Overview
Total knee arthroplasty is associated with severe postoperative pain — up to 60% of patients experience severe pain in the first 24 hours. Effective analgesia is critical not only for comfort but for facilitating early mobilisation and physiotherapy, which directly determines functional outcome and length of stay.
The key challenge in TKA analgesia is providing comprehensive knee coverage — anterior, medial, and posterior compartments — while preserving quadriceps motor function to allow early ambulation. This has driven the transition from femoral nerve blocks (which cause quadriceps weakness) toward the current standard of adductor canal block (ACB) + iPACK + local infiltration analgesia (LIA).
PROSPECT 2022 summary (Lavand'homme et al., Eur J Anaesthesiol): Paracetamol + NSAIDs/COX-2 as basic multimodal analgesia; single-shot adductor canal block + peri-articular LIA as regional strategy; IV dexamethasone; opioids as rescue only. Femoral nerve block is no longer recommended as first-line due to quadriceps weakness.
Analgesic Pathway — At a Glance
- Paracetamol 1g PO/IV
- COX-2 inhibitor (e.g. celecoxib 200 mg PO)
- Gabapentin 300 mg PO (selected patients — see notes)
- Pregabalin 75–150 mg (alternative to gabapentin)
- Routine opioid premedication — avoid
- Spinal or GA (spinal preferred — see anaesthesia section)
- Adductor canal block (ACB) — 15–20 mL ropivacaine 0.5%
- iPACK block — 15–20 mL ropivacaine 0.25%
- LIA by surgeon — ropivacaine 0.2% 100–150 mL
- Dexamethasone 8 mg IV
- Paracetamol 1g IV (if not given preop)
- Femoral nerve block — not recommended (quadriceps weakness)
- Paracetamol 1g QDS regular
- COX-2 / NSAID regular (≤5 days)
- Opioid PRN rescue (oxycodone 5–10 mg PO)
- Cryotherapy to knee
- Early physiotherapy — Day 0 mobilisation target
- Regular opioid prescription — avoid
- Continuous femoral nerve catheter
✓ Recommended | ◎ Optional/conditional | ✗ Not recommended. Based on PROSPECT 2022.
Systemic Analgesia
Basic Multimodal — PROSPECT Recommended
Paracetamol + NSAIDs or COX-2 inhibitors form the backbone of systemic analgesia for TKA. Both should be given regularly (not PRN) throughout the perioperative period unless contraindicated. Combined, they reduce opioid consumption by 30–50%.
| Agent | Dose | Route | Frequency | Duration | Notes |
|---|---|---|---|---|---|
| Paracetamol | 1 g | IV/PO | QDS | Throughout | Reduce to 500–750 mg if <50 kg |
| Celecoxib | 200 mg | PO | BD | ≤5 days | COX-2 preferred — less GI risk |
| Etoricoxib | 60–90 mg | PO | OD | ≤5 days | Once daily — good compliance |
| Ibuprofen | 400 mg | PO | TDS | ≤5 days | Add PPI; avoid if renal impairment |
| Dexamethasone | 8 mg | IV | Single dose intraop | — | Analgesic + PONV prophylaxis; extends block |
Gabapentinoids — Conditional Use Only
PROSPECT 2022 position: Gabapentinoids (pregabalin, gabapentin) may be considered as part of multimodal analgesia in TKA, but only in selected patients. The evidence shows modest opioid-sparing but significant sedation and dizziness risk. Avoid in elderly patients, OSA, and those on concurrent CNS depressants. Not recommended as routine for all TKA patients.
Opioids — Rescue Only
| Agent | Dose | Route | Notes |
|---|---|---|---|
| Oxycodone IR | 5–10 mg | PO PRN 4–6h | First-line oral rescue; predictable PK |
| Morphine | 2.5–5 mg | IV PRN | PACU titration; caution in renal impairment |
| Tramadol | — | — | Avoid in elderly Seizure risk, serotonin syndrome |
Regional Analgesic Strategy
The modern TKA regional strategy combines three complementary techniques to achieve complete knee coverage without motor blockade:
Adductor Canal Block (ACB)
PROSPECT ✓Blocks saphenous nerve — anterior and medial knee coverage. Motor-sparing (quadriceps strength preserved). Primary regional technique for TKA.
iPACK Block
PROSPECT ✓Infiltration between Popliteal Artery and posterior Capsule of the Knee — blocks posterior capsular innervation (genicular branches, tibial nerve articular branches).
Local Infiltration Analgesia (LIA)
PROSPECT ✓Peri-articular infiltration by surgeon — covers entire joint capsule, periosteum, and soft tissues. Complementary to ACB + iPACK.
