How effective are drain tip cultures at predicting surgical site infections after hip arthroplasty?

doi:10.21203/rs.3.rs-683668/v2

Background: Postoperative surgical site infections (SSIs) are a common complication of surgical procedures; however, the use of drain tip cultures to diagnose SSIs in patients is controversial. The objective of this study was to evaluate the efficacy of drain tip cultures for the prediction of postoperative SSIs in patients recovering from hip arthroplasty.

Study design: The data was compiled from 1204 patients in 15 years and statistical analysis was performed to evaluate the diagnostic value of drain tip culture in determining surgical site infection. We also used this data to evaluate whether preexisting conditions such as hypertension or diabetes affected the probability of a patient getting an SSI.

Results: Drain tip cultures were positive in 12 of 1,112 cases of primary hip arthroplasty, but only one of these 12 patients were ultimately diagnosed with an SSI (Sensitivity, 12.5%; specificity, 99.0%; p = 0.0834). Results from postoperative drain tip cultures performed in patients undergoing revision arthroplasty included 2 false positives and 3 false negatives; interestingly, no true positives were detected in any of the revision arthroplasty cases we evaluated (sensitivity, 0％; specificity, 97.8％; p = 0.9355).

Conclusion: Our results indicate that drain tip cultures have no statistically significant predictive value for the diagnosis of postoperative SSIs and thus should not be used as a primary diagnostic or predictive tool for SSIs. We recommend exploring other diagnostic tools for the postoperative diagnosis of SSIs. Standardized guidelines should therefore be established to improve the predictive value of the different methods.

Orthopedics

Orthopedic Surgery

Surgical Obstetrics & Gynecology

bipolar hip arthroplasty (BHA)

drain tip culture

revision total hip arthroplasty

surgical site infection

total hip arthroplasty (THA)

Surgical drains are inserted after total hip arthroplasty (THA) and bipolar hip arthroplasty (BHA) procedures to prevent the formation of a hematoma at the surgical site. Bacterial cultures from the tips of the drainage tubes are routinely performed after drain removal, but the efficacy of such drain tip cultures for detecting and diagnosing postoperative surgical site infection (SSI) remains unclear. SSIs are perioperatively diagnosed using samples taken from the synovial capsule. Although the incidence of SSI after hip arthroplasty is between 1-3%, the complications of SSIs associated with this procedure are often severe and require immediate intervention [1-3]. It is therefore important to evaluate the effectiveness of the diagnostic tools and protocols used to diagnose SSI after hip arthroplasty.

Several previous studies have documented specific correlations between the results of drain tip cultures and the incidence of SSIs after total knee arthroplasty and spinal surgery [4]. However, these studies only included a small number of patients and drain tip samples, and thus the likelihood of statistical errors was high. Petsatodis et al. [5] determined that a minimum of 1,000 cultures would be required for an accurate conclusion regarding the efficacy of drain tip cultures for diagnosing SSIs after hip arthroplasty. Because only one study to date has achieved such a large sample size, the efficacy of drain tip cultures remains controversial. Achieving a clear conclusion therefore requires increasing data availability while maintaining standard surgical procedures.

This study aimed to evaluate the effectiveness of drain tip cultures for predicting and diagnosing SSIs in patients who underwent hip arthroplasty, intending to obtain a large enough sample size for a robust and accurate assessment. To that end, we performed a retrospective analysis of drain tip cultures from 1,087 primary THA patients, 25 primary BHA patients, and 92 patients who underwent revision arthroplasties between 2005–2019 at Edogawa Hospital in Japan. To comprehensively evaluate the relationships between drain tip cultures and SSI diagnoses, we merged our data with data from three previous publications [5–7] and analyzed this combined data set. This approach allowed us to perform a more robust assessment of the prognostic value of drain tip cultures for the diagnosis of SSIs. Using our data, we tested the hypothesis that drain tip cultures are not an adequate predictor of SSI.

