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Knee Injuries in Your Dog

ACL Anterior Cruciate Ligament

Problems - Their Repair And Treatment



Ron Hines DVM PhD

Lots of my articles are plagiarized and altered on the web to market products and services. There are never ads running or anything for sale with my real articles. Try to stay with the ones that begin with http://www.2ndchance.info/ in the URL box or find all my articles at ACC.htm.

It is 2016. I wrote this article in 2009. More studies now confirm that neutering your pet before it is 1 year old (or its first heat cycle) can make cruciate ligament problems considerably more likely to occur. I know that is of no help to you at this point; but you might want to spread the word around. You can read some of those more recent studies here, here, here and here .

The Anterior Cruciate Ligament (ACL) and the Cranial Cruciate Ligament (CCL) are the same thing. Our knee is our pet's stifle. Physicians describe the ligament as "anterior" because it is toward our front. Veterinarians describe it as "cranial" because it is toward the pet's head.

August 2015: Not all large dogs will mend with conservative treatment. A new - less traumatic - modification to the tightrope procedure was announced by Arthrex this month. Click here to see how the new surgery is done. Here to see the original procedure.







What Are The Cruciate Ligaments And

What Happened To Them In My Dog ?

Your dog’s knee is also called its stifle. The two most common problems that involve this joint are torn or stretched cruciate ligaments and dislocating kneecaps, which you can read about in a separate article here . The condition of your pet's cruciate ligaments and its patella (knee caps) always need to be evaluated together (ref).

Your pet's stifle is the joint that bridges the upper and lower leg bones, the femur and tibia (click "full size" here or above). Your pet's stifle is an amazingly complex joint. To add stability to the joint, Nature has provided some very strong ligaments. Two of these are attached in a crosswise fashion, hence the names, anterior and posterior cruciates or “cross” ligaments. These ligaments act together with two outer bands of fibrous ligament, the lateral collateral ligaments, and the kneecap to maintain your pet's knee stability through a wide range of motion.

A small group of dogs suffer torn cruciates as a true sports injury. These are dogs that test the physical limits of their bodies through over-exertion, agility trials, roughhousing, dock jumping, and Frisbee catching.

But veterinarians see cruciate ligament damage much more frequently in overweight, neutered, middle-aged dogs. Veterinarians used to think of cruciate tears as a relatively simple and straightforward problem - the dog made a sudden incorrect move that tore the ligament. But recent research has shown that cruciate problems are anything but simple and straightforward in their cause and treatment.

For instance:

Research has shown that dogs over 4 years old that are spayed or neutered are considerably more likely to suffer cruciate tears than dogs that remain sexually intact.

We used to think that cruciate problem appeared suddenly – after a sudden twisting movement or due to jumping up or out of an elevated location. But we now know that this problem has usually been brewing for some time. There is even some evidence that these ligaments may tear after your pet's joint becomes inflamed (lymphoplasmacytic synovitis) - rather than becoming inflamed because of a torn ligament as we had once supposed.

Whatever the cause or causes, something more than a simple accident is usually occurring because it is common for the pet's second knee to go out sometime after the first.

Another group of dogs that suffer from this disease are those receiving corticosteroid medications for long periods. It is uncertain if these pets develop the problem because they gain weight or because corticosteroids decrease ligamental strength. A similar over-abundance of corticosteroid occurs if your pet develops Cushing's disease.


How Is A Cruciate Problem Diagnosed In My Pet?

Examination of a painful stifle (knee) in your pet is best done under anesthesia or heavy sedation. Besides being painful, the muscles of your pet's joint will probably be in spasm, making diagnosis difficult or impossible in un anaesthetized pets.

After relaxing the pet, I place one hand on the thigh to immobilize the femur and with my other hand I attempt to move the tibia anteriorly and posteriorly as the white arrow indicates in the diagram. A normal joint will not move in these directions because intact cruciate ligaments prevent it. Only in knees where the cruciate ligaments have snapped or stretched is this forward and backwards motion possible. We call this motion the “anterior drawer” effect. The term was taken from human medicine many years ago. (As performed on dogs or cats it is actually more similar to the Lachman Test which you can view here. As I mentioned, to give valid results, the test needs to be performed by your veterinarian while the pet is sedated. That is usually at the same time that x-rays of the stifle (knee) are taken.)

