Operating in ultraclean air and the prophylactic use of antibiotics have been found to reduce the incidence of joint sepsis confirmed at re-operation, after total hip or knee-joint replacement. The reduction was about 2-fold when operations were done in ultraclean air, 4·5-fold when body-exhaust suits also were worn, and about 3- to 4-fold when antibiotics had been given prophylactically. The effects of ultraclean air and antibiotics were additive. Wound sepsis recognized during post-operative hospital stay was, however, reduced by these measures only when it had been classed as major wound sepsis. This was reported after 2·3% of operations done without antibiotic cover in conventionally ventilated operating rooms.

Joint sepsis was much more frequent after wound infection and especially after major wound sepsis, although most cases of joint sepsis were not preceded by recognized wound sepsis. This was particularly noticeable after major wound sepsis associated with Staphylococcus aureus; after 37 such infections the same species was subsequently found in the septic joint of 11 patients. The sources of wound colonization with Staph. aureus, when this was not followed by joint sepsis, appeared to differ widely from those where joint sepsis occurred later. Operating-room sources could bo found for most of the latter and the risk of infection appeared to be similar with respect to any carrier in the operating room whether a member of the operating team or tho patient. For wound colonization that was not followed by joint sepsis, operating-room sources could only be inferred for fewer than half and of these more than one half appeared to be related to strains carried by the patient at the time of operation.

During tho follow-up period, which averaged about 2¼ years with a maximum of four years, there were, in addition to the 86 instances of deep joint sepsis confirmed at re-operation, 85 instances in which sepsis in the joint was suspected during this period but was not confirmed, because re-operation on the joint was not done. The incidence of suspected joint sepsis was, like that of confirmed joint sepsis, less after operations done in ultraclean air: 1/2·5, or with prophylactic antibiotics, 1/2·3

Although re-operation was more frequent on tho knee-joint than on the hip, and pain after the initial operation was more frequent after knee operations, there was no evidence that this was the result of any increased risk of infection.

There was some indication of an increased risk of joint sepsis and of major wound sepsis, after operations on patients with rheumatoid arthritis compared with other diagnoses. The increase could have been as much as twofold but, because of the small numbers involved, the statistical limitations of the study render these differences only marginally significant.

When wound washout samples had been obtained from the surgical wound after the insertion of the prosthesis the risk of subsequent joint sepsis was found to be considerably greater for those patients from whose wounds larger numbers of bateria were isolated than from those of other patients at the same hospital.