The Long Pastern bone of the horse (aka “P1”) is not symmetric — it has two non-zero angular parameters that we will call “Tilt” and “Twist”. The “Tilt” is the angular misalignment between the pastern-joint-axis and the fetlock-joint-axis as seen in a DP radiograph. The “Twist” is an angular twist about the long axis of the bone. One way to notice the Twist: place the bone on a flat surface – it won’t lie flat – you can rock it, due to the Twist angle. In our measures, the typical P1 bone has a Tilt of about 3 degrees and a Twist of about 6 degrees. See ‘The Hoof‘ book for more.