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Equine digital biomechanics
MORRIS ANIMAL FOUNDATION MEETING The Morris Animal Foundation held its annual meeting June 13, 1987 at the Hyatt Regency Hotel, Indianapolis, Indiana. Following are summaries of some information presented:
(
From MAF
)
EQUINE DIGITAL BIOMECHANICS D.M. Hood DVM, Ph.D. One of the many things that separates man from animals is his desire to take medicine: this peculiar need is exceeded, however, by a compulsive drive to give "medicine" to his animals. Evidence of this is seen in the many things done to the horse in an attempt to improve the hoof: 1. The horse is fed various diets, potions, and elixers (some smelling distinctly of dead fish). Most of these are some mixture of proteins, amino acids, vitamins, and "secret ingredients" designed to make the foot grow stronger and faster. 2. The coronary band is painted with various substances to enhance its growth rate. 3. The wall is painted with a number of different compounds for both aesthetic reasons and in hopes of altering its mechanical properties. 4. The foot is forced into specific shapes for medical, aesthetic, and performance purposes, and 5. The foot is shod in order to protect it, treat it, and to obtain an increase in performance. The arguments for using any of these various therapies are supported by what we think to be the "Facts" about the physiology or function of the horses foot- These facts may be obtained from books, by word of mouth, or deductions from observations of horses or other species. Fortunately most of what is done to the horse's foot is totally innocuous, neither helping nor hurting. A small percent of the time we actually (measurably) help the foot in some way. Unfortunately, a fairpercent of the time we are potentially or actually doing harm to the horse. Equally unfortunately, most of the time, we don't know which of the above we are accomplishing. This is the direct result of the lack of real knowledge about the function of this vitally important part of the horse. The question then becomes, "What do we really know about the foot and hoof of the horse?" This question could be made more specific by asking what we know about the mechanical function of 236
the foot, blood flow to the foot, or the growth and nutrition of the fool What we will examine here is the source, completeness, and accuracy of some of the facts in regard to the mechanical aspects of the footWhen we think of the mechanical function of the foot, one of the first questions considered is, "How does the foot and hoof handle the forces applied during weight-bearing?' The literature states that when a horse puts his weight down on his foot, the foot is subjected to a significant force or load. This force is divided into two components because of the consU-uction of the joints between bones of the foot. One part of this force is directed from the fetlock, pushing the coffin bone down and forward. The other force, a larger component, is vertically downward from the coffin hone and is transfered via the deep digital flexor tendon causing the tip of the hone to he pulled down. The result of both of these forces is the collective movement of the coffin bone, that of sinking and rotating. Similarly the idea that the coffin hone is suspended from the hoof wall by the laminar structures is well accepted.This is envisioned as occurring through the large internal surface area created by the interdigitating lamina. It is upon these statements of fact that most theories of shoeing and trimming are based. Adams utilizes these concepts in writing his book on lameness, as do many articles by other authors. Most textbooks on farriery either cite Adams or articles which say essentially the same things as Adams. Based upon these concepts, cutting of the accessory check ligament and digital flexor tendons is advocated as a treatment of laminitis. Upon these theories multiple mathematical calculations, have been done which absolutely define the internal forces operating inside the digit. Based partly upon these hypotheses the effect of lengthening or shortening the toe of the foot has been argued for some period of time. Since these statements figure so dramatically in our understanding of the physiology of the normal and the pathology of the abnormal foot, it would seem to be a prerequisite to know how accurate these facts are. One method of establishing the validity of the facts is to find the supporting data and evaluate its accuracy and consistency. The earliest statement regarding the forces operating inside the hoof (quoted above) can be found in German and Polish veterinary publications (circa 1890-1900). The only basis for these statements was the correlation of gross and microscopic anatomical studies with what "might, be happening inside the digit. These original statements have been handed down essentially intact without any concentrated effort to prove or disprove them. Thus these ideas must be regarded as unsubstantiated hypotheses. From the middle of the 1800's to the present, man's understanding of digital biomechanics has been largely dictated by his technical ability to make the needed measurements. The earliest recorded measurements in the area of digital biomechanics were done in 1840 by a Frenchman named Marcy. Using devices (rubber bails filled with India ink) attached to the bottom of the EQUINE VETERINARY SCIENCE
