To investigate the effects of modified continuous adductor block on motor function after total knee arthroplasty (TKA).

A total of 80 patients were enrolled in the study. All the patients were in grade I to III of American Society of Anaesthesiologists (ASA), in normal preoperative cognitive function and assigned for elective total knee arthroplasty. Patients with history of contralateral knee surgery within three months, spinal surgery within six months and allergy to local anaesthetics were excluded from the study. The patients were randomly divided into a modified adductor canal block group (as modified group) and a femoral nerve block group (as femoral group), with 40 cases per group. The primary assessments of postoperative outcome were the muscle strength of quadriceps at four, eight, 12, 24 and 48 h, and the time-up-and-go test (TUG) on first and second day after surgery. Secondary assessments of postoperative outcome included resting at four, eight, 12, 24, and 48 h after surgery, 45° knee flexion and visual analogue scale (VAS) of activity, also the number of patients with popliteal hypoanalgesia and the number of patients received remedial analgesia within 48 h after surgery. Serum C-reactive protein (CRP) and interleukin-6 (IL-6), also the circumference of the middle patella were monitored on the first day and third day after surgery. Repeated measurement of variance was used to evaluate the repeated measurement data, and the independent sample t test was employed for comparison between groups.

The muscle strength of quadriceps and TUG tests in the modified group were better than in the femoral group at 48 h after surgery (F=11.680, t=12.155, 5.892, all P<0.05). Twelve patients (34.3%) in the modified group had popliteal hypoalgesia at four hours after surgery (P<0.001) and five (14.3%) at eight hours. There was no popliteal hypoalgesia in the femoral nerve group. There was no statistically significant differences between the two groups in postoperative VAS score, ropivacaine dosage, and number of patients with remedial analgesics, inflammatory reaction and incidence of complications. (all P>0.05).

Modified continuous adductor canal block after TKA has less influence on quadriceps muscle strength, but to promote an early postoperative effect on popliteal analgesia. It can significantly improve the postoperative movement of patients.