Diagnostic injections are injections designed to better understand your pain generator. This typically is an anesthetic agent like lidocaine injected to block pain-sensing nerves in a specific structure guided by imaging (x-ray and/or ultrasound). Other diagnostic injections use contrast, a special dye, used to assess the integrity of different structures and if they are pain generators.
By using a local anesthetic like lidocaine, the nerves that pick up the pain signals are blocked. Once the anesthetic has fully taken effects, your physician can re-examine the painful area and hopefully movement, range of motion, and/or strength has improved. We also will ask you to go home and try to do certain activities that will typically provoke your symptoms. If your pain is much less, then we can more confidently say the structure we targeted with the injection is the source of your pain.
This depends largely on two things; the choice of anesthetic we use and if the structure targeted is actually your pain generator.
Shorter acting anesthetics like lidocaine or novocaine is typically 30 seconds to 2 minutes. These last anywhere from 2-4 hours on average. Longer-acting agents like bupivacaine take slightly longer to work at about 5 minutes, but last about 4-6 hours or longer. Some of this depends on the individual metabolisms of each patient as well.
If we injected the structure, you should experience significant pain relief within the first 5 minutes. However, you may not feel any different or only part of your pain is gone. This may mean you have multiple pain generators contributing to your symptoms.
This is a very valid question. The reason is that if we are not quite sure what is causing your pain, the risk of side effects from adding another medicine may outweigh the potential benefit and we are using the injection to better understand your symptoms.
Overall medication exposure is a risk and benefit analysis that must be considered by you and your physician based on physician examination findings and understanding of your medical history. See our post about steroid injections to better understand the risks and potential side effects of steroids.
Dr. Niteesh Bharara
Orthopedic Specialist - Non-Surgical Sports Medicine
Director of Regenerative Medicine
Reviewed by: Dr. Christopher Good, MD, FACS.