Horses with too-long feet and heavily-padded shoes are most at risk. Other horses can develop capped elbows and hocks because of poor stable management. Lying on hard ground can promote the development of both.Recently many more capped elbows and hocks are appearing.. Most likely because  people believe that using rubber mats in stalls means that there is little or no bedding required. Not true. Stalls will be easier to clean if there are mats under the bedding, and it is sometimes possible to use less bedding, but in no case should the stall be bare, nor should the "bedding" consist of a light sprinkling of shavings over the top of the stall mats. Even if the mats are very cushiony, there should still be at least a 4" to 6" layer of absorbent bedding between the horse and the mats.