I am not 100% sure whether you are referring to shin splints, or bony spurs, so I shall address both for you.
What you will need to know in both cases, is that bone is continually going through a process of remodeling and changes, based on the stresses that are placed on it. Bone changes over a period of time, and there are specific cells in bone that are able to build bone, or absorb (remove) it. Exercise and the horse`s movement and work load play a great role in the stresses being placed on bone and how it responds to those stresses.
Bony spurs are small bony growths that develop, usually at a joint margin. They are often referred to as `osteophytes`. If you imagine the joint surface, covered by its protective layer of cartilage and you imagine in a working horse that there are of course many stresses being placed on the bone and the cartilage. Any stresses that are more than the bone and cartilage can handle, or any type of degenerative disease in the cartilage or bone, will cause an inflammation reaction at the site of the stress and will cause the cartilage to wear down or thin. In order to relieve the stress and protect the exposed area in the joint or on the bony surface, the body lays down more hard bone, and this will result in a small bony growth. Also, where ligaments, tendons and joint capsules attach to bone, muscle and joints, there can also be excessive stress leading to the development of bone, especially where fibres tear out of bone, causing painful inflammation (shin splints!). These types of bony spurs are called enthesiophytes.
Treatment of these bony growths depend on a host of factors, such as site and size of growth, whether the growth is active and inflamed or has settled, the age of the horse, expected level of work and competition, and so on. Treatments include corrective shoeing, systemic and topical anti-inflammatory agents, support bandages/ boots, extra-corporeal shock wave therapy, cartilage protectants, and joint injections. The keys to remember are that bone spurs are radiographic findings that are symptomatic of damage and not a specific disease themselves. They can occur as a result of multiple causes. Treatment is for the underlying cause, and a specific diagnosis is critical to establishing a therapeutic plan.
Shin Splints are a form of bony spur that develops between the splint bones and the thick cannonbone because there is a small amount of movement possible in the splint bones. When the movement becomes too much to quickly, the very small fibres holding the splint bones to the cannon bone tear out of the cannon bone, resulting in pain and inflammation. To keep the splint bones still and reduce the tearing, the body lays down bone around the area causing a characteristic bony lump on the forelimb. A splint can also develop that is not easily seen at all, and is often referred to as a `blind` splint.
They can also be caused by direct trauma to the leg, damaging the periosteum (membrane covering the bone), but the cause is most often concussion and overwork - especially in young and unfit horses. Bone needs time to adapt to work loads being placed on it.
The treatment of shin splints can be very successful if done properly and if treatment commences as quickly as possible, and often there is a very good prognosis for the horse.
The horse`s workload should be decreased immediately, for at least three weeks, or longer if the heat and swelling has not improved by then. Ideally, the horse should be stabled, and hand walked twice to three times daily, taking care that the horse does not knock the swollen area while walking, causing even more damage. (The walking is an important part of recovery!) Several days of cold hosing, anti-inflammatories and bandaging may help, but the essential ingredient to a successful recovery is time. Herbal remedies may also be considered, such as Devils Claw, or a product by Hilton Herbs called Rest and Recover (A pure dried herbal blend for horses and ponies containing Devils Claw, Meadowsweet, Hawthorn, Valerian, Vervain, Chamomile and Cleavers. This combination blend helps to maintain mobility and a calm outlook during any period of enforced inactivity). Topical anti-inflammatories and cooling gels can also be tried, as well as Comfrey compresses and Arnica. Surgery to remove the excessive bone deposits is also an option but is very rarely successful, as the surgery may stimulate even more bone formation. This should be discussed with your Vet.Horses normally return to work very successfully, however the owner should be very careful to determine the cause of the splint - overworking your horse, working on rock-hard surfaces or not giving the horse`s bone time to adapt to training should be addressed. Things to also consider are shoeing and correct hoof balance and even diet. (Feeding too much bran- high phosperous low calcium content - has been implicated in splints, although this has yet to be proven scientifically).
I hope this has answered your question - let me know if you would like any more information. I would consult a vet if you are worried about your horse, also never be scared to get a second opinion!