A tendon is the attachment of a muscle to bone. The equine flexor tendons are highly specialized and vitally important structures in the lower limb. The muscles that attach to these tendons are in the upper limb, but the tendons run down the rear of the lower limb, below the carpus of the front limb or the hock of the hind limb. Here they attach to the pastern bones or P3 (depending upon the tendon), below the level of the fetlock. The flexor tendons support the full weight of the horse in weight bearing and normally tolerate tremendous tension.

Tendons have very little blood supply and therefore heal very slowly. When examined under the microscope, ligaments and tendons are composed of highly organized dense connective tissue that is extremely strong. Generally, they heal through the formation of scar tissue, which is never as strong or as flexible as the original structure. Due to this, re-injury is common.

A strained tendon is one in which tendon fibers have been torn or damaged.

When strained, these tendons become enlarged and bulge out, and this appears as a long vertical swelling that gives the affected leg a distinctly "bowed" contour. New injuries are soft, warm and painful to the touch. Over time the injuries become firmer and cool, as they are mostly scar tissue. Initially, horses with strained flexor tendons are moderately to severely lame, depending upon the tendon involved and the severity and location of the tear.

Flexor tendon injuries are common in performance horses of various disciplines and breeds. Bowed tendons are also more commonly seen in horses with long weak pasterns, and as a result of improper shoeing. These can be severe injuries that take a long time to heal due to the mechanics of the flexor tendons. In addition, re-injury is common in performance horses.

Diagnosis requires a clinical lameness exam, and careful assessment of the affected area. Ultrasound is by far the most useful diagnostic for assessing these soft tissue injuries.

There are now many more treatments available, including the regenerative therapies, which are being claimed to be far more effective than prior treatments. There is little proof of this at this time. Regardless of the injury, a critical part of effective treatment is a graded return to fitness and gradual strengthening and repair and remodeling of the injured tendon.