Apostoperative wound infection following total joint replacement is a
complication that is dreaded by surgeon and patient alike. Much emphasis has
been placed on decreasing infection rates in order to ensure a more successful
operative outcome. Reduced infection rates have been associated with
controlling for various environmental factors in the operating room with a
great variety of means, including systemic
antibiotics1-3,
laminar
airflow1,2,
antibiotic-loaded bone
cement3,4,
and ultraviolet
lighting5-11.
Contamination most often occurs as a result of bacteria that are emitted
from the various surgical personnel in and around the operating
room12. At some
facilities, laminar airflow is used as an environmental control because it
reduces the number of bacteria in the air, and thus, the possible number of
infectious colony-forming units. The use of ultraviolet radiation to minimize
the number of bacteria in the air has been studied since the
1930s7. Although
typically associated with laminar airflow, ultraclean air (air with <10
colony-forming units/m3) has been documented in association with
the use of high-intensity (290 µW cm-2 s-1)
ultraviolet light8.
The use of lower intensities (25 to 30 µW cm-2 s-1)
of ultraviolet light along with body exhaust suits and filtered air has been
associated with low infection rates, perhaps as the result of a cumulative
effect4,10,11.
The purpose of the present study was to compare the infection rates
following procedures performed by one surgeon before and after the
implementation of surgical ultraviolet lighting in order to determine the
efficacy of ultraviolet radiation as an infectious environmental control
during total joint replacement surgery.
Prior to September 16, 1991, all operations at the Center for Hip and Knee
Surgery involved the use of only horizontal laminar airflow. In September
1991, ultraviolet lighting (American Ultraviolet, Lebanon, Indiana) was
installed in all four operating rooms. After that date, one surgeon
exclusively used ultraviolet lighting without using laminar airflow. The
present study represents a consecutive series and includes all of the total
joint replacements that were performed by this surgeon over the included
time-period. Perioperative antibiotics were given to all patients
preoperatively at the time of surgery and postoperatively for twenty-four
hours. The present retrospective study was approved by the institutional
review board.
All of the operations that involved the use of horizontal laminar airflow
were performed so that none of the surgical personnel could be in the path of
the clean airflow. This placement of personnel was accomplished by positioning
the instrument table parallel to the face of the laminar airflow unit. The
operating table was then placed perpendicular to this flow wall and the two
tables (patient and instrument) were connected to one another with sterile
drapes. Body exhaust suits were used for all operating personnel.
With the implementation of ultraviolet lighting in the operating room,
protective clothing was needed for all surgical staff. Besides the standard
cotton short-sleeve blouses and pants, all nonsterile personnel wore
long-sleeve jackets, hoods, and protective eye-shields. The surgical team wore
long-sleeve gowns as well as body exhaust systems with an ultraviolet
protective face shield. Exposed skin required the application of sunscreen.
The patient was protected with eye ointment or an eye shield, and any exposed
areas other than the incision site were covered with blankets.
During each operation, the ultraviolet lights were turned on once all
personnel were gowned and the patient was fully prepared and draped for
surgery, or approximately two to three minutes prior to incision. The
ultraviolet lights remained on until the wound was closed and the dressings
were in place. They were off between procedures and were turned on again when
the next patient was fully prepared for surgery. The operating room was kept
at a temperature of 60°F to 70°F (16°C to 21°C) and at a
humidity of 30% to 50%.
The intensity of the lights was set by the circulating nurse at 23 µW
cm-2 s-1 and at a frequency of 2537 Å as this
frequency has been found to have the maximum bactericidal
effect7. To ensure
proper intensity levels, the ultraviolet lights were calibrated once a week at
night with a radiometer that was calibrated annually. In addition, the lights
were cleaned once a week and as needed with an alcohol-soaked cloth.
