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Signs and Symptoms of a Torn Knee Ligament in Dogs

Torn Knee Ligament in Dogs

A torn knee ligament in dogs is likely to produce various signs, but the symptoms of a torn knee ligament in dogs can often be confused with other orthopedic problems. The best way to determine whether your dog has injured his knee ligament (anterior cruciate ligament), is to have your dog evaluated by your vet. You vet can diagnose knee ligament problems in dogs by manipulating the affected leg and looking for some tell-tale signs of torn ligaments. Following are some possible symptoms pointing to a torn knee ligament in dogs, but again, only your vet can properly diagnose it.


Predisposing Factors

Certain dogs are more likely than others to rupture their anterior cruciate ligaments. For instance, consider size. Larger dogs are more predisposed than smaller dogs in general, even though tears in small dogs are not unheard of. If statistics are looked at, it is found that dogs weighing over 22 kg (over 48.5 pounds) had a higher prevalence of a rupture, compared to dogs weighing less than that amount.

Breed is also a factor. According to a study published in the Journal of the American Veterinary Medical Association, the breeds of dogs most predisposed for rupture of the cranial cruciate ligament include the Neapolitan Mastiff, Akita, Saint Bernard, Rottweiler, Mastiff, Newfoundland, Chesapeake Bay Retriever, Labrador Retriever, and American Staffordshire Terrier.

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Age is also a factor. According to another study, when it comes to age, the rupture is more likely to happen as dogs became older, with a greater prevalence in dogs aged between 7 and 10 years old.

A History of Trauma

running dog

When a dog tears a ligament, it's often the result of some traumatic event to the leg. Not always though dog owners notice the happening. Dog owners often report a sudden onset of rear leg limping.

A common triggering event is when the dog's lower hind leg is kept still (like it happens when it gets stuck in a hole or gets caught on a string), while the upper leg is in forward motion, explains veterinarian Dr. Fiona.  However, the injury can also happen with any activity that causes the dog to pivot on a hind leg.

It's often assumed that the poster child of such injury is a young athletic dog who loves to play rough or some canine athlete engaged in demanding canine sports, but a ruptured ACL in dogs can often occur in other events rather than a sporting event gone wrong, as it often happens in humans.

An older large dog who has weakened ligaments, and happens to stretch the ligament gradually or partially tears it, is a common happening. This partial rupture may only become evident when the ligament ruptures completely which can happen when the dog steps off the bed or takes a small leap, explains veterinarian Dr. Wendy C. Brooks.  Damage can also occur from slipping on ice or a hardwood floor. In such a scenario, the injury may be acute or more gradual as often seen in chronic joint diseases.

Not Bearing Weight

Leg cramps in dogs

The most obvious sign of a problem with a dog's knee ligament is not putting weight on the affected leg. This is a prominent sign of pain that is often underestimated. Dogs are not people, and therefore they are not prone to vocalize as much as we do when it comes to feeling pain.

Yes, dogs yelp in pain when something acute and sudden happens such as somebody stepping on their feet or walking on a thorn, but many times dogs will not manifest pain vocally as humans do. The fact that a dog doesn't put weight on a leg is therefore a sign of significant pain.

When dog owners say "my dog is not bearing weight on his leg, yet he's fine and is not showing pain" they are missing the most important sign of pain: not putting weight on the leg in the first place! Dogs don't go lame for no reason, and the lameness is therefore the most evident sign of pain.

Toe touching in a dog with a knee ligament tear

Toe touching in a dog with a knee ligament tear

Toe-Touching When Standing

One sign of a potential ligament tear in dogs is toe-touching. In toe-touching, the dog keeps most of the paw off the ground, but the tip of the toe may slightly touch the ground as seen in the picture. The purpose of toe-touching is to bear a limited amount of weight on the injured knee.

Interestingly, toe touching is mostly seen when the dog is standing or walking. This is because slow movements are more challenging for affected dogs.

