Ruptured Cranial Cruciate Ligament (ACL) in Dogs

Ruptured Cranial Cruciate Ligament (ACL) in Dogs

A vet bandages a dog's front leg.A vet bandages a dog's front leg.
A vet bandages a dog's front leg.A vet bandages a dog's front leg.

Overview of Ruptured Cranial Cruciate Ligament in Dogs

The cranial cruciate ligament, also referred to as anterior cruciate ligament or ACL, is located within the stifle (knee) joint and acts to stabilize the femur on the tibia. The ligament can be torn as a result of an acute traumatic event or more commonly it ruptures due to a slow progressive breakdown of the ligament.

When the tear is sudden and complete, lameness may be severe and such that your dog refuses to bear weight on the leg. When the tear is partial or incomplete an intermittent lameness that is more noticeable after heavy exercise may be seen. Your dog may seem more lame on some days than others.

In large dogs (greater than 30 pounds), the joint usually becomes arthritic and the joint thickens if surgical stabilization is not performed.

What to Watch For

Symptoms of Ruptured ACL in dogs include:

  • Sudden onset of rear limb lameness
  • Gradual onset of lameness in a rear limb

Diagnosis of Ruptured Cranial Cruciate Ligament in Dogs

The diagnosis is generally made by your veterinarian during the physical examination. Your veterinarian will want to know whether the lameness occurred gradually or suddenly, whether it is intermittent or continuous, and whether or not it is exacerbated by exercise.

Your dog will be observed at rest, walking and trotting. The leg will be palpated (felt) and the knee joint will be evaluated for swelling, evidence of pain, thickening, “clicking” on flexion and extension, and the range of motion (flexion and extension) determined.

Specific tests to evaluate the integrity of the cranial cruciate ligament include a cranial drawer test or a tibial compression test, which are used to determine if there is increased movement in the joint. The movement in one knee will be compared to the movement in the other rear limb.

Both stifle joints may be radiographed for comparison. X-rays may show joint swelling and various degrees of arthritis depending on the length of time the rupture has been present.


Treatment of Ruptured Cranial Cruciate Ligament in Dogs


  • Small dogs (less than 30 pounds)

    Small dogs often do well without surgery. Your veterinarian may recommend that you strictly confine your dog for six weeks, may suggest that your dog lose weight if he is overweight and may prescribe a short course of anti-inflammatory medication.

    If your dog fails to improve over a 6 to 8 week period, surgery may be recommended.

  • Large dogs (greater than 30 pounds)

    Large dogs clearly benefit from surgery because medical management usually results in chronic lameness. There are many different surgical options. The basic principle of the surgery is to stabilize the femur on the tibia. This can be accomplished by placing implants within the knee joint, or around the knee joint, or by altering the dynamics of the joint itself. Your veterinarian may prefer a certain surgical technique or suggest referral to a veterinary surgical specialist for consideration of some of the more complex surgical procedures.


Home Care and Prevention

Depending on the type of surgery that has been performed, your dog may go home with a soft padded bandage on the leg. If this is the case, check the toes daily for swelling or discomfort and keep the bandage clean and dry by putting a plastic bag over the foot when your dog goes outside to go to the bathroom.

If there is no bandage, the incision can be monitored for swelling, redness or discharge.

Stitches or staples should be removed at 10-14 days.

Regardless of the surgical technique used, your dog should be kept quiet for a period of six weeks, with no jumping on or off furniture. Don’t let your pet go up or down stairs if possible and allow only short leash walks to go to the bathroom.

Anti-inflammatory medication may be prescribed for the first week following surgery.

After six weeks you can begin to increase your dog’s exercise slowly and gradually until he returns to his normal levels approximately sixteen weeks after surgery.

In cases of acute cruciate ligament rupture there is nothing to prevent the injury from occurring. When the problem is intermittent and more chronic, prompt veterinary attention and treatment can reduce the amount of arthritic damage that will occur within the knee joint.