horse's feet, Marey initiated the science of gait analysis and locomotion. An American named Muybridge advanced the field of gait analysis significantlywith the introductionof photographic techniques in 1877. It is an indication of the lack of technical progress that Muybridge's original photographic plates were used in 1977 for further studies in gait analysis. The next series of advances in the field of digital biomechanics occurred when the technique of force plate analysis was introduced and subsequently combined with devices mounted on the hoof wall or shoe. These technical advances now allow accurate measurements of the external force of impact, speeds of acceleration and deceleration, as well as the duration of the various phases of the stride. Gait analysis is perhaps reaching its peak with the introduction of computerized systems which are allowing gait analysis to be used diagnostically for both medical and performance purposes. These quantified measurements of external load and speed have been combined with the hypothetical concepts that predict the magnitude of the forces existing within the digit. While these computed forces seem logical they are only as accurate as the hypothesis. As has been said already these internal forces have not been accurate in the past because of a lack of technical ability. Now, using specially designed technology, investigations attempting to define the forces within the digit are now possible through the use of devices placed inside the hoof wall and studies done on the components of the foot. An example of these studies is the accurate determination of the strength and elasticity of the hoof wall. Work in the author's laboratory is beginning to quantitatively define the direction and magnitude of the forces acting between the coffinbone and the hoof wall, and between the hoof wall and the coronary band. These studies are being completed using detectors surgically placed inside the foot, a detector which determines the mass or force being placed on the digit, and a computer which calibrates, records, and analyzes the signals from the detectors. An example of this systemis the DisplacementForce Transducer (DFO the use of which the Morris Animal Foundation was able to support a year ago. This DFT was designed to measure how much the hoof wall moves relative to the coffin bone when the foot is subjected to varying amounts of weight. The results from this detector are an index of the stability of the foot. Using the DFI" we have been able to look at the stabilityof the foot in the normal horse and in the horse affected with chronic laminitis. We have also studied the effect that various shoes and trimming techniques have on the stabilityof the foot In general the results of this study indicate that the coffin bone moves in a rather complex fashion during weightbearing. The bone appears to move down and away from the wall and then back toward the wall. The effect of different shoes is not always predictable. Most of the time, shoes which give sole support (heartbar shoe or pads) make the foot more stable. In other horses the opposite appears to be true, especially in the horse with laminitis. The data coming from studies such as these will have the initial effect of adding some confusion to our understanding of how the foot functions.This confusion is the product of two things, the first thing being that the data is insufficient. The problem of insufficient data can best be understood by
Volume 7, Number 4, 1987
trying to interpet the data from the DFF study. It appears from the data that forces acting between the coffin bone and the hoof wall are much more complex than previously thought Before all of the data can be interpeted it will have to be known if the wall is being deformed or if the coffin bone is coming into contact with the ground or if some other factor is involved. This, unfortunately is the point where the project ran out of money and as yet none has been available to continue this investigation. The problem of insufficient data can be rather easily overcome. In these days of biotechnology and bioengineering the technical aspects are of little concern. The problem now is insufficient time and money to perform the needed studies. This is unfortunatelyconnected to that second item which is a key for the advancement of knowledge. This second problem can be referred to as preconceived knowledge and defined as the unwillingnessto accept new ideas. This problem, applied to the foot, would be seen in the person (scientist, veterinarian, or horseman) that says, "I know how the foot works mechanically and we know that all horses can be cured of laminitis using the "XXX" shoe or technique so there is no use spending money working on the biomechanics of the foot." The problem, or course, with this statement is that the data shows that we don't understand how the foot works and that not all horses are "cured" of laminitis by any one shoe or technique. The current effect of preconceived knowledge is that it has resulted in a decrease in the number of studies being done on the biomechanics of the fooL It is extremely frustrating to see horse after horse affected with laminitis, being treated to the best of anyone's ability, continue to suffer the unrelentingpain associated with the disease. The frustration is compounded knowing that the key to the improved treatment of the patients is waiting to be turned, but cannot be due to a lack of research dollars. This then is where we stand, on the edge of knowing more about how the foot of the horse works but unable to proceed in a meaningful fashion. The technical aspects are not the problem. The only real holdup is the desire to know what we need to know, the willingness to test what we have long thought to be the facts and to discover new ways to use our knowledge to help the horse.
(
r ,m MAF HEALTH SEMINAR EQUINE COLIC SURVEY Nat T. Messer IV, D.V.M.
