Download Revisiting anterior leg anatomy and analgesia after

Revisiting anterior leg anatomy and analgesia after total
knee replacement
P.J. Cowlishaw
P. Kotze
Optimal anaesthesia and analgesia for total knee arthroplasty (TKA) presents a unique
challenge for Anaesthetists. Elderly patients with significant co-morbity are subjected
to major tissue trauma resulting in severe prolonged acute pain and systemic stress
response. Successful surgical outcome is reliant on safe and early patient
mobilisation. Common obstacles in preventing this are pain, muscle weakness,
sedation and confusion. These can be minimised by using an opiate sparing
multimodal anaesthetic and analgesic regimen utilising continuous regional
anaesthesia. Publications investigating the best regimen have filled the orthopaedic
and anaesthetic journals over the last couple of decades. It remains a huge source of
debate. Many regional anaesthesia techniques can be used to achieve neural blockade
from the central nervous system (epidural), to the major peripheral nerves (sciatic,
femoral and obturator nerve blocks) through to the terminal branches and plexuses
(local infiltration at the surgical site). There are benefits and risks and protagonists
and antagonists for all. A thorough appreciation and understanding of the neuroanatomy is paramount.
The knee is innervated by three nerves:- femoral, obturator and sciatic. Anatomy of
the sciatic nerve is not included in this review.
The femoral nerve arises from the dorsal divisions of the second, third and fourth
lumbar nerves. The nerve runs in the muscle fibres of psoas and emerges on its lateral
border. From here it courses between iliacus and psoas below the iliacus fascia. After
passing under the inguinal ligament it immediately branches in to the anterior and
posterior division.
Within the femoral triangle the anterior division splits in to the a) intermediate and
b) medial cutaneous femoral nerves and two muscular branches which supply
pectineus and sartorius.
a) The intermediate (middle) femoral cutaneous nerve pierces the fascia lata
forming the roof of the femoral triangle and descends superficially to supply
the skin of the anterior thigh.
b) The medial (internal) femoral cutaneous nerve divides high in the thigh in
front of the femoral artery. The anterior branch runs deep on sartorius and
pierces fascia lata in the mid-thigh. Here it divides in two, one innervates the
medial side of the knee and the other the lateral side of patella
(communicating with the infrapatella branch of saphenous nerve). The
posterior branch descends along medial side of sartorius giving off several
cutaneous branches.
The posterior division supplies the quadriceps and knee joint and forms the
saphenous nerve. Branches to rectus femoris and vastus lateralis leave with or above
the lateral femoral circumflex artery within the femoral triangle. The vastus medialis
branch descends further down the thigh with the saphenous nerve and femoral artery
in the adductor canal. This nerve divides further and usually has a terminal branch
which supplies the knee.
The saphenous nerve lies first lateral, then anterior and eventually medial to the
femoral artery deep to the sartorius muscle in the adductor canal. It emerges between
the tendons of gracilis and sartorius. At the middle of the thigh it gives off a branch
which forms part of the subsartorial plexus. On the medial side of the knee a large
branch leaves innervating the patella forming part of the infrapatella plexus. Terminal
branches of the obturator often form part of this plexus.
The obturator nerve originates from the ventral division of the second, third and
fourth lumbar nerves. It also descends through the fibres of psoas and emerges on the
medial border near the pelvic brim. It enters the thigh through the obturator foramen
and divides into anterior and posterior branches. The anterior branch innervates
the adductor longus and pectineus. It communicates with the anterior cutaneous and
saphenous nerve at the lower border of adductor longus contributing to the
subsartorial plexus. The posterior branch supplies the adductor brevis and magnus
and usually gives off an articular knee filament. This is sometimes absent but usually
perforates the adductor magnus and passes through the opening which transmits the
femoral artery.
Research suggests that continuous blockade of the femoral nerve provides excellent
analgesia for knee replacement surgery with or without the addition of continuous
sciatic blockade1,2. The femoral nerve innervates many of the hip flexors (iliacus,
rectus femoris, pectineus and Sartorius) and all the knee extensors (quadriceps).
Dense motor blockade inhibits early mobilisation and may increase the risk of falls
post TKA surgery 3,4. Selective sensory and articular blockade of the femoral nerve
could provide optimal conditions for patient satisfaction and surgical outcome. Recent
clinical studies have investigated blockade of the femoral nerve in the adductor canal.
These studies have shown that ‘adductor canal blocks’ provide similar analgesia to
traditional femoral nerve blockade with preservation of quadriceps function: Thus
facilitating early and safe mobilisation.5-7
Using MRI imaging and cadaver dissection we set out to find an anatomical
explanation for these clinical findings. In a pilot cadaver study we inserted catheters at
the proximal start of the adductor canal using an in-plane ultrasound guided
technique. The entry point of the catheter was 10-13 cm below the midpoint of the
inguinal ligament. 20 mls of 0.25% Aniline blue (2.5 g in 1000 ml Saline (0.9%) = 2.5
mg/ml = 25%) was injected through the catheter. Careful dissection revealed that the
dye had spread down the adductor canal to the adductor hiatus in all three cadavers.