In old injuries to the knee, scarring may prevent some of this characteristic motion, but not the pain. In old injuries, the lateral collateral ligaments that stabilize the knee may be stretched and loose as well.

In most cases it is the anterior, rather than posterior cruciate ligament that has torn. When there is any question in my mind as to the diagnosis, I compare the looseness of the affected joint with the normal one. Particularly when the tear is old, the affected knee may pop and click when it is manipulated. On occasion, these joints are puffy with excess fluid. Specialized veterinary centers confirm cruciate tears in a more sophisticated way. When the dog's size allows, an arthroscope can be inserted into the joint to actually see if the cruciate ligament is torn or if the meniscal cartilage is damaged.

X-rays will not detect the damaged ligaments in your pet when they occur, but they will pick up later arthritic changes as they develop in the unstable joint. It is also quite common for cruciate ligament damage to be misdiagnosed as a hip dysplasia problem and some dogs actually do have both hip and knee problems simultaneously. In the rare instances where both legs are affected simultaneously, the diagnosis can be mistaken for a spinal nerve injury.

What Treatment Would Be Best For My Pet ?

Veterinarians treat pets with cruciate ligament tears medically or surgically.

Conservative Medical Treatment

Publications like Veterinary Practice News, help veterinarians keep abreast of current therapy choices. In their October 2012 issue, Dr. Narda Robinson, Director of the Comparative and Integrative Pain Medicine Center at Colorado State Veterinary School, published a well-researched article on conservative treatment options for pets that have injured their cruciate ligament. You can read it here , and her 2013 update here.

If your dog's optimum weighs is 55 pounds or less, medical treatment is probably the best choice. Most of these lighter pets will improve with a conservative treatment of rest, restriction of strenuous exercise, hydrotherapy and anti-inflammatory medications. More than two thirds of the dogs that weight under thirty pounds will be nearly normal in six months.

Some veterinary hospitals have specialized tanks and whirlpools for hydrotherapy or will refer you to a center that does this. Stretch/range-of-motion exercises also seem to be quite helpful. Others practice treatment with less documented benefits such as cryotherapy, laser therapy and neuromuscular electrical stimulation – treatments commonly used in sports and rehabilitative human medicine.

Orthotic knee braces are also an option for residual pain, rehabilitation, as an alternative to surgery or to aid in post surgical recovery. When knee braces have good design and fits well, they can be a great help for dogs with knee problems - with or without surgery. However, they only work well when they fit well and when your dog does not destroy them in an attempt to get them off. Some dogs accept them readily and think nothing more about them. Others plot throughout the day on ways to get them off. Tight fitting braces cut off circulation and irritate the skin. Loose fitting braces fall off and do not give adequate support to the knee. It is just like wearing a set of shoes that are not your exact size or somebody else's eyeglasses.

I am dubious about services that plan to mail your dog a brace based on x-rays, size or breed. The results will be like ordering a new suit without having the tailor measure you in person. Maybe you will be lucky and it will fit; but maybe you won't. Ideally, bring your dog to the orthotic specialist to be fitted. If that can not be done, have a cast prepared of your dogs leg and have the specialist use that as a mannequin to construct the brace. Be sure their re-fit, refund and return policy is given to you in writing before your purchase. Be sure they are not gong to reach on the shelf and select a brace that approximates your dogs size. If they refer to the brace by a # or letter, it is most probably off-the-shelf.

Even in large breeds, lameness due to this injury usually decreases with conservative treatment and time. However, if instability of the knee remains, it may lead to arthritis of the joint and eventual reluctance to use the affected leg. But no current surgical technique is a guarantee that arthritis will not occur.

Also important for long-term management of your pet, is returning it to its optimum body weight when it is overweight. Providing regular moderate exercise and increasing your pet's exertion level very very gradually is also important. Be sure to cut back the level of exercise at the first sign of knee discomfort in your pet.

