Fetlock boots are used on the hind legs to protect brushing injuries to the inside of a horse's lower leg from the opposite leg or hoof brushing against or striking the leg.

Brushing injuries are commonly due to the conformation of the horse and occur mostly on horses whose hooves swing inwards although brushing injuries can also occur in young, tired, lazy horses, or from working on uneven ground and can be severe particularly if the horse is shod.

Fetlock boots are used with tendon boots and are popular with show jumpers as they provide protection to the sides of the fetlock area whilst still allowing the horse to feel a pole if it brushes or knocks it with its leg whilst jumping so that is encouraged to be more careful next time.

Fetlock boots often have a hard moulded plastic outer shell but may also be made of leather or other material.

Leather fetlock boots tend to have straps and buckles to fasten them, but synthetic fetlock boots are usually fixed with several velcro fastenings which fasten around the horse's leg or which pass through a ring and fasten back on themselves. Some have double velcro straps that overlap and these are more secure than single velcro straps. Fetlock boots with velcro fastenings make putting on and taking the boots off quick and easy, and are more adjustable than straps and buckles.

Fetlock boots should have a soft lining to prevent any soreness occurring and it is important that the fetlock boots fit the horse comfortably to avoid any rubbing. There are fetlock boots available with fleece or skeepskin lining for extra comfort and these linings may be removable for easy cleaning. Fetlck boots will inevitably get dirty and so it is important that they can be easily and regularly cleaned.