Background and Aims:
Adductor canal block (ACB) is mainstream for pain management after total knee arthroplasty (TKA). Ultrasound visualization identifies the proper administration of proximal ACB (pACB); however, the large volume of local anesthetics spread proximally may lead the quadriceps deficit. The trial evaluated the potency of pACB with a large or small amount (with the same dose) of levobupivacaine with a double-blinded manner.

Methods:
The informed consents were received from all subjects and approved by IRB (UMIN31890). Subjects was randomized to receiving 25 mg of 0.125% (20mL) or 0.5% (5mL) levobupivacaine. A tibial nerve block and multimodal analgesia protocols were provided. We evaluated the attained hours for the discharge criteria (ambulation, adequate knee flexion, using only oral non-opiate analgesics) as a primary outcome, in addition to the knee flexion beyond 120 degrees, the ability of the straight leg raise (SLR) and other postoperative parameters.

Results
We analyzed each 62 subjects. Median of the hours of the discharge criteria was 55.5 hours in 0.5% and 66 hours in 0.125% (p=0.04). The day of the knee flexion beyond 120 degrees was 6 days in 0.5% and 7 days in 0.125% (p=0.013). The frequency of SLR was 85.4% in 0.5% and 66.1% in 0.125% at immediately after surgery (p=0.02) and 93.5% in 0.5% and 77.4% in 0.125% (p=0.02) on the postoperative day 1.

Conclusions:
The results suggest only small volume (5mL) of 0.5% levobupivacaine administration into pACB attained the earlier discharge, the deep knee flexion, and the quadriceps-sparing after TKA.

2 - Proximal adductor canal block for total knee arthroplasty: randomized trial for comparing two volumes at the same dose