Anterior Cruciate Ligament Rupture

Cranial Cruciate Ligament Rupture

Ruptures of the cranial cruciate ligamaent are one of the most common orthopedic injuries in the dog. It is the major cause of arthritis of the stifle or knee joint. The strength of a dog's cranial cruciate ligament deteriorates with age. Large breed dogs develop these changes at an earlier age. Dogs with cruciate ligament rupture frequently are overweight. Obesity places additional stress on the ligament and can contribute to rupture in many cases.

There are three major types of cruciate injury. One is the athletic rupture that occurs just like in human athletes from landing wrong or twisting the rear leg while running or playing. This is the minority of cases. Often the rupture occurs acutely during normal levels of activity. The dog may have been jumping off the couch or deck, or running in the yard. The injury occurs from twisting the knee during partial flexion or hyper-extending the joint. The dog may vocalize and hold up the injured leg. In other cases the rupture may occur secondary to a medial patella luxation (small breeds most commonly) as the patella rides abnormally out of the groove on the inside of the leg and puts abnormal stress on the ligament. This is why we highly recommend fixing medial patella luxation (lateral in large breed dogs) to prevent this from happening.

Lastly, and most commonly, there is a more chronic degenerative course without a single traumatic event. In these cases the dog may have a chronic, episodic lameness that worsens with vigorous exercise and begins with a mild limp that often resolves in a short time. Some patients have a history of limping on and off for over a year! The ligament is a double banded structure made up of many smaller bands and it is covered with a layer of tissue called the synovium. The collagen fibers of the ligament are therefore not exposed to the joint fluid inside the knee or the immune system. Once the synovium tears along with a few fibers of the ligament the body does not recognize the ligament as "self" and treats it like foreign material just as if it was a bacteria or a splinter. This immune reaction leads to inflammation and further breakdown of the ligament. The inflammation causes joint effusion (fluid on the knee) and arthritis which can both cause pain and discomfort. Unlike a complete traumatic tear that leaves the joint unstable and allows us to easily palpate abnormal movement of the knee (anterior drawer), a "partial tear" is more difficult to diagnose early in the course of the disease.

Experienced surgeons can usually diagnose a partial tear by examination and radiographs (often sent to a board certified veterinary radiologist for interpretation). Sometimes we need to tap the joint and submit the joint fluid to the laboratory for analysis to differentiate ligamentous injury from infection or lymphoplasmacytic synovitis. Rarely dogs can also get a synovial carcinoma (cancer) of the joint that mimics a cruciate rupture. Additionally, the meniscus (cartilage) can also be damaged when the ligament is ruptured (usually a complete rupture) and only surgery can repair this as meniscus have no blood supply and do not heal. Removing the torn portion is the only way to treat the pain associated with the injury. Unfortunately, since partial tears are so difficult to determine in many cases, by the time the injury is finally diagnosed significant arthritis can be present in the knee. In people, diagnosis is made simpler by doing MRI exams, but because most pet owners do not have pet health insurance, this cost of this test makes it difficult to justify in veterinary medicine.

In many cases, especially smaller breed patients, there can be a hormonal imbalance of too little thyroid (hypothyroidism) or too much cortisone (Cushing's disease) that weakens the ligament. If your veterinarian suspects one of these conditions, they can be diagnosed with blood tests. Rarely, an autoimmune disease similar to rheumatoid arthritis, will cause the body to attack the soft tissues of the joint (as opposed to joints in rheumatoid) and weaken the ligaments as well.

Normal Anatomy

The cranial cruciate ligament originates on the lateral or outside aspect of the femur (thigh one), crosses the knee joint at an angle to attach to the front, inside aspect of the tibia (shin bone). The ligament prevents forward movement of the tibia, internal rotation and hyperextension of the knee. Rupture of the ligament results in instability of the knee. This results in pain, lameness and later arthritis. The instability or cranial drawer motion is used for diagnosis of the problem.

There is a medial and lateral meniscus in the knee joint. These are made of fibrocartilage, are crescent shaped and are situated between the femur and tibia. Damage to the medial meniscus is present in a significant number of dogs with cruciate ligament ruptures. The medial meniscus may be torn acutely at the time of the initial cruciate rupture or more often becomes damaged as a result of the chronic instability. An audible click may be heard during flexion and extension of the knee in dogs with meniscal damage. The surgeon will evaluate the meniscus at the time of surgery and if damaged, a partial or complete removal of the meniscus will be performed.

