How do i know if i have a meniscus tear, any ligament damage, or arthritis?

By clinical exam: The diagnosis generally can be made by a physician specializing in musculoskeletal medicine(physiatry, orthopedics) by simply an examination. Diagnostic tests can then be used to support the clinical diagnosis. Many people in your age group will have abnormal xray and MRI studies but the studies must be correlated with your clinical findings.