Canine Cranial Cruciate Ligament (ACL) Disease

A brisk northwesterly wind swept across the yucca and cholla-choked plains of Southeastern Colorado as my hunting partner’s cherished pointer searched for aromatic affirmation that there were birds in the neighboring environs. The pointer gracefully hurdled and bounded over the greasewood and sand-sage common in Colorado scaled quail country in search of any evidence of birds. Suddenly, a jackrabbit shot up and loped across the plains sending the pointer on a dead run after the impish creature. Frantically, my friend cussed and bawled for his pointer to “Whoa Dimmitt Whoa!” Shamefully, the pointer broke chase and returned to us 3-legged lame on the right pelvic limb.

The above paragraph is a very common scenario of how athletic dogs rupture or damage their cranial cruciate ligament (This is a common injury in people and is referred to as a torn or ruptured ACL). ACL rupture is a relatively common injury in athletic dogs and is the most common cause of degenerative joint disease or osteoarthritis in the stifle (knee joint). The role or function of the cranial cruciate ligament in the stifle joint is to limit internal rotation and forward or cranial displacement of the tibia in relationship to the lower femur bone. The ligament also plays a role in preventing the stifle from hyperextension during strenuous exercise.

Injury to the ACL occurs when excessive internal rotation and hyperextension are added to forces greater than the ligament’s inherent strength, ultimately leading to damage of the fibers of the ligament. Diagnosis of the injury is made based on history of the injury, clinical signs associated with the dog, and radiographs of the stifle joint.

Most dogs with an ACL strain or tear will be non-weight bearing for the first couple of weeks due to the amount of swelling and intense pain associated with the injury. The most common clinical sign veterinarians look for is the failure of the dog to sit normally. They fail the sit test when they swing the affected leg away from the body as the patient tries to move into the sit position. Radiographs of the stifle are also an effective tool to aid in the diagnosis because they help highlight the swelling in the joint that is commonly associated with a strain or tear of the ACL. Finally, palpation of the joint for pain and swelling and a forward motion of the femur relative to the tibia or Drawer’s Motion can aid in the proper non-invasive diagnosis of an ACL rupture. Partial or incomplete ruptures can be diagnosed by arthroscopic examination of the joint prior to surgical repair on dogs where ACL damage is strongly suspected.

There are numerous other environmental and genetic factors that can lead to damage of the ACL in dogs that generally do not apply to our well-conditioned and athletic bird dogs, so I will not address them in much detail.  These conditions can include such things as inadequate conditioning, obesity, hypothyroidism, and poor conformation, luxating or slipping kneecaps and chronic inflammation or arthritis in the stifle joint.

Once your dog has been properly diagnosed with pathology of the ACL, treatment options should be considered and initiated to get your bird dog back to top hunting performance. The goal of treatment should be to return your bird dog to the level of performance it was at prior to injury. The sooner surgical repair and stabilization are initiated, the better the outcome that can be expected. If left untreated, the unstable joint leads to damage of the articular cartilage and eventually osteoarthritis that can be performance limiting or stopping.

The two most common surgical techniques offered for ACL repair are Tibial Plateau Leveling Osteotomy (TPLO) and the new Tightrope CCL Technique. I will briefly describe both procedures in the following paragraphs.

The tibial plateau (the top of the tibia which is the bottom bone beneath the femur—both bones articulate to form the stifle joint) of the canine stifle is sloped and when the ACL is torn the femur slides down the tibia.  Some people have used the analogy of a car on a hillside tied to a rope. When the rope breaks, the car starts to roll down hill. However, when the car is placed on a level surface, it stays in the same spot and does not need to be tied in place. This is the simplified concept of the TPLO surgery.

Rupture of the ACL, and the sloping of the canine tibial plateau create what is termed as tibial thrust along with the forces exerted by the muscles of the calf and quadriceps. This tibial thrust creates excessive wear and tear on the joint causing damage to the cartilage and swelling which ultimately causes severe pain. A TPLO essentially levels the playing field and eliminates the tibial thrust, thus creating a dynamically stable and pain free gait.

