The accuracy of reporting of periprosthetic joint infection to the Australian Orthopaedic Association National Joint Replacement Registry

Introduction

The total number of people living with at least one arthroplasty in Australia is more than 800,000 and growing rapidly.¹ In 2019, 125,600 primary hip, knee, and shoulder arthroplasties were performed in Australia. One of the most devastating complications of arthroplasty is periprosthetic joint infection (PJI). In the same year, the incidence of PJI in Australia was estimated at between 2,200 to 2,900 cases per year.² A 2017 study looking at 3,705 Australian primary hip and knee arthroplasties revealed a two-year PJI rate of 1.7% (0.6% within four weeks, and 1.1% between four weeks and two years).³

National arthroplasty registries evaluate the outcome of joint arthroplasty surgery by linking primary procedures to subsequent revisions. Kaplan-Meier estimates of survival are used to report revision rates for all-cause revision and their indication. A revision is defined by the replacement, addition or removal of any component of the arthroplasty hardware. Recent publications assessing the validity of national joint registries in capturing infection as a complication have exposed gaps in reporting accuracy. Registries from Scandinavia and New Zealand under-report infection by up to 40%.^4-7 To assess the validity of PJI reporting, these studies compared PJIs captured by arthroplasty registries to data for the same cohort of patients collected by complementary registries or from hospital discharge diagnostic codes. Although these provide estimates of the proportion of under-reported PJIs, the denominator datasets may not provide patient-specific granular data to explore the patient and surgical factors associated with under-reporting. This might have particular relevance for under-reporting of reoperations for infection which would not be considered reportable. For the present study there were two distinct, but complementary aims. First, we aimed to test the validity of the Australian Orthopaedic Association’s National Joint Arthroplasty Registry (AOANJRR) in identifying infection as an indication for revision and the clinical and surgical factors associated with PJI reporting accuracy. Second, we aimed to use this data to refine estimates of the true burden of PJI in Australia.

Methods

Results

The PIANO study identified 561 Australian cases of confirmed PJI, 501 (89.3%) of which were matched with data available through the AOANJRR (Figure 1). From the data received from the registry, 373 recorded a revision procedure for infection while 128 did not. Only three of the 128 cases with an infection diagnosis were managed nonoperatively (and therefore not reportable to the registry), meaning that a total of 125 cases (25.0%) were not reported to the registry as an infection, despite receiving operative management for a confirmed PJI. The clinical and microbiological characteristics, indication for index arthroplasty, and initial surgical management strategy for participants with confirmed PJI according to reporting status to the registry are shown (Table I).

Fig. 1

Flowchart of study cases. AOANJRR, Australian Orthopaedic Association National Joint Arthroplasty Registry.

The overall median age of all cases matched to the AOANJRR was 69 years (IQR 61 to 77; range 31 to 99), with 269 males and 232 females. There were 200 hip, 277 knee, 21 shoulder, one ankle, and two elbow arthroplasties. Debridement, antibiotics, and implant retention (DAIR) was the initial management strategy for the majority of cases (318; 63.5%). This was followed by two-stage revision (96; 19.1%), suppressive antibiotics (41; 8.2%), single-stage revision (23; 4.6%), “no clear plan” (19; 3.8%), then excision arthroplasty (four; 0.8%).

Bivariable comparisons between reported and not-reported cases demonstrated highly significant differences in PJI type and the initial management strategy (Table I), which were included in the most parsimonious logistic regression model. When compared with late acute PJI, early (within 30 days of implantation) PJIs were less likely to be reported (aOR 0.56 (95% CI 0.34 to 0.93); p = 0.020). There were no significant differences for chronic or other PJI types. Compared with DAIR procedures, two-stage revision procedures were more likely to be reported correctly as a PJI to the registry (aOR 5.3 (95% CI 2.37 to 14.0); p = <0.001). There were no significant differences for other procedures. Age, sex, location of index joint, and microbiological characteristics were not associated with reporting to the registry. There were no significant regional differences in reporting.

Discussion

It has been shown previously that arthroplasty registries under-report infection by up to 40%.^4-7,10 With near universal coverage for arthroplasty operations in Australia, the AOANJRR successfully identified 75%, but did not capture 125 cases of PJI (25%). Only three of the 501 cases matched between the two databases were managed nonoperatively, meaning that a significant proportion of the PIANO population evaded detection by the AOANJRR, despite undergoing some form of operative management for their confirmed PJI. Comparable data from Scandinavia and New Zealand suggests that the Australian registry is performing better than other registries in this regard, with reporting accuracy of 63%, 67%, and 67% PJI for New Zealand, Denmark, and Sweden, respectively.^4-7

To date, there are few data exploring factors associated with reporting accuracy of revision for infection to registries. In the present study, patient demographics, location of joint, microbiological features, or any regional differences between states did not influence the reporting of PJIs to the AOANJRR. The temporal type of PJI influenced rates of reporting, with early (within 30 days of implantation) PJIs being less likely to be reported when compared with late acute PJI (OR 0.56 (95% CI 0.34 to 0.93); p = 0.020).

