SUMMARY: A torn ACL in dogs. It’s a common condition, but that doesn’t make it less scary when it’s your dog who is limping. In this ultimate guide, integrative veterinarian Dr. Julie Buzby shares tips, information, X-rays, and even a video on diagnosing an ACL tear. By chronicling the story of Bailey, a Labrador Retriever with a torn ACL, you’ll learn the facts—from diagnosis through recovery. Hope and help are here.
How your dog’s knees function
Did you know that dogs have knees? It’s true, they do! Further, the anatomy is very similar to ours. A dog’s knee is the joint on the hind leg where the bone of the upper thigh (femur) meets the shinbone (tibia and fibula). Just like humans, the canine knee is complex and intricate. Because the joint is composed of bones (patella, femur, fibula, and tibia), ligaments (medial and lateral collateral, cranial/anterior and caudal/posterior cruciate, patellar), and shock absorbers (menisci), there are a lot of structures that can be easily injured. To have a functioning knee, every part must work in perfect harmony.
The most common canine knee injury is a torn ACL in dogs
We all know the feeling of witnessing a player injured in a football or soccer game. The medics rush onto the field, as the silent crowd watches. The trainers pinpoint the injury to the leg and the commentators quietly speculate, “Could this be a cramp, Bob? He’s had those before…or do you think he tore his ACL?”
Most of us are familiar with the term ACL, but we may not know what it means. ACL stands for anterior cruciate ligament, and it is an important stabilizing structure in the human knee. But did you know that dogs share this anatomy? They have a very similar ligament, technically called the cranial cruciate (CCL). The term changes even though “anterior” and “cranial” are basically synonyms. The former is used to indicate a location (closer to the head) in humans and the latter refers to the same direction/position in animals.
Because most people are much more familiar with the term ACL when describing this injury, it is commonly referred to as a torn ACL in dogs, even among veterinarians. (I’ll use the terms interchangeably in this article.)
The anterior/cranial cruciate ligament has three critical functions:
- Prevents the tibia from thrusting forward in relation to the femur, like a drawer pulled forward from a dresser
- Prevents the knee from hyperextending
- Prevents the tibia from rotating internally
The cause of a torn ACL is multifaceted
In humans, tearing is generally associated with trauma, like the sports scenario above. This is usually not the case in our canine companions. In dogs, the CCL tends to weaken over time. The reasons for this aren’t well understood. Current research focuses on whether early spay and neuter could predispose to this. The role of hormones in the development and health of ligaments is poorly understood in dogs, as is the risk of taking those hormones away at a young age. We do suspect that hormones can play a role in human ACL tears, so it’s natural to conclude that they would for dogs too.
A review of over one million dogs from the 1960s-2000 showed that neutering increased the risk of suffering a torn ACL in dogs, and females were slightly more likely than males. (The gender distribution holds true for humans too.) Trauma can precipitate a tear, but in most cases, the cruciate is already weakened. As with many injuries, the cause is multifaceted.
Breeds that are at increased risk for an ACL injury
I’ve diagnosed a torn ACL in dogs of all sizes and shapes (and even cats), but large breed dogs older than four years of age are most often affected. Genetics also seem to play a role in the likelihood of a torn ACL in dogs because certain breeds appear to be at increased risk for the injury:
- Labrador Retriever
- Golden Retriever
- Neapolitan Mastiff
- St. Bernard
- Chesapeake Bay Retriever
- American Staffordshire Terrier
Diagnosing a torn ACL in dogs
The diagnosis of a torn ACL in dogs is made based on several things. The “history” is always important, meaning the backstory as reported by the dog’s family. Often, dogs with complete cruciate tears will have a history of mild, waxing/waning lameness and stiffness in a hind leg. They may have previously been treated with a combination of non-steroidal anti-inflammatory medications, joint supplements, physical therapy, acupuncture, and/or laser therapy. This is because chronic inflammation and cruciate degeneration often happen over time. Eventually, a complete tear occurs.
The physical exam is next, which may include a gaiting exam. (If the lameness is not super obvious, I take my patients out to the parking lot and ask the owners to pretend like they are in the ring at Westminster to watch the dog travel at a walk and trot.)
