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1 Quality Measures for Total Ankle Replacement, -day readmission and reoperation rates within year of surgery: a data linkage study using the NJR dataset Journal: BMJ Open Manuscript ID bmjopen-0-0 Article Type: Research Date Submitted by the Author: -Jan-0 Complete List of Authors: Zaidi, Razi; UCL, Institute of Orthopaedics and Musculoskeletal Science MacGregor, Alex; University of East Anglia, Norwich Medical School Goldberg, Andrew; University College London, Institute of Orthopaedics and Musculoskeletal Science <b>primary Subject Heading</b>: Surgery Secondary Subject Heading: Health informatics Keywords: Foot & ankle < ORTHOPAEDIC & TRAUMA SURGERY, ankle replacement, national joint registry, data linkage BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

2 Page of BMJ Open Quality Measures for Total Ankle Replacement, -day readmission and reoperation rates within year of surgery: a data linkage study using the NJR dataset Mr Razi Zaidi BSc MBBS MRCS Prof Alexander J Macgregor MA, MD, PhD, FRCP Mr Andy Goldberg OBE MD FRCS(Tr&Orth) Correspondence to Razi Zaidi, razizaidi@doctors.net.uk UCL Institute of Orthopaedics and Musculoskeletal Science (IOMS) Royal National Orthopaedic Hospital (RNOH), Brockley Hill, Stanmore HA LP Norwich Medical School University of East Anglia Bob Champion Research & Education Bldg.0 BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

3 Page of Copyright for authors The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, a worldwide licence to the Publishers and its licensees in perpetuity, in all forms, formats and media (whether known now or created in the future), to i) publish, reproduce, distribute, display and store the Contribution, ii) translate the Contribution into other languages, create adaptations, reprints, include within collections and create summaries, extracts and/or, abstracts of the Contribution, iii) create any other derivative work(s) based on the Contribution, iv) to exploit all subsidiary rights in the Contribution, v) the inclusion of electronic links from the Contribution to third party material where-ever it may be located; and, vi) licence any third party to do any or all of the above. Conflict of Interest We have read and understood the BMJ Group policy on declaration of interests and have no relevant interests to declare. Authorship RZ, AG and AM were all involved in the conception of the study. RZ and AG were responsible for obtaining the linked data. AM was involved in gaining approval for all the data used. RZ and AM did the data analysis and logistic regression analysis. AG was involved in data interpretation. RZ, AG and AM involved in drafting, revising and final approval of the version to be published. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

4 Page of BMJ Open Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. Data Sharing No additional data available. Abstract Objective To report on the -day readmission rate as well as the rate of additional or revision surgery within months following total ankle replacement. Design Data-linkage study of the UK National Joint Registry (NJR) data and Hospital Episodes Statistics (HES) database. These two databases were linked in a deterministic fashion. HES episodes months following the index procedure were isolated and analysed. Logistic regression was used to model predictors of reoperation and revision for primary ankle replacement. Participants All primary and revision ankle replacement patients captured on the NJR between February 00 and February 0. Results -day readmission following primary and revision ankle replacement was.% and.% respectively. In the months following primary and revision ankle replacement the revision rate (where implants needed to be removed) was.% with increased odd in those orthopaedic units preforming less than 0 ankle replacements per year and patients with a preoperative fixed equinus deformity. The reoperation other than revision (where implants were not BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

5 Page of removed) in the months following primary and revision TAR was.% and.% respectively. Rheumatoid arthritis, cemented prosthesis and high ASA grade significantly increased the odds of re-operation. Conclusions TAR has -day readmission rate of.%, which is similar to knee replacement but lower than total hip replacement..% of patients undergoing primary TAR require a reoperation within months of the index procedure. Early revision rates are significantly higher in low volume centres. Article Summary Article Focus -day readmission rate following ankle replacement. Revision rate in the months following ankle replacement. Risk factors for re-operation. Key Message The odds of reoperation following primary TAR were increased with rheumatoid arthritis, patients with a high ASA Grade and surgery where bone cement is used. The odds of revision were significantly higher in units preforming less than 0 ankle replacements per year. Strengths and limitations of this study World s largest cohort of ankle replacements. Data-linkage methodology reduces biases that are present in single surgeon, single centre reports of ankle replacement. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

