Medial Patellar Luxation (MPL)

How often have you seen a little dog walk along with an extra skip in their step? It might look cute until you learn that the most common cause for that skip is pain from Medial Patellar Luxation. If your dog is experiencing patellar luxation, it’s important to address it promptly because the sooner it's treated, the less damage is incurred and the less invasive measures will be required to fix it.

How Does Patellar Luxation Happen?

Medial Patella Luxation is a hereditary condition, most common in small and toy breeds, and typically affects both legs. The patella (aka the kneecap) is held in place by the patellar tendon, which connects the thigh muscles to the tibia (the main lower leg bone) and sits within the trochlear groove of the femur. As your dog’s leg moves, the patella slides up and down in that groove. 

If the patella is too thick, the trochlear groove is too shallow, the patellar tendon’s attachment points aren’t quite right, and/or the dog’s femur or tibia are malformed, the patella gets pulled to the side which causes it to grind up against one side of the trochlear groove. For dogs with MPL, the patella will get pulled inward to their midline - think towards your dog’s belly button. Over time, that grinding erodes that side of the trochlear groove, allowing the patella to luxate (slide out) of the groove when the leg is in movement and then slide back into the groove in the next step. This hurts, hence the skipped steps.

The longer MPL is allowed to occur, the more bone erosion takes place, the more pain the dog experiences, the less they want to use the leg, and the weaker the tendon becomes, all of which continue to exacerbate the issue.

The Four Grades of MPL

Grade 1: This is the earliest stage of MPL and can be tough to catch unless your veterinarian is looking for it. At this point, the patella will only luxate when pressure is applied, but it returns to normal position once released. This stage can be addressed with physical rehabilitation.

Grade 2: At this stage, the patella will sometimes luxate when your dog flexes (bends) their leg and will remain out until the leg is fully extended (straightened) again, at which point it will slide back into place. This stage can be addressed with physical rehabilitation to decrease to a Grade 1.

Grade 3: The patella now spends more time luxated than not, but it can be physically manipulated back into place. Surgery is required once your dog reaches this point. At CROC, we do not wish to cause more pain or suffering to a pet. Though you can find places that will exercise your dog on a dislocated kneecap, we believe that if your dog is a surgical candidate at grade 3, your time and resources are better spent on surgery than Physical Rehabilitation.

Grade 4: This is the most severe stage of MPL. The patella is now permanently luxated and unable to be manipulated back into place. Surgery is required once your dog reaches this point. At CROC, we do not wish to cause more pain or suffering to a pet. Though you can find places that will exercise your dog on a dislocated kneecap, we believe that if your dog is a surgical candidate at grade 4, your time and resources are better spent on surgery than Physical Rehabilitation.

Diagnosing MPL

A change in your dog’s gait (the way they walk) is often the earliest outward sign that there’s something wrong. They might skip a step, intermittently limp, or you might see them struggle to bend the leg until they stretch it out to get the patella to pop back in place.

Gait analysis is included in exams for all CROC patients because it can tell us so much about a dog’s pain, structural abnormalities, or neurological deficiencies.

MPL can be diagnosed by your veterinarian after brief palpation of your dog’s stifle. They will move the leg to feel for any palpable changes in the bone structure or reduction in range of motion and apply pressure to the patella to see if it moves abnormally. If there are any abnormal findings, your Veterinarian will likely recommend radiographs (x-rays) to evaluate how much bone damage has occurred and if your dog’s legs have any other structural abnormalities. Sometimes MPL isn’t identified until a patient presents with pain elsewhere in the body. For example, a dog that is compensating for MPL may experience back pain or stiff front legs from trying to reduce the workload on the MPL leg. 

Contributing Factors

Selective breeding may help decrease a dog’s risk for MPL, but it cannot otherwise be prevented. However, there are multiple controllable factors that can increase your dog’s chances for luxation.

Weight: This is the easiest way to decrease risk! Every ounce of excess weight puts extra strain on an already compromised joint. That means more pressure on the patellar tendon, making luxation more likely. Diet is the most impactful influence and it’s easy to not realize how the treats and table scraps add up. Your dog should be on a measured amount of an AAFCO approved diet and if they’re getting treats too, their main meal should be reduced to account for those extra calories. Take a look at our article, Body Condition Score & Canine Weight Loss, for tips and tricks to help your pup get to a healthy weight.

