We performed a randomised, blinded, controlled study with adult patients scheduled for primary total knee arthroplasty under spinal anaesthesia. The aim was to investigate the analgesic effects of adductor canal block using catheter-based repeated boluses, either through a new suture-method catheter or a standard perineural catheter, compared with a single-injection technique. All patients received an adductor canal block after surgery with an initial bolus of 20 ml ropivacaine 0.75%, followed by 20 ml of ropivacaine 0.2% every 8 h in the standard and suture-method catheter groups, and sham boluses for the single-injection group. The primary outcome measure was total opioid consumption (intravenous morphine equivalents) from the end of surgery until 12:00 on postoperative day 2. Secondary outcomes were pain, muscle strength and ambulation. We randomly assigned (1:1:1) and analysed 153 patients. Total opioid consumption was median (IQR [range]) 24 (11–37 [0–148]) mg in the suture-method group, 38 (17–51 [0–123]) mg in the standard catheter group and 37 (14–57 [0–158]) mg in the single-injection group (p = 0.049). Differences were not statistically significant after Bonferroni correction (α = 0.05/3). There were no differences between groups on postoperative day 1. On postoperative day 2, there were no differences between catheter groups, but muscle strength and ambulation were improved compared with the single-injection group. We conclude that providing repeated boluses via a catheter did not decrease opioid consumption or pain compared with a single injection, but improved muscle strength and ambulation on postoperative day 2. The two types of catheters were similar.