Fig. 26.1
Skeletal model showing anatomical landmarks for posterior gluteal sciatic nerve blockade
Fig. 26.2
Surface landmarks for posterior gluteal sciatic nerve block
The patient is placed in the lateral decubitus position with the legs flexed at the hip and knee. Surface landmarks include:
Greater trochanter of the femur
Sacral hiatus
Posterior superior iliac spine
The point of needle entry when using the landmark technique is where a perpendicular line drawn at the midpoint between the greater trochanter and posterior superior iliac spine intercepts a line drawn between the greater trochanter and the sacral hiatus.
26.2.2 Nerve Stimulation Technique
The approach described here is a modification of the landmark-based approach described by Winnie [1] with simplified landmarks and is typically easier to perform than the lateral or anterior approach [2].
Nerve stimulation in conjunction with ultrasound guidance is recommended for enhanced nerve localization using a posterior approach due to the depth of the sciatic nerve in the gluteal region.
26.2.2.1 Needle Insertion
A flowchart illustrating the needle insertion site and procedures is shown in Fig. 26.3.
Fig. 26.3
Flowchart of needle insertion and procedures for posterior gluteal sciatic nerve block
With the operator facing the patient’s back, a 50–80 mm, 22G–25G needle (depending on the age and size of the child) is inserted perpendicular to the skin at the landmark described above and advanced in the direction of the ischium.
The sciatic nerve may be reached at a variable depth, depending on the child’s size and adiposity, but the depth may be approximated as about 1 mm per kg of weight (especially between 20 and 40 kg) with relatively less depth for younger children and greater depth for older children [2].
If there is bony contact, the needle may either be touching the iliac bone or the ischial spine. In these cases, the needle tip has been placed too cephalad or too medial, respectively, or the needle is too deep.
The inferior gluteal and internal pudendal vessels are at risk for puncture if the needle is directed too medially.
26.2.2.2 Current Application and Appropriate Responses
Figure 26.4 illustrates the procedure for employing nerve stimulation techniques for lumbar plexus block.
Fig. 26.4
Flowchart for employing nerve stimulation technique for posterior gluteal sciatic nerve block
Initially, set the nerve stimulator to apply a current of 1–1.5 mA (2 Hz, 0.1–0.2 ms), and aim to elicit motor twitches at a current intensity threshold of 0.4 mA (0.1–0.2 ms) once the nerve is localized. Motor response cessation at currents less than 0.2 mA indicates that the needle is probably at an intraneural location.
Visible or palpable twitches of the hamstring, calf muscles, foot, or toes verify stimulation of the sciatic nerve.
Inversion of the foot or plantar flexion is sought, with inversion producing a more rapid onset and increased success of complete block than plantar flexion. Foot eversion indicates stimulation of the superficial peroneal nerves only and is associated with incomplete block [3].
See Table 14.4 for expected motor responses during nerve stimulation.
Clinical Pearl
A double-injection technique has been used for proximal and popliteal sciatic nerve blocks in order to accurately localize the two components of the sciatic nerve and thus provide greater block success (with shorter latency) and allow lower total doses of local anesthetic. However, this may increase the potential risk of needling trauma.
26.2.2.3 Modifications to Inappropriate Responses (Table 26.1)
Table 26.1
Responses and recommended needle adjustments for use with nerve stimulation during sciatic nerve block (posterior gluteal approach)
Correct response from nerve stimulation |
Visible or palpable twitches in any of the hamstring or calf muscles, foot, or toes, at 0.2–0.5 mA. Up to 1.0 mA may be required in some patients (diabetic, peripheral vascular disease, sepsis) |
Other common responses and needle adjustment |
Muscle twitches from electrical stimulation |
Gluteus maximus (local twitch from direct stimulation) |
Explanation: needle tip too superficial |
Needle adjustment: advance needle tip |
Deep muscle layer (local twitch of inferior or superior gemellus, obturator internus, or quadratus femoris muscles) |
Explanation: needle advanced too deep and beyond the nerve |
Needle adjustment: withdraw needle to the skin and redirect slightly medially or laterally |
Vascular puncture |
Inferior gluteal or internal pudendal vessels puncture |
Explanation: needle tip placed too medially |
Needle adjustment: withdraw needle to skin and reinsert more laterally |
Bone contact |
Iliac bone (close to gluteus insertion) |
Explanation: needle tip too superior |
Needle adjustment: withdraw completely and reinsert according to protocol (check landmarks) |
Ischial spine |
Explanation: needle inserted at too medial position or angled in a medial direction |
Needle adjustment: withdraw completely and reinsert in a more lateral direction |
An algorithm of modifications in case of inappropriate responses to nerve stimulation is shown in Fig. 26.5.
