There is much debate about the ideal angle for the pedal bone to sit at in relation to the ground. Some sects suggest a palmar angle of 0 degrees as an ideal, while the widely accepted normal range lies between 2 – 7 degrees.
But what are the implications for palmar angles, what plays a role in creating them and what decides what they should be?
Fig.1 The palmar angle (PA) is shown in purple.
The PA has a fluid relationship with the other angles of the digit. Heel angle will directly affect PA and PA will directly affect phalangeal alignment and hoof angle. Understanding this and the influences on the factors directly affecting PA begin to tell us what the ideal for our horse should be.
Firstly lets establish, as the opening paragraph states, there is a widely accepted range of palmar angles (PA’S) that fall within the ideal, this is down to natural variation and biodiversity.
Fig.2 Hoof Angle is made up of PA and bone angle.
If we accept phalangeal alignment as ideal, which we will explore later, with the knowledge that horses will have different pedal bone angles (Fig.1.2) as a matter of natural biodiversity, then it would suggest that they would require different PA’s in order to achieve the same alignment. Fig.2 shows some palmar angles both within the normal accepted range and some outside of that range. While the majority of horses will fall within the range stated previously there will always be some outside of this range that require much higher palmar angles in order to still have a straight alignment, some of these will possibly be pathological some not.
Alignment becomes our first and perhaps most important factor in deciding on appropriate palmar angle. Studies stating a range of normal palmar angles are limited, Parkes (2003) stated a normal range anywhere between 2-10 degrees and Professor Weller expresses a palmar angle below 2 degrees as pathological. However studies suggesting alignment as an ideal are widespread. This has direct implications for what becomes acceptable as a range for PA because as PA becomes lower it becomes increasingly difficult and rare to have a straight bone column alignment as a result.
Dorner et al. (2017) looked at the relationship between PA and radiographic changes in the navicular, it found a negative correlation between the navicular score and the palmar angle and negative correlation between the navicular score and the hoof angle. Importantly what it showed was a lower palmar angle was more likely to show radiographic changes in the navicular bone. This study shows the same results as many studies before it.