Incidence and risk factors for surgical infection after total knee replacement

Scandinavian Journal of Infectious Diseases, 2007; 39: 890 895 ORIGINAL ARTICLE Incidence and risk factors for surgical infection after total knee replacement YURI BABKIN 1,2, DAVID RAVEH 1, MOSHE LIFSCHITZ 2, MENACHEM ITZCHAKI 2, YONIT WIENER-WELL 1, PUAH KOPUIT 1, ZIONA JERASSY 1 & AMOS M. YINNON 1,3 From the 1 Infectious Disease Unit and 2 Department of Orthopaedics, Shaare Zedek Medical Centre, affiliated with the Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, and the 3 Hadassah-Hebrew University Medical School, Jerusalem, Israel Abstract Surgical site infection (SSI) after total knee replacement (TKR) is a devastating complication. We performed a retrospective study of all consecutive TKRs performed during a 2-y period. Surgical site infection (SSI) was defined by standard criteria. All patients were examined 1 y following surgery. Of 180 patients undergoing TKR, 10 (5.6%) developed a superficial (3, 1.7%) or deep (7, 3.9%) SSI. Two independent risk factors for SSI were detected: left knees became infected more often (9/ 92, 9.8%) than right knees (1/88, 1.1%) (Relative Risk 6.7995% CI 1.726.8); and 7/72 (9.7%) patients receiving a type-1 prosthesis developed infection versus 3/104 (3.1%) receiving a type-2 prosthesis (RR 4.7, 95% CI 1.1818.4). Investigation of the operating room revealed 3 problems: there was significant traffic through the door on the left of the patient; a nonstandard horizontal-flow air conditioner had been installed above that door; a tool-washing sink was in use on the other side of that door. Infection control guidelines were rehearsed: the sink was removed, the air conditioner was disconnected, and the door was locked. In a prospective survey performed 2 y later only 1/45 patients (2.2%) undergoing TKR developed a superficial SSI (p0.5). Correction of independent risk factors for infection following TKR led to a decrease in SSI rate. Introduction Hospital acquired infections in general are a challenging problem in all health care systems. They require broad-spectrum antibiotic treatment, lead to additional suffering and prolonged hospitalization and increased mortality. Most of the patients admitted to orthopaedic departments undergo surgical treatment, which usually includes internal fixations and prostheses. An infected foreign body often requires removal in a second operation, prolonged immobilization and antibiotic treatment and a subsequent third operation. Therefore, preventing infections in operations where foreign bodies are inserted is of paramount importance [1 5]. Periodic self-assessment to determine the wound infection rate and associated risk factors is a crucial part of the ongoing efforts to improve outcome. During the y 2000, we conducted a 3-month prospective survey to evaluate the rate of infections among 203 consecutive orthopaedic operations. The overall rate was similar to published data, but somewhat higher in total knee replacements (TKR). However, the number of patients (21) who underwent this type of operation was too small to draw conclusions. A prospective study would have been the most reliable method of investigation, but timeand labour-intensive, and we sought quick answers to a possible problem. We therefore conducted a retrospective review of all patients undergoing TKR during a 2-y period (1999 2000) in order to determine the infection rate and to detect associated risk factors. Methods Shaare Zedek Medical Centre is a 550-bed, university-affiliated general hospital, Jerusalem s second largest, which also includes a department of orthopaedic surgery. One specific operating room is Correspondence: A.M. Yinnon, Infectious Disease Unit, Shaare Zedek Medical Centre, P.O. Box 3235, Jerusalem 91031, Israel. Tel: 972 2 6555076. Fax: 972 2 6666840. E-mail: Yinnon@SZMC.org.il (Received 3 August 2006; accepted 5 April 2007) ISSN 0036-5548 print/issn 1651-1980 online # 2007 Taylor & Francis DOI: 10.1080/00365540701387056

Surgical site infection after total knee replacement 891 designated for all orthopaedic procedures, including elective and urgent patients. Thus, bacterial crosscontamination from other surgical or medical specialities is practically eliminated. The operating room volume is 144 m 3 and is ventilated by a conventional air-conditioning system without laminar airflow. 