Week 5 - Sciatic and Popliteal Nerve Blocks

Question 1

What is the Sacral nerve formed by?

Answer 1

The Ventral rami of L4, L5, and S1-S3

Question 2

What is the Tibial nerve formed by?

Answer 2

L4, L5, and S1-S3

Question 3

What is the Common Peroneal nerve formed by?

Answer 3

L4, L5, S1 and S2

Question 4

What is larger, peroneal nerve or tibial nerve?

Answer 4

Per PM, Tibial

Question 5

Sciatic Nerve…

Answer 5

The LARGEST peripheral nerve in the body.

Question 6

Lumbar plexus…

Answer 6

Know all the nerves and where they come from.. Drawing of lumbar plexus on Youtube - http://www.youtube.com/watch?v=AnZkTuVjaWs

Question 7

Indications for sciatic nerve block

Answer 7

Lower limb surgery

Question 8

True of False: Sciatic block should always be performed alone?

Answer 8

False: Almost always needs to be combined with a supplemental block. (often combined with Femoral or Psoas compartment block)

Question 9

Contraindications:

Answer 9

Pt. refusal, local infection at site of insertion, coagulopathy, preexisting central or peripheral nervous system disorders, allergy to LA.

Question 10

What two things should you know if someone is coming in for an ORIF of an ankle?

Answer 10

Where incision is going to be, and if there will be a tourniquet used. (want to make sure the right ares are blocked)

Question 11

Femoral Nerve blocks are always sufficient enough for Total Knee surgeries. True of False?

Answer 11

False… many times they require sciatic blocks as well to innervate the posterior portion of the leg.

Question 12

What forms the sacral plexus?

Answer 12

Union of lumbosacral trunk with first three sacral nerves.

Question 13

Strictly speaking what nerve roots form the sacral plexus?

Answer 13

L4-S3

Question 14

Where is the common peroneal nerve in relation to Tibial nerve?

Answer 14

LATERAL, LATERAL, LATERAL

Question 15

Common peroneal nerve CDE -

Answer 15

C - common Peroneal nerve D - dorsiflexion E - eversion

Question 16

Tibial nerve TIP -

Answer 16

Tibial Inversion Plantaflexion

Question 17

Tibial nerve motions

Answer 17

Knee extension, plantar flexion, toe flexion

Question 18

Peroneal nerve motions

Answer 18

Knee flexion, foot flexion (away from knee)

Question 19

Deep superficial nerve motions

Answer 19

Dorsiflexion of foot and ankle (toe’s point up to knee)

Question 20

Common dose (amount) of LA for sciatic nerve blocks?

Answer 20

30 ml (stick with this for now per PM)

Question 21

You get a local twitch of the gluteus muscle… what do you do?

Answer 21

Continue advancing the needle.

Question 22

Needle contacts bone but local twitch of the gluteus muscle is not elicited… what do you do?

Answer 22

Slightly laterally and caudally redirect the needle

Question 23

Needle encounters bone and sciatic twitches elicited… what do you do?

Answer 23

withdraw the needle and redirect slightly medially or laterally (5-10 degrees)

Question 24

Hamstring twitch… what do you do?

Answer 24

Accept and inject local anesthetic!!

Question 25

The needle placed deep (10 cm) but no twitches elicited and no bone contact… what do you do?

Answer 25

Withdraw and redirect needle slightly laterally, or cephalad (toward the head).

Question 26

Paresthesia of the genital organs.. what do you do?

Answer 26

If you like the person, probably want to redirect needle slightly cephalad and laterally! :)

Question 27

Clinical Pearls …

Answer 27

1. Twitches of hamstring, calf, foot, or toes at 0.2-0.5 mA is acceptable. 2. Inadequate skin anesthesia despite an apparent timely onset of the blockade can occur 3. It can take up to 30 MINUTES for full sensory-motor anesthesia to develop 4. LA infiltration at the site of injection by the surgeon is often all that is needed to allow the surgery to proceed.

