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ANALGESIA

The Posterior Approach to the Sciatic Nerve in the Popliteal Fossa: A Comparison of Single- Versus Double-Injection Technique

Xavier March, MD^*, Olga Pineda, MD^*, Maria M. Garcia, PhD, Dolores Caramés, MD^*, and Antonio Villalonga, PhD^*

From the *Servei d’Anestèsia, Reanimació i Terapèutica del Dolor and Institut de Investigació Biomédica de Girona, Hospital Universitari de Girona Dr Josep Trueta, Girona, Spain.

Address correspondence and reprint requests to Xavier March, MD, Servei d’Anestèsia, Reanimació i Terapèutica del Dolor, Hospital Universitari de Girona Dr Josep Trueta, Carretera de França s/n. Girona. Spain. Address e-mail: h416uxmm{at}htrueta.scs.es.

Abstract

We compared single-injection and double-injection of the sciatic nerve with nerve stimulation in the posterior popliteal approach using mepivacaine 1% in a prospective, randomized and single-blind study to evaluate effectiveness, delay of onset, and complications in patients undergoing foot and ankle surgery. In the single-injection group (Group S, n = 30), 25 mL of mepivacaine 1% was administered after eliciting foot inversion or plantar flexion. In the double-injection group (Group D, n = 30), 12.5 mL of the solution was injected after eversion or dorsiflexion and 12.5 mL after plantar flexion of the foot. Mean differences (sd) between the two groups from onset time to complete sensory block were not significant (21.9 [14.2] min vs 22.1 [13.8] min) except for the superficial peroneal nerve block (18 [13] min vs 11.4 [7.5] min, Group S and D, respectively; P < 0.05) and, in Group D, between the superficial peroneal and tibial nerve blocks (11.4 [7.5] min vs 22.3 [11.3] min, respectively; P < 0.05). Complete analgesia was achieved in 77% of Group S patients and in 87% of Group D (P = 0.22). Complete analgesia of the deep peroneal nerve was achieved in 80% and 97% in Group S and D, respectively; P < 0.05. There were more paresthesias during block procedure in Group D (17% vs 40%) (P < 0.05). We conclude that double-nerve stimulation of the sciatic nerve gives similar complete onset times and overall success rate to single-nerve stimulation and more paresthesias during block performance.

The anatomical variations at the level at which the sciatic nerve is divided into the tibial and peroneal components have been considered as possible causes for incomplete blocks at the popliteal level. Following the study of Vloka et al. (1), we proposed that stimulation of the sciatic nerve at the popliteal level 10 cm from the popliteal crease will block the sciatic nerve close to the point of separation. In earlier studies at the level of the sciatic nerve, some authors have found a longer onset time and less effectiveness with single stimulation, whereas others have not (2–5). Our aim was to compare the onset time and effectiveness of single- and double-injection techniques at this site. We hypothesized that double stimulation of the sciatic nerve close to the point of separation would not be more successful than single stimulation, but would result in a reduction in the onset time.

METHODS

After approval by our hospital’s ethical committee, informed written patient consent was obtained. Sixty ASA 1–3 patients programmed for foot and ankle surgery with an age of >18 yr were randomly assigned to one of two groups: single stimulation (Group S) or double stimulation (Group D).

Exclusion criteria were contraindications to regional anesthesia, diabetes mellitus, and neurological alterations of the limb.

Midazolam was administered at 0.5–2 mg and alfentanil from 100 to 400 µg IV and oxygen at 4 L/min.

A 22 gauge 50-mm long short-bevelled insulated needle (Stimuplex A; Braun, Melsungen, Germany) was used connected to a peripheral nerve stimulator (Stimuplex DIG, Braun).

Patients were placed in the prone position. The skin and the subcutaneous tissue were infiltrated with 2 mL of mepivacaine at 1%.

Nerve stimulation with a frequency of 2 Hz and duration of 0.1 ms was started with 1.5 mA and local anesthetic was administered (mepivacaine 1%) when a satisfactory response was obtained at 0.5 mA. In Group S, 25 mL of local anesthetic was injected, while in Group D 12.5 mL was injected for each of the responses.

In Group S, local anesthetic was administered when the inversion (preferred) or plantar flexion of the foot was achieved, whereas in Group D the anesthetic was given when the eversion or dorsiflexion response for the peroneal nerve and plantar flexion for the tibial nerve was obtained.