Normal Radiograph
Normal Radiograph
Abnormal Anatomy
Abnormal Anatomy

Clinical Signs and Diagnosis

The diagnosis of cruciate ligament rupture is based on history, physical examination, and possibly radiographic evaluation or joint taps to rule out other problems. The diagnosis is confirmed during exploratory arthrotomy surgery. The history typically involves an acute onset of lameness after minor trauma. Generally the dog will initially not bear any weight on the leg and will begin to place some weight on the leg after two to three weeks. However, the dog will remain mild to moderately lame on the leg. The lameness may worsen with the development of a meniscal injury or secondary arthritis.

In acute cases physical examination will reveal increased fluid within the joint. In chronic cases, the knee will be very thickened with a firm swelling at the inside of the knee. During the physical examination cranial drawer motion will be present in cases of cranial cruciate ligament rupture. Such motion is the ability to move the tibia forward while holding the femur stable. In very large or tense dogs, sedation or even anesthesia may be necessary to produce cranial drawer motion or administer steroids ahead of time to decrease swelling and facilitate the examination.

Radiographs may be taken to eliminate other possible causes of lameness. The actual cruciate ligament rupture is not visible radiographically, but many times we will see the soft tissue swelling of the joint capsule and displacement of the tibia forward. In chronic cases of cranial cruciate ligament rupture, arthritis will be present in the knee joint and can be demonstrated radiographically.

Medical Treatment

Rupture of the cranial cruciate ligament will produce progressive arthritis or degenerative joint disease due to instability in the knee joint. Close confinement for 4 to 8 weeks has been reported to yield satisfactory results in the majority of small dogs (less then 15 pounds) if no meniscal damage is present. All these animals develop advanced arthritis. It is our recommendation that the best treatment for this injury is surgical stabilization of the joint. This is not considered an emergency surgery; however, it is advisable to have surgery performed within a few weeks of the injury.

If surgery is postponed too long, arthritis will develop, chances of meniscal injury increase, and the benefit of surgery will be decreased.

Surgical Treatment

If causing persistent problems, and especially in larger dogs, the condition is best treated with surgery to stabilize the knee. There are many different surgical techniques for treating the condition and even specialty surgeons disagree regarding the best option. There is a lack of good scientific data to guide the surgeon and pet owner and surgeon preference for a particular technique is an important factor.

Some of the common surgical techniques used to treat the condition include:

  • Over-the-top fascial graft technique
  • Lateral fabellar imbrication suture (most common method of repair)
  • Tightrope
  • Tibial plateau leveling osteotomy (TPLO)
  • Tibial Tuberosity Advancement (TTA)

There is no agreement as to which is the best technique. Recent data would suggest that if there are differences between the techniques, these are minimal.

In the long run, all joints with cruciate ligament rupture will develop some degree of osteoarthritis. However, for most dogs the response to surgery is good and the osteoarthritis is minimized in patients having surgery compared to patients that do not.

We prefer the lateral fabellar imbrication suture technique for small dogs and Tightrope for patients over 40-50 pounds during which we open the joint to inspect the cruciate ligaments, menisci, joint lining and cartilage. The torn ends of the cruciate are removed and the menisci may be removed if damaged. The joint is then closed and the remainder of the surgery is performed under the skin and muscle, but outside the joint. The technique involves placing heavy gauge Fiberwire suture material either around the fabellar bone and through a bone tunnel drilled tibial tubercle. Most surgeons use nylon fishing line which is fine but we find that Fiberwire has better results as it does not break or stretch. The sutures are secured very tight to eliminate almost all instability. In larger patients, we utilize a newer technique called Tightrope which uses a larger form of Fiberwire material that is anchored through bone tunnels and secured over titanium buttons. In chronic cases with a large amount of joint swelling, your veterinarian may elect to administer some steroids pre-operatively to decrease this swelling. These patients will almost always develop some degree of joint laxity after surgery as the additional swelling subsides, but this is normal. Ultimately all surgical repairs rely on fibrosis or scar tissue formation to achieve long term joint stability.

Since virtually all techniques have very similar outcomes at six months according to many studies, we recommend focusing on cost and complications. We feel the techniques we utilize have the most economical costs and least number of complications compared to other techniques utilized by other surgeons in the area. Dr. Newman was trained to perform the Tightrope technique by the developer of the surgery, Dr. Jimi Cook at the University of Missouri.

