Luxatio patellaLuxatio patella

LUXATIO PATELLA CASE REPORTLUXATIO PATELLA CASE REPORT

A 2 year old FS miniature A 2 year old FS miniature poodle, weighing 3kg (body poodle, weighing 3kg (body type 5) presented to the type 5) presented to the hospital for a progressive hospital for a progressive history of hopping on one history of hopping on one leg. The owners describe leg. The owners describe their dog running & their dog running & periodically skipping/hopping periodically skipping/hopping on the right hindleg and then on the right hindleg and then going back to normal. They going back to normal. They describe that it happens describe that it happens about 10-20 times a day. about 10-20 times a day. The dog is otherwise fine, The dog is otherwise fine, non-painful and willing to non-painful and willing to exercise normally. exercise normally.

PathophysiologyPathophysiology

Patella luxations may be congenital or Patella luxations may be congenital or developmental, and there may be a developmental, and there may be a genetic component.  This may explain genetic component.  This may explain why we see them in the same breeds why we see them in the same breeds over and over again.  The cause of over and over again.  The cause of patella luxations is related to the patella luxations is related to the complex function of the hip joint, complex function of the hip joint, femur, patella, stifle joint and tibia.  femur, patella, stifle joint and tibia.  Some conformations that have been Some conformations that have been incriminated are coxa vara or coxa incriminated are coxa vara or coxa valga, and femoral and tibial valga, and femoral and tibial deformities.  These conformations can deformities.  These conformations can cause a shift of the patella out of the cause a shift of the patella out of the trochlear groove of the femur due to a trochlear groove of the femur due to a shift of the weight-bearing forces over shift of the weight-bearing forces over the patella.  There is wearing of the the patella.  There is wearing of the trochlear ridge and flattening of the trochlear ridge and flattening of the groove, which leads to abnormal groove, which leads to abnormal articular cartilage in the groove.  articular cartilage in the groove. 

Patella luxations have four classifications.  Patella luxations have four classifications.  Clinically, the amount of lameness Clinically, the amount of lameness associated with this condition is variable.  associated with this condition is variable.  Some dogs will have patella luxations their Some dogs will have patella luxations their entire lives with no clinical symptoms.  entire lives with no clinical symptoms.  Others will suddenly become more Others will suddenly become more symptomatic after a period of soundness.  symptomatic after a period of soundness.  Animals with grade 4 luxations are often Animals with grade 4 luxations are often severely affected and have severe skeletal severely affected and have severe skeletal deformities as well. deformities as well.

Grade 1 Grade 1 The patella is in the groove normally and The patella is in the groove normally and can be manually luxated.  It returns to the can be manually luxated.  It returns to the groove spontaneously when released. groove spontaneously when released.

Grade 2Grade 2Mild anatomic changes are present.  The Mild anatomic changes are present.  The patella is in the groove more than it is out, patella is in the groove more than it is out, but can be manually luxated and will luxate but can be manually luxated and will luxate spontaneously.  The patella will remain spontaneously.  The patella will remain luxated until relocated manually or by luxated until relocated manually or by extension and derotation of the joint. extension and derotation of the joint.

Grade 3Grade 3Mild to moderate anatomic changes are Mild to moderate anatomic changes are present.  The patella is out of the groove present.  The patella is out of the groove more than it is in.  It will luxate more than it is in.  It will luxate spontaneously, can be manually reduced, spontaneously, can be manually reduced, but will luxate upon release.  but will luxate upon release. 

Grade 4Grade 4Moderate to severe anatomic changes are Moderate to severe anatomic changes are present. The patella is out of the groove all present. The patella is out of the groove all the time and cannot be manually the time and cannot be manually replaced. Surgical intervention is required replaced. Surgical intervention is required for reduction. for reduction. Click here to open a picture of the stance of Click here to open a picture of the stance of a dog with bilateral grade 4 luxation. a dog with bilateral grade 4 luxation.

RadiographsRadiographsThese radiographs illustrate a grade 4 These radiographs illustrate a grade 4 patellar luxation.  Note the position of patellar luxation.  Note the position of the patella, the rotation of the femur, the patella, the rotation of the femur, and the deformity of the tibia on the and the deformity of the tibia on the cranial-caudal view.  On the lateral cranial-caudal view.  On the lateral view, note the position of the patella.  view, note the position of the patella. 

Trochleoplasties can be done one of four ways.

Abrasion trochleoplasty involves rongeuring or rasping the articular surface of the groove down to subchondral bone. This will fill in with fibrocartilage and remain deep as long as the patella rides in the groove.

The patellar groove is deepened with a rasp. The end result is a more stable patellar groove.

A wedge recession trochleoplasty involves cutting and removing a V-shaped wedge out of the groove. The resulting groove is enlarged, and the removed wedge is replaced into the groove. This retains the original hyaline cartilage in the groove and is particularly good in young animals.

A hobby saw is used to remove a wedge-shaped portion of the patellar groove.

The groove is widened by removing an additional piece.

The original wedge is replaced in the groove, recessed from its original position.0

Trochleoplasties, continued:

Other options include trochlear chondroplasty, which involves elevating the hyaline cartilage flap with no bone, rongeuring the underlying bone and then replacing the cartilage flap in this deepened groove. This only works in dogs younger than 10 months, because their cartilage is thicker and more pliable than older dogs. Block trochleoplasty (seen below) is virtually identical to a wedge recession, except the removed piece is rectangular instead of wedge-shaped, and some surgeons feel it provides a deeper recess and greater stability.

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