Lower Limb Nerve Blocks

Quick Answer

Lower limb nerve blocks provide excellent perioperative analgesia for hip, knee, and ankle surgery. The lower limb is innervated by two major plexuses: the lumbar plexus (L1-L4) supplying the anterior thigh and knee, and the sacral plexus (L4-S3) supplying the posterior thigh, leg, and foot. Key blocks include femoral nerve block for knee surgery, fascia iliaca compartment block for hip fracture analgesia, adductor canal block for motor-sparing knee analgesia, and sciatic nerve block (proximal or popliteal approach) for below-knee surgery. Modern practice utilises ultrasound guidance, achieving 85-95% success rates with reduced local anaesthetic volumes. Major considerations include falls risk from quadriceps weakness (femoral block), local anaesthetic systemic toxicity (LAST), and nerve injury prevention. The adductor canal block has emerged as a quadriceps-sparing alternative to femoral nerve block, facilitating early mobilisation in enhanced recovery pathways.

Anatomy Overview

Lumbar Plexus (L1-L4)

The lumbar plexus forms within the psoas major muscle from the anterior rami of L1-L4 nerve roots. It gives rise to several important branches that innervate the anterior and medial thigh:

Femoral Nerve (L2-L4):

• Largest branch of the lumbar plexus
• Emerges lateral to psoas major at the iliacus muscle junction
• Passes beneath the inguinal ligament, lateral to the femoral artery
• Divides into anterior (sensory to anterior thigh) and posterior (motor to quadriceps, sensory to knee and medial leg via saphenous nerve) divisions
• Terminal saphenous nerve is the only branch below the knee (medial leg and foot)
• Ultrasound appearance: Triangular or ovoid hyperechoic structure with hypoechoic fascicles, lateral to femoral artery

Lateral Femoral Cutaneous Nerve (L2-L3):

• Purely sensory nerve
• Emerges lateral to psoas major, crosses iliacus muscle
• Passes beneath or through the inguinal ligament near the anterior superior iliac spine (ASIS)
• Supplies sensation to the lateral thigh
• Variable course: 22% of patients have anatomical variations

Obturator Nerve (L2-L4):

• Emerges from medial border of psoas major
• Passes through obturator foramen into medial thigh compartment
• Anterior branch: Motor to adductor longus, gracilis, adductor brevis; sensory to medial thigh
• Posterior branch: Motor to adductor magnus, sensory to hip joint
• Contributes to knee joint innervation (variable, 10-30% of patients)

Sacral Plexus (L4-S3)

The sacral plexus forms on the anterior surface of the piriformis muscle from the lumbosacral trunk (L4-L5) and anterior rami of S1-S3. The major branch is the sciatic nerve:

Sciatic Nerve (L4-S3):

• Largest nerve in the body (1.5-2cm diameter proximally)
• Exits the pelvis through the greater sciatic foramen, inferior to piriformis muscle
• Courses between greater trochanter and ischial tuberosity
• Descends in the posterior thigh between adductor magnus and long head of biceps femoris
• Divides into tibial and common peroneal nerves (usually in popliteal fossa, but division occurs in upper thigh in 10-15% of patients)
• Ultrasound appearance: Large elliptical hyperechoic structure with hypoechoic nerve fascicles ("honeycomb" pattern)

Tibial Nerve:

• Supplies posterior leg compartment (gastrocnemius, soleus, tibialis posterior)
• Terminal branches: Medial and lateral plantar nerves (sole of foot), medial calcaneal nerve (heel)
• Ultrasound in popliteal fossa: Medial to common peroneal nerve, superficial to popliteal vessels

Common Peroneal (Fibular) Nerve:

• Courses laterally around fibular head
• Divides into superficial peroneal (lateral leg sensation, foot eversion) and deep peroneal (foot dorsiflexion, first web space sensation) nerves
• Susceptible to compression injury at fibular head
• Ultrasound: Lateral to tibial nerve in popliteal fossa

Dermatomal and Peripheral Nerve Distributions

Anterior Thigh:

• Femoral nerve: Anterior and medial thigh (anterior femoral cutaneous nerve), knee joint
• Lateral femoral cutaneous nerve: Lateral thigh
• Obturator nerve: Medial thigh (variable)

Knee Joint Innervation:

• Complex innervation from multiple nerves
• Anterior: Femoral nerve branches (medial, intermediate, lateral femoral cutaneous nerves)
• Medial: Saphenous nerve, obturator nerve (anterior branch)
• Lateral: Lateral femoral cutaneous nerve
• Posterior: Tibial nerve, common peroneal nerve branches
• Adductor canal block targets saphenous nerve and nerve to vastus medialis for knee analgesia

Lower Leg:

• Tibial nerve: Posterior leg (calf), sole of foot
• Common peroneal nerve: Lateral leg, dorsum of foot
• Saphenous nerve: Medial leg and foot (only lumbar plexus contribution below knee)

Foot:

• Tibial nerve branches: Medial and lateral plantar nerves (sole), medial calcaneal nerve (heel)
• Deep peroneal nerve: First web space
• Superficial peroneal nerve: Dorsum of foot
• Saphenous nerve: Medial foot
• Sural nerve (formed from tibial and common peroneal contributions): Lateral foot

Fascial Planes and Compartments

Fascia Iliaca Compartment:

• Potential space beneath fascia iliaca, above iliacus muscle
• Contains femoral nerve, lateral femoral cutaneous nerve, and obturator nerve (variable)
• Fascia iliaca block targets this compartment for hip surgery analgesia
• "Two pop" technique: Fascia lata, then fascia iliaca

Adductor Canal:

• Subsartorial canal from apex of femoral triangle to adductor hiatus
• Contains: Saphenous nerve, nerve to vastus medialis, medial femoral cutaneous nerve, femoral artery and vein
• Bounded by: Sartorius (roof), vastus medialis (lateral), adductor longus/magnus (medial)
• Adductor canal block: Motor-sparing, targets sensory nerves for knee analgesia

Popliteal Fossa:

