Cruciate rupture – knee injury in dogs

The knee (or stifle) is a complicated joint. It comprises the femur above, the tibia below and the kneecap (patella) in front, with the small bony fabella behind. The femur sits on C-shaped cartilages at the tibial plateau acting like cushions for movement. Various ligaments hold these bones in place to allow for normal movement.

There are two cruciate ligaments that cross inside the knee joint, the cranial (towards the head) cruciate and the caudal (towards the tail) cruciate. They form an X-shape, hence the term cruciate ligament. The cranial cruciate ligament stops the tibia sliding forward relative to the femur.

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Finding the Rupture

A ruptured cruciate ligament is the most common knee injury in the dog. Dogs with sudden non-weight bearing lameness in a hind limb more often than not have ruptured their cruciate ligament. Dogs most often present in the acute stage, close to when the injury occurred or in the chronic stage, weeks to months after the injury occurred.

The key to diagnosis is a simple test to see if the tibia slides forward relative to the femur, as a normal knee will not generally show this sign, due to the cruciate ligaments function. Clients are often surprised at how quickly the veterinarian comes to the diagnosis. If the rupture occurred some time ago or the joint has been progressively degenerating over time, a swelling on the inside of the knee may be present know as medial buttress. This is often a sign of maturing arthritis.

If the animal is tense in the consultation room, the tensed muscles may artificially stabilise the joint and the common clinical signs will be less evident. This may also be the case if the ligament is only partially ruptured. A sedation may allow for better manipulation and allow for x-rays to be conducted to confirm the diagnosis. It is important to x-ray the stifle before surgical repair to identify any other possible complications.

Arthritis present in the joint may slow the recovery after corrective surgery. However, surgical correction can often slow or prevent further arthritis development.

How Rupture Happens

Several clinical presentations may be seen with ruptured cruciate ligaments. One is a young athletic dog playing enthusiastically injuring the knee. Often these dogs are large breed dogs. At risk dogs include: Labrador retriever, Golden retriever, Rottweiler, Newfoundland, Akita, St. Bernard, Chesapeake Bay retriever and American Staffordshire terrier.

Alternatively, older dogs, especially if overweight, can have progressively weakened ligaments that partially tear or tear with less activity. These dogs often suffer rupture of the other cruciate ligament within one to two years.

Smaller dogs often rupture their cruciate ligaments and may have concurrent medial luxating patella in the same knee. Medial luxating patella is where the kneecap pops in and out of place and the owner may have observed intermittent hopping for much of the dog’s life. This condition may result in extra strain on the cruciate ligament.

Surgical Repair or None

There are several different surgical repair options for addressing a cruciate rupture. The different types may have varying costs to the client and can be discussed if the diagnosis is made, as well as which procedure may benefit the animal most.

Occasionally the animal may not require surgical intervention, although in most cases surgical repair may prevent the progression of osteoarthritis. A case by case assessment will be undertaken with each client before a treatment strategy is devised.