Exercise: Of course, this goes hand in hand with diet to maintain a healthy body weight, but there’s a less obvious culprit here. If you do not exercise, you do not build muscle.

In fact, muscle starts to degrade after just 72 hours of inactivity.

If your dog’s leg muscles are underdeveloped, their stifle (knee joint) will not have the support it needs and it will be that much easier for luxation to occur. Maintaining beefy quads (thigh muscles) help pull the patella tightly into the patellar groove, making luxation less likely and less severe. Plus exercise is just good for overall physical and mental health! Read our article, Motion is the Lotion to learn more.

Time: We frequently hear from owners that they were told about their dog’s MPL when they were young but it wasn’t a problem until they got older. The truth is that the dog has been dealing with MPL their whole life, but it only became apparent to the owner once the dog could no longer hide the pain it was experiencing and the physical deficiencies that were compensated in youth are no longer able to be ignored. By addressing this condition early, you save your dog from irreversible orthopedic injury and pain while also potentially sparing you from the cost of surgery.

How long you wait to address this condition will directly influence the severity of your dog’s symptoms because the longer the patella is allowed to luxate, the more permanent damage occurs.

MPL & Cranial Cruciate Ligament Rupture (CCLR)

There is a correlation in risk between MPL and CCLR because the CCL and the patellar tendon are both extremely important structures that work alongside several others to stabilize the stifle. When the patella is not in the correct position, there is an increase of rotational forces on the stifle, which over time can lead to CCL rupture.

If your dog has MPL, they are also more likely to develop a CCL injury.

Addressing the MPL sooner rather than later can help decrease that risk. To learn more, read our article about Cranial Cruciate Ligament Injury.

What about Lateral Patellar Luxation (LPL)?

When a dog has LPL, the mechanics are very similar to MPL but the patella is being pulled outward away from the body. This condition is less common than MPL and can be hereditary or acquired after trauma. While LPL can occur in any dog, it is most common in large and giant breeds, especially Labrador Retrievers, Great Danes, Boxers, and St. Bernards.

So, your dog has Grade 1 or 2 MPL. What do you do now?

You’re in luck! Surgery is usually not required. Physical Rehabilitation Therapy can reduce a Grade 2 to a Grade 1 and a Grade 1 can be reduced to nearly zero.

A Rehab treatment plan for the MPL patient consists of multiple modalities to address the entire body; not just the MPL leg(s). Your dog has been compensating by walking and/or standing differently and putting more weight on their other legs. This often means that their other legs are overworked and sore. Back pain is not uncommon after spending so much time walking with poor ergonomics. Therapy often begins with Thermotherapy, Massage, and Stretching. Thermotherapy and Massage help to relax tense muscles and increase blood flow to the tissues. Stretching is necessary to maintain your dog’s full range of motion in all joints, but should not be performed until after Thermotherapy and Massage. Stretching should only be performed with great care as inappropriate stretching can make MPL worse, but prescribed stretches will help keep the Patellar Tendon soft enough to work with. Laser therapy is an excellent tool to promote healing and relieve pain and inflammation. 

However, recovery takes more than just the “feel goods”. The goal is to restore your dog’s comfort and mobility by improving how the patella is held in place.

This will only improve with careful exercise!

Low impact Target exercises that avoid any twisting movements will be prescribed to your dog in order to address any deficiencies and encourage normal limb use. You will be instructed to have your dog do some of these exercises at home on a daily basis. Hydrotherapy using an Underwater Treadmill provides a high resistance but very low impact workout, encouraging muscle growth needed to support the joint. Take note that Hydrotherapy in an Underwater Treadmill is recommended, but due to less benefit and higher risks, swimming is not. 

Our article The Deep Dive Into Swimming provides a visual and more detailed explanation for this, but we’ll briefly explain here too. When dogs swim, they generally paddle fiercely with their front legs while keeping their back legs tucked up alongside their body. This type of movement means they are over-working their already strained front legs and barely working the back legs that actually need the exercise. If they do kick their back legs, it is generally in a quick, spastic movement that does not encourage muscle building but does put more stress on a compromised joint. . 

So, your dog has Grade 3 or 4 MPL. What do you do now?

Sadly, the patella’s displacement is now so significant that surgery is required.

