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Physiologic horseshoeing
Foot Science Physiologic Horseshoeing Stephen E. O’Grady, BVSc, MRCVS, and Derek A. Poupard, CJF
A
dherence to basic principles of physiologic horseshoeing is essential in maintenance of hoof health and soundness. Most horses do not require special trimming or shoeing techniques. Familiarity with a few basic concepts can help the veterinarian recognize when changes in trimming or shoeing might be expected to help the performance of a sound horse or to help restore the performance of one that is lame.
There may be no other routine procedure performed on the equine athlete that has more influence on soundness than hoof preparation and shoeing. Physiologic horseshoeing could be defined as that which promotes a healthy functional foot and biomechanical efficiency and prevents lameness.1 Because the veterinarian is responsible for the total care of the horse, a working knowledge of farriery is essential. Trimming and shoeing can affect a variety of important parameters, including: the manner in which the foot lands; the duration of the stance phase of the stride and breakover; normal foot function; and injuries related to landing and weight bearing. A thorough knowledge of proper traditional horseshoeing1-3 enables the veterinarian to interact with the farrier to enhance and promote quality hoof care. Important aspects include hoof balance, hoof length, and hoof angulation. HOOF BALANCE The term hoof balance was seldom used in the early farrier texts. Hoof balance should be considered a concept because it has no universal definition. Indeed, when the term “balance the hoof” is used, multiple questions may arise because hoof balance can be further divided into geometric, dynamic, and natural balance. Unfortunately, it may not be possible to satisfy all these concepts simultaneously. Geometric balance, which observes the horse at rest, means the foot should be symmetric (ie, the foot is trimmed so that the ground surface of the hoof is perpendicular to the long axis of the limb). Although it is a useful and readily identifiable concept, the problem with relying on geometric balance alone is that it does not consider the landing pattern of the foot
nor does it consider any potential relationship between leg and foot conformation. Dynamic balance, which observes the horse in motion, implies that a balanced foot should land symmetrically (ie, the foot should land flat with the hope that this places force uniformly on the solar surface of the hoof wall). The problem here is that often it is not possible to achieve a flat strike pattern because of leg conformation. Furthermore, it may be detrimental to the horse if the hoof is trimmed to land in a flat strike pattern if abnormal leg conformation is present. Recently, the term natural balance has been introduced. This suggests that foot conformation should be modeled after the foot in its natural state (ie, feral horses). It is unknown whether this type of balance allows maximum functional strength, whether it does not take into account the specific athletic activity of the horse, and whether it is largely incompatible with traditional horseshoeing techniques.4 Hoof balance encompasses both dorsal palmar/plantar balance and mediolateral balance. Improper mediolateral hoof balance has been associated with foot problems such as sheared heels, distorted hoof walls, and hoof cracks. These problems arise from disproportionate forces placed on the lateral or medial aspects on the foot.5 A problem arises with the exclusive use of either geometric or dynamic balance to address mediolateral trimming, as each may produce a foot with a different shape if the landing pattern or limb conformation deviates from normal. Because of this, no one standard method of trimming will achieve optimum mediolateral balance for every horse. HOOF LENGTH Hoof length (toe length) is determined with measurement from the toe at the ground surface proximally to the end of the horny wall at the coronary band. Guidelines for appropriate toe length have been established for most breeds on the basis of body weight (Table).6 With these guidelines, it becomes necessary to consider anatomic variations in: the relative position of the third phalanx within the hoof capsule; the thickness of the hoof wall; the hoof shape; and the horse’s athletic endeavor. HOOF ANGLE
Reprint requests: Stephen E. O’Grady, BVSc, MRCVS, Northern Virginia Equine, 7135 Mt Eccentric Rd, The Plains, VA 20198. From equipodiatry.com. Reprinted with permission. doi: 1053/jevs.2003.36
Volume 23, Number 3
The angle of the hoof is the angle formed at the junction of the dorsal hoof wall and the ground surface of the foot. Until recently, the veterinary and farrier literature recom123
Table
Guidelines for hoof length on basis of weight of horse Horse weight
Horse size Small Medium Large
Kg
Lb
360-400 800-900 425-475 950-1050 525-575 1150-1250
Toe length Cm
In
7.60 8.25 8.90
3.00 3.25 3.50
