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What Is Medial Patellar Luxation in Dogs? Explained Clearly

What Is Medial Patellar Luxation in Dogs? Explained Clearly

Medial Patellar Luxation

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Owners

Learn what medial patellar luxation in dogs is, its causes, signs, treatment options, and how early care improves your dog’s health and mobility

By 

Sustainable Vet Group

Updated on

July 17, 2026

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This article is for informational purposes only and is not a substitute for professional veterinary advice. Every case is unique, so always consult your veterinarian for guidance specific to your pet.

This content is intended for veterinary professionals for educational purposes. It does not replace clinical judgment or tailored advice. Always rely on your training, expertise, and the specific context of your patients.

What Is Medial Patellar Luxation in Dogs? Explained Clearly

Your dog takes a few steps, then suddenly skips on one back leg. A second later, everything looks normal. You wonder if you imagined it.

You didn't. That skipping gait is one of the most recognizable signs of medial patellar luxation, one of the most common orthopedic conditions in dogs. Understanding what's actually happening in your dog's knee makes it much easier to know what to do next.

 

What it is: Medial patellar luxation (MPL) means your dog's kneecap (patella) slips out of its normal groove and moves toward the inside of the leg.Who gets it: Mostly small and toy breeds, though any dog can be affected.How common: MPL is diagnosed in about 7% of puppies, according to the American College of Veterinary Surgeons.What happens: Some dogs skip occasionally with no obvious pain. Others develop persistent limping, stiffness, or a bowed-leg appearance.

 

Key takeaways

  • The kneecap slips inward: In MPL, the patella moves toward the inside of the knee, not outward.
  • It's mostly genetic: The condition is inherited in most dogs, not caused by injury or lifestyle.
  • Small breeds are most at risk: Chihuahuas, Pomeranians, and Maltese are among the most commonly affected.
  • It ranges from mild to severe: Four grades describe how often the kneecap slips and how bad the impact is.
  • Surgery isn't always needed: Mild cases are often managed without surgery, especially in dogs with few symptoms.
  • Arthritis is a long-term risk: Left untreated in moderate to severe cases, MPL can lead to permanent joint damage.

How your dog's kneecap is supposed to work

The patella is a small bone embedded in the tendon that runs along the front of your dog's knee. It sits inside a groove at the end of the thighbone (femur) and slides smoothly up and down when your dog moves.

This movement acts like a pulley system, helping the large thigh muscles straighten the leg efficiently. When everything is aligned correctly, the kneecap stays centered in its groove with each step.

In a dog with MPL, the groove is often too shallow, or the bones of the leg are angled in a way that pulls the kneecap off track. Over time, this repeated displacement wears down the joint and can cause arthritis.

What causes MPL in dogs

Abnormal bone development

The most common cause is a skeletal alignment problem that develops as the puppy grows. The thighbone, shinbone, or hip socket may form at slightly abnormal angles.

This pulls the entire "extensor mechanism" (the muscle-tendon-kneecap system) off-center. As Cornell University's College of Veterinary Medicine explains, dogs with MPL typically have a shallow femoral groove or general limb malalignment.

Genetic predisposition

MPL is considered an inherited condition in most dogs. Certain breeds carry genes that make the condition far more likely, which is why some breeds appear in veterinary offices with MPL at much higher rates than others.

According to research, MPL is 12 times more common in small dogs than in large dogs.

Trauma

In some cases, a fall, collision, or leg injury can damage the soft tissue structures around the knee, allowing the kneecap to shift. This is less common than the developmental cause but does occur, particularly in adult dogs with no prior history of the condition.

Which breeds are most commonly affected

Small and toy breeds are most at risk for MPL. The following breeds are among those most frequently diagnosed:

  • Chihuahua
  • Pomeranian
  • Maltese
  • Miniature and Toy Poodle
  • Yorkshire Terrier
  • Bichon Frise
  • Boston Terrier
  • French Bulldog

Large breeds can develop MPL too, though it's less common. According to the American College of Veterinary Surgeons, the condition is diagnosed primarily in small dogs but is increasingly recognized in larger breeds as well.

For a full breakdown of how the condition presents differently based on size, see how MPL differs in small vs large breeds.

What MPL looks like from the outside

The signs vary considerably depending on how severe the luxation is. Some dogs show almost no symptoms for years. Others are noticeably uncomfortable from an early age.

