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What Causes Cruciate Ligament Tears in Dogs?

What Causes Cruciate Ligament Tears in Dogs?

TPLO

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Owners

Learn what causes cruciate ligament tears in dogs, including risk factors, symptoms, and prevention tips for your pet’s joint health.

By 

Sustainable Vet Group

Updated on

August 13, 2026

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This article is for informational purposes only and is not a substitute for professional veterinary advice. Every case is unique, so always consult your veterinarian for guidance specific to your pet.

This content is intended for veterinary professionals for educational purposes. It does not replace clinical judgment or tailored advice. Always rely on your training, expertise, and the specific context of your patients.

What Causes Cruciate Ligament Tears in Dogs?

CCL rupture in dogs is not the same injury as ACL rupture in humans.

In humans, the anterior cruciate ligament typically tears during sudden trauma a pivoting fall on a ski slope, a tackle on a football field.

In dogs, the same ligament almost always fails through slow, progressive degeneration that began months or years before the day the dog comes in lame.

Understanding why the canine CCL fails and which dogs are most at risk is essential for prevention strategies and for recognizing early warning signs.

 

Quick answer: The canine CCL fails through progressive degeneration, not sudden trauma. Key risk factors are breed, obesity, poor fitness, tibial slope, and genetics. At least 50% of dogs that rupture one CCL will rupture the other within 1 to 2 years.

 

Key takeaways

  • CCL rupture results from degeneration, not trauma: ACVS confirms slow, progressive degeneration rather than acute injury to a healthy ligament
  • Obesity is the most modifiable risk factor: excess weight increases compressive and shear forces on the CCL with every step
  • High-risk breeds include Labrador, Rottweiler, Newfoundland, Mastiff, and Akita: genetic inheritance has been demonstrated in Newfoundlands and Labradors
  • Partial tears almost always progress to complete rupture: ACVS confirms this and notes progression is the rule, not the exception
  • At least 50% of dogs rupture the opposite CCL within 1 to 2 years of the first rupture
  • Neuter status increases CCL risk: spayed and neutered dogs show higher rates in multiple studies

Why dog CCL disease differs from human ACL injury

Colorado State University: "In humans, trauma (such as skiing, football, or soccer injuries) is the most common reason for injury of the ACL.

This 'traumatic' rupture can happen in dogs but is quite rare."

CSU: "Most commonly, CCLD is caused by a combination of many factors, including aging of the ligament (degeneration), obesity, poor physical condition, conformation, and breed."

In humans, a healthy ACL tears from a single high-energy event. In dogs, the ligament is already weakened before it ruptures.

The moment of obvious lameness is the endpoint of a months-long degenerative process.

ACVS: ligament rupture is "the result of subtle, slow degeneration that has been taking place over a period of time rather than the result of sudden trauma to an otherwise healthy ligament."

Fitzpatrick Referrals: "In the vast majority of dogs, the CrCL ruptures as a result of long-term degeneration, whereby the fibres weaken and fray over time, losing their structure and function."

The main causes and risk factors

Degeneration (aging and immune-mediated)

The underlying degenerative process in CCL disease involves progressive breakdown of collagen fibers within the ligament.

PMC (Cranial Cruciate Ligament Rupture Review): "The structural weakening of this joint due to the progressive degeneration of the ligament is the most accredited etiopathogenetic hypothesis."

The degeneration appears to involve both mechanical fatigue and immune-mediated inflammatory processes within the joint.

Synovitis (joint inflammation) often precedes complete rupture and may be detected during veterinary examination before full failure occurs.

Breed and genetics

ACVS: "Certain dog breeds are known to have a higher incidence: Rottweiler, Newfoundland, Staffordshire Terrier, Mastiff, Akita, Saint Bernard, Chesapeake Bay Retriever, and Labrador Retriever."

ACVS: "A genetic mode of inheritance has been shown for Newfoundlands and Labrador Retrievers."

Fitzpatrick Referrals: "Genetic factors are likely very important, with certain breeds being predisposed including Labradors, Rottweilers, Boxers, West Highland White Terriers, and Newfoundlands."

Breeds with low CCL disease incidence include Greyhounds, Dachshunds, Basset Hounds, and Old English Sheepdogs.

Fitzpatrick: "Supporting evidence for a genetic cause was obtained by assessment of family lines and the knowledge that many animals rupture both knees relatively early in life."

Obesity

ACVS: "Poor physical body condition and excessive body weight are risk factors for the development of CrCLD. Both of these factors can be influenced by pet owners."

PMC: "A predisposing factor is obesity, in which the concentrations of circulating inflammatory mediators increase, such as the concentrations of pro-inflammatory adipokines released from adipose tissue, which may contribute to degenerative phenomena."

Obesity matters in two ways: it increases the mechanical load on the CCL with every step, and it elevates systemic inflammation, which accelerates ligament degeneration.

A dog 10% overweight places significantly more stress on both stifle joints with every stride.

Tibial plateau angle (conformation)

The tibial plateau is the top surface of the tibia. In dogs, it slopes caudally. During weight-bearing, this slope creates a cranial shear force on the tibia that the CCL normally resists.

Fitzpatrick: "Increased tibial plateau angle (backwards slope at the top of the tibia) may play a role" in CCL disease.

Dogs with steeper tibial plateau angles experience greater cranial thrust with each step, increasing CCL load.

