A subchondral cyst is a type of bone abnormality that can appear near joints. These fluid-filled sacs, while a common finding, can vary in their presentation and implications for joint well-being. Understanding their nature, development, and management is important for individuals seeking clarity on these bony lesions.
What is a Subchondral Cyst?
A subchondral cyst, also referred to as a bone cyst or geodes, is a fluid-filled sac that forms within the bone directly beneath the joint cartilage. The term “subchondral” means “below the cartilage.” These cysts are filled with hyaluronic acid, a component of the synovial fluid that lubricates joints.
Subchondral cysts are frequently found in weight-bearing joints such as the knee, hip, and shoulder, but can also occur in the spine. While they are fluid-filled cavities, they are not considered tumors. Their presence is often detected incidentally during imaging for other joint concerns.
When Subchondral Cysts Become Problematic
Many subchondral cysts do not cause any symptoms and are discovered incidentally during imaging tests performed for other reasons. However, these cysts can become problematic, particularly if they grow in size or indicate an underlying joint condition. When they expand, they may affect joint function or press on surrounding soft tissues, leading to discomfort.
Problematic subchondral cysts can cause localized pain, which may worsen with activity and be noticeable upon waking. Other symptoms include joint stiffness, swelling around the affected joint, and a reduced range of motion. Some individuals may also experience a grinding or scraping sensation when moving the joint. While the cysts themselves may not directly cause symptoms, any pain experienced is frequently due to an associated underlying joint disease, such as osteoarthritis.
Why Subchondral Cysts Develop
Subchondral cysts often develop as a response to joint stress and cartilage damage. The most common underlying condition linked to their formation is osteoarthritis (OA), a degenerative joint disease characterized by the breakdown of cartilage. As cartilage wears away, the normal smooth gliding of bones within a joint is disrupted, leading to increased friction and stress on the subchondral bone.
This increased stress and altered mechanics in the joint can lead to microfractures in the subchondral bone, potentially causing fluid to enter and form a cyst. Damage to the subchondral bone and the overlying cartilage are contributing factors. Trauma or injury to a joint can also lead to subchondral cyst development, even without pre-existing osteoarthritis. Inflammatory joint conditions, such as late-stage rheumatoid arthritis, may also contribute to their formation.
Identifying and Addressing Subchondral Cysts
Subchondral cysts are identified through various imaging techniques. X-rays can reveal these hollowed-out areas within the subchondral bone, although they may sometimes be indistinct. For a more detailed and three-dimensional view, Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scans are often used to assess the cyst’s size, exact location, and its impact on the surrounding joint structures. A doctor will also review a patient’s medical history, symptoms, and risk factors to confirm the diagnosis.
Management and treatment approaches for subchondral cysts vary based on their size, the severity of symptoms, and the underlying joint pathology. For small, asymptomatic, or mildly symptomatic cysts, conservative measures are recommended. These include:
- Lifestyle modifications, such as adopting low-impact exercises (e.g., swimming or cycling) to reduce joint stress, and maintaining a healthy weight to alleviate pressure.
- Pain management, often involving over-the-counter anti-inflammatory drugs like ibuprofen.
- Physical therapy, focusing on strengthening muscles around the joint, improving flexibility, and enhancing joint stability.
- Corticosteroid or hyaluronic acid injections, which may provide temporary relief by reducing inflammation and lubricating the joint.
Surgical intervention, such as draining the cyst with a needle or more involved procedures like subchondroplasty or joint replacement, may be considered if conservative treatments fail, if the cyst causes significant pain or functional impairment, or if it contributes to severe joint damage.