Why ACB over femoral nerve block? The femoral nerve block (FNB) provides equivalent anterior knee analgesia but causes quadriceps motor blockade in up to 80% of patients — delaying ambulation, increasing fall risk, and impeding rehabilitation. ACB preserves quadriceps strength in ~95% of patients. PROSPECT 2022 explicitly recommends ACB over FNB for TKA.
Adductor Canal Block (ACB)
Anatomy
The adductor canal (Hunter's canal) is an aponeurotic tunnel in the mid-thigh running from the femoral triangle to the adductor hiatus. It contains the saphenous nerve (terminal sensory branch of femoral nerve), the nerve to vastus medialis, and the medial femoral cutaneous nerve, along with the femoral artery and vein. Blocking at this level provides sensory analgesia to the medial thigh, medial knee, and medial leg without affecting the motor branches to quadriceps (which arise proximally).
Technique — Ultrasound-Guided
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Position & probe placement
Patient supine, hip slightly abducted and externally rotated. Place high-frequency linear probe (10–15 MHz) on the anteromedial thigh at the mid-thigh level (approximately midway between ASIS and patella). Orient probe transversely.
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Identify the adductor canal
Identify the sartorius muscle (superficial), femoral artery (pulsatile, compressible), and the saphenous nerve — a hyperechoic triangular or oval structure anteromedial to the artery. The vastoadductor membrane forms the anterior wall of the canal.
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Needle insertion — in-plane, lateral to medial
Insert the needle lateral to the probe, in-plane, advancing beneath the sartorius muscle into the canal. Target the anteromedial aspect of the femoral artery where the saphenous nerve lies. Aspirate before injection.
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Injection
Inject 15–20 mL of ropivacaine 0.5% in 5 mL increments. Observe LA spread surrounding the saphenous nerve and filling the canal. The femoral artery should be displaced but not compressed.
Dosing
| Agent | Concentration | Volume | Onset | Duration | Notes |
|---|---|---|---|---|---|
| Ropivacaine | 0.5% | 15–20 mL | 10–20 min | 8–14 h | Standard choice; good duration |
| Ropivacaine | 0.25–0.375% | 20 mL | 15–25 min | 6–10 h | Reduced concentration — may ↓ motor effects further |
| Bupivacaine | 0.5% | 15–20 mL | 15–25 min | 12–18 h | Longer duration; use if extended analgesia needed |
| Levobupivacaine | 0.5% | 15–20 mL | 15–25 min | 12–18 h | Preferred over bupivacaine in frail/elderly |
+ Dexamethasone 4–8 mg IV (not perineural) extends duration by 6–8h. MEV90 with ropivacaine 0.275%: ~18 mL (Wang et al. 2023).
iPACK Block
iPACK (Infiltration between the Popliteal Artery and the Capsule of the Knee) was first described by Sinha et al. in 2012. Meta-analysis (Guo et al. 2022, 7 RCTs) shows that adding iPACK to ACB significantly reduces posterior knee pain, opioid consumption (by ~20%), and hospital length of stay compared to ACB alone, without additional motor effects.
Anatomy & Target
The posterior knee capsule is innervated by articular branches of the tibial nerve, common peroneal nerve, and the obturator nerve. The iPACK injects LA into the plane between the popliteal artery and the posterior knee capsule, bathing these articular branches without entering the popliteal fossa or affecting the main tibial/peroneal nerves (preserving foot motor function and plantar flexion).
Technique — Ultrasound-Guided
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Position & probe placement
Patient in lateral decubitus (operative side up) or supine with knee flexed. Place the linear probe in the popliteal fossa transversely to identify the popliteal artery, tibial nerve, and common peroneal nerve.
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Identify the target plane
Trace the popliteal artery proximally to the level of the posterior femoral condyles. The target is the plane immediately posterior to the artery and anterior to the posterior knee capsule. The tibial and common peroneal nerves should be visible and avoided.
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Needle insertion — medial to lateral, in-plane
Insert the needle medially (or laterally), in-plane, aiming to place the tip between the popliteal artery and the posterior capsule. Advance under real-time visualisation, keeping the needle superficial to the artery.
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Injection
After negative aspiration, inject 15–20 mL of ropivacaine 0.25% in incremental aliquots. Observe spread in the plane between the artery and capsule. The LA should spread proximally and distally along the capsule.