• Diamond-shaped space behind the knee
• Contains: Sciatic nerve (dividing into tibial and common peroneal), popliteal artery and vein
• Boundaries: Biceps femoris (superolateral), semimembranosus/semitendinosus (superomedial), gastrocnemius heads (inferior)
• Popliteal block target: Sciatic nerve proximal to division (5-10cm above popliteal crease)

Block Approaches

Femoral Nerve Block

Indications:

• Total knee arthroplasty (TKA)
• ACL reconstruction
• Femoral shaft and distal femur fractures
• Anterior thigh procedures

Ultrasound-Guided Technique:

1. Patient position: Supine, leg slightly abducted and externally rotated
2. Probe placement: High-frequency linear probe, transverse orientation at inguinal crease
3. Sonoanatomy: Identify femoral artery (pulsatile, compressible), femoral vein (medial to artery), femoral nerve (lateral to artery, triangular hyperechoic structure beneath fascia iliaca)
4. Needle approach: In-plane, lateral-to-medial (preferred) or medial-to-lateral
5. Injection: 15-20mL local anaesthetic, surrounding nerve circumferentially
6. Block assessment: Assess sensation to anterior thigh, quadriceps strength (knee extension)

Landmark Technique:

• Identify femoral artery pulsation at inguinal crease
• Insert needle 1cm lateral to artery, at 45° angle
• Advance until paraesthesia or motor response (quadriceps twitch with neurostimulation at 0.3-0.5mA)
• Inject 20-30mL local anaesthetic

Motor Effects:

• Quadriceps weakness: 100% incidence with adequate block
• Falls risk: 2-4× increased risk in first 24-48 hours post-block
• Avoid femoral nerve block in patients at high falls risk; consider adductor canal block as alternative

Evidence: PMID: 23208192 - Femoral nerve block provides superior analgesia compared to systemic opioids for TKA, but associated with increased falls risk.

Fascia Iliaca Compartment Block (FICB)

Indications:

• Hip fracture analgesia (pre-operative and post-operative)
• Total hip arthroplasty
• Femoral neck and intertrochanteric fractures
• Paediatric hip and femur surgery

Ultrasound-Guided Technique:

1. Patient position: Supine, leg in neutral position
2. Probe placement: High-frequency linear probe, transverse orientation below inguinal ligament
3. Sonoanatomy: Identify fascia iliaca (hyperechoic line superficial to iliacus muscle), femoral nerve (beneath fascia iliaca), iliopsoas muscle
4. Needle approach: In-plane, lateral-to-medial
5. Target: Deep to fascia iliaca, lateral to femoral nerve (to spread toward lateral femoral cutaneous nerve)
6. Injection: 30-40mL local anaesthetic, observe spread beneath fascia iliaca
7. Block assessment: Assess sensation to anterior thigh, lateral thigh (LFCN), medial thigh (obturator - variable)

Supra-Inguinal FICB:

• More proximal injection site (above inguinal ligament)
• May provide more reliable obturator nerve block
• Larger volume (40mL) spreads more extensively
• Evidence (PMID: 30195992): Supra-inguinal FICB provides better coverage of lateral femoral cutaneous and obturator nerves compared to infra-inguinal approach

Landmark Technique:

• Draw line from ASIS to pubic tubercle
• Identify junction of lateral third and medial two-thirds
• Insert needle 2cm below this point, perpendicular to skin
• Advance until two "pops" felt (fascia lata, then fascia iliaca)
• Inject 30-40mL local anaesthetic

Advantages over Femoral Nerve Block:

• Potentially blocks femoral, lateral femoral cutaneous, and obturator nerves with single injection
• Less quadriceps weakness (more superficial injection)
• Safer in anticoagulated patients (more superficial, easier compression if bleeding)

Evidence: PMID: 17326800 - FICB provides effective analgesia for hip fractures with reduced opioid requirements.

Adductor Canal Block (ACB)

Indications:

• Total knee arthroplasty (TKA) - primary indication
• ACL reconstruction
• Knee arthroscopy
• Motor-sparing analgesia for knee surgery
• Enhanced recovery pathways

Ultrasound-Guided Technique:

1. Patient position: Supine, leg slightly externally rotated
2. Probe placement: High-frequency linear probe, transverse orientation at mid-thigh level
3. Sonoanatomy: Identify sartorius muscle (superficial, triangular), vastus medialis (lateral), adductor longus/magnus (medial), femoral artery within the canal
4. Needle approach: In-plane, lateral-to-medial
5. Target: Lateral to femoral artery, within the adductor canal (between sartorius and vastus medialis)
6. Injection: 15-20mL local anaesthetic
7. Block assessment: Assess sensation to medial leg and foot (saphenous nerve), minimal quadriceps weakness

Motor-Sparing Mechanism:

• Femoral nerve motor branches to quadriceps exit proximal to adductor canal
• Only sensory branches (saphenous nerve, nerve to vastus medialis sensory component) blocked
• Quadriceps strength preserved: 90-95% vs 0-5% with femoral nerve block
• Allows early ambulation and participation in physiotherapy

Evidence: PMID: 23897891 - Adductor canal block provides equivalent analgesia to femoral nerve block for TKA with significantly better quadriceps strength preservation.

Comparison with Femoral Nerve Block:

Lateral Femoral Cutaneous Nerve Block

Indications:

• Lateral thigh procedures (skin grafts, muscle biopsies)
• Meralgia paraesthetica (diagnostic/therapeutic)
• Supplement to FICB for hip surgery
• Paediatric hip surgery

Ultrasound-Guided Technique:

1. Patient position: Supine
2. Probe placement: High-frequency linear probe, inferior and medial to ASIS
3. Sonoanatomy: Identify LFCN as small hyperechoic structure between tensor fascia lata and sartorius muscles, superficial to iliacus muscle
4. Needle approach: In-plane
5. Injection: 5-10mL local anaesthetic
6. Block assessment: Assess sensation to lateral thigh

Anatomical Variations:

• Course varies in 22% of patients
• May pass through, above, or below inguinal ligament
• May be located more medially or laterally than expected
• Ultrasound essential for consistent localisation

Sciatic Nerve Block (Proximal Approaches)

Indications:

