Cannula vs. Needle for Dermal Fillers

Over the last ten years, the use of cosmetic fillers has become increasingly popular. Historically, delivery of cosmetic tissue fillers has been through a sharp hypodermic needle. However, new blunt-tipped needles, called microcannulas, are gaining popularity with aesthetic injectors. The decision to use needle vs. cannula is the choice of the injector, but the advantages of using a blunt-tipped cannula make them the preferred option for some.

Let’s start with a brief introduction to cannulas. Microcannulas are blunt-tipped metal cylinders with a side port that can be used in lieu of needles. Puncture with a larger bore needle precedes the insertion of a microcannula through the opening. One of the benefits of cannula is the single point of entry, reducing the number of injection points during facial rejuvenation. In addition, cannulas are typically at least 1 inch in length, allowing for a larger area to be treated.

Can we deliver the same results safely with a cannula as we historically have with needles?

Needles

• • Pros:
    • PRECISION: With a sharp needle, placement of the needle tip is considered very precise especially when placing supraperiosteal
    • LEARNING CURVE: easier for clinicians who are already using needles to inject other substances
  • Con:
    • TRAUMATIC: increased risk of bruising and vascular events

In theory, the use of needles results in increased precision of injection. We are able to target and deliver the injected substance into the desired anatomic planes. However, there may be risk of spread if the substance tracks upward with the perpendicular movement of the needle. Cannulas are long and inserted at an oblique angle, theoretically confining the material into the desired plane of injection. However, using a longer needle may minimize retrograde migration along the trajectory of the needle path.

Cannulas

• • The blunt tip may act to displace blood vessels rather than lacerate them
    • Decrease risk of bruising, edema, and pain
    • Decrease risk of inadvertent injection into a blood vessel resulting in a vascular event
  • Long length allows for greater coverage through fewer injection points
    • Decreased pain with procedure

Although cannulas may be more comfortable for patients, the sensation of the cannula moving through tissue may be disconcerting. There is an increased chance of vasovagal reaction. This can be perturbed by discussing with the patient what to expect and having an open dialogue during the procedure.

In a recent study evaluating the efficacy of needle vs. cannula for dorsal hand rejuvenation, there was comparable improvement between both techniques. However, there was 12% greater patient satisfaction with the cannula technique.

In terms of efficacy, both needle and cannula deliver comparable aesthetic results. It has been suggested that the use of blunt microcannulas increases volume efficiency and decreases treatment time. However, optimal placement and results ultimately depend upon the knowledge and skill of the injector. With proficient use of cannula, practitioners can deliver similar aesthetic results.

Currently, there are 4 FDA approved indications for cannula use:

• • Restylane Silk – Lips – 2017
  • Restylane Lyft – Cheeks – 2018
  • Juvederm Voluma – Cheeks – 2019
  • Juvederm Voluma – Chin/Prejowel sulcus – 2020

Why adopt a new and initially more difficult technique? Minimizing the rare catastrophic events of needle injection, necrosis, and blindness is a major reason to consider use of cannula. However, are cannulas really safer?

In a recent retrospective cohort study of 370 participating dermatologists, the risk of vascular occlusion appeared exceedingly low (1 in 6410 syringes via needle and 1 in 40,882 via microcannula injector) when board-certified dermatologists used needles or cannulas for filler injection.

The blunt tip of a cannula is thought to laterally displace vessels preventing vascular penetration. However, the risk of inadvertent vascular injection is not completely eliminated with cannula use. There is greater force required to pierce a vessel with cannula compared to needle.

In a study comparing the arterial wall penetration forces in needles versus cannulas, it was shown that when using a 27-gauge needle or cannula, an artery could be penetrated with a similar force independent of whether the injector was utilizing a needle vs. cannula.

Forces needed to penetrate vessels significantly decreased with smaller diameter cannulas. Cannulas require greater forces for intraarterial penetration compared with correspondingly sized needles, confirming the safety of larger diameter cannulas such as 22-gauge cannulas. Therefore, the more nar­row the microcannula, the more potential to cause neurovascular injury or even to penetrate a blood ves­sel if passed through tissue with inappropriate force.

Injection force may be related to cannula shape as well. More fine-tipped cannulas are easier to use and move through tissue planes, however, it is also associated with increased risk for inadvertent arterial injection. Cannula location and direction matter as well. Large cannulas can tear the arterial wall if the artery wall is relatively fixed, for example against bone or from scar tissue after surgery. It is proposed that the artery cannot be displaced and is unable to avoid injury. Arterial location perpendicular to the cannula trajectory carries the most risk, especially if the artery is fixed.

Overall, in reviewing these studies, it can be concluded that cannulas appear to be associated with lower occlusion risk when compared with needles.

For many patients, a combination of blunt microcannula, as well as needle injection of fillers, may represent the optimal balance of safety and efficacy, by providing minimally traumatic diffuse contouring plus precise shaping.

Dr. Terrence Keaney’s tips for optimal outcomes:

• • Inject on bone when possible (zygomatic arch, jawline, chin)
  • If in soft tissue, use a 22-gauge cannula and keep the cannula moving
  • Inject slow and small boluses, less than 0.2cc per depo
  • Compress when injecting on nose
  • Be cautious to inject previous surgery patients or in areas of previous scarring

Summary

• • Both cannula and needle deliver similar aesthetic outcomes
  • Microcannulas can treat a large area from a single insertion point
  • There are 3 things to consider in terms of cannula safety: size, shape, and direction
  • There is less patient discomfort with microcannula
  • Optimal results are best achieved with a combination of needle and cannula

This information was presented by Dr. Terrence Keaney at the ODAC Conference held January 14-17, 2021. The above highlights from his lecture were written and compiled by Mojgan Hosseinipour, DO, FAAD.

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