In-depth Information on Canine Ruptured Cranial Cruciate Ligament

Sudden onset hind leg lameness following cruciate ligament injury can be so severe as to produce lameness as profound as a long bone fracture. Unlike a fracture, swelling and pain are restricted to the stifle (knee) joint.

Other Causes of Hind Limb Lameness

  • Medial patella luxation or a dislocated knee cap can produce bouts of sudden onset lameness or a more insidious lower grade problem. Differentiation between these diseases is made during the physical examination, although the two can occur at the same time.
  • Any traumatic injury to the hind limb can produce a lameness similar to an acute cruciate rupture, such as a dislocated hip, deranged or dislocated stifle or Achilles tendon rupture. These disorders are usually traumatic in origin, sudden in onset and easily differentiated from a torn cranial cruciate ligament.
  • Meniscal injury occurs in approximately 50 percent of completely torn cranial cruciate ligaments. It is therefore part and parcel of the cruciate problem and is not seen as a separate entity in its own right.
  • Caudal cruciate ligament rupture is extremely uncommon and the result of severe direct trauma to the front of the tibia. Abnormal motion of the knee can be found on palpation; in this instance, what is described as a “caudal drawer” is obtained.



In-depth Information on Diagnosis

It is important to discuss the history of the lameness, whether the problem was sudden in onset or appeared gradually over a period of months, improving with rest but always getting worse after exercise.

  • Observation. Your veterinarian will observe your dog at rest, taking note how your pet stands in the examination room and how he sits. The dog may not touch the leg to the ground in an acute injury or just touch the toes down. Most dogs with cruciate problems will not sit squarely, deviating a partially flexed knee out to the side. A walk, followed by a trot, will be most helpful to define a more subtle lameness perhaps due to a partial cruciate tear.
  • Palpation. Your veterinarian will carefully palpate the knee to assess for joint swelling and thickening. More long standing cruciate injury results in thickening on the inner aspect of the knee to produce a firm bump called a “medial buttress.”
  • Flexion and extension. The knee will be put through flexion and extension to assess the range of motion prior to evaluation for abnormal range of motion. Popping or clicking of the knee may occur during flexion and extension, which is suspicious for, but not diagnostic of, meniscal injury.
  • Cranial drawer or tibial compression tests. Performing these tests is extremely important. Both tests are looking for abnormal sliding of the tibia on the femur, a motion that should not be produced with an intact cruciate ligament. Certain partial tears will only produce a cranial drawer sign in knee flexion, and some partial tears will not produce a drawer sign at all.
  • Radiographs of the knee joint. X-rays can help to evaluate joint swelling and early subtle bony arthritic changes. In more chronic cases, the x-rays can help define the amount of arthritis that already exists to help in discussions about overall prognosis.
  • Arthroscopy or MRI. In certain cases of suspected partial cruciate injury, these further diagnostic techniques may prove helpful prior to an exploratory surgery of the knee.

In-depth Information on Treatment

The majority of small dogs (86 percent in one study) did not require surgical intervention and did just as well with strict rest, weight loss and the use of short courses of anti-inflammatory medication. Should the lameness persist, then surgery is recommended. Restriction like this for 6-8 weeks will not detrimentally affect the surgical outcome, should it prove necessary later on.

Surgical Options For Treating Torn ACL’s in Dogs

Broadly speaking there are two categories of surgery known as intracapsular techniques, where an effort is made to replace the damaged cruciate ligament with a natural or synthetic replacement, or extracapsular techniques, which aim to restore the function of the cruciate rather than the ligament that was damaged. Over recent years, intracapsular techniques have become less popular. The following are major extracapsular techniques:

