REFEREED In Vitro Assessment of the Equine Hoof Wall Strains in Flat Weight Bearing and After Heel Elevation Maria Ce ´lia Ramos Bellenzani, PhD, Associate Professor, a Ju ´lia Maria D’andrea Greve, PhD, Professor-Physiatrics, b and Ce ´sar Augusto Martins Pereira c ABSTRACT Horseshoeing is a common practice, but effects on the hoof wall are poorly understood. Strain gauges were used to document and compare hoof behavior in vitro during flat weight bearing and after artificial heel eleva- tion. Ten front limbs of Thoroughbred race horses, shod with conventional flat shoes, were used. Eight strain gauges were symmetrically distributed around the toe, quarters, and heels. Each limb was mounted to a testing machine (Kratos K5002; Kratos Dyna- mo ˆmetros, Ltda., Cotia-SP-Brazil) and subjected to a load equivalent to 30% of the donor’s body weight. Strains (m3) were acquired by means of a computerized system and the results compared using Friedman and Wilcoxon statistical tests. There was greater strain varia- tion when the heels were elevated. Compression predo- minated during flat weight bearing, with a tendency to horizontal traction after heel elevation. The changes in strain caused by heel elevation were not always symmet- rical. Elevation of the heels tensed the toe and the medial quarter horizontally, increased load at the posterior por- tion of the hoof capsule, and hindered its expansion. Keywords: Equine; Hoof wall; Heel elevation; Strains; Strain gauges INTRODUCTION Lameness is the major cause of poor performance in athlete horses, 1 particularly forelimb lameness. 2,3 The hoof cap- sule, a conical structure made of hard keratin 4 that encloses the third phalanx and adjacent structures to form the equine digit, is often the source of pain; causes are commonly re- lated to inadequate trimming and shoeing practices. 5 The art of farriery is an old one and relies more on tradi- tion than on science. Its consequences on hoof physiology and biomechanics are poorly understood, and research on this field is quite limited. Biomechanical studies tend to focus on the behavior of joints, tendons, and ligaments, rather then on the hoof itself. The shod hoof is more stable close to the weight-bearing surface than proximally. 6 Among other possible effects, shoeing restricts hoof wall flexion, induces earlier spreading of the heels, and delays expansion of the remaining portions of the wall. 7.8 These would reflect force redistribution through the wall and should not be regarded as harmful. 9 One of the most common practices of so-called orthope- dic shoeing is to elevate the heels to relax the deep digital flexor tendon and alleviate stress on the navicular bone, 10-13 but comparatively little information exists regarding its effects on the hoof capsule. Hoof material is anisotropic and behaves in a complex manner, showing greater flexibility in a vertical direction, along the tubular material. 14,15 As wall thickness decreases from dorsal to palmar or plantar, rigidity decreases from the toe to the quarters and the heel. 16 Force transmission through the hoof wall has been as- sumed to occur in the direction of the horn tubules, but part of such forces actually parallel the horizontally distrib- uted intertubular material. 17 Different studies, employing different methods, have demonstrated that the direction of principal strains on the hoof wall do not match the ori- entation of the tubules. 18,19 Internal forces also act on the dorsal wall as a result of the pull of the deep digital flexor tendon and produce a dorsoconcavity. 17 Other forces af- fecting the hoof are the shearing effects generated by changes in hoof shape. 13 Heel expansion occurs during weight bearing 7 and, in contrast to older theories, is primarily a response to expan- sion of the quarters. 13 In fact, it has been shown that hoof capsule expansion is unrelated to frog pressure, 8 although frog pressure may be one of the factors involved in heel movement, together with hoof anatomy and the frictional effect of the ground surface. 20 Heel movement also occurs toward the dorsal toe, particularly at the lateral heel. 18 Compressive strains predominate during the stance phase, with vertical forces reflecting weight transmission and horizontal forces reflecting hoof deformation. Such ORIGINAL RESEARCH From the Pontifı´cia Universidade Cato´lica (PUC), Poc ¸os de Caldas –MG and UNIPINHAL, Espı´rito Santo do Pinhal, Sa˜o Paulo – SP, Brazil a ; Instituto de Ortopedia e Traumatologia, School of Medicine, Sa˜o Paulo University (FM-USP), Sa˜o Paulo – SP, Brazil b ; and the Instituto de Ortopedia e Traumatologia, School of Medicine, Sa˜o Paulo University (FM-USP), Sa˜o Paulo—SP, Brazil. c Reprint requests: Maria Ce´lia Ramos Bellenzani, Rua Nelson Frank, 61 Jardim Olı´mpia, CEP 05542-170 Sa˜o Paulo—SP, Brazil. 0737-0806/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2007.10.003 Journal of Equine Veterinary Science  Vol 27, No 11 (2007) 475