Bone sequestrum in a yearling red deer (Cervus elaphus) hind in New Zealand.

Abstract

Osseous sequestration is a common orthopaedic condition of horses and cattle (Firth 1987), and is frequently associated with trauma that results in cortical ischemia and bacterial invasion (Huber 2011). Although deer were introduced into New Zealand in the nineteenth century (Husheer et al. 2003), commercial deer farming itself only became legal in New Zealand in 1969 following the introduction of the New Zealand government’s Noxious Animals Amendment Act 1967 and the Deer Farming Regulations 1969 (Challies 1991). Interest in deer farming increased rapidly in the early 1970s (Pollard and Wilson 2002), with exports of venison, antler, and by-products now worth around NZD$240 million for the year ended September 2020 (B+LNZ 2021). Most of the deer farmed in New Zealand are Cervus elaphus, including the European red deer, North American wapiti, and their hybrids, with a smaller number of fallow deer (Dama dama) also farmed (Mason 1994). There have been a small number of reports of musculoskeletal problems in New Zealand deer including fractures (Wilson 1981; Audigé et al. 2001), osteochondrosis secondary to copper deficiency (Thompson et al. 1994; Audigé et al. 1995), angular limb deformities (Beatson et al. 2011), epiphysitis and osteomyelitis (Badger 1982), foot abscesses (Wilson 1981), polydactyly in red and sika deer (Daniel 1967; Davidson 1971) and outbreaks of lameness associated with Bacteroides nodosus (Skerman 1983) and Fusobacterium necrophorum (Ingram and Gill 2010). However, there have been no reports of bone sequestra in deer in New Zealand, and a literature search conducted using the search terms “deer AND sequestrum AND lameness” in Web of Science on 12 January 2022, found no further results from overseas. On 13 August 2021 a rising 1-year-old (R1) red deer hind weighing 86 kg with a body condition score (BCS) of 2.5/5 presented with severe lameness of the right rear leg. The hind was part of a group of 55 weaned R1 deer, grazing at pasture. Examination of the leg identified a soft, painful swelling on the medial aspect of the metatarsal bone, mid-way between the hock and fetlock. The swelling was not freely movable and seemed adherent to the underlying bone, no crepitus or mobility was noticed on palpation or manipulation of the metatarsus. Differential diagnoses included osteomyelitis with or without bone sequestration, incomplete fracture, and neoplasia although this was less likely due to the patient’s signalment. Radiographic imaging of the leg was sought to confirm the diagnosis. However, the SARS-CoV-2 lockdown response mandated by the New Zealand Government (https://www.health.govt.nz/) meant this had to be postponed until after restrictions were lifted. The deer was treated with 20 mg/kg S/C oxytetracycline (Bivatop 200 Injection, Boehringer Ingelheim (NZ) Ltd., Auckland, NZ). One month later, lockdown restrictions eased, and imaging could be conducted. Two views of the right metatarsus were obtained while the hind was standing and minimally restrained, including mediolateral and plantarodorsal views centred at the mid-diaphyseal region. In addition, there was now a discharging fistula present (Figure 1A). The firm swelling and pain response had increased markedly since first examination, consistent with the periosteal reaction. The results of the radiograph confirmed the presence of an osseous sequestrum, and osteomyelitis (Figure 1B) and arrangements were made to perform a sequestrectomy. The hind was treated again with 20 mg/kg S/C oxytetracycline and this was repeated 3 days later. One week after the radiograph was taken, the hind was sedated with 0.8 mg/kg 5% xylazine (Phoenix Xylazine 5% injection; Phoenix PharmDistributors Ltd.), Auckland, New Zealand) given by I/M injection into the neck. Once recumbent a tourniquet was placed just below the hock, and the leg clipped. The tourniquet remained in position throughout the surgery. Intravenous regional anaesthesia using 5 mL 2% lignocaine (Nopaine 2%, Phoenix Pharm Distributors Ltd.), diluted to 20 mL with sterile water, was injected under pressure into a superficial vein identified on the anterior lateral aspect of the metatarsus, using a 19-gauge butterfly needle. A total of 15 mL of diluted lignocaine was injected. The site was surgically scrubbed and prepared whilst the I/V regional anaesthesia took effect. An elliptical skin incision was made longitudinally around the fistula using a number 15 scalpel blade. Blunt dissection was then used to extend the incision to the periosteum, using the fibrous tissue surrounding the fistula as a guide to locate the sequestrum. The skin edges were retracted using a small Gelpi retractor. A mallet and 6-mm osteotome were then used to remove sufficient periosteal new bone from the cloaca (the cavity in the bone surrounding the sequestrum) to allow removal of the sequestrum using haemostats (Figure 1C). The bone sequestrum measured 30.0 mm × 11.2 mm× 4.9 mm (Figure 1D). The operation site was then flushed with sterile normal saline (Baxter Sodium Chloride for Irrigation; Baxter Healthcare Ltd, Auckland, NZ) and the edges of the wound loosely opposed using Glycolide & eCaprolactone (SilverGlide Pty Ltd, Castle Hill, NSW, Australia) gauge 1–0 suture material. A Robert Jones pressure bandage was then placed over the surgery site, encompassing the whole lower limb, including the foot, and removed 4 days later. At completion of