Finally, a thorough orthopedic exam of the leg(s)/pelvis will be done. The following findings increase the suspicion for a torn ACL in dogs:
- Decreased range of motion in the affected leg.
- Decreased thigh muscle circumference in the affected leg (due to disuse/favoring the leg). We call this muscle atrophy.
- The presence of a medial buttress, a thickening on the medial (inner) surface of the leg indicating long-standing inflammation.
- An awkward sitting posture in which the painful leg is held out to the side or the dog refuses to sit squarely.
- A positive cranial drawer test. This is best accomplished with sedation because pain can make this test difficult to perform with accurate results. The dog will be placed in lateral recumbency (lying on his side). One hand should be placed on the patella (knee cap) and the other on the tibia. With pressure, the joint should feel tight and stable. If there is appreciable movement of the tibia forward in relation to the patella, this is considered a positive cranial drawer sign. (It mimics a drawer opening from a dresser, as mentioned above).
- Tibial thrust can also be checked under sedation. One hand is placed over the stifle, and the foot is flexed with the other. If there is strong movement of the tibia forward in relation to the patella, this is considered positive.
I mention the details of the last two signs, not to teach you how to perform them or expect you to fully understand them, but more so to illustrate that the best way to diagnose a torn ACL in dogs is through a hands-on exam and diagnostic manipulation by your veterinarian.
A video of a cranial drawer and tibial thrust performed by a veterinarian
There are several surgical options available for repairing a torn ACL in dogs. Despite what you may read on the internet, none of these is THE perfect surgery. (If there were one perfect treatment option, we wouldn’t have several surgical options to choose from.)
Treatment should be tailored to individual patients. It is dependent on breed, size, and lifestyle. A large, athletic dog that competes in agility will need a different approach than a couch potato pug that goes on walks twice a day!
What a torn ACL in dogs looks like in real life: Bailey’s Story
Bailey was a rotund, lazy Labrador when I met him at 13 years of age. He’d always been perfectly healthy, other than an unfortunate meeting with a copperhead several years prior. Since that incident, he’d been healthy but preferred life in the house—away from venomous yard dwellers. He and his owner, Randy, were perfectly happy sitting on the couch, sharing snacks, and watching Netflix.
One day, Bailey hopped down from the couch, walked a few steps, and then stopped. Randy noticed that he was favoring his left rear leg; in fact, he held it dangling in the air. Randy then remembered that Bailey had limped on that leg a little for the past few years, but it had never worried him since it seemed minor. Now Bailey wouldn’t touch the paw to the ground. He just held it up.
That was what he explained to me when I questioned him about Bailey’s history. Bailey hadn’t fallen. He hadn’t been chasing rabbits or playing ball. He’d just been getting off the couch.
A head-to-toe exam for Bailey
Kneeling next to Bailey, I started my head-to-toe examination. We checked his vitals including his weight, and I went through a thorough “systems check,” much like a commercial airline pilot.
Then I focused on his left rear leg. The inside of his left knee was thickened and very firm. I could feel what is called a “medial buttress.” This bony remodeling occurs in a knee with a chronic cruciate problem creating inflammation over time. I suspected that Bailey had had a partial tear for years, and the tear had now become complete.
Randy helped me place Bailey on his side with the assistance of some peanut butter. While Bailey focused his tongue on the decadent treat, I placed one hand on his stifle and the other on the bottom of his foot, flexing his hock and knee. I felt the tibia move forward under my hand, indicating tibial thrust. I then checked for a drawer sign. Bailey was fairly relaxed, but he tensed when I attempted this maneuver and lifted his head to inspect my work, indicating discomfort. I was not surprised; it is challenging to assess cranial drawer in an awake dog that is painful.
Sitting back on my heels, I sighed. “Randy,” I explained, “I think Bailey has torn his cruciate ligament. We need to sedate him so I can better palpate his knee and take some X-rays.” Randy agreed to whatever we needed to do.
