Analgesic efficacy of the intra-articular administration of high doses of morphine in patients undergoing total knee arthroplasty.

BACKGROUND AND OBJECTIVES Although the efficacy of intraarticular (IA) morphine is still controversial, it has been shown that higher doses promote better results and consequently decrease postoperative analgesic consumption, characterizing a dose-dependent peripheral action. A controlled, randomized, double-blind study was undertaken to evaluate the efficacy of the intra-articular administration of 10 mg of morphine in patients undergoing total knee arthroplasty. METHODS Fifty patients undergoing total knee arthroplasty were randomly divided into two groups: the treatment group received 10 mg (1 mL) of intra-articular morphine diluted in 19 mL of NS, while the control group received the intra-articular administration of 20 mL of NS, both after closure of the capsule at the end of the surgery. On demand subcutaneous morphine was available for residual pain. The following parameters were evaluated: pain severity according to the numeric scale (NS), 2 h (M1), 6 h (M2), 12 h (M3), and 24 h (M4) after the IA injection; time until the first request of analgesic; analgesic consumption, and side effects. CONCLUSIONS The treatment group had lower NS than the control group in M1 and M2, while significant differences were not observed in the other moments. The time until the first request of analgesics was significantly higher in the treatment group, and analgesic consumption in the first 24 hours was also lower in this group. The incidence of side effects did not differ between both groups. We concluded that the postoperative IA administration of 10 mg of morphine promoted a longer period without rescue analgesics and reduced their consumption in the first 24 hours.