  • Lateral suture technique. This procedure is quite straight forward and works well on many dogs, particularly those less than 70 to 80 lbs. Under anesthesia, having examined the inside of the knee joint to tidy up the remnants of the cruciate ligament and assess and address meniscal injury, a suture is passed around the knee joint, below the skin, in a configuration that will restore the normal position and stability of the femur on the tibia, acting to produce the same result as an intact cruciate ligament. With time, the implant may give a little, may stretch or even break, which will lead to increased thickening of the soft tissue around the knee and progression of bony arthritis. Despite this, the vast majority of dogs do well with this technique.
  • Fibular head transposition. This procedure uses a natural ligament, the lateral collateral ligament, to stabilize the femur on the tibia by modifying its normal position and function, by changing its attachment to the fibular, the smaller of the two bones below the knee joint. Some surgeons are very pleased with the clinical results they can achieve with this technique.
  • Tibial plateau leveling osteotomy (TPLO). This surgery has been described and patented by Dr. Barclay Slocum of Eugene, Ore. In simple terms, the femur slides on the tibia, in fact, the tibial plateau, because a slope exists, a slope, that to a large extent, is combated by virtue of an intact cruciate ligament. So, in a normal knee, no sliding takes place, but if the cruciate is damaged, the sliding, as seen with a cranial drawer test, occurs every time the dog puts weight on the leg.

    The idea behind this surgery stems from the fact that any kind of replacement for the cruciate ligament, be it natural or synthetic, can never be as good as the original. So, instead of trying to replace the damaged ligament, why not try to make it redundant, by getting rid of the slope that it was trying to offset. In other words, if we make the slope, the tibial plateau, level, then there is no need for a cruciate ligament; the ligament becomes redundant. This is a complicated surgical procedure and requires certification from Dr. Slocum in order to be performed.

Follow-up Care for Dogs with Torn ACL’s

Following surgery, many dogs remain hospitalized overnight in order to be monitored for full anesthetic recovery and to receive appropriate analgesic medication.

The use of a soft padded bandage to cover the leg after the procedure varies with the surgery and the surgeon. The bandage offers some comfort and reduces some of the postoperative swelling but, in fact, offers minimal support. If a bandage is used it should be kept clean and dry by placing a plastic bag over the foot every time the dog goes outside. The toes should be felt at the bottom of the bandage and assessed for swelling, sweating or pain, at least once a day.

If there is no bandage present, the incision can be assessed for swelling redness or discharge. In the case of a TPLO surgery, there is also a small incision lower down the leg, toward the ankle. Some swelling around the ankle may occur. This is not uncommon and usually responds well and quickly to the use of hot compresses.

Stiches or staples should be removed in 10-14 days.

Strict rest is essential for the first six weeks following surgery which means, ideally, no going up or down stairs, no jumping on or off furniture, avoiding slippery surfaces and walks, and going out on a leash for bathroom purposes only. With the TPLO surgery in particular, many dogs can recover extremely quickly. Owners should beware of this “false sense of security” afforded by dogs doing very well very early following surgery, and continue the rest for the full six week period.

Anti-inflammatory medication can be helpful for the first week following surgery, such as deracoxib, aspirin or carprofen (Rimadyl®).

After six weeks of rest, a slow, gradual increase in exercise should begin, with slow leash walks getting longer and longer in small increments such that over a further six weeks your dog is going on thirty minute walks, with short periods off the leash with far greater freedom around the house, including the use of stairs. By sixteen weeks after surgery, there should be no restriction on exercise.

Prognosis For Dogs with Ruptured ACL Ligaments

Early diagnosis and treatment an help minimize the progression of arthritis in the knee joint so the sooner you make a decision on treatment the better for your dog.

It is estimated that about half (30% to 50%) of dogs that tear one ACL will tear the opposite ACL with 2 years. For dogs that are overweight – there is a 25% risk of rupture of the opposite leg in the 3 – 6 months after the leg ACL due to increased stress on the other leg.

The American College of Veterinary Surgeons documents that 40-60% of dogs with will develop a similar problem in the other knee at some “future time”. It is common for some dogs to have a partial tear in one knee that eventually develops into a full tear.

Prevention of Ruptured ACL Ligaments in Dogs

Obesity can be a risk factor for tearing the ACL in dogs.  A regular exercise routine and keeping your dog at healthy weight and help minimize the risk.

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