Intraoperative bone defect measurement in the acetabulum using a navigation system: The influence of bone porosity on the digitalization process.

The aim of the study was to evaluate how bone porosity affects intraoperative volume measurement of the acetabulum in a plastic bone model study and to validate the measurement method on cadaveric acetabula. Point cloud collection was performed using a navigation system and compared to CT measurements as well as theoretical calculations on sawbones with different porosities and validated on cadaveric specimens. The grade of porosity had a significant influence on the volume measurement. In high porous materials volume calculation (61.5 cm²) was overestimated when using a digitalizer, while in materials with low porosity the volume was underestimated (57.0 cm²) in comparison to the known size of the defect (59.4 cm²). Digitalization time of the acetabulum was between 1 and 4 min. Validating the measurement on cadaveric bones no statistical significant difference could be found between digitalized volumes and theoretically calculated volumes. As digitalization of the acetabulum can be carried out in a reasonable time it could be used as a measurement tool to estimate the amount of allografts needed for filling bone defects.