Koala Kyphoscoliosis: Radiographic and CT Features of Abnormal Vertebral Column Curvature in Koalas (Phascolarctos cinereus) of the Mount Lofty Ranges, South Australia.

Abnormal vertebral column curvature is sporadically reported in koalas of the Mount Lofty Ranges, South Australia. This study evaluates the imaging features of 23 koalas from the Mount Lofty Ranges presenting with abnormal vertebral column curvature between 2015 and 2023 using digital radiography and computed tomography (CT). All images were evaluated by four reviewers to assess curve morphology, severity and Cobb angles for both scoliosis and kyphosis. For Cobb angle measurement, radiography performed similarly to CT with good agreement as measured by intraclass correlation coefficient (0.835 and 0.825 respectively) and Lin's concordance correlation coefficient (>0.85). The apex vertebra was always located between T7 and L6. For both scoliosis and kyphosis apex vertebrae, the thoracolumbar region was the most common location (8/22 and 9/19, respectively). For scoliosis, the caudal thoracic and lumbar regions were equally common (7/22 each), whereas for kyphosis, the caudal thoracic region (7/19) was more frequent than the lumbar region (3/19). Vertebral body rotation was a common component particularly in severely affected individuals, in which complex or 'S' shaped curves also occurred. Severity ranged from minimal or mild (6/23) to moderate (5/23) and severe (12/23), with simultaneous kyphosis and scoliosis present most frequently (21/23). As a result, the term, kyphoscoliosis is the most appropriate morphological description for abnormal vertebral curvature in koalas and may have pathophysiologic commonalities with human idiopathic scoliosis. This study is the first to describe imaging features of abnormal vertebral column curvature in koalas and evaluate inter-modality and interobserver agreement between radiography and CT.