Jewel's injury leaves little hope for return And daylight second: Atlantic Jewel romps to victory in the Caulfield Stakes. Champion Atlantic Jewel sustained a tendon injury at Flemington on Tuesday morning that will end this campaign and probably end her career. All trainers fear a bowed tendon as they know that what starts as a seemingly innocuous swelling in the leg, often without soreness, can finish a racehorse's career. There is no human equivalent to a bowed tendon, but there are similarities to a ruptured Achilles tendon. Atlantic Jewel's injury site. So what is a bowed tendon, why does it occur and why with today's advances in veterinary science is it still a career-ending injury? A bowed tendon is the lay or descriptive term for a strain or tearing to the superficial flexor tendon. The tendon runs down the back of the cannon bone or shin. It is a long thin band of tough, slightly elastic tissue stretching over about 40 centimetres from just above the knee to just above the hoof. It is thin and straplike, only half a centimetre thick and two centimetres wide, somewhat similar to the human Achilles tendon. It may be small but it has a vital function, serving as one of the main structural supports and shock absorbers for the fetlock and lower leg. The biomechanics of a galloping action mean that at some stage only one front leg is on the ground and all the forces are placed on the tendons and fetlock of that leg. Indeed, during a gallop, the back of the fetlock touches the ground as the leg absorbs the forces of a 500 kilogram horse galloping at speeds of 50km/h. The shock-absorbing role of the tendon during this loading is what leads to a tendon injury, but it is the nature of the healing that presents such a bleak prognosis. If we look at the tendon under a microscope, we see it is made up of thousands of tiny fibres of collagen all running parallel up and down the leg. These fibres give the tendon its shock-absorbing capacity as they can absorb huge loads, stretch slightly and recoil into the original shape. Tendons are supported by other muscles which keep them taut like a "bow string" to absorb these loads. With a bowed tendon, there is overloading of the tendon which is stretched too far, resulting in tearing of the collagen fibres. This leads to bleeding which causes the tendon to swell slightly. Clinically, a horse with a bowed tendon presents with a slightly swollen tendon which is hot and painful to touch though often these horses are not lame. As this is an overload injury, it tends to occur after a race or a trial rather than during regular training. During a race, the horse fatigues and the muscles tire which can lead to overloading of the tendon and the resultant strain. The real problem with a bowed tendon relates to how it heals. The body sends in new cells to repair the damage and lay down new collagen. But this new repair collagen or scar tissue is not arranged parallel to the original fibres but is simply a disorganised lump of scar tissue. Therefore it is not as elastic as the original and is a weak spot prone to re-injury. An analogy would be to cut a nylon rope in half and then simply glue the cut ends together. This inherent weakness in a healed bowed tendon means that these horses almost always re-tear the injury when it is loaded under race conditions. For this reason this is a frustrating injury to rehabilitate as often everything looks good during all the early training right up to the first trial or race when it often recurs. Advances in veterinary medicine technology, such as ultrasound, have meant that the diagnosis of a bowed tendon is much more precise. The ultrasound shows the tendon to be swollen with a hole where the fibres have broken. But similar advances have not been made in modifying the body's healing or repair function to improve the quality of the scar tissue in the repaired tendon. Many techniques have been tried, including surgery, tendon injections, tendon implants and, more recently, stem cell therapy. Some of these treatments, together with a controlled exercise program, try to force new collagen fibres to align parallel to the original fibres. While there has have been some improvements in treatment, we are yet to find a technique that can return tendon function to normal. As a result, tendon injuries still have a bleak prognosis. He is a specialist in equine surgery and consults both here and overseas.