Surgical Treatment Of Torn Cruciate Ligaments

There are a large number of surgical techniques that are purported to
to repair the knees of pets that have been destabilized by a torn cruciate ligament. Some of these techniques insert devices that attempt to stabilize the knee and require opening the joint (intra capsular techniques). Others attempt to add strength to the structures surrounding the joint to compensate for the torn cruciate. These are called extra capsular techniques. Two techniques (TPLO, TTA) are based on the assumption that the knee can be rebuilt in a way that no longer requires central stabilization.

None of them available as of 2015 work as satisfactorily as one might hope.

The problem with current surgical techniques is that they do not restore stability to your pet's joint. Without stability, the dog’s femur “rattles” around (oseochondral injury) on its tibia destroying the remaining cartilages and leading to eventual arthritis, loss of mobility and pain. When drastically different techniques, based on competing theories and explanations of what underlies cruciate ligament tears, ALL give about 85% limitted improvement; one must wonder if it is not just the post-surgical scaring and tightening of the joint capsule, the post-surgical rest , physiotherapy and rehabilitation that account for that improvement. (ref)

No surgical technique will restore your pet's knee if it does not replace the torn cruciate with a material of similar elastic consistency placed in the same crucial location as the original ligament. The stifle is a perfectly designed joint for what it must do – and God placed the cruciate where it is for a reason. This natural ligament is in the ideal location to modulate the forces of motion as your dog walks. Current surgical techniques ignore this point because the cruciate is located in such an inaccessible location. This can be very hard for owners and veterinarians, alike, to accept.

The cruciate is a crucial part of a hinge – similar to the ones on your door. It has to be in the right place and made of the right materials to work. Place it somewhere else on the door and it will not open or close correctly. Eventually it will fail. Construct it out of the wrong materials and it will not last long or work right. A replicate cruciate ligament for your pet would need to have the same superb elastic and strength characteristics of the original elastic cartilage.

Until biomedical engineers and surgeons come up with elastic material, placed in the appropriate place, it will remain a very imperfect surgery with generally disappointing results. Perhaps someday, nanotechnology or regenerative medicine will help these pets. But for now we have an unsolved engineering and materials question that needs a solution.

"If all you have is a hammer, everything looks like a nail"

This fact is very hard for owners and veterinarians to accept. Owners desperately want a cure for the pet they love. So much so that, according to one source, they spent 1.32 billion dollar in 2003 attempting to help their pets through cruciate pain. Currently, five times as many dogs undergo cruciate surgery in the US as people - even though people outnumber dogs nearly five to one.

The sheer number of surgical techniques currently in use show that no one is really satisfied with their results. The ones touted as being the best tend to be the ones that have been around the shortest period – the “fresh faces on the block”. The highest success rate statements are generally for the procedures being done for the shortest length of time. If past history is any guide, as time goes by, more complications and lower success rates will appear and surgeons will move on to another procedure. One of the few scientifically conducted studies on the success rate of these techniques was conducted in 2005 at Iowa State University. It can be faulted when used as a verdict on success rates because the pets involved had meniscal cartilage damage as well as cruciate tears - not all cruciate cases do – but it is the only impartial study of its kind that I know of.

Here are some of the techniques your pet may be offered:

LSS (lateral suture stabilization)

A 2005 study found that 14.9% of dogs undergoing this surgery
returned to normal leg function - no greater than the number that would have recovered without surgery. In 40% some improvement was noticed.

ICS (intra capsular over-the-top stabilization surgery)

The same 2005 study found that 15% of dogs undergoing this surgery
returned to normal leg function – no greater than the number that
would have recovered without surgery. In 15% some improvement was noticed.

TPLO (tibial plateau leveling osteotomy surgery)

This technique changes the angle at which the tibial portion of the pet's knee rides on the pet's femur on the theory that a functional stifle can be obtained by redirection of forces. However, in a study of 150 dogs published in 2008, researchers found that there was no evidence that the a pet’s TPA (tibia plateau angle) predicted the rupture of the second knee cruciate in dogs. That is, extremes in the angle this surgery corrects do not in themselves cause the cruciate to rupture.

