NYSORA - The New York School of Regional Anesthesia: Popliteal Block For Foot Surgery: Posterior Or Lateral Approach?

Popliteal Block For Foot Surgery: Posterior Or Lateral Approach?
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Vijay Patel on 19/03/2009 16:40:00

The aim of this study was to test the clinical utility of the lateral approach
to popliteal block and compare its effectiveness and patient acceptance to that
of the posterior approach.

SIGNIFICANCE
Figure 1. A cadaveric model for the lateral approach to popliteal block: A
cross-sectional anatomy of the popliteal fossa. The sloped lines represent two
different angles of needle insertion. Circles represent injectates at 30 degree
angle and squares injectates at 60 degree angle.
The need to position the patient in the prone position is the main disadvantage
of the posterior approach to the sciatic nerve block in the popliteal fossa
(popliteal block). This may preclude the use of the popliteal block in patients
who could benefit the most from this technique (i.e. advanced pregnancy, morbid
obesity, spine and hemodynamic instability, mechanical ventilation). A recent
study in a human cadaver model demonstrated that the sciatic nerve in the
popliteal fossa can also be reliably accessed in the supine position using the
lateral approach, Figure 1 (1).
A needle inserted seven cm above the knee in the groove between the biceps
femoris and vastus lateralis muscles, and advanced at a 30 degree downward angle
relative to the horizontal plane, resulted in a reliable approximation of the
needle tip to the popliteal nerve. While the study in cadavers provided guidance
for the design of the lateral approach to the popliteal block, its ease and
effectiveness has not yet been examined in clinical practice. The aim of this
study was to test the clinical utility of the lateral approach to popliteal
block and compare its effectiveness and patient acceptance to that of the
posterior approach.
METHODS
Fifty patients undergoing lower leg surgery were randomized to receive a
popliteal block using either the lateral or the posterior approach. All patients
received midazolam 10 to 30 µcg/kg and fentanyl 1 to 2 µcg/kg intravenously
prior to introduction of the anesthetic. Additional doses of midazolam and
fentanyl in increments of 1 mg and 50 µcg, respectively, were administered as
necessary during the block performance and surgery, in order to allay any
accompanying anxiety and discomfort. The nature and exact origin of the
discomfort were elicited from the patients before any additional sedatives or
analgesics were given. When it was determined that patients experienced pain on
surgical instrumentation, additional infiltration with a local anesthetic by the
surgeon was implemented or an alternative anesthetic was considered.
Technique Of The Popliteal Block Using The Lateral Approach
*
Figure 2. A 100 mm longus is inserted in a horizontal plane between the biceps
femoris and the vastus lateralis muscles until the femur is contacted.
The patients were in the supine position with their legs extended in the knee
joint. 	*The long axis of the foot was placed at a 90 degree angle to the table.
 	*A 100 mm long, 21G insulated stimulating needle attached to a nerve
stimulator was inserted in a horizontal plane 7 cm cephalad to the most
prominent point of the lateral femoral epicondyle, in the groove between the
biceps femoris and the vastus lateralis muscles (Figure 2) until the shaft of
the femoral bone was intentionally contacted. 	*When the femur was not contacted
within the depth of approximately 50 mm, the needle was reinserted 5 to 10 mm
anteriorly (above) to the first insertion.  	*After the femur was contacted, the
needle was withdrawn to the skin, and redirected posteriorly at a 30 degree
angle to the horizontal plane, Figure 3.  	*If the stimulation of the sciatic
nerve was not obtained, the needle was withdrawn to the skin and reinserted
through the same skin puncture, first 5 to 10 degrees anterior and then 5 to 10
degrees posterior relative to the initial insertion (30 degree) plane. 	*If
these redirections (1st attempt) did not result in nerve localization, the same
technique was repeated through new skin punctures (subsequent attempts) in 5 mm
increments posterior to the initial insertion plane.
Figure 3. The needle is inserted posteriorly at a 30 degree angle to the
horizontal plane.
Technique Of The Popliteal Block Using The Posterior Approach
*The patients were in the prone position (2,3). With the leg fully extended and
the long axis of the foot perpendicular to the horizontal plane a 50 mm
insulated block needle attached to a nerve stimulator was inserted perpendicular
to the skin at the midpoint between the tendons of biceps femoris and
semitendinosus muscles, 7 cm above the popliteal fossa crease (Figure 3), Figure
4. 	*The innitial stimulating current was 0.8 mA.  	*The needle was slowly
advanced while seeking a plantar or dorsiflexion of the foot or toes.  	*When
the nerve was not localized on the first needle insertion, the needle was slowly
withdrawn to the skin and reinserted through the same skin puncture. 	*The first
reinsertion was at an angle of 5 and then at 10 degrees laterally to the initial
insertion plane (1st attempt).  	*Failure to obtain the sciatic nerve
stimulation prompted removal of the needle, and repeating the same maneuvers,
but through a new puncture site 5 mm laterally to the initial insertion site
(2nd attempt).  	*This technique was repeated through new insertion sites
(subsequent attempts) in 5 mm incremental lateral insertions, until the desired
response was obtained.
