What is the cranial cruciate ligament (CCL)?
The cranial cruciate ligament (known as the anterior cruciate ligament, or ACL, in humans) is one of several ligaments in the stifle (knee) that connect the femur (thigh bone) to the tibia (shin bone). The CCL has 3 main functions: (1) prevent cranial displacement of the tibia in relation to the femur (cranial drawer sign) (2) prevent hyperextension of the knee, and (3) prevent internal rotation of the tibia.
Why does the CCL rupture?
Unlike human athletes, rupture of the CCL in dogs is rarely the result of a traumatic injury. Rather, animals tend to experience CCL “disease”, meaning that the ligament degenerates or weakens over time due to genetic, conformational, and/or immune mediated processes within the joint. The weakened ligament may partially or completely rupture following activities such as running or jumping. Unfortunately, the condition leading to CCLR is often present in both knees, and about 30- 50% of dogs will rupture both CCLs within 1-2 years of each other. CCL rupture is one of the most common orthopedic disease seen dogs, and CCL repair is the most common orthopedic surgery performed by veterinary surgeons.
Are any other parts of the joint affected when the CCL ruptures?
Quite often, yes. The medial meniscus (MM) is a fibrous pad attached to the top of the tibia that acts as a cushion inside the joint (there is also a lateral meniscus, but it is less often injured). The MM can be injured at the time of CCLR, but is more often damaged after prolonged instability of the stifle joint. Without the support of the CCL, the femur puts abnormal pressure on the MM which can lead to tearing or shredding of the meniscus.
What signs will I see if my dog ruptures a CCL?
There are three potential scenarios that can occur with CCLR: acute rupture, chronic rupture, and partial tears.
Following an acute rupture, your dog will likely be painful and partial to non-weight bearing lame in the affected hind limb. The lameness will likely improve over the next several weeks, however a sudden worsening may be seen if the MM becomes damaged, and your dog will not return to normal function without some evidence of lameness. An audible clicking or popping may be heard if the MM is torn.
With chronic CCLR, an inciting incident may not have been noticed, but persistent lameness is evident. Over time, the body tries to stabilize the stifle by surrounding the joint with scar tissue. This will look like a swollen knee and range of motion of the joint may be compromised. Arthritis will develop inside of the joint as a result of chronic instability.
Partial CCL ruptures are less obvious—your dog may appear lame with exercise, but improves with rest. However, the ligament will continue to weaken and the joint will become increasingly unstable. Eventually, the ligament will likely rupture completely and lameness will not improve with rest.
How will a veterinarian diagnose a ruptured CCL?
The diagnosis of CCLR is typically based on the presence of the “cranial drawer sign”. In order to feel this, you dog will be placed on his/ her side, and the veterinarian will feel the knee for cranial drawer motion. This procedure is not painful; however, some dogs may be too tense to allow thorough palpation. If this is the case, a sedative may be given in order to complete the examination. Patients with chronic ruptures associated with a large amount of scar tissue and arthritis may not exhibit cranial drawer. Other signs of CCL rupture include “medial buttress” (thickening or scarring on the inside of the knee), and “tibial thrust” (another method to check for cranial displacement of the tibia). X-rays will also be taken in order to rule out other potential causes of hind-limb lameness and to evaluate the extent of arthritis within the joint.
What are my treatment options?
Surgical stabilization of the stifle joint is the treatment of choice for complete CCLR in dogs. In addition to surgery, physical rehabilitation will be recommended.
There have been many different procedures described in order to treat CCLR. No procedure completely halts the development of arthritis within the joint, but surgical stabilization is believed to result in better functional results than conservative therapy alone. The success rate with surgery is about 90% (meaning that most dogs return to good or excellent function following surgery and proper post-operative care).
Currently, there are three procedures recommended and performed at the UFVH. Regardless of the stabilization procedure, the stifle joint will be explored, “cleaned out”, and the MM will be examined and removed if damaged.
- Extra-capsular stabilizing suture
This procedure attempts to mimic the functions of the CCL by placing a heavy gauge suture across the stifle joint in a similar orientation to the normal CCL. The suture is placed on the outside of the joint (extra-capsular). Outcomes are very good in dogs weighing less than 30-40 pounds (and in cats). It is possible to perform this procedure on larger dogs; however, the results are not as predictable and breakage of the suture may be more likely.
