LOWER LIMB ANATOMY FOR FRCA LUMBAR PLEXUS: FORMATION
Dorsal division Upper and lower divisions Lat cut n. of thigh
Ventral division L1
Iliohypogastric nerve
L2
Genitofemoral nerve Ilioinguinal nerve
L3
L4
Femoral nerve
Obturator nerve
Branch to lumbosacral trunk
LUMBAR PLEXUS: BRANCHES Quadratus Lumborum
Ilio-hypogastric N. Ilio-inguinal N.
Psoas minor lying on psoas major
Lat. Cut. N. of thigh Genitofemoral N. Femoral N.
Inguinal Ligament
4th lumbar sympathetic ganglion
Obturator N.
1
CUTANEOUS NERVES OF THE LOWER LIMB
2
LUMBAR PLEXUS ANATOMY SUMMARY
NERVE
SPINAL SEGMENT
ILIOHYPOGASTRIC
T 12-L1
ILIOINGUINAL
L1
GENITOFEMORAL
L1-L2
LAT FEMORAL CUTANEOUS (LAT CUT N OF THE THIGH)
L2-L3
FEMORAL
L2 – L4
MOTOR INNERVATION
MOTION OBSERVED*
SENSORY INNERVATION
ARTICULAR BRANCHES
Int/Ext Oblique
Ant abdominal wall
None
Int Oblique
Ant abdominal wall
Cremaster
Testicular
None
Sensory Nerve
Inferior abd wall Upper lat quadrant of buttock Inferior to medial aspect of inguinal ligament Portion of genitalia Inferior to mid portion of inguinal ligament Spermatic cord Anterior lateral and posterior aspects of thigh terminating in prepatellar plexus
Sartorius
Medial aspect of the lower Thigh Adductors of thigh Knee extension, patellar Ascension Sensory
Ant medial skin of the thigh
None
Thigh adduction
ANT DIVISION Pectineus Quadriceps POST DIVISION Saphenous
OBTURATOR
None
None
None
None Ant Thigh
Knee and Hip
Medial leg from the tibia to the medial aspect of the foot
None
Variable, posterior medial thigh, medial knee
Hip
L2 – L4
ANT DIVISION
POST DIVISION
Gracilus, adductor brevis & longus pectineus Obturator externus, adductor magnus
Thigh adduction with lateral hip rotation
Knee
LUMBAR PLEXUS BLOCK CLINICAL APPLICATIONS: Analogous to the brachial plexus block near the clavicle, the three nerves of the lumbar plexus that are important for neural supply to the lower extremity (femoral nerve, lateral femoral cutaneous nerve,
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obturator nerve) are located very closely together. This means that a single injection at this site is sufficient to anaesthetise all three nerves completely. POSITION: Lateral, similar to that used in spinal anaesthesia, with the legs bent and the leg to be blocked uppermost. LANDMARKS: Spinous process of the 4th lumbar vertebra (L4), the posterior superior iliac spine (PSIS) and the highest point on the iliac crest. APPROACH 1 The puncture site is on the line joining the L4 spine and the posterior superior iliac spine (PSIS), at the junction of the medial 2/3rd and lateral 1/3rd. The stimulating needle is advanced perpendicular to the skin. In case of bony contact with the transverse process of the 5th lumbar vertebra (L5), the needle should be directed cranially to walk over the transverse process. The femoral nerve is normally contacted at the depth of 1.8 - 2 cm beyond the transverse process. Contractions of the femoral quadriceps muscle show that the needle is in the direct vicinity of the nerve. Once a threshold current of 0.2 -0.3 mA is reached, 20-30mls local anaesthetic is injected.
PSIS 3 1/ 3 2/
Spine
L3
L4
L5
APPROACH 2 In this approach 3 lines are drawn, first line is line connecting the spinous processes. The second line passes cranially from the PSIS and lies parallel to the 1st line. The 3rd line cuts these two lines and passes from the highest point on the iliac crest (Tuffier’s line). The part which lies between the 1st and the second line is then divided into medial 2/3rd and lateral 1/3rd. The puncture site 4
lies 1-2 cm cranial to this point. Using a 100mm insulated needle, puncture is made keeping the needle perpendicular to the skin. Aim is to hit the transverse process of L4 and walk off it by 1.8-2.0 cm to seek the femoral (L 24)
stimulation.
