IPACK matched a selective tibial nerve block for posterior knee pain, without peroneal weakness

Design

Randomised, triple-blinded controlled trial

Population

90 adults having total knee arthroplasty under spinal anaesthesia with femoral triangle block

Primary outcome

Cumulative intravenous morphine on postoperative day 1

Effect

6 mg (IPACK) vs 5 mg (tibial); p = 0.36; peroneal motor block 9% with tibial block

In a triple-blinded randomised trial (Anaesthesia, 18 October 2026), 90 patients having total knee arthroplasty under spinal anaesthesia with a femoral triangle block received either IPACK (19 ml ropivacaine 0.2%) or a selective tibial nerve block (5 ml ropivacaine 0.75%) for posterior knee pain. All had paracetamol, ibuprofen and morphine PCA.

Cumulative day-1 intravenous morphine was similar (mean 6 vs 5 mg; p = 0.36), as were pain scores to day 3, quadriceps strength, walking distance and range of motion. Four patients (9%) in the tibial group had motor block of the common peroneal nerve.

The trial was designed to show IPACK superior and did not. For practice, either block is reasonable; the occasional peroneal motor block with the tibial approach can cause foot drop that complicates early mobilisation and assessment for nerve injury, which may tip the choice towards IPACK.

• Either IPACK or a selective tibial nerve block is reasonable for posterior knee pain after knee replacement.
• Consider IPACK where early mobilisation matters; the tibial approach caused peroneal motor block in 9%.
• If you use a tibial block, check and document foot dorsiflexion before mobilising.
• Warn ward staff that foot drop after a tibial block may be the block, not surgical nerve injury, but examine to confirm.

Why it matters

When two blocks give the same pain relief, the side effect becomes the deciding factor.

Don't overread it

With 45 patients per group, the trial could miss small differences, and the peroneal block finding is based on four patients.

The statistics, in plain English

Mean morphine of 6 vs 5 mg with standard deviations of 6-7 mg means the distributions overlap almost completely; p = 0.36 is consistent with no difference.

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