Question 28

When sciatic block is combined with a femoral or lumbar plexus block….

Answer 28

anesthesia of almost the entire leg can be achieved.

Question 29

Know all the dermatomes BELOW the knee

Answer 29

Question 30

Technique

Answer 30

Position: Lateral Decubitus position with slight tilt forward. Foot on side to be blocked should be visible to observe twitches when present.

Sterilize site, infiltrate with LA, depress skin firmly to decrease needle-nerve distance, insert needle perpendicular to skin, set stimulator to 1.5 mA, first visible twitches will be gluteal muscles, once twitches of hamstring, calf, foot, or toes is observed, DECREASE YOUR CURRENT…

Injection: Aspirate, Inject 15-25 ml, if resistance withdraw slightly and reattempt

Question 31

What is neuropraxia?

Answer 31

Damage to a nerve

Question 32

What is the double crush phenomenon?

Answer 32

If you impede blood flow (via use of LA) to a patient in an already compromised area (IE neuropathy) you risk increasing damage to the area.

Question 33

Landmarks of Sciatic nerve block (must know all these for test)

Answer 33

1. Greater Trochanter
2. Posterior Superior Iliac spine
3. Sacral hiatus

Question 34

Complications of Sciatic nerve block and how to avoid them….

Answer 34

1. Infection - use asceptic technique
2. Hematoma - Avoid multple insertions,
3. Vascular puncture - (not common) avoid deep needle insertion
4. LA toxicity - (not common) Avoid using large volumes of LA’s in single poses, ensure frequent aspiration checks.
5. Nerve injury - BIG ONE HERE - Sciatic has a unique predisposition for mechanical and pressure injury - Use slow needle insertion and nerve stimulation. If stimulation occurs < 0.2 mAs, your too close, withdraw needle slightly. pain or pressure, STOP.
6. Perforation of pelvic organs - directing the needle medially should be exercised.
7. Avoid use of turniquet when possible.
8. Anesthesia of the pudendal nerve - a branch of sacral plexus, can occur by diffusion of LA for this block… inform patients of the potential for this problem.

Question 35

Block of the Sciatic nerve WITHIN the Popliteal Fossa

Answer 35

1. Simple technique - good for calf, tibia, fibula, ankle, and foot.
2. Most commonly used for analgesia of foot, ankle, and lower leg surgery… ensure patient has a BOOT to walk in.
3. Can performed by either posterior or lateral approaches.
4. Lateral popliteal block with 0.5& bupivocaine lasted 18 hrs!!!! (versus ankle block at 6.2 hrs)

Question 36

Indictaions for Sciatic block within popliteal fossa

Answer 36

Corrective foot surgery, foot debridement, saphenous vein stripping (may need saphenous block for this as well) , repair of achilles tendon,

Difference between this block and the more proximal sciatic nerve block, THIS block anesthetizes the distal leg to the hamstring mucles, allowing patients to RETAIN knee flexion!

Question 37

Regarding Nerve stimulating needles… Red and black leads go where?

Answer 37

Red = patient

Black = device

Question 38

The sciatic nerve is a nerve bundle consisting of what two separate nerve trunks?

Answer 38

1. Tibial (medial)
2. Common Peroneal (lateral)

Question 39

Which nerve is the larger of the two divisions?

Answer 39

Tibial is larger - gives rise to the medial and lateral plantar nerves as well as sural and posterior tibial nerves.

-when stimulated causes Plantar FLEXION

Question 40

Common Peroneal nerve has terminal branches where? What happens when stimulated?

Answer 40

The Deep and Superficial Peroneal nerves. When stimulated they cause **dorsiflexion and everision **

(CDE)

Question 41

Where does the Popliteal Sciatic block distribute to? (where does it innervate?)

