Does parallel versus perpendicular catheter placement for a subsartorius approach to a continuous adductor canal block influence injectable distribution? A comparative cadaveric study
Year: 2025
Type: article
Abstract: INTRODUCTION Catheter insertion for continuous adductor canal block (CACB) typically requires positioning the catheter perpendicularly, with its tip adjacent to the saphenous nerve (SN) within the adductor canal (AC). However, despite proper fixation to the skin, the catheter tip can dislocate from the canal, particularly during postoperative physical therapy.[1] An alternative technique involves placing the catheter parallel to the nerve, with the needle positioned anteriorly through the sartorius muscle (SM) and aligned longitudinally along the SN.[2] Another approach places the catheter perpendicularly, with its tip situated between the SM and the superficial femoral artery,[3] a technique similar to our routine procedure.[4] Studies suggest a lower incidence of migration compared to the classical technique. Research on continuous peripheral nerve block migration indicates that catheter displacement is less frequent when placed parallel rather than perpendicular to a nerve.[5,6] However, previous studies have focused on single peripheral nerve placements, unlike CACB, which targets multiple nerves, including the SN and the nerve to vastus medialis (NVM). Variations in catheter placement for continuous targeted blockade of multiple nerves may affect the solution distribution to each nerve, and differing infusion concentrations within the AC might impact blockade effectiveness. This cadaver study aims to: (1) compare the anatomical distribution patterns of dye between parallel and perpendicular CACB catheter placements using a subsartorial approach, (2) evaluate the extent of dye staining on the SN and NVM within the adductor canal, and (3) assess the spread of dye beyond the adductor canal with each technique. We hypothesised that different catheter orientations would result in different patterns of dye distribution within the anatomical spaces. METHODS This study was exempted by the Institutional Review Board of the Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand (IRB approval no.: 0870/67 dated November 3, 2024, certificate no. 077/2024) in accordance with international guidelines for human research protection, including the Declaration of Helsinki, The Belmont Report, CIOMS Guidelines, and International Conference on Harmonization in Good Clinical Practice. The study was conducted between September and November 2024. Four modified Thiel soft-embalmed cadavers (two women and two men) were selected from donations to the Department of Anatomy, Chulalongkorn University. Additional consent was not required for the study. Cadavers with defects or scars in the hip, thigh, or knee regions were excluded. Each technique was applied randomly to the limbs by using a coin toss. The first technique was assigned to one limb, and the other technique was applied to the contralateral limb. A single investigator (WK) performed all the procedures. Parallel technique for CACB: Cadavers were positioned supine with thighs abducted and externally rotated. An ultrasound-guided bolus of 10 mL (0.5 mL methylene blue and 9.5 mL normal saline) was injected, followed by a continuous infusion of 0.05% methylene blue at 5 mL/h using an elastomeric infusion pump (Surefuser, NIPRO Corp., Osaka, Japan) and a 13–3 MHz linear probe (Sonimage HS1, Konica Minolta, Japan). The proximal AC was identified where the SN lies laterally to the femoral artery (FA), encircled by the SM, vastus medialis, and adductor longus muscles. A transducer was then rotated to obtain a long-axis view of the SN and FA. An 80-mm, 18-G needle was inserted in a cephalad-to-caudad direction using an in-plane approach and advanced through the SM to the subsartorial space [Supplementary File Video 1].[2] Once the needle tip was adjacent to the nerve, ~5 mL of methylene blue was injected to establish a channel for catheter placement. The catheter tip was positioned anterior to the vessel and nerve on ultrasound images, and residual dye was injected until it expanded around the SN in the short-axis view. The catheter was then secured to the skin using sutures. {"href":"Single Video Player","role":"media-player-id","content-type":"play-in-place","position":"float","orientation":"portrait","label":"Video 1","caption":"","object-id":[{"pub-id-type":"doi","id":""},{"pub-id-type":"other","content-type":"media-stream-id","id":"1_c18iemk6"},{"pub-id-type":"other","content-type":"media-source","id":"Kaltura"}]} Perpendicular technique for CACB: The cadavers were positioned, and equipment was prepared as described above. Using ultrasound guidance, the SN was identified in the short-axis view, with the FA located approximately beneath the midpoint of the SM. The needle was inserted from a lateral-to-medial direction by using an in-plane approach and advanced beneath the SM to the subsartorial space. The catheter tip was positioned anteromedial to the FA, and dye was injected to facilitate placement and expansion [Supplementary File