The best way is to try to find the patella and go two finger breadths, which is approximately three centimeters below the inferior aspect of the patella and two centimeters medial. So typically in most adults the blue 25 millimeter needle will be the right needle of choice, but you have to account for soft tissue depth. You might have to step up to the yellow or 45 millimeter needle, so choose the right needle for the right patient. After prepping the skin, which I've already done in this case, you want to apply the needle to the driver. It's a magnet that holds the needle in place. You want to stabilize the hub while you remove the cap. You want to insert the needle through the skin until you hit bone, and you want to make sure you see the five millimeter black mark to ensure that you have enough needle to get through the cortex. Gently advance the needle until you're essentially flush with the skin. You want to make sure you feel that drop or loss of resistance and then advance another one or two centimeters. In most adults you're going to apply this so that it's flush with the skin, and you want to make sure you're perpendicular to the plane of the tibia.

procedure demonstration

needle insertion

patella

needle choice

soft tissue depth