TPLO surgery involves arthroscopic examination of the stifle joint to clean up the damaged ends of the ligament and to inspect the medial and lateral meniscus to see if they were damaged as well. Then the tibial plateau of the tibia is cut and the plateau is rotated to level the slope to about 2 to 14 degrees. The tibia is then secured back into place with a surgical plate and multiple screws.

The healing process after TPLO surgery requires 8 to 12 weeks of serious commitment. In my experience, patients are usually touching their toes on the ground a few days post-op. Patients need to be confined to leash walking and cage rest for a minimum of 8 weeks. Follow-up radiographs are recommended at 6 weeks, 8 weeks and 12 weeks to insure that the bone is healing properly without any complication of infection or broken hardware. At 8 weeks, patients are allowed to go on longer leash walks and after about 4 months post-op, most exercise restrictions have been lifted. Patients can usually be hunting or performing by 6 months post-op.

With TPLO surgery, it is estimated that 90% of the patients will return to the level of performance they were pre-injury while about 10% develop osteoarthritis that may limit or even stop their athletic ability. Many surgeons recommend that the patient be radiographed annually to determine the amount of degeneration in the joint. All bird dogs that have suffered an ACL injury that required surgery should be on glucosamine/chondroitin sulfate, omega-3 Fatty Acids (fish oils), niacinamide or Vitamin B-6, and joint supportive diets (Please see other Strideaway articles on Canine Osteoarthritis).

Radiograph showing severe swelling or joint effusion due to rupture of the ACL.

Radiograph of the same dog after TPLO surgery.  Note the cut in the tibial plateau and the plate/screws.

Dr. James Cook, a veterinarian from the University of Missouri, recently developed the Tightrope CCL Technique to address some of the shortcomings of other ACL repair techniques including the aforementioned TPLO surgery. Dr. Cook fashioned this technique on a procedure used in humans with ankle surgery because human ankle injuries are very similar to canine ACL disease. The Tightrope  (TR) procedure was developed to stabilize the stifle without the invasive process of cutting the tibial plateau as takes place with the TPLO surgery.

The TR technique also includes arthroscopic visualization of the structures within the stifle to remove the damaged ligament and inspect the medial and lateral meniscus. Then small tunneling holes are drilled through the femur and tibia bones so that the TR (which is made of Kevlar) can be passed through and anchored to stabilize the stifle joint.

Tightrope Procedure/Technique showing anchor points (drawing courtesy of James L. Cook, DVM, PhD, Diplomate ACVS, Director, Comparative Orthopaedic Laboratory, University of Missouri)

Opening of the stifle joint to clean out the torn ligament and remove the damaged medial meniscus prior to Tightrope Procedure.

Drilled holes in the tibia and femur for the Tightrope to be placed.

Tightrope being placed.

There is still a required 10 to 12 week recovery period to insure that there is adequate healing time with this surgical procedure. One of the most common complications that I have heard from surgeons in the Denver area is infection associated with the Tightrope. TR surgical technique appears to have similar return to function rates as the TPLO surgery.

ACL damage is by far the most common orthopedic disease that we see as veterinarians. Dogs that rupture one ligament are very likely to rupture the other at some point in time. On a positive note, I see it more commonly with obese patients and that rarely includes our hunting and field trialing dogs. Traumatic rupture of the cranial cruciate ligament accounts for only about 20% of all the ACL disease in the canine population. Having a basic knowledge of what occurs with ACL disease will help us as bird dog owners to get our 3-legged lame partners to the veterinarian sooner to aid in a healthier recovery. One final note, it’s never a bad idea to get more than one opinion before you commit to any surgical procedure for your hunting partner.

Shawn will be happy to answer questions. We will be adding a logo link to his site shortly. You can find Shawn at Bird Dog Doc’s Chronicles