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REGIONAL ANESTHESIA

Postoperative Analgesia with Continuous Sciatic Nerve Block After Foot Surgery: A Prospective, Randomized Comparison Between the Popliteal and Subgluteal Approaches

Pia di Benedetto, MD^*, Andrea Casati, MD, Laura Bertini, MD^*, Guido Fanelli, MD, and Jaques E. Chelly, MD, PhD, MBA

*Department of Anesthesiology, CTO Roma, Italy; Department of Anesthesiology, IRCCS H San Raffaele, Vita et Salute University, Milano, Italy; Department of Anesthesiology, University of Texas Medical School, Houston, Texas

Address correspondence and reprint requests to Andrea Casati, MD, Department of Anesthesiology, IRCCS H San Raffaele, Via Olgettina 60, 20132 Milan, Italy. Address e-mail to casati.andrea{at}hsr.it

	Abstract

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To compare the posterior popliteal and subgluteal continuous sciatic nerve block for anesthesia and acute postoperative pain management after foot surgery, 60 ASA physical status I and II patients undergoing elective orthopedic foot surgery were randomly assigned to either a Subgluteal group (n = 30) or Popliteal group (n = 30). Before surgery and after performing a femoral nerve block with 15 mL of 2% mepivacaine, we performed the sciatic nerve block with 20 mL of 0.75% ropivacaine using either a subgluteal or posterior popliteal approach, and the placement of a catheter came afterward. In the recovery room, the catheter was connected to a patient-controlled analgesia pump to infuse 0.2% ropivacaine (basal infusion rate of 5 mL/h, incremental bolus of 10 mL, and a lockout time of 60 min). There were no technical problems in catheter placement. Intraoperative efficacy of nerve block was similar in the two groups. Postoperative catheter displacement and occlusion were recorded in four patients in the Popliteal group and two patients in the Subgluteal group (P = 0.67). Both approaches provided similar postoperative analgesia. We conclude that the subgluteal approach is as effective and safe as the previously described posterior popliteal approach for continuous sciatic block and can be considered a useful alternative to anesthesia and acute postoperative analgesia after foot procedures.

IMPLICATIONS: Comparing two different approaches for continuous sciatic nerve block after orthopedic foot surgery, this prospective, randomized study demonstrated that the subgluteal approach is as effective and safe as the previously described posterior popliteal approach, and can be considered a useful alternative to anesthesia and acute postoperative analgesia after foot procedures.

	Introduction

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The degree of pain induced by foot surgery is often severe and prolonged, requiring large parenteral doses of analgesics (1,2). Regional anesthesia has become increasingly popular, and several studies have demonstrated the usefulness of blocking the sciatic nerve at different levels for analgesia after foot surgery (2–6). However, even if long-acting anesthetic solutions are used, single-shot nerve blocks provide adequate pain relief for 10–20 h (4,7). To prolong the postoperative benefit of perineural blocks, Singelyn et al. (8) reported the use of continuous sciatic nerve block using a posterior popliteal approach.

We recently described an easy and reliable technique to block the sciatic nerve at the subgluteal level (9). This posterior approach is a useful alternative to the more traditional Labat’s approach in patients undergoing foot surgery, also allowing the placement of a perineural catheter to prolong the postoperative sciatic block (10). The aim of this prospective, randomized study was to describe the subgluteal approach for continuous sciatic nerve block and compare it with the continuous popliteal sciatic nerve block for postoperative analgesia after foot surgery.

	Methods

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With the approval of the Ethical Committee, written informed consent was obtained from 60 ASA physical status I and II patients undergoing elective orthopedic foot procedures (hallux valgus, hallux rigidus, and surgical corrections of foot deformities requiring osteotomies, arthrodesis, or both). Patients with contraindications to regional anesthesia, as well as patients with respiratory or cardiac disease, diabetes, peripheral neuropathy, and patients receiving chronic analgesic therapy, were excluded.

All patients were premedicated with oral diazepam (10 mg) 30 min before performing the blocks. Next an IV line was placed at the forearm and 5 mL · kg^-1 · h^-1 of crystalloid infusion was infused. Nerve blocks were performed using a nerve stimulator (Plexival, Medival, Italy). The stimulation frequency was set at 2 Hz and duration of pulse stimulation at 0.1 ms. The intensity of the stimulating current, initially set to deliver 1 mA, was gradually decreased to 0.5 mA while maintaining the appropriate motor responses. Because all surgeries were performed using a tourniquet placed at the thigh, a femoral nerve block was performed with 15 mL of 2% mepivacaine according to the technique (4,7). A sciatic nerve block was then performed, and patients were randomly assigned to either a subgluteal (Subgluteal group, n = 30) or a posterior popliteal (Popliteal group, n = 30) approach.

