Early Aseptic Loosening of a Total Knee Arthroplasty …
A specific radiological evaluation of hip joint infections does not exist to our knowledge. However, several authors have used different radiological systems that have been primarily developed for determining acetabular and femoral defects at the site of an aseptic loosening of hip arthroplasties also in the assessment of infected total hip replacements. The Paprosky- [, ], and the AAOS (American Academy of Orthopedic Surgeons) [-] classifications belong to the most widely used ones.
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Due to emergence of new multiresistant bacterial strains, modifications in the treatment philosophy of infected joints as well as an increasing number of comorbidities among patients that suffer from joint infections, staging and classification systems should be routinely updated over the years. In an evaluation of the McPherson staging system, Hanssen and Osmon recommended consideration of excluding infection chronicity as a separate variable in the local wound grade because this variable is redundant by already being accounted for in the categorization of infection type . Hereby, additional variables that should be considered for inclusion in the staging system include primary versus revision surgery, classification of the magnitude of acetabular and femoral bone loss, use of massive structural allografts, and the presence of multiresistant bacteria, such as methicillin-resistant staphylococci or vancomycin-resistant enterococci.
The time of infection manifestation is also an important factor in classifying hip joint infections. Historically, infections have been classified in acute and chronic ones. Over the years it has become apparent that a further differentiation depending on the exact time of infection manifestation is required. Therefore, hip joint infections are actually categorized into early, delayed, and late infections [, ]. Although these terms are widely accepted, a discrepancy regarding the precise differentiation of the time periods still exists. Some authors define all infections within the first 6 postoperative weeks as early, whereas others extend this period until the first 12 postoperative weeks. Early infections are attributed to an intraoperative contamination. Between this specific time and the first 24 months after surgery, infections are defined as delayed. Delayed infections are also attributed to an intraoperative contamination, however, an infection manifestation has not evolved due to a small bacteria number, low virulence of the causative organism or adverse local conditions for bacteria growth. Late infections emerge after the first 2 postoperative years. These infections are hematogenously acquired, whereas in 20-40 % of the cases the primary infection source remains unidentified . In the past years, the term of a low-grade infection has also been introduced for describing subacute, prolonged infections with lack of any typical local infection signs. Histopathological and microbiological findings might be positive. Practically, all these definitions are an attempt to separate surgically from nonsurgically acquired infections, and the problem is where to draw the line. Clearly, not every early infection is surgically acquired and not all late infections are from other sources.