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Knowledge about ossification of the lateral cartilages (sidebone)
The horse's hoof looks very rigid from the outside, but contains several elastic structures inside. Among them are the lateral cartilages, which sit on the inner and outer wing of the coffin bone in every hoof (see anatomy). When these cartilaginous structures ossify, this is called ossification of the lateral cartilages (sidebone). This can affect either one or both lateral cartilages in a hoof and can occur in one or more hooves. The front hooves are affected more often than the hind hooves.
How does sidebone develop?
Sidebone develops due to frequent or persistent overloading of the hoof, especially through concussion (e.g. very hard ground, often in combination with metal shoeing) or incorrect loading due to conformation faults. In particular, toe-out or toe-in conformation favours ossification of the lateral cartilages, since in this case the inner or outer side of the hoof is permanently overloaded. But heels that are too high or heel contraction can also lead to sidebone. In rare cases a single trauma can lead to ossification of a lateral cartilage.
In addition, heavy breeds or horses with a low height at the withers compared to body mass (i.e. with relatively short legs) are more often affected by ossification.
The hoof essentially tries to counteract the overload by slowly converting the flexible cartilage into stable bone substance. In English the term "sidebone", i.e. "lateral bone", is therefore used.
In addition, the nutrition factor must also be taken into account: cartilage is not supplied by blood vessels but has to be actively "flushed" with nutrient-rich fluid. However, this only happens during loading and unloading, i.e. with movement. It is therefore not only important that the horse is balanced in terms of minerals, but also that it is in constant movement, so that the cartilage tissue is well supplied and remains healthy. Undersupplied cartilage is more susceptible to ossification.
Prevention, detection and healing of sidebone
The best prevention against ossification of the lateral cartilages is to avoid the overloads mentioned above as well as to keep and feed your horse in a species-appropriate manner.
Nevertheless, sidebone is very widespread - however, in the initial stage horses often show no lameness, which is why the ossification is often only recognised at an advanced stage or as an incidental finding. In severe cases the ossifications can even be felt at the coronet or recognised with the naked eye as a kind of "bump". Otherwise, an X-ray provides clarity: sidebone is visible there as a cloud-like outgrowth in the rear part of the hoof.
Many horses live completely pain-free with sidebone. Depending on severity, however, the mobility of the hoof may be restricted, which can cause changes in gait (e.g. stumbling). Due to reduced elasticity in the hoof, blood supply within the hoof may also be reduced, which in turn can result in poorer horn growth.
In some horses, sidebone leads to problems because the newly formed bony structures can press on sensitive tissue (e.g. ligaments) and so the horses sometimes show diffuse lameness. These typically appear on hard ground or in tight turns.
In rare cases the ossified lateral cartilages can also fracture - like any other bone - and therefore lead to clear lameness.
Sidebone cannot be cured because the ossification process is irreversible. But with good management the progression can be stopped or at least slowed down. To do this, it is necessary to eliminate the causes as far as possible, e.g. correct conformation faults, reduce excess weight, adapt training, avoid hard ground etc.
Apart from that, lameness can be reduced by providing the horse with relief using a glue-on shoe (Klebebeschlag). Such a plastic Bekleb offers good shock absorption and can thus provide a degree of compensation for the ossified lateral cartilage.
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