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Association between surgeon training grade and the risk of revision following unicompartmental knee replacement: An analysis of National Joint Registry data
Association between surgeon grade and the risk of revision following unicompartmental knee replacement
https://orcid.org/0000-0002-8195-0993
Fowler Timothy J. Conceptualization Data curation Formal analysis Funding acquisition Investigation Methodology Project administration Resources Software Validation Visualization Writing – original draft Writing – review & editing 1 *
Howells Nicholas R. Writing – review & editing 1
Blom Ashley W. Conceptualization Funding acquisition Methodology Resources Supervision Visualization Writing – review & editing 2
https://orcid.org/0000-0001-7452-5043
Sayers Adrian Conceptualization Data curation Formal analysis Investigation Methodology Resources Software Supervision Visualization Writing – review & editing 1 ‡
Whitehouse Michael R. Conceptualization Funding acquisition Investigation Methodology Project administration Resources Supervision Validation Visualization Writing – review & editing 1 3 ‡
1 Musculoskeletal Research Unit, Translational Health Sciences, Bristol Medical School, Southmead Hospital, Bristol, United Kingdom
2 Faculty of Health, The University of Sheffield, Sheffield, United Kingdom
3 National Institute for Health Research Bristol Biomedical Research Centre, University Hospitals Bristol NHS Foundation Trust, University of Bristol, Bristol, United Kingdom
MRW, AWB and AS report holding a contract with The Healthcare Quality Improvement Partnership/The National Joint Registry in the form of the Lot 2 contract (FTS 010307-2022: Statistical Analysis, Support and Associated Services), during the conduct of the submitted work. MRW and AWB were supported by the NIHR Biomedical Research Centre at University Hospitals Bristol and Weston NHS Foundation Trust and the University of Bristol (IS-BRC-1215-20011), during the conduct of the submitted work. MRW and AWB report grants from the NIHR investigating the outcomes of joint replacement, outside the submitted work; MRW and AWB are editors of an Orthopaedic textbook for which they receive royalty payments from Taylor Francis. MRW conducts teaching on courses sponsored by Heraeus and DePuy for which his institution receives market rate payments. All other authors declare no conflicts of interest.

‡ These authors are joint senior authors on this work.

* E-mail: t.j.fowler@bristol.ac.uk
10 9 2024
9 2024
21 9 e100444529 2 2024
19 7 2024
© 2024 Fowler et al
2024
Fowler et al
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Background

Unicompartmental knee replacements (UKRs) are performed by surgeons at various stages in training with varying levels of supervision, but we do not know if this is a safe practice with comparable outcomes to consultant-performed UKR. The aim of this study was to use registry data for England and Wales to investigate the association between surgeon grade (consultant, or trainee), the senior supervision of trainees (supervised by a scrubbed consultant, or not), and the risk of revision surgery following UKR.

Methods and findings

We conducted an observational study using prospectively collected data from the National Joint Registry for England and Wales (NJR). We included adult patients who underwent primary UKR for osteoarthritis (n = 106,206), recorded in the NJR between 2003 and 2019. Exposures were the grade of the operating surgeon (consultant, or trainee) and whether or not trainees were directly supervised by a consultant during the procedure (referred to as “supervised by a scrubbed consultant”). The primary outcome was all-cause revision surgery. The secondary outcome was the number of procedures revised for the following specific indications: aseptic loosening/lysis, infection, progression of osteoarthritis, unexplained pain, and instability. Flexible parametric survival models were adjusted for patient, operation, and healthcare setting factors.

We included 106,206 UKRs in 91,626 patients, of which 4,382 (4.1%) procedures were performed by a trainee. The unadjusted cumulative probability of failure at 15 years was 17.13% (95% CI [16.44, 17.85]) for consultants, 16.42% (95% CI [14.09, 19.08]) for trainees overall, 15.98% (95% CI [13.36, 19.07]) for trainees supervised by a scrubbed consultant, and 17.32% (95% CI [13.24, 22.50]) for trainees not supervised by a scrubbed consultant. There was no association between surgeon grade and all-cause revision in either crude or adjusted models (adjusted HR = 1.01, 95% CI [0.90, 1.13]; p = 0.88). Trainees achieved comparable all-cause survival to consultants, regardless of the level of scrubbed consultant supervision (supervised: adjusted HR = 0.99, 95% CI [0.87, 1.14]; p = 0.94; unsupervised: adjusted HR = 1.03, 95% CI [0.87, 1.22]; p = 0.74).

Limitations of this study relate to its observational design and include: the potential for nonrandom allocation of cases by consultants to trainees; residual confounding; and the use of the binary variable “surgeon grade,” which does not capture variations in the level of experience between trainees.

Conclusions

This nationwide study of UKRs with over 16 years’ follow up demonstrates that trainees within the current training system in England and Wales achieve comparable all-cause implant survival to consultants. These findings support the current methods by which surgeons in England and Wales are trained to perform UKR.

Timothy J. Fowler and colleagues investigate whether the grade of the operating surgeon has an impact on the rate of re-operation following unicompartmental knee replacement in England and Wales.

Author summary

Why was this study done?

Unicompartmental knee replacement (UKR) is an alternative to total knee replacement (TKR) in patients with symptomatic osteoarthritis. The National Institute for Health and Care Excellence (NICE) recommends that patients with isolated medial compartment OA should be offered a choice of UKR or TKR.

Proposed advantages of UKR over TKR include superior functional outcomes, reduced length of stay, fewer medical complications, greater cost-effectiveness, and lower mortality. However, UKR revision rates are considerably higher than TKR revision rates.

The British Association for Surgery of the Knee (BASK) and European Knee Society (EKS) have recommended that knee surgeons should have exposure to and training in UKR.

UKRs are performed by surgeons at different stages in training with varying levels of supervision. However, we do not know if UKRs performed by trainees last as long as those performed by fully trained consultant surgeons.

What did the researchers do and find?

We analysed data from the National Joint Registry for England and Wales (NJR), which is the largest joint replacement registry in the world. We included over 100,000 primary UKRs performed between 2003 and 2019.

We were interested in whether the procedure was performed by a fully trained consultant surgeon, or a trainee. We were also interested in whether or not trainees were directly supervised by a consultant during the operation. The primary outcome was all-cause revision surgery. We used a specialist statistical method called “flexible parametric survival modelling” to analyse the data.

We found no association between surgeon grade and all-cause revision. Trainees achieved comparable outcomes to consultants, regardless of the level of consultant supervision.

What do these findings mean?

These data suggest that within the current training system in the England and Wales, UKRs performed by trainee surgeons last as long as those performed by fully trained consultant surgeons.

The findings of this study are reassuring and support the current methods by which surgeons are trained to perform UKR in England and Wales.

Limitations of this study relate to its observational design. A notable limitation is that we used a binary exposure (consultant, or trainee), which does not capture variations in the level of experience between trainees.

National Joint Registry FTS 010307-2022 Whitehouse Michael R. National Joint Registry FTS 010307-2022 Blom Ashley W. http://dx.doi.org/10.13039/100015250 NIHR Bristol Biomedical Research Centre IS-BRC-1215-20011 Whitehouse Michael R. http://dx.doi.org/10.13039/100015250 NIHR Bristol Biomedical Research Centre IS-BRC-1215-20011 Blom Ashley W. NIHR Academic Clinical Fellowship https://orcid.org/0000-0002-8195-0993
Fowler Timothy J. http://dx.doi.org/10.13039/501100000265 Medical Research Council MR/L01226X/1 https://orcid.org/0000-0001-7452-5043
Sayers Adrian Posts of members of the research team were funded by a contract grant from the National Joint Registry, in the form of the Lot 2 contract (FTS 010307-2022: Statistical Analysis, Support and Associated Services – MRW, AWB and AS). This study was also supported by the National Institute for Health Research (NIHR) Biomedical Research Centre at the University Hospitals Bristol NHS Foundation Trust and the University of Bristol (IS-BRC-1215-20011 – MRW and AWB). TF was supported by a NIHR Academic Clinical Fellowship. AS was supported by an MRC strategic skills fellowship (MR/L01226X/1). The funders had no role in study design, data collection and analysis, the preparation of the manuscript, or the decision to publish. Data AvailabilityThe data used in the study are available from The National Joint Registry (NJR) (https://www.njrcentre.org.uk). Restrictions apply to the availability of these data, which were used under license for the current study, and are therefore not publicly available. Data access applications can be made to the NJR Research Committee. With NJR permission in place, the data underlying the presented results will be available to access via the NJR data access network. The authors of this manuscript are not the data owner and do not have permission to share the data.
Data Availability

The data used in the study are available from The National Joint Registry (NJR) (https://www.njrcentre.org.uk). Restrictions apply to the availability of these data, which were used under license for the current study, and are therefore not publicly available. Data access applications can be made to the NJR Research Committee. With NJR permission in place, the data underlying the presented results will be available to access via the NJR data access network. The authors of this manuscript are not the data owner and do not have permission to share the data.
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pmcIntroduction

Unicompartmental knee replacement (UKR) is an alternative to total knee replacement (TKR) in patients with symptomatic osteoarthritis (OA) isolated to a single compartment [1]. The National Institute for Health and Care Excellence (NICE) recommends that patients in England and Wales with isolated medial compartment OA should be offered a choice of UKR or TKR [2]. The British Association for Surgery of the Knee (BASK) and European Knee Society (EKS) have recommended that knee surgeons should have exposure to and training in UKR [3]. Proposed advantages of UKR over TKR include superior functional outcomes, reduced length of stay, fewer medical complications, greater cost-effectiveness, and lower mortality [4,5]. However, UKR revision rates are considerably higher than primary TKR revision rates [6,7]. Previous studies have suggested that UKRs performed by low-volume surgeons are associated with an increased risk of revision compared to UKRs performed by experienced higher volume surgeons [8,9]. This raises the question of whether or not it is safe for these procedures to be performed by trainees.