2.1 Literature search strategy, selection criteria, and generation of combined data set

We performed a literature search on MEDLINE, Pubmed, and grey literature to identify published reports from 1989 to 2020 that examined the use of drain tip cultures to predict SSIs after hip arthroplasty. The search keywords included "drain tip culture," "surgical site infection," and "hip." No language restrictions were applied. The search resulted in only one relevant study [6]. Following further hand searching, we identified six more studies directly relevant to our work. This literature review was conducted to understand past studies' conclusions and obtain additional patient data that could be combined with ours. When multiple articles for a single study had been published, we used the latest and supplemented it. Two independent reviewers evaluated each potentially relevant study (A.T and A.B) discrepancies were resolved by consensus and consultation with (R.I). From our analyses, we identified three studies [5-7] that met our selection criteria and merged our results with data from three other research groups [5–7] that used similar protocols to what we did to perform statistical analysis (Figure 1)— resulting in a total of 2,616 drain tip cultures after primary hip arthroplasty.

2.2 Participants and procedures

We performed a retrospective evaluation of findings from 1,112 of the 1,159 patients who underwent primary hip arthroplasty at our hospital over the past 15 years and 92 patients who underwent revision hip arthroplasty. Forty-seven cases that did not include records of drain tip cultures were eliminated from further consideration. Patients were between 25-94 years of age (average: 65.9 years) and included 232 males (20.8%) and 880 females (79.1%).　The primary indications for hip arthroplasty included osteoarthritis (895 cases, 80.5%), idiopathic necrosis of the femoral head (102 cases, 9.2%), and other conditions including rheumatoid arthritis and osteonecrosis (115 cases, 10.3%). 105 patients with diabetes, 462 patients with hypertension, and 654 patients with an abnormal body mass index (BMI) above 25 or below 18.5.

All surgical procedures were performed using either a posterior approach or an anterolateral supine approach by one of two surgeons using the same aseptic techniques. Specifically, we used the same asepsis protocol and antibiotic regimen in all cases, the same range of implant types and a standardized drain removal protocol to control for as many variables as possible. The asepsis protocol for these procedures included preoperative scrubbing with iodopovidone (Betadine) and draping. Cefazolin (1.0 g) and Amikacin (200 mg) were administered intravenously 30 min before surgery and then every 12 hours for three days after surgery. Cephalexin (250 mg) was taken orally four times a day for the subsequent seven days. Due to an abundance of high-risk patients such as an increased smoking population, diabetics, and geriatric patients, the standardized antibiotics protocol included an extended prophylaxis period. [8]

Surgical sites were cleaned with pulsed lavage both before and after implantation of the prosthesis. The fascia was closed using a standard closure technique. Before closure, the operative site was copiously irrigated with iodopovidone, which was also reapplied to the incision site using a sterile sponge. A 3mm diameter catheter was inserted under the fascia lata at the time of closure to promote drainage and infused with a solution of 10 mL 0.75% anapeine, 10 mL 10% tranexamic acid, and 40 mg gentamicin. Sterile technique was maintained through the insertion and removal of the catheter. The wound was covered using a water- and film-proof dressing with a transparent hydrogel pad. The closed suction drainage system clamped shut during surgery, was opened two hours after surgery to allow for adequate suction and was eventually removed 48 hours after surgery.

After removal, the catheter was cut approximately 2 cm from the tip and submitted to the laboratory for culturing. Catheter samples were submitted in a sterile spitz with saline and then centrifuged for 10 min at 3500 rpm. The supernatant was decanted after centrifugation and the sample was smeared onto chocolate agar (carbon dioxide culture), liquid agar (aerobic culture), blood agar (anaerobic culture), bromothymol blue agar (aerobic culture), and Gifu anaerobic semi-fluid medium. All cultures were incubated at 37°C for 24 hours. Samples with visible bacterial growth were then Gram-stained, and samples without visible growth were cultured for one extra day. Additional biochemical tests to identify specific bacterial species were performed on any culture that produced visible bacterial growth. Samples in which no bacterial growth was observed even after an additional day of culturing were considered negative for infection.

To validate the results from the tip cultures, surgical sites were inspected post-operatively for signs of SSI by a healthcare staff member according to guidelines from the Centers for Disease Control (CDC) [9].

