| JOURNAL HOME | CME HOME | THIS MONTH | PAST ISSUES | ETOC | COLLECTIONS |
| AUTHORS | REVIEWERS | EDITORIAL BOARD | FEEDBACK | RSS | HELP |
 
|
|
|
||
|
|
Anesth Analg 2004;98:1785-1788 © 2004 International Anesthesia Research Society doi: 10.1213/01.ANE.0000117224.99190.A8
Denise J. Wedel Section Editor |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
To improve the incidence of block of the posterior femoral cutaneous nerve (PFCN) when using an anterior approach as described recently, we hypothesized that the distance between the inguinal line and the puncture site depends on the patient’s height. A preliminary radiological study performed in 13 patients established a formula describing the relationships between the patient’s height and the puncture site "S." A line was drawn between the anterior iliac spine and the superior angle of the pubic tubercle (inguinal line) and another line from the midpoint of the inguinal line to the puncture site "S." "S" was calculated from the midpoint of the inguinal line as "S" = (height in cm – 100)/10. A prospective study was conducted in 53 patients. Results are presented as median (range, 0.25–0.75). Two minutes were required to locate the sciatic nerve at a depth of 12 cm (10.5–13.0 cm). Complete sciatic and PFCN blocks were observed in 92% of the patients. We conclude that consideration should be given to the patient’s height when the sciatic nerve is blocked using an anterior approach. This technique seems to improve the success of block of the PFCN, essential to tolerate a thigh tourniquet.
IMPLICATIONS: This prospective but noncomparative work was performed to evaluate a new anterior technique of sciatic block, an adaptation of the anatomic landmarks described by Chelly and Delaunay, to patient height.
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Among the various approaches to perform regional blocks on the sciatic nerve (SN), the anterior approach is considered to be the most difficult (1). It requires minimal movement of the patient, a benefit in trauma cases, when movement may be severely limited or painful. When combined with a femoral nerve block, the anterior SN block provides complete anesthesia of the lower extremity.
Beck (2) was the first to describe the anterior approach in 1963. His approach located the SN near the lesser trochanter using the anatomic landmarks of the anterior superior iliac spine, lateral border of the pubic symphysis, and the greater trochanter. This technique often yielded inconsistent results because of difficulty in locating the greater trochanter, requirements for special equipment (a 150-mm needle), and problems in landmark identification in obese individuals. As such, the anterior approach was mostly abandoned in favor of the lateral and posterior approaches (3).
In 1999, Chelly and Delaunay (4) described a new anterior approach to the SN without using the greater trochanter as a landmark. Their technique involved drawing a line between the inferior border of the anterior iliac spine and the superior angle of the pubic tubercle (essentially the inguinal line). The puncture site was on a perpendicular line from the midpoint of the inguinal line, 8 cm caudal, anatomically located near the lesser trochanter. This puncture point more or less is located near Beck’s puncture point.
In Chelly and Delaunay’s (4) technique, the results for the SN were good; however, block of the posterior femoral cutaneous nerve (PFCN) was inadequate in 45% of patients (5). Block of PFCN is essential if a thigh tourniquet is to be used (Fig. 3 describes the cutaneous sensory distribution of the PFCN).
|
We noted that previously described techniques disregard patient height in their approach. The aim of our study was to adapt Chelly and Delaunay’s (4) technique to locate the SN in a more cephalic and medial position, above the lesser trochanter, using a simple height adjusted mathematical formula. The added benefit of this approach is locating the PFCN in the same anatomic space as the SN. We analyzed the success and complications of our technique.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
We started by performing a preliminary radiographic study on 13 healthy volunteers to determine how an individual’s height is related to the length of the femoral neck. After obtaining these data, we devised a simple mathematic formula using the patient’s height to estimate the theoretical needle entry point for each person. Then we performed a second radiographic study on the same 13 volunteers, comparing the theoretical needle localization with the neck of the femur and lesser trochanter using a radio-opaque target on the skin to simulate the needle entry point.
