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5 Bacterial Resistance
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org/10.1103/PhysRevLett.93.098102.
“Diagnosis ofBone andJoint
Infections fromSample toCulture”
FerdinandoDa Rin de Lorenzo
6
The prevention of surgical site infections (SSI) is
a priority within the objectives of the National
Health System. The negative consequences that
postoperative infections entail (morbidity, length
of hospitalization, and mortality) represent particularly serious events both for the individual
patient and for the community, in consideration of
the healthcare resources necessary to treat them.
Therefore, prevention is the watchword for these
pathologies, but also the diagnosis, as early as
possible. Before carrying out an evaluation of the
tests to arrive at a diagnosis of periprosthetic joint
infection (PJI), an answer must be given to what a
periprosthetic infection is. There are many guidelines for identifying a PJI, such as that of the
Infectious Diseases Society of America [1], that
of the European BJIS [2], that of Musculoskeletal
Infection Society (MSIS) [3], and that from
WAIOT [4] [Fig. 6.1]. We will examine what was
reported by the Philadelphia Consensus
Conference [5–7] and that is, an infection occurs
when:
• two positive cultures are taken with pheno-
typically identical organisms,
or
F. Da Rin de Lorenzo
Codivilla-Putti Institutes, National Reference Center
for the diagnosis and treatment of bone infections,
Cortina d’Ampezzo, Italy
e-mail: darin.ferdinando@iol.it
• the presence of a stula in communication
with the outside,
or
• having three of the following minor criteria:
(a) C-reactive protein (CRP-PCR) and erythro-
cyte sedimentation rate (ESR) in serum
elevated;
(b) elevated white blood cell (WBC) count O++;
(c) change in the leukocyte esterase stripe in the
sampled uid;
(d) high percentage of polymorphonuclear neu-
trophils (PMN%) in the collected uid;
(e) positive histological analysis of the tissue in
the peri-lesional area; and.
(f) a single positive culture. (85%).
Based on what is stated above, it is easy to
understand that the diagnosis is based on a set of
factors and elements which combined can give us
a denitive diagnosis. It is also clear that being
faced with bone exposure leaves no doubt about a
diagnosis of infection.
On the basis of what has been reported, we
must take into consideration the various tests
that we should do to arrive at a certain diagnosis,
but before doing this we must do a clinical exam-
ination, but, alas, the clinical signs of pain, joint
stiffness, fever [8], of the redness, swelling, and
increase in temperature in the periprosthetic
region, are to be considered signs and symptoms
with low specicity for a PJI [9].
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2025
P. Ruggieri et al. (eds.), Bone and Joint Infections, https://doi.org/10.1007/978-3-031-96383-4_6
45
46
e
1 of the 2 Major CriteriaORMinor criteria scoring ≥6 Infected
3–5 Possibly infected
≥1 Positive Criteria
(˝Consider further molecular diagnostics
such as next-generation sequencing˝)
<3 Not infected*
*˝Proceed with caution in: adverse local
tissue reaction, crystal deposition disease,
slow growing oranisms"˝
1. Pur ulence around the prosthesis or sinus
tract
Major:
1. Sinus tract with evidence of
(>2,000 cells/mL or >70 % granulocytes)
3. Positive histopathology
4. Confirmatory microbial growth in synovial
2. Increase synovial fluid leukocyte count
communication to the joint or
visualization of the prosthesis
2. Two positive growths of the same
organism using standard culture
flui<t periprosthetic tissue, or sonication cultur
(˝Confirmatory microbial growth in
periprosthetic tissue: if positive in ≥1 specimen
in highly virulent organisms or ≥2 in low
vilulent pathogens; sonication culture
considered positive if >50 colony-forming
methods
Minor:
(a) Elevated CRP (>100 mg/L for acute
infections; >10 mg/L.. for chronic
infections) or D-Dimer (unknown
threshold for acute infection; >860
units/mL of sonication fluid.˝)
