Classification and management options for prosthetic joint infection

Classification of prosthetic joint infections

Classification schemes for periprosthetic joint infections (PJIs) have been shown to be beneficial in terms of predicting the most appropriate treatment strategy.

The most widely accepted classification of periprosthetic infections of total joint replacements has been proposed by Coventry (1) and divides the occurrence of the infection into three stages: stage I (acute, within the first three months); stage II (more than 3 months after surgery); stage III (2 years after infection) (Table 1). Perhaps the most frequently cited classification of PJI is the one formulated by Tsukayama et al. (2) which proposed a system which categorized infections into four groups (Table 2):

• Positive intra-operative cultures;
• Early postoperative infection occurring before 4 weeks;
• Late chronic infection (>4 weeks), and;
• Acute hematogenous infection.

A similar system was proposed by Toms et al. (3), who otherwise consider early postoperative infections those being detected <6 weeks. Similarly, Cui et al. classified infection into four types according to onset of symptoms and positivity to intra-operative cultures (4).

Zimmerli et al. (5), distinguish between early PJIs (within 3 months postoperatively), delayed (3 to 24 months) or late (more than 24 months). A period of 3 months after surgery as the cut-off between acute or not has been mentioned also by Parvizi et al. (6). Recent recommendations reported by Osmon et al. (7) have achieved widespread acceptance internationally.

The timing of intervention is important. A short duration of symptoms is commonly considered the best prognostic factor in terms of eradication of infection (8,9). However, clarifications are needed in borderline cases, as the cut-off of an acute PJI ranges between 0–4 weeks (2) and 0–3 months (5,6). Based on available literature, robust scientific evidence correlating the duration of symptoms with the clinical outcome is lacking.

For these reasons a comprehensive seven point PJI classification has been proposed by Romanò et al. (10). This classification system focuses on several issues including the host status, responsible microorganisms, bone and soft tissue defects, aetiopathogenesis, and anatomical and pathological features, from acute, with rapid-onset pain, swelling and wound purulence with or without systemic features of infection, to chronic, with serious discomfort, decreased movement and presence of sinus tract.

This system seems intuitive as, given that multiple factors influence PJI, it is illogical that timing alone influences management and outcomes.

More recently, in order to address ambiguities arising in current guidelines ant to encompass the cases which do not conform to the available classification systems, a different perspective has been introduced (11) (Table 3).

This new classification proposal focuses on the identification of different patterns of infection based on the topography of the infectious process: this theory relies on the identification of the exact location of the bacterial colonization and provides guidance for the treating surgeons, allowing them to decide between a conservative or a more radical intervention irrespectively of the timing (11).

In order to accurately localize the focus of infection contemporary imaging modalities such as nuclear scanning may be used; which may allow to improve localization and to better understand PJI patterns compared to conventional radiographs. Radiolabeled white blood cells (WBC) imaging, possesses the accuracy to distinguish between septic and aseptic loosening (12-14). Single-photon emission computed tomography (SPECT) is currently overtaking planar scintigraphy with a more detailed 3D localization (15), and the recent introduction of integrated SPECT/CT has allowed a more precise anatomic localization (16).

With this idea in mind, by using radiolabeled WBC by SPECT/CT to accurately localize the focus of infection, three different patterns can be identified:

• Infection involving the joint space (Figure 1);
  

  Figure 1 Radiolabeled white blood cells (WBC) imaging documenting the location of the infection in the joint space (red arrows).
• Infection involving the bone-implant interface (Figure 2);
  

  Figure 2 Radiolabeled white blood cells (WBC) imaging documenting the location of the infection at the bone-implant interface.
• Infection involving both compartments (Figure 3).
  

  Figure 3 Radiolabeled white blood cells (WBC) imaging showing infection involvement of both compartments.

This new approach, by taking advantage of recent nuclear imaging modalities, could improve current management of PJIs allowing useful selection criteria enhancing therapeutic strategies (Figure 4).

