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Cruciate Ligament Rupture in Dogs

Jul 18 2022

What is Cruciate Ligament Rupture in Dogs?

What and where are the cruciate ligaments in your pet's body?

The word cruciate means 'to cross over' or 'form a cross. The cruciate ligaments are two bands of fibrous tissue located within each stifle (knee) joint. They join the femur and tibia (the bones above and below the knee joint) together so that the knee works as a stable, hinged joint.

One ligament runs from the inside to the outside of the knee joint and the other from the outside to the inside, crossing over each other in the middle. In dogs and cats, the ligaments are called the cranial and caudal cruciate ligaments. “In dogs, the most common knee injury is a rupture or tear of the cranial cruciate ligament. Most dogs with this injury cannot walk normally and experience pain. The resulting instability damages the cartilage and surrounding bones and leads to osteoarthritis (OA) in the knee joint. “

The severity of degeneration seems to be directly proportional to body size, with animals weighing more than 15 kg showing the most changes. Humans have a similar anatomical structure to the dog knee, but the ligaments are called the anterior and posterior cruciate ligaments. An anterior cruciate ligament (ACL) rupture is a common knee injury in athletes.

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How does a cranial cruciate injury occur?

Based on its anatomy, the knee joint is a hinge joint. It is relatively unstable because there are no interlocking bones in the joint. Instead, it is held together by several ligaments, including the cruciate ligaments, which allow it to move back and forth like a hinge but restrict its side-to-side motion.

The function of the cranial cruciate ligament is to constrain the stifle joint by limiting internal rotation and cranial displacement of the tibia relative to the femur and to prevent hyperextension.

The exact mechanism of injury is poorly understood. The two most common causes of cranial cruciate rupture are:

  • Traumatic Injury: most often the ligament is injured when the stifle is rotated rapidly with the joint in 20 to 50 degrees of flexion or when the joint is forcefully hyperextended. Acute or traumatic cruciate rupture is caused by a twisting injury to the knee joint. This occurs most often when the dog (or athlete) is running and suddenly changes direction. This place the majority of the body weight on the knee joint, and excessive rotational and shearing forces are placed on the cruciate ligaments. Hyperextension probably occurs most frequently by stepping into a hole or depression at a fast gait. This injury usually affects the anterior or cranial (front) ligament. A cruciate ligament rupture is usually extremely painful and the knee joint becomes unstable, resulting in lameness.

  •  Degeneration of the ligaments within the joint. The more common injury scenario is thought to be a progressive degenerative process that leads to a partial or full ligament tear. A more chronic form of cruciate damage occurs due to progressive weakening of the ligaments as a result of repeated trauma or arthritic disease. Initially, the ligament becomes stretched or partially torn and lameness may be only slight and intermittent. With continued use of the joint, the condition gradually gets worse until a complete rupture occurs. Obese dogs appear to be more predisposed to developing a cruciate rupture. In these dogs, the injury may occur with minor trauma to the knee, such as stumbling over a rock while walking. Dogs with other knee problems such as a luxating patella (“Luxating Patella in Dogs") may also be predisposed to rupturing their cruciate ligaments. Concurrent patellar luxation is seen fairly often in toy breeds of dogs. Dogs who rupture one cranial ligament are more predisposed to rupturing the cranial cruciate ligament in the other knee. Approximately 40% to 50% of dogs sustaining a cruciate ligament rupture will rupture the opposite ligament within 2 years. Concurrent bilateral problems are even more common in young adult dogs (1 to 2 years) of specific breeds, particularly the Newfoundland, Rottweiler, and Labrador retriever.

How do you Diagnose Cruciate Injury?

With traumatic cruciate rupture, the usual history is that the dog was running and suddenly stopped or cried out and was then unable to bear weight on the affected leg. Many pets will 'toe touch' and place only a small amount of weight on the injured leg.

During the lameness examination, the veterinarian will try to demonstrate a particular movement, called a cranial or anterior drawer sign. This abnormal forward movement of the tibia (lower leg bone) in front of the femur (thigh bone) indicates laxity in the knee joint and is called a positive drawer sign. It may be necessary to administer a sedative to relax the dog enough that the veterinarian can perform this test.

Cranial Drawer motion should be tested in flexion, normal standing angle, and extension. With acute injuries and gross instability, drawer motion may be evident. The joint effusion may be noted for several days after injury.

To palpate direct drawer movement, the index finger of one hand is placed on the proximal patellar region while the thumb is placed caudal to the lateral fabella. The index finger of the opposite hand is placed on the cranial aspect of the tibial crest, and the thumb is placed on the caudal aspect of the fibular head. With the femur stabilized, the tibia is pushed forward and then pulled backward. This is repeated several times in both flexion and extension. This maneuver is performed gently but quickly to detect 1 to 10 mm of movement of the tibia in relation to the femur.

The tibial compression or “thrust” test produces indirect drawer movement. With the stifle angle held in extension, the metatarsal region is dorsiflexed as far as possible. The index finger of the opposite hand detects the forward movement of the tibial tuberosity if drawer movement is present.