The survival of a joint replacement, defined as the absence of revision surgery over time, is the principal metric used for comparing the longevity of implant components and is a commonly used measure of surgical performance. Our current understanding of the survival of UKRs in the context of surgical training is based on a small number of observational studies, which are discussed in our recent systematic review on this subject [10]. Bottomley and colleagues conducted an observational study of 1,084 UKRs, of which 673 (62.1%) were performed by trainees. They reported no significant difference in implant survival between the groups, with 9-year cumulative survival estimates of 93.9% and 93.0% for consultants and trainees, respectively [11]. A New Zealand Joint Registry (NZJR) study of 8,854 UKRs, of which 304 (3.4%) were performed by trainees, reported no difference in the revision rates of supervised senior trainees compared to attending surgeons [12]. This study did not report survival estimates and the overall number of trainee cases in the cohort was insufficient to facilitate meaningful comparison between the supervised and unsupervised trainee groups. The survival of UKRs according to surgeon grade and supervision remains poorly understood. It is not clear if current training practices are safe, or whether trainees achieve comparable outcomes to consultants.

The aim of this research was to use National Joint Registry (NJR) data from England and Wales to investigate the association between surgeon grade, the supervision of trainees, and the risk of revision following UKR.

Methods

Patients and data sources

We performed an observational study using prospectively collected data recorded in the NJR. The initial NJR data set was 1,502,564 linked knee procedures performed between 1 April 2003 and 31 December 2019. We included primary UKRs in adult patients (aged ≥18 years) performed for an indication of OA only. Patellofemoral joint replacements were excluded. Cases were included if the operating surgeon grade was recorded as any of the following: Foundation Year 1 (F1) to Specialty Trainee Year 2 (ST2); ST3-ST8; fellow; or consultant. The process of mapping grade classifications to account for variations in terminology used in different versions of the NJR Minimum Data Set (MDS) form is outlined in S1 Appendix.

Analysis plan

The study protocol was designed prior to commencing the study, including defining the study population, exposures, outcomes of interest, and statistical methods. The main analyses were planned prior to commencing the study and these are documented throughout this methods section. However, data-driven changes to the analysis took place and these are summarised in detail in S2 Appendix, which justifies the model selection and construction.

Data processing

The base data set used in the current study is based on the same cut of NJR data that is used in the 17th Annual Report [13]. NJR data are annually linked to other healthcare system data sets, including Civil Registration Authority data, using unique patient identifiers. This linkage, which was carried out by the NJR prior to us obtaining the data set, is approved by the Health Research Authority under Section 251 of the NHS act 2006 [13]. The steps taken in data processing and are summarised in the study flow diagram in Fig 1 and illustrated in greater detail in S1 Fig. All exclusions are consistent with the exclusion criteria of this study and the stage at which these occurred is clearly documented.

10.1371/journal.pmed.1004445.g001 Fig 1 Study flow diagram.

Exposures

The primary exposure (exposure A) was surgeon grade. This is a binary variable, which was categorised according to the grade of the operating surgeon: (1) consultant; or (2) trainee. Procedures performed by surgeons of the following grades were categorised under the variable “trainee”: F1-ST2; ST3-ST8; and fellow. Consultants have completed their formal training in orthopaedic surgery and been appointed to a senior position in which they can practice independently and supervise trainees.

F1-ST2 represents the first 4 years of postgraduate training after graduating from medical school (F1, F2, ST1, and ST2). ST2 doctors who have completed the Membership of the Royal College of Surgeons (MRCS) examination are eligible to apply to Specialty Training. Specialty Training in Trauma and Orthopaedic Surgery is typically a six-year programme (ST3-8). ST3-ST8 trainees are referred to as “specialty trainees,” or “registrars.” Progression through training levels is dependent on the successful completion of training requirements and competencies. Trainees who have completed ST6 are eligible to sit the examination for Fellowship of the Royal College of Surgeons (FRCS), which is mandatory for Certification of Completion of Training (CCT). Trainees subsequently progress to post-CCT fellowship training prior to applying for a consultant position. The term “consultant” is synonymous with “attending”, and the term “registrar” is synonymous with “resident” in many healthcare settings including the United States of America. A schematic summary of the stages of surgical training in the United Kingdom is included in S3 Appendix [14].

The secondary exposure was whether or not trainees were directly supervised by a consultant during the procedure (exposure B). We refer to direct consultant supervision as “supervised by a scrubbed consultant” throughout this paper. Therefore, trainee cases were subcategorised as follows: (1) trainee supervised by a scrubbed consultant; or (2) trainee not supervised by a scrubbed consultant. Cases were categorised as “supervised by a scrubbed consultant” if the first assistant was recorded as a consultant.

Given the variability in the level of experience between individual trainees, we performed a sensitivity analysis by recategorising cases according to the specific training grade of the operating surgeon (exposure C: consultant; F1-ST2; ST3-ST8; or fellow). Cases were further subcategorised according to the level of scrubbed consultant supervision.

Outcomes of interest

The primary outcome was all-cause revision, which was defined as any procedure to add, remove, or modify one or more components of an implant construct for any reason [13]. The secondary outcome measure was the number of procedures revised for the following specific indications, which are listed as the 5 most common indications for knee replacement revision by the NJR: aseptic loosening/lysis, infection, progression of OA, unexplained pain, and instability [13].

Statistical analysis

Frequencies and percentages were used to describe categorical variables. The mean, standard deviation (SD), and interquartile range (IQR) were used to describe continuous variables. Unrevised cases were either administratively censored on 31 December 2019, or the date of death, depending on which was earliest. Unadjusted estimates of net implant failure were calculated using the Kaplan–Meier (KM) method.

We performed a comprehensive exploratory analysis using Cox regression. A combination of graphical plots, Schoenfeld residuals, and likelihood ratio testing (comparing proportional and non-proportional hazards models) were used to assess the proportional hazards (PH) assumption at each level of adjustment and to assess the time-dependent effects of each confounding variable [15]. Adjusted analyses did not satisfy the PH assumption, which was due to the time-dependent effects of multiple confounding variables included in the models (age, sex, IMD, approach, fixation, bearing mobility, year of operation, and funding source). Surgeon grade (exposures A) did not demonstrate a time-dependent effect.

To account for non-proportionality, we used flexible parametric survival modelling (FPM) [15,16], which has been used in previous NJR analyses [17–20]. This method uses restricted cubic spline functions to model the baseline hazard and account for the time-dependent effects of specified variables. Graphical assessment, AIC, BIC, and likelihood ratio testing were used to optimise the fit and complexity of the final model [15]. This process of model selection, construction, and justification is described in greater detail in S2 Appendix.

Analyses were adjusted for categorical confounding variables in the following manner. Model 1 was unadjusted. Model 2 was adjusted for patient-level factors (age, sex, American Society of Anaesthesiologists (ASA) grade, and index of multiple deprivation (IMD) decile). Model 3 was further adjusted for operation-level factors (anaesthetic, approach, fixation, and bearing mobility). Model 4 was further adjusted for healthcare setting factors (funding source and year of operation). In each case, the baseline category was the most frequently occurring (as detailed in S4 Appendix).

Body mass index (BMI) is missing in a large proportion of NJR records. It has been reported that approximately 40% of patients did not have a BMI recorded in the NJR in 2009, compared to approximately 18% in 2016 [21]. Due to the significant proportion of records with missing values, BMI was not included as a confounding variable in the analyses. This is consistent with the approach used in previous NJR studies and this decision was made prior to initiating the study based on the known pattern of missing data [22,23].

We performed separate analyses for all-cause revision and the 5 specific indications for revision (aseptic loosening/lysis, infection, progression of OA, unexplained pain, and instability), which were examined as separate survival endpoints. Separate FPM analyses were performed for each exposure and analyses were incrementally adjusted for confounding variables.