Figure 4 New classification treatment algorithm proposal focusing on the topography of the infectious process.

Management options

Several factors related to the host, infecting species and the surgeon influence the choice of treatment. Irrespective of the classification used the management should focus on eradicating the infection and restoring the pain free function of the affected limb. At present, treatment strategies for PJIs are based on the progression of the infectious process and clinical involvement. Long term antibiotic suppression therapy is an option if surgical treatment it precluded (17).

Current surgical management relies on debridement, antibiotics and implant retention (DAIR), which is traditionally performed at early stages following the onset of symptoms, 1- or 2-stage revision arthroplasty which is usually limited to chronic stages. In addition, in severe cases, definitive articulating antibiotic spacer (shoulder), excision arthroplasty (hip), arthrodesis or amputation (knee) can be performed.

Typically, DAIR is considered to be the treatment of choice in patients with a short duration of symptoms, which allows implant preservation, good functional outcomes and shorter hospital stays (18-26).

A 2-stage exchange strategy is commonly considered to be the ‘gold standard’ for the management of PJI, since it is advocated to provide effective infection eradication, although it is a complex surgical procedure usually which can itself result in bone and soft tissue damage (27).

The one-stage approach possesses the advantages of avoiding multiple major invasive surgical procedures and prolonged hospitalization however it needs strict criteria to be applied as it has to be performed in healthy patients Type A hosts (1) with healthy soft tissues and with minimal or moderate bone loss and in whom the infecting organism and the antibiotic sensitivities are known.

Several authors have reported similar rates of infection recurrence following one and two-stage revisions (28-32), and the use of one-stage revision surgery is gaining popularity.

Recently, satisfying results following partial implant retention during revision total arthroplasty for septic failures have been reported (33-36).

In a study by Ekpo et al. (33), a success rate of 89.4% (17 out of 19) has been reported at a minimum of 2 years follow-up after partial revision arthroplasty (range, 2–11 years). Similarly, a low reinfection rate (6.6%) has been reported by Morley et al. (34) 6.8 years following partial hip revision surgery. El-Husseiny et al. (36) reviewed 18 patients with infected THAs treated with selective implant retention at a minimum of 5 years follow-up (range, 5–9.9 years). Three patients (16.6%) had recurrent infection at the site of the prosthesis. Postoperative average Harris hip score was 78 (range, 46–89). These positive outcomes may demonstrate that bacteria have not invaded all implant components, and that the identification of the exact location of the infection may allow selective implant retention (11).

The use of a permanent cement spacer and resection arthroplasty may be considered viable treatment options in elderly, low-demand patient with severe medical comorbidities, as well as patients with limited bone stock, poor soft tissue coverage, or infections due to highly resistant organisms in whom surgery is deemed too high risk (37-41).

Similarly arthrodesis represents a salvage option for the septic prosthetic knee joint infection once multiple revision procedures have been exhausted providing acceptable functionality and satisfactory quality of life when bone stock is insufficient (40,41).

In case no measures to salvage a functional TKA can be pursued, knee arthrodesis or above-knee amputation should be considered as salvage procedures to eradicate the infectious process, and sometimes saves the patients’ life. Knee arthrodesis may allow limb preservation and residual joint functionality in absence of sufficient bone stock (42). Amputation should be the last option considered in presence of serious and permanent tissue damage, although may be appropriate in selected cases (43,44).

Conclusions

The classification of PJI can be used to guide clinicians with therapeutic decision making. There are however several classification systems which vary in their definition of what constitutes an acute infection as well as what prognostic factors are important in patients with PJI. Multicentre prospective randomized controlled trials are required to help to define these important issues.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editors (Nemandra A. Sandiford, Massimo Francescini and Daniel Kendoff) for the series “Prosthetic Joint Infection” published in Annals of Joint. The article has undergone external peer review.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/aoj-20-86). The series “Prosthetic Joint Infection” was commissioned by the editorial office without any funding or sponsorship. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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