The incidence of postoperative periprosthetic femoral fracture following total hip replacement: An analysis of UK National Joint Registry and Hospital Episodes statistics data

Jonathan Nicholas Lamb; Jonathan Thomas Evans; Samuel Relton; Michael Richard Whitehouse; J Mark Wilkinson; Hemant Pandit

doi:10.1371/journal.pmed.1004462

. 2024 Oct 1;21(10):e1004462. doi: 10.1371/journal.pmed.1004462

The incidence of postoperative periprosthetic femoral fracture following total hip replacement: An analysis of UK National Joint Registry and Hospital Episodes statistics data

Jonathan Nicholas Lamb ^1,^2,^‡, Jonathan Thomas Evans ^2,^3,^4,^‡,^*, Samuel Relton ⁵, Michael Richard Whitehouse ², J Mark Wilkinson ^6,^‡, Hemant Pandit ^7,^‡

¹Centre for Hip Surgery, Wrightington Hospital, Wigan, United Kingdom

²Musculoskeletal Research Unit, Translational Health Sciences, Bristol Medical School, Southmead Hospital, Bristol, United Kingdom

³Exeter Medical School, University of Exeter, St Lukes Campus, Exeter, United Kingdom

⁴National Institute for Health and Care Research Exeter Biomedical Research Centre, Royal Devon University Healthcare NHS Foundation Trust and University of Exeter, Exeter, United Kingdom

⁵Leeds Institute of Health Sciences, School of Medicine, University of Leeds, Leeds, United Kingdom

⁶Division of Clinical Medicine, School of Medicine and Population Health, University of Sheffield, Sheffield, United Kingdom

⁷Leeds Institute of Rheumatic and Musculoskeletal Medicine (LIRMM), University of Leeds, C/O Chapel Allerton Hospital, Leeds, United Kingdom

HP is a NIHR senior investigator and MHRA advisor. In the latter role, he advised MHRA regarding the incidence and risk factors associated with the post-operative peri-prosthetic femoral fractures. In particular, this was to identify the risks associated with one of the commonly used stems (CPT manufactured by Zimmer Biomet). This was a voluntary role and no funding from MHRA was/is associated with it. HP (as a Chief Investigator) receives institutional funding from Zimmer Biomet, Depuy Synthes, Allay Therapeutics, Paradigm Pharma and Invibio. In particular, Zimmer Biomet has funded University of Leeds in relation to the on-going and previous research in the field of peri-prosthetic fractures. HP is a paid consultant to Zimmer Biomet for the work in the field of peri-prosthetic fractures and arthroplasty related teaching / training. HP has also received personal funding from the following industry organisations (unrelated to the topic of this work): Invibio, Medacta International, Smith and Nephew, MATOrtho, Microport, Teleflex, Allay Therapeutics and Paradigm Pharmaceuticals. HP has a stock option with Allay Therapeutics. HP holds two patents (through University of Leeds - in the field of implantable sensors and recharging apparatus). None of these roles / funding from any of the industry organisations (either to HP or to his institution) influenced the design; collection, analysis, and interpretation of data presented in this manuscript)

‡ JNL and JTE share first authorship on this work. JMW and HP are joint senior authors on this work.

^✉

* E-mail: j.t.evans@exeter.ac.uk

Roles

Jonathan Nicholas Lamb: Conceptualization, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft, Writing – review & editing

Jonathan Thomas Evans: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing

Samuel Relton: Formal analysis, Investigation, Methodology, Writing – review & editing

Michael Richard Whitehouse: Conceptualization, Funding acquisition, Investigation, Methodology, Supervision, Writing – review & editing

J Mark Wilkinson: Investigation, Methodology, Supervision, Writing – review & editing

Hemant Pandit: Investigation, Methodology, Supervision, Writing – review & editing

PMCID: PMC11444412 PMID: 39352892

Abstract

Background

Postoperative periprosthetic femoral fracture (POPFF) after total hip replacement (THR) requires complex surgery and is associated with a high morbidity, mortality, and cost. Although the United Kingdom based National Joint Registry (NJR) captures over 95% of THRs treated with revision, before June 2023 it did not capture POPFF treated with fixation. We aimed to estimate the incidence and epidemiology of POPFF treated with either surgery in England.

Methods and findings

We performed a retrospective analysis of a mandatory, prospective database (NJR) linked to Hospital Episode Statistics (HES). All linkable primary THRs between 01/01/2004 and 31/12/2020 were included. Revision or fixation of POPFF were identified using a combination of procedural and diagnosis codes.

We identified 809,832 THRs representing 5,542,332 prosthesis years at risk. A total of 5,100 POPFF were identified that had been surgically treated by revision, fixation, or both, and 2,831 of these fractures were treated with fixation alone, meaning 56% were not represented with revision data alone. The incidence of POPFF needing surgery was 0.92 (95% CI 0.90, 0.95) per 1,000 prostheses years. This incidence was higher in patients over the age of 70 at the time of primary THR (1.31 [95% CI 1.26, 1.35] per 1,000 prostheses years) and for patients who underwent THR for hip fracture (2.19 [95% CI 1.97, 2.42] per 1,000 prostheses years). This incidence appears to be increasing year on year. The cumulative probability of sustaining a POPFF within 10 years of THR was 1% and over 15% of patients died within 1 year of surgery for a POPFF.

Conclusions

To date, the incidence of POPFF may have been underestimated with over 50% of cases missed if the case identification in this study is correct. After including these cases, we observed that POPFF is the largest reason for major reoperation following THR and patients sustaining these injuries have a high risk of death. The prevention and treatment of POPFF and requires further resource allocation and research.

Jonathan Nicholas Lamb and colleagues perform a retrospective analysis of UK data sources to investigate the true incidence of periprosthetic femoral fracture following total hip replacement.

Author summary

Why was the study done?

When the thigh bone supporting a hip replacement breaks because of injury, it is called a periprosthetic fracture of the femur. Patients are usually treated with major surgery, which is associated with significant risk of complications, high cost, and even death.
Currently the best estimates of how often these injuries occur after hip replacement in England are made using data which only counts when fractures are treated with one surgical method, revision and therefore miss a large proportion of cases.
This study is the first large study combining hospital data and the best currently used source to get a much more complete picture of when these fractures occur. In addition to revision, the study was able to capture the other common treatment method, i.e., fixation, thereby providing a comprehensive and more meaningful review.

What did the researchers do and find?

A very large data set of all hip replacements performed in England were matched to health data on hospital admissions to find patients who were treated with either exchange of implants (revision) and fixation of the fracture without exchange of implants.
This study found that previous estimates of periprosthetic fractures only represented about half of the actual number treated in hospitals over the past 2 decades. When cases treated with revision and fixation are combined, periprosthetic fracture appears to be the most common cause of major re-operation after hip replacement.
Patients who go on to sustain a fracture tended to be older and frailer at the time of the first hip replacement than those who do not go on to break. One in 25 patients with fractures died within 30 days of their operation, and the hospital length of stay was over 2 weeks.

What do these findings mean?

These results suggest that periprosthetic fracture after hip replacement is the biggest problem facing patients with a hip replacement and the scale of the problem has previously been underestimated.
Health care providers and researchers should prioritise the prevention and care for these vulnerable patients.

