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EQUINE VETERINARY EDUCATION / AE / JANUARY 2017
1991; Belknap et al. 1993; Wilmink et al. 2002; Mespoulhes- Riviere et al. 2008; Elliot et al. 2012). Several detrimental sequelae to this type of injury exist including a disruption in vasculature, flexor or extensor tendon dysfunction, wound and synovial structure sepsis, fracture, sequestration, exuberant granulation tissue, and scarring (Foland et al. 1991; Belknap et al. 1993; Mespoulhes-Riviere et al. 2008). Decreased or absent post traumatic perfusion to the distal limb is the main clinical finding leading to euthanasia after metatarsal extensor tendon injuries (Elliot et al. 2012). Thus, the assessment of the distal limb vasculature is of primary importance in cases with severe distal limb lacerations. The arterial supply to the distal limb is thought to be
Fig 3: Parasagittal sections of the distal pastern and hoof of Case 2: a) normal left hindlimb, b) affected right hindlimb hoof. In the affected hoof, there is complete separation of the coronary and laminar dermis from the hoof wall secondary to ischaemic dermal necrosis. The connective tissues are diffusely expanded by oedema and there is imbibition of haemoglobin causing red discolouration of the tissues.
horizontally oriented bands of small calibre, often empty, dilated, blood vessels lined by hypertrophic endothelial cells. There were small numbers of perivascular lymphocytes and plasma cells within the dermis and areas of fibrosis. Distal to the laceration in the medial and lateral sections of skin and subcutaneous tissues, there was full thickness coagulative necrosis of the epidermis, dermis and panniculus characterised by loss of cellular detail, cytoplasmic hypereosinophilia and faded or pyknotic nuclei. Large calibre blood vessels had fibrinoid necrosis of the vascular wall and often contained fibrin thrombi. There was also secondary necrosuppurative dermatitis and cellulitis characterised by multifocal areas of eosinophilic cellular and karyorrhectic debris, fibrin, degenerate neutrophils and myriad colonies of cocci bacteria. No significant findings were noted in the left hindlimb. The histological results confirmed the CT findings of ischaemic necrosis to the distal right hindlimb (Fig 4).
Discussion
Lacerations in the mid-diaphyseal region of the cannon bone are commonly encountered in equine practice (Foland et al.
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consistent amongst the species of the Equidae family (Bordalai and Nigam 1977) and primarily courses down the palmar/plantar aspect of the metacarpus/metatarsus distally, therefore, lacerations to the dorsal aspect of the metacarpus/metatarsus do not typically result in vascular disruption to the distal limb. In contrast, the dorsal third metatarsal artery is a primary parent vessel to the hindlimb digital arterial plexus and courses from dorsal to plantar at the proximal third of the metatarsus (Ghoshal 1975). As a result, dorsoproximal metatarsal lacerations can cause a significant vascular disruption to the distal hindlimb. Fortunately, the presence of robust collateral vasculature in the equine digit often permits complete coronary plexus perfusion when at least one vessel is patent, as demonstrated in Case 1. Other documented aetiologies of arterial thrombosis to the extremities resulting in avascular necrosis in horses include septicaemia (Forrest et al. 1999; Brianceau and Divers 2001), atrial septal defects (Spier 1985), and the application of a tourniquet and intra-arterial injection of stem cells (Sole et al. 2012). Clinical signs of avascular necrosis can be delayed for many days after the initial time of insult (Bell et al. 1995; Mespoulhes-Riviere et al. 2008) and any attempts to repair distal limb injuries are thought to be futile if the distal limb arterial vasculature is interrupted for a prolonged period of time (White 1983). Thus, the need for an accurate assessment of distal limb perfusion is imperative. Several diagnostic methods to assess the distal limb
vasculature of equids have been described. Most studies have been designed to determine the effect of laminitis on distal limb vasculature leaving a paucity of information regarding post traumatic assessment of distal limb vasculature. The most common modalities include radiographic arteriography (Ackerman et al. 1975; Bordalai and Nigam 1977; Rosenstein et al. 2000), nuclear scintigraphy (Galey et al. 1990; Trout et al. 1990; Bell et al. 1995; Ritmeester et al. 1998), Doppler ultrasonography (Adair III et al. 2000; Aguirre et al. 2013), and CTA (Collins et al. 2004). Contrast magnetic resonance imaging has also been used in order to determine distal extremity vascularity in man (Connell et al. 2002); however, to our knowledge this has yet to be described in large mammals. The use of radiographic angiography after catheterisation
of the palmar arteries has been used to describe the normal arterial anatomy of the distal limb (Rosenstein et al. 2000) as well as the vascular alterations seen in chronic laminitis (Ackerman et al. 1975). Radiographic angiography can be effective after traumatic injury; however, interpretation can be difficult due to the limited 2-dimensional nature of the diagnostic modality. Furthermore, distal limb arterial catheterisation can be technically challenging especially in the face of cellulitis and has been attributed to arterial
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