Factors affecting the incidence of infection in hip and knee replacement

Transcription

1 Factors affecting the incidence of infection in hip and knee replacement AN ANALYSIS OF 5277 CASES C. A. Willis-Owen, A. Konyves, D. K. Martin From Sportsmed SA, Adelaide, Australia Infection remains a significant and common complication after joint replacement and there is debate about which contributing factors are important. Few studies have investigated the effect of the operating time on infection. We collected data prospectively from 5277 hip and knee replacements which included the type of procedure, the operating time, the use of drains, the operating theatre, surgeon, age and gender. In a subgroup of 3449 knee replacements further analysis was carried out using the tourniquet time in place of the operating time. These variables were assessed by the use of generalised linear modelling against superficial, deep or joint-space post-operative infection as defined by the Australian Surgical-Site Infection criteria. The overall infection rate was.98%. In the replacement data set both male gender (z = 3.97, p =.195) and prolonged operating time (z = 4.325, p <.1) were predictive of infection. In the knee subgroup male gender (z = 2.25, p =.2447), a longer tourniquet time (z = 2.867, p =.414) and total knee replacement (versus unicompartmental knee replacement) (z = -2.52, p =.42) were predictive of infection. These findings support the view that a prolonged operating time and male gender are associated with an increased incidence of infection. Steps to minimise intra-operative delay should be instigated, and care should be exercised when introducing measures which prolong the duration of joint replacement. C. A. Willis-Owen, FRCS(Trauma & Orth), Orthopaedic Fellow A. Konyves, FRCS(Trauma & Orth), Orthopaedic Fellow D. K. Martin, MS(Orth), FRACS, FAOrthA, Orthopaedic Surgeon Sportsmed SA, 32 Payneham Road, Stepney, South Australia 569, Australia. Correspondence should be sent to Mr C. A. Willis-Owen; cawillisowen@gmail.com 21 British Editorial Society of Bone and Joint Surgery doi:1.132/31-62x.92b $2. J Bone Joint Surg [Br] 21;92-B: Received 21 December 29; Accepted after revision 24 March 21 Replacement of the hip or knee is one of the most successful surgical procedures in improving the quality of life. 1-6 However, infection is a feared complication and usually leads to removal of the implant and revision surgery. 7-1 The introduction of laminar flow operating theatres and antibiotic prophylaxis has led to considerable reduction in the incidence of surgical-site infection after joint replacement Nevertheless, we must continue to identify factors which may contribute to infection in order to devise ways of reducing the incidence even further. Many factors have been investigated in regard to the increased incidence of infection after knee replacement including age, gender, body mass index and medical co-morbidities. The results of these studies have been conflicting. Chesney et al 16 found no statistically significant correlation between age, gender, obesity or co-morbidity and infection, whereas Jämsen et al 17 showed that male gender, rheumatoid arthritis and previous fracture carried an increased risk of re-operation because of infection. There is a commonly held belief that longer operating times are associated with an increased incidence of infection, but definitive evidence to support this is sparse and debate continues. 18 Numerous studies have failed to show an association, but most have involved small numbers of patients Peersman et al 23 found that an operating time for knee replacement of more than 2.5 hours was associated with an increased incidence of infection in a retrospective study performed in the 199s, and that the operating time can predict those patients at risk. 24 Kessler et al 25 observed that a longer operating time was associated with increased overall morbidity, including infection, bleeding or thromboembolic events, in revision hip replacement. The association between tourniquet time and infection has not been investigated previously. As the complexity of replacement increases and new methods are introduced, we have sought to re-assess the potential impact of age, gender, type of operation, the use of surgical drains, operating time and tourniquet time on the incidence of infection in both hip and knee replacement. We used multivariate analysis to 1128 THE JOURNAL OF BONE AND JOINT SURGERY