Postoperative Care and Prognosis

We have a very detailed handout (which you may request) on home care and rehabilitation after surgery. In summary though, the patients are restricted to very short leash walks only with no free running, jumping or playing for at least 6 weeks after surgery. We will recheck your dog and remove the sutures 10- 14 days after surgery. We then request a second recheck exam 6 weeks after surgery to monitor recovery. At that time we may suggest gradually increasing levels of activity over the next several weeks. Most dogs are returned to normal activity within 3 to 4 months of surgery but chronic cases will take longer. It takes six months for complete recovery and improvement from surgery. Remember, all dogs will develop some arthritis but the surgical results are generally very good. Owners may report an occasional lameness or stiffness in the leg, particularly after a large amount of activity, after lying down for extended periods or in very cold weather.

Complications are very few with these procedures. Infection occurs in 1 to 2% of the cases. We routinely administer antibiotics at the time of surgery. Rarely, the dog will be overly active the first few weeks after surgery and can breakdown the repair. Fortunately, that only occurs in 1 or 2 % of the cases. In 1-2% of the cases, the dog may have a reaction or infection associated with the heavy gauge suture material and it may need to be removed. Generally this occurs after the joint is stable and it can be removed without requiring any additional stabilization. Damage to the peroneal nerve which runs alongside the knee can occur with suture placement, but this is also very rare. Up to 40% of the dogs will go on to eventually rupture the cranial cruciate ligament in their opposite knee (60% if overweight). Unfortunately, it is difficult to prevent this problem unless there is a treatable underlying cause like hormone disorders, and keeping the dog's weight under control. It is not uncommon to rupture the other leg during surgical recovery as it will be carrying all or most of your pet's weight for the first month or so after surgery.

Cruciate Rupture in Cats

Cruciate ligament ruptures are rare in the cat. Up to 16% are due to trauma and the remainder is of unknown cause. Diagnosis is based on lameness and a positive cranial drawer sign or instability. Conservative treatment is recommended for the majority of cats. This consists of confinement indoors, restricted activity and weight loss in obese cats. Most cats will return to full use of the leg without surgery in an average of 4.8 weeks. Surgery is indicated in cats when lameness persists despite conservative treatment or if other problems exist. In either case, the prognosis for cats with cruciate ligament injuries is very good.

What Surgery Is Best For My Pet's Cruciate Ligament Rupture

Having done thousands of cruciate repairs since graduating in 1980, I consider myself very knowledgeable regarding cruciate disease and surgery. Ruptured anterior cruciate ligament (RACL) repair represents fully one third of my surgical practice. There is a great deal of research underway to understand what causes this common problem and studies are constantly being done to evaluate all the different surgical procedures. There are twenty two different surgical procedures for cruciate repair in dogs and cats and numerous scientific studies have shown that outcomes are very similar. None of these many studies have shown any single procedure to be superior in outcomes despite individual surgeon's claims to the contrary.

Surgery is almost always the best option for dogs that rupture their anterior cruciate ligament. Just like people, without surgery, degenerative arthritis can form leading to chronic discomfort, swelling and pain. Surgery is much less effective once this happens as one of the major reasons for performing surgery is to minimize arthritis as well as quickly alleviate pain and discomfort. Additionally, although the instability in the stifle will eventually heal in most cases without surgery, the healing process can take months and during that time your pet will be uncomfortable and is at risk for tearing the medial meniscus if it is not already damaged. During this lengthy healing process, your pet will be favoring their "good" leg and is at risk of weakening the anterior cruciate in the good leg or possibly rupturing that side before the first side heals! Even with surgery, 40% of dogs will rupture the other side within eight months (60% if overweight). One dog in five that I operate on has partial or full tears on the "good" leg at the time of surgery. The healing time and discomfort is dramatically shortened when the damage is surgically repaired. Additionally, if your pet has a torn meniscus, this could take a very long time to heal as the meniscus has no blood supply and almost always need to be removed to stop the pain and swelling. People with meniscal tears need arthroscopic surgery to remove the torn meniscus.

