It can be confusing for people to actually visualise what is happening inside the hooves of their laminitic horse, so we’ve drawn some pictures for you! But first, before we go into what’s ‘abnormal’ we need to have an understanding of what’s ‘normal’… So here’s a little info about hoof anatomy. Don’t worry, we’ll keep it very simple with lots of pictures!
The inner structures of the horse’s hoof are surrounded, supported and protected by what’s known as the ‘hoof capsule’. This is made up of the hoof wall, sole and frog, and is attached to the inner structures and the bone by connective tissue called laminae.
In a normal and healthy hoof, the bone inside the hoof capsule, the pedal (or coffin) bone (also known as the 3rd phalanx or P3), sits high and has a tight connection via the laminae to the hoof wall (see diagrams 1). The angle of the front of the pedal bone is parallel with the dorsal (front) hoof wall angle.
The laminae hold the bone and the hoof wall firmly together from the coronet (hairline) to the toe. The top of the pedal bone is level with the coronary band or hairline, and the bottom edge has an angle of between 3-5 degrees to the ground plane. The point on the toe where the hoof tips forward and leaves the ground for takeoff is referred to as the break-over point. This point should be underneath and in line with the dorsal (front) angle of the pedal bone.
The term ‘laminitis’ describes inflammation in the laminae and this can cause it to weaken, losing its bond with the bone inside the hoof capsule. The breakdown of this connective tissue results in a lack of support for the pedal bone, which consequently drops down in the hoof capsule (sinks) and ‘rotates’ away from its tight connection with the hoof wall.
The pedal bone can move inside the hoof capsule in several different ways or in a combination of ways. This is why it helps to have radiographs (x-rays) taken to determine the exact position of the bone before trimming the hoof. Just to give you a basic idea of what can happen, the pictures below illustrate some of the ways that laminitis can affect the position of the pedal bone and hoof capsule.
In the Normal Hoof, the pedal bone sits high in the hoof capsule with a nice tight laminar connection and the pedal bone is parallel to the angle of the hoof wall.
The next picture – Rotated Hoof – shows a pedal bone that has rotated away from the bottom half of the hoof wall, the laminar connection has been compromised and has given way.
The Sunk picture shows a pedal bone that has dropped down in the hoof capsule. Often this occurs when a horse sufferer from chronic laminitis. The pedal bone can also rotate AND sink at the same time, see Rotated and Sunk picture.
In the Capsular Rotation picture, you can see that the laminae have given way BUT the pedal bone is still in correct alignment with the ground and other bones within the hoof. In this case, it’s the hoof capsule that has rotated away from the pedal bone. It is particularly important to note that in the case of capsular rotation, the point of a break over moves forward which then, in turn, puts more mechanical upward stress on the hoof and laminar connection. In a perpetuating cycle, the mechanics of the excessive toe leverage then causes further laminar stretching and tearing.
Note in the Rotated & Sunk picture especially, how close the tip of the pedal bone is to the ground, the sole is very thin and this will cause the horse to be very sore. If the condition gets bad enough the bone will penetrate right through the bottom of the foot!
This occurrence is extremely painful for the horse and results in the classic founder stance – below.
Springtime Laminitis has started already and it's not even Spring! Here is Zoe of Missy's Bucket talking about some of the key approaches that will help prevent the onset of this terrible disease.