100% fresh air, pre-filtered by high-efficiency particulate apparatus (HEPA) filter of 95% efficiency enters the room through 6 diffusers located on the ceiling, delivering 3800 m 3 per h. Air is exhausted at a rate of 1900 m 3 per h through 4 registers located low on the walls. A positive pressure gradient is thus maintained in the operating room, relative to the pressure in the corridors of the operating wing. 26 complete air changes per h are provided. We reviewed the charts of all consecutive patients who underwent total knee replacement (TKR) during 2 y (1999 2000), and retrieved the following information: 1) pre-operative factors, including age, gender, underlying diseases and comorbidities, medications, American Society of Anesthesiologists (ASA) score, status of the knee joint (previous operations or infections), and indication for total knee replacement; 2) intra-operative factors, including name and seniority of the operating surgeon, those of surgical assistants, anaesthesiologists and nurses, side of surgery, the surgeon s position to the right or left of the patient, right- or left-handedness of the surgeon, size and type of prosthesis, duration of surgery and usage of tourniquet; 3) post-operative factors, including use of a closed-suction drainage system and the drainage volume, range of motion achieved at discharge from the hospital, any concomitant infection other then surgical site infection (SSI), presence or absence of redness, swelling or secretion from the wound and its duration, positive cultures obtained from the joint, body temperature, white blood count, sedimentation rate, C-reactive protein, plasma biochemistry results, each before and after operation until discharge from hospital. The minimal follow-up was 1 y after the operation: the patients hospital and outpatient clinics charts were reviewed and, if detailed documentation was lacking regarding 1-y follow-up, the patient was called and invited for a subsequent clinic visit. Our hospital s orthopaedic team also staffs the ambulatory clinics of the city s Kupat Cholim Health Maintenance Organization. Therefore, complete 1-y follow-up could be achieved. We used the case definition criteria for surgical site infection (SSI) as published by the Centers for Disease Control (CDC) because of their widespread acceptance and reproducibility [6]. Cases consisted of patients diagnosed with superficial, deep or organspace SSI within 1 y of the procedure. Briefly, superficial SSI involves only skin and subcutaneous tissue; deep SSI involves fascial and muscle layers; and organ/space SSI involves any part of the anatomy other than the incision, opened or manipulated during the operative procedure. SSI must meet at least 1 of the following criteria: the infection occurred within 30 d (superficial incisional SSI) or within 1 y after the operation; an organism was isolated from an aseptically obtained culture of fluid or tissue from the incision, deliberately opened by the surgeon; an abscess or other evidence of infection was detected on direct examination, during reoperation, or by histopathological or radiographic examination; or SSI was diagnosed by a surgeon or attending physician. Controls consisted of the remainder of the patients. Results of the described retrospective analysis led to a careful epidemiological investigation of the single operating room where all orthopaedic surgery is performed. Detected problems were amended, as subsequently described. In 2004, 1.5 y after these improvements were made, a small prospective survey of 45 consecutive patients undergoing TKR was conducted, employing the same methods and definitions as described for the retrospective study, including the 1-y follow-up requirement for diagnosis of surgical site infection. Results of the 2 surveys were compared. The conduct of these surveys was considered routine epidemiological practice; however, approval was sought and received from the hospital s internal review board (Helsinki Committee). Data were entered, processed and analysed using Epi Info 6.04d software (CDC, Atlanta, USA). Proportions were compared using the x 2 or 2-tailed Fisher s exact test, where appropriate. Continuous variables were compared by the Student s t-test. All p-values were 2-tailed, and a p-value of B0.05 was considered statistically significant. Logistic regression analysis was performed using EpiInfo 2000 (CDC, Atlanta, USA) and SPSS version 10.0, to identify factors independently associated with the development of infection following total knee arthroplasty. We included in the logistic regression models selected variables having p values B0.08 in the bivariate analysis, as well as several central variables regardless of their p-value. Results During the y 1999 and 2000, 181 consecutive total knee arthroplasties (TKR) were performed. None of the patients received an operation of both knees during the study period. The preoperative factors are shown in Table I. All patients were admitted to the department on the d of the surgery. Each patient received preoperative antimicrobial prophylaxis (i.e.

