The cranial cruciate ligament (CrCL) is one of the structures connecting the femur (thigh bone) to the tibia (shin bone). An intact CrCL stabilizes your dog's knee during weight-bearing activity, limits hyperextension, and prevents the tibia from internal rotation and cranial thrust (tibia shifting forward).
What is a ligament?
The CrCL is a ligament. Ligaments are connective tissue made of collagen fibers that act like strong, firmly attached ropes tethering one bone to another. They stabilize joints as they move and prevent excessive motion.
What happens when the CrCL tears?
As the CrCL degenerates and loses its ability to control extension, internal rotation, and cranial slippage of the tibia against the femur, it's repeatedly stretched to the point of failure. Most CrCL tears develop gradually over time and do not occur suddenly, i.e., this is most often not a high energy, high impact sport-related trauma.
There's no exact reason for CrCL insufficiency in every dog, but excessive tibial plateau angle (TPA) may be a predisposing cause. Additional factors include genetics, obesity, poor fitness level, hormonal effects, immune-mediated disease and conformational structure. Any dog can tear their CrCL, but those with the most significant risk are middle-aged and large breeds.
The problem isn't limited to the ligament. Some dogs have a femur that slides backward (caudally) down a steeply angled tibial slope as they move. This repetitive shearing motion scrapes sensitive cartilage surfaces, causing synovitis (painful joint inflammation) worsening lameness and an increased likelihood for secondary meniscus tears.
Chronic slippage between the femur and tibia stretches the CrCL until it frays and loses strength. Think of a healthy CrCL like a piece of tightly wound rope solidly attaching two bones and torn ligament fibers resembling a mop head.
A partial CrCL rupture results in intermittent lameness and will generally progress to a complete tear within weeks or months, and full tears cause more consistent lameness. Besides limping, dogs with torn CrCLs have difficulty changing from one position to another. They often sit to the side with the painful leg tucked under their body or stretched out to the side.
Once a ligament has frayed, the knee joint loses stability and results in faulty movement patterns, inflammation, pain and eventual osteoarthritis.
Can a torn CrCL heal without surgery?
No. Minimal blood supply makes torn ligaments and meniscus cartilage poor healers, and because this is a degenerative process in dogs, those that rupture their CrCL may have up to a 60-70 percent likelihood of tearing the CrCL in the opposite hind limb.
The surgeon performs a thorough physical and orthopedic exam. X-rays are essential and assure bones are healthy and that other serious conditions aren't causing lameness. Surgeons expect diagnostic quality x-rays, which necessitate specific patient positioning, which is why surgeons may need to get new images.
ACOSM surgeons always evaluate the joint using arthroscopy, which allows them to identify and remove damaged meniscus and CrCL tissue.
Treatment of CrCL Tears:
Make no mistake - a CrCL tear is a surgical problem. That said, management of the CrCL tear in dogs can be medical or surgical. We believe all dogs, at least for a short time, require early medical management to reduce knee swelling, which includes things such as:
Surgeons recommend some combination of pain medications, joint supplements, or physical therapy during the early treatment phase to improve comfort.
How do we decide on treatment?
Treatment decisions, including continued longer-term medical management versus surgical management, revolve around three major concerns:
What is your dog's activity level?
How do you describe your pet-centric lifestyle in terms of activity? In other words, where do you go, and what do you do with your dog?
What are the athletic goals and outcome expectations for your dog?
Not all CrCL surgical procedures are the same.
We divide the two major categories of operations into dynamic and static procedures. Each approach is very different.
Dynamic procedures involve bone-cutting techniques focused on changing joint geometry to change weight-bearing knee mechanics. Each is a functional "workaround" solution to the deficient CrCL.
There are five more common dynamic techniques:
Tibial Plateau Leveling Osteotomy (TPLO)
CORA-based Leveling Osteotomy (CBLO)
Cranial Closing Wedge Osteotomy (CCWO)
Tibial Tuberosity Advancement (TTA)
Triple Tibial Osteotomy (TTO)
Besides dynamic surgeries, static techniques give early support to the knee by using a heavy suture implant to tighten or constrain the joint. Think of it as an internal brace for the knee until the joint capsule thickens or scars by natural mechanisms. These procedures vary widely based on the number of sutures used, suture material and size, and how they're attached to bone (tunnels, buttons, anchors, etc.).
Lateral suture stabilization may be an effective solution for dogs weighing less than 30-pounds. However, more recent research supports the use of TPLO in small breed dogs, and most surgeons may prefer TPLO over the lateral extracapsular suture, even in this subset of patients. In medium and large breed dogs greater than 30-pounds, increasing evidence-based literature shows improved outcomes with TPLO over other commonly performed procedures.
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Make no mistake, all surgical procedures are serious. Get the information you need and know your options. Then make an informed decision. Like any service, not all veterinary services are equal. Call to schedule or ask questions.
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