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Medial Patella Luxation
ABOUT MEDIAL PATELLA LUXATION
At VetLove Advanced Surgery, we understand the distress and pain that Medial Patella Luxation (MPL) can cause for both you and your pet.
When specialist hospital care is not an option or remaining at the clinic you know and trust is preferred, our compassionate team, along with Dr. Chris Lisowski, are dedicated to providing comprehensive care at a clinic close to your home and ensuring your pet feels comforted throughout their recovery journey. With a wealth of experience in MPL surgeries, Dr. Chris has performed hundreds patella alignment procedures, including complex cases with angular limb deformities and combination MPL and cruciate surgeries.
Dr. Chris’s methodical surgical style and friendly, open approach ensure that you are informed and confident in making the best decisions for your pet. By understanding MPL and the available treatment options, you can make well-informed plans and decisions. Rest assured, your beloved pet is in capable and caring hands at VetLove.
Dr Chris Lisowski (BVSc, MSc, BSc, MANZCVS)
VetLove Senior Surgeon
Medial Patella Luxation (MPL)
The patella, or kneecap, is a small bone situated within the tendon of the quadriceps muscle group. This muscle group is responsible for extending the stifle (knee joint). For proper function, the patella must track up and down a groove at the front of the femur, known as the trochlea. This mechanism allows the patella to direct the force exerted by the quadriceps muscle, enabling smooth and efficient movement of the knee joint. In dogs with Medial Patella Luxation (MPL), the patella slips outside the trochlea, disrupting stifle extension and leading to secondary changes such as angular deformities, cranial cruciate ligament disease, and osteoarthritis. These secondary changes result in pain and lameness, and in some cases, can become severely debilitating.
MPL can be caused by several factors, with the condition most commonly affecting smaller breeds. In smaller breeds, it is considered a developmental disease resulting from congenital deformities of the femur and tibia. These deformities can include angular changes and internal rotation of the tibia, contributing to the patella’s tendency to slip out. Occasionally, traumatic injuries can also result in patella luxation. Additionally, genetic predisposition plays a significant role, as certain breeds such as Boston Terriers, Chihuahuas, and Pomeranians are more prone to developing MPL. Larger breeds, including Chinese Shar Pei and Akitas, have also shown an increasing incidence of this condition in recent years.
The development of MPL is often due to congenital or developmental misalignment of the entire extensor mechanism. Factors contributing to this condition include:
Abnormal Conformation of the Hip Joint: Conditions like hip dysplasia can alter the alignment of the limb, predisposing the patella to luxate.
Femur Malformation: Abnormal angulation and torsion (rotation) of the femur can affect the patella’s tracking.
Tibia Malformation: Changes in the shape and structure of the tibia can contribute to patellar instability.
Deviation of the Tibial Crest: The tibial crest, where the patellar tendon attaches, may be misaligned, leading to improper tracking.
Tightness or Atrophy of the Quadriceps Muscles: The quadriceps muscles may become tight or atrophied, acting like a bowstring and pulling the patella out of its groove.
Potentially Long Patellar Ligament: An elongated patellar ligament can affect the stability of the kneecap.
When an MPL has been diagnosed, it is then graded in terms of its severity. Frequently Grade 1 MPL are treated conservatively, Grade 2 MPL may have surgery recommended if the condition is significantly impacting day to day life. Grade 3 and 4 MPL are recommended to have surgery to reduce the negative impacts the constant displacement of the patella has on the healthy of the joint, the ligaments within and surrounding the joint, and the shape of the tibia and femur.
Grade I
The kneecap can be manually displaced but returns to its normal position when released. This grade is often discovered during routine exams and usually doesn’t require treatment.
Grade II
The kneecap occasionally slips out of its groove, causing intermittent lameness. It can be manually repositioned. Treatment depends on the frequency and duration of lameness.
Grade III
The patella is permanently dislocated but can be manually repositioned. Dogs may exhibit persistent lameness, a crouched stance, or a bow-legged appearance. Surgery is often recommended.
Grade IV
The patella is permanently dislocated and cannot be manually repositioned. This grade causes significant pain and lameness, and the leg may appear deformed. Surgery is usually necessary, but full resolution may not be possible.
