Patella Luxation in Dogs
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What is patella luxation in dogs?
The patella, or kneecap, is a bone that sits within the tendon of the quadriceps muscle at the level of the stifle (knee) joint.
As the stifle is flexed and extended the patella moves up and down in a groove (the trochlear) on the bottom of the femur (thigh) bone. The underneath of the patella is concave to articulate with the curved surface of the femur.
The trochlea groove has ridges on either side which help maintain the position of the patella. There are ligaments on either side of the patella, which also aid this.
The quadriceps tendon, which contains the patella, joins on to the front of the tibia (shin bone) in a region called the tibial crest.
In dogs with patella luxation (dislocation) the patella does not sit within the trochlear of the femur but can dislocate out of this position.
This can be either laterally to the outside of the knee or medially, to the inside of the joint. Medial luxation is most commonly seen. In some cases the patella is permanently out of position, but in other cases it moves between a normal position and a luxated one.
The frequency of this varies between cases. Both stifles can be affected but the severity may be different. Patella luxation is seen most commonly in dogs, but cats can also be affected.
Patella luxation causes and symptoms
Most cases of patella luxation occur as a result of a developmental malalignment of the quadriceps mechanism.
This refers to rotational and angular deformities of the femur and tibia, and malformation of the trochlear groove.
There may be a genetic component as the condition is seen more commonly in certain breeds. Traumatic luxation is also seen but this is much less common.
The most common age of presentation is from six to twelve months but milder cases may not present until later in life.
This is usually due to a result of cartilage erosion or osteoarthritis development as a result of the ongoing luxation. Dogs with patella luxation present with varying degrees of lameness ranging from intermittent mild skipping to persistent lameness with a crouched hindlimb gait.
There can also be acute episodes of lameness if the patella luxates suddenly. Some dogs will have a bow legged appearance.
What dog breeds are prone to patella luxation?
Patella luxation is most commonly seen in the toy and miniature breeds such as Yorkshire terriers and miniature Poodles.
Other breeds such as Jack Russell terriers, Cavalier spaniels and Staffordshire bull terriers are also often affected.
Although generally less common in large breeds, Labradors and Mastiffs are over represented.
Luxating patella diagnosis
Patella luxation is usually diagnosed on physical examination, either at a routine check or because an abnormal gait or lameness has been noted. Radiographs (x-rays) of the stifle will also be required and in some cases advanced imaging, using CT, may also be necessary.
Luxating patella is graded 1 – 4 based on severity.
Luxating patella grading system
Grade I: The kneecap is in position but can be luxated by the examiner under digital pressure.
Grade II: The kneecap spontaneously luxates out of the groove during normal activity but will return to its normal position.
Grade III: The kneecap is permanently luxated but can be returned to the groove manually.
Grade IV: The kneecap is permanently luxated and cannot be returned to its normal position in the groove.
Luxating patella treatment options
Patella luxation is usually diagnosed on physical examination, either at a routine check or because an abnormal gait or lameness has been noted. Radiographs (x-rays) of the stifle will also be required and in some cases advanced imaging, using CT, may also be necessary.
Non-surgical treatment
In mild cases of patella luxation that have been diagnosed as an incidental finding non surgical treatment may be an option. This includes weight management, exercise control, physiotherapy, hydrotherapy and anti-inflammatory medication.
Early treatment of skeletally immature dogs may be beneficial to try and prevent more severe abnormalities developing.
Surgical treatment
Surgical treatment is indicated for dogs with a grade II luxation and clinical signs of lameness. Surgical treatment is usually indicated in dogs with grade III and IV luxations.
Surgical treatments aim to correct the alignment of the quadriceps mechanism and involve procedures to address both the soft tissue and bone components. Each case is assessed on an individual basis to determine which combination of procedures are indicated to restore the normal patella position.
Soft tissue correction
Soft tissue corrections involve releasing procedures on the side that the patella dislocates to and tightening procedures on the opposite side.
Tibial tuberosity transposition surgery
Tibial tuberosity transposition surgery involves cutting the tibia where the quadriceps tendon inserts and moving the bone to realign the patella within the trochlear groove. This is secured in the new position with pins and wire, and usually takes six to twelve weeks to heal.
Trochleoplasty
Trochleoplasty is a procedure used to deepen the groove that the patella runs in. A block or wedge of cartilage and bone is removed from the trochlear and preserved. The bone behind this is removed and then the cartilage is replaced into its new, deeper position. If the grove is very shallow, malformed or there is significant osteoarthritic change then a patella groove replacement (PGR) surgery may be indicated. This is where all the trochlear groove is removed and an artificial groove is screwed into position.
In some cases the femur can have significant bowing and a straightening procedure is indicated to correct this. This is called a distal femoral osteotomy (DFO) and involves removing a wedge of bone from the femur and then fixing it in the corrected position with a plate and screws. CT is often indicated in these cases to allow full assessment of the deformity, and in some cases custom made 3D guides can be created to optimise the outcome of the surgery.
Frequently Asked Questions
Is patella luxation preventable?
Patella luxation is not preventable, but if the condition is picked up while the dogs is still growing it is possible that relatively minor surgical procedures may prevent the condition worsening. Early intervention in a skeletally mature dog may reduce the chance of cartilage erosion and slow osteoarthritic development.
How much does luxating patella surgery cost?
The cost of luxating patella surgery will depend on the level of pre-surgical imaging and the surgical interventions that are required for an individual case. If you contact the practice we can discuss this with you.
What happens if luxating patella is left untreated?
If patella luxation is left untreated there is likely to be ongoing episodes of lameness as a direct result of the luxation. The severity and frequency of these will vary between cases. It is also likely to lead to cartilage erosion and osteoarthritis which will also manifest as lameness.
Can delaying treatment cause more damage?
Delaying treatment may result in more cartilage erosion and osteoarthritic change in the affected joint.
Will my dog be able to exercise normally after patella luxation surgery?
Once your dog has recovered from the surgery and the bone and soft tissues have healed then they should be able to exercise as normal. There is usually a period of six to twelve weeks post surgery where exercise restriction is required.
Can a dog live with luxating patella?
A dog can live with a luxating patella if this occurs infrequently, and the subsequent lameness is mild and resolves quickly.
Does luxating patella get worse over time?
In some cases the lameness associated with patella luxation will get worse over time due to cartilage erosion and osteoarthritic development.
Are dogs in pain with luxating patella?
When the patella is in its normal position the condition is not always painful, but when it luxates it can cause pain. This is due to stretching of the soft tissues surrounding the knee and mechanical restriction to the joint movement. Over time cartilage erosion and osteoarthritis may also cause inflammation in the affected joint, which will subsequently lead to pain.
Arranging a referral for your pet?
If your dog has been diagnosed with patella luxation and you would like us to carry out an assessment and surgery all you have to do is ask your veterinary surgeon to refer you to us.
They can do this easily via our website, by email or by phone call.
If you can let us know when you have made the request we will know to expect the referral and can follow it up if required.
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