by Elizabeth Hofheinz, M.P.H., M.Ed.
While spinal anesthesia confers benefits when administered during primary total hip arthroplasty (THA) and total knee arthroplasty (TKA), say the authors of a new Mayo Clinic study, the long-acting local anesthetics result in a “slow” and “unpredictable” return of lower-extremity motor function.
Their double-blinded, randomized clinical trial, “More Predictable Return of Motor Function with Mepivacaine Versus Bupivacaine Spinal Anesthetic in Total Hip and Total Knee Arthroplasty,” was published in the June 26, 2020 edition of The Journal of Bone and Joint Surgery.
Co-author Matthew Abdel, M.D. is Professor of Orthopedic Surgery at the Mayo Clinic College of Medicine and Consultant of Adult Reconstruction at the Mayo Clinic. Dr. Abdel told OSN, “Over the past several years, I co-chaired a surgical efficiency project at the Mayo Clinic entitled OASIS (Orthopedic Surgery and Anesthesiology Surgical Improvement Strategies). Through that, we identified limitations within the practice, and noticed one area for improvement was short-acting spinal anesthetics that were more reliable in duration.”
Would another local anesthetic—mepivacaine—come with a more consistent return of motor function?
To begin to answer that question, the researchers conducted an internal pilot study before the trial, finding that 154 patients were necessary in order to achieve the 80% power level. A 1:1 randomization was undertaken, and participants were stratified based on procedure, age group, sex, and body mass index. Postoperative motor function was assessed every 15 minutes in the nonoperative lower extremity.
“Among patients who received mepivacaine, 1% achieved motor function return beyond 5 hours compared with 11% of patients who received bupivacaine,” wrote the authors. “The mean time to return of lower-extremity motor function was 26 minutes quicker in patients who received mepivacaine (185 minutes; 95% confidence interval, 174 to 196 minutes) compared with low-dose bupivacaine (210 minutes; 95% confidence interval, 193 to 228 minutes) ). There were no significant differences in safety outcomes including pain scores, time to participation in physical therapy, incidence of orthostatic hypotension, urinary retention, or transient neurologic symptoms in patients receiving mepivacaine compared with low-dose bupivacaine.”
Dr. Abdel told OSN, “The key finding in this study was that mepivacaine allowed for more consistent return of lower-extremity motor function compared with low-dose bupivacaine. In the future, we plan on looking at smaller doses of mepivacaine spinals, as well as other methods to mitigate opioid use when performing lower extremity total join arthroplasty.”