Treatment Options:
For dogs with mild MPL, conservative (non-surgical) treatment options may be considered as the impact of low grade MPL is often mild and intermittent.
Weight Management
Maintaining a healthy weight to reduce stress on joints, which helps alleviate symptoms and prevent further deterioration.
Activity Modification
Avoiding overly strenuous activities like jumping and running can reduce wear on the knee joint. Gentle exercises, such as controlled leash walks, can help maintain muscle mass and joint mobility.
Physical Therapy and Hydrotherapy
These therapies can improve joint mobility, strengthen supporting muscles, and delay the progression of arthritis. Hydrotherapy, in particular, is beneficial for low-impact exercise.
Pain Management
Monitoring and managing pain with medications such as non-steroidal anti-inflammatory drugs (NSAIDs) and joint supplements can help keep your dog comfortable and active.
Surgical Treatment Options
Several surgical techniques can correct MPL, with intra-operative decision-making tailored to the dog’s specific needs:
Trochleoplasty:
This procedure involves deepening the trochlear groove using techniques such as Trochlear Wedge Recession or Trochlear Block Recession. By creating a deeper groove, the patella is less likely to slip out of place.
Tibial Tuberosity Transposition:
This surgery redirects the quadriceps muscle action by moving the tibial tuberosity laterally and is a main component of the re-alignment procedure. A portion of the tibial tuberosity containing the point of insertion of the patella tendon is cut free by what is known as an osteotomy. This small piece of bone is then moved laterally, moving the point of insertion of the patella tendon and subsequently pulling the patella into the trochlear groove. The piece of bone is then anchored in place by placement of small pins and occasionally a wire for additional security.
Lateral Imbrication and Medial Release:
During surgery, the soft tissues surrounding the patella may be adjusted. Medial release involves cutting contracted tissues on the inside of the knee to allow the patella to return to its normal position. Lateral imbrication involves tightening the tissues on the outside of the knee to maintain patella stability.
Concurrent MPL and Cranial Cruciate Ligament Insufficiency:
In cases where MPL is accompanied by cranial cruciate ligament insufficiency, procedures like TPLO (Tibial Plateau Leveling Osteotomy) may be performed simultaneously to correct both conditions.
Often the re-alignment of the patella during surgery requires intra-operative assessment and decisions based on how and when the patella is displacing from the trochlear groove and how each individual surgical steps improves the stability and tracking of the patella tendon.
Complications
While the prognosis for dogs undergoing MPL surgery is generally positive, complications can occur, including:
Recurrence of Kneecap Instability:
While uncommon post operatively, recurrence of MPL can occur after surgery. The alignment of the patella is confirmed in surgery by manipulation of the limb, however bending the pelvic limb isn’t the same as the patient contracting the quadriceps mechanism to create extension of the stifle. In addition, as the surgery heals, the pull of the patella medially by the quadriceps mechanism can re-stretch the tissues on the lateral side permitting increased mobility of the patella and recurrence of MPL. Fortunately, the recurrence of MPL can often be corrected by a minor revision of the lateral imbrication.
Migration or Breakage of Surgical Implants:
Rarely, the implants used to stabilize the bones may migrate or break, requiring additional intervention. While this can be a catastrophic event in serious cases, the risk of implant related complications can be minimised by following the recovery and rehabilitation plan provided to you by your veterinarian.
Infections:
Surgical sites can become infected in roughly 3% of cases. This is a rare complication is usually be managed successfully with antibiotics. In some cases, the implants may need to be removed once the osteotomy of the tibial tuberosity transposition has healed.
Prognosis
Over 90% of dog owners report satisfaction with their pet’s progress after MPL surgery. However, the prognosis may be less favourable in larger dogs, especially when combined with other abnormalities such as excessive angulation of long bones or hip dysplasia. Most dogs experience significant improvement in function and quality of life following surgery. Working closely with your veterinary surgeon to develop a personalized treatment plan is crucial for optimal outcomes.
MPL Surgery
Recovery Process
During the first eight weeks, the implants (pins and wire) provide 100% of the stability of the surgery site. It takes a minimum of eight weeks for bone to heal and good scar tissue to form. This process can take longer in geriatric pets or those with other systemic health conditions.
During the
first 8 weeks:
Your pet should be confined to a kennel or small room until radiographs show good bone healing.
