Cranial cruciate ligament injuries are quite common in domestic dogs. Fortunately, they are not particularly difficult for skilled veterinarians to diagnose. When presented with a patient limping on one or both of its hind legs, the veterinarian with initially do several things. First, she will take a thorough history from the dog’s owner, paying particular attention to whether the dog had any recent trauma that may have caused an injury to the affected leg (such as jumping off the couch, running too quickly down the stairs, jumping out of the back of the truck, zooming around the yard and skidding in the mud, etc.). She will especially want to know whether the lameness came on slowly or suddenly. Next, the veterinarian will examine the dog physically, from nose to tail. She will observe the dog’s posture when sitting, standing up and walking. She will palpate (feel) the muscles and bones of the legs, usually starting at the feet and working upward. The veterinarian will be assessing the stability or instability of the stifle on the affected hind leg. There are special manipulations that she will do on the rear legs that will identify whether the cranial cruciate ligament has been ruptured, torn or stretched. Most dogs accept these gentle manipulations quite well, without the need for sedation. However, depending on the severity of the injury, sedation may be appropriate for the dog’s comfort.
It is important for owners to take hind limb lameness in their dogs seriously and to seek veterinary advice and assistance as soon as possible. Without treatment, the underlying reason for the lameness can progressively worsen and ultimately become permanent.
After the initial evaluation, most veterinarians will recommend routine blood work, which includes a complete blood count (CBC) and a serum chemistry panel, together with a urinalysis. The blood sample will be taken from the dog’s jugular vein or from one of the large veins in a leg. The urine sample will be collected “free catch” (if the veterinary technician is lucky), or more easily by a procedure called “cystocentesis,” which involves inserting a sterile needle through the abdominal wall directly into the bladder, and retrieving a sterile urine sample by pulling back on the plunger of the attached syringe. Neither of these samples requires sedation. The results of blood work and a urinalysis will provide a snapshot of the dog’s overall health. If a damaged CCL is the only problem affecting the dog, the test results typically will be normal. However, it’s always a good idea to check a dog thoroughly, to get a complete picture of what may be contributing to its symptoms. For example, lameness can be caused by many things other than a blown cruciate ligament. Cancer, soft tissue injuries and bacterial infections in muscles or joints can all cause lameness. Evaluation of a blood sample will show whether the dog’s white blood cells are elevated, which happens when the dog’s immune system is fighting an infection.
The attending veterinarian will probably also recommend that radiographs (X-rays) be taken of the stifle joints of both rear legs, even if the dog is only lame in one leg. It is important to look at both legs for comparison purposes. The veterinarian will assess the angles of the bones that come together at the stifle. In some cases, radiographs of the whole legs may be recommended, especially if physical limb deformity or some other structural or conformational defect is suspected. Sedation may be necessary to get good films.
Arthroscopy and/or magnetic resonance imaging (MRI) may be recommended to confirm the diagnosis, especially if the cruciate ligament is only stretched or partially torn. “Arthroscopy” is the examination of the inside of a joint using an arthroscope (endoscope), which is a wand-like instrument with a camera at its tip. “Magnetic resonance imaging” involves placing the dog into a large tube-like structure under general anesthesia. The MRI instrument produces a very strong magnetic field around and through the dog. Radiofrequency signals are sent to a computer and processed in cross-sectional images, which the veterinary radiologist will carefully evaluate. MRIs are best used in veterinary medicine to assess soft tissue injuries. This diagnostic test is usually only available at veterinary teaching hospitals and highly specialized veterinary clinics.
Arthrocentesis, which involves sampling the synovial fluid from inside a joint capsule, can also be done to help to rule out infectious causes of lameness. Biopsies of the affected ligament may be taken during a surgical exploration or repair procedure, especially when the injury is not thought to have been caused by acute trauma. The sample will be sent to a diagnostic laboratory for microscopic assessment, to try and figure out what caused the ligament to fail.
Owners should not blame themselves if their pet injures its cranial cruciate ligament. Normal roughhousing and romping, and even more strenuous activities, are important to a dog’s overall fitness and physical and mental health. These activities should not be restricted just to prevent possible damage to the stifle. CCL injuries are fairly common in domestic dogs, and usually can be treated surgically with great success.