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The term "ACVS Diplomate" refers to a veterinarian who has been board certified in veterinary surgery.

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Cranial Cruciate Ligament Disease

The term "ACVS Diplomate" refers to a veterinarian who has been board certified in veterinary surgery. Only veterinarians who have successfully completed the certification requirements of the ACVS are Diplomates of the American College of Veterinary Surgeons and have earned the right to be called specialists in veterinary surgery.

Your ACVS board-certified veterinary surgeon completed a three-year residency program, met specific training and caseload requirements, performed research and had research published. This process was supervised by ACVS Diplomates, ensuring consistency in training and adherence to high standards. After completing the residency program, the individual passed a rigorous examination. Only then did your veterinary surgeon earn the title of ACVS Diplomate.

Overview: 

The cranial cruciate ligament (or CCL, see Figure 1.) is one of the most important stabilizers inside the knee (also called ‘stifle’) joint, the middle joint in the back leg. In humans the CCL is called the anterior cruciate ligament (or ACL). 

The meniscus (Figure 1) is a ‘cartilage-like’ structure that sits in between the thigh and shin bones. It serves many important functions in the joint such as shock absorption, position-sensing, and load-bearing and is frequently damaged when the CCL is injured. 

Rupture of the CCL is one of the most common reasons for hind limb lameness, pain and subsequent arthritis. Since the development of this problem in dogs is much more complex than in humans, and dogs suffer from different degrees of rupture (partial or complete), the condition is referred to as ‘cranial cruciate ligament disease’ (or CCLD). While the degree of lameness with CCLD varies, it invariably causes arthritis in the long-term

Traumatic rupture can happen in dogs but it is extremely rare. Most commonly CCLD is caused by a combination of many factors, including aging of the ligament (degeneration), obesity, poor physical condition, conformation and breed. Ligament injury is a result of subtle, slow degeneration that has been taking place over a few months or even years rather than the result of acute (sudden) trauma to an otherwise healthy ligament. This difference between people and dogs explains two important features of canine CCLD:

  1. Half of the dogs that have a cruciate ligament problem in one knee will likely, at some future time, develop a similar problem in the other knee.  
  2. Partial tearing of the CCL is common in dogs and frequently progresses to a full tear over time. 

Cruciate disease affects dogs of all sizes and ages and rarely cats. Certain dog breeds are known to have a higher incidence of CCLD (such as Rottweiler, Newfoundland, Staffordshire Terrier, Mastiff, Akita, Saint Bernard, Chesapeake Bay Retriever, and Labrador Retriever) while others are less often affected (such as Greyhound, Dachshund, Basset Hound, and Old English Sheepdog). 

Female and neutered dogs are at greater risk of developing CCLD. The exact reason for this finding is unknown and the benefits of neutering your pet (such as decreased risk of cancer) certainly outweigh this increased risk. A genetic mode of inheritance has been shown for Newfoundlands.  

Poor physical condition and excessive body weight are risk factors for the development of CCLD. Both of these factors can be influenced by pet owners. A good fitness level of regular activity is advised and will also help avoid obesity

Signs and Symptoms: 

As mentioned, progressive degeneration of the CCL from very mild partial tearing to a complete tear in the later stages of the disease is common in dogs. You may not notice a severe lameness initially, especially if both knees are affected. One common symptom is that dogs will not sit ‘square’ anymore but rather put their leg(s) out to the side when they sit down. 

You may also observe that your dog has:

  • difficulty rising
  • trouble jumping into the car
  • decreased activity level
  • muscle atrophy (decreased muscle mass in the affected leg)
  • decreased range of motion of the knee joint
  • a popping noise (which may indicate a meniscal tear)
  • swelling on the inside of the shin bone (fibrosis or scar tissue) 

Many dogs will shift their weight away from the damaged leg when they stand but the lameness is less obvious during walking especially with partial tears of the CCL. When a partially damaged ligament ruptures completely or the meniscus becomes damaged your dog may also become non-weight bearing lame and may hop on three legs. This change in lameness may happen suddenly, usually without major trauma (a minor traumatic event may cause the partially torn ligament to rupture completely). Dogs with chronic (late stages) of CCLD usually show symptoms associated with arthritis, such as:

  • decreased activity
  • stiffness
  • unwillingness to play
  • pain  
Diagnostics: 

Diagnosing complete tears of the CCL is easily accomplished by a combination of observation of your pet’s gait, palpation of the knee, and radiographs (x-rays). Early partial tears can be a bit more complicated and may sometimes require advanced imaging such as MRI or surgical exploration to physically examine the ligament.

