Subchondral Bone Cysts in People With Osteoarthritis

A subchondral cyst is a fluid-filled sac that forms in the bone beneath the cartilage of a joint such as the hip, knee, or shoulder. It's also known as a bone cyst. "Subchondral" means below the cartilage.

These cysts can develop in people with osteoarthritis. This article provides an overview on subchondral bone cysts, why they appear, how they're diagnosed, what the symptoms are, and common treatment options.

How Osteoarthritis Progresses

Osteoarthritis is caused by the breakdown of cartilage in the joints. Cartilage serves as a cushion between joint bones, allowing them to glide over each other and absorb the shock from physical movements. When it's damaged, bone spurs, bone cysts, and other problems result.

Osteoarthritis typically develops in the following stages:

1. At disease onset, the space between the joint bones begins to narrow due to cartilage degeneration.
2. As the joint tries to repair itself, the remodeling of bone can often be haphazard and lead to the formation of bone spurs (osteophytes) and the development of subchondral sclerosis (joint stiffening due to increased bone mass).
3. As cartilage loss continues, subchondral bone cysts may start to form.
4. The increasing depletion of cartilage will eventually cause bone to rub against bone, triggering pain and the loss of mobility.

Causes and Symptoms

Subchondral bone is the layer of bone just below the cartilage. With osteoarthritis, the blood supply to these areas increases as the body tries to repair the joint damage.

The exact way subchondral bone cysts form is unknown, but damage to the subchondral bone and overlying cartilage are key factors.

Not all people with osteoarthritis will develop subchondral cysts. It's not clear why some people develop the condition and others don't.

Diagnosis

Subchondral bone cysts are diagnosed with an X-ray.

They will appear as hollowed-out areas in the subchondral bone but are often poorly defined and difficult to spot. In such cases, a magnetic resonance imaging (MRI) scan may be ordered to provide the doctor with a more three-dimensional view.

The X-ray or MRI results, along with a review of the person's symptoms and risk factors, are usually enough to confirm the diagnosis.

Risk factors for bone cysts include:

• Obesity
• Smoking
• Abnormal joint alignment
• Abnormal joint shape
• Prior joint injury
• Family history of osteoarthritis

Treatment

Bone cysts are not treated directly. Instead, the doctor will find ways to help alleviate the acute and long-term symptoms of the underlying osteoarthritis.

Subchondral cyst treatment options include:

• Nonsteroidal anti-inflammatory drugs (NSAIDs), like Advil or Motrin (ibuprofen) and Aleve (naproxen), to treat pain
• Weight loss to relieve pressure on the joints
• Low-impact exercise (like biking, swimming, or ellipticals) to retain or improve joint flexibility
• Physical therapy
• Ultrasound therapy

If none of these options provides relief, the doctor may recommend a joint replacement surgery.