Introduction

Total hip replacement (THR) is the mainstay of treatment for end stage osteoarthritis of the hip and, in general, is safe and effective [1]. While most hip replacements are expected to last over 25 years, failures do occur and this results in severe pain and disability for the patient as well as the need for revision surgery [2], which is costly to both the patient and the health service [3,4]. Hip replacements can fail and need revision for several reasons including infection, joint instability, wear and/or loosening of the hip replacement components, unexplained pain, or when the femur supporting the hip replacement fractures [5]. When this occurs, it is known as a postoperative periprosthetic femoral fracture (POPFF) and is sudden, painful, and debilitating [6]. In most cases, patients are unable to stand and will need to be admitted to hospital for urgent surgery to stabilise the hip replacement allowing the patient to stand and walk. This stabilisation can be in the form of revision to a different type of hip replacement, or retention of the existing implants and internal fixation. Qualitative work has told us that the impact of these fractures is sudden, resulting in patients feeling “powerless” and in “dreadful, dreadful pain” [6]. Patients are often left waiting for days for urgent surgery, not knowing what is going on while specialist equipment is made available and until appropriate surgeons are available [7]. Even after surgery, patients report a loss of independence and confidence in their own mobility which can go on for years [6].

The outcomes of all hip replacements in England and Wales have been continuously monitored as part of the mandatory National Joint Registry (NJR) since 2003 and at the time of the 2023 20th annual report, held information on 1,488,541 primary hip replacement procedures [5]. Until June 2023, the NJR only collected information on hip replacements that had been revised (with additional, removal or modification of THR components) and not those that had been internally fixed with the existing implant remaining in place. This means that research relying on this data was missing fractures treated by fixation alone. As a result, it is impossible to estimate the full scale of the problem which limits the ability to plan and adequately resource the departments managing these injuries [8]. In 2019, the National Hip Fracture Database (NHFD) started collecting information on POPFF and suggest that as many as 60% of POPFF that are treated with surgery are treated with internal fixation, suggesting that the number of patients sustaining these life changing injuries may be twice as many as previously thought [9]. Bottle and colleagues used disease coding to identify patients with any periprosthetic fracture and found large numbers of patients with periprosthetic fractures, and incidence increased over the study period. Over 85% underwent surgical procedure but only 1 in 10 underwent revision operations. Findings were limited by the fact that they could not identify which part of the body the fracture related to and that the international classification of diseases (ICD-10) code they used to identify fractures had only recently been introduced and therefore uptake was unknown [10]. Researchers combining Swedish Arthroplasty Registry and routinely collected health data have estimated a rate of POPFF of 1.4 cases per thousand THR, but application of these estimates to a UK population is problematic where risk factors such as age, comorbidity, indication, and implant use are not equivalent [11,12].

The aim of this study was to identify reoperation for POPFF after primary total hip replacement using a linked implant registry and healthcare data set. This will allow us to investigate the incidence, changes in incidence, demographics of patients sustaining surgically managed POPFF, and outcomes after fracture including length of stay and mortality.

Methods

Ethics statement

This study was approved by the NJR research subcommittee, registration(s): Establishing risk profiles for incident periprosthetic fractures, associated health care costs, and projections for the future [RSC2017/20 HQIP REF: 198] and Periprosthetic fractures around primary total hip replacement [RSC2019/07].

We performed a retrospective review of prospectively collected data for all patients who had details of a primary THR submitted to the NJR. Data was accessed through the NJR research portal and analysed with R (4.2.0). Approval for the study and the planned methodology was granted by the NJR research subcommittee (RSC2017/20 and RSC2019/07) prior to data access and no data driven changes to analyses took place. Hospital Episode Statistics (HES) data is collected on NHS funded procedures performed in the NHS or independent sector in England but are not collected in Wales, Northern Ireland, or the Isle of Man. This study is reported as per the Reporting of studies Conducted using Observational Routinely collected health Data (RECORD) Statement (S1 Checklist).

The study population was all THRs implanted in the NJR from 1 January 2004 and 31 December 2020 with data linkable to HES and consent for their data to be used in research. Linkage was completed by the NJR and data were accessed through the NJR research portal. THRs with incomplete or inconsistent data or using metal-on-metal bearings (previously shown to demonstrate poorer survival) [13] were excluded, as were cases where the implant design was not known.

Patients were included if they had undergone primary THR between 1 January 2004 and 31 December 2020 and had undergone a first reoperation for POPFF after the day of primary surgery. A combination of ICD10 and OPCS4 codes in the HES data were used to identify fractures that had undergone surgery, occurred on the same side as the linked primary hip replacement and after the date of the primary (see S1 Table). This set of codes has not been independently validated for specificity in identifying POPFF. In addition, HES data were used to identify patients that had undergone revision THR and not been reported to the NJR by using the ICD10 and OPCS4 codes already provided by the NJR for use in the annual data quality audit.

Statistical analysis

The primary outcome was incidence of surgically managed POPFF. This consisted of fractures around hip replacement femoral components that were treated with either revision of the implant, internal fixation, or a combination [13,14]. Incidence was estimated using a count of new cases per year or prosthesis time incidence rate (PTIR), which was number of new events per 1,000 years that a prosthesis has cumulatively been in place. The choice of primary outcome (either revision of any part of the THR for any reason (NJR definition) or internal fixation of a POPFF) was made in partnership with the Patient Experience Partnership in Research (PEP-R) group. They advised us that the need to undergo any further surgery is the most important outcome to them regardless of the reason for the surgery [15]. Secondary outcomes included patient survival to an endpoint of POPFF, patient survival to an endpoint of mortality, length of stay, and inpatient bed stay cost. Survival until POPFF was calculated using the Kaplan–Meier (KM) method for all included THRs, censored either by death, or administratively on 31 December 2020 [14]. Mortality was estimated using the KM method for all patients in the study. Length of stay was estimated as the number of whole days between date and time of admission and time of discharge from hospital. Inpatient stay costs were estimated by multiplying total inpatient bed days by an estimated cost of £586.59 per bed day [16]. All analyses were unadjusted.

Results

There were 1,128,684 primary THRs available for analysis of which 864,793 were linkable to the HES database by a unique national identifier. There were 38,703 hips excluded as they had a metal-on-metal bearing surface and 16,256 with an unknown implant design. A flow chart of data sources, inclusions, and exclusions can be seen in Fig 1.

A total of 5,100 POPFF were identified that had either been treated with revision surgery or internal fixation, and 2,831 fractures were treated with internal fixation meaning that 56% were not represented in NJR reports and analyses that captured revision only and in previous research based upon these data. There were 520 additional revisions identified using OPCS4 codes that were not already in the NJR, this is roughly in keeping with results of the NJR annual data quality audits [5].

Fig 2 shows the most common reasons for revision, classified into the subgroups used in the NJR annual report but calculated using our study data set. The grey bars in the figure represent revision operations and the black area represents the additional POPFF treated with internal fixation identified by this study.

Demographics

The demographics of our study population (primary THRs that were linkable with HES data) were representative of the overall NJR population described by the NJR 2023 annual report with the majority of patients being female, ASA 2, and undergoing THR for predominantly osteoarthritis [5]. The full table of demographics can be seen in Table 1.

