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“You may be a needle person or a cannula person, but it doesn’t have to be that way,” he said during the Orlando Dermatology Aesthetic and Clinical Conference. “There are pros and cons of both techniques, but I think there’s a place for both.”
Dr. Terrence Keaney
With a sharp needle, placement of the tip is considered precise, especially when delivering a supraperiosteal injection. “From a learning curve, especially for us as dermatologists, it’s easier because we’re used to injecting lidocaine, and we’re using needles on a day-to-day basis for injectables and other applications,” said Dr. Keaney, a dermatologist who is founder and director of SkinDC in Arlington, Va. “However, use of a needle is traumatic; it creates an increased risk of bruising and we’re cutting through tissue. We can potentially puncture a blood vessel and create a vascular event.”
Clinicians may consider filler delivery by sharp needle as being more precise, but in an observational cadaver study of cannula vs. sharp needle for placement of tissue fillers, investigators found an increased risk for spread of filler to more superficial layers along the needle trajectory, as well as a higher risk of intra-arterial injection. “This may explain why, when you’re injecting on a tear trough, you may still get some swelling in the area,” Dr. Keaney said. “You may see some swelling and some product, because it’s tracking along the injection point. One can argue that you can reduce this risk by using a longer needle or cannula.”
With a longer cannula, the blunt tips may act to displace blood vessels rather than to lacerate them. “They allow for greater coverage through fewer injection points and they approach the injection site at a more oblique angle, so it’s harder for the product to track,” he explained. “Cannula patients tend to faint on me a lot more than my needle patients do, so while the cannula may be more comfortable, it can be more nerve-wracking for patients.”
Recent studies have shown that with cannula proficiency, clinicians can achieve results on par with using sharp needles for dermal filler treatments (Dermatol Surg. 2020 Apr;46[4]:465-72; Dermatol Surg. 2012 Feb;38[2]:207-14). A recent head-to-head comparison found no significant differences in the use of needles vs. cannulas for the treatment of the dorsal hand with diluted calcium hydroxylapatite, though patients reported 12% greater satisfaction with the cannula technique (Dermatol Surg. 2020 Oct;46 Suppl 1:S54-61).
“Based on these articles, we can feel comfortable that with proficient use, you can deliver similar results with the cannula as you would with the needle,” said Dr. Keaney, a clinical associate faculty member in the department of dermatology at George Washington University, Washington. “As a result, we are seeing Food and Drug Administration–approved indications for the use of cannulas for dermal fillers: Restylane Silk for lips, Restylane Lyft for cheeks, Juvederm Voluma for cheeks, and Juvederm Voluma for the chin.”
Such emerging data present a conundrum, though. If someone is comfortable injecting dermal filler with needles, why switch to using cannulas? After all, a case study reported arterial penetration with blunt-tipped cannulas using injectables . “Cannulas are not 100% safe,” Dr. Keaney said. “One of my mentors once said, “If a vascular event has not happened to you yet, you have not injected enough. These things can happen even in the most experienced hands, whether you use a needle or a cannula.”
However, safety data from a recently published retrospective study demonstrated that cannulas are less likely to be associated with occlusions compared with needles (a risk of 1 occlusion per 40,882 injections vs. 1 occlusion per 6,410 injections (P less than .001).
“Cannulas are generally safer because the blunt tip kind of dissects tissue and pushes vessels away,” he said. “That doesn’t mean it can’t get into a vessel, it just requires greater force to penetrate facial arteries with a cannula. Finer tips may be easier to use.”
Larger cannulas can tear into an arterial wall when the artery wall is relatively fixed, so it cannot slide aside enough to avoid injury, Dr. Keaney continued. “Arterial location perpendicular to cannula trajectory carries the most risk,” he said. Meanwhile, filler-induced blindness, which he characterized as “the worst possible outcome,” is often due to the retrograde embolization of the product. This can occur with injection pressures greater than the sum of the systolic arterial pressure and the frictional forces due to viscous flow.
Dr. Keaney said he uses both needles and cannulas in his clinical practice. “I use a needle to inject on bone if I want to mimic bony projections along the zygomatic arch or jawline or chin,” he said. “I think a needle can get those boluses to develop that projection that you want. If I’m injecting within soft tissue plane, I use a 22 G cannula and keep the cannula moving within the tissue. I inject slowly and less than 0.2 cc per bolus. I compress when injecting on the nose and I’m cautious to inject previous patients who have undergone plastic surgery or in areas of previous scarring.”
Dr. Keaney reported that he is a consultant to and/or an advisory board member for several pharmaceutical companies.