The Complete Guide to Canine Knee Anatomy

The canine knee is a complex joint that plays a crucial role in a dog's mobility and overall health. The knee joint is made up of three bones: the femur (thigh bone), the patella (kneecap), and the tibia (shin bone).

The femur and tibia are connected by a hinge joint, which allows for flexion and extension of the knee. This joint is stabilized by ligaments, including the cruciate ligaments, which are essential for maintaining knee stability.

The patella, or kneecap, sits in a groove at the front of the knee joint and helps to facilitate movement by reducing friction between the femur and tibia.

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Trauma from injuries like skiing or football is the most common reason for ACL injuries in humans, but it's rare in dogs. In dogs, cruciate ligament disease (CCLD) is often caused by a combination of factors including aging, obesity, poor physical condition, conformation, and breed.

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Degeneration of the ligament over time is a significant contributor to CCLD in dogs. This subtle, slow degeneration can occur over months or even years, leading to a full tear of the CCL.

Dogs with CCLD in one knee are likely to develop a similar problem in the other knee at some point in the future. Partial tearing of the CCL is also common in dogs and can frequently progress to a full tear over time.

Certain breeds, such as Rottweiler, Newfoundland, and Labrador Retriever, are known to have a higher incidence of CCLD. Female and neutered dogs are also at greater risk of developing CCLD, although the exact reason for this is unknown.

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Trauma from skiing, football, or soccer injuries is the most common reason for ACL injuries in humans. However, in dogs, traumatic ruptures are relatively rare.

Aging of the ligament, or degeneration, is a significant contributor to CCLD in dogs. This process can take months or even years to develop.

Obesity is another factor that increases the risk of CCLD in dogs. In fact, being overweight can put additional stress on the ligament, making it more prone to injury.

Poor physical condition and conformation can also play a role in CCLD. This means that dogs with certain physical characteristics or a lack of physical fitness may be more susceptible to ligament injuries.

In dogs, CCLD often occurs due to a combination of these factors, rather than a single traumatic event. This is in contrast to humans, where ACL injuries are often the result of a sudden, traumatic incident.

At least half of dogs with a cruciate ligament problem in one knee will likely develop a similar problem in the other knee at some point in the future.

Partial tearing of the CCL is common in dogs and frequently progresses to a full tear over time.

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Cruciate disease affects dogs of all sizes and ages, but rarely cats. Certain dog breeds are more prone to CCLD, including Rottweiler, Newfoundland, Staffordshire Terrier, Mastiff, Akita, Saint Bernard, Chesapeake Bay Retriever, and Labrador Retriever.

Female dogs and neutered dogs are at a greater risk of developing CCLD. The benefits of neutering may outweigh this increased risk.

Newfoundlands have a genetic mode of inheritance for CCLD.

Dogs with CCLD often don't show 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.

Difficulty rising, trouble jumping into the car, and a decreased activity level are also common signs of CCLD.

Muscle atrophy, or decreased muscle mass in the affected leg, can be a symptom of CCLD.

A popping noise, which may indicate a meniscal tear, can also be a sign of the condition.

Swelling on the inside of the shin bone, or fibrosis or scar tissue, can be another symptom of CCLD.

Dogs with CCLD may shift their weight away from the damaged leg when they stand.

In some cases, the lameness may become more obvious, especially if the ligament ruptures completely or the meniscus becomes damaged.

Dogs with chronic CCLD may show symptoms associated with arthritis, such as decreased activity, stiffness, and pain.

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Dogs with CCLD often don't display severe lameness at first, especially if both knees are affected.

One common symptom is that dogs will no longer sit "square" but rather put their leg(s) out to the side when they sit down.

You may observe that your dog has difficulty rising, trouble jumping into the car, or a decreased activity level.

Muscle atrophy (decreased muscle mass in the affected leg) is another symptom you may notice.

Dogs with CCLD often 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.