ug/L for chronic infection) (score 2)
F. DaRindeLorenzo
evated synovial WBC count (>10,000
(c) El
cells/mL for acute infections; >3,000
cells/mL for chronic infections) OR
(score 3)
(d) Elevated synovial PMN% (>90% for
Leukocyte Esterase (++ for acute and
infections) (score 1)
chronic infections) OR Positive alphadefensin
(b) Elevated ESR (no role for acute
infections; >30 mm/hr for chronic
acute infections; >70% for chronic
infections) (score 2)
(score 3)
(e) Single positive culture (score 2)
(f) Positive histology (score 3)
(g) Positive intraoperative purulence
IDSA 2013 [4]ICM 2013 [5]ICM 2018 [7] Proposed EBJIS 2018 [8]
MSIS 2011 [1]
Source
Definition
1 of the 2 Major CriteriaOR≥3 of 5 Minor Criteria*
≥1 Positive Criteria*
1 of the 2 Major CriteriaOR≥4 of 6 Minor Criteria*
Scoring
system
*˝PJI may be present without
meeting these criteria,( ... ).˝
Major
1. A sinus tract communicating with
the joint
2. Two positive periprosthetic
criteria are not met ( .. .)˝
*˝The presence of PJI is possible even if the above
1. Sinus tract communicating with the prosthesis
2. Purulence without other etiology surrounding the
prosthesis
3. Acute inflammation seen on histopathological
*˝PJI may be present if fewer than
four of these criteria are met˝
Major:
1. Sinus tract communicating with
the prosthesis;
2. A pathogen is isolated by culture
cultures with phenotypically
identical organisms,
Minor:
(a) Elevated ESR (>30 mm/hr) and
CRP (> 100 mg/L for acute
examination of the periprosthetic tissue
4. ≥2 intraoperative cultures or combination of
preoperative aspiration and intraoperative cultures
yielding an indistinguishable organism (the growth of a
virulent microorganism (e.g., Staphylococcus aureus) in
a single specimen of a tissue biopsy or synovial fluid is
or fluid samples obtained from
from at least two separate tissue
the affected prosthetic joint
Minor:
(a) Elevated ESR (>30 mm/hr) and
infections)
(b) Elevated synovial fluid WBC
infections; >10 mg/L.. for chronic
also considered as indicative of a PJI]
CRP (>10 mg/L) concentration
(b) Elevated synovial leukocyte
COWlt
(c) Elevated PMN% (>90% for acute
infections; >80% for chronic
count (>10,000 cells/mL for acute
infections; >3,000 cells/mL for
chronic infections) or ++ change
on leukocyte esterase test strip
(c) Elevated PMN%
(d) Purulence in the affected joint
(e) Isolation of a microorganism in
one culture of periprosthetic
tissue or fluid
(f) Greater than five neutrophils
Criteria
infections)
(d) Positive histological analysis of
periprosthetic tissue (> 5
neutrophils per high-power field
in five high-power fields
per high-power field in five
high-power fields observed
from histologic analysis of
periprosthetic tissue at ×400
magnification
observed on periprosthetic tissue
at ×400 magnification)
(e) A single positive culture
outlines major and minor criteria for each source, including factors like sinus
tract communications, elevated inammatory markers and positive cultures.
Each column details specic diagnostic criteria and notes, highlighting differ-
ences and similarities across the guidelines
Fig. 6.1 Comparison of the diagnostic criteria, adopted in ve periprosthetic
joint infection (PJI) denitions, published from 2011 to 2018. (Reproduced
from [4] under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/)). The table
6 “Diagnosis ofBone andJoint Infections fromSample toCulture”
47
Before delving into the tests to be considered,
it is good to make a distinction by giving the denitions of some terms used in the evaluation of
tests, namely sensitivity, specicity, negative predictive value (NPV), and positive predictive value
(PPV). Sensitivity= Probability that the test is
positive if an individual is sick. Ability to cor-
cyte sedimentation rate (ESR). Normal ESR values in humans are 1–10 mm, and 1–15 mm in
women. Normal C-reactive protein (CRP) values
are the same for men as for women 0–0.8mg/dl.
It should be considered that normal values of
these two elements do not indicate the absence of
infection, and this can happen [17–22]:
rectly classify sick subjects.
