Patellar luxation in dogsPatellar luxation (dislocation of the kneecap) is a young dog's problem. It manifests itself in a very typical gait change in which the corresponding hind leg is completely unloaded for one or more steps. In between the dog runs normally. The problem is clearly influenced by heredity, which is why patellar luxation can mean breeding exclusion for certain dog breeds.
What is the patella?
The patella is the kneecap. Four bones are involved in the knee joint: The thigh bone (femur). The shinbone (tibia) share the main load. The fibula is very thin in dogs compared to humans. Can be practically neglected.
According to common derivation, the patella (knee cap) is actually a reinforcement of the tendon that connects the knee extensor (large thigh muscle) to the lower leg. The patella protects this tendon during flexion. Stretching the knee joint from too much wear and tear. Such bones as the kneecap are called sesamoid bones.
However, recent research results now indicate that the patella was a bony process of the thigh (an apophysis) in genetically ancient animals. There muscles set. Apparently it came then in the course of the development over millions of years to the solution of this extension, because a faster locomotion became necessary.
How does the knee joint of a dog work?
A total of 13 ligaments are involved in the dog's knee joint function. The most important are the straight patellar ligament (from the patella to the tibia), the two collateral ligaments, and the two cruciate ligaments, which connect the femur and tibia in a cross and prevent them from moving each other forward or backward.
The meniscus performs an important buffer function. It is a kind of cushion between the femur and the tibia and guides the bones during movement. Finally, all the muscles that surround the knee joint are jointly responsible for proper function. In particular, the big knee-stretcher (M. quadriceps) has a great influence on the good guidance of the patella in the groove on the lower thigh.
Dog knee joint from the side, patella as reinforcement of the tendon of the knee extensor.
Normal dog knee, patella is held in position by cartilaginous lateral wings.
How does a patellar luxation develop in a dog?? It is clear: In a luxation, the patella moves out of the guide groove in the lower part of the thigh. Lies outside (inside or outside) of its important joint function. As a result, the joint capsule tears. The extension mechanism of the joint is disturbed. The dogs are in pain. Losing quality of life.
Still unclear, but well on the way to discovery, is why dislocation occurs in the first place.
A 2021 study shows that dogs with a wide stance of the hind legs, such as bulldogs, rotate more in the knee joint than dogs with a narrow stance.
While in the standing phase of a hind leg, the lower leg is virtually fixed, the upper leg rotates outwards.
The patella can only partially participate in this movement because it is attached to the lower leg by the ligament and therefore dislocates outwards.
The study and the current status of the results can be viewed here. It is still under development, but already opens new horizons concerning the origin and could show the way to breeding.
Which dog breeds suffer from patellar luxation most often?
Patellar luxation occurs mainly in small dog breeds in the first year of life. These include Maltese, Yorkshire Terrier, Pinscher, Bulldog, Bolonka, Poodle, Shih Tzu, Chihuahua, Boston Terrier and many more. The trend towards miniaturization promotes the occurrence of luxation. Inheritance of this health problem has been proven in two breeds with 25% to 30%. Most luxations go inward (medial). An outward (lateral) dislocation is rarely encountered.
Large breeds with a tendency to medial luxation are: Appenzeller Mountain Dogs, Flat Coated Retrievers and Newfoundlands.
How do I recognize a patellar luxation in my dog?? The typical symptom of a patellar dislocation is a bouncing gait with normal weight bearing on all legs at times. Temporary complete relief of the corresponding hind leg. It is called intermittent lameness. This bouncing gait is not always painful. Is sometimes considered a "playful variation" when walking. But be careful: when lifting the leg, the knee biomechanics are permanently disturbed and there is a risk of consequential damage!
Video: Gait pattern of a dog with a patellar luxation
In many dog breeds this study, resp. the finding "no luxation" (respectively maximum "luxation grade 1") is a prerequisite for breeding permission. Dogs with dislocation grades from 2 to 4 usually limp badly. Usually have to be treated surgically.
Dogs with a dislocation grade 1 or 2 can often be treated with physical therapy so that the patella stays in place through directed muscle traction. The formation of arthrosis is usually small, but if the patellar luxation is left untreated for years, the cartilage between the patella and the thigh is worn away, which cannot be rebuilt even after surgery.
