Does your dog skip or have trouble walking?
From time to time does your dog skip on a back leg? Or perhaps they hop a few steps and then run perfectly fine.
A common reason for this skipping gait is a loose kneecap over the stifle joint; or to give it the correct name, patellar luxation.
This article answers the following questions:
- What is patella luxation in dogs?
- What causes patellar luxation?
- Patellar luxation grades of severity
- Is patellar luxation painful?
- What’s the best patellar luxation surgery?
Of course, there’s more to lameness than wobbly kneecaps, so always get a diagnosis from your vet. But for those who already have a label of ‘patellar luxation’, but are puzzled about the implications, this is a great place to start.
What Is Patellar Luxation in Dogs?
Don’t you love it when good plain English is dressed up in fancy terms?
In this case, ‘patella’ simply means kneecap, and ‘luxation’ means side-to-side movement. Hence, how patellar luxation and wobbly or loose kneecaps are an interchangeable term.
Why does a loose kneecap matter?
Rather than being there for ornamentation, the kneecap has a job to do. It provides a fulcrum, or pulley-point, on which the quadriceps muscle group pulls.
When these big thigh muscles contract they pull on the kneecap, which is anchored on the shinbone (tibia). This causes the leg to straighten. Thus the patella has an important role in taking steps forward.
Pulley Systems and Skipped Steps
But much like a pulley, if something slips out of place, things don’t run smoothly.
In this case, it’s the patella jumping to the left or right of centre that causes a medial patellar luxation (if the kneecap moves inwards) or lateral luxation (if it pops outwards).
Then when the muscles pull it’s no longer in a straight line, but off to one side. This causes the leg to lock up and makes it mechanically difficult to straighten out. Hence the skipped step.
The Short and Long of It
In the short term, a loose kneecap is often no more than a minor inconvenience. But in the long term, there is the potential for problems. This depends on:
- How much movement there is in the kneecap
- If complications have set in, such as arthritis or cruciate disease.
Again, best check in with your vet who can assess the severity of the luxation.
What Causes Patellar Luxation?
Loose kneecaps are usually an inherited condition, rather than the result of an accident or trauma.
Is Patellar Luxation Hereditary?
Yes, there are strong breed links to this condition, especially small breed dogs. This may be down to the dog breed confirmation requiring them to have short, bendy legs.
In theory, affected dogs should not be bred from. This is all well in principle, but some breeds have such bendy legs that it’s hard to find a dog that doesn’t have some degree of patellar luxation.
The poster-dogs for patellar luxation are:
- Yorkshire terrier
- Lhasa Apso
- Shih Tzu
- Boston terriers
In contrast to small dogs, luxation of the patella is relatively uncommon in large breeds. However, there are exceptions, the best known of which is the Labrador Retriever.
That said, don’t feel smug if your dog is a mix or not one of these breeds. Any dog, large or small, can have patellar luxation if they have poor knee anatomy.
A loose kneecap is a mechanical problem, down to angles and pulley systems. But for our dogs we’re not talking ropes and wooden blocks, so much as bone angles and groove depths.
The most important anatomy quirks that cause patellar luxation are:
- A slack joint capsule that fails to hold the kneecap firmly in place
- A shallow (rather than deep) trochlear groove for the kneecap to rest in. The lack of depth makes it easier to flip the patellar out of place.
- A bow or twist in the thigh bone (femur), which means the muscles don’t pull straight and the patella luxates when they contract.
- A bow or twist in the shin bone (tibia), particularly the beak of bone that the kneecap is anchored to
Any individual dog may have one, two, or all of the above issues, hence the severity of the luxation varies between dogs.
Patellar Luxation Grades of Severity
- Grade I: A Barely Noticeable Problem
- Grade II: A Hop, Skip, & a Jump
- Grade III: The Persistent Lameness
- Grade IV: The Locked-up Leg
Having a loose kneecap isn’t like being pregnant. It’s NOT an all-or-nothing condition.
Some dogs have the merest hint of a niggly knee, whilst others are disabled by it.
Indeed, when a vet assesses a patellar luxation, they will ‘Grade’ or assign a level of seriousness to the condition. This better allows them to work through which dogs just need pain relief and those that need patellar luxation surgery.