892 Y. Babkin et al. Table I. Demographic and clinical characteristics of 180 patients who underwent total knee replacement (TKR) during a 2-y period (19992000). Characteristics n (%) Gender: Male 61 (34) Female 119 (66) Age, in y9sd (range) 72.497.4 (4194) Comorbid factors: Ischaemic heart disease 41 (23) Congestive heart failure 18 (10) Chronic lung disease 32 (18) Diabetes mellitus 37 (21) Obesity 34 (19) First versus repeat knee surgery: First 158 (88) Repeat 22 (12) Indications for TKR: Osteoarthritis 162 (90) Rheumatoid arthritis 5 (3) Avascular necrosis 2 (1) Psoriatic arthritis 1 (1) Aseptic loosening 5 (3) Infected loosening 5 (3) Pre-operative ASA score* 02 158 (94) 35 11 (6) Total NNIS index* 0 128 (80) 1 25 (15) 2 6 (4) 3 2 (1) Pre-operative glucose, in mg/dl (range) 118938 (58 304) Operative factors: Drain volume, in ml9sd 4429295 Duration, in h9sd (range) 1.790.6 (15.2) Prolonged operation 15 (9%) Post-surgical factors: Any infection, except SSI: 31 (17) Bacteraemia/sepsis 3 (2) Pneumonia 3 (2) Urinary tract infection 25 (14) One-y follow-up Outpatient clinic 150 (83) Telephone callvisit 30 (17) TKR: total knee replacement; SSI: surgical site infection. *Data were not available for all patients. within 1 h prior to surgery) with cefonicid or, in case of penicillin allergy, vancomycin. Early range-ofmotion exercises and early ambulation were the standard treatment protocol. The minimal followup was 1 y. Detailed follow-up information was attained for all 181 patients. Applying the CDC case-definition criteria for SSI, we detected 3 superficial wound infections and 7 organ-space infections. All 7 deep infections were confirmed during the revision operation, as in all of the cases there were clear signs of infection and positive cultures. Five patients were treated with 1-stage debridement, while 2 patients were treated by exchange revision 2-stage arthroplasty. In 1 additional case (0.6%), a diagnostic tap was made because of persistent pain and swelling 3 months after the operation, out of which coagulase-negative Staphylococcus was isolated. The patient was treated with oral antibiotics and further follow-up was uneventful. This patient did not meet the CDC case definition of a SSI; however, because of uncertainty regarding the local findings, it was decided to exclude this patient from further analysis. The analysed study group therefore consisted of 180 patients, of whom 10 (5.6%) developed infection 3(1.7%) superficial and 7 (3.9%) organspace infections. Table II shows the factors that were significantly associated with SSI. Two risk factors were independently associated with SSI on multivariate analysis: first, left knees were infected 4 times more often than right knees and, second, use of the Johnson & Johnson prosthesis was associated with infection 4 times more often than that of the Biomet prosthesis. In addition, if the first surgeon was positioned on the left side of the operated patient, there was an increase in the infection rate. Finally, as the number of surgeons and/or anaesthesiologists increased, the rate of wound infection was also higher. However, the latter factors closely approached but did not reach statistical significance. 100% of patients received antibiotic prophylaxis, consisting of 1 dose of 1 g cefonicid, provided within 1 h prior to surgery. Exact timing of prophylaxis was recorded in a minority of patients only, but was observed in a previous study and found to be given at the appropriate time in 100% of patients [7]. Use of tourniquet, suction drainage and peri-operative use of low molecular weight heparin (enoxapirin) was recorded for all patients, i.e. for all those with and without subsequent SSI. A relatively higher preoperative leukocyte count was associated with a higher rate of SSI upon bivariate analysis (p0.056), as was a past history of a cerebrovascular accident or cellulitis involving the operated leg (p B0.05); none of these factors was found to be significant in the multivariate models. Additional variables, which upon bivariate analysis were not found to be significant risk factors for surgical site infection (SSI), included: the preoperative glucose level and the preoperative erythrocyte sedimentation rate; the preoperative ASA score and NNIS index; the duration of operation; presence of haematomas; and development of a post-operative infection other than a SSI. The findings of the study led to the careful examination of the single operating room in which these operations were performed. The following

