have been evaluated specifically in patients with
inflammatory arthritis with PJI or in patients on
immunomodulatory agents. This remains an area
for potential research.
With regards to radiology, plain X-rays may
be useful for operative planning and for
demonstration of loosening of the prosthesis
but have a low specificity and sensitivity in
differentiating septic and aseptic osteolysis.
Plain CT may be used in determining periosteal
reaction or soft tissue accumulation. MRI is the
most sensitive modality for detection of pus but
is limited by its cost and the time the scan takes.
Both MRI and CT can be limited by metal artefacts
in patients with prosthetic joints. Nuclear
medicine scans and FDG PET are useful tools for
detection of infection. However, in a patient with
RA, there may be difficulties determining the
difference between inflammatory arthritis and
an infected joint.
The most common pathogens in PJI are
Staphylococcus aureus and Coagulase-negative
Staphylococcus. However, other bacteria (for
example, Streptococcus, Enterococci, Diptheroids,
Gram negatives and Anaerobes) can also
frequently cause infection. Moreover, PJI
infections are often polymicrobial, which can
make antimicrobial therapy challenging. The
incidence of polymicrobial infection in RA in one
cohort was 15%. 6 Pathogens causing infection are
broadly similar in patients with and without RA
– perhaps with a higher incidence of Staphylococcus
aureus than the general population. 6,7
Obtaining a microbiological diagnosis is key to
securing optimal treatment. It is recommended
that a deep joint aspirate is collected aseptically
– ideally in theatre by a specialist to prevent
contamination and further infection of the joint.
It should be Gram stained and cultured. If the
patient is febrile blood cultures should be taken.
Ideally cultures should be collected before
commencing systemic antibiotics to increase
culture sensitivity.
If atypical organisms are suspected, for
example where a history suggests tuberculosis,
the microbiology lab must be alerted so that
appropriate culture methods can be used and
laboratory safety precautions taken.
Mycobacterial infection should be investigated
and managed by an experienced physician,
looking for a history of exposure or previous
infection and examination and imaging for
disseminated infection. Fluid should be sent for
mycobacterial culture and Mycobacterial
Obtaining a
microbiological
diagnosis is
the key to
securing optimal
treatment
TABLE 1
Atypical pathogens: not isolated from standard
bacterial culture methods
Pathogen
Mycobacteria including
Mycobacterium tuberculosis
Risk factors
Previous exposure or treatment for
mycobacterial infection
Symptoms and signs of disseminated
Mycobacterial infection
Fungal infection
Immunocompromised (for example,
patients on chemotherapy, solid organ
transplant patients, bone marrow
transplant)
15
HHE 2019 | hospitalhealthcare.com
polymerase chain reaction (PCR).
If the patient is felt to be at risk of fungal
infection, fluid and blood cultures should be sent
with fluid being cultured on fungal selective agar.
Blood markers such as beta glucan and
Aspergillus antigen, if available locally, should be
sent. These cases should be discussed with local
Infection specialists to ensure correct specimens
are sent.
In the setting of culture-negative PJI, that is,
one where no pathogen has been isolated, the
patient should be evaluated for the likelihood for
a less typical pathogen. There should also be
discussion with an infection specialist about
empirical antimicrobial therapy, which is usually
directed at Staphylococcus species. Tissue samples
can also be sent for 16S and 18S PCR analysis to
improve sensitivity of detection of bacteria and
fungi respectively. This may be useful if the
sample was taken on antimicrobials. The
limitations with PCR can be availability, possible
contamination (and therefore detection of
organism that is not the infecting pathogen)
and the lack of antibiogram data.
Histological analysis can be used for the
diagnosis of PJI. A systemic review of intra-
operative frozen sections demonstrated it was
a very good predictor of culture positive joint
infection and moderate at predicting culture
negative cases based on the presence or not of
acute inflammation, that is, >5 PMN in at least
five separate high powered fields. 8 Stains can also
be performed for fungi or mycobacterial
infection. However there was no subgroup
analysis of patients with inflammatory arthritis
and whether this affects histological diagnosis.
The presence of acute inflammation may not be
present in less virulent organisms, for example,
Cutibacterium acnes.
Management
The management of PJI in general comprises
both medical and surgical options with a
multidisciplinary team including orthopaedic
and plastic surgeons, infection specialists and
rheumatologists. Conventional surgical options
for the infected joint replacement are retention
and debridement, one or two stage revision
procedures, resection of arthrodesis or, as a last
resort, amputation.
During surgery, multiple (five to six) deep
samples should be taken for Gram stain and
culture, each with fresh sterile instruments
and without passing through a sinus in order
to prevent contamination.
Sonicade and bead milling are newer
intraoperative techniques to increase culture
sensitivity.
Sonicade involves placing bone tissue in sterile
water then passing ultrasound waves through
this media. It has been shown to increase the
sensitivity of culture and also PCR detection. 9
Bead mill processing involves grinding of bone
fragments and then processing in blood culture
and agar which appear to decrease turnaround
times.
There have been several studies looking at the
outcomes in surgical management in patients
with RA. 6,7 One retrospective study looking at 246
episodes of PIJ in patients with RA showed that
as per the general population, a two-stage