Lameness in show jumpers is often caused by forelimb tendon injury. The superficial digital flexor tendon (SDFT) is most frequently injured, followed by the interosseus tendon (IT), and the accessory ligament (AL), while the deep digital flexor tendon (DDFT) is rarely injured. Repetitive landings over high fences produce significant forces on these tendons. Past studies have calculated combined forces on the forelimb tendons without analyzing each limb or each tendon separately. However, it is actually the trailing forelimb in a landing that experiences the greatest forces, and those forces most certainly increase with increasing fence height.

This study used living horses to analyze the forces on each tendon of the trailing limb during landings over fences of increasing height. Cadaver limbs were also subjected to various forces in the laboratory.

The investigators discovered that forces during landing over two- to three- foot fences were lowest on the DDFT (and AL), higher on the IT, and highest on the SDFT. Forces on the SDFT actually exceeded the force necessary for tendon breakage in the laboratory. Increasing fence height up to four feet substantially increased forces on the SDFT, but barely affected the forces on the IT and AL beyond what was experienced over low fences. In fact, forces on the IT and AL only increased as the horse became increasingly fatigued.

The authors concluded that increasing fence height increased the risk of injury to the SDFT. However, there might be an effect of genetics and/or conditioning in elite jumpers that protects them from injury, which is why the SDFT in these animals can handle forces that rupture tendons in less conditioned animals. Lowering fences and preventing fatigue in less competitive horses could provide some protection from troublesome tendon injury.

Equine Veterinary Journal Supplement, 33: 6-10, 2001.