Introduction

The avian skeleton is light but strong. Fractures frequently result if a bird sustains trauma. However, bone healing is rapid and most cases heal well if appropriately supported.

CASE PRESENTING SIGNS

A 6-month-old Socorro dove (Zenaida graysoni) presented with suspected tibiotarsal fracture.

Husbandry

The dove was part of a breeding colony held in a zoological collection as part of an international ex situ conservation project (Box 12.1). It was housed individually in an indoor aviary at the time of the incident. The aviary was approximately 2 × 2 × 3 m, and comprised solid walls with a wire mesh front. Several natural branches were present for enrichment and perching. The diet provided was a proprietary pigeon seed mix supplemented with chopped fruit and greens.

BOX 12.1 Ecology of Socorro doves

• Socorro doves originate from the island of Socorro in the Revillagigedo Islands, Mexico. Previously they were common in forest areas higher than 500 m above sea level.

• Socorro doves are frugivores, with free-ranging birds depending on ferns and euphorbias.

• The bird is highly terrestrial, and they have been extirpated by feral cats. Other factors such as human predation and grazing of the bird’s food sources by sheep may have also contributed to their decline. The IUCN now describes Socorro doves as Extinct in the Wild.

• The species are predominantly solitary, with pairs forming for breeding. Young are chased away as soon as they can fend for themselves, and the male and female separate outside the breeding season.

• Ex situ breeding programmes are expected to provide stock for reintroduction after cats and sheep have been eradicated from the island.

Case History

The bird was noted to be 10/10ths lame on its left leg late one evening. A brief conscious examination revealed a palpable fracture in the tibiotarsus. Analgesia was provided using meloxicam (0.1 mg/kg PO). No other signs of illness were noted.

Clinical Examination

Reassessment of the bird the following day was performed:

• Body weight 98 g, good body condition (keel palpable but good pectoral muscle coverage)

• Plumage in good condition

• Oral examination, palpation of abdominal region, auscultation of air sacs – no abnormalities detected

• Orthopaedic examination:

• Nails appropriate length, no foot lesions

• Left leg: non-weight bearing, bruising evident mid-tibiotarsus, skin intact, tibiotarsus unstable (suspected fracture site), deep pain present

• No abnormalities on right leg or either wing.

DIFFERENTIAL DIAGNOSES

Although it may not be possible to easily differentiate lameness from ataxia in a small bird, the differential diagnoses lists (for avian species) are slightly different.

The differentials for lameness are:

• Trauma resulting in fracture, dislocation, or soft tissue injury

• Note that systemic illness (e.g. hypocalcaemia, central nervous system lesions) may result in weakness, ataxia or seizures and predispose to injuries after falling

• Metabolic bone disease (MBD) or neoplasia will also result in bone weakness and predispose to pathological fractures

• Overgrown claws

• Infection, e.g. bumblefoot, septic arthritis

• Arthritis, e.g. older bird, after traumatic injury

• Neoplasia (particularly budgerigars): renal (e.g. adenocarcinomas, embryonal nephromas), gonadal (e.g. ovarian or testicular tumours) or adrenal. Neoplasms act as a space-occupying lesion, pressing on the sciatic or pudendal nerves that run between these organs and the bony synsacrum

• Other causes of organomegaly (commonly renomegaly) pressing on sciatic nerve intra-coelomically

• Intra-articular gout

• Bruising in the pelvic regions after or during egg laying (females)

• Spinal pathology.

The differentials for ataxia are:

• Infectious diseases:

• Viruses, e.g. paramyxoviruses (there are at least nine known serotypes), polyomavirus, central lesions with proventricular dilatation disease (PDD, mostly affecting psittacines), togaviruses (e.g. West Nile virus), influenza A, reovirus

• Bacteria, e.g. Chlamydophila psittaci (especially chronic infections), granulomas or abscesses (with Listeria monocytogenes and Mycobacterium spp), septic arthritis (e.g. at joints between notarium and synsacrum, with abscess compressing spinal cord), encephalitis (with Staphylococcus aureus, Enterococcus spp, Pasteurella spp, Klebsiella spp)

• Fungi, e.g. aspergillosis (due to secondary cerebral infarction or toxin-induced peripheral neuropathies), mycotoxins in food

• Parasites, e.g. CNS infection with Filaroides spp and Sarcocystis spp, cerebrospinal Baylisascaris procyonis (in North America)

• Toxicity: heavy metal toxicity

• Metabolic disease: hypocalcaemia, hepatic encephalopathy, renal disease, hypoglycaemia

• Malnutrition, e.g. hypovitaminosis E/selenium, hypovitaminosis B2 (riboflavin deficiency), hypovitaminosis B1 (uncommon)

• Trauma (as above)

• Neoplasia, e.g. peripheral neuropathy (including aetiologies outlined above, and also schwannomas and malignant schwannomas), central nervous system pathology (e.g. astrocytomas, oligodendrogliomas, teratomas, lymphosarcomas and meningiomas)

• Congenital defects (uncommon).

Case Work-Up

The dove was anaesthetized with isoflurane (see box on page 91).

Radiographs

Lateral and ventro-dorsal views of the body (Fig. 12.1) were taken to assess for any concomitant illness – no evidence was seen. Further views with the X-ray beam collimated on the left leg confirmed the presence of a mid-shaft transverse fracture of the left tibiotarsus (Fig. 12.2).