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Loose Body in the Knee

A loose body in the knee is a small fragment of bone, cartilage or other tissue that is free within the knee joint. Loose bodies may move around the joint and can sometimes become caught between the joint surfaces, causing pain, catching or locking of the knee.

Some loose bodies cause few or no symptoms and are discovered incidentally on an X-ray or MRI scan. Others can cause recurrent mechanical symptoms and may require treatment.

What causes a loose body in the knee?

Loose bodies can develop for several reasons. Common causes include:

• Cartilage or osteochondral injury – an injury may dislodge a fragment of cartilage or a piece containing both cartilage and underlying bone.
• Osteoarthritis – degenerative changes within the knee can result in fragments of cartilage or bone becoming loose within the joint.
• Osteochondritis dissecans (OCD) – a segment of cartilage and underlying bone can become unstable and, in some cases, detach.
• Synovial chondromatosis – a condition in which multiple cartilage nodules develop from the lining of the joint. These nodules may detach and form multiple loose bodies.
• Previous knee injury or surgery – occasionally, loose fragments may develop following previous trauma or procedures involving the knee.

Determining the cause is important because treatment may need to address the underlying knee condition as well as the loose body itself.

What are the symptoms of a loose body in the knee?

A loose body does not always cause symptoms. When symptomatic, patients may experience:

• Pain within the knee
• Swelling
• Clicking or catching
• A sensation of something moving inside the knee
• Intermittent locking
• Difficulty fully bending or straightening the knee
• Sudden episodes in which the knee becomes temporarily stuck

Symptoms can be intermittent because a mobile loose body may move to different parts of the knee.

Can a loose body cause the knee to lock?

Yes. A loose body can occasionally become trapped between the moving surfaces of the knee and produce mechanical locking.

This may cause the knee to suddenly become stuck or prevent full extension. The obstruction may subsequently move, allowing the knee to move normally again.

However, not every episode of knee locking is caused by a loose body. Meniscus tears, cartilage injuries and other knee conditions can produce similar symptoms, so an assessment is useful when locking is recurrent.

How is a loose body in the knee diagnosed?

Assessment usually begins with a history and physical examination. Your doctor will ask about previous injuries, swelling, locking or catching and whether symptoms occur during particular movements.

X-rays

Loose bodies containing sufficient bone or calcium may be visible on an X-ray. X-rays can also demonstrate associated conditions such as osteoarthritis.

MRI scan

An MRI scan of the knee can identify loose bodies that may not be visible on X-rays and assess the cartilage, menisci, ligaments and other structures within the knee.

MRI can also help determine where a loose body originated and whether there is an underlying condition that requires treatment.

What is synovial chondromatosis?

Synovial chondromatosis is an uncommon condition affecting the lining, or synovium, of a joint. Multiple small cartilage nodules form within the synovium and may subsequently detach, producing multiple loose bodies within the knee.

These loose bodies may increase in size and some may eventually calcify or ossify, making them visible on X-rays.

Patients may develop pain, swelling, stiffness, reduced movement, catching or locking.

Treatment depends on the severity of symptoms and the extent of the condition. In symptomatic cases, surgery may involve removal of the loose bodies together with treatment of abnormal synovial tissue where appropriate.

Does every loose body need to be removed?

No.

A small loose body discovered incidentally that is not causing symptoms may not necessarily require surgery. Treatment depends on factors including:

• Whether the knee is painful or swollen
• Whether there is recurrent catching or locking
• The size and location of the loose body
• Whether the loose body is mobile
• The underlying cause
• Associated cartilage or meniscus damage

Observation and treatment of the underlying knee condition may be appropriate when mechanical symptoms are absent.

When is arthroscopic removal considered?

Knee arthroscopy may be considered when a loose body causes persistent pain, recurrent swelling, catching, mechanical locking or restriction of movement.

Arthroscopy is a keyhole procedure in which a small camera is introduced into the knee through small incisions. The joint can be inspected systematically and loose fragments can be identified and removed using arthroscopic instruments.

Importantly, arthroscopy also allows the surgeon to assess the source of the loose body and other structures within the knee.

Depending on the findings, additional treatment may be required for associated cartilage injury, an unstable osteochondral lesion or abnormal synovial tissue.

Learn more: Knee Arthroscopy in Singapore →

Arthroscopic treatment of synovial chondromatosis

When synovial chondromatosis produces multiple symptomatic loose bodies, arthroscopic surgery can be used to locate and remove loose bodies from different compartments of the knee.

A synovectomy, involving removal of affected areas of abnormal synovial tissue, may also be performed when indicated.

The exact procedure depends on the number and location of loose bodies and the extent of synovial involvement. Occasionally, disease in areas that are difficult to access arthroscopically may require a different surgical approach.

What happens after arthroscopic loose body removal?

Recovery depends on what is found and treated during surgery.

When the procedure consists primarily of loose body removal, patients can often begin moving the knee and bearing weight relatively early. If additional procedures are performed for cartilage, meniscus or osteochondral pathology, rehabilitation may need to be modified accordingly.

Return to work and sport therefore depends not simply on removal of the loose body, but also on the underlying condition and any additional treatment performed.

Can loose bodies come back?

A loose body that has been completely removed does not itself grow back. However, new loose bodies can develop if the underlying condition remains active.

This is particularly relevant in synovial chondromatosis, which can recur after treatment. Follow-up may therefore be recommended depending on the underlying diagnosis and extent of disease.

When should I see a knee specialist?

Consider assessment if you have:

• Recurrent locking or catching of the knee
• Persistent knee swelling
• Difficulty fully straightening or bending the knee
• An X-ray or MRI report describing a loose body
• An osteochondral fragment within the knee
• Multiple loose bodies or suspected synovial chondromatosis
• Persistent symptoms despite non-operative treatment

The aim of assessment is not simply to determine whether a loose body is present, but to establish why it developed and whether it is responsible for your symptoms.

Loose Body and Knee Arthroscopy in Singapore

Dr Puah Ken Lee is an orthopaedic surgeon with an interest in sports knee injuries and arthroscopic surgery. He assesses patients with knee pain, mechanical locking, cartilage and osteochondral injuries, meniscus injuries and loose bodies within the knee.

Where appropriate, symptomatic loose bodies can be treated using arthroscopic (keyhole) surgery, while addressing associated abnormalities within the knee during the same procedure.

Learn more about Knee Arthroscopy →

Book an appointment with Dr Puah →

Related Pages

You may also find these pages helpful:

• Knee Conditions
• Meniscus Tear
• Knee Arthroscopy
• Sports Knee Injuries
• Knee Specialist Singapore
• Knee Treatments

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Dr Puah is regularly invited to teach arthroscopy internationally

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Loose bodies in the knee are common. Early diagnosis and appropriate management can improve outcomes and prevent long-term problems.
Dr Puah Ken Lee is an orthopaedic surgeon in Singapore specialising in shoulder, elbow and sports injuries at 360 Orthopaedics, Mount Elizabeth Novena. Patients with persistent locking, stiffness or pain in the knee are encouraged to seek specialist evaluation.