Brief Answer: Ligament or meniscal injury Detailed Answer: Hello, Thanks for your query. From description it seems you might develop ligament or meniscal injury and that might be the cause of popping out or instability of knee. I would suggest getting this evaluated by an orthopedician for an accurate diagnosis and appropriate management. You may get the X-ray/MRI of the area affected under his/her guidance. In the interim,apply ice packs to the affected area,anti-inflammatory drug like motrin to reduce pain and inflammation. Avoid putting weight and rest well. I do hope that you have found something helpful and I will be glad to answer any further query. Take care

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