2 FACTORS AFFECTING THE INCIDENCE OF INFECTION IN HIP AND KNEE REPLACEMENT 1129 Table I. Details of the Australian surgical site infection (SSI) definitions for superficial, deep and joint or organspace infection Type of infection Superficial incisional: Infection involves only skin and subcutaneous tissue of this incision occurs within 3 days after the operative procedure has at least one of the following from the superficial incision: 1. Purulent discharge (NOT stitch abscess) 2. Organisms isolated from an aseptically collected culture of fluid or tissue. Note: a positive wound swab (in contrast to wound aspirate) without other significant evidence of infection is not adequate for diagnosis of infection 3. Displays at the site of incision any of the following signs and symptoms of infection: pain or tenderness localised swelling redness or heat the incision is deliberately explored by the surgeon resulting in a positive wound culture Note: A culture-negative finding does not meet this criterion unless the patient was on antibiotics immediately before diagnosis 4. Diagnosis or antimicrobial treatment of superficial incisional infection by the operating surgeon or registrar Deep incisional/organ space: Involves deep soft tissues (e.g. fascial and muscle layers) organs/spaces opened or manipulated during an operation occurs within 3 days after the operative procedure if implant not present OR within one year if implant in situ has either 1 and/or 2: 1. Purulent drainage from deep soft tissue or drain that is placed through a stab wound into the organ/ space 2. Spontaneous dehiscence at the incision site or the round is deliberately explored by a surgeon with the patient showing evidence of one or more of the following signs or symptoms: Fever > 38 C, localised pain or tenderness with culture positive specimen. A culture-negative finding does not meet this criterion unless the patient was on antibiotics immediately prior to the wound being explored and/or the culture being taken; Organisms isolated from aseptically obtained culture of fluid or tissue obtained from an organ/space; An abscess or other evidence of infection involving a deep/organ space is found on direct examination, during re-operation, or by histopathological or radiological examination; or Diagnosis of, or antimicrobial treatment of a deep incisional or organ/space SSI by the operating surgeon or registrar investigate the factors related to infection at the operation site in a large series of patients undergoing primary hip or knee replacement using the latest measures for the prevention of infection. Patients and Methods At our specialist private orthopaedic hospital data relating to every surgical procedure carried out have been prospectively collected and stored. The variables of age, gender, type of procedure, the time from entering to leaving the operating theatre, the time from inflation to deflation of the tourniquet, the use of drains, the operating theatre and the surgeon, assistant and scrub staff are all recorded. Post-operative complications are identified and recorded in every patient using a mandatory standardised form. The surgeons are audited on their collection rate of data on complications and face penalties for incomplete records. All cases of potential superficial, deep or jointspace infection are recorded and reported. This surveillance is conducted by an infection control nurse using the Australian Infection Control Association Surgical-Site Infection (SSI) definitions 26 (Table I). These definitions are similar to those in the United Kingdom. 27 Patients and their general practitioners are specifically instructed to contact the hospital if there are any concerns regarding wound infection before taking antibiotics. Those who do not attend for follow-up appointments are routinely contacted by telephone to establish the reason, and if they are receiving treatment elsewhere, appropriate details are sought. Each case of suspected infection is discussed with the treating surgeon to ensure that the details are recorded. As a result we believe that we have a relatively accurate and complete prospectively collected record of post-operative infective complications. Infection control measures. Since 21 all patients undergoing replacement have received intravenous antibiotic prophylaxis for 24 hours with 24 mg of gentamicin and 2 g of cephalothin at the induction of anaesthesia followed by three further doses of cephalothin in the following 24 hours. All the procedures have taken place in one of five operating theatres of similar design. Each has a filtered-air laminar-flow system. In every patient the operating site was shaved and pre-prepared with povidone iodine (or chlorhexidine in cases of iodine sensitivity) in the ward within one hour prior to entry to the operating theatre. All the patients then received a second skin preparation. Disposable drapes and occlusive drapes were used. All surgeons used double gloves for all cases and patients were catheterised only when clinically indicated. All the patients were nursed in individual rooms for the duration of their hospital stay in one of two dedicated elective orthopaedic wards. Bed occupancy rates were typically in the region of 8%. VOL. 92-B, No. 8, AUGUST 21

