Cranial Cruciate Ligament Rupture

TL;DR. Cranial cruciate ligament rupture is a common, painful knee injury in dogs and cats that causes hindlimb lameness and joint instability, often requiring surgical stabilization to prevent progressive arthritis.

Cranial cruciate ligament rupture is a common cause of hindlimb lameness in dogs.

What is it?

Cranial cruciate ligament rupture (CCLR), also known as cranial cruciate ligament insufficiency or disease, is one of the most common orthopedic conditions encountered in veterinary medicine. The cranial cruciate ligament (CCL) is a vital band of tough, fibrous tissue located inside the stifle (knee) joint of dogs and cats. It is structurally and functionally analogous to the anterior cruciate ligament (ACL) in humans.

In a healthy joint, the CCL connects the femur (thigh bone) to the tibia (shin bone), preventing the tibia from sliding forward relative to the femur during weight-bearing activities. It also prevents internal rotation of the limb and hyperextension of the knee. When this ligament undergoes a partial or complete rupture, the structural integrity of the knee is lost. This leads to immediate joint instability, inflammation, and pain.

Unlike ACL tears in human athletes, which are typically the result of sudden, acute trauma, CCLR in dogs is most often a progressive, degenerative disease. The ligament slowly weakens over time due to cellular changes, microscopic tearing, and chronic joint inflammation. Eventually, even normal daily activities like running in the yard or jumping off a couch can cause the weakened ligament to tear completely. In cats, while the condition is less common, it can occur due to trauma, obesity, or age-related degeneration.

Causes & risk factors

The exact cause of cranial cruciate ligament degeneration is multifactorial, involving genetics, conformation, body weight, and inflammatory processes.

• Conformation and Joint Angulation: Dogs with a steep tibial plateau angle (the slope of the top of the shin bone) experience constant, increased stress on the CCL during normal standing and walking, accelerating wear and tear.
• Obesity and Body Condition: Excess body weight significantly increases the mechanical load placed on the stifle joints, accelerating ligament degeneration and increasing the likelihood of a complete rupture.
• Inflammatory and Immune-Mediated Factors: There is ongoing scientific investigation into the role of joint inflammation in ligament breakdown. A leading veterinary internal medicine reference notes:

An alternative theory is that lymphoplasmacytic synovitis is a primary immune-mediated disorder that causes joint laxity and instability, eventually leading to rupture of the cranial cruciate ligament. Some investigators have estimated that perhaps as many as 10% to 25% of cruciate ruptures in dogs are caused by this immunologic disorder, but this is a controversial claim.

• Breed Predispositions: Certain large and giant breed dogs are highly predisposed to developing CCLR, suggesting a strong genetic component. These include the Rottweiler, Newfoundland, Staffordshire Bull Terrier, and Labrador Retriever.

Signs to watch for

The clinical signs of CCLR can appear suddenly or develop gradually over several weeks or months, depending on whether the tear is acute or chronic, and partial or complete.

• Rear limb lameness (cardinal): This is the most prominent sign. Your pet may limp persistently, hold the affected leg up entirely, or show intermittent lameness that worsens after exercise.
• Stifle instability (cardinal): The knee joint may visibly slip or give way when your pet attempts to bear weight.
• Pain (common): Your pet may resist having the hind leg touched, extended, or bent. They may also sit awkwardly with the affected leg splayed out to the side (known as the "sit test").
• Joint effusion (common): Swelling or fluid buildup within the knee joint, which can make the knee look larger or feel puffy compared to the healthy side.
• Medial collateral ligament hypertrophy (occasional): In chronic cases, the body attempts to stabilize the loose joint by building up thick fibrous tissue on the inside of the knee. This firm swelling is often referred to as a "medial buttress."

A classic 'toe-touching' lameness in a dog with a ruptured cranial cruciate ligament.

How vets diagnose it

Diagnosing CCLR requires a thorough physical and orthopedic evaluation by your vet. Because pets often tense their muscles when stressed or painful, some parts of the exam may require mild sedation to ensure accuracy and patient comfort.

• Palpation of the stifle: This remains the most critical diagnostic tool. Your vet will feel the joint for swelling (effusion), pain, thickening (medial buttress), and range of motion. As noted in a prominent veterinary surgical textbook:

Diagnosis of cranial cruciate ligament insufficiency is based on historical and clinical evidence of rear limb lameness. Palpation of the stifle is the most useful tool to make a diagnosis of cranial cruciate ligament insufficiency.

• Cranial drawer test: Your vet will stabilize the femur with one hand and attempt to slide the tibia forward with the other. If the tibia moves forward like a drawer opening, the CCL is ruptured.
• Tibial compression test: Your vet will flex the ankle (hock) joint while stabilizing the knee. If the tibia thrusts forward during this movement, it indicates joint instability.
• Radiographs (X-rays): While X-rays cannot directly show the ligament itself, they are essential for identifying joint effusion, ruling out other bone diseases, and assessing the severity of degenerative joint disease (arthritis).
• Advanced Diagnostics: In complex or ambiguous cases, your vet may recommend Magnetic Resonance Imaging (MRI), joint ultrasonography, nuclear scintigraphy, synovial fluid analysis (to rule out infectious or joint-specific immune diseases), or a biopsy of the ligament and joint lining (synovium).
• Arthroscopy: This minimally invasive surgical technique uses a small camera inserted into the joint. It is the gold standard for directly visualizing the ligament, assessing partial tears, and inspecting the menisci (the cartilage shock absorbers in the knee) for damage.

