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

Ultrasound-Guided Measurement of Piriformis Muscle Thickness to Diagnose Piriformis Syndrome

Background: Piriformis syndrome (PS) is a neuromuscular condition caused by the entrapment of the sciatic nerve at the level of the piriformis muscle (PM). Diagnosing PS remains challenging despite recent invasive and non-invasive diagnostic methods. Response to invasive nerve block is still one of the most reliable diagnostic modalities because there is no gold standard test for PS. As early diagnosis may prevent delayed diagnosis that results in chronic somatic dysfunction and muscle weakness, a screening test with high sensitivity could guide clinicians in performing the next appropriate step in diagnosing PS.

Aim: The purpose of this study is to determine the sensitivity, specificity, and best cut-off point of ultrasound-guided PM thickness in PS.

Method: This case-control study was conducted in a general hospital in Tangerang during a 3-month period. We recruited 58 patients clinically diagnosed with PS and 58 healthy patients (without a history of hip and buttock pain) during their visits to the outpatient clinic. All patients underwent ultrasound assessment to measure bilateral PM thickness. Sex, age, body mass index, history of micro-/macro-trauma, and prolonged sitting duration were recorded. Statistical analyses were performed using the Statistical Package for the Social Sciences version 25.

Result: The PS and control groups predominantly comprised female subjects, with mean ages of 51.79 ± 14.10 and 50.09 ± 13.26 years on PS and healthy subjects, respectively. The mean ultrasound-guided PM thickness was higher in PS subjects compared to healthy subjects with mean thicknesses of 1.16 ± 0.13 and 0.85 ± 0.11 cm, respectively (p < 0.05). The area under the receiver operating characteristic curve of the PM was 0.970 (95% confidence interval 0.943–0.998, p < 0.05). The best cut-off point defined by Youden's J index was 0.9950 cm for all PS subjects.

Conclusion: We propose 0.9950 cm as the cut-off point for diagnosing PS by ultrasound, which has the sensitivity and specificity of 94.8 and 87.9%, respectively.

Lower extremity regional anesthesia: essentials of our current understanding

The advent of ultrasound guidance has led to a renewed interest in regional anesthesia of the lower limb. In keeping with the American Society of Regional Anesthesia and Pain Medicine's ongoing commitment to provide intensive evidence-based education, this article presents a complete update of the 2005 comprehensive review on lower extremity peripheral nerve blocks. The current review article strives to (1) summarize the pertinent anatomy of the lumbar and sacral plexuses, (2) discuss the optimal approaches and techniques for lower limb regional anesthesia, (3) present evidence to guide the selection of pharmacological agents and adjuvants, (4) describe potential complications associated with lower extremity nerve blocks, and (5) identify informational gaps pertaining to outcomes, which warrant further investigation.

Noninvasive Measurement of Sciatic Nerve Stiffness in Patients With Chronic Low Back Related Leg Pain Using Shear Wave Elastography

OBJECTIVES

The purpose of this study was to determine whether sciatic nerve stiffness is altered in people with chronic low back-related leg pain by using shear wave elastography.

METHODS

In this cross-sectional study, the sciatic nerve shear wave velocity (ie, an index of stiffness) was measured in both legs of 16 participants (8 with unilateral low back-related leg pain and 8 healthy controls). Sciatic stiffness was measured during a passive ankle dorsiflexion motion performed at 2°/s in an isokinetic dynamometer. The ankle range of motion and passive torque, as well as muscle activity, were also measured.

RESULTS

In people with low back-related leg pain, the affected limb showed higher sciatic nerve stiffness compared to the unaffected limb (+11.3%; P = .05). However, no differences were observed between the unaffected limb of people with low back-related leg pain and the healthy controls (P = .34).

CONCLUSIONS

People with chronic low back-related leg pain have interlimb differences in sciatic nerve stiffness, as measured by a safe and noninvasive method: shear wave elastography. The changes found may be related to alterations in nerve mechanical properties, which should be confirmed by future investigations.

Sciatic nerve stiffness is not changed immediately after a slump neurodynamics technique

Background

Neurodynamics techniques aim to assess and improve neural mechanosensitivity. However, there is no in vivo evidence regarding the mechanical effects of these techniques in the nerve stiffness. This study examined the immediate effects of a slump neurodynamics technique in the sciatic nerve shear wave velocity (SWV. i.e. an index of stiffness) using ultrasound-based elastography.

