Abstract
Purpose
Infections and deep vein thrombosis (DVT) after total hip arthroplasty (THA) are challenging problems for both the patient and surgeon. Previous studies have identified numerous risk factors for infections and DVT after THA but have often been limited by sample size. We aimed to evaluate the effect of operative time on early postoperative infection as well as DVT rates following THA. We hypothesized that an increase in operative time would result in increased odds of acquiring an infection as well as a DVT.
Methods
We conducted a retrospective analysis of prospectively collected data using the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database from 2006 to 2015 for all patients undergoing primary THA. Associations between operative time and infection or DVT were evaluated with multivariable logistic regressions controlling for demographics and several known risks factors for infection. Three different types of infections were evaluated: 1) superficial surgical site infection (SSI), an infection involving the skin or subcutaneous tissue, 2) deep SSI, an infection involving the muscle or fascial layers beneath the subcutaneous tissue, and 3) organ/space infection, an infection involving any part of the anatomy manipulated during surgery other than the incisional components.
Results
In total, 103,044 patients who underwent THA were included in our study. Our results suggested a significant association between superficial SSIs and operative time. Specifically, the adjusted odds of suffering a superficial SSI increased by 6% (CI=1.04–1.08, p<0.0001) for every 10-minute increase of operative time. When using dichotomized operative time (<90 minutes or >90 minutes), the adjusted odds of suffering a superficial SSI was 56% higher for patients with prolonged operative time (CI=1.05–2.32, p=0.0277). The adjusted odds of suffering a deep SSI increased by 7% for every 10-minute increase in operative time (CI=1.01–1.14, p=0.0335). No significant associations were detected between organ/space infection, wound dehiscence, or DVT and operative time either as continuous or as dichotomized.
Conclusion
Prolonged operative times (>90 min) are associated with increased rates of superficial SSIs, but not deep SSIs, organ/space infections, wound dehiscence, or DVT.
Level of Evidence
III
Keywords: Total hip arthroplasty, operative time, infection
Introduction
As the growing population continues to age, the number total hip arthroplasties (THA) performed is also expected to increase [1]. With more joint replacements performed, there will likely be a proportional increase in the absolute number of complications.
Common complications following THA include aseptic loosening, periprosthetic fracture, dislocation, and infection. Infection, in particular, can be a challenging problem for the surgeon to face. Superficial surgical site infection rates in THA range anywhere from 1.4% to 4.4%, with deep surgical site infection rates ranging from 0.4% to 2.2% [2]. Previous studies have identified multiple risk factors for infection including age, male gender, obesity, lower socioeconomic status, lack of antibiotic prophylaxis, poor skin preparation, metal on metal hips, bilateral procedures, history of methicillin resistant staphylococcus aureus colonization (MRSA), and prolonged hospital stay [3–10].
Another proposed risk factor is length of surgery. The vast majority of evidence has indicated that prolonged surgeries are likely to increase the risk of infection [3–12] while a few have found no relationship between length of surgery and infection [13, 14]. This discrepancy could be attributed to relatively small patient cohorts, variations in surgical protocols between individual institutions, or data collected from precarious health care systems.
The American College of Surgeons National Surgical Improvement Program (ACS NSQIP) database is a unique resource in which surgical outcome data is prospectively collected from hundreds of institutions. This allows researchers to evaluate thousands of patients at a time. Although the association between operative time and infection or deep vein thrombosis (DVT) has been studied previously, to our knowledge, this is the largest database study evaluating these complications after primary THA. The purpose of this study was to determine if operation time in primary THA has any correlation with infection, wound dehiscence, and deep vein thrombosis. We hypothesized that there would be an increase in each of these complications with prolonged surgical times.
Methods and Materials
The ACS NSQIP database used in this study contains publicly available de-identified patient data, thereby exempting this study from Institutional Review Board approval. This database contains protected data from patients undergoing major surgical procedures from hundreds of participating institutions. Patient data including demographics, preoperative risk factors, intraoperative variables, and 30-day postoperative outcomes are collected by trained surgical clinical reviewers at each participating institution [15].