Figure 4. The needle is inserted perpendicularly at the midpoint between the
tendons of the biceps femoris and semitendinosus muscles.
Figure 5. The stimulating current is controlled using a foot-controlled
stimulator. This allows a single anesthesiologist to perform the block without
the need for an assistant.
While the techniques of the popliteal block differed between the lateral and
posterior approach, the preparation for the block, local anesthetic solution
used for the blocks, and the technique of nerve stimulation were similar.
In both techniques the following procedure was followed:
*The skin was prepared with a solution of povidone iodine, and the site of
needle insertion was infiltrated with 2 mL of 1% lidocaine using a 25 gauge
needle. 	*The nerve localization was achieved using insulated needles connected
to a nerve stimulator. A 100 mm long 21G needle was used for the lateral
approach and 50 mm long 22G for the classical approach.  	*The stimulating
needle was connected to the negative lead of the constant voltage nerve
stimulator (DualStim" DX, Professional Instruments, Houston, TX), (DualStim(tm)
DX, Professional Instruments, Houston, TX) while the reference electrode was
connected to the lateral calf via an EKG electrode ("Red Dot," 3M, London,
Ontario).  	*The initial current of 0.8 mA (1 Hz) was gradually decreased by a
single operator using a foot-controlled unit (Hadzic A, Vloka JD.: U.S. Patent
Serial No. No. 08/419,419 for "Apparatus for Locating and Anesthetizing
Peripheral Nerves and a Method Therefore"), Figure 5.  	*The localization of the
nerve was considered successful when either tibial nerve response (plantar
flexion), or common peroneal response (lateral inversion-dorsal flexion) was
obtained.  	*The output current of the nerve stimulator was adjusted to the
lowest current at which these responses were still observed.  	*At this point,
after inadvertent intravascular placement of the needle was ruled out by gentle
aspiration, 40 mL of 1.5% alkalinized mepivacaine (1 mEq of NaHCO3 per 30 mL of
mepivacaine) with 1:200,000 epinephrine was injected.  	*When stimulation of the
nerve required a current of greater intensity than 0.4 mA, an attempt was made
to stimulate the division of the popliteal nerve that predominantly innervated
the surgical area.  	*When necessary, a supplementary block of the saphenous
nerve was performed at the level of the tibial tuberosity using 8 to 10 mL of
pH-adjusted 1.5% mepivacaine with 1:200,000 epinephrine (4).
The data collected included: patient demographics, time from the first needle
insertion to successful nerve localization (time required for performance of the
block), number of attempts to localize the popliteal nerve (defined as a number
of skin punctures). The presence of sensory block in the distribution of the
peroneal and tibial nerves was ascertained using the pinprick method every 5
minutes following injection of the local anesthetic, for up to 30 minutes. The
presence of motor block was assessed by testing the ability of the patient to
perform plantar or dorsal flexion of the foot 30 minutes following the
injection. A successful block was defined as a complete sensory block affecting
both divisions of the sciatic popliteal nerve within 30 minutes and absence of
pain on surgical instrumentation. Surgery proceeded once sensory anesthesia in
the surgical field was documented by pinching the skin by the surgeon using a
hemostat clamp.
Postoperative pain assessments were performed by postanesthesia care unit
(PACU) nurses blinded to the purpose of the study. Patients were assessed every
15 minutes from the time of admission to PACU (Phase 1 recovery) until their
discharge home or transfer to the floor. The time to the first administration of
analgesics was evaluated only among inpatients, since the data could not be
reliably obtained in all patients who were discharged to their homes. All
patients were interviewed by an anesthesiologist (blinded to the popliteal block
technique) in person (inpatients) or by telephone (outpatients) 24 hours after
the operation. During the interview, patients' responses to questions relating
to discomfort and pain during block placement, and satisfaction with anesthesia
technique were recorded. Pain and discomfort during block placement were rated
as: no pain, slightly painful, moderately painful, painful and extremely
painful. Patient satisfaction with the anesthetic technique was assessed by
questioning as to whether they would choose the same anesthesia technique for
any eventual subsequent surgery, or if they would recommend the popliteal block
technique to their friends.