We improved upon the CDC guidelines by diagnosing an SSI based on (1) the isolation of a bacterial pathogen in conjunction with (2) local pain or tenderness, swelling, redness, heat, and (3) elevated serum levels of C-reactive protein (CRP). In cases where the diagnosis remained unclear, we consulted multiple physicians and reached a collective decision, ensuring the diagnosis's reliability and decreasing the chance of a misdiagnosis.

Results from all patients in this 15-year study were compiled in Microsoft Excel® spreadsheets and analyzed for evidence that was part of our criteria. The language used in the spreadsheet was consistent across all patients and agreed upon by the research team and the inputting physician. We calculated the correlation between positive drain tip cultures and SSI diagnoses using a one-tailed Fisher's exact test with a confidence interval of 95% (i.e., the null hypothesis was rejected if p < 0.05). We also calculated the positive predictive value, which measures the effectiveness of a test at predicting a particular condition. In our case, we measured whether drain tip culture can accurately predict an SSI when it occurs. We therefore used the positive predictive value as an indicator for effectiveness, as our goal was to determine the prognostic value of positive drain tip cultures for the diagnosis of SSI.

Of the 1,112 patients who underwent primary hip arthroplasty at Edogawa Hospital from 2005-2019, twelve patients had positive drain tip cultures (Table 1) and eight patients (0.72%) were suspected of having a postoperative SSI. However, only one SSI case was associated with a positive drain tip culture. Of the seven SSI cases with negative tip culture results, four (0.36%) required washing and surgical debridement. All eight SSI cases were diagnosed as superficial. Based on these results, the sensitivity of drain tip culture for postoperative SSI was 12.5% and the specificity was 99.0%, with a positive predictive value of 8.3% and a negative predictive value of 99.4%. A Fisher's exact test performed on this data showed no statistically significant correlation between drain tip culture results and the onset of an SSI (p = 0.0834).

In the single case of suspected SSI with a positive drain tip culture, the drain tip culture was positive for methicillin-resistant S. epidermidis. The other 11 patients with false-positive drain tip cultures had no symptoms or indications of SSI, and their drain tip cultures were positive for bacteria that are part of the native skin flora, which may not result in infection. The bacterial strains detected in these false-positive drain tip cultures included Staphylococcus epidermidis (n = 3), S. cohnii (n = 2), and Escherichia coli (n = 2; Table 2).

In addition to obtaining samples from patients undergoing primary hip arthroplasties, we also performed drain tip cultures in 92 patients who underwent revision hip arthroplasties. Neither of the two patients with positive drain tip cultures was diagnosed with an SSI (Table 3), resulting in a drain tip culture sensitivity of 0.0%, a specificity of 97.8%, a positive predictive value of 0.0%, and a negative predictive value of 96.7%. Overall, there was no statistically significant correlation between the results of drain tip culture and the incidence of SSI in patients that underwent revision hip arthroplasties (One-tailed Fisher's exact test, p = 0.936). However, due to the modest sample size, Fisher's exact test may not provide a decisive conclusion regarding the effectiveness of tip culture for predicting SSI in these patients. The two positive drain tip cultures were positive for E. coli and Burkholderia cepacia, respectively (Table 4). These false-positive results suggest that detecting these bacteria, which are components of the normal skin flora, may not indicate infection.

To improve the robustness of our statistical conclusions, we combined our data for primary hip arthroplasties with the results from three other research groups [5–7] for a total of 2,646 drain tip cultures. Despite this larger sample size, we still found no correlation between positive drain tip cultures and the incidence of SSIs (p = 0.128). In this more extensive data set, drain tip culture had a sensitivity of 8.3%, specificity of 98.9%, positive predictive value of 3.3%, and negative predictive value of 99.6% (Table 5). To determine whether preexisting patient factors affected the chance of developing SSI, we also evaluated the incidence of SSI with various patient characteristics including age, gender, hypertension, diabetes, steroid use, and BMI (Table 6). However, none of these factors significantly correlated with developing an SSI.

There has been much recent debate on the utility of drain tip cultures for predicting and diagnosing postoperative SSIs. Studies published before 2004 concluded that drain tip culture results were positively correlated with SSI diagnoses in cases of total hip arthroplasty. However, these studies all had small sample sizes (approximately 100 patients), making the conclusions of these retrospective analyses controversial, as small sample sizes can sometimes lead to fallacious results.

