Overview of Canine Lateral Patella Luxation
Lateral patella luxation (LPL) is a condition in which the patella, or knee-cap, no longer glides within its natural groove in the femur, the upper bone of the stifle or knee joint that can occur in dogs. It becomes displaced to the outside of the joint and can be partial or complete, intermittent or permanent. LPL can occur as a result of trauma, develop during the first year of an animal’s life in large and giant breeds of dogs or occur when they are more mature in small breeds.
Medial patella luxation (MPL) is more common in all breeds of dog than LPL. LPL is seen in large and giant breeds more frequently than small breeds of dog, such as Great Danes, St. Bernards and Irish wolfhounds. In the large and giant breeds, LPL is more common in both knees. Animals may show symptoms during the first year of life, particularly if the abnormality is severe, or any time later in their life if the problem is lower grade and leads to a more progressive, chronic lameness. Traumatic patella luxation can occur at any age and is usually secondary to being hit by a car.
Lameness can vary from an occasional hitch of the leg, like an intermittent skipping, to a persistent weight bearing lameness. Traumatic luxations are more likely to result in a non-weight bearing lameness.
Diagnosis of Lateral Patella Luxation in Dogs
Initial observation is important. The animal is observed walking and trotting. In a standing position, the knee joint of the affected leg is compared to the opposite side.
The veterinarian will put the knee joint through a normal range of motion to feel the tracking of the patella during flexion and extension of the joint. Depending on the severity of the problem, the patella may move only slightly toward the outer aspect of the joint or may pop completely and audibly out of position.
X-rays of the knee can be helpful to document the luxation.
Treatment of Lateral Patella Luxation in Dogs
Low grade LPL may be an incidental finding in which no treatment is necessary other than being aware of the clinical signs that may develop and closely observing your pet for development of this problem. In some cases LPL may be managed conservatively with restricted exercise and non-steroidal anti-inflammatory medication.
More severe grades of LPL should be addressed surgically. There are a variety of surgical options depending on which factors within and around the knee joint contribute to the luxation.
Home Care and Prevention
Following surgery your dog may be sent home with the leg in a soft padded bandage. This should be kept clean and dry at all times and the toes at the bottom of the bandage checked twice daily for swelling and/or pain. For many large and giant breeds of dog, keeping a bandage in place following surgery can be difficult and therefore may not be deemed worthwhile.
Most animals will require exercise restriction for the first four to six weeks following surgery. The bandage and stitches are removed at 10 to 14 days. Passive flexion and extension of the knee can be helpful to reduce joint stiffness and this will be demonstrated by your veterinarian if appropriate.
Congenital LPL is commonly a bilateral problem, that is it affects both hind legs, though not necessarily to the same degree. When selecting a dog, ask the breeder about the history of patella problems in the bloodline.
Be on the lookout for your dog developing a knock-kneed stance that may be indicative of LPL during the growing months of life.
Since trauma can occasionally lead to development of LPL, your dog should remain on a leash when walking and have a properly fenced in yard at home.
In-depth Information on Lateral Patella Luxation in Dogs
Related Symptoms or Diseases
There are many other causes of lameness referable to the knee joint. These diseases would be considered during the history taking and the physical examination. Some examples would include the following:
Medial patella luxation. The same clinical signs as lateral patella luxation are present, but the displacement is to the inside rather than the outside of the knee. This disorder occurs more frequently in smaller breeds of dog.
Cranial cruciate ligament rupture. Like patella luxation this injury can result from an acute traumatic event or develop as a chronic lower grade lameness. It is not uncommon to have combinations of patella luxation and a torn cranial cruciate ligament.
Collateral ligament injury. The collateral ligaments are located on the inner (medial) aspect and outer (lateral) aspect of the knee joint. They are most commonly injured in major trauma to the whole joint called stifle luxation or a deranged stifle. The medial collateral ligament and the cranial cruciate ligament are often both torn together with damage to the cartilage shock absorber, the meniscus, that lies between the two major bones of the knee joint. The patella is not normally affected in this injury.
Patella fractures are uncommon and would present as an acute traumatic lameness, usually as a result of a direct blow.
Patella tendon rupture is even less common and results in the patella being displaced above the knee joint, not out to one side or the other.
In young dogs, the position of the knee-cap may be altered due to a fracture at the attachment of the patella ligament to the bone below the knee joint, the tibia. This fracture is called an avulsion of the tibial tuberosity and requires surgery to return the fragment, the tendon and the knee-cap to their appropriate positions.
In-depth Information on Diagnosis
Following a general medical history your veterinarian will ask questions concerning the nature of your pet’s lameness. This will include:
The duration, that is acute versus chronic.
Does the lameness vary or stay the same?
Is it worse in the morning or at night?
Is it worse when your pet first gets up after lying down or worse after exercise?
Is there a hopping or skipping component to the gait? Perhaps your dog runs, then hitches up the leg for a few steps and then places it down again and carries on as normal.
Is one side worse than the other?
Is the problem getting worse?
Does the problem improve with rest?
In the case of a traumatic LPL, this questioning is not as important as the physical examination. Other body systems will take priority over lameness issues.
With congenital or developmental LPL, the lameness usually varies, is often worse when first getting up after lying down, may produce some skipping during exercise or low grade partial weight bearing lameness that is slowly becoming more noticeable and does not change much despite rest.