Methods

Fourteen healthy participants were included in this experiment. Sciatic SWV and ankle passive torque were measured during a passive ankle dorsiflexion motion (2°/s), before and immediately after 3 minutes of slump neurodynamics technique, randomly applied to one lower limb. The contralateral limb served as control.

Results

The slump intervention did not change the sciatic SWV (P=0.78), nor the dorsiflexion passive torque (P=0.14), throughout the ankle dorsiflexion motion. Excellent values of intra-rater repeatability (ICC=0.88, 0.68-0.96), and low values of standard error of measurement (0.59 m/s, 0.35-1.15m/s), were observed for the SWV measurements.

Conclusions

The sciatic nerve stiffness of healthy participants did not change immediately after a slump neurodynamics technique, suggesting a compliance of the neural tissue to tensile loads. However, these results ought to be confirmed using other neurodynamics techniques and in other populations (e.g. peripheral neuropathies).

Level of evidence

III.

Holistic ultrasound in trauma: An update

Holistic ultrasound is a total body examination using an ultrasound device aiming to achieve immediate patient care and decision making. In the setting of trauma, it is one of the most fundamental components of care of the injured patients. Ground-breaking imaging software allows physicians to examine various organs thoroughly, recognize imaging signs early, and potentially foresee the onset or the possible outcome of certain types of injuries. Holistic ultrasound can be performed on a routine basis at the bedside of the patients, at admission and during the perioperative period. Trauma care physicians should be aware of the diagnostic and guidance benefits of ultrasound and should receive appropriate training for the optimal management of their patients. In this paper, the findings of holistic ultrasound in trauma patients are presented, with emphasis on the lungs, heart, cerebral circulation, abdomen, and airway. Additionally, the benefits of ultrasound imaging in interventional anaesthesia techniques such as ultrasound-guided peripheral nerve blocks and central vein catheterization are described.

Surgical anatomy of the sciatic nerve: A meta-analysis

The sciatic nerve has varying anatomy with respect to the piriformis muscle. Understanding this variant anatomy is vital to avoiding iatrogenic nerve injuries. A comprehensive electronic database search was performed to identify articles reporting the prevalence of anatomical variations or morphometric data of the sciatic nerve. The data found was extracted and pooled into a meta-analysis. A total of 45 studies (n = 7068 lower limbs) were included in the meta-analysis on the sciatic nerve variations with respect to the piriformis muscle. The normal Type A variation, where the sciatic nerve exits the pelvis as a single entity below the piriformis muscle, was most common with a pooled prevalence of 85.2% (95%CI: 78.4-87.0). This was followed by Type B with a pooled prevalence of 9.8% (95%CI: 6.5-13.2), where the sciatic nerve bifurcated in the pelvis with the exiting common peroneal nerve piercing, and the tibial nerve coursing below the piriformis muscle. In morphometric analysis, we found that the pooled mean width of the sciatic nerve at the lower margin of the piriformis muscle was 15.55 mm. The pooled mean distance of sciatic nerve bifurcation from the popliteal fossa was 65.43 mm. The sciatic nerve deviates from its normal course of pelvic exit in almost 15% of cases. As such we recommend that a thorough assessment of sciatic nerve variants needs to be considered when performing procedures in the pelvic and gluteal regions in order to reduce the risk of iatrogenic injury. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1820-1827, 2016.

Minimum effective local anesthetic volume for surgical anesthesia by subparaneural, ultrasound-guided popliteal sciatic nerve block: A prospective dose-finding study

