Mepivacaine versus bupivacaine spinal anesthesia for return of motor function following total knee arthroplasty: a randomized controlled trial.

Background: Demand for same-day discharge pathways and early ambulation following knee arthroplasty continues to increase. While spinal anesthesia with mepivacaine versus bupivacaine may promote return of motor function and ambulation, there are limited randomized trials evaluating this in knee arthroplasty patients. This study hypothesized that spinal mepivacaine would result in earlier return of motor function, promoting ambulation and same-day discharge.

Methods: Patients undergoing primary total knee arthroplasty (n=163) were enrolled and randomized patients to mepivacaine (60 mg) or isobaric bupivacaine (10 mg) for spinal anesthesia. The primary outcome was time to return of motor function. Additional outcomes included time to first ambulation, distance at first ambulation, same-day discharge rate, length of stay, postoperative pain, opioid consumption, and side effects.

Results: Patients receiving a mepivacaine spinal anesthetic had faster median (95% CI) time to return of motor function, (210 min (200, 216) vs 229 (223, 237) min, p<0.001) and lower rates of urinary retention (36% vs 57%, p=0.007). Mepivacaine patients exhibited higher pain scores in the post-anesthesia care unit (32.4 vs 9.5 mm, p<0.001) but no differences at 6, 24, or 48 hours postoperative. Opioid consumption did not differ at any time point (p=0.769). There were no differences in time to first ambulation, distance at first ambulation, same-day discharge rate, length of stay, nausea, vomiting, pruritus, or transient neurological symptoms between groups.

Conclusions: Although mepivacaine expedited return of motor function after knee arthroplasty, a clinically relevant 20% reduction was not observed. Ambulation times and same-day discharge rates did not differ.

Trial registration number: NCT05765682.