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It sounds like you are descring patella luxation. In layman's terms, this means wiggly kneecaps. The dog might flex his leg to pop the kneecap in place or hop if it is out.
There are effective surgeries that can help with this if is causing pain for the dog. You can also use anti-inflammatories.
If he is not in pain, you probably don't have to do anything to fix it.
Let me know if you still have questions about this.
It's not the same thing but it's a similar surgery.
Do you have more specific questions?