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Abstract
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Background and Aims The adductor canal block relieves pain on the anterior aspect of the knee after arthroplasty. Pain on the posterior aspect might be treated either by partial local infiltration analgesia of the posterior capsule or by a tibial nerve block This randomised, controlled, triple-blinded trial tested the hypothesis that a tibial nerve block would provide superior analgesia than a posterior capsule infiltration in patients scheduled for total knee arthroplasty under spinal anaesthesia with an adductor canal block.
Methods Sixty patients were randomised to receive either an infiltration of the posterior capsule by the surgeon with ropivacaine 0.2%, 25mL or a tibial nerve block with ropivacaine 0.5%, 10mL. Sham injections were performed to guarantee proper blinding.
Results The primary outcome was intravenous morphine consumption at 24h. Secondary outcomes included intravenous morphine consumption, pain scores at rest and on movement, and different functional outcomes, measured at up to 48h. When necessary, longitudinal analyses were performed with a mixed-effects linear model. The median (interquartile range) of cumulative intravenous morphine consumption at 24h was 12mg (4–16) and 8mg (2–14) in patients having respectively the infiltration or the tibial nerve block (p=0.20). Our longitudinal model showed a significant interaction between group and time in favour of the tibial nerve block (p=0.015).
Conclusions No significant differences were present between groups in the other above-mentioned secondary outcomes. In conclusion, a tibial nerve block does not provide superior analgesia when compared to infiltration. However, a tibial nerve block might be associated with a slower increase in morphine consumption along time.