Rupture or tearing of the cranial cruciate ligament is one of the most common orthopedic injuries affecting dogs and is considered the major cause of degenerative joint disease (DJD) of the stifle (knee) joint. The cranial cruciate ligament is located inside the stifle joint and is one of the stabilizing structures connecting the femur and the tibia bones. Its primary function is to constrain the joint by limiting internal rotation and forward displacement of the tibia relative to the femur, (cranial drawer motion) and to prevent hyperextension.
The ligamentous injury may be a complete rupture in which there is gross instability and the animal is non weight baring, or a partial tear with less instability with an increased lameness after exercise and seems to recover after a few days of rest. The majority of partial tears will become full ruptures. Rupture of the CrCl results in pain, swelling and obvious lameness and chronic instability causes excess wear and tear of the cartilage, ongoing inflammation, as well as leading to secondary injury to other structures with in the joint such as the menisci. The meniscus maybe torn acutely at injury but more often damaged as a result of chronic instability and repetitive crushing shredding injuries to the caudal horn.
Mechanisms of injury can be related to normal functions; most often the ligament is ruptured when the knee is rotated rapidly with the joint in 20 to 50 degrees of flexion while the foot is planted on the ground. This puts extreme internal rotation on the tibia which puts stress on the CrCl and increases the forward tibial thrust in relation to the femur.
Other contributing factors;
larger young straight legged breeds (mastiffs, chows, labs, pit bulls. rottweilers etc.):
The angle of the tibial plateau – the steeper the slope the more tension on the ligament (the opposite leg is a mirror image, thus 30-40% of ruptures will become bilateral)
The degree of force placed or anterior-forward thrust of the joint.
Hyperextension – rabbit holes and Frisbee dogs
Medial patellar luxation in smaller breeds as patella and ligament are also stabilizers of the joint.
Obesity increased weight increased concussion and stress forces
Diagnosing the injury involves observing the dogs' gait which typically shows a weight baring shift and shortened stride, palpating the joint for the telltale instability (drawer motion), internal rotation of the tibia and a toed in appearance, and a positive sit test in which the dog will often hold the leg extended and slightly abducted from the body trying to avoid increased flexion of the joint. Radiographs are of little value in the typical rupture other than to document the amount of osteoarthrosis present, and for preoperative planning.
Modes of therapy --- Instability resulting from CrCl insufficiency leads to a progressive degenerative process and the sooner intervention is done less of these changes occur. Conservative treatment by splinting, confinement for 4-8 weeks and water treadmills have been advocated and shown to yield satisfactory function in the majority of small dogs (<15kg). Clinical experience though leads us to recommend surgical treatment of all dogs and cats when financially feasible as even the cases with chronic or advanced DJD or lame for months will show 75-95% clinical success rate after surgery. Most stifle joints are explored via a medial arthrotomy regardless of the stabilization technique performed which allows visualization on the cruciate remnants and the menisci. The meniscus is either left alone, partially or completely excised or a meniscal release performed to prevent future entrapment of a torn meniscus.
A lot of procedures have been done over the years but the top three procedures with the best predictable outcomes will be discussed.
1. Extracapsular techniques involve the use of heavy gauge suture material to decrease the instability by preventing forward and internal rotation of the tibia in similar way the intact ligament would. These procedures are usually reserved for small dogs and cats.
2. Tibial Tuberosity Advancement (TTA); Removes the need for an anterior cruciate ligament by placing the function on the patellar ligament and the quadriceps and hamstrings. Advancement of the tibial tuberosity provides stability by maintaining a weight baring alignment while not loading either the cranial or caudal cruciate ligaments in the normal standing angle.
3. Tibial plateau leveling osteotomy (TPLO); Also removes the need for a CrCl by counteracting the tibial thrust that occurs during weight baring. The proximal tibia is cut in an elliptical manner and rotated a predetermined amount to change the tibial slope to an ideal 5-to-7-degree slope and thus prevents the tibial thrust from the caudal slope of plateau.
Both the TPLO and TTA require placement of a plate to secure the osteotomy until healing occurs over 6-12 weeks.
Effective pain management in a proactive approach and tailored to the individual to ensure pet remains comfortable and generally include the use of pre- and post-operative narcotics, epidural nerve block, long-acting local nerve blocks, and nonsteroidal medication to address pain and inflammation associate with surgery.
Confinement and controlled activity (house arrest and leash control) are important during the healing process as too much activity before osteotomy has healed can result in poor healing or in complications. Typically, most patients are expected to be weight baring in the first 5-7 days after surgery, return to restricted exercise in 2 months and return to full working activity in 6 months. Radiographs are obtained at 4-6 weeks post op to evaluate bone healing and integrity of implants and activity level addressed accordingly.
Unfortunately, nothing will reverse the arthritis but surgery can help to minimize its progression and lead to a more rapid recovery better range of motion develop less arthritis and have a better return to working or athletic activity.
Alan A. Cuthbertson, DVM