After receiving approval by the local IRB, we prospectively included 53 patients over 6 mo undergoing surgery on the lower extremity amenable to regional anesthesia. Informed consent was obtained. Patients included were more than 18 yr old and ASA physical status I or II. They did not have local anesthetics allergy, cutaneous infection at the puncture site, inguinal adenopathy, or sciatic neuropathy. Patients were excluded when there was inadequate data collection.
All patients were positioned supine on a firm surface, avoiding thigh flexion, with the patella positioned midline (requiring slight medial rotation of the foot). The landmarks were located by drawing a line between the inferior border of the anterior superior iliac spine and the superior border of the pubic symphysis (inguinal line). From the midpoint of this line, we drew a caudal perpendicular line to the puncture site "S." The distance to "S" was defined by our mathematical formula, which was "S" = (height in cm – 100)/10. For example, for a patient of height 160 cm, "S" = 6 cm, and for a height of 185 cm, "S" = 8.5 cm (Fig. 1).
|
Before performing the block, sedation was provided with sufentanil 5–10 µg, midazolam 2 mg IV, or both because the procedure can be painful. Nerve stimulation was performed using a Stimuplex stimulator (B-Braun Medical®, Sheffield, United Kingdom),and a 15-cm insulated Stimuplex needle (B-Braun Medical®). After sterile preparation with Betadine solution, the needle was introduced perpendicular to the skin (Fig. 2). The initial stimulator settings were then set at pulse current = 1.2 mA, frequency = 2 Hz, and duration = 0.3 ms.
|
If upon skin entry the femoral nerve was stimulated, the intensity of the stimulation was decreased to 0.5 mA to verify that the needle was not in contact with the femoral nerve. If stimulation continued at 0.5 mA, we concluded that there was a risk of nerve injury if the needle was introduced deeper. The needle was pulled out to the skin and reintroduced 1–2 mm laterally. If no response was obtained at 0.5 mA, the needle was advanced deeper (Fig. 2) until sciatic stimulation was obtained (foot eversion, foot dorsal flexion, or toe dorsal flexion for the common peroneal nerve; plantar foot flexion, toe flexion, or foot inversion for tibial nerve). Upon this stimulation, the current was reduced to 0.5 mA before the injection. Anesthetic solution was chosen according to the surgical indication (lidocaine, ropivacaine, or bupivacaine).
During needle positioning, if the femur was encountered, the needle was reintroduced medially. When the needle reached the border of the lesser trochanter, bony resistance was felt. The SN was usually located 1–2 cm beyond this resistance. If the patient experienced pain or motor response in the gluteal muscle (PFCN), the needle direction was assumed to be too medial.
In 94% of the patients, a femoral nerve block was also used (inguinal paravascular technique). It was never performed before the sciatic block to avoid potential injury to the femoral nerve.
For each patient, we noted the time required to perform the block, difficulties encountered, minimal stimulations required, and motor response obtained. We documented the latency of sensory analgesia (cold sensation and pinprick tests every 5 min after performing the blocks for SN, femoral nerve, and PFCN). Success of the blocks was based on the criterion of no pain to either incision (SN and femoral nerve) or tourniquet inflation (PFCN). Results are presented as median and percentiles (25–75).
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
To obtain our height-adjusted landmarks for locating the needle puncture point, 13 patients were evaluated. In 11 cases, the needle puncture point was above the lesser trochanter (1–2 cm above the highest point of the lesser trochanter). For one patient, who was also obese (120 kg and 186 cm), the point was in the middle of the femoral diaphysa near the lesser trochanter. In the final patient, the point was at the inferior border of the lesser trochanter.
In the clinical portion of the study, of the 53 patients enrolled, 35 had a fracture of the leg or foot, and 18 were undergoing elective surgery (arthrographic knee exploration or toe surgery). Nine different anesthesiologists performed the blocks on these 53 patients. Characteristics of the providers included 6 attending physicians, all with extensive experience with regional anesthesia, and 3 supervised resident physicians.
