The physician’s fingers and thumb are wrapped around the proximal tibia to stabilize it; the hand should not be placed directly behind the insertion site (to avoid self-puncture). Instead, a towel may be placed behind the knee to support it. The physician holds the needle firmly in the palm of the other hand, directing the point slightly away from the joint space and growth plate. The needle is inserted with moderate pressure and a rotary motion, which is stopped as soon as a pop indicates penetration of the cortex. Some needles have a plastic sleeve, which can be adjusted to prevent them from being pushed too deeply into or through the bone.