Table 1. Demographics of overall cohort at time of primary joint replacement.

	Overall
n	809,832
Age (years) (median [IQR])	71.00 [63.00, 77.00]
Patient gender (%)
Female	496,576 (61.3)
Male	313,249 (38.7)
Non-binary	7 (0.0)
ASA at primary THA (%)
P1—Fit and healthy	101,097 (12.5)
P2—Mild disease not incapacitating	556,756 (68.7)
P3—Incapacitating systemic disease	146,984 (18.1)
P4—Life threatening disease	4,922 (0.6)
P5—Expected to die within 24 h with or without an operation	73 (0.0)
Ethnicity (%)
White	688,336 (85.0)
Unknown	109,167 (13.5)
Non white	12,329 (1.5)
Indication for primary THA (%)
Osteoarthritis	715,289 (88.3)
Acute trauma including NOF	34,856 (4.3)
AVN	19,802 (2.4)
Chronic trauma	8,802 (1.1)
Inflammatory arthritis	10,918 (1.3)
Malignancy	1,072 (0.1)
Other	4,874 (0.6)
Paediatric disease	13,347 (1.6)
Previous arthrodesis	236 (0.0)
Previous infection	636 (0.1)
Operation funding (%)
Independent	14,391 (1.8)
NHS	783,225 (96.7)
Unknown	12,216 (1.5)

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Table 2 demonstrates the demographics (at the time of primary THR) that went on to sustain POPFF and underwent surgery for the fracture. These patients appeared to be older, with a higher ASA and had their primary surgery for indications other than solely osteoarthritis.

Table 2. Demographics of patients (at time of primary hip replacement) who went on to sustain a POPFF.

	No fracture		POPFF
n	804,732		5,100
Age (mean (SD))	69.37	(11.04)	73.73	(9.95)
ASA (%)
P1—Fit and healthy	100,639	(12.5)	458	(9.0)
P2—Mild disease not incapacitating	553,397	(68.8)	3,359	(65.9)
P3—Incapacitating systemic disease	145,751	(18.1)	1,233	(24.2)
P4—Life threatening disease	4,872	(0.6)	50	(1.0)
P5—Expected to die within 24 h with or without an operation	73	(0.0)	0	(0.0)
Indication for primary THR (%)
Acute trauma including NOF	34,476	(4.3)	380	(7.5)
AVN	19,659	(2.4)	143	(2.8)
Chronic trauma	8,673	(1.1)	129	(2.5)
Inflammatory arthritis	10,861	(1.3)	57	(1.1)
Malignancy	1,066	(0.1)	6	(0.1)
Osteoarthritis	710,975	(88.3)	4,314	(84.6)
Other	5,705	(0.7)	41	(0.8)
Paediatric disease	13,317	(1.7)	30	(0.6)

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POPFF, postoperative periprosthetic femoral fracture; THR, total hip replacement.

Incidence

We observed that 22,647 of the 809,832 patients (2.8%) underwent surgery for revision (for any cause) or POPFF fixation, during a total of 5,542,332 patients years giving an incidence rate of 4.09 (95% CI 4.03, 4.14) reoperations (for revision or fixation) per 1,000 prostheses years, and 5,100 of the 809,832 included THRs (0.6%) underwent surgery for POPFF giving an incidence rate of 0.92 (95% CI 0.90, 0.95) POPFF per 1,000 prostheses years. The number of new cases of POPFF among patients who had a primary hip replacement recorded in the NJR increased each year (Fig 3).

Fig 3 — POPFF, postoperative periprosthetic femoral fracture.

Analyses restricted by age and indication

There were 407,894 THR performed in patients over the age of 70, leading to 10,691 revision or fixation for POPFF over an exposure time of 2,613,659 years, giving an overall PTIR for revision for any cause or POPFF fixation of 4.09 (95% CI 4.01, 4.17) per 1,000 prostheses years, and 3,417 hips had surgically managed POPFF giving a PTIR for POPFF was 1.31 (95% CI 1.26, 1.35) per 1,000 prostheses years.

There were 94,543 primary THR performed for an indication other than osteoarthritis alone, leading to 3,582 revision or fixation for POPFF over an exposure time of 564,820 years, giving an overall PTIR for revision for any cause or POPFF fixation of 6.34 (95% CI 6.14, 6.55) per 1,000 prostheses years. A total of 786 patients had surgically managed POPFF giving a PTIR for POPFF was 1.39 (95% 1.30, 1.49) per 1,000 prostheses years.

There were 34,856 THR performed for neck of femur fracture, leading to 1,282 revision or fixation for POPFF over an exposure time of 173,650 years, giving an overall PTIR for revision for any cause or POPFF fixation of 7.38 (95% CI 6.98, 7.80) per 1,000 prostheses years. A total of 380 patients had surgically managed POPFF giving a PTIR for POPFF of 2.19 (95% CI 1.97, 2.42) per 1,000 prostheses years.

Timing of fracture

Fig 4 demonstrates that after an early peak, the rate of fracture is relatively consistent. At 10 years, the cumulative probability of sustaining a POPFF requiring surgery was 1% (95% CI 1.0, 1.0).

Mortality

Of the 5,100 patients who had a POPFF identified, 2,347 died during the follow-up period of this study. Death within 30 days of operation to treat the fracture was 4.2% (95% CI 3.6, 4.7), 90 days was 6.7% (95% CI 6.0, 7.4), and within 1 year of injury was 15.4% (95% CI 14.4, 16.4) versus mortality following revision for non-periprosthetic fracture causes which was 0.9% (95% CI 0.8, 1.1) within 30 days, 1.2% (95% CI 1.0, 1.3) within 90 days, and 4.7% (95% CI 4.3, 5.0) within 1 year. The median survival time following fracture was 6.2 years (95% CI 5.9, 6.6 years). A KM plot with death after fracture as the outcome can be seen in Fig 5.

Fig 5 — Shaded area indicates the cumulative incidence estimate 95% confidence interval. POPFF, postoperative periprosthetic femoral fracture.

Length of stay

The median length of overall stay in the acute hospital was 16 days (IQR 10, 26) with patients waiting a median of 3 days prior to receiving surgery (IQR 1, 5). The distribution of length of stay can be seen in S1 Fig.

Cost

Every year since 2015 has seen a total of over 10,000 acute hospital bed days per calendar year for the treatment of POPFF. The estimated cost of inpatient stay alone was £5,865,900 a year, not accounting for the surgical management of the injury, facilities, subsequent rehabilitation, and complications [16].

Discussion

Statement of principal findings

We have observed that in our study population, postoperative periprosthetic femoral fracture is the single most common indication for major reoperation following a total hip replacement. Previous estimates were based on revision surgery alone. We have demonstrated that 56% of fractures were not identified by the NJR, which does not capture those that are treated with fixation without revision of components.

Patients with POPFF were older and frailer than patients without POPFF and 90-day mortality for patients who have undergone revision or fixation of a POPFF was greater than 5 times more than for any other type of revision operation for hip replacement [17]. The cost of looking after patients with these injuries (in bed days alone) may be over £5 million a year without accounting for theatre time, equipment, follow up, and subsequent complications. These results emphasise the significant vulnerability of this patient group in relation to other groups of patients with problematic hip replacement.

