Subchondral Bone Cysts: What They Are and How They're Treated

Fluid-Filled Sacs in Joint Bone Are a Sign of Osteoarthritis

Knee, semiology elderly person
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A subchondral bone cyst is a fluid-filled sac that forms inside of and extends from the bone of a joint. It is seen on x-rays in cases of osteoarthritis. These cysts are not treated. They are a sign of osteoarthritis, although they do not occur in all cases.

How Osteoarthritis Progresses

Osteoarthritis is caused by the breakdown of cartilage in one or more of your joints. Cartilage serves as a cushion between the bones of your joints, allowing the bones to glide over one another and absorb the shock from your physical movements.

Osteoarthritis progresses in stages. Here is the typical pattern that you can expect to see in a joint with osteoarthritis:

  1. Joint space begins to narrow as a result of cartilage degeneration.
  2. Bone tries to repair itself and there is bone remodeling in the forms of subchondral sclerosis and osteophytes.
  3. As cartilage loss continues, subchondral cysts may form within and extend from the bone underlying the joint space.
  4. Joint space disappears as cartilage wears away and bone rubs on bone

Formation of Subchondral Bone Cysts in Osteoarthritis

Subchondral cyst formation is characteristic of osteoarthritis and can be routinely found on x-rays. A subchondral cyst is a fluid-filled sac that extrudes from the joint, consisting of thickened joint material. This material is mostly hyaluronic acid, a substance found in the normal joint fluid that serves to lubricate the joint.

Subchondral bone is the layer of bone just below the cartilage.

When someone has osteoarthritis, there is increased blood flow and other changes that develop in the subchondral layer—subchondral sclerosis (increased bone density), subchondral cyst formation, and increased pressure within the bone—all of which may cause osteoarthritis pain.

Significance of Subchondral Bone Cysts

A subchondral cyst formation is indicative of progressive osteoarthritis.

It is often the case that the subchondral cyst improves without medical attention, although the disease itself does not go away.

The subchondral bone cysts may have a destructive role in osteoarthritis progression. When they intrude into the subchondral plate and calcified cartilage, they can cause more destructive processes in the bone and cartilage.

While subchondral bone cysts are considered a cardinal radiological finding for knee osteoarthritis, a study of 806 patients with knee osteoarthritis found them in only 30.6 percent of the cases, more often in females. Meanwhile, the other characteristics were far more common, with 99.5 percent showing narrowed joint space, 98.1 percent osteophytes, and 88.3 percent subchondral sclerosis.

Treatment for Subchondral Cysts

If the subchondral cyst causes discomfort, Nonsteroidal anti-inflammatory drugs (NSAIDs) may provide relief. It may also be recommended that you try to avoid activities that irritate the joint that is involved with osteoarthritis. Lower-impact activities would be better than higher-impact activities for knees and hips.

The recommended treatment for a subchondral cyst is to just leave it alone. A subchondral cyst should not be lanced or removed, especially because removal would cause an increased risk of infection or possible problems with wound healing.

Instead, symptom relief, lifestyle modification and eventual joint replacement are the usual courses of treatment.


  • Guangyi Li, Yin J, Gao J, et al."Subchondral bone in osteoarthritis: insight into risk factors and microstructural changes." Arthritis Res Ther. 2013; 15(6): 223.
  • Han Xinyun Audrey, Hamid Rahmatullah Bin Abd Razak,* and Tan Hwee Chye Andrew. "The Truth Behind Subchondral Cysts in Osteoarthritis of the Knee." Open Orthop J. 2014; 8: 7–10.
  • Radiographic Assessment of Osteoarthritis. Swagerty DL. et al. American Family Physician.