Fitzpatrick Referrals
Orthopaedics + Neurosurgery

Rupture Of The Cranial Cruciate Ligament

What is the cranial cruciate ligament?

The cranial cruciate ligament in dogs is the same as the “anterior” cruciate ligament in humans. It is a band of tough fibrous tissue, which attaches the femur (thigh bone) to the tibia (shin bone), preventing the tibia from shifting forward (cranially) relative to the femur. It also helps to prevent the knee joint from over-extending or rotating.

What happens when the cranial cruciate ligament ruptures?

The main effect of a cranial cruciate ligament rupture is laxity (i.e. looseness) of the knee, with the tibia tending to shift forward relative to the femur when the dog stands on the leg (known as “tibial thrust”). This causes discomfort (e.g. as the soft tissues around the knee are stretched), inflammation and development of osteoarthritis. The cartilage within the joint may also become eroded, including tearing of the menisci (cartilage shock-absorbing pads within the knee).

Why does the ligament rupture?

Much as in humans (especially footballers and golfers), it is possible for dogs to damage their cruciate ligaments by “trauma”, such as by sudden twisting or over-extension of the knee. However, this is extremely rare as a sole cause in dogs and usually only occurs in very athletic dogs (e.g. working sheep dogs).

In the vast majority of dogs, the cranial cruciate ligament ruptures as a result of long-term degeneration, whereby the fibres within the ligament weaken over time. We do not know the precise cause of this, but genetic factors are probably most important, with certain breeds being predisposed (including Labradors, Rottweilers, Boxers, West Highland White Terriers and Newfoundlands). Other factors such as obesity, individual conformation (i.e. shape of legs), hormonal imbalance and certain infections may also play a role.

Will my dog develop osteoarthritis?

As soon as cranial cruciate ligament degeneration starts to develop, osteoarthritis (inflammation of the joint and associated bones) immediately starts to develop too. Once present, osteoarthritis cannot be cured, but in most patients, it can be effectively managed.

What are the symptoms of cranial cruciate ligament rupture?

Hind limb lameness is the most common presenting symptom. Swelling and obvious instability (such as a clicking noise when the dog walks) are also identified in some dogs, particularly if the cruciate ligament is fully ruptured at the time of diagnosis. Many dogs are reluctant to bend the affected knee, so when they sit, the affected leg may stick out to the side of their body instead of being bent under their hind-quarters.

Many dogs will have degenerative changes of the cranial cruciate ligament in both knees. In this circumstance, lameness may be less obvious, but affected dogs may appear stiff, reluctant to exercise or play, or may seem generally depressed. This is sometimes erroneously perceived as a different problem, such as a spinal or hip issue.

How is cranial cruciate ligament rupture diagnosed?

Diagnosis in dogs with complete rupture of the cranial cruciate ligament is usually based on examination by an experienced orthopaedic surgeon, with demonstration of laxity of the joint by specific manipulations of the knee. In dogs with partial tears or early degeneration of the ligament, other tests may be necessary, including X-rays, CT or MRI scans, and laboratory tests. In most dogs, exploratory surgery or arthroscopy (keyhole surgery) is used to confirm the diagnosis, and to investigate for possible cartilage tears or other diseases.