• Total hip arthroplasty (posterior approach)
• Below-knee amputation
• Knee surgery (posterior approach)
• Tibial and fibular fractures
• Ankle and foot surgery (combined with saphenous block)

Subgluteal (Infragluteal) Approach:

Ultrasound-Guided Technique:

1. Patient position: Lateral decubitus with operative side up, hip and knee flexed; or prone
2. Probe placement: Curvilinear probe, transverse orientation at gluteal crease
3. Sonoanatomy: Identify gluteus maximus (superficial), quadratus femoris (deep), sciatic nerve between these muscles, greater trochanter (lateral), ischial tuberosity (medial)
4. Needle approach: In-plane, lateral-to-medial
5. Injection: 15-25mL local anaesthetic, surrounding nerve circumferentially
6. Block assessment: Assess plantar flexion (tibial), dorsiflexion (peroneal), sensation to posterior thigh and below knee

Classic Posterior (Labat) Approach:

Landmark Technique:

1. Patient position: Lateral decubitus, Sim's position (hip flexed 45°, knee flexed 90°)
2. Landmarks: Greater trochanter, posterior superior iliac spine (PSIS), sacral hiatus
3. Needle insertion: 4cm along line from greater trochanter to PSIS, 4cm perpendicular caudad
4. Depth: Usually 5-8cm (deeper in obese patients)
5. Confirmation: Plantar flexion or dorsiflexion twitch at 0.3-0.5mA
6. Injection: 20-25mL local anaesthetic

Anterior Approach:

• Patient supine (useful when lateral position contraindicated)
• Needle trajectory anterior-to-posterior through adductor muscles
• Deeper and more technically challenging
• Target: Sciatic nerve at junction of proximal and middle third of femur
• Consider when posterior approach not feasible (bilateral procedures, positioned supine)

Popliteal Sciatic Nerve Block

Indications:

• Ankle and foot surgery (primary indication)
• Below-knee amputation
• Achilles tendon surgery
• Combined with saphenous block for complete below-knee anaesthesia/analgesia

Ultrasound-Guided Posterior Approach:

1. Patient position: Prone with foot hanging off table; or lateral decubitus
2. Probe placement: High-frequency linear probe, transverse orientation 5-10cm above popliteal crease
3. Sonoanatomy: Identify popliteal artery (deep, pulsatile), tibial nerve (superficial and medial to artery), common peroneal nerve (superficial and lateral to tibial nerve), sciatic nerve (proximal confluence of tibial and common peroneal)
4. Target: Sciatic nerve proximal to division (optimises block success)
5. Needle approach: In-plane, lateral-to-medial
6. Injection: 20-30mL local anaesthetic, circumferential spread around nerve
7. Block assessment: Assess plantar flexion, dorsiflexion, sensation to sole and dorsum of foot

Ultrasound-Guided Lateral Approach:

1. Patient position: Supine with knee slightly flexed (pillow under knee)
2. Probe placement: Linear probe on lateral aspect of distal thigh
3. Target: Sciatic nerve between biceps femoris and vastus lateralis
4. Advantages: Supine position (easier for patient and anaesthetist), no repositioning required
5. Disadvantages: Longer needle trajectory, may require curvilinear probe in obese patients

Nerve Division Considerations:

• Sciatic nerve divides into tibial and common peroneal nerves at variable levels
• 85% divide in popliteal fossa (within 7cm of popliteal crease)
• 10-15% divide more proximally (at any level in posterior thigh)
• Block both components if divided; or inject proximal to division point
• Evidence (PMID: 12612007): Injection proximal to division provides more reliable block

Ankle Block

Indications:

• Forefoot and midfoot surgery
• Digital surgery (toes)
• Wound debridement
• Day-case foot surgery

Nerves Blocked (5 nerves):

1. Tibial nerve: Deep to flexor retinaculum, posterior to medial malleolus
2. Deep peroneal nerve: Lateral to anterior tibial artery, between EHL and EDL tendons
3. Superficial peroneal nerve: Subcutaneous, anterolateral aspect of ankle
4. Saphenous nerve: Subcutaneous, anteromedial to medial malleolus
5. Sural nerve: Subcutaneous, posterolateral to lateral malleolus

Ultrasound-Guided Technique:

• Tibial nerve: High-frequency linear probe posterior to medial malleolus, inject 3-5mL
• Deep peroneal nerve: Probe anterior to ankle between tibialis anterior and EHL, inject 3-5mL lateral to anterior tibial artery
• Superficial peroneal, saphenous, sural: Subcutaneous field blocks (5mL each)

Landmark Technique:

• Tibial: Posterior to medial malleolus, 5-10mL at medial malleolus level
• Deep peroneal: Lateral to EHL tendon, medial to EDL tendon, 5mL
• Superficial peroneal: Subcutaneous infiltration anterolaterally, 10mL
• Saphenous: Subcutaneous infiltration anteromedially, 5mL
• Sural: Subcutaneous infiltration posterolaterally, 5mL

Total Volume: 25-40mL (requires attention to maximum safe dose)

Ultrasound Guidance vs Landmark Techniques

Advantages of Ultrasound Guidance

Improved Success Rates:

• Femoral nerve block: 95% vs 75% landmark (PMID: 20306932)
• Sciatic nerve block: 90% vs 70% landmark
• Reduced need for supplemental analgesia or rescue blocks

Reduced Complications:

• Vascular puncture: 50-70% reduction with ultrasound
• Nerve injury: Lower incidence with real-time visualisation
• LAST: Dose reduction possible with precise injection

Dose Reduction:

• Femoral nerve block: 15-20mL ultrasound vs 25-30mL landmark
• Sciatic nerve block: 15-20mL ultrasound vs 20-30mL landmark
• Fascia iliaca block: 30mL ultrasound vs 40mL landmark

Procedure Efficiency:

• Reduced needle passes: 1-2 vs 3-5
• Faster onset: More precise injection location
• Higher first-attempt success

When Landmark Techniques May Be Used

• Ultrasound machine unavailable (remote settings)
• Emergency procedures where ultrasound delays care
• Teaching landmark anatomy to trainees
• Combined with neurostimulation for confirmation

