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Lower Extremity Blocks
TEXTRegional II · 9 min read
Femoral, popliteal sciatic, adductor canal, iPACK, ankle block. Match block to surgery + preserve motor when possible.
After this lesson you can
4 min read8 sections- Choose femoral, adductor canal, sciatic, or popliteal for the case.
- Recall LA volume + duration expectations.
- Anticipate motor block effects on rehab.
- Manage continuous catheter complications.
Anatomy refresher — what each nerve covers
Sacral plexus (L4-S3): SCIATIC (largest peripheral nerve) — splits in popliteal fossa to TIBIAL (plantar foot) + COMMON PERONEAL (lateral leg + dorsum of foot); POSTERIOR FEMORAL CUTANEOUS — posterior thigh skin.
Knowing which nerve to block depends on which structures are in the surgical field.
Femoral nerve block — uses + tradeoffs
Provides ANTERIOR thigh + MEDIAL knee/calf (via saphenous branch) anesthesia and analgesia.
- hip fracture (transport + pre-op analgesia)
- patellar surgery
- anterior thigh procedures
- ACL repair
- traditional TKA
SIGNIFICANT QUADRICEPS WEAKNESS post-block high fall risk if patient ambulates with assistance — must be educated and supervised.
This concern drove the shift to adductor canal block for ERAS protocols where patients ambulate POD#0.
Adductor canal block — preserves motor
Mostly SENSORY branches at this level — minimal quadriceps motor block.
Provides equivalent analgesia to femoral block for TKA and knee arthroscopy while preserving ambulation strength.
PREFERRED for ERAS TKA pathways.
Add iPACK (interspace between popliteal artery + capsule of knee) for posterior knee coverage.
Standard modern TKA regional combo: adductor canal + iPACK + periarticular surgeon injection (cocktail of LA + ketorolac + epi + ± steroid).
Popliteal sciatic block — foot + ankle
Sciatic nerve at the popliteal fossa, ideally targeted JUST PROXIMAL to the bifurcation into tibial + common peroneal (the LA fills the common epineural sheath and bathes both branches faster, more reliable block).
Covers below-knee surgery EXCEPT medial foot/ankle (which is saphenous from femoral — supplement with saphenous block if needed).
Approaches: posterior (prone — uncomfortable for awake patient), lateral (supine via biceps femoris/vastus lateralis groove — easier and increasingly preferred).
Duration with bupivacaine 12-18 hours, with ropivacaine 8-12 hr.
- foot + ankle surgery
- calf compartments
- ankle fracture
- Achilles repair
Ankle block — five nerves at the ankle
Technique: subcutaneous infiltration; no neurostimulator typically used.
Reliable for hallux valgus, forefoot reconstruction, toe surgery, neuroma excision.
Preserves all proximal motor function — patient ambulates immediately after surgery.
Combined blocks for major lower extremity surgery
Achieves quad-preserving analgesia + early ambulation + POD#1 discharge in selected patients.
12-24 hr analgesia.
Continuous catheter blocks
48-72 hr post-TKA analgesia.Popliteal sciatic catheter for major foot/ankle surgery.
Femoral catheter occasionally for hip fracture pre-op analgesia.
- secure with tegaderm + tape + bridge
- label clearly
- monitor for catheter dislodgement + LA leak
Programmed intermittent boluses (PIEB) increasingly preferred over continuous infusion for catheter pain pumps — better spread, less motor block, lower total LA dose.
Patient-controlled boluses (PCRA) commonly enabled with lockout.
Send patient home with disposable elastomeric pump (e.g., ON-Q, ambIT) for 48-72 hr.
LA selection + max dose limits + LAST awareness
- bupivacaine
2 mg/kgplain (3 mg/kg with epi) - ropivacaine
3 mg/kg - lidocaine
4.5 mg/kgplain (7 mg/kg with epi)
- peri-oral numbness
- tinnitus
- metallic taste
- dizziness
- agitation
- seizure
- then bradycardia/asystole
1.5 mL/kg bolus + 0.25 mL/kg/min infusion, modified ACLS (reduced epi dose ≤1 mcg/kg, avoid vasopressin/CCB/beta-blockers).
⚠ Common pitfalls
- Femoral block before knee surgery without considering quad weakness — falls risk.
- Sciatic block alone for TKA — doesn't cover the medial knee (saphenous).
- Forgetting popliteal block for foot surgery — best motor-sparing option above ankle.
- Catheter in place >72 hr without inspection — infection risk.
💎 Clinical pearls
- Adductor canal = sensory > motor; preserves quad strength for early ambulation post-TKA.
- Popliteal sciatic: 20-30 mL 0.5% bupivacaine, ~12-18 hr motor block.
- Fascia iliaca block is the simplest alternative to femoral for hip fracture analgesia.
- Ankle block (5 nerves) avoids tourniquet pain + ideal for foot surgery.
Recap
- Adductor canal = sensory > motor; preserves quad strength for early ambulation post-TKA.
- Popliteal sciatic: 20-30 mL 0.5% bupivacaine, ~12-18 hr motor block.
- Fascia iliaca block is the simplest alternative to femoral for hip fracture analgesia.
- Ankle block (5 nerves) avoids tourniquet pain + ideal for foot surgery.
Mark each section done to complete the module.