Rehab for Grade 1 or 2 MPL is focused on building muscle, but because the Grade 3 or 4 stifle is so painful and/or completely luxated, exercise would be excruciating and unethical to pursue. We recommend getting a consultation with a board-certified veterinary orthopedic surgeon and making sure your dog gets some pain relief in the meantime. Your dog’s condition will likely get worse the longer you wait and as your dog ages, their anesthetic risks often increase. Remember that they are also compensating for their luxating patellas by putting extra strain on other parts of their body, which frequently leads to pain or even injury of those parts. For these reasons, we recommend having your dog’s MPL corrected as soon as possible.

Initiating therapy after surgery can improve your dog’s recovery by addressing their muscle atrophy, increasing their range of motion, stimulating healing, and relieving any pain that might remain.

Your dog’s surgeon will decide when your dog can begin therapy, but they may want to take follow up x-rays to confirm appropriate healing beforehand. Every case will be different, so recommended commencement of therapy can range anywhere from 2 to 8 weeks after your dog’s surgery.

Can I brace my dog’s knee instead of pursuing surgery?

We absolutely understand the desire to avoid surgery but for most cases, we will strongly advise against the use of a brace. While a brace might provide some degree of stabilization, it does so by restricting movement of the joint, reducing the knee’s Range of Motion.

A joint without its full Range of Motion will become more stiff, more inflamed, and more painful.

This restriction in movement also causes significant muscle atrophy. Muscles that aren’t exercised waste away. Just like if you have your leg in a cast for several weeks, when the cast finally comes off, your leg muscles will have atrophied from lack of use. Reduced musculature will only make your dog's situation worse because the joint will have even less support when it needs it most.

Surgical Options

Tibial Tuberosity Transposition (TTT) or Tibial Crest Transposition (TCT)

The Tibial Tuberosity is an attachment point on the tibia for the Patellar Tendon. If the Tibia is malformed or the Tibial Tuberosity just isn’t in the right spot, it ruins the alignment of the stifle joint and the Patella can get pulled off to the side when the Quadriceps flex. This surgery involves cutting into the bone to release the Tibial Tuberosity, then uses pins and wire to reattach it in the new position to restore the joint’s alignment and redirect the forces from the Quadriceps.

Trochlear Wedge Recession or Trochlear Block Recession

The Trochlear Groove is the “valley” of the femur that the patella slides up and down in. The groove is lined with cartilage to ensure smooth movement. A Trochlear Groove that is too shallow is a common cause of MPL so this surgery aims to deepen the groove, making luxating less likely. First, part of the cartilage is temporarily removed to allow access to the bone underneath. Some of the bone is removed to carve a deeper groove, then the cartilage is put back in place followed by the patella.

Lateral Capsular Imbrication

This surgery is often used in conjunction with the other surgical procedures. The soft tissues on the inside of the stifle can become tight over time and continue to pull the patella medially (toward your dog’s belly). Similarly, the soft tissues on the outside of the stifle can become overly stretched from chronic luxation. This technique creates an incision to release the tissues that are too tight on the inside and uses overlapping sutures to tighten up the loose tissues on the outside. 

Post Operative Recovery

Recovery from stifle surgery can be challenging as it typically requires several weeks of strict exercise restriction to allow the bone to heal. Limiting your dog’s activity according to the surgeon’s recommendations is not optional. 

Too much activity too soon can be devastatingly destructive to a bone that is healing; potentially causing failure to heal, fractures, or even requiring additional surgery to repair the leg.

Use of an e-collar (aka the cone of shame) is incredibly important as any licking of the incision/stitches is likely to cause a serious infection of a fresh orthopedic surgery site.

Your dog’s surgeon will tell you when the e-collar is no longer needed. Pain medications and antibiotics are typically prescribed and should be given as directed. Do not stop or decrease these medications without consulting with the surgeon first. Some pets benefit from sedating or anti-anxiety medications during the recovery period to help keep them calm and less likely to over exercise.

It may be helpful to use baby gates to block off certain parts of your home during the recovery period, especially stairs or areas with slick floors. Good traction and controlled movements are key elements for safety and smooth recovery. If you have other pets in your home that typically play together, it is best to keep them separated during the first few weeks. Just like when we have a freshly broken bone, your dog will need to avoid any high-impact activities which sadly includes play time with housemates. Your surgeon may provide instructions for low-impact exercises as your pet heals. This may include Passive Range of Motion or standing exercises. Walks are typically restricted to slow and short outings, but can be increased each week as your surgeon recommends. Sticking to your pet’s prescribed exercises is important, not only to prevent over-stressing the surgical site, but also to maintain what muscle mass and flexibility they currently have. 

