Laminitis has afflicted the equine population for centuries and continues to be a substantial contributor to equine morbidity.1 It is believed that the cause of laminitis is likely multifactorial; therefore, it is difficult to identify a single mechanism of action. Many in vitro experiments have provided insight regarding potential pathways for the development of laminitis, but such pathways are difficult to confirm in vivo.2 The exact etiologies remain elusive, and the goals of treatment of acute laminitis are mainly supportive—relieve pain, halt or slow progression of the disease, and enhance recovery.3
There is considerable controversy regarding the best way to treat laminitis in the acute phase.4 An ideal approach to management of acute laminitis should include treatment aimed at the physiologic and biomechanical mechanisms of the disease while providing the horse with appropriate analgesia. Mechanistically, this would include an intervention that decreases the stresses placed on the laminar junction. The options for accomplishing this are to decrease the force exerted by the deep digital flexor tendon on the third phalanx, decrease the force acting in a vertical manner on the lamina, and increase the surface area across which the vertical load is distributed. Additionally, an ideal treatment should be easy to administer and cost-effective for owners. Deep digital flexor tenotomy is an effective way of removing the strain in the deep digital flexor tendon, but because of surgical complications and a poor prognosis for athletic soundness, this surgical intervention is reserved for salvage cases. Raising the heels is a less aggressive method of reducing strain in the deep digital flexor tendon by shifting the center of pressure palmarly (or plantarly), but results of a study5 in which a 59% increase in lateral hoof wall strain resulted from a 15° to 20° heel elevation suggest that severe wedging may be detrimental to successful laminitis treatment. Increasing the weight-bearing surface area of the foot distributes the vertical load over a larger area, thereby decreasing the load placed on the normal weight-bearing structures—mainly the hoof wall.6
A popular belief is that the support offered by applying industrial polystyrene foam insulation sheeting (known as blue foam) to the sole of the foot redistributes the weight of the horse, normally borne mainly by the hoof wall, to include the entire palmar surface of the foot.4,7 This would then decrease primary weight bearing by the hoof wall and presumably the laminar structures and redistribute weight to the sole and frog. In addition, it may provide support to the digital cushion and tissues between the distal phalanx and the sole. To this effect, prevention of laminar separation may be possible.
The purpose of the study reported here was to evaluate the ability of polystyrene foam sole supports to increase the weight-bearing surface area of the feet, decrease contact pressure, and move the center of pressure palmarly and validate its use as an effective means of minimizing load on hoof wall and presumably the laminar junction, with the long-term goal of providing an evidence-based approach to treatment of acute laminitis in horses. We hypothesized that the weight-bearing surface area in the forefeet of horses would be increased, the contact pressure decreased, and the center of pressure moved palmarly.
Matscan HR Mat 7101E, Tekscan Inc, South Boston, Mass.
Styrofoam, Dow Chemical Co, Midland, Mich.
Elasticon, Johnson & Johnson Co, Skillman, NJ.
HR Mat Research, version 6.3, Tekscan Inc, South Boston, Mass.
MIXED procedure, SAS System for Windows, version 9.1.3, Service Pack 4, SAS Institute Inc, Cary, NC.
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