We are developing what we call “The Bone Engine” which is a collection of software tools that can do various computations on scanned 3-D polygonal models of bones and other structures. As an example of one ability of the Bone Engine — it can compute the best approximation of the 3-D location of the axis of rotation for a given joint. The interesting thing about this method is that the computation is made purely from the 3-D shape of the condyles and epicondyles of the two bones that form the joint. The resulting location of the axis of rotation is derived purely from shape (not from motion data, nor someone’s opinion, nor other means). The 3 three video segments show how the axis of the fetlock joint of a horse’s front leg was determined from laser-scanned 3-D models of the long pastern and cannon bones.