Cruciate Disease
By Dr. Karen Burgess

What is a cruciate ligament?
There are two cruciate ligaments that help provide stability to the knee or stifle joint.  The anterior cruciate ligament is also known as the ACL and is the most commonly affected by disease in dogs.  The cruciate ligament is a band of tissue that helps connect the femur or thigh bone to the tibia or calf bone.  The cruciate ligament is one of many ways that stability is provided to the stifle or knee joint of dogs.  ACL injuries are relatively common in human sports including basketball, football, and skiing.

What is an ACL injury and how is it caused?
The ACL can be torn or partially torn.  Very often they occur when a pet is performing a normal activity such as running the backyard.  In some cases no known injury occurs prior to an ACL tear.  An abnormal twisting of the knee joint can also lead to an ACL injury.  In some breeds the angulation of the hip and knee may predispose to cruciate disease.  Unfortunately if a dog tears one cruciate ligament they have a significant chance of tearing their other ACL in the future.

What are symptoms of ACL disease?
Pets with a partial or complete tear of their ACL will often come up suddenly lame on a hind limb.  This functional injury causes a toe touching or non-weight bearing lameness.  Very often dogs are not extremely painful and still willing to run around three legged which helps differentiate an ACL injury from a fracture.  In the case of a partial tear an intermittent mild lameness may be noted until the point in time where the ligament tears completely.  Most discomfort from ACL disease comes from joint swelling as opposed to from the torn ligament.

How is ACL disease diagnosed?
In the case of a complete tear palpation by a veterinarian for what is called a “cranial drawer” sign is diagnostic.  This abnormal motion of the knee may require sedation or even palpation to detect in particular in heavily muscled or tense dogs.  Radiographs are also often diagnostic.  In the case of partial tears it can be much more difficult to diagnose.  Subtle changes such as joint swelling may be the only detectable sign.  In these cases scoping of the knee during general anesthesia may be required for diagnosis.

How is ACL injury treated?
Surgery is the definitive treatment and involves either creating a false ligament or changing the angle of the knee thereby creating stability.  In the long run, the goal is to return a pet to comfortable function and help avoid arthritis down the road.  There are several different types of surgery available for ACL tears and for larger pets (over 40#) this is the treatment of choice.  It is important to understand that while commonly performed today in veterinary medicine, devastating complications can occur.  For this reason, while it may be more expensive to have a surgeon (veterinarian that has received advanced training in surgery) perform the procedure, in the end it is often the safer option.  Other options for ACL injury include benign neglect, or doing nothing, and/or rehabilitation.  The body will eventually scar the injured joint providing a pain-free knee.  However the degree of function will be more greatly affected and return to normal function often does not occur.  In small dogs where less weight is being put on the knee joints scarring as a treatment is acceptable, but in larger dogs it is not optimal.  Weight control and joint protectant medications are also recommended with or without surgical treatment.

How long is recovery from ACL disease/surgery?
With surgery recovery typically takes six to eight weeks with a gradual increase in exercise thereafter.  For cases of self-healing, six weeks of limited and protected movement is recommended.  Physical therapy including water treadmill can help with the recovery process.