In order to expect the highest chance at success with treatment, it is important to ensure the injection is administered to the right place. For example, joint injections need to be administered within the joint space, and not the surrounding soft-tissues. Tendon injections should be administered in the tendon sheath, the structure that envelops the tendon, and not inside the tendon.
Traditionally, injections were administered "blind." This doesn't mean the practitioner isn't looking, but rather that they cannot see the medication as it leaves the needle. Instead, your doctor relies on experience, location, and feel to know if the injection is being given in the right spot:
- Experience: Over time, with many injections, doctors become comfortable with not only the visible anatomy, but also what lies beneath the skin. An experienced doctor knows the best ways to access a joint or tendon sheath, and relies on this experience to guide their injections.
- Location: Each joint has one or a few ways to best access the joint space. Knowledge of this can help increase the chance of getting the needle to the correct spot.
- Feel: Feel is very important both in that you can feel the tip of the needle passing through different structures to get to the right spot, and also you can feel the resistance to flow of the medication exiting the needle.
Image Guided InjectionsOne way to try to increase the chance of getting the injection into the right spot is to use an imaging device to allow you to "see" inside the body as the injection is being given. The most commonly used devise is an ultrasound machine. Ultrasound machines were used infrequently in an orthopedists office until a few years ago. At that time, better portable machines became available, and now many orthopedic surgeons, and other doctors, are using ultrasound to guide their injections to try to improve accuracy.
Ultrasound guided injections are administered in a similar fashion to traditional injections. The needle and syringe are the same. When ultrasound is used, a small probe attached to a video monitor is pressed against the skin--similar to the device used to see a fetus in a pregnant mother. The probe is placed next to the body part to be injected--commonly a joint or tendon sheath. Once your doctor has identified the anatomic landmarks, the injection is administered while watching the needle with the ultrasound. Ultrasound is an excellent way to visualize fluids, and therefore an experienced user can identify the fluid being injected, and ensure this is in the proper location.
Are Ultrasound Guided Injections Better?This is a question of great debate. The reason why it is debated is that some people, including many insurers, feel that doctors only use these injections because they can submit a bill and capture a fee for this service. Ultrasound is quick and relatively easy, and aside from the initial cost of the machine, there is little ongoing cost to using this technology. Most doctors charge anywhere from $100 or more each time they use this technology. In addition, many people, including some doctors, feel that experience and feel should be sufficient to properly administer most injections--that ultrasounds may not improve accuracy.
On the flip side, there are a number of studies that demonstrate improved accuracy of the ultrasound guided injections. This is especially important with injections that may be in a more anatomically difficult location, such as a hip joint or deep tendon, rather than a superficial, easily felt joint or tendon. The best recommendation is to ask your doctor about whether it is necessary to use this technology for your injection. If you are going to be responsible for some or all of the cost, you may want to ask how much difference the ultrasound is likely to make. In addition, an ultrasound machine, like any medical technology, is only as good as the person using it. Appropriate training and experience are necessary to use this technology properly. Ask your doctor how long they have been using the technology and how they were trained to use it.
Lee DH, et al. "Sonographically guided tendon sheath injections are more accurate than blind injections: implications for trigger finger treatment" J Ultrasound Med. 2011 Feb;30(2):197-203.
Park Y, et al. "Comparison of sonographically guided intra-articular injections at 3 different sites of the knee" J Ultrasound Med. 2011 Dec;30(12):1669-76.