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When the foot impacts with the ground the pastern joint dorsiflexes into the close-packed position (Figure 1) and, normally, remains in that position until the foot lifts-off from the ground. The close-packed position is that position of a joint in which the two joint surfaces have maximum surface area in contact with each other. It is the position of greatest congruity of the joint surfaces. It is true, though the argument will not be developed here, that as the joint dorsiflexes, the bones spin around their long axes from medial to lateral (Figure 2). There is, then, a twisting or screw-like motion of the pastern joint as it dorsiflexes. This spinning occurs because the medial part of the joint is larger than the lateral part. Again, without