The objective of our study was to evaluate the association between acute
periprosthetic joint infection (APJI) and radiographic measurement of soft-tissue thickness in elective total hip replacement surgery. A case-control study was conducted to compare the soft-tissue thickness
radiographic measurement (SRM) at the hip in patients diagnosed with APJI
based on Tsukayama et al. (2003) criteria after total hip replacement with patients
that were not infected, at a single institution from 2013 to 2019. To
minimize selection bias, each case was matched with two controls using the
following methodology: patients of the same sex, with an age variation of
± 5 years, and nearest in surgery date to the cases were selected. All
postoperative radiographs were performed in the first 24 h after total hip arthroplasty (THA)
surgery as it is protocolized in our institution. Soft-tissue thickness
radiographic measurement was defined as the distance from the tip of the
greater trochanter to the skin following a perpendicular line to the femoral
diaphysis in postoperative anteroposterior hip radiographs. In total, 78 patients were included (26 cases and 52 controls). The SRM median of the cases
was 76.19 mm (SD: 26.518) and 53.5 mm (SD: 20.47) in controls. A multivariate
logistic regression model showed an independent association between APJI and
SRM (odds ratio (OR) = 1.033, 95 % confidence interval (CI) 1.007–1.059, p=0.012). Patients with an SRM
greater than 60 mm had a 7-fold increase in the odds of APJI
(OR = 7.295, 95 % CI = 2.364–22.511, p<0.001). The results of our study suggest an association between large SRM at the hip
and the risk of APJI in patients with primary total hip arthroplasty. SRM
may be a helpful and easy tool for evaluating the risk of APJI before
elective primary total hip replacement surgery.
Introduction
Acute periprosthetic joint infection following total hip arthroplasty (THA)
can dramatically modify a patient's postoperative expectations, increasing
the challenge of postoperative management, sometimes even requiring revision
surgery to eradicate infection and reconstruct a functional hip
(Triantafyllopoulos et al., 2015).
APJIs not only cause an important adverse impact on patient outcomes but
also in healthcare economic systems. Prevalence estimations have predicted an
increase in total hip replacement procedures in future years, and it is
fitting to assume an increase in APJI.
Host susceptibility to infection has emerged as an important predictor of
APJI. Several risk factors for acute postoperative wound complications and
infection following THA have previously been identified. These include
diabetes, immunosuppression, inflammatory arthropathy, primary bone
malignancy, prior lower-extremity fracture, renal or hepatic diseases, age,
alcohol, parenteral drugs or tobacco abuse, vascular insufficiency, and
obesity (Wright et al., 2012).
Although preoperative risk assessment is multifactorial, radiographically
measured soft-tissue thickness at the incision site has been associated with
postoperative surgical site infection after cardiac, cervical spine, and
lumbar spine surgery (Kozlow et al., 2014; Lee et al., 2016; Mehta et al., 2013). Also,
computerized-tomography-measured abdominal soft-tissue depth has been
correlated in abdominal and spine surgery (Fuji et al., 2010; Lee et al., 2011).
Increased anterior knee subcutaneous fat thickness measured in radiographs
has been associated with a significantly increased risk of early reoperation
for wound complications following primary total knee arthroplasty (TKA) and
had a greater predictive value than body mass index (BMI) (Watts et al., 2016;
Wagner et al., 2018). However, few studies have investigated the potential
association between increased peritrochanteric soft-tissue thickness and
APJI following primary THA.
The exact measurement of soft-tissue thickness can only be assessed
intraoperatively. For this reason, preoperative detection of patients at a
higher risk of acute periprosthetic joint infection is challenging, and
preventive strategies are limited.
The objective of our study was to evaluate the association between acute
periprosthetic joint infection (APJI) and soft-tissue thickness measured
with an X-ray after elective total hip replacement surgery following the
methodology previously described by Bernaus et al. (2019).
This study hypothesizes that large measurements of local soft tissue around
the hip, measured with radiographs, are associated with an increased risk of
APJI after total hip replacement.
Materials and methods
A case-control study was conducted to compare soft-tissue thickness
radiographic measurement (SRM) at the hip in patients diagnosed with APJI
after total hip replacement with patients that were not diagnosed with APJI.
