Despite progress in prosthesis science and design, as well as in surgical techniques and perioperative care, infection of the prosthetic knee remains constant in the range of 0.4% to 2% during the first year after knee arthroplasty [1-5].

However, although the percentage of patients developing infections after knee replacement surgery is low, the absolute number is reaching intolerable levels, due to the enormous quantity of such operations being performed. Some authors have projected that in the USA the demand for primary knee arthroplasty will grow to 3.48 million patients by 2030 [5]. If 2% of them develop an infection, as many as 69,000 patients could require treatment for periprosthetic knee infection each year. The potential economic burden to any healthcare system is very considerable and strategies to better treat and to prevent total knee arthroplasty infections should be investigated.

Regarding infection after total knee arthroplasty (TKA), several classification schemes have been proposed and these are used to determine the treatment applied, especially whether the prosthesis should be removed or retained. These classification systems are mainly based on the clinical presentation, as follows: (a) positive intraoperative culture; (b) early postoperative infection (superficial or deep); (c) late chronic infection; d) acute haematogenous infection [6]. The choice of the most appropriate treatment for a given type of infection after TKA is critical for its control. According to the literature, physicians should only seek to retain the prosthesis in cases of acute infection. The latter may be early postoperative or acute haematogenous infections. By definition, the first of these occurs within one month of implantation, whereas the second is caused by a blood stream seeding the joint from another primary site of infection.

The goal of treatment of an infection at the site of a TKA is eradication of the infection and the restoration of a painless, well-functioning knee. In some cases, the aim is achieved only partially and it is not possible to recover good joint function. Treatment options include chronic antibiotic suppression, irrigation and debridement with component retention, one or two-stage exchange arthroplasty, or salvage procedures such as resection arthroplasty, arthrodesis or even amputation. Of these treatment options, two-stage exchange arthroplasty using an antibiotic-laden cement spacer is considered the gold standard protocol, providing a high rate of infection control, ranging from 85% to 100%.

However, two-stage revision is associated with pain and limited mobility between stages, and high costs; moreover, it can provoke skeletal defects and soft tissue loss, resulting in the possible need for a constrained prosthesis. To avoid these complications, irrigation and debridement has been considered for treating acute postoperative TKA infection.

Rates of infection healing following treatment with prosthesis retention and irrigation plus debridement range from 18% to 83% [7-9]. However, direct comparison of infection control rates for different treatment options is difficult because of the many variables that can influence the success of the procedure, such as the exact duration of symptoms after which prosthesis retention is less likely to result in infection eradication (from 2 days [10] to 4 weeks [11]), immunity-impairing host condition, virulence of the infecting organism, implant state, operation history or type of surgery, as well as the absence of randomised, controlled, prospective comparison studies.

One of the variables that could influence the success of the procedure would be the application of a continuous irrigation system, thus enabling the administration of high-dose antibiotics and the drainage of debris and blood clots. The literature contains few reports of debridement combined with an associated continuous irrigation system; we found only one other series [12], used in the treatment of septic natural knees, and one concerning case reports [13] on its use for infected TKA (PKI). Therefore, the role of this procedure has yet to be clearly defined.

The purpose of the present study is to determine the overall success of irrigation and debridement with retention of the prosthesis in controlling infection and to examine whether the application of a continuous irrigation system after the surgery improves this success rate. Our operational hypothesis was that irrigation, debridement and the application of a continuous irrigation system after the intervention is likely to provide a better success rate than irrigation and debridement alone; the null hypothesis was that the use of a continuous irrigation system after surgery makes no difference, and the alternative hypothesis was that the use of a continuous irrigation system is associated with a higher failure rate than irrigation and debridement with prosthesis retention alone.

According to our definitions of successful and failed treatment, ID with prosthesis retention was successful in 25 patients (73.5%) and failed in 9 patients (26.5%), after the conclusion of follow up. Overall infection rates were similar in both intervention groups, at 75% in the CCIS and 71.4% in the control group, with no statistically significant differences between them (P=1).

