Last updated 17 June 2020
Needle Vs Cannula – what are the differences when injecting dermal filler?
Traditionally, dermal fillers have been injected using needles. In fact, most dermal fillers still come packaged with two short (1/2 inch) needles as the recommended means of injecting the product. However, there are several advantages of not using the supplied needle, and instead, using a blunt-tipped cannula for the injection of dermal fillers. One of the key advantages of using blunt-tipped cannulas is the reduced likelihood of penetrating blood vessels, especially arteries. Injection of filler into arteries can have disastrous consequences including blindness, stroke, and death of parts of the skin injected.
The overwhelming majority of practitioners still use needles to inject fillers, although cannula use is on the rise. Technically, it is much more difficult to use a cannula. A significant amount of feel is required to use a cannula, whereas a needle simply pierces through tissues. Because the tip of a sharp needle is extremely fine, it is essentially a force multiplier. This is the reason why only a small amount of pushing force is required to channel a needle through the face. The learning curve associated with using a cannula combined with the additional cost to purchase cannulas could account for the lack of usage amongst practitioners, despite their advantages.
When using a needle, the sharp tip of the needle penetrates through the skin and down to the depth where the filler is injected. In contrast to this, a cannula has a blunt tip, and therefore cannot pierce the skin. A needle is required to make an entry point for the cannula that just passes through the skin. The cannula is then used to pass through the entry point to the areas beneath the skin. The blunt-tipped cannula can re-enter the same entry point again without having to hurt the patient with another needle puncture.
Because the cannula is blunt, it is not as indiscriminate as a needle as it passes through the tissues. Needles, being sharp-tipped, may more easily pass into or through a vein or artery. This can cause significant bruising or swelling, and at worst, intravascular injection (injection of filler into the artery or vein, which can cause serious complications). Cannulae (plural for cannula), being blunt, are less likely to pass into a vein or artery, and therefore cause less bruising or swelling and tend to avoid intravascular injection. Instead, the blunt tip tends to push veins or arteries aside as they are passed through the tissues. Furthermore, the practitioner is able to feel resistance from structures that a cannula pass through, allowing them to judge when and how to apply pressure or manipulate the direction of the cannula. Finally, cannulae tend to be longer than most needles and therefore reach more areas with fewer entry points into the skin.
To summarise, there are many advantages of using a blunt-tipped cannula for the injection of dermal fillers instead of needles. There are advantages for the patient and the practitioner.
- Cannulae are blunt, which mean that they are less likely to pierce a through a vein or artery. This results in less swelling, bruising and intravascular injection of filler.
- The practitioner has more feel about what structures are being passed by the tip of the cannula.
- Cannulae are longer, allowing for fewer injections and entry points through the skin.
- Can go in through the same entry point multiple times without hurting the patient.