Positioning the Catheter Tip Anterior or Posterior to the Saphenous Nerve in Continuous Adductor Canal Block: A Mono-Centric Retrospective Comparative Study

Background and aim: Ultrasound-guided continuous adductor canal block (cACB) is a conventional choice in patients undergoing total knee arthroplasty (TKA) for the management of the postoperative pain. This study aims to compare different catheter tip locations for cACB relative to the saphenous nerve (anteriorly vs posteriorly) in terms of efficacy and complications. Methods: At the department of Surgical Sciences, Orthopedic Trauma and Emergencies of the University of Naples Federico II (Naples, Italy), between January 2020 and November 2021, retrospective comparative study was executed. Patients planned for TKA were included in the study if they met the follow inclusion criteria: patients undergone TKA; aged 50-85 years; body mass index (BMI) of 18-35 kg/m2; American Society of Anesthesiologists (ASA) physical status classification from I to III; subarachnoid technique for anesthesiology plane; continuous adductor canal block performed by an anesthetist with considerable experience. Patients were assigned to receive cACB with the catheter tip located anteriorly (Group 1, G1) or posteriorly to the saphenous nerve (Group 2, G2). Postoperative pain, ambulation ability, episodes of pump block and rate of catheter dislodgement and leakage were evaluated and analyzed. Results: Altogether, 102 patients were admitted to the study (48 in G1 and 54 in G2). After the first 8 postoperative hours, in G1 17 patients (35.4%) had a VAS greater than 4, while in group 2 only 3 patients (5.6%) had a VAS greater than 4 (p-value <0.01). All patients of both groups showed ambulation ability in the postoperative period. No episode of leakage was recorded. While the catheter displacement rate was similar in the two groups (2.1% for G1 vs 3.7% for G2; p-value >0.05), the episodes of pump block were significantly less in G2 than in G1 (3.7% vs 20.8%; p-value <0.01). Conclusion: In cACB for TKA, we found that positioning the catheter tip posteriorly to the saphenous nerve may lead to a greater postoperative analgesia and reduce the risk of pump block compared to placing the catheter tip anteriorly to the nerve.