Because of its rapid onset time, recent years have seen an increase in the use of ultrasound (US)-guided popliteal sciatic nerve block (PSNB) via subparaneural injection for induction of surgical anesthesia. Moreover, in below-knee surgery, combined blocks, as opposed to sciatic nerve block alone, have become more common. These combined blocks often require a large volume of local anesthetic (LA), thus increasing the risk of local-anesthetic systemic toxicity (LAST). Thus, to decrease the risk of LAST, it is important to know the minimum effective volume (MEV) required for an adequate block. We, therefore, aimed to determine the MEV of ropivacaine 0.75% for induction of surgical anesthesia by the method of US-guided popliteal sciatic nerve block via subparaneural injection.Thirty patients underwent a US-guided PSNB with ropivacaine 0.75% at a 20-mL starting volume. Using a step-up/step-down method, we determined injection volumes for consecutive patients from the preceding patient's outcome. When an effective block was achieved within 40 minutes after injection, the next patient's volume was decreased by 2 mL. If the block failed, the next patient's volume was increased by 2 mL. The sensory and motor blockade was graded according to a 4-point scale. The block was considered a success if a combination of anesthesia and paresis (a score of 3 for both the sensory and motor nerves) was achieved within 40 minutes. The primary outcome measure was the MEV resulting in a successful subparaneural block of the sciatic nerve in 50% of patients (MEV50). Additionally, the data were processed with a probit regression analysis to determine the volume required to produce a complete sciatic nerve block in 90% of subjects (ED90).The MEV50 of 0.75% ropivacaine is 6.14 mL (95% confidence interval, 4.33-7.94 mL). The ED90 by probit analysis for a subparaneural injection was 8.9 mL (95% CI, 7.09-21.75 mL).The 6.14-mL MEV50 of ropivacaine 0.75% represents a 71% reduction in volume compared with neurostimulation techniques and a 14.7% reduction in volume compared with US-guided PSNB using the alternative perineural injection technique.

Non-invasive assessment of sciatic nerve stiffness during human ankle motion using ultrasound shear wave elastography

Peripheral nerves are exposed to mechanical stress during movement. However the in vivo mechanical properties of nerves remain largely unexplored. The primary aim of this study was to characterize the effect of passive dorsiflexion on sciatic nerve shear wave velocity (an index of stiffness) when the knee was in 90° flexion (knee 90°) or extended (knee 180°). The secondary aim was to determine the effect of five repeated dorsiflexions on the nerve shear wave velocity. Nine healthy participants were tested. The repeatability of sciatic nerve shear wave velocity was good for both knee 90° and knee 180° (ICCs ≥ 0.92, CVs ≤ 8.1%). The shear wave velocity of the sciatic nerve significantly increased (p<0.0001) during dorsiflexion when the knee was extended (knee 180°), but no changes were observed when the knee was flexed (90°). The shear wave velocity-angle relationship displayed a hysteresis for knee 180°. Although there was a tendency for the nerve shear wave velocity to decrease throughout the repetition of the five ankle dorsiflexions, the level of significance was not reached (p=0.055). These results demonstrate that the sciatic nerve stiffness can be non-invasively assessed during passive movements. In addition, the results highlight the importance of considering both the knee and the ankle position for clinical and biomechanical assessment of the sciatic nerve. This non-invasive technique offers new perspectives to provide new insights into nerve mechanics in both healthy and clinical populations (e.g., specific peripheral neuropathies).

Location of the sciatic nerve at the popliteal fossa in the adult population: Relationship with gender and anthropometric data studied. Implications for daily practice

OBJECTIVE

To determine whether the location of the sciatic nerve (SN) at the popliteal fossa is related to anthropometric variables in the adult population, and to identify possible anatomical variations and their possible implications for clinical practice.

MATERIALS AND METHOD

Prospective observational study in elective ambulatory surgery patients. Patients were examined using ultrasound, looking at depth, laterality and distance at which the SN bifurcates at the level of the popliteal fossa. These measurements were linked to gender and the anthropometric data of the patients.

RESULTS

A total of 62 patients were included, with 124 measurements. A statistically significant association was found between SN depth and the diameter of the thigh measured at 10 cm from the popliteal crease (P<.001). Mean depth: 3.32 ± 0.8 cm, mean laterality: 1.43 ± 0.9 cm, mean SN bifurcation distance: 61.78 ± 12 mm and mean SN diameter: 7.45 ± 1.17 mm. There were no statistical differences when comparing the measured variables with the age and gender. Similar results were obtained between measurements when comparing both lower limbs in the same patient. There was no statistical difference between height and distance at which the SN bifurcates.

CONCLUSIONS

The depth and laterality of SN are independent of gender, weight and height. The depth at which the SN is located at the level of the popliteal fossa is related to the diameter of the thigh. The bifurcation of SN in popliteal fossa is not related to height.

