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 (which in cats is known as the stifle joint). Medial luxation is more common than lateral. If this is not resolved, arthritis can develop in the affected joint(s) over time.
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. It is buried by the patellar tendon which is a strong, flat tendon that attaches from the bottom of 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, meaning a bone that is embedded with a tendon or muscle. The function of sesamoid bones 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.
There are several possible causes of patellar luxation cats.
Physical trauma – Traumatic luxations tend to be more painful and often run concurrently with other physical injuries. It may occur in one joint or both.
Congenital (present at birth) – This type of patellar luxation tends to be bilateral (affecting both knees). In dogs, this condition is inherited, however, it has not been proven that this is the case in cats. Congenital patellar luxation is 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 may slip out of place is the trochlear groove is too shallow, if the tendon attachment is off centre or if the bones are bowed.
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.
Diagnosis of patellar luxation is based on x-ray images which will be taken from different angles to view not only the patellar but the depth of the trochlear groove. He will also look for arthritic to the joint as a result of the condition.
Once patellar luxation has been diagnosed it will be graded from 1 to 4, with 4 being the most severe.
The patellar is normal.
The patellar luxates with manual pressure upon full extension of the stifle joint but easily returns to the trochlear groove when released.
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.
The patellar is permanently luxated, it can be manually returned to the trochlear groove on extension but re-luxates when released.
The patellar is permanently luxated and can not be re-positioned in the trochlear groove. The trochlear groove may be shallow or completely absent.
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:
Tibial crest transposition: Repositioning the attachment of the tendon at the tibial crest so that the patellar is re-aligned with the trochlear groove. The bone is cut and then re-attached in the correct position and pinned into place.
Trochleoplasty: Deepening and/or widening of the trochlear groove.
Lateral or medial imbrication: It is common for the soft tissue surrounding the patellar to become stretched over time, this may need to be tightened during surgery to help hold the patellar in place.
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. It is usually performed on dogs who have bowed legs.
The success rate of this surgery is usually very high, particularly if caught in time before arthritis has developed.
Follow your veterinarian’s instructions to the letter. Your cat will be sent home with pain killers, anti inflammatory medication and antibiotics. 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. Rehabilitation is an important part of recovery.
He will need to be confined to a crate or a room until he has recovered, this generally takes two weeks although excessive activity and jumping should be restricted for up to 3 months. It is advisable you keep your cat confined indoors during this period.
It is not advised to breed with cats who have patellar luxation.
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