X-rays are usually taken to:

  • confirm joint effusion (fluid accumulation in the joint which indicates that there is a problem within the joint)
  • evaluate the degree of arthritis
  • aid in surgical planning
  • rule out concurrent disease conditions such as bone cancer

For certain treatments (TPLO, TTA) specific X-rays are required and hence your board-certified surgeon may need to repeat radiographs of the knee even if your primary care veterinarian has already taken some.  

Specific palpation techniques that veterinarians use to confirm a problem with the CCL are the ‘cranial drawer test’ and the ‘tibial thrust test’. These tests confirm abnormal motion in the knee and hence a rupture of the CCL. 

X-rays do NOT show the status (i.e. intact or damaged) of the CCL or the meniscus since those structures cannot be seen on X-rays. It is crucial that the surgeon evaluate both of these structures (meniscus and the cruciate ligament) when performing the selected surgical repair. This can be accomplished either via an arthrotomy (opening of the joint) or with the use of a minimally invasive camera (arthroscope) and is generally combined with the surgical stabilization procedure itself since both procedures require full anesthesia and clipping of the animal. 

Treatment: 

Many treatment options are available for CCLD. The first major decision is between surgical treatment and non-surgical (also termed conservative or medical) treatment/management. The best option for your pet depends on many factors such as your pet’s activity level, size, age, and conformation, as well as the degree of knee instability. Pet owners should contact an ACVS board-certified as soon as they notice signs and symptoms in order to achieve the best results.

Surgical treatment is generally recommended for CCLD since it is the only way to permanently control the instability in the stifle joint and to evaluate the structures within the joint. Surgery addresses the two major problems seen with CCLD.

  • stifle instability because of loss of the CCL
  • damage to the medial meniscus commonly seen in conjunction with CCLD

Again, meniscal injury will be addressed by your surgeon by removing the damaged parts of the meniscus when performing surgery to stabilize the knee. To address stifle instability many surgical treatment options are available. These different techniques can be categorized into two groups based on different concepts:

  1. Osteotomy techniques require a bone cut (osteotomy) which changes the way the quadriceps muscles act on the top of the shin bone (tibial plateau). Stability of the stifle joint is achieved without replacing the CCL itself but rather by changing the biomechanics of the knee joint. This can be accomplished by either advancing the attachment of the muscle (Tibial Tuberosity Advancement - TTA) or by rotation the plateau (slope) of the shin bone (Tibial Plateau Leveling Osteotomy - TPLO).

Many surgeons prefer these techniques for large, active dogs:

  1. Tibial Plateau Leveling Osteotomy (TPLO) involves making a circular cut in the tibial plateau and rotating the contact surface of this bone until it attains a relatively level orientation that puts it at approximately 90 degrees to the attachment of the quadriceps muscles (Figure 2). This orientation of the tibial plateau renders the knee relatively stable, independent of the CCL. The cut in the bone needs to be stabilized by the use of a bridging bone plate and screws (Figure 3). Once the bone has healed, the bone plate and screws are not needed, but are seldom removed unless there is an associated problem.

    The greatest advantage of this technique is the perceived superior outcome (limb function and less progression of arthritis) compared to traditional suture techniques especially in young, large breed dogs.

