated nerves or plexuses such as the infraclavicular block for the upper extremity
and lumbar plexus and sciatic nerve blocks for the lower extremity. Transitioning from nerve stimulation to ultrasound-guided blocks alone or in combination is beneficial
in certain scenarios. However, not every patient undergoing regional anesthesia technique benefits from the use of ultrasound, especially when circumstances resulting
in difficult visualization such as deep nerve blocks and/or block performed by inexperienced ultrasonographers. The use of ultrasound does not replace experience and
knowledge of relevant anatomy, especially for visualization of deep structures. In certain scenarios, ultrasound may not offer additional value and substantial amount of time
may be spent trying to find relevant structures or even provide a false sense of security, especially to an inexperienced operator. We look at available literature on the role of
ultrasound for the performance of deep peripheral nerve blocks and its benefits.
Anesthesiology Research and Practice 07/2011; 2011:262070. DOI:10.1155/2011/262070
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