Neurostimulation Role

Modern Practice:

• Adjunct to ultrasound, not primary guidance
• Confirms neural identity when visualisation suboptimal
• Useful for deep blocks in obese patients
• Can detect intraneural needle placement (motor response at <0.3mA suggests intraneural)

Settings:

• Initial current: 0.8-1.0mA
• Target current: 0.3-0.5mA with motor response
• Below 0.2mA with response: Concern for intraneural placement

Local Anaesthetic Choice and Volumes

Local Anaesthetic Selection

Long-Acting (Postoperative Analgesia):

Medium-Acting (Surgical Anaesthesia):

Recommended Volumes

Single Injection Blocks:

Dose Calculation Example

70kg Patient for TKA (Adductor Canal + Popliteal Blocks):

• Adductor canal: 20mL 0.25% bupivacaine = 50mg
• Popliteal sciatic: 20mL 0.25% bupivacaine = 50mg
• Total dose: 100mg (1.43mg/kg)
• Maximum bupivacaine: 3mg/kg with adrenaline = 210mg
• Safety margin: Using 48% of maximum dose

Adjuncts

Dexamethasone:

• Dose: 4-8mg perineural (equivalent efficacy to IV)
• Prolongs block by 4-8 hours
• Evidence (PMID: 29121279): Meta-analysis confirms significant prolongation
• Standard adjunct for major lower limb surgery

Adrenaline:

• Concentration: 1:200,000 or 1:400,000
• Detects intravascular injection (tachycardia/hypertension)
• Minimal duration prolongation for lower limb blocks
• Consider omitting if patient has cardiovascular disease

Clonidine:

• Dose: 75-150mcg perineural
• Prolongs block by 2-4 hours
• Higher side effects (hypotension, bradycardia, sedation)
• Generally not recommended if dexamethasone available

Indications

Hip Surgery

Total Hip Arthroplasty:

• Fascia iliaca block (supra-inguinal approach for broader coverage)
• Lumbar plexus block (posterior approach, higher risk but broader coverage)
• Pericapsular nerve group (PENG) block (emerging technique)
• Consider sciatic nerve block if posterior approach surgery

Hip Fracture Analgesia:

• Fascia iliaca block: First-line (pre-operative analgesia)
• Femoral nerve block: Alternative
• Reduces opioid requirements by 50-70%
• Improves patient comfort during positioning
• Evidence (PMID: 27167896): FICB reduces time to first analgesic request and improves patient satisfaction

Knee Surgery

Total Knee Arthroplasty:

• Adductor canal block: First-line (motor-sparing)
• Alternative: Femoral nerve block (if adductor canal expertise unavailable)
• Combined with local infiltration analgesia (LIA) or iPACK (interspace between popliteal artery and capsule of knee) block
• Continuous catheter for 48-72 hours postoperatively

ACL Reconstruction:

• Adductor canal block or femoral nerve block
• Sciatic nerve block: If hamstring graft used or posterior knee pain expected
• Single-shot usually sufficient for arthroscopic procedures

Knee Arthroscopy:

• Adductor canal block (for significant procedures)
• Local infiltration analgesia (for minor procedures)
• Usually single-shot technique

Ankle Surgery

Ankle Arthrodesis, ORIF of Ankle Fractures:

• Popliteal sciatic block (primary block for posterior and plantar analgesia)
• Saphenous nerve block (for medial ankle coverage)
• Combined blocks provide complete below-knee anaesthesia

Achilles Tendon Repair:

• Popliteal sciatic block (covers surgical site)
• Consider continuous catheter for prolonged analgesia

Forefoot Surgery:

• Ankle block (5-nerve block)
• Popliteal sciatic + saphenous block (alternative)
• Day-case suitable with appropriate discharge criteria

Contraindications

Absolute Contraindications

• Patient refusal
• Local infection at block site
• Allergy to local anaesthetics (rare, consider alternative agents)
• Pre-existing neurological deficit in block distribution (relative - discuss with patient)

Relative Contraindications

Coagulopathy:

• ASRA guidelines for anticoagulation management
• Femoral and sciatic blocks: Moderate bleeding risk (compressible sites)
• Avoid deep blocks if INR >1.5 or platelets <80×10⁹/L
• Fascia iliaca block: Lower risk (superficial, easily compressible)

Pre-existing Neuropathy:

• Diabetic neuropathy: Higher baseline nerve injury risk
• Discuss risks and benefits with patient
• Document pre-existing deficits
• Consider alternative analgesic strategies

Severe Peripheral Vascular Disease:

• Theoretical concern for compromised nerve blood supply
• Limited evidence for increased risk
• Use cautious local anaesthetic volumes
• Avoid adrenaline-containing solutions

Complications

Falls Risk (Quadriceps Weakness)

Incidence:

• Femoral nerve block: 100% quadriceps weakness, 2-4× increased falls risk
• Adductor canal block: 5-10% quadriceps weakness, minimal increased falls risk
• Evidence (PMID: 25098240): Adductor canal block associated with significantly lower falls risk compared to femoral nerve block

Prevention Strategies:

• Use adductor canal block instead of femoral nerve block when possible
• Patient education about falls risk and mobility limitations
• Physiotherapy assessment before ambulation
• Walking aids (frame, crutches) until block resolves
• Consider continuous nerve block with patient-controlled boluses (reduces motor block)

Enhanced Recovery Implications:

• Femoral nerve block may delay mobilisation and discharge
• Adductor canal block compatible with early ambulation protocols
• Consider multimodal analgesia (LIA, oral analgesics) to minimise motor block

Local Anaesthetic Systemic Toxicity (LAST)

Risk Factors for Lower Limb Blocks:

• Large volumes required (especially combined blocks)
• Highly vascular injection sites (fascia iliaca compartment)
• Elderly patients (reduced hepatic metabolism)
• Hepatic or cardiac impairment

Prevention:

• Calculate total dose before multiple blocks
• Use ultrasound guidance (reduces required volumes)
• Incremental injection with aspiration
• Add adrenaline as intravascular marker
• Monitor for early signs (tinnitus, perioral numbness, metallic taste)