Specicity=Probability that the test will be nega-
• In low virulence infections such as
tive if an individual is healthy. Ability to correctly
classify healthy subjects. PV = probability of
presence or absence of disease given the positive
or negative test result and the likelihood
ratios=measures of informativeness of the diagnostic test dene by how much the probability of
• In fungal infections.
• In tuberculosis.
• In Staphylococcal epidermidis infections.
• In patients using anti-inammatories, immudisease is changed to positive or negative given
the test result [10–13]. It is not possible to iden-
• In immunosuppressed patients.
tify an acceptable value for the predictive and
negative value of a diagnostic test in the context
of peri-prosthetic infection (PIJ) because the negative or positive probabilistic diagnosis is
achieved through an ordered series of diagnostic
tests starting from those with the least invasiveness or frequently through a minimal basis of
diagnostic tests that modify the a priori probability of disease given by the clinical history, physical examination and risk factors for PPH. The
only generic indication that we are allowed to
give is to use less invasive tests with a high negative predictive value at the beginning of the diagnostic process which can more likely allow us to
values can remain high postoperatively for up to
6 weeks [23] after a prosthesis operation. It is
useful to carry out a preoperative hematochemical evaluation of both ESR and CRP, which can
be based on postoperatively because in patients
with autoimmune rheumatic diseases, the values
are already high without the presence of ongoing
infections. In the postoperative period, the trend
will therefore be followed based on the previous
blood sample and noting the stability or decrease
in values; an increase in the blood should lead to
suspicion of an ongoing infection.
exclude the disease and interrupt the diagnostic
process for the majority of patients tested. In the
population testing positive for these tests, further
investigations will be carried out to exclude false
positives [14–16].
which is an inammatory cytokine produced in
response to infection or inammation by mono-
cytes and macrophages and is more elevated than
in aseptic mobilizations and normalizes in the 6h
following surgery.
6.1 Blood Chemistry Tests
as D-dimer can be evaluated. D-Dimer is assum-
ing an interesting diagnostic value from a diagThese are generally the rst tests done when PJI
nostic point of view in PJI [24, 25].
is suspected as they are not very invasive and can
already give us information, especially if associated with a clinic which, although not specic,
can alarm us.
Let us start with the hematochemical dosage
of polymerase chain reaction (PCR) and erythro-
to a protein fragment (of brin), the result of the
natural degradation of the clots present in our
organism. It tends to be detectable in the blood if
we are faced with a phenomenon of brinolysis,
i.e., when the counterbalancing process of blood
Cutibacterium acnes or
Propionibacteriumacnes.
nosuppressants, or antibiotics.
It should be considered that the ESR and CRP
Another hematological test is interleukin 6,
Also in the blood sample, other elements such
When we talk about D-dimer, we are referring
48
F. DaRindeLorenzo
coagulation starts (vascular or tissue damage can
trigger it). This process, therefore, allows the formation of the D-dimer: how? The body must block
any hemorrhage (blood loss) with the formation of
clots (composed of networks of brin and platelets). After repairing the damage, the networks are
no longer necessary and the clots are slowly
destroyed by plasmin (enzyme), giving rise to
mini-fragments, the D-dimer. Usually, the doctor
can request the measurement of the D-dimer when
the patient shows symptoms linked to a possible
deep vein thrombosis or pulmonary embolism.
The D-dimer is not present in physiological conditions in human blood (or, more correctly, it is present in very low concentrations); the normal and
reference values of the D-dimer are less than or
equal to 500ng/mL Fibrinogen Equivalent Units
(FEU). The molecular weight of the D-dimer is
around 180,000 daltons, and the half-life is equal
to 4–6h, in other words, this means that during
this time interval, its plasma concentration is
halved. Therefore, it does not have a specic biological function. Its measurement, however, provides very useful indirect information about the
activation of the patient’s coagulation system.