In response to the peer review process, we conducted an additional sensitivity analysis to explore the lack of independence between observations in patients who underwent bilateral procedures (on the same day, or on different days). We examined the primary outcome measure using a fully adjusted (Model 4) multilevel mixed effects parametric survival model to introduce a frailty term and account for time-dependent effects [24]. All analyses were performed using Stata (Version SE 15.1; StataCorp LP, USA). This study is reported as per the Reporting of studies Conducted using Observational Routinely collected health Data (RECORD) Statement (S1 RECORD Checklist) [25].

Patient and public involvement

Patient representatives sit on the committee structure of the NJR. The research priorities of the NJR are identified by this committee and approved by the patient representatives. Patients were not involved in setting the research question or the outcome measures nor were they involved in the design, implementation, or interpretation of the results of this study. We are unable to disseminate the results of this study directly to study participants due to the anonymous nature of the data. We plan to disseminate our findings through the NJR communications team to relevant individuals who determine the provision of joint replacement and to the general population through local and national press.

Ethics statement

The NJR supports public health surveillance and wider clinical decision-making and holds data that are anonymous to the researchers who use it. NHS Health Research Authority guidance dictates that the secondary use of such data for research does not require approval by a research ethics committee. Therefore, separate research ethics committee approval was not required for this study. Patients are consented for inclusion in the NJR according to standard practice, with permission under the Health Service (Control of Patient Information) Regulations, otherwise referred to as Section 251 support [26].

Results

Descriptive analysis

We included 106,206 UKR procedures in 91,626 patients, of which 4,382 (4.1%) were performed by trainees. Trainees were supervised by a scrubbed consultant in 66.1% (n = 2,898) of trainee-performed cases (Table 1 and Fig 1).

10.1371/journal.pmed.1004445.t001 Table 1 Descriptive statistics for patient, operation, and healthcare setting factors for included UKRs.

Variable	Surgeon grade and supervision (n = 106,206)	
Consultant
(n = 101,824)	Trainee (overall) (n = 4,382)	Trainee supervised by a scrubbed consultant (n = 2,898)	Trainee not supervised by a scrubbed consultant (n = 1,484)	
Mean age (SD)	63.8 (9.7)	65.5 (9.6)	65.4 (9.7)	65.7 (9.5)	
Age groups (%)					
 <55	18,562 (18.2)	594 (13.6)	408 (14.1)	186 (12.5)	
 55–64	35,656 (35.0)	1,416 (32.3)	938 (32.4)	478 (32.2)	
 65–74	33,057 (32.5)	1,541 (35.2)	1,014 (35.0)	527 (35.5)	
 75–84	13,132 (12.9)	745 (17.0)	474 (16.4)	271 (18.3)	
 >85	1,417 (1.4)	86 (2.0)	64 (2.2)	22 (1.5)	
Female (%)	46,972 (46.1)	2,105 (48.0)	1,410 (48.7)	695 (46.8)	
Side (%)					
 Right	50,989 (50.1)	2,138 (48.8)	1,396 (48.2)	742 (50.0)	
IMD decile (%)*					
 1–2 (most deprived)	9,778 (9.6)	496 (11.3)	356 (12.3)	140 (9.4)	
 3–4	14,969 (14.7)	712 (16.3)	501 (17.3)	211 (14.2)	
 5–6	22,054 (21.7)	886 (20.2)	588 (20.3)	298 (20.1)	
 7–8	25,655 (25.2)	1,013 (23.1)	660 (22.8)	353 (23.8)	
 9–10 (least deprived)	29,368 (28.8)	1,275 (29.1)	793 (27.4)	482 (32.5)	
BMI (kg/m 2 )					
 <19 (underweight)	140 (0.1)	5 (0.1)	3 (0.1)	2 (0.1)	
 19–24.9 (normal)	8,049 (7.9)	264 (6.0)	190 (6.6)	74 (5.0)	
 25–29.9 (overweight)	27,948 (27.5)	1,032 (23.6)	699 (24.1)	333 (22.4)	
 >30 (obese)	37,431 (36.8)	1,571 (35.9)	1,101 (38.0)	470 (31.7)	
 Missing	28,256 (27.8)	1,510 (34.5)	905 (31.2)	605 (40.8)	
ASA grade (%)					
 ASA I	21,663 (21.3)	686 (15.7)	466 (16.1)	220 (14.8)	
 ASA II	71,562 (70.3)	3,107 (70.9)	2,021 (69.7)	1,086 (73.2)	
 ASA ≥III	8,599 (8.4)	589 (13.4)	411 (14.2)	178 (12.0)	
Anaesthetic (%)					
 Spinal	57,928 (56.9)	2,193 (50.1)	1,544 (53.3)	649 (43.7)	
 General	47,812 (47.0)	2,164 (49.4)	1,380 (47.6)	784 (52.8)	
 Epidural	4,290 (4.2)	331 (7.6)	174 (6.0)	157 (10.6)	
 Nerve block	16,847 (16.6)	948 (21.6)	607 (21.0)	341 (23.0)	
Approach (%)					
 Lateral parapatellar	3,310 (3.3)	111 (2.5)	89 (3.1)	22 (1.5)	
 Medial parapatellar	90,149 (88.5)	3,982 (90.9)	2,593 (89.5)	1,389 (93.6)	
 Mid-vastus	3,968 (3.9)	131 (3.0)	109 (3.8)	22 (1.5)	
 Sub-vastus	1,595 (1.6)	44 (1.0)	29 (1.0)	15 (1.0)	
 Other	2,802 (2.8)	114 (2.6)	78 (2.7)	36 (2.4)	
Fixation (%)					
 Cemented	79,206 (77.8)	3,208 (73.2)	2,123 (72.2)	1,085 (73.1)	
 Uncemented	20,209 (19.9)	1,036 (23.6)	666 (23.0)	370 (24.9)	
 Hybrid	2,409 (2.4)	138 (3.2)	109 (3.8)	29 (2.0)	
Bearing mobility (%)					
 Fixed	34,268 (33.7)	912 (20.8)	695 (24.0)	217 (14.6)	
 Mobile	62,011 (60.9)	3,153 (72.0)	1,978 (68.3)	1,175 (79.2)	
 Monobloc poly tibia	5,545 (5.5)	317 (7.2)	225 (7.8)	92 (6.2)	
Funding source (%)					
 NHS	77,595 (76.2)	4,370 (99.7)	2,893 (99.8)	1,477 (99.5)	
 Private	24,229 (23.8)	12 (0.3)	5 (0.2)	7 (0.5)	
Year of operation (%)					
 2003–2011	35,054 (34.4)	2,080 (47.5)	1,241 (42.8)	839 (56.5)	
 2012–2019	66,770 (65.6)	2,302 (52.5)	1,657 (57.2)	645 (43.5)	
Data are n (%) or mean (SD); denoted where applicable

*IMD deciles used for analysis.

ASA, American Society of Anaesthesiologists; BMI, body mass index; IMD, index of multiple deprivation; NHS, National Health Service; UKR, unicompartmental knee replacement.

The mean age of patients operated on by trainees was 1.7 years older than patients operated on by consultants (65.5 versus 63.8 years). Trainees operated on a lower proportion of ASA I patients (15.7% versus 21.3%) and a higher proportion of ASA ≥III patients (13.4% versus 8.4%). A higher proportion of trainee procedures utilised uncemented implants (23.6% versus 19.9%) and a mobile bearing (72.0% versus 60.9%) (Table 1).

The maximum duration of follow up was 16.8 years. Mean follow up was 6.5 years (SD 4.3; IQR 2.6 to 10.1 years) for trainee UKRs and 5.6 years (SD 4.00; IQR 2.2 to 8.6 years) for consultant UKRs. A total of 6,920 UKRs were revised at a mean of 4.3 years (SD 3.5; IQR 1.5 to 6.5 years).

Missing data

Details of missing data are documented in S2 Fig. Fewer than 5% of cases (n = 5,120) had missing data. Complete-case analysis was used in all analyses and records with missing data in any confounding variable field used in subsequent statistical models were excluded from the relevant model. This is based on the assumption that the pattern of missingness of NJR data is independent of the primary exposure and the outcome. Considering the large data sets, the small proportion of incomplete cases and the assumed pattern of missingness, any potential improvement in efficiency from using multiple imputation compared to complete-case analysis is likely to be negligible [22,27].

All-cause revision

The unadjusted cumulative probability of failure at 15 years was 17.13% (95% CI [16.44, 17.85]) for consultants, 16.42% (95% CI [14.09, 19.08]) for trainees overall, 15.98% (95% CI [13.36, 19.07]) for trainees supervised by a scrubbed consultant, and 17.32% (95% CI [13.24, 22.50]) for trainees not supervised by a scrubbed consultant. Failure estimates (one minus survival) for all intervals of follow up are presented in Table 2, and graphically displayed as a one minus KM plot in Fig 2.

