Stress Fractures in the Young Thoroughbred Racehorse
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Vet Forum: The Expert View By Stuart Williamson BVSc MRCVS stress fractures that are not evident when investigated with other imaging Stress fractures in the young modalities. The opportunity to obtain a firm diagnosis and therefore more accurately plan further training of the horse often outweighs the additional thoroughbred racehorse expense and transport to a hospital. Whilst scintigraphy is an excellent stress fracture is a partial the resorption of bone tissue. During of rest are over-represented in the tool for highlighting areas of excessive or complete bone fracture exercise, bone adaptation is triggered affected population. bone remodelling, there remains a risk A that occurs as a result of the by a change in the number of strain A thorough clinical examination of of a negative or an inconclusive result if repeated application of stress at a cycles and the magnitude, the rate the limb may identify a painful response these animals are presented too early. level lower than the stress required to of change and distribution of strain. in the affected area and this can guide For this reason, delaying scintigraphic fracture the bone in a single loading. In other words, increasing levels of radiography or ultrasonography. examination until ten to 14 days post- Stress fractures are common injuries exercise results in increased bone If a painful focus is not identified, injury permits the appropriate bone in both human and equine athletes remodelling. Training over further survey radiography of the limb and remodelling to occur that will be more whose bones are placed under constant distances, galloping at faster speeds ultrasonography of the pelvis are easily identified upon scintigraphic strain whilst undergoing rigorous and not allowing a sufficient rest period performed in order to examine those examination. training regimes. First described by between training sessions can all push sites commonly affected by stress In human medicine, magnetic Aristotle in 200 BC, stress fractures this remodelling adaptation to the fracture pathology, and to rule out resonance imaging (MRI) examination were initially recorded in the medical limit. This can alter the continuum of other possible injuries. is the gold standard for the diagnosis literature in 1855 by the Prussian adaptive and non-adaptive responses Unfortunately, regardless of the of stress fractures but unfortunately military physician Breithaupt, who of bone and result in fracture. level of lameness, initial radiographic the size of the equine patient and the described what is now known as a and ultrasonographic examinations design of the machines available in “march fracture”, or a stress fracture of How do we diagnose stress may prove non-diagnostic as changes most hospital set-ups limits its use to the metatarsals within the foot. Much fractures? are too subtle to be detectable with evaluation of the lower limb. early research was based upon military The diagnosis of a stress fracture each of these modalities at the onset personnel, however, as the general is based upon a combination of of lameness. Further bone remodelling How do we manage stress population engaged in more vigorous the presenting clinical signs, the can be required in the areas of these fractures? and weight-bearing sporting activities, training history of the horse and the stress fractures in order for them Primary management is dependent these injuries became of interest to the radiographic, ultrasonographic or to become visible on radiography upon the level of lameness. In most wider medical field. gamma scintigraphic (bone scan) and ultrasonography. If no definitive cases, a period of box rest is advised, Paula Radcliffe received media findings. Lameness can vary from mild abnormalities are identified at this until the horse is sound and can A specimen of the equine pelvis. The red arrows indicate the left and right ilial wings attention following the news that she (often indicating early stress fracture stage then the horse is box rested commence walking exercise. Those whilst the blue arrows indicate the left and right ilial shafts had sustained a stress fracture of her pathology) to severe (this can be and a repeat imaging examination with a marked or a non-weight bearing femur in the lead-up to the Beijing associated with a complete fracture of is performed ten to 14 days later. acute lameness are often cross-tied PELVIS be catastrophic if a sharp fractured Olympics in 2008. In the racing media, the bone). Generally it is recognised Alternatively, scintigraphy may be until a definitive diagnosis is established Ilial stress fractures can occur in either portion of the bone lacerates one of Jack Hobbs was reported to have that two-year-olds undertaking their employed. and a complete bone fracture has been the wing or in the shaft portion of the arteries closely associated with it. sustained a pelvic stress fracture having first pieces of fast work and horses Scintigraphy (bone scan) is the gold ruled out. Following completion of box this bone. Ilial wing stress fractures Whilst cases of ilial stress fractures been pulled up in the Group 2 Jockey returning to exercise following a period standard approach for identifying many rest, equal periods of both walking and are more commonly identified. Those do not necessarily present with any Club Stakes at Newmarket in late April trotting exercise (generally three to that involve the shaft of the ilium are localising clinical signs, mild early 2016. four weeks) are recommended before generally more serious, particularly cases of ilial stress fractures may The occurrence of these injuries, cantering exercise is resumed. Imaging if complete and displaced. They may resent firm palpation over the pelvic ›› often at vital points in training monitoring may occasionally be used to programmes, underlines the importance tailor the rehabilitation programme for of early recognition allied with an a specific injury. accurate diagnosis. Both are essential to ensure the appropriate management, Common stress fracture to permit a timely return to training and locations to reduce the risk of recurrence in the TIBIA next training phase. Tibial stress fractures have been This article reviews the more identified as the most common commonly identified stress fractures, musculoskeletal injury of the young the pathology underlying their thoroughbred in training. Lameness development, their diagnosis and the frequently precedes the radiographic subsequent management. changes and indeed many of these tibial stress fractures remain Why do stress fractures occur? radiographically subtle or silent, Bone is an active tissue that is prompting scintigraphic examination constantly changing in response to the to obtain a definitive diagnosis. Most forces placed through it. Osteoblasts cases will require six to ten weeks out are the cells that are the building of cantering exercise. The prognosis Left: bone scan image demonstrating an area of increased radionucleotide uptake on blocks involved in the creation and Lateromedial radiographs of the bottom of the tibia demonstrating bony callus for a return to full athletic function the back edge of the left ilial wing (red arrow). Right: ultrasonographic appearance mineralisation of new bone, whilst characteristic of a distal tibial stress fracture. Both radiographs are of the same following a tibial stress fracture is of the ilial wing stress fracture (red arrow) identified on the bone scan image on the osteoclasts are the cells involved in injury on day one (left) and day 21 (right) generally considered to be excellent. left. Note the disrupted contour of the ilium and the associated callus 102 THE OWNER BREEDER THE OWNER BREEDER 103 Vet Forum: The Expert View ›› area. More significant fractures frequently display muscle spasm and guarding over the gluteal musculature. Diagnosis can be made by ultrasound examination of the ilium. As with other stress fractures, the absence of ultrasound findings does not rule out injury, especially with ilial shaft stress fractures as these can be difficult to visualise. In the absence of ultrasonographic findings, scintigraphy could follow. Alternatively, horses can be treated symptomatically and rested as they would with a definitive diagnosis. The prognosis following ilial stress fractures is varied. Non-displaced wing and shaft fractures carry a good prognosis. Displaced wing fractures Left: bone scan image demonstrating increased radionucleotide uptake at the generally carry a good prognosis bottom of the humerus (red arrow). Right: bony callus noted on the outer aspect of though pelvic asymmetry can often the bottom of the humerus (red arrow) be marked, whilst displaced shaft fractures carry a guarded prognosis UPPER CANNON Subtle radiographic abnormalities may for a return to racing. Most ilial stress This stress injury of the upper be noted but scintigraphy is often fractures do not produce a bony callus cannon can also involve pathology required for diagnosis of this particular that would encroach on the birth canal within the proximal suspensory injury. and preclude a broodmare career. ligament and is a common cause of lameness in young racehorses. Both Summary HUMERUS radiography and ultrasonography In summary, stress fractures are Humeral stress fractures typically are frequently unremarkable, with common injuries in the thoroughbred occur without any history of preceding MRI the modality of choice following racehorse as a result of the intense lameness. Whilst they can be noted localisation