Overview
A loose body in the knee is a small fragment of bone and/or cartilage that becomes separated inside the joint. It can come from an osteochondral injury, osteochondritis dissecans, degenerative cartilage damage, or less commonly conditions that cause abnormal cartilage growth. When the fragment moves, it can irritate the joint lining and interfere with smooth knee motion, leading to pain, swelling, and mechanical symptoms. Even though the fragment is inside the knee, conservative care can often reduce inflammation and improve function while you evaluate the need for further management.
Symptoms
You may notice intermittent catching, clicking, or a sensation that the knee is "stuck," especially when bending or straightening. Pain is often activity-related and may come with swelling after flare-ups. Some people develop reduced range of motion, a feeling of instability, or difficulty fully straightening the knee. Symptoms can worsen with twisting, deep squats, or repetitive bending.
Causes
Loose bodies typically form after a joint injury that damages cartilage or bone, allowing a fragment to detach. They can also develop gradually from wear-and-tear osteoarthritis or from osteochondral defects where cartilage separates from the underlying bone. In some cases, synovial conditions such as synovial chondromatosis can generate multiple loose fragments over time.
Risk Factors
Your risk is higher if you have a history of knee trauma, prior cartilage injury, or osteoarthritis. Repetitive high-impact activities, participation in sports with cutting and pivoting, and activities that place the knee under frequent twisting stress can contribute to cartilage breakdown. Age-related degeneration and certain underlying joint disorders can also increase the likelihood of loose-body formation.
Prevention
To reduce risk, protect the knee from injury by using appropriate technique for sports and avoiding unsafe pivots or sudden changes in direction when you are fatigued. Strengthening the quadriceps and hip muscles, improving flexibility, and maintaining a healthy body weight can lower joint stress. If you have knee osteoarthritis or recurrent swelling, early activity modification and supervised rehabilitation can help reduce cartilage irritation that may lead to fragments.
How the Diagnosis Is Evaluated
A clinician typically starts with your history of catching, locking, pain pattern, and any prior knee injury. Physical examination may reveal joint-line tenderness, swelling, painful range of motion, or mechanical motion limits such as reduced ability to fully extend. Imaging is used to confirm and characterize the loose body; plain X-rays may show calcified fragments, while MRI is often used to detect non-calcified cartilage pieces and evaluate the cartilage surface and any osteochondral injury. Ultrasound is sometimes used to assess effusion, but MRI or X-ray is more definitive for identifying the loose fragment.
Nonsurgical Treatment Options
Conservative care focuses on reducing inflammation, improving motion, and minimizing mechanical irritation. Activity modification, relative rest during flares, and weight-bearing adjustments can help calm symptoms while you maintain mobility. Physical therapy commonly targets range-of-motion restoration, quadriceps and hip strengthening, and movement control to decrease painful stress. NSAIDs or other anti-inflammatory pain relief may be used if safe for you. If symptoms are driven by joint inflammation, a corticosteroid injection into the knee may help temporarily, but it does not remove the loose fragment. If you also have osteoarthritis, treatments such as hyaluronic acid (for example, Orthovisc-type viscosupplementation) or platelet-rich plasma (PRP) may be considered for pain control, recognizing they do not directly eliminate the mechanical loose body.
When to Seek Medical Attention
Seek prompt medical attention if your knee repeatedly locks, you cannot bear weight, or you have sudden loss of motion that does not quickly improve. You should be evaluated urgently for major swelling, redness, fever, or severe pain that could suggest infection or a significant injury. Contact a clinician soon if symptoms are worsening, recur frequently, or you develop persistent instability. Get urgent care if you notice new numbness or progressive weakness in the leg.
Frequently Asked Questions
Sometimes symptoms improve if the fragment settles or inflammation quiets down, but the loose body usually remains and may continue to cause catching or locking.
Locking usually means the knee cannot move normally, often because the fragment blocks motion during bending or straightening.
Next Steps
If you have recurrent catching, episodes of locking, or swelling after activity, arrange an in-person evaluation to confirm the cause and determine the best conservative plan. If you have inability to bear weight or true locked knee that will not unlock, seek urgent care. Bring any prior imaging or injury history so your clinician can guide next diagnostic steps efficiently.