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What's Wrong with My Dog's Knee?

Cranial Cruciate Ligament Rupture

Nancy Peterson, DVM, CCRT, CVA, CVSMT

Pawsitive Strides Veterinary Rehabilitation & Therapy of Des Moines

Your dog is limping on one of his rear legs. Or when he sits, one leg is always off to the side. When he stands, he doesn’t put his leg all the way to the ground, or he limps more after exercise. You may be wondering: what is wrong with my dog’s knee? 

Your dog may have injured the cranial cruciate ligament (CCL) in his knee or stifle. CCL rupture is one of the most common orthopedic diseases seen in dogs, and CCL repair is the most common orthopedic surgery performed by veterinary surgeons.

What is the cranial cruciate ligament (CCL)?

The cranial cruciate ligament (known as the anterior cruciate ligament, or ACL, in humans) is one of four ligaments that join the tibia (shin bone) and femur (thigh bone) together to create a stable dog knee joint (stifle joint).

The CCL has 3 main functions:

  1. Prevent displacement of the tibia in relationship to the femur. When your pet is standing, a compression force created in the stifle joint (dog knee) that causes the tibia to thrust forward. This forward (Cranial) tibial thrust would cause the tibia (shin bone) to thrust forward. The tibia bone has a slope to it close to the knee joint and the cranial cruciate ligament (CCL) acts like a “emergency brake” preventing the forward motion “down the hill” of the tibia by the "car" or the femur, preventing the forward (cranial) tibial thrust.
  2. Prevent hyper-extension of the stifle (knee joint).
  3. Prevent internal rotation of the tibia (shin bone).

Why does the CCL rupture?

We often think that a dog ruptures a CCL when they jump off the sofa or chase a ball but unlike people, the rupture of the cruciate ligament in pets is rarely the result of traumatic injury. In dogs this tear is often the result of subtle, slow degeneration that has been taking place within the ligament rather than the result of trauma to an otherwise healthily ligament. This is why about half of the dogs that have a cruciate ligament problem in one knee will, are at high risk to, develop a similar problem in the other knee in the future. Animals tend to experience CCL “disease”, meaning that the ligament weakens over time due to genetic, conformational, and/or immure mediated processes within the joint. Then the weakened ligament may partially or completely rupture following activities such as jumping off the sofa or chasing that ball. Obesity or excessive weight also increases the risk for cruciate ligament injury by increasing the load on the joints and therefore the wear and tear.

A CCL rupture or tear leads to:

  • Stifle (knee) pain and instability
  • Inflammation
  • Accumulation of fluid in the joint (effusion)
  • Arthritis
  • The medial meniscus (acts like a cushion inside the joint) can be damaged at the time of the CCL tear, but is more often damaged after prolonged instability of the stifle joint and can result in a torn meniscus and more pain and discomfort.

What are the signs of a ruptured cruciate ligament (CCL)?

  • Lameness (limping) in the hind limbs
  • “Toe-touching “at rest- when standing your pet may not bear weight properly on the affected leg but will just touch the toes to the ground without full weight.
  • Reluctance to walk or exercise
  • Noticeable change in the muscle mass (muscle atrophy) in the affected leg with chronic changes.
  • With a partial cranial cruciate tear the signs are less obvious- your dog may appear lame with exercise but improves with rest.
  • Shifting weight to other legs

How will a veterinarian diagnose a ruptured CCL? 

Diagnosing a cruciate ligament injury or tear includes:

  • Observing the gait
  • Palpation of the leg and stifle (knee) by the veterinarian and testing the stability of the joint and ligaments.
  • X-rays or radiographs
  • Sometimes it is more complicated or a subtle injury and requires advanced imaging or surgical exploration of the knee.

What are the treatment options?

Surgical stabilization of the stifle joint is the treatment of choice for complete CCL ruptures in dogs. In addition to surgery, physical rehabilitation is recommended. Just like physical therapy for people after an ACL tear, our dogs recover better and more completely with physical rehabilitation after surgery. There is good evidence that perioperative rehabilitation therapy by a trained veterinary rehabilitation practitioner can advance and hasten the recovery from surgery.

There are many different surgical procedures described in order to treat CCL tears. Click here for a good article on ruptured anterior (Cranial) Cruciate Ligaments and the discussion of surgical options.

No procedure completely halts the development of arthritis within the joint after the injury but timely surgery and rehabilitation therapy can be very beneficial to minimize the development of this serious complication to CCL tears.

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