Fig. 26.5
Flowchart of modifications to inappropriate responses to nerve stimulation during posterior gluteal sciatic nerve block
26.2.3 Ultrasound-Guided Technique
For a summary of ultrasound guidance techniques for posterior gluteal sciatic nerve blocks, see Fig. 26.6.
Fig. 26.6
Flowchart of ultrasound guidance technique for posterior gluteal sciatic nerve block
Major anatomical structures of the sciatic nerve in the gluteal region as captured by MRI and VHVS images are shown with the corresponding ultrasound image in Fig. 26.7a.
Fig. 26.7
(a) VHVS and MRI images of anatomical structures surrounding the sciatic nerve in the posterior gluteal region. (b) Ultrasound image of the posterior gluteal sciatic nerve block location
Prepare the needle insertion site and skin surface with an antiseptic solution. Prepare the ultrasound probe surface by applying a sterile adhesive dressing to it prior to needling as discussed in Chap. 4.
There are some differences between adults and children in terms of their anatomical landmarks and sonoanatomy. The ischial tuberosity is very thin in children under 1 year of age and may be more difficult to palpate or view sonographically [4]. Laterally, the medial aspect of the greater trochanter will appear largely hypoechoic, although its size will depend on the age of the child, and it will only become highly recognizable at 6–8 years of age [5]. The femoral condyles are cartilaginous between the first and third years of life and do not ossify and develop their distinctive shape with visible sonographic appearance until 7–9 years of age; therefore, the borders of the femur may not be as hyperechoic in young children.
26.2.3.1 Scanning Technique
The choice of ultrasound probe for this block will depend on the size of the patient. For young children, a high-frequency linear probe (10–5 MHz) can be used, although in older or larger patients, a curved, lower-frequency (5–2 MHz) probe may be required for increased depth of penetration.
The probe is moved cephalad and caudad in the gluteal region to examine the ischial bone (a hyperechoic line with bony shadowing). Locate the widest portion of this bone that includes the ischial spine in the medial aspect.
The gluteus maximus muscle will be visible superficial and posterior to the sciatic nerve.
Alternatively, the sciatic nerve can be first located in the subgluteal region at approximately the midpoint between the greater trochanter and ischial tuberosity and traced proximally.
Identification of the internal pudendal artery and vein adjacent to the ischial spine, as well as the inferior gluteal artery immediately adjacent to the sciatic nerve, may be facilitated with color Doppler.
26.2.3.2 Sonographic Appearance
The sciatic nerve is hyperechoic and often appears wide and flat in short axis (Fig. 26.7b).
Overlying the sciatic nerve is the distinctive gluteus maximus, which has a “starry night” pattern, and the inner muscle layers (superior and inferior gemellus muscles and quadratus femoris muscle) are often indistinct.
26.2.3.3 Needle Insertion
Both in-plane (IP) and out-of-plane (OOP) approaches are appropriate for ultrasound-guided sciatic nerve block using the posterior gluteal approach.
OOP approach (Fig. 26.8): the needle is inserted inferior to the probe in a cephalo-anterior direction. Since the nerve is deep at the gluteal region, needle insertion at a steep angle immediately next the transducer may increase the visibility of the needle tip.
Fig. 26.8
Out-of-plane needling technique for ultrasound-guided posterior gluteal sciatic nerve block. Blue rectangle indicates probe footprint
IP approach (Fig. 26.9): the needle may be advanced in a lateral-to-medial direction, penetrating the gluteus maximus muscle prior to reaching the sciatic nerve above the ischial bone.
Fig. 26.9
In-plane needling technique for ultrasound-guided posterior gluteal sciatic nerve block. Blue rectangle indicates probe footprint
26.2.4 Local Anesthetic Application
Ensure negative aspiration of blood prior to injection of local anesthetic.
Dalens et al. [2] described the use of four anesthetic solutions, each with 1:200,000 epinephrine (15 patients in each group): (1) 1 % lidocaine, (2) 0.5 % bupivacaine, (3) a mixture of equal volumes of 0.5 % bupivacaine and 1 % lidocaine, and (4) a mixture of equal volumes of 0.5 % bupivacaine and 1 % etidocaine. The local anesthetic solution was administered on a weight basis: 0.5 mL/kg in patients weighing less than 20 kg and 10 mL plus 0.25 mL/kg of patient’s weight exceeding 20 kg, up to 25 mL maximum injected volumes.
Small amounts of local anesthetic (0.3–0.5 mL/kg of 0.5 % bupivacaine for single limb blocks and 0.3 mL/kg 0.25 % bupivacaine per side for bilateral blocks) have also proven effective [6–8].
