Morphometric analysis of saw marks on human bones throug micro-CT

Introduction: The analysis of saw mark characteristics on bones can provide useful information about the type of saw used to produce the injury/mark. This study aims at testing micro-computed tomography (micro-CT) analysis of false start saw marks produced on human bones by different types of saws in order to correlate the metrical characteristics of the saw with those of the mark. Material and Methods: This study was performed on 40 human defleshed metacarpal, metatarsal and phalanx bones, collected from individuals who donated their body to the University of Padua for research purposes. The saw marks examined in this study were generated using 5 new saws, including: 3 saws with alternating set and different teeth per inch (TPI; 5, 8 and 10, respectively) and 2 saws with wavy set and different TPI (18 and 24, respectively). All marks were inflicted manually by the same operator, holding the saw perpendicularly to the long axis of the bone, applying a single unidirectional stroke with an excursion of 15 cm in length, in order to simulate a false start. Each bone sample was scanned by a Skyscan 1172 HR micro-CT (Skyscan, Aartselaar, Belgium) with the following parameters: 14 μm isotropic voxel size, 51 Kv, 194 uA, exposition time 6050 ms, rotation step 0.7, frame averaging 2, 1280 x 1024 pixel Field of View. Reconstructions were performed by N-Recon Software (Skyscan, Aartslaar Belgium), subsequently, the bitmap files were converted in DICOM using the DICOM Converter® Software. Osirix (Open Source Software, Version 7.0.1) was used to perform all the measurements and elaborate the multiplanar (MPR) and 3D volumetric reconstructions. For each bone sample, on the MPR images, the following features were assessed: number of isolated marks on each bone, shape of the mark on the sagittal plane (rectangular or triangular), maximal depth and height measured on the sagittal plane and presence of metal residues. Results: All saw marks were detected by micro-CT. Marks produced by saws with 5, 8 and 10 TPI showed two incisions with different shapes and dimensions, which were in some cases in continuity one with the other. Saw marks produced by saws with 18 and 24 TPI showed a single mark with rectangular shape and different dimensions. Metallic residues were observed in several cases. Conclusions: The preliminary results of the study suggest that micro-CT could be a useful tool for the analysis of saw marks produced on human bones. The possibility to assess the morphometric features of each lesion indicates that this technique might provide accurate and precise information about the characteristics of the type of saw used. However, further studies including a wider number of samples and using a higher variety of cutting weapons need to be performed to fully assess the potentiality of the presented radiological technique.