- Email: [email protected]
Understanding and evaluating the unique lameness of horses with chronic laminitis – Parts 1, 2, and 3
592
Abstracts / Journal of Equine Veterinary Science 31 (2011) 562-609
[1,5,6]. If these assertions are to be believed, then the barefoot horse might be expected to outperform its shod competitors. That has not proven to be the case in the equestrian disciplines at the Olympic Games. While there is no official record of the footwear worn by horses competing in the Olympic Games, there appear to be no accounts of barefoot horses winning medals in any equestrian events. It is possible that some barefoot medalists have been overlooked. Even so, it would have to be considered exceptional for a barefoot horse to succeed at the highest levels of athletic competition. There are several accounts of endurance horses training without shoes; however, many of these horses are shod prior to some of the more difficult events such as the Olympic Games. When it comes to human athletes, there are several reports that document potential advantages to performing barefoot. Oxygen consumption has been measured to be 2% lower in barefoot runners than in runners wearing shoes [7], which may translate into ability to perform for longer before tiring. Also, individual impact patterns are more varied in barefoot runners, with lower impact force and the potential for decreased risk of injury, particularly among runners with a mid-foot, lateral foot strike [8]. In addition, human runners take a longer stride when shod than when barefoot, and they are more inclined to land heel-first when wearing shoes [9], which may increase the ground impact force. However, the potential for increased levels of performance is not supported by track records. Since 1960, only two runners have won Olympic medals barefoot. In 1960, Ethiopian marathon runner Abebe Bikila established a world-record time in winning the gold medal barefoot, and South African/Briton Zola Budd also won medals competing barefoot. Interestingly, both athletes later turned to competing with shoes. Bikila competed in the 1964 Olympic Games wearing shoes and set a new world record when he won his second gold medal. Zola Budd, who trained and competed both in shoes and barefoot during her career, now states: “I no longer run barefoot. As I got older I had injuries to my hamstring. I found that wearing shoes gives me more support and protection from injuries” [10]. Is there sufficient information to justify the choice of barefoot over shoes?: In the equine hoofcare field, the anecdotal evidence far outweighs the scientific data, and the anecdotal evidence could support either stance on the issue. Horses certainly evolved over thousands of years without orthotics; however, foot problems appear to have been present even before horses were domesticated. A study of fossilized equine remains suggests the presence of navicular disease long before the time of any human involvement with horses. Furthermore, the research indicates that the severity of lesions in the navicular bone were related to the size of the animal [11]. The United States Navy examined this question and concluded that there was some evidence supporting the efficacy and safety of barefoot-style running shoes, such as the Vibram FiveFinger shoes which allow the foot to function naturally without added support or cushioning. (These shoes were originally designed as boat shoes.) The list of “pros” for the use of minimalist shoes includes stronger feet, reduced impact force, heightened
proprioception, and improved balance. The list of “cons” includes less overall support and protection for the foot, and the need for a transition period. Minimalist shoes are not recommended for those successfully using foot orthotics or for those with preexisting foot problems. Ultimately, the Navy concluded that there is insufficient evidence to either support or refute the efficacy and safety of the barefoot-style running shoes for military personnel. Conclusions: With all of the resources available in the field of human footwear research, there is no consensus as to what constitutes “ideal” footwear. Although there are many advocates of barefoot running, the use of minimalist-style running shoes is more common. Orthotics that provide selected characteristics such as protection while minimally changing the barefoot stride characteristics are now available from several different shoe companies. While many advocates of leaving horses barefoot are opposed to the use of any orthotics, in recent years there has been an increase in the use and availability of many nontraditional orthotics for horses, including various styles of hoof boot, molded urethanes, glue-on shoes, and hoof casts. Although the use of any of orthotic is, strictly speaking, not “barefoot,” it does represent an interesting middle ground. Future studies that investigate the effects of these orthotic devices on foot morphology, function, and athletic performance might lead to the development of new products designed to provide the horse with the mechanical necessities while limiting undesirable effects of hoof orthotics. So, where does all this science and anecdote leave the practitioner considering whether to ditch the shoes? The “evidence is not concrete for or against barefoot or shod running,” said Allison H. Gruber, a doctoral candidate at the University of Massachusetts. “If one is not experiencing any injuries, it is probably best to not change what you're doing.”