Patients in the Popliteal group were placed in the prone position. The introduction site of the needle was 9 cm from the popliteal crease and 1 cm lateral to midline (10). After local skin infiltration, a 10-cm, 18-gauge insulated Tuohy needle (Plexolong, Pajunk, Germany) connected to a nerve stimulator was introduced with the tip oriented cephalad at an angle of 45–60 degrees. The stimulating needle was advanced until stimulation of the sciatic nerve with either flexion plantaris (tibial nerve) or dorsiflexion of the foot (common peroneal nerve) was observed. The needle position was adjusted to maintain the motor response with a stimulating current of 0.5 mA. Then, 20 mL of 0.75% ropivacaine was injected slowly in 5-mL increments, with careful aspiration after every increment. The introduction of a 20-gauge epidural catheter through the Tuohy needle 3–4 cm beyond the tip came afterward. The needle was then removed, and the catheter was secured to the skin with 12 mm x 100 mm stery strips (3M Health Care, St Paul, MN) and covered with a transparent Tegaderm (3M Health Care).

Patients in the Subgluteal group were placed in the lateral decubitus position, with the leg to be blocked uppermost and rolled forward with the knee flexed at a 90-degree angle (Sim’s position) (9,10). A line was drawn from the midpoint of the greater trochanter to the ischial tuberosity. From the midpoint of this line, a second line was drawn perpendicularly and extended caudally for 4 cm. At this level, a skin depression can be palpated representing the groove between the biceps femoris and semitendinous muscles. This point represented the site of introduction of the needle (Fig. 1). After local skin infiltration, a 10-cm, 18-gauge insulated Tuohy needle connected to a nerve stimulator was introduced with the tip oriented cephalad at an angle with the skin of about 80 degrees. The stimulating needle was advanced until eliciting a sciatic mediated motor response. The position of the needle was adjusted to maintain the good motor response with a stimulating current of 0.5 mA. Then, 20 mL of 0.75% ropivacaine was injected slowly in 5-mL increments, ensuring negative aspirations for blood between aliquots. The introduction of a 20-gauge epidural catheter through the Tuohy needle 3–4 cm beyond the tip came afterward. The needle was then removed, and the catheter was secured to the skin.

View larger version (148K): [in this window] [in a new window]   Figure 1. Landmarks to perform continuous subgluteal sciatic nerve block. A line was drawn from the greater trocanter to the ischial tuberosity. From the midpoint of this line, a second line was drawn perpendicularly and extending caudally for 4 cm. This point represented the site for needle insertion.

In the recovery room after the surgery, the sciatic catheter was connected to a patient-controlled analgesia (PCA) pump set to deliver a continuous infusion of 0.2% ropivacaine at a rate of 5 mL/h, with an incremental bolus of 10 mL and a 60 min lockout time. In addition, all patients also received 30 mg IV of ketorolac every 8 h until discharge from the hospital. Five milligrams of morphine was given subcutaneously as a rescue analgesia (maximum every 4 h) if the visual analog pain score (VAS) was >30 mm.

An independent observer who was not involved with either anesthesia or postoperative analgesia evaluated the degree of pain using a VAS score every 6 h. The amount of rescue morphine required during the first 24 h after surgery, as well as the occurrence of complications or side effects, were also recorded. The acceptance of the analgesic technique was assessed 24 h after surgery using a three-point score: 1 = excellent, 2 = good, and 3 = insufficient.

At discharge from the orthopedic ward and 3 wk after hospital discharge (during routine postoperative orthopedic examination), patients were questioned about the occurrence of neurological complications.

Statistical analysis was performed using the program Systat 7.0 (SPSS Inc, Chicago, IL). The Mann-Whitney U-test was used to compare continuous variables, whereas categorical data were analyzed using the contingency table analysis with Fisher’s exact test. Unless otherwise indicated, results were presented as a median (range) or as a number (percentage). A P value of 0.05 was considered statistically significant.

	Results

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No differences in demographic variables were reported between the two groups. Median age was 59 (18–80) yr in the Popliteal group and 55 (20–78) yr in the Subgluteal group (P = 0.51). Weight was 65 (48–85) kg in the Popliteal group and 62 (50–87) kg in the Subgluteal group (P = 0.68). Height was 165 (152–183) cm in the Popliteal group and 164 (154–176) cm in the Subgluteal group (P = 0.72). Sex distribution was 12 men and 18 women in the Popliteal group and 9 men and 21 women in the Subgluteal group (P = 0.99).

The sciatic nerve was identified with 1 or 2 needle redirections in 26 patients in the Popliteal group (86%) and 27 patients in the Subgluteal group (90%) (P = 0.99) although the sciatic catheters were successfully placed in all patients. Intraoperative fentanyl supplementation was required in three patients in the Popliteal group (10%) and two patients in the Subgluteal group (6.6%) (P = 0.99), with no differences in total amount within the two groups (dose range, 50–150 µg). No patient required conversion to general anesthesia in either group; therefore, all patients enrolled were included in the study.