Table II. Factors associated with developing wound infection after total knee replacement. Surgical site infection after total knee replacement 893 Risk factor Total n (%) Infected n (%) p (2-tailed) bivariate RR (95% CI) p multivariate RR (95% CI) Gender NS (0.09) NS Male 61 (34) 6 (9.8) 1.07 (0.981.17) Female 119 (66) 4 (3.4) CHF NS (0.6) NI Yes 18 (10) 0 1.07 (1.021.11) No 162 (90) 10 (6.1) Diabetes mellitus NS (0.69) NI Yes 37 (21) 1 (2.7) 1.04 (0.971.11) No 143 (79) 9 (6.3) First vs repeat* surgery NS (0.35) NI First 158 (88) 8 (5.1) 0.53 (0.105.53) Repeat 22 (12) 2 (9.1) Knee operated 0.01 B0.01 Left 92 (51) 9 (9.8) 9.01 (1.2203) 6.69 (1.726.8) Right 88 (49) 1 (1.1) Prosthesis type 0.056 0.03 Johnson & Johnson 72 (40) 7 (10) 3.6 (0.818.4) 4.7 (1.1818.4) Biomet 104 (58) 3 (3) Revision of TKR 4 (2) 0 (0) No. of surgeons NS (0.32) NS Two 72 (40) 2 (2.8) 1.05 (0.981.12) Three 108 (60) 8 (7.4) No. of TKR/surgeon 0.045 NS 114 (n9) 40 (22) 5 (12.5) 3.86 (0.8317.6) ]15 (n4) 140 (78) 5 (3.6) Preoperative ASA score NS (1.0) NI 02 158 (94) 10 (6.3) 35 11 (6) 0 Prolonged operation NS (1.0) NI Yes 15 (8) 0 No 165 (92) 10 (6) Presence of urinary catheter NS (1.0) NI Yes 8 (4) 0 No 172 (96) 10 (5.8) RR: relative risk; 95% CI: confidence interval; NS: non-significant; WBC: white blood count; the x 2 calculation of the prosthesis type was done omitting the revision surgery cases. *Repeat indicates any kind of previous surgery of the knee subsequently undergoing TKR; NS: not significant; NI: not included in the multivariate model due to high p-value in the bivariate model. major breaks were detected in adherence with standard infection control recommendations. First, this operating room has 3 doors, allowing frequent entrances and exits of the team, principally through the main door located to the left of the patient. Secondly, a non-standard horizontal-flow air-conditioner was detected that had been installed above the left, main door several y earlier. Thirdly, a washing sink on the other side of the main door was found to be in very active use for washing of used tools before sterilization, potentially leading to contamination of the operating room air. The implications of these findings were explained to the operating room nursing staff and the orthopaedic team, who were urged to improve adherence with surgical infection control guidelines. The sink was removed, the horizontal air conditioner was disconnected, and the door was locked during these operations. In 2004, 1.5 y after these improvements were made, a small, prospective survey of 45 consecutive patients undergoing TKR demonstrated only 1 superficial SSI (2.2%) (p0.5), i.e. a clinically significant improvement in SSI rate, although statistical significance was not reached, most probably because of the small number of patients in the prospective study. Discussion This retrospective study of 180 patients undergoing total knee replacement during 2 y (19992000)

894 Y. Babkin et al. revealed 3 superficial wound infections (1.7%) and 7 deep infections requiring re-operation (3.9%), out of a total of 10 surgical site infections (SSI) (5.6%). These figures are within the range of published data (0.5 5%), although at the upper limit of the spectrum, justifying the conduct of this survey [816]. Two independent risk factors for wound infection were detected, in addition to several factors that nearly reached statistical significance. The independent risk factors were the operation involving the left rather than the right knee and the kind of prosthesis used. Subsequently we will discuss the major findings of this study. In the operating room, patients were always placed in the same position with their left side to the described, main entrance. Sterile surgical instruments were laid out on trays on the right side of the operating table. Whenever the surgeon stood on the left side of the operated patient, he and his assistant were between that horizontal-flow air conditioner and the operative wound. Bacteria shed from the surgical team could have been carried by the airflow onto the patient s wound [9,10,14,15]. Salvati et al. [17] reported an increased incidence of post-operative organ space SSI from 1.9% to 3.9% while comparing total knee replacements performed in rooms ventilated by conventional air-conditioning system and in rooms