For this study, we included all patients diagnosed with APJI admitted to our
hospital for total hip replacement from 2013 to 2019. All the patients were
diagnosed with hip arthritis.
All patients were operated on by the same surgical team (Francesc Angles Crespo, Agustí Bartra Ylla, and Silvia Maria Miguela Álvarez)
from the Hip Unit at our institution. Antibiotic prophylaxis dosing adjusted
by weight was performed with a second-generation cephalosporin for
non-allergic patients, clindamycin for allergic patients, and teicoplanin
for patients with colonization with methicillin-resistant Staphylococcus aureus. A posterolateral approach was performed in all cases. No drains were
used.
All patients were included in a fast-track program with mobilization on the
same day of the surgery.
Patients and variables
Cases were defined as patients diagnosed with APJI (those diagnosed less
than 4 weeks after surgery) after total hip replacement. To minimize
selection bias, each case was matched with two controls using the following
methodology: patients of the same sex, with an age variation of ±5
years, and nearest in surgery date to the cases were selected. All
participants had high-quality anteroposterior pelvis X-rays available. The
principal variables collected were soft-tissue thickness radiographic
measurement and acute periprosthetic joint infection. Secondary variables
collected included age; gender; BMI; operating time; American Society of
Anesthesiologists (ASA) physical status classification; and comorbidities
such as diabetes mellitus, rheumatoid arthritis, transfusion, liver
cirrhosis, current use of corticosteroids, smoking, and parental drug use.
Criteria for APJI diagnosis
The clinical diagnosis of acute periprosthetic joint infection (APJI) was
based on Tsukayama et al. (2003) criteria: local inflammatory signs, purulent
drainage through the wound, and elevated C-reactive protein during the first
4 weeks after the index surgery.
Surgical technique and antibiotic therapy
Surgical debridement was performed in all patients with a clinical
diagnostic suspicion of APJI. During the surgery, at least five to seven
different samples were taken to obtain a microbiological diagnosis, and
modular components were changed. Synovial fluid samples were inoculated in
blood culture flasks (Font-Vizcarra and Soriano, 2010). After surgery, broad-spectrum
intravenous antibiotic therapy with antibiofilm activity was started
following the protocol at our institution: teicoplanin, amikacin, and
rifampicin until results from intraoperative cultures were available. Then,
targeted antibiotic therapy was started according to the antibiotic
sensibility of the specific microorganism for 8 weeks. Oral medication
was preferred when possible.
Methodology for assessment of SRM
Once cases and controls were identified and included, the distance from the
tip of the greater trochanter to the skin was measured by two different
blinded orthopedic surgeons following a perpendicular line to the femoral
diaphysis in anteroposterior hip radiographs. Standardized anteroposterior
pelvis X-rays (Figs. 1 and 2) in the supine position and
15∘ of internal rotation of the hips were obtained for all
patients.
The distance from the tip of the greater trochanter to the skin
was measured following a perpendicular line to the femoral diaphysis in
anteroposterior hip radiographs.
SRM, in this example, is 26.4 mm.
To obtain precise measurements, the first step required calibrating X-rays.
In patients with THA, the known diameter of the dome/cup component was
introduced into the TraumaCad X-ray viewer program (Brainlab Ltd.,
Petach Tikva, Israel) and set as a reference. Once this calibration process
was performed, we proceeded to obtain the measurement from the tip of the
greater trochanter to the skin as previously described. These measurements
were taken in the postoperative X-ray performed in the first 24 h after
THA.
Statistical analysis
Qualitative or ordinal variables were described using absolute frequencies
or percentages while quantitative variables were described as mean or median
values when necessary. Univariate analyses were performed using the
Student's T test, Fisher test, or chi-squared test for quantitative and
dichotomous variables. SRM was analyzed as a continuous variable and as a
dichotomous variable using the median of our measurements as a threshold. We
performed a multivariate logistic regression model with those significant
variables in univariate analysis. A multivariate logistic regression model
was used to estimate the risk of presenting infection as an odds ratio (OR)
and with a 95 % confidence interval (CI). All analyses were performed using SPSS
for MAC v22 (SPSS Inc., Chicago, IL, USA). The level of statistical significance
was established at p≤0.05 (two-tailed).
