Being able to perform accurate injections is vital in confirming the diagnosis. Equally important in diagnosis and treatment is choosing the right substance to inject. This decision is based on the tissue type, the nature of the injury, and the goal of the injection. For example, when someone has severe shoulder pain during reaching movements, it can sometimes be difficult to tell if the pain is coming from inside the joint, or from the rotator cuff, which is outside the joint. Injecting a small amount of lidocaine around the rotator cuff can immediately determine the pain source, and the appropriate medication can then be delivered to the correct target. This is important because we want to minimize the exposure of healthy tissue to needles and medication. In other words, if we are going to perform an injection, we need to make it count.