An inter- and intra-rater agreement assessment of a novel classification of pyogenic spinal infections

Purpose Pola et al. described a clinical-radiological classification of pyogenic spinal infections (PSI) based on magnetic resonance imaging (MRI) features including vertebral destruction, soft tissue involvement, and epidural abscess, along with the neurological status. We performed an inter- and intra-observer agreement evaluation of this classification. Methods Complete MRI studies of 80 patients with PSI were selected and classified using the scheme described by Pola et al. by seven evaluators. After a four-week interval, all cases were presented to the same assessors in a random sequence for repeat assessment. We used the weighted kappa statistics (w kappa) to establish the inter- and intra-observer agreement. Results The inter-observer agreement was substantial considering the main categories (w kappa = 0.77; 0.71-0.82), but moderate considering the subtypes (w kappa = 0.51; 0.45-0.58). The intra-observer agreement was substantial considering the main types (w kappa = 0.65; 0.59-0.71), and moderate considering the subtypes (w kappa = 0.58; 0.54-0.63). Conclusion The agreement at the main type level indicates that this classification allows adequate communication and may be used in clinical practice; at the subtypes level, the agreement is only moderate.