The equine flexor tendons are rope-like structures located in the rear part of front and rear lower limbs. They have critical structural, shock absorbing and slinging functions in the lower limb. They are under tremendous tension as the horse bears weight.

The deep digital flexor tendon runs down the back of the cannon bone, through the back of the fetlock, down along the back of the pastern, and dives between the heel bulbs and into the hoof. Here it runs over the navicular bone and bursa, and attaches on the rear part of the coffin bone. The full weight of the horse is borne through the deep flexor tendon; it is under great strain normally.

Tendinitis is strain and tearing of the fibers of a tendon, usually from overload of the structure.

These injuries have been thought to occur from overload in deep footing or injury when a horse steps in a hole. There are likely many other reasons for injury and predisposing factors too.

Pain in the back half of the equine hoof has historically been difficult to differentiate using ultrasound and radiography. Much of it has been attributed to the navicular bone. As MRI has become more commonly performed, we have recognized a whole range of tears and injuries that occur to the deep digital flexor tendon within the hoof.

Tearing of the deep digital flexor tendon within the hoof may be part of the same process that causes degeneration of the navicular bone and inflammation within the navicular bursa. This is an important cause of lameness that is localized to the heel with nerve blocks.

Diagnosis requires lameness exam, nerve blocks, ultrasound and especially MRI. It is almost impossible to definitively diagnose this condition without MRI. Ultrasound is useful but we are limited by our ability to see the structures within the hoof.

Treatment centers on rest, but may include a variety of other treatments including regenerative therapies.