The effect of hoof angle variations on dorsal lamellar load in the equine hoof G. D. RAMSEY*, P. J. HUNTER and M. P. NASH † Auckland Bioengineering Institute and † Department of Engineering Science, The University of Auckland, Auckland, New Zealand. Keywords: horse; equine hoof; biomechanics; finite element analysis; model; hoof angle Summary Reasons for performing study: In the treatment of laminitis it is believed that reducing tension in the deep digital flexor tendon by raising the palmar angle of the hoof can reduce the load on the dorsal lamellae, allowing them to heal or prevent further damage. Objective: To determine the effect of alterations in hoof angle on the load in the dorsal laminar junction. Methods: Biomechanical finite element models of equine hooves were created with palmar angles of the distal phalanx varying from 0–15°. Tissue material relations accounting for anisotropy and the effect of moisture were used. Loading conditions simulating the stages in the stance where the vertical ground reaction force, midstance joint moment and breakover joint moment were maximal, were applied to the models. The loads were adjusted to account for the reduction in joint moment caused by increasing the palmar angle. Models were compared using the stored elastic energy, an indication of load, which was sampled in the dorsal laminar junction. Results: For all loading cases, increasing the palmar angle increased the stored elastic energy in the dorsal laminar junction. The stored elastic energy near the proximal laminar junction border for a palmar angle of 15° was between 1.3 and 3.8 times that for a palmar angle of 0°. Stored elastic energy at the distal laminar junction border was small in all cases. For the breakover case, stored elastic energy at the proximal border also increased with increasing palmar angle. Conclusions and potential relevance: The models in this study predict that raising the palmar angle increases the load on the dorsal laminar junction. Therefore, hoof care interventions that raise the palmar angle in order to reduce the dorsal lamellae load may not achieve this outcome. Introduction In equine hooves affected by the disease laminitis, the mechanical strength of the lamellae attaching the hoof capsule to the distal phalanx (Fig 1) is compromised. A common consequence is that the hoof capsule rotates in relation to the distal phalanx or vice versa (Stashak 2002). In the treatment of laminitis, it is current practice to raise the hoof angle, since this reduces the force in the deep digital flexor tendon (DDFT) (Lochner et al. 1980; Riemersma et al. 1996; Willemen et al. 1999) and it is believed that it also reduces the mechanical stress on the dorsal lamellae (Hood 1999; Stashak 2002; Parks and O’Grady 2003; O’Grady and Poupard 2003; Redden 2003) allowing them to be unloaded to aid healing. However, whether this unloading of the dorsal lamellae actually occurs in practice remains unknown (Leach 1983; Hood 1999). An alternative hypothesis for the biomechanics of distal phalanx loading was described by Coffman et al. (1970) and predicts that the predominant force is the bodyweight of the horse applied to the distal phalanx through the second phalanx. They considered the force of the DDFT to have less consequence because its point of attachment corresponds with the hypothesised centre of rotation during failure and recommended lowering the heels as a strategy for relieving the stress on the dorsal lamellae. Leach (1983) suggested that even though raising the heel decreases the strain in the DDFT, excessive elevation could change the orientation of the load exerted on the distal phalanx by the second phalanx, resulting in a potentially damaging loading situation at the laminar junction. Leach also reported that both raising and lowering the heels have historically been recommended as laminitis treatments. Thomason et al. (2005) used a model to investigate the morphology of the laminar junction and found a correlation between the lamellar spacing and magnitude of the predicted stress. Their study indicated that the stress in the laminar junction is greater proximally than distally, but did not report on its variation with hoof angle. The effect on the hoof capsule of raising and lowering the heels was modelled by Hinterhofer et al. (2000), who found that raising the heels lowered the peak stress and deflections in the capsule. Their model did not include the laminar junction. Strain measurements by Bellenzani et al. (2007) revealed that raising the heels hindered their expansion but, in contrast to the results of Hinterhofer et al. (2000) caused a greater variation of strain within the capsule. Hobbs et al. (2009) found a large reduction in radial strain in the proximal part of the toe wall when the heels were raised by 10°. To test the hypothesis that raising the hoof angle decreases the load in the dorsal lamellae, we created biomechanical finite element models to represent normal hooves with palmar angles of *Corresponding author email: g.ramsey@auckland.ac.nz [Paper received for publication 03.05.10; Accepted 07.09.10] © 2011 EVJ Ltd 536 EQUINE VETERINARY JOURNAL Equine vet. J. (2011) 43 (5) 536-542 doi: 10.1111/j.2042-3306.2010.00319.x