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' Luxating Patella '

Dislocating kneecaps or luxating patella can be inherited, or acquired through trauma.  It occurs in Toy Breed dogs mainly but also can be found in larger breeds. 

In dogs the patella is a small bone which protects the front of the stifle joint (like our kneecap).  It is anchored in place by ligaments, and slides in a groove in the femur.   The Trochlear groove is not deep enough to keep the patella in place.  If this groove is not deep enough, the patella can "fall out" of it, causing the luxation.  

There are 4 grades of Patella Luxation, those being:

GRADE 1  The knee is nearly normal and the patella can only be dislocated if the knee is expanded and digital pressure applied (in other words pushed off the joint).  
GRADE 2 The patella can be dislocated in extension and remains out of place when the knee is flexed and can be returned by manual pressure.  Dogs with this grade can be subject to a disease of the joint cartilage and secondary osteo-arthritis due to the rubbing effect as the patella constantly dislocates.  
GRADE 3 The patella is dislocated most of the time.  It can manually be put back into place when the leg is extended, but it flips out easily again.   Dogs with this degree can also be a high risk of rupture of the anterior cruciate ligament in the stifle (knee joint).  
GRADE 4 The patella is dislocated all of the time and cannot be put back into place. The dog affected by this grade exhibits lameness and an inability to walk and needs surgical intervention.  

Cavaliers with Grade 3 and 4 usually require surgery.


Normal V's Abnormal Patella


The red arrow is showing the trochlear groove.  This is where the patella normally "rides".  This femur would be described as having a deep groove, which has plenty of space to keep the patella where it belongs.



The red arrow is pointing again to the trochlear groove. Notice how shallow it looks.  There is not much space for the patella, and would be quite easy for the patella to slip out or luxate.


This picture shows a normal trochlear groove with the patella.  Notice how the patella fits in securely and is unlikely to fall out or luxate.


This picture shows an abnormal or shallow trochlear groove.  The patella has no groove to fit into and can easily slip out  to either side (see red arrows).


Clinical Signs of Luxating Patella

Clinical signs depend on the Grade of the luxation, how long the dog has been affected and whether the dog has any additional health problems.

Signs May Include:

* Mild intermittent rear leg lameness

* Inability to fully bend rear leg

* Hopping or skipping

* Kicking leg out behind dog

* Bowlegged or crouched position

* Reluctance to jump


Treatment and Prognosis

Surgery is most often required if the dog has a severe grade of patella luxation (some grade 3's and all grade 4's). Occasionally if the dog is overweight , placing the dog on a diet will ease the side effects as there is less strain on the legs. The goal is to correct the bone defects that predispose the patella to luxating.

The surgical technique is called Trochleoplasty.  This surgical operation deepens the trochlear groove, making it deeper so he patella is less likely to slip out or luxate.

Another surgical technique veterinarians use is called Tibial Tubercle Transposition. This procedure is used when the femur and tibia bones dont line up quite right, which can lead to the luxation of the patella.  A piece of bone is cut from the tibia and moved, which helps to straighten the muscles around the knee. 

The prognosis for dogs with surgical treatment is good to excellent.  There is a 90-95% success rate, if the problem is detected and treated early.



How Am I Supposed To Live Without You - Michael Bolten

© Braydnvale Cavaliers 2004