- Maria Soroko
Wroclaw University of Environmental and Life Sciences, Poland
Thermography has found a broad range of applications in equine sport and veterinary medicine. Thermographic diagnosis is useful in monitoring changes of horse surface temperature resulting from exercise allowing evaluation of the work of individual parts of the body in racing performance. Regular assessment of body surface temperature allows the detection of training overloads and identification of pathological conditions of the musculoskeletal system during the racing training cycle. The usefulness of thermography in veterinary medicine has been proved in detecting pathological conditions associated mainly with inflammation processes of the distal parts of the limbs and back. The main advantage of thermography is the detection of subclinical signs of inflammation before the onset of clinical signs of pathology, providing great value in veterinary medicine diagnosis. Thermography has also found application in detecting illegal performance procedures to improve horse performance and in assessing the saddle fit to the horse’s back.
Thermography in equine veterinary medicine was introduced in 1965 and since that time has been considered for use in a wide range of applications (Delahanty & Georgi, 1965).
Thermography enables abnormal patterns in skin surface temperatures (and hence vascularity and metabolic activity within and below the skin surface) due to injury to be detected (Turner, 1991). One of the clinical signs of inflammation is heat, related to metabolic activity and an elevated local circulation, recognised thermographically as a ‘hotspot’ (Ring, 1990). Other pathological conditions reduce blood circulation due to either vascular shunts, thrombosis or autonomic nervous system abnormalities and are recognised as ‘coldspots’ (Turner, 1991; von Schweinitz, 1999).
Therefore thermography has been used increasingly in equine veterinary practice as an efficient tool for detection of injuries of the musculoskeletal system in sport horses (Turner et al., 2001). It has been employed especially in the racing industry, where the physical demands put on racing horses are extreme (Figure 1). Constant overload of the musculoskeletal system due to regular training and racing can cause abnormalities associated with painful conditions or diseases, leading to loss of performance (Jeffcott et al., 1982; Rossdale et al., 1985). Injuries are mainly associated with soft tissue or bone fractures of the distal parts of limbs (Jeffcott, 1999; Parkin et al., 2004; Head, 2009). They are often variably clinically manifested, ranging from overt lameness but also pain on palpation or gait alterations (Jeffcott, 1999; Denoix, 1999; Haussler et al., 1999).
|Figure 1. Thermogram of a racehorse with the rider from the lateral aspect|
Lameness is a significant disorder for racehorses, recognized as an abnormality associated with painful conditions or mechanical injuries, which affect the horse’s way of movement. Numerous reports describing lameness incidence in racehorses have been recorded in the United Kingdom. Investigations presented by Buchner et al. (1996), Ramdy (1997), Oliver et al. (1997), Jeffcott (1999), Kane et al. (2000), and Keegan et al. (2000) indicated that lameness is the main reason for training days being lost and wastage in the horse industry. In the study presented by Jeffcott et al. (1982), out of 163 Thoroughbred racehorses 53% suffered from lameness, which was the main cause of elimination of the horses from performance. A more recent study involving Thoroughbred racehorses recorded an 81% incidence of lameness (Williams et al., 2001).
One of the main problems with injuries is the long period of rehabilitation. Additionally, the reduced tissue functionality decreases the chance of the horse returning to its previous performance and soundness. It was reported that 70% of Thoroughbred horses failed to return to regular training after injury (Oikawa & Kasashima, 2002). Monitoring the impact of racehorse exercise programmes through the measurement of body surface temperature can help to detect potential injuries, maintain horse health and condition, and extend a horse’s career in sport.
Potential equine veterinary applications of thermography in identifying areas of pathology have been described (Purohit & McCoy, 1980; Bowman et al., 1983; Turner et al., 1983; Turner, 1991). These reports mostly address the detection of injuries, especially at the back and the distal parts of the limbs (Vaden et al., 1980; von Schweinitz, 1999; Turner et al., 2001; Turner, 2003; Soroko et al., 2013).
Clinical diseases of the distal limbs including tendonitis, carpal and tarsal joint inflammation and bucked shins have been recognized and characterized by thermography (Purohit & McCoy, 1980; Bowman et al., 1983; Turner et al., 1983; Turner, 1991; Soroko, 2011a). Thermography is also useful in recognizing abnormal conditions of the hoof including navicular syndrome, laminitis, sole abscesses, corns and other hoof-related structural pathologies (Purohit & McCoy, 1980; Turner et al., 1983; Turner, 1991). Thermography not only provides additional information about localizing the problem but also evaluates the degree of associated inflammation.
