Styrofoam's Effects on Forefoot Pressure and Load Distribution (AAEP 2010)

Laminitis is a critical cause of lameness in horses: Not only is the exact cause not known in all cases, but considerable controversy persists about how to treat and manage this disease. At the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md., Jennifer Schleining, DVM, MS, Dipl. ACVS-LA, a clinician in the department of veterinary clinical science at Iowa State University, discussed the common practice of using industrial Styrofoam to increase weight-bearing surface area while decreasing total contact pressure on the bottom of a painful hoof. This method is used primarily as the first line of defense in an acute case of laminitis when veterinarians are trying to prevent permanent mechanical damage, but no studies had previously been conducted on the benefits of Styrofoam.

Schleining reviewed the significant financial impact of lameness, including laminitis, with costs of $675 million for all lamenesses reported in a 1998 USDA study. According to that study, each lameness event resulted in an average of 110 days of lost use as well as an emotional impact on owners and veterinarians. Laminitis is the second leading cause of equine death, behind colic--nearly 200,000 horses were diagnosed with laminitis in 2007.

In the developmental stage of laminitis, Schleining explained that a shift in weight bearing is not evident before clinical signs are recognized--the typical laminitis stance is not seen until after the coffin bone has displaced. Treatment goals are to diminish or eliminate the inciting cause, to minimize pain, and to prevent permanent damage and mechanical collapse of hoof laminae (the sensitive tissues that connect the coffin bone to the interior of the hoof wall).

"No one technique benefits all patients," Schleining reported, explaining that approaches to mechanical support are attempted in numerous ways with the Lily pad, roll gauze taped to the frog, heart-bar shoes, Stewart clogs, shoes or hoof casts with fillers, or Styrofoam. She commented that, based on previous studies, Lily pads increase laminitic pain in the initial five days, roll gauze has no peer review to substantiate claims that it works, and the efficacy of controversial heart-bar shoes is dependent on farrier skill in application. Hoof wall casts with 15-20-degree heel elevation decrease hoof wall strain by 60% at the toe, yet she said the effects are disappointing since lateral hoof wall strain along the sides of the hooves increases 35%.

In the study Schleining and colleagues hoped to show that industrial Styrofoam (1½-inch blue foam) increases the weight-bearing surface area, decreases contact pressure, and results in pressure shifts toward the heel. She said the study, which the team performed on normal horses, corroborated this hypothesis. The result was immediate benefit through decreased hoof pressures.

An unexpected shift of the center of pressure toward the toe did not significantly move toward the heel until 24-48 hours after placement. Eighty percent of the horses had areas devoid of weight-bearing in the center of the foot, likely due to standing on wood shavings over rubber mats.

Shift of the center of pressure toward the heels is beneficial to decrease the pull of the deep digital flexor tendon on the coffin bone, thereby lessening the risk of coffin bone rotation. Schleining suggests that better results might be achieved by using less thick Styrofoam initially and then adding an additional layer after 24 hours, or by applying a 1-2° wedge prior to placing the Styrofoam.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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