A tear of the cruciate ligament can be suspected if most of these features are present:
A definable injury or event
Patients with a torn cruciate generally recall the moment that the cruciate ligament gave out. Although the injury may be a contact or a non-contact injury, it usually involves a twisting of the femur bone and tibia bone in relation to one another.
A loud 'pop' at the time of injury
As the cruciate snaps apart during the injury, very often the patient hears a loud 'pop' which may even be audible to others nearby.
Unable to continue with activity
Immediate knee swelling
Because the cruciate ligament has blood vessels in it, usually the knee swells up rapidly with blood (a haemarthrosis). This may become tense and painful and may need aspiration (sucking out with a syringe and needle).