Treatment options

Treatment for CCLR is categorized into surgical stabilization and medical management. Because the disease is progressive, surgery is almost always the recommended path for dogs to restore function and slow down the onset of arthritis.

Surgical Stabilization (First-Line Therapy)

Surgical intervention is highly recommended for most dogs, regardless of whether the tear is partial or complete. A leading veterinary surgical reference emphasizes this necessity:

Because rupture of the cranial cruciate ligament results in progressive degenerative joint changes within the joint, most such injuries should be repaired. In the authors' experience, many large breed dogs present with partial cranial cruciate ligament tears. The authors currently recommend repair in these cases even though they may not be grossly unstable.

Common surgical techniques include:

• Tibial Plateau Leveling Osteotomy (TPLO): This procedure involves making a curved cut in the top of the tibia, rotating the bone to flatten the slope of the joint, and securing it with a specialized bone plate. This changes the biomechanics of the knee so that the CCL is no longer needed to stabilize the joint during weight-bearing.
• Extracapsular Suture Stabilization: Often used in smaller dogs and cats, this technique involves placing a strong, medical-grade suture outside the joint capsule to mimic the stabilizing function of the lost ligament.
• Meniscal Evaluation: During surgery (via arthroscopy or open joint inspection), the surgeon will evaluate the menisci. A torn meniscus is highly painful and must be partially removed or repaired to ensure a successful outcome.

Medical and Immunological Management (Second-Line Therapy)

In cases where surgery is absolutely not an option due to severe concurrent medical conditions, or in specific cases where an underlying primary immune-mediated joint disease (lymphoplasmacytic synovitis) is suspected, medical therapy may be utilized:

• Glucocorticoids (Corticosteroids): Used to suppress severe, immune-mediated joint inflammation.
• Azathioprine (Immunosuppressant): A purine antagonist used as a second-line therapy to control immune-mediated joint destruction when corticosteroids alone are insufficient or cause unacceptable side effects.
• Conservative Management: This includes strict cage rest, non-steroidal anti-inflammatory drugs (NSAIDs) for pain relief, joint supplements (glucosamine, chondroitin, omega-3 fatty acids), and physical rehabilitation. While conservative management may help very small dogs (under 15 kg) and cats, it rarely provides satisfactory long-term stability for larger dogs.

X-rays help veterinarians assess joint effusion and secondary arthritis associated with CCLR.

Prognosis

The prognosis for pets with CCLR is generally favorable to excellent if they receive timely surgical stabilization and appropriate postoperative care. Most dogs return to normal, pain-free activity levels within 3 to 4 months following surgery.

However, the prognosis can be poor or unfavorable in chronic, long-standing cases where severe pre-existing degenerative joint disease (arthritis) has already developed. While surgery can stabilize the joint, it cannot reverse existing arthritic changes. These pets will require lifelong management of osteoarthritis, including weight control, joint supplements, and intermittent pain medications.

It is also important to note that up to 40% to 60% of dogs that rupture the CCL in one knee will eventually rupture the ligament in the opposite knee, often within 1 to 2 years of the first injury.

Prevention

While you cannot completely prevent degenerative ligament disease, you can take steps to significantly reduce your pet's risk:

• Maintain a Lean Body Weight: Keeping your dog or cat at an ideal body condition score is the single most effective way to protect their joints from excessive mechanical stress.
• Consistent Exercise: Avoid the "weekend warrior" syndrome. Ensure your pet gets regular, moderate daily exercise rather than intense, sporadic activity.
• Careful Breeding: Because certain breeds are highly predisposed, responsible breeders should screen their breeding stock for overall joint health and avoid breeding dogs with a history of early-onset CCLR.

When to call your vet

You should schedule an appointment with your vet if you notice any persistent limping, stiffness when rising, or reluctance to run and jump.

Seek immediate veterinary attention if your pet suddenly becomes completely non-weight-bearing on a hind limb, exhibits severe distress or vocalization when the leg is touched, or is unable to stand on both hind limbs simultaneously.

For specific breeds

If you own a Rottweiler, Newfoundland, Staffordshire Bull Terrier, or Labrador Retriever, you must be extra vigilant. These breeds have a documented, suspected genetic predisposition to cranial cruciate ligament disease. Monitor their growth closely during puppyhood, maintain a strict lean body weight, and consult your vet at the first sign of any hindlimb stiffness or subtle gait changes. Early detection of partial tears can prevent catastrophic complete ruptures and minimize long-term joint damage.

Sources

• Current Techniques in Small Animal Surgery, 5th Edition, pages 1095, 1103, 1104.
• Internal Medicine, 5th Edition, page 1155.