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Diagnosis of Cruciate Ligament Disease

So I hope you've read through the initial information on cruciate ligaments in dogs. The next bit is to understand how we diagnose this problem.

Diagnosis of cruciate ligament disease, can be the easiest and quickest diagnosis to make, and sometimes also one of the hardest. This is because as said before, the ligament doesn't always fully rupture when a dog is still consistently painful, and also some of our patients have had such a long history of progress ligament weakening, there is a lot of scar tissue built up around the joint which makes instability harder to feel.

The simplest method of diagnosis of cranial cruciate ligament rupture diagnosis is performed in the consulting room - and is called the 'Cranial Drawer Test' 


This is a test where the vet shows the instability of a ruptured cruciate by pushing the tibia forwards, while keeping the femur still - it is not possible to do this in a dog with a normal knee. This single test is simple, cheap and absolutely diagnostic of a ruptured ligament. Sometimes in very strong dogs it is necessary to sedate or even induce anaesthetic to allow them to be sufficiently relaxed to accurately perform this test. I often find myself proven wrong when I tell an owner, the ligament isn't fully ruptured when their 40kg Rottweiler is conscious, only to find under anaesthetic the ligament has completely gone. A partially torn ligament might prove painful when a drawer test is performed, but not always.

The second test is perhaps more sensitive for a partially torn cruciate ligament, but it also diagnostic for a fully torn ligament, it is the 'Tibial Compression Test'. In this test, the vet mimics load bearing by fixing the knee in a walking angle, and then pushing up on the foot, to mimic load. The tibia will slide forward under this load, and with a partially torn ligament will often be painful.

Sometimes the best way to show that the knee is the problem is just to extend the knee to its fullest extent, which is often painful when dogs have a partially torn ligament.

X-rays do not actually confirm the diagnosis of cruciate ligament disease, although they sometimes can, if a knee's instability has been so long standing it has led to a dislocation remodelling of the joint.

In most cases x-rays are used to:

1. Rule out other conditions - occasionally bone tumours are found lurking in a dog with a cruciate ligament rupture.

2. Get an early feel for the level of arthritis pre-existing in a dog's knee (indicative of a slowly progressive cruciate disease)

3. Measure angles for surgery

4. Examine an individual dog's knee for anatomical differences which might mean one type of surgery is selected over another.

X-rays are always taken at our clinic prior to surgery, even if the rupture of the ligament has been diagnosed in the consulting room. It is not possible to perform the correct surgery for an individual case without x-rays first. If the incorrect technique is chosen, then the outcome might be compromised.

This X-ray shows evidence of swelling within the knee joint, visible as a fluffy white cloud in the triangle on the front of the joint, this is typical of a relatively recent cruciate ligament rupture.

If the signs on x-rays, and clinical examination tests are not conclusive, it is possible to relatively non-invasively diagnose the cruciate ligament as the source of the pain, by using an arthroscope. Here at Peninsula Vetcare when I perform a cruciate surgery, I examine the joint to check for cartilage tears with an arthroscope, but occasionally when a lameness has been long standing, and there is no concrete evidence of cruciate ligament disease, except for a painful knee joint, we do use the 'scope to confirm our suspicion that the ligament is involved.

Dr Chris Franklin (Jan 2018)