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Dog owners are often surprised that their dog, despite being injured, is capable of running. Truth is, when a dog is running, his paws hardly touch the ground, and this explains why dogs are often capable of running on three legs.

If your dog is lame, but yet is capable of running, don't be fooled and underestimate the problem. See your vet if there is severe limping or the limping is lasting more than 24 hours, suggests veterinarian Dr. Sandra Truli.

"The symptoms seen are usually a sudden onset of hind-end lameness, with toe touching seen at standing and walking, but the dog often carries the leg when running." ~Dr. Fiona

Sloppy Sitting in Dogs

dog symptoms of acl

If your dog is "sitting sloppy" lately, suspect a torn cruciate ligament. What exactly is a sloppy sit in dogs? In a healthy dog, with healthy knees, the act of sitting is completely pain free and the dog has no problems sitting squarely, with the hind legs nicely tucked up.

In dogs suffering from a torn cruciate ligament, sitting is actually painful as it requires to bend the knee. So instead of flexing the knee, the affected dog will extend it outwards. Some people describe sloppy sits as the posture seen in the old days when ladies were riding horses, with the the legs placed sideways.

'Sloppy sits" also known as "lazy sits" because they are often chalked up to dogs being lazy (but in most cases, they are not, they're just in pain!) therefore often denotes some sort of physical problem and a common issue is a torn ligament, especially if it is accompanied by other potential signs.

“Hip dysplasia patients will usually sit square—i.e. symmetrically with both knees flexed—whereas ACL dogs will often have one leg extended because their stifle hurts in flexion.” Dr. Bernard Paré

Positive Drawer Test 

This is an exam that only veterinarians should do. It consists of moving the affected leg in such a way as to determine whether the tibial bone slides forward in relation to the femur bone. This sliding movement is not seen in dogs with a normal knee, and therefore it's diagnostic for a ligament tear when it happens, explains veterinarian Dr. John.

However, things can get tricky at times. Consider that when dogs are at the vet's office, it can be quite normal for them to feel anxious and tense. What does this mean when it comes to a torn ligament? It means that tense muscles can temporary stabilize the knee, causing a false negative drawer test.

This is often why vets will request to have a drawer test done under sedation in order to get a better evaluation of the knee, especially when it comes to large dogs, explains veterinarian Dr. Wendy C. Brooks. Another test vets may conduct is the cranial tibial thrust test.

Did you know? The drawer test gets its name from the fact that the movement of the dog's femur in relation to the tibia is very similar to the movement that occurs when pulling out and back in the drawer of a cabinet.


Changes on X-Rays

One main problem associated with ruptured ligaments is the onset of degenerative changes. The knee ligament helps keep the knee stable. When the ligament ruptures, the knee bones and cartilage rub against each other. Dogs may develop bone spurs as soon as 1 to 3 weeks after the rupture which result in pain and loss of normal function.

While x-rays cannot reveal a cruciate rupture, several degenerative changes that occur as a result of the rupture can be seen on x-rays. X-rays come also handy to help rule out other serious disorders such as bone cancers and synovial cell sarcomas.

Did you know? A study published by the Journal of the American Veterinary Medical Assn. reported that as many as 32 percent of dogs that were referred to a surgeon for hip dysplasia actually turned out having a torn ACL!



  • Breed, sex, and body weight as risk factors for rupture of the cranial cruciate ligament in young dogs. Duval JMBudsberg SC , Flo GL , Sammarco JL Journal of the American Veterinary Medical Association [01 Sep 1999, 215(6):811-814]
  • Epidemiology of cranial cruciate ligament rupture in dogs. Whitehair JG , Vasseur PB , Willits NH Journal of the American Veterinary Medical Association [01 Oct 1993, 203(7):1016-1019]
  • Veterinary Practice News: How To Confirm Partial ACL Tear
  • DVM360: Bad hips and knees: Is it hip dysplasia or a torn cruciate ligament?

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