The 2005 study found that 10.9% of dogs undergoing TPLO surgery
returned to normal leg function - no greater than the number that would have recovered without surgery. In 34% some improvement was noticed.

An article in the November 2007 issue of Clinicians Brief states that TPLO does not stop or reverse the progress of osteoarthritis in the knees of dogs with cruciate ligament tears.

The chairman of the Orthopedics Department at U. of Pennsylvania's School of Veterinary Medicine has bee quoted as saying: "The TPLO doesn't seem to have any great advantage over more conservative forms of treatment". and, in another correspondence, as stating : “There is no evidence based studies to show that the results are any better than traditional surgeries and the invasiveness & cost is much higher. The morbidity is also much higher & therefore at U of P- we do not do it”.

Tightrope (TR CCL) surgery procedure

This rather-recent procedure attempts to temporarily stabilize the pets loose stifle with a fiber tape. The theory presented is that permanent scaring of the pet’s joint capsule will eliminate or improve joint stability. Of all the surgical options, this is my favorite. Besides offering reasonable results it is considerably less invasive than TPLO. Because of that, I believe it is less likely to lead to post-surgical infections that occur in 2.5 to 15.8% of TPLO procedures. (ref) See how veterinarians perform the tightrope procedure here and here (if you did not view it in an earlier link).

A white paper from the manufacturer states that 6-months outcomes are “as good or better than TPLO”. Considering the questionable results of TPLO, this is nothing to brag about.

If you do decide that your pet must undergo knee surgery, I suggest an extracapsular technique similar to this one. Less damage is done within the joint, recovery is faster and results are as satisfactory as any. There is also less risk of infection than when the joint is opened. Be sure that antibiotics are prescribed after surgery. (ref)

TTA (tibial tuberosity advancement surgery)

This new surgical method uses the same defective reasoning used to justify TPLO surgery. Its chief advantage is that it is a less-involved extra-capsular procedure that does less damage to the joint than TPLO and costs less to perform.
The website for the Swiss manufacturers of one of these systems states their system is “without clinical evidence at this time [that], TTA may show less long-term joint degeneration” [than TPLO]

FHT (fibular head transposition surgery)

Research published in 1994 identified this once widely-performed surgical procedure for torn cruciates in pets as worthless .

So Why Is My Vet Recommending This Surgery?

All veterinarians want to heal pets. Veterinarians in general practice know that they have no silver bullets to deal with cruciate ligament tears. So they are likely to pass you along to a specialist, just as your general practice physician will do when he suspects a difficult case. There are many very good general-practice vets who truly believe these procedures work and want you to be aware of them. But there are also several problematic incentives for sending you to a veterinary surgeon rather than advising patience.

If your veterinarian advises patience, physical therapy and medical management of your pet’s knee and it gets better, the outcome for the vet is neutral. But if it gets worse or does not return to full function (as it may), you might blame the vet.

In many states in the US, there can also be severe licensing and liability repercussions to your veterinarian if he does not refer you to a specialist.

Orthopedic surgeons, human or veterinary, feel the need to practice their specialty. If they were not enthusiastic about their craft, they would work in other fields. But this exuberance can lead to excesses. For example, commonly performed arthroscopic surgery for knee arthritis in humans is usually worthless. and many feel that surgical cruciate repair in people is often unnecessary as well.

I am very proud of the free enterprise and entrepreneurship that exists in the veterinary profession in the United States. Because of it, your pet has better health options here than anywhere else on Earth. But making intelligent pet health choices will always pit pet owners against the never-changing nature of commerce and enterprise – when you visit the fresh fish store, what are you likely to leave with ?

Your orthopedic physician is under similar pressure to do surgery for patients who come to them with severe knee pain. A common procedure was arthroscopic surgery to "smooth" the joint surfaces or remove portions of torn meniscus. Recent studies have found that, in many cases, surgery is no more beneficial than careful physical therapy and some weight loss. (ref1, ref2)

How Can I Avoid Cruciate Ligament Problems In My Pets In The Future ?