Thermography and radiography are complementary diagnostic tools for the study of inflammation diseases of distal parts of the limbs (Collins et al., 1976). They cooperate together in diagnosis of joint diseases, as radiography recognizes osseous changes, while thermography indicates changes associated with capsulitis and synovitis in joints. Cooperation between those two methods was successfully applied for diagnosis of osteoarthritis. The study presented by Vaden et al. (1980) indicated that thermography can be a useful tool for chronic tarsal joint arthritis diagnosis together with radiography, and also in the early stages of joint disorders, when no changes are detected in radiography examinations. Similar conclusions were indicated in the case of carpal inflammatory joint disease (Bowman et al., 1983).
Thermography and ultrasonography are also used as complementary tools for the examination of tendons in the distal parts of the limbs. While ultrasonography evaluates morphology of the tendonitis (the size and the shape of the injury), thermography localizes the injury. Moreover thermography can be useful to follow the healing process. As the tendon heals the thermal pattern becomes more uniform, but the temperature remains abnormally elevated compared with a normal tendon (Stromberg, 1972; 1974). Later in the recovery process, as the scar tissue is deposited, the skin over the injured area may actually show a decrease in temperature. According to Hall et al. (1987), ultrasonographic assessment of the structural reorganization of the tendon during healing did not correlate with the thermal changes. However a correlation between thermography and ultrasonography examinations was demonstrated at the time of diagnosis of the clinical signs of tendon inflammation (Soroko et al., 2012a).
Thermography has been shown to be useful in monitoring the healing process, being able to detect inflammation in cases with no clinical signs of injury (Bowman et al., 1983). Additionally, thermography was used to grade the significance of the inflammation during the recovery phase. In the study presented by Purohit and McCoy (1980) thermography monitored the response to anti-inflammatory drugs in the area of the front splints bones. Thermographic images confirmed the reduction of inflammation, however when no heat was detected manually at the affected area, the image continued to suggest increased blood circulation.
Other studies indicated the effectiveness of thermography in monitoring the development of cast sores in the distal parts of the limb. Thermographic evaluations of sored limbs were performed between 18-31 days after the cast. It was found that the technique was able to detect superficial and deep dermal sores. The results indicate that thermography can be useful in monitoring casts and the complications associated with them (Levet et al., 2009).
In the case of back abnormalities, thermography can diagnose muscular and spinous process inflammation of the thoracic vertebrae (Turner et al., 1996; Kold & Chappel, 1998). It has also been used to diagnose clinical cases of lumbosacral muscle tension (Turner, 1991; Turner et al., 1996). In another study thermography diagnosed the clinical signs of neuromuscular disease as caused by nerve dysfunction of the thoracolumbar region (von Schweintiz, 1999). Thermography has been compared with radiographic examination to detect an area of subluxation of the third lumbar vertebrae. The large mass of soft tissue meant that radiographic images did not detect the site of injury, whereas thermography was effective in identification of the exact site of the pathology (Purohit & McCoy, 1980). Thermography was shown to be an effective diagnostic tool in finding active or degenerative places of lesion. Another study presented by Kold and Chappel (1998), investigated the effectiveness of thermography in detecting inflammation along the spine in acute stages. Diagnoses were successful in identification of increased activity of the superficial soft tissue of the thoracic spine and symmetrically over the sacroiliac area. It has been suggested that additional thermography diagnosis can help to locate the site of pain allowing other diagnosis to work more effectively (Turner, 2003). In another study, thermography (along with ultrasonography) was efficient at detecting supraspinous and interspinous ligament inflammation, dorsal intervertebral osteoarthritis and kissing spines of the thoracolumbar spine (Fonseca et al., 2006). Thermography has also been used as a first examination tool for the detection of subclinical inflammation, before the onset of clinical signs of injury. It diagnosed subclinical signs of tendonitis and joint arthritis prior to the appearance of clinical signs of inflammation (Stromberg, 1974; Vaden et al., 1980; Bowman et al., 1983). Recent studies also report possible detection of subclinical inflammation in racehorses (Turner, 1991; Turner et al., 2001; Soroko, 2011a; Soroko et al., 2013). In the study presented by Turner et al. (2001), out of 127 specific limb problems in racehorses, 120 abnormalities were predicted 2 weeks before they became evident clinically. Thermography may therefore help to avoid future loss of soundness by applying treatment or by changing the training program.
