Background Perineural catheters placed parallel to the nerve course are reported to have lower migration rates than those placed perpendicular to it. However, catheter migration rates for a continuous adductor canal block (ACB) remain unknown. This study compared postoperative migration rates of proximal ACB catheters placed parallel and perpendicular to the saphenous nerve.
Methods Seventy participants scheduled for unilateral primary total knee arthroplasty were randomly assigned for parallel or perpendicular placement of the ACB catheter. The primary outcome was the migration rate of the ACB catheter on postoperative day (POD) 2. Catheter migration was defined as being unable to confirm saline administration via the catheter around the saphenous nerve at the mid-thigh level under ultrasound guidance. Secondary outcomes included active and passive range of motion (ROM) of the knee on postoperative rehabilitation.
Results Sixty-seven participants were included in the final analyses. The catheter migrated significantly less often in the parallel group (5 of 34 (14.7%)) than in the perpendicular group (24 of 33 (72.7%)) (p<0.001). The mean (SD) active and passive knee flexion ROM (degrees) improved significantly in the parallel than in the perpendicular group (POD 1: active, 88.4 (13.2) vs 80.0 (12.4), p=0.011; passive, 95.6 (12.8) vs 85.7 (13.6), p=0.004; POD 2: active, 88.7 (13.4) vs 82.2 (11.5), p=0.036; passive, 97.2 (12.8) vs 91.0 (12.0), p=0.045).
Conclusion Parallel placement of the ACB catheter provided a lower postoperative catheter migration rate than perpendicular placement of the ACB catheter along with corresponding improvements in ROM and secondary analgesic outcomes.
Trial registration number UMIN000045374.
- nerve block
- pain, postoperative
- regional anesthesia
- lower extremity
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A continuous proximal adductor canal block (ACB) is a widely used technique for analgesia after total knee arthroplasty (TKA),1 2 although the possibility of catheter migration is a major drawback of continuous nerve block techniques.3 Perineural catheters can be placed either perpendicular or parallel to the nerve course.4–6 For ultrasound-guided perpendicular catheter placements, the entire boundary of the nerve tissue and the whole needle can be seen, possibly improving the safety of nerve blocks.5–8 However, this technique may lead to insufficient postoperative analgesia due to the frequent occurrence of catheter migration,9 10 compared with that with perineural catheters placed parallel to the nerve.11 12 The difference in catheter migration rates between catheter placement techniques for ACB remains unknown.
This randomized controlled study aimed to evaluate the hypothesis that ACB catheters placed parallel to the nerve would be less likely to migrate from the proximity of the saphenous nerve beneath the sartorius muscle than those placed perpendicular to the nerve.
Written informed consent was obtained from all participants before enrolment. Participants were recruited from Kansai Medical University Hospital between September 2021 and May 2022. Patients aged ≥20 years with American Society of Anesthesiologists physical status I–III who were scheduled for primary unilateral TKA were eligible to participate. The exclusion criteria were as follows: pre-existing lower limb neuropathy, chronic opioid use, allergy to local anesthetics, and inadequate capacity to consent. Participants were randomly allocated to either the parallel or perpendicular group based on a computer-generated randomization table. Sealed opaque envelopes containing individual allocation results were disclosed at the beginning of the peripheral nerve block procedures. Experienced regional anesthesiologists (TF, TN, and AH) performed all peripheral nerve blocks.
First, we marked the mid-thigh, that is, the midpoint between the anterior superior iliac spine and the base of the patella,13 14 on the skin of the participants in a supine position. After sterilizing around the puncture site and giving local infiltration of the skin with 3 mL 1% lidocaine, we performed an ACB and placed a catheter either parallel or perpendicular to the nerve course according to the allocation result.
Under ultrasound guidance (SONIMAGE HS1, KONICA MINOLTA, Tokyo, Japan), a linear transducer (L11-3, KONICA MINOLTA) covered with a sterile sleeve was placed at the mid-thigh to identify the saphenous nerve, located anterolateral to the femoral artery surrounded by the sartorius, vastus medialis, and adductor longus muscles. At the point where the femoral artery lies beneath the medial one-third of the sartorius muscle, the transducer was rotated to obtain a long-axis view of the nerve. Subsequently, a 100 mm 18-gage needle (Contiplex Ultra 360; B. Braun, Melsungen, Germany) was inserted approximately 4–5 cm superolateral to the superior end of the ultrasound transducer and advanced along the course of the saphenous nerve using an in-plane technique. The needle passed through the interfascial plane beneath the sartorius muscle (ie, the subsartorial space) while hydrodissecting the plane with saline. The needle tip was positioned anterolateral to the SN, and 20 mL of 0.25% levobupivacaine was administered to create space for catheter advancement. Afterwards, a catheter with three side holes around the tip (Perifix ONE, B. Braun) was threaded through the needle and further advanced in a direction parallel to the saphenous nerve through the subsartorial space to reach the mid-thigh level. With the transducer placed at the mid-thigh to see the short-axis view of the saphenous nerve, the correct tip position around the saphenous nerve was confirmed sonographically by injecting 1–3 mL of 1% lidocaine via the catheter. The catheter was withdrawn and repositioned when necessary until the appropriate tip position was achieved (figures 1A and 2A).
