METHOD: For the purpose of mathematical modeling, we assumed a left tibial length of 470 mm, a left femoral length of 460 mm, and the distance between the hip and foot of the supine patient to be 570 mm. These numbers are based on a typical tibiofemoral ratio of 1 to 1.26 , and a knee angle of approximately 900. Since under these assumptions the femur, tibia, hip-foot distance create a triangle of known dimensions, it was possible to use trigonometry to calculate the angles of the triangle. From these angles, it was then possible to compute, for given changes in the length of the right leg bones, changes in the height and Y-axis position of the knee. We also explored the mathematical consequences of one hip being drawn up cephalad compared with other, while the feet are kept even at the foot of the table (thus increasing the hip-foot distance on one side).
RESULTS: The knee altitude is diminished with either femoral or tibial length reduction. The knee is shifted cephalad when the femur is reduced in length. Shortening of the femur has an approximately 25% greater impact on knee Y-axis location than tibial shortening, whereas tibial length reduction has an approximately 25% greater impact than femoral shortening on knee altitude.
DISCUSSION: Irrespective of nomenclature, our modeling shows that the traditional interpretation of the test may be flawed. Although it may detect a leg length inequality, the test does not appear to detect what some individuals have said. This study is limited by the fact that it is pure modeling, and it will take a clinical study to see if its predictions are borne out. The simple model we describe may not be an entirely appropriate representation of a flesh and blood leg, with the complexity of its joint kinematics. Future studies may address the interexaminer and intraexaminer of this type of visual check, and compare its results against an accepted gold standard for a leg length inequality, such as the scanogram x-ray.
There are significant discrepancies in the literature on the description of the Allis/Galleazzi test, which appears relevant only to infants, and is performed with the hip at 90°.The procedure chiropractors commonly perform closely resembles what Magee calls the Weber-Barstow procedure. The modeling we performed refutes what Magee and others have said on the interpretation of the test. Either a short tibia or femur lowers the knee seen from the foot of the table, by similar amounts, and cannot discriminate between a leg length inequality due to one or the other. In the side view, a short femur brings the knee cephalad, and a short tibia brings it caudad, by similar amounts.
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