With chronic injuries and with partial tears, drawer motion is much less evident and often requires very careful examination under sedation. With chronic cruciate ligament instability, periarticular tissues become thickened and fibrotic, with only limited stretching possible. Drawer motion in these patients may be almost imperceptible, but any drawer motion is abnormal in the adult dog.

With partial cruciate ruptures, a small amount of Cranial drawer motion will be appreciated only in flexion, emphasizing the need to check drawer motion in extension, neutral, and flexion. Pain may also be elicited on full extension of the stifle when a partial tear is present. Testing the joint for increased internal rotation of the tibia is helpful in animals with chronic conditions and in those with partial rupture. The amount of torsion of the tibia can be compared with that of the opposite limb. Fibrosis of the joint capsule and associated structures partially stabilizes the joint but not sufficiently to prevent its continual deterioration. Animals of all ages often have periarticular fibrosis on the medial surface of the joint between the medial collateral ligament and the proximal tibial (“buttress sign”). The significance of this tissue hypertrophy is unknown.

Other common exam findings include stifle joint effusion when standing, as noted by the lack of a finite edge to the medial aspect of the patella tendon, and resistance to fully flexing the knee when sitting (“sit test”).

Is other joint damage common?

Inside the knee joint are pieces of cartilage called menisci. The menisci act as shock absorbers between the femur and tibia. The menisci are often damaged when the cruciate ligaments rupture. They are usually repaired at the same time as ligament surgery. The medial meniscus may be torn acutely upon injury but is more often damaged as a result of chronic instability of the joint, producing crushing and eventual shredding of the caudal horn of the medial meniscus.

While the diagnosis is made on orthopedic examination, radiographs are essential to document the degree of osteoarthrosis and to rule out fracture or neoplasia.

The following observations should be noted when radiographs are taken:

  1. Osteophytes. These are seen especially around the distal patella, the supratrochlear region, the tibial and femoral margins, and fabellae.

  2. Fat pad sign. On the lateral projection, a normal triangle of radiolucent fat is present from the distal patella to the femur and tibia. The cruciate ligaments and menisci account for the normal radiodensity just caudal to this triangle. With synovial effusion or fibrosis of the fat pad region, the area cranial to the femur becomes whiter. Good-quality soft-tissue technique films are necessary to define this change.

  3. Cranial drawer position. Normally with cruciate rupture, the unstressed leg lies in a neutral drawer position. If a cranial drawer position is detected on the radiograph, it may indicate the presence of a torn meniscus wedging the tibia forward.

Is an operation always necessary?

Dogs weighing less than 10 kg (22 lbs) may heal without surgery, provided they have severe exercise restrictions such as strict cage rest for six weeks. Dogs over 10 kg (22 lbs) usually require surgery to stabilize the knee. Unfortunately, most dogs will eventually require surgery to correct this painful injury.

What options are there for repairing my dog’s torn CCL? 

When the cranial cruciate ligament is torn, surgical stabilization of the knee joint is often required, especially in larger or more active dogs. Surgery is generally recommended as soon as possible to reduce permanent, irreversible joint damage and relieve pain.

"Surgery is generally recommended as soon as possible to reduce permanent, irreversible joint damage and relieve pain."

Several surgical techniques are currently used to correct CCL rupture. Each procedure has unique advantages and potential drawbacks.

There are various surgical techniques performed to stabilize the knee joint following cruciate rupture.

These techniques can be broken down into three groups: extracapsular, intracapsular, and tibial osteotomy:

  • Extracapsular methods embrace a wide variety of stabilization techniques for the cruciate-deficient stifle joint. Most of these involve the use of heavy-gauge sutures to decrease joint instability.

  • Intracapsular methods usually involve anatomical (or near-anatomical) replacement of the cruciate ligament with autogenous or autologous grafts or synthetic materials.

  • Tibial osteotomy techniques are thought to provide dynamic stabilization by neutralizing the shear forces (cranial tibial thrust) seen in the stifle during weight bearing. EG TPLO and TTA Extraarticular methods work well in smaller breeds but have often been considered less satisfactory in the larger, athletic animal with a cranial cruciate ligament rupture.

These are four commonly performed techniques.  Each technique has its own advantages and disadvantages.

  • Cranial Cruciate Ligament Repair: Extracapsular Repair (MRIT),

  • TightRope Procedure (TightRope).

  • Tibial plateau leveling osteotomy (TPLO).

  • Tibial tuberosity advancement (TTA.)

A systematic review of the literature on surgical treatments of cranial cruciate ligament disease strongly supports the ability of the TPLO to provide superior functional recovery when compared with the extracapsular fabella suture technique.

No surgical technique consistently stops the development or progression of DJD. It is hoped that less DJD develops as a result of surgical stabilization than if no surgery is performed.

"Your veterinarian will guide you through the decision-making process and advise you on the best surgical option for your pet based on your weight, age, activity, and body condition of your pet.

There is no right or wrong answer when it comes to choosing your pet's surgery, only what is most likely to achieve the desired outcome."


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