Patients undergoing staged bilateral total knee arthroplasty (TKA) can gain greater relief from tertiary hyperalgesia if treated with magnesium sulphate, according to a study presented here at the World Congress on Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (WCO).
“Administration of magnesium significantly reduced postoperative pain and the difference in pain intensity between the first and second operated knee in staged bilateral TKA. These observations suggest that magnesium attenuates tertiary hyperalgesia induced by surgical injury,” stated Hyun-Jung Shin, PhD, Department Anesthesiology and Pain Medicine/Seoul National University Bundang Hospital, Seongnamsi, Republic of Korea, and colleagues on April 15.
The repeated invasive surgery that is inevitable in staged bilateral TKA can result in tertiary hyperalgesia. The increased pain sensitivity may to the result of central sensitisation, a process in which the nervous system becomes regulated in a persistently high reactive state. Magnesium sulphate dampens N-methyl-D-aspartate receptor activity, which diminishes central sensitisation.
The foregoing prompted the researchers to examine the possible benefit of magnesium sulphate on tertiary hyperalgesia in 44 patients undergoing staged bilateral TKA. At random, 22 patients were given oral magnesium sulphate 50 mg/kg 15 minutes before surgery, with intravenous infusion provided continuously throughout surgery. The other 22 patients received a sham pill and the same volume of saline intravenously during surgery (control group).
Resting postoperative pain was ranked by use of a numerical rating scale. The quality of patient-controlled fentanyl and intravenous ketoprofen used as rescue analgesics in the first 48 hours after the 2 surgeries were compared between the 2 groups.
Resting postoperative pain was greater in the control group than in the magnesium group at 24 and 48 hours postoperative in the first TKA and in the second TKA (all P < .001).
More rescue analgesics were used in the 48-hour postoperative period after the second TKA in the control group than in the magnesium group (P = .001). Postoperative patient-controlled fentanyl use was significantly greater in the control group than in the magnesium group at 24 (P = .014) and 48 (P = .001) hours.
In the control group, surgery on the second knee was more painful, with 24- and 48-hour postoperative pain scores significantly higher (P < .001 and P = .006, respectively) and greater quantities of rescue analgesics used (P = .011 and.004, respectively) than after the first knee surgery. Fentanyl use in the first 48 hours after surgery was greater after the second TKA than after the first TKA (P < .001).
In the magnesium group, postoperative pain was not significantly different at 24 or 48 hours between the first and second knee surgeries. However, in the second surgery, more rescue analgesic was used in the first 24 (P = .021) and 48 (P = .004) hours after surgery.
The results indicate the benefit of magnesium sulphate as a method of pain relief in staged bilateral TKA. The easily performed measure warrants more consideration.