Two-stage revision procedures were more likely to be reported correctly as a PJI to the registry when compared with other surgical management (OR 5.3 (95% CI 2.37 to 14.0); p ≤ 0.001). These results accord with a smaller cohort from New Zealand, which identified debridement and modular exchange procedures, rather than two-stage revision procedures, as a possible risk for under-reporting.⁷

Although the logistic regression model identified broad independent predictors for non-reporting, our data suggest that outside these factors the specific reasons for non-reporting are multifactorial and inconsistent. It is also important to note that there may be valid reasons for not capturing every PJI in the registry. The basic concept for reporting to the AOANJRR is that events are recorded in relation to revision procedures. For most surgeons this would imply the exchange or removal of at least one of the arthroplasty components. Therefore, operations without component exchange may not be recorded as a revision for PJI and may therefore be responsible for some of the missed PJIs. Indeed, of the 96 revisions for PJI that were not recorded in the joint registry, 77 had a DAIR procedure, and of these, 27 had no component removed. It is plausible that this observation could be explained by surgeons not wanting to be recorded as having a PJI on the registry or being unaware that a liner exchange is considered reportable to the registry.

Timing of the operation may also be important for accurate reporting. Notification of the indication for revision is completed for the AOANJRR at the time of surgery. A delayed or unexpected diagnosis of infection may elude capture by the registry especially if microbiological confirmation is reported days or weeks after the procedure. In our study, this was evidenced by the variety of reported indications reported to the registry according to heterogeneous PJI types and surgical management strategies. The 29 patients with an alternative indication for revision (loosening, lysis, or metal-related problems) might reflect delayed and perhaps unexpected microbiological confirmation of PJI, rather than deliberate misreporting by surgeons. One proposed solution to this is to postpone reporting, which may allow further details and definitive culture reports to become available. The trade-off for this delay is that it might impact on completeness of reporting.¹⁰

The key strength of this study lies in the reference cohort with confirmed PJI, which was based on a large prospective observational study collected across 22 sites within Australia. By recruiting from multiple institutions these data are generalizable in terms of PJI characteristics and management approaches across the country.⁸ A significant amount of detailed data was collected for all patients involved in this study allowing exploration of the clinical, laboratory, and microbiological characteristics associated with PJI reporting.

Our study has limitations. We did not examine the individual reporting forms or intraoperative findings of each case and so cannot confirm the accuracy of the reported information. The AOANJRR reporting forms are often filled out by non-surgical personnel or nursing staff at some point during the procedure and so may either not reflect the correct initial diagnosis or may not account for intraoperative developments, such as infective findings during revision procedures. Another limitation is that PJIs managed without operative intervention with suppressive antibiotics, which are not reportable to the AOANJRR and therefore may not be reflected in the reported incidence of PJI. The PIANO study identified 41 cases of PJI that were managed with suppressive antibiotics; all but three of these cases progressed to a revision procedure at some stage. As noted in the consort diagram, these latter patients were ‘correctly’ not reported to the registry. The final limitation is the representativeness of the institutions contributing to the PIANO data, which might have affected the reporting rates. While we recruited from 22 secondary and tertiary institutions across different Australian states, comprising public and private institutions, it is possible that this might not be reflective of PJI reporting for all institutions across Australia.

The AOANJRR correctly identified 75% of patients in the PIANO study. There are global calls to nest PJI registries within arthroplasty registries to monitor secular trends in PJI, and as a platform for large scale intervention trials.¹¹ To improve the overall capture rate of all PJI, our data suggest that ‘mandatory’ reporting of all DAIR procedures, regardless of whether the liner was exchanged would reduce under-reporting by ~60%. The other major modification to improve PJI reporting accuracy would be to automate linkage of microbiological data collected at the time of surgery.^8,10 This would capture microbiologically confirmed cases that may not have been expected at the time of operative management. Linked microbiological data would also be integral to enable large scale nested randomized controlled trials within the AOANJRR. One further measure would be to enable more than one diagnosis to be reported on the reporting form. This could include ‘suspected infection’, alongside other possible indications for revision.

Of the patients not matched to the AOANJRR, 14 of the 60 unmatched cases preceded the establishment of the registry. Overall, 46 cases had their primary arthroplasty procedure after data recording commenced, but still evaded capture by the AOANJRR. This is concerning as this number is higher than expected given Australia’s near complete reporting compliance, and it is unclear to us why this has occurred. An error in data matching between our study databases or an error in the initial collection of patient demographics by the registry are our most likely hypotheses.