Prolonged disuse of a leg can cause Muscle Contracture, a condition where atrophy has become so severe that adhesions form between the bone, periosteal tissues (a thin layer of tissue that surrounds the bone), and quadriceps muscles, essentially locking the thigh muscles down and preventing normal movement of the leg.

Atrophy and reduced range of motion is the most common post-operative complication that we treat. 

Muscle contracture is very painful and extremely difficult to resolve, often requiring multiple therapy sessions a week for several months to give a patient the best chance at regaining normal limb use.

Long Term Care

The most impactful thing you can do at home to keep your pet comfortable and active is to maintain a lean body weight and good musculature. Even with surgery, your pet will develop Osteoarthritis (albeit slower than a dog that did not have surgery) and as they get older, it will only become more challenging for them to build muscle and lose weight. By keeping them lean and well-muscled from the start, you are giving your dog a solid foundation for a longer, more active, and healthier life. For more information, check out our article Crunchy Doggos - Managing Osteoarthritis.

If your dog has only had MPL diagnosed in one knee, you should prepare yourself for the likelihood that your dog’s other knee will also be affected and potentially require surgical intervention.

Some activities are more likely to aggravate patellar luxation than others, so we recommend removing them from your routine or reducing them as much as possible. Fetch involves a lot of twisting movements to quickly turn and run for the ball, then turn and rush back so fetch should be replaced with a safer game. Jumping on and off furniture or in and out of vehicles forces your dog’s joints to absorb a hefty impact, so we recommend assisting your dog or providing stairs or ramps. Slow, controlled exercise will always be preferred.

What If Surgery Is Not An Option?

Because surgery is the only way to resolve a Grade 3 or 4 MPL, it will always be the top recommendation. However, there are some circumstances that make surgery a poor choice. Often, financial constraints are the first to come to mind. We get it; it’s an expensive option! However, without surgery, your dog will require long term treatments like medications and pain relief focused Rehab. If your dog is a young dog, you will likely spend at least the same, but likely more money on these “band-aids” than if the surgery was performed at the beginning.

If your pet is a senior or geriatric pet, it may not make sense to put them through anesthesia and a big surgery. Pets with co-morbidities like heart disease, liver shunts, or clotting disorders can also be high-risk anesthetic candidates. Certain auto-immune conditions may complicate your pet’s ability to heal or fight off infection.

In these cases, your goal will be to maintain your pet’s comfort and mobility as best as possible. As the damage to the bone worsens, they will begin to experience more pain and therefore be more likely to rely on their other legs instead, setting them up for compensatory injury. Pain medications, supplements, and Rehab are all good options for relieving pain and inflammation. Check out our Pain Meds & Supplements article for more information regarding commonly prescribed pain medications, our favorite supplements, and how to choose quality products.

To Summarize

MPL is painful but it doesn’t have to keep your dog on the sidelines forever. Utilizing services from a board-certified veterinary surgeon and a certified veterinary rehab specialist is likely to give your dog the best results.

While the expense of surgery may be off-putting, in the long run, it is usually cheaper to invest in the surgery early on rather than paying for a lifetime of pain relief.

While braces and medications might be appealing solutions, they will not resolve your pet’s condition and are likely to make it worse. 

With the right home routine and/or surgery, your dog can enjoy good, pain-free mobility. For dogs that cannot undergo surgery, there are options to help control their pain and increase their limb strength which, depending on the severity of luxation, may resolve their symptoms. However, surgery is still the most effective solution for grade 3 & 4 MPL cases.

If you still have questions about Medial Patellar Luxation, our team of licensed veterinary professionals at Canine Rehab of Orange County is happy to consult with you.

The CROC Team is Here for You!

MPL is among the most common conditions that we see and we aim to help you find the best options for you and your dog. In some instances, we start therapy before surgery to maintain comfort and muscle mass as much as possible. We frequently see MPL patients after surgery to help them achieve the best and fastest recovery. Feel free to reach out to us with any questions or if you would like to move forward with a consultation, visit our New Patients page to get started.