Remember, your pet's activity, weight, muscularity, age, tibial plateau angle, as well as other orthopedic issues like hip dysplasia or cruciate tears on the opposite limb can also affect whether your pet needs surgery and which kind of repair is best for your individual pet. Since no one procedure has superior outcomes, it makes sense to take a critical look at costs and complications when deciding what is best for your pet.

it is important to realize that most dogs do not rupture their cruciate ligament due to trauma or physical activity. Although we do see the occasional pet that hurt their leg "playing ball", in most cases, the ligament was already partially damaged due to a degenerative process that we still do not fully understand. In rare cases, your pet may have an immune mediated disease called lymphoplasmacytic synovitis which, much like rheumatoid arthritis in people, is a result of the body thinking the ligament is a foreign material that needs to be removed by the body's immune system.

If your veterinarian has felt "anterior drawer" or "tibial thrust" (instability) in your pet's stifle along with a medial buttress sign (swelling on inside of stifle), there is no doubt about the presence of an anterior cruciate ligament tear and I do not have to examine your pet before surgery. In cases of partial tears where there is minimal instability or chronic tears where scar tissue makes palpating the stifle difficult, a radiologist can almost always diagnose the condition with well positioned quality radiographs sent to them by digital camera and the internet. Rarely, I will need to examine your pet and take some fluid from the stifle for analysis to confirm the diagnosis

You can often find veterinarians who will offer to repair your pet's RACL for a seemingly very low and affordable fee. It is important to ask if the are using hard, medical grade "fishing line" with grommets or Fiberwire suture; if they are doing an arthrotomy to clean out the stifle and examine the meniscus for tears; if they have joint retractors and special tools to remove the damaged meniscus; if they are doing epidurals with morphine for pain; and what anesthetic and monitors they are using to keep your pet safe while under anesthesia. I would also ask how many they have done in the past six months. When I perform surgery on your pet, we utilize a half million dollar human mobile surgical suite with state of the art air filters, monitors for pulse oximetry, respiration, carbon dioxide, blood pressure, temperature, and oxygen sensors. We also have a ventilator and defibrillator if necessary. With that said, if your budget simply does not permit you to utilize our services, cleaning out the joint and placing a nylon lateral suture is always better than doing nothing. In fact, studies have shown that just cleaning out the joint without any stabilization has decent outcomes when compared to doing nothing (see Budget Surgery Without Stabilization below).

Dogs Under 25 Pounds

Pets that fall in this category do not always need surgery. Many patients will heal on their own with fibrosis (scar tissue) and do fairly well, but arthritis can still form and cause future discomfort that requires lifetime pain medication and joint supplements. If your pet is improving week by week, we often suggest waiting on surgery unless you want your pet to heal as fast as possible with the least amount of discomfort. Often smaller patients have a luxating patella that predisposes the stifle to ligament damage and must be repaired at the same time.

If your pet is severely lame after two weeks with little or no improvement, surgery is almost always necessary in order to remove a damaged meniscus and stabilize the torn ligament. In almost every case, a simple arthrotomy to clean out the joint is performed and a lateral suture is placed to stabilize the joint. Most surgeons use a medical grade "fishing line" of monofilament nylon for this purpose. I utilize a much more expensive material called Fiberwire. Fiberwire is made of a Kevlar like material that is very strong. While nylon can stretch and break and often needs metal grommets to secure the suture, Fiberwire is much smaller diameter and can be tied in a small surgical knot. Fiberwire rarely breaks and hardly stretches at all making it ideal for this surgery. Fiberwire is routinely used in human surgery for ligament repair and shoulder surgery and is very safe.

In select cases, a mini-tightrope is utilized instead of a lateral suture if the small bone we anchor the suture to (fabella) is highly mobile or avulsed. This adds several hundred dollars to the cost of the procedure.

Dogs 25 to 40 Pounds

Pets that fall in this category should always have surgical intervention to repair the damaged ligament. Surgery should be performed within three weeks of the injury as arthritis can start forming after that time period. Again, a lateral suture anchored to the fabella bone with larger Fiberwire is the best way to repair this sized dogs. Interestingly, larger patients need larger medical grade fishing line but the larger the suture, the more it stretches. Fiberwire has been shown to be stronger than nylon for larger patients but most surgeons still use nylon and grommets. Patients repaired with Fiberwire have less instability post-operatively and therefore develop less arthritis and start using their leg sooner than patients repaired with nylon. Lateral suture has a 6-8% failure rate and on rare occasions, the patient develops an allergic reaction to the suture and it has to be removed in a simple surgical procedure.

