What is an ACL/CrCL Extracapsular Repair?

An extracapsular repair is a surgical procedure performed to address a torn cranial cruciate ligament (ACL or CrCL). In order to understand this procedure, a review of canine stifle (knee) anatomy is in order. The stifle is composed of the bottom of the femur (thigh bone), which is shaped into two rounded condyles with a deep furrow running between them (the intercondylar fossa), the top of the tibia (shin bone), which provides a relatively flat surface with a mild downward slope from front to back (called the tibial plateau), and the patella (kneecap). As the knee flexes and extends, the femoral condyles rock back and forth atop the tibial plateau, and the patella slides up and down within the trochlear groove running along the front of the bottom of the femur. A number of ligaments are present within and around the knee joint to maintain stability as the limb is used. Two of these, the cranial and caudal cruciate ligaments, run between the intercondylar fossa of the femur and the middle of the tibial plateau within the joint. The cranial cruciate ligament (analogous to the anterior cruciate ligament, or ACL, in humans) starts far back on the femur and runs toward the front of the tibia, while the caudal cruciate does the opposite, starting toward the front of the femur and running to the back of the tibia. The cranial cruciate ligament performs the important job of preventing backward sliding of the femur on the sloped tibial plateau when the animal bears weight on the limb.

When the cranial cruciate ligament is torn, the stifle becomes unstable, as the femoral condyles slide backward on the tibial plateau whenever weight is placed on the affected limb. This causes pain and inflammation that, if not addressed, will ultimately result in significant degenerative joint disease. The extracapsular repair surgery aims to stabilize the knee by installing a synthetic substitute for the torn ligament outside of the joint against its lateral (outer) surface. First, the surgeon enters the joint and removes any damaged portions of the cranial cruciate ligament and medial meniscus. After closing the joint, the surgeon passes a thick, heavy suture—most commonly composed of nylon, around the lateral fabella, a small round bone located behind the lateral femoral condyle. The suture is then brought forward across the lateral aspect of the stifle joint, and one end is passed under the patellar ligament to the inner (medial) side of the stifle. It is then passed back to the lateral side through a bone tunnel drilled in the top of the front portion of the tibia. The two ends of the suture are brought together and adjusted to the appropriate tension, then a tiny metal clamp is used to secure the two strands together. This nylon loop now runs in the same direction from the front to the back of the knee as the torn cranial cruciate ligament, effectively assuming the job of preventing the femur from backsliding on the tibial plateau. Over the months following surgery, scar tissue is laid down along and around the suture, providing essential reinforcement, as the suture will inevitably weaken and loosen with time and use. 

What patients can benefit from an extracapsular ACL/CrCl Repair?

The extracapsular repair can be performed on any dog or cat with a torn cranial cruciate ligament, but it is generally considered to be most suitable for patients who weigh less than 30 pounds and have a relatively inactive lifestyle. This is because heavier patients and those who are highly active are at a higher risk of stretching out the synthetic ligament before scar tissue has been laid down, resulting in the return of instability. Additionally, patients who have an abnormally high tibial plateau slope will generally have a better outcome with a TPLO, even if they are relatively small. 

What post-operative care is required?

Most of our pet patients are able to go home the day after surgery with oral medications to treat pain and inflammation. Instructions are provided on how to perform physical rehabilitation techniques such as cryotherapy (ice packing), stretches, and range of motion exercises. The key to a successful outcome following this surgery is strictly limiting physical activity for the first two months. By limiting activity to short, slow leash walks, strain on the synthetic suture, and subsequent loosening, is minimized. Recheck appointments are scheduled at 2, 4, and 8 weeks following surgery to monitor the progress of healing. After 8 weeks, physical activity can be gradually increased, with return to full activity expected between three and four months following surgery. 

What are the potential risks or complications with this surgery?

Several complications may be encountered following extracapsular repair surgery. Stretching or breakage of the suture, resulting in a return of instability, can occur if a patient is too active during the first two months following surgery, or if the suture used was too small relative to the patient’s body size. A second surgery is necessary in these cases to replace the suture and restore stability. Dogs weighing more than thirty pounds are at an increased risk of this complication. Infection of the surgery site is also possible, and may necessitate eventual removal of the suture. 

What is the prognosis with this surgery? 

The prognosis for return to normal or near-normal function following surgery is very good to excellent for patients weighing less than thirty pounds who avoid high-impact activity during the first two months after surgery. A functional outcome is certainly possible for larger dogs, but the risk of implant failure is higher. Because a slight amount of instability inevitably remains following surgery, mild progression of arthritis is expected over time. This is typically manageable with medications, supplements, and physical rehabilitation therapy. Also owing to this slight persistent instability, a small percentage of patients will go on to tear their meniscus in the months or years following surgery. Treatment for a meniscal tear typically involves another surgery on the stifle.


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