Bacterial contamination of irrigation fluid and suture material during ACL reconstruction and meniscus surgery

Although knee arthroscopy is generally considered an effective and safe procedure, it is not free from complications [14]. Among these, postoperative joint infections are rare but severe adverse events with an overall incidence of less than 1%. Comparing different arthroscopic procedures, with an incidence ranging from 0.3 to 1.7%, ACL reconstruction is responsible for postoperative infection more often than, e.g. meniscus surgery (incidence 0.15–0.84%) [1, 7, 11]. This study demonstrates that time-dependent contamination of irrigation fluid and bacterium stained suture material are key determinants in post-arthroscopic site infection after ACL reconstruction and meniscus repair. In contrast to other potentially contagious factors, as listed in the national nosocomial infections surveillance score (NNIS), fluid and suture contamination is an avoidable risk and knowledge about their impact, therefore, a key factor in the prevention of postoperative adverse events.

Risk factors for joint infection after surgery can be divided into surgery related and patient related. Smoking and obesity, for example, are known to be major positive predictors concerning deep and superficial infection. On the procedural side, e.g. complexity and duration of the surgical procedure are associated with a higher risk of postoperative infection [11].

To prevent joint infection, orthopedic surgery requires a highly sterile environment since the joint is a secluded compartment with a scarcity of immune cells [20]. Despite additive preventive measures such as single-shot antibiotic prophylaxis or laminar airflow, the risk for septic arthritis after arthroscopic knee surgery remains up to 1.1% [6, 19].

The continuous flush with a sterile solution, which is inherent to arthroscopic surgery, is one basic measure for the intraoperative prophylaxis against infection. In animal models, intensified lavage of contaminated wounds achieved a clear reduction in microbial load [21]. However, fluid residues accumulating from the remains of irrigation fluid, blood and debris on the surgical drape also provide a potential reservoir for pathogenic bacteria [2]. Suction devices, commonly used to remove accumulating irrigation fluid, also showed substantial bacterial contamination during total knee arthroplasty [15].

To what extent the even bigger fluid reservoirs in arthroscopic procedures remain sterile over the course of surgery or whether there is a time-dependent increase in their contamination has not been investigated so far. Therefore, the objective of the current study was to investigate whether pathogenic microbes can be identified in the irrigation fluid of arthroscopic ACL and meniscus surgery and to determine potential operation time thresholds for increased fluid contamination.

Our hypothesis was that despite the continuous flush in arthroscopic surgery, an increasing rate of microbiological contamination of the irrigation fluid and suture material over time would be observed. Respective to fluid, this has already been shown for joint replacement surgery, but has not yet been examined for knee arthroscopies. Suture material has not been evaluated in this context yet, despite its critical role in arthroscopic procedures.

The study was approved by the institutional review board of the Charité, Universitätsmedizin Berlin (EA4/069/17). All patients gave written informed consent prior to study inclusion.

The patient population comprised 67 women and 88 men with an average age of 33.7 years (SD, 12.6 years). The average duration for ACL reconstruction was 65 min, for meniscus surgery 36 min and for ACL reconstruction and meniscus repair 75 min.

The most important finding of this study was a surgical time-dependent contamination of irrigation fluid and suture material in ACL reconstruction and meniscus repair. We are not aware of any comparative studies on this subject with respect to knee arthroscopy.

Our data show for the first time that in arthroscopic knee surgery irrigation fluid reservoirs on surgical covers are prone to increasing bacterial contamination over time. Furthermore, as postoperative knee infection is attributed to a multitude of different microorganisms, which are predominantly part of the physiological skin flora [12, 22], bacterial contamination of irrigation fluid and suture and fixation material first investigated in this study may not necessarily imply, but could be the potential source of surgical site infection.

To the best of our knowledge, this study is the first to show the progression of contamination over time at short intervals and to compare the pathogen colonization of suture material with the colonization of the irrigation fluid. Gowd et al. showed operative time to be an independent risk factor for complications including surgical site infection in knee arthroscopy without further investigating its underlying mechanisms [17]. Fuchs et al. demonstrated a contamination rate of 22% for fluid residues in knee arthroplasty after 60 min of surgery [15]. Pauzenberg et al. showed increased skin contamination at the end of shoulder arthroscopy despite perioperative preventive measures. At the end of shoulder arthroscopy, 64.6% of patients showed at least one culture positive for C. acnes [22].

