Background: Adductor canal (AC) catheters are being used to provide continuous postoperative analgesia after total knee arthroplasty (TKA) surgery. There are anatomical arguments that most AC catheters are being inserted into the femoral triangle (FT) compartment of the thigh rather than the AC compartment. The clinical relevance of this is unknown with respect to motor weakness, quality of analgesia, and opioid consumption. We hypothesised that AC catheters provide superior functional mobilisation on postoperative Day 1 after TKA as measured using the Timed Up and Go (TUG) test. Methods: In this multinational, multicentre, double-blinded RCT, catheters were inserted under ultrasound guidance into the anatomical AC and FT compartments. The standardised protocol included spinal anaesthesia without intrathecal morphine, fixed catheter infusion rates, and oral analgesia. Results: Of 151 subjects recruited, 75 were in the AC group and 76 in the FT group. There was no statistically significant difference in TUG on postoperative Day 1 between AC (38 [29e55] s) and FT subjects (44 [32e64] s) (median [inter-quartile range]); P¼0.11). There was no difference in TUG Day 2, AC (38 [27e53] s) vs FT (42 [31e59] s); P¼0.66. There were no statistically significant differences for secondary endpoints of pain level, effectiveness of pain relief, interference of functional activities and interpersonal relationships by pain, and opioid consumption between groups. Conclusions: There were no differences in immediate postoperative functional mobility, analgesia, and opioid consumption provided by catheters inserted into the AC vs FT locations for TKA surgery. Clinical trial registration: ANZCTR12617001421325.