From July 9, 1986 to July 15, 2005, one surgeon performed 5980 total joint
replacements in 3846 patients at our facility. The procedures included 4071
total knee replacements (68.1%) and 1909 total hip replacements (31.9%), with
5428 (90.8%) of the operations being primary procedures and 552 (9.2%) being
revisions. The preoperative diagnoses associated with all procedures (primary
and revision) included osteoarthritis (5171 procedures; 86.5%), failed total
hip replacement (346 procedures; 5.8%), failed total knee replacement (206
procedures; 3.4%), osteonecrosis (119 procedures; 2.0%), rheumatoid arthritis
(ninety-seven procedures; 1.6%), and other diagnoses (forty-one procedures;
0.7%). Among the 552 revision procedures, 346 (62.7%) were hip replacements
(of which thirteen [3.8%] were performed because of prior infection) and 206
(37.3%) were knee replacements (of which thirty-nine [18.9%] were performed
because of prior infection). Overall, there were 2317 female patients (60.2%)
and 1529 male patients (39.8%).
Of the 5980 total joint procedures, 4909 (82.1%) were performed with use of
ultraviolet lighting without laminar airflow and 1071 (17.9%) were performed
with use of laminar airflow without ultraviolet lighting
(Table I). Of the 4909 total
joint replacements performed with use of ultraviolet lighting, 1519 (30.9%)
were hip replacements and 3390 (69.1%) were knee replacements. Of the 1519 hip
replacements performed with use of ultraviolet lighting, 261 (17.2%) were
revision procedures. Ten (3.8%) of these hip revisions were performed because
of prior hip infection. Of the 3390 knee replacements performed with use of
ultraviolet lighting, 163 (4.8%) were revision procedures. Twenty (12.3%) of
these revisions were performed because of prior knee infection. Of the 1071
procedures performed with laminar airflow and without ultraviolet lighting,
390 (36.4%) were hip replacements and 681 (63.6%) were knee replacements. Of
the 390 hip replacements performed without ultraviolet lighting, eighty-five
(21.8%) were revision procedures; three (3.5%) of these revision procedures
were performed because of prior hip infection. Of the 681 knee replacements
performed without ultraviolet lighting, forty-three (6.3%) were revision
procedures; nineteen (2.8%) of the 681 knee replacements were performed
because of prior knee infection.
Two thousand and twenty-two joint replacements were performed as unilateral
procedures, and 206 of these were revisions. Two thousand four hundred and
seventy-eight joint replacements were performed as simultaneous procedures
involving two joint replacements in one patient, and fifty-five of these
procedures were revisions. Furthermore, fifty-two of these joint replacements
were performed as contralateral or ipsilateral procedures. Nine hundred and
twenty-eight joint replacements also involved two joint replacements in one
patient; however, the operations for the two joints were staged. One hundred
and forty-four of these staged joint replacements were revisions. Three
hundred and three joint replacements involved three staged or three
simultaneous joint replacements in one patient. Nine of the 303 joint
replacements were performed as simultaneous procedures in one patient, and the
remainder were staged. Seventy-five of the 303 joint replacements were
revisions. One hundred and eighty-eight joint replacements occurred in
patients with a total of four total joint replacements. Forty-nine of these
joint replacements were revisions. Sixty-one joint replacements were performed
in patients who had five or more joint replacements. Twenty-three of these
joint replacements were revisions.
An infection was classified as deep if it was deep to the fascia with a
delay in wound-healing or persistent
discharge11. Total
joint replacement was considered to have failed if the joint had a deep
infection, excision, and/or revision because of infection.
Statistical Analysis
Patient-related and operative factors associated with the rate of infection
were analyzed by means of logistic regression, the chi-square statistic, and,
in limited instances, the two-sample t test. The factors that were analyzed
included the age of the patient at the time of surgery, the preoperative body
mass index, the presence of ultraviolet light at the time of surgery, the
joint being replaced (hip or knee), the type of procedure (primary or
revision), the type of fixation (cemented or uncemented), the diagnosis at the
time of surgery (osteoarthritis, rheumatoid arthritis, or osteonecrosis), and
the performance of revision surgery because of a prior infection.