PSIS 1/3 Spine
L3
L4
2/3 L5
FEMORAL TRIANGLE BOUNDARIES: Superior: Inguinal Ligament Lateral: Medial border of Sartorius muscle Medial: Medial border of adductor longus Roof: fascia lata Floor: Iliacus, Psoas (Iliopsoas), Pectineus, and adductor Brevis & longus muscles. It also has the anterior division of the Obturator nerve on its surface Femoral Nerve
Femoral Sheath
Lat Cut Nerve of the Thigh
Ilio-psoas Adductor Brevis and Longus
Pectineus Sartotius Ant Branch of Obturator Nerve
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CONTENTS: •
Femoral Nerve
•
Femoral artery
•
Femoral Vein
•
Deep Inguinal Nodes FEMORAL SHEATH AND CANAL
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FEMORAL NERVE AND BRANCHES FEMORAL NERVE
L2
PELVIS
L3 ILIACUS
POST DIVISION
L4
ANT DIVISION
LAT CIRCUMFLEX FEMORAL ARTERY
HIP JOINT RECTUS FEMORIS
PECTINEUS SARTORIUS MED FEMORAL CUT NERVE
LATERALIS VASTUS
INTERMEDIATE FEMORAL CUT NERVE
INTERMEDIUS MEDIALIS
FEMORAL ARTERY
KNEE JOINT
DEEP FASCIA BELOW KNEE INFRAPATELLAR BRANCH SAPHENOUS NERVE
The femoral nerve is the largest branch of the lumbar plexus. It arises from the second, third, and fourth lumbar nerves. The nerve descends through the fibers of the psoas muscle, emerging from the psoas at the lower part of its border, and passes down between the psoas and the iliacus. (see fig: Lumbar Plexus branches) Eventually, the femoral nerve passes underneath the inguinal ligament into the thigh, where it assumes a more flattened shape. As the femoral nerve passes underneath the inguinal ligament, it is positioned immediately lateral and slightly deeper than the femoral artery. Fascia Iliacus
Fascia Latae
Ilio-psoas Femoral sheath Femoral Nerve
Femoral Artery and vein
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At the femoral crease, the nerve is covered by the fascia iliaca and separated from the femoral artery and vein by a portion of the psoas muscle and the ligamentum ileopectineum. This physical separation of the femoral nerve from the vascular fascia explains the lack of the spread of a "blind paravascular" injection of local anesthetics toward the femoral nerve FEMORAL NERVE BLOCK CLINICAL APPLICATIONS: Anaesthesia for knee arthroscopy in combination with intra-articular local anaesthesia •
Analgesia
for
femoral
shaft
fractures,
anterior
cruciate
ligament
reconstruction (ACL), and total knee arthroplasty (TKA) as a part of multimodal regimens. Use of nerve blocks for complex knee operations is associated with lower pain scores and fewer hospital admissions after same-day surgery. ANATOMY RELATED TO NERVE STIMULATION: As the nerve emerges under the inguinal ligament it soon divides into the posterior and anterior divisions and undergoes extensive arborisation. While performing femoral nerve block, it is the anterior branch that is most commonly identified (97% of the time), stimulation of this branch causes the contraction of the sartorius muscle on the medial aspect of the thigh and should not be accepted. It is the posterior branch that provides the articular and muscular branches. LANDMARK AND TECHNIQUE: The puncture site is located approximately in the region of the inguinal fold, 1.5 cm lateral of the femoral artery, approx. 2-3 cm below the inguinal ligament (IVAN = Inner Vein Artery Nerve). The stimulation needle (40 - 50 mm) is inserted at an angle of approx. 30º to the skin and advanced in a cranial direction. After reaching a depth of around 2-4 cm, the femoral nerve is encountered. Contractions of the quadriceps femoris muscle (post division)
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signal the direct proximity to the nerve. Stimulation of the rectus muscle of the thigh is crucial for the block to be effective.