10.1371/journal.pmed.1004445.g002 Fig 2 Kaplan–Meier plot (one minus survival) demonstrating the cumulative probability of UKR failure (i.e., all-cause revision) according to surgeon grade (exposure A).

10.1371/journal.pmed.1004445.t002 Table 2 The unadjusted cumulative probability of all-cause failure of UKRs according to surgeon grade (exposure A) and supervision (exposure B).

Follow up (years)	Consultant	Trainee (overall)	Trainee supervised by a scrubbed consultant	Trainee not supervised by a scrubbed consultant	
Number at risk*	Number of revisions	% Failure (95% CI)	Number at risk*	Number of revisions	% Failure (95% CI)	Number at risk*	Number of revisions	% Failure (95% CI)	Number at risk*	Number of revisions	% Failure (95% CI)	
1	101,824	986	1.02 (0.96, 1.10)	4,382	47	1.12 (0.84, 1.49)	2,898	29	1.05 (0.73, 0.15)	1,484	18	1.26 (0.80, 2.00)	
3	90,264	2,121	3.63 (3.51, 3.76)	3,954	105	4.01 (3.43, 4.68)	2,605	64	3.74 (3.06, 4.57)	1,349	41	4.52 (3.52, 5.80)	
5	67,809	1,150	5.50 (5.34, 5.67)	3,119	65	6.22 (5.46, 7.08)	2,009	47	6.29 (5.34, 7.40)	1,110	18	6.16 (4.95, 7.65)	
7	49,530	867	7.43 (7.23, 7.64)	2,475	49	8.28 (7.36, 9.32)	1,532	24	7.92 (6.80, 9.21)	943	25	8.93 (7.34, 10.77)	
10	35,199	874	10.52 (10.24, 10.81)	1,916	35	10.35 (9.23, 11.59)	1,180	21	10.10 (8.70, 11.71)	736	14	10.86 (9.08, 12.96)	
13	17,425	461	14.44 (13.99, 14.91)	1,125	39	14.74 (13.05, 16.63)	629	23	14.87 (12.62, 17.49)	496	16	14.76 (12.30, 17.67)	
15	5,117	98	17.13 (16.44, 17.85)	369	4	16.42 (14.09, 19.08)	208	2	15.98 (13.36, 19.07)	161	2	17.32 (13.24, 22.50)	
Data are the number at risk, the number of revision events, the unadjusted cumulative probability of failure and the 95% CI.

*Number at risk at the beginning of interval.

Unadjusted FPM analysis comparing UKRs performed by consultants and trainees (exposure A), indicated that surgeon grade was not associated with the risk of all-cause revision (Model 1: HR = 1.05, 95% CI [0.94, 1.17]; p = 0.40). This finding, which is documented in Table 3, persisted despite incremental adjustment for patient, operation, and healthcare setting factors (Model 4: HR = 1.01, 95% CI [0.90, 1.13]; p = 0.88). Further analysis was performed according to the level of senior supervision (exposure B). Neither crude nor adjusted models demonstrated an association between the level of supervision of trainees and the risk of all-cause revision (Table 3).

10.1371/journal.pmed.1004445.t003 Table 3 Results of flexible parametric models (FPMs) according to surgeon grade (exposure A) and supervision (exposure B).

Indication for revision	Exposure subgroup	Exposure	Revisions (n)*	Model 1 (unadjusted)	Model 2 (adjusted for †)	Model 3 (adjusted for †, ‡)	Model 4 (adjusted for †, ‡, §)	
n = 106,206	n = 106,206	n = 106,206	n = 106,206	
HR	95% CI	p-value	HR	95% CI	p-value	HR	95% CI	p-value	HR	95% CI	p-value	
All-cause revision	A	Consultant	6,576	1.00			1.00			1.00			1.00			
Trainee (overall)	344	1.05	0.94, 1.17	0.40	1.09	0.98, 1.21	0.13	1.05	0.94, 1.17	0.40	1.01	0.90, 1.13	0.88	
B	Consultant	6,576	1.00			1.00			1.00			1.00			
Trainee supervised	210	1.02	0.89, 1.17	0.75	1.05	0.92, 1.21	0.46	1.03	0.90, 1.18	0.70	0.99	0.87, 1.14	0.94	
Trainee unsupervised	134	1.09	0.92, 1.29	0.32	1.15	0.97, 1.36	0.12	1.08	0.91, 1.29	0.36	1.03	0.87, 1.22	0.74	
Progression of OA	A	Consultant	2,161	1.00			1.00			1.00			1.00			
Trainee (overall)	110	0.96	0.79, 1.16	0.64	0.98	0.81, 1.19	0.84	0.97	0.80, 1.17	0.77	0.99	0.82, 1.21	0.95	
B	Consultant	2,161	1.00			1.00			1.00			1.00			
Trainee supervised	77	1.10	0.87, 1.37	0.43	1.11	0.88, 1.40	0.36	1.11	0.88, 1.39	0.38	1.13	0.90, 1.42	0.31	
Trainee unsupervised	33	0.74	0.52, 1.04	0.08	0.77	0.54, 1.08	0.13	0.76	0.54, 1.07	0.11	0.78	0.55, 1.10	0.16	
Aseptic loosening/lysis	A	Consultant	1,877	1.00			1.00			1.00			1.00			
Trainee (overall)	95	1.02	0.83, 1.25	0.86	1.07	0.87, 1.32	0.52	1.03	0.84, 1.27	0.78	0.96	0.78, 1.19	0.72	
B	Consultant	1,877	1.00			1.00			1.00			1.00			
Trainee supervised	60	1.03	0.79, 1.33	0.84	1.08	0.83, 1.39	0.57	1.05	0.81, 1.36	0.70	0.99	0.77, 1.29	0.96	
Trainee unsupervised	35	1.00	0.72, 1.41	0.97	1.06	0.76, 1.48	0.74	0.99	0.71, 1.39	0.97	0.92	0.65, 1.28	0.61	
Unexplained pain	A	Consultant	1,236	1.00			1.00			1.00			1.00			
Trainee (overall)	72	1.24	0.98, 1.57	0.08	1.25	0.98, 1.58	0.07	1.20	0.95, 1.53	0.13	1.08	0.85, 1.37	0.54	
B	Consultant	1,236	1.00			1.00			1.00			1.00			
Trainee supervised	38	1.02	0.74, 1.41	0.90	1.03	0.75, 1.43	0.85	1.01	0.73, 1.39	0.98	0.92	0.66, 1.27	0.60	
Trainee unsupervised	34	1.62	1.15, 2.28	0.01	1.63	1.16, 2.29	0.01	1.54	1.10, 2.17	0.01	1.34	0.95, 1.89	0.09	
Instability	A	Consultant	1,052	1.00			1.00			1.00			1.00			
Trainee (overall)	44	0.86	0.64, 1.16	0.33	0.92	0.68, 1.25	0.59	0.86	0.63, 1.16	0.31	0.80	0.59, 1.09	0.16	
B	Consultant	1,052	1.00			1.00			1.00			1.00			
Trainee supervised	27	0.83	0.57, 1.22	0.35	0.89	0.61, 1.31	0.56	0.85	0.58, 1.24	0.40	0.80	0.54, 1.17	0.25	
Trainee unsupervised	17	0.90	0.56, 1.46	0.67	0.97	0.60, 1.57	0.90	0.87	0.54, 1.41	0.57	0.81	0.50, 1.32	0.41	
Infection	A	Consultant	359	1.00			1.00			1.00			1.00			
Trainee (overall)	22	1.31	0.85, 2.02	0.22	1.32	0.86, 2.04	0.20	1.30	0.84, 2.00	0.24	1.30	0.84, 2.01	0.25	
B	Consultant	359	1.00			1.00			1.00			1.00			
Trainee supervised	13	1.21	0.69, 2.09	0.51	1.22	0.70, 2.13	0.48	1.21	0.70, 2.11	0.50	1.22	0.70, 2.13	0.49	
Trainee unsupervised	9	1.50	0.77, 2.90	0.23	1.51	0.78, 2.93	0.22	1.44	0.74, 2.79	0.29	1.43	0.73, 2.79	0.30	
Data are the number of revisions for each indication, hazard ratio, 95% CI, or p-value.

†Patient factors: age; sex; ASA; IMD decile.

‡Operation factors: anaesthetic; approach; fixation; bearing mobility.

§Healthcare setting factors: funding; year of operation.

*Some cases were revised for more than one indication.

