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This is a condition where the patella (kneecap) dislocates from the groove of the bottom of the femur (thigh bone). The condition is more common in small breed dogs such as Pomeranians and Yorkshire Terriers. Often the patella dislocates to the inside of the knee (medial luxation) but can occasionally displace to the outside of the knee (lateral luxation).
Patellar luxation is caused by many factors. Occasionally, it may be the result of a traumatic incident but often it is caused by a genetic influence. Several abnormalities in the anatomy of the affected leg can lead to development of a luxating patella. Commonly, the muscles and major bones of the leg are deformed and malaligned.
At Acorn, the most commonly reported sign by owners is an intermittent lameness. The animal may cry in discomfort, hop or limp for several steps (then stretch the leg and appear normal again) or walk abnormally. If the condition persists for a long time, the stifle (knee) joint will often develop osteoarthritis (degenerative joint disease) from the abnormal motion of the patella, which will cause pain and lameness.
Patellar luxation is most commonly diagnosed by an examination of the leg during a consultation. Often veterinarians may detect a luxating patella during a routine check-up (e.g. vaccination) before any clinical signs have been noted. We normally grade the severity of the luxation on a scale of 1 to 4.
· Grade 1 – patella can be manually displaced but when released, it returns to its normal position.
· Grade 2 – The patella may manually or spontaneously luxate but normally needs to be replaced to the normal position by either manual manipulation or by extending the leg.
· Grade 3 – The patella is constantly dislocated but can be manually returned into the normal position but re-luxates once the pressure is released.
· Grade 4 – This is the most severe form when the patella is permanently luxated and cannot be returned to the normal position.
At Acorn, we often recommend x-rays of the leg to assess the anatomical abnormalities and to aid us to decide the best measures to take to correct the condition.
In animals, with no clinical signs, we may recommend a conservative approach where we monitor movement or any discomfort that may develop in the leg. There are several surgical techniques we may use to stabilize the position of the kneecap to allow proper alignment. The most common techniques include one or a combination of:
· Deepening of the trochlear groove of the femur where the patella sits by a recession trochleaoplasty.
· Re-locating the tibial crest (shin bone which is attached to the patellar tendon) to release the abnormal pull on the kneecap.
· Sutures that imbricate (strengthen) the supporting soft tissues and joint capsule that pull the patella to the normal position.
· A releasing incision on the side which the patella is luxated to release the pulling tension.
· In severe cases, we may perform a corrective osteotomy to realign the patella by straightening the femur (and possibly the tibia).
After surgery, in most cases, the prognosis is good and the leg can return to a good function.