Increased flexion and reduced hospital stay with continuous intraarticular morphine and ropivacaine after primary total knee replacement: open intervention study of efficacy and safety in 154 patients.

Background: A single injection of bupivacaine after wound closure reduces the need for analgesics and increases flexion after total knee replacement (TKR). We have therefore studied the effect of continuous injection of morphine and ropivacaine after TKR on range of movement and length of hospital stay.

Patients and methods: In an open intervention study, we assigned 154 consecutive patients who had primary unilateral TKR for osteoarthrosis. The intervention was continuous intraarticular injection of morphine 20 mg/mL, 0.5 mL plus ropivacaine 2 mg/mL, 100 mL; bolus 20 mL and 2 mL/hour from 24 to 72 hours postoperatively. Group 1 (10 women and 8 men) received standard postoperative analgesics and group 2 (11 women and 7 men) also received continuous intraarticular morphine and ropivacaine as described above. Group 3 (14 women and 4 men) received double this dose (4 mL/hour) from 24 to 72 hours postoperatively. To assess the safety of the intraarticular treatment, an additional group of 100 consecutive patients was followed (group 4).

Results: At discharge, flexion was 70 degrees (60-100) in group 1, 100 degrees (70-115) in group 2 and 110 degrees (90-130) in group 3. Hospital stay was reduced from 9 (7-11) days in group 1, to 7 (5-10) days in groups 2 and 3. Number of days elapsed until the patient was walking with crutches was reduced from 5 (3-8) to 4 (3-6) and 3 (3-9), respectively. In the intervention groups, the need for analgesics was reduced during the hospital stay. Deep infection was registered in 1 patient.

Interpretation: Continuous intraarticular morphine and ropivacaine reduce pain and enhance rehabilitation after total knee replacement. Before advocating this as a standard procedure, further large-scale randomized studies will be needed to assess the safety of this regimen.