15% of foreign bodies are not visualized on plain radiographs. (Morgan WJ, J Hand Surg Br. 1984;9(2):194-196).
Stone, wood, and glass are often not well visualzed on plain xrays. Consider ultrasound or CT if suspected.
Foreign Body References
Bodne D, Quinn SF, Cochran CF. Imaging foreign glass and wooden bodies of the extremities with CT and MR. J Comput Assist Tomogr. 1988;12(4):608-611.
Russell RC, Williamson DA, Sullivan JW, Suchy H, Suliman O. Detection of foreign bodies in the hand. J Hand Surg Am. 1991;16(1):2-11.
Crawford R, Matheson AB. Clinical value of ultrasonography in the detection and removal of radiolucent foreign bodies. Injury. 1989;20(6):341-343.
De Flaviis L, Scaglione P, Del Bò P, Nessi R. Detection of foreign bodies in soft tissues: experimental comparison of ultrasonography and xeroradiography. J Trauma. 1988;28(3):400-404.