Medial Patellar Luxation: A Vet's Guide to Understanding MPL in Dogs

We all know the sinking feeling we get in our stomachs when our dogs start to limp. Is it just a tweak or something more? Back leg issues in our dogs are common, and today I want to dig a bit deeper into the world of canine orthopedic challenges, specifically medial patellar luxation (MPL). Through my time as a veterinarian, I've encountered numerous cases of MPL, yet it is still not super well known amongst the pet parent community.

Whether you're a concerned pet parent noticing signs of knee discomfort in your dog or simply seeking to expand your knowledge about canine health let’s unravel the intricacies of MPL, from its underlying causes and varied severity to innovative treatment options and preventative measures. Let’s take on Medial Patellar Luxation, explore behind the limp, and help our dogs bounce back.

What is the Patella, and its Role in Dogs?

The patella, or kneecap, is a small bone located in the front of the knee joint. In our canine friends, just as in humans, the patella plays a critical role in the mechanics of the knee, aiding in the extension of the joint and serving as a fulcrum for the quadriceps muscles. This small bone is nestled within the tendon of these muscles and glides smoothly within a groove in the femur (thigh bone) during leg movement.

The long-winded answer to the primary function of the patella is to increase the leverage of the tendon, enhancing the power of the quadriceps and stabilizing the knee during activities such as walking, running, and jumping. But what is most important for pet parents to understand is that the efficient and smooth motion of the knee joint is what aids in the overall mobility and agility of both dogs and humans. So when the patella moves into an inappropriate position, you will see it in your dog's gait or lack thereof.

Patellar Luxation of dog.

Medial Patellar Luxation in Dogs

Let’s break it down. Medial Patellar Luxation (MPL) is a condition where the patella dislocates from its normal position, usually towards the inside of the leg. This condition can occur in many different ways, often involving a combination of genetic predispositions and physical triggers.

Certain breeds, particularly smaller ones like Pomeranians, Yorkshire Terriers, and Boston Terriers, are more genetically prone to MPL. The luxation can be a result of congenital anomalies where the dog is born with structural misalignments in the leg bones, muscles, or ligaments that make the knee joint unstable.

Activities that place unusual stress on the knee joint, such as jumping from heights or abrupt changes in direction while running, can exacerbate this predisposition and lead to luxation. Even normal play and routine activities can trigger a luxation event in a dog with a predisposed structural weakness in the knee. Regular vet check-ups can help in the early detection and management of this condition, especially in breeds known to be at higher risk.

MPL Grades

There are different levels of Medial Patellar Luxation(MPL) in dogs. We categorize them into four distinct grades, each representing the severity of the condition. These grades help veterinarians determine the most appropriate treatment plan. Here’s a brief overview of each grade:

  • Grade 1: This is the mildest form of MPL. In this grade, the patella luxates (dislocates) only occasionally, typically when pressure is applied in a certain way, and it easily returns to its normal position either spontaneously or when manipulated back in place manually. Dogs with Grade 1 MPL may show few, if any, symptoms and often do not require surgical intervention unless the condition progresses.
  • Grade 2: In this stage, the patella luxates more frequently, though it can still be manually repositioned back into the trochlear groove (in the thigh bone). Dogs with Grade 2 MPL may exhibit occasional lameness, especially after exercise. This grade may require surgical treatment, especially if the condition leads to persistent discomfort or lameness.
  • Grade 3: This is a more severe form, where the patella is dislocated most of the time but can still be manually repositioned back into place. Dogs with Grade 3 MPL often display a more consistent lameness and may adapt their gait to compensate for the discomfort. Surgical treatment is usually recommended to prevent further joint damage and alleviate pain.
  • Grade 4: This is the most severe grade of MPL. The patella is permanently dislocated and cannot be manually repositioned due to severe malformations of the leg bones. Dogs with Grade 4 MPL typically show significant lameness and may have difficulty walking. Surgical intervention is almost always necessary and may involve complex procedures to realign the joint and correct the bone deformities.

Symptoms and Diagnosing MPL

The symptoms of MPL can vary depending on its severity but commonly include intermittent lameness, an unusual gait, or a visible reluctance to use the affected leg. Dogs might also exhibit a 'skipping' motion when they run, as they try to avoid bending the affected knee when the patella is out of place. In more severe cases, persistent limping or an abnormal stance may be observed.

Diagnosing MPL typically involves a thorough physical examination by a veterinarian. During the exam, we will palpate the knee to check for luxation and assess the dog's reaction to certain movements. Radiographs, or X-rays, are used to evaluate the extent of the condition, including any underlying bone deformities and the grade of luxation.Diagnostic Orthopedic X-rays often require sedation to be able to painlessly and properly position your pet.

It's important to note that early detection plays a big role in the effective management of MPL. If you notice any signs of knee discomfort or irregularities in your dog's walk, consult with your veterinarian as soon as possible. They can provide a comprehensive assessment, recommend the best course of action for your pet, and help navigate through any issues.

Havanese after patellar surgery, MPL on dog.

Surgical Repairs for MPL

Surgical intervention is often recommended, especially for higher grades of MPL. The goal is to realign the patella, relieve pain, and restore normal function. Common surgical procedures include:

  • Reconstruction of Soft Tissues: Loosening the joint capsule on the side of the luxation and tightening it on the opposite side to realign the patella.
  • Deepening of the Trochlear Groove: This involves deepening the groove in the femur where the patella sits to prevent dislocation.
  • Tibial Tuberosity Transposition (TTT): The bony prominence where the patellar tendon attaches to the tibia is realigned to ensure the tendon runs straight.
  • Correction of Bone Deformities: In some cases, correcting the underlying bone deformity is necessary for a long-term solution.

Secondary Injuries

Because the patella luxation leaves the knee joint without proper support, it is possible that other injuries to the knee can occur at the same time. These injuries may include:

  1. Tearing or stretching of the Cranial Cruciate Ligament
  2. Meniscal tearing or damage
  3. Cartilage damage within the joint

Post-Operative Care and Rehabilitation

If your dog has surgery, making a quick, complete recovery hinges on effective post-operative care. This includes a well-managed pain relief plan, carefully monitored exercise, and targeted physical therapy. Rehabilitation exercises enable your pet to regain full joint function and muscle strength. These exercises help in healing and significantly enhance your dog's overall mobility and quality of life post-surgery.

Prevention and Management

Genetics certainly have a major influence on the development of Medial Patellar Luxation in dogs, but don't underestimate the power of a healthy lifestyle. Keeping your dog at an optimal weight and ensuring they get regular exercise can be incredibly effective in managing MPL, particularly in its less severe forms.

Catching and addressing the condition early on is also a game-changer – it can significantly reduce the risk of more serious complications down the line. So, regular check-ups and staying watchful for any signs of knee discomfort in your dog can make a big difference in their long-term health and mobility!

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This information was first seen on Urban Veterinary Associates.

Contributing DVM