Infection after primary hip arthroplasty. Epidemiology, time trends and risk factors in data from national health registers. The Norwegian Arthroplasty Register
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Every year, more than 10,000 Norwegians undergo hip replacement (7,360 THAs and 3,214 HAs in 2011). This may be due to osteoarthritis (OA), inflammatory joint disease, fractures, fracture sequelae, aseptic femoral head necrosis or sequelae after childhood hip disease. The native hip joint is replaced by a total hip arthroplasty (THA) or a hemiarthroplasty (HA). The implants constitute large foreign bodies that could be predilection spots for adherence of microorganisms, and postoperative infections are a feared complication. Such infections are difficult to treat and impose increased morbidity and mortality on the patients.
To meet the challenge of prosthetic joint infection, several risk factors have been identified and prophylactic measures have been introduced. The Norwegian Arthroplasty Register (NAR) has had several publications on antibiotic prophylaxis, systemically and in bone cement, for THA, and probably contributed to that Norwegian orthopaedic surgeons changed their routines. The starting point of the present PhD project was to assess whether these changes in antibiotic prophylaxis had changed the risk of revision due to infection.
We found that, in spite of the anticipated improved antibiotic prophylaxis, the risk of revision due to infection after primary THA had increased threefold from 1987-1992 to 2003-2007 (Paper I). In the Nordic Arthroplasty Register Association’s (NARA) dataset from Denmark, Finland, Norway and Sweden, a similar increase in risk of revision due to infection after primary THA was found between 1995-1999 and 2005-2009 (Paper III). The reason for this increase could not be explained by any known changes in the risk factors assessed in the two studies (Papers I and III). The possibility of a true increase in prosthetic joint infection and other possible explanations were discussed.
In Norway there are no systematic registrations of true prosthetic joint infection. Revisions due to infection should be reported to the NAR and the Norwegian Hip Fracture Register (NHFR), and surgical site infections should be reported to the Norwegian Surveillance System for Healthcare-Associated Infections (NOIS). In Paper II we assessed risk factors and risk patterns for these two endpoints for both THA and HA. The first-year incidence of surgical site infection after primary arthroplasty was found to be nearly five times higher than the first-year incidence of revision due to infection. There also seems to be differences in the risk patterns between surgical site infection and revision due to infection and between HA and THA.
The risk factors associated with increased risk of revision due to infection after primary THA were male sex, advanced age (70-90 years when adjusted for comorbidity), comorbidity (ASA class > 1), long duration of surgery (> 100 minutes), uncemented or hybrid fixation, bone cement without antibiotics, laminar air flow in the operation room, NNIS risk index higher than one, and THA performed due to inflammatory disease, hip fracture or femoral head necrosis.
Risk factors of surgical site infection after THA was advanced age (> 80 years), comorbidity (ASA class > 2), and short duration of surgery (< 60 minutes).
For primary HAs the only risk factor associated with increased risk of revision due to infection was young age (< 60 years), whereas no statistically significant risk factors of surgical site infection were identified.
The overall conclusion of this thesis is that the risk of revision due to infection after primary THA has been increasing. Definite causes of this increased risk could not be established in the three papers. Considering risk factors and possible confounders we still believe that there might have been a true increase in the incidence of prosthetic joint infection.