Читать книгу Fractures in the Horse - Группа авторов - Страница 18

The Farm Vet published by an anonymous veterinarian in 1914 noted that ‘chloroform can be used to render animals insensible and relaxes muscles which oppose the necessary extension of limbs in order to get fractured bones in apposition’. Horses are noted as ‘the worst subjects for fractures and sheep the best. Horses must be able to work sound. Sheep and cattle need only to put on sufficient flesh to bring them to the block.’

In 1905, Wotley Axe [26] commented on the emergency care of equine fractures; ‘if an ambulance cart can be procured without much delay, it would be desirable to convey him at once where he may be required to go’ and that ‘it should be kept in mind that the success of treatment is greatly facilitated by the speedy readjustment of the broken bone’. Potential limitations of temperament were also recognized; ‘a horse's highest intelligence fails to realise the advantage of that perfect quiet upon which the surgeon sets so much store, in guarding against an extension of the injury and in bringing about its reparation. The moment the fracture is suspected every means should be adopted at once to restrain the animals movements and to provide as far as possible against any undue use or disturbance of the injured limb.’

Röentgen discovered X‐rays in 1895 and the potential of radiographic diagnosis in horses was first recognized as early as 1927 [27]. Radiographs produced on photographic films were first documented in equine fracture evaluation in 1950 [28]: until this time diagnosis was entirely clinical [20]. Radiographic diagnosis came to public attention in 1966 with the diagnosis of a distal phalangeal fracture in champion steeplechaser Arkle.

The 1962 publication of the eponymous ‘Lameness in Horses’ [29] signalled the arrival of the speciality. It also provided a series of radiographic images of equine fractures and recommended specific treatments including suitability for fragment removal. Although at this time the desirability for reconstruction was recognized, techniques and suitable equipment were not yet available. In 1963, Salter and Harris [30] described a classification of growth plate fractures in children. Its applicability to horses was soon recognized, and its adoption into veterinary orthopaedics was rapid and enduring.

Internal fixation of fractures was first reported by Lambotte in 1913 [cited in 31]. Techniques for active repair of fractures in horses appeared in the first half of the twentieth century, but progress was slow. Roberts [cited in 17] concluded that intramedullary pins were impractical in horses because of fragment rotation and implant bending. Problems associated with plates available at this time included bending at screw holes and shearing of screws. These issues were addressed by the combined mathematical, physical, engineering and medical collaboration in establishing the Arbeitsgemeinschaft fűr Osteosynthesfragen (AO) group in 1958. This was translated in the United States into the Association for the Study of Internal Fixation (ASIF). The terms are synonymous, interchangeable and sometimes used concurrently (AO/ASIF). Central to the early AO goals were accurate anatomic reconstruction, fracture compression, rigidity of fixation and preservation of blood supply [32]. This promoted primary bone healing, a concept first published in 1947 [33]. In 1968, an osteotomized third metacarpal bone was repaired in vivo with a human plate [22]. AOVET was founded in 1969, and in the following year a report documented the repair of diaphyseal fractures of third metatarsal bones in two ponies using primordial compression plates and cortical screws [34]. Initial progress was slow. In a well‐documented seven‐hour marathon surgery in 1972, a third metacarpal lateral condylar fracture was repaired in Derby winner Mill Reef. The owner was charged £25 000 [35] (which equated to approximately £330 000 in 2020). As interest increased, an exponential growth in the publication of papers on equine fractures followed (Figure 1.1). 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].