Sesamoiditis: At the back of the fetlock is two sesamoid bones. Sesamoiditis occurs when these bones are damaged or inflamed. Acute lameness is generally present and the fetlock will swell. Long pasterns and repetative concussion to the area is the usual cause. This is a serious condition and the horse will need to be immobilized. Treatment: Long rest period (12 monthes). Pain relief and lower leg treatments. Splints: Splints are very common and are usually not serious. A splint is a hard and bony swelling on either side of the cannon bone.