OBJECTIVE The authors conducted an unfunded randomized controlled trial approved by the Brooke Army Medical Center (BAMC) Institutional Review Board (IRB) to determine the possible efficacy of intra-articular morphine for pain in acute knee injuries. METHODS Patients presenting to the emergency department at San Antonio Military Medical Center (SAMMC) from May 2012 to August 2013 with knee pain due to an acute injury were consented and then enrolled based on a convenience sample. Patients were randomized to one of three intervention arms (morphine, lidocaine, or morphine and lidocaine) and were blinded to the intervention. The respective solution was injected into the knee joint using standard techniques. The patients self-reported their levels of knee pain via a standard 100mm visual analogue scale (VAS) at the time of injection and 30 minutes, 60 minutes, 90 minutes, 2 hours, 6 hours, and 24 hours postinjection. At 24 hours, the patients also reported the estimated amount of time they applied ice to the knee and the amount of oral analgesia consumed in the previous 24 hours. RESULTS The primary outcome was relative pain reduction as measured by the VAS. Secondary outcomes were the total cumulative use of ice and analgesics during the first 24 hours. Although this was a small study, the results showed a possible trend toward better pain control at all time intervals with injections containing morphine compared with lidocaine-only injections. Ice and oral analgesia usage was equivalent between the three intervention arms. CONCLUSIONS Further investigation with a larger sample is required to explore whether these results are statistically significant and the possible superiority of intra-articular morphine to lidocaine for acute knee pain.