References [1] King M. Barefoot vs. shod. The Horse Magazine 2008. article: 12778. [2] Phys Reynolds G, editor. Is running barefoot better for you? The New York Times; 2009; Oct 21. [3] Bedwell SF, Cressman LS. Fort Rock Report: Prehistory and environment of the pluvial Fort Rock lake area of south-central Oregon. In: Aikens CM, editor. Great Basin Anthropological Conference, Selected Papers. Eugene: University of Oregon Anthropological Papers 1; 1970. p. 1-25. [4] Trinkaus E, Hong S. Anatomical evidence for the antiquity of human footwear. Journal of Archaeological Science 2008;35:1928-33. [5] Strasser H. Shoeing: A Necessary Evil? 2nd edn. Sabine Kells, Qualicum Beach; 2000. pp 46–48. [6] Teskey TG. The unfettered foot: a paradigm change for equine podiatry. 2006; http://www.easycareinc.com/TeskeyTrim.pdf [7] Hanson NJ, Berg K, Deka P, et al. Oxygen cost of running barefoot vs. running shod. International Journal of Sports Medicine 2011;32:401-6. [8] Lieberman D, Venkadesan M, Werbel W, et al. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 2010;463:531-5. [9] Wegener C, Hunt AE, Vanwanseele B, et al. Effect of children's shoes on gait: a systematic review and meta-analysis. J Foot Ankle Res 2011; 4:3. [10] Friedman S. After the fall: Zola Budd's running story. Runner's World 2009; Oct. [11] Thompson ME, McDonald G, Østblom LC. Equine navicular syndrome in the fossil record. Hoofcare and Lameness; 76:34–40.
Practical – Laminitis: Treatment by Design Understanding and evaluating the unique lameness of horses with chronic laminitis – Parts 1, 2, and 3 David M. Hood DVM, PhD Hoof Diagnostic and Rehabilitation Clinic, Bryan TX
Take-Home Message: It's not just sore feet. Within the hoof, multiple pathologic and physiologic factors combine to initiate the signaling that produces the altered gait and stance which characterizes the chronically foundered horse. In addition, nonlaminitic digital pathologies as well as nondigital pathologies
Abstracts / Journal of Equine Veterinary Science 31 (2011) 562-609
frequently are present in horses with very chronic laminitis. Identifying all of the elements that are contributing to the lameness is essential to optimizing rehabilitation. Introduction: The treatment and management of lameness is a major component of rehabilitation in horses with chronic laminitis. To better understand and reduce the impact of the lameness in these sometimes difficult cases, there are three key research goals. First is the development of lameness evaluation systems that have greater objectivity, sensitivity, and accuracy than the commonly used subjective grading systems. Second is research that specifically identifies the underlying pathologies and factors that contribute to the lameness in these horses. Third is the development and testing of diagnostic, prognostic, and therapeutic paradigms that target the mechanisms responsible for the observed lameness. This paper summarizes recent research conducted by our group in each of these areas. 1. Objective Assessment of Lameness Severity in Chronic Laminitis: Clinically, the assessment of lameness severity is largely subjective and primarily involves assigning lameness scores to affected horses. However, in rehabilitation research the qualitative nature of subjective grading systems, and the large differences in lameness severity that can exist between the specific grades within a scoring system, combine to limit the consistency, comparability, and accuracy of the data derived from them. The goal of this study was to investigate the clinical usefulness of a force plate-based technology for quantifying lameness severity in horses with chronic laminitis. Material and methods: This cross-sectional study involved 30 horses with naturally occurring chronic laminitis, admitted for rehabilitation and/or rehabilitation research. Lameness severity was subjectively graded in each horse using accepted methods. A load cell-based force plate system was used to determine the percentage of total ground reaction force experienced by the individual feet. The pattern of average distribution of foot load and displacement of the center of load vector (COLv) from its normal position during stancedtermed the mean load stance patterndwas determined for each horse. The strength of association between lameness severity and stance pattern was determined using Spearman's rank correlation. Results: The mean load stance patterns shown by horses with chronic laminitis varied with subjective lameness severity. A significant correlation was found between lameness severity and the degree of change in mean COLv magnitude from that of normal horses. In addition, stance analysis detected significant differences in foot loading in horses subjectively identified as being bilaterally lame, and indicated a high prevalence of rear limb lameness in horses with chronic laminitis. Discussion: The mean load stance pattern displayed by the horse as well as COLv magnitude and direction are the result of voluntary changes in applied limb loads during quasi-static loading. The variation in mean load stance pattern with subjective lameness severity is interpreted as reflecting the combined effects of differences in pain avoidance between limbs and the physiologic/mechanical factors associated with changes in foot conformation, therapeutic shoeing, and learned behavior. The mean load stance pattern and the direction of COLv thus are both presumptive indicators of relative limb involvement in an individual horse. Although the correlation between the magnitude of COLv and subjective lameness severity is circumstantial, it does support the use of this measure as a valid index of lameness severity between individual limbs of an individual horse and between horses. 2. Application of Load Stance Analysis to Understanding the Lameness of Chronic Laminitis: As with any disease, rehabilitation in horses with chronic laminitis is most effective when it is based on protocols designed to identify and address the specific pathologies and factors responsible for producing the clinical
