Background photographs

On the far left stained dark blue is the distal phalanx (pedal bone), stained light blue is the laminar corium with 'fingers' sensitive laminae extending towards the brown stained horny primary laminae. The white areas within the laminar corium are blood vessels.

Secondary laminae are visible on each primary laminae, this arrangement of primary and secondary laminae increases the surface area of attachment to the distal phalanx.

This tightly packed structure will only be able to accommodate small amounts of hoof capsule distortion before it becomes damaged.

The general shape of the hoof wall is an arch extending from one heel to the other, this is an incredibly strong shape.

The orientation of the laminae around this arch is towards the apex of the frog, therefore the laminae at the widest part of the hoof point towards each other, while the laminae at the toe are aligned at 90° to those at the widest part.

The combination of an arched wall and arched sole gives the hoof capsule tremendous structural strength.

Horn is very resistant to compression, it must be to carry the weight of the horse.

The more serious laminitis cases will be equines with stronger hoof capsules.

Horn when grown at differential rates will grow in a curved way, this is used in nature very frequently. This ram is exploiting differential horn growth to produce left and right spiraling horns.

Chronic laminitic horn growing at differential rates will lift the dorsal wall from the underlying bone (also referred to as 'capsular rotation'). The horn in the toe region is not compressed in this example, the heels have grown more quickly.

Round hoof capsules distort more generally so the laminae become distended around the circumference of the hoof. The distended laminae are aligned radialy as the circumference of the hoof wall has expanded. In extreme cases the distal phalanx sinks in round shaped hooves.  

When a long narrow hoof capsule distorts the laminae at the toe become distended. Note that the distended laminae are aligned parallel to each other, indicating that the hoof wall has moved away from its original position. In extreme cases the distal phalanx will rotate.

As the hoof wall is lifted, the sole is pulled towards the distal border of the distal phalanx (solar surface of the pedal bone), the bruising highlighting the outline of the bone. Blood flow through the solar corium will be restricted by compression of the vascular structures. The position of the hoof wall and orientation of the distended laminae trace the movement of the hoof wall. 

Confirmation that distortion is dependent on hoof shape is provided by asymmetric hoof shapes - which have one side round and the other straight in shape.

When an asymmetric hoof capsule distorts it will not be uniform, distension or damage to the laminae will be greater on one side of the hoof than the other. In severe cases the distal phalanx will partly sink and partly rotate.