3 113 C. A. WILLIS-OWEN, A. KONYVES, D. K. MARTIN Table II. Details of the cases included in the main analysis Gender Male 261 Female Procedure * THR 175 TKR 2423 UKR 114 Males (%) 6 4 Mean age in years (range) (17.8 to 95.7) Mean operating time in mins (range) (6 to 315) 2 Use of drains Used 5132 Not used 145 * THR, total hip replacement; TKR, total knee replacement; UKR, unicompartmental knee replacement Fig. 1a Statistical analysis. Data regarding all primary hip and knee replacements from 22 to 28 were gathered from our database and analysed using the statistical software package R (R package, V CRAN 29, the Foundation for Statistical Computing). Binomial generalised linear models were fitted to the data, incorporating a range of putative predictor variables and a binary outcome measure, the post-operative infection status. Putative predictors included age, gender, surgeon, operating theatre, the time of entry to the operating theatre to the time of exit, the presence or absence of a drain and the operative procedure (total hip replacement (THR), total knee replacement (TKR) and medial unicompartmental knee replacement (UKR)). All cases which were complicated by a superficial infection, a deep infection or a joint-space infection were identified, and this provided the basis for a binary outcome measure. This analysis was repeated in a subgroup of data containing all cases of knee replacement. Every case involved the use of a pneumatic tourniquet. Thus in this subgroup the role of the duration of application of the tourniquet was assessed instead of the total operating time. Two observations from the replacement data set and three from the knee subgroup were removed since the data was incomplete. Results Data were available for a total of 5277 patients who had undergone primary replacement between 21 and 28. Their clinical details are given in Table II. There were 51 patients with a confirmed infection at the operation site, representing an infection rate of.98%. Based on a nominal alpha threshold of 5%, two predictors were significant. These were gender (z = 3.97, p =.195) and operating time (z = 4.325, p <.1). Male gender was associated with a higher rate of infection (Fig. 1a). In the non-infected group 2561 (49.%) of the patients were male, whereas in the infected group 39 (76.5%) were male. Longer operating times were also associated with a higher incidence of Mean operating time (mins) 15 5 Fig. 1b Graphs showing a) the percentage of males in infected and non-infected patients in the replacement group, b) the mean operating time in infected and non-infected patients in the replacement group (error bars represent the SEM). infection (Fig. 1b). The mean operating time in the noninfected group was 12 (6 to 315) minutes compared with 125 (8 to 21) minutes in the infected group. Surgeon, age, operative procedure and the use of drains were not found to have any significant predictive value. There were 3449 patients in the subgroup of those with knee replacement and complete data on the tourniquet time. The clinical details for these are given in Table III. Male gender was also associated with a higher rate of infection in this subgroup (z = 2.25, p =.2447). In the non-infected group 1592 (46.5%) of patients were male and in the infected group 18 (72.%) were male (Fig. 2a). Likewise, longer tourniquet times were also significantly associated with a higher incidence of infection (z = 2.867, p =.414). The mean tourniquet time in the non-infected group was 76 (4 to 185) THE JOURNAL OF BONE AND JOINT SURGERY

4 FACTORS AFFECTING THE INCIDENCE OF INFECTION IN HIP AND KNEE REPLACEMENT 1131 Table III. Details of the cases included in the analysis of the knee subgroup Gender Male 161 Female 1839 Procedure * TKR 2369 UKR 18 Males (%) Mean age in years (range) (29.1 to 89.7) Mean tourniquet time in mins (4 to 185) (range) Use of drains Used 3353 Not used 96 * TKR, total knee replacement; UKR, unicompartmental knee replacement 2 Fig. 2a 14 minutes compared with 9 (59 to 156) minutes in the infected group (Fig. 2b). Of the remaining putative predictors only the type of procedure had a nominal 5% threshold of significance (z = -2.52, p =.42). UKR was associated with a lower incidence of infection compared with TKR with only 9% of the infected group having the former compared with 31% of the non-infected group. The use of the Bonferroni correction is recognised as being a highly conservative approach for dealing with multiple testing. We have described two analyses, yielding a Bonferroni-corrected significance threshold of p =.25. At this conservative threshold the effects of both gender and time (total operating/tourniquet) retain significance in the total and knee subgroup data sets, thereby reinforcing the validity of these findings. In the knee subgroup the operative procedure (TKR/UKR) finding did not meet this robust threshold, and was lost after Bonferroni correction. Mean tourniquet time (mins) Fig. 2b Discussion Well-executed studies examining factors associated with infection after joint replacement are difficult to conduct. Prospective studies with meticulous collection of data have problems in achieving sufficient numbers to be effectively statistically powerful because infection is a rare event. Large registry-based studies often rely on readmission or re-operation as a surrogate measure of infection and hence miss numerous infections successfully treated conservatively. It has also been shown that registry data have a considerable potential to miss prosthetic joint infections. 28,29 Our large prospective single-unit study showed a statistically significant correlation of prolonged operating time and wound infection, with longer operations having a higher incidence of infection. This finding was independent of other variables. Our findings contradict those of a number of small studies which have failed to show an effect of operating time on the incidence of infection Graphs showing a) the percentage of males in infected and non-infected patients in the knee subgroup, b) the mean tourniquet time in infected and non-infected patients in the knee subgroup (error bars represent the SEM). However, in a retrospective review, Peersman et al 24 showed a link between operating time and infection and in a registry-based study, Ridgeway et al 3 had similar findings. Our study in a strictly-controlled, single-hospital setting corroborates and extends these findings in primary hip and knee replacement. Similar effects have been shown in abdominal surgery. 31 When the tourniquet time was used as a measure of operating time for knee replacement the same effect was observed. This association has not been described previously, but in a small, randomised study, avoidance of the use of a tourniquet has been shown to be associated with fewer superficial infections. 32 The use of a pneumatic tour- VOL. 92-B, No. 8, AUGUST 21

