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The importance of identifying lower and upper limb lameness

VETERINARYWeb Master
  In thoroughbred racing, injuries to the limbs are a major welfare and safety concern and are the leading reason for horses to be out of training. Lameness is the number one reason for a high turnover in racing stables and, as many trainers know, it has huge financial implications for the owner, trainer, and the racing industry in general. Previous investigators have found that just over 50% of horses in training in England and Germany experience lameness during training and approximately 20% of horses in the UK suffer lameness that prevents them from returning to training. With this amount of horses on lay-up, it can be difficult to run a profitable racing stable.         In addition to having an impact on the horse’s welfare and future career, severe musculoskeletal injury also poses a serious safety concern for jockeys. The main reason for a jockey to suffer injury in a race is a horse sustaining a catastrophic injury or sudden death.  Researchers in the US found that a jockey was 171 times more likely to be injured when a horse they were riding in a race died. In thoroughbred racing, the most common life-threatening injury to horses involves fractures of bones in the fetlock. Therefore, the best way we can improve safety and welfare of both horses and jockeys is to highlight risk factors for fractures in an attempt to prevent these catastrophic injuries from occurring.         While the majority of injuries occur in the lower limb, such as condylar fractures or suspensory/tendon injury, up to 30% can occur in the upper limb. Several colleagues and I have recently investigated fractures of the upper limb and pelvis in racehorses at the Hong Kong In addition to the welfare of the horse and jockey, severe injuries that occur on race day have an impact on the public perception of racing. This is becoming more apparent in recent times, with an increasing number of animal right activists and the wide availability of social media. It is unknown in the future if certain races will be banned and emphasises how important research in this field is to decrease the number of these fatal injuries.         Jockey Club (HKJC). Although these fractures are less common, they still pose a serious risk when they occur. These include fractures of the radius, humerus, scapula, tibia, femur, and pelvis. These bones are very large and considering the weight of the average racehorse, once a complete fracture of these bones occur there is limited chance of repairing them. It has been demonstrated by previous researchers that these fatal injuries are often the end result of a repetitive or stress-related injury. Therefore, if we could identify these horses during training before they develop a complete fracture we may be able to prevent these fatalities.         Fractures of the upper limb and pelvis can affect horses in numerous different ways. Typically, if a horse has sustained a stress fracture it shows as a severe lameness following fast work, and it improves with rest. However, sometimes these stress fractures can present as a mild lameness with an insidious onset, making it difficult for trainers or riders to observe. As a result, these early injuries can often be mistaken as something less serious, such as a sore foot. Not only is it difficult for the trainer and rider, these cases of lameness are often not straightforward for the veterinarian either. As a result, multiple tools such as radiographs, ultrasound, and bone scan may be required to make a firm diagnosis.         To understand this concept, it is important to understand the mechanism of bone injury. This is similar in both horses and humans. Bone is a versatile structure composed of minerals, collagen, and water. The minerals provide stiffness and strength to the bone, while the collagen and water make it tough and give it a degree of elasticity. Although we do not associate elasticity with bones, if they did not have this property they would be extremely brittle and break very easily.          There are a few important cells in bone that are worth mentioning. Osteoblasts help build new bone and osteoclasts help dissolve and remove old bone so that it can be replaced by fresh, healthy bone. When a lot of stress is placed on bone, such as in certain periods of race training, this stimulates a biological response to increase the size and shape of the bone and additional bone is formed in areas of stress (bone modelling). Also, repetitive loading of the bone, from regular gallops and races, can result in small cracks forming within the bone tissue. These microcracks can join together to form stress fractures. If no extra strain is placed on this bone these microcracks can heal; however, if work is continued this can result in a catastrophic fracture developing. It is a key point to note that during the microcrack formation a lameness may be evident. If the horse is rested at this point, the cells that break down the damaged bone (osteoclasts) cause bone resorption. This results in a temporarily weakness until the new bone is formed. Therefore, if the horse returns to work during this period of new bone formation he is at increased risk of developing a fracture. The resorption phase can occur in as quick as two weeks, but the formation of new healthy bone may take between two and four months, although this is not the same for every injury, every bone, or every horse. This means that if a horse is out of work for whatever reason for more than a few days, he may be at an increased risk of developing a fracture when put straight back into work.         