X-rays support the ACL diagnosis
We gave Bailey an IV sedative and pain reliever, and positioned him for palpation and X-rays. With Bailey now fully cooperative and relaxed, I could easily feel a positive cranial drawer sign. We proceeded with X-rays to confirm my physical exam findings. As I’ve already mentioned, I considered the diagnosis made based on my exam findings, but I have personally misdiagnosed a dog with a ruptured ACL, who actually had bone cancer, and know colleagues who have done the same. Radiographs help support the torn ACL diagnosis and rule out other conditions that can cause the same symptoms.
Whenever orthopedic X-rays are taken, there are two key elements:
- The radiographs should be positioned perfectly to be diagnostic quality. Often sedation is necessary to get good orthopedic X-rays in all but the calmest dogs, if for no other reason than pain. It’s hard (and unkind) to torque a painful dog’s leg into the perfect position for a radiograph while the dog is fully conscious.
- It’s always important to get both legs in the films. This allows for comparison so that abnormalities are easier to see.
Bailey’s right knee looked normal, but his left definitely had fluid (effusion) in the stifle. On an X-ray, this looks like cloudiness in the joint space. The tibia also looked cranially (forward) displaced. Everything pointed to an ACL/CCL tear.
I relayed this information to his owner. We had some decisions to make. Bailey was 13, and surgery was no small undertaking, not to mention he would require an extended rehabilitation period afterward (up to six weeks).
While we’d been taking X-rays, Randy had been consulting Google. He’d already realized that I would recommend surgery. He had found a brace advertised to help dogs with cruciate injuries. He showed it to me, wondering if it would be an option rather than surgery.
This was a legitimate question. After all, Bailey was 13. Was he fit enough to handle a surgical procedure? And could he and Randy handle the recovery period?
Talking with your vet about surgery
This is yet another example (there are many throughout our blog) of the priceless value of having an open and trusting relationship with your veterinarian. Randy knew me. He knew that I would only recommend the best option for Bailey. That was surgery.
When one cruciate tears, the other usually follows within a one year period. If that happened, Bailey would have two bum hind legs. Further, since Bailey was already a “couch potato dog,” I knew he could handle the long period of rest after surgery.
Without surgery, Bailey’s body would start to scar over the tear and stabilize the joint by laying down extra bone. He would eventually be able to use the leg again (though it would always be his “Achilles heel,” prone to reinjury), but arthritis would set in, causing chronic pain and lessening his quality of life.
I explained all this to Randy, and, after much consideration, he elected to take Bailey to a board-certified orthopedic surgeon for a consultation and surgery.
Surgical treatment options for a torn ACL in dogs
Surgical options to repair the ACL/CCL include:
- TPLO (tibial plateau leveling osteotomy)
- TTA (tibial tuberosity advancement)
- aCBLO (anatomic cora-based leveling osteotomy)
- Tightrope (lateral fabella suture)
- Simitri Stable in Stride
(You can read more about these surgeries in detail by visiting the American College of Veterinary Surgeons website. )
In small dogs (less than 15 kg), who have a comparably small amount of mass to move around, conservative management with rest and pain management may be an acceptable approach. Unfortunately, no studies exist that compare this option to others, so it remains up for debate.
In one older study (1984), for dogs over 15 kg, less than 20% had an acceptable outcome with conservative management. As a result, for larger dogs, surgery is the treatment of choice.
But which surgery? If you put 10 veterinary orthopedic surgeons in a room, you’ll likely get 11 different opinions! And maybe some bloodshed! It’s a hotly contested topic.
As a veterinary student, I was taught about the tibial plateau leveling osteotomy procedure (TPLO). In this common procedure, a large piece of the tibia is removed, rotated to a specific angle, and reattached with a plate and screws. This changes the dynamics of the knee so that when weight is borne, the tibia doesn’t thrust forward, inherently making the knee more stable.
In 2016 a study was published in the Journal of Veterinary Surgery which reported on a very promising new procedure called the Simitri Stable in Stride—an implant placed in the knee that stabilizes the joint. Early results are very promising, but it is not widely used yet. You can learn more by visiting this website and reading, Simitri: a new option for an age-old problem.
