What is Patellar Luxation?
Patella luxation is a common cause of hindlimb lameness in dogs, and rarely in cats. The patella acts as a fulcrum during normal extension of the knee joint which improves the ability of the knee joint to glide as it moves. Patella luxation occurs when the patella is displaced from its normal position in the groove of the femur to the inside of the leg (medial patellar luxation), or the outside of the leg (lateral patellar luxation). This may be a permanent luxation, or the patella may intermittently slide in and out of the groove. The consequence of this luxation is an inability to properly extend the knee joint. As the patella moves over the groove in the femur, it can damage the cartilage of both the patella and the femur. This causes a painful response and leads to osteoarthritis. The abnormal mechanics of the stifle in an animal with patellar luxation can increase the stresses on other soft tissues within the stifle, including the cranial cruciate ligament.
What is the cause of patellar luxation?
Medial patellar luxation is the most common. It is not present at birth in most cases, but the abnormalities in skeletal structure that predispose to patellar luxation are present. It is most common in animals with bow-legged conformation – when the powerful quadriceps mechanism starts to displace in this direction, it acts as a bowstring and causes the femur and tibia to deform into a pronounced outwards bow. The groove that normally houses the patella does not develop properly, and the limb deformities become self-perpetuating at this stage.
In some instances, the luxation is traumatic, due to tearing of the tissues that hold the patella in place.
What breeds of dog are affected?
Medial patellar luxation is most common in small-breed dogs with bow-legged hind limb conformation but can also occur in large breed dogs. Lateral patellar luxation is most common in large breed dogs.
How can I tell if my pet has patellar luxation?
Patellar luxation is a common condition. The age at onset of clinical signs is variable. Most animals start to show signs as puppies or young adults, although onset of signs in mature dogs is also common.
A characteristic non-painful “skipping” lameness is often seen, where animals will limp for a few steps and then quickly return to normal. Some animals will limp continuously and some dogs affected by patellar luxation in both knees will have a stiff, awkward gait with knees that do not extend properly.
As the grade of patellar luxation worsens, your pet may develop a ‘crouched’ gait as the dog does not extend its leg properly.
Animals affected by patellar luxation often have a bow-legged conformation of the hind limbs.
How is patellar luxation diagnosed?
Patellar luxation is diagnosed during physical examination by your primary care vet during routine health check, or when you have highlighted an abnormal gait or ‘skipping’ during exercise.
A grading system exists for medial patellar luxation, which depends on the severity of your pets’ condition and will be established during physical examination. Observing your pet at a walk and trot will be performed to evaluate their conformation and to determine the degree of lameness. Physical examination will also rule out other conditions such as cranial cruciate ligament injury.
During your initial consultation at North Coast Veterinary Specialist and Referral Centre your dog will be examination by one of our orthopaedic vets. Following this, your dog will be admitted to the hospital to perform radiographs of the affected stifle joints under sedation or general anaesthesia.
Your dog will receive one-to-one nursing care throughout the process by one of our nurses from the prep nursing team who are all highly trained and experienced in anaesthesia and sedation. The radiographs will enable us to confirm a diagnosis and assess the presence of any arthritic changes in the stifle joint. Following diagnostic imaging your dog may require corrective surgery.
How is patellar luxation treated?
Patellar luxation may be diagnosed incidentally during a routine physical examination. In adult dogs with this incidental finding, non-surgical treatment may be the best option. In immature animals, and animals showing clinical signs of patellar luxation, surgical management may be more appropriate to try to prevent the development of severe limb deformities. The decision for surgical or non- surgical management will be made on an individual basis, and depends on the grade of patellar luxation, the degree of skeletal deformity and the degree of arthritic changes present in your pet.
Non-surgical treatments for patellar luxation
Non-surgical management for your pet with patellar luxation involves body weight management, physiotherapy, exercise modification, and pain relief medication. These same techniques are also important in the short-term management of dogs who are treated surgically, although the primary surgical aim is to minimize the requirement for long-term exercise restriction and medication.
