AbdelQadir, Y. H., A. E. Nabhan, E. A. Abdelghany, A. G. Mohamed, A. S. E. Tokhey, A. A. Elmegeed, A. Z. Nourelden, and K. M. Ragab. “Efficacy and Safety of Intrathecal Morphine in Total Knee Arthroplasty: A Systematic Review and Meta-Analysis”. Journal of Opioid Management, vol. 17, no. 5, Sept. 2021, pp. 405-16, doi:10.5055/jom.2021.0674.