Other tests may include:
Your veterinarian will ask you to walk and then trot your dog, in order to observe the lameness.
With your pet in a standing position, the affected side will be compared to the opposite side, for muscle wasting, patella position while standing, swelling of the knee joint, thickening of the joint, position and thickness of the patella tendon and its attachment to the tibia, the bone below the joint.
The stifle joint will be put through a normal range of motion, paying particular attention to the tracking of the patella through its groove and the ability to push the knee cap manually in or out of its normal position.
The curvature and shape of the femur and tibia will be observed as the knee joint often twists inward (knock-kneed) in dogs with LPL.
The knee will be assessed for abnormal motion such as side to side looseness or laxity due to collateral damage, and front to back laxity or “drawer” due to a damaged cranial cruciate ligament.
The patella luxation will be assigned a grade, from 1 being mild, without clinical signs, through to 4, being severe with a permanently displaced patella. Dogs with grades 2, 3 and 4 are often candidates for surgery.
All other joints, bones and soft tissues on the affected side would also be palpated and put through a normal range of motion to ensure the problem is isolated to the knee.
It is important to check out your dog’s hip joints as hip dysplasia is not uncommon in association with LPL.
X-rays of the affected knee are not always essential but may be helpful to evaluate bony deformity and arthritic change as a result of the luxation. X-rays will be important following traumatic luxation of the patella, to ensure that the bones around the joint are not fractured.
X-rays may be unremarkable with regard to the position of the patella unless the problem is a grade 3 or 4.
There are no laboratory findings specific for LPL but blood may be obtained prior to a general anesthesia to ensure that no other concurrent problems are present.
In-depth Information on Treatment
Dogs with grade 1 LPL should be managed conservatively with a period of rest and a short course of non-steroidal anti-inflammatory agents. If the lameness persists or worsens they should be re-evaluated.
Some dogs will fall into a gray zone, with grade 2 LPL but minimal clinical signs. If the lameness is very occasional and not progressive then surgery is probably not indicated. But where this grade is associated with a more marked lameness or serial x-rays show significant progression of arthritis, surgery would be appropriate.
There are a variety of surgical techniques available, but they all aim to restore the patella to tracking permanently in its correct plane within the groove (sulcus) of the femur. To achieve this goal the groove may be artificially deepened either by abrading the existing surface or cutting a v-shaped wedge into the bone. The joint capsule surrounding the knee may be too tight on the outside, pulling the patella in that direction, and so may need to be loosened or “released” while the opposite side (inner, medial aspect) of the capsule is tightened. Finally, the attachment of the patella itself may deviate to the lateral or outer aspect of the tibia, and therefore need to be restored to a straight attachment. This is usually achieved by cutting the tendon at its bony interface, and fixing this with pins and wire into a new straighter location on the tibia.
In some dogs the LPL is associated with severe angular or torsional deformities of the bones around the knee joint and these may need to be addressed at the same time. Such surgical corrections are best performed by a board certified surgeon with the necessary training, experience and equipment.
Follow-up care for Dogs with Lateral Patella Luxation
A soft-padded bandage is usually placed on the leg following surgery to offer comfort, reduce some of the normal postoperative swelling, and provide some support. This can be difficult in some long-legged giant breeds as they tend to telescope down the leg.
Because it is not possible to observe the surgical incision for any problems, it is imperative to check the toes on a daily basis for swelling, excessive heat or pain. If your pet is persistently trying to chew the bandage and is not behaving normally in any other respect, a bandage change might be helpful to evaluate the surgical site.
The bandage must stay clean and dry which means putting a plastic bag or trash can liner over the bandage every time your dog goes outside.
Some dogs just do not tolerate a bandage very well, despite the absence of complications at the surgical site. Elizabethan collars can be helpful in most instances, but in some cases the bandage should be removed if it becomes more trouble than it is worth.
Your pet should have the bandage and stitches removed at 10 to 14 days following surgery and be strictly rested for 4 to 6 weeks. This would require, in most cases, confinement to a single room, no going up or down stairs, avoiding slippery surfaces such as tile, hardwood floors or linoleum, and leash walk to go to the bathroom only.
Putting the knee through a passive range of motion, that is gentle flexion and extension of the knee, can be demonstrated by your veterinarian, and will often encourage earlier weight bearing.
The prognosis for dogs with LPL is not as good as for dogs with MPL. Having said this the overall prognosis is still good for return to function.
Prevention of Lateral Patella Luxation in Dogs
It is not possible to prevent developmental LPL; however, when selecting a dog, ask about the breed line and whether there is any history of knee related problems.
Certain breeds of large and giant dogs are more prone to LPL – reportedly those more likely to get hip dysplasia.
Good or excellent hip scores in the sire and dam will not guarantee normal knee development but certainly should be viewed more favorably.
At the first sign of lameness or gait abnormality, have your dog evaluated by a veterinarian. The position and tracking of the patella can be assessed. As discussed earlier, not all LPL’s necessitate surgical intervention. The problem may just need to be monitored and evaluated periodically during your pet’s development and subsequent veterinary check-ups. In cases of more severe LPL, the prognosis is improved with early detection and surgical correction, as this improves joint function and alignment while the animal is still developing.
In the unusual event that trauma was the underlying cause, leash restrictions on your dog together with adequate yard fencing can help prevent this sort of problem from occurring.