Internal and external factors have a significant effect on body surface temperature distribution. The proper use of thermography to evaluate surface thermal patterns therefore requires a controlled environment, and the physiological state of the horse must be considered in order to reduce variability and eliminate errors of interpretation (Head & Dyson, 2001; American Academy of Thermology, 2013; Soroko & Davies – Morel 2016).
Indoor thermography measurement standards have been established in equine veterinary practice (Purohit, 2009). To enhance the diagnostic value of thermography, the thermographic examination should be performed in an area sheltered from the sunlight, in the absence of air drafts (Palmer, 1981; Turner, 2001; Westermann et al. 2013). The ambient temperature of the examination room should be maintained between 21°C to 26°C. Slight variation in some cases may be acceptable, but room temperature should always be cooler than the animal’s body temperature and free from bright lights. It is also recommended to acclimatise the horse for 15-20 minutes prior to imaging in the room where thermography will take place. A longer period of equilibration may be required in cases where the animal is transported from an extreme cold or hot environment. According to Tunley and Henson (2004), the thermographic pattern does not change significantly during acclimatization, but the time taken for stabilisation of the absolute temperature of the body surface is between 39 and 60 minutes. The major factor affecting this equilibration time is the temperature difference between the original environment and that in which the images are to be obtained. Therefore a stabilisation period of one hour is suggested after exposure to a different ambient temperature (Palmer, 1983). Another factor affecting the quality of thermograms is sweating. Therefore imaging should be performed prior to exercise (Purohit, 2009). The examimed horse must have a clean, dry hair coat and should be groomed at least one hour before the examination. Artifacts can be produced by any material on the body surface such as dirt, thick coat, scars and bands (Stromberg, 1974; Palmer, 1981). The feet should be brushed to remove external contamination. Anti – inflammatory medications, vasoactive drugs, regional and local blocks, sedation and tranquilisation should be avoided because of their effect on superficial perfusion (Purohit, 2009). Blankets should be removed at least 30 minutes before thermographic examination, and any bandages should be removed at least two hours before imaging (Palmer, 1981).
Emissivity of the hair coat is generally assumed to be 1, but a lack of precise knowledge of this value will have a small impact on accuracy of perhaps a few tenths of a degree Celsius (Soroko & Davies-Morel, 2016).
Hair coat has been shown to be an effective insulator by blocking heat emission from the skin (Turner, 1991). It has been found that clipping does not cause any change in the thermal distribution but does result in an increase in overall thermal emission. This indicates that clipping is not necessary for a reliable thermogram, however it is necessary that the hair coat be short, of uniform length, and lay flat against the skin to permit thermal conduction (Turner et al., 1983). This is important in the feet area, where some horses can have long “feathers”.
The effect of the coat on thermal distribution has many considerations, because its emission presents a rough surface causing an error in reading the surface temperature. The coated animal surface seen by the camera includes some layers within the coat. Its equilibrium temperature in air is determined by the balance between the loss of heat by radiation and convection to the surrounding environment, and heat conduction through the coat, (Cena, 1974). Clark and Cena (1973) described the transmission of thermal radiation through animal coats of various colours and the related effects of environmental factors. The influence of radiant solar energy on pigmented and non-pigmented areas of the coat was also examined. There was a significant difference in coat surface temperature, up to 8°C between hotter black pigments compared to white areas. It was concluded that skin temperature differences are clearly expressed on the thermal image, but the effect of environmental factors can disturb a reliable thermal image of the animal. In a later study, it was confirmed that under direct sun exposure, black areas of the skin are significantly warmer compared to unpigmented areas. However, indoor examination did not present a significant difference between pigmented and non-pigmented areas (Palmer, 1981). It was also suggested that solar energy absorption depended on the shape and posture of exposed areas to sun (Clark & Cena, 1973). Errors of reading can also be influenced by curvature of the anatomical surface, variations in coat thickness, or pigmentation differences (Clark & Cena, 1977; Turner et al., 1983).
Notes of the thermographic examination should include age, gender and breed of the horse, type of performance and training intensity, and also information about saddle fit. A medical history is also required, including results of other veterinary examinations like radiography, ultrasonography and palpation. This is crucial because many musculoskeletal injuries can be detected by thermography not only in the acute or chronic but also the subclinical stage of inflammation (Soroko & Davies-Morel, 2016).
