EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2017


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a)


b)


Dorsal fetlocks


Fig 1: Vascular phase scintigraphy of a horse with traumatic disruption of the suspensory apparatus showing vascular disruption in the left forelimb (appears to the right of a, and in lateral view in b) due to vessel trauma during fetlock hyperextension during injury. Note normal perfusion on right distal limb in comparison (to the left in a).


require general anaesthesia to perform. Scintigraphic evaluation, which can be easily performed under sedation without general anaesthesia and readily evaluates vascular integrity (vascular phase), can be very useful in these cases. The authors of this commentary have effectively and reliably used this modality as a determinant of vascular integrity in clinical cases (see Fig 1). As the authors of the case series state, these diagnostics are not likely to be applicable in the majority of limb injury cases; however, in cases where there is a query over vascular integrity in the period between injury and before hoof wall loss (approximately 10 days post injury based on this case series) then scintigraphy can be a very useful modality that can greatly influence clinical decision making.


Treatment of ALI in man is quite effective but when


delayed longer than 6–12 h can result in permanent disability, amputation and/or death. Treatments are generally aimed at restoring blood supply to the ischaemic segment using either surgical interventions (vascular grafts, thrombectomy) or pharmaceutically (tissue plasminogen activator or anti-clot medications, such as Plavix). One author (B.A.) has successfully used tissue plasminogen activator to re-establish vessel patency in a unilaterally affected plantar metatarsal artery. The key factor with all treatment options is that they are most effective when applied early in the process of ALI; however, intervening during this timeframe is an extremely difficult, if not impossible, task in most cases of equine ALI and we are often left with treating substantially later or simply evaluating if there is any vascular perfusion left at all. In man,


the diagnosis of ALI is based on paralysis (inability to wiggle fingers or toes) and anaesthesia (loss of light touch) but aside from these symptoms, signs of acute ischaemia are nonspecific or are inconsistent. In horses, it is not possible to determine paralysis in distal limb injury due to the absence of muscle. Similarly, in horses with traumatic wounds, the


determination of subtle regional anaesthesia to the degree that is possible in man is not realistic. As such, in cases of traumatic injury such as these three reported cases or cases of TDSA especially in racehorses (which are a similar type of hyperextension [quasi luxation] of the fetlock joint as occurs in human knee luxations) there is likely to be trauma to the vascular wall of the arterial supply to the distal limb. To cause ALI similar to that in man, all the vessels supplying the distal limb of the horse would appear to have to be affected as unilateral vascular transection that is relatively common does not result in spontaneous hoof wall loss. It is interesting to note that in this series of 3, 2 had trauma at the level of the pastern or ‘lower limb’ and one was an almost circumferential injury of the distal metatarsus (Ruzickova et al. 2017). At these levels, the important vascular supply to the distal limb is relatively exposed to trauma and this may be an important factor for equine veterinarians to consider when evaluating lacerations of the distal limb in horses as a potential risk factor for spontaneous hoof wall loss. The cellulitis/lymphangitis that was seen in this case series may have simply represented a clinical progression/consequence of ALI in these cases, rather than a contributing factor to the hoof wall loss. This is supported by the numerous cases of severe cellulitis that occur in routine equine practice that do not result in hoof wall loss. This case series highlights the infrequent but major


complication of spontaneous hoof wall loss that can occur secondarily to lower limb trauma in horses. Veterinarians should pay close attention to assessment of vascular integrity and consider early treatment if the timeframe of injury to presentation allows. Alternatively, in cases where assessment of vascular integrity is the objective (early treatment window passed) consider the use of scintigraphy/contrast arteriography to determine vessel patency to allow for accurate treatment decisions and case prognostication.


© 2016 EVJ Ltd


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