mended that the normal hoof angle be 45 to 50 degrees for the forefeet and 50 to 55 degrees for the hind feet. These recommendations have been proven erroneous because they do not take into consideration the conformation of the horse’s individual limbs.7 Ideal hoof angulation occurs when a line drawn down the dorsal surface of the hoof wall and a line drawn along the surface of the heel are in alignment or parallel to a line drawn through the 3 phalanges. The foot is trimmed appropriately and the hoof angle is correct for the individual horse when the dorsal hoof wall and the dorsal surface of the pastern region are parallel. This is known as the hoof pastern axis. For confirmation of this hoofpastern axis visually, the horse should be on a hard level surface and must stand squarely on all 4 feet with the cannon bones positioned vertically. The terms low hoof angle and high hoof angle can be used simply to describe a nonlinear relationship between the dorsal hoof wall and the dorsal pastern region. In the normal foot, a vertical line drawn from the center of the lateral condyle of the distal second phalanx to the ground should bisect the bearing surface of the foot.8 This line would mark the center of rotation of the distal interphalangeal joint and would coincide with a line drawn across the solar surface of the foot through the middle one third of the frog. This line drawn across the solar surface should equal the widest part of the foot. FUNCTIONAL CONSIDERATIONS Foot conformation (shape) is important because of its relationship to the foot’s biomechanical function. Any changes made to the bottom of the horse’s foot will have an effect on the angulation of the hoof, the hoof-pastern axis, and the alignment of the hoof capsule under the center of rotation. Variation away from optimum for these parameters may result in decreased biomechanical efficiency. Perhaps the most commonly discussed functional element of hoof movement is breakover. Breakover is defined as the phase of the stride between the time the horse’s heel lifts off the ground and the time the toe lifts off the ground. The toe acts as a fulcrum around which the heel rotates under the influence of the deep digital flexor tendon. The suspensory ligament to the navicular bone and the impar ligament are under maximal stress just before breakover.9 Changes in toe length, hoof-pastern axis, and hoof angle all affect breakover and the tensile forces on the deep digital flexor tendon. However, it may not be possible to predict what
124
changes in breakover will occur as a result of a particular trimming modification, nor will such changes necessarily occur at all gaits. In general, breakover is significantly delayed with the presence of a long toe and acute hoof angle because the long toe acts as a long lever arm, requiring more time and forces to rotate the heel around the toe. In addition, it is believed that tension exerted by the deep digital flexor tendon against excessive toe length results in lamina tearing, which may lead to hoof distortion. Low hoof angles, where the angle of the dorsal hoof wall is lower than the angle of the dorsal pastern, create a broken-back hoof-pastern axis. This type of foot configuration is commonly caused by the long-toe/underrun-heel foot conformation. A low hoof angle causes coffin joint extension and increased strain on the deep digital flexor tendon and promotes toe-first landing. This, in turn, may cause increased stress on the soft tissue structures associated with the navicular bone and may delay the speed of breakover. There is experimental evidence that a low hoof angle will compromise circulation in the heel area of the foot.10 This abnormal hoof conformation is known to contribute to navicular syndrome, chronic heel pain (bruising), coffin joint inflammation, quarter and heel cracks, and interference problems. High hoof angles, where the angle of the dorsal hoof wall is higher than the angle of the dorsal pastern, create a brokenforward hoof-pastern axis. An extremely high hoof angle is often classified as a “club foot.” Some horses with extremely upright pasterns may be falsely identified as having a club foot. A high hoof angle causes coffin joint flexion, promotes heelfirst landing, and increases pressure in the heel. Some injuries associated with a high hoof angle are coffin joint inflammation from abnormal loading of this joint, sole bruising, and increased strain on the suspensory ligaments of the navicular bone. (Edited from Proceedings of Alamo Pintado Equine Medical Center Symposium 2003.)
REFERENCES 1. Butler KO. The prevention of lameness by physiologically-sound horseshoeing. Proc 31 Annu Cony Am Assoc Equine Pract 1985;465-75. 2. Curtis S. Farriery-foal to racehorse. Newmarket: R&W Publications; 1999. p. 1-11. 3. Hickman J, Humphrey M, editors. Hickmans farriery, 2 ed. London: J.A. Allen; 1988. p. 136-75. 4. Hood DM, Jackobson AC. The principles of equine hoof wall conformation. Proc Hoof Project 1997;2-19. 5. Moyer W, Anderson J. Sheared heels: diagnosis and treatment. J Am Vet Med Assoc 1975;166:53-5. 6. Turner T. The use of hoof measurements for the objective assessment of hoof balance. Proc 38 Annu Cony Am Assoc Equine Pract 1992;389-95. 7. Bach O, Butler D, White K, Metcalf S. Hoof balance and lameness: improper toe length, hoof angle, and mediolateral balance. Compend Contin Educ Pract Vet 1995;17:1275-82. 8. Colles C. Interpreting radiographs. 1. The foot. Equine Vet J 1983;15:297-303. 9. Clayton H. The effect of an acute hoof angulation on the stride kinematics of trotting horses. Equine Vet J (suppl) 1990;9:86-90. 10. Colles C. Concepts of blood flow in the etilogy and treatment of navicular disease. Proceedings of the 29th Annual Convention of the American Association of Equine Practitioners 1983;265-70.
