EQUINE VETERINARY EDUCATION / AE / JANUARY 2017


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prevent metatarsophalangeal joint hyperflexion. The mule remained on i.v. antibiotics for 18 days. Gentamicin was transitioned to enrofloxacin (5.0 mg/kg bwt i.v. q. 24 h) 5 days after treatment initiation due to rising creatinine levels. On Day 19, she was transitioned to oral enrofloxacin (7.5 mg/kg bwt per os q. 24 h) and oral flunixin meglumine (1.1 mg/kg bwt per os q. 24 h). Additionally, the case was maintained on omeprazole (20 mg/kg bwt per os q. 24 h) and pregabalin (2.2 mg/kg bwt per os q. 8 h) for the duration of her hospitalisation and for 14 additional days after discharge. After 21 days of hospitalisation, she was discharged with instructions for intensive wound management. The wound continued to granulate in until a healthy granulation bed was achieved 14 weeks after initial injury. At this time, pinch skin grafting was performed and 90% graft viability was achieved. The wound was fully epithelialised 4 weeks later. The mare is fully functional with an acceptable cosmetic appearance 18 months post injury.


Case 2 A 7-month-old 245 kg Standardbred colt was referred for evaluation of a severe right mid-diaphyseal metatarsal laceration 6 days after initial injury. The limb had become entangled in a metal wire electric fence. Attempts at releasing the entrapped limb resulted in the subsequent laceration. At the time of initial injury, the colt was nonweightbearing lame. The third-metatarsal bone was exposed, however, involvement of synovial structures, flexor tendons, the suspensory ligament or plantar vasculature was not suspected following examination. Primary closure was attempted using a series of stented vertical mattress sutures. Bandaging was performed without distal limb splinting which resulted in periodic hyperflexion of the metatarsophalangeal joint. Antibiotic (procaine penicillin G 22,000 iu/kg bwt i.m. q. 12 h and gentamicin 6.6 mg/kg bwt i.v. q. 24 h) and anti- inflammatory (phenylbutazone 2.2 mg/kg bwt per os q. 12 h) treatment was initiated. The repair failed, lameness persisted and the colt developed intermittent pyrexia (39°C) so the antibiotic therapy was transitioned to chloramphenicol (45 mg/kg bwt per os q. 8 h) 4 days after injury. Five days after initial injury, it was noted that the distal limb was severely hypothermic. The colt was referred to our hospital for determination of distal limb vascular viability and potential wound management. Upon presentation to the Cornell University Equine Hospital,


the bandage was removed from the right hind distal limb. Digital examination of the wound revealed a circumferential laceration on the dorsal aspect of the right mid-diaphyseal metatarsus sparing the most plantar aspect. The flexor tendons, suspensory ligament, axial aspect of metatarsal bones 2 and 4, and plantar vasculature did not appear to be affected. The wound edges were necrotic and the repair was dehiscing. Severe diffuse cellulitis was present extending from the coronary band to the femoropatellar joint. The skin distal to the metatarsophalangeal joint was diffusely hypothermic on palpation. A 16 gauge needle was used to create 4 punctures through the dermis at the plantar aspect of the medial and lateral pastern and heel bulb resulting in a delayed exudation of dark purple blood. A full limb compression bandage with a dorsal splint was applied. The previously prescribed medical therapy was continued. On the day following presentation, 16 gauge 15 cm catheters were placed in both jugular veins, the colt was


a)


b) P2


c)


d) P2


Fig 2: Computed tomography scans of the normal left-pelvic limb (a, b) and the injured right-pelvic limb (c, d) following injection of intravenous contrast material in a 7-month-old Standardbred colt: a, c) surface rendered 3-dimensional volume reconstruction using a bone display, plantar view; b, d) transverse reconstructions at the level of the middle phalanx (P2) using a soft-tissue display, dorsal is at the top. In the normal limb, there is fair-to-good vascular opacification throughout the entire limb (black arrows, black circles). In the injured limb, the digit is diffusely swollen, covered with bandage material, and contains subcutaneous and deep gas (white arrows): note that contrast enhancement is not detected bilaterally, indicating that avascular necrosis is possible.


induced under general anaesthesia, and nonselective CTA of both distal hindlimbs was performed (see imaging section for technical details). In the right hindlimb, contrast enhancement of the medial and lateral plantar arteries was absent just proximal to the level of the laceration. Computed tomographic evaluation of the limb revealed invasion of gas into facial planes and joint spaces. No laminar arterial contrast enhancement was present and gas attenuation was noted within the plantar digital arteries and between the sensitive and insensitive laminar corium (Fig 2). Complete vascular perfusion was achieved with no abnormalities detected in the left hindlimb. The colt was humanely subjected to euthanasia while under general anaesthesia due to a presumptive clinical diagnosis of vascular necrosis of the right distal limb based on the clinical and CTA findings (Fig 2). A post mortem examination was performed, which confirmed the clinical diagnosis of avascular necrosis and loss of laminar integrity, resulting in the separation of the laminar corium (Fig 3).


Histology


After euthanasia of Case 2, samples of the dermis and associated subcutaneous tissues were collected from the medial and lateral aspect of the right hindlimb both proximal and distal to the laceration. Matched histology samples were taken from the left hindlimb acting as a control. Proximal to the laceration in the medial and lateral sections of skin and subcutaneous tissues, there was expansion of the panniculus by oedema and fibroplasia interspersed with bands of neovascularisation. The oedema and fibroplasia were characterised by haphazardly arranged fibroblasts separated by abundant loose, fibrillar, pale eosinophilic, extracellular matrix material. The neovascularisation was characterised by


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