Unusual penetrating injury of the knee joint. A case report.

: Although not commonly recognized, glass may be radiopaque in soft tissue. Its density can be similar to that of bone, and it may be misinterpreted as fracture fragments. The radiodensity of glass is dependent on its varying quantities of iron, silicon, dioxide, aluminum, calcium, magnesium, and sodium salts. The awareness that the radiodensity of glass can be similar to that of human bone on roentgenogram can help the surgeon avoid the pitfall of misdiagnosis. Roentgenograms may be used to detect intraarticular glass and to assist in a localization of glass imbedded in the soft tissue.