Results
A total of 81 patients (27 cases and 54 controls) were included in this
analysis. Three patients had to be excluded, two controls (women) and one
case (man), as the postoperative X-ray did not include the skin. From those
78 patients (26 cases and 52 controls), there were 31 (39.7 %) female
patients and 47 (60.3 %) male patients. The mean age of APJI patients was
67 years (SD = 12.7) and 68.54 years (SD = 12.4) for non-APJI patients.
In the univariate analysis, the distribution of previously studied risk
factors between cases and controls did not show significant differences
except for soft-tissue thickness radiographic measurement, patients with an ASA
score of 3, operating time, and BMI (Table 1).
A correlation study resulted in a positive correlation between the variables
that showed an association in the univariate model (operating time, BMI, and
SRM). Operating time and SRM showed a weak uphill (positive) linear
relationship (Pearson correlation coefficient = 0.4). BMI and operating
time showed a weak uphill (positive) linear relationship (Pearson
correlation coefficient = 0.3). BMI and SRM showed a moderate uphill
(positive) relationship (Pearson correlation coefficient = 0.561). All
correlations showed statistical significance.
Finally, we performed a multivariate logistic regression model to
investigate the association between APJI and variables that showed
association in the univariate model (operating time, BMI, and SRM). This
analysis showed an independent association between APJI and SRM (OR = 1.033,
95 % CI 1.007–1.059, p=0.012). The other variables analyzed (operating
time and BMI) were progressively excluded from the equation when the Wald
method was used.
The median for the SRM at the hip for all patients was 60 mm (range 15–141).
The mean SRM for cases was 76.19 mm (SD = 26.52) and 53.5 mm (SD = 20.47)
for controls. The median for the case group was 79 mm (15–141) and 48.5 mm
(25–128) for the control group. When participants were separated into two
groups based on the median as a threshold, a significant association between
APJI and SRM was found for patients with greater measurements. Patients with
an SRM greater than 60 mm had a 7-fold increase in the odds of APJI
(OR = 7.295, 95 % CI = 2.364–22.511, p<0.001) compared to those with smaller measurements.
A subanalysis based on different sex was performed to test the correlation
between BMI and SRM. We expected a different fat distribution between sexes
but the correlation between BMI and SRM was still present. This may be
explained by the inclusion of muscle and not only subcutaneous fat in the
measurement.
Discussion
Since the appearance of total joint arthroplasty, antibiotic prophylaxis
and improvements in surgical technique have reduced APJI rates. However,
with an increasing number of yearly total hip replacements, a substantial
population remains at risk of infection-related complications following this
procedure.
Accurate preoperative infection-risk stratification is an important step
toward further reducing APJI rates. In this way, surgeons could thoroughly
discuss with their patients the infection risk of surgery, possible
non-surgical alternatives, and especially possible means of risk reduction.
A non-invasive tool for detecting those patients at increased risk of APJI
could allow additional prevention strategies. Some studies have determined
that infection risk can be objectively determined in a preoperative setting
with an APJI risk-assessment score attending to patient comorbidities
(Everhart et al., 2016; Poultsides et al., 2018), but these do not take into account local
conditions around the joint.
Multiple explanations can be considered as to why an increased local fat
distribution at the hips is associated with an increased risk of APJI.
Having an increased physical space implies technical difficulties for
surgeons leading to larger dissections, soft-tissue damage, aggressive
retraction, an increased surgical time, and subsequently a higher risk of
infection.
The prevalence of obesity continues to rise in parallel with the demand for
total hip arthroplasty (Pirruccio et al., 2019). A relationship between surgical
site infection (SSI) and morbid obesity or diabetes has consistently been
reported; although both conditions are often concurrent, both diabetes and
morbid obesity independently contribute to SSI risk. Moreover, obesity has
previously been demonstrated to be an independent risk factor for increased
complications after total hip and knee arthroplasties (Dowsey and Choong, 2008; Ma et al.,
2016; Chee et al., 2010; Zingg et al., 2016).
BMI is also known to be a predictive factor for wound complications
following both THA and TKA (Wallace and Judge, 2014; Shearer et al., 2020). Adhikary et al. (2016) suggested that there was a positive correlation between BMI and
incidences of 30 d postoperative complications in both TKA and THA.