Common signs include:

  • Intermittent skipping: The dog lifts one back leg for a few steps, then puts it back down as if nothing happened. This is the classic MPL presentation.
  • Occasional leg shaking or extension: Some dogs kick their leg out to the side to pop the kneecap back into place.
  • Lameness after rest: Stiffness when getting up after sleeping or lying down.
  • Reluctance to exercise or jump: The dog avoids activities that stress the knee.
  • Bow-legged appearance: In young puppies with more severe MPL, the rear legs may appear bowed outward.

For a complete list of what to watch for, visit signs and symptoms to watch for.

How MPL is diagnosed

Your veterinarian will diagnose MPL through a physical examination. The vet manually palpates the knee while flexing and extending the joint to feel whether the kneecap slides out of the groove and back in again.

X-rays may be taken to evaluate the degree of bone deformity, the depth of the femoral groove, and whether any arthritis is already present.

The examination assigns your dog a grade from 1 to 4, which reflects how easily the kneecap displaces, how often it stays out, and whether it returns to the groove on its own.

For a clear explanation of what each grade means for your dog's treatment and outlook, read about the four grades of patellar luxation.

Once your dog has a confirmed grade, the next decision is whether treatment is needed and what kind. For guidance on when surgery is necessary, including which grades typically require intervention and which can be managed conservatively, that article walks through the decision in full.

How serious is MPL?

The severity depends heavily on the grade and how quickly it progresses.

GradeWhat happensImpact
1Kneecap pops out only when manually pressedOften no visible symptoms
2Kneecap slips out occasionally on its ownIntermittent skipping or lameness
3Kneecap is out of the groove most of the timePersistent limping; harder to manage without surgery
4Kneecap is permanently displacedSignificant lameness; leg function impaired

 

Grades 1 and 2 often have good outcomes with conservative management. Grades 3 and 4 typically require surgery for meaningful improvement.

Can MPL be prevented?

Because MPL is primarily genetic, true prevention is not possible in dogs who carry the relevant genes. However, early detection matters.

For puppies from at-risk breeds, regular veterinary checkups from an early age allow the condition to be identified and graded before it progresses or causes joint damage.

For information on reducing risk in young dogs and what early intervention looks like, see whether MPL can be prevented in puppies.

When MPL affects both knees

MPL occurs in both knees in many dogs. Some dogs have it in only one knee; others have different grades in each knee.

Bilateral MPL (both knees affected) is common, particularly in small breeds. It changes the treatment planning and recovery process.

For more on how bilateral cases are managed, see what bilateral MPL means and how to tell if your dog has MPL.

Frequently asked questions

Is MPL painful for dogs?

It depends on the grade. Mild MPL (Grade 1 or 2) often causes little obvious pain, though the joint is still being stressed with each luxation. More severe grades (3 and 4) typically cause persistent lameness and discomfort. Long-term, repeated luxation causes arthritis, which becomes increasingly painful over time.

How do I know if my dog has MPL or just hurt their leg?

The intermittent skipping pattern is the biggest clue. If your dog skips, then resumes walking normally within a few steps, MPL is a likely explanation. A traumatic leg injury typically causes consistent limping rather than this on-and-off pattern. Your vet can confirm through a physical exam.

My dog was just diagnosed with MPL. Does that mean surgery right away?

Not necessarily. Grade and symptom severity guide the treatment recommendation. Many dogs with Grade 1 or 2 MPL are managed with physical therapy, weight management, and monitoring rather than immediate surgery. Your vet will assess which path is appropriate for your dog specifically.

Can a dog live a normal life with MPL?

Many dogs do, particularly those with low-grade MPL. Dogs with higher grades may have quality-of-life limitations that surgery can significantly improve. The key is getting an accurate grade assessment and following the treatment plan your vet recommends.

MPL is one of the most common orthopedic conditions in small dogs, but being common doesn't mean it's simple. The range from mild and barely noticeable to severe and debilitating is wide, and the treatment path depends entirely on where your dog falls within it. A clear grade and an honest conversation with your vet is the right starting point for every MPL case.

Resources

  • American College of Veterinary Surgeons. Patellar Luxations. acvs.org
  • Cornell University College of Veterinary Medicine. Patellar Luxation. vet.cornell.edu
  • VCA Animal Hospitals. Luxating Patella in Dogs. vcahospitals.com

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