5 1132 C. A. WILLIS-OWEN, A. KONYVES, D. K. MARTIN niquet in TKR has been shown to cause persisting wound hypoxia to a level related to inflation pressure, but not to tourniquet time. 33 At our institution the tourniquet is inflated immediately before the start of surgery, and released as soon as dressings have been applied. Hence this measure is very closely related to the actual duration of surgery. Because of the way we use tourniquets it is not possible to separate the effects of operating time and tourniquet time. It may be informative to carry out similar studies in situations in which the tourniquet is used for only part of the operation. The finding that males have a higher incidence of infection is in keeping with those of a registry-based study by Jämsen et al. 17 Numerous previous studies have failed to demonstrate an effect from gender, but it is known that there are gender differences in skin colonisation 34 which may be associated with differences in skin ph, sebum production or skin thickness. 35 The lower rate of infection seen in UKR is in keeping with previous registry-based studies. 29,36 This finding was independent of other factors in our analysis and may reflect the smaller incision and minimally invasive nature of the procedure. Meticulous soft-tissue handling is thought to be important in reducing wound infection. It may be argued that surgeons taking longer over their procedures were either more or less careful with soft-tissue handling, but our findings were independent of the operating surgeon. Our study has a number of limitations. The actual duration of surgery was measured as the total time spent in the operating theatre. The time from incision to application of the dressing was not recorded. Other studies have not clearly defined how operating time was measured and therefore there is no consensus definition. 22 While this surrogate measure of operating time is imperfect, it can be assumed that the time after entering the theatre before starting the operation, and the time between finishing surgery and leaving the theatre is relatively constant regardless of the duration of surgery. Hence any error introduced would tend to have a proportionally greater effect on shorter operating times than longer times. As a result it is unlikely that we have overestimated the importance of the operating time, but may have somewhat underestimated it. The second part of the study, using the more accurate surrogate measure of tourniquet time, corroborated the results from the first, suggesting that this finding is robust. It was not possible to be certain that all episodes of wound infection had been included in our data collection, but we took all possible measures to identify every case. The incidence of wound infection was similar to that reported in the literature for specialist elective units suggesting that we did not miss a significant number of infection episodes. 37,38 In order to capture the maximum number of episodes of infection and to attain sufficient statistical power we chose to combine superficial, deep, and joint-space infections to provide one measure of infection. It may be argued that superficial infections are less clinically significant and that attention should focus on deep infections. The difference between a deep and a superficial infection is complex and may relate to the time of presentation, the extent and timing of the treatment and definition with superficial infections having the potential to spread and to involve the joint space. We feel that identifying factors contributing to any form of infection of the operation site is important. We did not include the potential confounding factors of comorbidities such as diabetes mellitus, rheumatoid arthritis, obesity or previous fracture. These factors have been suggested to be associated with an increased risk of infection in joint replacement, 17,39 and could prolong the operating time. Further studies in this area might establish whether it is the comorbidity, the increased operating time or a combination of both which leads to the increased rate of infection. While surgical procedures should not be hurried many avoidable factors can introduce unnecessary delay. Familiarity of the staff with the procedure and the use and location of equipment should be addressed before beginning surgery. Pre-operative planning and templating can reduce the amount of time spent making decisions during the procedure and can allow anticipation of any additional requirements for equipment. The design of the implant and instruments can minimise the number of steps required to carry out the procedure. Accurate jigs and their careful use can avoid the need to repeat steps. Appropriate and timely preparation of cement can reduce wasted time. Specific equipment which may speed up a procedure should be considered on the grounds of operating time saved as well as absolute necessity. Our data suggest that caution should be taken when considering introducing new steps or technologies to a surgical procedure which may be expected to increase the operating time. Antibiotic prophylaxis reduces the risk of infection in joint replacement surgery. 4 Current regimes depending on the half life of the antibiotic used, typically involve further doses if the surgical time exceeds four hours. This has been shown to be effective. 41 Before the advent of general anaesthesia the surgeons were measured by the speed at which they would operate. 42 While we do not advocate a return to such practice we do suggest that orthopaedic surgeons remain aware as our study shows that taking longer to do a hip or knee replacement is associated with an increased risk of infection. Supplementary material A further opinion by Mr R. Grimer is available with the online version of this article on our website at No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. THE JOURNAL OF BONE AND JOINT SURGERY

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