6 Page of BMJ Open Limited by linkage rate of %. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

7 Page of Introduction Nearly million people in the UK have sought treatment for osteoarthritis [] and is a huge burden to the National Health Service (NHS) which spends approximately 0 billion ($.Bn,.Bn) annually on musculoskeletal care []. Joint replacements have been available since the 0 s [] and hip replacement is one of the most common orthopaedic interventions carried out globally and is recognised as one of the most cost effective interventions in medicine [], however, the proliferation of implants with little outcome data led to the creation of Joint Registries to capture real world data. Indeed the UK now has one of the most advanced National Joint Registry programmes in the world[], and has captured more than million records since its inception in 00.[] The NJR now captures data on all hip, knee, ankle, shoulder and elbow replacements carried out in England and Wales. Ankle replacements have been captured on the NJR since April 00 and although this is a less common procedure than hip or knee replacement, the UK registry of, ankle replacements makes this the largest database of its kind in the world. [] The burden of ankle arthritis is growing and in the UK approximately,000 patients each year present to ankle specialists with symptomatic ankle arthritis.[] Once non-operative interventions have failed, there are two main surgical treatment options available, ankle arthrodesis (fusion) or total ankle replacement (TAR). At present, approximately 00 procedures are performed each year on the NHS[] of which the ratio of fusion to replacement is approximately :.[] BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

8 Page of BMJ Open TAR has been shown to provide patients with an improved functional outcome[] and an increasing patient demand, coupled with evidence of TAR s cost-effectiveness [] is likely to see a rise in the use of this technology over the coming years. However there are more than prostheses types on the market with published survival rates of TAR vary between % to % at ten years and a cumulative annual failure rate of.%[], which is a significantly higher failure rate than hip replacements which is about 0.%.[] Patients with ankle arthritis need to have access to quality and outcome data to enable informed decision making [0] and the aim of the current study was to report on reoperation and revision rate within a year from the index TAR by linking the UK NJR to the Hospital Episodes Statistics (HES) database, which captures data on all NHS admissions and operations. In addition, -day readmission rates are used in the UK and internationally as a marker of quality of care[] and in the UK the data is published by the Health & Social Care Information Centre (HSCIC) routinely for hip and knee replacement [] but not for TAR. Using similar methodology, we therefore also aimed to define the -day readmission rate following TAR. Methods and Material Data linkage Data from the NJR was linked to HES data in a deterministic fashion. Deterministic linkage requires an exact match of the fields being linked from both datasets in order to say that they BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

9 Page of from the same patient. This is in contrast to probabilistic linkage which estimates the likelihood that two records are for the same individual, even if they disagree on some fields.[] The linkage was conducted by the HSCIC. This was in line with best linkage practice with application of the separation principle to allow the most ethical workflow.[] This principle is used to protect patient data with patient identifying components and clinical components of a dataset are kept separate. Identifying data is used by a group to perform data linkage while the research group uses non-identifying data to perform the analysis. Since there was extract deterministic linkage between the common fields in both datasets all of these revision and reoperation procedures from the HES dataset had a linked A (Primary TAR) NJR form which contained the demographic data for analysis from the patient s primary procedure., NJR records had more than months of time following the index procedure and hence were linked. The, NJR records were linked to five years of HES records. NJR-HES linkage was based on a hierarchy of deterministic criteria based on nine fields (Figure ). NJR data was captured on minimal dataset forms completed by the surgeon at the time of surgery and submitted by the performing hospital. This is a mandated requirement in the UK National Health Service. For a primary ankle replacement the form is entitled an A form and for a revision ankle replacement, an A form.[] The forms capture patient demographics such as patient age, gender, and BMI. The unit where the surgery is performed is also captured with the grade of surgeon performing the surgery. The grade of surgeon is sub-divided into a consultant surgeon or trainee. Indication for surgery and details of pre-operative deformity and range of motion. Further to this the prosthesis type, surgical approach, associated procedures, intra-operative complications and prophylaxis against venous thromboembolic disease are recorded.[,] BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

