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

If it is the anterior cruciate ligament that is torn, usually the patient is unable to go on with the activity. Sometimes it is possible to continue if only the PCL is torn.

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).

The instability may not be immediately apparent as the person is likely to be helped to a position of rest, but this tends to become a key symptom as soon as the patient tries to walk again.