Synovial chondromatosis, also referred to as synovial osteochondromatosis, is a rare, non-cancerous (benign) disorder affecting the synovium, the thin layer of tissue that lines the joints. This condition most commonly develops in the knee joint, although it can impact other joints throughout the body.

Despite being a benign condition, synovial chondromatosis can cause significant joint damage, which may lead to osteoarthritis if left untreated. Early intervention is essential to reduce pain and protect the joint from further deterioration.

Anatomy of Joints and Synovium

A joint is the point where two or more bones connect, such as the knee, shoulder, or ankle joints. In a healthy joint, the bones’ surfaces are cushioned by articular cartilage, a smooth, slippery tissue that enables bones to move freely and without friction.

The joint is enclosed by a joint capsule, which is composed of thick bands of tissue that provide stability. The inner layer of the joint capsule is the synovial membrane or synovium, responsible for producing synovial fluid, which acts as a lubricant for the joint, facilitating smooth and pain-free movement.

The knee joint is the most commonly affected location for synovial chondromatosis. Although not visible in standard imaging, the condition starts in the thin synovial membrane that lines the joint. This is where abnormal growth occurs, leading to the development of the characteristic cartilage nodules.

Description of Synovial Chondromatosis

In synovial chondromatosis, the synovium—the tissue lining the joint—undergoes abnormal growth and begins producing cartilage nodules. These nodules may occasionally detach from the synovium and become loose bodies within the joint.

The size of these loose cartilage bodies can vary, ranging from a few millimeters (the size of a small pill) to a few centimeters (similar to the size of a marble). Once free within the joint, these bodies are nourished by the synovial fluid, which can cause them to grow, calcify (harden), or even ossify (transform into bone). When this happens, the loose bodies may move freely around the joint space.

As these loose bodies roll around, they can damage the smooth articular cartilage that lines the joint, which often leads to osteoarthritis. In osteoarthritis, the damaged cartilage becomes worn and frayed, causing pain when the bones rub against the exposed joint surface.

In more severe cases of synovial chondromatosis, the loose bodies can grow large enough to fill the entire joint space or even invade surrounding tissues, further complicating joint function and leading to discomfort.

In these X-rays of the elbow joint (left) and ankle joint (right), the loose bodies associated with synovial chondromatosis are clearly visible.
(Left) Reproduced from Johnson TR, Steinbach LS (eds.): Essentials of Musculoskeletal Imaging. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2004, p. 297.

Commonly Affected Joints and Demographics

Synovial chondromatosis most frequently affects the knee joint, but it can also occur in the hip, elbow, or shoulder. Typically, this condition only impacts one joint in the body. It primarily occurs in individuals between the ages of 30 and 50, with men being twice as likely to develop the condition as women.

Cause of Synovial Chondromatosis

The exact cause of synovial chondromatosis remains unknown, and the condition occurs spontaneously. It is not linked to any hereditary factors and does not run in families.

Symptoms of Synovial Chondromatosis

The most common symptoms of synovial chondromatosis are similar to those associated with osteoarthritis, and include:

• Joint pain
• Joint swelling
• Limited range of motion in the affected joint

Other potential signs and symptoms may include:

• Fluid accumulation in the joint
• Tenderness in the joint area
• A creaking, grinding, or popping sound (known as crepitus) during movement

In some cases, the cartilage nodules can be felt in joints located close to the surface of the skin, such as the knee, ankle, and elbow joints.

Doctor Examination and Diagnosis

Seeking early treatment for synovial chondromatosis is crucial for reducing pain and preventing further joint damage or the progression of osteoarthritis.

Physical Examination

During a physical examination, your doctor will discuss your general health and medical history, as well as any symptoms you’ve been experiencing. The affected joint will be examined for:

• Swelling
• Tenderness
• A limited range of motion
• Grinding or creaking noises during movement, which indicate bone-on-bone friction

Diagnostic Tests

To diagnose synovial chondromatosis, your doctor will order a series of imaging tests. These tests are important not only for confirming the diagnosis but also for differentiating this condition from osteoarthritis.

• X-rays: X-rays provide clear images of dense structures like bones. Larger loose bodies that have calcified or ossified are typically visible on X-rays. However, smaller or non-calcified loose bodies may not show up on X-rays.

(Left) In this X-ray of a knee joint, the small loose bodies are barely visible (indicated by arrows). (Right) In this MRI scan, a cross-sectional image of the same knee shows the loose bodies more clearly (arrow).

 

(Left) X-ray of an elbow joint reveals two large ossified loose bodies (indicated by arrows). (Right) The MRI scan provides a cross-sectional image of the same elbow.

Reproduced from Ahmad CS, Vitale MA: Elbow arthroscopy: setup, portal placement, and simple procedures. Instructional Course Lectures, Vol. 60. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2011, pp. 171-180. 

• Other Imaging Tests: If X-rays do not reveal the loose bodies, your doctor may request a magnetic resonance imaging (MRI) or computed tomography (CT) These scans can offer a more detailed view of the joint and usually detect loose bodies. MRI and CT scans can also help identify any additional issues, such as joint fluid accumulation, or signs of osteoarthritis, like joint space narrowing or the presence of bone spurs.

Treatment of Synovial Chondromatosis

Nonsurgical Treatment

Observation: In some cases, particularly when symptoms are mild, observation may be a suitable treatment option. Your doctor will carefully evaluate several factors to determine if this approach is appropriate for you. During this observation period, the doctor will monitor the affected joint for signs of osteoarthritis progression or worsening of symptoms.

Surgical Treatment

For most patients with synovial chondromatosis, surgery is the recommended treatment to remove the loose cartilage bodies. In some instances, the synovium (the tissue lining the joint) may also be partially or fully removed through a procedure called synovectomy. Surgery can be performed using one of two techniques: open surgery or arthroscopy.

The choice of technique will depend on various factors, such as:

• The number of loose bodies present in the joint
• The size of the loose bodies
• The overall condition of the synovium

During an open surgical procedure, the surgeon makes one or two incisions to remove a large number of loose bodies from the knee joint.

In a traditional open procedure, the surgeon makes one or two large incisions to access the joint and remove the loose bodies. In contrast, an arthroscopic procedure involves smaller incisions, through which miniature surgical instruments are used to perform the surgery.

Both open surgery and arthroscopy can yield similar outcomes, and your doctor will discuss which option is best suited for your specific case.

Calcified loose bodies removed from the knee joint of a patient with synovial chondromatosis. 

 

Recovery After Surgery for Synovial Chondromatosis

The recovery time following surgery for synovial chondromatosis can vary based on the specific procedure performed and the joint affected. Your doctor will provide you with tailored instructions to support your rehabilitation and help you return to daily activities as safely and quickly as possible.

Although surgery is effective, synovial chondromatosis may recur in up to 20% of patients. To monitor for any recurrence, your doctor will schedule regular follow-up visits. During these check-ups, they will also assess the joint for signs of osteoarthritis progression.

The likelihood of developing osteoarthritis depends on the extent of joint damage caused by synovial chondromatosis prior to surgery. Your doctor will keep a close eye on your joint health to ensure any complications are addressed promptly.