Loose bodies may develop in any synovial joint, though the knee is most common. Sometimes known as ‘rice bodies’ or ‘knee joint mice’, they most often affect athletes and older individuals with knee arthritis.
The ‘loose bodies’ themselves are typically made of cartilage or bone. In rare cases, such as after an open fracture, they can be foreign debris or elements left after a previous surgery. Rarer conditions such as synovial chondromatosis may also cause them.
Patients affected by a loose body in the knee may experience:
· Knee pain and swelling (especially worsening with activity)
· Limited range of motion in the affected joint
· Warmth and tenderness to the touch
· The knee feeling ‘locked’ or ‘caught’
· Creaking, grinding, or popping noises when moving the knee
· Limited range of motion (especially due to pain or stiffness)
· A solid lump beneath the knee’s skin that they can feel.
Note that these symptoms are not specific to loose bodies, and may indicate other knee conditions. For a full assessment, ask your doctor for a referral to Orthopaedics SA.
Loose bodies are most often caused by knee trauma. Small fractures, bleeding inside the knee joint, and tissue death from tuberculosis or arthritis can cause sections of bone and cartilage to break away (become ‘loose’) and float around inside the knee joint. These fragments may produce minimal symptoms or none whatsoever, but sometimes becomes caught in the joint and cause difficulty with movement.
Knee surgery also causes loose bodies on occasion. The procedure itself or the injury which warrants it may impact blood supply to the knee’s bones and make their tissues more likely to separate. Less commonly, an object left in the knee after surgery becomes loose and requires further surgery to be removed.
Orthopaedic surgeons generally begin diagnosing loose bodies in the knee with a physical exam. This involves asking questions about your symptoms and how long you have been experiencing them, your levels of pain, and your family history of knee or other orthopaedic conditions. The surgeon may also ask you to attempt certain movements or manually manipulate the knee to assess its function.
Most doctors then refer for an X-ray to assess bony fragments and deformities. If your pain is caused by another condition (such as knee arthritis), this test may hint toward an alternative or complementary diagnosis.
As X-rays often do not clearly show damage to the cartilage, your doctor may request an MRI scan to evaluate the joint’s softer structures. The MRI may also show inflammation or ligament damage that an X-ray cannot detect.
Your treatment options depend on the number of loose bodies present in the knee, their size, and whether other structures in the knee are damaged.
Observation and activity modification are the best treatments for loose bodies which do not produce significant pain or functional impairment. Your doctor may recommend an over-the-counter painkiller (like Nurofen or Advil) and recommend follow-up appointments to monitor your function and pain levels. Surgery is sometimes indicated if symptoms worsen and impact your day-to-day life.
Surgical treatment generally consists of arthroscopic knee debridement. This minimally invasive procedure involves a surgeon making several small incisions in the knee’s skin, which they use to pass a small camera and tiny tools into the joint space. The tools and camera are used to identify and remove the loose bodies. If needed, your surgeon can partially or completely remove the knee’s synovium (perform a synovectomy) in the same procedure.
Cases where the loose bodies are large or there are a great number of them may warrant an open knee debridement. This procedure has the same goals and outcome, but is performed through a single large incision instead of several small ones. Open debridement allows the surgeon to better visualise the operative environment, but produces larger scars and may carry a higher risk of some complications.