retention. Patients were excluded if the infected prosthesis
was a megaprosthesis for bone tumour surgery or if the primary
surgical treatment was prosthesis removal. During the
study period, a protocol existed where ‘early’ Gram-negative
PJI (3 months from implantation) was
treated with retention of the prosthesis and surgical debridement
by arthrotomy. The subsequent antibiotic regimen consisted
of an initial period of intravenous b-lactam antibiotic
followed by a course of oral ciprofloxacin. The treating clinician
had the authority to vary from the treatment protocol
with regard to the number of surgical debridement procedures
and the duration of intravenous and oral antibiotics,
depending on the clinical situation. The exact reasons for
variation from the protocol were not always available from
the medical record
Definitions
A Gram-negative PJI was defined by the isolation of Gramnegative
bacilli from at least two deep, peri-prosthetic culture
specimens; or the isolation of Gram-negative bacilli
from one specimen plus the presence of purulence around
the joint, a sinus tract communicating with the joint or acute
inflammation on histopathology of surgical specimens [3].
Treatment failure was defined as persistence or recurrence
of symptoms or signs of prosthetic infection, the isolation of
the same or different organisms from subsequent operative
samples or the removal of the prosthesis while antibiotic
therapy continued.
Microbiological methods
Susceptibility testing of isolates was performed according to
CLSI (NCCLS) guidelines. The MicroScan WalkAway (Dade
Behring Inc., Deerfield, IL, USA) and agar dilution methods
were used for isolates from 1998 to 1999 and the Vitek-2
(bioMerieux, Marcy l’Etoile, France) was used for isolates
from 2000 until 2007.
Statistical analysis
The Kaplan–Meier method was used to estimate the 2-year
survival rate free of treatment failure. A Fisher exact test
was used for analysing categorical data.
Results
Study population
Over the study period 1919 total knee replacement and
1912 total hip replacement operations were performed at