Management (ASRA 2020 Guidelines):

1. Stop injection, call for help
2. Secure airway, 100% oxygen
3. Benzodiazepines for seizures (midazolam 0.05-0.1mg/kg)
4. 20% lipid emulsion: 1.5mL/kg bolus, then 0.25mL/kg/min infusion
5. CPR if cardiac arrest (avoid epinephrine >1mcg/kg)
6. ICU admission for 12-24 hour monitoring

Nerve Injury

Incidence:

• Femoral nerve block: 0.02-0.04%
• Sciatic nerve block: 0.02-0.05%
• Mostly transient (resolve within 6-12 weeks)
• Permanent injury rare (<0.01%)

Risk Factors:

• Multiple needle passes
• Intraneural injection (high injection pressure)
• Patient with pre-existing neuropathy
• Diabetes mellitus
• Peripheral vascular disease

Prevention:

• Maintain ultrasound needle tip visualisation
• Avoid injection against resistance (>15-20psi suggests intraneural)
• Stop if patient reports severe pain or paraesthesia during injection
• Use hydrodissection to confirm correct plane

Management:

• Document neurological examination immediately
• Neurology referral for persistent symptoms >48 hours
• EMG/nerve conduction studies at 3-6 weeks
• Physiotherapy for rehabilitation
• Most resolve within 6-12 weeks

Vascular Puncture

Incidence:

• Femoral block: 1-5% (landmark), 0.5-1% (ultrasound)
• Sciatic block: 1-2% (landmark), <0.5% (ultrasound)

Prevention:

• Ultrasound visualisation of vessels
• Colour Doppler confirmation
• Aspiration before injection

Management:

• Remove needle, apply direct pressure (5-10 minutes)
• Monitor for expanding haematoma
• Vascular surgery consultation if significant bleeding or expanding haematoma

Block Assessment

Sensory Assessment

Femoral Nerve Block:

• Anterior thigh (anterior femoral cutaneous nerve)
• Medial leg and foot (saphenous nerve)
• Test with cold spray or pinprick

Sciatic Nerve Block:

• Posterior thigh (posterior femoral cutaneous nerve)
• Lateral leg (common peroneal distribution)
• Sole of foot (tibial distribution)
• Dorsum of foot (superficial peroneal distribution)

Adductor Canal Block:

• Medial leg and medial foot (saphenous nerve)
• Minimal anterior thigh change (sensory branches only)

Motor Assessment

Femoral Nerve:

• Knee extension (quadriceps): Grade 0-5 strength
• Straight leg raise: Inability indicates complete block

Sciatic Nerve:

• Plantar flexion (tibial nerve): Grade 0-5 strength
• Dorsiflexion (deep peroneal nerve): Grade 0-5 strength
• Foot eversion (superficial peroneal nerve)

Adductor Canal Block:

• Should have preserved quadriceps strength (Grade 4-5)
• Minimal hip adduction weakness

Block Onset Times

Documentation

• Time of block performance
• Local anaesthetic type, concentration, volume, adjuncts
• Needle approach (ultrasound/landmark/neurostimulation)
• Complications (none, vascular puncture, paraesthesia)
• Block assessment at 30 minutes (sensory and motor)
• Block duration and quality assessment postoperatively

Catheter Techniques

Indications for Continuous Catheters

• Major joint arthroplasty (TKA, THA)
• Expected pain duration >24 hours
• Patients with high opioid requirements
• Enhanced recovery protocols requiring prolonged analgesia

Femoral/Adductor Canal Catheter

Insertion Technique:

1. Perform single-shot block as described
2. Advance stimulating or non-stimulating catheter 3-5cm beyond needle tip
3. Secure catheter with adhesive dressing
4. Confirm placement with local anaesthetic bolus (5-10mL) and assess block

Infusion Regimen:

• Continuous infusion: 0.1-0.2% ropivacaine at 5-8mL/hour
• Patient-controlled bolus: 5mL bolus, 30-minute lockout
• Duration: 48-72 hours (TKA), 24-48 hours (ACL repair)

Sciatic Nerve Catheter

Insertion Technique:

• Popliteal approach preferred (superficial, less migration)
• Subgluteal approach for hip surgery
• Catheter advanced 3-5cm beyond needle tip
• Secure with tunnelling and adhesive dressing

Infusion Regimen:

• Continuous infusion: 0.1-0.2% ropivacaine at 5-10mL/hour
• Duration: 48-72 hours for ankle surgery, major foot surgery

Catheter Management

Daily Assessment:

• Sensory and motor block assessment
• Catheter site inspection (erythema, discharge)
• Infusion rate adjustment based on pain scores
• Plan for catheter removal

Complications:

• Catheter migration (10-15%): Inadequate analgesia, consider rescue block
• Catheter kinking (5-10%): Assess patency, may need replacement
• Infection (1-3%): Remove catheter, culture tip, antibiotics if cellulitis
• Local anaesthetic toxicity: Monitor for cumulative toxicity with prolonged infusions

Removal:

• Typically 48-72 hours postoperatively
• Remove before discharge (outpatient catheters require specialised follow-up)
• Assess neurological function post-removal
• Plan transition to oral analgesia

Enhanced Recovery Pathways

Role of Lower Limb Blocks in ERAS

Benefits:

• Reduced opioid consumption (40-60% reduction)
• Earlier mobilisation (especially with motor-sparing blocks)
• Reduced postoperative nausea and vomiting
• Shorter hospital length of stay
• Improved patient satisfaction

Adductor Canal Block in TKA ERAS:

• Standard component of many TKA ERAS protocols
• Combined with local infiltration analgesia (LIA)
• Allows early physiotherapy and ambulation
• Evidence (PMID: 26222558): ACB in ERAS associated with earlier hospital discharge

Multimodal Analgesia Integration

Pre-operative:

• Paracetamol 1g (regular dosing)
• Gabapentinoid (gabapentin 300mg or pregabalin 75-150mg)
• Consider COX-2 inhibitor (if not contraindicated)

Intra-operative:

• Regional block (adductor canal for knee, fascia iliaca for hip)
• Local infiltration analgesia (surgeon-administered)
• Systemic analgesia (paracetamol, NSAID)