During stimulation, sciatic motor response involved the peroneal nerve in 57% of the patients, the tibial nerve in 26% of patients, and both in 17% of patients. (These data are presented in Table 1.) During approach to the nerve, the femur was contacted in 56% of the cases and the femoral nerve was stimulated in 50% of the cases.
|
The volume of local anesthetic was defined at 30 mL in all cases except for 2. One case involved injecting 25 mL for a small size woman (155 cm and 50 kg) and 40 mL in another case during which there was concern about needle movement during the injection. The type of local anesthetic was left to the discretion of the anesthesia provider.
Of the 53 patients receiving the study block, there were 4 failures. One was an obese patient (120 kg and 168 cm) in whom cutaneous landmarks were not easy to determinate (pubic symphysis) and the minimum stimulation achieved before the injection was only 0.8 mA (no block was observed in this patient after injection). In two patients, the technique was abandoned secondary to pain and agitation of the patients. Finally, in the fourth, no explanation could be derived for failure.
In all the cases where the block was successful (92%), the SN block and PFCN block were satisfactory. However, in six cases, the regional block had to be supplemented by general anesthesia secondary to failure of the femoral block. During all blocks performed, there were no intravascular injection nor any clinical neurologic deficit noted.
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
In the study population of 53 patients, a 92% overall success rate for SN and PFCN anesthesia using the modified anterior approach method was observed. However, the number of subjects studied did not provide adequate power to comment on population differences (such as sex, age, height/weight relation, etc.). These will be objectives of further studies.
The puncture site localization seemed to be correct to directly stimulate the SN. The result of 50% bony contact is probably wrong, overestimated by the resistance of the tendinous insertion of the iliopsoas muscle at the lesser trochanter and misinterpreted at the beginning of the study.
Compared with the posterior approach to the SN, the anterior approach is associated with more intense pain during placement of the block, possibly requiring more sedation (cutaneous local anesthesia was not used to preserve femoral nerve of injury during needle progression). However, the technique requires minimum movement of the patient, which is an advantage with spinal and lower extremity trauma.
A direct comparison of our technique to the one described by Chelly and Delaunay (4) shows that our puncture site was generally higher and more medial. We have found that the anatomic landmarks must be carefully identified in performing all blocks, but especially in those in which a formula or geometrical associations is applied. Incorrect identification of landmarks can lead to failure of blocks, especially in obese patients.
In Chelly and Delaunay’s (4) technique, there was 100% success of sciatic blockade in 22 patients. However, in a subsequent study, they described a 50% success rate on PFCN anesthesia (5). Our technique has a global success rate of 92% on SN and PFCN anesthesia.
Our modified approach may yield superior block of the PFCN, but a randomized, comparative study using Chelly and Delaunay’s (4) technique should be performed to confirm these results.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
- Dalens B. Anesthesie locorégionale de la naissance à l’âge adulte. In: Pradel, ed. Paris: Blocs proximaux des nerfs du plexus sacré. 1993: 353–74.
- Beck GP. Anterior approach to sciatic nerve block. Anesthesiology 1963; 24: 222–4.[Web of Science][Medline]
- Zetlaoui PJ. Blocs des nerfs sciatiques. Cah Anesthesiol 1996; 44: 119–26.[Medline]
- Chelly JE, Delaunay L. A new anterior approach to the sciatic nerve block. Anesthesiology 1999; 91: 1655–60.[Web of Science][Medline]
- Delaunay L, Chelly JE. Nouvelle approche antérieure du nerf sciatique. Ann Fr Anesth Reanim 2000; 19: 121–2.
This article has been cited by other articles:
|
|
 |
|
  R. Fuzier, P. Hoffreumont, S. Bringuier-Branchereau, X. Capdevila, and F. Singelyn Does the Sciatic Nerve Approach Influence Thigh Tourniquet Tolerance During Below-Knee Surgery? Anesth. Analg., May 1, 2005; 100(5): 1511 - 1514. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. E. Chelly and L. Delaunay Block of the Posterior Femoral Cutaneous Nerve Anesth. Analg., February 1, 2005; 100(2): 597 - 597. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
