Subchondral Bone Cysts in People with Osteoporosis

A subchondral bone cyst (SBC) is a fluid-filled sac that forms in the bone just beneath the cartilage of a joint, such as the hip, knee, or shoulder. These cysts can develop in people with osteoarthritis and are usually not treated.

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.

Osteoarthritis typically develops in the following stages:

1. At the onset of disease, the space between the joint bones will begin 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 (the stiffening of the joint due to increased bone mass).
3. As cartilage loss continues, SBCs may begin 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 is typically increased as the body tries to repair the joint damage. Damage to the subchondral bone and overlying cartilage are key factors, but exactly how SBCs form remains unknown.

Not all people with osteoarthritis will develop SBCs, and it is not even entirely clear why some people develop the condition and others don't.

Diagnosis

SBCs 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 a more three-dimensional view.

This, along with a review of the person's symptoms and risk factors, is usually enough to confirm the diagnosis.

The risk factors for SBC include:

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

Treatment

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

Options may include:

• Nonsteroidal anti-inflammatory drugs (NSAIDs), such as Advil or Motrin (ibuprofen) and Aleve (naproxen), to treat pain
• Weight loss to alleviate pressure on the joints
• Low-impact exercise (such as biking, swimming, or elliptical machines) 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.