593
signs, in this case lameness. Preliminary and ongoing research indicates that the lameness typical of chronic laminitis is a composite of a variety of pathologies, physiologic/mechanical processes, and learned behavior. The goal of this study was to better characterize the underlying causes and mechanisms associated with the lameness of chronic laminitis. Specific objectives included identifying the anatomic source(s) of lameness, determining the association between lameness severity and the extent of distal phalanx displacement and altered hoof conformation, and characterizing potential paininducing mechanisms within the digit. Material and methods: A change in lameness severity in response to regional anesthesia was used to localize the site(s) of pain in a group of horses with chronic laminitis. Sequential ascending nerve blocks were used to determine the relative contribution made to the lameness by structures located within specific areas of innervation. A second group of horses was used to determine the association between lameness severity and the presence and severity of specific digital pathologies or other gait-altering mechanisms. Therapeutic intervention was used to confirm the role of specific mechanisms. These experiments used changes in subjective lameness and mean load stance analysis as response criteria. Spearman's rank correlation, repeated measures analysis, and paired t-test were used for statistical analysis. Results: Differential regional anesthesia revealed the following: 1. Not all of the lameness in horses with chronic laminitis is the direct result of pain avoidance. 2. In the majority of chronically foundered horses, the lameness originates within the solar and heel regions, rather than in the dorsal laminar interface. 3. Nondigital lameness frequently is superimposed on lameness of digital origin. 4. There is an apparently high incidence of rear limb lameness in horses with chronic laminitis. There was a moderate association between hoof capsule deformation and lameness severity at the walk, but not at rest, in most horses. Intervention studies indicated that digital pain was principally associated with inflammatory mediators and focal pressures generated between the displaced distal phalanx and the hoof capsule. However, the analgesic response to NSAIDs was delayed in these horses. Stronger associations were found between lameness severity and 1) digital instability and 2) the healing response at the sublaminar and laminar interface. Discussion: The failure of regional anesthesia of the foot to totally abolish the lameness indicates that there are factors other than pain contributing to the altered gait and stance in some horses with chronic laminitis. Potential mechanisms include both learned responses and mechanical/physiologic dysfunction. In the horses evaluated, the component of the lameness unassociated with pain appeared to be related to chronic elevation of the heels and/or contracture of the flexor tendons and suspensory apparatus. These acquired hoof malformations alter the gait and stance via interference with the myotactic reflex or by mechanically altering digital biomechanics. The component of the lameness determined to be not of digital origin was clinically interpreted to arise from degenerative joint disease and/or injury to the suspensory apparatus, both of which were presumed to be secondary to chronic laminitis. The high prevalence of rear limb lameness was attributed to repeated overloading of the rear limbs in attempts to rise without fully loading the forefeet. There is little question that the lameness seen in horses with chronic laminitis is, at least in part, the product of diseasedinduced mechanical failure within the foot. However, the low
594
Abstracts / Journal of Equine Veterinary Science 31 (2011) 562-609
association between distal phalanx displacement and lameness severity infers that the pain is not primarily related to the presence or magnitude of displacement associated with mechanical failure. Rather, the association between lameness severity and both digital instability and the healing response at the dorsal laminar interface argues that disease-induced alterations in the material properties of the laminar interface are important in lameness induction. The delayed response to NSAIDs in horses with long-standing laminitis is consistent with a state of upregulation of nociceptors in the digit. 3. Pain and Lameness Management in Horses with Chronic Laminitis: Pain and lameness severity are used clinically to grade disease severity, gauge the relative success of specific treatments, as a prognostic indicator, and as a criterion for euthanasia. This section summarizes some important features of lameness diagnosis, prognosis, and management as it pertains to the horse with chronic laminitis. Diagnostic paradigms for the lameness of chronic laminitis: It is obvious that a major contributor to the lameness seen in horses with chronic laminitis reflects a pain-avoidance response to pathologies directly or indirectly associated with laminitis. However, as our data show, not all of the lameness is directly caused by pain; nor does the pain result exclusively from laminitis-associated digital pathology. Other contributors to the lameness may include digital pathology unassociated with laminitis and pathology beyond the digit that may or may not be a result of laminitis. Hence the need for thorough diagnostic assessment in horses with chronic laminitis. A three-tiered diagnostic protocol is used at our clinic: 1. Determine the relative contributions made by pain avoidance, mechanical factors, and learned behavior. 