Ivani et al. [9] suggested a bolus dose of 0.4–0.6 mL/kg of 0.2 % ropivacaine for postoperative analgesia and a higher concentration of 0.5 % ropivacaine if intraoperative pain control is required. They also described the use of clonidine 2 μg/kg in their local anesthetic mixture.
The same group also suggested that ropivacaine and levobupivacaine are probably the best choice for longer operations when pain is more intense and long-lasting [10].
Due to the anatomy of the nerves in children (smaller diameter and shorter distance between the nodes of Ranvier), larger volumes with lower concentrations are key to obtaining effective analgesia [11].
We recommend the use of ropivacaine 0.2 %, bupivacaine 0.25 %, or levobupivacaine 0.25 %, with a volume of 0.25–0.5 mL/kg.
As a guideline, lower concentrations should be used in children below the age of 6 years. Based on clinical experience, 6–12 h of analgesia can be expected [12].
The dose of local anesthetic should not exceed the maximum toxic dose.
Ultrasound Considerations
Performing a test dose with D5W is recommended prior to local anesthetic application to visualize the spread and confirm nerve localization. Deposit the local anesthetic solution over and around the sciatic nerve.
26.3 Infragluteal/Subgluteal Sciatic Nerve Block Approach
In contrast to the Labat/gluteal sciatic nerve block, the infragluteal/subgluteal approach targets the sciatic nerve at a more superficial location.
26.3.1 Surface Anatomy (Fig. 26.10)
Fig. 26.10
Skeletal model showing anatomical landmarks for subgluteal sciatic nerve blockade
The patient can be placed in the lateral decubitus position with the hip flexed and knee slightly extended, or they may be positioned prone. Surface landmarks include:
Ischial tuberosity
Greater trochanter
26.3.2 Nerve Stimulation Technique
The authors recommend combining nerve stimulation with ultrasound guidance for infragluteal/subgluteal sciatic blocks.
26.3.2.1 Needle Insertion
A flowchart illustrating the needle insertion site and procedures is shown in Fig. 26.12.
Fig. 26.12
Flowchart of needle insertion and procedures for subgluteal sciatic nerve block
A 50–80 mm, 22G–25G needle (depending on the child’s age and size) is inserted perpendicularly to the skin until a loss of resistance is felt upon entrance to the common sheath.
The depth of the sciatic nerve will be variable and age dependent.
In situations of needle contact with bone:
Touching the iliac bone: needle tip is placed too cephalad.
Touching the hip joint: needle is located too deep and lateral.
Touching the ischium: needle is deep and medial.
26.3.2.2 Current Application and Appropriate Responses
Figure 26.13 illustrates the procedure for employing nerve stimulation techniques for subgluteal sciatic nerve block.
Fig. 26.13
Procedure for employing nerve stimulation technique during subgluteal sciatic nerve block
Applying an initial current of 1–1.5 mA (2 Hz, 0.1–0.2 ms) is sufficient for stimulation of the sciatic nerve. After obtaining the appropriate motor response, the current is reduced to aim for a threshold current of 0.4 mA (0.1–0.2 ms). Motor response cessation at currents less than 0.2 mA indicates that the needle is probably in an intraneural location.
Visible or palpable twitches of the hamstring or calf muscles, foot, or toes verify stimulation of the sciatic nerve.
Twitches in the foot indicate stimulation of the tibial and common peroneal nerves rather than the proximal branches of the sciatic nerve and suggest optimal needle placement. Ideally, inversion of the foot, which is indicative of tibial nerve stimulation, is sought [3].
See Table 14.4 for expected motor responses during nerve stimulation.
26.3.2.3 Modifications to Inappropriate Responses (Table 26.2)
Table 26.2
Responses and recommended needle adjustments for use with nerve stimulation during sciatic nerve block (subgluteal approach)
Correct response from nerve stimulation |
Twitches (visible or palpable) in any of the hamstring or calf muscles, foot, or toes, at 0.2–0.5 mA. Up to 1.0 mA may be required in some patients (diabetic, peripheral vascular disease, sepsis) |
Other common responses and needle adjustments |
Muscle twitches from electrical stimulation |
Gluteus maximus (local twitch from direct stimulation) |
Explanation: needle tip too superficial |
Needle adjustment: advance needle tip |
Bone contact |
Iliac bone (close to gluteus insertion) |
Explanation: needle tip too superior |
Needle adjustment: withdraw completely and reinsert according to protocol (check landmarks) |
Ischial or hip joint |
Explanation: needle missed the plane of the sciatic nerve and the tip is placed too far medially (ischial) or laterally (hip) |
Needle adjustment: withdraw completely and reinsert with a 5–10° angle adjustment |
No response despite deep placement |
Deep (10 cm) but no response; it is likely that the needle has been placed in the greater sciatic notch |
Explanation: needle tip too inferior and medial |
Needle adjustment: withdraw completely and reinsert slightly superiorly |
An algorithm of modifications in case of inappropriate responses to nerve stimulation is shown in Fig. 26.14.
