Patellar Luxation (Dislocated Knee)

Nancy McDonald RN, BSN, (retired)


The most common orthopedic problem found in the Bichon Frise is patellar luxation, which can lead to rupture of the cruciate ligament.  Occasionally Bichons suffer hip dysplasia, but this condition occurs more often in large breeds, while patellar luxation is more common in small breeds, as is Legg-Calve-Perthes Disease.

The patella is the kneecap, part of the structure of the stifle (knee) joint. It is a small bone located within the tendon of the extensor muscles (the quadriceps muscles) of the thigh and normally rides in a groove within the femur in the knee.  When the kneecap (patella) rides outside the femoral groove in a flexed leg, it is considered luxating and the knee cannot extend properly and stays bent.  In about half of all cases, patellar luxation affects both knees, potentially resulting in discomfort and loss of function.

One cause of luxating patella is an injury to the knee when a dog may step in a hole or get its leg caught.  This injury may include a rupture of the anterior cruciate ligament.  In the absence of trauma, patellar luxation results from a congenital or developmental misalignment of the entire extensor mechanism.  Because this condition is at least part genetic, a dog diagnosed with patellar luxation should not be bred

Symptoms of patellar luxation very according to the severity of the disease.  Most dogs affected by this disease will occasionally carry the affected leg up for a few steps looking as if the dog is skipping or trying to extend or shake the leg before using it again.  With the knee cap out of place, stress on the rear leg is altered and, in time, changes occur in the hips and long bones in addition to arthritis development.

The diagnosis is made by a veterinarian’s orthopedic examination of the knee.  Additional tests such as palpating the knee under sedation, X-rays of surrounding structures, CT or CAT Scan, may be needed for the surgeon to evaluate the correct treatment.  Medial patellar luxations are graded to assess severity:

Grade 1: The kneecap can be moved out of place but it returns easily to its normal position.  No surgery is required.

Grade 2: When the kneecap is moved, the kneecap does not move back to its normal position without the dog extending its leg.  The dog may develop arthritis but there is controversy whether grade 2 dogs should have surgery.

Grade 3: The patella is out of place all the time. It can be manipulated back into place but doesn’t stay in place.  This dog is a candidate for surgery.

Grade 4: The patella is out all the time and cannot be manipulated back into place.  The dog has extreme difficulty extending his knees and walks with its knees bent all the time.  The dog needs surgery.

Surgical treatment strategies will be determined by the surgeon depending of the cause of the disease and experience of the surgeon.  If you have any questions, you can always seek a second opinion.  Depending on the surgery, recovery may take as little as 3 to 4 weeks but in most cases, it takes 6 to 8 weeks and may include physical therapy.  The post-op dog should avoid running, jumping and active play during recovery and should be crated when not under close supervision.  Limit outside time to the few minutes necessary to relieve himself keeping him on a leash.  He should be carried up and down stairs.  Watch for signs of infection and keep the bandage dry.  If he wants to chew the bandage, check for problems and consider using an Elizabethan collar or restrict his ability to reach the knee bandage by securing a folded hand towel around his neck.  This “thick collar” will allow him to move around without the weight of an Elizabethan collar but he will not be able to get his mouth on the surgical area.

Repetitive dislocation of the patella will only worsen the condition and arthritis may occur.  Surgery should not be dangerous for an otherwise healthy dog and permanent repair means an active life for your pet for years to come.  Keeping weight down to a normal level on any dog with signs of patellar luxation may enable to avoid damage in the first place and makes for faster healing if he does need surgery.

This article was referenced from: