REGIONAL ANESTHESIA AND PAIN MANAGEMENT SECTION EDITOR DENISE J. WEDEL

Lateral Approach to the Sciatic Nerve in the Popliteal Fossa Paul J. Zetlaoui, MD*, and Herv6 Bouaziz, Mm *Dhpartement d’Anesth&ie-Rkanimation, HBpital de Bic&tre, Le Kremlin-Bic&tre; and -tDepartement d’Anesth&ie- Reanimation, HBpital Antoine B&l&e, Clamart, France

We describe a modification of the sciatic nerve (SN) block in the popliteal fossa through the lateral ap- proach. After a brief anatomic study using previously reported landmarks, we propose a new needle orienta- tion associated with a double injection technique after identification of the tibia1 and the common peroneal nerve. Thirty-four patients undergoing ankle or foot surgery were enrolled in this study. With patients in the supine position, the upper edge of the patella and the groove between the posterior border of the vastus late- ralis and the anterior border of the tendon of the biceps femoris were identified. The needle was directed poste- riorly with a 20-30” angle relative to the horizontal plane and slightly caudal. Both nerves were individu- ally located with a nerve stimulator and blocked with a

mixture of lidocaine-bupivacaine and clonidine. In all but one case, the two nerves were easily located, and no vascular puncture was evident. Effective analgesia was obtained for a minimum of 15 h (first analgesic de- mand). We conclude that this technique, with a modi- fied direction of the needle and a double stimulation, provides a very high rate of success for SN blockade in the popliteal fossa. Implications: We describe a new lateral approach to the sciatic nerve in the popliteal fossa. The needle was directed caudad and posteriorly while seeking with a nerve stimulator for the tibia1 and the peroneal nerves, which were blocked separately. This technique was very successful.

(Anesth Analg 1998;87:79-82)

T he classic posterior approach to the sciatic nerve (SN) in the popliteal fossa requires placement of the patient in the prone position (l), which may

be contraindicated in pregnant women or impossible in trauma patients.

Three studies have suggest a lateral approach to the SN in the popliteal fossa (2-4). Our clinical experience using these techniques were disappointing because we sometimes experienced difficulty localizing the SN when the needle entered perpendicular to the femoral shaft. Furthermore, when only the tibia1 nerve (TN) was blocked, in some cases, the common popliteal nerve (CPN) was not blocked. Vloka et al. (5) pre- sented an anatomical study of the lateral approach to the SN in the popliteal fossa, which showed that the SN is more easily encountered when the needle is directed posteriorly. Moreover, Bailey et al. (6) showed that a double injection technique (i.e., block- ing the TN and the CPN separately) via the Labat approach at the buttock provides better clinical results

This study was presented as an abstract at the annual meeting of the Soci&6 Francaise d’Anesth&ie et de Rkanimation, Paris, France, September 1996.

Accepted for publication March 31, 1998. Address correspondence to Paul J. Zetlaoui, Departement

d’Anesth&ie-Rkanimation, HBpital de Bic&re, 48 rue du G&-&al Leclerc, 94275 Le Kremlin-Bic@tre, France. Address e-mail to darkb@imaginet.fr.

01998 by the International Anesthesia Research Society 0003.2999/98/$5.00

than a single injection. Thus, after a short anatomic study, we conducted a clinical study of SN blockade via the lateral approach in the popliteal fossa.

Methods Anatomic Study

After the insertion of a lo-cm needle according to the techniques of Collum and Courtney (2) and McLeod et al. (3), the popliteal fossa in three cadavers (six legs) placed in the supine position was dissected (with the needle in place) to identify the position of the needle relative to the neurologic and vascular structures in the popliteal fossa.

Patient Study

After institutional review board approval and written, informed consent had been obtained, 34 patients un- dergoing ankle or foot surgery were enrolled in the study. SN block was the sole anesthesia technique for 20 patients, whereas 14 others requested sedation or light general anesthesia during surgery. In all cases, SN block was performed after mild sedation using IV fentanyl (0.5 pg/kg) and midazolam (l-2 mg). Gen- eral anesthesia, if requested, was administrated after evaluating the extension of the block. Blocks were

Anesth Analg 1998;87:79-82 79

80 REGIONAL ANESTHESIA AND PAIN MANAGEMENT ZETLAOUI AND BOUAZIZ ANESTH ANALG SCIATIC NERVE BLOCK IN THE POPLITEAL FOSSA 1998;87:79-82

--- ^.._ ____ __ “.“.-- I_ _” ‘--.

