We agree with Drs. Wardhan and Nimma that the suture-catheter system is simpler in design than conventional through-the-needle catheters and that no system will be perfect in design, ergonomics, or ease of placement.1 However, our experience with the catheter insertion system differs from their suggestion that relative to a straight needle, the suture shape is more difficult to visualize. As our study progressed, we were somewhat surprised to discover that the 19-gauge suture needle visualized at least as well, if not better, than a Tuohy needle of the same gauge. Drs. Wardhan and Nimma note that “lateral forces exerted on [a] straight needle tip leading to curvature may lead to an unpredictable needle trajectory which cannot always be assumed to be straight or even in a single two-dimensional plane.” We concur and suggest that the suture-shaped needle remains within a two-dimensional plane precisely because of its curvature, which appears to greatly strengthen the needle: It is extraordinarily rigid and resists bending laterally (in a direction other than its curvature).
Furthermore, as our colleagues note, straight needles often bend, resulting in the end being “obscured by shadows or poor reflection back to the probe.” We agree, and we found that the suture design did not exhibit this weakness, possibly because the gently curved needle is comparatively parallel to the ultrasound probe when it reaches the target nerve.
Lastly, we respectfully disagree with our colleagues’ statement that we “struggle to visualize the needle clearly at meager depth of possibly just a few (2 to 4) centimeters as evident in [our] figure 3.” To the contrary, the needle appears clearly for its entire length (within the ultrasound field) in the first two panels of figure 3. Any distortion is an artifact of the static image, which was originally viewed in real-time. This can be best appreciated in the supplemental videos associated with the article, which demonstrate how the suture-catheter can be seen moving through tissue in real time.2
We join our colleagues in calling for additional research to provide actionable information for clinicians to optimize benefits—and minimize risks—of perineural catheter delivery systems.
Ferrosan Medical Devices (Søborg, Denmark) provided an unrestricted research grant and suture-type perineural catheters used in the original study to the University of California. This institution has also received funding and product for other research projects from Myoscience (Fremont, California), Epimed (Farmers Branch, Texas), InfuTronix (Natick, Massachusetts) and SPR Therapeutics (Cleveland, Ohio). In addition to the above, Dr. Ilfeld’s institution has received funding for a different research project from Heron Pharmaceuticals (San Diego, California).