Variable selection for the logistic regression was performed with the
forward stepwise procedure, with entry and removal criteria as defined by a
parameter estimate level of significance of 0.10. Separately, each
nonsignificant explanatory variable was tested along with the significant
variable of ultraviolet lighting for the final reported p values. For
significant p values, there was one final overall total joint replacement
model reported, one final model for knees reported, and one final model for
hips reported. For logistic regressions that selected only one explanatory
variable, the chi-square test or Fisher exact test was reported, either when
appropriate or when the odds ratio was not appropriately calculated.
Forty-seven deep infections were identified in association with 5980 total
joint replacements that were performed over a nineteen-year period
(prevalence, 0.79%). The average duration of follow-up was 5.2 ± 4.0
years (range, 0.2 to 18.5 years), and 712 joints (11.9%) were completely lost
to follow-up. Within one month, one-half of all infections had occurred; the
median time to infection was one month (thirty days). The most frequently
reported time to infection was fourteen days, with 19% (nine) of the
forty-seven infections occurring at that time. Thirty-five (74%) of the
forty-seven infections occurred within four months.
The binomial distribution indicates that for the 712 joints that were lost
to follow-up, we can expect 5.6 ± 2.4 additional infections (95%
confidence interval, 0.8 to 10.4). Statistically, there was an approximately
95% chance of observing between one and ten additional infections among the
712 joints that were lost to follow-up.
As it is most likely that the 712 joints that were lost to follow-up
populated both the infected and noninfected subsets in a similar fashion and
ratio as the 5980 joints that were originally observed (with six expected
infections among the 712 joints that were lost, compared with forty-seven
observed infections among the 5980 joints in the original group), there is a
95% chance of observing any reported result within the 95% confidence interval
of the rate reported in the present study. Furthermore, although it is
difficult to calculate the impact of each possible alternate scenario had we
been able to include the 712 lost joints, at a minimum we have the usual
statistical confidence that the results would not have been highly altered by
the inclusion of the lost joints, primarily because of the large number of
cases (5980) and the reasonable size of the group of lost joints (11.9%; 712
of 5980).
Previous studies of total joint replacement have óexamined the
effect of cases that are lost to
follow-up13, with
the observation that missing cases do not necessarily represent poor results.
With respect to the outcomes of revision and satisfactory results following
total knee arthroplasty, missing patients actually tended to do better than
returning patients. In that report, 440 of 563 patients were followed and 123
(21.8%) were lost to follow-up.
In the present study, the infection rate was 1.77% (nineteen of 1071)
following procedures performed without the use of ultraviolet lighting and
0.57% (twenty-eight of 4909) following procedures performed with the use of
ultraviolet light (p < 0.0001). After separating the data according to the
type of total joint replacement (hip or knee), the data revealed that the
infection rate associated with total hip replacement decreased from 1.03% to
0.72% after the installation of ultraviolet lighting (p = 0.5407)
(Table II). A post hoc power
analysis demonstrated that 32,000 total hip replacements would be needed to
demonstrate a significant difference at this rate. The infection rate
associated with total knee replacement decreased from 2.20% to 0.50% when
ultraviolet light was utilized (p < 0.0001)
(Table III).
The odds of infection were 3.1 times greater (95% confidence interval, 1.8
to 5.6) for all joint procedures performed without ultraviolet lighting as
compared with those performed with ultraviolet lighting (p < 0.0001). With
the numbers available, revision surgery (p = 0.1528), body mass index (p =
0.1117), patient age (p = 0.7261), the use of a cemented prosthesis (p =
0.5206), rheumatoid arthritis (p = 0.9381), osteonecrosis (p = 0.9304), and a
history of infection (odds ratio = 2.1, p = 0.0557) were not found to be
associated with an elevated risk of infection, regardless of whether or not
ultraviolet lighting was utilized. In the years following the implementation
of ultraviolet lighting in the operating room, the average patient age
decreased and the average body mass index increased
(Table I). When body mass index
is taken into account, despite the fact that it was not a significant effect,
the odds ratio for an infection increased to 6.9 (95% confidence interval, 4.0
to 13.5) (p < 0.0001).
