Description of Injections
There are several different types of injections for the shoulder, hip, and knee. The most common are steroid, hyaluronic acid, and platelet rich plasma (PRP). While all of these can be used in the shoulder, hip, and knee, hyaluronic acid is only FDA approved for injection into the knee. An ultrasound is frequently used to identify key anatomy and to ensure that the needle is placed in the precise location.
1. Steroids are powerful anti-inflammatory medications, which act on the cells to turn off their inflammatory response. This results in decreased pain and swelling. The injected solution contains both the steroid and lidocaine, which is a numbing medication that lasts for a couple hours. The steroid takes a day or two to start working, but provides pain relief for 2-3 months on average. Almost all patients receive some pain relief from the steroid injection, but the amount of pain relief and duration varies. Steroid injections into the joint for arthritis can be repeated every 3 months with low risk of any adverse side effects; however, steroid injections around tendons such as the subacromial bursa can weaken the tendon and potentially cause tendon ruptures, so these are generally limited to 1-2 injections.
2. Hyaluronic acid (HA) is a normal component of the fluid in joints. This can be made synthetically or isolated from chicken products. There are several different types of HA. Some are administered as a single injection, but most are administered as a series of 3 injections that are given one week apart. Hyaluronic acid was initially thought to provide lubrication to the arthritic joint, but actually acts to block inflammatory signals in the joint, but in a way that is different than steroid. A lower percentage of patients respond to HA injections, but they can provide 6-12 months of relief. Most insurances cover HA injections, which are typically authorized every six months.
3. Platelet rich plasma (PRP) is obtained from a sample of blood, which is then spun in a centrifuge. This stratifies the blood into different layers, one of which is PRP. Many of the body’s own healing factors that are held in platelets are concentrated in PRP, which is then injected into the knee. A high percentage of patients respond to this treatment, which can also provide 6+ months of pain relief. PRP is a newer treatment that is not typically covered by insurance. PRP injections can be repeated every six months.