    The major disadvantage is the need to perform an osteotomy. Any osteotomy requires healing of the bone, and if a problem is observed (such as implant failure, failure of the bone to heal), it may require revision surgery and the outcome may be poor. Luckily, such complications are rare, especially when the procedure is performed by an experienced board-certified surgeon.
  2. Tibial Tuberosity Advancement (TTA) requires a linear cut along the front of the shin-bone. The front of the tibia, called the ‘tibial tuberosity’ is advanced forward until the attachment of the quadriceps is oriented approximately 90 degrees to the tibial plateau (Figure 4). This is simply another way to accomplish the same orientation as the TPLO. This orientation renders the knee stable, independent of the CCL. Similar to the TPLO, the cut in the bone is stabilized by the use of a specifically designed bridging bone plate and screws. The decision between TPLO and TTA is based upon concurrent problems and your surgeon’s judgment. The anatomic configuration of some dog’s knees may not lend them to safe or effective application of this technique.

  1. Suture techniques can be divided into intra-articular (within the joint) and extra-articular (outside the joint) procedures. In humans intra-articular replacement of the ACL using some form of ACL replacement is the most common procedure. This approach has been studied extensively in dogs and found not to be successful mainly because of the difference in anatomy and underlying disease process. Many companies and surgeons are revisiting this possibility utilizing novel developments. Because of the disappointment with intra-articular techniques to date, suture techniques are currently performed in an extra-articular fashion in dogs. The most commonly performed technique is called extra-capsular suture stabilization and utilizes strong suture material that is placed just on the outside of the knee joint (but under the skin) to mimic the CCL and stabilize the joint. A variation of this technique is called Tightrope® and allows the surgeons to use bone tunnels and toggles.
    1. Extra-capsular suture stabilization (also called “Ex-Cap suture”, “lateral fabellar suture stabilization” and the “fishing line technique”) has been performed for many years. While there are many variations of this technique (different suture materials, ways to tie the suture, how to attach the suture to the bone and so forth), the general concept of this procedure is to replace the function of a defective CCL on the outside of the joint. This is usually accomplished by utilizing a strong suture placed along a similar orientation to the original cruciate ligament. The suture needs to stabilize the knee joint, while allowing normal knee movement, until organized scar tissue can form and assume the stabilizing role.

      The most common complications after this procedure involve failure of the suture and progressive development of arthritis. Suture failure tends to be more common in larger, active dogs; hence many surgeons reserve this technique for small breeds, older, and/or inactive dogs. The main advantages of this technique include the lower cost and the lack of a bone cut (meaning that complications associated with the bone cut are not seen with this technique).
    2. The Tightrope® is a novel technique that has been developed to provide an alternative to osteotomy techniques for large breed dogs providing similar outcome without the complications associated with these techniques (such as failure of the bone to fuse or slow bone healing). It utilizes a specifically developed suture/toggle implant that allows drilling holes through both bones (thigh and shin bones) and using a toggle to attach the suture (Figure 5).

      Advantages of this technique over the traditional suture repair techniques include more accurate placement of the suture and stronger fixation. This technique also allows for minimally invasive placement of the suture. A study comparing TPLO and Tightrope did not find a significant difference between the two techniques at 6 months after surgery.

Non-surgical treatment usually involves a combination of medications, exercise modification, joint supplements, and possibly braces/orthotics:

  1. Activity restriction and anti-inflammatories – The lameness associated with CCLD usually waxes and wanes and generally improves significantly with administration of pain medications (please note that dogs should not be given Aspirin) and rest. Especially in small dogs and with partial tears, the lameness may completely disappear with this treatment but usually some degree of lameness remains in larger dogs. Attempts to return to normal activity levels will often be limited by the progression of arthritis. The combination of pain medications and rest is not a treatment per se because it does not stabilize the knee. Therefore, this treatment is generally not advised, but it may be appropriate for individual dogs due to some combination of their very small size, inactive lifestyle, or other concurrent injuries or diseases. 
  2. Rehabilitation therapy - There is ample evidence that rehabilitation therapy by a trained rehabilitation practitioner can advance and hasten the recovery from surgery. However, there is little evidence to suggest that this is a consistent and predictable alternative to surgical management for most dogs. Occasionally the combination of concurrent injuries or diseases, advanced age, patient size, and financial limitations may make this an attractive alternative option.
  3. Custom knee bracing/orthotics – Custom knee bracing is relatively new to canine orthopedics and hence there is little scientific evidence available. This treatment is valuable for the selected patient. However, it is a temporary solution and therefore not ideal for young, active animals.  
Aftercare and Outcome: 