Journal of Equine Veterinary Science
March 2003
A
dherence to basic principles of physiologic horseshoeing is essential in maintenance of hoof health and soundness. Most horses do not require special trimming or shoeing techniques. Familiarity with a few basic concepts can help the veterinarian recognize when changes in trimming or shoeing might be expected to help the performance of a sound horse or to help restore the performance of one that is lame.
There may be no other routine procedure performed on the equine athlete that has more influence on soundness than hoof preparation and shoeing. Physiologic horseshoeing could be defined as that which promotes a healthy functional foot and biomechanical efficiency and prevents lameness.1 Because the veterinarian is responsible for the total care of the horse, a working knowledge of farriery is essential. Trimming and shoeing can affect a variety of important parameters, including: the manner in which the foot lands; the duration of the stance phase of the stride and breakover; normal foot function; and injuries related to landing and weight bearing. A thorough knowledge of proper traditional horseshoeing1-3 enables the veterinarian to interact with the farrier to enhance and promote quality hoof care. Important aspects include hoof balance, hoof length, and hoof angulation. HOOF BALANCE The term hoof balance was seldom used in the early farrier texts. Hoof balance should be considered a concept because it has no universal definition. Indeed, when the term “balance the hoof” is used, multiple questions may arise because hoof balance can be further divided into geometric, dynamic, and natural balance. Unfortunately, it may not be possible to satisfy all these concepts simultaneously. Geometric balance, which observes the horse at rest, means the foot should be symmetric (ie, the foot is trimmed so that the ground surface of the hoof is perpendicular to the long axis of the limb). Although it is a useful and readily identifiable concept, the problem with relying on geometric balance alone is that it does not consider the landing pattern of the foot
nor does it consider any potential relationship between leg and foot conformation. Dynamic balance, which observes the horse in motion, implies that a balanced foot should land symmetrically (ie, the foot should land flat with the hope that this places force uniformly on the solar surface of the hoof wall). The problem here is that often it is not possible to achieve a flat strike pattern because of leg conformation. Furthermore, it may be detrimental to the horse if the hoof is trimmed to land in a flat strike pattern if abnormal leg conformation is present. Recently, the term natural balance has been introduced. This suggests that foot conformation should be modeled after the foot in its natural state (ie, feral horses). It is unknown whether this type of balance allows maximum functional strength, whether it does not take into account the specific athletic activity of the horse, and whether it is largely incompatible with traditional horseshoeing techniques.4 Hoof balance encompasses both dorsal palmar/plantar balance and mediolateral balance. Improper mediolateral hoof balance has been associated with foot problems such as sheared heels, distorted hoof walls, and hoof cracks. These problems arise from disproportionate forces placed on the lateral or medial aspects on the foot.5 A problem arises with the exclusive use of either geometric or dynamic balance to address mediolateral trimming, as each may produce a foot with a different shape if the landing pattern or limb conformation deviates from normal. Because of this, no one standard method of trimming will achieve optimum mediolateral balance for every horse. HOOF LENGTH Hoof length (toe length) is determined with measurement from the toe at the ground surface proximally to the end of the horny wall at the coronary band. Guidelines for appropriate toe length have been established for most breeds on the basis of body weight (Table).6 With these guidelines, it becomes necessary to consider anatomic variations in: the relative position of the third phalanx within the hoof capsule; the thickness of the hoof wall; the hoof shape; and the horse’s athletic endeavor. HOOF ANGLE
Reprint requests: Stephen E. O’Grady, BVSc, MRCVS, Northern Virginia Equine, 7135 Mt Eccentric Rd, The Plains, VA 20198. From equipodiatry.com. Reprinted with permission. doi: 1053/jevs.2003.36
Volume 23, Number 3
The angle of the hoof is the angle formed at the junction of the dorsal hoof wall and the ground surface of the foot. Until recently, the veterinary and farrier literature recom123
Table
Guidelines for hoof length on basis of weight of horse Horse weight
Horse size Small Medium Large
Kg
Lb
360-400 800-900 425-475 950-1050 525-575 1150-1250
Toe length Cm
In
7.60 8.25 8.90
3.00 3.25 3.50