Sensitivity analysis was performed following further subcategorisation of cases according to specific training grade (exposure C) and supervision. There was no evidence of an association between any specific training grade (F1-ST2, ST3-ST8, or fellow) and an increased risk of all-cause revision, regardless of the level of supervision (Table 4). It should be noted that very few UKRs were performed by surgeons in the most junior category (F1-ST2).

10.1371/journal.pmed.1004445.t004 Table 4 Sensitivity analysis: Results of flexible parametric models (FPMs) for all-cause revision according to the specific training grade (exposure C) and supervision.

Exposure	Number of cases	Number of revisions	Complete cases (n = 106,206)	
HR	95% CI	p-Value	
Model 1 (unadjusted)						
Consultant	101,824	6,576	1.00			
F1-ST2 supervised by scrubbed consultant	25	2	2.16	0.70, 6.71	0.18	
F1-ST2 not supervised by scrubbed consultant	19	2	1.17	0.29, 4.69	0.82	
ST3-ST8 supervised by scrubbed consultant	2,746	193	1.04	0.90, 1.20	0.59	
ST3-ST8 not supervised by scrubbed consultant	1,244	99	1.07	0.87, 1.30	0.52	
Fellow supervised by scrubbed consultant	127	14	0.76	0.45, 1.28	0.31	
Fellow not supervised by scrubbed consultant	221	33	1.16	0.83, 1.64	0.39	
Model 2 (adjusted for †)						
Consultant	101,824	6,576	1.00			
F1-ST2 supervised by scrubbed consultant	25	2	2.08	0.67, 6.45	0.21	
F1-ST2 not supervised by scrubbed consultant	19	2	1.15	0.29, 4.64	0.84	
ST3-ST8 supervised by scrubbed consultant	2,746	193	1.08	0.93, 1.24	0.32	
ST3-ST8 not supervised by scrubbed consultant	1,244	99	1.12	0.92, 1.37	0.25	
Fellow supervised by scrubbed consultant	127	14	0.75	0.45, 1.27	0.29	
Fellow not supervised by scrubbed consultant	221	33	1.23	0.87, 1.73	0.23	
Model 3 (adjusted for †, ‡)						
Consultant	101,824	6,576	1.00			
F1-ST2 supervised by scrubbed consultant	25	2	1.99	0.64, 6.17	0.23	
F1-ST2 not supervised by scrubbed consultant	19	2	1.08	0.27, 4.34	0.91	
ST3-ST8 supervised by scrubbed consultant	2,746	193	1.06	0.91, 1.21	0.46	
ST3-ST8 not supervised by scrubbed consultant	1,244	99	1.08	0.88, 1.32	0.45	
Fellow supervised by scrubbed consultant	127	14	0.71	0.42, 1.19	0.19	
Fellow not supervised by scrubbed consultant	221	33	1.11	0.79, 1.56	0.56	
Model 4 (adjusted for †, ‡, §)						
Consultant	101,824	6,576	1.00			
F1-ST2 supervised by scrubbed consultant	25	2	1.93	0.62, 6.01	0.25	
F1-ST2 not supervised by scrubbed consultant	19	2	1.03	0.26, 4.12	0.97	
ST3-ST8 supervised by scrubbed consultant	2,746	193	1.02	0.89, 1.18	0.74	
ST3-ST8 not supervised by scrubbed consultant	1,244	99	1.03	0.84, 1.26	0.77	
Fellow supervised by scrubbed consultant	127	14	0.66	0.39, 1.12	0.12	
Fellow not supervised by scrubbed consultant	221	33	1.04	0.74, 1.46	0.84	
†Patient factors: age; sex; ASA; IMD decile.

‡Operation factors: anaesthetic; approach; fixation; bearing mobility.

§Healthcare setting factors: funding; year of operation.

F1 = Foundation Year 1; ST = Specialty Trainee (number denotes year of training). F1-ST2 is the most junior category, followed by ST3-ST8.

An additional sensitivity analysis was performed to explore the lack of independence between observations in patients who underwent bilateral procedures. The results were very similar, and we found no evidence of an association between surgeon grade (Model 4: HR = 1.01, 95% CI [0.90, 1.13]; p = 0.89) and the risk of all-cause revision.

Indication for revision

The 3 most common indications for revision in this cohort were progression of OA (n = 2,271), aseptic loosening/lysis (n = 1,972), and unexplained pain (n = 1,308). Crude and adjusted analyses demonstrated no evidence of an association between surgeon grade (exposure A) and an increased risk of revision for any indication, including aseptic loosening/lysis, infection, progression of OA, unexplained pain, or instability (Table 3).

Further analysis was performed according to the level of trainee supervision (exposure B). We found no evidence of an increased risk of revision for any indication when trainees were supervised by a scrubbed consultant. However, both crude and adjusted analyses (Models 1–3) demonstrated that procedures performed by trainees without scrubbed consultant supervision were associated with an increased risk of revision for unexplained pain, compared to procedures performed by consultants (Model 1: HR = 1.62, 95% CI [1.15, 2.28]; p = 0.01). This was not observed in the fully adjusted model (Model 4: HR = 1.34, 95% CI [0.95, 1.89]; p = 0.09) (Table 3).

Discussion

This analysis of 106,206 primary UKRs with over 16 years’ follow up represents the largest study to date of UKR outcomes in the context of surgical training. We have demonstrated that when comparing UKRs performed by consultants and trainees, there was no evidence of an association between surgeon grade and the risk of all-cause revision. Trainees achieved comparable outcomes to consultants regardless of the level of scrubbed supervision. There was no evidence that UKRs performed by trainees who were supervised by a scrubbed consultant were associated with an increased risk of revision for any specific indication (including aseptic loosening/lysis, infection, progression of OA, unexplained pain, and instability) compared to consultant-performed UKRs. We found evidence that UKRs performed by trainees who were not supervised by a scrubbed consultant were more likely to be revised for unexplained pain compared to consultant-performed UKRs. However, this was not observed in the fully adjusted model. Revision for unexplained pain following UKR has previously been attributed to low-volume surgeons, but not unsupervised trainees [8]. The most common indication for revision was progression of OA. The NJR defines revision as any procedure to add, remove, or modify one or more components of an implant construct for any reason [13]. Revision for progression of OA in the context of previous UKR implies progression of arthritis in previously unreplaced compartments of the knee. This includes procedures such as revising the UKR to a TKR, or the addition of another UKR (medial, lateral, or patellofemoral) to a previously unreplaced compartment. It does not necessarily imply failure of the individual implant components but is recorded by the NJR as a failure of the construct. We found no evidence of an association between surgeon grade, or the level of supervision and the risk of revision for progression of OA, which suggests that trainers are selecting appropriate cases for their trainees.

We included over 100,000 UKRs, which makes this significantly larger than any previous study of the association between surgeon grade and UKR outcomes [10,28]. Despite limiting our study period to predate the anomalous period of elective orthopaedic practice during the COVID-19 pandemic, our findings are current and represent UKRs with over 16 years of follow up. The data were recorded in a mandatory, nationwide prospective register, which improves the external validity and generalisability of our findings by reducing sampling bias. We employed FPM to model the time-dependent effects of confounding variables and account for non-proportionality. Furthermore, our incremental approach to confounding adjustment increases transparency by demonstrating the relative contribution of patient, operation, and healthcare setting factors to the adjusted results.

Despite these strengths, our study has limitations. This is an observational study and there is likely to be a nonrandom allocation of cases by consultants to trainees. We have attempted to account for this by adjusting for a comprehensive range of confounding variables. However, we acknowledge that there may be residual confounding and confirm that, to our knowledge, there are no further steps to take to adjust for factors that might have influenced the allocation of cases. While this may make it difficult to understand what the true training effect is, our results suggest that the current process of allocating UKR cases to trainees in England and Wales is safe and effective. Implant survival is an important objective metric of success. However, we did not consider other measures that may be relevant when evaluating the success of a joint replacement, such as patient-reported outcome measures, or postoperative complications other than failure, as they are not currently reported by the NJR. OA was the only indication, which along with adjustment for confounding variables, accounts for measurable variations in case complexity between the groups. However, our findings remain susceptible to residual confounding. For example, we did not adjust for BMI which, consistent with other NJR studies, was missing in a high proportion of records [21]. We performed multiple testing for various reasons for revision which may account for the association between unsupervised trainees and revision for unexplained pain that attenuated with adjustment. The distinction between medial and lateral UKRs is not routinely reported by the NJR. The NJR data collection process did not distinguish between medial and lateral UKRs until the introduction of MDS version 7 in 2018 and this information was not available within the data set [13].

The binary variable “surgeon grade” does not capture variations in the level of experience between individual trainees. We have attempted to address this through sensitivity analysis, by categorising cases according to the specific training grade of the surgeon; however, this categorical variable has similar limitations. Furthermore, supervision is recorded by the NJR as a binary variable according to the grade of the first assistant, which does not capture the spectrum of supervision that is necessary in the training process [29]. Thus, these categorical variables do not account for procedures that may have been part-performed by a trainee, or in which a trainee was supervised by an unscrubbed consultant.

