Revision for prosthetic joint infection following hip arthroplasty

Article focus

• Hip prosthetic joint infection (PJI) is an uncommon, but serious, complication of hip arthroplasty.

• Epidemiological evidence from the United Kingdom on revision for PJI is out of date and the majority of available studies are single-centre retrospective cohorts.

• We identified no contemporary studies reporting the frequency or changes in use over time of single- and two-stage revision procedures.

Key messages

• The overall risk of revision for PJI was 0.4% after primary total hip arthroplasty (THA) and 1.6% after aseptic revision THA.

• Between 2005 and 2013, there was an increase in the risk of revision due to PJI in the three months following index THA, with no increase after three months.

• The annual volume of revision hip procedures for treatment of PJI increased 2.6-fold between 2005 and 2013, with an increase in the use of single-stage revision from 18% in 2005 to 39% in 2014.

Strengths and limitations

• The dataset on which this analysis was performed is one of the largest joint arthroplasty registers.

• The recording of PJI as an indication for surgery is according to the opinion of the treating surgeon at the time of surgery. As such, the diagnosis has not necessarily been referenced against a benchmark set of criteria.

• While the National Joint Registry now represents a mature dataset with long-term follow-up, there is still a substantial number of patients undergoing revision THA where there is no record of a linked primary THA.

Introduction

Hip prosthetic joint infection (PJI) is an uncommon, but serious, complication of hip arthroplasty,¹ with an incidence of 0.6% to 2.2%.^2-4 Analysis of national registry data from four Nordic countries between 1995 and 2009 demonstrated an increase in the proportion of primary hip arthroplasties revised for PJI.² Evidence available from the United Kingdom is out of date and primarily derived from single-centre retrospective cohort studies.^3,5

Surgical site infections can have a devastating effect on patients and these infections are sometimes fatal.⁶ PJI may be managed with surgical debridement, antibiotic treatment and implant retention with exchange of modular components (DAIR).⁷ This is commonly used for treatment of acute PJI with pathogens susceptible to antibiotics and in patients unfit for major surgery. However, lifelong suppressive antibiotic treatment may be required and 45% to 52% of patients receiving DAIR may subsequently need revision of their implants.⁸ Rates of revision of implants following treatment with DAIR may be lower with strict selection criteria,⁹ but larger single-centre cohort studies suggest that the rate of revision of implants is around 20% by two years.⁷ About half of patients who are diagnosed with PJI subsequently undergo major revision surgery.^3,10 Single-stage or two-stage revision surgery may be undertaken. For many surgeons, the revision of hip arthroplasties for PJI by a two-stage approach is considered the benchmark¹¹ but there is increasing support for a single-stage approach.¹² Both interventions achieve eradication of infection in about 90% of cases in the two years following revision¹² and are associated with significant morbidity and cost.¹³ We identified no contemporary studies reporting the frequency of use or changes in use over time of the different revision strategies.

We analysed the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR), a large arthroplasty database established in April 2003,¹⁴ to obtain representative and contemporary evidence on the burden of revision surgery for hip PJI in England and Wales.

Our specific aims were to:

• - describe the prevalence rates of revision surgery for the treatment of hip PJI and their time trends broken down by time from index surgery to revision for infection;

• - describe the cumulative incidence functions;

• - estimate the national burden of hip PJI at health service level by accounting for all of the revisions and re-revision surgeries performed for hip PJI registered in the NJR.

The above aims are reported by type of index surgery, i.e. primary or revision surgery for aseptic indications.

Materials and Methods

Results

There were 623 253 primary and 63 222 aseptic revision hip arthroplasties (n = 686 475) recorded in the NJR between April 2003 and December 2013 (Table I). A total of 7040 patients required at least one revision surgery (7585 procedures) due to hip PJI between 2003 and 2014 (primary hip arthroplasty revised for PJI, n = 2705 (2926 procedures), aseptic revision re-revised for PJI, n = 997 (1113 procedures), revision for PJI but no index surgery recorded in the NJR, n = 3338 (3546 procedures)) (Fig. 1).

Fig. 1

Description of procedures recorded in the National Joint Registry (NJR).

Surgeon perspective

Around 0.43% (95% CI 0.42 to 0.45) of the primary hip arthroplasties recorded in the NJR were subsequently revised due to PJI and 1.58% (95% CI 1.48 to 1.67) of the aseptic revision hip arthroplasties were similarly revised due to PJI (Table I).

