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Medial patellar luxation, or MPL, is a common orthopedic abnormality found in dogs, particularly small breeds. If your veterinarian has made a diagnosis of a medial patellar luxation and discussed the potential need for surgery to correct this, we are here to help.

What is medial patellar luxation?

Simply put, an MPL is a knee cap (patella) that slips out of place (luxates) towards the inside (medial side) of your dog's leg. Many dogs have luxating patellas that do not cause any significant problems or pain; however, if your pet is limping due to this condition or your veterinarian has discussed surgery with you, surgical correction is likely to increase your pet’s quality of life by reducing pain, as well as decreasing the risk for more serious problems down the road.

What causes the patella to luxate?

There are many reasons a patella will luxate or slip out of place. It is also possible that there may be more than one cause. The most common reason the patella luxates is that the femoral groove in which it is supposed to sit is too shallow. Other causes of patellar luxation include abnormal shape of the femur and tibia (the bones that make up the knee), as well as overly tight or loose soft tissue structures around the knee joint. 

How is MPL diagnosed?

Diagnosing a luxating patella is typically done by performing an orthopedic exam. However, as stated before, determining the exact cause is more challenging. Advanced imaging such as computed tomography (aka a CT Scan) will provide the most detail regarding the underlying structures involved in contributing to an MPL. Due to the cost of putting a dog under anesthesia and performing a CT scan, this is often cost prohibitive for many pet owners. If a CT is not a practical option for you, careful examination and correctly positioned radiographs can often indicate which underlying issues are the most likely cause. The exact diagnosis and surgical plan for correction would then be made while performing the surgery and evaluating the structures with the surgeon's hands and eyes.

After my pet is diagnosed with MPL, what are the next steps?

If your pet has been diagnosed with a luxating patella, the first step is to determine whether your pet's MPL can be best addressed at Helping Hands. We will carefully review your pet’s medical chart and history to determine if there is a high probability we can help. In some cases caused by certain factors, your best option will be to consult with a board certified orthopedic specialist. 

If our doctors determine that your pet is likely a good candidate for surgery at Helping Hands, the next step is to bring your pet in for an orthopedic evaluation. During this evaluation we will perform a physical and orthopedic exam, perform and evaluate preanesthetic blood work, and take x-rays in specific positions to obtain the best possible images for the surgeon. In order to obtain these images your pet will need to be safely sedated and monitored. After careful evaluation of your pet, their blood work, and their x-rays, our doctors will discuss the best surgical plan for your pet.

What exactly does MPL surgery entail?

The most commonly performed surgery to correct a luxating patella is called a Trochleoplasty. There are several techniques used to perform this surgery, all of which are designed to deepen the groove within the femur in which the patella should sit. By making a deeper groove, the patella will be much less likely to slip out of place. It is not uncommon to find that the soft tissue structures surrounding the knee are overly tight or loose, in which case we will also attempt to correct this at the time of surgery.

In some cases, deepening the groove in the femur may not be enough to keep the patella in place. Some dogs may have abnormal conformations of the bone where the ligament of the patella attaches at the bottom of the knee, causing it to pull the patella out of place. This attachment point is called the tibial crest and may need to be moved over to the center of the knee. If this is determined to be contributing to your dog's MPL, the surgeon may perform a Tibial Crest Transposition. This involves making an incision into the tibia near the tibial crest and re-attaching it with orthopedic wires to its new location. The need for this procedure can only be determined once the surgery has begun.

What kind of care does my pet need after MPL surgery?

Most dogs who have MPL surgery do very well. Minor complications after surgery may include swelling, mild pain, or bruising. Major complications are uncommon but include infection of the bone or rejection of any implants used.

In order to reduce the risk of complications, careful compliance to our post operative care instructions will be necessary. We will go over these instructions in greater detail at the time of surgery, but typically your pet will need to be strictly rested in a crate for 2 weeks following surgery, and then very gradually allowed to have longer or more frequent walks over the next 2-3 months. We highly recommend pursuing follow up care with a veterinary physical therapist and will be happy to find one near you.