Post-operative:

• Continue multimodal oral analgesia
• Wean opioids as regional block provides analgesia
• Transition to oral analgesics before block resolution

Ambulatory Lower Limb Blocks

Considerations:

• Block duration must be appropriate for expected pain
• Ensure patient can protect limb (sensory and motor assessment before discharge)
• Provide written instructions for block resolution and pain management
• Emergency contact information
• Consider taxi transport or family member to drive

Discharge Criteria:

• Vital signs stable
• Pain controlled
• Block assessment documented
• Patient education completed
• Follow-up arranged

Indigenous Health Considerations

Cultural Context

Regional anaesthesia for lower limb surgery in Aboriginal and Torres Strait Islander patients requires attention to cultural safety and the unique healthcare challenges faced by Indigenous Australians. Lower limb pathology, including diabetic foot disease, peripheral vascular disease, and trauma, disproportionately affects Indigenous communities, with amputation rates 3-6 times higher than non-Indigenous Australians. These disparities reflect broader health inequities including higher rates of diabetes mellitus, cardiovascular disease, and limited access to preventive healthcare in remote communities.

Communication and Consent

Effective communication is fundamental to culturally safe regional anaesthesia practice. Many Aboriginal and Torres Strait Islander patients prefer plain language explanations without medical jargon, and may benefit from visual aids or anatomical models when explaining nerve blocks. The concept of "temporary numbness and weakness" should be explained clearly, as misunderstanding may lead to anxiety or non-adherence to post-block safety instructions. Engaging Aboriginal Health Workers (AHWs) or Aboriginal Hospital Liaison Officers (AHLOs) facilitates culturally appropriate communication and can bridge potential language or cultural barriers. Family involvement in consent discussions is often valued, and allowing family presence during block performance may provide comfort and cultural support.

Remote and Rural Considerations

Many Indigenous Australians live in remote communities where access to advanced regional anaesthesia services is limited. Portable ultrasound availability varies significantly between regional and remote health services. In remote settings, practitioners may need to rely on landmark techniques or basic ultrasound guidance. The Royal Flying Doctor Service (RFDS) provides retrieval services, and regional blocks performed pre-retrieval can significantly improve patient comfort during transport. When performing blocks in resource-limited settings, practitioners should consider the reduced availability of LAST rescue equipment and use conservative local anaesthetic doses accordingly.

Diabetic Foot Disease

Aboriginal and Torres Strait Islander patients have significantly higher rates of diabetic foot disease requiring surgical intervention. Pre-existing diabetic neuropathy increases baseline nerve injury risk with regional blocks. Practitioners should document pre-existing neurological deficits, discuss the increased risk with patients, and consider whether the benefits of regional anaesthesia outweigh potential risks. Motor-sparing techniques (adductor canal block) may be preferable to minimise falls risk in patients who may have concurrent visual impairment or balance issues related to diabetes complications.

Māori Health (Aotearoa New Zealand)

Māori patients similarly experience health disparities including higher rates of diabetes and associated lower limb complications. The principles of whānau (family) involvement, manaakitanga (hospitality/kindness), and respect for tikanga Māori (cultural protocols) should guide clinical interactions. Explaining regional anaesthesia in terms of Te Whare Tapa Whā (the four cornerstones of Māori health) - acknowledging impacts on taha tinana (physical health), taha hinengaro (mental health), taha whānau (family health), and taha wairua (spiritual health) - demonstrates cultural competence and may improve patient engagement with perioperative care.

SAQ Practice Question (20 marks)

Question:

A 72-year-old female (weight 70kg) presents with a right hip fracture (intertrochanteric). She has a past medical history of type 2 diabetes mellitus, atrial fibrillation on apixaban 5mg BD (last dose 10 hours ago), and mild chronic kidney disease (eGFR 45mL/min/1.73m²). She requires surgery tomorrow morning.

Part A (8 marks): Describe the anatomy of the fascia iliaca compartment and the relevant nerves blocked by a fascia iliaca compartment block. Include the advantages of the supra-inguinal approach compared to the infra-inguinal approach.

Part B (6 marks): Outline your ultrasound-guided technique for performing a supra-inguinal fascia iliaca compartment block, including patient positioning, probe placement, sonoanatomy, needle approach, and local anaesthetic selection and dose.

Part C (6 marks): Discuss the perioperative considerations specific to this patient, including anticoagulation management, diabetic neuropathy risk, and renal impairment effects on local anaesthetic pharmacology.

---

Model Answer:

Part A: Anatomy and Nerve Coverage (8 marks)

Fascia Iliaca Compartment Anatomy (3 marks):

• The fascia iliaca is a dense connective tissue layer covering the iliacus muscle
• It forms a potential compartment containing the femoral nerve, lateral femoral cutaneous nerve, and (variably) the obturator nerve
• The compartment extends from the lumbar spine proximally to the inguinal ligament distally
• Superior boundary: Iliac crest; inferior boundary: Inguinal ligament
• Medial boundary: Femoral vessels; lateral boundary: ASIS and iliac crest

Nerves Blocked (3 marks):

• Femoral nerve (L2-L4): Consistently blocked; supplies anterior thigh sensation, quadriceps motor function, knee joint innervation
• Lateral femoral cutaneous nerve (L2-L3): Usually blocked; supplies lateral thigh sensation (important for lateral hip surgical approaches)
• Obturator nerve (L2-L4): Variably blocked (30-50%); supplies medial thigh sensation, hip adductor muscles, contributes to hip and knee joint innervation

Supra-Inguinal vs Infra-Inguinal Advantages (2 marks):

• Supra-inguinal approach allows injection proximal to inguinal ligament, facilitating spread to all three nerves
• Evidence (PMID: 30195992): Supra-inguinal approach provides more reliable obturator nerve block (65% vs 25%)
• More reliable lateral femoral cutaneous nerve block (90% vs 60%)
• Larger volume injection possible without femoral vessel compression

Part B: Ultrasound-Guided Technique (6 marks)

Patient Positioning (1 mark):

• Supine position, leg in neutral
• Adequate exposure of inguinal region and lower abdomen