2. Use the diagnostic findings to determine whether the resulting goal is treatment or simply management of the lameness. 3. Identify the presence and severity of specific lamenessinducing pathologies. Lameness severity as a prognostic indicator in chronic laminitis: Severe, unremitting pain justifies euthanasia in horses with chronic laminitis. However, the fact that the absence of pain does not preclude significant digital pathology and that significant lameness can be present without severe pathology adds an extra degree of complexity to the use of lameness as the sole criterion for euthanasia. A more logical approach is to use the combination of 1) specific digital pathologies that preclude successful rehabilitation and 2) response to pain management. Therapeutic approaches to lameness in horses with chronic laminitis: Major questions remain regarding the management of pain and lameness in horses with chronic laminitis. The arguments that 1) pain is a protective mechanism which serves to limit further injury to the feet, and 2) given the potential for adverse affects, NSAIDs should be given for only a limited time, are countered by the argument that pain is pathological and has consequences that limit the success of rehabilitation. Lameness management decisions are made even more complex by considering the question of whether lameness severity should be used as a primary criterion for therapeutic success. Few clinical studies have been published that provide data with which to resolve these issues. In practice, two approaches to the lameness of chronic laminitis are used. Treatments can be directed at the underlying digital pathologies, with the goal of decreasing lameness severity by reducing nociceptor stimulation. Alternatively, the lameness can be managed with the use of drugs that modify the pain signaling pathways or centers involved in pain perception.
The approach used in our practice is founded on three important premises: 1. Pain management is critical to successful rehabilitation. 2. NSAIDs can be used for prolonged periods when necessary. 3. While the goal of successful rehabilitation includes significant reduction in lameness, it is often a poor indicator of the efficacy of specific treatments. Conclusions: The successful management of lameness in horses with chronic laminitis is critical to their rehabilitation. As with any disease symptom, management must be based on diagnosis of the underlying pathology, which requires an appreciation of pain physiology. Analysis of mean load stance provides an objective assessment of lameness severity that can be used to compare horses and to determine the response to treatment in individual horses. As the lameness associated with pain avoidance can arise from multiple digital and even extra-digital pathologies, the rehabilitation of horses with chronic laminitis is enhanced by using diagnostic protocols designed to 1) accurately assess lameness severity, 2) determine to what extent the lameness is due to pain avoidance, and 3) identify the specific lesion(s) contributing to pain avoidance. Optimal clinical management of the lameness of chronic laminitis, whether supportive or pharmacologic, is most effective when it is based on protocols designed to target the specific lesion(s).
Laminitis in feral horses: where, when, and why? Brian Hampson School of Veterinary Science, The University of Queensland Take-Home Message: Chronic laminitis occurs in feral horses. As in domesticated horses, pasture-based nutrition appears to be the cause in some populations, while in others it may be longdistance travel over hard surfaces. Introduction: Although much recent research has focused on the pathogenesis of acute laminitis, too little is known about chronic laminitis. Whether feral horses living in wilderness environments are susceptible to laminitis is worthy of study, as it has been proposed that the free-roaming lifestyle and free-choice diet of the feral horse may be preventive. This study investigated the incidence of laminitis in 4 feral horse populations living in a variety of habitats in New Zealand (NZ) and Australia (AUS), using histopathologic and histomorphologic features that have been documented as characteristic of chronic laminitis in the horse. The NZ population was grazing highly palatable pasture grasses selected for exotic sheep that often would have been high in nonstructural carbohydrates (NSC). Long day lengths at high altitudes in the Kaimanawa Ranges of NZ, coupled with overnight temperatures below freezing, produce the ideal scenario for pasture-induced laminitis. The 3 populations of horses in AUS were all living in semi-arid areas of the Australian outback. Materials and Methods: Lamellar samples from the left forefeet of 56 feral horses from the Kaimanawa Ranges of NZ and 45 feral horses from 3 different populations in the AUS outback were examined using light microscopy. The presence of laminitis was determined and the histopathologic lesions described. Horses were grouped as laminitic or non-laminitic, and histomorphologic analysis was compared between groups. Gross morphologic and radiographic findings were also evaluated. Results: In the NZ samples, 45% of the horses had evidence of chronic laminitis. There was a trend toward increased length of the
