Ultrasound guidance for a lateral approach to the sciatic nerve in the popliteal fossa

The influence of patient position on ultrasound examination of the sciatic nerve in the popliteal fossa: A cross-sectional study

Introduction/Purpose

Ultrasound-guided popliteal fossa sciatic nerve (PFSN) blocks are performed with patients in the supine, lateral or prone position. No known studies compare the quality of images obtained from each approach. This study examines the quality of supine and prone PFSN ultrasound images.

Methods

Thirty-eight adult volunteers were sorted into two groups. Five regional anaesthesiologists performed ultrasound examinations of the PFSN on volunteers in supine and prone positions. Popliteal fossa sciatic nerve image quality was analysed with grayscale techniques and peer evaluation. Popliteal fossa sciatic nerve depth, distance from the popliteal crease and time until optimal imaging were recorded.

Results

The grayscale ratio of the PFSN vs. the background was 1.83 (supine) and 1.75 (prone) (P = 0.034). Similarly, the grayscale ratio of the PFSN vs. the immediately adjacent area was 1.65 (supine) and 1.55 (prone) (P = 0.004). Mean depth of the PFSN was 1.6 cm (supine) and 1.7 cm (prone) (P = 0.009). Average distance from the popliteal crease to the PFSN was 5.9 cm (supine) and 6.6 cm (prone) (P = 0.02). Mean time to acquire optimal imaging was 36 s (supine) and 47 s (prone) (P = 0.002). Observers preferred supine positioning 53.8%, prone positioning 22.5% and no preference 23.7% of the time. Observers with strong preferences preferred supine imaging in 70.9% of cases.

Conclusions

Supine ultrasound examination offered quicker identification of the PFSN, in a more superficial location, closer to the popliteal crease and with enhanced contrast to surrounding tissue, correlating with observer preferences for supine positioning. These results may influence ultrasound-guided PFSN block success rates, especially in difficult-to-image patients.

Identification of the popliteal sciatic nerve through the above-knee lateral approach provides superior echogenicity and ultrasound visibility: a patient volunteer trial

BACKGROUND

Distinguishing light-echoed nerves from surrounding structures is challenging but may be important in nerve block administration. We evaluated the effect of patient characteristics on the echogenicity or visibility of the popliteal sciatic nerve (PSN).

METHODS

This study included adult patients who presented to the operating room as volunteers. The primary outcome was the success rate of nerve identification by ultrasound using different PSN access paths. The secondary outcome included the PSN visibility score (VIS), scan time, and PSN depth. Logistic regression analysis was used to identify factors associated with the PSN identification success rate. The body mass index (BMI) proximal-based cut-off was used to compare the PSN identification success rate through different access paths.

RESULTS

The PSN was successfully identified in 89.7% of the volunteers. The access paths (P < 0.01) and BMI (P = 0.01) were identified as independent predictors of successful PSN identification. A higher PSN identification success rate (P = 0.01), a higher VIS (P < 0.01), a more superficial PSN depth (P < 0.01), and a shorter scan time (P < 0.01) were observed in the above-knee lateral approach. Among volunteers with BMI ≥ 26.77 kg/m2, the PSN identification success rate through the above-knee lateral approach was significantly higher (P < 0.01), and PSN depth was shallower (P < 0.01) than through the medial approach.

CONCLUSIONS

The ultrasound-guided above-knee lateral approach for PSN block improved the PSN identification success rate, ensured a more superficial nerve location, and provided a clearer image.

Diabetic neuropathy increases stimulation threshold during popliteal sciatic nerve block

BACKGROUND

Peripheral nerve stimulation is commonly used for nerve localization in regional anaesthesia, but recommended stimulation currents of 0.3-0.5 mA do not reliably produce motor activity in the absence of intraneural needle placement. As this may be particularly true in patients with diabetic neuropathy, we examined the stimulation threshold in patients with and without diabetes.

METHODS

Preoperative evaluation included a neurological exam and electroneurography. During ultrasound-guided popliteal sciatic nerve block, we measured the current required to produce motor activity for the tibial and common peroneal nerve in diabetic and non-diabetic patients. Proximity to the nerve was evaluated post-hoc using ultrasound imaging.