Within the 24 h observation period, four catheters (13.3%) were either occluded (2) or displaced (2) in the Popliteal group versus only two catheters (6.6%) in the Subgluteal group (one displaced and one occluded) (P = 0.67). Patients with catheter displacement were excluded from further evaluation. In those patients with catheter occlusion, the catheter insertion site was evaluated to eliminate possible kinking. Then patients were given a 10-mL bolus of 1% lidocaine to confirm correct catheter placement, and the ropivacaine infusion was restarted. Median postoperative consumption of 0.2% ropivacaine was 160 mL (120–270 mL) in the Popliteal group and 130 mL (120–260 mL) in the Subgluteal group (P = 0.83).

Figure 2 shows the degree of pain measured during the first 24 h after surgery in studied patients. No differences in the VAS were observed between the two groups. Rescue morphine administrations were required in 3 patients in the Popliteal group (10%) and 7 patients in the Subgluteal group (23%) (P = 0.29). No difference in median morphine consumption was observed between the Popliteal group (0 mg [0–30 mg]) and the Subgluteal group (0 mg [0–30 mg]) (P = 0.42).

View larger version (8K): [in this window] [in a new window]   Figure 2. Visual analog pain score (VAS) during the first 24 h after surgery in patients receiving a continuous popliteal sciatic nerve block (Popliteal group, n = 30) or continuous subgluteal sciatic nerve block (Subgluteal group, n = 30) after elective foot procedures. Values are expressed as median (range).

View larger version (23K): [in this window] [in a new window]   Figure 3. Acceptance of the analgesia technique in patients receiving either a continuous popliteal (Popliteal group, n = 30) or subgluteal (Subgluteal group, n = 30) block of the sciatic nerve after elective foot procedures.

	Discussion

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In 1997, Singelyn et al. (8) described an original technique of continuous posterior popliteal sciatic nerve block for postoperative analgesia after foot surgery. They demonstrated that this technique was more effective than either IM opioids or continuous epidural analgesia and led to less undesirable side effects. The authors also reported an incidence of associated postoperative technical problems as frequent as 25% in the continuous sciatic group. In the present investigation, we experienced 13% of postoperative technical problems in similar conditions. The reasons for this difference may be related to either differences in the equipment or the technique used for catheter placement. Thus, Singelyn et al. (8) used a Seldinger technique eliciting the specific sciatic mediated motor response with a stimulating current of 1 mA, whereas we accepted a current of 0.5 mA before the catheter introduction. In agreement with this hypothesis, Choyce et al. (11) demonstrated that producing a motor response at 0.5 mA or less is a reasonable threshold to aim for when placing peripheral nerve blocks. Furthermore, catheters were inserted no more than 3–4 cm beyond the tip of the Tuohy introducer needle. It is possible that this may also account for a reduced incidence of inappropriate placement of the catheter. Thus, Ganapathy et al. (12) demonstrated that introducing a femoral catheter 15 cm or more beyond the tip of the introducer needle resulted in only 40% of appropriate catheter placement. Technological improvements in the quality of perineural catheters may be required to minimize this problem even further. Another point to consider is how perineural catheters are being secured.

In the present investigation, the sciatic catheters were infused using a PCA technique with 5 mL/h and a 10-mL bolus. Singelyn et al. (13,14) compared different modes of continuous peripheral nerve blocks including a continuous infusion, a basal infusion with incremental boluses, and only PCA boluses maintaining the same volume per hour. They demonstrated that a basal infusion rate of 5 mL/h combined with patient-controlled boluses resulted in the lowest consumption of local anesthetic solution for the same efficacy. Similar findings were also reported by other authors with continuous interscalene block (15).

Several approaches to the sciatic nerve have been described in the literature (16–18), but few of them can be easily used to place a perineural catheter. In this respect, the subgluteal approach has been proven to be as easy and successful as the previously described posterior popliteal approach (8). Furthermore, this approach required minimal mobilization of the patients and may be useful, especially in overly obese or trauma patients. Our data also seem to suggest that displacement of the catheter is unlikely with this approach. Our data also demonstrate that the use of a subgluteal approach is as well accepted as the classic posterior popliteal approach.

In conclusion, this prospective, randomized study indicates that continuous subgluteal sciatic nerve block is as effective and safe as the previously described posterior popliteal approach. This indication suggests that the subgluteal approach can be a useful alternative to prolonged postoperative analgesia in patients undergoing foot and ankle surgery if a proximal approach to the sciatic nerve is required during the procedure according to the surgical site or the surgeon’s requirements (e.g., need for thigh tourniquet placement).

	References

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999