Patellar luxation – grade 1
Grade 1 means that the patella spontaneously goes back to its normal position, causing little lameness.
Patellar luxation – grade 2 – 3
The differences between grade 2 and 3 are fluid and sometimes difficult to distinguish. In both, the patella is often not in the groove, which is why these dogs cannot transmit the force and relieve the leg.
Patellar luxation – grade 4
at grade 4 the patella can no longer be displaced from the luxation position, which is sometimes overlooked, because the dogs walk quite stable for a few months to years before massive arthrosis sets in.
What are the treatment methods?
The best therapies are those that surgically restore the correct relative position of the patella and femur. This means that the attachment of the straight patellar ligament is loosened with a piece of lower leg bone and moved either outward or inward, so that the patella again sits correctly over the groove in the thigh. The sawed-off piece of the lower leg is stably fixed with a so-called tension belt (two metal pins, wire).
In addition, the guide groove of the patella on the thigh is deepened using a wedge or block technique. This makes it less easy for the patella to pop out of the groove. Soft tie restraints are used to secure the bone sections.
The prognosis is very good. Sometimes migrating nails have to be pulled later on.
Since 2021, it has been possible to replace the traction belt made of metal pins and a wire with an impact plate (Swiss Patella Plate, SPP®). This has the advantage that it is hardly necessary to remove the metal pins. The first series of this new technique is very promising, the dogs load early and it could one day replace the previous technique.
Figure left: Patellar Groove on the model (© Kyon AG, Zurich), Figure right: X-ray image of terrier with Patellar Groove half prosthesis .
At what age is patellar luxation ideally operated on??
Dogs can be vaccinated approx. be operated on from the sixth month of life onwards. In the case of high-grade dislocations, an earlier operation is possible, in which case the groove is deepened by means of cartilage elevation and bone marrow curettage. If both knees are affected in a dog, the operations are performed separately and at least six weeks apart.
What is the prognosis for patellar luxation surgery??
Patellar dislocation surgeries are generally associated with a good prognosis. Osteoarthritis formation is low, even when the operation is performed on the adult dog. Complications are usually caused by the metal pins moving or the skin rubbing over their ends. Then removal is indicated. The smaller the dogs, the more likely implant removal will be recommended.
X-rays of the knee joint of an Appenzeller man after correction of a patellar luxation 3. Grades.
The recovery period after surgery lasts four to six weeks. Usually a bandage is applied for a few days and painkillers and cartilage protection preparations are administered. Physiotherapy is highly recommended. After removing the hemisphere, swimming training is also advised.
Four to six weeks after the operation, a control X-ray is taken to check the fit of the implants and to counteract possible complications at an early stage.
With the new SPP® method, there are hardly any implant removals.
How can I prevent patellar luxation in my dog??
A prevention is practically not possible. There are no known influencing factors that would prevent patellar luxation in puppyhood. Targeted muscle training can stabilize the patella, but the effect is not permanent. As already mentioned, patellar luxation is genetically transmitted. Therefore exists only in a certain number of dog breeds. Therefore, the only effective measure against patellar luxation can only be responsible breeding with patellar luxation-free dogs.
It must be consistently observed that a serious evaluation and registration is carried out by a licensed veterinarian. So when buying a dog, inform yourself among other things about any patellar luxation problems of the parent animals.
Common misconceptions
– Unfortunately, the "funny bounce" is very often misinterpreted by dog owners. But it is a serious knee problem – By the way: In Jack Russell Terriers it can sometimes be difficult to correctly diagnose patellar luxation, because luxation is difficult to trigger – Furthermore, every veterinarian should check not only the luxation inwards, but also outwards – In Shelties, the patellar luxation-typical gait is often the result of a jumping tendon over the heel bone and has nothing to do with the knee
Conclusion
Patellar luxation is a common problem in small dogs. If the breeding efforts were consistently implemented, we would already encounter fewer patellar luxations today. The treatment of patellar luxation is mostly surgical and has a good prognosis, even more so if it is detected and treated at an early stage.
Further links:
– Professional article: The dog in growth – Guidebook: Nutrition& Exercise for the growing dog – professional article: The cruciate ligament rupture in dogs
This post was written by Dr. med. vet. ECVS Daniel Koch, Daniel Koch Small Animal Surgery AG. Updated March 2021.