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What is Anterior Cruciate Ligament?

When your dog’s anterior cruciate ligament ruptures or tears, the knee becomes unsecured and the femur and tibia can freely move back and forth across each other. The ACL can become damaged when your dog twists on their hind legs, slips on a slippery surface, is hit by a car or makes sudden turns when running. Overweight dogs are at a higher risk of tearing their ACL as the excess weight wears on the joint and causes the ACL to degenerate and weaken. There are certain breeds that are more prone to anterior cruciate ligament problems including the St. Bernard, Rottweiler, Bichon Frise, Newfoundland and Labrador Retriever. 

Your dog’s knee has several ligaments and tissues holding the three bones, the femur, tibia and patella, in place. There are two ligaments that crisscross inside the knee from the femur to the tibia. These ligaments are called cruciate ligaments. The ligament that is closer to the front of the leg is the anterior cruciate ligament or ACL and the ligament that is behind the leg is the posterior cruciate ligament.

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Symptoms of Anterior Cruciate Ligament in Dogs

If your dog tears or ruptures their anterior cruciate ligament they will appear to suddenly go lame. They will usually not want to put weight on the affected leg and will therefore hold the foot up and shift their weight to the three unaffected legs. If you notice your dog is limping or not wanting to bear weight on one of their hind legs, contact your veterinarian for an appointment. Other symptoms to look for include:

  • Swollen knee
  • Difficulty getting up from a sit
  • Trouble jumping
  • Decreased activity
  • Unwillingness to play or run
  • Lameness of differing severity
  • Decreased range of motion of the knee joint
  • Popping noise when the knee joint is moved
  • Swelling on the inside of the shin bone
  • Muscle atrophy 
  • Pain 
  • Stiffness

Causes of Anterior Cruciate Ligament in Dogs

The knee is made up of several ligaments that hold essentially hold three bones together and allow them to work as one cohesive unit. When one of the main ligaments ruptures or tears, that allows the bones to freely move against each other causing lameness and pain. The anterior cruciate ligament crisscrosses the inside of the knee from femur to tibia. The ACL keeps the femur and tibia from colliding or rubbing against each other. 

Some dog breeds are more prone to anterior cruciate ligament ruptures or tears, although any dog can experience it. Dogs that stand on their hind legs and twist can easily rupture their ACL. Dogs that run and turn too fast or fall on slippery floors can also rupture their ACL. 

Small dogs should not be allowed to jump up or down off of furniture to prevent them from experiencing luxation in their patellas. Luxation in the patella can also cause the anterior cruciate ligament to stretch and then rupture.

Diagnosis of Anterior Cruciate Ligament in Dogs

When you arrive for your veterinary appointment, have your dog’s medical history readily available, especially if this is a new veterinarian that is not familiar with your dog. Your veterinarian will begin by conducting a physical examination of your dog and will watch them walk, paying close attention to the affected leg. Your veterinarian will closely palpate the knee joint, probably by placing a hand on the femur and a hand on the tibia and applying pressure on the knee. Your veterinarian will be feeling for any abnormal movement of the femur and tibia. 

An x-ray and an ultrasound will also be conducted. This will verify that the anterior cruciate ligament has indeed ruptured. Your veterinarian will also be able to assess the extent of the tear to the ACL and determine the best treatment plan for your dog.

Treatment of Anterior Cruciate Ligament in Dogs

Once your dog has been diagnosed with an anterior cruciate ligament tear, your veterinarian will assess the extent of the tear and will discuss treatment options with you.  If the ACL has been completely torn, surgery will be necessary, especially if your dog is a larger dog. 

Synthetic Sutures

The anterior cruciate ligament can be repaired using synthetic suture material or part of the adjacent fibrous tissue. The ACL is basically removed and a new one is created when the ligament has completely torn. The sutures or fibrous tissue stretched and extended from the outside of the femur to the inside of the tibia.

TPLO

Your veterinarian may opt to perform a TPLO, or tibial plateau leveling osteotomy. This is where a part of the tibia is severed and then reattached to a different part of the tibia using plates and screws. This stabilizes the knee. TPLO is a difficult surgery to perform but the prognosis is very good. Generally, TPLO surgery is recommended for large dogs, weighing over 50 pounds. 

TTA

This surgery is called TTA or tibial tuberosity advancement and a portion of the tibia is severed and then allowed to heal at an angle that will change the stresses that are put on the knee. This is a complex surgery that will require specialized equipment and a veterinarian that has been properly trained in this procedure. 

Post-surgical instructions will include keeping your dog confined for two weeks. Your dog will not be allowed to run, jump or have excessive exercise during this time. They should be kept in a small space, preferably their crate to minimize their activity. You may notice that by day 10, following surgery, your dog is beginning to touch their toes of the affected leg to the ground. They should also start putting a little weight on their affected leg. 

Restricted exercise will be required for 4 to 6 weeks following your dog’s 2 week follow up. This means that you will be able to take your dog for short walks on leash to keep them from re-injuring their ACL.

Medical Treatment

This is necessary when the ACL is partially torn, your dog is older or your dog suffers from medical conditions that will keep them from properly healing from surgery. This consists on minimizing your dog’s activity levels for 8 to 12 weeks. Your veterinarian may suggest low impact exercise on a controlled basis to keep your dog’s muscle strength. NSAIDS are often used to reduce any inflammation in the knee. Your veterinarian may also recommend a glucosamine chondroitin or other chondroprotective supplement.

Recovery of Anterior Cruciate Ligament in Dogs

Your dog’s recovery time will depend on the type of treatment that is given. Your veterinarian will discuss with you the expected recovery time for your dog. Follow your veterinarian’s treatment plan as prescribed. 

If your dog’s torn ACL is not treated, then arthritis can set in, causing more pain. In dogs that have not been treated, many cases show that the ACL in the unaffected leg ruptures because of the over-compensation being made by favoring the initially injured leg.