How can i know whether it's a stretch or a tear of the meniscus or the acl?

Some it is confusing: Stretch should cause as much symptoms as tear, swelling will be less and improvement without the surgery will happened, but with tear symptoms will persist and cause more trouble (giving out, swelling). Of course your orthopedic surgeon when he examine you he could tell the difference between the two. Mri is the test to tell also the difference between the two.

Need an exam.: You'l need to be examined by a sports medicine trained orthopedic knee specialist. Then an MRI may be ordered to get you an answer, particularly about the meniscus.