D-dimer can be increased in various physio-
logical and pathological conditions:
Physiological Causes
• Advanced age (increase in elderly subjects
>65years, perhaps related to less mobility and
atherosclerosis)
• Neonatal period
• Pregnancy (expression of the increased hyper-
coagulability inherent to the condition)
• Menstrual cycle
• Laboratory limitations (more frequent with
the classic latex test: interference from plasma
proteins, haemolysis, cross-reacting substances, and antibodies)
Pathological Causes
• Hospitalized and/or severely disabled
subjects
• Current infections (sepsis due to Gram-
negative bacteria)
• Major trauma
• Brain stroke
• Myocardial infarction
• Heart failure
• Tumors
• Disseminated intravascular coagulation (DIC)
• Surgical interventions
• Liver disease
• Nephropathies
• Chronic inammatory diseases such as lupus
erythematosus and rheumatoid arthritis)
• Venous thromboembolism
• Thrombolytic therapy
The test has a sensitivity between 93 and 95%
and approximately 50% specicity in the diagnosis of thrombotic disease, while in a work by
Qian Hu etal. [26] on a sample of 40 patients
affected by PJI, 37 patients with aseptic loosening and 59 patients with extra-articular infection,
the sensitivity of the D-dimer was 87.50% and a
specicity of 78.38%, while for the sum of the
CRP and ESR values the sensitivity was 75.00%
and the specicity of 83.78%. Shahi and other
authors [27] compared 245 patients; 23 with primary prosthesis, 56 with revision prosthesis for
aseptic loosening, 57 revision prosthesis for PJI,
and 29 reimplantations and evaluated CRP, ESR,
and D-dimer and the result was very interesting:
the median D-dimer level was signicantly
higher (p<0.0001) for patients with PJI (1110ng/
ml [range, 243–8487 ng/ml]) compared to
patients with aseptic failure (299ng/mL [range,
106–2571 ng/mL]). Using the Youden index,
850ng/mL was determined to be the optimal cutoff value for serum D-dimer for diagnosis of
PJI.Serum D-dimer outperformed both ESR and
serum CRP, with a sensitivity of 89% and specicity of 93%. ESR and CRP had a sensitivity of
73% and 79%, respectively, and a specicity of
78% and 80%. The sensitivity and specicity of
the combined ESR and CRP were 84% (95%
condence interval [CI], from 76% to 90%) and
47% (95% CI, from 36% to 58%).
They concluded that it appears that serum
D-dimer is a promising marker for the diagnosis
of PJI.This test can also be of great use in determining the optimal time for replantation.
6 “Diagnosis ofBone andJoint Infections fromSample toCulture”
49
However, some factors must be considered:
• False positives: can be due to various causes
such as liver disease, a high rheumatoid factor
value, inammation, malignant tumors,
trauma, pregnancy, recent surgery, as well as
advanced age.
• False negatives: occur in particular if the sample is collected too soon after the formation of
thethrombus or if the test is performed with a
serious delay (in the order of several days).
• Furthermore, ongoing anticoagulant treatment
can make the test negative because it prevents
the extension of the thrombus.
• False values can be obtained if the sample
tube is not sufciently lled (a falsely low
value is recorded if it is underlled and a
falsely high value if overlled). This is due to
the dilution effect of the anticoagulant (the
sample is collected correctly when the bloodanticoagulant ratio is equal to 9:1).
• In elderly patients, the D-dimer has a reduced
specicity and is therefore less useful.
However, it is possible to construct agedependent cut-off values in order to adapt and
make the execution of the test is useful even in
elderly subjects.
• The evaluation laboratory testing is different
between the various laboratories, and, furthermore, the evaluation is different whether on
serum or on plasma, even if the latter data is
not signicant as demonstrated by Korte and
Riesen [28]. Therefore, even if the cut-off was
detected for the PJI of 850, it is thought that
this is not a value identifying the PJI because it
can also be detected in aseptic mobilizations.
The D-dimer has entered the evaluation
parameters of a possible PJI, but neither the
mechanism by which it is formed in a PJI nor
what is the cut-off value that can give us a diagnosis is still clear certain of PJI.There will certainly be further studies that will provide these
answers in the future.
