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Q:  My 5 1/2 year old Yorkie was recently diagnosed with a luxating patella after falling down a flight of stairs.  He was given anti-inflammatory medication which he took for 2 weeks and is now on Glucosamine.  Although he seems to be getting better, I still notice that he would occasionally lift the injured leg when walking.  He does not appear to be in any pain.  He has a follow-up visit in a month to see if things have gotten better however if he does not, my vet suggest that he sees a orthopedic veterinarian.  I’d like to know if anyone has had the same problem and if they opted for surgery.


A.   The patella, or knee cap, is a small bone burred in the tendon of the muscles that extend the knee joint. The knee cap normally rides in a groove at the end of the thigh bone (femur) at the knee joint.  Above the patella, the quadriceps muscles attach to the pelvis.  Below the patella, the patellar tendon attaches to the tibial crest, a bony prominence just below the knee.  The quadriceps muscle, the patella and its tendon form the “extensor mechanism” and are normally well-aligned with each other.  Patellar luxation is a condition where the knee cap rides outside the femoral groove when the knee joint is flexed.  It can be further characterized as medial or lateral, depending on whether the knee cap rides on the inner or on the outer aspect of the knee joint.

Patellar luxation is one of the most common congenital anomalies in dogs, diagnosed in about 7% of puppies and is now thought to be a component/consequence of a more complex congenital condition that affects the overall alignment of the hind leg .  The condition affects primarily small dogs, especially breeds such as Boston terrier, Chihuahua, Pomeranian, miniature poodle and Yorkshire terrier.  The incidence in large breed dogs has been on the rise over the past 10-15 years, and breeds such as Chinese shar pei, flat-coated retriever, Akita and Great Pyrenees are now considered predisposed to this disease.  Patellar luxation affects both knees in 50% of all cases, resulting in discomfort and loss of function.

Clinical signs associated with patellar luxation vary greatly with the severity of the disease: this condition may be an incidental finding detected by your veterinarian on a routine physical examination or may cause your pet to carry the affected limb up all the time.  Most dogs affected by this disease will suddenly carry the limb up for a few steps, and may be seen shaking or extending the leg prior to regaining its full use.  As the disease progresses in duration and severity, this lameness becomes more frequent and may even become continuous. In young puppies with severe medial patellar luxation, the rear legs often present a “bow-legged” appearance that worsens with growth.  Large breed dogs with lateral patellar luxation may have a “knocked-in knee” appearance.

Patellar luxation, as in your pets case, occasionally results from a traumatic injury to the knee, causing sudden non-weight-bearing lameness of the limb.  The lameness associated with a traumatic patellar luxation may initially respond to rest and anti-inflamatory therapy to some degree.

The diagnosis of patellar luxation is essentially based on palpation of an unstable knee cap on orthopedic examination and the severity of the luxation can be graded on a scale of 0 to 4.  Additional tests, such as palpation of the knee under sedation, radiographs of the knees and pelvis, and occasionally CT scan of the hind limbs, may be needed to help diagnose conditions often associated with patellar luxation and to help the surgeon recommend the most appropriate treatment for your pet.   Patellar luxations that do not cause any clinical sign should be monitored but do not typically warrant surgical correction, especially in small dogs.  Surgery is considered in grades 2 and over.  Surgical treatment of patellar luxation is more difficult in large breed dogs, especially when combined with other associated orthopedic conditions.

One or several of the following surgical strategies may be required to correct patellar luxation:

  • Reconstruction of soft tissues surrounding the knee cap to loosen the side toward which the patella is riding and tighten the opposite side.
  • Deepening of the femoral groove.
  • Moving  the bony prominence where the patellar tendon attaches below the knee.
  • Correction of abnormally shaped thigh bones (femurs).

The procedures that will best address the problem are selected on an individual basis by the surgeon that has examined the patient.

Studies have shown that over 90% of pet owners are satisfied by the results of surgical treatment for patellar luxation.  As alluded to earlier, the prognosis is less favorable in large dogs, especially in individuals where patellar luxation is combined with other orthopedic abnormalities.

Remember, you should seek veterinary advice if you have any concern about the gait of your pet.  Your primary veterinarian may wish to refer you to a surgeon specializing in orthopedic disease for treatment of patellar luxation if it requires surgery.

[doctor name = <Arthur A. Fettig>]