Abstracts / Journal of Equine Veterinary Science 31 (2011) 562-609
[1,5,6]. If these assertions are to be believed, then the barefoot horse might be expected to outperform its shod competitors. That has not proven to be the case in the equestrian disciplines at the Olympic Games. While there is no official record of the footwear worn by horses competing in the Olympic Games, there appear to be no accounts of barefoot horses winning medals in any equestrian events. It is possible that some barefoot medalists have been overlooked. Even so, it would have to be considered exceptional for a barefoot horse to succeed at the highest levels of athletic competition. There are several accounts of endurance horses training without shoes; however, many of these horses are shod prior to some of the more difficult events such as the Olympic Games. When it comes to human athletes, there are several reports that document potential advantages to performing barefoot. Oxygen consumption has been measured to be 2% lower in barefoot runners than in runners wearing shoes [7], which may translate into ability to perform for longer before tiring. Also, individual impact patterns are more varied in barefoot runners, with lower impact force and the potential for decreased risk of injury, particularly among runners with a mid-foot, lateral foot strike [8]. In addition, human runners take a longer stride when shod than when barefoot, and they are more inclined to land heel-first when wearing shoes [9], which may increase the ground impact force. However, the potential for increased levels of performance is not supported by track records. Since 1960, only two runners have won Olympic medals barefoot. In 1960, Ethiopian marathon runner Abebe Bikila established a world-record time in winning the gold medal barefoot, and South African/Briton Zola Budd also won medals competing barefoot. Interestingly, both athletes later turned to competing with shoes. Bikila competed in the 1964 Olympic Games wearing shoes and set a new world record when he won his second gold medal. Zola Budd, who trained and competed both in shoes and barefoot during her career, now states: “I no longer run barefoot. As I got older I had injuries to my hamstring. I found that wearing shoes gives me more support and protection from injuries” [10]. Is there sufficient information to justify the choice of barefoot over shoes?: In the equine hoofcare field, the anecdotal evidence far outweighs the scientific data, and the anecdotal evidence could support either stance on the issue. Horses certainly evolved over thousands of years without orthotics; however, foot problems appear to have been present even before horses were domesticated. A study of fossilized equine remains suggests the presence of navicular disease long before the time of any human involvement with horses. Furthermore, the research indicates that the severity of lesions in the navicular bone were related to the size of the animal [11]. The United States Navy examined this question and concluded that there was some evidence supporting the efficacy and safety of barefoot-style running shoes, such as the Vibram FiveFinger shoes which allow the foot to function naturally without added support or cushioning. (These shoes were originally designed as boat shoes.) The list of “pros” for the use of minimalist shoes includes stronger feet, reduced impact force, heightened
proprioception, and improved balance. The list of “cons” includes less overall support and protection for the foot, and the need for a transition period. Minimalist shoes are not recommended for those successfully using foot orthotics or for those with preexisting foot problems. Ultimately, the Navy concluded that there is insufficient evidence to either support or refute the efficacy and safety of the barefoot-style running shoes for military personnel. Conclusions: With all of the resources available in the field of human footwear research, there is no consensus as to what constitutes “ideal” footwear. Although there are many advocates of barefoot running, the use of minimalist-style running shoes is more common. Orthotics that provide selected characteristics such as protection while minimally changing the barefoot stride characteristics are now available from several different shoe companies. While many advocates of leaving horses barefoot are opposed to the use of any orthotics, in recent years there has been an increase in the use and availability of many nontraditional orthotics for horses, including various styles of hoof boot, molded urethanes, glue-on shoes, and hoof casts. Although the use of any of orthotic is, strictly speaking, not “barefoot,” it does represent an interesting middle ground. Future studies that investigate the effects of these orthotic devices on foot morphology, function, and athletic performance might lead to the development of new products designed to provide the horse with the mechanical necessities while limiting undesirable effects of hoof orthotics. So, where does all this science and anecdote leave the practitioner considering whether to ditch the shoes? The “evidence is not concrete for or against barefoot or shod running,” said Allison H. Gruber, a doctoral candidate at the University of Massachusetts. “If one is not experiencing any injuries, it is probably best to not change what you're doing.”