Femoral sheath
Fascia lata
Femoral Nerve Pectineus Iliopsoas
Femoral Artery and Nerve
Iliacus Fascia
Contractions of the sartorius muscle (ant division) are usually not sufficient. In case of anterior division stimulation, the needle should be reinserted slightly laterally and with a deeper direction to encounter the posterior branch of the femoral nerve. Stimulation of this branch is identified by patellar ascension as the quadriceps contract (dancing of the patella). While performing femoral nerve block it is utmost important to continually aspirate before injecting the local anaesthetic. Keeping distal pressure ensures cranial spread allowing for blocking branches arising above the inguinal ligament. This can also be accomplished by lifting up the leg. DEFINING THE 3-IN-1 BLOCK: During femoral nerve block, it is commonly believed that using a higher volume of local anaesthetic and applying distal pressure during and a few minutes after injection blocks the femoral, lateral femoral cutaneous, and obturator nerves, the so-named “3-in-1 block”. However, despite many efforts to consistently produce a 3-in-1 block, the effectiveness of these manoeuvres has not been shown. In most reports, the femoral nerve is the only nerve consistently blocked with this approach. Blockade of the lateral femoral cutaneous nerve occurs through lateral diffusion of local anaesthetic and not 9
through proximal spread to the lumbar plexus. The obturator nerve is less frequently anesthetised during 3-in-1 block than the lateral femoral cutaneous (LFC), which is not surprising given the number of fascial barriers between these structures at the level of the inguinal ligament. Despite the lack of scientific support for the term 3-in-1, many authors still continue to refer to the anterior femoral nerve block as a 3-in-1 block. FASCIA ILIACA BLOCK: Femoral nerve can also be blindly blocked using this technique. The landmark for this is the inguinal ligament. The ligament is divided into thirds. The point of needle insertion is 1-2cm below the junction of the medial 1/3 and the lateral 2/3. A short bevelled needle is used for this technique. After piercing the skin two distinct ‘pops’ are felt as the needle passes through the fascia lata and then the ant iliacus fascia.
Fascia lata
Pectineus Iliacus Fascia
Iliopsoas Muscle
LATERAL FEMORAL CUTANEOUS ( LFC) NERVE BLOCK: CLINICAL APPLICATIONS: This block is useful for skin graft harvesting and can be used in concert with other peripheral nerve blocks for complete anaesthesia of the lower extremity ANATOMY RELATED TO THE BLOCK: The lateral femoral cutaneous nerve or the lateral cutaneous nerve of the thigh (L2 and L3) emerges at the lateral border of the psoas muscle
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immediately caudad to the ilioinguinal nerve. It descends under the iliac fascia to enter the thigh deep to the inguinal ligament 1 to 2 cm medial to the anterior superior iliac spine (ASIS). The nerve emerges from the fascia lata 7 to 10 cm below the ASIS and divides into anterior and posterior branches. The skin of the lateral portion of the thigh from the hip to midthigh is supplied by the posterior branch; the anterior branch supplies the anterolateral thigh to the knee. Internal oblique muscle
Iliacus Fascia
External oblique Aponeurosis ASIS Iliacus Muscle Lat Cutaneous Nerve of Thigh Inguinal ligament
Fascia Lata
POSITION: Supine LANDMARK AND TECHNIQUE: A point is marked 2 cm medial and 2 cm caudad to the anterior superior iliac spine. A short-bevel 22-gauge, 4-cm needle is advanced perpendicular to the skin entry site until a sudden release (pop) indicates passage through the fascia lata. As the needle is moved fanwise laterally and medially, 10 to 15 mL of solution is injected, depositing local anaesthetic above and below the fascia. The nerve can also be blocked just medial and posterior to the anterior superior iliac crest with 10 mL of solution. Combining the two techniques (beltand-suspenders method) increases the success rate, but the total volume of solution used may be limiting. Because this is a pure sensory nerve, electrical stimulation is not helpful in performing this block.
