Cranial or Anterior Cruciate Ligament (CCL/ACL) Rupture
Cranial or anterior cruciate ligament (CrCL, CCL or ACL) injury is an all-too frequent disorder affecting dogs. Cats are affected as well, but much less commonly. The cranial cruciate is one half of crossing ligaments in the knee or stifle joint. The caudal/posterior cruciate is the other half and is of no concern here as it is rarely damaged. These two cruciates help stabilize the knee by anchoring the bottom of the femur to the top of the tibia. A normal intact cranial cruciate ligament (CrCL) prevents excess forward motion of the tibia in relation to the femur. When the CrCL is torn, excess forward motion of the tibia occurs and is defined as cranial drawer. During a physical exam, this excess motion is the basis of diagnosing a torn CrCL. Difficulty obtaining a definitive diagnosis happens with a partial tear that doesn’t allow this excess play in the joint. Partial CrCL tears will frequently lead to intermittent or ongoing lameness.
As to why CrCL tears occur with regularity in dogs is unknown. It seems likely genetics play a role but it also seems likely there are multiple factors involved. Nutrition, growth, activity (too much or little), early spay/neuter, angle of the joint, and inflammation are considerations. Ultimately, abnormal early weakening of the CrCL is responsible for the majority of cases. There are also some athletic and trauma induced CrCL ruptures resulting from more stress than a normal cruciate can withstand.
Instability from a torn CrCL typically causes a severe sudden onset rear limb lameness. It also inevitably leads to arthritis. It is universally accepted that surgery to stabilize the joint improves function, but stifle arthritis will occur after a torn CrCL even with surgical correction. Without surgery there tends to be prolonged disuse, less return to function, and more debilitating arthritis. It is not uncommon for a dog to tear the CrCL in their opposite leg too. Meniscus cartilages also reside in the stifle joint sandwiched between the femur and tibia bones. Due to a grinding motion, meniscus tears are a common consequence of CrCL rupture. Surgery is indicated after a torn CrCL since the opposite CrCL is in jeopardy and most dogs improve substantially following surgery, plus meniscus tears require surgical treatment.
A normal CrCL is Mother Nature’s way of counteracting the force pushing forward on the tibia created by walking and running. Surgery for torn CrCLs is designed to eliminate or counteract this forward pushing of the tibia that occurs with weight bearing. The mechanical force that pushes the tibia forward is known as tibial thrust.
A number of CrCL surgeries exist, three of which are in popular use.
1. Tibial Tuberosity Advancement (TTA). A procedure where a bony prominence at the top front of the tibia, the tibial tuberosity, is cut and moved forward. This tibial tuberosity is where the patella tendon attaches so it too gets advanced in the process. Tibial thrust is eliminated by the way the quadracep muscles, that attach to the patella tendon, then pull the tibia up and back instead of forward in the act of weight bearing. Pros: Becoming the treatment of choice for medium and large breed dogs, permits the stifle joint to bend and flex like a normal joint, early rehabilitation, and probable improved athleticism. Cons: moderate cost.
2. Extracapsular Lateral Suture Stabilization. This uses a suture or multiple sutures to connect the tibia and femur similar to the CrCL. The sutures(s) run along the outside of the joint instead of inside like a normal CrCL. This procedure is performed at Pet Care Veterinary Hospital. Pros: Good for small dogs, early rehabilitation and less cost. Cons: Possibly less chance of return to athleticism.
3. Tibial Plateau Leveling Osteotomy (TPLO). A referral procedure in which the top of the tibia bone is cut in an arc and rotated. It is stabilized to heal with a bone plate and screws. This “levels” the top of the tibia and changes forward tibial thrust to downward tibial thrust when the animal bears weight on the leg. Pros: Similar to TTA for improved return to athletic ability. Cons: Six or more weeks cage rest after surgery and more costly.
Anti-inflammatory and pain medications, glucosamine/chondroitin nutritional supplements, and rehabilitation therapy are also important components of treatment after repair of a torn CrCL. Nearly ninety percent of stabilized knees successfully result in good limb use. There are however some individuals who respond with disappointing results. We help almost all patients with CrCL tears utilizing surgery, although some decline in joint function is still possible.
