Study Compares Perpendicular and Parallel Techniques of Analgesia for continuous abductor canal block

Recent study investigates the differences in anatomical dye distribution patterns and nerve blockade effectiveness between two catheter placement techniques for continuous adductor canal block (CACB) using a subsartorial approach. The comparison focuses on parallel and perpendicular orientations of catheter tips in relation to the saphenous nerve (SN) and the nerve to vastus medialis (NVM). An initial motivation for the study stems from documented complications associated with catheter dislocation, particularly during postoperative rehabilitation, which could impact analgesic outcomes.

Research has indicated that catheters placed parallel to nerves might experience less migration than traditional perpendicular placements. However, existing studies had mostly examined single nerve blocks rather than CACB, which targets multiple nerves. This study, therefore, aims to assess how variations in catheter orientation influence dye distribution to the SN and NVM and to evaluate any implications for postoperative analgesia.

Conducted with four modified Thiel soft-embalmed cadavers, the study utilized a randomized approach to assign each limb to either the parallel or perpendicular technique. Using ultrasound guidance, a dye approach involving methylene blue was employed, with both a continuous infusion method and bolus injections to visualize dye spread. The primary measurements included the dye diffusion patterns, intensity of staining on the SN and NVM, and any spread beyond the adductor canal.

Results show that both techniques led to substantial staining of the SN; however, the NVM exhibited intense staining using the perpendicular method, while staining intensity varied with the parallel technique. The dye distribution revealed a narrower downward spread with the parallel approach, contrasting with the more diffuse and extensive spread achieved with the perpendicular orientation. Notably, the parallel method demonstrated a tendency for dye penetration into the posterior knee compartment through the adductor hiatus, an occurrence not observed with the perpendicular placement.

Implications

The findings suggest that while the perpendicular catheter placement reliably targets both the SN and NVM, the parallel placement predominantly influences only the SN but allows for extended influence into the posterior compartment of the knee. This distribution pattern may have implications for pain control post-surgery, as effective analgesia often necessitates adequate blockade of nerves supplying the posterior knee region.

Limitations

The study acknowledges significant limitations, including the small sample size and the challenges of translating results from cadaveric examinations to living patients, particularly given that the opioid spread in awake subjects may vary considerably from cadaveric models. Additionally, variations in catheter usage techniques or infusion durations could also confound the results.

Conclusion

Concluding, the study emphasizes that while perpendicular catheter placements for CACB target both the SN and NVM effectively, the parallel technique might be preferred in certain clinical settings, given its potential for greater posterior compartment influence. These findings could shape future techniques in regional anesthesia, guiding clinicians toward optimal analgesic strategies and possibly reducing complications related to catheter migration. Further research in living subjects will be essential to validate these observations and improve application in clinical contexts.

Key Points

- The study investigates the anatomical dye distribution patterns and effectiveness of nerve blockade between two catheter placement techniques (parallel vs. perpendicular) for continuous adductor canal block (CACB), specifically examining their impact on the saphenous nerve (SN) and the nerve to vastus medialis (NVM).

- Existing research indicates that parallel catheter placements might reduce migration compared to traditional perpendicular placements, yet previous studies primarily focused on single nerve blocks rather than the multi-nerve targeting inherent in CACB.

- Utilizing four modified Thiel soft-embalmed cadavers, the study employed a randomized design involving ultrasound guidance to visualize dye spread from both continuous infusion and bolus injections, analyzing patterns and intensity of staining on the SN and NVM.

- Results demonstrate that while both techniques stained the SN significantly, the perpendicular method yielded intense staining of the NVM with a more extensive dye spread, whereas the parallel technique resulted in a narrower downward spread but notable penetration into the posterior knee compartment.

- The findings imply that although the perpendicular technique effectively targets both SN and NVM, the parallel method, primarily affecting the SN, could allow for extended analgesic influence into the posterior knee compartment, which may enhance postoperative pain control.

- Limitations of the study include a small sample size, difficulties in translating findings from cadavers to live patients, and potential variations in clinical techniques affecting results; further research on living subjects is necessary to confirm these insights and enhance clinical application.

Reference –

Kampitak W, Thamrongskulsiri N, Purngpiputtrakul P, Kertkiatkachorn W. Does parallel versus perpendicular catheter placement for a subsartorius approach to a continuous adductor canal block influence injectable distribution? A comparative cadaveric study. Indian J Anaesth 2025;69:405-9.