Strengths and weaknesses of the study

This is the largest study of its kind identifying fractures around THR stems. The strength of this study is the size and documented completeness of the large mandatory national registry. Although registry data is now considered highly reliable, the initial years (2004 to 2008) of the NJR were less complete and there will be both primary and revision cases missing from these analyses. In this study, information from hospital coding data has been used to identify a greater number of revision operations, which may have previously been missed. These methods are likely to improve accuracy of the data and subsequent observations. We have successfully identified POPFF treated with internal fixation and added them to the already known revisions within the NJR but have not addressed the same issue for two other key reasons for failure infection and dislocation. Dislocated THRs treated with closed or open reduction without modification or changing of the implants will not be identified in this cohort, this is hard to assess using admitted patient HES data (as in this study) as many dislocations are treated with closed reduction in the Emergency Department and may not be admitted to hospital which will not be captured in the available linked data. Recent evidence has demonstrated that the cumulative incidence of dislocation may be as high as 0.9% within 30 days but as few as 11% of these patients undergo revision surgery for dislocation [18]. In a similar manner, infected THRs treated with a debridement and no exchange of implants were not captured prior to June 2018. Operations for infection including debridement and implant exchange will have been captured in the NJR data set. Reoperation for infection is associated with large volume blood loss [19]. Addition of operations for dislocation and infection will improve the validity of large registry data sets in the future and allow for accurate planning and prioritisation of resource allocation and focus for future research. The codes used to identify POPFF in the linked database have not been formally validated as both sensitive and specific to identify only true cases as the pseudonymised data does not allow this. As a result, this may result in over or under identification of cases, the ratio of cases treated with revision and fixation is however consistent with data collected by the NHFD [7,9].

Strengths and weaknesses of the study in relation to other studies

We estimate that the overall prevalence of periprosthetic fracture was 0.6% which was at least double that of previous estimates from large national registries [20–22]. These results are in keeping with previous smaller studies linking the Swedish Arthroplasty Register to national health data, which demonstrated that registry estimates alone under reported the incidence of surgically treated POPFF [11]. This study will not have identified patients who had POPFF treated without surgery, i.e., patients with a stable fracture pattern or those too unwell to tolerate surgery as we were reliant on OPCS4 operative codes to link the side of injury to an initial primary THR. These patients undoubtedly represent an important cohort and in the NHFD have been reported to represent approximately 20% of the total POPFF cohort. These extra patients may still require admission to hospital and will still require significant rehabilitation and social care support and need to be included in an overall health economic estimate of the burden of POPFF. This study identified an increase in the incidence of POPFF in the last decade; this must be interpreted with caution however as NJR data quality and compliance was less reliable in the first part of the last decade [11]. Although we have been unable to investigate the reasons behind delays in taking patients to theatre, this has in some way been addressed by the Facilities Audit of the 2021 National Hip Fracture Database, which cited surgeon availability as the largest cause for preoperative delay. An ongoing study by Imperial College London aims to investigate variations in care between hospitals and regions and further understand the metrics by which care of these patients should be judged [23]. This will be important in guiding further research in this area.

Unanswered questions and future research

Previous failings in the identification of patients who have suffered periprosthetic fracture mean that this population has not been prioritised appropriately. Given the relative scale of the problem, focused efforts should be made to tackle POPFF with adaptation of surgical training, health care pathways, and funding for care and research. Future work using national data sets must also consider both unreported revision and fixation events to build a true picture of implant performance as well as POPFF treated without surgery. Implant survival estimates from the NJR may change once these additional reoperations are included as an endpoint of implant survival, and this effect should be explored in further work. A non-revision reoperation data collection form was added to the NJR in June 2023 but the uptake of this and capture rate is not yet known. As implant registers turn from implant monitoring tools to research tools, efforts should be made to increase the clinically important data captured so that results are reflective of the real-world patient experience.

Further work is needed to understand the causes of POPFF and whether it represents a true fragility fracture or is more related to implant-associated mechanical causes. Methods of preventing fractures such as bone protection and falls prevention may prove important and this warrants further investigation. We have focussed on fracture following THR, but this needs to be expanded to look at other replaced joints as well. The effect of POPFF on the patient experience in the short and longer term requires further investigation, with reference to the specific outcomes of fixation and revision as treatment methods.

Conclusion

Periprosthetic femoral fracture may be the largest cause for major re-operation following THR. Revision only data analysis appears to miss over half of patients who sustain this life changing injury if our method of data capture is accurate. POPFF is associated with high mortality and long stays in hospital both before and after surgery. Research is needed to improve care for this under researched patient group.

Patient and public involvement

The pre-analysis plan for this project was approved by the patient representatives on the NJR research subcommittee which includes 2 patient representatives. The PEP-R group at the Musculoskeletal Research Unit at the University of Bristol advised on the primary outcome of interest and in the interpretation of the results, onward implications, and need for further research as well as aiding in the production of materials for dissemination of results.

Supporting information

S1 Table. Codes used in identifying fractures.

(DOCX)

pmed.1004462.s001.docx^{(23.5KB, docx)}

S2 Table. Breakdown of reasons for revision including items contained within “Other”.

(DOCX)

pmed.1004462.s002.docx^{(14.7KB, docx)}

S1 Fig. Histogram depicting length of stay in the acute hospital after identification of postoperative periprosthetic femoral fracture (POPFF).

(DOCX)

pmed.1004462.s003.docx^{(28.2KB, docx)}

S1 RECORD Checklist. Checklist indicating how this study met the RECORD reporting guidelines.

(DOCX)

pmed.1004462.s004.docx^{(19.1KB, docx)}

Acknowledgments

We are grateful to the continued input and support of our patient group who have helped to shape the design and conduct of this study. We thank the patients and staff of all the hospitals who have contributed data to the National Joint Registry. We are grateful to the Healthcare Quality Improvement Partnership (HQIP), the NJR Research Committee and staff at the NJR for facilitating this work. The authors have conformed to the NJR’s standard protocol for data access and publication.

The views expressed represent those of the authors and do not necessarily reflect those of the National Joint Registry Steering Committee, Research Subcommittee, or the Healthcare Quality Improvement Partnership (HQIP) who do not vouch for how the information is presented.

The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the National Institute for Health Research, or the Department of Health and Social Care.

The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care.

Abbreviations

HES: Hospital Episode Statistics
KM: Kaplan–Meie
NHFD: National Hip Fracture Database
JR: National Joint Registry
PEP-R: Patient Experience Partnership in Research
POPFF: postoperative periprosthetic femoral fracture
PTIR: prosthesis time incidence rate
THR: total hip replacement

Data Availability

Data cannot be shared publicly because they are protected as part of a mandatory national audit. Anonymised data are available from the NJR Research Sub Committee for researchers who meet the criteria for access to confidential data. The process for applying for the data underlying the results presented in the study are available from https://www.njrcentre.org.uk/research/research-requests/. HES Admitted Patient Care data was made available via same route under sublicensing agreement between NJR and NHS England.

