Luxating Patella in Dogs

  • By: Mick Whitefield
  • Time to read: 10 min.

When your dog is limping on the back leg it can be concerning, with older dogs it is often hip problems that are age related, but when it is a young pup and you see that they are in pain it can be very worrying. A visit to the vet follows and he says “ it’s a luxating patella”. So lets take a good look and give you a description of this worrying condition.

What is a luxating patella? Patellar luxation or luxating patella is sometimes called a “floating kneecap,” and refers to the fact that the kneecap dislocates or becomes dislodged. The kneecap (patella) is normally held in place by the ridges of the femoral groove, these cartilaginous ridges at the base of the femur should hold it in line securely whilst allowing free movement (bending) of the knee joint (stifle). When the ridges of the femoral groove are not as pronounced as they should be, or if the groove is too shallow, the kneecap (patella) can slip or dislocate out of place. Like any dislocation it can slip back in, but if it continues to slip out it may require surgical intervention to keep it in place.

What causes a floating kneecap in dogs?

In most cases it is caused by muscle and skeletal abnormalities present at birth (congenital) as it is often an inherited genetic defect. This condition can be exacerbated by obesity or caused by an accident such as a knock to the leg.

It is more prevalent in small dog breeds but some large breeds also suffer from this and can often be found in puppies as young as six weeks old up to six months of age.

The bones of the knee joint are made up of the thigh bone (femur), the two shin bones (tibia and fibula), and the knee cap (patella).

Knee Diagram Stifle
A healthy knee joint

The kneecap sits in a groove at the bottom of the femur and is called the trochlear groove. Ligaments connect these bones which support and stabilize the joint.

We then have the quadricep muscles which are a set of four muscles on the front of the femur that come together near the patella to form the patellar ligament. This ligament can be felt between the patella and a prominence on the tibia (tibial tuberosity) over the front of the knee. The quadricep muscles work to extend or straighten the knee.

The patella acts as a lever arm for the quadricep muscles and exerts tension from the muscles on the patellar ligament. Any normal functioning knee joint works because all of the joining components of the knee joint (bones, ligaments, tendons and muscles) are lined up correctly. In dogs with patellar luxation, one or more of the components either is malformed, dysfunctional or becomes so as the puppy matures.

The patella should sit in the cartilaginous groove at the base of the femur at the stifle (knee). It is a condition of the knee which in a dog means it only affects the back legs. It can cause pain and create difficulty in walking.

Luxated Patella
On the right the patella has popped out of position (luxated)

Some dogs as opposed to puppies can develop this condition later in life, usually due to trauma or, a combination of a congenital abnormalities and then subsequent wear.

In veterinarian terms Dogs with a luxation of the patella usually have one or more of the following abnormalities: abnormal angulation between the head and shaft of the femur, medial displacement of the quadriceps, lateral twisting or bowing of the femur just above the joint, a shallow trochlear groove, or medial displacement of the tibial tuberosity where the patellar ligament attaches.

A Close Up Of A Tool

Description Automatically Generated
The leg will stand straight or twist to the outside (medial) or twist to the inside (lateral)

The picture above shows a normal knee with the patella sitting tightly into the trochlear groove the other two pictures show that the patella has slipped out of place and dependant upon left or right rotation is called a Medial or a Lateral Luxating Patella.

There are differing theories as to which deformity initiates the problem and results in the luxation. Most widely the accepted theory is that an abnormal angulation between the head and shaft of the femur causes the quadriceps muscle to move medially and pull the patella with it.

Three other theories for the development of the condition include:-

1) Hormonal influences on the bone formation and growth that result in the development of a shallow trochlear groove in the femur.

2) Various Hip diseases or incorrect hip positions that cause dogs to walk abnormally thus making the knee compensate inappropriately.

3) Abnormally positioned attachments of the muscles that cause the patella to be displaced medially.

There is not always a single condition that is responsible, and it may be that your dog has a mix of the possible causations which is why a vet needs to examine your dog.

Regardless though there can be several unwanted consequences if this condition is not treated. With the patella out of place, the cartilage on the surface of the patella, tibia and femur wears down, causing pain and restricting movement, eventually leading to arthritis.

Other problems that can develop include the rupture of the cranial cruciate ligament, one of the ligaments that attach the femur to the tibia. This ligament can tear completely if the patella is displaced.

Patellar luxation in dogs that are still growing will get worse as the bones continue to grow unless it is corrected surgically.

Similarly, without the normal pressure exerted by the patella on the trochlear groove of the femur, the groove does not deepen as it should. As a result, the groove will become too shallow to retain the patella in position, even if it is popped back into place.

Thus, as you can see it is vital that a proper diagnosis by a veterinarian is made so that the correct treatment can be given particularly for puppies and young dogs.

A Veterinarians View of Patella Luxation Severities

Patellar luxation is ranked on a grading scale of 1 to 4, depending on the severity, recurrence rate and prognosis of the condition.

  • Grade 1 refers to cases where the kneecap can be physically manipulated to pop or slip out of place but will then return to its normal position of its own accord.
  • Grade 2 occurs when the patella can be physically manipulated out of place, or if it can be made to pop out on its own by flexing of the stifle (knee) joint. Then if the patella will not return to its place automatically but will return to its place if manually pushed back. Or, if the joint is extended and rotated to correct it.
  • Grade 3 of the condition is when the patella will slip and remain out of joint on its own most of the time, but it can be manually pushed back into place temporarily.
  • Grade 4 occurs when the patella is permanently luxated out of position and cannot be pushed back into place manually, not even temporarily.
A Close Up Of An Animal

Description Automatically Generated

Treating Patellar Luxation

Grade 1

The patella can be forced out of the femoral groove but pops back into place when the joint pressure is released. Causing occasional limping.