Bailey’s surgeon elected to repair his cruciate rupture with a TPLO.
Recovery from surgery and why following post-op instructions is critical
Bailey’s surgery was a huge success! This was in large part due to the dedication of Randy. He kept Bailey strictly rested for 6 weeks post-operatively. Bailey was only allowed short leash walks outside to use the bathroom.
Otherwise, he was confined to his crate. Despite Randy’s passion for sitting on the couch with his canine companion and watching Netflix, Bailey was not allowed on the furniture while he recovered. Randy continued their movie night tradition, but sat on the floor with Bailey instead.
He was also strict about keeping the Elizabethan collar on at all times to prevent Bailey from chewing his stitches. Trust me, I get that it’s not called “the cone of shame” for nothing. And there are viable alternatives to the e-collar, which are probably more comfortable for dogs. But my point is that strictly following the post-op instructions is critical to success.
Pain medications and supplements
Randy administered Bailey’s pain medication diligently. Post-operative pain medications usually include a non-steroidal anti-inflammatory like carprofen or deracoxib, as well as gabapentin and/or tramadol. Randy and I also discussed adjunctive modalities like laser therapy and acupuncture and set up a course of treatments. Joint supplements such as green-lipped mussel, New Zealand deer velvet, and glucosamine/chondroitin are also valuable in my experience, although data is lacking on these therapies.
After orthopedic surgery in human medicine, it is assumed that rehab or PT will be a part of the recovery process. Veterinary rehabilitation for dogs is one of the fastest-growing aspects of veterinary medicine. It is now recommended by many orthopedic surgeons after the initial healing period. Doggie PT can speed recovery by building muscle tone and improving strength and balance. This option was not available in our area for Bailey, but you can search for a certified rehabilitation practitioner by state at the American Association of Rehabilitation Veterinarians’ website.
Avoiding post-surgical complications
Some of the most common postoperative complications of stifle repair are avoidable. Infection secondary to chewing and licking at the incision is common. Failure of the TPLO plate can also happen if a dog is allowed to be active too soon after surgery. One of my dearest patients had this experience. Though her intentions were pure, Hope’s owner only half-heartedly restricted her activity post TPLO surgery and the plate shifted. Hope spent the rest of her life challenged by this, but her story has a happy ending and also dramatically changed the course of my life. For the rest of the story, please read A Foreshadowed Hope.
Randy, the quintessential compliant client, mitigated all of these things by following the post-op instructions from the surgeon to the letter and following up with Bailey’s surgeon for post-op rechecks. If your dog is facing knee surgery, it is important to know that even after surgery, follow up visits are necessary to ensure that everything is healing appropriately.
Can cruciate tears be prevented?
One of the hazards of being a conscientious pet owner is a propensity toward “mom guilt”. When I diagnosed Bailey, Randy wanted to know if he inadvertently contributed to the injury or could have prevented it.
Cranial cruciate ruptures aren’t well understood. The causes are multifactorial, as mentioned above. But one risk factor is known and within your control—obesity! In one study, obesity quadrupled the risk of a cranial cruciate tear. Keeping dogs slim and fit is certainly helpful in not only preventing cruciate tears but in preventing many other disease processes. To learn more about keeping your dog fit, please read my article, Canine Body Condition Score: Learn Your Dog’s Number.
Speak with your veterinarian about treatment options
I diagnosed my first torn cruciate ligament in a middle-aged Golden Retriever during my very first week of veterinary practice. Since then I have seen hundreds upon hundreds of partial and complete tears in dogs. If your dog has been diagnosed with a torn ACL/CCL, I want you to know you’re not alone. This is a very common condition in dogs, and thankfully one for which excellent treatment options exist. Your dog can recover from this injury and go on to lead a happy, active life —running on all four paws.
Ready for more ways to help your dog live the happiest, healthiest life possible?
Get Dr. Buzby’s latest tips, articles, and promotions. Plus, receive a FREE e-book Seven Ways to Love Your Senior Dog!
What questions do you have about a torn ACL in dogs?
Please comment below. We can all learn from each other.