Thermographic examination of the horse for veterinary diagnosis should include a lateral aspect of the whole body from both sides (Eddy et al., 2001). In these views there should be equal loading of four all limbs with the lateral and medial aspects of the limbs visible. Imaging distance should be about 7 m. The distal parts of the forelimbs and hindlimbs can be imaged from a distance of approximately 2 m (Van Hoogmoed & Snyder, 2002) and should include dorsal, palmar/plantar, lateral and medial aspects. Symmetrical limbs imaged together for palmar or dorsal aspects in one thermographic image should be positioned next to each other; the horse should stand straight without lateral and medial rotation, and the limbs should be evenly loaded.
It is also important to include both lateral aspects of the head, neck, thoracic and pelvic areas, imaged from a distance of around 3 m. The thoracolumbar and sacral parts of the spine should be imaged in the dorsal aspect (von Schweinitz, 1999) from a height of approximately 1.2 m and at a distance of 1.5 m.
Thermographic patterns of the healthy horse have been described, enabling improved diagnostic interpretation of equine thermography (Soroko & Davies-Morel, 2016). It was found that every horse has its own individual and reproducible thermographic pattern, which is related to the vasculature and tissue metabolism and is influenced by ambient air temperature (Purohit & McCoy, 1980; Waldsmith & Oltmann, 1994). However, a number of studies have demonstrated repeatability of body surface temperature distribution on the same areas in different horses (Vaden et al., 1980; Purohit & McCoy, 1980; Palmer, 1981). The skin overlying major vessels will appear warm, whereas areas distal to a major blood supply will appear cooler. Normally veins are warmer compared to arteries because they are in metabolically active areas and closer to the skin surface. Venous drainage from tissue with a high metabolic rate is warmer than venous drainage from normal tissue. The temperature of skin overlying a muscle mass depends on muscle activity.
Based on the above findings, some generalisations can be made regarding the thermal pattern of the horse. The midline of the horse is warm, including the back, chest, and the area between the hindlimbs along the ventral midline (Turner, 1991). Temperature over the limbs decreases from the proximal to the distal part.
Studies by Purohit et al. (1977), Purohit and McCoy (1980), Turner (1991) and Tunley and Henson (2004) has established normal thermographic patterns of the distal parts of the limbs and the back for clinical use.
The patterns obtained in the distal parts of the limbs are characterised by right and left temperature symmetry. Also the thermal symmetry was found to be identical between distal parts of forelimbs and hindlimbs (Purohit & McCoy, 1980). Variations in local blood supply determine the thermal pattern. Areas of increased temperature follow the vascular patterns, including the 3rd metacarpal/metatarsal from the medial and lateral aspects, and coronary band arteries in the dorsal aspect (Vaden et al., 1980; Turner, 1991). In the dorsal aspect joints are cooler compared to the surrounding structures, except the tarsal joint which has a vertical area of increased temperature medially corresponding to the saphenous vein. The route of the median palmar vein in the forelimb and the metatarsal vein in the hindlimb produces a warm region between the 3rd metacarpal/metatarsal and the flexor tendons (Figure 2). Therefore the medial metacarpal/metatarsal region is warmer than the lateral. In contrast, areas distant from major blood vessels appear cooler, including the 3rd metacarpal/metatarsal bone, fetlock, and pastern from the dorsal and palmar/plantar aspects (Turner et al., 1996) (Figure 3, 4).
|Figure 2. Thermogram of lateral aspect of the distal part of right forelimb and medial aspect of distal part of left forelimb. Areas of increased temperature follow the vascular patterns in 3rd metacarpal region|
|Figure 3. Thermogram of dorsal aspect of the distal part of forelimbs. The highest temperature is in the coronary band. Lower temperatures follow the tendons|
|Figure 4. Thermogram of palmar aspect of the distal part of forelimbs. Increase in the heat between the heel bulbs. Lower temperatures follow the tendons|
The highest temperature is in the coronary band, as it is situated close to the major arterio-venous plexus (Kold & Chappell, 1998; Turner, 2001) (Figure 3). The coronary band is 1-2°C warmer than the remainder of the hoof. The surface temperature of the hoof becomes gradually cooler towards the ground, because of the specific anatomic build of the hoof (Verschooten et al., 1997). Tendons have a low blood supply and will appear cold in the dorsal and palmar/plantar aspects because of their location far from superficial vessels. From palmar/plantar aspects, a high surface temperature is indicated in the area between the bulbs of the heels (Turner, 1991) (Figure 4).