Dosing
| Agent | Concentration | Volume | Notes |
|---|---|---|---|
| Ropivacaine | 0.25% | 15–20 mL | Standard; motor-sparing concentration |
| Ropivacaine | 0.2% | 20 mL | Lower concentration — adequate for analgesia, maximum motor sparing |
| Bupivacaine | 0.25% | 15 mL | Alternative — longer duration |
Calculate total LA dose: When combining ACB + iPACK + LIA, ensure total ropivacaine dose does not exceed 3 mg/kg. For a 70 kg patient: max 210 mg. ACB 20 mL × 5 mg/mL = 100 mg + iPACK 20 mL × 2.5 mg/mL = 50 mg + LIA 100 mL × 2 mg/mL = 200 mg = 350 mg total — exceeds limit. Adjust concentrations accordingly, or reduce LIA volume.
Local Infiltration Analgesia (LIA)
Peri-articular LIA provides circumferential coverage of the knee joint capsule, periosteum, ligaments, and soft tissues. It is complementary to ACB + iPACK — covering areas not reached by the nerve blocks. The technique involves systematic injection by the surgeon before wound closure.
Standard LIA Protocol
| Agent | Concentration | Volume | Total Dose | Notes |
|---|---|---|---|---|
| Ropivacaine | 0.2% | 100–150 mL | 200–300 mg | Standard — ensure total dose <3 mg/kg when combined with nerve blocks |
| Levobupivacaine | 0.25% | 60–80 mL | 150–200 mg | Lower volume needed; watch total dose |
Some centres add ketorolac 30 mg and/or adrenaline 1:200,000 to LIA mixture. Adrenaline reduces systemic absorption and prolongs duration. Ketorolac in LIA mixture is off-label in most countries.
Anaesthetic Technique
| Technique | PROSPECT | Advantages | Notes |
|---|---|---|---|
| Spinal anaesthesia | Preferred | Lower opioid use, reduced PONV, better outcomes in meta-analyses, may allow earlier ambulation | Hyperbaric bupivacaine 0.5% 2–3 mL ± intrathecal morphine 100 mcg (hospitalised patients only) |
| General anaesthesia | Acceptable | Familiar, controllable depth, suitable when spinal contraindicated | Add IV multimodal analgesia; regional blocks remain essential |
| Intrathecal morphine | Conditional | 12–18h analgesia without motor block | 100 mcg only; PONV, pruritus, respiratory depression risk; hospitalised patients only — not day-case |
Not Recommended — PROSPECT 2022
FNB causes significant quadriceps motor blockade, delaying mobilisation and increasing falls risk. ACB provides equivalent anterior knee analgesia with preservation of motor function. FNB is no longer recommended as first-line for TKA.
Continuous FNB provides no analgesic benefit over single-shot when combined with ACB + LIA, and adds motor blockade, infection risk, and catheter complications.
Epidural provides bilateral lower limb effects, urinary catheter requirement, hypotension, and delays mobilisation. No superiority over ACB + LIA. Not recommended for routine TKA.
Sciatic nerve block causes foot drop and peroneal motor blockade without sufficient analgesic benefit to justify its use routinely. The iPACK block covers posterior knee pain without this risk.
Insufficient evidence to recommend routine IV ketamine for TKA. May be considered in opioid-tolerant patients or those with chronic pain as part of individualised strategy.
Practical Analgesic Protocol
Suggested protocol for a typical adult patient (70 kg, eGFR >60, no NSAID contraindication) undergoing primary unilateral TKA under spinal anaesthesia:
LA dose check: Always calculate total ropivacaine dose when combining ACB + iPACK + LIA. For patients <70 kg or with hepatic impairment, reduce LIA volume proportionally. Use the Drug Calculator to check max dose before starting.
References
- Lavand'homme PM, Kehlet H, Rawal N, Joshi GP; PROSPECT Working Group. Pain management after total knee arthroplasty: PROSPECT recommendations. Eur J Anaesthesiol. 2022;39(9):743–757. PMID 35852550 ↗
- Hussain N, Brull R, Vannabouathong C et al. Analgesic effectiveness of motor-sparing nerve blocks for total knee arthroplasty: network meta-analysis. Anesthesiology. 2023;139:444–461.
- Guo J, Hou M, Shi G et al. iPACK + adductor canal block vs adductor canal block in TKA: systematic review and meta-analysis. J Orthop Surg Res. 2022. PMC9373358 ↗
- Wang Q et al. Minimum effective volume of ropivacaine for ACB + iPACK block in TKA. J Orthop Surg (Hong Kong). 2023. PubMed ↗
- Albrecht E et al. Motor-sparing regional anaesthesia for TKA: narrative and systematic review. Br J Anaesth. 2023;78:188–196. BJA ↗
- ESRA PROSPECT. Total Knee Arthroplasty. esraeurope.org ↗
- Moucha CS et al. Multimodal pain management and enhanced recovery after surgery protocols in total joint arthroplasty. J Bone Joint Surg Am. 2016;98(11):932–940.