One-sided contracted hoof (spread contracted hoof) is caused by the extremities being strained on one side. If substantial one-sided horn abrasion of the inside or outside wall of the hoof is not corrected, the load will be shifted onto that half of the hoof. The greater horn loss causes the bearing surface to be shortened faster on that side than on the opposite side not subject to this strain. This means that the hoof is lower on that side. At the same time, the opposite side of the hoof leverages the hoof upwards on the other side, thus shifting a proportionally greater amount of weight onto the side wall subject to strain. However, that side is already too low and suffers under a greater load. This puts the lower wall in a steep position in relation to the ground, preventing the side wall from being outwardly resilient under load and making the side of the hoof tend to get narrower (under load).
Hoof orthopaedics corrects one-sided contracted hoof by counteracting uneven horn abrasion. Abrasion is increased on the side of the hoof with a lesser load in order to restore balance. One way to do this is to thin out the bearing wall on this side so that it offers less abrasion resistance towards the ground and will be able to wear faster.
Double-sided contracted hoof generally develops in connection with narrow steep hooves and is always the result of a lack of or improper treatment. The horn capsule and in particular the rear section of the hoof is hardly subject to any widening from the counterpressure from the ground due to the steep straight bearing walls that narrow hooves have. If the hoof is left untreated or treated improperly, the opposite may develop, namely inner leverage. The rear parts of the side walls that are in a vertical position in relation to the ground develop into "supersteep" walls such as the heel walls and they are increasingly shaped in the inward direction under the pressure from the ground. This is caused by the rear hoof area being subject to a lesser load. There may also be less of a load if the hoof is improperly positioned (acquired tendon contracture or club foot) and due to pathological changes in the area of the navicular bone (navicular disease). The hoof becomes increasingly steep and narrow due to the reduced load on the heel involved with these processes and the horn abrasion in the area of the toe wall is increases accordingly.
Overloading the rear section of the hoof may turn narrow individual hooves into contracted hoofs. This development is also due to improper or lacking hoof treatment. An example of this is excessive abrasion on the heels under iron horseshoes combined with excessive shortening of the heel area (when trying to cut the hoof to a certain shape that the owner imagines to be ideal). This may transfer an excessive a load onto the rear areas of the hoof. This forces the bearing horn tubules (that are already supersteep in relation to the ground in narrow hooves) inwards due to the increased load from the counterpressure from the ground. The toe wall has a more slanted angle to the ground by tilting the hoof backwards, meaning that the bearing surface becomes wider. A more slanted angle and higher width slow down horn abrasion in this area. The horn tubules in the toe wall and in the area of the edge of the sole wear down less than the horn structures in the rear area of the hoof. The abrasion in the area of heels under more and more pressure increases on a similar scale. In addition, the narrowing of the central and collateral grooves also favours the settlement of putrefactive bacteria and the development of thrush. The maceration of the frog horn (and often also that of the ball horn) makes the hoof even narrower.
The main work of hoof orthopaedics is geared towards minimising the imbalanced load. The procedure depends upon the specific situation. If the rear sections of the hoof are overloaded as described above, the hoof treatment will be aligned towards distributing the load in the direction of the toe. In contrast, if contracted hoof is caused by a lesser load in the rear of the hoof, hoof orthopaedics thins out the bearing surface in the heel area and rear side wall area to attempt to ensure that the hoof receives more abrasion in spite of a lower load in the heel area. This and other work also prevents improperly positioned (acquired tendon contracture or club foot) or unhealthy extremities (navicular disease) from becoming more and more steep in the rear due to less abrasion.