Efficacy and safety of intrathecal morphine in total knee arthroplasty: A systematic review and meta-analysis

Objective: Morphine is a potent analgesic used to manage the pain following total knee arthroplasty (TKA). We aim to assess the safety and efficacy of intrathecal morphine (ITM) compared with placebo following TKA. Methods: We systematically searched four databases for trials that study the safety and efficacy of ITM in TKA. From relevant studies, data were extracted and pooled as mean difference (MD) or standardized mean difference (SMD) with 95 percent confidence interval (CI) using Review Manager software (Version 5.3). Results: We included six randomized controlled trials in our study. ITM significantly reduced pain scores at 4 hours (SMD = -0.82, 95 percent CI [-1.52, -0.12], p = 0.02) and 24 hours (MD = -2.01, 95 percent CI [-2.93, -1.09], p = 0.0001) after surgery compared to placebo. No statistically significant difference in cumulative morphine use or nausea episodes was observed after 24 hours. ITM increased the risk of pruritus more than placebo (relative risk [RR] = 4.82, 95 percent CI [2.34, 9.93], p<0.0001). Conclusion: ITM reduces pain at 4 and 24 hours post-operatively with no effect on cumulative morphine consumption. The only feared side effect is pruritus.