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| Journal of the New Zealand Medical Association,
25-January-2008, Vol 121 No 1268
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The influence of steroid injections on the incidence
of infection following total knee arthroplasty
Geoffrey Horne, Peter Devane, Andrew Davidson, Kathryn
Adams, Gordon Purdie
The initial management of patients with arthritis of the
knee should be non-operative. Joint aspiration and intra-articular steroid
injection are techniques that may be used to improve synovitis in these
patients.1 However, total knee arthroplasty is
the most effective treatment for the relief of pain in severe arthritis of the
knee.1,2
The most severe complications of TKA are wound and joint
infection which occur in about 0.5–2% of operations
performed.1–6 The mortality rate for
prosthetic joint infection may be as high as
2.5%.7 Infection may occur early in the
postoperative period, in which case the joint may be salvaged by exploration and
synovectomy, or it may be a late, deep joint phenomenon where complete removal
and revision of the joint in a two step process is
indicated.1,5,7
Risk factors that have been identified as being related to a
higher risk of surgical site infection or deep wound infection include obesity,
diabetes mellitus, malignancy, smoking, renal failure, urinary tract infection,
rheumatoid arthritis, previous knee surgery, and prolonged postoperative
drainage for longer than 6
days.1,2,4,5,8,9
Recent research has demonstrated an increase in deep
infection rate and wound healing problems after intra-articular steroid hip
injection (IASHI). prior to arthroplasty.10,11
These findings support the outcome of a systematic, comprehensive survey of the
expert opinion and current practice of orthopaedic surgeons in Ontario, Canada,
that reveal that a substantial number of surgeons believe that the infection
rate related to THA may be increased after intra-articular steroid hip
injection.12
To date, published studies that assess the effect of
intra-articular steroid injections on the risk of infection following total
arthroplasty in knees, have offered differing
results.13,14
For example, Joshy et al, in a recent retrospective cohort
study found no significant difference in the numbers of patients who received
intra-articular steroid injection between the infection and non infection
groups.13 They concluded that infection
following total knee replacement is due to multiple factors and that the use of
intra-articular steroids does not alter the incidence of deep infections
following total knee arthroplasty.
Conversely, in a more recently published retrospective
study, Papavasiliou et al reviewed 231 patients who had undergone total knee
replacement over a period of 2.5 years.14 These
researchers concluded that the decision to administer intra-articular steroids
to a patient who may be a candidate for total knee replacement should not be
taken lightly because of a risk of postoperative deep infection.
In the light of these recent differences in research
findings, this case-control study aimed to assess the influence of preoperative
intra-articular corticosteroid injection on the incidence of postoperative wound
healing problems and infection in patients undergoing total knee joint
replacement surgery at two university-affiliated tertiary hospitals in
Wellington, New Zealand.
It was hypothesised that a corticosteroid injection into the
knee joint at any time prior to the operation would increase the risk of wound
healing problems and infection of the joint following surgery, with resultant
worsened knee symptoms as reported by patients on Oxford Knee Scores. We also
aimed to assess whether the outcome was influenced by the person who
administered the injection, for example, whether it was the patient’s
general practitioner, orthopaedic surgeon or rheumatologist.
As well as the rate of wound healing problems and
infections, quality-of-life measures have been shown to be valuable in assessing
the success of joint replacement surgery.15
Oxford scores are considered a simple and effective method for assessing quality
of life.16
The Oxford Knee Score (OKS) contains 12 questions, each of
which has five options graded 1 to 5. The scores are summed. Higher scores
indicate more severe symptoms from the knee in question.
MethodsThe study was a retrospective, case control design. The
two groups for the study were a control group of patients who had undergone
total knee joint replacement without subsequent infective complications, and a
group of patients who had either had postoperative wound healing problems or
revision surgery for deep infection at any stage following initial
surgery.
A list of all patients who underwent primary total knee
arthroplasty at Hutt Hospital, Wellington between July 1999 and December 2002,
and at Wellington Public Hospital between January 1992 and December 2002 was
obtained from the computerised medical records systems at the two hospitals.
From these lists it was determined which patients
either had a subsequent revision surgery on the same knee that was replaced, or
were readmitted within 6 months with wound healing problems, that is, proven
infection, but not requiring re-operation. Further data was then gathered,
finding all patients who underwent revision to a total knee joint arthroplasty
between January 2003 and December 2004 at each of the two hospitals.
The clinical records of all patients who had either
been readmitted within 6 months for wound healing problems or had revision knee
joint surgery were then reviewed to determine which cases were in fact due to
suspected infection and which were due to other problems such as mechanical
failure.
Patients who had either a deep joint infection
requiring revision surgery, or who had a wound healing problem with suspected
infection requiring readmission were included in the study group.