At North Coast Veterinary Specialist and Referral Centre we can provide you and your dog with a rehabilitation plan for patellar luxation. This is coordinated through our in-house rehabilitation service with our physiotherapist team who are very experienced in the management of patellar luxation. Your orthopaedic clinician will coordinate an appointment with a member of our physiotherapy team whereby a thorough clinical examination will be performed, and a rehabilitation plan will be uniquely designed for your dog including an exercise plan for you to follow at home. Most appointments are attended as an out-patient and your physiotherapist will regularly evaluate your dogs’ progress and amend your home exercise plan as necessary.
Surgical treatments for patellar luxation
Surgical treatments are recommended for dogs with an intermittent or permanent lameness due to patellar luxation. It is essential in higher grades of patellar luxation where it is difficult or impossible for the patellar to return to its normal position.
There are many different surgical techniques available for the treatment of patellar luxation; the primary aim is to restore normal alignment of the quadriceps muscle relative to the entire limb to realign the patella within the groove of the femur and ensure pain-free function of the limb. This requires reshaping of the bones and reconstruction of soft tissues, often by a combination of surgical techniques.
● Trochleoplasty techniques:
Trochleoplasty widens and deepens the trochlear groove to enable the patella to remain in position. There are many different types of trochleoplasty techniques, all of which aim to preserve the cartilage of the femur, and result in the least amount of arthritis developing. There are several different trochleoplasty techniques, including trochlear sulcoplasty, trochlear chondroplasty, trochlear wedge recession and trochlear block recession. The optimal technique for your pet will be decided based on clinical examination and radiographic findings and will be explained to you at consultation.
● Tibial Tuberosity Transposition:
The patella is attached to the tibia by a very strong ligament. By realigning the attachment of this ligament to the tibia, the patellar can be redirected and encouraged to remain within the groove of the femur. In this technique, the front (tuberosity) of your pet’s tibia will be cut using a bone saw to allow the tuberosity to be moved to an ideal position. It is then stabilised with wires or pins, and the bone heals over the following 4-8 weeks.
● Soft tissue reconstruction:
Often in dogs affected by patellar luxation, the soft tissues on one side of the patella are too tight, and those on the other side are too loose. Reconstructive techniques aim to correct this imbalance; by either loosening tight tissues or tightening loose tissues which enables the patella to remain in its normal position.
● Anti-rotational techniques:
The tibia of your pet may be internally rotated which is contributing to patellar luxation. In young animals, early correction of this may correct the deformity.
● Distal Femoral Corrective Osteotomy:
Abnormal femur conformation can contribute to patella luxation; this is most common in large breed dogs. To correct this conformation, a bone cut (osteotomy) is made in the femur, and the femur is realigned to straighten the limb. The osteotomy is stabilised using a bone plate and screws, and the bone heals over the following 4-8 weeks.
Are there any complications associated?
Complications can include delayed bone healing, fixation failure at osteotomy sites, relaxation of the patellar, infection, persistent patellar luxation and osteoarthritis.
What is the prognosis?
The prognosis varies with the grade of patellar luxation – is it good for lower grade luxations, and fair to good for higher grade luxations. In cases with severe conformational deformities and arthritis, the prognosis decreases.
Most cases do well clinically and have a slow radiographic progression of arthritis.
Will my dog be able to exercise normally after patellar luxation surgery?
Your dog will initially have to undergo a standard period of 6-week rest, usually involving cage restriction at home, combined with a limited lead exercise program prescribed by your orthopaedic surgeon.
At North Coast Veterinary Specialist and Referral Centre we will provide you with post operative support as well as further advice on physiotherapy options all of which can be provided on an out-patient basis through our physiotherapy service. During your initial appointment, a member of our physiotherapy team will assess your dog and design a program specific for their condition.
Following 6-week post-op reassessment (including radiographs, if implants were placed) with our orthopaedic surgeon and providing your dog is making good progress there is no reason why your pet cannot enjoy the same exercise as before surgery.