Answer 41

The entire distal two-thirds of the lower extremity, with the EXCEPTION of the medial aspect of the leg which is supplied by the saphenous nerve ( a superficial terminal branch of the femoral nerve)

Question 42

Technique for Politeal sciatic block

(POSTERIOR)

Answer 42

1. Prone position
2. Allow foot to protrude off the bed - helps detect even the slightest movements
3. Landmarks: Popliteal fossa crease, tendon of biceps femoris (laterally) and tendons of semitendinous and semimembranous (medially)
4. Insert needle 7cm above crease between tendons
5. After twich observed, inject 35-45 (more volume here to try and hit both nerve branches in one shot)

Question 43

Technie for

CONTINUOUS POPLITEAL BLOCK

Answer 43

• Is an advanced technique, best to master the Single-shot block first.
• Similar to single shot except slightly cephalad needle angulation is required to allow the catheter to be threaded.

Question 44

Popliteal Block Troubleshooting…

Responses and Corrective Actions

Answer 44

1. Local twitch of the biceps (yes.. its biceps) muscle - Withdraw the needle and redirect slightly medially (5-10 degrees)
2. Local twitch of the semitendinosus/membranosus muscles - withdraw the needle and redirect slightly laterally (5-10 degrees)
3. Twitch of the calf muslces WITHOUT foot or toe movement - Disregard and continue advancing the needle until the foot/toes twitches are obtained.
4. Vascular puncture - withdraw and redirect
5. Bone contact - Withdraw needle slowly and look for the foot twitch; if twitches are not seen, reinsert in another direction.

Question 45

Technique

Popliteal sciatic block

(LATERAL)

Answer 45

Main Advantage: Patient does not have to take a prone position. This block is perfomed while patient is supine.

Sciatic nerve is poisitioned between the biceps femories and semitendinous muscles

Common peroneal nerve is usually stimulated first (65% of the time) - why? Is more lateral

100mm needle -

Landmarks : Popliteal Crease, vastus lateralis, and biceps femories muscles.

Question 46

Lateral Popliteal block troubleshooting

Response - Corrective Action

Answer 46

1. Local twitch of the biceps - Advance the needle deeper
2. Local twitch of vastus lateralis muscle - withdraw the needle and reinsert posterior
3. Twitch of the calf muscles without foot or toe movement - disregard and continue advancing the needle until the foot/toes twitches are obtained.
4. Vasular puncture - Withdraw and redirect laterally
5. Twitches of the foot or toes - Accept and inject local anesthetic

Question 47

Complications of politeal block

Infection - how do we prevent?

Answer 47

Aseptic technique

Question 48

Complications of Popliteal block

Hematoma - How do we prevent?

Answer 48

Avoid multipe needle passes with a continues block needle; the larger needle diameter and/or Tuohy design may result in a hematoma of the biceps femoris or vastus lateralis muscles. When the nerve is not localized on first two or three needle passes, localize the nerve using a smaller guage, single-shot needle first… then reinsert with continuous needle using the exact same angle.

Question 49

Complications of Popliteal block

Vascular puncture - How do we prevent?

Answer 49

Avoid too deep insertion of needle because the vascular sheeth is positioned medially and deeper to the sciatic nerve.

When the nerve is not localized within 2 cm after the local twitches of the biceps muslce cease, the needle should be withdrawn and reinserted at a different angle, rather than deep

Question 50

Complications of Popliteal block

Nerve injury - how do we prevent?

Answer 50

Uncommon; use nerve stimulation and slow needle advancement; do not inject when patient complains of pain or pressure, do NOT with stimulation at < 0.2 mA. Avoid combination of epinephrine in LA and application of a tourniquet over injection site to decrase risk of prolonged ischemia of the nerve.

Question 51

Complications of Popliteal block

Pressure necrosis of the heal - How do we prevent it?

Answer 51

Instruct patient on the care of the insensate extremity

Use heel padding and frequent repositioning