The odds of infection were 4.5 times greater (95% confidence interval, 2.3
to 9.3) for knee procedures performed without ultraviolet lighting as compared
with those performed with ultraviolet lighting (p < 0.0001). Logistic
regression analysis revealed that, in the setting of revision surgery, the
odds of infection were 3.5 times greater (95% confidence interval, 1.003 to
12.2) for procedures performed without ultraviolet lighting as compared with
those performed with ultraviolet lighting (p = 0.0494). Following primary knee
replacement, the infection rate was 1.9% (twelve of 638) for procedures
performed without ultraviolet lighting and 0.5% (seventeen of 3227) for
procedures performed with ultraviolet lighting (p = 0.0003)
(Table III). Following revision
knee replacement, the infection rate was 7.0% (three of forty-three) for
procedures performed without ultraviolet lighting and 0.0% (zero of 163) for
procedures performed with ultraviolet lighting (p = 0.0086)
(Table III). With the numbers
available, body mass index (odds ratio = 1.05 per unit of body mass index; p =
0.0887), age (odds ratio = 0.96 per year of age; p = 0.0712), the diagnosis of
rheumatoid arthritis (odds ratio = 3.8; p = 0.0887), the diagnosis of
osteonecrosis (p = 0.9798), or a history of previous infection (odds ratio =
2.1; p = 0.0685) were not found to be significantly associated with infection.
There were no uncemented knee replacements in the current cohort.
The odds of infection were 1.4 times greater for hip procedures performed
without ultraviolet lighting than for those performed with ultraviolet
lighting; however, this finding was not significant (p = 0.5407). With the
numbers available, revision surgery (odds ratio = 1.5; p = 0.6238), body mass
index (p = 0.9377), age (p = 0.1572), a cemented prosthesis (p = 0.3878), the
diagnosis of rheumatoid arthritis (p = 0.6530), the diagnosis of osteonecrosis
(odds ratio = 2.8; p = 0.1536), or a history of previous infection (p =
0.7607) were not found to be associated with infection.
The overall infection rate following primary joint replacement was 0.77%
(forty-two of 5428). The infection rate was 1.70% (sixteen of 943) following
primary procedures performed without ultraviolet lighting and 0.58%
(twenty-six of 4485) following primary procedures performed with ultraviolet
lighting. The overall infection rate following revision was 0.91% (five of
552). The infection rate was 2.34% (three of 128) following revisions
performed without ultraviolet lighting and 0.47% (two of 424) following those
performed with ultraviolet lighting. The infection rate for joints with a
prior infection was 1.9% (one of fifty-two). The infection rate was 0.40% (ten
of 2488) for joints undergoing a simultaneous bilateral procedure and 0.1%
(one of 928) for those undergoing a staged bilateral arthroplasty (in this
case, with the infection occurring after the second stage). The infection rate
for patients after three or more procedures was 0.63% (one infection among 159
patients undergoing 552 total joint replacements), and the infection rate for
those undergoing four or more procedures was 0% (zero infections among
fifty-eight patients undergoing 249 total joint replacements).
In 1937, Duke University implemented ultraviolet radiation in the operating
room after infection rates at their facility remained elevated for a period of
five years. Since 1940, the infection rate at Duke University remained below
0.5% for all orthopaedic procedures through 1973, demonstrating the strong
bactericidal effect of ultraviolet
light5. There have
been many changes in the operating room since 1973, but little has been
reported with regard to ultraviolet
lighting5-11.
In 1964, the National Research Council carried out a double-blind, randomized
study that involved the use of ultraviolet lighting at five
institutions7. The
investigators reported that the only procedures with significant improvement
due to ultraviolet radiation in the operating room were those procedures
involving refined-clean wounds. Today, this wound category would contain joint
replacement procedures. In this category, which represented 19.2% of all
infections in the study, the postoperative infection rate decreased from 3.8%
to 2.9%.