Grade 1: A Barely Noticeable Problem
Your dog is fine, and you probably aren’t even aware there is an issue. This is the luxation the vet finds as part of a routine vaccination checkup. The kneecap can be gently pushed out of place by a helping hand, but isn’t inclined to do so of its own accord.
Grade 2: A Hop, Skip, & a Jump
This is the dog that skips a step when walking or running, but it doesn’t slow them up any. It might happen once in a blue moon or regularly, but aside from the odd twinge, doesn’t bother them.
Grade 3: The Persistent Lameness
This is the kneecap, which naturally prefers to sit in the wrong position, but hasn’t fused there yet. Lameness and knee pain are common, and can impact on the dog’s ability to jump or get around.
Grade 4: The Locked-up Leg
This leg is permanently locked in the wrong position, and it’s really difficult to relocate the patella back to its rightful place. These dogs are often permanently lame on the leg and do require surgical treatment to keep them mobile.
Is Patellar Luxation Painful?
Anyone with a ‘clicky’ joint, appreciates an abnormal movement isn’t necessarily painful.
The same goes for patellar luxation in the dog.
In mild patellar subluxation (Grades 1 & 2) the problem is more mechanical rather than painful. Much like putting a door wedge under the door, the knee is physically locked in the wrong position. That dramatic skipping, isn’t down to discomfort, but due to the knee locking up.
However, if the knee repeatedly locks up, this causes inflammation. When the inflammation is severe enough, this causes knee pain. Hence, why mildly affected dogs may need pain MEDs from time to time.
Going back to the door analogy, if you repeatedly slam the door against the wedge, forcing it closed, eventually you damage the door. Similarly, for patellar luxation grades 3 & 4. The repeated insult leads to remodelled bone, early arthritis, and knee pain.
These guys are sore, and it places extra strain on the other legs. Surgery is the best option to get these dogs back on their paws again.
For the less serious cases where the patella pops back into the normal position after a step or two, they may require occasional pain relief, such as an anti-inflammatory medication, in order to keep them comfortable.
What’s the best patellar luxation surgery?
There are several techniques for surgical correction of patellar luxation. The surgeon decides which patellar luxation surgery is needed by assessing each individual dog’s issues. This requires a thorough physical examination along with x-rays.
This helps grade the severity of the condition and exclude other conditions affecting the hind legs, which can also cause lameness, such as cranial cruciate ligament damage, hip dysplasia, and soft tissue damage.
Thus, the vet can be sure the clinical signs and limping are fully attributable to the kneecap, rather than a different problem.
Take the example of a dog with straight legs but the kneecap sits in a shallow groove. The lack of depth allows the patella to pop out of place. All that’s needed is to surgically deepen that groove and then the kneecap can sit tight.
At the other end of the scale, is a dog with severely bowed legs. The forces pulling on the patella are all over the place, so simply deepening the groove won’t cut it. These guys need complex procedures to realign part of the shin bone.
When deciding on appropriate patellar luxation surgery the options out there include:
- Tightening the Joint Capsule: Just as tightening your belt holds your trousers up, so tightening the joint capsule keeps the kneecap in place
- Deepening the Kneecap Groove: This gives the kneecap better footing to sit in
- Tibial Crest Transposition: This involves breaking a beak of bone (the tibial crest) and reattaching it in a better position. The idea being to make forces on the patella pull in a straight line.
Patellar Luxation Surgery Cost
For low grade problems most first opinion vets are happy to tighten the joint capsule and deepen the kneecap groove. The procedure needs to be done under general anaesthetic and usually costs several hundred pounds.
For more complex problems, referral to a specialist veterinary orthopaedic surgeon may be needed. Rebuilding the knee joint is complex and the costs can mount accordingly, into thousands of pounds. We have pet insurance guides that cover specific patellar luxation surgery cost relating to specific breeds in more detail here.
A Hop, Skip, & a Jump: Patellar Luxation and Your Dog
If you’re suspicious your dog has patellar luxation, see your vet. They can advise you as to the best way forward.
In addition, look after the dog’s joints. You may wish to consider giving a joint supplement (Chondroitin and Glucosamine tablets are a good place to start) to make the knee more resilient.
And for puppy owners of breeds at risk of patellar luxation, take out pet insurance. Then, if the worst does happen, you can decide what’s best based on surgical advice rather than the depth of your pocket.
Keep those tails wagging, everyone!