The cranial cruciate ligament (CrCL, see Figure 1.) is one of the most important stabilizers inside the canine knee (stifle) joint, the middle joint in the back leg. In humans the CrCL is called the anterior cruciate ligament (ACL).
The meniscus (Figure 1) is a ‘cartilage-like’ structure that sits in between the femur (thigh) and tibia (shin) bones. It serves many important purposes in the joint such as shock absorption, position-sensing, and load-bearing and can be damaged when the CrCL is ruptured.
Rupture of the CrCL is one of the most common reasons for hind limb lameness, pain, and subsequent knee arthritis. Since the development of this problem in dogs is much more complex than in humans, and they experience different degrees of rupture (partial or complete), the canine condition is referred to as ‘cranial cruciate ligament disease’ (CrCLD). While the clinical signs (symptoms) associated with CrCLD vary, the condition invariably causes rear limb dysfunction and pain.
Most commonly CrCLD is caused by a combination of many factors, including 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). This difference between people and dogs explains two important features of canine CrCLD:
- 40-60% of dogs that have CrCLD in one knee will, at some future time, develop a similar problem in the other knee.
- Partial tearing of the CrCL is common in dogs and progresses to a full tear over time.
Cranial cruciate ligament disease can affect dogs of all sizes, breeds, and ages, but rarely cats. Certain dog breeds are known to have a higher incidence of CrCLD (Rottweiler, Newfoundland, Staffordshire Terrier, Mastiff, Akita, Saint Bernard, Chesapeake Bay Retriever, and Labrador Retriever) while others are less often affected (Greyhound, Dachshund, Basset Hound, and Old English Sheepdog). A genetic mode of inheritance has been shown for Newfoundlands and Labrador Retrievers.
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. Consistent physical conditioning with regular activity and close monitoring of food intake to maintain a lean body mass is advisable.
Dogs with CrCLD may exhibit any combination of the following signs (symptoms):
- difficulty rising from a sit
- trouble jumping into the car
- decreased activity level
- lameness (limping) of variable severity
- muscle atrophy (decreased muscle mass in the affected leg)
- decreased range of motion of the knee joint
- a popping noise (which may indicate a meniscal tear)
- swelling on the inside of the shin bone (fibrosis or scar tissue)
- unwillingness to play
Diagnosing complete tears of the CrCL is easily accomplished by a veterinarian using a combination of gait observations, physical examination findings, and radiography (X-rays). By contrast, partial CrCL tears may be more challenging to diagnose.
X-rays allow your veterinarian to:
- confirm the presence of joint effusion (fluid accumulation in the joint, indicating that there is an abnormality present)
- evaluate for the presence/degree of arthritis
- take measurements for surgical planning
- rule out concurrent disease conditions
Specific palpation techniques that veterinarians use to assess the CrCL include the ‘cranial drawer test’ and the ‘tibial compression test.’ These tests can confirm abnormal motion within the knee consistent with rupture of the CrCL.
Postoperative care at home is critical. Premature, uncontrolled or excessive activities risk complete or partial failure of any surgical repair. Such failure may require extensive surgery to address. Proper postoperative care will be explained to you in detail by your dog’s surgeon before and after surgery.
Studies show that physical rehabilitation can speed a dog’s recovery and improve final outcomes regardless of the chosen surgical technique. This rehabilitation should start immediately after surgery and usually includes a regime of passive range of motion, balance exercises, controlled walks on leash and so forth. Additional details should be discussed with a board-certified surgeon and/or a primary care veterinarian.
The long-term prognosis for animals undergoing surgical repair of CCLD is good, with reports of significant improvement in 85-90% of the cases. While, arthritis can progress regardless of treatment type, it’s expected to be slower when surgery is performed. Therefore, multimodal osteoarthritis management is recommended for any dog with CrCLD regardless of treatment. What this management might entail should be discussed with your dog’s surgeon and/or primary care veterinarian.
Obesity in pets has numerous health issues associated with it that go beyond CrCLD. Weight loss should be considered critical to any overweight pet with CrCLD. Your veterinarian can help you to determine the ideal weight of your pet and how best to reach it.