Cranial Cruciate Ligament Tear/Rupture

HPIM0644The cranial cruciate ligament (CCL), also known as the anterior cruciate ligament (ACL) in humans, is durable tissue that connects the femur (thigh bone) to the lower leg bone (tibia) and serves to stabilize the knee joint. A torn/ruptured CCL is the most common orthopedic injury in dogs, and generally requires expensive surgical intervention.

This website has given significant attention to the metabolic and behavioral effects that spay/neuter has on its unsuspecting victim – the family dog. However, studies have determined that orthopedic disorders (i.e., hip dysplasia, elbow dysplasia, and steep tibial plateau angle (TPA) which leads to CCLtear/rupture), are also byproducts of spay/neuter – thus completing the trifecta of deleterious outcomes attributable to spay/neuter. The most common of these spay/neuter related orthopedic injuries is the CCL tear/rupture which, because it is not strictly a wear and tear injury, can render a dog lame at an abnormally young age. According to the Canadian Veterinary Journal:

“Rupture of the canine cranial cruciate ligament (CCL) remains the most common orthopedic problem seen in veterinary practice around the world”.145 

Our dog Billy experienced debilitating tears of his cranial cruciate ligament in both of his knees. Billy underwent TPLO surgery to repair both knees. It was disturbing to us that we never understood why the ligament tears occurred in the first place. Billy was not obese, not even slightly overweight. He exercised regularly, including a 6 mile run in the forgiving soft sand of Ocean Beach every morning. What went wrong? Our primary care vet and the orthopedic surgeon had no answers for us.

What the public is told

Banfield, a nationwide chain of some 1000 veterinary clinics, provides their clients the following information regarding cranial cruciate ligament injury:

“The cranial cruciate ligament (CCL) is the most common ligament to be injured, and is similar to when humans injure their anterior cruciate ligament (ACL). Injures to the CCL happen when too much stress is placed on the joint in any given direction, resulting in complete or partial tears of the ligament. Most commonly, these injuries occur during active play, jumping or by trauma…Any dog can injure the CCL, although larger breed dogs or dogs that are very active tend to account for the majority of pets seen with a CCL injury. Pets that are overweight can be at a higher risk for ligament injuries due to the increased weight that puts greater stress on their joints.”

The ASPCA Pet Insurance online forum explains CCL tear/rupture as follows:

“The cruciate ligaments help stabilize the knee joint. Injuries to these ligaments can start out as partial tears that eventually rupture completely and cause the knee to be very unstable with lameness and pain. The complete rupture of the ligament is often the result of gradual degeneration that can take place over months or years and can be influenced by a number of factors, for instance:

  • Obesity – puts added weight on joints and ligaments (this is the most common risk factor for ligament damage)
  • Intermittent strenuous activity — “weekend warriors” dogs who only get out for vigorous exercise once a week or less are prone to this injury
  • Poor overall health
  • Age of the dog — because it’s a degenerative disease, the ligament may weaken over time”

According to the American College of Veterinary Surgeons (ACVS) Small Animal Topics (a series of short educational write-ups intended to educate pet guardians about surgical procedures), Cranial Cruciate Ligament Disease  (CrCLD) is caused by a combination of many factors. These would include aging of the ligament (degeneration), obesity, poor physical condition, genetics, conformation (skeletal shape and configuration), and breed. With CrCLD, ligament rupture is a result of subtle, slow degeneration that has been taking place over a few months or even years rather than the result of acute (sudden) trauma to an otherwise healthy ligament (which is very rare). Further, the ACVS reports 40-60% of dogs that have CrCLD in one knee will, at some future time, develop a similar problem in the other knee.

It is difficult for the dog guardian to make sense of the information provided to them by veterinary professionals. One source indicates CCL rupture/tear is an abrupt injury, while others characterize it rather as a disease, a degenerative condition. All sources highlight obesity as an important contributing factor, with one source specifying that obesity is the most common risk factor for ligament damage. The ACVS write-up is the only source of the three to acknowledge skeletal shape or conformation as a predisposing factor. What is abundantly clear is that in the communications to pet guardians regarding the major causes for this injury, the blame seems to fall in large part upon the dog guardian – too much food, too little exercise, too much exercise all at once and so on. Alternatively, CCL tear could be the result of breed or conformation – circumstances certainly out of the control of the veterinarian.

What the vets are discussing among themselves

Once you leave the realm of information designed to educate the public, and delve into the research and publications for veterinary professionals, the story with respect to CCL tear/rupture is decidedly different. For many years, university-based research has produced substantial evidence that early spay/neuter may indeed affect the development (conformation) of the tibia and other long bones in a dog. It is this improper development of the tibia that predisposes the dog to CCL tear/rupture. The longer tibia results in a knee joint with a tibial plateau angle (TPA) that is more steep than is normal. Almost two decades ago, it was acknowledged in the Journal of the American Veterinary Medical Association:150

“Dogs with CrCL injuries have a significantly greater TPA than dogs without CrCL injury…TPA measurements may be used to screen dogs suspected of being susceptible to CrCL injury.”