A recent systematic review identified a small number of observational studies relating to this subject [10]. In their NZJR study, Storey and colleagues found no significant difference in the revision rate of UKRs performed by supervised senior trainees (n = 276) compared to attending surgeons (n = 8,550). They also reported that supervised senior trainees achieved comparable functional outcomes (Oxford Knee Score) to attending surgeons at 6 months. With only 14 cases in each group, the authors acknowledge that they had insufficient data for any meaningful analysis of the outcomes of UKRs performed by supervised junior trainees and unsupervised senior trainees. Furthermore, the indication for revision was not reported, and the description of the statistical methodology employed is limited [12]. Of note, a similarly low proportion of UKRs are recorded as performed by trainees in the NZJR (3.3%) and NJR (4.1%).

Bottomley and colleagues conducted a single-centre observational study of 1,084 Oxford medial UKRs (Zimmer Biomet, Swindon, UK). Trainees performed 673 UKRs (62.1%) and were supervised by a scrubbed consultant in 48% of cases. They reported no difference in implant survival between the groups, with 9-year cumulative survival estimates of 93.9% (95% CI [90.2, 97.6]) and 93.0% (95% CI [90.3, 95.7]) for consultants and trainees, respectively. In a subgroup analysis, they showed that trainees who had performed fewer than 10 UKRs had a failure rate of 5.1% compared to a failure rate of 4.7% in those who had undertaken more than 10 UKRs; a difference that was not statistically significant [11].

In comparison to the existing literature, the current study is significantly larger, has methodological advantages, longer follow up, and provides novel insight into the importance of scrubbed consultant supervision. Our findings are generally concordant with published data from another national joint registry [12], which suggests that our findings might be generalisable to other countries.

Our findings suggest that current training practices for UKR in England and Wales are safe, when defined by equivalence of survival outcomes. However, only a small proportion of UKRs in these countries are performed by trainees and it should be noted that very few UKRs were performed by surgeons of the most junior specific training grade (F1-ST2). It is likely that UKRs are typically performed by more experienced, senior trainees. However, we were unable to quantify this in the current study, due to the broad categories used by the NJR to record the grade of the operating surgeon.

It is presumed that trainers select appropriate cases for their trainees and permit trainees to operate without scrubbed supervision only when they have reached a subjective threshold of expertise commensurate with safe independent surgical practice. Our study suggests that in this context, trainees achieve comparable all-cause UKR survival to consultant surgeons. In terms of revision for unexplained pain, trainees might achieve their best outcomes when supervised by a scrubbed consultant. However, this association was not observed in the fully adjusted analysis. We propose that trainees should ideally be supervised by a scrubbed consultant when performing UKR, particularly during the early stages of training. When experienced senior trainees operate without scrubbed supervision, careful case selection is required, and scrubbed consultant supervision should be readily available.

The findings of this study are reassuring and support the current methods by which surgeons are trained to perform UKR in England and Wales. This is of particular importance in the context of current NICE guidelines, which recommend that patients with isolated medial compartment OA should be offered a choice of UKR or TKR [2]. This requires future generations of surgeons to be trained in both procedures, or for there to be easily accessible referral networks in place to allow surgeons that do not perform UKR to refer appropriate patients on to surgeons that do.

Conclusion

This nationwide study of UKRs with over 16 years’ follow up demonstrates that trainees in England and Wales achieve comparable all-cause implant survival to consultants. Our findings support the current methods by which surgeons in England and Wales are trained to perform UKR.

Supporting information

S1 RECORD Checklist Reporting of studies Conducted using Observational Routinely collected health Data (RECORD) Checklist.

(DOCX)

S1 Fig Detailed study flow diagram showing sequential exclusions.

(TIF)

S2 Fig Detailed study flow diagram showing exclusion of missing data.

(TIF)

S1 Appendix Process of accounting for changes in NJR operating surgeon grade categories.

(DOCX)

S2 Appendix Model selection, construction and justification.

(DOCX)

S3 Appendix Schematic summary of surgical training in the UK.

(DOCX)

S4 Appendix Model specification summarising the exposures and confounding variables used in the analyses.

(DOCX)

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 National Joint Registry Steering Committee (NJRSC), and staff at the NJR Centre for facilitating this work.

The views expressed in this publication are those of the authors and do not necessarily reflect those of the NHS, the NIHR, the UK Department of Health and Social Care, the NJRSC, or the HQIP.

Abbreviations

BASK British Association for Surgery of the Knee

BMI body mass index

CCT Certification of Completion of Training

EKS European Knee Society

FPM flexible parametric survival modelling

FRCS Fellowship of the Royal College of Surgeons

IMD index of multiple deprivation

IQR interquartile range

KM Kaplan–Meier

NICE National Institute for Health and Care Excellence

NJR National Joint Registry

NZJR New Zealand Joint Registry

OA osteoarthritis

PH proportional hazard

SD standard deviation

TKR total knee replacement

UKR unicompartmental knee replacement

10.1371/journal.pmed.1004445.r001
Decision Letter 0
Sunny Syba Senior Editor
© 2024 Syba Sunny
2024
Syba Sunny
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version0
4 Mar 2024

Dear Dr Fowler,

Thank you for submitting your manuscript entitled "Association between surgeon training grade and risk of revision following unicompartmental knee replacement: an analysis of a National Joint Registry Data" for consideration by PLOS Medicine.

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10.1371/journal.pmed.1004445.r002
Decision Letter 1
Sunny Syba Senior Editor
© 2024 Syba Sunny
2024
Syba Sunny
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version1
12 Apr 2024

Dear Mr Fowler,

Many thanks for submitting your manuscript “Association between surgeon training grade and the risk of revision following unicompartmental knee replacement: an analysis of a National Joint Registry Data” (PMEDICINE-D-24-00668R1) to PLOS Medicine. The paper has been reviewed by three subject experts and a statistician; their comments are included below and can also be accessed here:

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As you will see, the reviewers were positive about the paper but they raised a number of questions about specific study details and the methodological approach. After discussing the paper with the editorial team and an academic editor with relevant expertise, 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 of all of the original reviewers*, and of course we cannot provide any guarantees at this stage regarding publication.

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Editorial comments:

The editorial team all agree that you present a very interesting study and, we are grateful that you gave us the opportunity to consider your work. We are pleased that the peer reviews were positive. However, we do also agree with the reviewers’ points regarding your data analyses (please see below) which could be more robust and additionally informative. All reviewer comments will need to be addressed before we can consider the manuscript further. Please see below for specific comments and respond in full.

----------------------------

Comments from the reviewers:

Reviewer #1:

This study uses a national joint registry to compare the revision rate of UKR when the primary surgeon was either a trainee or a consultant to establish whether the current training model is appropriate with respect to the longevity of the implant. The conclusions were that there is little difference between the revision outcomes between trainees and consultants, including those cases where the trainee is "supervised" or "non supervised" and that the current training model does not disadvantage patients.

Generally the methodology is satisfactory within the framework of using registry data. The authors do not distinguish between lateral and medial UKR which I find a little unusual when we know that lat UKR especially with a mobile bearing are technically more difficult with a higher revision rate. It would be interesting to know if there is indeed a difference in the UK. If the authors cannot easily separate the med from lat UKRs then I would like to see a section relating to this in the limitation section.

Progression of OA was the commonest cause for revision and I would like the authors to expand on the implications of this cause for revision within the framework of the study - progression of OA is hardly a failure of the implant and more likely to be due to inappropriate patient selection (overstuffing may have occurred but is probably much less likely to cause progression of OA especially as we know that there continues to be subsidence of both cemented and uncemented implants over time), not being aware of OA elsewhere at the time of surgery, which is likely to be a decision event which is outside of the trainee's brief. Although the actual revision rate for progression of OA is similar across all surgeons a comment on this would be useful.

The authors comment on the limitation of no PROMs data which is a significant limitation, especially when considering unexplained pain, however within the confines of registry data this is acceptable.

Otherwise I believe the authors should be congratulated for a robust and sound study.

Reviewer #2: See attachment

Michael Dewey

Reviewer #3:

The authors evaluated patient outcomes following unicompartmental knee joint replacement surgery upon the variable of whether the surgeon was a consultant or trainee and demonstrated that there was no difference in the primary outcome - need for revision surgery with long term follow up. This is a national registry study and is subject to limitations which the authors transparently discussed. Given that this is the most common method of training surgical trainees, I think this is a valuable contribution to the literature and provides insight into potential risk or lack thereof with our current methods.

Reviewer #4:

The authors investigated the revision rate of UKA in the NJR, by controlling for trainee vs consultants.

Please add line numbers to facilitate review.

