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”. In a DP radiograph, there is an “Apparent Tilt” – the angular misalignment between the pastern-joint-axis and the fetlock-joint-axis in that image. But this apparent tilt is primarily due to the “Twist” of the P1 bone due to its slope when imaged. 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.