Lateral and medial aspects of the distal part of the limb are more reliable than the palmar/plantar aspects for detecting and monitoring abnormalities in increased blood flow.
The thermographic image of a clinically healthy back presents with left and right temperature distribution symmetry along the midline of the spine (Kold & Chappell, 1998). Similar conclusions were found in another study where the thoracolumbar spine was divided into 6 horizontal lines along which the temperatures were measured. All thermograms indicated increased temperature along the midline of the spine, with a temperature 3°C higher at the midline at the thoracic and lumbar vertebrae (Tunley & Henson, 2004). A possible explanation is a high number of superficial subcutaneus blood vessels in that area (von Schweinitz, 1999) (Figure 5).
|Figure 5. Thermogram of dorsal aspect of back. Increased temperatures follow the midline of the spine in the thoracic and lumbar vertebrae with temperature symmetry between right and left side of the back|
Any thermal asymmetry between compared bilateral surfaces can indicate abnormalities (Verschooten et al., 1997). However, not every asymmetry should be defined as an abnormal condition (Kold & Chappell, 1998). Temperature variations up to 1ºC between the compared limbs represents normal variation. Where there is a temperature difference of more than 1°C over 25% of the compared body area, it is considered to be abnormal (Turner, 1991). Temperature differences of 1.25°C between the right and left distal parts of limbs indicated subclinical inflammation of the superficial digital flexor tendon and bucked shins in racehorses (Soroko et al., 2013). In another study, the early stages of bucked shins (Figure 6) were diagnosed when local temperatures over the dorsal 3rd metacarpal bone were 1°C to 2°C higher compared to the surrounding distal limb areas (Turner, 1991) .
|Figure 6. Thermogram of dorsal aspect of distal part of forelimbs. Subclinical inflammation of the right and left 3rd metacarpal bone|
In the early phase of laminitis, the coronary band had significantly increased surface temperature compared to the distal hoof wall and soles of the hooves (Noeck, 1997). In navicular disease, there was a reduction of the blood flow, especially in the heel region, because of vascular constriction. Affected horses presented with a lack of temperature increase in the suspected limb after exercise. The results were correlated with radiography findings, which showed an increased vascular foramina of the affected navicular bone (Turner et al., 1983). Therefore navicular disease can be recognized by thermography in the early stages, with the decreased blood flow appearing as a cooler area (Waldsmith & Oltmann, 1994).
Not every temperature asymmetry may lead to pathological conditions (Kold & Chappell, 1998). In the distal parts of the limbs, local skin temperature variations may be associated with the horse’s homeostatic response to ambient temperature extremes. At low ambient temperature there is a maximal temperature gradient between the skin and the environment, because of vasoconstriction of the local vasculature in the extremities to conserve metabolic energy. At high ambient temperatures, vasodilation causes warming of the extremities, encouraging heat loss to the environment. Bilateral symmetry of the limbs is clinically valid throughout the range of ambient temperature (Palmer, 1983).
Body surface temperature distribution depends on movement, and the type of physical exercise performed, as the skin overlying muscle is subjected to an increase in temperature during muscular activity (Turner et al., 1996). Thermograms documenting the changes of horse surface temperature resulting from exercise could be useful in the evaluation of the work of individual parts of the body in racing performance (Purohit & McCoy, 1980; Waldsmith & Oltmann, 1994; Jodkowska et al., 2001; Jodkowska, 2005).
The study presented by Simon et al. (2006) highlighted the influence of exercise on body surface temperature changes in the forelimbs and hindlimbs. Thermal images of examined horses were taken before and after exercise on a treadmill. The skin temperature overlying muscle surfaces after exercise was increased by 6°C, whereas areas of distal parts of the limbs were increased by 8°C. There was a significant temperature difference during the first 15 minutes after exercise, whereas thermographic examinations performed 45 minutes after exercise were not influenced by the mechanism of thermoregulation. It was also found that muscular areas in the upper part of the body returned more quickly to the basal temperature compared to the dorsal parts of the limbs. In the study by Turner et al. (2001), racehorses had an increased hoof surface temperature for almost 24 hours after an intensive gallop.