Over the years, surgeons discovered that surgeries which merely repaired the ligament (as we do for humans) had only short-term success. Enterprising surgeons concluded that the TPA must be leveled to allow the repaired cranial cruciate ligament to function long-term. The Tibial Plateau Leveling Osteotomy (TPLO) surgery was developed to flatten the TPA in the 1980’s and became more mainstream starting in 1995.

TPA Corrected by TPLO Surgery

Remarkably, research designed to benefit female human athletes (who often stop menstruating and suffer increased ACL injury as compared to male athletes) utilized dogs as subjects because researchers felt that in the dog, most external factors that may affect ACL injury either do not apply or can be minimized. (Note: The ACL in humans is the equivalent of the CCL in dogs). Therefore, effects of internal differences such as sex, hormone status, or removal of ovaries or testes on ACL injury prevalence can be assessed accurately. Unlike previous studies which focused only on university-based practices, these researchers looked at a rural community practice, possibly eliminating selection bias inherent to specialty referral centers.

The research findings, as presented at the 50th Annual Meeting of the Orthopaedic Research Society in 2004, concluded:

” Gonadectomy [removal of ovaries or testes] increased the prevalence of ACL injury across sizes and breeds of dogs of either sex. We conclude that ACL injury occurs with a high prevalence in dogs, and that spaying or neutering significantly increases the prevalence of this injury.”

In 2007, a study 67 was conducted at the Veterinary School of Colorado State University whose objective was to identify risk factors for development of excessive tibial plateau angle (TPA) in large-breed dogs with cranial cruciate ligament disease. This study documented a threefold increase in excessive TPA for dogs neutered (or spayed) early. The explanation is fairly simple. The long bones (e.g. the tibia in the knee joint) have a growth plate which closes (and terminates growth) when the bone has grown to its genetically determined proper length. The closure of bony growth plates generally occurs when the dog is between the ages of 4 and 18 months and is regulated by sex hormones. Spay/neuter drastically alters the sex hormones in female and male dogs at least for a time after the surgery. It is well documented that if a dog is spayed or neutered before the growth plates in the long bones at the elbow, knee or hip joint have closed, the closure of the growth plates will be delayed.61 The variability with respect to dogs developing excessive TPA is dependent upon the time frame chosen for the spay/neuter and the actual genetically determined time frame for closure of growth plates in the individual dog. Additionally we have the variable ability of each dog to compensate for the loss of the sex hormones. Depending upon the length of delay, the long bones continue to grow longer – beyond their genetically determined length. In the knee, the longer tibia creates an excessive tibial plateau angle (TPA), which predisposes the dog to CCL tear/rupture.

For those of you who have gone through a TPLO procedure with your dog, you know the outcome is generally excellent. However, the initial injury and recovery are very painful, and we believe the post operative pain is worse than the veterinarians tell us. We know post-operative pain in humans is severe after bone fracture or the cutting of bone by the surgeon as in a hip replacement. Your dog’s pain is no different. Researchers are currently utilizing animal models to try and find new techniques to minimize post-operative pain in humans. The painful healing period for your dog after TPLO surgery is 8 weeks, and the forced inactivity is difficult psychologically for the dog and their guardian.

In most cases, a rupture in the untreated knee will occur and also require TPLO surgery. In those exceptional situations where the dog does not require TPLO surgery on the other, untreated knee, usually changes have been made by the dog guardian with respect to their dog’s physical activities. Although the expense and downtime of a second TPLO surgery might be avoided, the limiting or elimination of a dog’s favorite recreational activities over a lifetime significantly diminishes their physical and mental well-being.

It should be pointed out that with any surgical procedure, there are risks, and TPLO surgery is no exception. Complications may arise from inappropriate candidate selection, imperfect surgical technique, or poor owner compliance. 192 10% to 34% of dogs treated with TPLO develop a complication, with up to 4% requiring revision surgery. 193

The most common TPLO surgical complications are surgical site infection (SSI) whose incidence ranges from 1.3% to 25.6% 192; and residual instability which is present postoperatively in one-third of TPLO-treated patients.195 Reported risk factors for development of post-TPLO SSI include German shepherd breed, heavier body weight, undergoing a meniscectomy, inexperienced surgeon, and prolonged duration of surgery and anesthesia. One study also evaluated increased SSI rate after TPLO in dogs with dermatitis; thus, the authors recommend giving consideration to surgical delay and controlling dermatitis prior to elective orthopedic surgery, particularly when dermatitis is severe or within the surgical site.194 The issue of SSI is a critical one, and the orthopedic surgeon who performed Billy’s TPLO surgeries took the unprecedented step of having all surgical instruments and the implants for his TPLO surgery sterilized at a nearby hospital for humans, in an effort to ensure absolute sterility of the surgical process. If an SSI occurs, immediate and aggressive wound management, bacterial culture, and antibiotic therapy are all recommended to control the infection while the bone heals. Even superficial soft tissue infections can progress to implant-associated infections and osteomyelitis, especially if not treated appropriately, and can result in delayed union, nonunion, or persistent infection. 193  In rare cases, infection cannot be controlled, bone healing cannot be achieved, and amputation or euthanasia is required.192

Unfortunately, the TPLO surgery does not prevent arthritis in the repaired joint, and in fact it has been shown arthritic changes start almost immediately after surgery.64  The ACVS write-up confirms rupture of the CrCL  is one of the most common reasons for hind limb lameness, pain, and subsequent knee arthritis.