Our study, which included 1,112 patients who underwent primary hip arthroplasty, agrees with previous studies that do not support using routine drain tip culture after hip replacement to diagnose postoperative infection [5, 6, 10]. The incidence of SSI in our study aligns with international reported literature. To bolster our conclusions about the overall prognostic value of drain tip cultures, we additionally analyzed a larger data set that combined our data from patients who underwent primary total hip arthroplasty with data from three previously published studies with similar protocols [5–7] (Table 7). Even in this sample of 2,646 cultures, we still found no correlation between positive cultures and the incidence of SSIs. The low positive predictive value (3.3%) suggests that the prognostic value of drain tip cultures is minimal, the likelihood of false-negative results is high, and, overall, that it is ineffective for predicting or diagnosing an SSI in postoperative patients.

The false-positive results in the combined data could result from contamination during drain tip removal, transport, or culturing. Drain tip contamination has not been emphasized in other studies; however, based on the type of bacteria we found and the lack of clinical findings indicative of an infection, we suggest that drain tip contamination is a possible cause of false-positive culture results. Relying on the results of drain tip cultures could lead to the unnecessary use of antibiotics, thus increasing the risk of side effects and healthcare costs. Skin flora contamination is may have contributed to findings reported in all similar studies published to date [11, 12]. The length of time that the drain remains in the operative site could also affect the likelihood of developing an SSI and the risk of skin flora contamination of the drain tip culture [13]. It is therefore essential to standardize the time the drain is removed.

We also evaluated the incidence of SSI with patient age, gender, BMI, and history of hypertension, diabetes, and steroid use. Age, gender, and the tested comorbidities were not statistically significantly correlated with the development of SSI. Understanding the relationships between patient comorbidities and the incidence of SSI may allow for patient-specific SSI screening procedures to be introduced which may prove better than drain tip cultures .

There are limitations associated with all the studies considered here, including the present study:

All studies were retrospective, although in our case, using a standard and uniform clinical protocol throughout the study period mitigated potential confounds associated with variation among surgeons or procedures.
All SSIs diagnosed in patients undergoing primary hip arthroplasty were superficial, meaning that the infection only involved the skin or subcutaneous tissue and did not extend down to the muscle, fascia, or organ space. We identified only one case of deep tissue infection in a patient who underwent revision hip arthroplasty. Therefore, our results are unclear whether drain tip cultures effectively predict deep tissue or organ/space SSIs.
We recognize that it is difficult to compare across studies because of variations in postoperative antibiotic protocols, asepsis techniques, implant types, and surgical approaches.

Other problems include the lack of universal guidelines for diagnosing and preventing SSIs and the additional expense of drain tip cultures, which may act as a barrier to their clinical use [14]. In addition, given the low incidence of SSI associated with hip arthroplasty procedures, an ideal study would include a substantially larger patient cohort in which many patients tested positive for SSI.

Because drain tip cultures are also routinely used in spinal procedures and knee arthroplasty, continuing to evaluate the effectiveness of drain tip cultures is vital for the broader field of orthopaedic surgery. Although Enhanced Recovery After Surgery (ERAS) protocol is increasingly being adopted, many hospitals remain to use closed suction drainage catheters following hip arthroplasty [15]. Hospitals within Japan and other countries remain to utilize drain tip cultures as a diagnostic tool to detect SSI; however, based on the results of our study as well as a systematic review of the existing literature, drain tip cultures do not have a high enough positive predictive value to be used as an effective diagnostic tool.

Given the present studies and the general lack of statistical support for the routine use of drain tip cultures, other diagnostic tools should be explored as potential alternatives. Such tools may include screening for hematoma, as previous studies have observed a correlation between the incidence of hematoma and SSIs, or diagnostic tools such as physical examination [16].

Funding. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authorship. All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship for this article, take responsibility for the integrity of the work as a whole, and have given their approval for this version to be published.

Editorial assistance. The authors would like to thank Medical Journal Editors (MJE) for assistance with the editing of our manuscript. This assistance was funded privately by the authors.

Disclosures. The authors declare that they have no conflicts of interest with respect to the work presented herein.

