Integrated Biomaterials Science

Infection and Sterilization 821
steel, cobalt chromium alloys, high-density polyethylene, in vivo prepolymerized
and polymerized polymethylmethacrylate. In control cases,
no implants were applied. These authors noted that all of the implants
were significantly associated with S. aureus infections in comparison
with controls. The incidence of E. coli and S. epidermidis infections in
in vivo polymerized polymethylmethacrylate was higher than in the other
implants.
The resistance of the biomaterial surface to infections can be maintained
by sterilization and antibiotic impregnation or by improving colonization
by host tissue cells.
With regard to the origin, many infections are likely to be related to
the endogenous flora of the patient. Focuses of infections in the organism
may also be involved. Antibiotic administration after stomatologic or
urological procedures is suggested in patients with hip prosthesis to prevent
hematogenous dissemination of bacteria (Shaw and Greer, 1994). The role
of bacteriemia in the onset of prosthetic infections is, however, controversial.
Experimentally, Moore (1987) observed that the intravenous infusion in
dogs of S. aureus during vascular grafting surgery or in the early
postoperative period led to the infection of all the grafts. Late infusion
(3 to 12 months) was followed by a rate of infections ranging from 30%
to 57%. Once pseudointimal healing had occurred, no infections were
registered.
Environmental contamination, as well as contamination from medical
devices such as venous or cardiac catheters, endotracheal tubes, and bladder
catheters, should be considered, too. Air-borne implant contamination can
be reduced by using laminar flow in the operating theater. This seems to be
demonstrated for total joint arthroplasty (Ritter, 1984; Fitzgerald and
Peterson, 1984).
Another possible factor of infection is the positioning of the prosthesis
in a traumatic—and therefore likely to be contaminated—area. In such a
clinical situation, the appropriate use of prophylactic antibiotics, adequate
wound debridement, and timely soft tissue coverage is recommended
(McClinton and Helgemo, 1997). The scarce vascularization of the tissues,
such as in bone or joint capsule, may be a first cause for the lack of
protective factors in the implant site. The surface of a prosthesis is usually
a wide area to which bacteria can adhere, and therefore a relatively small
number of microorganisms can cause infection. On the other hand, vascular
and heart valve prostheses, which are in direct contact with blood, are more
protected, and a larger amount of germs is required to cause infection.
Finally, an important role in the onset of implant infections is played
by the patient’s condition or diseases. Systemic illnesses, such as diabetes or