Fig. 26.14
Flowchart of modifications to inappropriate responses to nerve stimulation during subgluteal sciatic nerve block
26.3.3 Ultrasound-Guided Technique
For a summary of ultrasound guidance techniques in subgluteal sciatic nerve blocks, see Fig. 26.15.
Fig. 26.15
Flowchart of ultrasound guidance technique for subgluteal sciatic nerve block
Major anatomical structures surrounding the sciatic nerve using a subgluteal approach as captured by MRI and VHVS images are shown with the corresponding ultrasound image in Fig. 26.16.
Fig. 26.16
(a) VHVS and MRI images of anatomical structures surrounding the sciatic nerve in the subgluteal region. (b) Ultrasound image of the subgluteal sciatic nerve block location
Prepare the needle insertion site and skin surface with an antiseptic solution. Prepare the ultrasound probe surface by applying a sterile adhesive dressing to it prior to needling as discussed in Chap. 4.
26.3.3.1 Scanning Technique
A high-frequency (10–5 MHz) linear probe is appropriate for most children. Larger children and adolescents may require the use of a curved, low-frequency (5–2 MHz) probe.
Position the probe to obtain a short-axis view of the sciatic nerve, usually between the ischial tuberosity and the greater trochanter of the femur.
Tilt and/or rotate the probe to optimize the ultrasound image of the sciatic nerve.
If the sciatic nerve is hard to localize at the subgluteal region, it can be traced proximally from the bifurcation point at or near the apex of the popliteal fossa
26.3.3.2 Sonographic Appearance
On the lateral side, the greater trochanter appears round with a hyperechoic edge and associated hypoechoic bony shadowing.
The sciatic nerve in the subgluteal region appears predominantly hyperechoic and is often elliptical in a short-axis view (Fig. 26.16b).
26.3.3.3 Needle Insertion
An OOP technique will result in the shortest possible needle path (Fig. 26.17). Since the nerve is deep, inserting the needle at a steep angle immediately next the transducer may increase the visibility of the needle tip.
Fig. 26.17
Out-of-plane needling technique for ultrasound-guided subgluteal sciatic nerve block. Blue rectangle indicates probe footprint
An IP alignment (Fig. 26.18) may allow for greater ease of needle shaft and tip recognition than OOP alignment. Use color Doppler to identify any blood vessels, such that the needle trajectory can be modified to avoid vascular puncture.
Fig. 26.18
In-plane needling technique for ultrasound-guided subgluteal sciatic nerve block. Blue rectangle indicates probe footprint
26.3.3.4 Local Anesthetic Application
See Sect. 26.2.4.
Ultrasound Considerations
Ultrasound guidance may allow for lower volumes of local anesthetic compared to the nerve stimulation technique.
Local anesthetic is injected following careful aspiration and injection of a test dose of D5W to visualize the spread and confirm nerve localization.
Deposit local anesthetic next to, but not directly within, the sciatic nerve structure in the subgluteal region. A hypoechoic local anesthetic fluid collection is often seen around the hyperechoic nerve during injection.
26.3.4 Case Study
Sciatic Nerve Block (Subgluteal Approach) (Contributed by A. Sawardekar)
A 10-year-old girl, 40 kg, with no previous medical history, presented with a left ankle fracture after falling while playing basketball. The fracture was confirmed by X-ray. Open reduction and internal fixation of the ankle was scheduled, and a left sciatic nerve block was chosen for pain control. An ultrasound-guided sciatic nerve block with a subgluteal approach was administered. A 22G, 80 mm needle and a 13–6 MHz linear high-frequency probe were used; the sciatic nerve was visualized at the subgluteal-parabiceps area, medial to the femur (Fig. 26.19). Ten mL 0.25 % bupivacaine was injected, and the block lasted for 8 h. Duration of surgery was 120 min. No additional analgesics were needed in the recovery room. The patient was discharged home after 2 h in the recovery room and was given instructions to take oral hydrocodone once sensation had returned to the operative extremity.
Fig. 26.19
Ultrasound-guided sciatic nerve block using a subgluteal approach. SN sciatic nerve, arrowheads indicate needle position (see Case Study for details)
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