The term colic, as defined by the Morris Animal Foundation's Colic Panel, describes the clinical signs of pain resulting from potentially life threatening diseases of the gastrointestinal tract of the horse. Equine colic is a significanteconomic problem for the horse industry and a cause of considerable personal concern to owners. Most cases of colic seen by veterinarians are medically manageble and make uneventful recoveries with ~'eatment Some cases require more extensive and costly treatment, including surgery. The decision to perform surgery can be difficult and must be made expediently. Prognosis, i.e., the probability of survival, is informationthe owner needs in advance of the decision to perform surgery. The Morris Animal FoundationColic Survey was under-
237
(
From MAF
)
EQUINE DIGITAL BIOMECHANICS D.M. Hood DVM, Ph.D. One of the many things that separates man from animals is his desire to take medicine: this peculiar need is exceeded, however, by a compulsive drive to give "medicine" to his animals. Evidence of this is seen in the many things done to the horse in an attempt to improve the hoof: 1. The horse is fed various diets, potions, and elixers (some smelling distinctly of dead fish). Most of these are some mixture of proteins, amino acids, vitamins, and "secret ingredients" designed to make the foot grow stronger and faster. 2. The coronary band is painted with various substances to enhance its growth rate. 3. The wall is painted with a number of different compounds for both aesthetic reasons and in hopes of altering its mechanical properties. 4. The foot is forced into specific shapes for medical, aesthetic, and performance purposes, and 5. The foot is shod in order to protect it, treat it, and to obtain an increase in performance. The arguments for using any of these various therapies are supported by what we think to be the "Facts" about the physiology or function of the horses foot- These facts may be obtained from books, by word of mouth, or deductions from observations of horses or other species. Fortunately most of what is done to the horse's foot is totally innocuous, neither helping nor hurting. A small percent of the time we actually (measurably) help the foot in some way. Unfortunately, a fairpercent of the time we are potentially or actually doing harm to the horse. Equally unfortunately, most of the time, we don't know which of the above we are accomplishing. This is the direct result of the lack of real knowledge about the function of this vitally important part of the horse. The question then becomes, "What do we really know about the foot and hoof of the horse?" This question could be made more specific by asking what we know about the mechanical function of 236
the foot, blood flow to the foot, or the growth and nutrition of the fool What we will examine here is the source, completeness, and accuracy of some of the facts in regard to the mechanical aspects of the footWhen we think of the mechanical function of the foot, one of the first questions considered is, "How does the foot and hoof handle the forces applied during weight-bearing?' The literature states that when a horse puts his weight down on his foot, the foot is subjected to a significant force or load. This force is divided into two components because of the consU-uction of the joints between bones of the foot. One part of this force is directed from the fetlock, pushing the coffin bone down and forward. The other force, a larger component, is vertically downward from the coffin hone and is transfered via the deep digital flexor tendon causing the tip of the hone to he pulled down. The result of both of these forces is the collective movement of the coffin bone, that of sinking and rotating. Similarly the idea that the coffin hone is suspended from the hoof wall by the laminar structures is well accepted.This is envisioned as occurring through the large internal surface area created by the interdigitating lamina. It is upon these statements of fact that most theories of shoeing and trimming are based. Adams utilizes these concepts in writing his book on lameness, as do many articles by other authors. Most textbooks on farriery either cite Adams or articles which say essentially the same things as Adams. Based upon these concepts, cutting of the accessory check ligament and digital flexor tendons is advocated as a treatment of laminitis. Upon these theories multiple mathematical calculations, have been done which absolutely define the internal forces operating inside the digit. Based partly upon these hypotheses the effect of lengthening or shortening the toe of the foot has been argued for some period of time. Since these statements figure so dramatically in our understanding of the physiology of the normal and the pathology of the abnormal foot, it would seem to be a prerequisite to know how accurate these facts are. One method of establishing the validity of the facts is to find the supporting data and evaluate its accuracy and consistency. The earliest statement regarding the forces operating inside the hoof (quoted above) can be found in German and Polish veterinary publications (circa 1890-1900). The only basis for these statements was the correlation of gross and microscopic anatomical studies with what "might, be happening inside the digit. These original statements have been handed down essentially intact without any concentrated effort to prove or disprove them. Thus these ideas must be regarded as unsubstantiated hypotheses. From the middle of the 1800's to the present, man's understanding of digital biomechanics has been largely dictated by his technical ability to make the needed measurements. The earliest recorded measurements in the area of digital biomechanics were done in 1840 by a Frenchman named Marcy. Using devices (rubber bails filled with India ink) attached to the bottom of the EQUINE VETERINARY SCIENCE