Despite the benefits of laminar airflow in reducing the number of bacteria
at the wound site during total joint replacement, it has been shown that the
infection rate associated with total knee replacement can actually increase
when horizontal laminar airflow is used. This discrepancy is related to the
placement of operating personnel during
surgery14. This
positioning problem has been controlled to a degree for more than thirty years
at our hospitals by positioning the instrument table and the operating table
so that the operating personnel are in a less risky position. However, the
operating personnel still lean into the path of the air on occasion to check
the position of their instruments and the alignment of the knee. This factor
may account for the elevated infection rates following total knee replacement
as compared with total hip replacement.
The infection rate in our operating room decreased significantly, from
1.77% to 0.57%, in association with the use of ultraviolet lighting, even with
the elimination of laminar airflow. The decrease in the infection rate for
total knee replacement from 2.2% to 0.5% was significant (p < 0.0001).
Reduction in the operative time could have been a positive factor influencing
this result. Over these years, one would expect our techniques to improve and
the operating times to decrease. We used the exact same knee arthroplasty
system during the entire period of time. We evaluated all of the knee
procedures in March of 1991 and March of 2003 with regard to the duration of
surgery; the average duration was sixty-three minutes (range, forty-eight to
115 minutes) in 1991 and fifty-eight minutes (range, fifty to 113 minutes) in
2003. Therefore, shortened operating time probably was not a factor.
The use of ultraviolet lighting as an environmental control brings about
several concerns, especially the safety of the patient and the operating room
personnel. The recommended intensity for ultraviolet lighting is 25 to 30
µW cm-2 s-1 in order to prevent
overexposure10. Eye
protection for both the patient and the operating room personnel is critical
in order to prevent severe conjunctivitis. Even two to three minutes of direct
exposure is enough to cause conjunctivitis. Longer periods of exposure without
proper protection may lead to blindness. In order to prevent the superficial
erythema that can result after fifteen to twenty minutes of ultraviolet
exposure, a hood, jacket, and gloves must be worn when ultraviolet lights are
in use. Failure to comply with these protective measures may result in serious
burns of the cornea and skin. At our facility, we provided an educational
video about ultraviolet lighting and effective protection for all staff in
order to guarantee awareness of the dangers of noncompliance. Because of these
concerns, many of the personnel find the use of the ultraviolet lights an
inconvenience. Nevertheless, they have adapted well to the change in
environment.
Additional concerns with ultraviolet lighting include the temperature and
humidity of the room. High temperatures may cause excessive sweating, whereas
low temperatures may reduce the efficiency of the ultraviolet
lights5. A decrease
in efficacy is seen at >60% humidity, and the ultraviolet lights become
almost ineffective at 80% humidity. For this reason, we keep the temperature
in our operating rooms between 60°F and 70°F (16°C and 21°C),
and we keep the humidity level between 30% and 50%.
One feature that makes ultraviolet lighting so attractive is the relatively
low cost of its installation and maintenance. In 1989, ultraviolet lighting
was thirty-four times less expensive than the ultraclean air enclosure
unit9. At our
facility, each operating room was equipped with ultraviolet lighting for
approximately $2000. In contrast, laminar airflow enclosures for the same room
cost approximately $200,000. With appropriate and relatively simple safety
measures, ultraviolet lighting appears to be a cost-effective environmental
control that can maintain relatively low infection rates.
Postoperative infection after total joint replacement is a devastating
event for all those involved, often resulting in a failed arthroplasty and
substantial patient morbidity. The use of ultraviolet lighting in the
operating room appears to be an effective adjunct to ultraclean air enclosures
for reducing the rate of infection following total joint replacement,
particularly total knee replacement. In situations in which a particular
surgeon or procedure has an elevated infection rate, we highly recommend
ultraviolet lighting as an effective environmental control to minimize the
infection risk. ?