References [1] King M. Barefoot vs. shod. The Horse Magazine 2008. article: 12778. [2] Phys Reynolds G, editor. Is running barefoot better for you? The New York Times; 2009; Oct 21. [3] Bedwell SF, Cressman LS. Fort Rock Report: Prehistory and environment of the pluvial Fort Rock lake area of south-central Oregon. In: Aikens CM, editor. Great Basin Anthropological Conference, Selected Papers. Eugene: University of Oregon Anthropological Papers 1; 1970. p. 1-25. [4] Trinkaus E, Hong S. Anatomical evidence for the antiquity of human footwear. Journal of Archaeological Science 2008;35:1928-33. [5] Strasser H. Shoeing: A Necessary Evil? 2nd edn. Sabine Kells, Qualicum Beach; 2000. pp 46–48. [6] Teskey TG. The unfettered foot: a paradigm change for equine podiatry. 2006; http://www.easycareinc.com/TeskeyTrim.pdf [7] Hanson NJ, Berg K, Deka P, et al. Oxygen cost of running barefoot vs. running shod. International Journal of Sports Medicine 2011;32:401-6. [8] Lieberman D, Venkadesan M, Werbel W, et al. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 2010;463:531-5. [9] Wegener C, Hunt AE, Vanwanseele B, et al. Effect of children's shoes on gait: a systematic review and meta-analysis. J Foot Ankle Res 2011; 4:3. [10] Friedman S. After the fall: Zola Budd's running story. Runner's World 2009; Oct. [11] Thompson ME, McDonald G, Østblom LC. Equine navicular syndrome in the fossil record. Hoofcare and Lameness; 76:34–40.
Practical – Laminitis: Treatment by Design Understanding and evaluating the unique lameness of horses with chronic laminitis – Parts 1, 2, and 3 David M. Hood DVM, PhD Hoof Diagnostic and Rehabilitation Clinic, Bryan TX
Take-Home Message: It's not just sore feet. Within the hoof, multiple pathologic and physiologic factors combine to initiate the signaling that produces the altered gait and stance which characterizes the chronically foundered horse. In addition, nonlaminitic digital pathologies as well as nondigital pathologies
Abstracts / Journal of Equine Veterinary Science 31 (2011) 562-609
frequently are present in horses with very chronic laminitis. Identifying all of the elements that are contributing to the lameness is essential to optimizing rehabilitation. Introduction: The treatment and management of lameness is a major component of rehabilitation in horses with chronic laminitis. To better understand and reduce the impact of the lameness in these sometimes difficult cases, there are three key research goals. First is the development of lameness evaluation systems that have greater objectivity, sensitivity, and accuracy than the commonly used subjective grading systems. Second is research that specifically identifies the underlying pathologies and factors that contribute to the lameness in these horses. Third is the development and testing of diagnostic, prognostic, and therapeutic paradigms that target the mechanisms responsible for the observed lameness. This paper summarizes recent research conducted by our group in each of these areas. 1. Objective Assessment of Lameness Severity in Chronic Laminitis: Clinically, the assessment of lameness severity is largely subjective and primarily involves assigning lameness scores to affected horses. However, in rehabilitation research the qualitative nature of subjective grading systems, and the large differences in lameness severity that can exist between the specific grades within a scoring system, combine to limit the consistency, comparability, and accuracy of the data derived from them. The goal of this study was to investigate the clinical usefulness of a force plate-based technology for quantifying lameness severity in horses with chronic laminitis. Material and methods: This cross-sectional study involved 30 horses with naturally occurring chronic laminitis, admitted for rehabilitation and/or rehabilitation research. Lameness severity was subjectively graded in each horse using accepted methods. A load cell-based force plate system was used to determine the percentage of total ground reaction force experienced by the individual feet. The pattern of average distribution of foot load and displacement of the center of load vector (COLv) from its normal position during stancedtermed the mean load stance patterndwas determined for each horse. The strength of association between lameness severity and stance pattern was determined using Spearman's rank correlation. Results: The mean load stance patterns shown by horses with chronic laminitis varied with subjective lameness severity. A significant correlation was found between lameness severity and the degree of change in mean COLv magnitude from that of normal horses. In addition, stance analysis detected significant differences in foot loading in horses subjectively identified as being bilaterally lame, and indicated a high prevalence of rear limb lameness in horses with chronic laminitis. Discussion: The mean load stance pattern displayed by the horse as well as COLv magnitude and direction are the result of voluntary changes in applied limb loads during quasi-static loading. The variation in mean load stance pattern with subjective lameness severity is interpreted as reflecting the combined effects of differences in pain avoidance between limbs and the physiologic/mechanical factors associated with changes in foot conformation, therapeutic shoeing, and learned behavior. The mean load stance pattern and the direction of COLv thus are both presumptive indicators of relative limb involvement in an individual horse. Although the correlation between the magnitude of COLv and subjective lameness severity is circumstantial, it does support the use of this measure as a valid index of lameness severity between individual limbs of an individual horse and between horses. 2. Application of Load Stance Analysis to Understanding the Lameness of Chronic Laminitis: As with any disease, rehabilitation in horses with chronic laminitis is most effective when it is based on protocols designed to identify and address the specific pathologies and factors responsible for producing the clinical