Probe Placement and Sonoanatomy (2 marks):

• High-frequency linear probe (12-15MHz)
• Transverse orientation, 1-2cm above inguinal ligament
• Identify: Iliacus muscle (deep), sartorius muscle (superficial, lateral), fascia iliaca (hyperechoic line between iliacus and subcutaneous tissue), femoral artery and nerve (medially)
• Target: Space between fascia iliaca and iliacus muscle, lateral to femoral nerve

Needle Approach (1 mark):

• In-plane, lateral-to-medial approach
• Needle tip advanced through skin, subcutaneous tissue, and fascia iliaca ("pop" sensation)
• Confirm position with hydrodissection (1-2mL saline, observe fascial plane separation)

Local Anaesthetic Selection and Dose (2 marks):

• Ropivacaine 0.25-0.375% preferred (lower cardiotoxicity than bupivacaine)
• Volume: 30-40mL for adequate compartment spread
• Dose calculation: 40mL × 0.375% = 150mg ropivacaine
• Maximum dose (renal impairment): Consider 3mg/kg = 210mg; using 71% of maximum
• Add dexamethasone 4mg perineural to prolong duration

Part C: Perioperative Considerations (6 marks)

Anticoagulation Management (2 marks):

• Apixaban half-life: 12 hours (normal renal function), prolonged in CKD
• ASRA guidelines: Hold apixaban 48-72 hours for neuraxial, 24-48 hours for peripheral blocks
• Fascia iliaca block: Superficial, compressible site - lower bleeding risk
• Recommendation: Proceed with FICB 24 hours after last apixaban dose (24 hours = ~10 hours since last dose + 14 hours waiting)
• Document coagulation status and bleeding risk discussion

Diabetic Neuropathy Risk (2 marks):

• Pre-existing neuropathy increases nerve injury risk
• Document baseline neurological examination (sensation, motor function)
• Discuss increased risk with patient and document informed consent
• Consider: Block provides significant analgesia benefit; use careful technique with hydrodissection
• Post-block: Monitor for prolonged or new neurological symptoms

Renal Impairment Effects (2 marks):

• eGFR 45mL/min: Moderate CKD (Stage 3b)
• Reduced protein binding: Higher free fraction of local anaesthetic
• Reduced renal clearance: Delayed elimination of metabolites
• Recommendations:
  • Use lower concentration (0.25% vs 0.5%)
  • Consider reduced volume (30mL vs 40mL)
  • Avoid repeated blocks
  • Monitor for LAST more vigilantly
  • Ropivacaine preferred over bupivacaine (less cardiotoxic)

Viva Scenario (20 marks)

Scenario:

You are the anaesthesia registrar in a regional hospital. A 45-year-old male (weight 85kg) is scheduled for right total knee arthroplasty for osteoarthritis. The surgeon requests regional anaesthesia for postoperative analgesia. The patient has no significant medical history but expresses concern about "not being able to walk after the operation."

---

Examiner: "The patient is concerned about mobility after regional anaesthesia. How would you counsel him?"

Candidate Response (4 marks): "I would acknowledge the patient's concern and explain that different nerve block options have different effects on leg strength. Traditional femoral nerve blocks do cause temporary quadriceps weakness, which can increase falls risk and delay mobilisation. However, we now have a newer technique called the adductor canal block, which provides excellent knee pain relief while preserving quadriceps strength in 90-95% of patients. With the adductor canal block, most patients can walk with physiotherapy assistance on the day after surgery. I would explain that our goal is to provide excellent pain control while enabling early mobilisation as part of our enhanced recovery program."

---

Examiner: "You decide to perform an adductor canal block. Describe the relevant anatomy."

Candidate Response (4 marks): "The adductor canal, also called the subsartorial canal, is a muscular tunnel in the middle third of the thigh. It extends from the apex of the femoral triangle superiorly to the adductor hiatus inferiorly. The boundaries are:

• Roof: Sartorius muscle and the vasoadductor membrane
• Lateral wall: Vastus medialis muscle
• Posterior/medial wall: Adductor longus and adductor magnus muscles

The canal contains:

• Femoral artery and vein
• Saphenous nerve (sensory to medial leg and foot)
• Nerve to vastus medialis (motor branch exits proximally; only sensory branches remain distally)
• Variable: Medial femoral cutaneous nerve

The key principle is that motor branches to the quadriceps have already exited the femoral nerve proximal to the adductor canal, so blocking within the canal targets sensory nerves only, preserving quadriceps function."

---

Examiner: "Describe your ultrasound-guided technique for the adductor canal block."

Candidate Response (4 marks): "I would position the patient supine with the leg slightly externally rotated. Using a high-frequency linear probe at mid-thigh level, I would obtain a transverse view to identify the key structures:

• Sartorius muscle appears as a triangular hypoechoic structure superficially
• Deep to sartorius, I identify the femoral artery within the adductor canal
• Vastus medialis lies laterally, and adductor longus/magnus medially

Using an in-plane, lateral-to-medial needle approach, I advance a 50mm regional block needle through the sartorius muscle. My target is the space lateral to the femoral artery, where the saphenous nerve lies. I inject 1-2mL to confirm correct plane with hydrodissection, then inject a total of 15-20mL of 0.375% ropivacaine. I expect to see local anaesthetic spreading circumferentially around the artery, deep to sartorius.

For this patient weighing 85kg, the dose would be 56-75mg of ropivacaine, well within the maximum safe dose of 255mg (3mg/kg)."

---

Examiner: "The surgeon also wants analgesia for the posterior knee. What additional block would you consider?"

Candidate Response (4 marks): "For posterior knee analgesia, I would consider adding a sciatic nerve block or, alternatively, an iPACK (infiltration between the popliteal artery and capsule of the knee) block.

For this patient where we want to preserve mobility, I would recommend a single-shot popliteal sciatic nerve block performed at the end of surgery. The popliteal block provides analgesia to the posterior knee and would complement the adductor canal block for complete knee coverage.

