Loose Bodies in Joints (Joint Mice)
Loose Bodies are free-floating fragments of bone or cartilage inside the joint space. They can cause mechanical symptoms like locking and catching.
1. Etiology
- Osteoarthritis (OA): Broken osteophytes (Most common in elderly).
- Osteochondritis Dissecans (OCD): A piece of subchondral bone dies and detaches (common in young athletes, Knee/Elbow).
- Synovial Chondromatosis: Synovium undergoes metaplasia, producing hundreds of cartilaginous loose bodies ("Snowstorm" appearance).
- Trauma: Chip fractures.
2. Clinical Features
- Locking: Sudden inability to move the joint (mouse gets trapped).
- Palpable: Patient can often feel the "mouse" moving around subcutaneously.
- Pain & Swelling: Intermittent effusion.
3. Management
- Arthroscopic Removal: The gold standard for symptomatic loose bodies.
- Fixation: Large OCD lesions in young patients may be pinned back in place.
25 Practice MCQs
Q1. Loose bodies are colloquially known as:
Answer: A). Because they dart around inside the joint.
Q2. Most common site for loose bodies is:
Answer: A). Large joint space.
Q3. Synovial Chondromatosis involves:
Answer: A). Can produce hundreds of pearl-like bodies.
Q4. Osteochondritis Dissecans (OCD) most commonly affects:
Answer: A). Classic location.
Q5. The primary symptom of a loose body is:
Answer: A). Mechanical block.
Q6. "Snowstorm" appearance on X-ray indicates:
Answer: A). Many calcified bodies.
Q7. Fibrinous loose bodies (Rice bodies) are seen in:
Answer: A). Not bone, but fibrin.
Q8. Treatment for a symptomatic loose body is:
Answer: A). Removal prevents cartilage damage ("pebble in the shoe").
Q9. Can loose bodies damage the joint?
Answer: A). Like sand in a gearbox.
Q10. Clanton classification is for:
Answer: A). Grades stability of the lesion.
Q11. Which imaging is best for cartilaginous (non-ossified) loose bodies?
Answer: A). X-ray only shows calcified bodies.
Q12. Panner's Disease is:
Answer: A). Similar to OCD but involves the whole ossific nucleus.
Q13. Is Wilson's Test used for OCD?
Answer: A). Impinges the lesion on the tibial spine.
Q14. Drilling (Microfracture) is used for:
Answer: A). Brings marrow cells to the surface.
Q15. A "nidus" is:
Answer: A). Layers of cartilage grow around it.
Q16. Are all loose bodies visible on X-ray?
Answer: B). Need MRI or Arthroscopy.
Q17. Secondary Synovial Chondromatosis is due to:
Answer: A). Fewer bodies than primary type, varying sizes.
Q18. Fixation of OCD is preferred if:
Answer: A). To restore the articular surface.
Q19. Melon seed bodies are seen in:
Answer: A). Fibrin bodies.
Q20. Which joint is the second most common site for OCD?
Answer: A). Talar dome lesions.
Q21. Can loose bodies reattach spontaneously?
Answer: B). They grow (fed by synovium) but don't reattach.
Q22. OATS procedure stands for:
Answer: A). Plugs of healthy cartilage/bone moved to the defect.
Q23. "Joint Mouse" usually refers to:
Answer: A). It moves away when you try to touch it.
Q24. Synovectomy is required for:
Answer: A). Because the synovium is the source of the bodies.
Q25. A loose body in the posterior knee compartment is:
Answer: A). Requires specialized portals.
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