mended that the normal hoof angle be 45 to 50 degrees for the forefeet and 50 to 55 degrees for the hind feet. These recommendations have been proven erroneous because they do not take into consideration the conformation of the horse’s individual limbs.7 Ideal hoof angulation occurs when a line drawn down the dorsal surface of the hoof wall and a line drawn along the surface of the heel are in alignment or parallel to a line drawn through the 3 phalanges. The foot is trimmed appropriately and the hoof angle is correct for the individual horse when the dorsal hoof wall and the dorsal surface of the pastern region are parallel. This is known as the hoof pastern axis. For confirmation of this hoofpastern axis visually, the horse should be on a hard level surface and must stand squarely on all 4 feet with the cannon bones positioned vertically. The terms low hoof angle and high hoof angle can be used simply to describe a nonlinear relationship between the dorsal hoof wall and the dorsal pastern region. In the normal foot, a vertical line drawn from the center of the lateral condyle of the distal second phalanx to the ground should bisect the bearing surface of the foot.8 This line would mark the center of rotation of the distal interphalangeal joint and would coincide with a line drawn across the solar surface of the foot through the middle one third of the frog. This line drawn across the solar surface should equal the widest part of the foot. FUNCTIONAL CONSIDERATIONS Foot conformation (shape) is important because of its relationship to the foot’s biomechanical function. Any changes made to the bottom of the horse’s foot will have an effect on the angulation of the hoof, the hoof-pastern axis, and the alignment of the hoof capsule under the center of rotation. Variation away from optimum for these parameters may result in decreased biomechanical efficiency. Perhaps the most commonly discussed functional element of hoof movement is breakover. Breakover is defined as the phase of the stride between the time the horse’s heel lifts off the ground and the time the toe lifts off the ground. The toe acts as a fulcrum around which the heel rotates under the influence of the deep digital flexor tendon. The suspensory ligament to the navicular bone and the impar ligament are under maximal stress just before breakover.9 Changes in toe length, hoof-pastern axis, and hoof angle all affect breakover and the tensile forces on the deep digital flexor tendon. However, it may not be possible to predict what
124
changes in breakover will occur as a result of a particular trimming modification, nor will such changes necessarily occur at all gaits. In general, breakover is significantly delayed with the presence of a long toe and acute hoof angle because the long toe acts as a long lever arm, requiring more time and forces to rotate the heel around the toe. In addition, it is believed that tension exerted by the deep digital flexor tendon against excessive toe length results in lamina tearing, which may lead to hoof distortion. Low hoof angles, where the angle of the dorsal hoof wall is lower than the angle of the dorsal pastern, create a broken-back hoof-pastern axis. This type of foot configuration is commonly caused by the long-toe/underrun-heel foot conformation. A low hoof angle causes coffin joint extension and increased strain on the deep digital flexor tendon and promotes toe-first landing. This, in turn, may cause increased stress on the soft tissue structures associated with the navicular bone and may delay the speed of breakover. There is experimental evidence that a low hoof angle will compromise circulation in the heel area of the foot.10 This abnormal hoof conformation is known to contribute to navicular syndrome, chronic heel pain (bruising), coffin joint inflammation, quarter and heel cracks, and interference problems. High hoof angles, where the angle of the dorsal hoof wall is higher than the angle of the dorsal pastern, create a brokenforward hoof-pastern axis. An extremely high hoof angle is often classified as a “club foot.” Some horses with extremely upright pasterns may be falsely identified as having a club foot. A high hoof angle causes coffin joint flexion, promotes heelfirst landing, and increases pressure in the heel. Some injuries associated with a high hoof angle are coffin joint inflammation from abnormal loading of this joint, sole bruising, and increased strain on the suspensory ligaments of the navicular bone. (Edited from Proceedings of Alamo Pintado Equine Medical Center Symposium 2003.)
REFERENCES 1. Butler KO. The prevention of lameness by physiologically-sound horseshoeing. Proc 31 Annu Cony Am Assoc Equine Pract 1985;465-75. 2. Curtis S. Farriery-foal to racehorse. Newmarket: R&W Publications; 1999. p. 1-11. 3. Hickman J, Humphrey M, editors. Hickmans farriery, 2 ed. London: J.A. Allen; 1988. p. 136-75. 4. Hood DM, Jackobson AC. The principles of equine hoof wall conformation. Proc Hoof Project 1997;2-19. 5. Moyer W, Anderson J. Sheared heels: diagnosis and treatment. J Am Vet Med Assoc 1975;166:53-5. 6. Turner T. The use of hoof measurements for the objective assessment of hoof balance. Proc 38 Annu Cony Am Assoc Equine Pract 1992;389-95. 7. Bach O, Butler D, White K, Metcalf S. Hoof balance and lameness: improper toe length, hoof angle, and mediolateral balance. Compend Contin Educ Pract Vet 1995;17:1275-82. 8. Colles C. Interpreting radiographs. 1. The foot. Equine Vet J 1983;15:297-303. 9. Clayton H. The effect of an acute hoof angulation on the stride kinematics of trotting horses. Equine Vet J (suppl) 1990;9:86-90. 10. Colles C. Concepts of blood flow in the etilogy and treatment of navicular disease. Proceedings of the 29th Annual Convention of the American Association of Equine Practitioners 1983;265-70.
Journal of Equine Veterinary Science
March 2003