$TODAY we have many sensitive and specific tools that are used by veterinary surgeons to diagnose the cause of lameness. These include radiography, scintigraphy, ultrasound and MRI. These however not all suitable for regular routine monitoring. Ultrasound, due to its nature, can be used more frequently than the other techniques but its use is focused to soft tissue and in a limited area, e.g. tendons. These are diagnostic modalities rather than techniques for monitoring. The most common tools the trainer uses to monitor horses with respect to lameness are eyes and hands. Visual observation of a horse’s gait is used universally. However, several studies have shown that even trained and experienced veterinary surgeons differ in subjective visual lameness assessment. That is, even wh en examining the same horse they may assign different grades of lameness, disagree on the site of the lameness, and sometimes even disagree on which leg the horse is lame; this is especially true when the lameness is mild! (see Keegan et al. American Journal of Veterinary Research , 1998) The problem with visual observation is that it is subjective. It may be hard, if not impossible, to see very slow deterioration in a horse over several weeks. There has been a move towards developing objective lameness assessment devices, such as the Lameness Locator. These have the potential to be used routinely for monitoring a horse’s gait over time. However, the cost and technical aspects mean they will likely be used by clinicians rather than trainers. And whilst they may identify a horse as lame, they may not give any clues as to the location of the problem and will not identify a problem in the early stages i.e. when there is inflammation but no effect on gait. Running hands down a horse’s legs is the second technique used widely. The limitation here is that our hands are relatively insensitive. We may be able to detect a difference of around 1°C between legs. Some people may only appreciate a difference when this exceeds 2°C. In many cases the difference in temperature of injured tissues may be less than we can detect by hand. The areas of the body over which we use our hands are also fairly limited. When muscle or tendon or even bone or cartilage is damaged or injured, blood flow is usually increased in an attempt to repair the damage. This is what leads to the increase in temperature that we may be able to detect with our hands and which has lead to the use of thermography (thermal imaging) as technique to visualise heat patterns on the surface. Thermal cameras actually only measure the surface temperature of whatever they are pointing at. So if it’s the back of the front leg we are looking at the temperature of the hairs rather than the skin. But, if there is inflammation under the skin, then this will result in warmer hairs. And even if the damage is deep down in the tendon, if the degree of inflammation is sufficient, the heat being generated can be conducted through the tendon to the surface. Thermography has been around for a long time. People seem to fall into one of two categories when it comes to the use of thermography. There are those that are totally invested in it and convinced by it as a technique, and there are those that have no time for it. There’s no middle ground. Thermal cameras even as recent as 15-20 years ago yielded relatively poor quality fuzzy pictures and lacked sensitivity. They were also heavy, unwieldy, and very expensive. Modern cameras offer much higher resolution images with greater sensitivity. The big question is, do they offer any advantage to the trainer looking to monitor horses for signs of orthopaedic problems that may lead to lameness? Infrared thermography is a monitoring tool that allows us to quickly and efficiently identify trauma in an injured animal. It allows early detection of physiological injury, stress, and trauma; it also acts as an aid to monitor racehorses in recovery from injury. By identifying the location of the injury we can prevent further trauma, make a decision on treatment needed, and monitor the recovery. It has also been used by some as a tool to help ensure effective training methods and to help achieve peak performance. With the use of an infrared camera we can see and measure the thermal energy (heat) from an object. Thermal or infrared energy is light that is not visible to the naked eye because its wavelength is too long to be detected by us. It is the part of the electromagnetic spectrum that we perceive as heat unlike visible light. In the infrared world everything with temperature above absolute zero emits heat; even very cold objects, like ice cubes, emit infrared. The higher the object temperature the greater the infrared radiation emitted. In other words infrared allows us to see what our eyes cannot; it also allows us to see what our hands cannot feel. So when using thermography with racehorses, this technology gives us a pictorial representation of the surface temperature of the animal; it represents the measured heat emitted from the skin surface. The skin of an animal is approximately five degrees cooler than core body temperature (in temperate conditions; it may be even greater when its very cold) and variations in skin temperature result from tissue perfusion and blood flow in superficial veins. It also reflects alteration of the circulation in deeper tissues and so detects areas of inflammation. Because inflamed tissue has increased circulation, injury will then show up as ‘hot spots’ or, in the case of nerve damage or an abnormal accumulation of fluid in the tissue reducing circulation, ‘cold spots.’ For a thermographer to understand what a scan is showing, it is firstly important for them to understand what is normal. Once that is established they can then identify what is abnormal. A normal, sound horse should show symmetric thermal patterns in its anatomic structures when compared to the same region on the opposite side of the body. Where there are breaks in the thermal patterns or asymmetry we would investigate further; this may mean the application of another diagnostic tool that would give more detailed information on the animal’s physical state. Thermography has a wide range of clinical applications. The most common is the evaluation of the tendons and ligaments of the limbs with a great capacity for preventative applications. Tendon and ligament injuries have been known to be identified up to three weeks before the onset of clinical lameness. Laminitis, characterised by the inflammation of the laminar structures, has been identified by thermography. Other applications are foot abscesses, navicular, foot imbalances, and back injuries such as kissing spine and sacroiliac injuries. Thermography has also been proposed to be useful in the early diagnosis of stress fractures in the third metacarpal bone, the radius, and the tibia, which could prevent catastrophic bone failure. Inflammation in the joint produces a characteristic thermal pattern in the overlaying skin. Normal thermal patterns of joints should be cool compared to the surrounding tissues. One of the greatest potential applications is for monitoring the muscles in the upper limbs and back. In the upper forelimb, the pectoralis and biceps brachii musculature are most commonly associated with temperature asymmetry. In the upper hind limb, the distal quadriceps musculature, the semitendinosus, and biceps femoris muscles have been most commonly isolated as areas of injury and abnormal thermal patterns. Without the aid of thermography, these injuries can be difficult to identify. Additionally, injuries of the gluteal musculature, dorsal spinous ligament desmitis, and sacroiliac desmitis are often demonstrated as hot spots thermographically. Once a muscle injury is diagnosed with thermography, ultrasonography can be used to characterise the lesion. Due to the ability to detect physiological changes quickly, safely, non-invasively, and without any limitation on how often it is used, thermography’s benefits for the trainer should be in its ability to detect small changes that occur. Being able to identify when training is resulting in more frequent or more severe damage and when it is detrimental to the horse could represent a huge leap towards prevention of injury in the racehorse. To maximise the advantages for the racehorse, thermography should probably be used as a regular monitoring tool before and after training, after racing, and also as a monitoring tool for recovery from injury. Thermography should ideally be applied by a qualified thermographer who has been trained by a reputable longstanding organisation, and he or she must be supported by a veterinary surgeon. The aim of thermography is early identification of abnormal thermal patterns, the cause of which can then be investigated and diagnosed by a veterinary surgeon. Both thermal imaging technology (i.e. cameras) and understanding of how to interpret thermal images have developed over the past 15 years. Thermal imaging has the potential to be a useful tool in the racing yard. Only time will tell if the advances in technology translate into more widespread use and a clear advantage over the considerably cheaper and time honoured technique of... using our hands!$

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