A sudden change in lameness, often without major trauma, can occur if a partially damaged ligament ruptures completely or the meniscus becomes damaged.

Dogs with chronic CCLD may show symptoms associated with arthritis, such as decreased activity, stiffness, and unwillingness to play.

A popping noise, which may indicate a meniscal tear, can also be a symptom of CCLD.

Swelling on the inside of the shin bone (fibrosis or scar tissue) is another possible symptom.

Diagnosing a complete tear of the CCL is easily accomplished by a combination of observation of your pet's gait and palpation of the knee.

Observation of your pet's gait can be a key indicator of a CCL issue, as abnormal movement can be a sign of a problem.

Palpation of the knee by a veterinarian can also help confirm the presence of a CCL issue, as they use specific techniques such as the "cranial drawer test" and the "tibial thrust test" to check for abnormal motion in the knee.

X-rays are often taken to confirm the presence of joint effusion, which indicates a problem within the joint, and to rule out concurrent disease conditions such as bone cancer.

X-rays are also used to aid in surgical planning and to determine the degree of arthritis in the joint.

However, X-rays do not show the status of the CCL or the meniscus, making it crucial for a surgeon to evaluate these structures during surgery.

This evaluation is typically done via an arthrotomy (opening of the joint) or with the use of a minimally-invasive camera (arthroscope).

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Surgical treatment is often recommended for CCLD because it's the only way to permanently control the instability in the stifle joint.

The best option for your pet depends on many factors such as their activity level, size, age, and conformation, as well as the degree of knee instability.

Surgery addresses the two major problems seen with CCLD: stifle instability because of loss of the CCL and damage to the inside meniscus commonly seen in conjunction with CCLD.

The damaged parts of the meniscus are removed by your surgeon when performing surgery to stabilize the knee.

Many surgical treatment options are available to address stifle instability, which can be grouped into two main concepts.

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A craniomedial approach is used to access the stifle joint, starting between the sartorius muscle bellies proximally and extending distally through the tendinous insertion of the pes anserinus muscle group.

The surgeon makes a fascial incision, releasing the medial border of the cranial tibial muscle, and carefully incises the insertions of the gracilis and sartorius muscles to visualize the medial collateral ligament.

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The medial meniscus is often affected in CCLD, with pathology ranging from partial-thickness tearing to full-thickness bucket-handle tears or crushing injuries.

To address medial meniscal pathology, the surgeon excises the pathologic segment of the medial meniscus while protecting the caudal cruciate ligament.

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, rendering the knee relatively stable, independent of the CCL.

Arthrotomy and meniscal procedures are crucial steps in surgical treatment for CCLD. Surgical treatment is recommended for CCLD because it's the only way to permanently control the instability in the stifle joint.

A medial parapatellar arthrotomy is performed routinely to evaluate the structures within the joint. The cranial and caudal cruciate ligaments, medial and lateral menisci, long digital extensor tendon, synovial lining, and joint cartilage are all evaluated during this procedure.

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The cranial cruciate ligament is débrided as appropriate, and a small Hohmann retractor is used to protect the caudal cruciate ligament from inadvertent laceration. This helps facilitate visualization of the menisci.

Medial meniscal pathology is often present, and it can vary from partial-thickness tearing to a full-thickness bucket-handle tear to a severe crushing injury. The surgeon should excise the pathologic segment of the medial meniscus using caution to protect the caudal cruciate ligament.

Suction is essential during this procedure, and headlight illumination is helpful. If the meniscus is intact, a medial meniscal release can be performed to decrease the incidence of delayed meniscal injury.

Osteotomy techniques are a type of surgical treatment for CCLD that involve making a cut in the bone to change its shape and alignment. This can be done to stabilize the stifle joint without replacing the CCL itself.

Osteotomy techniques can be used to address stifle instability by changing the biomechanics of the knee joint. There are two main types of osteotomy techniques: tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA).