RESULTS

Average stimulation currents did not differ between diabetic (n=55) and non-diabetic patients (n=52). Although the planned number of patients was not reached, the power goal for the mean stimulation current was met. Subjects with diminished pressure perception showed increased thresholds for the common peroneal nerve (median 1.30 vs. 0.57 mA in subjects with normal perception, P=0.042), as did subjects with decreased pain sensation (1.60 vs. 0.50 mA in subjects with normal sensation, P=0.038). Slowed ulnar nerve conduction velocity predicted elevated mean stimulation current (r=-0.35, P=0.002). Finally, 15 diabetic patients required more than 0.5 mA to evoke a motor response, despite intraneural needle placement (n=4), or required currents ≥2 mA despite needle-nerve contact, vs three such patients (1 intraneural, 2 with ≥2 mA) among non-diabetic patients (P=0.003).

CONCLUSIONS

These findings suggest that stimulation thresholds of 0.3-0.5 mA may not reliably determine close needle-nerve contact during popliteal sciatic nerve block, particularly in patients with diabetic neuropathy.

CLINICAL TRIAL REGISTRATION

NCT01488474.

The significance of tibial and common peroneal nerves in nerve blocks

PURPOSE

The aim of this study was to elucidate the anatomical location of tibial nerve (TN) and common peroneal nerve (CPN) in the popliteal crease for specific nerve block.

METHODS

Fifty fresh specimens from 27 adult Korean cadavers (16 males and 11 females, age 35-87 years) were investigated. Five of the 27 cadavers were used to determine the depths of nerves in cross-section.

RESULTS

Tibial nerve was located 50 % from the most lateral point of the popliteal crease and 1.4-cm deep to the surface. In 20 % of the 50 specimens, the medial sural cutaneous nerve branched out below or at the popliteal crease, whereas the CPN was located at 26 % from the most lateral point of the popliteal crease and 0.7-cm deep from the surface. Furthermore, in 6 % of specimens the lateral sural cutaneous nerve branched out below or at the popliteal crease.

CONCLUSION

The results concerning the location of the TN and CPN at the popliteal crease offer a good guide to optimal nerve block.

Tibial and common fibular nerve block in the popliteal fossa with single puncture using percutaneous nerve stimulator: anatomical considerations and ultrasound description

BACKGROUND AND OBJECTIVES

Techniques of peripheral nerve block have gained popularity over the last two decades becoming a growing anesthetic option for limb surgeries. This study proposes a technical approach of the tibial and common fibular nerves in the popliteal fossa with single puncture using percutaneous nerve stimulator, considering the correlation with an anatomical and ultrasound study.

METHODS

This prospective, observational, randomized study was performed with 28 patients scheduled for foot surgeries. After localizing the tibial and common fibular nerves through percutaneous stimulation, the puncture was performed at the point of tibial nerve stimulation with a 5-cm needle (B.Braun, Stimuplex 50), and 10 mL of levobupivacaine were injected. The needle was pulled back and redirected to the point of common fibular nerve stimulation looking for the corresponding motor response, and 10 mL of the local anesthetic were injected. Imaging study of the popliteal region was performed by ultrasound to correlate the anatomy with the technique used.

RESULTS

Adequate anesthesia was obtained in all cases. The mean time to localize the tibial and common fibular nerves suing the percutaneous stimulator was 57.1 and 32.8 seconds, respectively, and with the nerve stimulator it was 2.22 and 1.79 minutes, respectively. The mean depth of the needle into the tibial nerve was 10.7 mm.

CONCLUSIONS

The approach for tibial and common fibular nerves with single puncture in the popliteal fossa using peripheral nerve stimulator is a good option for anesthesia and analgesia for foot surgeries.

Ultrasound-guided medial mid-thigh approach to sciatic nerve block with a patient in a supine position

We report the use of a ‘medial mid-thigh approach (medial approach),’ a new approach for performing ultrasound-guided sciatic nerve blockade (SNB) with patients in a supine position. Fifty-four patients undergoing knee surgery under general anesthesia and a combined femoral nerve block (FNB) and SNB were included in the study. After FNB, an ultrasound-guided medial approach was used to perform the SNB. The patient was placed in a supine position, and the hip and knee joints were flexed with the leg rotating externally. A linear ultrasound transducer was positioned perpendicular to the skin at the level of the upper mid-thigh. The sciatic nerve was identified in all patients using ultrasound imaging, and the distance to the nerve was 3.0–5.5 cm. A combined ultrasound- and nerve stimulator-guided SNB was then performed, and 0.375% ropivacaine was administered. The block was successful in all patients, and the mean duration of the sensory and motor blockade was 11.9 and 8.2 h, respectively. In this study, the medial approach was highly successful and easy to perform. As performing a simultaneous FNB and SNB with patients in a supine position has several potential advantages, future studies should compare this approach with other more proximal approaches for performing SNB.