Figure 1. Computed tomographic scan of the popliteal fossa at the level of needle insertion. a = Direction of the needle when intro- duced strictly horizontally, b = direction of the needle when intro- duced posteriorly with a 30” angle, VL = vastus lateralis, F = femur, BF = biceps femoris, PV = popliteal vessels (artery and vein), CPN = common peroneal nerve, T = tibia1 nerve.

performed by the two authors (n = 15) or by residents (n = 19).

Patients were positioned supine. The upper edge of the patella and the groove between the lateral border of the vastus lateralis and the tendon of the biceps femoris were palpated and drawn on the skin. To facilitate identification of the groove, patients were asked to flex their knee, and the leg was then straight- ened again. A line was drawn vertically from the upper edge of the patella. The puncture site was lo- cated at the intersection of this line with the intermus- cular groove. After standard skin preparation, a 22- gauge, 50-mm insulated needle (Stimuplex; B/Braun, Boulogne-Billancourt, France) was inserted 20-30” posterior to the horizontal plane with a slight caudad direction (Figure 1). The two components of the SN were located with a nerve stimulator (Stimuplex). Af- ter identifying the CPN, the needle was directed fol- lowing the same axis to find the TN. The CPN and the TN were identified by their muscular response, plan- tar flexion, or inversion of the foot for the TN and dorsiflexion or eversion of the foot for the CPN (7). For each nerve, 10 mL of a local anesthetic solution was injected when the intensity of nerve stimulation was <l mA. According to our clinical practice, the local anesthetic solution was a mixture of 2% lidocaine and 0.5% bupivacaine (50%/50%) with epinephrine (1:200,000) and clonidine (1 pg/kg). For the first 10 patients, 10 mL of iopamidol 350 was added to the local anesthetic solution for radiological evaluation of the diffusion of the injected solution.

In cases of surgery involving the area of the saphe- nous nerve, this nerve was blocked as described by Bouaziz et al. (8), with 10 mL of the same anesthetic solution.

Table 1. Demographic Data

Age W Height (cm) Weight (kg)

Mean t SD

51 ? 19 165 t: 7.0

66 ? 13

Range

14-84 152-178

52-112

Patient characteristics, success or failure of the tech- nique, incidence of vascular puncture by repeated as- piration and blood return in the needle, minimal nerve stimulation intensity for each nerve, order of localiza- tion of the two nerves, distance between the two nerves, and time to perform the block were recorded. Motor and sensory blockade were assessed every 5 min for 30 min using a 3-point scale rating (2 = no block, 1 = paresis or hypoesthesia, 0 = paralysis or anesthesia). Motor blockade was assessed by asking the patient to plantar flex (TN) or dorsiflex (CPN) the foot. Sensory blockade was assessed for TN (sole of the foot) and CPN (dorsal area of the foot) by pinprick with a blunted needle. Postoperative analgesia was assessed using a verbal scale as excellent, good, or poor. Duration of analgesia was defined as the time elapsed between SN blockade and the first analgesic demand for subcutaneous morphine (5 mg).

Results are expressed as mean + SD.

Results Anatomic Study

When the needle is directed horizontally through the lateral popliteal groove, as recommended in previous studies (2,3) there is a risk of vascular puncture. The findings of our study showed, in all six cadaveric legs, that the popliteal vessels are at the same level as the lateral groove of the popliteal fossa. The tibia1 and peroneal nerves were always located posterior to the vascular structures; therefore, the needle must be di- rected posteriorly with a 2030” angle relative to the horizontal plane.

Patient Study

Of the patients enrolled in the study, 22 were women and 12 were men. Demographic data are reported in Table 1. A tourniquet was used in 22 cases, and a saphenous nerve block was required in 19 cases. Time to perform the block was 4.10 + 1.26 min. In all patients but one, the two nerves were easily located, and all blocks were successful for ankle or foot sur- gery. Stimulation intensity was 0.66 ? 0.15 mA to block the CPN and 0.63 + 0.15 mA to block the TN. In 28 patients, the CPN was the first nerve identified; in the other 6 patients, the TN was located first. The mean distance between the two nerves was 21 mm (range 14-36 mm). No vascular puncture was noted.

ANESTH ANALG REGIONAL ANESTHESIA AND PAIN MANAGEMENT ZETLAOUI AND BOUAZIZ 81 1998;87:79-82 SCIATIC NERVE BLOCK IN THE POPLITEAL FOSSA

0 5 10 15 20 25 30 Tlme(mm)

0 No block Hypoesthesia I Anesthesia

Figure 2. Schematic representation of onset of sensory blockade as a function of time after sciatic nerve block through the lateral approach in the popliteal fossa. CPN = common peroneal nerve, TN = tibia1 nerve. Sensory blockade was assessed using a 3-point rating scale (2 = no block, 1 = hypoesthesia, 0 = anesthesia).