Funding Statement

This work was funded by Orthopaedic Research United Kingdom (ORUK) Grant number 540 - Epidemiology of periprosthetic femoral fracture. (JTE) MRW is Principal Investigator (PI) of the National Joint Registry lot 2 contract (statistical analysis) team which is hosted by his employer, the University of Bristol; JTE is a member of the lot 2 contract team. HP (as a Chief Investigator) receives institutional funding from Zimmer Biomet, Depuy Synthes, Allay Therapeutics, Paradigm Pharma and Invibio. In particular, Zimmer Biomet has funded University of Leeds in relation to the on-going and previous research in the field of peri-prosthetic fractures. This study was supported by the National Institute for Health and Care Research Exeter Biomedical Research Centre. This paper presents independent research supported by the National Institute for Health Research (NIHR) Leeds Biomedical Research Centre (BRC). This study was supported by the NIHR Biomedical Research Centre at the University Hospitals Bristol NHS Foundation Trust and the University of Bristol. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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PLoS Med. doi: 10.1371/journal.pmed.1004462.r001

Decision Letter 0

Syba Sunny

11 Apr 2024

Dear Dr Evans,

Thank you for submitting your manuscript entitled "Postoperative periprosthetic femoral fracture is the leading cause of reoperation following total hip replacement: An analysis of linked data from the National Joint Registry and Hospital Episodes Statistics." for consideration by PLOS Medicine.

Your manuscript has now been evaluated by the PLOS Medicine editorial staff and I am writing to let you know that we would like to send your submission out for external peer review.

However, before we can send your manuscript to reviewers, we need you to complete your submission by providing the metadata that is required for full assessment. To this end, please login to Editorial Manager where you will find the paper in the 'Submissions Needing Revisions' folder on your homepage. Please click 'Revise Submission' from the Action Links and complete all additional questions in the submission questionnaire.

Please re-submit your manuscript by the end of Monday 15th April. If you require more time, please just let me know.

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Feel free to email our support team at plosmedicine@plos.org if you need help with inputting your metadata, etc. Otherwise, please feel free to email me directly on ssunny@plos.org

Kind regards,

Syba Sunny, MBBS, MRes, FRCPath

Associate Editor

PLOS Medicine

ssunny@plos.org

PLoS Med. doi: 10.1371/journal.pmed.1004462.r002

Decision Letter 1

Syba Sunny

16 May 2024

Dear Dr. Evans,

Thank you very much for submitting your manuscript "Postoperative periprosthetic femoral fracture is the leading cause of reoperation following total hip replacement: An analysis of linked data from the National Joint Registry and Hospital Episodes Statistics." (PMEDICINE-D-24-01147R1) for consideration at PLOS Medicine.

The paper has been reviewed by two subject experts and a statistician; their comments are included below and can also be accessed here:

[LINK]

As you will see, the reviewers were positive about the paper but, they raised a number of questions about specific study details and the interpretation of data. After discussing the paper with the editorial team, I’m pleased to invite you to revise the paper in response to the reviewers’ comments. We plan to send the revised paper to some or all of the original reviewers*, and of course we cannot provide any guarantees at this stage regarding publication.

When you upload your revision, please include a point-by-point response that addresses all of the reviewer and editorial points, indicating the changes made in the manuscript and either an excerpt of the revised text or the location (e.g. page and line number) where each change can be found. Please submit a clean version of the paper as the main article file and a version with changes marked should as a marked-up manuscript. Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper.

We ask that you submit your revision by Jun 06 2024 11:59PM. However, if this deadline is not feasible, please contact me by email, and we can discuss a suitable alternative.

Please don’t hesitate to contact me directly with any questions (ssunny@plos.org). If you reply directly to this message, please be sure to ‘Reply All’ so your message comes directly to my inbox.

Kind regards,

Syba

Syba Sunny MBBS, MRes, FRCPath

Associate Editor

PLOS Medicine

ssunny@plos.org

*Please note: If your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

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Editorial comments:

1) The editorial team agree that the authors should be commended on undertaking research on an important complication of total hip replacements, and we are grateful for the opportunity to consider your work. However, we do agree with the reviewers’ points with regards to the handling and reporting of data, and also the need to further justify some of the assertions made. All reviewer comments will need to be addressed in full before we can consider the manuscript further.

2) Financial Disclosures

Please provide further information about the funding body, including the funder’s name in full. Also, please describe any affiliations or contracts with the National Joint Registry, if applicable.

3) Data Availability

Thank you for including a statement regarding data availability. Please also include a statement about accessing Hospital Episode Statistics data.

4) Reporting guidance

Please ensure that the study is reported according to the RECORD (STROBE if you feel it is more appropriate) guideline and include the completed RECORD checklist as Supporting Information. Please add the following statement, or similar, to the Methods: "This study is reported as per the Reporting of studies Conducted using Observational Routinely-collected health Data (RECORD) Statement (S1 Checklist)."

When completing the checklist, please use section and paragraph numbers, rather than page numbers.

The relevant guidance can be found here: https://www.equator-network.org/reporting-guidelines/

5) Statistical reporting

Please quantify the main results with 95% CIs and p values.

When reporting p values please report as <0.001 and where higher as p=0.002, for example. When reporting 95% CIs please separate upper and lower bounds with commas instead of hyphens as the latter can be confused with reporting of negative values.

Please include the actual amounts and/or absolute risk(s) of relevant outcomes (including NNT or NNH where appropriate), not just relative risks or correlation coefficients. (example for absolute risks: PMID: 28399126).

Please include any important dependent variables that are adjusted for in the analyses.

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Did your study have a prospective protocol or analysis plan? Please state this (either way) early in the Methods section.

a) If a prospective analysis plan (from your funding proposal, IRB or other ethics committee submission, study protocol, or other planning document written before analyzing the data) was used in designing the study, please include the relevant prospectively written document with your revised manuscript as a Supporting Information file to be published alongside your study, and cite it in the Methods section. A legend for this file should be included at the end of your manuscript.

b) If no such document exists, please make sure that the Methods section transparently describes when analyses were planned, and when/why any data-driven changes to analyses took place.

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Please address past research and explain the need for and potential importance of your study. Indicate whether your study is novel and how you determined that. If there has been a systematic review of the evidence related to your study (or you have conducted one), please refer to and reference that review and indicate whether it supports the need for your study.

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Please present and organize the Discussion as follows: a short, clear summary of the article's findings; what the study adds to existing research and where and why the results may differ from previous research; strengths and limitations of the study; implications and next steps for research, clinical practice, and/or public policy; one-paragraph conclusion.

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Comments from the reviewers:

Reviewer #1:

Realising that NJR data only captures revision procedures, this study linked data from the NJR to Hospital Episode Statistics to also detect re-operations for post-operative periprosthetic fracture that were treated by fracture fixation without revision. They found over half of re-operations were fracture fixations and therefore not included in the NJR. Further analysis of patient demographics, timing of fracture and cost of treatment is included.

The messages from this study are important and highlight a number of concerns about POPFF, however the paper has a number of areas in which it could be improved.

The major problem is that the authors state (in multiple places in the paper) that this study is of the "true" incidence of POPFF, but it is not, as they also point out that some POPFF are treated non-operatively and these are not included. This paper therefore studies only re-operation for POPFF, and this needs to be made clear in the manuscript.

A second major problem is that re-operation for POPFF is compared to only revision for other causes (such as dislocation and infection), so the claim that POPFF is the major cause of re-operation may be incorrect. While there is some discussion about this point, the comparison is unbalanced, and should be better qualified or removed. This consideration also needs to be applied to comparisons of demographic groups and mortality.