Influence of Leg Position on the Depth and Sonographic Appearance of the Sciatic Nerve in Volunteers

We investigated the effect of leg position on the depth of the sciatic nerve and quality of ultrasound images taken at the proximal and mid-thigh level. Twenty-one volunteers with average body mass index were recruited to represent the younger population receiving sciatic nerve blocks for sports injury surgery. The volunteers were placed in the lateral position, with the hip flexed and with the hip in a neutral (extended) position. A single operator imaged the uppermost leg and the best images of the sciatic nerve at the proximal and mid-thigh level were saved. Sciatic nerve depth was measured at each level. Eleven clinicians experienced in ultrasound-guided regional anaesthesia assessed the paired images. In the proximal thigh, the sciatic nerve depth was greater with the hip flexed compared to the neutral position (median 30 vs 23 mm, P=0.0002). There was no consistent difference in the mid-thigh. More clinicians favoured the proximal sciatic image with the leg in the neutral position. Although statistically significant, the depth difference is probably not a major clinical consideration in most patients with an average body mass index. We suggest clinicians place the leg in the most ergonomically favourable position when performing sciatic nerve blocks in the proximal thigh in these patients.

Lower limb blocks

The advances in regional techniques for blocks of the lower limb have been driven primarily by the need to produce effective analgesia in the postoperative period and beyond. These techniques are commonly performed before or after central neuraxial blockade when this technique is used to provide anaesthesia and analgesia for the surgical procedure. Increasingly, modern practice demands a shorter hospital stay, improved patient expectations and early mobilisation. This article describes the current methods and reasons for performing specific blocks to the lower limb and the management of these blocks particularly in the postoperative period.

Electrical stimulation versus ultrasound guidance for popliteal-sciatic perineural catheter insertion: a randomized controlled trial

BACKGROUND

Sciatic perineural catheters via a popliteal fossa approach and subsequent local anesthetic infusion provide potent analgesia and other benefits after foot and ankle surgery. Electrical stimulation (ES) and, more recently, ultrasound (US)-guided placement techniques have been described. However, because these techniques have not been compared in a randomized fashion, the optimal method remains undetermined. Therefore, we tested the hypotheses that popliteal-sciatic perineural catheters placed via US guidance require less time for placement and produce equivalent results, as compared with catheters placed using ES.

METHODS

Preoperatively, subjects receiving a popliteal-sciatic perineural catheter for foot and/or ankle surgery were randomly assigned to either the ES with a stimulating catheter or US-guided technique with a nonstimulating catheter. The primary end point was catheter insertion duration (in minutes) starting when the US transducer (US group) or catheter-placement needle (ES group) first touched the patient and ending when the catheter-placement needle was removed after catheter insertion.

RESULTS

All US-guided catheters were placed per protocol (n = 20), whereas only 80% of stimulation-guided catheters could be placed per protocol (n = 20, P = 0.106). All catheters placed per protocol in both groups resulted in a successful surgical block. Perineural catheters placed by US took a median (10th-90th percentile) of 5.0 min (3.9-11.1 min) compared with 10.0 min (2.0-15.0 min) for stimulation (P = 0.034). Subjects in the US group experienced less pain during catheter placement, scoring discomfort a median of 0 (0.0-2.1) compared with 2.0 (0.0-5.0) for the stimulation group (P = 0.005) on a numeric rating scale of 0 to 10.

CONCLUSIONS

Placement of popliteal-sciatic perineural catheters takes less time and produces less procedure-related discomfort when using US guidance compared with ES.

Ultrasound-guided sciatic nerve block in the popliteal fossa using a lateral approach: onset time comparing separate tibial and common peroneal nerve injections versus injecting proximal to the bifurcation

BACKGROUND

We hypothesized that blocking the tibial and common peroneal nerves individually using ultrasound distal to sciatic bifurcation would decrease time to complete block compared with a block proximal to the bifurcation.

METHODS

Seventy-six patients undergoing foot or ankle surgery received a sciatic nerve block either proximal or distal to the point of bifurcation. A mixture of 28 mL 1.5% mepivacaine with 100 microg clonidine and 1 mL 8.4% sodium bicarbonate for a total of 30 mL was used. Ultrasound was used to guide needle adjustments to achieve circumferential spread. Block success was defined as a loss of sensation to pinprick in both nerve distributions within 46 minutes.

RESULTS

Patients in the tibial-peroneal group had significantly faster time to complete block than the sciatic group (19.2 vs 26.1 minutes; P = 0.006).