Minimum Effective Anaesthetic Volume of 0.5% Ropivacaine for Ultrasound-Guided Popliteal Sciatic Nerve Block in Patients Undergoing Foot and Ankle Surgery: Determination of ED50 and ED95

Compared to nerve stimulation or classic paraesthesia techniques, ultrasound (US)-guided popliteal sciatic nerve block requires a smaller volume of local anaesthetic. The up-and-down method was used to determine the minimum effective anaesthetic volume of 0.5% ropivacaine necessary for US-guided popliteal sciatic nerve block to achieve successful surgical anaesthesia for foot and ankle surgery. The study included 32 patients receiving an US-guided popliteal sciatic nerve bock. The starting dose of 0.5% ropivacaine was set at 30 ml, which was decreased by 3 ml if the block succeeded and increased by 3 ml if the block failed. After the injection of local anaesthetic, the degree of sensory and motor blockade of the tibial and common peroneal nerves was assessed every 5 minutes for 30 minutes. The ED50 and ED95 volumes of local anaesthetic were 6 ml and 16 ml, respectively. The success rates of sensory blockade of the tibial nerve and common peroneal nerve were 69% and 88%, respectively. The success rates of motor blockade of these nerves were 75% and 90%, respectively. The ED50 and ED95 of 0.5% ropivacaine for US-guided popliteal sciatic nerve block were 6 ml and 16 ml, respectively.

Use of ultrasound for lower extremity

PURPOSE OF REVIEW

To explore the recent advances in the use of ultrasound for lower extremity blocks, including approaches to the lumbar and sacral plexus blocks.

RECENT FINDINGS

Procedures of the lower extremity often require blocks of the lumbar and sacral plexuses. The use of ultrasound offers some advantages, including the possibility to directly visualize the distribution of local anesthetics.

SUMMARY

Lower extremity blocks under ultrasound guidance often require advanced skills because of the depth of target nerves. This review summarizes the recent advances in the use of ultrasound guidance over traditional techniques.

Tibial nerve excursion during lumbar spine and hip flexion measured with diagnostic ultrasound

Ultrasound imaging provides a method for non-invasive in vivo measurement of nerve motion resulting from joint movement. This study measured the proximal excursion of the tibial branch of the sciatic nerve at the popliteal fossa during forward bending in healthy subjects. Long-axis image sequences of the nerve were analysed using frame-by-frame cross-correlation software that calculated the longitudinal and axial movement of the nerve. Proximal excursion was calculated from the hypotenuse of these values. The mean proximal excursion recorded was 12.2 mm (SD 2.2 mm, n = 24). The reliability of three repeat measurements was found to be excellent (ICC 0.97, 95% CI 0.93-0.99; SEM 0.7 mm, n = 21). The protocol described provides a reliable method for analysing tibial nerve movement that could prove useful in future clinical studies.

Ultrasound-guided infragluteal sciatic nerve block: a comparison between four different techniques

OBJECTIVE

Ultrasound guided sciatic block can be performed by different techniques. We compared namely short or long axis views of the sciatic nerve with in-plane or out-of-plane needle insertion techniques for the infragluteal sciatic nerve block (ISNB).

METHODS

One hundred twenty patients with American Society of Anesthesiologists physical status I-III, scheduled for foot surgery were assigned into four groups. Group SI: patients received ultrasound-guided SNB using short axis (S) view of the SN and in-plane (I) insertion of needle. Group LI: patients received SNB using long axis (L) view of SN and (I) insertion of the needle. Group SO: patients received SNB using (S) view of SN and out-of-plane (O) insertion of the needle. Group LO: patients received SNB using (L) view of SN and (O) insertion of the needle. Primary outcomes included the time to perform the block (recognition and performance time) and the level of patient discomfort during block placement.

RESULTS

The recognition time and performance time were shortest in LI group (51 ± 16.4 and 87.7 ± 14.8 s), while they were longest in LO group (138.7 ± 21.4 and 160.3 ± 17.5 s). There were no significant differences between the groups as regards the number of attempts and needle redirections to elicit sciatic motor response. The level of patient discomfort was significantly less in the LI group in comparison with the SI and LO groups.

CONCLUSION

The LI approach required less time to complete the infragluteal sciatic nerve block procedure and it was more comfortable for the patients in comparison to the SO, SI and LO approaches.

Ultrasound guidance for deep peripheral nerve blocks: a brief review

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.

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.

Fifteen years of ultrasound guidance in regional anaesthesia: Part 2-recent developments in block techniques

The use of ultrasound guidance for regional anaesthesia has gained enormous popularity in the last 10 yr. The first part of this review article provided information on safety, technical developments, economic aspects, education, advantages, needle guidance techniques, and future developments in ultrasound. The second part focuses on practical and technical details of individual ultrasound-guided nerve blocks in adults. We present a comprehensive review of the relevant literature of the last 5 yr with a commentary based on our own clinical experience in order to provide information relevant to patient management. Upper limb blocks, including interscalene, supra- and infraclavicular, and axillary approaches, are described and discussed. For the lower limb, psoas compartment, femoral, obturator, sciatic, and lateral cutaneous nerve blocks are described, as are some abdominal wall blocks. The potential role of ultrasound guidance for neuraxial block is addressed. The need for further large-scale studies of the role of ultrasound is emphasized.