Other criticisms include:

Introduction:

Common use descriptions (such as thigh bone, re-do surgery) should be removed as this is a scientific manuscript not a lay article.

The aims of the study need to be more clearly stated.

Methods:

The inclusion/exclusion criteria need to be clearly stated in one place. Some of this information is in the first paragraph and some in the second.

How incidence of POPFF is calculated needs to be stated.

It is unclear what sensitivity analyses were carried out.

There is no mention of how hospital LOS data were obtained or information on hospital costs.

The patient/public involvement would be better placed toward the end in the acknowledgement section.

Results:

In this section the results should be clearly stated and interpretation left for the discussion. For example, comments about previous studies using NJR data, or bimodal distribution of fractures.

Figure 2 is the "reasons for revision" not "failure", as some revisions are carried out with a well-functioning prosthesis, such as for infection. Also what is the difference between the 7th reason for revision "other indication for revision" and the last reason "other"? This figure "shows" the frequency of each reason for revision, the reader "visualises". Part 2 of this should be removed for the reason above.

Similarly, the word "failure" should be removed from the total incidence rate per 1000 patient years. These are re-operations not failures. This is also a mis-leading calculation as it does not include all re-operations.

Figure 3 shows the number of POPFF by year, not the incidence as stated in the text.

The term PTIR needs definition.

I do not understand how the calculated overall incidence of revision and fracture fixation per 1000 patient years is the same as for those over 70 at time of THR (4.09 for both). I would expect these to be different. A comparison of those 70 and over with those less than 70 would be helpful.

Comparison by primary diagnosis may be clearer if grouped into OA, Fractured NOF and Other.

The timing of fracture treatment section needs to simply state the result.

Figure 4 should be titled the cumulative incidence of POPFF.

The display of mortality after fracture treatment may be more easily interpreted if shown as survival. Additionally, a comparison of survival after fracture treatment to survival after revision for other causes in figure 5 would be helpful.

The calculation of cost is difficult to follow without knowing the mean LOS. If in 2015 for instance the number of POPFFs was 410 (as shown graphically), and the median LOS is used, the result is far short of 10,000 hospital bed days. The LOS needs to be at the upper confidence level of 26 to achieve this.

Discussion:

The statement about POPFF being the greatest reason for re-operation needs to be qualified.

I don't understand how frequency, mortality and cost results make this group "vulnerable".

In the discussion there should be mention that only 80% of revisions for POPFF were captured in the NJR, and the implications of this.

The discussion should include the timing of the fracture and how it differs from previous presumptions.

The discussion could include mention of the patient impact.

I don't understand how patients with POPFF are "underserved". They all would have been adequately treated.

Implant survival estimates in the NJR will not change by adding fracture fixation data, as the implant will still be un-revised.

The discussion lacks detail of how this study compares to previous studies looking at POPFF with only one mentioned.

It may be helpful to the reader to have a comparison of the groups treated by revision +/- fixation to those treated by fixation alone.

There is no discussion of prosthesis characteristics for those treated for a POPFF.

Reviewer #2:

Thank you for opportunity to review this interesting paper. I think that the main findings highlight the previously under-estimated burden of periprosthetic fractures. However, in my opinion, the manuscript need some reconstruction. I would also prefer line numbers in the manuscript to make the communication easier.

Specific comments:

Abstract: Please report confidence intervals for incidences.

Introduction:

In general I would prefer shorter introduction. Some parts may be considered to shortened or moved to the discussion. Some previous epidemiology of the periprosthetic femoral fractures should be included, including the estimated incidence and predisposing factors.

"In 2019, the National Hip Fracture Database (NHFD) started collecting information on POPFF but these data are crude, do not include implant information and do not yet appear to be universally completed.1" Please define "universally complete"? What is missing?

If you cite Bottle et al., please shortly repeat their main findings, not only some part of discussion and weaknesses of their study.

Methods

Please define all outcomes you are reporting in the results. Now the results section is very heterogeneous and does not match the outcomes defined. For example, some calculation of the costs are reported in the results but not once mentioned in the methods.

Statistical analysis-paragraph includes mostly information that should not be under statistics-section in my opinion. Please restructure the methods section and leave only part that consider the statistical analyses here.

Results

Figure 2 highlights the missing POPFFs in the NJR data. However, in the limitations of the study you mention that THA infections treated with debridement without change of components are not recorded in the data. Therefore, if I have understood correctly, this figure gives false comparison of the burden of POPFFs compared with infections. Also, the dislocations treated with closed reposition are missing. I find this figure misleading and would consider removing or altering it. If you decide to keep this figure, this problem should be clearly mentioned in the discussion.

"The incidence of POPFF amongst patients who had a primary hip replacement recorded in the NJR appears to be rising by year (Figure 3). This figure must be interpreted with caution however as the early part of the chart represents a time where not as many hips had been input into the NJR and were therefore at risk of POPFF"

This type of speculation inn valid, however it should be in discussion, not in results.

"It is commonly considered that POPFF occur early after implantation (and may represent a missed intraoperative fracture) or that they occur late after implantation (e.g. 10 years or more) secondary to loosening and/or lysis.15" Never use references in the results section, again, this to the introduction or to discussion.

Demographics: Start the result section with demographics and give it short.

Mortality: The mortality rate is known to be high in periprosthetic fractures. Could you compare the mortality rates between patient who suffered a POPFF and those who did not?

Discussion

The first paragraph should focus on the main finding of this study. The following part of the first paragraph could be moved to later discussion and partly added in the conclusions: "A non-revision reoperation data collection form was added to the NJR in June 2023 but the uptake of this and capture rate is not yet known. 90-day mortality for patients who have undergone revision or fixation of a POPFF was greater than five times more than for any other type of revision operation for failing hip replacement.5 The cost of looking after patients with these injuries (in bed days alone) may be over £5 million a year without accounting for theatre time, equipment and follow up/subsequent complications. These results emphasise the significant vulnerability of this patient group in relation to other groups of patients with problematic hip replacement."

Please compare your results in previous studies. What has been the estimated incidence of POPFFs inn the previous studies?

Conclusions: The economic burden could be mentioned here, but not in the principal findings of the study since this was not a cost-analysis study.

Reviewer #3:

Using data from the English(?) National Joint Registry and the National Health Service, the incidence of post-operative periprosthetic femoral fracture after total hip replacement from 2004-2020 inclusive was estimated.

1. Please state what country's national joint registry is being used in the title and in the Background section of the Abstract.

2. Were the 5100 POPFF identified as having been treated with revision surgery or internal fixation those identified in the NJR only? Were the 2831 fractures those identified in the NHS data only? Were any fractures identified in both datasets? That is, please clarify that the 2831 fractures are not included in the NJR dataset.

3. Figure 2 - please state which figure corresponds to before and after inclusion of POPFF in the caption. Is the only difference between the top and bottom histogram the addition of the 2831 fractures identified in the NHS data?

4. Please include the number of patient-years the 809,832 included THRs represents when describing incidence.

5. What is PTIR? This acronym appears first just after Figure 3 but is not defined.

6. What is the shaded area on Figure 4? Please include counts of THAs and events at 0, 5, 10, 15 and 20 years below this figure.