Any running (inside or outside), jumping on or off furniture, or playing could lead to severe complications.
At approximately eight weeks following surgery radiographs are recommended to verify complete bone healing before returning to normal activity.
Incision Care:
You must prevent your pet from licking or chewing the incision site. Licking or chewing at the incision may cause premature removal of the sutures and/or incisional site infection, both of which may require additional procedures to repair. Until the surgical incision has healed and unless otherwise instructed by your veterinary surgeon, an E-collar must always be in place when your pet is not under your immediate supervision.
Recheck Appointments
Recheck appointments are an important part of the recovery process. These appointments allow your veterinarian to assess the rate of recovery as well as identify and discuss any concerns you may have.
A wound dressing is placed after surgery and a recheck should be performed within 3-5 days to have it removed and for the surgery site to be assessed.
Your pet should be evaluated 10-14 days post-operatively to evaluate healing of the incision; any external skin sutures placed during surgery are removed at this time.
Weekly or fortnightly appointments are then recommended until the bone has healed and your pet has recovered from surgery.
REHABILITATION
Physical rehabilitation protocols have been found to be beneficial in the recovery following MPL.
If at any time during the recovery period there is a decline in function and comfort, it is important that your pet is seen by your veterinarian so any complications can be identified early and any modifications to the rehabilitation plan can be instituted.
Weeks 1 and 2
Controlled leash walks
- Walks are best performed on a short leash. Go slowly at first to help gradually improve strength. Walking slowly may help encourage use.
- Walks can be done two to three times per day for five minutes at a time for elimination purposes.
- Using a sling or folded bath towel under your dog’s belly can be used for support when walking on slick surfaces such as tile or wood floors, and even on other surfaces if they are unsteady on the surgical limb. The sling can also be used to help slow your pet’s pace down if they are pulling hard on the leash.
- No off-leash activity is permitted or recommended
Passive Range of Motion (PROM)
- Lay pet on their side with surgical limb up.
- Flex and extend the joints of the affected limb gently to resistance.
- Gently support the knee to prevent twisting or rotation of the limb.
- Repeat 2 – 3 times daily for 10 to 15 repetitions.
- PROM should not cause pain, discomfort or negative reaction. If any negative reactions occur, PROM should be stopped and consultation with your veterinarian is advised for advice, modification of technique, and for any modification to the pain relief plan.
Ice and Heat therapy
- Use of ice packs after walks and PROM during the first 3 to 4 days after surgery.
- Drugstore packs, crushed ice in a Ziploc bag, or frozen peas or corn can be used.
- Ice around as much of the circumference of the knee as possible.
- While a paper or thin towel can be used to absorb moisture from the ice pack, a thick towel may prevent icing from being effective.
- Ice for 15 minutes per session.
- Icing should not cause pain, discomfort or negative reactions.
- Use heat packs prior to PROM after initial 3 to 4 days.
- Drugstore packs or socks filled with uncooked rice heated in a microwave work well.
- Test pack on your wrist first. If it is too hot for your skin, it is too hot for your dog.
- Insulate the heat pack with a thin cloth.
- Use for five to ten minutes before starting PROM.
- Heat packs should not cause pain, discomfort or negative reactions.
- If your pet fails to begin using his leg during the first two weeks, please contact your veterinarian.
- A recheck should be performed at two weeks so the incision site can be evaluated as well as the degree of use and comfort of the surgery limb.
Weeks 3 and 4
- PROM can be reduced to twice per week.
- Continue ice therapy as needed if your pet seems sore after walking/exercise.
- Increase leash walks to ~8 minutes in week 3 and ~10 minutes in week 4 as long as your pet continues to show comfort using the surgical limb.