Symmetrical temperature distribution on both sides from the front and from the back aspect should be present at rest, and also after exercise (Jodkowska et al., 2001). Any temperature asymmetry after training could be useful in the evaluation of the work of individual parts of the body in sport performance. Jodkowska (2005) determined a model of horse temperature before and after exercise. During the study the rectal temperature, pulse rate and blood parameters, as well as environmental factors were correlated with changing temperature patterns. It was concluded that body surface temperature patterns depend on exercise performance. Surface temperature examination of the distal limbs and back was helpful in assessing the quality of exercises and preparation of a horse for training. It was also found that the optimum period for measurements of body surface temperature was the time before exercise, or on the day after exercise.
Thermography was also confirmed as a valuable aid in regular assessment of racehorses by Turner et al. (2001). Thermographic imaging of the distal parts of the limbs and back at rest during the training season facilitated identification of inflammation affecting performance (Soroko at al., 2013). In the study presented by Turner et al. (2001) there was a high correlation between Thoroughbred racehorse trainers’ and veterinary diagnosis supported by thermographic assessment. Additionally, in most cases subclinical inflammation was detected 2 weeks before clinical problems were noted. This finding confirmed reports in a previous paper that indicated injury of the superficial digital flexor tendon of racehorses prior to the appearance of clinical signs of inflammation (Stromberg, 1974) (Figure 7). The injured area showed increased temperature on the thermographic image even though radiogram did not show any changes. Stromberg (1974) concluded that thermography can predict tendon injures up to 14 days before clinical signs appear and can play an essential role in preventing lameness in racehorses.
|Figure 7. Thermogram of lateral aspect of the distal part of left forelimb and medial aspect of distal part of right forelimb. Subclinical inflammation of superficial digital flexor tendon of right forelimb|
The type of training has an influence on changes of body temperature distribution. Horses in training put more strain on the forelimbs, especially on the digital flexor tendons and bones (Nilson & Bjorck, 1969). Regular thermographic examination of racehorses found thermal abnormalities of forelimbs associated with strains and overloads (Soroko, 2011b; Soroko et al., 2014). This confirms that racehorses are more likely to develop injury associated with the forelimb than the hindlimb (Peloso et al., 1994). The same conclusions have been presented in another study, where more signs of injuries in 4-year-old Standardbreed Trotters were recorded in the left forelimb compared to the right one (Magnusson, 1985). Possibly, as horses during racing and exercise were loaded on the right forelimb due to the clockwise race track, when resting they were overloading the opposite side.
Increased body surface temperature in the back area may indicate pathological conditions caused by intensive performance of a horse, the rider’s imbalance, or an incorrectly fitted saddle (Harman, 1999; De Cocq et al., 2004; Arruda at al., 2011). The study by Jeffcott et al. (1985) proved that injuries of the paraspinal muscles and the ligaments were diagnosed in 25% of horses in intensive training. Other research indicated body temperature surface variations in the sacroiliac joint region, which were found to be typical injuries for show jumping horses with indicated abnormalities of hind limb movement patterns (Haussler et al., 1999). Racehorse back surface temperature distribution changes were characterised in response to increasing training intensity in long-term training by Soroko et al. (2012b). The study found that the spine had the highest temperature in the thoracic vertebrae compared to the lumbar vertebrae and sacroiliac joint area. Higher temperatures in the thoracic vertebrae could be associated with riding techniques in trot. Peham et al. (2010) detected the highest load on the horse’s back at the sitting trot (2112 N), followed by the rising trot (2056 N) and the two-point seat (1688 N). Saddles, analysed for the pressure distribution over the thoracic vertebrae during movement, indicated the highest pressure at trot (Latif et al., 2010).
Gradual increments of training intensity in long – term training caused a decrease of average temperature differences between thoracic vertebrae compared to the lumbar vertebrae and sacroiliac joint areas in racehorses at rest (Soroko et al., 2012b). Regular thermographic examination of racehorse performance indicated an increment of the temperature at the back and the distal parts of the forelimbs at rest (Soroko, at al., 2015). In another study, the best performing racehorses were warmer than their poorer performing peers at all body sites. Differences in temperature between the groups were significantly higher at the carpal joint, 3rd metacarpal bone, fetlock joint, the short pastern bone, the tarsus joint, (although only on the left side) and also the thoracic vertebrae (Soroko et al., 2014). This temperature difference may reflect an increased physiological training impact on the best performing horses. According to Evans et al. (1992), strains and overloading of the musculoskeletal system due to physical work under demanding exercise results in increased blood circulation in a defensive adaptation process, predisposing the animal to future lameness injuries. This agrees with Estberg et al. (1995) who confirmed that training intensity and regular exercise predispose horses to fatal skeletal injures. According to Soroko et al. (2014) identification of the most reliable body regions recommended for monitoring the impact of training should facilitate the detection of pathological conditions during the training cycle. This is particularly important in racehorses, where immediate diagnosis might help to maintain their health and condition, positively influencing their further career in sport.