The saphenous nerve was displayed in the short-axis view of the mid-thigh. At the same level, the needle was inserted perpendicular to the nerve using an in-plane approach in a lateral-to-medial direction under ultrasound guidance. Like the parallel placement, the needle was advanced into the interfascial subsartorial plane using the hydrodissection technique. Afterwards, 20 mL of 0.25% levobupivacaine was administered around the saphenous nerve, and the needle was advanced into the region where the local anesthetic had spread. The catheter was inserted beyond the needle tip by approximately 3 cm, perpendicular to the saphenous nerve, and 1–3 mL of 1% lidocaine was injected through the catheter to confirm the appropriate catheter tip position around the nerve. The catheter was withdrawn and repositioned when necessary until the correct tip position was achieved (figures 1B and 2B).
All catheters were secured to the skin using cyanoacrylate adhesive and a transparent dressing in both groups.
A selective tibial nerve block was performed immediately after ACB catheter placement, with participants in the supine position with their hip and knee joints flexed. A 10 mL of 0.25% levobupivacaine was injected into the proximity of the tibial nerve using an in-plane approach with an 80 mm 22-gage needle (Perican, B. Braun).
After the peripheral nerve blocks, all participants underwent general anesthesia with a supraglottic airway. Anesthesia was induced with propofol, remifentanil, and rocuronium, and was maintained with remifentanil and sevoflurane during surgery. Additionally, all participants received dexamethasone (6.6 mg) intravenously as an antiemetic drug. In all participants, the same surgical team performed TKA using the medial parapatellar approach, employing a thigh tourniquet intraoperatively. Local infiltration anesthesia was not used intraoperatively. Following the surgical procedure, acetaminophen 1000 mg was administered intravenously. A continuous ACB with 0.125% levobupivacaine at a 4 mL/hour rate was initiated immediately after surgery using an elastic infusion pump with no bolus option. Approximately 30 min after emerging from general anesthesia, participants were transferred to the ward. Postoperatively, all participants received 500 mg of oral acetaminophen four times daily and 60 mg of loxoprofen as rescue analgesia. Participants attempted to ambulate with the caregiver’s assistance on postoperative day (POD) 1. A postoperative standardized rehabilitation program was performed once daily from POD 1.
The primary outcome was the migration rate of the ACB catheter assessed after rehabilitation on POD 2. Secondary outcomes included: (1) the Numerical Rating Scale for pain (NRS) (no pain, 0 and worst pain imaginable, 10) at rest and during knee flexion 2 hour postoperatively; (2) NRS at rest and during rehabilitation on POD 1 and 2; (3) 6 min ambulation distance measured when asked to walk as long as possible on POD 1 and 2; (4) knee range of motion (ROM) during rehabilitation on POD 1 and 2; (5) participant satisfaction on a scale of 0–10 (complete absence of satisfied, 0 and very satisfied, 10); (6) the total number of rescue analgesic use 48 hours postoperatively; (7) catheter insertion length from the skin to the catheter tip; and (8) postoperative complications, including knee buckling, postoperative nausea and vomiting, falls, and local anesthetic leakage around the skin of the catheter insertion site.
We assessed the occurrence of catheter migration by administering 10 mL saline at a rate of approximately 2 mL/sec via the catheter under ultrasound at the predefined mid-thigh level. Videos of the saline injection process were recorded. An experienced regional anesthesiologist (TY) blinded to the group allocation determined the occurrence of catheter migration based on the clips. Catheter migration was defined as the absence of the administered saline via the catheter within the perineural space of the saphenous nerve surrounded by the sartorius, vastus medialis, and adductor longus muscles. Pain scores and function-related outcomes were evaluated during rehabilitation conducted on POD 1 and 2 by physical therapists blinded to the allocation. The ward nurses blinded to the allocation examined participant satisfaction after catheter removal.
