Difficulties in distinguishing between an atlas fracture and a congenital posterior atlas arch defect in postmortem analysis

•Approximately 1% of atlas present different anatomical variations.•Atlas fractures can be mistaken for posterior arch defects in post-mortem studies.•Arch defects, fractures and post-mortem osseous loss can be found in the same atlas.•Differentiate dry atlas arch defects from fractures is more difficult than expected.

We found one atlas from a sample of 148 skeletons (0.67%) that presented different anatomical variations which made it difficult to determine whether the vertebra had an atlas fracture, an unusual Type B posterior atlas arch defect, or a combination of both. We carried out a stereomicroscopy, radiographic, and computerized tomography scan study that revealed that the dry atlas we found presented a very uncommon congenital Type B posterior atlas arch defect, simulating a fracture. In short, the present paper has revealed that differentiating Type B posterior atlas arch defects from fractures in post-mortem dry vertebrae is more difficult than expected. Thus we believe that it can be easier than expected to mistake Type B posterior arch defects for fractures and vice versa in postmortem studies.