Thermography is able to diagnose an area of inflammation associated with superficial muscles or muscle groups. Muscle inflammation is usually identified as an area of increased temperature directly overlying the affected muscle. Although thermography measures only skin surface temperature it also reflects alterations in the circulation of deeper tissue. The most common cause of muscle inflammation is muscle strain, which can be detected by thermography, however it has not been well documented in studies. Turner (1998) detected by thermography inflammation of muscles in forelimbs including the pectoralis muscles and biceps brachialis muscles. In the upper hindlimb, the gluteal muscles and the biceps femoris muscles appeared warmer when the croup region was injured (Turner et al., 1996). In another study horses with croup and caudal thigh myopathy were diagnosed. Thermography was recommended as a tool for detecting upper limb lameness, by confirming inflammation of sore areas requiring further diagnostics (Turner, 1998). Figures 8-10 present examples of thermographically detected muscle inflammation processes in four cases of sport horses. Thermography was able to detect upper limb problems associated with: gluteus muscles inflammation (Figure 8), tensor fasciae latae muscle inflammation (Figure 9) inflammation of the semitendinosus (Figure 10) and biceps femoris muscles (Figure 11). Once abnormalities have been detected, thermography can determine the effectiveness of different types of therapeutic and rehabilitation applications (Turner, 1991; Turner, 1998).
|Figure 8. Thermogram of dorsal aspect of hindlimb. Inflammation of left and right gluteus muscles|
|Figure 9. Thermogram of lateral aspect of left hindlimb. Inflammation of tensor fasciae latae muscle|
|Figure 10. Thermogram of caudal aspect of hindlimb. Inflammation of left semitendinosus muscle|
|Figure 11. Thermogram of lateral aspect of right hindlimb. Inflammation of biceps femoris muscle|
In racing performance horses intensively trained for high level racing, musculoskeletal injures can impair the horse’s ability to perform and can lead to dismissal from competition. Common areas which are frequently a source of lameness in racing horses are the distal parts of limbs and back. Therefore regular thermographic analysis will enable horseback overloads to be monitored and facilitate identification of pathological conditions during the training cycle. With the veterinarians and breeders working together, new heights in performance can be reached when training and conditional diagnosis are combined.
Thermography has also found application in detecting abnormal temperature caused by chemical and mechanical abrasion of performance horses. In equestrian events intense competition promotes the use of procedures designed to illegally enhance performance including application of counterirritants, subdermal injections, irritants or use of regional nerve block via chemical or surgical neurectomies. The majority of these methods are an attempt either to mask lameness from veterinarians or enhance a horse’s natural gait by artificially producing more action or suspension. Some techniques are not detectable, and may be difficult to prove, using conventional methods.
In 1970 the passage of the US federal Horse Protection Act put a legal ban on the use of chemical or mechanical means of soring horses. Five years later Nelson and Osheim (1975) demonstrated that chemical and mechanical soring caused definite abnormalities in the radiation emission patterns of the horse’s digit. In a later publication, thermography detected illegal procedures in show horses, detecting the application of irritants to the perineal region to enhance rail evaluation (Turner & Scroggins, 1989). Therefore thermography became an appropriate tool for the detection of illegal performance procedures. Thermography successfully detected limb sensitivity, which refers to the sensation perceived by horses in their limbs. When the sensation is increased above normal limits it is called hypersensitivity, as from traumatic or surgical cutting of the nerves in that area of the limb (neurectomy). It is practiced to encourage sport horses to jump more carefully and higher. In a study presented by Van Hoogmoed et al. (2000) thermography was used to investigate the detection and duration of counter-irritants applied topically and injected subdermally, and induction of hypersensitisation using limb bandages containing metallic objects. Counter-irritations were applied to the dorsum of the pastern, and metallic irritants contained in limb bandages were applied to the metacarpal area to induce hypersensitivity of that area. Thermography images were found useful to detect and monitor the effect of changed thermal patterns after a single application of an irritant: mercuric iodine for 6 days, and the effect of metallic bottle caps within the leg wraps for 24h after application, presenting thermography as a sensitive tool for detecting hypersensitisations in horses.