Radiographic measurement of soft-tissue thickness has been correlated with
postoperative surgical site infection in other surgical fields such as
general and cardiac surgery (Kozlow et al., 2014; Lee et al., 2011).
In general surgery, Lee et al. (2011) found that abdominal subcutaneous fat
measured in CT is an independent predictor of superficial incisional SSI
after midline laparotomy, and Fuji et al. (2010) also reported an increased
risk of SSI in patients with greater radiographically determined subcutaneous fat thickness
after undergoing elective colorectal resection.
A similar study on elective lumbar spine surgery shows the utility
of local soft-tissue thickness radiographic measures as a simple independent
risk assessment tool for surgical site infection (Lee et al., 2016). In cervical
spine fusion procedures, Mehta et al. (2013) demonstrated that the thickness
of subcutaneous fat measured by CT scan is a factor in the development of
surgical site infection.
DeMik et al. (2018) established that the impact of obesity on postoperative
complications is more profound for THA than TKA. Morbidly obese patients
undergoing THA were also found to have significantly higher rates of wound
complications, deep infection, and reoperation rate. Moreover, DeMik took
into account the fat distribution differences between the knee and hip soft
tissues. The tendency of adipose tissue to deposit in the gluteal region and
the resulting soft-tissue envelope may contribute to the differences between THA
and TKA postoperative complications.
All hip arthroplasties in our study were implanted using a posterolateral
approach. A recent study by Purcell et al. (2018) found there was no
difference in deep infection rates between a direct anterior and posterior
approach.
In a series of morbidly obese patients undergoing primary TKA, Watts et al. (2016) found increased anterior knee subcutaneous fat thickness using plain
radiographs to be a more predictive measurement of wound complication than
body mass index. In a recent study, Shearer et al. (2020) found that BMI
is a better predictor of periprosthetic joint infection risk than
radiographic measures of adipose tissue after TKA, as opposed to Watts. In
our study, 4 patients had a normal BMI with > 60 mm SRM. It is
important to take into consideration that fat distribution is different
between the knee and hip when comparing these results.
The impact of SRM in elderly patients with surgically treated hip fractures
was previously studied (Bernaus et al., 2019). The analysis demonstrated an
association between the SRM at the hip and the risk of SSI. They found that
patients with an SRM greater than 6.27 cm had a 7-fold increase in the
odds of surgical site infection compared to those with smaller measurements.
In the same way, patients with infection had a 2.24 cm greater mean SRM.
Increased peritrochanteric soft-tissue thickness following primary total hip
arthroplasty and its association with APJI has been barely studied. Bell et
al. (2019) performed a case-control study matched on age, sex, and BMI which
did not demonstrate an association between radiographically measured
peritrochanteric fat and infectious or wound complications following THA.
They also performed the surgery using a posterior surgical approach.
Peritrochanteric fat thickness was reliably measured, with Pearson's
correlation coefficients > 0.90 in all cases. Also, Mayne et al. (2020) analyzed 1220 primary THAs and measured, intraoperatively, the
vertical soft-tissue depth from the most prominent part of the greater
trochanter to the skin. Surgery was performed through a posterior approach
as we did in our study. They did not find a relationship between
peritrochanteric fat depth and the risk of surgical complications for the
initial 12-month follow-up period. Patients with BMI > 40 kg/m2 or
more had a significantly increased risk of infection compared to those with
BMI < 40 kg/m2. They also found females had a significantly greater
fat depth at the greater trochanter in comparison to males, although no
significant differences in BMI were observed between sexes. Fat depth showed
a weak correlation with BMI.
The results of our study suggest an association between the SRM at the hip
and the risk of APJI in patients after total hip replacement surgery. Sprowls et al.
(2020a) retrospectively reviewed 1110 patients, identifying increased lateral
soft-tissue thickness and body mass index as factors associated with
surgical site infection and deep infection and lateral soft-tissue thickness
with revision surgery as well. A value > 5 cm was predictive of
surgical site infection, deep infection, and revision surgery. All surgeries
were performed through a lateral incision (posterior, lateral, or
anterolateral approach). The measurement of lateral soft-tissue thickness
was measured as the horizontal distance from the most lateral point of the
greater trochanter to the skin edge, using the standing hip radiographs
obtained within 1 year of the surgery date. Increased lateral soft-tissue
thickness was associated with risk for revision surgery (OR 1.02 per
increasing millimeter).
