Regional Block

Popliteal Sciatic Nerve Block

The popliteal sciatic nerve block targets the sciatic nerve in the popliteal fossa, approximately 5–7 cm proximal to the popliteal skin crease. The sciatic nerve (L4–S3) divides into the tibial nerve (medial) and common peroneal nerve (lateral) at or above the popliteal crease. At the level of the popliteal fossa, both nerves are still enclosed within a common epineural sheath. The injection above the bifurcation within this common sheath produces faster and more complete block than injecting below the bifurcation. The sciatic nerve is located posteromedial to the biceps femoris tendon and deep to the biceps femoris and semitendinosus muscles in the popliteal fossa.

Onset20–30 minutes for complete block

Duration14–24 hours with bupivacaine/levobupivacaine

CoverageTibial nerve: plantar foot, heel, posterior leg

Clinical Note

DO NOT perform popliteal sciatic block if compartment syndrome is suspected. Motor and sensory block will prevent monitoring of the 6 Ps (pain, pallor, pulselessness, paraesthesia, paralysis, pressure). This can lead to delayed diagnosis and catastrophic limb loss.

Indications

Foot and ankle surgery (ankle arthroscopy, calcaneal fracture, Achilles repair)
Below-knee amputation analgesia
Ankle fracture reduction and fixation
Total ankle arthroplasty
Foot debridement and diabetic foot surgery
Calcaneus fractures
Hindfoot procedures
Acute lower leg compartment syndrome assessment (Note: controversial — consult senior; regional blocks may mask early compartment syndrome)
Tourniquet analgesia in below-knee surgery (combined with saphenous/femoral block)

Contraindications

Patient refusal
Infection or abscess in popliteal fossa
Significant coagulopathy (risk-benefit)
Known allergy to local anaesthetic
Suspected compartment syndrome of the lower leg (relative/absolute — blocks may mask deterioration)
Pre-existing sciatic neuropathy (relative)

Technique

Patient positioned prone (preferred) or lateral decubitus with operative limb uppermost
High-frequency linear probe placed transversely in popliteal fossa
Identify popliteal artery (pulsatile); vein lies superficial; sciatic nerve lies posterior-lateral to vessels
Scan proximally to identify the point of bifurcation of tibial and common peroneal nerves
Target 2–5 cm proximal to bifurcation (within common epineural sheath)
In-plane needle approach from lateral (preferred) or out-of-plane
Advance needle to just outside epineural sheath (perineural)
Inject 20–30 mL LA with Doppler confirmation of no intravascular injection
Visualise circumferential spread around sciatic nerve (donut sign)
LATERAL APPROACH: patient supine, probe on lateral thigh — accesses nerve from lateral side without repositioning

Drug Doses

Agent	Concentration	Volume	Total Dose	Notes
Ropivacaine	0.5%	20–30 mL	100–150 mg	Most commonly used. Good sensory block. Max 3 mg/kg. Duration 12–18h.
Bupivacaine	0.375–0.5%	20–30 mL	75–150 mg	Long duration. Max 2 mg/kg (not >150 mg). Excellent for overnight analgesia.
Levobupivacaine	0.375–0.5%	20–30 mL	75–100 mg	Preferred in patients with cardiac history. Max 2 mg/kg.
Combined with Saphenous Block	Add ropivacaine 0.5% 5 mL	5 mL additional	Calculate cumulative dose	Complete foot/ankle block requires adding saphenous nerve block (femoral nerve territory, medial lower leg). Cumulative dose must not exceed maximum safe doses.

Onset

20–30 minutes for complete block; common peroneal component often faster than tibial

Duration

14–24 hours with bupivacaine/levobupivacaine; 12–18 hours with ropivacaine

Complications

Foot Drop (Common Peroneal Nerve Palsy)

Expected motor block: plantar/dorsiflexion weakness. Foot drop from injury to common peroneal nerve is rare but serious. Ensure padding and splinting to prevent pressure injury to foot. Educate patient.

LAST

Large volumes used (20–30 mL). Popliteal fossa is moderately vascular. Aspirate before each injection increment. Popliteal vein and artery identified by Doppler before injection.

Nerve Injury

Intraneural injection is most significant complication. Do not inject against resistance. Symptoms: paresthesia on injection (stop immediately).

Vascular Puncture / Haematoma

Popliteal vessels lie deep to the nerve. Ultrasound with Doppler reduces risk. Apply compression if puncture occurs.

Incomplete Block

Failure to inject within common sheath (below bifurcation) is the most common cause. Saphenous nerve (medial lower leg) requires separate block for complete foot/ankle anaesthesia.

Landmarks

Popliteal crease (skin fold at back of knee)
Biceps femoris tendon (lateral border of popliteal fossa)
Semimembranosus/semitendinosus tendons (medial border)
Popliteal artery and vein (deep to nerve)
Target: sciatic nerve 5–7 cm above popliteal crease

Sensory Coverage

Tibial nerve: plantar foot, heel, posterior leg. Common peroneal nerve: dorsum of foot, anterior lower leg, lateral lower leg (superficial peroneal). Does NOT cover: medial lower leg/medial foot (saphenous nerve — femoral territory). For complete foot anaesthesia: popliteal sciatic + saphenous nerve block.

Clinical Pearls

Identify bifurcation first, then inject 3–5 cm proximal for most reliable complete block

Lateral approach allows block to be performed without repositioning supine patient

Continuous catheter in popliteal fossa provides excellent post-operative analgesia for major foot surgery

Document: patient must not weight-bear with operative limb due to motor block

Saphenous nerve block is required if medial leg/foot territory must be covered

Avoid in suspected compartment syndrome — motor/sensory block will mask signs

Background & Evidence

The popliteal sciatic nerve block is the workhorse block for foot and ankle surgery, providing excellent analgesia below the knee (sciatic territory). It is technically reliable with ultrasound guidance. The key anatomical distinction is the bifurcation point — injection within the common epineural sheath proximal to bifurcation gives the most rapid and complete block. Combined with a saphenous nerve block, it provides complete foot and ankle anaesthesia.

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