Another study evaluated the ability of thermography to detect procedures used to obscure lameness, ranging from local injections of various pharmaceuticals. The injection of analgesic agents was applied to horses’ limbs and backs. Thermographic images were recorded before, and 30, 60, 90 and 120 min. after the experimental procedures, until temperature differences from the opposite non-treated site were no longer significant. A single injection of neurolitic agents in the area of lumbar vertebrae and in the suspensory ligament caused an increase of temperature which persisted for 2 days. The highest temperature differences peaked at 60 min. and later declined. The study identified thermography as potential tool for detecting temperature changes in heat patterns compared to control regions. In the same study, the application of thermography was investigated for detecting and monitoring palmar digital neurectomy. Horses with palmar digital neurectomy did not show a persistent increase in temperature compared to the control limb. The significantly increased temperature was present on the first day of treatment in the limb with neurectomy compared to opposite control limb. However, no temperature differences between limbs were detected by day 6. It is suspected that nervous interruption causes a vasodilator effect, persistent for a short period of time until the vascular system compensates, influencing a return to normal circulation (Van Hoogmoed & Synder, 2002). It has been concluded that thermography is sensitive enough to detect changes in heat patterns from innervated regions, however it is not specific enough to discriminate between procedures and injury inducing an inflammatory response.
Since 2002 thermography has been recommended as a potential screening technique for illegal limb sensitivity of competition horses by the International Federation for Equestrian Sports. If the examining veterinarians observe excessively sensitive, or insensitive limbs together with abnormal thermal patterns detected by thermography, a horse can be disqualified from competition on the basis of horse welfare and fair play.
Thermography was also used for examination of the correct fit of the saddle to the horse’s back (Turner, 1991). Tack related problems can be identified by the thermal patterns caused by the tack while the horse is being ridden. Thermal image assessment of the dynamic interaction between the saddle and the back of the horse showed not only the heat generated in areas of greater interaction with the saddle, but also the physiological effects of riding on the back of the horse (Turner et al., 2004; Arruda et al., 2011).
Thermography is becoming increasingly popular as an aid to assist the diagnosis of musculoskeletal and neurological injuries in racehorses. It can detect subclinical problems at least 2 weeks before they are visually detectable. It helps veterinarians to diagnose the exact site of injury and follow the response to treatment. Thermography detects training overloads and muscle strains which can lead to injury, allowing the trainer to make decisions about the horse’s training programme and management. It is more sensitive than palpitation for detecting subtle temperature variations (Turner, 2001). This high sensitivity makes it useful in conjunction with other veterinary diagnostic tools that provide more specific information. Thermography, as a non-invasive tool, allows the horses to be examined without being touched, thus causing no stress or discomfort to the animal.
Infrared imaging technology has improved extraordinarily in recent years. New generations of thermographic imagers are user-friendly, portable and have a high temperature sensitivity. Current thermographic equipment is sensitive enough to detect skin temperature differences of 0.1°C.
The development of infra-red technology and better availability of this type of equipment should contribute to more extensive use of this diagnostic method, applicable not only to horses, but also to other animals.
This research was previously published in Innovative Research in Thermal Imaging for Biology and Medicine edited by Ricardo Vardasca and Joaquim Gabriel Mendes, pages 264-286, copyright year 2017 by Medical Information Science Reference (an imprint of IGI Global).
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Bucked Shines: A repetitive loading injury of the third metacarpal bone. It occurs when the periosteum tears away from the front of the cannon bone. As the result of this this tear, there is bleeding with the formation of a hematoma, where new bone if forming.
Distal Parts of the Limbs: Limb from carpal joint do hoof in forelimb and from tarsal joint to hoof in hindlimb.
Laminitis: Laminitis is a crippling disease in which there is a failure of attachment of the epidermal laminae connected to the hoof wall from the dermal laminae attached to the distal phalanx.
Long Term Training: One racing training season which lasts 10 months from January till October, during which horses are regularly trained and raced.
Navicular Disease: Is an arthrosis developing on the surfaces of the navicular bone and the deep flexor tendon.
Subclinical Sign of Inflammations: Very early stage of inflammation when no clinical signs of inflammation: pain, heat, lameness, swelling and concerns of trainers are present.
Tendonitis: Inflammation of a tendon.