Practice matters


Introduction to needle and cannula

Let’s begin by reviewing the shape and purpose of a needle. I have here a typical needle, and we will notice that if I remove the protective cover, the needle is hollow, sharp, and open at the end. Accordingly, the injected product will exit from the end of the needle. A needle allows us precision, but the disadvantage is that the sharpness of the needle can damage vulnerable structures like blood vessels.


In comparison, a cannula has some major differences. The end of the cannula is blunt and closed. If you look very carefully you will notice there is a small, open port at the side of the cannula just before the distal tip. As it is blunt, a cannula cannot penetrate the skin, so we need to create an entry hole. When we use a cannula, we will use a sharp needle first to make a hole in the skin and then insert the cannula through the hole.


The cannula gives us greater safety, but it is less precise than the needle. We may also use more product when using the cannula compared to using the needle. The cannulas differ in gauge and length. Let’s look at these two cannuli here. The one on the right is a 25 gauge, 38 mm cannula and the one on the left is a 27 gauge, 50 mm cannula. You will notice that the longer, thinner cannula is very flexible, and this makes it harder to control. Whereas this shorter, thicker one is more robust and behaves more like a needle. If you are a beginner, try to use a thicker cannula and the shortest length that will suffice.