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Cranial Cruciate Tears

Find out more about this common injury in dogs

Cranial cruciate tears are a common cause of lameness in the dog. These tears are seen in many breeds and types of dogs but are generally a greater problem in the larger breeds such as Rottweilers, Labradors, Golden Retrievers/Boxers, Shepherds Mastiffs and Bull Terriers. They may present as an acute painful lameness or as a more gradual chronic lameness/soreness.

  • There are in fact two cruciate ligaments in your dogs knee (stifle) joint. One goes from front to back the other from back to front. They form a cross in the knee and act as a point about which the knee hinges.

     

    Also found in the canine knee are the menisci. These are two C shaped pieces of cartilage that sit between the femur and tibia and act as cushions within the knee joint.

  • The exact cause is unknown. We believe there are several factors involved including a weak or degenerative ligament and overloading of the ligament.

     

    An important difference between your knee and that of your dog is the weight bearing part of the tibia in the dog slopes backwards. This means the femur is constantly trying to drop backwards and it is the job of the cranial cruciate to hold on or anchor the femur to the tibia. So even when your dog is standing the cruciate ligament is under strain.

     

    Once the ligament tears the knee then becomes very unstable and painful. Sadly the ligament never repairs or heals properly because of a poor blood supply and the ongoing shearing action of the knee's anatomy.

  • The general stability of the knee is lost and because the knee is then used abnormally, degenerative changes begin which will lead to a progressive amount of arthritis and pain.

     

    Often dogs are seen with cruciate tears with a seemingly gradual onset of lameness that suddenly gets worse. This is because the ligament may have stretched or torn over a period of time leading to more and more instability and more degenerative joint disease/osteoarthritis.

  • If your dog is really unlucky they will also damage their menisci. Approximately one third of cruciate tears will have some meniscal damage. This is caused by a scuffing action of the femur as the knee is bent and straightened . This would normally be stopped by the anchoring action of the intact ligament. These meniscal tears are acutely painful and significantly worsen the disease and prognosis for a full recovery. The longer the knee is left unstable the greater the risk of tearing the menisci and the more degenerative joint disease.

  • The clinical examination and symptoms are the most important factor in diagnosis. Radiographs will be taken while your dog is under general anaesthetic (GA). This will allow us to see the degree of boney changes present within the knee. While under GA we can also check for the presence of a cranial draw sign. This is where the tibia can be shunted forward which will show how unstable the joint is. Also from the X-rays we can assess the slope of the tibial table.

We use two main surgeries to treat cruciate tears:

1. Lateral Stabilising Suture

This involves replacing the ruptured ligament with a loop of hard nylon wire. The wire passes around a small bone at the back of the knee (lateral fabella) then through two bone tunnels drilled in the tibia.

Over 90% of dogs with this surgery show considerable improvement. Unfortunately 40-50% will still exhibit some form of lameness albeit intermittent.

This was until recently the main stay of our surgical treatment of cruciate ruptures and still remains a valuable option. However some patients, particularly larger dogs, may remain stiff and a full return to athletic potential is not achieved.

The inadequacy of this technique is that firstly we don’t have a ligament replacement that is stronger than the original ligament but retains the elasticity. Secondly it does not address one of the causes of the rupture i.e. the slope of the tibia.

2. Tibial Tuberosity Advancement

This is technically more demanding and requires specialised instruments and implants. The tibial tuberosity (the top part of the shin) is cut and moved forward then reattached to the tibia with custom made titanium implants.

Effectively this changes the position of the patellar ligament relative to the tibial table thus removing the effect of the backward slope of the tibia, so now there is no need for the anchoring of the cruciate ligament.

We have been performing TTAs for several years and the results are very exciting. Many dogs both working and pets make a full recovery to athletic ability often with little or no long term painkillers.

The other huge benefit from a TTA is there is significantly less degenerative joint disease and arthritis as these dogs get older compared to other treatments. This is the most important feature of TTAs.

Summary

Cranial cruciate tears are a common, debilitating condition of the dog's knee. It will produce arthritis, pain and lameness all of which will progressively worsen with time. However with correct treatment and care we can now expect all our patients to exercise happily and enjoy a good quality of life.

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