- Incorporate the following exercises into leash walks, to build strength and body awareness:
- Walk in large figure 8 pattern
- Stepping slowly up onto and down off of a curb in an S pattern
- Gentle inclines (a mild slope on a street or a driveway)
- The following exercises can also help build balance and core strength. Perform these exercises on a non-slip surface, with 5-10 repetitions each
- Gently nudge the hind end from side to side while standing
- Sit to Stand exercise – have your pet repeatedly sit down, then stand up
- Three-Legged Standing Exercise – Have your dog in a standing position, then lift one leg off the ground at a time for 10 to 15 seconds (alternate with all but surgical leg)
- No off-leash activity
Weeks 5 through 8
- Icing and heat-packing can be discontinued
- Continue performing the previously mentioned exercises
- Week 5 increase length of walks up to ~12 minutes up to 3-5 times a day
- Week 6 increase length of walks up to ~15 minutes up to 3-5 times a day
- Week 7 increase length of walks up to ~18 minutes up to 3-5 times a day
- Week 8 increase length of walks up to ~20 minutes up to 3-5 times a day
- No off-leash activity
Weeks 8 through 12
Radiographs will be taken at about 8 weeks to confirm appropriate bone healing. Assuming the tibia is healing:
- Continue performing the previously mentioned exercises
- Continue to gradually increase the duration of the walks
- Gradually introduce off-leash activity, starting week 9 with about 5 minutes of off-leash activity 3-5 times a day, week 10 up to 10 minutes of off-leash activity 3-5 times a day, week 11 up to 15 minutes of off-leash activity 3-5 times a day, week 12 up to 20 minutes of off-leash activity 3-5 times per day.
Is your dog still limping?
There are multiple reasons why a patient may not want to bear weight on a limb following surgery. If your pet is not bearing weight within 7 days of surgery or develops an acute onset of lameness any time after surgery, please contact your veterinarian immediately for an assessment. Below are some of the more common reasons why a pet may limp following surgery.
Overdid it
As with people, it is not uncommon for pets to “overdo it” leading to an acute onset of lameness. Sometimes during the post-operative recovery patients may be more active than is recommended (jump down from a sofa, chase the cat, etc.) or even just take a funny step, leading to a lameness of varying severity. Fortunately, this most common cause of discomfort after surgery resolves with some additional rest and anti-inflammatory medication.
Meniscal tear
Infection
Approximately 3-5% of all patients undergoing a TPLO will develop a surgical site infection. Some infections are more superficial and may clear up after a short course of antibiotics. In approximately 3% of all TPLO cases, an infection may be deeper and become associated with the plate and screws. Patients may show signs of lameness or pain, swelling/redness at the surgery site, and or discharge. In these cases, patients are placed on antibiotics until the bone is healed (based on x-rays) and the bone plate can be removed.
Implant-associated pain
Until the bone has healed, we are completely relying on the bone plate to stabilize the surgical site. In situations where a pet is allowed excessive high impact activity, the bone plate or screws can bend or break. Thankfully, this is a very rare complication (<0.1%). If this occurs, the surgical site may be unstable which in many instances would require further surgery. In other rare instances, patients may simply be uncomfortable with the presence of the plate. In these cases, removal of the plate after the bone has healed will typically resolve the lameness.
MPL Frequently Asked Questions:
What medications will my pet be sent home with?
The exact medications sent home will be dependent on the individual, however, below is a typical post-operative medication protocol.
- Anti-inflammatory: Most pets will be sent home with a course of an anti-inflammatory. Anti-inflammatories help to reduce inflammation at the surgical site and act as a pain reliever.
- Pain-reliever: A transdermal opioid patch is commonly applied after large procedures to provide a continual pain relief over a period of 72 hours. Often only one patch is required, but depending on the individual, replacement patches may be placed.
- Antibiotic: A short course of antibiotics are generally provided post-operatively to minimize the risk of a surgical site infection until the surgical wound has healed superficially.
Should I be concerned if my pet hasn't urinated or defecated since the surgery?
It is not uncommon for pets to have delayed urination or bowel movements after surgery. Pets are often kept off food and sometimes water for 12 hours prior to surgery. Medications given during surgery can alter gut motility. Additionally, pets may urinate or defecate while under anaesthesia, or hospital staff may express their bladder to prevent them from waking up with a full bladder. After surgery, pets might not have an appetite or want to drink for a day, and they may have difficulty posturing to urinate or defecate, especially if surgery involved their legs. For these reasons, it can take a few days for pets to resume normal urination and bowel movements. Rest assured, when they need to urinate or defecate, they will.
Should I be concerned if my dog isn’t eating normally after surgery?
