In a normal knee, the patella (knee-cap) is positioned in the middle of the knee joint. As the knee is bent and straightened, the patella slides up and down in a groove on the far end of the femur (thigh bone). A luxating patella no longer travels in this groove; instead it slips (luxates) to one side of the groove. Most often it slips to the inside of the knee, however sometimes it can slip to the outside.
The patella may luxate infrequently, or frequently. It may pop out of place as the knee bends, and back into place as it straightens, or it may be permanently fixed in the abnormal position. Young and old dogs of any breed can be affected, though toy-small breed dogs are the most commonly affected.
The Problem with Luxating Patellas
Your pet’s luxating patella is likely to lead to problems that cause your pet pain and discomfort. You may have already noticed some symptoms, such as hopping, holding the leg off the ground, whimpering when jumping, or reluctance to jump and climb stairs. Problems can arise suddenly, or develop slowly. Such developments include-
- The knee ligaments may tear under the extra stress of joint instability (cruciate rupture) and cause sudden severe knee pain, lameness and non-weight bearing in the affected leg.
- Cartilage and bone development in affected young dogs may be impaired, and result in pain, lameness, deformity as the limbs continue to grow, and early onset osteoarthritis in the affected knee.
- Rapid cartilage wear of the bones involved, leading to early onset degenerative joint disease and osteoarthritis.
Causes of Patellar Luxation
Most commonly, the patella slips out of place because there are pre-existing muscular and skeletal deformities within the leg.
Your pet may have one or more of the following-
- Displaced quadriceps muscles
- Bowing of the femur (thigh bone)
- Outward rotation of the femur at knee level.
- Knee joint instability
- Abnormal trochlear groove shape (eg. too shallow)
- Abnormal tibial (shin bone) shape
In growing dogs, a luxated patella rapidly exaggerates deformities, by exerting abnormal forces on the growing muscle and bone. This inturn exacerbates joint degeneration, lameness and pain.
Correction of Patellar Luxation
Surgical repair is required to stop the luxation and prevent further problems from occurring. Surgery targets repair of the abnormalities causing the luxation. Your veterinarian will assess the conformation of your pet’s leg, and will then discuss with you the surgical techniques that will be needed to normalize the structure and alignment of the muscles and bones.
How effective is the surgery?
There is an EXCELLENT prognosis for RETURN TO NORMAL LIMB FUNCTION!
Does your dog need a surgical repair?
Surgery is strongly advised for growing or young dogs with symptomatic luxating patellas, as the surgery is very successful at preventing further deformity and very early cartilage wear. Repair greatly delays the onset of osteoarthritis.
Surgery is highly recommended for dogs of any age that are lame from their patellar luxations, as surgery significantly resolves lameness and the risk of ligament rupture.
Your veterinarian will happily discuss all therapeutic options with you.