Lateral Patellar Luxation in Large Dogs. A Challenging Therapeutical Approach
Luis de Morais, DVM and Alameda D. Afonso Henriques
The lateral luxation of the patella in large breed dogs is a pathologic process of the knee, relatively less frequent as the medial patellar luxation. It can be congenital, associated with the development, or acquired, as a consequence of trauma, for instance.
Usually, we found the description of the lateral patellar luxation associated to the medial luxation, in most cases, reflected as a very similar orthopaedic problem, with a similar surgical resolution.
It's a fact that has been classified, described and sometimes treated in the same way that the medial luxation, as if the former was the especular image (on the mirror) of lather. This situation, in our point of view, does not seem to correspond to the reality, and that's what we will look for to explain in our presentation.
The great majority of the lateral patellar luxation we have seen, show different clinical expressions, as the ones seen on the medial side. For instance, much more precocious in its appearance and origin, and when not properly corrected, morphologic alterations of such importance that, frequently, they are responsible for evident lameness and, many times, irreversible injuries of the joint.
The etiopathogeny is not clarified. For some authors is a consequence of hip dysplasia, by anteversion of the femoral head, meanwhile others, pointed coxa valga the main cause; but for others, it's still the wrong position of the anterior tuberosity of the tibia and /or atrophy of the medial quadriceps, what exaggerate the influence of the lateral quadriceps and, consequently, displacement of the patella and the patellar ligament to a lateral position. In our point of view, they are quite all responsible in simultaneous. We are not able, however, to classify their importance. On a fact, in the great majority of cases we have seen, we found an exaggerate angle of anteversion of the femoral head (> 20°);coxa valga (> 145°) and consequent medial rotation of the distal femur as well as poor alignment of the leg extensor apparatus (quadriceps muscle group, patellar ligament, femoral trochlea and anterior tibial tuberosity ). But we also found serious deformation (rotation) of the proximal tibia responsible for a very peculiar position of the foot-pointed laterally. This alteration, when not considered is responsible for failure in the therapeutical approach.
If not let us see: If in fact did not exist, it seems to us evident that the medial transposition of the anterior tibial tuberosity to correct the deformation would be enough so alone. We know, however, that it is not true. The medial transposition of tibial anterior tuberosity, associated or not to others techniques, as deepening of the femoral inter-trochlear groove and, eventually, to the osteotomy for lateral rotation of the distal femur does not solve, normally, the problem.
And why? First because femur and tibia are firmly attached by the femoro-tibial ligaments, the patellar ligament and the joint capsule. Torsion of the femur will drag, necessarily, the same to the tibia in the same sense and direction. Therefore abduction of the member verified initially will increase. In the post-op alignment of the leg extensor apparatus could be corrected, but with an enormous deformation of the foot, incompatible with walking.
Secondly hypoplasia of lateral condyle origins ostheoartrosis of the knee.
Then, if we are right, how can we treat this situation?
We think first we must decide precociously. On a fact, we consider of extremely importance to act before serious morphologic alterations are evident. The first therapeutically approach is osteotomy of the medial tibial shaft for internal rotation of the tibia and later osteotomy of medial femoral shaft for external rotation when it seemed indispensable. It seems to us of little importance medial transposition of the anterior tibial tuberosity.