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EQUINE VETERINARY EDUCATION / AE / JANUARY 2017


the animal’s attempts to free the limb. The wound was bandaged by the owner and a veterinary examination was performed on the following day. At initial examination, the affected limb was completely covered with skin; however, the skin on the dorsal aspect of the right metatarsus was discoloured and indurated. The distal limb was subjectively hypothermic to the touch so colour-flow Doppler ultrasonography of the plantar digital arteries was performed and no blood flow was documented. No lameness was present so conservative treatment was elected including daily bandaging, antimicrobial (trimethoprim sulfamethoxazole 30 mg/kg bwt per os q. 12 h) and anti-inflammatory administration (flunixin meglumine 1.1 mg/kg bwt per os q. 12 h). At recheck evaluation 5 days post injury no lameness or hindlimb cellulitis was noted. Necrotic tissue apparent on the margins of the wound was sharply debrided. Colour-flow Doppler ultrasonography was again performed on the affected limb and plantar digital arterial flow was documented. The treatment plan was continued until 7 days after initial injury when the mare became lame and the wound became exudative. She was then referred to our hospital for evaluation of distal limb vasculature and further treatment of her wound. Upon presentation to the Cornell University Equine Hospital,


the bandage was removed from the right hindlimb and the wound was observed. The wound was 15 cm in length and circumferential with complete granulation tissue coverage over the flexor tendons. The long digital extensor tendon was completely severed resulting in an inability of the metatarsophalangeal joint to extend. The wound margins were necrotic with regions of exposed third metatarsal bone. The wound was aseptically prepared and explored with a sterile probe, which indicated that the digital tendon sheath and metatarsophalangeal joint were not involved. Aerobic and anaerobic bacterial culture successfully identified isolates from 3 different bacterial species. Four standard view radiographs were taken and no osseous abnormalities were noted. The pastern and coronary band regions were cold to the touch. A 16 gauge needle was used to create 4 punctures through the dermis at the medial and lateral plantar aspect of the pastern and heel bulb region resulting in a delayed exudation of dark purple blood. A 16 gauge 15 cm catheter was placed in the left jugular vein and the mare was transitioned to intravenous antibiotics (potassium penicillin 22,000 iu/kg bwt q. 6 h and gentamicin 6.6 mg/kg bwt q. 24 h) and anti-inflammatories (flunixin meglumine 1.1 mg/kg bwt per os q. 12 h). A chemistry panel and complete blood count were unremarkable and a bandage with a plantar splint was applied to prevent hyperflexion of the metatarsophalangeal joint.


One day following presentation, an additional 16 gauge


15 cm catheter was placed in the right jugular vein and the mare was induced under general anaesthesia. Nonselective CTA of both distal hindlimbs was performed (see imaging section for technical details). Lateral and medial plantar and plantar digital arteries could be visualised in the right hindlimb, although they were diffusely smaller and less opaque than the arteries in the contralateral limb. Contrast enhancement could not be identified at a 3 cm section beginning at the lateral aspect of the mid first phalanx extending to the lateral aspect of the mid second phalanx. Arterial contrast enhancement was present distal to the anastomosing medial and lateral arteries of the second phalanx and the presence of contrast in


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the small laminar vessels was similar bilaterally (Fig 1). Subcutaneous gas was noted in the soft tissues surrounding the metatarsus and metatarsophalangeal joint; however, gas attenuation could not be detected within the synovial compartments. Complete vascular perfusion was achieved with no abnormalities detected in the left hindlimb. After distal limb vascular viability was confirmed, the mule


was immediately taken to the operating theatre where surgical debridement of the wound was performed. Post operative wound management included 18 days of vacuum assisted closure at 125 mmHg continuous suction with dressing changes every 72 h. A plantar splint was maintained to


a)


b) MtIII 1 4


5 6 23


c) P1 f) P1


e) MtIII


d) P2


g) P2


Fig 1: Computed tomography scans of the normal left-pelvic limb (a–d) and the injured right-pelvic limb (e–g) following injection of i.v. contrast material in a 3-year-old miniature mule mare: a) surface rendered 3-dimensional volume reconstruction using a bone display, plantar view; b–g) transverse reconstructions at the level of the third metatarsal bone (MtIII), proximal phalanx (P1) and middle phalanx (P2), using a soft-tissue display and same degree of zoom – dorsal is at the top, and medial is to the right (b–d) or left (e–f). In the normal limb (first 2 columns), there is excellent opacification of blood vessels throughout the entire limb: (1) distal perforating branch of the third dorsal metatarsal artery; (2) lateral terminal branch of 1; (3) medial terminal branch of 1; (4) superficial branch of second common plantar digital vein; (5) lateral plantar digital vein; and (6) medial plantar digital vein. Note that contrast material (white arrows) is visible both medially and laterally. In the injured limb (third column), the limb is diffusely swollen, contains subcutaneous gas (arrow heads), and has variable vascular opacification (white arrows). Excellent opacification is seen medially; good-to-absent, laterally. Proximal (e) and distal (g) to the laceration, contrast material is seen both medially and laterally; at the level of the laceration (f) contrast material is seen only medially. In the distal limb (g), restitution of blood flow laterally was attributed to collateral circulation, distal to the laceration, through the terminal arch, formed by the anastomosis of the medial and lateral plantar digital arteries.


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