The main issue is controlling for consultant surgeon, in light of the data on UKA.

There is sufficient evidence demonstrating that UKA should be performed on a regular basis to decrease revision. Thus, comparing low volume consultant surgeons with trainees might omit the true data.

In these papers, the cut-off of consultant with at least 100 knee arthroplasty was used, which is a more fair comparison. I suggest adding this analysis.

10.1007/s00167-021-06650-4

The paper is otherwise well written.

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

[LINK]

----------------------------

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---------------------------------------------------------

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Attachment Submitted filename: fowler.pdf

10.1371/journal.pmed.1004445.r003
Author response to Decision Letter 1
Submission Version2
11 May 2024

Attachment Submitted filename: Response.docx

10.1371/journal.pmed.1004445.r004
Decision Letter 2
Sunny Syba Senior Editor
© 2024 Syba Sunny
2024
Syba Sunny
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version2
5 Jun 2024

Dear Mr. Fowler,

Thank you very much for re-submitting your manuscript "Association between surgeon training grade and the risk of revision following unicompartmental knee replacement: an analysis of a National Joint Registry Data" (PMEDICINE-D-24-00668R2) for review by PLOS Medicine.

We are grateful for your detailed responses to the editorial and reviewer comments. I am pleased to say that the reviewers were satisfied with your revision. Please see below for further comments which we require that you address prior to publication.

***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 revising the manuscript for further consideration here, please ensure you address the specific points made by each reviewer and the editors. In your rebuttal letter you should indicate your response to the reviewers' and 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.

We expect to receive your revised manuscript within 2 weeks. Please email us (ssunny@plos.org or plosmedicine@plos.org) if you have any questions or concerns.

Please note, at the point of acceptance, 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 Wednesday 19th June.   

Sincerely,

Syba

Syba Sunny, MBBS, MRes, FRCPath

Associate Editor 

PLOS Medicine

ssunny@plos.org

------------------------------------------------------------

Comments from Reviewers:

Reviewer #1: I am satisfied that the authors have addressed my concerns satisfactorily

Reviewer #2: The authors have addressed all my points

Reviewer #4: The authors performed a thorough revision.

------------------------------------------------------------

Editorial comments:

GENERAL

Many of the editorial requests detailed below pertain to specific formatting and content requirements. Some may have already been incorporated into the manuscript and some may not apply, but please review the complete list of items and ensure that each item is included as necessary.

Our Academic Editor commented that your rebuttal letter was ‘thoughtful and thorough’ and only had one small suggestion at this stage: that your abstract should report absolute risks and not just relative risks.

OBSERVATIONAL STUDIES

In the manuscript text, please indicate: (1) the specific hypotheses you intended to test, (2) the analytical methods by which you planned to test them, (3) the analyses you actually performed, and (4) when reported analyses differ from those that were planned, transparent explanations for differences that affect the reliability of the study's results. If a reported analysis was performed based on an interesting but unanticipated pattern in the data, please be clear that the analysis was data-driven.

DATA AVAILABILITY

Please provide a URL or email address for data applications to the Census Bureau.

COMPETING INTERESTS

Thank you for acknowledging that members of the research team were funded by a contract grant from the National Joint Registry (NJR). Could you provide more details please? What does this contract entail? The funding statement should include: specific grant numbers, initials of authors who received each award, URLs to sponsors’ websites, etc. I see that you write that the NIHR had no role in the design and conduct of the study, etc – I would be grateful if you could include a similar statement (where it applies) with regards to the NJR.

ABSTRACT

In the final sentence of the abstract methods and findings section, please detail the limitations of the study.

AUTHOR SUMMARY

Thank you for including this Author Summary.

Line 7 – Please briefly expand on the statement that ‘there is a growing demand for surgeons to be trained in [UKR]’ – it would be useful for readers to know why there is such a demand within this summary.

Line 11 onwards – Please re-phrase your sentences here to help readers who do not have specialist knowledge to better understand exactly what you did and/or why. For example, ‘parametric survival models’ or ‘scrubbed consultants’ may not be well-understood. Please revise for accessibility to the non-scientific reader avoiding the use of what might be considered medical and/or scientific ‘jargon’.

In the final bullet point of ‘What Do These Findings Mean?’, please describe the main limitations of the study in non-technical language.

Line 21 – suggest ‘These data suggest…’ or similar.

INTRODUCTION

Our journal readership is global – please consider revising the sentences here to reflect that you are referring to UK-based observations and guidelines.

STATISTICAL REPORTING

Throughout, 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).

DISCUSSION

Please re-phrase ‘We included over 100,000 knees…’ to ‘We included over 100,000 knee operations…’ (or similar).

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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.

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MAIN TEXT - MISCELLANEOUS

Throughout your manuscript, please avoid the use of the term ‘retrospective’ to describe your study and instead refer to it as ‘observational’. In the Abstract, for example. Please check and amend throughout.

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Please ensure you apply all guidance detailed above to the supporting information files.

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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.

10.1371/journal.pmed.1004445.r005
Author response to Decision Letter 2
Submission Version3
27 Jun 2024

Attachment Submitted filename: Response.docx

10.1371/journal.pmed.1004445.r006
Decision Letter 3
Sunny Syba Senior Editor
© 2024 Syba Sunny
2024
Syba Sunny
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version3
10 Jul 2024

Dear Mr Fowler,

Thank you very much for re-submitting your manuscript "Association between surgeon training grade and the risk of revision following unicompartmental knee replacement: an analysis of a National Joint Registry Data" (PMEDICINE-D-24-00668R3) 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 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 revising the manuscript for further consideration here, please ensure you address the specific points made by the editors. In your rebuttal letter you should indicate your response to the reviewers' and 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.

We expect to receive your revised manuscript within 1 week. Please email me directly if you have any questions or concerns.

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.

We look forward to receiving the revised manuscript by Jul 17 2024 11:59PM.   

Sincerely,

Syba

Dr Syba Sunny, MBBS, MRes, FRCPath

Associate Editor 

PLOS Medicine

ssunny@plos.org

------------------------------------------------------------

Requests from Editors:

Many thanks again for submitting your revised manuscript. I have discussed your response to ‘Comment 1’ with the academic editor and he would be happy for you to report the cumulative probabilities in your abstract. In addition to this, I have detailed below some other points that I would ask you to address.

Title: Please revise the latter part of your title for clarity, e.g. replace ‘an analysis of a National Joint Registry Data’ with ‘an analysis of National Joint Registry Data’ or similar.

Please mention the location (i.e. England and Wales) in the Background section of the Abstract.

We suggest that you revise the statement in your abstract that reads ‘Unsupervised trainee cases were associated with an increased risk of revision for unexplained pain compared to consultant-performed UKRs, in all but the fully adjusted model’. Given that there was no difference in the fully adjusted model, it would seem to us that essentially there was no real difference to be found here.

Please replace ‘all cause’ with ‘all-cause’ (i.e. with a hyphen) throughout your manuscript.

Thank you for revising the phrase ‘scrubbed consultant’ in line 11 of your earlier version of the manuscript. Please revise the phrase in the Methods and Findings section of your abstract too.

In the conclusions section of your abstract, please insert an apostrophe after the word ‘years’ in the phrase ‘16 years follow up’, so it reads ‘16 years’ follow up’.

In your Author Summary, could you briefly expand here why UKR is better than the more usual alternative; why is this recommended by NICE, etc?

Under your Exposures subheading, you mention ‘scrubbed consultants’. This is completely acceptable here, but it might make better reading if you qualify what this term means in the first instance of mentioning it and then state something along the lines of ‘henceforth referred to as scrubbed consultants…’ (or similar).

On page 11 of your manuscript, replace the square brackets for ASA, IMD and BMI with parentheses, i.e. ().

On page 12, line 6, there is a missing word ‘in’. The sentence ‘…more were they involved the design’ should have an ‘in’ before the word ‘the’.

In the section named Contributors, I note that the initials used for the authors used is not consistent with those used in the Financial Disclosures section – could this be revised for consistency please?

10.1371/journal.pmed.1004445.r007
Author response to Decision Letter 3
Submission Version4
18 Jul 2024

Attachment Submitted filename: Response.docx

10.1371/journal.pmed.1004445.r008
Decision Letter 4
Sunny Syba Senior Editor
© 2024 Syba Sunny
2024
Syba Sunny
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version4
19 Jul 2024

Dear Mr Fowler, 

On behalf of my colleagues, I am very pleased to inform you that we have agreed to publish your manuscript "Association between surgeon training grade and the risk of revision following unicompartmental knee replacement: an analysis of National Joint Registry Data" (PMEDICINE-D-24-00668R4) in PLOS Medicine.

Prior to publication, could you replace the capital D in the word Data in your full title with a lower case d please? The title should then read: ‘Association between surgeon training grade and the risk of revision following unicompartmental knee replacement: an analysis of National Joint Registry data’. (Apologies, this was my oversight!)