Postoperative care at home is critical. Premature, uncontrolled or excessive activity, risks complete or partial failure of the surgical repair. When choosing a suture repair, this failure may simply mean that the surgery has to be performed again but when choosing an osteotomy technique this failure may mean that a much more invasive approach is now needed. Proper postoperative care limits activity to leash walking for a minimum of 8 weeks and no running, jumping, rough-housing, or off-leash activity. While it is important to control activity it is also important to maintain muscle mass and joint function (range of motion). 

Studies show that physical therapy can speed the recovery and improve final outcome regardless of the chosen surgical technique. This rehabilitation should start immediately after surgery and usually includes a regime of passive range of motion, balance exercises, controlled walks on leash and so forth. Discuss details with your board-certified surgeon and/or primary care veterinarian.

The long term prognosis for animals undergoing surgical repair of CCLD is good, with clinical reports of improvement in 85-90% of the cases. Unfortunately, arthritis progresses regardless of treatment, however much slower when surgery is performed. Therefore, medical arthritis management/prevention is recommended for any dog with CCLD regardless of the chosen surgicalIt is important to realize that arthritis is a progressive disease and develops fairly quickly in an injured (or damaged) stifle joint. 

The most common complication caused by CCLD is long-term impairment due to arthritis. Other complications associated with arthritis and CCLD include loss of range of motion in the joint, muscle atrophy, and loss of full function of the limb, as well as decreased activity. Unfortunately, neither human nor veterinary surgeons are able to completely restore normal joint anatomy and function. Even with surgery some progression of arthritis is expected. It is important to understand that arthritis is an irreversible disease and hence everything should be done to prevent its development or progression.  Therefore, two steps are crucial when treating CCLD:

  1. surgical repair and
  2. medical management of arthritis  

The second most common complication caused by CCLD is tearing of the meniscus. Due to the instability in the knee joint, the inside (medial) meniscus frequently gets damaged. This can happen during the initial injury or even later after surgical repair of the CCL. Meniscal damage in dogs is addressed by removing the damaged parts of the meniscus since it is too small to repair. A meniscal tear is very painful and if a damaged meniscus is left in place the animal will not regain full function. Removal of the damaged parts of the meniscus (if present) will be performed by your board-certified surgeon during the chosen procedure to address the knee instability.

As previously mentioned, rupture of the CCL in the opposite limb happens in more than half of the animals.

When choosing the best treatment for your dog, possible complications should be considered. Complications that can be observed with any technique include complications associated with:

  • anesthesia
  • wounds
  • infection
  • patellar (knee cap) luxation (dislocation)
  • failure to return to normal function
  • progressive arthritis 

Complications specific to the osteotomy techniques include delayed healing of the bone, non-healing of the bone, healing in an incorrect position (i.e. with rotation of the limb), fracture of the bone, and failure/breaking of the screws/plates. These complications can be serious and may require multiple revision surgeries. Again, serious complications that require a second surgery are rare when the procedures are performed by an experienced surgeon and exercise-restriction guidelines are followed.

If your dog is overweight, a weight loss program might be advisable. Your veterinarian will gladly help you to determine the ideal weight of your pet. Regular, daily activity is another important component of CCLD prevention. 

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This Animal Health Topic was written by and reviewed by Diplomates of the American College of Veterinary Surgeons.  Any opinions stated in this article are not necessarily the official position of the American College of Veterinary Surgeons.

The American College of Veterinary Surgeons recommends contacting an ACVS board-certified veterinary surgeon or your general veterinarian for more information about this topic.

To find an ACVS Diplomate, visit www.acvs.org/find-a-surgeon.