UC Davis has produced a series of studies wherein they combined the incidence of all three joint disorders that have shown evidence of being increased by spay/neuter (i.e., hip dysplasia, cranial cruciate ligament tear, and elbow dysplasia) and tabulated them as a single incidence. This means that if a dog suffers from one or more of these joint disorders, it counts simply as one dog whose orthopedic health has been adversely affected by spay/neuter.

The 2014 UC Davis study revealed that in Labrador Retrievers, spay/neuter at less than 6 months doubled the incidence of one or more of the three joint disorders in both sexes. In the same study Golden Retrievers spayed/neutered at less than 6 months had an increased incidence of one or more joint disorders to 4-5 times that of intact dogs.61  In spite of these devastating outcomes, UC Davis continues to train their students to perform spay and neuter, forgoing any training in hormone-sparing procedures such as vasectomy or tubal ligation. This study also acknowledges that in the last three decades, the practice of spaying female dogs and castrating males (both referred to in this study as neutering) has greatly increased, even as the data substantiating the harm conferred by these procedures has become irrefutable. Further, despite all the evidence of harm due to early spay/neuter, spay/neuter is advocated prior to 6 months at UC Davis.

In 2016, a UC Davis study of German Shepherds reveals that in males and females, neutering or spaying within the first year of life is associated with a highly significant, threefold risk of acquiring at least one joint disorder, with CCL tear being the most likely to occur.108

These studies in 2014 61 and 2016108 at UC Davis also made efforts to calculate the effect of obesity or poor physical condition upon the likelihood of incurring a rupture/tear of the CCL. There is a body score system utilized in dogs that is similar to the BMI measurement for humans. It is called the Body Condition Score (BCS).

UC Davis utilized the nine point BCS scale. The median BCSs for both male and female neutered dogs with joint disorders related to neutering were compared with BCSs of neutered dogs without the joint disorders. The median BCSs for both male and female neutered dogs with a joint disorder were the same as, or close to, the ideal score of 5, as were BCSs of neutered dogs without the disorder. Clearly, obesity and poor physical condition are not scientifically established as the major reasons for the proliferation of this painful, damaging injury. The researchers concluded that body weight probably plays a role in the development of a joint disorder in overweight dogs. However, the researchers also acknowledged that the increase in joint disorders in neutered dogs is at least partially due to the effect of gonadal hormonal removal in delaying long-bone growth plate closure. From a common sense perspective we ask how, exactly, would overeating or poor exercise habits create a skeletal deformity in the tibia, causing an excessive TPA?

Because the expense of this injury is so significant, we feel the need to explore the financial aspect of this condition as well as the other adverse outcomes of early spay/neuter. We have created a “Hidden Cost of Spay/Neuter” page, where you will see TPLO surgery costs up to $5,500.00/knee. The other troubling issue surrounding this injury is that despite our specific questions, early neutering as the underlying cause of Billy’s CCL tears/ruptures was never revealed to us by our primary care vet or the orthopedic surgeon. It does seem that the veterinary profession is withholding this vital information from the dog guardian. One could almost characterize it as a campaign of disinformation if you review the literature made available to the pet guardian by the veterinary community.

We discovered a study published in the Journal of the American Veterinary Medical Association many years ago, in 2003. The study’s objective was to assess the economic impact of this injury. The study estimated that owners spent $1.32 billion for the treatment of Ruptured Cranial Cruciate Ligament (RCCL) in the United States in 2003.146  It is reasonable to conclude that we are spending much, much more to address this single adverse outcome of spay/neuter today. It is also not surprising to see (on our “Hidden Cost of Spay/Neuter” page) that the economic impact of ALL the adverse outcomes of spay/neuter are indeed huge today.


It is acknowledged in veterinary studies that joint disorders such as hip dysplasia, elbow dysplasia and CCL tear can be directly associated to early spay/neuter. These disorders are painful for the dog and create a burden for those caring for the dog.108  Still, the veterinary community fails to openly acknowledge early spay/neuter as the primary cause of CCL tear/rupture and other orthopedic problems, as well as all the other adverse outcomes of spay/neuter as chronicled on this website. We can only conclude there appears to be an economic conflict of interest which could account for the failure of the veterinary community to adequately inform dog guardians as to what the risks and benefits of spay/neuter are, as well as the other options for sterilization. We believe this failure to inform* the dog guardian is what allows the practice of early spay/neuter to persist.

* The State of California has a legal requirement for “informed consent“. Therefore, the risks, benefits and options for any recommended procedure must be disclosed to the guardian before they can technically consent to that procedure.