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SAPHENOUS NERVE BLOCK: CLINICAL APPLICATIONS: Saphenous is a purely sensory nerve supplying the skin on the medial side of the leg below the knee. It is commonly blocked along with the sciatic nerve to complete the anaesthesia of the leg for procedures on the tibia & fibula and the ankle.
FEMORAL VEIN AND ARTERY SARTORIUS
SAPHENOUS NERVE
GENICULAR BRANCHES
POSITION: Supine LANDMARK AND TECHNIQUE: There are multiple approaches at different levels to the saphenous nerve block. SEEKING PARESTHESIA (TRANS SARTORIAL APPROACH)
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In an awake and cooperative patient, electrical nerve stimulation can be used to seek paresthesia. The compartment between the vastus medialis and sartorius muscles is identified at about 2 - 4 cm above and medial to the patella. Here, the stimulation needle is inserted perpendicular to the table until it reaches the subsartorial fatty tissue. At a pulse duration of 1.0 ms and an amplitude of 0.3 - 0.5 mA, electrical paresthesia can be elicited and 10 to 15 ml of local anaesthetic injected. [In many cases, the saphenous nerve is still accompanied by a muscular branch of the femoral nerve which innervates the vastus medialis muscle. In such cases, a motor stimulatory response from the vastus medialis muscle can be judged as successful. A catheter can be placed without any trouble.] INFILTERTION TECHNIQUES: The saphenous nerve can be blocked just below the knee joint or at the level of the ankle by subcutaneous infiltration. At the level of the knee, subcutaneous infiltration is carried out from the medial head of the gastrocnemius up to the tibial tuberosity. OBTURATOR NERVE BLOCK: ANATOMY RELATED TO THE BLOCK: The obturator nerve is derived primarily from the third and fourth lumbar nerves (L3,4)with an occasional minor contribution from L2. The nerve lies deep in the obturator canal, having descended from the medial border of the psoas muscle. As the nerve leaves the obturator canal, it divides into anterior and posterior branches. The anterior branch supplies an articular branch to the hip and the anterior adductor muscles and a variable cutaneous branch to the lower medial thigh. The posterior branch innervates the deep adductor muscles and may send an articular branch to the knee. CLINICAL APPLICATIONS: Blocked as part of regional anaesthesia for knee surgery. Primarily a motor nerve, it is rarely blocked on its own; however, obturator nerve block can be useful in treating or diagnosing the extent of adductor 13
spasm in patients with cerebral palsy and other muscle or neurological diseases affecting the lower extremities prior to surgical intervention (adductor tenotomy).