This is why TPLO and CBLO surgery (which reduce the tibial plateau angle) neutralize the instability rather than replacing the torn ligament.

Neuter status

Multiple studies have found that spayed and neutered dogs have higher rates of CCL disease than intact dogs. The relationship is stronger in some breeds than others.

Proposed mechanisms include the loss of sex hormones that influence joint development and ligament maturation, longer bone growth periods in dogs neutered before skeletal maturity, and altered body composition.

Contralateral (opposite knee) risk

NCBi (Radiographic Risk Factors study): "Among dogs presented with unilateral CCL rupture, a large proportion will develop contralateral CCL rupture within 12 to 24 months of initial diagnosis.

This risk is in the range of 22 to 54% at 6 to 17 months of diagnosis."

CSU: "At least half of the dogs that have a cruciate ligament problem in one knee will likely, at some future time, develop a similar problem in the other knee."

This bilateral risk reflects the systemic nature of CCL degeneration both ligaments are affected by the same genetic, hormonal, and conformation factors.

Partial tears: the warning stage

The CCL typically does not rupture all at once. Partial tears are common and produce intermittent hind limb lameness that owners sometimes attribute to a sprain.

CSU: "Partial tearing of the CCL is common in dogs and frequently precedes complete rupture."

ACVS: "Partial tearing of the CCL is common in dogs and almost always progresses to a full tear over time."

A dog with a partial CCL tear that receives cage rest and returns to activity will almost always eventually progress to complete rupture.

Surgical intervention at the partial tear stage can be considered for active dogs, though evidence on whether it prevents eventual complete rupture is limited.

Signs of CCL disease

  • Hind limb lameness, especially after exercise
  • Sudden onset of non-weight-bearing on a back leg
  • Stiffness when getting up, especially after rest
  • Muscle atrophy on the affected hind limb
  • Thickening on the inside of the knee joint (medial buttress)
  • Positive cranial drawer test or tibial compression test on orthopedic examination

Can CCL tears be prevented?

Risk cannot be eliminated in predisposed breeds, but it can be reduced.

ACVS: "Consistent physical conditioning with regular activity and close monitoring of food intake to maintain a lean body mass is advisable."

Evidence-based prevention strategies:

  • Maintain healthy body weight (most impactful modifiable factor)
  • Consistent, regular exercise rather than intermittent intense activity
  • Avoid sudden load increases (the "weekend warrior" pattern)
  • Discuss neutering timing with your vet, particularly in high-risk breeds

For the surgical treatment of CCL rupture, see CBLO surgery in dogs: cost, recovery, and success rate. For the surgery vs. conservative management decision, see canine cruciate injuries: surgery vs. conservative management.

For meniscal injury that often accompanies CCL tears, see torn meniscus surgery cost in dogs. For when CCL disease requires specialist referral, see when to refer for orthopedic surgery.

Frequently asked questions

My dog tore its CCL running in the yard. Wasn't that traumatic?

The event may have looked sudden, but the ligament was almost certainly already degenerated.

ACVS: the rupture is "the result of subtle, slow degeneration... rather than sudden trauma to an otherwise healthy ligament." The yard run was the last straw, not the cause.

Which dog breeds are at highest risk for CCL tears?

ACVS identifies Rottweilers, Newfoundlands, Staffordshire Terriers, Mastiffs, Akitas, Saint Bernards, Chesapeake Bay Retrievers, and Labrador Retrievers as high-incidence breeds. Fitzpatrick Referrals adds Boxers and West Highland White Terriers.

Does obesity really make that much difference?

Yes. Obesity increases both mechanical load on the CCL and systemic inflammation via adipokines from fat tissue.

It is the most modifiable risk factor maintaining healthy body weight is the single most impactful thing an owner can do for CCL disease prevention.

My dog had surgery on one knee. How long before the other goes?

NCBi data: the risk of contralateral CCL rupture is 22 to 54% within 6 to 17 months of the first diagnosis. Monitoring the other knee closely after the first diagnosis is important.

Maintaining lean body weight and avoiding abrupt increases in activity are the main protective strategies.

Can a dog with a partial CCL tear be managed without surgery?

Conservative management (rest, weight loss, physical therapy) may be attempted for partial tears, particularly in small dogs. But ACVS states partial tears "almost always progress to a full tear over time."

Discuss with an orthopedic specialist whether surgery at the partial tear stage is appropriate for your dog.

What is the difference between CCL and ACL?

CCL (cranial cruciate ligament) is the correct term in dogs; ACL (anterior cruciate ligament) is the human equivalent. They are anatomically similar structures that stabilize the knee joint.

The key clinical difference: in humans, ACL tears are usually traumatic; in dogs, CCL tears are almost always degenerative.

Resources

  • ACVS. Cranial Cruciate Ligament Disease. acvs.org
  • CSU Veterinary Health System. Canine Cruciate Ligament Injury. vetmedbiosci.colostate.edu
  • Fitzpatrick Referrals. Cruciate Ligament Disease or Injury. fitzpatrickreferrals.co.uk
  • NCBi PMC. Radiographic Risk Factors for Contralateral Rupture in Dogs with Unilateral CCL Rupture. ncbi.nlm.nih.gov
  • PMC. Cranial Cruciate Ligament Rupture in Dogs: Review on Biomechanics, Etiopathogenetic Factors and Rehabilitation. ncbi.nlm.nih.gov

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