It’s not uncommon for dogs to lose their appetite following anaesthesia and it can take a few days for your pet’s appetite to return to normal. Generally, by the following morning they will be ready for at least a small meal.
Should I be worried if my dog has diarrhea and is vomiting after anaesthesia?
Some dogs may have mild diarrhea following anaesthesia due to the stress associated with the procedure. However, both diarrhea and vomiting can be serious, life-threatening symptoms. If your pet has diarrhea or is vomiting, it’s important to contact your veterinarian for advice.
When should I expect my dog to return to his normal behaviour post-surgery?
All dogs respond differently to anaesthesia, and it can take some pets longer than others to get back to their normal self. If your pet’s attitude isn’t back to normal within a few days of surgery, it is important to have them evaluated by a veterinarian.
Is it normal for my pet's ankle to swell after surgery?
While it doesn’t occur after every surgery, swelling around the ankle can develop approximately 2-5 days following TPLO surgery on the leg. It will typically go down without any treatment over the course of a few days. If it is painful, or you remain concerned, it is important to contact your veterinarian for advice.
Is it safe for my pet to climb stairs after surgery?
There is no universally approved rehabilitation or activity protocol established by all surgeons or rehabilitation specialists. Following MPL surgery, the pins and wire hold the tibial tuberosity to the tibia in its new position until the bone heals, which takes about 8-12 weeks. During this time, the pins and wire must endure all the stresses of weight-bearing. Excessive activity too soon can lead to implant failure. Generally, stairs should be avoided early in the recovery period. However, if stairs are unavoidable, it is typically acceptable for your pet to walk up or down them. It is crucial not to let your pet run up or down the stairs or jump off them. Always use a leash while your pet is healing, and a sling (or towel) can be used under the belly when navigating stairs to prevent slipping and falling. The sling also helps you control your pet’s pace.
Is it necessary to keep my dog in a kennel post-surgery, or is house confinement enough?
Following MPL surgery, the pins and wire hold the tibial tuberosity to the tibia in its new position until the bone heals, which takes about 8-12 weeks. During this healing period, the pins and wire must bear all the stresses of weight-bearing, and too much activity too soon can lead to implant failure. High-impact activities such as running through the house or jumping off furniture should be avoided as they could increase the risk of serious complications. If your pet is crate trained, it is recommended to confine them to the kennel when not outside on a leash to go to the restroom. If your pet is not crate trained, confine them to a small room in the home, such as an office, laundry room, or large walk-in closet. When you are watching TV or working at a computer, your pet can be with you, but ensure they are not allowed to run freely in the home.
Why must my dog stay on-leash for 8 weeks post-surgery?
Following MPL surgery, the pins and wire hold the tibial tuberosity to the tibia in its new position until the bone heals, which takes about 8-12 weeks. During this healing period, the pins and wire must endure all the stresses of weight-bearing. Excessive activity too soon can lead to implant failure, so high-impact activities are not advised. It is strongly recommended that off-leash activity is not allowed until radiographs confirm complete bone healing.
Why is my dog limping after running around post-MPL surgery?
There are multiple potential causes for lameness following MPL surgery, including simple soft-tissue inflammation due to over-activity, recurrence of MPL, or implant failure/fracture of the tibial tuberosity. If your pet appears sore, it’s best to contact your veterinarian. They will rule out various conditions, such as a simple soft tissue sprain or strain, infection, cruciate injury, meniscal injury, implant failure, and patella misalignment. Most complications following MPL surgery are minor and can be medically managed. In some cases, additional surgery may be required to remove an infected implant, manage a persistent MPL, address a newly occurred ligament injury, or restabilize the tibial tuberosity in cases of implant failure or fracture. To minimize the risks of postoperative concerns and complications, it’s important to keep your pet calm and on a leash for 8 weeks, and to follow the rehabilitation protocol provided by your veterinary surgeon as closely as possible.
What should I do if my dog is improved but not fully recovered 8 weeks post-surgery?
Every pet recovers from surgery at a different pace. While some pets appear to have made a full recovery within weeks of surgery, others may take months to reach their full potential. Studies have shown that it can take 6-12 months following surgery for patients to exhibit limb function indistinguishable from a control population. If your pet’s level of function is of concern, it is important to contact your veterinarian for recommendations to help get your pet back to peak function.
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