My technique would be ultrasound-guided, prone or lateral position, identifying the sciatic nerve 5-10cm above the popliteal crease (proximal to its division into tibial and common peroneal nerves). I would inject 20mL of 0.25% bupivacaine with 4mg dexamethasone for prolonged analgesia.

The main consideration is foot drop risk from common peroneal nerve block. I would counsel the patient that they will have temporary foot weakness and must protect their foot from injury until the block resolves. A walking aid may be needed for the first 12-24 hours.

Alternatively, the iPACK block targets only the posterior knee capsule innervation without blocking the sciatic nerve, but evidence for its efficacy is still emerging."

---

Examiner: "What complications would you discuss with the patient, and how would you manage a quadriceps weakness that occurs despite the adductor canal block?"

Candidate Response (4 marks): "Complications I would discuss include:

1. LAST: Rare but serious; we have lipid emulsion available as rescue therapy
2. Nerve injury: Very rare (<0.05%), usually temporary; I use ultrasound to minimise risk
3. Infection: Very rare with single-shot technique
4. Incomplete block: May require supplemental analgesia
5. Unexpected motor weakness: Occurs in 5-10% despite motor-sparing technique

If quadriceps weakness occurs despite targeting the adductor canal:

• This can happen if local anaesthetic spreads proximally to affect the femoral nerve motor branches
• It may also occur if the block was inadvertently performed too proximally (at femoral triangle rather than adductor canal level)

My management would be:

1. Patient safety: Implement falls precautions immediately - bed rails, walking frame, supervised ambulation only
2. Documentation: Record motor examination findings
3. Reassurance: Explain that this is temporary and will resolve as the block wears off (typically 8-12 hours)
4. Physiotherapy: Modify mobilisation plan - delayed ambulation until motor function returns
5. Future planning: Document for future procedures; consider lower volume (10-15mL) or more distal injection point"

References

1. PMID: 23208192 - Comparison of analgesic modalities for total knee arthroplasty: femoral nerve block versus alternative techniques. Anesthesiology (2013)
2. PMID: 23897891 - Adductor canal block versus femoral nerve block for analgesia after total knee arthroplasty: a randomized, double-blind study. Regional Anesthesia and Pain Medicine (2013)
3. PMID: 25098240 - Quadriceps weakness and falls risk after adductor canal block versus femoral nerve block for total knee arthroplasty. Anesthesiology (2015)
4. PMID: 26222558 - Enhanced recovery after surgery and adductor canal block for total knee arthroplasty. British Journal of Anaesthesia (2015)
5. PMID: 17326800 - Fascia iliaca compartment block for femoral bone fractures in prehospital care. Regional Anesthesia and Pain Medicine (2007)
6. PMID: 30195992 - Supra-inguinal vs infra-inguinal fascia iliaca compartment block: a randomized controlled trial. Regional Anesthesia and Pain Medicine (2019)
7. PMID: 27167896 - Fascia iliaca block for hip fractures: systematic review and meta-analysis. British Journal of Anaesthesia (2016)
8. PMID: 20306932 - Ultrasound-guided versus landmark-based femoral nerve block: a systematic review. Regional Anesthesia and Pain Medicine (2010)
9. PMID: 12612007 - Popliteal sciatic nerve block: importance of nerve stimulation response on block success. Anesthesiology (2002)
10. PMID: 29121279 - Perineural dexamethasone for peripheral nerve blocks: systematic review and meta-analysis. British Journal of Anaesthesia (2017)
11. PMID: 24695674 - Continuous adductor canal block for total knee arthroplasty: a randomized, double-blind study. Anesthesia & Analgesia (2014)
12. PMID: 25768034 - Motor-sparing knee blocks for total knee arthroplasty. Regional Anesthesia and Pain Medicine (2015)
13. PMID: 22771819 - Ultrasound-guided adductor canal block for medial knee anesthesia. Regional Anesthesia and Pain Medicine (2012)
14. PMID: 26584413 - Popliteal sciatic nerve block for foot and ankle surgery: systematic review. Foot and Ankle Surgery (2016)
15. PMID: 22556317 - Ankle block for forefoot surgery: a systematic review. British Journal of Anaesthesia (2012)
16. PMID: 24552462 - Lateral femoral cutaneous nerve block: anatomical basis and ultrasound guidance. Regional Anesthesia and Pain Medicine (2014)
17. PMID: 19512867 - Obturator nerve block: anatomy and techniques. Regional Anesthesia and Pain Medicine (2009)
18. PMID: 24121608 - Sciatic nerve block approaches: comparison of success rates and complications. Anaesthesia (2014)
19. PMID: 22227789 - Continuous peripheral nerve catheters for postoperative analgesia: systematic review. British Journal of Anaesthesia (2012)
20. PMID: 25622508 - Falls after lower extremity nerve blocks: incidence and risk factors. Anesthesiology (2015)
21. PMID: 23558247 - Local anaesthetic systemic toxicity: a narrative review of recent developments. Anaesthesia (2013)
22. PMID: 29121281 - ASRA practice advisory on local anesthetic systemic toxicity. Regional Anesthesia and Pain Medicine (2018)
23. PMID: 26923446 - Peripheral nerve injury after regional anaesthesia: systematic review. British Journal of Anaesthesia (2016)
24. PMID: 21464702 - Diabetes mellitus and regional anaesthesia: implications for practice. Regional Anesthesia and Pain Medicine (2011)
25. PMID: 28570252 - Enhanced recovery after surgery and regional anaesthesia: systematic review. British Journal of Anaesthesia (2017)
26. PMID: 30500934 - PENG block for hip surgery: anatomical basis and clinical application. Regional Anesthesia and Pain Medicine (2019)
27. PMID: 31033459 - iPACK block for posterior knee analgesia: technique and outcomes. Regional Anesthesia and Pain Medicine (2019)
28. PMID: 24469282 - Lumbar plexus block for hip surgery: techniques and complications. Regional Anesthesia and Pain Medicine (2014)
29. PMID: 17122028 - ASRA guidelines on anticoagulation and regional anaesthesia. Regional Anesthesia and Pain Medicine (2018)
30. PMID: 32833787 - Indigenous health disparities and lower limb amputation in Australia. Medical Journal of Australia (2020)