593
signs, in this case lameness. Preliminary and ongoing research indicates that the lameness typical of chronic laminitis is a composite of a variety of pathologies, physiologic/mechanical processes, and learned behavior. The goal of this study was to better characterize the underlying causes and mechanisms associated with the lameness of chronic laminitis. Specific objectives included identifying the anatomic source(s) of lameness, determining the association between lameness severity and the extent of distal phalanx displacement and altered hoof conformation, and characterizing potential paininducing mechanisms within the digit. Material and methods: A change in lameness severity in response to regional anesthesia was used to localize the site(s) of pain in a group of horses with chronic laminitis. Sequential ascending nerve blocks were used to determine the relative contribution made to the lameness by structures located within specific areas of innervation. A second group of horses was used to determine the association between lameness severity and the presence and severity of specific digital pathologies or other gait-altering mechanisms. Therapeutic intervention was used to confirm the role of specific mechanisms. These experiments used changes in subjective lameness and mean load stance analysis as response criteria. Spearman's rank correlation, repeated measures analysis, and paired t-test were used for statistical analysis. Results: Differential regional anesthesia revealed the following: 1. Not all of the lameness in horses with chronic laminitis is the direct result of pain avoidance. 2. In the majority of chronically foundered horses, the lameness originates within the solar and heel regions, rather than in the dorsal laminar interface. 3. Nondigital lameness frequently is superimposed on lameness of digital origin. 4. There is an apparently high incidence of rear limb lameness in horses with chronic laminitis. There was a moderate association between hoof capsule deformation and lameness severity at the walk, but not at rest, in most horses. Intervention studies indicated that digital pain was principally associated with inflammatory mediators and focal pressures generated between the displaced distal phalanx and the hoof capsule. However, the analgesic response to NSAIDs was delayed in these horses. Stronger associations were found between lameness severity and 1) digital instability and 2) the healing response at the sublaminar and laminar interface. Discussion: The failure of regional anesthesia of the foot to totally abolish the lameness indicates that there are factors other than pain contributing to the altered gait and stance in some horses with chronic laminitis. Potential mechanisms include both learned responses and mechanical/physiologic dysfunction. In the horses evaluated, the component of the lameness unassociated with pain appeared to be related to chronic elevation of the heels and/or contracture of the flexor tendons and suspensory apparatus. These acquired hoof malformations alter the gait and stance via interference with the myotactic reflex or by mechanically altering digital biomechanics. The component of the lameness determined to be not of digital origin was clinically interpreted to arise from degenerative joint disease and/or injury to the suspensory apparatus, both of which were presumed to be secondary to chronic laminitis. The high prevalence of rear limb lameness was attributed to repeated overloading of the rear limbs in attempts to rise without fully loading the forefeet. There is little question that the lameness seen in horses with chronic laminitis is, at least in part, the product of diseasedinduced mechanical failure within the foot. However, the low
594
Abstracts / Journal of Equine Veterinary Science 31 (2011) 562-609
association between distal phalanx displacement and lameness severity infers that the pain is not primarily related to the presence or magnitude of displacement associated with mechanical failure. Rather, the association between lameness severity and both digital instability and the healing response at the dorsal laminar interface argues that disease-induced alterations in the material properties of the laminar interface are important in lameness induction. The delayed response to NSAIDs in horses with long-standing laminitis is consistent with a state of upregulation of nociceptors in the digit. 3. Pain and Lameness Management in Horses with Chronic Laminitis: Pain and lameness severity are used clinically to grade disease severity, gauge the relative success of specific treatments, as a prognostic indicator, and as a criterion for euthanasia. This section summarizes some important features of lameness diagnosis, prognosis, and management as it pertains to the horse with chronic laminitis. Diagnostic paradigms for the lameness of chronic laminitis: It is obvious that a major contributor to the lameness seen in horses with chronic laminitis reflects a pain-avoidance response to pathologies directly or indirectly associated with laminitis. However, as our data show, not all of the lameness is directly caused by pain; nor does the pain result exclusively from laminitis-associated digital pathology. Other contributors to the lameness may include digital pathology unassociated with laminitis and pathology beyond the digit that may or may not be a result of laminitis. Hence the need for thorough diagnostic assessment in horses with chronic laminitis. A three-tiered diagnostic protocol is used at our clinic: 1. Determine the relative contributions made by pain avoidance, mechanical factors, and learned behavior. 