Therapeutic Shoeing for Tendon Injuries: Not One Size Fits All

A horse’s injured tendon is likely to heal better if it’s got less strain on it. Corrective shoeing that changes the hoof’s angle in relation to the ground can affect the strain on the tendons of the distal (lower) limb. But according to a new study, changing the hoof’s orientation doesn’t always relieve the superficial and deep flexor tendons in the intended way. In some cases, to reduce strain the angle would have to be modified so much it could create new problems.

“Popular shoeing recommendations to relieve fetlock-related structures through a change in hoof angulation often don’t work and cannot be generally assumed for each horse,” said Jenny Hagen, DrMedVet, of the Institute of Veterinary Anatomy, Histology, and Embryology in the Faculty of Veterinary Medicine at Leipzig University, in Germany.

The Study: 30 Horses and Six Hoof Wedges

In their study, Hagen and her fellow researchers placed wedges under the toes of heels of 30 barefoot horses. They used duct tape to attach three different sizes of wedges, creating six changes in hoof angle: 5°, 10°, and 20° each of toe and heel wedges. They then took radiographic and ultrasound measurements to see how the wedges affected various morphometric (size and shape) and biomechanical parameters.

They mainly observed how these angular changes affected the superficial digital flexor tendon (SDFT) and the deep digital flexor tendon (DDFT). Both these tendons run down the back of the leg between the carpus (knee) and the fetlock or the hock and the fetlock. The SDFT is the tendon closest to the outside, that you can feel when you run your hand down the back of your horse’s leg. The DDFT runs beneath the branches of the SDFT and over the navicular bone, inserting into the back of the coffin bone.

To estimate loading or relief on the tendons, the research team measured tendon width at different shoeing angles. Because tendons are elastic, it seemed logical that the thinner the tendon, the more tightly it’s being pulled, Hagen said. By contrast, the wider the tendon, the more relaxed and less strained it is.

Hagen’s group found that, overall, the 5° angle made little difference in the strain on the SDFT and the DDFT. While they did notice some relaxation of the SDFT and the DDFT with bigger angle changes (19°-20°), those changes in hoof orientation would probably be “uncomfortable” for the horse and might provoke secondary injuries at joints and soft tissue structures, she said. It would be somewhat similar to asking a human to run in high heels, she added.

Comparison to Previous Hoof Angle Studies

The research team’s findings contradict some established orthopedic concepts. “A French research group found that a steeper hoof angulation causes increased extension in the fetlock joint and higher load on the SDFT, and that a flatter hoof angulation leads to less extension in the fetlock joint related to a relief of the SDFT,” Hagen said. “And those findings became popular and influenced the design of commercially provided therapeutic horseshoes. But I could already see in my clinical work with therapeutic shoeing in the horseshoeing school here that this biomechanical principle was not working in each case of therapeutic shoeing to relieve tendon injuries, and my study supports that.”

The French study was based on five horses. In that small population, explained Hagen, the researchers found no obvious individual differences in reaction of the fetlock joint angle. And they didn’t examine the load or flexor tendon morphometrics in relation to the use of different wedges. She said the results from her study on six times as many horses suggests that not all equine tendons react the same way to a flatter or steeper hoof orientation.

“The individual reaction of the fetlock angle and the load on the tendons related to a change in hoof angulation is dependent on body conformation as well as the limb and hoof conformation of each horse,” she said. “In particular, the length and angulation of the pastern interacts with the effect of therapeutic shoeing. In addition, it is likely that muscle properties and tendon stiffness affect the influence of therapeutic shoeing on the stated parameters.”

Recommendations for Veterinarians and Farriers

Based on her study, Hagen said she has the following recommendations for farriers and veterinarians working on horses with tendon issues:

  • Take the time to evaluate every single patient carefully in stance (when the hoof is in contact with the ground) and walk with a focus on toe conformation and hoof-ground contact during motion.
  • Avoid standard solutions for specific orthopedic diseases.
  • Tape wedges to the foot before applying the final horseshoe to test the effects of hoof angulation changes on the biomechanics of the distal limb.
  • Work as a team and improve communication between owner, farrier, and veterinarian.
  • Work from a clear diagnosis to identify the injured structure before selecting a therapeutic shoeing approach.
  • Have each shoe manufactured on a case-by-case basis to avoid unnecessary side effects.
  • Keep ground conditions and rehabilitation status in mind when selecting shoeing type, because there’s often a difference in shoeing for static and dynamic conditions.
  • Keep therapeutic shoeing temporary, and always aim for standard shoeing or bare feet in the long run.
  • Have the owner adapt the horse’s management to the status of rehabilitation and shoeing.