Dogs 41 to 60 Pounds

Pets that fall in this category can be repaired with either a lateral Fiberwire suture or the new technique developed by Dr. Jimi Cook at University of Missouri called Tightrope. Tightrope is a larger, stronger form of Fiberwire that is flat and anchored with bone tunnels and titanium buttons. It has a 4-5% failure rate and a 10% complication rate overall. Most complications are not serious and resolve with medication or time. Some surgeons recommend a Tibial Plateau Leveling Osteotomy (TPLO) for this size range which involves cutting the top of the tibia with a special saw and rotating the bone. The rotated bone is then stabilized with a special bone plate to prevent the stifle from "thrusting" forward during weight bearing. Another procedure called Tibial Tuberosity Advancement (TTA) also utilizes a bone saw and titanium cage implant to move the tibial crest forward and stabilize the stifle. I call these two procedures "bone cutting" procedures. All bone cutting procedures are much more costly than lateral suture or Tightrope (TR) and have a 17-22% complication rate. If your pet has a severely abnormal tibial slope (angle of the top of the tibia) then a TPLO would be the best surgery for that pet. This represents around 1% of all patients.

Dogs Over 60 Pounds

Pets that fall in this category should always have a TR. If someone has financial constrains, I would always offer a lateral suture with Fiberwire, but for the extra $300-400 you are getting much better outcomes, faster use of the limb, and much less arthritis. Lateral suture has twice as many complications as TR. TR is so strong, you can pull a Mercedes Benz without it breaking. Again, we have good to excellent outcomes in 95.5% of our cases which means that 4.5% do not do well. It is impossible to know ahead of time which patients will have problems. If you are unfortunate enough to have a serious complication that needs a second surgery, we only charge cost for this second procedure which can involve explanting the tightrope, cultures, and biopsies to determine the cause of the failure. Infections are the biggest complication (although only 3% get infections). If caught early, aggressive antibiotic therapy can avoid more surgery. If caught late, the implant must be removed to resolve the infection.

Other options include the "bone cutting" described above (TTA and TPLO) and many general practitioners offer a lateral suture technique utilizing heavy gauge nylon at a reduced cost over the TR and the bone cutting surgeries. This technique is probably the most commonly performed surgery for RACL, but the main disadvantage is that nylon can stretch and/or break leading to excessive instability after surgery. The more instability you have, the more arthritis your pet develops.

Special Note About Boxers

Boxers are notorious for having very slow, insidious cruciate tears. They start as partial tears and get effusion (swelling in stifle) and limp on and off until the ligament finally completely tears often 4-6 months after the initial limping. Diagnosing these early and stabilizing the stifle with a TR before a complete tear occurs leads to much better outcomes.

Chronic RACL

If your pet has been limping for months or longer and has a very swollen stifle, this is usually known as a "chronic cruciate tear" as opposed to an acute tear. Chronic RACL's always take longer to operate on, longer to recover, and usually do not do as well as acute tears. Most patients will need to take pain medication and joint supplements with cold water fish oils for life. Cold weather and activity will usually cause increased discomfort. Even with an acute tear, a torn cruciate ligament is a devastating injury and the joint will never be good as new. But with proper repair, your pet will have good to excellent use of their leg even though 40% (50% if overweight) will eventually rupture the ligament on the other side within a year

Surgery Without Stabilization or Medical Management

As mentioned previously, studies have been done on pets that simply have the joint opened surgically and cleaned out and meniscal tears treated without doing any type of stabilization with bone cutting or lateral sutures and the outcomes are actually pretty decent. By removing the torn ligaments, the body does not have to fill the joint with fluid and special white blood cells (macrophages) to remove the tags of ligament remaining in the joint. This process takes a long time and the swelling (water on the knee) can cause chronic, low grade discomfort. A torn meniscus actually causes more pain than the torn ligment and while the body can repair the instability with scar tissue and remove the torn ligament, it cannot heal or remove the meniscus as there is no blood supply to this hard tissue. We tighten the joint capsule during closure in a procedure called "imbrication" to give some stability to the stifle but time and scar tissue eventually stabilize the joint with much more arthritis than would otherwise occur if a stabilization was performed. If your pet does not have a torn meniscus, weight loss, physical therapy, and joint supplements without any surgery can have a functional outcome.

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