7. The patient demographics section just after Figure 4 should appear as the first subsection of the Results. The Table of demographics of the overall cohort should appear in the main paper.

8. Table 1 provides p-values assessing the differences in various demographic factors for patients who developed POPFF or not. I don't think that Table 1 is particularly useful - if interest is in knowing what demographic factors are causally related to the development of a POPFF, then confounding of the relationship between each of these factors and the outcome must be considered in turn, adjusting for other factors to reduce confounding of this relationship (and a causal diagram should be constructed to aid in selection of these factors). I recommend deleting this and all discussion of this Table. (For an in-depth discussion of this issue, I recommend Hernan and Robins' textbook What if?) Also note that when p-values are presented, it is essential to state which statistical tests were used to generate these.

9. In Figure 5, include the sample size at each year along with cumulative number of events. Please also state what the pink shading is in the caption.

10. How many hospital stays in the Length of Stay section were concluded with discharge from hospital, and how many with in-hospital mortality?

Minor comments:

1. Introduction: please change "patient's report a loss" to "patients report a loss"

2. When it is stated in the Introduction that the NJR is linked to itself, does this mean that records from the same patient are linked to each other?

3. Please provide a reference for the statement "There are 520 additional revisions… this is roughly in keeping with results of the NJR annual data quality audits."

Any attachments provided with reviews can be seen via the following link:

[LINK]

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PLoS Med. 2024 Oct 1;21(10):e1004462. doi: 10.1371/journal.pmed.1004462.r003

Author response to Decision Letter 1

6 Jun 2024

Attachment

Submitted filename: Response_to_reviewers.docx

pmed.1004462.s005.docx^{(57.7KB, docx)}

PLoS Med. doi: 10.1371/journal.pmed.1004462.r004

Decision Letter 2

Syba Sunny

3 Jul 2024

Dear Dr Evans,

Many thanks for submitting your revised manuscript, entitled "Postoperative periprosthetic femoral fracture is the leading cause of major reoperation following total hip replacement: An analysis of linked data from the United Kingdom based National Joint Registry and Hospital Episodes Statistics." (PMEDICINE-D-24-01147R2) to PLOS Medicine. The paper has been re-reviewed by a subject expert and a statistician; their comments are included below and can also be accessed here: [LINK]

As you will see, the reviewers were, on the whole, satisfied with your revised manuscript. However, an academic editor with relevant expertise was also consulted and a concern was raised (see below). Your revised paper was also discussed with the wider editorial team; all were in agreement with the academic editor. As such, we invite you to submit a further revised manuscript addressing this issue and further comments below. Please note that we cannot provide any guarantees at this stage regarding publication.

When you upload your revision, please include a point-by-point response that addresses all of the reviewer and editorial points, indicating the changes made in the manuscript and either an excerpt of the revised text or the location (eg: page and line number) where each change can be found. Please also be sure to check the general editorial comments at the end of this letter and include these in your point-by-point response. When you resubmit your paper, please include a clean version of the paper as the main article file and a version with changes tracked as a marked-up manuscript. It may also be helpful to check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper.

We ask that you submit your revision by Jul 29 2024 11:59PM. However, if this deadline is not feasible, please contact me by email, and we can discuss a suitable alternative.

Don't hesitate to contact me directly with any questions (ssunny@plos.org).

Best regards,

Syba

Dr Syba Sunny, MBBS, MRes, FRCPath

Associate Editor

PLOS Medicine

ssunny@plos.org

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Editorial requests:

We thank you for your thorough revision and we continue to find your research interesting and of clinical importance. As mentioned previously, we invite you to submit a revised manuscript.

We ask that you address the academic editor's comments (below) in full; we believe she has highlighted a significant issue. It would be beneficial to state whether the strategy used to identify patients with postoperative periprosthetic femoral fracture (POPFF) was validated and, if not, we ask that you make an acknowledgement of this in your main text.

Considering the limitations of the data, we also ask if you would consider re-wording the conclusions asserted in all relevant sections to take into account that the incidence of POPFF as a complication of total hip replacement may not be as significant as stated in this and the original version of the manuscript.

Finally, there has been some comments about Figure 2 and the lack of inclusion of counts for 'other' causes of revision that might have been missed in the NJR for what appears to be similar reasons as with POPFF. We think that the readers would appreciate reading the counts for this and this might help them to better contextualise POPFF amongst other complications of total hip replacements. We ask that you address this point further in your second revision.

Thanks again.

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Comments from the academic editor:

The academic editor believed that the topic was 'interesting and clinically relevant' (in keeping with the sentiments of the reviewers and editors). However, she was concerned that the incidence of POPFF might be overestimated by the methods you have used here. She asked that the reliability of the combination of codes used to identify POPFF be clarified and the risk of misdiagnosis (with differential diagnoses) using these codes be discussed as a limitation.

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Comments from the reviewers:

Reviewer #1: A much improved manuscript with greater clarity.

Some simple grammar corrections required.

Perhaps figure 2 could be simplified by discarding the part 2 and a hatched portion added to the periprosthetic fracture column rather than repeating the whole histogram with only change.

Reviewer #3: I thank the authors for their responses to my comments on the previous version of this manuscript. I have no further comments.

PLoS Med. 2024 Oct 1;21(10):e1004462. doi: 10.1371/journal.pmed.1004462.r005

Author response to Decision Letter 2

25 Jul 2024

Attachment

Submitted filename: Response_to_reviewers_2.docx

pmed.1004462.s006.docx^{(4MB, docx)}

PLoS Med. doi: 10.1371/journal.pmed.1004462.r006

Decision Letter 3

Syba Sunny

14 Aug 2024

Dear Dr. Evans,

Thank you very much for re-submitting your manuscript "Postoperative periprosthetic femoral fracture is the leading cause of major reoperation following total hip replacement: An analysis of linked data from the United Kingdom based National Joint Registry and Hospital Episodes Statistics." (PMEDICINE-D-24-01147R3) for review by PLOS Medicine.

I have discussed the paper with my colleagues and the academic editor; I am pleased to say that, provided the remaining editorial and production issues are dealt with, we are now planning to accept the paper for publication in the journal.

The remaining issues that need to be addressed are listed at the end of this email.

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

In your rebuttal letter, you should indicate your response to the editors' comments and the changes you have made in the manuscript. Please submit a clean version of the paper as the main article file. A version with changes marked must also be uploaded as a marked up manuscript file.

Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper.

We expect to receive your revised manuscript within 1 week. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

We ask every co-author listed on the manuscript to fill in a contributing author statement. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT.

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript.

Please note, when your manuscript is accepted, an uncorrected proof of your manuscript will be published online ahead of the final version, unless you've already opted out via the online submission form. If, for any reason, you do not want an earlier version of your manuscript published online or are unsure if you have already indicated as such, please let the journal staff know immediately at plosmedicine@plos.org.

If you have any questions in the meantime, please contact me or the journal staff on plosmedicine@plos.org.

We look forward to receiving the revised manuscript by Aug 21 2024 11:59PM. Please do let us know if you need more time.