(figure 1).
dye
Figure 1 Dissection showing the muscular layer of the thigh form of the left leg. Dye are noted on
the facia of the subsartorial canal form the apex of the femoral triangle and approximating the
adductor hiatus.
In all 3 cadaver dissections there was no spread of dye in to the femoral triangle with
cephalad spread limited to 1-2 cm above the catheter. The fascia enveloping the
femoral triangle was thicker and less compliant. Dye did not stain the motor nerves to
sartorius, vastus lateralis, intermedius and rectus femoris. (figure 2)
Figure 2 Detailed dissection of the right femoral triangle showing the unstained femoral nerve as it
exits the femoral canal and branching 2cm distally. Key: 1 Femoral nerve, 2 M. Sartorius, 3
Motor nerve prior to split to quadriceps muscle, 4. Hip articular branch 5. Femoral vessel
MRI and ultrasound imaging was also performed on a patient undergoing total knee
arthroplasty. Figure 3 shows the ultrasound image and the catheter in situ after the
femoral artery has branched into profunda, superficial and lateral circumflex.
Figure 3 Catheter inserted between sartorius and rectus femoris distal to the splitting of the femoral artery
Figure 4 illustrates the high signal density (white) of the local anaesthetic spreading
under the sartorius muscle lateral to the femoral vessels. Figure 5 is a reconstructed
coronal view demonstrating the high signal density of local anaesthetic spreading
distally in the adductor canal but not cephalad.
Figure 4 MRI image of catheter and spread of local anaesthetic in the sub-sartorial space
Figure 5 Reconstructed coronal MRI image of thigh
This anatomical evidence provides an explanation to why continuous adductor canal
blocks can provide excellent analgesia with quadriceps sparing. In summary
cutaneous analgesia is achieved with blockade of the saphenous, medial cutaneous
nerve and sensory branches of the anterior obturator nerve. Knee analgesia is also
provided from blockade of the articular branches of the posterior femoral nerve which
lie in the adductor canal and possibly an articular branch of the posterior obturator
nerve. Innervation to sartorius, vastus lateralis, intermedius and rectus femoris
appears to be spared.
Published descriptions of the adductor canal block describe an in plane ultrasound
guided injection at a mid-thigh level when neurovascular bundle is tightly surrounded
by sartorius, vastus medialis and adductor longus. Our needle entry site is different: a
lateral in plane ultrasound guided approach 10-12cm below the inguinal ligament. The
needle endpoint is inferior to sartorius, medial to rectus femoris and lateral or inferior
to the superficial femoral artery. This catheter entry site is usually proximal to the
tourniquet and away from the surgical site and dressings. It is well below the inguinal
crease facilitating access and minimising infection risk.
Further clinical trials are required to optimise local anaesthetic infusion regimes and
catheter techniques.
1.
Cowlishaw PJ, Scott DM, Barrington MJ. The role of regional anaesthesia
techniques in the management of acute pain. Anaesth Intensive Care 2012;40:33-45.
2.
Wegener JT, Van Ooij B, Van Dijk CN, Hollmann MW, Preckel B, Stevens
MF. Value of single-injection or continuous sciatic nerve block in addition to a
continuous femoral nerve block in patients undergoing total knee arthroplasty: A
prospective, randomized, controlled trial. Regional Anesthesia and Pain Medicine
2011;36 (5):481-8.
3.
Johnson RL, Kopp SL, Hebl JR, Erwin PJ, Mantilla CB. Falls and major
orthopaedic surgery with peripheral nerve blockade: a systematic review and metaanalysis. Br J Anaesth 2013;110:518-28.
4.
Ilfeld BM, Duke KB, Donohue MC. The association between lower extremity
continuous peripheral nerve blocks and patient falls after knee and hip arthroplasty.
Anesth Analg 2010;111:1552-4.
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Kwofie MK, Shastri UD, Gadsden JC, et al. The effects of ultrasound-guided
adductor canal block versus femoral nerve block on quadriceps strength and fall risk:
a blinded, randomized trial of volunteers. Reg Anesth Pain Med 2013;38:321-5.
6.
Hanson NA, Allen CJ, Hostetter LS, et al. Continuous ultrasound-guided
adductor canal block for total knee arthroplasty: a randomized, double-blind trial.
Anesth Analg 2014;118:1370-7.
7.
Jenstrup MT, Jaeger P, Lund J, et al. Effects of adductor-canal-blockade on
pain and ambulation after total knee arthroplasty: a randomized study. Acta
Anaesthesiol Scand 2012;56:357-64.