Based on a previous report showing that 40% of postoperative popliteal sciatic catheters placed perpendicular to the nerve migrated postoperatively,13 we assumed that ACB catheters placed perpendicular to the nerve would have a similar chance of migration. Accordingly, 32 cases per group were required to statistically detect a 30% difference in the catheter migration rate between the two catheterization methods, with a type 1 error of 5% and power of 80%. Considering a drop-out rate of 10%, 70 participants (35 participants per group) were included in this study.
Normally distributed continuous variables were analyzed using Student’s unpaired t-test, whereas non-normally distributed continuous and discrete variables were analyzed using the Mann-Whitney U test. Categorical variables were analyzed using Fisher’s exact test. Values were presented as mean (SD) or as median (IQR (range)). Statistical significance was set at p<0.05, using a two-tailed analysis for the primary outcome assessment. No adjustments were made for multiple comparisons; thus, the secondary outcomes of this study should be considered suggestive findings. All statistical analyses were performed using GraphPad Prism V.9 for Mac OS X V.9.40 (GraphPad Software, San Diego, California, USA).
Seventy participants were randomly assigned to one of the groups, and 67 participants were ultimately analyzed (figure 3). In one patient of the perpendicular group, the catheter was found to be detached from an antibacterial filter on POD 1. Then, the whole catheter was removed immediately, considering contamination issues. In the parallel group, one patient’s catheter unintentionally came out entirely in the morning of POD 2 when a dressing over the catheter insertion site was removed due to sweating. These patients were included in the final analyses in an intention-to-treat analysis fashion, and the catheters were deemed as ‘migrated’ concerning the primary outcome. The participants’ demographics and characteristics at baseline are shown in table 1. The catheter migrated in 5 of 34 participants (14.7%) in the parallel group, whereas 24 of 33 participants (72.7%) in the perpendicular group experienced catheter migration (p<0.001). The maximum NRS scores at rest and during rehabilitation on POD 1 and 2 were significantly lower in the parallel group than in the perpendicular group (table 2). Knee flexion ROM on POD 1 and 2 was significantly greater in the parallel group (table 2). Additionally, the participant satisfaction score was significantly higher in the parallel group than the perpendicular group (table 2). The mean (SD) catheter insertion lengths from the skin puncture site to the catheter tip in the parallel and perpendicular groups were 14.9 (0.5) and 11.5 (1.4) cm, respectively (p<0.0001).
One participant in the parallel group experienced a fall after surgery. Moreover, four participants in the perpendicular group experienced local anesthetic leakage from the catheter insertion site, whereas no participants in the parallel group experienced leakage (p=0.053). No other block-related complications were observed.
Our study showed that proximal ACB catheters placed parallel to the saphenous nerve, through the subsartorial space, had a lower catheter migration rate than those placed perpendicularly to the saphenous nerve. Parallel placement of ACB catheter also improved knee flexion ROM and other analgesic outcomes after TKA.
This study has some limitations. First, the block performers knew the study allocation. Besides, because both catheter placement techniques used different insertion sites, it was challenging to blind the examiners who recorded the video of the saline injection process. Second, catheter migration was defined as the absence of perineural infiltration of saline at the mid-thigh; thus, the exact catheter tip position in both the parallel and the perpendicular groups may not have been observed. Moreover, the timing of catheter migration remains unclear. Third, we did not assess the actual area of sensory loss to confirm the success of the nerve blocks. Fourth, we used a relatively stiff catheter; thus, the current results may not apply to blocks using more flexible catheters. Also, suture-method catheters could better stay in situ than usual block catheters even with the perpendicular placement.15 Fifth, the average body mass index of this study participants could be smaller than that of similar patient populations in other countries. A bigger body habitus may make parallel catheter placement more difficult. Lastly, only one assessor determined whether the catheter tip stayed at the optimal position based on the video clips in the present study. The reproducibility of this assessment could have been evaluated if multiple assessors had been employed.
Compared with proximal ACB catheters placed perpendicular to the saphenous nerve, those placed parallel to the saphenous nerve provide a lower catheter migration rate, along with improved measures of ROM and postoperative analgesia.
Patient consent for publication
This study involves human participants and was approved by Ethical Committee of Kansai Medical University Hospital (approval number: 2021113). Participants gave informed consent to participate in the study before taking part.
The authors thank the nurses, anesthesiologists, physiotherapists, and orthopedic surgeons from Kansai Medical University Hospital who were involved in this study for their support, as well as Kota Kato from the Department of Anatomy and Life Structure at Juntendo University Graduate School of Medicine for the artwork.
TF and TN contributed equally.
Contributors TF, TN and TY: study conception and the design. TF and TN: participant recruitment. TF and TN, AH and TH: data collection and study conduct. TY: data analysis. TF: manuscript preparation. TN, TY and IK: Revision of drafts. All authors read and approved the final manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.