Fractures in the Horse. Группа авторов
The first Manual of Internal Fixation in the Horse was published in 1982 [36]. Development of an equine fracture documentation system was attempted [37], but the discipline progressed too quickly for this to be viable. In 1996, Alan Nixon edited the multi‐author ‘Equine Fracture Repair’ [38], which provided an excellent state of knowledge summary for the time. A second edition was planned 10 years later but did not reach fruition until 2020 [39]. In the interim, ‘AO Principles of Equine Osteosynthesis’ was published in 2000 [40]. The rapid relief of pain that follows a stable fracture repair is remarkable and, in addition to preventing secondary, and often life‐limiting clinical problems such as overload laminitis, has made a major contribution to animal welfare. On a personal basis, this remains one of the greatest motivating forces.
Implants used in equine fracture repair have also evolved; while cortical bone screws have been a consistent mainstay throughout, plate design has increased in sophistication. The originally used dynamic compression plate (DCP) [41] remains in use. Although not identified in horses, stress protection and remodelling osteoporosis were associated with DCP application in man and this led to development of first the limited contact dynamic compression plate (LC‐DCP) and subsequently the locking compression plate (LCP) [42].
Figure 1.1 Number of papers on equine fractures published in the veterinary literature between 1945 and 2016.
Source: Data from PubMed (https://www.ncbi.nlh.gov/pubmed/).
Safe and effective adaptation of AO/ASIF techniques relied on developments in anaesthesia, operating theatre and table design, asepsis, evolution of suture material, medication, cast materials and imaging. Fracture repair under general anaesthesia is almost always optimal. Justification for standing techniques was based on historic mortality risk data [43]. Development of anaesthesia training programmes, improvements in pharmacology and centralized hospital experience have subsequently resulted in significantly reduced risk [44].
Understanding the importance of soft tissues in successful fracture management has been an important although less well‐documented concept [45–47]. Refinements have occurred and prognoses improved by the use of minimally invasive surgical techniques, principally arthroscopy first in removing articular fracture fragments [48] and more recently in guiding reduction and repair [49, 50]. Minimally invasive plate application has also been adopted into clinical practice [51]. Accurate three‐dimensional imaging and the repeatability/predictability of work/fatigue fractures have also permitted percutaneous repair with consequent preservation of soft tissue.
Use of resin‐bonded fibreglass to create casts for horse limbs was reported in 1963 [52], and use of fibreglass to reinforce plaster of Paris casts was first documented in 1966 in treating people [53]. Equine use of an experimental tape was reported in 1971 [54], and its material advantages were documented in 1973 [55]. Subsequent commercial development of fibreglass casting materials suitable for use in horses [56–59] enhanced acute support before surgery and recovery from general anaesthesia. It has also permitted more protracted immobilization of fractures that are not amenable to reconstruction or to augment or protect constructs. Severely comminuted and/or complex fractures can also be managed with transfixation casts used alone or in conjunction with selective internal fixation [60, 61]. These techniques have now replaced external fixation devices for distal limb fractures [42, 62].
Distal limb amputations with replacement prostheses have been documented [63], but complication rates are high, longevity is usually limited and the ethics are questionable. Other prosthetic techniques have also not made a significant impact in equine orthopaedics [64]. Nonetheless, veterinarians have always been capable of lateral thought and have been prepared to try alternative approaches. Plato's adage that ‘necessity is the mother of invention’ is readily applicable to equine fracture management. Examples include standing fracture repair, long‐term suspension of horses [65, 66] and relief of load on fractured bones or limb segments [61, 62,67–71]. Attempts to hasten bone healing (Chapter 6) have largely been unfruitful.
Nuclear medicine (scintigraphy) was adopted into equine orthopaedics in the 1980s [72]. Determination of increased metabolic activity in bone allowed identification of suspected fractures in areas of limited imaging capability or in some cases in advance of identifiable (usually radiographic) morphologic changes [73].
After nearly a century of interpreting radiographic information on photographic film, digital imaging became the norm and with it substantially more information on bone structure and fracture identification. However, radiographs are two‐dimensional assessments of a three‐dimensional object with superimposition of other structures. They are therefore limited in assessing the geometry of fractures that are not simple and uniplanar. Introduction of computed tomography (CT) in the last decade provided three‐dimensional radiographic information and has been a great step forward resulting in the re‐classification of many fractures from incomplete to complete, uniplanar to spiral and simple to comminuted. Confident identification of fractures has not only directed optimal management but has also permitted minimally invasive repair.
Ex vivo (post‐mortem) use of CT and magnetic resonance imaging (MRI) to evaluate equine fractures was reported in 1995 [74]. Both produce sectional multiplanar images, but these are based on different information sources. CT relies on tissue attenuation of X‐rays; MRI principally maps the presence of hydrogen atoms (particularly in water and fat), and structural information of the skeleton is inferred from this [75]. CT identification of a two‐dimensional radiographically occult fracture was reported in 1999 [76], and in 2001 Tucker and Sande [77] identified the potential for CT to better delineate fracture orientation and assist in surgical planning in horses. Subsequent development and adoption of mobile in‐theatre units made this a reality, and CT is currently considered the gold standard in assessing and directing repair of equine fractures. In vivo diagnostic use of MRI for the evaluation of equine fractures started to appear in 2010 [78] with subsequent contributions to understanding pathogenesis [79], surgical planning [80] and risk assessment [81].
Inherent surgical limitations are now recognized in veterinary medicine [82]. Those who regularly deal with equine fracture repair understand the importance of team work, attention to detail, communication and planning. The ideas crystallized in the publications of Atul Gawande [83–85] are as relevant to equine surgeons as their human counterparts. An international World Health Organisation (WHO) study demonstrated that adoption of a surgical checklist reduced human post‐operative morbidity and mortality by 36% and 48%, respectively [86]. Multiple subsequent studies have upheld these findings in man, and similar results have been reported in veterinary anaesthesia [87] and small animal surgery [88, 89].
The Future
Ethereal debate centred on the question of ‘what is a fracture?’ is anticipated. The dictionary definition of ‘being broken, of a crack, division or split’ [90] is clear, but at what level? Division of a bone into two or more pieces is indisputable and all would agree that incomplete fissures in cortical or subchondral compacta are fractures. But should disrupted trabeculae in spongiosa be similarly classified? Do some enostoses represent fractures in trabecular bone [91]? Are the recently adopted terms of ‘bone failure’, ‘bone bruising’ and ‘fatigue failure’ manifestations of fractures at a microscopic level?
If the veterinary profession wishes to retain its role as guardians of animal welfare, then future endeavours will need to include measures targeting prevention or reduction of fracture incidence in horse sports, particularly racing. Elements of society have and will continue to question whether use of horses for competitive sport is ethical and, rather more directly, whether ‘horseracing is too dangerous?’ [92]. In some countries, animals are also gradually moving from the legal status of chattel to sentient beings: with that will come rights