WHAT IS BALANCE?
Balance occurs when the center-of-mass and the center-of-rotation are in alignment. Any deviation from the balanced position and the object is unbalanced and unstable. Therefore, the balanced position for the hoof is when the center-of-area of the sole of the hoof that is in contact with the ground and the first joint of rotation are in alignment. The first joint of rotation is the coffin joint (a.k.a. Distal Interphalangeal Joint (DIP)).
WHY DOES BALANCE MATTER?
Structural Engineers, like myself, use balance every day to design framing and foundation systems. We describe balance as when the sum of the forces is zero about a point of rotation. In other words, static equilibrium. Therefore, when I describe balance I use “Statics” to prove that the forces around the DIP joint are zero. To keep it simple, I ignore the acceleration forces. Force(F) is actually mass (m) times acceleration (a) (F=ma). I use statics because it keeps the math simple and it’s easier for horse owners to get the concept of what is occurring when the hoof is balanced vs. unbalanced.
This is a concept lesson to give you a general idea about how the forces or load is moving through the coffin bone and joint. When the horse is moving we are dealing with a dynamic loading situation in the X, Y, and Z planes. This includes knowing what the acceleration forces are in those directions plus, we can’t forget gravitational forces. The math gets complicated really quickly which is why I choose to ignore the acceleration. In other words, I’m freezing a moment in time to simplify the calculation.
When any object is out-of-balance it becomes unstable and unbalanced. When the hoof is out-of-balance the foundation of the horse is unstable. To maintain balance, another force has to counterbalance that instability. To maintain a stable platform while the hoof is out-of-balance, the horse has to engage the Deep Digital Flexor tendon, thus applying a torque at the DIP joint. Also, the digital cushion is not fully supporting the coffin, short pastern, and navicular bones. The percentage that the digital cushion is not supporting the bones above, the ligaments and tendon that hold/connect the joint are now engage in tension to provide the remaining support to the joint. They are experiencing strain to hold the joint and the bones in place. Left in the unbalanced position, the soft tissue for the joint becomes fatigued and will eventually fail. Many veterinarians and hoof care providers refer to this as Navicular Syndrome or Heal Pain. In reality, the whole body of the horse has to compensate for the unbalanced state of the hoof. The horse may look stiff, gait faults, and they may have back and hind end related issues to name a few potential side effects. Basically, the coffin joint and its soft tissue is being fatigued and prematurely aged due to manmade effects of being trimmed and/or shod out-of-balance.
Signs that your horse’s hooves are out-of-balance include tripping, stumbling, and forging. These are usually the earliest noticeable symptoms. Many horse owners and trainers choose to ignore these symptoms thinking the horse is clumsy or lazy. Don’t ignore them. Your horse is telling you something. If left untreated, your horse will develop more severe lameness symptoms, and become much more of a challenge to treat.
The following definitions are from Webster’s Ninth New Collegiate Dictionary:
LEVERAGE: The action of a lever or the mechanical advantage gained by it.
LEVEL: A measurement of the difference of altitude of two points by means of a level.
PERPENDICULAR: a) Standing at right angles to the plane of the horizon: exactly upright. b) being at right angles to a given line or plane.
BALANCE: Stability produced by even distribution of weight on each side of the vertical axis.
EQUILIBRIUM: A state of balance between opposing forces or actions that is either static (as in a body acted on by forces whose resultant is zero) or dynamic (as in a reversible chemical reaction when the velocities in both directions are equal)
STRAIN: Deformation of a material body under the action of applied forces
TORQUE: a) A force that produces or tends to produce rotation or torsion also: a measure of the effectiveness of such a force that consist of the product of the force and the perpendicular distance from the line of action of the force to the axis of rotation. b) a turning or twisting force.
This is a balanced hoof in x-ray. It’s the hoof of an Oldenburg gelding who’s self-maintaining his hooves. He’s boarded at a facility that specializes in barefoot hooves and lives in a hard-dry environment with lots of opportunity for pasture movement.
Looking at this cross-sectional view one can easily tell that this hoof is balanced (center of area of the bottom of the hoof and the first joint of rotation are in alignment). To check for balance, draw a horizontal line starting at the heal bearing point and terminating at the toe breakover point. Split that line in half and draw a perpendicular line to the horizontal line. The perpendicular line bisects the coffin joint. This is the balanced position. Thus, the horses’ weight is being distributed through the coffin joint and into the ground. The ground force (force normal) is pushing back with an equal-and-opposite force at the center of area of the bottom of the hoof. This hoof is at static equilibrium. Thus, the sum of the forces is zero.
Looking at the coffin joint, take note at how snug the coffin bone (P3), short pastern bone (P2), and the navicular bone is with each other (coffin joint area). This hoof also shows what a “strong digital cushion” looks like. It’s supporting the bone structure above. In structures the navicular bone is acting as a “rocker”. This allows the coffin joint to articulate. Take note of the alignment of P1, P2, and P3. Also note that the hoof wall is parallel with the coffin bone. This is the magic angle for a balanced hoof. No hoof gage required.