CONCLUSIONS

Blocking the tibial and common peroneal nerves in the popliteal fossa separately provides for a faster onset than a prebifurcation sciatic block.

Visualization of the course of the sciatic nerve in adult volunteers by ultrasonography

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Regional anesthesia meets ultrasound: a specialty in transition

Despite its well-known benefits, regional anesthesia has not attained the stature, simplicity, and safety of general anesthesia. Many of the challenges and clinical failures of regional anesthetic techniques can be attributed to fact that neurovascular anatomy is highly variable. Furthermore, current nerve localization techniques provide little or no information regarding the anatomical spread local anesthesia. Recently, ultrasound technology has been utilized by anesthesiologists in an attempt to minimize many of the drawbacks of traditional nerve block techniques. This review article will update the reader on the current status of ultrasound-guided regional anesthesia, provide an evidence-based context, and supply key facts regarding ultrasound physics. In the process, we will also highlight several possible limitations of ultrasound techniques including learning curve issues, costs, and artifact generation.

Ultrasound-guided sciatic nerve block: description of a new approach at the subgluteal space

Sciatic nerve block is frequently used for anaesthesia or analgesia during orthopaedic foot surgery and there are several different approaches to the sciatic nerve. This report describes a new approach to the sciatic nerve using ultrasound. Local anesthetic was injected into the 'subgluteal space' under ultrasound guidance which was effective in producing sciatic nerve block in a small series of five patients. The anatomy, sonographic features, technique of identifying the subgluteal space, and potential advantages of this approach to the sciatic nerve are discussed.

Ultrasound-guided peripheral nerve blockade

Peripheral nerve blockade (PNB) for orthopedic surgery is usually performed without visual guidance, relying mainly on surface anatomic landmarks and electrical stimulation to localize nerves. Moreover, multiple trial and error attempts to place a needle can frustrate the operator, cause unwarranted pain to the patient, and waste valuable time in the operating room. Inaccurate needle placement and spread of local anesthetic account for most PNB failures, whereas "trial and error" needle manipulations for nerve localization can cause complications. The recent application of ultrasound (US) to PNB affords real-time imaging of the target nerve, needle, and surrounding vasculature, such that needle proximity to the nerve is ensured and vascular puncture avoided. This article reviews the advantages, principles, and techniques of US for the most common types of PNB.

Anatomical evaluation of the tibial nerve within the popliteal fossa

The purpose of this study was to evaluate the inter-hamstring position (medial to lateral intertendinous position) of the tibial nerve within the popliteal fossa. A descriptive cadaver model study was performed to permit controlled and direct measures of the tibial nerve. Fourteen embalmed lower extremities (8 left, 6 right) from nine cadavers (4 males, 5 females; 84.3 +/- 10.7 years of age) were examined. Nine anatomical variables were measured. All measurements, except the diameter of the tibial nerve at the apex of the popliteal fossa, were performed at the level of the femoral condyles, at their widest medial-to-lateral point. The tibial nerve's diameter increased as it descended from the apex (3.95 +/- 0.50 mm; CI = 2.94-4.96 mm) to the condyles (4.46 +/- 0.92 mm; CI = 2.62-6.31 mm). The distance between the semimembranosus tendon and the biceps femoris tendon in the popliteal fossa (the mid-intertendinous distance) was 48.50 +/- 11.50 mm. The location of the tibial nerve between these two tendons was highly variable: 21.45 +/- 8.40 mm lateral of the semimembranosus tendon and 22.60 +/- 4.90 mm medial of the biceps femoris tendon. Therefore, in 95% of the patients the tibial N could be located within 48.2% of midpoint of the inter-hamstring distance.

Establishing a popliteal portal using the METRx system under ultrasound guidance

This report describes a special technique for safe establishment of a popliteal portal with the METRx system (Medtronic Sofamor Danek, Memphis, TN) under ultrasound guidance with the patient in the awake state. Herbert screws located at the posterior tibial plateau were removed via this portal in a minimally invasive way. Before surgery, we performed surface mapping of the screw tract with an image intensifier and target needling under ultrasound guidance. The METRx system was used to establish the soft-tissue corridor along the guide pin. Screw removal and tibial plateau resurfacing were performed with the Acufex Mosaicplasty system (Smith & Nephew Endoscopy, Andover, MA). In our review of the literature, no similar method establishing the knee popliteal portal was found. The method is recommended especially for minimally invasive surgery in regions rich with neurovascular structures.