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).
Figure 1. Illustration of the anatomy of the dog’s knee: Blue = cranial cruciate ligament; Red = meniscus; Green = caudal cruciate; the insert shows a ruptured cranial cruciate ligament (also note that the shinbone is displaced forward and is crushing the meniscus)
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.