The NSQIP database was queried for patients who underwent primary THA from 2006 to 2015 using the Current Procedural Terminology (CPT) code 27130 for primary total hip arthroplasty. Three different classifications of infections, as well as wound dehiscence and DVT, were evaluated with respect to operative time. The types of infections included superficial surgical site infection, deep surgical site infection, and organ/space infection.
Superficial surgical site infection (SSI) is defined by NSQIP as an infection involving only skin or subcutaneous tissue of the incision. Deep surgical site infection is defined as an infection involving the muscle and fascial layers deep to the skin and subcutaneous tissue. Last, organ/space infection (OSI) is defined by NSQIP as an infection that involves any part of the anatomy that was manipulated during an operation other than the incisional components (skin, subcutaneous tissue, muscle, and fascial layers).
Furthermore, to be classified as one of the aforementioned infections, at least one of the following criteria must be satisfied [15, 16]:
The presence of purulent drainage from a drain that is placed through a stab wound.
Organisms isolated from an aseptically obtained culture of fluid or tissue.
Presence of an abscess or other evidence of infection that is found on direct examination, during reoperation, or by histopathologic or radiologic examination.
Formal diagnosis of an infection by a surgeon or attending physician.
Patients’ demographics, comorbidities and operative variables were summarized as mean ± standard deviation (SD) for continuous variables and frequency (proportion) for categorical variables. The demographics included age, gender, body mass index (BMI), steroid intake, and smoking status. The comorbidities included preoperative hematocrit, dialysis status, and previous diagnosis of diabetes mellitus. These comorbidities have been proven to be associated with infections or DVT after joint replacement [3–10]. The operative variables included length of surgery (minutes), infections (superficial, deep, and OSI), wound dehiscence, and DVT. The association between infections/DVT and operative time were evaluated with multivariable logistic regressions controlling for patient demographics and comorbidities. The adjusted odds ratio and its 95% confidence interval were presented to indicate the strength of association. The operative time was initially analyzed as continuous variable and then dichotomized as prolonged operative time (≥90min) and normal (<90min). Due to its close proximity to the mean length of surgery of our patient cohort, we chose 90 minutes as a cutoff for prolonged operative time. Only cases with operative times greater than 25 minutes and less than 300 minutes were included in our final analysis to avoid potential transcription errors; however, all the cases with valid operative time were included in the sensitivity analysis. All statistical analysis was performed using SAS 9.4 (Cary, NC). The level of significance level was set as p < 0.05.
Results
In total, 103,044 patients with operative time ranging from 25 minutes to 300 minutes were identified as our study cohort, including 46,032 (44.7%) men and 57,012 (55.3%) women. Patients’ demographics, comorbidities and surgery related complications are summarized in Table 1. The average time of surgery was 94 minutes. The average age of the patients undergoing surgery was 65 years old and the average BMI of the study cohort was 30.1 kg/m2. The comorbidities included 3,846 (3.7%) patients on steroids at the time of surgery, 11,990 (11.6%) patients on medicine for diabetes at the time of the surgery, 13,800 (13.4%) patients with a history of smoking within one year, and 266 (0.3%) patients on dialysis pre-operatively. Of the 103,044 cases, there were 722 superficial surgical site infections (0.7%), 325 (0.3%) deep surgical site infections, and 233 (0.2%) organ/space infections recorded. Wound dehiscence was recorded in 118 (0.1%) of cases. There were 438 (0.4%) DVTs noted in the patient population.