Ultrasound-guided nerve blocks: efficacy and safety

The introduction of affordable, portable and high-resolution ultrasound machines has rejuvenated interest in regional anaesthesia. The inherent benefits of direct visualisation of nerves and surrounding anatomy, continual observation of the needle tip and spread of local anaesthetic make ultrasound-guided regional anaesthesia highly appealing. However, in the cost-conscious health-care setting and to convince sceptics, there also needs to be evidence of increased benefits and reduced complications. Ultrasound is a rapidly developing area of technology and some of the newer modalities are discussed. This article focusses on the recent growing evidence to support the benefits of its use in nerve and plexus blocks. Common complications of nerve blocks can be avoided with ultrasound but have still been reported. Anatomical variants have been demonstrated by ultrasound and it has proved to be useful in performing regional anaesthesia in difficult situations or where peripheral nerve stimulation is unsuccessful or inappropriate.

Soft tissue landmark for ultrasound identification of the sciatic nerve in the infragluteal region: the tendon of the long head of the biceps femoris muscle

BACKGROUND AND OBJECTIVES

The sciatic nerve block represents one of the more difficult ultrasound-guided nerve blocks. Easy and reliable internal ultrasound landmarks would be helpful for localization of the sciatic nerve. Earlier, during ultrasound-guided posterior approaches to the infragluteal sciatic nerve, the authors recognized a hyperechoic structure at the medial border of the long head of biceps femoris muscle (BFL). The present study was performed to determine whether this is a potential internal landmark to identify the infragluteal sciatic nerve.

METHODS

The depth and the thickness of this hyperechoic structure, its relationship with the sciatic nerve and the ultrasound visibility of both were recorded in the proximal upper leg of 21 adult volunteers using a linear ultrasound probe in the range of 7-13 MHz. The findings were verified by an anatomical study in two cadavers.

RESULTS

The hyperechoic structure at the medial border of the BFL extended in a dorsoventral direction between 1.4+/-0.6 cm (mean+/-SD) and 2.8+/-0.8 cm deep from the surface, with a width of 2.2+/-0.9 mm. Between 2.6+/-0.9 and 10.0+/-1.5 cm distal to the subgluteal fold, the sciatic nerve was consistently identified directly at the ventral end of the hyperechoic structure in all volunteers. The anatomical study revealed that this hyperechoic structure corresponds to tendinous fibres inside and at the medial border of the BFL.

CONCLUSION

The hyperechoic BFL tendon might be a reliable soft tissue landmark for ultrasound localization of the infragluteal sciatic nerve.

Impact of a regional anesthesia rotation on ultrasonographic identification of anatomic structures by anesthesiology residents

OBJECTIVE

The specific aim of this study was to determine the ability of anesthesiology residents to independently identify a series of anatomic structures in a live model using ultrasound, both before and after a 4-week regional anesthesia rotation that incorporates a standardized ultrasound training curriculum for peripheral nerve blockade.

METHODS

Ten CA2 and CA3 anesthesiology residents volunteered to participate in this study. Each resident was subjected to a pre-rotation practical exam, in which he attempted to identify 15 structures at four sites of peripheral nerve blockade, in a test subject. Each resident then received specific training for ultrasound-guided nerve blocks during a 4-week regional anesthesia rotation, and then completed a post-rotation exam. The mean number of structures correctly identified on the exams was compared for significant differences utilizing a paired t-test.

RESULTS

Residents were able to identify significantly more anatomic structures on the post-rotation exam as compared with the pre-rotation exam (mean 14.1 vs. 9.9, P<.001), as well as more peripheral nerve targets. The most frequently misidentified structures on the pre-rotation exam were the subclavian vein, the sciatic nerve in the popliteal fossa, and the femur.

CONCLUSIONS

Ultrasound-naive anesthesiology residents, who received instruction and experience with ultrasound-guided peripheral nerve blocks on a 4-week regional anesthesia rotation, significantly improved their ability to independently identify relevant anatomic structures with ultrasonography.