Patella Luxations



        Patellar Luxation is an intermittent or permanent displacement (dislocation) of the patellar (kneecap) from the Trochlear Groove (groove in which the kneecap fits). Medial (towards the midline of the body) patellar luxations are common in small dogs and sometimes in cats. Lateral (away from the midline of the body) patellar luxations are more common in larger dogs than small dogs. Both medial and lateral patellar luxations are an inherited abnormality and commonly seen bilaterally (both legs).

    Most of the patients with a luxating patellar have associated musculoskeletal abnormalities including the displacement of the quadriceps muscle group, lateral torsion and bowing of the distal (furthest from the midline of the body) femur, rotational instability of the stifle joint or Tibial deformity. The severity of the patellar luxation is related to which deformities are present. These abnormalities cause abnormal pressure exerted on the growth plate of the tibia, alter the growth of bone and affect the growth of cartilage.

    A normal patellar fits snuggly into a deep Trochlear Groove. Abnormal development of the Trochlear Groove exists in pets with patellar luxations. A pet with Grade I (mild) Patellar Luxation may have a Trochlear Groove deep enough so the patellar doesn’t luxate often. However, a pet with Grade IV (severe) Patellar Luxation may have a shallow Trochlear Groove or no groove at all, causing the patellar to permanently luxate.

     A common sign of this condition is acute, short-lived, non-weight bearing lameness. The patellar usually luxates when the pets’ stifle (knee) is flexed, as seen when they are running or jumping. This is commonly combined with a yelp, and followed by holding the leg up flexed for a few minutes. The pet then gains the courage to straighten the leg and thus, pop the patellar back in place. Extremely athletic dogs may cause trauma to their knees by a fall or twisting injury, which can also encourage the patella’s to luxate. In these cases, the patella ligament is strained, stretched or torn, thus causing lameness.

    Pets with patellar luxations are at risk of promoting arthritis (osteoarthritis) and increasing the possibility of rupturing the cruciate ligament in their stifle joint. When the patella is in a luxated position, the cruciate ligament is the only ligament stabilizing the knee. If the pet stops short, or pivots quickly, this cruciate ligament absorbs all the velocity and can be partial torn or completely torn.  A pet with a completely torn ligament will not walk on that limb at all, because the knee is so unstable. Surgery is absolutely necessary to fix the problem, prevent pain and give the pet a limb that it can use. If the pet has a partially torn ligament, severe exercise restriction is recommended for a month. It is possible that the partially torn ligament can be secured by scar tissue to will form.


Patella Luxations



Patellar

Lateral Collateral Ligament

Cranial Cruciate Ligament

Lateral Meniscus

Femur

Caudal Cruiate Ligament

Medial Meniscus

Medial Collateral Ligament

Tibia

Fibula

Trochlear Groove

Trochlear Rim



Quadriceps

Femur

Osteophytes (Arthritis)

Eroding Articular Cartilage

Fibular Head

Lateral Meniscus

Fibula

Tibia

Patellar Ligament

Medial Meniscus

Patella

Quadriceps Tendon

Worn Trochlear Rim

    

    Physical examination and palpation of the stifle joint can determine luxating patellas and torn cruciate ligaments.  Radiographs may be necessary to visualize any other changes in the stifle, such as arthritis. Keep in mind that Radiographs will only show a patella luxation if the patella is luxated at the time of the Radiograph.

     The treatment of patellar luxation may be medical or surgical, depending on the clinical history, physical findings, and the pet’s age. Patella Luxations, as well as Hip Dysplasia, are graded on a scale from 1 to 4. Pets with a Grade I or II, usually do not require surgery. However, such pets should not be used as breeding stock, since this is hereditary. Pets with Grade III and Grade IV, which is considered severe, will almost always require surgery.  Surgery is recommended for most pets with mild to severe luxations, which are symptomatic or asymptomatic, immature or adult. If you expect your dog to be an athlete, surgery is absolutely necessary. If your pet is a house pet, and nothing athletic is expected of him or her, then a lifestyle change will be necessary to prevent running and jumping.

       In addition, pets with Grade I and Grade II patella luxations are often gone unnoticed by the lay person and the everyday dog owner. Even though the patellas are luxating at Grade I and II,  they may not cause any continual or noticeable limping or discomfort. Depending on which breed the pet is, will often determine if luxating patella(s) will eventually cause a problem. The heavier the breed, the more likely the pet will require surgery at some point during his/her life. Occasionally, the problem becomes more severe as the pet ages. This is caused by years of the patella moving back and forth over the Trochlear Rim (lip of the groove) and thus wearing it down so much that there is nothing holding the patella in place.  Therefore, Luxating Patellas of Grade I and II can result in a Grade III or IV, by the time the pet reaches between 7 and 12 years of age. For this reason, Grade I and II MPL (medial patellar luxations) are not recognized until the pet reaches middle age. However, some pets with a Grade I and Grade II Luxating Patella’s never require surgery, and can run “like a Greyhound” and remain asymptomatic and non-clinical.  

        Most veterinarian do not routinely checks the knees of their patients, unless alerted by the owner that there is a problem with limping, etc. There are also some veterinarians who do not know how to palpate for patella luxations, let alone be familiar enough with the grading system - in order to grade the luxation correctly. If you suspect that your pet has a luxating patella, it would be best to seek the opinion on a Board Certified Veterinary Surgeon. Although, I have come across a FEW very “CUT-HAPPY”  Board Certified Surgeons in my day, even those that come highly recommended, so you may need to seek two ‘unassociated’ boarded surgeons.

    There are surgical procedures available to correct a luxating patella. There are also numerous surgical techniques aimed at restraining the patellar within the Trochlear Groove. Generally, a combination of techniques is required and performed all at the same time. Some of the techniques which would be done to promote the success in securing a luxating patella include the following: Tibial Tuberosity, medial restraint release, lateral restraint reinforcement, Trochlear Groove deepening (Trochleaoplasty), Femoral Osteotomy and Tibial Osteotomy, Tibial Crest Transplantation and Wedge Resection.

         Patella Luxations are very common in most small breeds of dog, not just the Pekingese. Patella Luxation is very commonly seen in the Miniature Poodle, Shih Tzu, Cavalier King Charles Spaniel, Cocker Spaniel,  Japanese Chin, Shiba Inu, Chihuahua, Maltese, Yorkshire Terrier, Pomeranian, Pug, Boston Terrier, and the Bichon Frise. Some larger breed dogs have been known to have laterally luxating patellas (LPL), which posses the same characteristics of an MPL.


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Patella Luxations