Torn ACL in Dogs: The Ruptured Cranial Cruciate Ligament

It’s the stuff of nightmares: Your active Labrador jumps for a ball, yelps, and limps away holding up a back leg. OK, perhaps he’s just sprained something. You take him home, put away the leash and insist he rests.  But when several days later, he’s still not using that leg and you start to worry he’s done something serious…like ruptured a cruciate ligament.

From pet dogs to Olympic athletes, a torn ACL in dogs (AKA a ruptured cruciate ligament) means a lengthy lay off from doing what they enjoy most. Worse still, especially from a pet parents perspective, a major operation is often required to get their dog back on his paws again.

So what’s so bad about a ruptured cranial cruciate ligament and what can be done to sort them?

 

Cruciate Facts in a Nutshell

To sort our knees from elbows, and ligaments from tendons, we take a deeper look at what a cruciate ligament is, the job it does, and why they’re so important.

 

What is a Cruciate Ligament?

The cruciate ligament in dogs serves the same purpose as the ACL in humans and is part of the knee joint.  Its job is to stop the thigh bone (femur) from sliding off the back of the shin bone (tibia) when the dog takes a step. This is done through a simple but clever arrangement with two cruciate (or ‘cross’) ligaments forming an ‘X’ within the knee joint, to allow hinge movements but not sliding.

What’s so Serious about Cruciate Ligament Rupture?

A Crancial Cruciate ligament rupture in dogs is like having a torn ACL in humans.  Of the two cruciate ligaments, the most important is the cranial cruciate as it’s under most strain. It anchors to femur and tibia relative to one another (like securing a ship fore-and-aft to a jetty) while allowing some movement. When the cranial cruciate snaps under pressure, the bones are no longer secured, and are able to move in a way nature never intended.

The mechanics of a ruptured cruciate mean that when the dog tries to put weight on the leg, the tibia shoots forward relative to the femur. This pinches the shock-absorbing menisci (cartilage pads) within the knee setting up inflammation. Now the dog not only has a mechanically insecure knee that doesn’t take his weight but one that’s sore and inflamed.

A cruciate rapture is so serious because the ligament can’t heal itself. In the short term the dog has a hot, swollen, painful knee, and in the longer term it will become arthritic.

 

What Causes a Ruptured Cruciate?

Now here’s a thing. Although your dog’s injury may seem sudden, the chances are ligament was already weakened, but failed suddenly. Many dogs suffer from cruciate disease as a stretching and weakening of the ligament (like an anchor rope fraying). It copes up to a point, only to snap when the dog jumps or twists with force.

As to why the cruciate weakens…great question! No one knows. There are various theories, including the immune system damaging the ligament, genetics, or hormonal factors, but in truth no one’s really sure.

What are the Signs of a Ruptured Cruciate?

The most common presentation is the dog chasing a ball, which pulls up completely lame on a back leg. However, sometimes there are subtle signs ahead of this. It might be the dog was regularly slightly lame after vigorous exercise but recovered with rest, or he was sound at the walk but lame at a gallop, until one day the ligament broke altogether.

A dog with a ruptured cruciate has a special way of standing. They tend to ‘toe-tip’ or stand with only the tips of the toes of the poorly leg, in contact with the ground.

 

How is Cruciate Disease Diagnosed?

Your vet does this through a combination of feeling for excessive movement in the joint (the ‘anterior draw’ test), joint anatomy (looking for a medial buttress or swelling on the inner aspect of the joint), and radiographs.

The x-rays help rule out other causes of lameness such as fractures, infection, or bone cancer. In addition the position of the tibia and femur relative to each other, along with the shape of the joint space all give vital clues.

 

What Happens if You Do Nothing?

Cruciate surgery is painful for the dog and expensive on your pocket. Is doing nothing an option?

For the vast majority of dogs ignoring the problem leads to complications such as severe arthritis in later life. Unfortunately, once ruptured the ligament doesn’t mend, and the best you can hope for is scar tissue eventually stabilizes the joint.

So what are the options?

 

Medical Treatment

Wouldn’t it be nice if rest and pain relief did the trick?

Here’s the rub. For small dogs, less than 10kg in weight, there’s a slim chance that six months’ worth of taking it easy may work. Their lesser size and weight means less strain on the knee, and eventually scar tissue will stabilize the joint.

But (and it’s a big ‘but’) there is a risk of premature arthritis developing as a result of bone rubbing on bone. If you decide on this route then consider giving a good quality nutraceutical supplement containing glucosamine and chondroitin. This ‘feeds’ the knee with healing chemicals and may help improve the eventual outcome to minimize damage.

 

Surgical Solutions

Most dogs need surgery, to improve their mobility and reduce the risk of arthritis. There are lots of different techniques that have developed over time. To summarize, here are the four most relevant options.

 

#1: Extracapsular Repair

This method involves using long-lasting artificial suture material, attached in a figure-of-8 loop, without entering the joint capsule. The suture stops the bones sliding over one another, whilst still allowing hinging, hence returning a normal movement. This op can be highly effective, especially in dogs under 25kg, and is especially suitable for those under 10kg.

This procedure has the huge advantage of being less invasive (and for this read less painful) than other methods. However, the limiting factor is the strength of the suture, which tends to snap in bigger, heavier dogs.

 

#2: Over-the-Top Technique (OTT)

This is a tried and tested procedure that’s been around for decades. It requires moderate surgical skills (not a beginner’s procedure, so ask if your vet has done this before!). The technique involves creating a graft using the dog’s own soft tissue fascia, which is passed through the knee joint to form a ‘new’ cruciate ligament.

Although effective, the OTT has fallen from favor as other more modern techniques have developed. Because the joint capsule is entered, this is a sore procedure. In addition, the new ligament takes several months until it reaches maximum strength, so the dog’s exercise is curtailed sometimes for as much as half a year.

 

#3: Tibial Plateau Leveling Osteotomy (TPLO)

This operation created quite a buzz when first developed, and with just cause. The thinking is brilliant, which is to change the angle at which the tibia meets the femur, so that when it takes weight the femur holds steady instead of falling off the back.

This requires the top of the shin bone (tibia) to be sliced like a cake and realigned in a new position. Special metal implants hold the knee bone in its new position. This all sounds drastic, but actually bone heals much faster than tendon (as in the OTT procedure) so the recovery time is reduced. In addition, the joint capsule is not entered, so this is less painful than an OTT.

So what’s not to like? Expertise is a must! This is all about angles, and to judge that correctly takes an expert orthopedic surgeon. This means referral to a specialist, which means $$$.

 

Tibial Tuberosity Advancement (TTA)

This op works on the same basic principle as the TPLO, which is to change the direction of forces on the knee so the femur no longer slides backwards.

The TTA is the love-child of the TPLO and the mechanics are even more complicated, making referral to a specialist even more important. The idea this time is to change the angle of a crest of bone on the front of the tibia, so that the major thigh muscles pull differently. This changed angle supports the femur in a forward direction and stops it rolling backwards.

 

To Take Things Further

Each dog is an individual and each case is different. Always speak to your vet about which options are best for your dog.

 

To find out more general information, Fitzpatrick’s Referrals and the University of Florida both have useful information on their websites.

 

Now skip to it and take that dog for a walk!

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