Degenerative discopathy is a common pathology which may require spine surgery. A metallic cylindrical pin is inserted into the vertebral body to maintain soft tissues and may be used as a reflector of ultrasonic wave to estimate bone density. The first aim of this paper is to validate a 3D model to simulate the ultrasonic propagation in a trabecular bone sample in which a metallic pin has been inserted. We also aim at determining the effect of changes of bone volume fraction (BV/TV) and of positioning errors on the quantitative ultrasound (QUS) parameters in this specific configuration. The approach consists in coupling finite difference time domain simulation with X-ray microcomputed tomography. The correlation coefficient between experimental and simulated speed of sound (SOS) (respectively broadband ultrasonic attenuation (BUA)) was equal to 0.90 (respectively 0.55). The results show a significant correlation of SOS with BV/TV (R = 0.82), while BUA values exhibit a non-linear behavior versus BV/TV. The orientation of the pin should be controlled with an accuracy of around 1° in order to obtain accurate results. The results indicate that using the ultrasonic wave reflected by a pin has a potential to estimate the bone density. SOS is more reliable than BUA due its lower sensitivity to the tilt angle.