Another easily identiable blood element is
brinogen (Fbg) [29–31], which is a protein
present in the blood whose main role is linked to
hemostasis, i.e., the set of physiological pro-
cesses that allows blood loss (hemorrhage) to be
stopped in any area of the body. Chemically, it is
a glycosylated protein (glycoprotein) which is
produced in the liver and endothelial cells in the
form of dimers with a molecular weight of
340kDa; the individual monomers that constitute
it, in turn, are made up of simple amino acid
chains. Its half-life in circulating plasma is
between 3 and 5days. High brinogen values are
usually associated with prothrombotic conditions, while low values correlate with hemorrhagic conditions. Fibrinogen values can be
detected through normal blood tests and normal
parameters, which indicate correct functioning of
the coagulation mechanism and are the
following:
• Women: 200–430mg/dl;
• Men: 200–375mg/dl.
• Normal values 200–393 mg/dL (Source:
Mayo).
The correlation between D-dimer, brinogen,
and brin degradation products is an indicator of a
septic condition as highlighted in various works
[26, 32–34]. Plasma Fbg showed similar diagnostic performance compared to CRP and ESR in predicting positive culture results in PJI. Plasma
D-dimer showed high specicity but low sensitivity. In the study by Xi Chen and AA, Fbg and
D-dimer did not show better diagnostic performance with different pathogens and different types
of PJI.Further studies are needed to investigate the
difference between serum D-dimer and plasma
D-dimer in the arthroplasty population [35].
If exposures and/or stulas are present, a cul-
ture examination and a supercial antibiogram
can be performed by taking a local sample. The
supercial sampling must be done with accuracy
because it could reveal germs that are not pathogenic ones, and therefore a sterile eld must be
created, and the performer must equip himself
with all the equipment as if he were carrying out
a simple surgical operation. Many authors discourage the performance of supercial swabs as
in many cases it is polymicrobial or does not correspond to deep-seated pathogens, creating difculties in antibiotic coverage [36, 37].
50
F. DaRindeLorenzo
Another test, but in this case a little more invasive, is the examination of the synovial uid, on
which many tests can be performed:
• The white blood cell count with the percent-
age of polymorphonuclear cells (PMN).
• The dosage of PCR and ESR (blood).
• Leukocyte esterase.
• Alpha defensin.
• D-Dimer.
• Calprotectin.
• Culture examination with antibiogram.
• The search for the germ with molecular and
other techniques.
Arthrocentesis [38] is indicated in the pres-
ence of an intra-articular effusion and increased
blood inammation indices, but also in the case
of negative serological tests, if there is a strong
clinical suspicion of PJI.In some cases, the technique makes use of ultrasound, especially in the
hip, while for the knee it is recommended to do it
with the knee exed so that the liquid collects
entirely in the intra-condylar space, even if normally the knee joint is entered in the subpatellar
space. Hip arthrocentesis is more difcult and
actually produces false positives from 3% to 16%
[39]. If there is not enough uid, some authors
recommend the introduction of physiological
saline in modest quantities [40–43]. In general
there are no contraindications to arthrocentesis
unless there is a skin infection in the area to be
punctured, the use of anticoagulants that could
create a hemarthrosis [44] or a systemic septic
disease that could be the act of arthrocentesis to
create a joint infection, but there are no studies
that support these risk conditions, even if being
an invasive gesture it can cause synovial irritation
and pain. In this way, with a single sample, more
data can be obtained [45]. This system is part of
the Point-of-Care (POCT). They are widespread
in many branches of medicine. Their name
derives from their location (at the patient’s bed)
and not from the type of examination they allow
to be performed. They are also sometimes called
rapid, satellite, or remote tests; in general, however, the term POCT refers to all those tests that
can be performed close to the patient or in the
place where health care is provided. The results
are ready in a short time and allow their immediate use. The rst evaluation that is done after having performed the arthrocentesis is to evaluate
the physical aspect, which can give us information, and thus the viscosity and color (Fig.6.2).
From this clearly invasive test, multiple pieces
of information can be obtained such as the white
blood cell count, with differential polymorphonuclear count, an important test to evaluate a
joint infection. In fact, it has an excellent specicity with a cut-off >3000 cells/μL and a percentage of neutrophils >80%, this value can be
differentiated between knee and hip [45–47]. To
be accurate, the white blood cell count should be
performed within 2h of arthrocentesis, as white
blood cells may agglutinate over time. In particularly viscous synovial uids, hyaluronidase can
be used (15U/ml for 15 min at 30°C), which
decreases the viscosity and allows greater
handling.
