What Is a Subchondral Bone Cyst?
It's a fluid-filled sac that forms in one or both of the bones that make up a joint. They're especially common at the knee or hip. The cysts show up just under the tough spongy tissue (called cartilage) that covers the bone near the joint.
Your doctor might call them:
- Osteoarthritic cysts
- Egger cysts (in the hip socket).
Causes of Subchondral Bone Cysts
Osteoarthritis (OA) is the most common. It breaks down the cartilage. OA can happen from simple wear and tear over time, or because of a sudden injury to a joint.
Either way, the normal, smooth, gliding of one bone against another in your joints starts to cause more friction. That leads to the cyst.
In other cases, a joint injury might lead to a cyst without OA.
Symptoms of Subchondral Bone Cysts
The cysts themselves don’t seem to cause symptoms. But in rare cases, they can push on soft tissue in the area. That can cause pain.
More often, if you have pain, it's due to the osteoarthritis that causes the cysts. The pain tends to come and go at first. But it gets worse over time, or if you're very active. It might be especially serious when you wake up. Eventually, the pain can become constant.
As OA gets worse, stiffness and swelling can make it harder for your joints to work the way they should. You might also feel weaker over time -- so much so that it gets harder to do simple things, like open a jar or bend down.
With OA of the hip or knee -- where cysts are more common -- you might have pain in your:
- Area behind the knee
You might also feel a grinding or scraping sound when you move your joint.
Over time, the cyst itself can start to damage your joint. That can keep you from being able to make some movements.
Diagnosis of Subchondral Bone Cysts
Your doctor will examine you and ask about any pain or stiffness you're having.
If you have pain, swelling, or stiffness that could be from OA or a joint injury, your doctor will order X-rays or other imaging tests. Any cysts you have will show up on these tests.
Subchondral cysts may not cause any symptoms. But sometimes, they continue to grow. That may start to change the way your joint works. If this happens, your doctor might suggest using a needle to drain the cyst.
Other than that, your doctor will try to treat the cause of your cyst -- in most cases, OA or a joint injury.
Though there is no cure for OA, your doctor can help you manage your symptoms with:
- Over-the-counter pain meds
- Prescription drugs
- Physical therapy, as well as splints, crutches, and other devices.
In rare cases, you might have surgery to replace a joint.
Talk with your doctor about which treatment might be best for you.