Video 2]. The catheter was secured to the skin by using sutures. The tip and catheter position were subsequently re-confirmed using ultrasound prior to the initiation of continuous infusion for both techniques. {"href":"Single Video Player","role":"media-player-id","content-type":"play-in-place","position":"float","orientation":"portrait","label":"Video 2","caption":"","object-id":[{"pub-id-type":"doi","id":""},{"pub-id-type":"other","content-type":"media-stream-id","id":"1_13d05ajr"},{"pub-id-type":"other","content-type":"media-source","id":"Kaltura"}]} Thirty minutes after the completion of the 3-hour continuous infusion for both techniques, two independent investigators (PP and NT) performed lower limb dissections using a longitudinal incision extending from the lower midpoint of the inguinal crease to the superior aspect of the medial femoral condyle. The skin, subcutaneous fat, and superficial vessels were dissected to expose the SM. The boundaries of the femoral triangle (FT) and the AC were defined to evaluate dye distribution before reflecting the SM laterally or medially. The femoral vessels, nerves, and branches, including the SN and NVM, were identified and examined. Additionally, the quality of nerve staining in each specimen was assessed. RESULTS Ultrasound-guided parallel (n = 4) and perpendicular (n = 4) techniques were assessed in two women and two men cadavers aged 60–85 years. Figure 1a–d shows typical dye distribution, and Table 1 summarises the results. Both techniques produced intense staining of the SN in all specimens. The NVM was intensely stained with the perpendicular technique in all specimens, whereas staining varied from mild to intense with the parallel technique. The dye was similarly distributed within the distal FT across specimens, but the parallel technique extended its distribution to the distal AC. In three specimens, the dye permeated through the adductor hiatus into the posterior compartment [Figure 1e].Figure 1: Ultrasound images and cadaveric dissections demonstrating parallel and perpendicular techniques for proximal adductor canal block by using the subsartorial approach. (a) and (c) represent the parallel technique, while (b) and (d) illustrate the perpendicular technique. (e) represents the dissection findings of a soft-embalmed cadaveric thigh specimen following the parallel technique. A = femoral artery; NVM = nerve to vastus medialis; S = sartorius muscle; SN = saphenous nerve; VMO = vastus medialis obliqueTable 1: Catheter insertion length, dye distribution, and nerve staining using perpendicular and parallel techniquesDISCUSSION This comparative small cadaveric study examined variations in dye distribution and staining intensity among the major nerves supplying the medial compartment of the knee joint when comparing perpendicular and parallel catheter placements for CACB by using a subsartorial approach. Dye distribution was directed downward and narrower with the parallel placement compared to the perpendicular technique. Consequently, staining of the NVM was reduced with the parallel placement, while the dye extended to the distal AC. This distribution pattern suggests an increased likelihood of dye penetration into the posterior knee compartment with parallel CACB compared to the perpendicular technique. Blocking the SN and NVM in the proximal ACB has demonstrated favourable analgesic outcomes in previous studies.[7,8] However, effective management of posterior knee pain after arthroplasty often requires targeting the popliteal fossa region.[9] Therefore, the findings of this study may have important clinical implications and warrant further clinical validation. This study has limitations, including a small sample of cadavers was included in this study. However, the sample size resembled those of other cadaveric studies that detail anatomy pertinent to the distribution of local anaesthesia.[10,11] Additionally, the inherent constraints of a cadaveric design indicate that although our study employed a modified Thiel’s solution embalming technique to obtain optimal physical and functional alignment of the limbs for ultrasound-guided regional anaesthetic procedures, the findings from immobile cadaveric studies may not reliably translate to real-life scenarios, particularly with respect to the increasingly used CACB catheter for patient mobilisation. Drug spread in live patients differs significantly from the dye spread observed in cadavers.[12] This discrepancy highlights the limitations of cadaveric models for predicting clinical outcomes. Lastly, the use of shorter continuous infusion durations might have influenced the results. CONCLUSION Our cadaveric findings indicate that perpendicular CACB consistently affects both the SN and NVM, whereas parallel CACB predominantly influences the SN. However, the parallel technique appears to extend its influence on the posterior knee compartment, an effect not observed with the perpendicular technique. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Source: Indian Journal of Anaesthesia
Language: English
Subfield: Surgery
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W4408408224