The group of patients from Wellington hospital who had
had total knee arthroplasty between 1992 and 2002 and not experienced a
subsequent infection was much larger than was required (1200), so a random
sample of 165 cases was taken from this sample to make it more manageable for
comparison with the study group. It was calculated that we would need sample
sizes of 152 controls and 38 infected to achieve a power of 80%, given an
estimated odds ratio of 3.0. This estimate was conservatively based on a
previous study that had found a relative risk of 4.0 in hips injected with
steroids.10
A reply-paid letter was then sent to all patients,
outlining the purpose of the study and asking patients whether they had ever had
an injection into their knee joint, at any stage before their total knee
arthroplasty (Appendix 1).
The patients were asked simply whether they received
any injection before surgery. They were not asked to identify the reason for the
injection. We also asked patients to indicate whether that injection was
performed by a rheumatologist, general practitioner or orthopaedic surgeon; how
many injections they received and how long before the operation the last
injection was given. The patients were also asked to indicate whether, at the
time of surgery, they had diabetes or they smoked cigarettes. They were also
asked to complete a validated knee assessment tool, the OKS (Appendix 2).
In all, 392 patients were contacted. 352 were controls
and 40 were infection cases. The reply rate was 65% overall after 4 weeks.
Two groups were thus produced:
Of the
non-responders we contacted the general practitioner of all of the infection
cases and a sample of one-third of all the control cases, to see if any had
changed address or were deceased. To improve the reply rate, especially for the
infection cases, those still living at the same address were contacted again by
mail.
The reply rates for this second round of letters
increased the overall reply rates to 69.6% for controls and 77.5%% for study
cases after one week, at which time we finalised our data set. After removing
patients who were deceased, or who failed to reply adequately we were left with
sample sizes of 219 controls and 29 study cases.
The data was then analysed statistically using EpiInfo
(Centers for Disease Control & Prevention, Atlanta, GA, USA) for an
association between preoperative intra-articular steroid injections and wound or
joint infection following operation.
Secondary relationships to be assessed were between
each of smoking, diabetes and infection; between infection and Oxford Knee
Score; and between injection by each of rheumatologists, general practitioners,
and orthopaedic surgeons and infection rate following surgery.
Finally we looked at whether the time before the
operation that the injection was given, and the numbers of injections given,
influenced infection rates.
ResultsThe overall reply rate for this study was 70.4%. The
infection case reply rate was 77.5% and for non-infection controls it was 69.6%.
The difference between rates of reply was not significant (Table 1).
Table 1. Reply rates by hospital and
overall
 For all respondents, 13 patients were deceased or unable to
reply. A further 15 controls were discarded due to an incomplete OKS or steroid
injection questionnaire. One patient filled in only the OKS, and 35 filled out
the injection questionnaire but did not fully complete the OKS. Patients who
adequately filled in one of the two sections were included in the study.
In all, 32.8% of patients had received a steroid injection
at some stage before knee replacement surgery. Of all patients, 7.3% claimed to
be smokers at the time of their surgery and 8.2% had diabetes. The average OKS
was 26.03 for all subjects. The national mean for OKSs at 6 months post-primary
TKA was 23.22 in 2003.
Most injections were delivered by general practitioners
(GPs) who gave 37%, with orthopaedic surgeons giving 35% and rheumatologists
administering 22%. The remainder reported more than one injection, given by
different doctors. The average number of injections (of all those who received
any injections) was 2.23 with a range of 1–15. The mean time before
surgery from the last injection was 16 months, with a range of 1 month to 45
years. A telephone call to the respondent verified the 45-year interval. 79% of
patients claimed that their last injection was within 12 months of surgery.
The rates of pre-operative injections in each of the control
and study groups were 32.0% (17/28) and 39.3% (70/219) respectively with an odds
ratio of 1.38 (95%CI 0.55–3.31). There was no significant difference
detected (p= 0.44).
The rates of diabetes were 7.3% and 14.3% in the control and
infection groups respectively (OR 2.09; 95%CI 0.47–7.22) and smoking
occurred at rates of 6.9% and 10.7% (OR 1.62; 95%CI 0.28–6.33). The rates
of reported diabetes and smoking were not found to be significantly different
between the two groups (p=0.21, p=0.46 respectively) (Table 2).
Table 2. Rates of injection, diabetes, and
smoking in the infection and control groups
 The administrators of steroid injections were relatively
mixed for the control group and mostly orthopaedic surgeons for the infection
group, however the difference between the two groups was not significant (Figure
1).
Figure 1. Injection
administrators
 The mean OKS was 25.3 for the control group (95%CI
23.8–26.8) and 31.9 for the infection group (95%CI 26.9–36.8). There
was a significant difference in this measure between the two groups
(p=0.014).
Table 3. Mean Oxford Knee Score (OKS) for
control and infection groups
 DiscussionThis case control study aimed to examine the effect of
pre-operative steroid injections on the rate of postoperative wound healing
problems and joint infection in the knees of patients undergoing total knee
arthroplasty. It was hypothesised that the results would mirror those of
previous studies that have found higher rates of post surgical problems in hips
that have been injected with steroids.
