Patellar Luxation Signs, Symptoms & Treatment Options
January 20th, 2015 | Posted in Medical Articles
The patella (knee cap) is the bone at the front of the knee. The trochlear groove in the end of the femur (thigh bone) allows the patella to glide up and down when the stifle joint (knee) is bent and extended. In doing so, the patella relays the action of the quadriceps muscle to the lower leg.
In some dogs, because of malformation or trauma, the ridges forming the trochlear groove are not prominent, and a very shallow groove results. This situation allows the patella to luxate (move out of the groove), usually medially (toward the inside). This causes the leg to ‘lock up’ with the foot held off the ground. When the patella is luxated from the trochlear groove, it usually cannot return to its normal position until the quadriceps muscle relaxes and increases in length.
Small breeds of dogs (Miniature and Toy Poodle, Pomeranian, Chihuahua, etc.) have the highest incidence of patellar luxation. Genetics likely plays a role in most cases. In some dogs, an abnormal shape of the femur and tibia contributes to the patellar luxation. The curvature of the bones in these cases works in conjunction with the forces of the quadriceps muscles to displace the patella medially.
Most dogs are young to middle-aged, with a history of intermittent (on again-off again) lameness in the affected rear leg(s). Patellar luxations are graded from 1 (least severe) to 4 (most severe), based on the amount of time the patella is out of the trochlear groove. An affected dog commonly stops and cries out as he is running, then will hold the leg up for seconds to minutes. Dogs with a grade 3 or 4 luxation in both hind legs may walk with the patellas in the luxated position using a wide bent-leg posture.
Pets with lower grade luxations may not require correction, however, when correction is warranted surgery is required. Medical therapy has little corrective ability in this disorder. Uncorrected, the trochlear ridges will continue to wear, the groove will become more shallow, the dog will become progressively more lame and arthritis will prematurely affect the joint.
Surgery may involve deepening of the trochlear groove, repositioning of the tibial tuberosity (bony protuberance at the attachment site of the quadriceps tendon, and/or imbrication (tightening) of the joint capsule and fascia. In patients with abnormal curvature of the femur or tibia, a corrective osteotomy may also be required. All of these procedures work well and the type performed depends on the individual case and the surgeon. The pet typically will respond quickly after surgery and is usually completely recovered in 2 to 3 months, and using his legs in normal fashion. Following instructions for activity restriction during the recovery period is important for a good final outcome.
Because of the strong genetic relationships, dogs with this disorder should not be used for breeding. They can still be excellent pets – and those that do require surgery will usually lead perfectly normal lives without any restrictions on activity.
Additional information regarding Patellar Luxations (and other common surgical disorders in dogs and cats) can be found on the website of the American College of Veterinary Surgeons.