1) Unless you plan to enter your pet in dog shows, purchase your pets from field trial or working lines rather than from show lines

2) Avoid larger-than-life litters – those from parents that exceed their traditional breed standard size. There tends to be a creep upward in the body size of many breeds. This often leads to a variety of health problems.

3) Do not purchase from breeders that have cruciate problem in their history. There is already evidence at this time that in Newfoundland’s, the tendency to torn cruciates is genetically inherited.
This has proven to be the case with joint problems in other breeds as well.

4) Do not choose the largest or smallest pup in the litter. It has been my experience that health problems often occur at the extremes.

5) Slow the growth of your large-breed puppy. Feed your puppies 25% less than they would consume free-choice. This is known to suppress later hip dysplasia and elbow dysplasia problems in dogs and increases life span. It might help avoid cruciate problems as well.

6) Do not neuter your pets too young. Sex hormones are involved in the development of bone, tendon and muscle. Early-age neutering is not a healthy choice. It is pushed by SPCAs that are desperate to halt the pet overpopulation problem. If you own a male dog, consider why you plan to have him neutered. It is currently politically correct and it will save you a few dollars in license fees in some areas but it is not going to make a dent in pet overpopulation – your male dog has no business running loose in the first place.

7) Keep your adult dog trim and lean. Do not overfeed it. Exercise your pet on a daily or biweekly basis. Work it into hard sports very gradually. Dogs will do anything for their owners without regard for the well-being of their body. Do not ask your dog to do too much.

8) Encourage the OFA and PennHip
to develop a grading system and databases that identify dogs at risk for cruciate ligament problems. The benefit would be two fold:

We would understand which characteristics make dogs prone to cruciate problems and thus how best to treat the condition.

If cruciate weakness proves to have identifiable genetic components, we may be able to remove the trait from our pets by breeding only dogs that do not carry the trait.

Are There Options When Knee Surgery Was Unsuccessful Or When Arthritis Within My Pet's Knee Is Already Severe ?

Yes, there is one. For a number of years, veterinary surgeons have attempted to place prosthetic (artificial) knees in dogs. These devices replace the entire natural joint and are patterned on the highly successful prosthetic knees used in people. As in humans, they are called TKRs (Total Knee Replacements). Much of this work was pioneered by a veterinary surgeon in Houston, TX (ref); but the procedure is now performed at Ohio State University, The Veterinary College, U. of Minnesota (ref), The Langford Veterinary Hospital at the University of Bristol in the UK (ref) , Helsinki, Finland (ref) as well as in Australia. (ref) I am sure there are more.

The implant commonly used is made of an upper, high-grade, metal alloy and a polyethylene plastic lower component. Currently, it's manufacturer suggested that it be used in dogs weighing more than 26 lbs.

The cost of the procedure and subsequent rehabilitation is said to be in the neighborhood of $6,500. I have no personal experience with this surgery - none of my client’s pets have had it performed. This procedure is still considered to be in the "clinical trial" stage, subject to modification as more long term results become known. Repair of a single knee is usually sufficient for dogs to rise, get out and about and lead a pain-free life. But both knees have occasionally been replaced successfully. (ref)


Since the early 1900s, horse veterinarians have relied on intentional inflammation (firing and blistering) to heal arthritic joints. When I was 18, a respected veterinarian at the Arlington Heights race track in Illinois I worked for told me that "firing" horses was the only way he could get trainers to give their horses the rest they needed for an injured joint to heal on its own. He believed that the treatment itself was worthless. I shared his belief in "constructive" inflammation - at least until now. But this week an article was published on a similar technique, prolotherapy, used to treat arthritic knees in people. It appears to have been a well-constructed study and it was published in a respected journal. You can read it here and some thought on why it might have helped here. So, perhaps, it is a valid treatment option for some pets too. A month ago, I would have placed prolothrapy in Complimentary/New Age Medicine - something I have no faith in; Now, I just don't know. Discuss it with your veterinarian.