Multiple researchers across the world have worked to identify risk factors that may predispose racehorses to developing a fracture. It must be considered that there are different racing and training regimes, racehorse surveillance programmes, and veterinary resources across racing jurisdictions, and therefore the risk factors may not be the same in every area. Sometimes conflicting results are found. Work from the UK suggests a detrimental effect on bone of the accumulation of long-distance workouts at slow speed and that there are potential benefits of the gradual buildup of high-speed exercise. In addition, short-distance, high-speed exercise has been shown to have a protective effect on skeletal injury.         There are many other risk factors to consider. Although not specifically looking at fractures, it has been shown that with increasing age, horses are at increased chance of sustaining a musculoskeletal injury that will prevent them from returning to racing. However, the risk for a fatal injury decreases with age. There are also certain injuries that are more likely in certain age groups, such as bucked shins and tibia stress fractures in two-year-olds and humeral stress fractures in three-year-olds. One would assume that this is associated with the development of the musculoskeletal system and its response to training regimes. The more we learn about this, the more aware trainers can become, such as, for example, knowing that a horse is more susceptible to bucked shins at a certain age and adjusting training regimes accordingly. There are numerous factors that have been found to affect the risk of injuries such as gender, quality of the race, hoof conformation, and racetrack surface. However, these factors are often inter-related in a complex manner, which often makes it difficult to accurately assess the risk posed by each individual factor. For example, it has been shown that the type of surface will affect the way that a horse lands and puts weight on his limbs, but the same horse doesn’t train on multiple surfaces for comparison. There will be different training regimes, shoeing practices, tack, riders, and weather conditions that will affect the way a horse will train. This makes training surfaces difficult to compare, and there are often confounding results.         In Hong Kong, we examined all of the racehorses in training over 11 racing seasons. Our aim was to find out what type of fractures of the upper limb they suffered, how many of these were fatal, how successful these horses were following fracture, and how this compared to the rest of the world. Our eventual goal is to look at risk factors in an attempt to help reduce the occurrence of injuries. The incidence of fractures of the upper limb and pelvis were low over this time period. There was a total of 102,785 starts in 8,147 races with most of these (90%) being on turf. In Hong Kong, horses typically start racing as three-year-olds rather than at two, and this may explain why we saw a greater number of fractures of the humerus compared to in the UK and US, where tibia fractures are more common. In most of the horses that developed a lameness it was obvious (grade 3 out of 5), but it is important to note that a large proportion of horses had a subtle lameness (grade 1 or 2). This is an important point, as horses in this bracket may have a very mild intermittent lameness that may go unnoticed. The lameness may typically improve with rest and then may form a complete fatal fracture during the next period of fast work. Therefore, as previously mentioned, careful attention must be given to horses that show even a mild lameness after fast work in order to obtain an accurate diagnosis and ensure that appropriate rest and treatment may be administered, if necessary. Lastly, we found that a large proportion of the horses that suffered from non-fatal fractures went on to lead successful racing careers after being given time to recover: 74% of horses with upper limb fractures went on to race again, and over half of these won a race.         In summary, fractures of the upper limb and pelvis are not as common as fractures and other injuries of the lower limb in racehorses. However, if lameness associated with this is not recognised early, these can develop into serious or fatal injuries. The more we research this topic the more we are learning about certain risk factors that may help decrease the occurrence of these injuries.

First published in European Trainer issue 58 - July - September 2017

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In thoroughbred racing injuries to the limbs are a major welfare and safety concern and are the leading reason for horses to be out of training.

Lameness is the number one reason for a high turnover in racing stables and, as many trainers know, it has huge financial implications for the owner, trainer, and the racing industry in general. Previous investigators have found that just over 50% of horses in training in England and Germany experience lameness during training and approximately 20% of horses in the UK suffer lameness that prevents them from returning to training. With this amount of horses on lay-up, it can be difficult to run a profitable racing stable.

In addition to having an impact on the horse’s welfare and future career, severe musculoskeletal injury also poses a serious safety concern for jockeys. The main reason for a jockey to suffer injury in a race is a horse sustaining a catastrophic injury or sudden death.  Researchers in the US found that a jockey was 171 times more likely to be injured when a horse they were riding in a race died. In thoroughbred racing, the most common life-threatening injury to horses involves fractures of bones in the fetlock. Therefore, the best way we can improve safety and welfare of both horses and jockeys is to highlight risk factors for fractures in an attempt to prevent these catastrophic injuries from occurring.