Luxating patellas are one of the most common orthopaedic conditions diagnosed in dogs. The condition primarily affects small dogs like Chihuahuas, Yorkies, and Jack Russells, but it can also affect larger breeds like the German Shepherd, Rottweiler and Labrador.
Symptoms of a luxating patella
Some dogs may not show any clinical signs, but symptoms can include:
- Intermittent lameness of variable severity
- Hopping or skipping, which quickly returns to normal
- Clicking
- Stiffness
Patella luxation
The patella, more commonly called the kneecap, sits underneath a ligament called the patellar ligament. This ligament attaches the large quadricep muscles (the thigh muscles) to a point on the front of the tibia (shin bone). When the thigh muscles contract, the force is transmitted through the patellar ligament, pulling on the tibia. This results in the extension or straightening of the knee. The patella slides up and down in its groove (trochlear groove) and helps keep the patellar ligament in place during this movement.
In some dogs, especially ones that are bowlegged, the patella may luxate, i.e. move out of alignment, because the point of attachment of the patellar ligament is not in the centre of the tibia. In these cases, it is almost always located too far toward the middle of the body or the inside of the leg. In these cases, as the quadriceps contract, the force applied to the patella pulls it to the inside of the knee. After several months or years of this abnormal movement, the inner side of the groove in the femur may wear down. Once this happens, the patella is then free to dislocate or slide toward the inside of the knee at any time. This type of luxation is referred to as a medial luxating patella. Many toy and small breed dogs, including Maltese, Chihuahua, French Poodle, and Bichon Frise, have a genetic predisposition for a medial luxating patella.
A laterally luxating patella (i.e. a patella that luxates to the outside of the dog’s leg) occurs less frequently. It is more common in medium or large-breed dogs, often in tandem with hip dysplasia.
Causes of patella luxation
Patella luxation can occur due to the conformation of the dog, which has a strong genetic component. However, it can also arise due to trauma to the area.
In all dogs affected by luxating patellas, one or both kneecaps may luxate, sometimes to different degrees. Approximately 50% of affected dogs have both knees involved.
As patellar luxation progresses, the patella dislocates more easily and frequently — persistently rubbing on the knee joint cartilage and leading to arthritis. The strain from the patella dislocating can also predispose dogs to other orthopaedic knee conditions, such as cranial cruciate ligament rupture. It is estimated that at least 15-20% of all dogs diagnosed with luxating patella will eventually rupture their cranial cruciate ligament due to the stress on the area.
There are four grades of patellar luxation, and a higher grade means that the condition is more severe.
Grade 1 = Occasional lifting of the affected leg is noticed in a hopping motion, but the issue corrects itself rapidly. Equally, the patella can be manipulated out of the groove but will return spontaneously.
Grade 2 = More lifting of the leg may be noticed, and the patella moves out of the groove more. However, the patella can still be replaced by manipulation.
Grade 3 = More permanent dislocation is seen as the patella is out of the trochlear groove most of the time. It can be replaced easily but will slide out again quickly.
Grade 4 = Permanent luxation occurs, and it proves impossible to return the patella to the trochlear groove.
Diagnosis
Your vet will provide a full examination and may be able to determine by palpation how much the patella moves, and then it can be graded as described above. However, X-Rays under sedation or full general anaesthetic may be required to assess the stifle joint more closely and evaluate the bony conformation.
Treatment
Not all dogs diagnosed with luxating patella require surgery. Some with low-grade issues are managed conservatively. Conservative management includes:
- Joint supplements
- Pain medication
- Weight control
- Hydrotherapy to encourage normal weight bearing, help build muscle strength and support the surrounding stifle structures.
- Massage therapy to help address any muscular tension, areas of overcompensation or muscle splitting and improve overall comfort levels.
For those dogs that require surgery (generally those with higher grade luxations), there are a variety of procedures available. While they may be used alone, they are more commonly used in combination. These techniques include:
- Deepening of the trochlear groove in the femur (called ‘sulcoplasty’)
- Moving the attachment point of the patella ligament on the tibia (called ‘tibial tubercle transposition’)
- Releasing the tight fascia around the patella
- Tightening any redundant fascia around the patella
- In exceptional cases, corrective femoral or tibial osteotomies (cuts into the bone) may be required to realign the limb.
Final thoughts
Luxating patella is a common orthopaedic issue in dogs that can significantly impact their quality of life. Understanding the different types of luxation is crucial for proper diagnosis and the development of an effective treatment plan. If you suspect your dog may have a luxating patella, it is essential to consult with a veterinarian promptly to explore the most appropriate course of action for your furry friend’s health and well being.
