Patella luxation: a common orthoapaedic problem
You may have never heard of patella luxation until you apply for pet insurance and receive a 'knee form'. Sometimes, that's also the time you discover your pet has it
Patella luxation (or kneecap instability/dislocation) is one of the most common orthopaedic problems we see in small breed dogs. But little dogs are not the only ones affected – all sizes of dogs and cats can have unstable kneecaps too.
What is patella luxation?
Patella luxation is a condition where the kneecap (patella) slips out of position (luxates). Normally the patella sits in a groove at the bottom of the thigh bone, there it rides up and down the groove as the knee bends and straightens. It's held in place by the groove itself as well as by the patella ligament, which runs from the patella to the top of the shin bone.
A patella that slips inward is called a medial patella luxation (MPL). If it slips outward, it's a lateral patella luxation (LPL). Medial luxations occur in all sizes of dog, but lateral luxations typically occur in larger breeds. Of the dogs that have the condition, 40–50% have it in both knees.
Patella luxation can be caused by a traumatic injury to the knee. But more often it's something that occurs due to genetics and/or developmental abnormalities. The abnormalities that are involved in patella luxation include:
a shallow groove
an alignment problem that causes the patella ligament not to be straight (eg bowed legs, pigeon toes, cow hocks)
hip joint problems (eg hip dysplasia)
How do I know if my pet has a luxating patella?
Although a luxating patella is usually a congenital condition (that is your pet is born with it), it often doesn't become symptomatic until around 2 years of age.
When the patella is out of position, your pet will usually feel some discomfort. This discomfort is displayed as lameness (reduced weight bearing). Some people describe it as hopping or skipping.
In small breed dogs, the typical scenario is your dog runs along, suddenly skips (ie holds a back leg up), then after a few steps, runs along on all four legs again. This can happen over and over again (see video). What's happening here is the patella has slipped out of the groove then slipped back in again.
Depending on the level of soreness and the severity of luxation, the lameness may be more persistent and your pet may even have difficulty straightening the knee, creating a crouching walk. We'll look at severity next.
Some pets show no symptoms and their luxating patellas are only discovered on physical examination – like when having a vet check for insurance.
How is patella luxation treated?
The only way to 'fix' a luxating patella is by surgically correcting the abnormalities that let allow it happen. But not all pets need surgery!! The treatment your pet needs is mostly based on symptoms and severity.
There are four grades of severity:
Grade 1 – the patella can be moved out of place manually (when the knee is straightened) but goes back into place when let go
Grade 2 – the patella occasionally slips out of its groove but goes back in on its own (like in the typical scenario above) or it can easily be moved out of place manually but tends to stay in place when moved back
Grade 3 – the patella is out of place all of the time but can be pushed back into its normal position manually (although it will not stay there)
Grade 4 – the patella is out of place all the time and cannot be manipulated back into the normal position – pets with this severity cannot straighten their knees completely and walk with knee bent all of the time.
So with grades 1 and 2, the patella is mostly in the normal position but can be temporarily luxated. With grades 3 and 4, the patella is permanently luxated. Grade 2 luxations can progress to grade 3 if the moving patella wears down the edge of the groove.
Here's how severity influences treatment:
Pets with grade 1 luxation don't usually require any treatment. They don't have symptoms and the general rule is to avoid surgery in asymptomatic pets
Pets with grade 2 luxation may not need treatment or they may require anti-inflammatory pain relief to relieve temporary soreness (lameness). If your pet is persistently lame, you might consider surgical correction
Pets with grade 3 or 4 disease usually have problematic symptoms and therefore you should consider surgery. Obviously, there can be situations where surgery is not an option (eg severe concurrent disease, finances) and longterm pain medication will be needed.
You might hear that even if your pet has no symptoms, surgery is beneficial to reduce the risk of degenerative joint disease (osteoarthritis) and cruciate ligament rupture. So far, there is no evidence that this 'preventive' surgery is actually beneficial.
What does surgery involve?
Surgery aims is to correct the abnormalities that allow the patella to slip out. That is, the various surgical techniques are all designed to do things such as re-align the patella ligament and deepen the groove.
The techniques include:
tibial crest transposition – where the bony bump on the skin bone that the patella ligament attaches to is moved to a new position that aligns the patella with the groove
trochlear modification – where the cartilage of the groove is lifted away, the bone underneath is cut away to form a deeper groove and then the cartilage is replaced
lateral imbrication – this is basically just creating a tuck in the joint capsule to make it tighter and allow less room for the patella to slip
Ridgestop implant – this is a new technique which involves using an implant to add height to the edges of the groove (thereby deepening it)
Often a combination of techniques are used (eg tibial crest transposition plus lateral imbrication). Because the best technique(s) vary for individual patients, there's no single price for fixing a luxating patella. If you would like to have your pet assessed for surgery and get an estimate of costs, make an appointment to see Dr Craig Goode, who does this surgery. Note that all orthopaedic surgery is done at Elwood Vet.
What are the risks?
The main risk of surgery is recurrence of luxation. The rate of recurrence is reported to be between 8% and 48%. The variation is due to surgeon skill, post-op care and size of dog (larger breeds are more likely to have recurrence).
What is the post-op process?
A supportive dressing is placed after surgery. This holds the knee in a fairly fixed position, which can be a bit awkward for some dogs (especially low to the ground ones with bandy legs). This dressing will usually stay on for 3–7 days.
Pain relief is given before your pet wakes up from surgery and then continues as needed. We often use a combination of opioid pain patches and oral anti-inflammatory medication to ensure your pet is as comfortable as possible.
Generally, you should expect a 6–8 week recovery period. While your dog should be using the leg within the first 2 weeks, activity needs to be restricted to short, easy walking for up to 8 weeks (depending on individual recovery).
Dogs that have become used to not bearing weight on the affected leg may need physio to retrain them to use the leg.