As discussed in our previous article, if your furry friend is a large breed dog having trouble in walking or running, it might be suffering from canine hip dysplasia. But if your furry friend is a small breed dog, it might suffer from a joint problem like patellar luxation. 

Like hip dysplasia, patellar luxation is a hereditary joint disease.  It is especially common in small and toy dog breeds including Miniature or Toy Poodles, Yorkshire Terriers, Chihuahuas, Pomeranians and Pekingese.  It can also be found in large breed dogs but small dog breeds are 10 – 12 times more likely to be affected than giant dog breeds.  Furthermore, females are 1.5 times more likely than males to suffer this condition where kneecap is permanently or temporarily dislocated.

There are two general types of patellar luxation: medial patellar luxation normally found in small dog breeds, and lateral patellar luxation commonly seen in large dog breeds. In both types, patellar luxation occurs when there is a shallow trochlear groove and abnormal conformation of the femur due to uneven forces of the quadriceps muscles. In such situation, the patella (or kneecap) cannot stay in its track and slipped, which in turn causes kneecap dislocation, torsion of the tibia, and anterior cruciate ligament disruption or tearing.

In terms of diagnosis, veterinarian can generally determine how severe the patellar luxation by palpating the knee joint.  The severity can occur within four levels, with each level displaying similar or unique symptoms:

Grade 1
No clinical signs seen.  External force can cause the kneecap pops out of place intermittently and the kneecap can then be easily put back into place when the external force disappears.

Grade 2
The kneecap will dislocate when the leg is bended or external force is applied on the area.  The kneecap can then be put back into place when the leg is extended or external force disappears.

Grade 3
The dislocated kneecap cannot reset itself.  One must apply force to massage the kneecap back into its trochlear groove, but the kneecap will pop back out again easily once the external force disappears.

Grade 4
The dislocated kneecap cannot reset itself and will not stay in its trochlear groove even when external force is applied.

Different treatments are used depending on the severity level of patellar luxation.  While some furry friends do fine with minimal treatment, some furry friends may require surgery.  You should consult your veterinarian for more details if you believe that your dog suffers from any sign or symptoms of canine hip dysplasia.