What is patella luxation?
Patella luxation in small animals such as dogs and cats is a very common finding. Whether the luxation is found in a general clinical examination or after an injury, our main aim is to ensure the pet has normal walking and running motion, and is pain free.
Luxation means ‘moving out of place’ also know as dislocation. A patella is referring to the kneecap that rides within the groove of the lower part of the main upper leg bone (the femur). The trochlear groove allows the patella to run smoothly over the knee joint.
In some animals, the patella either pops out of the groove or does not run smoothly within the groove, causing physical dysfunction of the leg and pain.
Why does your pet have patella luxation?
Animals that have a luxating patella either on one side or both, do so because of;
- A congenital (existing at birth) deformity in the anatomy of the leg.
- An injury causing the ligaments around the patella to become loose.
The patella normally sits within the trochlear groove and is attached above and below by ligaments and tendons. In an animal with normal anatomy, the attachments ensure that the patella runs vertically and so cannot pop out of alignment. In an animal with abnormal anatomy, the ligaments and tendons do not run vertically and as such direct the patella inwards. When the knee moves in certain planes during flexion and extension it is pulled and consequently allowed to pop out of position. The animal may correct this itself just by flexing or extending the knee. In a few animals the patella may permanently be sitting out of the groove.
Accident or injury
The patella is prone to dislocate in some animals after an accident or injury. It may be forcibly pushed out of joint causing immense pain and possible permanent loosening of the patella ligaments and tendons. It may be possible to relocate the patella back into the groove but it might then be too loose to remain in position.
How is patella luxation diagnosed?
The diagnosis of luxating patella may be done in a normal clinical consultation by manual palpation (feeling the knee). Occasionally, the degree of luxation, contributing anatomy, and chronic arthritic changes may need to be visualized by radiography (X-rays).
A grading score is used by vets to allow us a common understanding of to what degree the luxation has occurred.
Grade 1 – the patella can be moved by palpation to dislocate but pops back in when released
Grade 2 – the patella can be moved to dislocate or it can happen automatically when the knee is flexed. It stays in that position until pushed back in or until the animal extends its leg.
Grade 3 – the patella is luxated most of the time but can be pushed back into the groove on extending the knee. Moving the knee will cause it to pop out again though.
Grade 4 – the patella is permanently out of joint and cannot be replaced.
What is the treatment?
In animals with grade 1 and in some grade 2 cases, a conservative approach may be used as long as the patient is not experiencing extreme discomfort.
Veterinarians may recommend antinflammatories to ease inflammation and associated pain.
Exercise and physiotherapy can also help in these cases.
Unfortunately, constant luxation will translate in degenerative joint changes and osteoarthritis if left untreated.
The theory of the surgical approach is to tighten the patella ligaments and tendons, re-align the attachments and deepen the groove, so that the patella cannot dislocate anymore.
Trochleoplasty / sulcoplasty
This is the deepening of the trochlear groove. This can be done a number of ways depending on the view of the veterinarian.
A common method is to cut a wedge shape in the groove and temporarily remove that section. A second deeper groove is then cut and this cartilage removed. The initial wedge is then replaced into the groove. The initial wedge will now sit deeper within the groove hence allowing the patella to run better and have less chance of jumping out of the groove. This method can also be done as a square cut rather than wedged.
In this surgical method, the tibial tuberosity – the ridge on the shin bone – is partially removed from the bone while leaving the patella attachment – and re-positioned back on in a more lateral position.
The ridge is pinned back on with K-Wires (a stainless steel pin). This allows the moving patella to have a new direction to run in such that it is unlikely to want to jump out of the groove.
The closure of the knee will often involve tightening up the joint capsule on the outside (lateral side). This is done by slightly overlapping the layers as they are brought together to close the joint area
Post operative care
Patients return to normal use of the leg within 8-12 weeks, though many will be ready to take part in normal activity much earlier.
Antibiotics and pain relief are continued when the patient heads home and anti-inflammatories may also be prescribed to decrease post operative swelling and discomfort.
When you get your pet home it is very important that you restrict exercise to short walks on lead to toilet only. No running laps around the block! During recovery it is best to confine your pet to a small space, gradually increasing the duration and frequency of their walks as time goes on.
The surgery itself is only one part of the healing phase, the other part comes from the post operative care you provide to your pet at home, so you must restrict your pet from moving around too much.