Key Points

One of the important functions of the cruciate ligament is to prevent forward and backward sliding of the femur on the tibia bone, also known as drawer motion

Rupture of this ligament leads to debilitating lameness

The TTA surgery

• has a similar outcome as compared to the TPLO procedure
• can have complications, but typically are not as devastating versus those occasionally seen with the TPLO
• is not for every dog; your dog’s surgeon will help you make the decision whether TPLO or TTA should be performed

 

Anatomy

The canine knee joint, known as the stifle joint, is similar to a human’s knee in many regards. The joint is made up of the meeting of the femur (thigh bone), tibia (shin bone), and the patella (kneecap). The cranial and caudal cruciate ligaments (CCL), medial and lateral collateral ligaments, and the patellar (kneecap) ligament hold these bones in place.

Ligaments are strong, dense structures consisting of connective tissue that connect the ends of two bones across a joint. The function of ligaments is to stabilize a joint. The CCL plays a critical role in stabilizing the stifle (known as the knee in humans) against front-to-back forces. It prevents the tibia from shifting in front of the femur, controls excessive internal rotation of the joint and hyperextension, and is the structure most commonly injured. In fact, more than 600,000 dogs in the U.S. have surgery for this problem every year.

Diagnosis

The top of the tibia that is in contact with the bottom of the femur is angled and sloped toward the back of a dog’s leg. When the CCL is torn, weight-bearing movement causes the femur bone to slide down this slope. Not only is this painful, but also causes the stifle to “give out” during weight-bearing. As the femur slides down the slope of the tibia, the meniscal cartilage—a cushion between the bones that acts as a shock absorber may be crushed. In about 50% of the dogs with CCL injuries, the meniscal cartilage has been injured as well. This type of injury is often accompanied by a “click” that can be heard when a dog walks.

When the CCL is weakened or torn, the most significant long-term change in the joint is the development of arthritis. All joints with instability will develop arthritis; however the severity and the effect of the arthritis will vary from dog to dog. Most dogs with a complete CCL tear show an immediate onset of lameness. While there may be some initial improvement over several days, there usually is a dramatic decline in limb function over time. There is no benefit gained from taking a “wait and see” approach. Stabilization of the joint soon after the injury has occurred is recommended.

Treatment

In small dogs, nylon bands can be used to tighten the knee, however, this technique usually is not consistently effective in large breeds. There are two main types of surgery that are recommended for medium and large breed dogs that have CCL tears: the tibial tuberosity advancement (TTA) and the tibial plateau leveling osteotomy (TPLO). The TTA is a somewhat less invasive surgery and gives similar results to the TPLO. Dogs that receive the TTA procedure will recover quicker initially, however, by 4 months after surgery both procedures have similar outcomes.

The TTA procedure should not be used in dogs that have a steep tibial plateau, therefore your dog’s surgeon will make a decision which procedure is the best option for your companion. The TTA procedure involves making a cut in the front part of the tibia bone (tibial tuberosity) and advancing this portion of bone forward in order to realign the patellar ligament so that the abnormal sliding movement within the knee joint is eliminated. A specialized bone spacer, plate and screws are used to secure the bone in place. Bone graft is collected from the top of the tibia and placed in the gap in the bone to stimulate healing.

Biomechanics of the TTA

Now this will seem complicated when you look at the forces that are applied to the knee, but let me try to explain. There are opposing forces that affect the stability of the knee. The forces that come from the patellar ligament (from the pull of the quadriceps muscles), Fq, oppose the other forces applied (Fn and Ft). Because the patellar ligament is angled greater than 90 degrees to the top of the tibial slope (dashed line), there is a resultant shear force that causes the tibia bone to slide forward with weight-bearing; this force is normally neutralized by the cranial cruciate ligament. However, when the cruciate ligament is torn, this force causes the knee “give out” with every weight-bearing stride. After the TTA procedure has been completed, the angle of the patellar ligament approaches 90 degrees to the tibial slope and the opposing forces become cancelled, thus the tibia bone remains in place when weight is placed on the limb.

Aftercare and Results

After surgery, you can continue to give your pet a prescribed pain reliever to minimize discomfort. It’s also extremely important to limit your dog’s activity and exercise level during this post-operative period. Rehabilitation exercises can be done at your home or if you choose, by professionally trained therapists at an animal rehabilitation center. Rehabilitation therapy should be continued until your dog is bearing weight well on the operated limb (typically 8 weeks after surgery). Detailed instructions will be given to you after the surgery.

The healing process will be monitored by the surgeon with two follow-up exams. The first is scheduled at two weeks after the surgery and the second is at eight weeks after the surgery. By 8 weeks after surgery, the bone will be healed together. By 16 weeks after surgery, most dogs are fully weight-bearing on the operated limb, and exercise restrictions can be lifted at this time.

Complications are possible following TTA surgery; however, as the surgeon performs more and more of these procedures the complication rate also will decrease, but will not be totally eliminated. Anesthetic reactions are uncommon and rarely result in mortality under the care of trained specialists. Although infection may develop in the surgical site, this is uncommon, as strict sterile technique is used during the surgery. If your dog is receiving medications such as chemotherapy or steroids, the bone may not heal well, therefore it is imperative that you inform the surgeon prior to surgery that your dog is receiving these medications. Over activity in the postop period may also result in poor bone healing, loosening of the screws or breakage of the implant. In addition, if your dog falls, the tibia may fracture. Arthritis (bone spurs) is usually present at the time of diagnosis of a cruciate ligament rupture and likely will progress regardless of surgical procedure performed. At this time (Jan 2008) there is no report that demonstrates that the TTA procedure will slow the progression of arthritis. If the arthritis progresses, medications can be used to help relieve these signs. Reports indicate that there is about a 9 to 10% risk of developing a meniscal tear after TTA surgery (another report demonstrated greater than 20% meniscal tears), therefore most surgeons perform a meniscal release at the time of the surgery to prevent this complication. In comparison, only about 2% of TPLO cases develop a meniscal tear after surgery (with no meniscal release being performed). If the patient develops an infection in the surgical site and the implants need to be removed it can be a total nightmare for the surgeon to remove the implants. The cage that is frequently embeded in the bone will require drilling of the bone to remove it.

The TTA and TPLO procedures offer multiple benefits in comparison to older techniques which include: faster recovery, earlier use of the limb after surgery, better chance to return to full activity, and better range of motion of the joint. The TTA and TPLO procedures are currently the best methods available for stabilizing a dog’s knee. At the time of this writing (Jan 2008), no study demonstrated that working dogs receiving the TTA procedure will return to their peak athletic performance. Until supportive data comes out, I still recommend the TPLO surgery for athletes (agility, hunting, police dogs etc). In addition, I would not recommend this procedure for show dogs for two reasons: first, the tibial crest protrudes more, therefore a short-coated dog will have a visible difference in the appearance of the operated limb; second, following TTA surgery, the dog may walk with the stifle in a more flexed angle. Overall, the TTA appears to be a good treatment option for dogs that have ruptured the cranial cruciate ligament.

 

References

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