Can a piece of cartilage get stuck under the kneecap? what are the symptoms of having a acl problem? please help

Yes: Yes, you can definitely have what ine or more "loose bodies" which can float in the knee and cause pain and swelling, they often will arise from a cartilage source. An ACL injury, when complete, will often cause the knee to feel unstable, like it gives way. Don't hesitate to be seen for a specific diagnosis.

Knee pain: These are two very different problems.When a piece of cartilage gets stuck under your kneecap you will have a locking or catching type problem. You could have problems flexing or extending your knee and certainly problems with going up and down steps. With an ACL injury,there is usually a sense of instability and a sense of the knees shifting.There's usually a sense of apprehension with activities