with horizontal unidirectional filtered airflow. They found that during total knee replacement (TKR), team members were periodically required to stand between the source of the horizontal air stream and the exposed wound. Our infection-rate pattern (Table II) confirms these observations. The use of the Johnson & Johnson prosthesis was associated with an infection rate that, at 11%, was 4 times higher than that of use of the Biomet prosthesis (3%). We doubt whether this different infection rate is due to the small difference in structure between these prostheses. Operation time was somewhat longer when Johnson & Johnson prostheses were implanted (1.890.7 h) compared to 1.690.4 h for Biomet implants (p0.029). However, length of operation was not significant in the multivariate analysis. It is a well-known fact that the primary source of deep post-operative SSI is contamination from airborne bacteria. About 95% of wound contamination is derived from airborne sources and only 5% to 15% from the patient s own skin flora [15]. We also found that as the number of orthopaedic surgeons or anaesthesiologists was higher during an operation, the rate of infections increased as well. Although this trend did not reach statistical significance, it is obvious that the number of operating room personnel is an important factor in disseminating bacteria by airflow [14,15,18]. As mentioned above, the implications of both the retrospective study and the epidemiological investigation were explained to the operating room nursing staff and the orthopaedic team, who were urged to improve adherence with surgical infection control guidelines. The sink was removed, the horizontal air conditioner was disconnected, and the door was locked during operations. However, the use of the Johnson & Johnson prosthesis actually increased, to 75% of all implants used. The prospective survey conducted in the beginning of 2004, 1.5 y after improvements were made, employing the same CDC case definitions of SSI, let to detection of only 1 superficial wound infection out of 45 total knee replacements (2.2%), while 75% of the used prostheses were of the Johnson & Johnson type. This suggests that the use of the latter prostheses possibly requires a longer learning period, associated with an initially higher complication rate, which subsequently entirely dissipates. Quite possibly, other undetected factors were involved which were corrected unintentionally. Our study has several limitations. First, the retrospective nature of the study could have led to underdetection of wound infection. However, as 100% 1-y follow-up was achieved, we believe that deep or organ-space infection could not have been missed, although under-diagnosis of superficial SSI is a distinct possibility. Such minor infections, if indeed missed, certainly did not lead to reported adverse effects for ambulation and did not require further admission or re-operation. Accordingly, the impact of this bias is in our view negligible. Secondly, although we collected data for almost 100 demographic, clinical, surgical and laboratory parameters, there may have been additional risk factors for infection, which we did not include in the study, such as timing for antibiotic prophylaxis. Repeat surveillance surveys have indicated appropriate timing of antimicrobial prophylaxis ([7], and unpublished data), but this factor was not assessed in the present study. Therefore we believe that there is only a small possibility that additional risk factors for SSI were missed. Total quality management requires frequent determination of wound infection rates, evaluation of possible risk factors, correction of detected problems, and a repetition of these measures, in order to achieve and maintain the best possible outcome. Ongoing surveillance may lead to detection of a higher than expected infection rate, but often fails to lead to the possible cause or causes. A carefully designed prospective surveillance project may lead to detection of risk factors, but is often time- and labour-intensive, and therefore expensive. The usual approach is the retrospective, case-control study, in

