A loose body in the knee is a fragment of bone, cartilage, or other tissue that has broken off and floats within the knee joint. These fragments vary in size and may be single or multiple. While some loose bodies might not cause immediate issues, they often move freely, leading to discomfort and mechanical problems. This condition is common and can affect knee function if left unaddressed.
Understanding Loose Bodies
A loose body is a detached piece of material residing within the knee joint’s synovial fluid. These fragments are primarily composed of articular cartilage, the smooth tissue covering bone ends, or a combination of cartilage and bone. They can also include fragments of the meniscus or other foreign objects. Loose bodies are classified as unstable, meaning they float freely, or stable, if trapped in a fixed position within the joint. The size of these fragments can range from microscopic particles to pieces as large as a quarter or even a golf ball in rare cases.
How Loose Bodies Form
Loose bodies form due to conditions that cause tissue to detach from joint surfaces. Common causes include acute trauma or repetitive stress injuries, such as those from sports or accidents. Direct blows, fractures, or severe twisting injuries can dislodge bone or cartilage pieces.
Degenerative conditions, particularly osteoarthritis, are a frequent source. As cartilage wears away, fragments can break off. Inflammatory conditions affecting the knee can also contribute. A less common condition, synovial chondromatosis, involves abnormal growth of the synovium, producing cartilage nodules that can break off.
Recognizing the Symptoms
Loose bodies in the knee can cause various symptoms, depending on the fragment’s size, location, and movement. Pain is a primary symptom, which can be sharp or dull and may occur in different knee areas. This pain is often intermittent, coming and going as the loose body shifts.
Patients may experience clicking, popping, or a grating sound during knee movement. A common mechanical symptom is the knee locking or catching, where the joint temporarily gets stuck and cannot fully extend or flex. This can make walking difficult and may cause the knee to feel unstable. Swelling around the knee joint can also occur, especially after activity.
Diagnosis and Treatment Options
Diagnosing a loose body in the knee begins with a physical examination and a review of the patient’s medical history. Imaging tests are crucial for confirming their presence. X-rays are often the first imaging used, especially for larger, bony fragments. However, purely cartilaginous loose bodies may not appear on an X-ray.
Magnetic Resonance Imaging (MRI) is the most effective imaging for visualizing loose bodies, particularly those made entirely of cartilage, and for assessing the overall condition of the knee joint. A CT scan provides more detailed views, especially if bone fragments are suspected. An arthrogram, involving dye injection before an X-ray or CT scan, can help highlight fragments.
Treatment varies based on symptom severity and impact on joint function. For less severe cases, conservative management may be attempted, including rest, ice, activity modification, anti-inflammatory medications, and physical therapy to improve flexibility and strength. However, loose bodies often cause mechanical symptoms that only resolve with removal. Surgical intervention is recommended in most symptomatic instances to prevent further cartilage damage and alleviate symptoms.
Arthroscopic surgery is the preferred method for removal. This minimally invasive procedure uses small incisions for a camera and instruments to locate and extract fragments. During arthroscopy, the surgeon can also address associated cartilage damage. Open surgery (arthrotomy) may be used for very large or numerous loose bodies but is less common due to invasiveness. Following surgery, rehabilitation, including physical therapy, is necessary to restore knee strength and mobility.