This grade of luxation is difficult to spot by many owners and they generally just make a passing comment to the vet during a health check that the dog keeps limping on occasions.

If the dog affected has a grade 1 rating, you may decide in consultation with your vet to simply leave it be and monitor any changes. It has been shown that with correct physio exercising such as Hydrotherapy (swimming therapy) that the muscular area around the knee can be built up and with this type of regular exercise it is possible to avoid surgery. The same has been shown to be highly successful in humans, but the correct exercise participation in humans may be easier to action.

If this condition is left to its own devices at grade 1, then it will usually progress to a point where the listing grade is increased and as such it will then require surgery. Physio for muscle building at this point must be given serious work (pretty much daily) under physio to avoid surgery.

Hydrotherapy For An Australian Cattle Dog 1
Above is an Australian Cattle Dog having Hydrotherapy

Grade 2

If the condition is causing walking difficulty and/or much pain then it is rated as a Grade 2, 3, or 4.

Grade 2 is often the most common stage that anything wrong is first noticed by owners and will often appear during exercise or perhaps when the dog is washed or groomed.

Correct physio can even save a dog from surgery at grade 2 assuming that lifestyle changes for the dog are put in place, but agreement with your vet as to the comfort level of pain and the type of physio will need to be discussed.

Grade 3 and 4

Both these grades will require surgery, the measure and type of surgery required will be determined by;

  • The formation of the patellar ridges,
  • Whether the kneecap slips bilaterally or laterally,
  • How far and how often the slippage occurs,
  • Whether the patella can be held in place at all.

In Grade 3 the displacement of the patella is commonplace and although it can be manipulated back into place it is unlikely to stay there once the joint is moved.

Grade 4

In Grade 4 the patella cannot be put back into place or there may be no ridge or groove available to hold the patella in place. This is the most severe of cases and is rare unless it has been completely ignored by the owner or it is a major congenital condition (born with it).

Once surgery has been achieved you will still need physio and most likely some change of lifestyle for your dog which will likely involve a mix of physio, supplements (joint), and such things as ramps or steps for things like getting in and out of the car.

Treatment for Patellar Luxation in Dogs

Depending upon the Grade of the luxation here is an idea of what can be done, bear in mind that it may take a mixture of any of the following dependant upon the grade severity:-

  • Muscular physio to help build up the strength of the muscles and ligaments to enable the kneecap to remain where it should be.
  • Steroidal or collagen injections.
  • Supplements such as glucosamine, Vitamins C and E.

Surgery which may include:-

  • Sulcoplasty which is to deepen the femoral groove.
  • Tibial tubercle transposition, which means to move the point of attachment of the ligament on the tibia.
Vet Operating On A Knee
Vet operating on a knee
  • A Releasing of the Fascia – The Fascia are an integral part of the connective tissue that attach and stabilise muscles and ligaments.
  • A Tightening of the Fascia around the patella.
  • Femoral or tibial osteotomies – cutting or trimming of the leg bones and occasionally the addition of titanium pins.

Then post-operative care as the vet may see fit probably to include physio such as Hydrotherapy as in Grade 1, various supplements and anti-biotics to avoid infections.

Small Dog With Leg Injury
Recovery can take a while

Breeds that suffer Luxating Patella

This is often a condition that appears more commonly in small dog breeds such as Boston Terriers, Cavalier King Charles Spaniels and other similar sized Spaniels, Chihuahua, Dachshund or Doxie, Jack Russel’s, Miniature and Toy Poodles, Pomeranians, Pekingese, Papillons, Shiba Inus, Shih Tzus, West Highland Terriers, and Yorkshire Terriers to name but a few, I pick these breeds as they often have inherited or congenital traits.

West Highland Terrier Pup 1
This condition can be difficult to spot at the early stage on small dogs

Some of the larger dogs that have this as a common disorder are Akitas, Australian shepherds, Boxers, Golden Retrievers, Huskies, Labradors, Malamutes and St Bernard’s.

Symptoms of Luxating Patella

Your dog will appear lame (limp) at frequent intervals or all the time in severe cases. It is likely that the dog will continually look at the leg or lick the leg. Some dogs will refuse to walk altogether or at certain points on your daily walk until the kneecap pops back in to place.

Your dog will have trouble putting his hind leg to the floor or it will continually hold the leg up and will be hopping on 3 legs.

Your dog may sit in an unusual position.

Your dog may stand in an unusual way i.e. bow legged

Luxated Diagram Of Bowed
In a severe case when both knees are affected you can get a bow legged stance as shown above and below
Luxated Patellas With Bowed Legs

They may struggle to get up from a prone position to a standing position.

Your dog may not want to get up at all.

The foot may appear to be pointing at a strange angle and then suddenly appear to be ok.

They may not be able to bend the knee.

Whining, growling or baring teeth at you (this being out of character) when you attempt to examine the leg.

Ears and tail constantly down, these signs are often evident with many conditions but is an indication that something is wrong with them.

Your dog may be struggling with going to the toilet but again this would be an additional sign that there is a problem.

Luxating Patellar – The Conclusion

As clearly seen in the section what can the vet do for luxation? Early intervention is preferable, it’s also less costly and less stressful for both you and your dog.

This is not a condition to ignore and hope that it goes away, if you have any suspicions at all regarding this condition – Go see a Veterinarian.

So much pain and cost can be avoided if caught early. This may not be the case with older dogs but please do not ignore the problem if you think it may be there.

This is not a majorly common problem, but it is far better to spend five mins with the vet to be sure rather than months of pain, surgery and therapy.

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