Surgical site infection after total knee replacement 895 which each case with a SSI is matched with 1 or more control patients who did not develop wound infection. Our approach, in which all patients with a detected SSI were compared with all patients who evidently did not develop infection, provided valuable information and clues regarding possible underlying causes of infection, which were corrected. The prospective survey subsequently conducted demonstrated only 1 superficial SSI, i.e. a significant improvement in SSI rate. Ongoing observation suggests that the rate of SSI after TKR remains below 2.5%. It is impossible to prove a direct link between these interventions and the improved outcome, although such an association is plausible. In conclusion, this retrospective study of 180 patients undergoing total knee replacement during a 2-y period and related epidemiological investigation led to detection of several distinct risk factors which, upon correction, resulted in a significant decrease in wound infection rate. Ongoing surveillance of wound infection rates is essential for all operations and in particular for operations with insertion of foreign material. Detection of a higher than expected SSI rate should lead to a retrospective case-control study in order to identify possible risk factors and implement appropriate interventions. References [1] Talbot TR, Kaiser AB. Post-operative infections and antimicrobial prophylaxis. In: Mandell GL, Bennett JE, Dolin R, editors. Principles and Practice of Infectious Diseases, 6th edn. Philadelphia: Churchill Livingstone; 2005. p. 353347. [2] Schwartz T, Agassi M, Peled T. (2000). Prevalence survey of nosocomial infections in Israeli general hospitals (1997 1998) (Hebrew). Israeli Ministry of Health Report No. 4003. [3] Larcom P, Lotke PA. Treatment of inflammatory and degenerative conditions of the knee. In: Dee R, editor. Principles of Orthopedic Practice. New York: McGraw-Hill Company; 1997. p. 9757. [4] Schierholz JM, Beuth J. Implant infections: a haven for opportunistic bacteria. J Hosp Infect 2001;/49:/87 93. [5] Lidwell OM. Sir John Charnly, Surgeon (191182): the control of infection after total joint replacement. J Hosp Infect ;23 1993;/23:/515. [6] SHEA, APIC, CDC, SIS Consensus paper. Consensus paper on the surveillance of surgical wound infections. The Society for Hospital Epidemiology of America; the Association for Practitioners in Infection Control; the Centers for Disease Control; the Surgical Infection Society. J Infect Control Hosp Epidemiol 1992;13:599608. [7] Vaisbrud V, Raveh D, Schlesinger Y, Yinnon AM. Surveillance of antimicrobial prophylaxis for surgical procedures. Infect Control Hosp Epidemiol 1999;/20:/6103. [8] American Academy of Orthopedic Surgeons (1996). Orthopaedic knowledge update 5 home syllabus. Rosemont, IL; 4901. [9] The American Academy of Orthopedic Surgeons. Common complications of total knee arthroplasty. J Bone Joint Surg 1997;79:278311. [10] Hanssen AD, Rand JA. Instructional course lectures, the American Academy of Orthopedic Surgeons: evaluation and treatment of infection at the site of a total hip or knee arthroplasty. J Bone Joint Surg 1998;/80:/910. [11] Grogan TJ, Dorey F, Rollings J, Amstutz HC. Deep infected knee arthroplasty: 10 y experience at the University of California at Los Angeles Medical Center. J Bone Joint Surg (Am) 1986;/68:/22634. [12] Segawa H, Tsukayama DT, Kyle RF, Becker DA, Gustilio RB. Infection after total knee arthroplasty. A retrospective study of the treatment of 81 infections. J Bone Joint Surg 1999;/81:/143445. [13] Bengson S, Knutson K. The infected knee arthroplasty: a 6- y follow-up of 357 cases. Acta Orthop Scand 1991;/62:/301 11. [14] Fitzgerald RH. Total hip arthroplasty sepsis, prevention and diagnosis. Orthopedic Clinics North Am 1992;/23:/ 25964. [15] Fitzgerald RH. Medical and surgical management of the patient with an infected total knee arthroplasty. In: Lotke PA, Garino JP, editors. Revision total knee arthroplasty. Philadelphia.: Lippincott-Raven Publishers; 1999. [16] Lidwell OM, Lowbury EJ, Whyte W, Blowers R, Stanley SJ, Lowe D. Effect of ultra-clean air in operating rooms on deep sepsis in the joint after total hip or knee replacement: a randomized study. Br Med J 1982;/285:/104. [17] Salvaty EA, Robinson RP, Zeno SM, Koslin BL, Brause BD, Wilson PD. Infection rates after 3175 total hip and total knee replacements performed with and without a horizontal unidirectional filtered air-flow system. J Bone Joint Surg Am 1982;/64:/52535. [18] Minnema B, Vearncombe M, Augustin A, Gollish J, Simor AE. Risk factors for surgical site infection following primary total knee arthroplasty. Infect Control Hosp Epidemiol 2004;/25:/47780.