All the blocks were performed by the first author. The block was considered to be successful when there was analgesia (absence of pain on pinprick) in the four areas of the foot depending on the sciatic nerve. Each territory was evaluated every 5 min by another anesthesiologist during a 45-min period and was complemented with midazolam, alfentanil, or propofol on initiating the surgery or another anesthesia as necessary.

The motor blockade of the foot was evaluated on a scale from 1 to 3: the absence of motor blockade, 1; almost complete motor blockade, 2; and complete motor blockade, 3.

The tourniquet was sited just above the ankle. Complications including vascular puncture, paresthesias during the performance of the block, hematomas, and neurological sequels were recorded.

Based on earlier studies, it was hypothesized that we would observe at least a 5 min difference in onset time to complete sensory block between the two groups. Accepting a risk of 0.05 and a ß risk of 0.20 in a unilateral comparison, 30 patients were required for each group in order to detect a difference equal to or more than 5 min in the onset time. A standard deviation of 7.5 min was assumed in both groups.

The results are expressed as percentages for categorical variables and as mean (sd). Proportions were compared using the ² test and the Student’s t-test or Mann–Whitney test were used to compare continuous variables between groups.

RESULTS

There were no significant differences between the two groups in demographic factors or duration and type of surgery (Table 1). No patient was excluded from the study. The inversion response was not found in three Group S patients leading to plantar flexion being used successfully. Two patients experienced some pain with the tourniquet and required sedation (not presented in Table 3). One patient required additional saphenous nerve block before surgery was begun, as the surgery involved the saphenous territory. The time to perform block was shorter in the single-injection group, and the success rate and the onset time to complete sensory block were similar in the two groups. Onset time for the superficial peroneal nerve block was shorter in Group D than Group S. Significant differences were found within Group D between the onset times of the superficial peroneal nerve and the tibial nerve (P < 0.05). There were more paresthesias in Group D (Table 2 and 3).

DISCUSSION

Nerve stimulation of the two branches of the sciatic nerve at the popliteal level with a posterior approach, at 10 cm from the popliteal skin crease, did not result in a reduced complete onset time or improved success rate when compared with that obtained with single stimulation. However, it proved to be more effective to block the deep peroneal nerve. Most studies comparing single and multiple nerve stimulation of the sciatic nerve along the whole of its course have found a decrease in the onset time with double nerve stimulation (2,3,5) and greater efficacy (2–4), although one study found no differences in the onset time (4) and another found no improvement in efficacy (5). In our study, only the superficial peroneal nerve was blocked earlier in Group D than in Group S. This might be explained by the fact that in Group S, the tibial nerve was stimulated and the anesthesia administered to this nerve has to diffuse to the superficial peroneal nerve. There was a significant difference in the onset time in Group D of the superficial peroneal nerve compared to the tibial nerve. This could be explained by the difference in thickness of the two branches of the nerve. Our findings regarding onset time are similar to those of earlier studies (4,6). The sural nerve was anesthetized in all patients and was the first to become blocked, presumably because it is formed of peripheral fibers of the peroneal and tibial nerves.

The effectiveness found in earlier studies with single nerve stimulation of the sciatic nerve at the popliteal level has been variable (7–9). There is no consensus in the literature with regard to which response elicited in single nerve stimulation of the sciatic nerve is most likely to result in successful regional anesthesia (10,11). Single stimulation of the sciatic nerve close to the division is more likely to result in successful blocks than more distal approaches (4). There were more paresthesias in the double injection group during the performance of the block, presumably due to the proximity of the two nerves.

In conclusion, double nerve stimulation of the sciatic nerve at 10 cm from the popliteal crease resulted in similar complete onset time, overall success rate, and more paresthesias when compared with single nerve stimulation. However, the onset time of the superficial peroneal was shorter and the success rate of the deep peroneal was increased with double stimulation. We recommend that a double stimulation technique be used when surgery involves the peroneal innervated regions.

ACKNOWLEDGMENTS

The authors thank Dolors Fauria Roma, Raquel Martínez Arancón, and Anna Plana Fernández, who are nurses at the Dr. Josep Trueta Hospital, for their assistance in the performance of the study.

Footnotes

Accepted for publication August 4, 2006.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by March, X. Articles by Villalonga, A. Search for Related Content PubMed PubMed Citation Articles by March, X. Articles by Villalonga, A. Related Collections Anesthetic Techniques Regional Anesthesia