horse's feet, Marey initiated the science of gait analysis and locomotion. An American named Muybridge advanced the field of gait analysis significantlywith the introductionof photographic techniques in 1877. It is an indication of the lack of technical progress that Muybridge's original photographic plates were used in 1977 for further studies in gait analysis. The next series of advances in the field of digital biomechanics occurred when the technique of force plate analysis was introduced and subsequently combined with devices mounted on the hoof wall or shoe. These technical advances now allow accurate measurements of the external force of impact, speeds of acceleration and deceleration, as well as the duration of the various phases of the stride. Gait analysis is perhaps reaching its peak with the introduction of computerized systems which are allowing gait analysis to be used diagnostically for both medical and performance purposes. These quantified measurements of external load and speed have been combined with the hypothetical concepts that predict the magnitude of the forces existing within the digit. While these computed forces seem logical they are only as accurate as the hypothesis. As has been said already these internal forces have not been accurate in the past because of a lack of technical ability. Now, using specially designed technology, investigations attempting to define the forces within the digit are now possible through the use of devices placed inside the hoof wall and studies done on the components of the foot. An example of these studies is the accurate determination of the strength and elasticity of the hoof wall. Work in the author's laboratory is beginning to quantitatively define the direction and magnitude of the forces acting between the coffinbone and the hoof wall, and between the hoof wall and the coronary band. These studies are being completed using detectors surgically placed inside the foot, a detector which determines the mass or force being placed on the digit, and a computer which calibrates, records, and analyzes the signals from the detectors. An example of this systemis the DisplacementForce Transducer (DFO the use of which the Morris Animal Foundation was able to support a year ago. This DFT was designed to measure how much the hoof wall moves relative to the coffin bone when the foot is subjected to varying amounts of weight. The results from this detector are an index of the stability of the foot. Using the DFI" we have been able to look at the stabilityof the foot in the normal horse and in the horse affected with chronic laminitis. We have also studied the effect that various shoes and trimming techniques have on the stabilityof the foot In general the results of this study indicate that the coffin bone moves in a rather complex fashion during weightbearing. The bone appears to move down and away from the wall and then back toward the wall. The effect of different shoes is not always predictable. Most of the time, shoes which give sole support (heartbar shoe or pads) make the foot more stable. In other horses the opposite appears to be true, especially in the horse with laminitis. The data coming from studies such as these will have the initial effect of adding some confusion to our understanding of how the foot functions.This confusion is the product of two things, the first thing being that the data is insufficient. The problem of insufficient data can best be understood by
Volume 7, Number 4, 1987
trying to interpet the data from the DFF study. It appears from the data that forces acting between the coffin bone and the hoof wall are much more complex than previously thought Before all of the data can be interpeted it will have to be known if the wall is being deformed or if the coffin bone is coming into contact with the ground or if some other factor is involved. This, unfortunately is the point where the project ran out of money and as yet none has been available to continue this investigation. The problem of insufficient data can be rather easily overcome. In these days of biotechnology and bioengineering the technical aspects are of little concern. The problem now is insufficient time and money to perform the needed studies. This is unfortunatelyconnected to that second item which is a key for the advancement of knowledge. This second problem can be referred to as preconceived knowledge and defined as the unwillingnessto accept new ideas. This problem, applied to the foot, would be seen in the person (scientist, veterinarian, or horseman) that says, "I know how the foot works mechanically and we know that all horses can be cured of laminitis using the "XXX" shoe or technique so there is no use spending money working on the biomechanics of the foot." The problem, or course, with this statement is that the data shows that we don't understand how the foot works and that not all horses are "cured" of laminitis by any one shoe or technique. The current effect of preconceived knowledge is that it has resulted in a decrease in the number of studies being done on the biomechanics of the fooL It is extremely frustrating to see horse after horse affected with laminitis, being treated to the best of anyone's ability, continue to suffer the unrelentingpain associated with the disease. The frustration is compounded knowing that the key to the improved treatment of the patients is waiting to be turned, but cannot be due to a lack of research dollars. This then is where we stand, on the edge of knowing more about how the foot of the horse works but unable to proceed in a meaningful fashion. The technical aspects are not the problem. The only real holdup is the desire to know what we need to know, the willingness to test what we have long thought to be the facts and to discover new ways to use our knowledge to help the horse.
(
r ,m MAF HEALTH SEMINAR EQUINE COLIC SURVEY Nat T. Messer IV, D.V.M.
The term colic, as defined by the Morris Animal Foundation's Colic Panel, describes the clinical signs of pain resulting from potentially life threatening diseases of the gastrointestinal tract of the horse. Equine colic is a significanteconomic problem for the horse industry and a cause of considerable personal concern to owners. Most cases of colic seen by veterinarians are medically manageble and make uneventful recoveries with ~'eatment Some cases require more extensive and costly treatment, including surgery. The decision to perform surgery can be difficult and must be made expediently. Prognosis, i.e., the probability of survival, is informationthe owner needs in advance of the decision to perform surgery. The Morris Animal FoundationColic Survey was under-
237