Figure 2 shows trends in primary surgeries revised for PJI within two years of the index surgery. The revision rates of a primary hip arthroplasty for PJI within three months of the index procedure increased over time, with the rate in 2013 twice that of the rate in 2005: rate ratio (RR) 2.29 (95% CI 1.28 to 4.08), time trend (likelihood ratio test, p < 0.0001). No evidence of time trends in the rates of revision within three to six months, six months to one year, and one to two years, was found between 2005 and 2013. The rates of late revision for PJI decreased over time (supplementary Fig. a): between two and three years (2011 compared with 2005), RR 0.52 (95% CI 0.32 to 0.84), time trend (likelihood ratio test, p < 0.0001); between three and four years (2010 compared with 2005), RR 0.49 (95% CI 0.31 to 0.80), time trend (likelihood ratio test, p = 0.001); and between four and five years (2009 compared with 2005), RR 0.44 (95% CI 0.27 to 0.73), time trend (likelihood ratio test, p = 0.028).

Fig. 2

Prevalence (95% confidence intervals) of revision for prosthetic joint infection within two years of the index primary surgery.

Figure 3 and supplementary Figure b show trends in aseptic revision surgeries revised for PJI. The proportion of aseptic revisions subsequently revised for PJI within three months of the procedure also increased over time, RR 3.00 (95% CI 1.06 to 8.51), time trend (likelihood ratio test, p = 0.002). No important differences were noted in the rates of revision for infection performed at any time beyond three months from the index revision surgery (all time trend, likelihood ratio test, p-values > 0.1).

Fig. 3

Prevalence (95% confidence intervals) of revision for prosthetic joint infection within two years of the index aseptic revision surgery.

Patient perspective

Figure 4 shows the probability over time of revision for infection in patients with an index primary or aseptic revision while accounting for the time at risk of revision for infection, the risk of death and revision for any indication other than infection. The probability of revision for PJI at one year following a primary hip arthroplasty was 0.15% (95% CI 0.14 to 0.16) compared with 0.69% (95% CI 0.63 to 0.76) following an aseptic revision hip arthroplasty. At two years, the probability was 0.26% (95% CI 0.24 to 0.27) and 1.06% (95% CI 0.98 to 1.14) respectively. At five years, it was 0.44% (95% CI 0.42 to 0.46) and 1.77% (95% CI 1.66 to 1.89), respectively. The probability of revision for PJI within the first ten years following primary hip arthroplasty was 0.62% (95% CI 0.59 to 0.65). The ten-year probability following an aseptic revision was much higher, with up to 2.25% (95% CI 2.08 to 2.43) of those procedures subsequently revised for PJI.

Fig. 4

Cumulative incidence function of revision for prosthetic joint infection following index primary and aseptic revision hip arthroplasty (CI, confidence interval).

Discussion

This study is the largest to date investigating the treatment of hip PJI, including 686 475 index primary and aseptic revision hip arthroplasty procedures and 7585 revision THAs performed due to a diagnosis of PJI. It has demonstrated that the probability of undergoing a revision for PJI is higher following aseptic revision hip arthroplasty than for primary hip arthroplasty, and that the risk of undergoing revision for PJI within three months of surgery has risen over time for primary and revision procedures. The majority of revisions performed for PJI are still two-stage procedures, but the use of single-stage revision is increasing. The total burden of treating PJI of the hip has risen substantially and this mirrors the rise in aseptic revision surgery recorded in the NJR rather than the increase in primary surgery over the period of observation.¹⁴

We have shown an elevated cumulative incidence rate of revision for PJI following aseptic revision hip arthroplasty (2.3% at ten years) compared with primary hip arthroplasty (0.6% at ten years). This is consistent with the findings of previous large cohort studies. In analyses of United States Medicare data, Mahomed et al¹⁹ and Zhan et al²⁰ noted a four- to five-fold increased risk of wound infection within 90 days of surgery in patients with revision, compared with primary hip arthroplasty. Similarly, in a United States surgical registry, both Bohl et al²¹ and Pugely et al²² observed an approximate fourfold greater risk of deep infection in the first 30 days after revision, compared with primary hip arthroplasty.