Leukocyte Esterase Test It is an enzyme present
in neutrophils and granulocytes (white blood
cells), whose main task is to degrade the proteins
that support the connective matrix (molecules
with the role of tissue support). It is carried out
using a stick, normally used for urinalysis
(Fig.6.3).
An extemporaneous exam that can be evaluated directly even if for greater objectivity it can
be evaluated by an optical reader (Fig. 6.4),
therefore, is no longer a personal evaluation but
given by an impartial and highly validated
system.
Alpha-defensin (Fig. 6.5) is a peptide with
antimicrobial action that is particularly abundant
in neutrophils where it is produced in response to
an infectious stimulus.
Viscosity
variable
Aspect
purulent or milky
Color
light yellow or citrine
greenish-yellow
Synovial fluid
y
septic
6 “Diagnosis ofBone andJoint Infections fromSample toCulture”
51
light yellow
dark yellow.
Fig. 6.2 Some macroscopic characteristics found in the various synovial uids
transparent
slightly cloudy
cloudy.
preserved
moderately reduced
reduced
non-inflammatory
moderately inflammator
frankly inflammatory
Fig. 6.3 As can be seen from the following images. Each test has a corresponding color range indicating levels from
negative to large, with specic reading times in minute andseconds
It presents some characteristics:
• It is not inuenced by the preventive administration of antibiotics.
• It covers a wide spectrum of potential
pathogens.
• It is not inuenced by other inammatory
conditions.
• It does not give valid results in the presence of
a high saline dilution of the sample.
• The aspiration of a hematoma not from a validation of the test.
• In metallosis from a false positive rate of 30%.
Fig. 6.4 Optical reader
52
Valid Test
developed
transparent
Invalid Test
F. DaRindeLorenzo
NegativePositivePositivePositive No appears
Fig. 6.5 Some examples of Synovasure-defensintest results
Leukocyte esterase has a very low cost and
has a specicity and sensitivity equal to alpha
defensing, which has a higher cost [48]. There
are many studies on alpha defensin but the comparison with esterase is similar [49].
Calprotectin is a very important substance for
diagnosing numerous inammatory diseases.
Calprotectin is a peptide (protein) present
throughout the body, but particularly concentrated especially in neutrophilic granulocytes and
also in monocytes and macrophages. Capable of
2%, with a 97 6% specicity, and the AUC was
0.993. The sensitivity of calprotectin of the
antibiotic- treated PJI group was 100% versus 90
9% of the nonantibiotic-treated PJI group.
Although 47.6% (ten cases) of the patients in the
PJI group received antibiotics before aspiration,
the diagnostic efcacy of calprotectin was not
affected. The sensitivity and specicity of ESR,
CRP, SF-WBCs, and SF-PMNs ranged from 76
(2%) to 90 (5%) and 64 (3%) to 85 (7%), respec-
tively [50].
binding to oxygen and zinc, the main function of
calprotectin consists in a counteracting action
against the growth of bacteria and fungi within
test line.
control
It must be considered that the presence of blood
inside the joint and the use of anticoagulants can
alter the diagnostic tests.
the body (the so-called antimicrobial activity).
The normal values of this protein should always
be lower than 500 mcg/g, while they begin to be
suspicious or doubtful when they are between 50
0 and 120 mcg/g; if they were to be higher than
120 mcg/g, however, the test can be said to be
completely positive for infection. Zeyu and A.A
[50]. tested 63 patients who were suspected of
having a PJI and the result was the following:
The median calprotectin level was 776μg/ml
(interquartile range [IQR] 536 5–1132) in the PJI
group and 54.5μg/ml (IQR, 38 75–78 0.25) in
the aseptic failure (AF) group (p<0 05). Using a
threshold of 173 μg/ml, the sensitivity was 95
The culture test from synovial uid has a high
specicity (approximately 98%) but low sensitivity (approximately 68%). A negative culture test
therefore does not exclude the presence of
PJI.On the other hand, a false positivity rate of
13% was reported. Shmerling in 1994 claims that
the “best reason” to perform an arthrocentesis is
the diagnosis of an infection [51, 52]. A positive
gram stain can in fact lead to a reasoned therapy
in a very short time, the positivity of a culture
allows a diagnosis, and a therapeutic choice
makes it possible to monitor the therapy and the
pathological course with a second blood sample
Line test
has not.
