•Osteoarthritis (OA), a debilitating and life-altering condition, presents an escalating health challenge as populations in the United States and other developed nations experience increased life expectancy and body mass index (BMI)1,2.

•Intrathecal morphine (ITM) provides effective postoperative analgesia in patients undergoing total knee arthroplasty (TKA) under spinal anesthesia when compared to control3.

•However, the ideal dose at which maximal analgesic effects can be delivered with minimal side effects is not clearly known.

•This retrospective study is aimed to compare two different doses of ITM with respect to analgesia benefits and side effects.