Table 1:
Summary statistics of study cohort.
| Demographic Information | (N) |
|---|---|
| Male | 46,032 (44.7%) |
| Female | 57,012 (55.4%) |
| Mean BMI (kg/m2) | 30.1 ± 6.3 |
| Mean Age at Surgery (Years) | 65.0 ± 11.8 |
| Mean Operative Time (Minutes) | 93.6 ± 36.8 |
| Mean Pre-op Hematocrit (Percent) | 40.7 ± 4.3 |
| Comorbidities | |
| Steroid Use for Chronic Condition | 3,846 (3.7%) |
| Diabetes Mellitus | 11,990 (11.6%) |
| Current Smoker | 13,800 (13.4 %) |
| Currently on Dialysis Pre-operatively | 266 (0.3%) |
| Complications | |
| Superficial Surgical Site Infections | 722 (0.7%) |
| Deep Surgical Site Infections | 325 (0.3%) |
| Organ/Space Infections | 233 (0.2%) |
| Wound Dehiscence | 118 (0.1%) |
| Deep Vein Thrombosis | 438 (0.4%) |
Our results suggested a significant association between superficial surgical site infections and operative time. Specifically, the adjusted odds of suffering a superficial surgical site infection increased by 6% (CI=1.04–1.08, p<0.0001) for every 10-minute increase of operative time. When using dichotomized operative time, the adjusted odds of suffering a superficial surgical site infection was 56% (CI=1.05–2.32, p=0.0277) higher for patients with prolonged operative times greater than 90 minutes. In addition, the adjusted odds of suffering a deep surgical site infection increased by 7% for every 10-minute increase in operative time (CI=1.01–1.14, p=0.0335); however, such association was not significant when using dichotomized operative time (adjusted-OR=1.50, p=0.1848). No significant associations were detected between organ/space infection, wound dehiscence, or DVT and operative time either as continuous or as dichotomized (Table 2). To evaluate whether excluding cases affect the results, we conducted a sensitivity analysis on all cases with valid operative times. The results were similar (data not shown).
Table 2.
Adjusted odds ratios between complications and operative time.
| Complications | 10 min increase in operative time | Prolonged operative time (>90 min) | ||
|---|---|---|---|---|
| Odds Ratio | P-value | Odds Ratio | P-value | |
| Superficial Surgical Site Infections | 1.06 (1.04, 1.08) | <0.0001 | 1.56 (1.05, 2.32) | 0.0277 |
| Deep Surgical Site Infection | 1.07 (1.01, 1.14) | 0.0335 | 1.50 (0.82, 2.73) | 0.1848 |
| Organ/Space Infection | 1.08 (0.99, 1.18) | 0.0704 | 1.68 (0.73, 3.86) | 0.2207 |
| Wound Dehiscence | 1.07 (0.97, 1.19) | 0.1800 | 1.39 (0.49, 3.96) | 0.5395 |
| DVT | 1.04 (0.98, 1.10) | 0.1718 | 0.81 (0.50, 1.34) | 0.4170 |
Discussion
The main finding of this study is a significant association between operative time and superficial surgical site infections. Specifically, the odds of a superficial surgical site infection increased by 6% for every 10 minutes of operative time, and the odds of suffering a superficial surgical site infection was 56% higher in patients with operative times greater than 90 minutes. Additionally, the odds of suffering a deep surgical site infection increased by 7% for every 10-minute increase in operative time. There was no significant association between operative time and DVT or wound dehiscence.
Risk factors for prosthetic infections have been widely investigated and well established in the orthopedic literature. For example, one study found that male gender, avascular necrosis, use of dual mobility cups, and a Rottinger anterolateral approach were all associated with increased odds of infection in primary total hip arthroplasty [17]. Ricciardi et al. reviewed 30-day readmission rates in 21,864 arthroplasties performed at their facility. They found that patients with longer procedure or tourniquet times who underwent either TKA or THA were more likely to be readmitted within 30 days [18]. Pulido et al. reviewed 9,245 patients between 2001 and 2006 who underwent total joint arthroplasty and found a significant increase in rates of infection with longer operative times in patients undergoing either TKA or THA [19]. A recent study by Duchman et al. also showed that operative times greater than 120 minutes in THA and TKA were associated with a significant increase in wound complications and infections [20].
