In the course of many operations foreign substances are introduced into the tissues and intentionally left there, for example, suture and ligature materials, steel or aluminium plates, silver wire or ivory pegs used to secure the fixation of bones, or solid paraffin employed to correct deformities. Other substances, such as gauze, drainage tubes, or metal instruments, may be unintentionally left in a wound.
Foreign bodies may also lodge in accidentally inflicted wounds, for example, bullets, needles, splinters of wood, or fragments of clothing. The needles of hypodermic syringes sometimes break and a portion remains embedded in the tissues. As a result of explosions, particles of carbon, in the form of coal-dust or gunpowder, or portions of shale, may lodge in a wound.
The embedded foreign body at first acts as an irritant, and induces a reaction in the tissues in which it lodges, in the form of hyperæmia, local leucocytosis, proliferation of fibroblasts, and the formation of granulation tissue. The subsequent changes depend upon whether or not the wound is infected with pyogenic bacteria. If it is so infected, suppuration ensues, a sinus forms, and persists until the foreign body is either cast out or removed.
If the wound is aseptic, the fate of the foreign body varies with its character. A substance that is absorbable, such as catgut or fine silk, is surrounded and permeated by the phagocytes, which soften and disintegrate it, the debris being gradually absorbed in much the same manner as a fibrinous exudate. Minute bodies that are not capable of being absorbed, such as particles of carbon, or of pigment used in tattooing, are taken up by the phagocytes, and in course of time removed. Larger bodies, such as needles or bullets, which are not capable of being destroyed by the phagocytes, become encapsulated. In the granulation tissue by which they are surrounded large multinuclear giant-cells appear (“foreign-body giant-cells”) and attach themselves to the foreign body, the fibroblasts proliferate and a capsule of scar tissue is eventually formed around the body. The tissues of the capsule may show evidence of iron pigmentation. Sometimes fluid accumulates around a foreign body within its capsule, constituting a cyst.
Substances like paraffin, strands of silk used to bridge a gap in a tendon, or portions of calcined bone, instead of being encapsulated, are gradually permeated and eventually replaced by new connective tissue.
Embedded bodies may remain in the tissues for an indefinite period without giving rise to inconvenience. At any time, however, they may cause trouble, either as a result of infective complications, or by inducing the formation of a mass of inflammatory tissue around them, which may simulate a gumma, a tuberculous focus, or a sarcoma. This latter condition may give rise to difficulties in diagnosis, particularly if there is no history forthcoming of the entrance of the foreign body. The ignorance of patients regarding the possible lodgment in the tissues of a foreign body—even of considerable size—is remarkable. In such cases the X-rays will reveal the presence of the foreign body if it is sufficiently opaque to cast a shadow. The heavy, lead-containing varieties of glass throw very definite shadows little inferior in sharpness and definition to those of metal; almost all the ordinary forms of commercial glass also may be shown up by the X-rays.
Foreign bodies encapsulated in the peritoneal cavity are specially dangerous, as the proximity of the intestine furnishes a constant possibility of infection.
The question of removal of the foreign body must be decided according to the conditions present in individual cases; in searching for a foreign body in the tissues, unless it has been accurately located, a general anæsthetic is to be preferred.