What is the cruciate ligament?
There are two cruciate ligaments in the knee joint, the cranial (or anterior) cruciate ligament and the caudal (or posterior) cruciate ligament. The cranial cruciate ligament is very commonly injured in dogs and this causes instability of the knee and may lead to other problems such as meniscal (cartilage) injury and osteoarthritis. It is rare for the caudal cruciate ligament to be injured.

What sort of dogs are affected?
Although in people, cruciate ligament rupture usually occurs during sports injuries incurred, for example, by skiers, soccer and rugby players, the situation in dogs is quite different. The cruciate ligament seems to weaken gradually in dogs, particularly in some larger breeds, and this means that the cruciate ligament may eventually rupture even during normal activity. Some large breed dogs can suffer cruciate ligament rupture from quite an early age (1-3 years) and often in both knees. Epidemiological evidence does indicate that certain breeds are at increased risk for cruciate rupture and these breeds include:

Labrador Retriever, Golden Retriever, Rottweiler, Mastiffs, Boxer, Newfoundland, West Highland White Terrier. However, many dog breeds can suffer from cruciate ligament rupture.

There is a suggestion that obesity also increases the risk of cruciate ligament rupture. This may be so, although further scientific information on this is required. Certainly avoiding obesity has been shown to reduce the severity of arthritis in other joints, so it seems to be sensible.

What causes cruciate ligament rupture?
The cause of the gradual degeneration of the cruciate ligament is not known. However, recent research indicates that even "normal" ligaments from dogs at risk of cruciate rupture are weaker compared to those breeds at low risk. It appears that the ligament structure is altered such that it is unable to function as it should and is prone to failure. Research continues to elucidate the reasons for ligament degeneration. This department currently has a research programme addressing this issue. Our recent finding will be published shortly and we have ongoing funding for further studies. In addition, we are also investigating the genetic basis for this disease through the UK Companion Animal DNA archive, in collaboration with other UK veterinary schools and the Animal Health Trust.

What are the signs of this condition?
Rupture of the cruciate ligament may occur suddenly or gradually and this can be reflected in the appearance of the signs of the condition which include lameness and stiffness of the knee. Full rupture of the cruciate ligament causes instability of the knee and this may lead to joint swelling and wasting (atrophy) of the muscles of the hindlimb, particularly the quardiceps muscle group. Dogs with cruciate ligament rupture often prefer to sit with the affected limb straightened out in front of them rather than tucked up; this is because they do not like to flex the knee.

How are these conditions diagnosed?
A clinical examination by a veterinary surgeon is the first step in diagnosis. If cruciate ligament rupture is suspected, further tests may be required, including x-rays, joint fluid analysis, arthroscopy, MRI, or exploratory surgery. Once the cruciate ligament is ruptured, about 40-60% of knees will also develop injury to one of the cartilages of the knee. Osteoarthritis will develop in all knees with cruciate rupture, but may not cause problems for many months or years.

This x-ray is from a dog with a recent cruciate ligament rupture. There is increased fluid inside the joint but otherwise the joint appears relatively normal. However, the process of osteoarthritis will have begun and will tend to progress with time.

What can be done to treat the condition?
If causing persistent problems, and especially in larger dogs, the condition is best treated with surgery to stabilise the knee. There are many different surgical techniques for treating the condition and even specialty surgeons disagree regarding the best option. There is a lack of good scientific data to guide the surgeon and pet owner and surgeon preference for a particular technique is an important factor. Some of the common surgical techniques used to treat the condition include:

Over-the-top fascial graft technique

Lateral fabellar inbrication suture

Tibial plateau levelling osteotomy (TPLO)
There is no agreement as to which is the best technique. Recent data would suggest that if there are differences between the techniques, these are minimal.

In the long run, all joints with cruciate ligament rupture will develop some degree of osteoarthritis. However, for most dogs the response to surgery is good and the osteoarthritis does not seem to cause problems for several years.

These three x-rays are from the same dog showing the progression of osteoarthritis during the 18 month period following cruciate ligament rupture. The progression os the arthritis will vary from dog to dog.

Publications on cruciate ligament rupture from Liverpool staff
1. Fernihough JK, Innes JF, Billingham MEJ, Holly JMP. Changes in the local regulation of insulin-like growth factors I and II and insulin-like growth factor-binding proteins in osteoarthritis of the canine stifle joint secondary to cruciate ligament rupture. Veterinary Surgery 2003;32(4):313-323.

2. Innes JF, Shepstone L, Holder J, Barr ARS, Dieppe PA. Changes in the canine femoropatellar joint space in the postsurgical, cruciate-deficient stifle joint. Veterinary Radiology & Ultrasound 2002;43(3):241-248.

3. Innes JF, Bacon D, Lynch C, Pollard A. Long-term outcome of surgery for dogs with cranial cruciate ligament deficiency. Veterinary Record 2000;147(12):325-328.

4. Innes JF, Sharif M, Barr ARS. Changes in concentrations of biochemical markers of osteoarthritis following surgical repair of ruptured cranial cruciate ligaments in dogs. American Journal of Veterinary Research 1999;60(9):1164-1168.

5. Innes JF, Sharif M, Barr ARS. Relations between biochemical markers of osteoarthritis and other disease parameters in a population of dogs with naturally acquired osteoarthritis of the genual joint. American Journal of Veterinary Research 1998;59(12):1530-1536.

6. Innes JF, Barr ARS. Clinical natural history of the postsurgical cruciate deficient canine stifle joint: year 1. Journal of Small Animal Practice 1998;39(7):325-332.

7. Innes JF, Barr ARS, Patteson MW, Dieppe PA. Scintigraphy in the evaluation of osteoarthritis of the canine stifle joint - Relationship with clinical, radiographic and surgical observations. Veterinary and Comparative Orthopaedics and Traumatology 1996;9(2):53-59.