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The TPLO technique involves making a circular cut in the tibial plateau and rotating the contact surface until it is relatively level. This is done to put the tibial plateau at approximately 90 degrees to the attachment of the quadriceps muscles, rendering the knee relatively stable.

The TTA technique involves making a linear cut along the front of the shin bone, advancing the tibial tuberosity forward until the attachment of the quadriceps is oriented approximately 90 degrees to the tibial plateau.

The decision between TPLO and TTA is based on concurrent problems, surgeon preference, and the anatomic configuration of the dog's knee.

Here are the key differences between TPLO and TTA:

Both TPLO and TTA can be effective in stabilizing the stifle joint and reducing the risk of further injury. However, each technique has its own advantages and disadvantages, and the best choice will depend on the individual dog and its specific needs.

When looking at a radiograph of a dog's knee, it's essential to understand the different components that make up this complex joint. The stifle joint, also known as the knee, is comprised of the distal femur, proximal tibia, and four sesamoid bones.

The patella normally articulates with the trochlear groove of the cranial distal surface of the femur. This is a crucial point to note when evaluating a radiograph, as any deviation from this normal articulation can indicate a problem.

The femoral and tibial condyles barely directly articulate in the normal stifle because of the menisci. These c-shaped fibrocartilage structures cover the tibial condyle and alleviate the incongruity between the two surfaces.

In a normal stifle joint, the fibular head forms a fibrous connective tissue joint with the proximal aspect of the lateral proximal tibia. This is an important anatomical relationship to understand when interpreting radiographs.

Here are the key components of the stifle joint to look for on a radiograph:

Understanding the normal anatomy of the stifle joint is crucial for accurately interpreting radiographs and making informed decisions about your dog's health.

Suture techniques can be divided into intra-articular and extra-articular procedures, with intra-articular replacement of the ACL being the most common procedure in humans, but not as successful in dogs due to anatomical differences.

Intra-articular techniques have been disappointing in dogs, leading to the use of extra-articular suture techniques, such as extra-capsular suture stabilization.

Extra-capsular suture stabilization has been performed for many years and is used to replace the function of a defective CCL on the outside of the joint.

This technique involves using a strong suture placed along a similar orientation to the original cruciate ligament to stabilize the knee joint.

The suture needs to allow normal knee movement until organized scar tissue can form and assume the stabilizing role.

Suture failure tends to be more common in larger, active dogs, so 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.

Aftercare is crucial for a successful recovery from CCLD surgery. Proper postoperative care limits activity to leash walking for a minimum of eight weeks and no running, jumping, rough-housing, or off-leash activity.

Physical therapy speeds the recovery and improves 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, etc.

Long-term prognosis for animals undergoing surgical repair of CCLD is good, with clinical reports of improvement in 85-90% of the cases.

Aftercare is a critical phase of recovery after surgery. Proper postoperative care is essential to prevent complications and promote healing.

Premature, uncontrolled, or excessive activity can risk complete or partial failure of the surgical repair. This is especially true for osteotomy techniques, where failure may require a more invasive approach.

For a minimum of eight weeks, it's crucial to limit activity to leash walking only. No running, jumping, rough-housing, or off-leash activity is allowed during this time.

Physical therapy plays a vital role in speeding up recovery and improving final outcome. Multiple studies have shown that rehabilitation starting immediately after surgery can make a significant difference.

A regime of passive range of motion, balance exercises, and controlled walks on leash are essential components of post-operative rehabilitation.

The prognosis for your furry friend is generally good, with a success rate of 85-90% for surgical repair of CCLD.

However, it's essential to understand that arthritis will still progress, even with treatment. This is because the disease is progressive and can develop quickly, especially in an injured stifle joint.

Arthritis management and prevention are crucial, regardless of the chosen surgical technique. This is why it's recommended to manage arthritis in dogs with CCLD.

Early surgical repair is advised by most surgeons, as it can help decrease the amount of arthritis that has developed and the chance of a meniscal tear.