Mechanical Axis

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- Discussion:
    - mechanical axis refers to the angle formed by a line drawn from the center of the femoral head
            to the medial tibial spine and a line drawn from the medial tibial spine and the center
            of the ankle joint;
            - this should not be confused w/ the wt bearing axis which runs from the center of the femoral
                  head to the center of the ankle;
    - w/ optimal alignment, the mechanism axis will form a straight line (overlapping the wt bearing axis)
    - mechanical axis passes thru the three demensional anatomic center of knee;
            - therefore, it also defines neutral alignment in every plane and is not subject to
                    projectional variation;
    - because hips are more widely separated than the knees and ankles, the
            mechanical axis is in 3 degrees of valgus from the true vertical
            axis of body, which extends from center of gravity to the ground;