poodle running on grass

Luxating Patella in Dogs

LAST UPDATED 19 JULY 2022

This article is written by Pet Circle's qualified veterinarians, Dr Hannah Vickery and Dr Gillian Hill

Has your dog been diagnosed with luxating patellas, or 'floating kneecaps'? Or perhaps you are a prospective puppy owner researching your favourite dog breed, but have discovered they are a breed prone to luxating patellas? Our handy guide should provide you with everything you need to know about patellar luxation in dogs.

Contents:

What is a luxating patella?

What causes luxating patellas?

Symptoms of luxating patellas

Diagnosis of luxating patellas

Treatment of luxating patellas

What is a Luxating Patella?

Source: PDSA

A luxating patella is a knee cap which dislocates, or 'luxates' - it pops sideways, out of place from the groove in the bottom of the femur bone that it normally sits in. It can occur medially (moves to the midline of the body or towards the other leg - which is the most common) or laterally (moves towards the outside/away from the other leg).

Grades of Luxating Patella

Luxating patellas are graded depending on severity:

While the luxation itself is not painful, the sliding of the patella in and out of the groove damages the lubricating cartilage and flattens the groove which can lead to osteoarthritis, or arthritis, reduced mobility and limb changes.

What Causes Luxating Patellas in dogs?

Luxating patellas are usually a developmental disease with the onset occurring during growth.

Risk factors for the development of luxating patellas include:
  • Mal-alignment of the quadriceps muscle - the quadriceps tendon attaches to the patella and can pull it out of it's proper alignment.
  • Bowing of the bottom part of the femur.
  • Deformity of the tibia.
  • Mal-alignment of the hip joint, often from hip dysplasia, which can cause the line of force of the quadriceps muscle to shift.
  • Trauma to the bone or soft tissues of the back leg, or contraction of muscles caused by nerve changes.
  • Instability of the knee joint, such as from previous surgery or injury to the cranial cruciate ligament.

Which Breeds are Prone to Luxating Patellas?

Luxating patellas can occur in both sexes in any breed of dog (and cat), but mostly occurs in toy and miniature breeds. Large breeds, such as Newfoundlands, have a higher percentage of lateral patella luxations compared to small breed dogs.

Patellar luxation has been shown to be heritable in toy spaniels and toy and miniature poodles.

Signs of Luxating Patellas

The signs and symptoms of luxating patellas will vary depending on the grade of luxation.

In grade 1 luxations, there are generally no noticeable symptoms, and the diagnosis is made as an incidental finding on physical examination.

Symptoms associated with a grade 2 luxation are usually occasional skipping in the affected back leg. The dog will flex the limb and hold it up for a few steps and then walk normally again. Occasionally, the tissues around the knee joint will become stretched and lead to lameness where the dog will not bear weight on the affected leg.

Over time, a grade 2 luxation can progess to a grade 3 luxation through the flattening of the groove, and can also lead to arthritis in the joint.

With grade 3 and 4 luxations, the symptoms tend to be more constant. These include:

  • Constant limp in the affected leg or legs.
  • Walking in a crouched or slanted position in the back legs
  • An unusual shape or angle to their hind legs
  • Reluctance to jump

More severe luxations will lead to arthritis in the knee joint. The common symptoms of arthritis are:

  • Lameness or limping which worsens after strenuous exercise
  • Appearing to have stiff joints, especially after rest
  • Slow to rise from sitting or lying
  • Reluctance to use stairs or jump into the car
  • Avoiding sitting or lying on hard surfaces
  • Loss of muscle mass in the rear legs

Diagnosis of Luxating Patellas

dog at vets

The diagnosis of patellar luxation is usually made on the basis of the symptoms and physical examination. Xrays are usually performed if surgery is planned as they can pick up other associated disorders such as cranial cruciate ligament tears and concurrent osteoarthritis

Treatment of Luxating Patellas

The treatment for patellar luxation will once again depend on the grade of the luxation.

Grade 1 luxations are managed conservatively with medical management. Grade 2 luxations may be treated medically, or surgery may be warranted based on the frequency of luxation and/or the level of lameness, or to prevent the condition progressing to higher grades. Grade 3 and 4 lucations should be treated surgically.

Medical Management

Medical management for patellar luxation is aimed at delaying the onset, or severity, of arthritis in the joint.

Joint Supplements

There are a number of natural extracts and herbal products with proven anti-inflammatory properties. Some are antioxidants, which slow the actual progression of arthritis, while others intercept the inflammatory cascade to limit pain and inflammation.