10 Page of BMJ Open Identification of concurrent procedures Concurrent procedures that took place at the time of primary or revision TAR were identified from the NJR data alone as they capture this on the A and A forms. Concurrent procedures then formed part of the regression analysis of re-operation and revision. Identification of -day readmssion From the linked dataset all index procedures with a HES entry within days of the index procedure were isolated. These were examined for the ICD-0 diagnostic codes and determined the rate and reason for re-admission. Definition of Revision and Re-operation In this study we used the definition of revision accepted by the NJR, which is any operation leading to exchange or removal of any of the prosthetic components with the exception of incidental exchange of the polyethylene insert in a mobile bearing ( component) ankle replacement.[] Any other surgery, such as joint debridement, washout or adjacent joint surgery would constitute a reoperation other than revision. The rate of reoperation used in this paper included all revisions. Identification of re-operation and revision Reoperation and revision were identified using the linked NJR-HES dataset. OPCS- (Office of Population Censuses and Surveys Classification of Interventions and Procedures version ) is the procedural classification used by clinical coders within National Health Service (NHS) hospitals BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

11 Page 0 of in the UK. OPCS codes were used to identify arthroscopy, bone debridement, calcaneal osteotomy, soft tissue operations, wound related operations, removal of metalwork and subtalar fusion in the months following the index operation. Removal of metalwork pertained to all metalwork unrelated to the implant (ie that was not the tibial or talar component of the TAR). Statistical Methods Analysis was performed using R v.0. (R Foundation for Statistical Computing, Vienna, Austria). Initially univariate analysis was performed with primary ankle replacement and revision dataset to analyse re-operation as a whole. Shapiro Wilk test tests were used to establish if data was normally distributed. For descriptive statistics Mann-Whitney or independent sample t-tests were used for continuous variables. For categorical data chi-squared or fisher exact tests were used. Logistic regression was used to model predictors of specific reoperations and was only used with the primary ankle replacement dataset. Every model was adjusted for patient characteristics including age, body mass index, comorbidity and ASA-grade. Multiple regression models were conducted in stepwise forwards and backwards fashion. We used Akaike Information Criterion (AIC) to calibrate the model which is an robust and objective way to determining which model is most parsimonious.[,0] Co-morbid conditions were defined using the Royal College of Surgeons Charlson Score applied to HES records in the months preceding the index operation for every patient. This is a validated tool that is a count of chronic co-morbid conditions that may affect the outcome of surgery.[] 0 BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

12 Page of BMJ Open For the purpose of analysis age was divided into three groups; less than, - and greater than. BMI was divided into three categories. A BMI of.- was classed as normal, below this we class the patients as underweight and above this overweight. Reoperation was also analysed in the in context of unit volume. We classed high volume units those carrying out 0 ankle replacements or more per year and low volume units those that performed less than 0 per year. The reason for this was that in a primary analysis we identified that those units performing more than 0 per year ( units) accounted for half of all ankle replacements performed and those that did less than 0 per year ( units) accounted for the other half. Indications for TAR on the NJR dataset are divided into osteoarthritis, rheumatoid arthritis, other inflammatory arthropathy and other. Inflammatory arthropathy includes psoriatic arthritis, pseudogout, ankylosing spondylitis, juvenile idiopathic arthritis, and systemic lupus erythematosus. Results There were a total of, NJR records comprising of, primary operations and 0 revisions. The overall match rate with HES was % with,0 matched primary procedures and revisions. Using the OPCS codes (Table ) [] for various different types of reoperation we searched linked episodes for occurrences after the index procedure. The most frequently used ankle prosthesis was the Mobility (DePuy Synthes, UK) (%) followed by the Zenith (Corin, UK) (0%). Mobile bearing prosthesis were the most frequently used with fixed bearing use in under % of cases (Figure ). BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

