Part 4 in the Owner Fact Files blog series, discussing Patellar Luxation (PL), an orthopaedic condition of the stifle (knee) joint.
What is Patellar Luxation?
The patella, or the knee cap, is a small sesamoid bone, in the stifle joint - sesamoid means the bone is embedded within a tendon. Luxation means the complete dislocation of a joint, so in the case of Patellar Luxation (PL), the patella moves out of place from where it should normally sit in the stifle.
In the healthy stifle joint the patella sits within a groove in the femur (thigh bone) underneath the patellar ligament, which attaches the thigh muscles to the tibia (shin bone). When the thigh muscles contract, the force is transmitted through the patellar ligament, causing a pull on the tibia. This effort extends the stifle, straightening the joint. As the stifle extends, the patella glides up and down within the groove, helping to keep the patellar ligament in place. This mechanism allows for smooth, pain free extension of the stifle joint.
In cases of PL, stifle extension cannot happen in the same way, read on to find out why, and how this effects the dog.
What causes Patellar Luxation?
In some dogs, the patella slips out of the normal groove that it should sit in. The primary reason for this is genetics, as selective breeding over time has produced more dogs with a bowed leg conformation.
Dogs will be born with normal knees, but problems begin to develop in their early life. The abnormal shape of the limbs puts stress on the muscles and soft tissues in the limb. This causes the muscle that sits above the patella, the quadriceps, and the patellar ligament, to shift to the inside of the joint.
This shift causes the thigh and shin bones to further deform, and the groove that the patella should sit in does not develop correctly. The groove does not become deep enough, meaning the patella is free to luxate/slide out of position.
There are several factors which are said to influence the development of PL in dogs. Genetics, is the primary factor, as the condition is hereditary, meaning that dogs with PL should not be bred from. Research has also shown that Sex plays a role, with females more likely to develop the disease, and neutered dogs appear to be at higher risk too.
PL is most often a condition that effects smaller breeds, with a 12 times higher incidence compared to large breeds. Breeds that are commonly affected include: Toy/Miniature Poodle, Pomeranian, Yorkshire Terrier, Chihuahua, French Bulldog, Maltese Terrier, Lhasa Apso, Cavalier King Charles Spaniel, Bichon, Pug, Bulldog, Westie, Jack Russell, and Shih-Tzu.
What's happening inside the joint? (the science bit)
As previously explained, when the muscles and patellar tendon shift towards the inside of the joint, the patella is also pulled that way, out of the groove. This movement occurs when the stifle is flexed, so when extension is attempted it is not possible, meaning the limb cannot straighten.
Over time, as this abnormal movement continues to occur, the femur (thigh bone) and the groove in the bone are worn down. This worsens the problem, as the groove becomes shallower, making it easier for the patella to luxate. The friction of the patella on the femur also wears holes in the cartilage of the stifle joint, which causes pain and triggers osteoarthritis as a secondary issue.
Luxations are graded according to their severity:
Grade 1 - the patella can be luxated with manual pressure, but otherwise stays in the groove. This grade is often found by accident, and the dog will not be affected with clinical symptoms.
Grade 2 - the patella will spontaneously luxate, and a skipping lameness will be seen. In these cases, the patella will mostly stay within the groove, and will also go back in after it has luxated.
Grade 3 - the patella is permanently luxated, but it can be manually replaced in the groove, however it will luxate again quickly.
Grade 4 - the patella is permanently luxated and cannot be manually replaced in the groove.
Symptoms
Signs of PL will mostly start to show in puppies, and the majority of cases are diagnosed before the age of 3. Around 50% of dogs will be affected in both limbs.
The sign that is seen is a 'skipping' or 'hopping' movement - the dog will hold the limb up for a few steps then return to normal movement. Other signs you may notice include;
- Continuous limp - Clicking of the joint
- Stiff awkward gait - Shaking the limb before use
- Restricted knee extension - Bunny hopping gait
- Crouched hind limb posture - Frequently attempts to stretch
- Suddenly stopping on walks the limb backwards
- Reluctance to go down slopes
If you see any of these signs in your dog and you have concerns, please speak to your vet for advice. PL can vary in severity, so you may not see all of these signs.
Treatment
The treatment selected for PL cases depends on the grade of the luxation. Grade 1 cases, the mildest form of PL, are treated conservatively, meaning surgery is not required. This type of management will also be used in some Grade 2 cases to see how the animal responds, and to possibly avoid surgery.
Conservative management includes; body weight reduction to take any excess weight off of the compromised joint. Physiotherapy, hydrotherapy, and exercise modification, to strengthen the soft tissue around the patella and support the joint. Medication to relieve pain and reduce inflammation.
Some Grade 2 cases will worsen over time, so surgery may be required. Surgery is always recommended for Grade 3 and 4 cases, to prevent the progression of osteoarthritis in the joint. The surgical options aim to realign the anatomy, and deepen the groove which the patella should sit in.
Tibial Tuberosity Transposition is a surgery which moves the bony prominence on the front of the tibia, where the patellar tendon attaches, to help realign the quadriceps muscle, the tendon itself, and the patella. The anatomy is moved to a more appropriate place and pinned to allow correct movement.
Femoral Vastus Osteotomy surgery is chosen when the femur (thigh bone) is severely bowed. A wedge of the bone is removed and the bone is repaired and straightened to reduce the inward pull on the muscles and tendon.
A Recession Sulcoplasty procedure is used when the groove in the femur is particularly shallow. A wedge of bone and cartilage are removed and replaced in a recessed position to deepen the groove for the patella.
The final procedure which may be used is Soft Tissue Reconstruction surrounding the patella. This helps to loosen the pull on the knee cap, and also tightens the opposing side, to keep the bone in position.
How can physiotherapy help?
I would recommend physiotherapy for the conservative management route and also in postoperative rehabilitation. My primary aim is pain management within the stifle joint, in the surrounding structures, and also in other areas of the body which may have been working harder to compensate for the PL. Pain would be managed with hot/cold therapy, massage, and electrotherapy treatment.
Physiotherapy further helps with a gradual return to exercise, focusing on building muscle around the stifle, and increasing the range of motion in the joint where it was previously restricted. This in turn will improve your dog's gait and get them moving correctly, without having to compensate and alter their movement. Remedial exercises which I prescribe for you to complete with your dog, are key in returning them to their previous activity levels, and allowing them to live a full and happy life.
For more information on how physiotherapy could benefit a dog with Patellar Luxation, please get in touch - vetphysionancy@outlook.com // 07795163445.
Prognosis
Following surgery, 6-8 weeks of rest and restricted exercise will be required. With good progress, dogs can return to their previous exercise levels.
If PL is treated before arthritis has set in, prognosis is very good. If arthritis has already developed, your dog may suffer with joint pain and secondary issues, which will require long term care to maintain joint health.
That brings me to the end of the PL Owner Fact File, if you have any questions please do contact me, and come back to read the next instalment in the series.
If you think there is anything I can do to help your animals please drop me a message - Nancy
M: 07795163445
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