In one case, the CPN was not located after 5 min but was easily blocked at the level of the head of the fibula. In two cases, the area of the medial cutaneous sural nerve, the mid-posterior part of the calf, was not blocked, but surgery was possible because this area was not involved in the procedure. Onset of sensory blockade on both components is represented in Figure 2. Motor blockade was always complete within 30 min. In eight cases, radiological opacifications showed a possible common sheath surrounding the two nerves, but in two cases, there was no evidence of a common sheath, allowing the diffusion from one nerve to the other (Figure 3). All patients had excellent or good postoperative analgesia that lasted 15-20 h.

Discussion Compared with the classic posterior approach, the lateral approach to the SN in the popliteal fossa offers the advantage of not requiring the patient to be posi- tioned prone. Collum and Courtney (2) and McLeod et al. (3) reported a strictly horizontal direction of the needle. In an anatomic study, Vloka et al. (5) demon- strated that when the needle is inserted in this direc- tion, the femoral shaft was contacted in most cases, and the branches of the SN are more easily encoun- tered when the needle is directed with a 30” angle posteriorly relative to the horizontal plane. This is consistent with the findings of our anatomic study. Furthermore, Vloka et al. (5) also reported that with a 30” posterior direction, the needle was always poste- rior to the vascular space, which reduced the hazard of vascular puncture. This risk is present when the nee- dle is inserted horizontally, as described by Collum and Courtney (2) and McLeod et al. (3).

In the study by Collum and Courtney (2), the blocks were performed either with a nerve stimulator or us- ing a blind technique. They did not report the total

Figure 3. Radiographs after the injection of 5 mL of iopamldol 350 diluted in 10 mL of local anesthetic solution. Left, After local- ization of the common peroneal nerve, only this nerve was opaci- fied, without evidence, at the level of the puncture, of a common sheath, within which is located the tibia1 and the common peroneal nerve. Right, After localization of the tibia1 nerve, this radiograph shows no evidence of a common sheath surrounding the tibia1 and the common peroneal nerve.

number of patients treated or the relative distribution between the blind and the nerve stimulator tech- niques. They also did not report the success and fail- ure rates of their technique. We think that the blind technique is difficult to teach. In our study, 19 blocks were successfully performed by residents using a nerve stimulator, after a brief description of the procedure.

Vloka et al. (5) showed that 7 cm above the femoral epicondyle, the SN runs in a sheath, which, when entered, allows the cephalic spread of an injected so- lution. This observation presumes that it is necessary to localize only one of the two branches of the SN to achieve a popliteal SN block. In the study by McLeod et al. (3), only the TN was located with the nerve stimulator. Postoperative analgesia was unsuccessful in 9 of 21 patients. In two cases, postoperative pain was related to a failed sciatic block. They hypothe- sized that some blocks were too medially placed to block the CPN, which was perhaps the cause of failed analgesia despite a TN block. Using the posterior ap- proach in the popliteal fossa in a group of 20 patients, Kilpatrick et al. (10) showed that identifying only the TN resulted in five failed blocks and six supplemen- tary blocks. Using the Labat approach at the buttock, Bailey et al. (6) showed that identifying both compo- nents of the SN-the TN and the CPN-improves the success rate and shortens the onset time of the block. Benzon et al. (9) reported that the TN and the CPN may be two separate nerves throughout their course,

82 REGIONAL ANESTHESIA AND PAIN MANAGEMENT ZETLAOUI AND BOUAZIZ ANESTH ANALG SCIATIC NERVE BLOCK IN THE POPLITEAL FOSSA 1998;87:79 -82

each surrounded by its own fascia. Furthermore, in the anatomic study of Vloka et al. (ll), in one of eight cases, the dye solution (15 mL) injected in the common sheath was unable to reach the division of the SN. Thus, based on our results, we believe that at the popliteal level, separate blockade of the two branches of the SN may offer more consistent blockade because, in some cases, the CPN is located several centimeters distant from the TN. Bailey et al. (6) and Benzon et al. (9) reported faster onset and more complete blockade when the two components of the SN were specifically localized and individually blocked. In our study, com- plete sensory and motor blockade was achieved within 30 min.

We conclude that, when blocking the SN in the popliteal fossa using a lateral approach, a very high success rate is achieved when the needle is directed with a 20-30” angle posterior to the horizontal plane and when the TN and the CPN are specifically located and individually blocked.

The authors thank I+. K. Mori for manuscript assistance

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