13 Page of Concurrent procedures The frequency of concurrent procedures with primary and revision TAR was % and % respectively. The most frequent procedure was Achilles lengthening followed by calcaneal osteotomy (Figure and Figure ). day readmission rate Following primary and revision TAR the rate of -day readmission was.% (%CI.-.) and.% (%CI 0.-.) respectively. There were a total of readmissions of which (%) were for wound infections, (%) were for medical issues (including cardiovascular and respiratory issues), (0%) were for re-operation, (%) were due to fractures around the prosthesis and (%) were due to pulmonary embolism. Reoperation rate The rate of reoperation within months of the primary and revision TAR was.% (%CI.-.) and.% (%CI.-0.) respectively (Table ). primary ankle replacements had reoperations; revision ankle replacements had reoperations. The odds of reoperation with a primary TAR were increased with rheumatoid, cemented operations and increasing ASA grade (Table ). With revision operations no risk factors were shown to be significant (Table ). Arthroscopy post primary TAR The rate of arthroscopy was.% (%CI -.) at a mean of 0 (SD±.) with the significant risk factors being pre-operative fixed equinus and preoperative reduced plantar flexion (to only - degrees) (Table ). BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

14 Page of BMJ Open Bone debridement post primary TAR The rate of bony debridement post TAR was 0.% (%CI 0.-0.) at a mean of (SD±.) (Table ). Rheumatoid arthritis the only significant predictor with an increase in odds of. (Table ). Calcaneal osteotomy The rate of a calcaneal osteotomy following TAR was 0.% (% CI 0.-0.) at a mean of 00 (SD±.)(Table ). Having had concurrent lateral ligament reconstruction was the only predictor of risk that emerged, increasing the risk five fold (Table ). Soft tissue operations The rate of these were 0.% (%CI 0.-0.) at a mean of 0 (SD±) days. procedures were performed in four patients to address the gastrocnemius, peroneal tendons, tibialis posterior, tibialis anterior and the joint capsule. Cemented TAR and having a fibular osteotomy during the initial procedure increased the odds these procedures (Table ). Wound related operation A total of wound related operations were performed in five patients. The rate of these procedures months following TAR was 0.% (%CI 0.-0.) at a mean of days (SD±.). Three patients each had a single procedure and patients had two procedures. Two patients had vascularised skin flaps and had the application of a VAC dressing. The odds of BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

15 Page of this type of reoperation were significantly increased in patients with rheumatoid arthritis, cemented prosthesis or concurrent subtalar or talonavicular fusion (Table ). Removal of metalwork The rate of this was 0.% (%CI 0.-0.) at a mean of 00 (SD±) days (Table ). Rheumatoid arthritis was the only significant predictor for this (Table ). Subtalar fusion Subtalar fusion was carried out in patients (0.% (%CI 0.-0.)) at a mean of (SD±) days (Table ). No predictors emerged for this (Table ). Revision The revision rate in the months following TAR was.% (%CI.-.) (Table ). Three of these were full revisions of the ankle replacement and had corresponding record for revision on the NJR (an NJR A form was submitted), were converted to ankle fusions (but did not have a corresponding NJR A form submitted) and were revisions of just one component, again without the NJR A form. Therefore 0 of the (%) revisions were identified through the HES linkage only and would not have been identified if reliance were only on the NJR forms being submitted. Fifty four per cent of the revisions were performed as result of loosening or fracture of any of the three components. The odds of revision were significantly higher in those orthopaedic units preforming less than 0 ankle replacements per year and patients with a preoperative fixed equinus deformity (Table ). BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

