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Anatomical ankle axis

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  • Anatomical ankle axis

    We have been having some discussions lately regarding the
    anatomical ankle joint axis (talo-crural) versus the mechanical
    axis that we incorporate into our ankle foot orthoses.
    Traditionally, the mechanical ankle joint axis has been
    determined by using the distal tip of the medial malleolus as a
    reference, and place the lateral joint axis at the same height.
    The anterior/posterior location of the joints are determined by
    using the distal tip of the medial maleolus again as a starting
    point, and then place the lateral joint in a position which sets
    the foot in about 5-7 degrees of external rotation.
    Our concerns have been in the area of mechanical alignment
    versus skeletal alignment of the joints. We have been
    experimenting with placing the joint axes in a more anatomical
    position by moving the lateral joint posterior to be more
    congruent with the lateral malleolus. Also, we have been tilting
    the joint axis a few degrees to match the angle of the medial
    versus the lateral malleolus. The end result is an orthosis
    which looks and acts quite differently from the traditionally
    aligned orthosis, but mimics the actual motion of the foot more

    Discussion points:

    How critical is mechanical joint alignment on an orthosis?

    Since tibial progression over the foot is made up of more than
    just talo-crural motion, do you think that skeletal alignment of
    the mechanical ankle joints is significant.

    Any info that could be used in the determination of more
    appropriate mechanical joint axes, using skeletal landmarks as
    reference points, would be helpful.

    Thank you very much.

    Paul E. Prusakowski, C.O.
    Shands Hospital at the University of Florida
    Orthotics and Prosthetics Dept.