STATISTICAL ANALYSES
Data are presented as mean +/- standard deviations for continuous variables and
as counts and percentages for nominal data. Differences between patients
receiving the posterior or the lateral approach with respect to continuous
variables (age, height, weight, intensity of the stimulating current, time to
complete the block, time to surgical incision, duration of operation) were
tested by Student's t-test for independent samples. Differences in proportions
of patients in the two groups with respect to nominal data (sex, type of
surgery, inpatient vs. ambulatory surgery, number of attempts, number of
successes) were tested by P 2, or by Fisher's exact test when numbers were
small. Discomfort was assessed by a P 2 for trend. All analyses were performed
using the Statistical Package for the Social Sciences (SPSS for Windows),
version 5.02 (Chicago, IL, 1993). Differences were considered significant at the
0.05 level.
RESULTS
Fifty patients were enrolled in the study. There were no significant diferences
in demographics (age, weight, height), ASA status, or type of surgical procedure
between the groups (Table 1 ).
Table 1: Patient demographics and surgical procedures.
Posterior Approach (n=25)
Lateral Approach (n=25)
Age (years)
51 +/- 16
49 +/- 14
Height (cm); mean +/- SD
Range (cm) 164 +/- 12
147-184 162 +/- 17
125 +/- 194
Weight (kg); mean +/- SD
Range (kg) 74 +/- 17
50-109 73 +/- 16
51-104
Sex (M:F)
11:14
16:9
ASA physical status
*I 	*II-III
11 (44%)
14 (56%)
13 (52%)
12 (48%)
Surgeries:
*Bunionectomy 	*TMTA 	*I&D foot 	*ORIF ankle 	*Achilles tendon 	*BKA 	*Other
9 (36%)
3 (12%)
2 (8%)
3 (12%)
3 (12%)
1 (4%)
4 (16%)
8 (32%)
5 (20%)
1 (4%)
3 (12%)
1 (4%)
1 (4%)
6 (24%)
Tourniquets used
*none 	*ankle 	*calf 	*thigh
5
10
9
1
7
11
7
0
Duration of operation (min)
64 +/- 40
60 +/- 37
Surgical setting
Inpatients
Ambulatory surgery
8 (32%)
17 (68%)
11 (44%)
14 (56%)
There were no significant differences in demographics, surgical procedures or
the use of tourniquets between patients receiving the popliteal block through
the posterior or through the lateral approach. Legend: TMTA-trans-metatarsal
amputation, I&D-incision and drainnage, ORIF-open reduction and internal
fixation, BKA-below knee amputation.
Both techniques resulted in successful blockade in all but one patient in the
lateral approach group, who underwent transmetatarsal amputation of the foot.
Despite adequate anesthesia on assessment, bone incision proved to be painful,
which required infusion of propofol (100-130 microgram/kg/min) for completion of
the procedure. On admission to PACU, however, the patient had a full sensory and
motor block, and did not require any analgesics for 630 minutes after surgery.
The time to the first analgesic in the posterior PNB group was 568 +/- 159
minutes (range 320-760 min) and 595 +/- 133 minutes (range 365-780 min) in the
lateral PNB group; p> 0.05.
Five saphenous nerve blocks (two in the posterior and three in the lateral
group) were judged as having failed. Although these patients required
supplemental injections of local anesthetics in the distribution of the
saphenous nerve, as well as additional doses of intravenous midazo-MTA-
trans-metatarsal amputation, I&D-incision and drainnage, ORIF-open reduction and
internal fixation, BKA-below knee amputation.
Both techniques resulted in successful blockade in all but one patient in the
lateral approach group, who underwent transmetatarsal amputation of the foot.
Despite adequate anesthesia on assessment, bone incision proved to be painful,
which required infusion of propofol (100-130 microgram/kg/min) for completion of
the procedure. On admission to PACU, however, the patient had a full sensory and
motor block, and did not require any analgesics for 630 minutes after surgery.
The time to the first analgesic in the posterior PNB group was 568 +/- 159
minutes (range 320-760 min) and 595 +/- 133 minutes (range 365-780 min) in the
lateral PNB group; p> 0.05.
Five saphenous nerve blocks (two in the posterior and three in the lateral
group) were judged as having failed. Although these patients required
supplemental injections of local anesthetics in the distribution of the
saphenous nerve, as well as additional doses of intravenous midazolam, propofol
or fentanyl, none of them required induction of an alternative anesthetic.
There was no difference in the popliteal block success rate between the two
techniques. However, while the majority of patients in the posterior group
required only one or two attempts, the majority of patients in the lateral group
required a third or fourth attempt in order to localize the nerve (Table 2).
This difference was statistically significant (p < 0.001). The initial response
to nerve stimulation also significantly varied between the two techniques, with
stimulation of the common peroneal nerve being the most common first response
(72%) in the lateral approach group, and the tibial nerve response being the
most common (76%) in the posterior approach group (Table 2).
Table 2. Ease of nerve localization and success rate.
Posterior Approach (n=25)
Lateral Approach (n=25)
p-value
Number of attempts1:
One
Two
Three
Four
13 (52%)
8 (32%)
4(16%)
0
2 (8%)
6 (24%)
10 (40%)
7 (28%)