Only few studies have yet dealt with the contamination of suture material in arthroscopic surgery [23, 26]. Roach et al. showed a relevant microbial colonization of subscapularis tagging sutures in shoulder surgery and again a significant association of procedure length and positive microbacterial finding (p = 0.03) [23]. There is no comparable study for the knee joint in the literature.

As there was only one postoperative joint infection in this series, no final assumption can be made whether positive suture or irrigation fluid culture is a more reliable factor for predicting the risk of surgical site infection. The reported infection was a Staphylococcus lugdunensis infection after positive fluid and suture specimens for this bacterium. This example indicates that in case of bacteria with high virulence such as Staphylococcus aureus or intermediate virulence such as S. lugdunensis, the contamination of the material and fluid can be relevant. However, the majority of contaminations did not lead to a postoperative infection. This might be due to the character of the arthroscopic surgery with continuous flushing of the operation site and the standard-of-care single-shot antibiotic, which might be sufficient in most cases to fight the evolvement of an infection.

Interestingly enough, only one out of four patients with same positive suture material and irrigation fluid results (only 0.6% of all patients and 2% of all culture-positive patients examined) developed a postoperative knee infection during the follow-up period. All other culture-positive patients remained free of any sign of infection in our 12-month follow-up.

The pathogen causing the only postoperative joint infection in this study, Staphylococcus lugdunensis, is involved in a wide range of severe infections. Frank et al. were the first to show S. lugdunensis to be a virulent CoNS that behaves similarly to Staphylococcus aureus in causing deep abscesses, skin and soft tissue infections, central nervous system infections and blood stream infections including sepsis, toxic shock syndrome and endocarditis complicated by embolic events [5, 18]. With its specific adhesions molecules, cytotoxins and biofilm synthesis system, S. lugdunensis, although a CoNS, shows a high pathogenicity comparable to S. aureus and is frequently verified in post-arthroscopic joint infections [3]. Therefore, single positive microbiological samples with S. lugdunensis should be treated as significant rather than as contamination [4, 13].

A discrepancy between high bacterial contamination rates and a low rate of postoperative infection was noticed. First, it is possible that most potential infections in those patients were successfully prevented by perioperative antibiotic prophylaxis [10, 24]. Second, the continuous flush of the knee joint during arthroscopic surgery leads to pathogen elimination in the case of a (low) bacterial contamination load. Third, there may be some yet unknown patient-related endogenous immunologic capacities, which enable patients to contain a certain number of pathogens inducing postoperative infections. Additional studies are surely necessary to clarify these questions.

Graft preparation with vancomycin is a well-known and investigated procedure to decrease infection after ACL reconstruction [10]. This proven concept might also be applied for all used suture and fixation material to reduce bacterial contamination and need to be evaluated in further studies.

Despite the efforts for a rigorous methodology, there are limitations to this study. Only one sample was examined at the respective times and thus contamination with a large dilution may not have been detected. Furthermore, all patients in this study received a single-shot perioperative cefazolin prophylaxis (or vancomycin in the event of cephalosporin intolerance) so that all samples were taken after administration of antibiotics. Although known from arthroplasty and periprosthetic joint infection studies that a single-shot antibiotic does not compromise the result of intra-articular biopsy [8, 9, 16, 25], this could have led to a certain selection phenomenon. Nevertheless, antibiotic prophylaxis is a common measure and is used as standard of care in everyday clinical practice. In addition, the relatively short follow-up period of 12 months may have not allowed to detect all, particularly low-grade infections. Therefore, the true rate of joint infection could be higher than the one we observed. To the best of our knowledge, the present study is the first one examining the correlation between the duration of the surgery and contamination rates of the pooled irrigation fluid. Thus, no data for a reliable a priori power analysis were available and we, therefore, have conducted the study in an explorative manner.

The data showed only one case of a postoperative infection accompanied by suture and irrigation fluid contamination. Nevertheless, the time-dependent increase of suture and fluid contamination should contribute to a more distinct awareness in the handling of these potentially contaminated materials during surgery, e.g. contact of surgical instruments with the fluid reservoir should be avoided as should be emptying it using the suction device.

Any direct contact with the collected irrigation fluid in the reservoir and any contact of suture material with skin or fluid reservoirs should be avoided.