Rupture of the Cranial Cruciate Ligament (CCL) is the most common orthopaedic injury that occurs in our canine patients in a year, which is referred to as the ACL or Anterior Cruciate Ligament in humans. In humans acute trauma is almost always the cause. In dogs, CCL injury can occur as an acute trauma or more commonly is the result of a degenerative process that leads to early and progressive arthritis. CCL insufficiency causes pain and lameness and increases the risk of injury to other structures of the knee, such as the meniscus. Techniques used to repair this injury in humans do not work well for dogs because of factors such as conformation. In dogs, the CCL cannot be repaired or reattached. Surgical options for dogs with this injury are based on stabilizing the joint with nylon (other options) using the extracapsular stabilization or dynamically altering the biomechanics of the joint using the TPLO or TTA.
Cranial Cruciate Ligament work?
The knee (or stifle as it is called in dogs) joint in dogs is similar to ours; the forces applied to the joint during weight bearing are vastly different. Because we stand upright, there is minimal stress to the ligaments in our knee. Dogs, however, stand with the ankle elevated and the knee forward. The top of the dog’s tibia (tibial plateau) is sloped and weight bearing creates a force that pushes the femur down the slope of the tibia. This force is called “tibial thrust” and it is the job of the CCL to prevent this motion. Each time the dog bears weight, the CCL is under tension. When the ligament is ruptured, each time the dog bears weight this motion occurs and causes discomfort. When the CCL is ruptured (even partially) the joint, there will be inflammation and swelling, referred to as synovitis and effusion. The two menisci are the “shock absorbers” of the knee and are located between the femur and the tibia. When the knee is unstable due to a CCL rupture, either complete or partial, the menisci are at risk for injury.
Rupture of the Cranial Cruciate Ligament
Rarely there may be a single incident which causes a sudden complete rupture of the ligament. If this occurs the dog is typically painful and non-weight bearing. A rupture can also occur over incrementally over a relatively long period. Dogs with a high tibial plateau angle (greater slope) have greater stress to the CCL and the ligament can tear partially. Dogs can also partially tear the ligament due to an incident. When a dog has a partial rupture, the dog typically has an intermittent lameness. Partial ruptures can progress to a complete rupture within weeks to months. Actions that could cause a rupture include hyperextension and internal rotation of the knee from sudden turns; include stepping into a hole, jumping, repetitive normal activities and degeneration with aging. Obesity is an increased risk of a rupture as can the “weekend warrior” routine, in which the pet is relatively inactive during the week but very active on weekends. Dogs that have ruptured the CCL in one knee have a 50% to 70% greater chance of rupturing the CCL in the other knee. Therefore, surgical correction is recommended as soon as possible to decrease the stress placed on the uninjured CCL, thereby decreasing the risk of CCL rupture to that knee.
What are symptoms that my pet has a rupture of the CCL?
Complete rupture results in a non-weight bearing lameness. In the case of a partial rupture, the pet will be weight-bearing lame or have an intermittent lameness. Lameness will often worsen with activity. Stiffness upon rising and/or a stiff gait is another common complaint. You may note that your pet sits with the affected leg out to the side. He or she may have difficulty rising and be less active. Physically, you may note a swelling or thickening of the knee and muscle atrophy (wasting) in the affected limb. Dogs that have ruptured the CCL in both knees do not have lameness in a particular limb since he or she does not have a good limb to stand on.
Diagnosis of CCL rupture
Muscle atrophy of the affected hind limb is common and thickening of the affected knee, called medial buttress, is noted. The patellar tendon, which runs along the front of the knee, is assessed. An effusion within the joint common to CCL injuries will make palpation of the patellar tendon less distinct. Joint stability can be assessed through manual manipulation. Instability detected by experienced clinicians will detect complete or partial rupture of the CCL. Radiographs of the stifle can be useful to evaluate the presence of effusion (excessive fluid within the joint) and arthritis. If these assessments are not completely diagnostic, arthroscopic evaluation of the joint and structures may be recommended. If arthroscopic evaluation reveals the ligament is injured, surgical correction can be performed at that time. There are four techniques for surgical stabilization of the stifle joint.
Extracapsular Stabilization/Lateral Suture Procedure
Extracapsular Stabilization stabilizes the stifle joint with placement of a non-absorbable suture material, typically a monofilament nylon such as fishing leader line, around the lateral fabella and through a hole in the tibial crest mimicking the pattern of the CCL. Although often referred to as an “artificial ligament”, the suture provides only temporary stabilization and will loosen over time. This technique relies on scar tissue to ultimately stabilize the joint. Recovery time following the Extracapsular Stabilization is approximately 3 to 5 months. While this technique can be successful, it is more likely to fail in large breed dogs as the prosthetic ligament can stretch or rupture. Another common complication is over-tightening of the prosthetic ligament with applies excessive compression of the joint. This can lead to cartilage damage, increased risk of meniscal injury, limited range of motion of the joint, and discomfort.
TightRope CCL
This technique differs from the traditional extracapsular stabilization in that it is a bone to bone fixation and utilizes a method for more accurate isometric implant placement. FiberTape®, an implant designed specifically for ligament repair, has superior strength and stiffness compared to conventional materials used for extracapsular stabilization. The FiberTape® is passed through these tunnels. Toggle buttons are inserted and used to apply appropriate tension to the FiberTape® providing stabilization of the knee
Tibial Plateau Levelling Osteotomy (TPLO)
The TPLO procedure is a dynamic procedure and stabilizes the knee by levelling the tibial plateau. The surgeon will measure the tibial plateau angle (slope) from X Rays and accurately and precisely determine the amount of rotation that is needed to reduce the angle to between 5 and 8 degrees. The basis of the TPLO procedure is that the surgeon will make a curved cut (Osteotomy) in the tibia and rotate the segment so that the load-bearing surface of the tibia is between 5 to 8 degrees. A plate and screws is then applied to hold the tibia in this position and allow for the bone to heal. Recovery time following the TPLO procedure is approximately 2 to 3 months. Following TPLO surgery, patients use the limb and are morecomfortable much sooner than following the Extracapsular Stabilization. Additionally, studies show that there is less arthritic development long term following the TPLO verses the Extracapsular Stabilization (Lazar T, Vet Surg, 2005).
TTA vs TPLO Diagram
TTA
The basis for the TTA is similar to the TPLO, in that the biomechanics of the stifle are altered to dynamically reduce or eliminate cranial tibial thrust. This is achieved by cutting the cranial aspect of the tibia and advancing it forward using a Titanium cage. By making the patella tendon perpendicular to the tibial plateau slope the stifle remains in neutral position.
Tibial Tuberosity Advancement (TTA)
TTA View of Implants
The TTA is a dynamic procedure similar in principal to the TPLO but relies on the patellar tendon to stabilize the knee. This involves moving the patellar tendon forward to the point that it is perpendicular (at 90 degrees) to the tibial plateau with the limb in a standing angle. This movement relieves the load of the CCL, applying that load to the patellar tendon. The amount of distance necessary to advance the patellar tendon to make it perpendicular to the tibial plateau is measured from preoperative radiographs.
TTA Post-Op X-Ray
The patellar tendon is attached to the tibial tuberosity (the front top portion of the tibia) and it is the tibial tuberosity that is actually advanced.
The tibial tuberosity is cut in a wedge fashion and moved forward the predetermined amount. It is held in place by a titanium cage, fork and tension band plate. Bone grows over and through the cage and fills in between the tibia and the advanced tibial tuberosity. This technique is not appropriate for dogs with tibial slopes greater than 27° to 30°.