Sincerely,

Syba

Syba Sunny, MBBS, MRes, FRCPath

Associate Editor

PLOS Medicine

ssunny@plos.org

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Requests from Editors:

Thank you for engaging so thoroughly with previous editor and reviewer comments. We have further comments/requests; however, most of these simply pertain to journal-specific formatting and content requirements. We ask that you address all in full in order to progress towards publication.

COMPETING INTERESTS

Thank you for the information provided in the Competing Interests section. We very much appreciate as much transparency as possible at PLOS, so we appreciate the authors’ efforts here. I only have one small ask – could you replace the initials ZB with the name of the company these represent, please?

TITLE

Please revise your title according to PLOS Medicine's style. Your title must be nondeclarative. Causality can be inferred only for an RCT. It could perhaps be changed to something like ‘The incidence of periprosthetic femoral fracture following total hip replacement: an analysis of UK National Joint Registry and Hospital Episodes Statistics data’, or similar, as you see fit.

ABSTRACT

Thank you for amending your abstract as requested previously. I note that this amended version hasn’t come across to the relevant ‘meta data’ section (though it is present in your main text) – could you have a look at this and correct this please? If this is not something you find you can correct, please link in with our Editorial Office who might be able to help; they can be contacted via plosmedicine@plos.org.

Also, please remove your funding statement from this section – this can be removed and transferred to the Financial Disclosure section (which forms part of the meta-data for the manuscript).

AUTHOR SUMMARY

Thank you for all your work on this section. Could you kindly address 3 small points in this section:

(1) In the section ‘What did the researchers do and find?’, please revise the sentence ‘When cases treated with revision and fixation are combined, periprosthetic fracture is the most common…’ so it reads ‘… periprosthetic fracture appears to be the most common…’

(2) Could you rename the section ‘ to ‘What Do These Findings Mean?’

(3) In this last section, please revise the sentence ‘These results demonstrate that periprosthetic fracture after hip replacement is the biggest problem facing patients with a hip replacement…’ to ‘These results suggest that …’ or similar.

TABLES and FIGURES

Throughout, including the supporting files, please provide titles/captions/footnotes which clearly describe the table/figure content without the need to refer to the text.

Please ensure all abbreviations including those used for statistical reporting are also clearly defined in the footnote.

Throughout please indicate whether your analyses are adjusted or unadjusted and where adjusted analyses are presented please also present unadjusted analyses for comparison.

Please also ensure to clearly detail in the footnote/caption the factors which are adjusted for.

Please refer to https://journals.plos.org/plosmedicine/s/figures#loc-pages for further guidance.

SOCIAL MEDIA

To help us extend the reach of your research, if not already done so, please detail any X (formerly Twitter) handles you wish to be included when we tweet this paper (including your own, your coauthors’, your institution, funder, or lab) in the manuscript submission form when you re-submit the manuscript.

PLoS Med. doi: 10.1371/journal.pmed.1004462.r007

Decision Letter 4

Syba Sunny

16 Aug 2024

Dear Dr Evans,

On behalf of my colleagues and the Academic Editor, I am pleased to inform you that we have agreed to publish your manuscript "The incidence of periprosthetic femoral fracture following total hip replacement: an analysis of UK National Joint Registry and Hospital Episodes Statistics data." (PMEDICINE-D-24-01147R4) in PLOS Medicine.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow up email. Please be aware that it may take several days for you to receive this email; during this time no action is required by you. Once you have received these formatting requests, please note that your manuscript will not be scheduled for publication until you have made the required changes.

In the meantime, please log into Editorial Manager at http://www.editorialmanager.com/pmedicine/, click the "Update My Information" link at the top of the page, and update your user information to ensure an efficient production process.

PRESS

We frequently collaborate with press offices. If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximise its impact. If the press office is planning to promote your findings, we would be grateful if they could coordinate with medicinepress@plos.org. If you have not yet opted out of the early version process, we ask that you notify us immediately of any press plans so that we may do so on your behalf.

We also ask that you take this opportunity to read our Embargo Policy regarding the discussion, promotion and media coverage of work that is yet to be published by PLOS. As your manuscript is not yet published, it is bound by the conditions of our Embargo Policy. Please be aware that this policy is in place both to ensure that any press coverage of your article is fully substantiated and to provide a direct link between such coverage and the published work. For full details of our Embargo Policy, please visit http://www.plos.org/about/media-inquiries/embargo-policy/.

Thank you again for submitting to PLOS Medicine. We look forward to publishing your paper.

Sincerely,

Syba

Syba Sunny, MBBS, MRes, FRCPath

Associate Editor

PLOS Medicine

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Table. Codes used in identifying fractures.

(DOCX)

pmed.1004462.s001.docx^{(23.5KB, docx)}

S2 Table. Breakdown of reasons for revision including items contained within “Other”.

(DOCX)

pmed.1004462.s002.docx^{(14.7KB, docx)}

S1 Fig. Histogram depicting length of stay in the acute hospital after identification of postoperative periprosthetic femoral fracture (POPFF).

(DOCX)

pmed.1004462.s003.docx^{(28.2KB, docx)}

S1 RECORD Checklist. Checklist indicating how this study met the RECORD reporting guidelines.

(DOCX)

pmed.1004462.s004.docx^{(19.1KB, docx)}

Attachment

Submitted filename: Response_to_reviewers.docx

pmed.1004462.s005.docx^{(57.7KB, docx)}

Attachment

Submitted filename: Response_to_reviewers_2.docx

pmed.1004462.s006.docx^{(4MB, docx)}

Data Availability Statement

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PERMALINK

The incidence of postoperative periprosthetic femoral fracture following total hip replacement: An analysis of UK National Joint Registry and Hospital Episodes statistics data

Jonathan Nicholas Lamb

Jonathan Thomas Evans

Samuel Relton

Michael Richard Whitehouse

J Mark Wilkinson

Hemant Pandit

Roles

Abstract

Background

Methods and findings

Conclusions

Author summary

Why was the study done?

What did the researchers do and find?

What do these findings mean?

Introduction

Methods

Ethics statement

Statistical analysis

Results

Fig 1. Flow diagram demonstrating data sources, matching, and exclusions. NJR, National Joint Registry.

Fig 2. Reasons for revision or reoperation of THRs.

Demographics

Table 1. Demographics of overall cohort at time of primary joint replacement.

Table 2. Demographics of patients (at time of primary hip replacement) who went on to sustain a POPFF.

Incidence

Fig 3. Count of postoperative POPFF identified by year.

Analyses restricted by age and indication

Timing of fracture

Fig 4. Cumulative incidence plot showing occurrence of POPFF.

Mortality

Fig 5. Cumulative mortality (unadjusted) following POPFF.

Length of stay

Cost

Discussion

Statement of principal findings

Strengths and weaknesses of the study

Strengths and weaknesses of the study in relation to other studies

Unanswered questions and future research

Conclusion

Patient and public involvement

Supporting information

Acknowledgments

Abbreviations

Data Availability

Funding Statement

References

Decision Letter 0

Syba Sunny

Roles

Decision Letter 1

Syba Sunny

Roles

Author response to Decision Letter 1

Decision Letter 2

Syba Sunny

Roles

Author response to Decision Letter 2

Decision Letter 3

Syba Sunny

Roles

Decision Letter 4

Syba Sunny

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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