Addition of Morphine to Femoral Nerve Block Improves Post-TKA Analgesia

Administration of epidural morphine during single-injection femoral nerve block may improve pain and quality of life in patients who have undergone total knee arthroplasty.

Administration of epidural morphine at a low dose during single-injection femoral nerve block may improve moderate to severe pain and quality of life within 48 hours, and may lower morphine consumption in patients who have undergone total knee arthroplasty, according to study results published in PLoS One.

A total of 110 patients were randomly assigned to receive morphine (2 mg in 5 mg normal saline) or 5 mg normal saline, both epidurally, during a single-injection femoral nerve block after having undergone total knee arthroplasty. All participants could, in addition, self-administer morphine using a patient-controlled intravenous analgesia pump. Patients were asked to evaluate pain intensity using a 0 to 10 numeric rating scale at 6, 12, 24, 36, and 48 hours after surgery.

Fewer patients who received epidural morphine vs saline reported moderate to severe pain (numeric rating scale score ≥4) within 48 hours of surgery (58.2% vs 76.4%, respectively; odds ratio, 0.43; P =.042). Cumulative morphine consumption was also lower in the intervention vs placebo group (18.4 mg vs 22.4 mg, respectively; P =.002). In addition, patients who were administered epidural morphine vs saline had a higher mental component summary score of 30-day quality of life (63.8 vs 61.9, respectively; P =0.008).

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All participants experienced complete recovery of motor blockage of lower limbs within 6 hours of surgery, and there were no significant between-group differences regarding adverse events.

Study limitations include the inability to generalize findings because of the use of a single setting at a tertiary clinic.

“Our results showed that, for patients following [total knee arthroplasty], the addition of low-dose epidural morphine to single-injection femoral nerve block reduced the percentage with moderate to severe pain within 48 hours. It also decreased the cumulative morphine consumption within 48 hours and improved the mental health-related quality of life at 30 days. This intervention did not increase the incidence of side effects,” concluded the study authors.

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Meng Z-T, Cui F, Li X-Y, Wang D-X. Epidural morphine improves postoperative analgesia in patients after total knee arthroplasty: a randomized controlled trial. PLoS One. 2019;14(7):e0219116.