Design: Triple-blinded randomised controlled trial
Population: 90 patients having total knee arthroplasty under spinal with femoral triangle block
Primary outcome: Cumulative intravenous morphine on postoperative day 1
Effect: 6 (7) mg vs 5 (6) mg, p = 0.36; peroneal motor block 9% with tibial block

This triple-blinded trial randomised 90 patients having total knee arthroplasty under spinal anaesthesia with a femoral triangle block to either IPACK with 19 ml ropivacaine 0.2% or a selective tibial nerve block with 5 ml ropivacaine 0.75%. All received paracetamol, ibuprofen and morphine patient-controlled analgesia.

Day 1 morphine use was 6 mg (SD 7) with IPACK and 5 mg (SD 6) with the tibial block, p = 0.36. Pain scores over three days, quadriceps strength, walking distance and range of motion did not differ. Four patients (9%) in the tibial group had motor block of the common peroneal nerve.

Both blocks cover posterior knee pain equally well when added to a femoral triangle block and good systemic analgesia. The deciding factor is the peroneal motor block, which can mimic or mask a surgical peroneal nerve injury and delay mobilisation. That argues for IPACK where it can be performed, or for careful post-block assessment if a tibial block is used.

Use either IPACK or a selective tibial block for posterior knee pain; analgesia was equal.
Check dorsiflexion before and after a tibial block, since 9% had peroneal motor block.
Document a pre-existing foot drop before any posterior knee block.
Tell the surgical team which block was given, so new foot weakness is interpreted correctly.

Why it matters

When two blocks work equally well, the side-effect profile decides, and here that favours IPACK.

The statistics, in plain English

Morphine use of 6 mg versus 5 mg with p = 0.36 means no meaningful difference. With 45 patients per arm, a small difference could be missed, but morphine use was low in both groups, so any missed difference is unlikely to matter clinically.