- TPLO (Tibial Plateau Leveling Osteotomy)
To date, the TPLO is considered by many experienced veterinary surgeons to be the most successful stabilization procedure available for dogs of any size, and is particularly successful in large dogs.
The TPLO changes the mechanics of the stifle joint rather than attempting to replace or mimic the CCL with a graft or suture. The tibia has a natural slope, and an intact CCL prevents the femur from “sliding” down the slope when a dog bears weight. When the CCL is ruptured, the femur is free to slide down the slope, or in other words, the tibia moves forward in relationship to the femur (cranial drawer) when weight is place on the effected limb. In a TPLO procedure, the tibia is cut (osteotomy) and rotated in order to flatten the tibial plateau (the top or joint surface of the tibia) and prevent the femur from sliding backwards. A plate is applied to the inside or medial surface of the tibia to stabilize the osteotomy. This procedure requires specialized equipment and is usually performed in veterinary teaching hospitals or a referral center. Proper post operative management is critical in TPLO patients since, essentially, a fracture has been created and the bone must heal.
- TTA (Tibial Tuberosity Advancement)
Like the TPLO procedure, the TTA changes the mechanics of the stifle joint in order to counter-act the abnormal forces placed on the joint following injury to the CCL. This is the latest surgical procedure designed for treating CCL ruptures and surgeons who have been performing TTA’s have been very satisfied with the results.
In order to change the joint mechanics, a cut is made in the tibia along the front edge (cranial surface) where the patellar (knee cap) ligament attaches. This segment of bone is advanced a pre-determined distance and stabilized using a titanium plate and screws.
Advantages of this procedure compared to the TPLO include a smaller, less invasive cut in the bone at an area that is not directly involved in weight bearing, earlier post-operative weight bearing, and potentially less severe complications. The primary disadvantage is lack of long term studies comparing this procedure to the TPLO and extra-capsular suture. We have been performing this procedure here at the UFVH since July 2005 and have seen comparable results to the TPLO. Dogs do tend to bear more weight on the limb earlier in the recovery period; however, strict exercise restrictions must be followed similar to the TPLO.
What will need to be done before my dog can have surgery?
X-rays must be taken prior to surgery. If x-rays were taken at your regular veterinarian, the films may suffice for dogs having extra-capsular repairs. A special view is needed for dogs having a TPLO or TTA, so it will be necessary to have x-rays taken here. Prior to anesthesia, routine blood work will be performed.
What will the recovery process be?
You will receive detailed instructions at the time of discharge from the hospital regarding post operative care. Regardless of the procedure, your dog will require at least 3 months of exercise restrictions. This will mean leash walks only (no free roam of the back yard), no running, jumping, or rough house play. However, physical therapy and rehabilitation will be essential and a detailed program will be outlined for you and your pet. This will involve leash walks of increasing duration and intensity along with therapeutic exercises to strengthen the muscles of the affected leg as well as the core stabilizing muscles. Most dogs are allowed to return to normal activity after 3-4 months (only once the bone has healed completely and the muscles have been rebuilt). Failure to follow the exercise restrictions dictated in the discharge instructions could result in severe complications necessitating further surgery.
The skin sutures or staples will need to be removed 2 weeks after surgery. This is often performed with your veterinarian. Recheck appointments at the Small Animal Hospital will be required at 4-6 weeks and 3 months after surgery, at which time x-rays will be taken to asses bone healing if a TPLO or TTA was performed.
What are the potential complications of surgery?
Any time an animal (or human) undergoes anesthesia there is the risk of adverse reactions to anesthesia, including death. However, blood work is performed prior to anesthesia in order to identify any underlying medical conditions which may influence anesthetic choices. In addition, there are board-certified anesthesiologists and an extremely experienced staff of anesthesia nurses here at the Small Animal Hospital that will take exceptional care of your pet.
Complications associated with surgery are uncommon and include excessive bleeding, infection, fracture of the tibial crest or fibula, and surgical implant failure. It will be essential that the post-operative instructions be followed precisely in order to prevent surgical site infections (usually due to dogs licking the incision), failure of the suture or implant (breakage of the suture or TPLO/ TTA plate) or fracture of tibia.