Understanding knee injuries requires a basic understanding of the anatomy of the joint. The stifle, or knee, is the joint in between the femur and the tibia. Between the two bones lies a cushion called the meniscus, which is composed of two C-shaped pieces of cartilage. The stifle joint is stabilized by a series of ligaments: the cranial and caudal cruciate ligaments, the medial and lateral collateral ligaments, and the patellar ligaments. The cranial and caudal cruciate ligaments cross over the front of the stifle joint, and are responsible for keeping the tibia from sliding too far forward, or too far backward, respectively. The medial and lateral collateral ligaments lie on either side of the knee, with the lateral being on the outer aspect of the joint, and the medial on the inner aspect. These two ligaments function to stabilize the sides of the joint, and keep the bones from sliding away from each other in a medial or lateral direction when the stifle is extended. The patellar ligaments are those that hold the patella, or kneecap, in place and allow for its movement when extending and flexing the knee. (diagram of stifle anatomy)
Injury to the lateral collateral ligament can result in a complete or partial tear of the ligament.
Any age, breed, or gender of dog can suffer lateral collateral ligament injuries. Cats can also be affected. In general, stifle injuries tend to occur in larger dogs, especially those that are overweight, and/or extremely active.
The most common clinical sign of lateral collateral ligament injury is lameness. The degree of lameness will vary among patients, and will differ based on the severity of the injury, i.e. if it is a strain, partial tear, or complete rupture. The dog will favor the affected leg, and may show signs of pain and discomfort.
Diagnosis of lateral collateral ligament injury is based on palpation, and can be used to determine the severity of the damage. Your veterinarian will test the integrity of the ligament by holding the limb in
extension, and performing a varus stress test. Using one hand to stabilize the femur, and the other to hold the end of the tibia, your veterinarian will apply and inward force (called adduction) to the joint. If the lateral collateral ligament is torn, an “opening” of the joint is apparent; in other words, the femur and the tibia will separate, because that ligament is not intact. Radiographs may also be taken to rule out any other concurrent problems, such as bone fragments.
Due to the anatomy and biomechanics of the joint, it is prone to a number of injuries, particularly in large, overweight dogs. Injury to the joint usually results occurs while the animal is exercising, or during a traumatic incident. Damage to the lateral collateral ligament specifically, is usually caused by a severe blow to the side of the joint or a twisting motion, especially at high speed. The affected ligament may be stretched, partially torn, or completely ruptured. It is important to note that lateral collateral ligament injuries are often secondary to other ligament damage of the stifle, such as rupture of the cranial or caudal cruciate ligament.
Lateral collateral ligament injuries can be treated medically or surgically, and deciding which approach to take is made based on the degree of injury, and whether or not damage to other structures of the stifle is present. Conservative treatment is used in less severe cases, and includes rest, exercise restriction, anti-inflammatories, and possibly placing a fiberglass cast for 2 weeks in order to immobilize the joint and allow it to heal. For patients with significant injury to the ligament, surgery is recommended. The surgical technique involves replacing the ligament to its normal anatomical position, and anchoring it in place with a screw. Alternatively, an anchor may be placed where the ligament normally attaches, and the ligament is sutured to this anchor. If it is a partial tear, the ends of the ligament can be sutured together, and then anchored with screws. After surgical repair, the limb is placed in a soft, padded bandage with a splint for 10 to 14 days. Exercise must be restricted to specific physical rehabilitation exercises and leash walking only for 6 weeks; the animal can then be gradually returned to normal physical activity over a 6-week period of time.
Unfortunately, there is no sure-fire way to prevent stifle injuries in dogs, other than keeping them from playing and running around exuberantly, which is not realistic, or in the animal’s best interests. Proper conditioning of athletic dogs is important in preventing injuries, and weight management is crucial in all dogs.
The prognosis for isolated collateral ligament tears is good to excellent. If multiple ligaments are torn, the prognosis is fair.