Revision hip arthroplasty is performed in a population with increased host and procedure risk factors for infection or further revision,²³ and involves prolonged operation time and also implantation of a greater volume of prosthetic material and adjuncts such as bone graft that may present a favourable environment for bacterial colonisation and subsequent PJI.²⁴

We have demonstrated a substantial time trend of an increased risk of revision for PJI within the first three months of an index procedure being performed. In their analysis of the Nordic Arthroplasty Register Association dataset, Dale et al² also noted increased revision rates due to hip PJI. Similar to our findings, the increased risk of revision was mainly in the three months after the primary index procedure. The trend for increased risk of early revision for hip PJI is likely to be multifactorial. Factors may include the increased accuracy of tests available to clinicians for the diagnosis of PJI,²⁵ and the increased risk factors for PJI among the population undergoing hip arthroplasty such as elevated body mass index²⁶ and increased bed occupancy.²⁷ It may also represent a progression towards earlier recognition and/or treatment in specialist centres with a subsequent benefit in terms of reduced long-term PJI. There may be a trend towards the use of revision surgery to manage PJI rather than suppressive treatment with antibiotics but we cannot comment on this as non-surgical management of PJI is not captured in the NJR. Risk factors recorded in the Nordic registries could not account for the increase in early revision rates, suggesting that the trend could reflect an actual increase in the risk of early PJI.²

The current rate of surgical revision performed as a consequence of hip PJI is approximately 1000 cases/year across the NJR. This represents a significant healthcare burden which has more than doubled over the last decade. The cost of revision hip arthroplasty due to PJI is more than three times that of primary hip arthroplasty, and over twice that of aseptic revision.²⁸ In the NHS, the cost is in excess of £20 000 per case, not accounting for the litigation costs.¹³ Single-stage revision offers an advantage over two-stage in both patient- and surgeon-derived utility values in the short and long term,²⁹ suggesting that this increased burden could be mitigated by the increased use of single-stage revision.

We have identified an increased use of single-stage, as compared with two-stage, revision for hip PJI. Currently in the NJR, the only option to record DAIR with modular exchange procedures is to record them as single-stage revisions.³⁰ This complicates their differentiation from single-stage surgeries where implants fixed to bone such as a acetabular component and stem (distal or non-modular) are revised. This represents a potential weakness of the data collection form as this may be subject to different interpretation by surgeons, despite the fact that recording of procedures in which any component is removed or inserted is mandatory. We have used component-level data for individual cases to identify DAIR procedures with modular exchange. A few single-stage revisions for PJI unlinked to an index procedure were considered as DAIRs in view of the components implanted (n = 43).

The importance of arthroplasty registries in identifying best clinical practice and improving health outcomes is recognised.³¹ The NJR is one of the largest joint arthroplasty registers, with comprehensive coverage of procedures undertaken, which is reassuring in terms of the generalisability of the data generated by the study. Issues relating to under-reporting, and thus potentially lower incidence estimates, are acknowledged.³² The data are prospectively entered into the registry and are observational which implies certain limitations. The recording of PJI as an indication for surgery is at the discretion of the treating surgeon at the time of surgery. As such, the diagnosis has not necessarily been referenced against a benchmark set of criteria and hence may be subject to misdiagnosis. Linkage to multiple other datasets, including those containing microbiology data and results, may improve the sensitivity and specificity of the diagnosis of PJI in these cases.³³ While the NJR now represents a mature dataset with long-term follow-up, there is still a substantial number of patients undergoing revision hip arthroplasty with no record of a linked primary hip arthroplasty. As anonymised data were provided to us, it is difficult to determine to what extent this might be due to issues related to the patient identification and linkage to their related index procedures in the original dataset. This is reflective of the fact that some PJI revisions were performed in the early days of the registry and relate to index procedures performed prior to the start of the registry or at a time data capture was still improving but incomplete. The proportion of patients with a revision for PJI reported in the NJR but unlinked to an index surgery has indeed reduced over time: from 79% in 2005 compared with 46% in 2009 and 36% in 2014. Survivorship of hip arthroplasty is high¹⁴ and it is also likely that some PJI revision procedures occur a long time after the index procedure due to PJI secondary to haematogenous spread: around 21% (280/1345) of revision procedures for PJI have been reported at greater than two years after the index surgery,³⁴ with 10% performed at five years or beyond. The sample we present is six times larger than previous reports and therefore it is likely that a certain volume of our unlinked procedures are late revisions of index procedures performed before 2003 or in the first years of the registry.

The number of revisions performed annually in England and Wales for infected hip arthroplasties is rising, as is the risk of revision for infection in the first three months following surgery. This has substantial implications for service delivery given the surgical burden and costs associated with performing revision hip arthroplasties for prosthetic joint infection. Single-stage revisions are still performed less frequently than two-stage revisions but are becoming more popular.