FEMORAL VESSELS
OBTURATOR NERVE FEMORAL NERVE
2Cms 2Cms
POSITION: Supine LANDMARK AND TECHNIQUE: Mark is made 1 to 2 cm lateral and 1 to 2 cm caudad to the pubic tubercle. A skin wheal is raised, and a short-bevel 22-gauge, 8-10 cm needle is advanced perpendicular to the skin entry site with a slight medial direction. The inferior pubic ramus is encountered at a depth of 2 to 4 cm, and the needle is walked in a lateral and caudad direction, until it passes into the obturator canal. The obturator nerve is located 2 to 3 cm past the initial point of contact with the pubic ramus. After negative aspiration, 10 to 15 mL of local anaesthetic is injected. A nerve stimulator can be successfully used for locating the obturator nerve; correct needle position produces contractions of the adductor muscles of the medial thigh
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SACRAL PLEXUS L4 L5 S1 S2 S3
SUP GLUTEAL NERVE
S4 S5 ANOCOCCYGEAL NERVE
PERFORATING CUT NERVE
INF GLUTEAL NERVE
POST FEMORAL CUT NERVE
C1
PUDENDAL NERVE
SCIATIC NERVE
SCIATIC NERVE AND BRANCHES
L4 L5 S1
Pelvis
S2 S3 piriformis Hip Joint Inf Gemellus Quad. femoris Semi-tendinosus
Sup Gemellus Obt Internus Short Head of Biceps femoris
Semi-membranosus Long Head of Biceps femoris
Thigh
Tibial L4,5, S1,2,3
Common Peroneal (fibular) L4,5 ,S1,2
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SACRAL PLEXUS ANATOMY: SUMMARY
NERVE
SPINAL SEGMENT
GLUTEAL NERVES
L4 – S2
SCIATIC, TIBIAL
L4 – S3
MOTOR INNERVATION
MOTION OBSERVED
SENSORY INNERVATION
ARTICULAR BARNCHES
Piriformis, sup/inf gemellus obturator internus, quadratus femoris
Buttocks with lat hip rotation
Upper medial aspect of buttock Hip
Hip
Biceps femoris, semitendinosus, adductor magnus
Hamstrings with knee extension
Medial and lat heel Sole of foot
Hip Knee and Ankle
Popliteus Knee flexion Plantar flexion Gastrocnemius, soleus, flexors of foot
Toe flexion
Knee and Ankle SCIATIC, PERONEAL
L4 – S3
SUPERFICIAL
DEEP
SURAL COMPONENTS FROM PERONEAL & TIBIAL POST CUT NERVE OF THIGH
None
S1 – S3
Short head of biceps femoris peroneus longus, brevis
Knee flexion Foot inversion
Distal anterior leg, dorsum of foot
Extensors of foot, toes
Dorsiflexion of foot, ankle
Web space of 1st toe
None
None
Post calf, lat border of foot and 5th toe
None
None
None
Distal medial quadrant of buttock perineum, post thigh including popliteal fossa
None
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SACRAL PLEXUS: BRANCHES (GLUTEAL REGION)
SCIATIC NERVE BLOCK: PARASACRAL APPROACH CLINICAL APPLICATIONS: The parasacral block targets the sciatic nerve at its most proximal point where it induces fast and full anaesthesia. POSITION: Seated or in the lateral recumbent position. The lateral recumbent position is preferred , given that, in combination with the psoas compartment block, the technique is especially suited for complex surgical interventions on the leg, and avoids the inconvenience of repositioning and re-draping of the patient between the two procedures. The side to be blocked is uppermost; the lumbar spine shows a kyphosis and the hip flexed to facilitate orientation. LANDMARKS AND TECHNIQUE: 17
The posterior superior iliac spine (PSIS) and the ischial tuberosity (IT) are marked. From the posterior superior iliac spine, the palpating finger follows the tuberosity until no more bony structures are encountered. Here, approximately 5 - 7 cm caudad to the posterior superior iliac spine, the puncture site is marked. The stimulation needle (80 -120 mm) is advanced perpendicular to the skin in the direction of the tuberosity until a stimulatory response is elicited from the peroneal or tibial part of the sciatic nerve. GT IT 5 – 7 Cms
PSIS
Sacral Hiatus
TIP OF COCCYX
Once the desired amplitude is reached (0.3 – 0.4 mA) 20 to 40 ml of local anaesthetic is injected. If no primary stimulatory response is achieved or bony resistance encountered, the needle is directed in a caudal and slightly lateral direction (pointing towards the mid point between greater trochanter and ischial tuberosity). Do not consider the contractions of the gluteal muscles as a sign of success. Always look for signs of stimulation of the tibial or peroneal components. SCIATIC NERVE BLOCK: LATERAL/ CLASSIC APPROACH ( LABAT’S) POSITION: Lateral recumbent position, with the leg to be blocked uppermost. The other leg is extended. The upper leg is bent approx. 30-40º at the hip joint and approx. 90º at the knee joint. The heel of the leg to be blocked should be touching the knee of the other leg. 18
LANDMARK AND TECHNIQUE: The greater trochanter (GT) and the posterior superior iliac spine (PSIS) at the dorsal end of the iliac crest should be identified and marked. A second line is drawn passing from the sacral hiatus to the greater trochanter. A line is then perpendicularly dropped from the midpoint of the first on to the second. The puncture site is marked at a point this line touches the second line (~4-5 cm).