The patient-specific characteristics were similar in both groups, including during the follow up period. No association was found between health status or host immunity [21] and any treatment group (Tables 1 and 2).

There were no statistically significant differences between the two groups with regard to the number or distribution of infected revision arthroplasties or type of infection, according to the classification of Tsukuyama et al. (p=0.672 and p=0.627, respectively).

Nine patients in our series presented intraoperative purulence around the prosthesis, (26.47%) and polyethylene was exchanged in 17 knees (50%), with no differences between the two treatment groups, (P=0.50 and P=0.36, respectively). There were no differences in outcome, based on the duration of symptoms; for the control group, the median value was 5.5 days, with a difference between the first and the third quartile of 13 days, and for the irrigation system group it was three days, with an interquartile range of 6.75 days (p=0.507). The need for additional surgical debridement procedures to control infection and the number of such interventions were not statistically different between the two groups (p=0.562).

There were no significant differences (p=0.704) between the two treatment groups regarding those infected with a single organism and those infected with multiple organisms. Twelve knees (35.29%) were infected with methicillin-susceptible S. aureus and there were no differences in this distribution between the two treatment groups (p=1).

Finally, the comparison of the length of stay, for the ID and the CCIS groups, revealed a significant difference: the median hospital stay of patients fitted with a closed system (CCIS) was 22 days vs 9 days for ID patients (p=0.000).

The costs of hospital stay, drugs and other expenses were calculated to be €349 per day. Since CCIS patients stayed for 13 days longer than ID patients, the extra cost for these 20 CCIS patients was €90,740.

Two-stage reimplantation for the treatment of TKA periprosthetic infection is currently considered the most effective approach to this major complication. However, the substantial morbidity associated with it must be taken into account. Accordingly, both patients and surgeons tend to view irrigation and debridement with prosthesis retention as an acceptable choice in the setting of acute periprosthetic infection [20].

Seventy-three per cent of the patients in our study achieved infection control and prosthesis retention. Similar high success rates have been reported before [1], for example, Mont et al. reported a success rate of 71% for late haematogenous infection and 100% for early postoperative TKA infections without removal of the prosthesis [22]. On the other hand, Silva et al. [11], in their review, reported an overall failure rate of 67.4% among infected knee arthroplasties treated with open debridement and prosthesis retention. Nevertheless, in most of the studies included in the latter review, the results of initial surgical treatment were evaluated and the need for any additional intervention was considered to represent a failure of infection control. In our review, repeated debridement was not considered a treatment failure.

We found no statistically significant difference between the two treatment groups with regard to the factors previously identified as being associated with a successful outcome, i.e., young, healthy patients with early postoperative infections, the short-term duration of symptoms, or methicillin-sensitive staphylococcus as the causative organism.

The purpose of this study was to determine the effectiveness of irrigation and debridement combined with the application of a continuous irrigation-suction system, considered to present the following theoretical advantages: diluting the enzymatically active material, diluting the concentration of the causative organism, increasing the efficiency of systemic antibiotics and persistently removing necrotic material.

Certain limitations are inherently present in our study. Data collection of all the variables was performed retrospectively, and so this is not a prospective randomised double blind study and does not provide the same level of evidence. Furthermore, we made no evaluation of clinical function, and so could not reach a clear conclusion as to the effect on the final outcome of multiple interventions required for infection control. These limitations are inherent to all retrospective studies in this field, and further research in which these methodological problems are resolved is needed.

In our study, patients who received open debridement and irrigation combined with the application of a continuous closed irrigation system did not have a different number of operations or a higher or lower success rate, but they did need a longer hospital stay than did patients who received open debridement and irrigation alone (median of 22 days vs 9 days). Therefore, avoiding the use of a closed irrigation-suction system dramatically reduces hospital stay time whilst maintaining the same success rate for infection control.

The authors confirm that this article content has no conflict of interest.