Investigating the Effect of Perioperative Chlorzoxazone On Acute Postoperative Pain After Total Hip and Knee Replacement Surgery

BACKGROUND AND AIMS: Severe pre- and acute postoperative pain have been associated with development of chronic postoperative pain. Chlorzoxazone (a muscle relaxant) has been suggested to enhance acute postoperative pain recovery but the lack of larger randomized controlled trials have however questioned the continued use. Despite this, chlorzoxazone is still used for acute postoperative pain management following total knee or hip replacement (TKR or THR). The currentrandomized, double blinded, placebo-controlled, parallel group, clinical trial aimed to assess the effect of chlorzoxazone for postoperative pain management following TKR or THR.

METHODS: 393 patients scheduled for TKR or THR were included in the trial. Patients were assigned to 250▒mg chlorzoxazone three times daily for the first seven days postoperative or placebo. The primary outcome was pain after 5 meter walk assessed 24-hours postoperative. Secondary outcomes included, changes in preoperative pain at rest, worst pain in the last 24 hours, and Oxford Knee or Hip Score compared with 12 months follow-up. In addition, adverse events were assessed in the perioperative period.

RESULTS: No significant differences were found for any of the outcome parameters after TKR or THR. For neither TKR or THR no effects were demonstrated for pain after 5 meters walk 24-hours after surgery (P>0.313), or for any of the secondary outcomes (P>0.288) or adverse event (P>0.112) in the group receiving chlorzoxazone compared with placebo.

CONCLUSIONS: The current study demonstrated no analgesic effects of postoperative chlorzoxazone administration compared with placebo on acute or chronic postoperative pain 12 months following TKR and THR.