GT IT
PSIS
Sacral Hiatus
The stimulating needle is inserted perpendicular to the skin surface (80 mm long). Sciatic nerve is usually contacted at a depth of 5 to 8 cm. Contractions of the calf musculature with plantar or dorsal flexion of the foot are considered as sign of successful localisation and after appropriate reduction in stimulation current is reached (0.3-0.4 mA) 20-30mL of local anaesthetic is injected. SCIATIC NERVE BLOCK: ANTERIOR APPROACH POSITION: Supine, with the leg in a neutral position, not rotated outwardly like in the femoral nerve block. LANDMARK AND TECHNIQUE: A line connecting the anterior superior iliac spine (ASIS) and the pubic tubercle is marked. A line passing through the greater trochanter (GT) lying parallel to the first is drawn. The length of the first line is divided into thirds. A
19
perpendicular line is dropped inferiorly from the medial third point to the second line. The puncture is made at the point of this intersection.
ASIS
GT
SCIATIC NERVE
Feel along the muscle compartment between the rectus femoris muscle and the vastus medialis and/or the sartorius muscle. The puncture is made lateral to this, thereby minimising the risk of hitting a vessel. Insert the stimulating needle (120 mm) at a 75-85° angle, guiding it in a dorsal and cranial direction. Stimulation of parts of the femoral nerve is sometime observed. At a depth of 6-10 cm, the post thigh compartment is reached. The sciatic nerve is sought by advancing the needle a bit further. The nerve is successfully located when plantar flexion (tibial part) or dorsal flexion (peroneal part) are elicited. SCIATIC NERVE BLOCK: HIGH LATERAL APPROACH POSITION: The patient is supine, with the leg in a neutral position or rotated slightly inwards. Padding placed under the lower leg and pelvis helps facilitate puncture, but is not imperative. LANDMARK AND TECHNIQUE: By passive rotation of the hip joint, it is possible to palpate and mark the greater trochanter, even in obese patients. The puncture site is located approx. 2 cm inferior and 4 cm distal to the greater trochanter. The direction of
20
insertion is horizontal and slightly cranial towards the ischial tuberosity. This approach requires needles of between 80 and 120 mm in length.
GT X
2 Cms
4 Cms
If the femur is encountered during puncture, the insertion point must be changed slightly dorsal. Should stimulation at a reasonable depth fail to achieve the desired response, a redirection in a slightly ventral direction and inward rotation of the hip sometimes helps. Stimulating catheters can also be placed using this approach. SCIATIC NERVE: LITHOTOMY APPROACH This is probably the commonest approach used by trainees in the UK. POSITION: Supine with the hip hyperflexed and the knee partially extended LANDMARKS AND TECHNIQUE: Ischial tuberosity and greater trochanter are the main landmarks. A line is drawn connecting this two landmarks and the midpoint on this line marked. The insertion point lies 2-3 cms distal to this point. A 50 - 80mm needle is sufficient to perform this block.
