This article discusses a common orthopedic condition in dogs, particularly smaller breeds, known as Medial Patellar Luxation (MPL), a condition that can often requires surgical correction.
Understanding Medial Patellar Luxation
The patella, or knee cap, is a small bone buried in the tendon of the extensor muscles (the quadriceps muscles) of the thigh. The patella normally rides in a groove within the femur (thigh bone) in the knee. The patellar tendon attaches on the tibial crest, a bony prominence located on the tibia (shin bone), just below the knee. The quadriceps muscle, the patella and its tendon form the “extensor mechanism” and are normally well-aligned with each other. Patellar luxation (dislocation) is a condition where the knee cap rides outside the femoral groove when the knee is flexed.
In medial patellar luxations, the kneecap moves inward, or medially (towards the dog’s body), which can be classified into different grades (Grade I to IV) based on severity:
1. Grade I: The patella can be manually luxated but returns to its normal position when released.
2. Grade II: The patella occasionally luxates on its own, causing occasional lameness, but can be replaced by manipulation.
3. Grade III: The patella is luxated out of its groove most of the time, causing persistent lameness and discomfort, but can still be manually replaced in the groove.
4. Grade IV: The patella is permanently luxated, leading to severe discomfort and deformity, and can not be manually replaced back into the groove.
Why Do Patellar Luxations Happen?
Several factors can contribute to MPL, including genetic predisposition, trauma, and developmental issues. Certain breeds are more susceptible, including Boston Terriers, Yorkshire Terriers, Pomeranians, Miniature Poodles, and Chihuahuas, among others.
The luxation can occur due to malformations in various components of the dog’s leg, such as the femur, tibia, or the supportive structures surrounding the knee joint. The misalignment leads to luxation of the patella out of the trochlear groove.
How Do I Know if My Dog has an MPL?
Symptoms associated with patellar luxation vary greatly with the severity of the disease. This condition may be an incidental finding detected by your veterinarian on a routine physical examination. Some signs that your dog may be experiencing MPL include:
- Limping or lameness in one or both hind legs that may start off intermittent. This lameness can become more frequent and continuous with worsening severity of MPL
- An abnormal gait, such as skipping or hopping. Many dogs affected by this disease will suddenly carry the limb up for a few steps (“skip”), and may be seen shaking or extending the leg prior to putting it down again.
- Reluctance to jump or run
- A “bow-legged” appearance, especially in young puppies with higher grade MPLs
If you notice any of these symptoms in your dog, it’s essential to visit your veterinarian for a proper diagnosis.
Over time, the knee cap may dislocate more and more often out of its groove, eroding cartilage and eventually exposing areas of bone which leads to arthritis and associated pain. Other structures in the knee may become more strained, potentially predisposing to a ruptured cranial cruciate ligament. In puppies, the abnormal alignment of the patella may also lead to serious deformation of the leg.
Surgical Correction of MPL
Mild cases (Grade I and some Grade II that are asymptomatic) may not require surgery and can be managed with lifestyle modifications, physiotherapy, and weight management. However, more severe cases (Grade III and IV, and symptomatic Grade II) usually require surgical correction for the best chance of a full recovery.
The choice of surgery depends on the specifics of each case, but generally, the goal is to realign the structures so the patella stays in place. There are various surgical techniques available, including:
1. Tibial Tuberosity Transposition (TTT): Here, the bony prominence on the tibia, where the patellar ligament attaches, is cut and repositioned to realign the quadriceps, patella, and its tendon.
2. Trochleoplasty: This procedure involves deepening the groove in which the patella lies to make it harder for the patella to luxate or move out of place.
3. Soft tissue realignment: Techniques like imbrication (tightening the tissues on the outside of the knee) and releasing tissues on the inside of the knee help correct patellar alignment.
4. Corrective Osteotomies: In severe cases where femoral deformity has developed, the abnormal shape of the femur can contribute to the patellar luxation. A corrective osteotomy involves cutting the bone, correcting the deformity to realign the patella, and stabilizing the bone with a bone plate.
In most cases, with proper post-operative care and physical therapy, dogs can regain good function of their leg. Over 90% of owners are satisfied with the outcome of surgical correction for medial patellar luxations.
Medial Patellar Luxation can significantly impact your dog’s quality of life. If you notice your dog exhibiting any of the clinical signs listed above, it’s best to consult with your veterinarian as soon as possible. Early detection and intervention are key to managing this condition.
If you have any more questions about MPL, feel free to ask your local vet or email us at info@apexvetsurgery.com