Compliance with ethics guidelines. This study was approved by the review board at Edogawa Hospital and was performed in accordance with the Helsinki Declaration. All study participants provided informed consent prior to being enrolled in the study.

Data availability. The datasets generated and/or analyzed during the current study are not publicly available due to the presence of confidential patient information within the data.

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Table 1 Correlation between postoperative SSI and the incidence of positive drain tip cultures from patients who underwent primary hip arthroplasty from 2005 to 2019. The p-value was 0.0834, indicating that there was no statistically significant correlation.

	Number of patients with SSIs*	Number of patients without SSIs
Positive cultures	1	11
Negative cultures	7	1093
Total	8	1104

*All SSIs diagnosed in this patient cohort were superficial in nature.

Table 2 Species identified in drain tip cultures from patients who underwent primary hip arthroplasty at Edogawa Hospital from 2005 to 2019.

Bacteria	Number of culture-positive drain tips (total n = 12)*
Staphylococcus epidermidis	3
Staphylococcus cohnii	2
Escherichia coli	2
Staphylococcus haemolyticus	1
Acinetobacter lwoffi	1
Methicillin-susceptible S. aureus	1
Enterobacter cloacae	1
Methicillin-resistant S. epidermidis	1
Fungi	1

* One patient returned to 2 bacteria in their culture result.

Table 3 Correlation between postoperative SSI and the incidence of positive drain tip cultures who underwent revision hip arthroplasty from 2005 to 2019. The p-value was 0.936, indicating that there was no statistically significant correlation.

	Number of patients with SSIs*	Number of patients without SSIs
Positive cultures	0	2
Negative cultures	3	87
Total	3	89

* One case of SSI after revision arthroplasty was deep in nature.

Table 4 Bacteria identified in drain tip cultures from patients who underwent revision hip arthroplasty at Edogawa Hospital from 2005 to 2019.

Isolated Bacteria	Number of culture-positive drain tips (total n = 2)
Escherichia coli	1
Burkholderia cepacia	1

Table 5 Statistical evaluation of the use of drain tip cultures to predict SSIs after primary or revision hip arthroplasty data in patients from the present study as well as in combination with data from three previous studies [5–7].

Outcomes	Primary arthroplasty (N = 1112 patients)	Revision arthroplasty (N = 92 patients)	Primary arthroplasty; merged data* (N = 2616)
Sensitivity	12.5%	0.0%	8.3%
Specificity	99.0%	97.8%	98.9%
Positive Predictive Value	8.3%	0.0%	3.3%
Negative Predictive Value	99.4%	96.7%	99.6%
P-Value	0.0834	0.936	0.128

* Results in this column were calculated from a data set that included our data and data from three previous studies that addressed drain tip cultures in primary hip arthroplasty [5–7].

Table 6 Incidence of positive drain tip cultures in relation to patient characteristics and pre-existing conditions. No statistically significant correlations were observed.

		SSI	No-SSI	P-Value
Gender	Male	3	229	0.2223
Gender	Female	5	875	0.2223
Age	Above 65	4	588	0.5143
Age	Under 65	4	473	0.5143
Hypertension	Hypertensive	4	458	0.4188
Hypertension	Non-hypertensive	4	673	0.4188
Diabetes	Diabetic	1	104	0.5583
Diabetes	Non-Diabetic	7	973	0.5583
BMI	Normal BMI	4	476	0.4603
BMI	Abnormal BMI	4	650	0.4603
Steroid Use	Steroid User	0	21	0.8558
Steroid Use	Non-steroid User	8	1064	0.8558

Table 7 Diagnosis of postoperative SSI vs. the number of positive drain tip cultures among patients who underwent primary hip arthroplasty. Data presented here are combined with findings from three previous studies [5–7]. The p-value was 0.128, indicating that there was no statistically significant correlation.

	Number of patients with SSIs*	Number of patients without SSIs
Positive culture	1	29
Negative culture	11	2605
Total	12	2634

*All SSIs in this patient cohort were superficial in nature.

How effective are drain tip cultures at predicting surgical site infections after hip arthroplasty?

Status:

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Abstract

Figures

Introduction

Materials And Methods

Results

Discussion

Declarations

References

Tables

Status:

Version 2