Before your manuscript can be formally accepted, you will also 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/.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. Additionally, PLOS ONE offers an option to publish peer-reviewed clinical study protocols. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols

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

ssunny@plos.org
==== Refs
References

1 Price AJ , Alvand A , Troelsen A , Katz JN , Hooper G , Gray A , et al . Knee replacement. Lancet. 2018;392 (10158 ):1672–82. doi: 10.1016/S0140-6736(18)32344-4 30496082
2 NICE: Joint replacement (primary): hip, knee and shoulder [NG157] 2023 [cited 24/06/2024]. Available from: https://www.nice.org.uk/guidance/ng157/chapter/Recommendations#procedures-for-primary-elective-knee-replacement.
3 Price A , Thienpont E , Catani F , Abram S , Troelsen A, Bask , et al . Consensus statement on unicompartmental knee replacement: A collaboration between BASK and EKS. Knee. 2023;41 :391–6. doi: 10.1016/j.knee.2023.03.015 37088518
4 Wilson HA , Middleton R , Abram SGF , Smith S , Alvand A , Jackson WF , et al . Patient relevant outcomes of unicompartmental versus total knee replacement: systematic review and meta-analysis. BMJ. 2019;364 :l352. doi: 10.1136/bmj.l352 30792179
5 Beard DJ , Davies LJ , Cook JA , MacLennan G , Price A , Kent S , et al . The clinical and cost-effectiveness of total versus partial knee replacement in patients with medial compartment osteoarthritis (TOPKAT): 5-year outcomes of a randomised controlled trial. Lancet. 2019;394 (10200 ):746–56. doi: 10.1016/S0140-6736(19)31281-4 31326135
6 Evans JT , Walker RW , Evans JP , Blom AW , Sayers A , Whitehouse MR . How long does a knee replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up. Lancet. 2019;393 (10172 ):655–63. doi: 10.1016/S0140-6736(18)32531-5 30782341
7 Hunt LP , Blom AW , Matharu GS , Kunutsor SK , Beswick AD , Wilkinson JM , et al . Patients Receiving a Primary Unicompartmental Knee Replacement Have a Higher Risk of Revision but a Lower Risk of Mortality Than Predicted Had They Received a Total Knee Replacement: Data From the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man. J Arthroplasty. 2021;36 (2 ):471–7 e6. doi: 10.1016/j.arth.2020.08.063 33011013
8 Baker P , Jameson S , Critchley R , Reed M , Gregg P , Deehan D . Center and surgeon volume influence the revision rate following unicondylar knee replacement: an analysis of 23,400 medial cemented unicondylar knee replacements. J Bone Joint Surg Am. 2013;95 (8 ):702–9. doi: 10.2106/JBJS.L.00520 23595068
9 Liddle AD , Pandit H , Judge A , Murray DW . Effect of Surgical Caseload on Revision Rate Following Total and Unicompartmental Knee Replacement. J Bone Joint Surg Am. 2016;98 (1 ):1–8. doi: 10.2106/JBJS.N.00487 26738897
10 Fowler TJ , Aquilina AL , Blom AW , Sayers A , Whitehouse MR . Association between surgeon grade and implant survival following hip and knee replacement: a systematic review and meta-analysis. BMJ Open. 2021;11 (11 ):e047882. doi: 10.1136/bmjopen-2020-047882 34758989
11 Bottomley N , Jones LD , Rout R , Alvand A , Rombach I , Evans T , et al . A survival analysis of 1084 knees of the Oxford unicompartmental knee arthroplasty: a comparison between consultant and trainee surgeons. Bone Joint J. 2016;98-B (10 Supple B):22–7. doi: 10.1302/0301-620X.98B10.BJJ-2016-0483.R1 27694512
12 Storey R , Frampton C , Kieser D , Ailabouni R , Hooper G . Does Orthopaedic Training Compromise the Outcome in Knee Joint Arthroplasty? J Surg Educ. 2018;75 (5 ):1292–8. doi: 10.1016/j.jsurg.2018.02.011 29574018
13 National Joint Registry: 17th Annual Report 2020 [cited 24/06/2024]. Available from: https://reports.njrcentre.org.uk/Portals/10/PDFdownloads/NJR%2017th%20Annual%20Report%202020.pdf.
14 Fitzgerald JE , Giddings CE , Khera G , Marron CD . Improving the future of surgical training and education: consensus recommendations from the Association of Surgeons in Training. Int J Surg. 2012;10 (8 ):389–92. doi: 10.1016/j.ijsu.2012.03.012 22449833
15 Royston P , Lambert PC . Flexible parametric survival analysis using stata: beyond the Cox model. College Station, Tex.: Stata; 2011.
16 Lambert PC , Royston P . Further development of flexible parametric models for survival analysis. Stata J. 2009;9 (2 ):265–90.
17 Smith AJ , Dieppe P , Vernon K , Porter M , Blom AW , National Joint Registry. Failure rates of stemmed metal-on-metal hip replacements: analysis of data from the National Joint Registry of England and Wales. Lancet. 2012;379 (9822 ):1199–204.22417410
18 Blom AW , Hunt LP , Matharu GS , Reed M , Whitehouse MR . The effect of surgical approach in total knee replacement on outcomes. An analysis of 875,166 elective operations from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man. Knee. 2021;31 :144–57. doi: 10.1016/j.knee.2021.04.009 34175672
19 Blom AW , Hunt LP , Matharu GS , Reed MR , Whitehouse MR . The effect of surgical approach in total hip replacement on outcomes: an analysis of 723,904 elective operations from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man. BMC Med. 2020;18 (1 ):242. doi: 10.1186/s12916-020-01672-0 32758226
20 Hunt LP , Whitehouse MR , Beswick A , Porter ML , Howard P , Blom AW . Implications of Introducing New Technology: Comparative Survivorship Modeling of Metal-on-Metal Hip Replacements and Contemporary Alternatives in the National Joint Registry. J Bone Joint Surg Am. 2018;100 (3 ):189–96. doi: 10.2106/JBJS.17.00039 29406339
21 Sayers A , Whitehouse MR , Judge A , MacGregor AJ , Blom AW , Ben-Shlomo Y . Analysis of change in patient-reported outcome measures with floor and ceiling effects using the multilevel Tobit model: a simulation study and an example from a National Joint Register using body mass index and the Oxford Hip Score. BMJ Open. 2020;10 (8 ):e033646. doi: 10.1136/bmjopen-2019-033646 32859657
22 Sayers A , Steele F , Whitehouse MR , Price A , Ben-Shlomo Y , Blom AW . Association between surgical volume and failure of primary total hip replacement in England and Wales: findings from a prospective national joint replacement register. BMJ Open. 2020;10 :e033045. doi: 10.1136/bmjopen-2019-033045 32928843
23 Fowler TJ , Aquilina AL , Reed MR , Blom AW , Sayers A , Whitehouse MR . The association between surgeon grade and risk of revision following total hip arthroplasty: an analysis of National Joint Registry data. Bone Joint J. 2022;104-B (3 ):341–51. doi: 10.1302/0301-620X.104B3.BJJ-2021-1389.R1 35227094
24 Crowther MJ , Look MP , Riley RD . Multilevel mixed effects parametric survival models using adaptive Gauss-Hermite quadrature with application to recurrent events and individual participant data meta-analysis. Stat Med. 2014;33 (22 ):3844–58. doi: 10.1002/sim.6191 24789760
25 Benchimol EI , Smeeth L , Guttmann A , Harron K , Moher D , Petersen I , et al . The Reporting of studies Conducted using Observational Routinely-collected health Data (RECORD) Statement. PLoS Med. 2015;12 (10 ):e1001885. doi: 10.1371/journal.pmed.1001885 26440803
26 National Joint Registry: Privacy Notice & GDPR 2024 [cited 24/06/2024]. Available from: https://www.njrcentre.org.uk/privacy-notice-gdpr/.
27 White IR , Carlin JB . Bias and efficiency of multiple imputation compared with complete-case analysis for missing covariate values. Stat Med. 2010;29 :2920–31. doi: 10.1002/sim.3944 20842622
28 Madanipour S , Singh P , Karia M , Bhamra JS , Abdul-Jabar HB . Trainee performed total knee arthroplasty is safe and effective: A systematic review and meta-analysis comparing outcomes between trainees and consultants. Knee. 2021;30 :291–304. doi: 10.1016/j.knee.2021.04.013 33984748
29 Intercollegiate Surgical Curriculum Programme: Trauma and Orthopaedic Surgery Curriculum 2021 [cited 24/06/2024]. Available from: https://www.iscp.ac.uk/iscp/curriculum/trauma-orthopaedic-surgery-curriculum/1-introduction/.
