The canine stifle ( knee ) is a complex joint that lacks a true ball and socket type design. The femoral condyles rest on a tibial plateau aided by two cartilage meniscus pads which are cupped and substitute as a socket for the femoral condyles to rest. The two main intra- articular ligaments that give stability to the knee are called Cruciate Ligaments. They are the Anterior Cruciate Ligament ( ACL ) and Caudal Cruciate Ligament ( CCL ) On occasion the medial cartilage pad (meniscus ) can be injured ( torn ) with or without concurrent cruciate ligament tears. This creates pain in the knee joint and subsequent lameness. Fortunately for dogs, they walk on 4 legs and often get along on 3 legs or transfer enough weight and appear to cope with a mild injury. This leads to intermittent lameness after exercise, medial swelling on the knee joint capsule ( medial buttress ) and osteoarthritis in the knee. Once completely torn the dogs often holds the leg up and are reluctant to want to weight bear on the leg. Most ligament tears occur in the ACL, less commonly in the CCL. Often with a meniscus tear a clicking noise can be heard and felt when the knee is flexed and extended.
In humans the tearing of the ACL is mostly the result of direct trauma. In dogs the onset of the lameness may appear to be from a trauma however, it is now know that a factor called the "tibial plateau angle" plays a significant role in predisposing the ACL to tears. The human knee has a tibial plateau that is just slightly off the horizontal plane by a few degrees. In the dog the plateau angle is quite significant, often in excess of 24 degrees in the posterior direction ( slopes backwards away from the front of the knee ). This slope places direct tension on the ACL that is directly related to the degree of slope. Over time this stretches, fatigues and weakens the ACL. Then the ligament can tear from a traumatic event and appear that the onset is acute ( sudden ).
Once the ACL is torn, surgery is the best option to get stability back in the knee and resume usage. There have been over 230 different surgical techniques developed over the years to address a torn ACL. To date, even with all of our advancements in surgery, there is no one technique that is the "magic bullet" for this condition. The most commonly used techniques for the dog are; Lateral Suture Imbrication, Tibial Plateau Leveling Osteotomy ( TPLO ) and Tibial Tuberosity Advancement ( TTA ). Recently, a second generation TTA2 procedure has been developed which uses less implants and speeds healing for selected cases.
Lateral Suture Imbrication involves applying a monofilament suture ( similar to fishing line ) to the outer aspect of the lateral joint capsule in such a direction as to mimic the line of tension of the ACL. This gives lateral stability to the knee, but little to no rotational stability. The knee functions more as a hinge joint. This predisposes the knee to meniscial injuries ( tears ). It is a relatively simple surgery and can be performed by veterinarians with good surgical technique and training
TPLO and TTA surgeries address the biomechanics of knee forces instead of the direct stability of the knee joint. They are often referred to as Geometric surgeries. These surgeries neutralize the cranial tibial thrust force. After surgery the knee will function in the abcense of an intact ACL.
TPLO has been a very popular technique and has had good success in returning dogs back to function. It involves making a curved cut in the proximal tibia separating the tibial plateau from the tibial shaft, rotating the plateau to 6 degrees off horizontal and fixing it with a bone plate. It has a few draw backs, in that the weight bearing axis is changed in the leg, the popliteal muscle is elevated off the tibial bone for the osteotomy procedure which results in some loss of rotational stability in the knee and tension is removed from the patella tendon which may lead to patellar tendonitis post op. Reported complication rates are as high as 28 to 30% post operatively. It requires special training and equipment and should not be attempted by veterinarians not proficient in Orthopedic Surgery.
TTA surgery also neutralizes the " cranial tibial thrust " force by an osteotomy to free up the tibial crest and advance it forward. The crest is fixed it in place with a metal cage and specialized fork plate. This techniques keeps the same weight bearing axis for the leg, does not affect the function of the popliteal muscle and maintains tension of the patellar tendon. The reported complication rate is about 6 to 8% post op. It too should be performed by surgeons experienced in Orthopedic Surgery. TTA2 is a variation of TTA and reduces the amount of implants needed for the procedure.
Here at Peterborough Pet Hospital Dr. Muise prefers and routinely performs TTA surgery and TTA2 for the treatment of Anterior Cruciate Ligament disease.