- Design
- Participant-blinded and assessor-blinded randomised controlled trial
- Population
- 94 patients undergoing primary unilateral total knee arthroplasty, all receiving iPACK block, periarticular infiltration and standardised oral analgesia
- Primary outcome
- Opioid consumption during the 24-48 hour postoperative period
- Effect
- Median 30 mg (IQR 15-60) with catheter vs 38.8 mg (22.9-69.4) single injection; 95% CI of median difference -22.50 to 7.00 mg, p=0.213; catheter buckling in 7%
Rebound pain after the adductor canal block wears off is the standing argument for a continuous catheter after total knee arthroplasty. Catheters cost time to place, need infusion equipment, complicate mobilisation and fail mechanically. This participant- and assessor-blinded randomised trial tested whether the catheter earns any of that.
94 patients having primary unilateral knee arthroplasty were randomised to a single-injection adductor canal block - 15 mL of 0.25% bupivacaine with 2 mg perineural dexamethasone - or the same single injection followed by a continuous catheter running 0.2% ropivacaine at 8 mL/hour for 50 hours. Both groups received the same multimodal regimen: iPACK block, periarticular infiltration and oral analgesia.
Opioid consumption during the 24-48 hour window - the period the catheter exists to cover - did not differ: median 30 mg (IQR 15-60) with the catheter against 38.8 mg (22.9-69.4) without, 95% CI of the median difference -22.50 to 7.00, p=0.213. Recovery room opioid use did not differ either. Catheter buckling occurred in 7% of the catheter group and none of the single-injection group, all transient. No difference in satisfaction, length of stay or functional recovery.
The trial is small at 94 patients and the confidence interval is wide enough that a real reduction of up to 22 mg cannot be excluded, so this is not proof of equivalence. What it does show is that the catheter's advantage, if any, was not demonstrable against a single injection containing perineural dexamethasone plus a good multimodal regimen - and the comparator matters, because a bare single-injection block without dexamethasone is a different comparison.
So where perineural dexamethasone, an iPACK block and periarticular infiltration are already in the pathway, the catheter is hard to justify. That conclusion travels well to Indian practice, where infusion pumps and catheter follow-up are the scarce resources and the single injection is deliverable everywhere.
- Add 2 mg perineural dexamethasone to the single-injection adductor canal block rather than placing a catheter
- Keep the rest of the multimodal regimen - iPACK, periarticular infiltration and oral analgesia were in both arms
- Note the comparator: this does not compare a catheter with a plain single injection
- Catheter buckling occurred in 7% - a real failure mode that costs ward time
- Ninety-four patients: the interval does not exclude a modest catheter benefit
The statistics, in plain English
A p value of 0.213 means no difference was demonstrated, not that the two are equivalent - the 95% interval for the median difference runs from -22.50 to +7.00 mg, so a clinically useful reduction of 20 mg morphine equivalent remains compatible with these data. With 94 patients and a highly skewed outcome, reported as medians with wide interquartile ranges, this trial was only ever going to detect a large effect. Note also that the prespecified secondary outcome was recovery room opioid use; everything else was exploratory and prespecified only in the local protocol, which is a weaker guarantee than trial registration.
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