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KNEE JOINT: NERVE SUPPLY AND MOVEMENTS Nerve Supply: Femoral Obturator via posterior division and Sciatic via both tibial and common peroneal branches Movements: Flexion : Semimembranosus, Semitendinosus, Biceps femoris, Gracilis, sartorius ( Gastrocnemius, Plantaris, Popliteus) Extension: Quadriceps femoris, Iliotibial tact ( Gluteus maximus, Tensor Fasciae latae) SCIATIC NERVE BELOW THE KNEE AND BRANCHES
SCIATIC NERVE
POPLITEAL FOSSA COMMON PERONEAL TIBIAL NERVE SURAL COMMUNICATING BRANCH
SUPERFICIAL PERONEAL
MED & LAT PLANTAR NERVES SURAL NERVE
DEEP RERONEAL
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POPLITEAL FOSSA Diamond shaped Borders: •
Upper medial – Semimembranosus (& Semitendinosus)
•
Upper lateral – Biceps Femoris
•
Lower medial – Gastronemius (Medial head)
•
Lower lateral – Plantaris & Gastronemius (Lateral head)
•
Roof –
Short saphenous & communicating veins Lateral sural cutaneous nerve Sural communicating nerve End of posterior femoral cutaneous nerve Fascia latae
RIGHT SUPERFICIAL POPLITEAL FOSSA
23
CONTENTS: Popliteal artery and vein Tibial nerve Common Peroneal Nerve Fat Lymph Nodes POLITEAL ARTERY: 8” Long Starts medial to Tibial Nerve Ends lateral to Tibila nerve Vein always between the artery and the Nerve ( unlike other places where Vein, Artery and Nerve follow the VAN pattern)
DEEP POPLITEAL FOSSA
24
SCIATIC NERVE BLOCK AT THE POPLITEAL FOSSA BLOCK CLINICAL APPLICATION: This technique affords a block of the sciatic nerve just superior to its bifurcation without any complicated positioning.
POPLITEAL FOSSA BLOCK (LATERAL APPROACH) POSITION: The patient is supine on his back, with the leg in a neutral position; padding is placed distally under the lower leg to allow the knee to hang suspended. LANDMARK AND TECHNIQUE: The compartment between the vastus lateralis muscle and the biceps femoris muscle is identified by palpation approx. 11 cm above the patella. This site is marked.
11 cm
A needle of 100 mm in length is usually sufficient for the puncture. The needle is inserted initially perpendicular to the skin. The needle in this position should come in contact with the femur. The needle is then withdrawn and the insertion direction changed to 30° dorsally and 5 - 10° cranially (towards the hip joint) looking for the tibial / peroneal response. 25
1 30O 2
Once the threshold electrical current is reached, 30 - 50 ml of local anaesthetic is injected. Compared to the proximal sciatic nerve blocks, onset of action is significantly longer, between 20 - 40 min. A catheter for continuous block can be positioned easily. One common error that is often made, searching for the nerve too ventrally and at a depth (The nerve's position is always more superficial and dorsal than one thinks).
POPLITEAL FOSSA BLOCK ( INTERTENDINOUS APPROACH) POSITION: The patient is either in the prone position or lying on the side that is not to be anaesthetised. The upper leg must then be well extended. The patient may also lie supine and the assistant can hold the leg with the hip flexed at 90o and the knee partially extended. LANDMARK AND TECHNIQUE: Landmarks for the intertendious approach to popliteal block are easily recognizable even in obese patients. All three landmarks should be outlined by a marking pen:
26
1. Popliteal fossa crease 2. Tendon of biceps femoris (laterally) 3. Tendons of semitendinosus and semimembranosus (medially) With the patient in one of these positions, the popliteal fossa is first identified and then demarcated medial to the semitendinosus muscle and lateral to the biceps femoris muscle.
Biceps femoris
ST 7-11 cms X
In this technique, the needle is introduced at the midpoint between the biceps femoris and semitendinosus tendons at about 7-11 cms from the popliteal crease. The nerve stimulator should be initially set to deliver 1.5 mA current (2 Hz, 100µsec) because this higher current allows detection of the inadvertent needle placement into the hamstrings muscles and stimulation of the sciatic nerve through the epineural sheath as the needle is approaching its target. When the needle is inserted in a correct plane, advancement of the needle should not result in any local muscular twitches; the first response to nerve stimulation is typically that of the sciatic nerve (foot twitch). Keeping fingers of the palpating hand on the biceps muscle is important for early detection of twitches of the biceps or semitendinosus muscles underneath the fingers.
