Lateral Patella Luxation in Dogs
Dr. Nicholas Trout
The duration, that is acute versus chronic.
Following a general medical history your veterinarian will ask questions concerning the nature of your pet's lameness. This will include:
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.
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.