Eighty-nine patients undergoing elective primary total knee arthroplasty (TKA) were randomized to receive an intraoperative intraosseous injection of morphine (10 mg) and vancomycin (500 mg) in normal saline or an identical intraosseous injection containing vancomycin without morphine. The outcomes of interest were postoperative pain scores, postoperative opioid consumption measured in morphine milligram equivalents (MME), nausea and vomiting events, post anesthesia care unit (PACU) pain scores, and PACU opioid consumption. Outcomes were assessed through patient-reported surveys collected six times daily for 14 days postoperatively. Overall, the results of the study revealed no statistically significant differences in postoperative pain scores or opioid consumption between the experimental and control groups. These findings suggest that intraoperative intraosseous morphine does not improve short-term postoperative pain control after TKA.