27
These local twitches are the result of direct muscle stimulation when the needle is placed too laterally or medially, respectively: When local stimulation of the biceps muscle is felt under the fingers of the palpating hand, the needle should be redirected medially. Local twitches of the semitendinosus muscle indicates a too medial needle insertion. The needle should be withdrawn to the skin level and reinserted laterally. ANKLE
AXIAL CROSS SECTION RIGHT ANKLE
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CUTANEOUS INNERVATION OF THE FOOT Saphenous Sural
Superficial Peroneal
Deep Peroneal
Medial plantar
Lateral plantar
CLINICAL APPLICATIONS: Ankle blocks are simple to perform and offer adequate anaesthesia for surgical procedures of the foot not requiring a tourniquet above the ankle. ANATOMY OF THE NERVES AROUND THE ANKLE: Four of the five individual nerves that can be blocked at the ankle to provide anaesthesia of the foot are terminal branches of the sciatic nerve: the posterior tibial, sural, superficial peroneal, and deep peroneal branches. The sciatic nerve divides at or above the apex of the popliteal fossa to form the common peroneal and tibial nerves. The common peroneal nerve descends laterally around the head of the fibula, where it divides into the superficial and deep peroneal nerves. The tibial nerve divides into the posterior tibial and sural nerves in the lower leg. The posterior tibial nerve becomes superficial at the medial border of the Achilles tendon near the artery of the same name, and the sural nerve emerges lateral to the Achilles tendon.
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POST TIBIAL AND SURAL NERVE BLOCKS:
POST TIBIAL NERVE
MEDIAL MALLEOLUS
SURAL NERVE MEDIAL MALLEOLUS POST TIBIAL ARTERY AND NERVE
ACHILLES TENDON
The posterior tibial nerve can be blocked with the patient in either the prone or the supine position. The posterior tibial artery is palpated, and a 22-gauge, 3cm needle is inserted posterolateral to the artery at the level of the medial malleolus. In an awake patient paresthesia can often be elicited; however, it is not necessary for a successful block. If a paresthesia is obtained, 3 to 5 mL of local anaesthetic should be injected. Otherwise, 7 to 10 mL of solution should be injected as the needle is slowly withdrawn back from the posterior aspect of the tibia. A nerve stimulator and / ultrasound can also be used for this block. Blockade of the posterior tibial nerve provides anaesthesia of the heel, plantar portion of the toes, and the sole of the foot as well as some motor branches in the same area. The sural nerve is located superficially between the lateral malleolus and the Achilles tendon. A 25-gauge, 3-cm needle is inserted lateral to the tendon and is directed toward the malleolus as 5 to 10 mL of solution is injected subcutaneously. This block provides anaesthesia of the lateral foot and the lateral aspects of the proximal sole of the foot.
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DEEP AND SUPER FICIAL PERONEAL & SAPHENOUS NERVE BLOCKS The deep peroneal, superficial peroneal, and saphenous nerves can be blocked through a single needle entry site. A line is drawn across the dorsum of the foot connecting the two malleoli. In an awake patient the extensor hallucis longus tendon can be identified by asking the patient to dorsiflex the big toe. The anterior tibial artery lies between this structure and the tendon of the extensor digitorum longus muscle and is palpable at this level. A skin wheal is raised just lateral to the pulsation between the two tendons on the intermalleolar line. A 25-gauge, 3cm needle is advanced perpendicular to skin entry site, and 3 to 5 mL of local anaesthetic injected deep to the extensor retinaculum to block the deep peroneal nerve. This technique anaesthetises the skin between the first and second toes and the short extensors of the toes.
SAPHENOUS NERVE
SUPERFICIAL PERONEAL NERVE
DEEP PERONEAL NERVE
SUPERFICIAL PERONEAL NERVE
The needle can now be directed laterally through the same skin wheal while injecting 3 to 5 mL of solution subcutaneously, thus blocking the superficial peroneal nerve and resulting in anaesthesia of the dorsum of the foot, excluding the first interdigital space. The same manoeuvre can now be performed in the medial direction, thereby anaesthetising the saphenous nerve, a terminal branch of the femoral nerve that supplies a strip along the medial aspect of the foot.
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