The same group (Sprowls et al., 2020b) examined the relationship between fat
thickness and 90 d postoperative complications and assessed the
intraoperative thickness of subcutaneous fat at the incision site for direct
anterior and posterior approaches for THA. In total, 124 patients were included and
reviewed retrospectively. Also, the lateral hip fat thickness was measured
from preoperative anteroposterior pelvis radiographs (taken within 6 months
of the THA procedure). Return to the operation room was significantly associated with
BMI, anterior soft-tissue incision site, and lateral soft-tissue incision
site. Periprosthetic joint infection (American Academy of Orthopaedic Surgeons (AAOS) diagnostic criteria) was
significantly associated with BMI and lateral incision site fat thickness.
Lateral hip fat thickness measured in radiographs strongly correlated with
measurements at the incision site. Regardless of BMI, sex, or age, more soft
tissue was encountered with posterior approaches compared to direct anterior
approaches. Excess incisional fat was associated with periprosthetic joint
infection after a posterior approach.
Likewise, our multivariate logistic regression model showed an independent
association between APJI and SRM (OR = 1.033, 95 % CI 1.007–1.059).
Patients with an SRM greater than 60 mm had a 7-fold increase in the
odds of APJI (OR = 7.42, 95 % CI = 3.01–18.28,
p<0.001) compared to those with smaller measurements. The
reliability of measurements using this method between observers was
previously corroborated by Bernaus et al. (2019). The overall agreement
between observers was good (intraclass correlation coefficient
score = 0.822, 95 % CI: 0.754–0.873, p<0.001).
There are some limitations in this study: it includes a small sample size
from a single institution that may compromise external validity, and for this
reason, we believe there is a need for further study in this area of
interest.
Postoperative radiographs were used for the measurement of distances as
25 % of calibrated preoperative radiographs did not include the skin. Three
patients had to be excluded as the postoperative X-ray did not include the
skin. Postoperative inflammation and hematoma formation can impact the soft-tissue thickness. However, hematoma formation is not an important issue with
the use of tranexamic acid.
All radiographs were taken in the first 24 h after THA surgery, as it is
protocolized in our institution. These radiographs were taken in a supine
position which could influence exact measurements. Some potential drawbacks
to the SRM could include different patient positioning, rotation of the
pelvis, and the orientation of the beam.
Contrary to other previously reported studies (Bell et al., 2019; Mayne et al., 2020),
radiographic measurement of soft-tissue thickness was a valid tool for
predicting APJI after primary total hip arthroplasty in this study. This
measure allows for long-term individualized prevention strategies to
decrease the soft tissue around the hip, especially in elective patients in
which time to surgery is not critical. This measurement could alert about
higher infection risk in patients with normal BMI values or without systemic
risk factors.
Prevention strategies, including preoperative weight control (which could
also decrease osteoarthritis symptoms), optimization of antibiotic
prophylaxis doses, the use of local antibiotics, or povidone iodine in cases
that preoperatively prove to be at higher risk, could be established as a
clinical routine.
Conclusions
The results of our study suggest an association between large SRM at the hip
and the risk of APJI in patients with primary total hip arthroplasty. SRM
may be a helpful and easy tool for evaluating the risk of APJI before
elective primary total hip replacement surgery. However, further studies are
necessary to confirm our results and to further evaluate its usefulness in
clinical practice.
Ethical statement
Informed consent was obtained from all individual participants included in
the study.
Data availability
Research data are not published but can be requested by email to the corresponding author.
Author contributions
SMA and LRF collected the data.
LFV performed the formal analysis, methodology, review, and editing.
FAC performed the conceptualization, supervision, review, and editing.
LRF prepared the original draft with contributions from all
co-authors.
ABY performed the supervision and review.
MCB performed the review and editing.
Competing interests
The authors declare that they have no conflict of interest.
Review statement
This paper was edited by Martin Clauss and reviewed by two anonymous referees.
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