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Sensitivity, specificity, and predictive value analyses of a method that can be used to detect pedicular wall perforation during pedicle screw insertion were assessed.To determine the accuracy of observing the fatty material expelled during pedicle screw insertion for detecting pedicular wall perforations.Although many methods for safe and accurate insertion of a pedicle screw are described, the rates of misplacement still are high, and complications may occur from improper placement of pedicle screws. Computer-assisted insertion techniques are reported to be very accurate, but these techniques are not yet commonly available.In this study, 74 pedicle screw insertions were observed for the material expelled after drilling for the pedicle screw. The outflows of blood and fatty particles were recorded separately. The position of the pedicle screws after surgery was verified by computed tomography. The specificity, sensitivity, positive and negative predictive values, and kappa statistics were assessed.Visible fatty particles were observed during 51 pedicle screw insertions. The histologic analysis showed that the fatty particles were coming from the bone marrow of the corpus. For the observation of fatty particles in detecting perforations along the pedicle screw pathway, the specificity was 98%, the sensitivity 73%, the positive predictive value 84%, the negative predictive value 95%, and the kappa statistic 0.74.The observation of fatty particles in the blood that comes out after drilling for the pedicle screw may indicate that there is no perforation along the pedicle screw pathway. The observation is easy to perform and does not require any special instruments. Therefore, it can be used alone or in combination with other methods to improve the accuracy of pedicle screw insertion.