NYSORA - The New York School of Regional Anesthesia: Simplified Landmarks For Popliteal Block

Simplified Landmarks For Popliteal Block
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In the current study an MRI simulation of the popliteal block was undertaken to
compare the accuracy of needle placement in relationship to the sciatic nerve
using the intertendinous and classical approaches.
Based on: Hadzic A, Vloka JD, Singson R, Santos AC, Thys DM. A comparison of
Intertendinous and Classical Approaches to Popliteal Nerve Block Using MRI
Simulation. Anesth Analg 2002; 94: 1321-4.
Introduction
Sciatic nerve block in the popliteal fossa (popliteal block) has several
advantages over other anesthetic techniques for lower extremity surgery (1). As
opposed to the more proximal approaches to the sciatic nerve block, the
popliteal block spares the hamstrings muscles and promotes postoperative
ambulation. Compared to spinal anesthesia, it results in a unilateral block,
carries no risk of "post dural" puncture headache, results in prolonged
postoperative analgesia, and it can be performed in patients being treated with
anticoagulant therapy. Despite these potential advantages, popliteal block is
not often used for lower extremity surgery in the United States (2). The reasons
for the infrequent use of this block may be related to inadequate training of
residents (2), concerns over operating room efficiency and a highly variable
success rate of the block (2-4).
The most frequently used technique for popliteal block is the classical,
posterior approach, where the needle insertion site is 7 cm above the popliteal
fossa crease and 1 cm lateral to the midline of the popliteal fossa triangle
(formed by the popliteal fossa crease, the semimembranosus and semitendinosus
muscles, and the biceps femoris muscles) (4). The needle is then advanced from
posterior to anterior until the sciatic nerve is identified (3). However, these
landmarks are rather unclear in many patients and often multiple attempts are
required to localize the sciatic nerve using this approach. Consequently, in our
clinical practice and training of residents, we have developed a new,
intertendinous approach to popliteal block (5). Using this approach, the needle
is inserted at the midpoint between the tendons of the biceps femoris and
semitendinosus muscles, rather than 1 cm lateral to the midline of the popliteal
fossa triangle as in the classical approach. In the current study an MRI
simulation of the popliteal block was undertaken to compare the accuracy of
needle placement in relationship to the sciatic nerve using the intertendinous
and classical approaches.
Material & Methods
After approval by the Institutional Review Board, 10 healthy, adult volunteers
were enrolled in the study after written consent was obtained. The anatomical
surface landmarks for needle insertion using the intertendinous and classical
approaches to popliteal block were identified by two attending anesthesiologists
familiar with popliteal block (authors of the study) and then labeled using
magnetic resonance imaging (MRI) contrast markers (vitamin E capsules). The
anesthesiologists jointly examined the extremities and agreed upon the landmarks
and the insertion points for both approaches in all patients. For the classical
technique, the needle "insertion site" (for off-line simulation) was labeled
with vitamin E capsules 7 cm above the popliteal fossa crease and 1 cm lateral
to the midline of the popliteal fossa triangle (identified by drawing a line
along the converging course of the bodies of the semimembranosus and biceps
femoris muscles) (4). For the intertendinous approach, the needle "insertion
site" was also labeled 7 cm above the popliteal fossa crease, but in contrast to
the classical technique, at the mid-point between the tendons of the
semimembranosus and biceps femoris muscles (Figure 1). The described landmarks
and needle insertion sites were done for both legs in all subjects.
Figure 1. Example on the left: Popliteal block - Intertendinous Approach.
Landmarks:1.Popliteal fossa crease 2.Tendon of biceps femoris muscle 3.Tendon
of semitendinosus/semimembranosus muscles Example on the right: The black arrow
indicates the needle insertion site in the "classical" approach to popliteal
block which utilizes the "popliteal fossa triangle" as a landmark. (Milwaukee,
WI) software was used by an independent, blinded interpreter. For both
approaches, the simulations were performed at 7 cm above the popliteal fossa
crease and at an angle perpendicular to the horizontal plane. A line simulating
the needle insertion path (simulated or virtual needle) was placed through the
labeled "insertion sites" on the image and extended anteriorly in a saggittal
plane (perpendicular to the horizontal plane), just as would be done in a
popliteal block (Figure 2) (4,5). The order of simulations was random so
approximately half of the simulations were first done with the intertendinous
and half with the classical approach. The spatial proximity of the needle
trajectory to the sciatic nerve and its distance (relationships) to the
structures important to popliteal block were measured for each simulation.
Figure 2. Simulation of the popliteal block using MRI images. The large arrow
indicates a typical needle path in the intertendinous approach, whereas the
small arrow shows too lateral insertion of the needle is common in the classical
(triangle) approach.
Data are expressed as means +/- standard errors for continuous measures. Since
both approaches were studied in the same volunteers, McNemar chi-square tests
were used to evaluate differences between the two approaches for the proportions
presented in Table 2. Statistical analyses were performed using the Statistical
Package for the Social Sciences (SPSS for Windows, version 5.0.2, Chicago, IL);
p
Table 1: Anatomical measurements Relevant to Popliteal nerve block (n=10).
Distances
Mean +/- SE (mm)
Range (mm)
Skin - PN*
36 +/- 4
25 - 41
PN - femur*
19 +/- 3
13 - 24
PN - PA**
9.0 +/- 4
2 - 18
* Measured in the saggital plane (postero-anterior)
**Measured as the closest distance between the popliteal nerve and popliteal
vein or artery
PN = popliteal nerve; PV= popliteal vessels
Table 2: Needle Trajectories Measurements in Relation to Popliteal Fossa
Structures
Classical
Intertendinous PNB
p-value
Needle-popliteal nerve contact
5 (25%)
14(70%)
=2 mm from popliteal nerve
14(70%)
4(20%)
REFERENCES:
1. Vloka JD, Hadzic A, Mulcare R, et al. Combined blocks of the sciatic nerve
at the popliteal fossa and posterior cutaneous     nerve of the thigh for short
saphenous vein stripping in outpatients: An alternative to spinal anesthesia. J
Clin Anesth     1997;9:618-22.
2. Hadzic A, Vloka JD, Kuroda MM et al. The practice of peripheral nerve blocks
in the United States. A national survey. Reg     Anesth Pain Med 1998:23:241-6.
3. Rorie DK, Byer DE, Nelson DO, et al. Assessment of block of the sciatic
nerve in the popliteal fossa. Anesth Analg, 1980;     59:371-6.
4. Brown DL: Popliteal nerve block. In: Brown DL, ed. Atlas of Regional
Anesthesia. Philadelphia: W.B.Saunders Co.,     1992:109-13.
5. Hadzic A, Vloka JD. A comparison of the posterior versus lateral approaches
to the block of the sciatic nerve in the     popliteal fossa. Anesthesiology
1998; 88:1480-6.