Knee pain. We all know it. It can quickly derail a successful snow sport season. Beyond ice, rest, acetaminophen, or ibuprofen, there are options. Knee injections can provide relief in mild to moderate arthritis flare-ups and some acute injuries when X-rays and MRI show no need for urgent surgery.
Cortisone
By far the most common injection is a steroid shot (cortisone), an anti-inflammatory that works by subduing cells that release substances leading to knee aggravation. The inflammation increases blood flow to the knee lining, recruiting cells that fight infection and are involved in inflammation. This can lead to an increase in fluid within the knee, manifesting as swelling. The swollen knee, in turn, stretches nerve endings in the knee lining, causing pain. There are two types of cortisone shots: a delayed-release formulation, which is thought to provide longer-lasting relief, and the standard-release formulation. Both are injected with a small amount of numbing medicine, with relief coming within a few days and lasting from three months to a year or more.
Hyaluronic acid
The second type of injection is a gel-like hyaluronate-based injection. Hyaluronic acid is a normal component of healthy joint fluid and aids in joint lubrication. These injections range from a single shot to a weekly series of 3 to 5 injections. They are indicated for mild to moderate arthritis pain. In early arthritis, joint fluid can be thinner than normal, which can aggravate pain from arthritic inflammation. Normal cartilage should look like the shiny end one sees on a chicken bone. In arthritis, the shiny portion breaks down and begins to look cracked or frayed, or even to have bare spots exposing bone and nerve endings. This causes inflammation in the lining of the knee and produces more fluid to lubricate the joint and enable smoother motion. Introducing a more normal joint fluid composition leads to symptom relief and better joint lubrication. These injections take a few weeks to up to six weeks to provide symptom relief.
PRP
The third type of injection is PRP (platelet-rich plasma). This more experimental intervention is used to heal acute injuries, to potentiate healing during surgery, and to treat cartilage defects due to mild arthritis. PRP injections are done by drawing some of one’s own blood and spinning it in a special centrifuge to separate out the platelets and associated plasma from the red blood cells. This fluid is then reinjected into your knee on the same day. PRP is high in concentrated growth factors, platelets, some white blood cells, and cytokines, which are all substances known to promote healing and regeneration. This type of injection takes at least a few weeks to take effect and can temporarily increase pain as the healing response is activated. Healing relies on some of the same cells and factors involved with inflammation, which is why PRP can initially cause more pain. Cortisone is not indicated at the same time as PRP, since it can blunt the healing response.
Stem Cell Injection
The newest and most experimental type of injection is the stem cell injection. Stem cells have the potential to differentiate into many specialized cell types, such as cartilage or bone. Cells are taken from your own bone marrow or fat and grown in a lab to separate out and increase the number of stem cells. These are then reinjected into your knee in the hopes of regrowing normal tissue. Because there are few scientific studies, the data are still unclear about how well stem cells work. However, this is an exciting area for continued research into potential treatments to delay or prevent the need for surgeries such as knee replacements.
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