The results to this study indicated that there was no
increased risk of postoperative wound healing problems or infection attributable
to patients receiving an injection into their knee before surgery. While the
response rate to the letters was satisfactory, due to the rarity of
postoperative infection, trial size of the infection group was based on
feasibility.
There was no detectable increased risk of wound or joint
problems related to either diabetes or cigarette smoking. Only 7.3% of patients
claimed to have been cigarette smokers at the time of surgery. The expected
number of cigarette smokers in a population of New Zealanders 50 years of age or
older, would be 10–15%.17
It was decided not to use time before operation and number
of injections given as measures since the replies were often non-specific and
the data was skewed by the occasional extreme case. As an example, one patient
reported that his last injection was 45 years before the operation. This patient
had a steroid injection into his knee following a rugby injury as a young adult.
His knee stiffened afterwards, so he determined never to have another injection
into the knee joint.
The overall mean OKS (26.03, 95%CI 24.55–27.52) was
slightly above the 2003 national mean for TKA recipients of 23.22. However, the
national mean figure was for patients reporting 6 months after surgery whereas
many patients in the study population would have been reporting at a much longer
interval following their operations. This could account for the knee symptoms of
the study group being of less severity than the national average.
A significant difference was found in OKS between the
control group and the infection group, with the latter reporting more severe
knee symptoms. This is not surprising, as those postoperative complications are
likely to have caused a less satisfactory state of the knee.
The person who administered injections into the knee was
thought to be a possible important variable by the authors of studies on hip
replacement surgery. This study did not find a significant difference in the
degree of safety with which general practitioners, rheumatologists, and
orthopaedic surgeons administered injections into the knee joint.
Some weaknesses were identified during the course of this
study. Patients who indicated that they had an injection into their knee before
surgery may not in fact have been injected with steroids, and the accuracy of
recall (particularly with an ageing study group) must be taken into
consideration. However the fact that an injection had been administered would
tend to over-estimate the influence of steroid injection if only local
anaesthetic were injected, and since there was no association found it is
extremely unlikely that steroid injection has an influence on infection
rates.
The strengths of this study included the high patient
response rate and the simplicity of the questionnaire which allowed patients to
provide useful information. It also provided a virtually exhaustive database of
infection and wound healing cases for the last 10 years, in the area
studied.
ConclusionOur results did not indicate that intra-articular steroid
injection was contraindicated in patients who are candidates for total knee
replacement surgery, although patients who had infective complications following
TKA did have a less favourable long-term knee function.
This is a small, retrospective study in a limited number of
patients, undertaken primarily to assess long-term outcomes of total knee
arthroplasty, comparing those who had prior intra-articular injections, to those
who did not.
This study suggests the outcome for patients who had
intra-articular injections prior to TKA, is no less successful than for those
who did not have injections. The findings indicate that if injections into the
knee do have an effect, then it is much smaller than that seen in hip
replacement surgery.
The recent published research on infection rate
relationships to prior intra-articular injections and total knee arthroplasty
have all been retrospective studies. For this reason, and because the fewer than
expected infected cases presented for this study, it is recommended that a
larger, prospective, multicentre study be undertaken, that could more
confidently determine these relationships.
Competing interests: None known.
Author information: Geoffrey Horne,
Orthopaedic Surgeon1; Peter Devane, Orthopaedic
Surgeon1; Kathryn Adams, Orthopaedic Research
Nurse1; Andrew Davidson, Medical
Student2; Gordon Purdie,
Biostatistician2
Acknowledgements: We thank
the New Zealand Orthopaedics Association for their support in this project as
well as George Serbiesku at Wellington Hospital and Pauline Barclay at Hutt
Hospital for their assistance with data collection.
Correspondence: Kathryn Adams, Orthopaedic
Research Nurse, Orthopaedic Department, Wellington Hospital, Riddiford Street,
Wellington, New Zealand. Fax: +64 (0)4 3855831; email Kathryn.adams@ccdhb.org.nz
References:
Appendix 1
Date
Address 1
Address2
Address3
Dear
We are currently conducting a
study looking at whether there may be an association between injections into the
knee before surgery and problems with wound healing after knee replacement
surgery.
We are trying to establish whether patients had an
injection into their knee at any time before the knee operation (into the same
knee that was operated on). You have been identified from hospital records at
Hutt Hospital or Wellington Hospital as having had a total knee replacement
operation between 1999 and 2002.
We would greatly appreciate it if you could answer
the following questions and fill out the attached questionnaire, returning the
completed forms to us in the envelope provided.
Yours sincerely
Andrew Davidson; Medical Student,
University of Otago
Professor JG Horne; Orthopaedics
Department, Wellington Hospital
1) Did you have an injection into your knee
from a GP, rheumatologist or orthopaedic surgeon, at any time before you had a
knee replacement operation?
Please tick
If yes:
________________________________________________
c) How long before your operation was the last
injection?
2 – At the time of surgery were
you:
a) Diabetic?
Please tick
b) A smoker?
Please tick
3) – Enclosed you will find
a knee scoring chart. Please fill this out with regards to the
current condition of your knee.
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