The hoof pastern axis (HPA) on both front and hind limbs can be assessed when, an imaginary line drawn through the centre of the phalanges is compared to the line of the dorsal wall of the hoof capsule, when viewed from the lateral aspect (Adams, 2002). When assessing for a correct HPA, the phalangeal axis should be parallel with the dorsal surface of the pedal bone. The dorsal wall of the hoof capsule should be free from flares/distortion, if it is going to be used as an accurate guide
NEGATIVE / BROKEN BACK HPA
This is an illustration of Negative Hoof Pastern Axis.
The blue line is completely straight (normal HPA) whereas the red line is broken at the yellow dot mark.
POSITIVE / BROKEN FORWARD HPA
The Red line also breaks at the yellow dot, but the opposite way.
⚠️ JUST A VISUAL ASSESSMENT, NOT A MEASUREMENT TECHNIQUE
True HPA is determined with clear lateral radiographs. You wouldn’t be able to have a true measurement with those observations only.