The cruciate ligaments are little cords within the knee that keep the joint stable. When one of them is ruptured, the knee will become unstable and painful and your dog will limp. If untreated, the condition can lead to significant problems with arthritis. The best treatment for cruciate ligament rupture depends on how big your dog is and how severe the signs are. Some smaller dogs will do well on rest and medication, but in many cases the condition requires surgery.
What are the cruciate ligaments?
There are two cruciate ligaments in the knee, called the cranial and caudal cruciate ligaments. They run between the thigh bone and the shinbone to hold the joint together and prevent unusual movements. The reason they are called 'cruciate' is because they cross over each other in the middle of the knee, as shown in the following animation.
It is usually the cranial cruciate ligament that ruptures – this ligament runs from further back on the thigh bone to further forward on the shinbone. The ligament can either rupture all the way through, or it can develop a partial tear. A full and partial rupture are shown in the following animations:
Full rupture:
Partial rupture:
Dogs with a partial tear are often less lame when they first show symptoms, but their signs may worsen if the weakened ligament tears further or progresses to a complete rupture.
How does the cruciate ligament get damaged?
Sometimes, a healthy cruciate ligament can be damaged by excessive force on the knee - for example if your dog gets their foot caught in a hole when they're running, or pivots around at speed on the one leg. However, cruciate rupture more often develops as a result of progressive ligament degeneration - the ligament becomes weakened over time and therefore does not require excessive force to rupture.
Cruciate ligament disease is more common in certain breeds such as the Labrador Retriever, Newfoundland, Rottweiler, Golden Retriever and West Highland White Terrier. It is also more common in overweight dogs.
What happens when the cruciate ligament ruptures?
When the cruciate ligament is ruptured, the knee joint becomes unstable. This means that your dog will show signs of lameness and pain in the knee.
The instability of the knee also causes arthritis to develop, and this will be worse the longer the knee is unstable. Diagnosing and treating the disease early will reduce the chances of problems with arthritis as much as possible.
How will my vet diagnose a cruciate ligament rupture?
The cranial cruciate ligament usually prevents the tibia (shinbone) from sliding too far forward in relation to the thigh bone. So, to diagnose a cruciate rupture, your vet will manipulate the knee and see whether it is possible to move the tibia unusually far forwards. This is called the 'cranial drawer' test. Cranial drawer is shown in the following animation.
Your vet will also talk through your dog's signs with you and examine the knee thoroughly. They may also advise X-rays or other imaging of your dog's knee to check for other problems and to work out what treatment will be best.
How is a cruciate ligament rupture treated?
There are various options for treating cruciate ligament rupture, and your vet will help you choose the best option for your dog. For some smaller dogs, it is possible to manage the condition conservatively with strict rest, anti-inflammatory painkillers, weight management, and sometimes physiotherapy or hydrotherapy.
In most cases, however, surgery is required to stabilise the knee. There are many different surgical techniques used. The simplest type of surgery is to replace the ligament with an artificial band, sometimes called a lateral suture. However, this technique is not often recommended in larger dogs as the artificial ligament may not be strong enough.
Other surgical techniques involve changing the anatomy of the knee such that the ligament is no longer necessary to keep the joint stable. These techniques include 'tibial tuberosity advancement' surgery, in which the front of the shinbone is moved forwards, and 'tibial plateau levelling osteotomy' (TPLO), in which the angle of the top of the shinbone is altered to make it flatter. A TPLO is shown in the following animation.
Animation illustrating the principle of TPLO surgery:
What will I need to do after surgery?
Recovery from cruciate surgery can take about three months and it is important to follow your vet's advice on aftercare during this time. Your vet is likely to recommend a period of strict rest, in which your dog is only taken out on the lead to toilet. After this, short lead walks can be introduced and your vet will advise on how and when to increase the length of these. Hydrotherapy and physiotherapy are also sometimes recommended. It is important to stop your dog from overloading the knee by jumping up or using stairs for as long as your vet advises.
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