Loose body

Damage to the joint cartilage may result in bits breaking off and floating free in the joint.

The joint fluid may nourish the cells of the loose body, and the fragment may actually grow.

A microscopic slice of a loose body showing the living joint cartilage tissue which is stained red.

• Knee mice
• Forum discussions

Knee mice

Loose bodies are often referred to as 'knee mice' or 'joint mice'.

The bits may start off quite small, but may grow, nourished by the joint fluid (synovial fluid). They may be washed into the gutters at either side of the joint (parapatellar gutters) or behind the joint in the popliteal space, but sometimes one sweeps out and gets caught between the bones, causing sudden pain and sometimes locking or giving way.

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Synovial chondromatosis

A rare condition - synovial chondromatosis - may result in the formation of multiple loose bodies that arise from abnormal cells in the joint lining.

Removal of loose bodies is surgical.

• Quote from peer-reviewed paper:

  "....arthroscopic synovectomy and removal of loose bodies.... [is indicated in] in synovial osteochondromatosis of the knee...."

  Citation: Leung OT, Lui TH. Arthroscopic Synovectomy and Removal of Loose Bodies in Synovial Osteochondromatosis of the Knee. Arthrosc Tech. 2023 Jun 5;12(7):e1057-e1063. doi: 10.1016/j.eats.2023.02.023. PMID: 37533918; PMCID: PMC10390706.

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