fully
Background
does not
become
10
97,7
ection
Chen AF et al. KSSTA 2016
SF ana
6 “Diagnosis ofBone andJoint Infections fromSample toCulture”
53
[53]. There are two methods for managing the
withdrawal:
A) Immediately, after collection, inoculate an
aliquot (≥ 1ml per bottle) into blood culture
bottles for aerobic and anaerobic microorganisms. Transfer the remaining aspirate into
sterile containers with anticoagulant for subsequent culture analyzes and with EDTA
(dithiothreitol) for the total leukocyte count
and differential neutrophil polymorphonuclear count.
B) Transfer the aspirate into sterile containers
with anticoagulant for subsequent culture
and EDTA analyzes for the total leukocyte
count and differential neutrophil polymorphonuclear count.
The samples must be kept at a temperature of
4°C and should reach the laboratory within 2h,
keeping in mind that there is a signicant loss of
bacteria already 6 h after sampling due to the
presence of killer bacteria. Antibiotics should be
discontinued at least 2weeks before arthrocentesis to ensure positive culture results; however, it
is necessary to know that antibiotic therapy can
inhibit the proliferation of some microorganisms
even for months [54].
0
80
60
40
20
0
lysis
The value of intra-articular tests has greater signicance
than blood chemistry tests. The examination of the synovial uid is, to date, the most important examination in the
diagnosis of PJI. (Based on data taken from Suan
S.Ahmad, Roland Becker, Antonia F Chen, Sandro Kohl EKA
survey: diagnosis of prosthetic knee joint infection
September 2016, Knee Surgery Sports Traumatology
Arthroscopy 24(10) https://doi.org/10.1007/
s00167- 016- 4303- y)
91,5
72,4
6,3
Tissue
Histology
EKA survey: Diagnosis of prosthetic Knee Joint inf
CRP
Sonication
36
The data set carries a score, as reported in the
following scheme developed at the Philadelphia
2018 consensus conference (Fig.6.6), differentiating the values between the acute form and the
chronic form.
Other biomarkers from synovial uid are
being evaluated. In a recent work, 16 biomarkers
were studied of which 5 gave a value of high
specicity and sensitivity: alpha-defensin, the
mutated ELA-2 gene, the Bactericial
permeability- increasing (BPI) protein, neutrophil
gelatinase-associated lipocalin (NGAL), and lactoferrin. Eight other biomarkers (IL-8, C-reactive
protein, resistin, thrombospondin, IL-1, IL-6,
IL-10, and IL-1) have showed AUC greater than
0.9 [55]. Results: Five biomarkers, including
human α-defensin 1–3, neutrophil elastase 2,bactericidal/permeability-increasing protein, neutrophil gelatinase-associated lipocalin, and
lactoferrin, correctly predicted the MSIS classication of all patients in this study, with 100% sensitivity and specicity for the diagnosis of
PJI. Eight additional biomarkers demonstrated
excellent diagnostic strength, with an area under
the curve of greater than 0 9.
Another very recent test about which there are
still some uncertainties and which can be performed when sampling synovial uid is molecu-
lar diagnostics for the identication of pathogens
in septic arthritis and periprosthetic infections
(PJI).
For this very recent topic, I availed myself of
the collaboration of Prof. Pier Francesco Indelli
and Doctor Emanuele Chisari whom I thank.
Next-generation sequencing (NGS) is a
molecular diagnostic method that offers a more
efcient, cost-effective, and validated technique
for identifying the pathogens responsible for
periprosthetic joint infections (PJIs). NGS outperforms traditional culture and PCR methods in
microbial detection, particularly in complex
cases like polymicrobial infections or when traditional biomarkers fail. It is especially useful for
identifying causative pathogens in culturenegative PJIs [56], which can occur due to previous antimicrobial therapy, user error, or
limitations of current detection methods. Because
of this, recent reports [57, 58] are recommending