At McDowall Veterinary Practice, we commonly see animals that have issues with their knees and are intermittently lame on their back legs. One of the most common conditions is a luxating kneecap (patella) which is particularly prevalent in small breeds of dog, who are often born with a predisposition to this condition. The article below explains this condition in depth and how we correct it.
The patella bone (also known as the kneecap) is a bone that sits in the middle and front of the hind leg in the dog. It is connected via the thigh muscles (quadriceps) and attached to the tibial crest (shin bone). The patella bone normally glides along a groove in the thigh bone (femoral groove).
Patella Luxation is a very common orthopaedic problem which occurs when the patella luxates out of the femoral groove, most commonly on the inside portion of the knee or toward the middle of the body (medial luxating patella). This problem generally affects both knees, and one is usually worse than the other.
A Medial Luxating Patella is common in small breeds but can occur in large breed dogs. It is a genetic problem that is commonly seen in dogs with bow-legged femurs/thigh bones.
Having a bowed-leg affects the normal muscle and bone development of the entire hind limb. In some puppies, a normal kneecap groove may not develop and further limb deformities become a self-perpetuating problem.
Typically, dogs will start skipping on three legs when running or bunny hopping if both hind legs are affected with a luxating patella. After a few skips the lameness sign can disappear and the gait abnormality may go back to normal when walking at a slower speed. Most dogs cannot extend/straighten their knee normally. The longer this condition is left, the more painful the luxation can be. Your pet is more likely to develop osteoarthritis as the kneecap continues to rip out of its socket. It can also put more stress onto the main anterior/cranial cruciate (ACL) ligament which is at higher risk of damage in those patients.
Most commonly a patella luxation is diagnosed during a routine health check. However, if you notice any lameness be sure to book an appointment with us so that we can check it out. Additionally, we would recommend filming any visible lameness as this may disappear by the time you arrive at the clinic for an appointment.
Your dog will likely need a short course of anti-inflammatories to ease the pain, and you will be advised if further action is required to surgically fix the luxating patella.
There are four different severities of grading a luxating patella:
Grade 1– the patella can be luxated from its groove by manual examination but returns into the socket immediately after manipulation. Generally, this grade is non-painful and does not require surgery.
Grade 2– The patella can spontaneously luxate, and skipping is sometimes noted when dogs are running and can be associated with pain. Surgical treatment is generally required and, if performed early, it will help avoid other problems.
Grade 3– The patella is permanently luxated, but can be manually reduced into the joint, but will pop straight back out afterwards. Ideally needs surgery and is more complex to fix than a Grade 2 luxation.
Grade 4– Like a grade 3 luxation, the patella is permanently luxated but cannot be replaced back into the groove with manual reduction. This may require specialist referral to correct the problem. Recurrence is more common with grade 3 and 4 luxations.
When you come in to see us, we will perform a detailed physical and musculoskeletal exam to grade the patella luxation and ensure that there are no other orthopaedic problems coexisiting. X-rays are organised of the hips, knees and lower spine and are taken under sedation/general anaesthesia to assess the need for surgery.
We commonly see Hip Dysplasia (hip joint abnormality) associated with medial luxating patellas. If luxating patellas are left untreated it may cause further deterioration of the knee joint including cartilage loss and will lead to osteoarthritis causing more pain and lameness for your dog. Prolonged stress on the knee joint can also result in anterior cruciate rupture. Dogs with both problems pose a greater challenge when trying to surgically correct their knees and often leads to a poorer outcome.
Surgery is the treatment of choice to correct a medial luxating patella and should be undertaken when temporary or permanent lameness signs are seen (skipping/ pain). The main aim is to realign the thigh muscles (quadriceps) that attach to the patella. The success rate for surgery is excellent if done before osteoarthritis has developed.
This is achieved through the following surgical techniques. Depending on the degree of luxation, multiple techniques are used to realign the patella appropriately.
Firstly, the patella (kneecap) groove located at the bottom of the thigh bone is deepened (if required) to allow the patella to be seated centrally. See the diagram below.
Second, a tibial transposition is performed. This means realigning the patella attachment in a straight line. The top of the shinbone (tibia) is cut and relocated laterally (pushed towards the outside of the knee). This is secured with two pins and sometimes wire to allow the bone to heal in the correct position.
Third, the inner thigh muscles are loosened whilst the outer thigh muscles are stitched together tighter (imbrication).
Complications are very uncommon (approximately <2%) and include infection, implant failure/loosening, and recurrence. These complications are minimised by confining your pet for 6-8 weeks post-operatively. At 6-7 weeks post-surgery we will take hind leg Xrays to ensure the surgery has been successful and that there is no need to remove the implants. By 3 months post-surgery most dogs have good function of there leg and are able to go on long walks again. At 6-12months most dogs have complete recovery and full use of their surgical leg.
We are fortunate to have several surgeons here at McDowall Vets who are very experienced and accomplished at performing these surgeries. We love seeing our patients become pain free and return to energetically living life to the full again. Let us know if you are concerned about a luxating knee cap in your pet, we will be only too happy to help make those knees less wobbly!
