Examination of a dog with a torn ACL will often reveal a swollen, painful knee joint. In acute cases, the knee may have fluid swelling within the joint, termed joint effusion, or more commonly referred to as "water on the knee". Dogs with chronic knee instability tend to develop scar tissue, which appears as a firm swelling on the inside of the affected knee. X-rays are used to support the diagnosis and to document the extent of arthritic changes in the joint. The most reliable diagnostic finding, however, is evidence of instability in the knee (known as the "anterior drawer sign"). When a veterinarian elicits a positive drawer sign, the lower bone of the knee joint, or tibia, is moved forward relative to the upper bone, or femur. Basic anatomy of the canine knee joint is shown in Figure 1. In some large or heavily muscled dogs, it may be necessary to use sedation or anesthesia in order to relax the joint enough to demonstrate the drawer sign.

Active or working dogs require surgical stabilization of the knee in order to have any chance of returning to their previous level of performance. It is advisable to have the surgery performed within a few weeks of the injury to reduce the chance of secondary arthritis in the joint. Veterinary surgeons have employed a large number of surgical procedures to stabilize the knees of dogs with ACL injuries. Many different techniques have been reported with varying success. The actual technique used will be determined by the dog's age and size, whether the injury is acute or chronic, and most importantly, by the surgeon's preference and experience. In sporting dogs, the repair should be performed by an experienced veterinary surgeon in order to enhance the chance that the dog can return to the field and perform satisfactorily. It is important to note, however, that there is no technique that will return an injured dog's knee joint to normal and some degree of arthritis will occur after surgery in most cases. The two major categories of surgical repairs used for canine knee injuries are those where stabilization is achieved inside the joint (intra-articular) and those done outside the joint (extra-articular). Satisfactory results have been reported for both forms of repair. The knee joint is explored in most cases with both types of surgical procedures in order to remove remnants of the torn ligament and to inspect for torn cartilage. One of the knee cartilages, referred to as the medial meniscus, is commonly damaged along with the ACL. Treatment of the torn cartilage is necessary to prevent continued pain after surgery.

External support of the knee is common following surgery in order to protect the repair during the early healing process. A padded bandage or light splint is used for no more than a week or two after surgery. Following removal of the external support, physical therapy is begun on the knee joint to help restore muscle tone and range of motion. During the recovery period, the dog's exercise must be restricted in order to prevent damage to the surgical repair. Only brief leash walks are permitted and the dog is not allowed to run, jump or play for a minimum of 8 weeks. This is a difficult time for most sporting dogs that are accustomed to a high level of activity. Most veterinary surgeons allow a gradual increase in exercise, with the majority of dogs returning to full activity within 3 to 4 months after surgery. Results are generally quite good when the injury is treated soon after it occurs. Chronic cases with more advanced arthritic changes at the time of surgery will tend to have less satisfactory results. These dogs frequently exhibit stiffness or lameness after rigorous exercise and may require medication for their arthritis. In colder climates, some dogs may exhibit a more pronounced lameness during the winter months.

The only realistic means of preventing a knee ligament injury is to keep your dog as fit as possible. Dogs that are too heavy and those with other orthopedic problems, such as hip dysplasia, are at increased risk for a torn knee ligament. As with any athlete, training programs should begin with less strenuous activity that is increased in regular intervals until peak performance is achieved. If a serious injury occurs, consult your veterinarian as soon as possible. Prompt treatment of an injury will improve the dog's chances for a satisfactory recovery.