2. Use the diagnostic findings to determine whether the resulting goal is treatment or simply management of the lameness. 3. Identify the presence and severity of specific lamenessinducing pathologies. Lameness severity as a prognostic indicator in chronic laminitis: Severe, unremitting pain justifies euthanasia in horses with chronic laminitis. However, the fact that the absence of pain does not preclude significant digital pathology and that significant lameness can be present without severe pathology adds an extra degree of complexity to the use of lameness as the sole criterion for euthanasia. A more logical approach is to use the combination of 1) specific digital pathologies that preclude successful rehabilitation and 2) response to pain management. Therapeutic approaches to lameness in horses with chronic laminitis: Major questions remain regarding the management of pain and lameness in horses with chronic laminitis. The arguments that 1) pain is a protective mechanism which serves to limit further injury to the feet, and 2) given the potential for adverse affects, NSAIDs should be given for only a limited time, are countered by the argument that pain is pathological and has consequences that limit the success of rehabilitation. Lameness management decisions are made even more complex by considering the question of whether lameness severity should be used as a primary criterion for therapeutic success. Few clinical studies have been published that provide data with which to resolve these issues. In practice, two approaches to the lameness of chronic laminitis are used. Treatments can be directed at the underlying digital pathologies, with the goal of decreasing lameness severity by reducing nociceptor stimulation. Alternatively, the lameness can be managed with the use of drugs that modify the pain signaling pathways or centers involved in pain perception.
The approach used in our practice is founded on three important premises: 1. Pain management is critical to successful rehabilitation. 2. NSAIDs can be used for prolonged periods when necessary. 3. While the goal of successful rehabilitation includes significant reduction in lameness, it is often a poor indicator of the efficacy of specific treatments. Conclusions: The successful management of lameness in horses with chronic laminitis is critical to their rehabilitation. As with any disease symptom, management must be based on diagnosis of the underlying pathology, which requires an appreciation of pain physiology. Analysis of mean load stance provides an objective assessment of lameness severity that can be used to compare horses and to determine the response to treatment in individual horses. As the lameness associated with pain avoidance can arise from multiple digital and even extra-digital pathologies, the rehabilitation of horses with chronic laminitis is enhanced by using diagnostic protocols designed to 1) accurately assess lameness severity, 2) determine to what extent the lameness is due to pain avoidance, and 3) identify the specific lesion(s) contributing to pain avoidance. Optimal clinical management of the lameness of chronic laminitis, whether supportive or pharmacologic, is most effective when it is based on protocols designed to target the specific lesion(s).
Laminitis in feral horses: where, when, and why? Brian Hampson School of Veterinary Science, The University of Queensland Take-Home Message: Chronic laminitis occurs in feral horses. As in domesticated horses, pasture-based nutrition appears to be the cause in some populations, while in others it may be longdistance travel over hard surfaces. Introduction: Although much recent research has focused on the pathogenesis of acute laminitis, too little is known about chronic laminitis. Whether feral horses living in wilderness environments are susceptible to laminitis is worthy of study, as it has been proposed that the free-roaming lifestyle and free-choice diet of the feral horse may be preventive. This study investigated the incidence of laminitis in 4 feral horse populations living in a variety of habitats in New Zealand (NZ) and Australia (AUS), using histopathologic and histomorphologic features that have been documented as characteristic of chronic laminitis in the horse. The NZ population was grazing highly palatable pasture grasses selected for exotic sheep that often would have been high in nonstructural carbohydrates (NSC). Long day lengths at high altitudes in the Kaimanawa Ranges of NZ, coupled with overnight temperatures below freezing, produce the ideal scenario for pasture-induced laminitis. The 3 populations of horses in AUS were all living in semi-arid areas of the Australian outback. Materials and Methods: Lamellar samples from the left forefeet of 56 feral horses from the Kaimanawa Ranges of NZ and 45 feral horses from 3 different populations in the AUS outback were examined using light microscopy. The presence of laminitis was determined and the histopathologic lesions described. Horses were grouped as laminitic or non-laminitic, and histomorphologic analysis was compared between groups. Gross morphologic and radiographic findings were also evaluated. Results: In the NZ samples, 45% of the horses had evidence of chronic laminitis. There was a trend toward increased length of the