There have been several more studies that focused specifically on hip arthroplasty data. Cordero-Ampuero et al. retrospectively reviewed 47 patients from their center diagnosed with a late infection following THA or hemiarthroplasty and compared these patients to 200 randomly selected patients that did not develop an infection [6]. They found that patients who developed late infections tended to have longer operative times than those without infection [6]. Ridgeway et al. studied 16,291 patients undergoing primary THA to identify risks factors for surgical site infection using the Surgical Site Infection Surveillance Service out of England [7]. Procedures that lasted over 120 minutes were associated with increased rates of surgical site infection [7]. Ong et al. identified 887 patients with prosthetic joint infections out of 39,929 patients undergoing primary THA from the Medicare national sample database from 1997–2006 [5]. Procedures lasting longer than 210 minutes had a significantly higher risk of infection compared to procedures lasting less than 120 minutes [5]. Maoz et al. looked at 3672 primary THAs and 406 revision THAs at a single hospital and identified surgical time as a modifiable risk for infection [8].
While the majority of studies have identified prolonged surgical times as a risk factor for infection, not all have. Hamilton et al. reviewed the 30-year data of 1993 THAs performed by a single surgeon [13]. In the cases that developed infection, the average surgical time was 114.9 minutes whereas in those without infection it was 111.2 minutes. They did not find a significant difference between these times.
Our study builds upon the previous literature and suggests that prolonged surgical time increases the risk of developing an early superficial surgical site infection. To our knowledge, this is the largest study performed to evaluate length of surgery on infection rates and to use a national database to eliminate single institution bias. Deep surgical site infection, organ/space infection, wound dehiscence, and DVT trended towards significance with prolonged surgical times, but ultimately were not significant. However, the odds of suffering a deep surgical site infection did increase with every 10 minutes of operative time. Higher infection rates with prolonged surgery may be associated with increased time of exposure to the environment, larger incisions from more complex surgeries, and higher amounts of soft tissue injury [7]. Further studies are required to help elucidate whether the length of the surgery itself or increased soft tissue injury from more complex surgeries is the cause of the higher infection rates.
Even though a large database was used, this study is not without limitations. Our study results demonstrated higher mean operative time than previous studies, which may indicate a disproportionally higher number of less experienced surgeons included in the database. Additionally, the infection rate identified in our study was lower than in previous literature [5], which may be attributable to our limited post-operative detection period. Although many risk factors have been reported in the literature, not all of them are included in this database. Therefore, some known and unknown confounders could not be controlled in our analysis such as surgeon experience and operative technique. Another important factor that we were unable to assess or control for was specific measures taken to decrease the risk of contamination. For example, it has been shown in the literature that increasing the number of times gloves are changed during a THA can reduce the risk of contamination or perforation [21]. Other confounding factors that limit our study are differences in individual skin preparation, MRSA colonization protocol, and proper administration of antibiotic prophylaxis. Nevertheless, compared to studies with small samples, our results from such large data could be more accurate and reliable.
Given that our study adds to a growing body of literature regarding operative time and infection, the potential impact of our research on the orthopedic community is an increased awareness of this relationship. Knowledge of this association by surgeons combined with further research efforts to understand this relationship may eventually contribute to a decreased rate of infection for patients undergoing total hip arthroplasty. Surgical operative time should be taken into consideration to aid in the future prevention of prosthetic hip infection.
Acknowledgements
Funding: This research was supported in part by the National Institute of Health (NIH) grant number UL1TR001417.
Footnotes
Conflict of Interest: The authors declare that they have no conflicts of interest to disclose.
Ethical Approval: All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. As this study was retrospective, formal consent was not required.
ACS NSQIP Disclaimer: The American College of Surgeons National Surgical Quality Improvement Program and the hospitals participating in the ACS NSQIP are the source of the data used herein; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors.
Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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