Patellar Luxation in Cats – Causes, Symptoms & Treatment

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What is patellar luxation?   What causes it?   Symptoms of patellar luxation   How is it diagnosed?   How is it treated?

What is patellar luxation?

Patellar luxation (meaning out of place) is a condition in which the kneecap (patellar) moves (or dislocates) out of the trochlear groove, and moves to the inside (medial) or outside (lateral) of the knee joint (known as the stifle joint in cats). Medial luxation is more common than lateral. Unresolved patellar luxation can lead to arthritis.

Luxating patellar in cats

The patellar is what most of us know as the knee bone, it is a small circular bone which sits in front of the knee joint, which consists of the femur in the upper leg and the tibia and fibula in the lower leg. It sits in a vertical groove at the lower end of the femur known as the trochlear groove.

As the hind leg moves, the patellar slides up and down the groove. Buried by the patellar tendon, a strong, flat tendon that attaches from the bottom of the quadriceps muscle of the thigh, over the patellar and attaches to the tibial crest, a bony prominence on the shin bone in the lower leg.

The patellar is a sesamoid bone, the function of which is to act like a pulley, by allowing the tendon to sit further away from the joint, which helps increase movement and strength as the joint straightens and bends. The patellar also helps to protect the knee joint and keep the tendon in place.

The condition can occur in cats of all ages and breeds, although there appears to be a higher incidence in Abyssinian, Devon Rex, British Shorthair, Siamese, Maine Coons, and Persians.

What causes patellar luxation in cats?

There are several possible causes of patellar luxation cats.

  • Physical trauma – Traumatic luxations are more painful. They frequently run concurrently with other physical injuries and can affect one joint or both.
  • Congenital (present at birth) – This type of patellar luxation tends to be bilateral, affecting both knees.  Congenital patellar luxation – Most often the result of abnormal bone development, as well as a shallow trochlear groove which often slopes towards the side of the luxation.

The patellar can slip out of place if;

  • The trochlear groove is too shallow
  • The cat has bowed bones
  • The tendon attachment is off centre

What are the symptoms of patellar luxation?

Cats with mild patellar luxation may not display any symptoms, particularly with congenital patellar luxation.

  • Cats with traumatic patellar luxation may develop sudden lameness.
  • Lameness on one or both of the hind legs which can come and go or be present all the time.
  • As your cat walks, he may skip or hop on the affected leg, he frequently pulls the leg up towards the body and skips.
  • Reluctance to jump and climb.
  • Stiffness of the hind limb(s).
  • Cats with medial patellar luxation may walk with a bowlegged gait.
  • Bowlegged appearance (more common in dogs).

How is patellar luxation diagnosed in cats?

In some cases, patellar luxation may be an incidental finding during a routine physical examination.

Your veterinarian will perform a thorough evaluation of your cat and obtain a medical history from you. He will manually evaluate the patellar to evaluate and grade the severity of the patellar luxation.

Xray images taken from different angles to view the patellar and the depth of the trochlear groove can confirm diagnosis.  He will also look for arthritic to the joint as a result of the condition.

After diagnosis, grading will occur to evaluate the severity.

Grade 0: Normal patellar.
Grade 1: The patellar luxates with manual pressure upon full extension of the stifle joint but easily returns to the trochlear groove when released.
Grade 2:  The patellar luxates with manual pressure or spontaneously luxate upon flexion of the stifle joint and remains luxated until it is repositioned in the trochlear groove manually.
Grade 3: The patellar is permanently luxated, it can be manually returned to the trochlear groove on extension but re-luxates when released.
Grade 4: The patellar is permanently luxated and cannot be re-positioned in the trochlear groove. The trochlear groove may be shallow or completely absent.

How is patellar luxation treated?

Grades 1 and 2 generally require no treatment, some cats manage to pop the patellar back into place themselves by extending the affected leg.  It is advisable to ensure your cat’s weight doesn’t creep up as excess weight places additional pressure on all of the cat’s joints.

Grades 3 and 4 require surgery, preferably before the onset of osteoarthritis. There are a number of surgical treatments for patellar luxation, which depend on the type of abnormality present. Some options include:

  1. Tibial crest transposition: Reposition the attachment of the tendon at the tibial crest to re-align the patellar with the trochlear groove.
  2. Trochleoplasty: Deepening and/or widening of the trochlear groove.
  3. Lateral or medial imbrication: It is common for the soft tissue surrounding the patellar to stretch over time. Tightening the tissue during surgery will help to hold the patellar in place.
  4. Osteotomy: Some grade 4 cases may require surgery to realign the tibia or fibula, this surgery involves cutting the femur and re-aligning it with clamps.

The success rate of this surgery is usually very high, particularly if caught in time before arthritis has developed.

Home care:

Follow your veterinarian’s instructions to the letter, antibiotics, painkillers, and anti-inflammatories will be provided upon discharge, administer all medications as prescribed.

Keep a close eye on the surgical site for signs of infection which includes swelling, redness, and oozing, if you notice any of these, see your veterinarian immediately.

Your veterinarian may recommend gentle exercises for you to perform on your cat during his recovery to help restore his normal range of motion, follow as instructed as rehabilitation is an important part of recovery.

Confine to a crate or room until recovered, which takes two weeks. Avoid excessive activity and jumping for three months, keep him indoors during this time.

Do not breed with cats who have patellar luxation.

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