Green Lipped Mussel (Perna canaliculus): Green Lipped Mussel for dogs contains key omega-3 polyunsaturated fatty acids, glycosaminoglycans (a source of chondroitin), vitamins and minerals which have been shown to have beneficial anti-inflammatory effects in dogs with arthritis. Similar to other joint supplements, it may take several weeks to notice visible effects, however it has been shown to play a role in reducing inflammation and pain in the joints.

Glucosamine and Chondroitin: Glucosamine for dogs and Chondroitin are the building blocks of normal healthy cartilage. Despite a lack of strong evidence in the veterinary literature, some veterinarians and owners have found supplementation to be helpful. With minimal side effects compared to some of the common pain relief medications, they are a good option for mild cases and to use alongside other therapies.

Omega Fatty Acids: Omega 3 fatty acids DHA and EPA have been demonstrated to have anti inflammatory properties, and as far as supplements for arthritis go, they are backed by the most convincing evidence. Omega 3's can be obtained from lots of difference sources including fish oil, green lipped mussel powder, flaxseeds and nuts. Marine sources of omega fatty acids (such as fish, fish oil and green lipped mussel) are the most effective for dogs.

Shop All Dog Joint Supplements

Pain relief

Your veterinarian will determine the most appropriate pain relief regime for your dog. In some cases, multiple medications may be recommended to achieve the best results. Some forms of pain relief aren't suitable for some dogs due to concurrent health issues, so every case is assessed on an individual basis.

Chondroprotective / Disease-Modifying Drugs

Your vet may also prescribe a course of injections to help manage arthritis. The brand name of these injections can vary (Zydax, Cartrophen, Pentosan), however the the active ingredient, Pentosan Polysulfate, is the same. Pentosan polysulfate is of plant origin and acts within the joint to preserve joint health and provide pain relief. It is usually given as a series of injections, one injection per week for 4-6 weeks, followed by a booster injection at a time frame specificed by your vet.

Weight Control

Weight control is the single most important strategy in the management of arthritis in dogs. Extra weight results in increased stress on the joints and also makes dogs less likely to move around. Fat cells also release inflammatory mediators which can contribute to inflammation and pain in the body.

Just like for humans, weight control relies on diet and exercise. There are numerous low-calorie diets available in both wet and dry varieties - and even special diets with joint care ingredients.

Shop All Dog Weight Control and Mobility Diets

Natural Remedies for Luxating Patellas

When it comes to exercise, balance is key. It is important to not overdo it and cause excessive luxation of the patella, which can lead to discomfort and accelerated cartilage destruction. Low impact exercise options such as swimming or hydrotherapy can be great for dogs with luxating patellas or those that suffer from arthritis.

Environmental enrichment is a great way to get your dog moving without overstressing the joints and provides them with important emotional enrichment also.There is a range of interactive dog toys and puzzle feeding toys available to encourage activity and keep your dog entertained.

Surgical Treatment for Luxating Patellas

Surgery is indicated for grade 3 and 4 luxating patellas, and also grade 2 depending on the dog's age, clinical signs and likelihood of the luxation progression to higher grades.

A number of different techniques have been developed with the aim to secure the patella within the trochlear groove. Usually, a number of different techniques are used for best results.

Trochlear Resection - in this technique, the trochlear groove which the patella should sit within, is deepened, to help prevent the patella from slipping out.

Lateral Reinforcement - for medially luxating patellas, the tissues on the outside, or lateral side, of the knee joint are reinforced in a number of different ways, to help pull the patella laterally and help it to remain in the groove.

Tibial Crest Transposition - the top of the tibial bone where the quadriceps muscle attaches is removed and replaced in order to realign the mechanical forces of the quadriceps muscle.

Ridgestop Implant - this is a new technique which involves the addition of an implant to the inside edge of the trochlear groove, to prevent the patella from slipping out.

Most dogs make an excellent recovery and return to normal limb function following surgery. However, if there are other concurrent abnormalities, such as limb deformities, hip dysplasia or cruciate ligament injury, the prognosis may not be as good.

Further Reading

Want to know more? Check out some of our other articles:

Arthritis in dogs: what causes it and how do I know if my dog is affected?

Obesity in pets: why it's a problem and what to do about it

How the right diet can make old dogs young again

Boredom busters for dogs

Your guide to fleas, ticks and worms

References:

Brooks, W., Veterinary Partner, accessed 12 July, 2022, Medial Luxating Patella in Dogs, https://veterinarypartner.vin.com/default.aspx?pid=19239&id=4952566.

Fossum, T.W., (2002), Small Animal Surgery, 2nd Ed., Mosby, Inc.