Cruciate ligament disease can typically be diagnosed by an experienced vet when they examine the painful knee. The examination process can be divided into: evaluation of standing patient, gait observation and orthopaedic examination. Judgement and skill are required at each of these steps to enable an accurate diagnosis in all cases. Understand that the anterior cruciate ligament that tears cannot be seen on an x-ray. Avoid thinking that your vet has to take an x-ray to make the diagnosis, it is almost always tentatively diagnosed based on physical examination techniques. Arthroscopy is the least invasive method to establish a definitive diagnosis (100% guarantee).