Negative Palmar Angle Syndrome. Could this be your horse?

Could this be your horse?

I think that the start to any discussion on feet involves putting into perspective their importance. Horses are 4 legged creatures and they carry 60% of their weight on their front legs. They do not have an articulation joint between the front legs and the body. You can imagine that you carry your weight on your legs and distribute this weight through your hip joints. Horses have a muscular sling made up by the superficial and deep pectoral muscles that distribute this weight to their front legs. The back end of the horse is responsible for propulsion and the front end is responsible for steering and carrying the majority of the weight.
When we look at the proportion of lameness’s we see in horses, more often than not they are lame in front and of those front limb lameness’s, 80% of the time the problem is below the knee.
The reason we spend so much time and energy discussing feet, chatting to farriers and trying to perfect our shoeing is because the hoof is the most common cause of horses being off work and it is a dynamic structure. It changes through the seasons and it changes in response to our shoeing techniques.
At this point I want to do a brief overview of the anatomy of the hoof. 

This is a diagrammatic representation of what the angles on a radiograph should look like. The pedal bone is suspended by the lamella within the hoof structure. The digital cushion at the base of the pedal bone provides the shock absorbing function to the foot.

The hoof is a highly evolved and very complex structure. The most common cause of lameness in spring is normally sole bruising and hoof abscessation.  Horses can either bruise through pressure being applied from the outside of the sole, for example they will play around in the paddock and stand on a stone, land a little awkwardly after a jump  or get a bit of sole pressure from a shoe. Or they can get pressure being applied from the inside of the hoof, where the angle between the pedal bone and the ground is so narrow that it pinches the sole, resulting in deep seated corns. Basically bruising of the sole is like any tissue that becomes bruised, the tissue becomes damaged, and blood and inflammatory mediators are found in the area of damage. These mediators are responsible for the pain we see on hoof testers and lameness under saddle. Often they can be worse in the soft going as the sand moulds into the shoe and applies more pressure to an already sensitive sole. This bruising creates a marvellous environment for secondary bacterial infection. If there is standing water and mud in the horse’s environment, like during our Cape winters, then often bruising will develop into a hoof abscess. 
Some horses appear to be more susceptible to hoof problems than others. This is normally when we start to suspect that the conformation of the pedal bone within the hoof may well be the cause of the problem. We did a hoof survey towards the end of 2010 and were surprised to find that a large proportion of horses had what we call negative angles, or Negative Palmar Angle Syndrome.

This is a radiograph of a fairly normal foot. If you compare this to the diagrammatic representation you will note that the Palmar angle, the angle between the base of the pedal bone and the shoe is fairly normal. The following radiograph shows what the anatomy looks like when the angle is negative.