16 Page of BMJ Open Discussion This paper constitutes the first output from the world s largest database of ankle replacements (the UK National Joint Registry) and has shown a -day readmission following primary and revision TAR to be.% and.% respectively. -day readmission is a proxy measure for quality of care used by the NHS and this rate for TAR is comparable to the % reported -day readmission following knee replacement[] but lower than the.% reported rate for hip replacement.[] The reoperation rate within months following a primary TAR was.%. This is lower than that for both hip replacement[] and knee replacement[], which have re-operation rates within months of the index procedure of.% and % respectively. For TAR, we identified three significant predictors, rheumatoid, cemented operations and increasing ASA grade. Whilst rheumatoid and high ASA grade seem straightforward, it is not clear whether cemented procedures increase complications or whether surgeons elect to use cement in more complicated procedures[], explaining the higher reoperation rate. Indeed, the majority (>%) of TAR s performed in the NJR are uncemented. Reoperation rate following revision was.% but numbers were small and no predictors emerged. Previous studies with longer follow-up have shown age to be a predictor of reoperation with increased risk at the at the extremes of age but there was no indication of this from our data.[] BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

17 Page of We found that reoperation related to wound complication within year of the index primary TAR was 0.% with rheumatoid arthritis being a significant risk factor. This is a similar finding to Raikin et al also showed a times increase in wound complication requiring reoperation in patients with rheumatoid arthritis.[] In our paper, we have defined revision as being any operation leading to exchange or removal of any of the prosthetic components with the exception of incidental exchange of the polyethylene insert in a mobile bearing ( component) ankle replacement.[]. All other procedures are referred to as re-operations other than revision. Revision rate within year of primary TAR was.%. The majority of these were change of only one component. Metaanalysis of joint registry data from Sweden, Finland, Norway and New Zealand[] has shown the yearly failure rate to be.%, almost double that from the UK thus far, although numbers in the UK register are much greater. A major strength of this study was that we used another database (HES) to identify revision procedures. We could have used intra-database linkage by trying to link all the primary procedures on the NJR to revision procedures, however this would have greatly underestimated the revision rate as not all revisions were captured on the NJR resulting in reporting bias.[] TAR carried out in a low volume centres (<0 per year) was found to be risk factor or early implant failure. The reason for the cut-off of 0 was that the analysis identified that those units performing more than 0 TAR operations per year ( units) accounted for half of all ankle BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

18 Page of BMJ Open replacements volume performed and those that did less than 0 per year ( units) accounted for the other half. This finding contrasts with a Norwegian registry study that examined TAR and found no difference in survival by unit volume.[] This difference may be attributable to the greater power of the current study as a result of significantly larger numbers of TAR included. Limitations This study had a limited power to detect risk factors for specific reoperations due to small numbers of patient end points. A further limitation was the dependence on OPCS- procedural coding systems as any errors in coding may have misrepresented an event. In orthopaedics % of procedures have been shown to be inaccurately coded, but training and education combined with continued national audit of coding has led to improvement.[] In this study we are unable to divide the osteoarthritis group into primary and post traumatic as this data is not captured in the NJR, however, this distinction is, in practice, very subjective as it is possible that patients have a combination of both primary and post traumatic arthritic changes. Hence we believe that any papers that classify primary versus post-traumatic OA, are likely to also be subject to similar errors. The linkage rate of the NJR data to the HES data was %. Of the unlinked data % ( ankle replacements) were carried out in the independent (private) sector and had no relevant HES records to interrogate. Since there are very few emergency admissions units in the private sector BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

19 Page of we believe that complications in the main are picked up in public sector. However, we cannot be certain that complications were not dealt with in the private sector, where no HES record would be recorded and hence the -day readmission rates and the -year reoperation other than revision rates could be higher than as described in this paper. As with any paper reporting on large national datasets, data incompleteness can be an issue. With regards primary TAR there was missing data regards BMI and surgical approach (Table ) and with revision BMI and operation type (Table ). We did not consider this had a major impact on the study results. Compliance with completion of NJR forms is also an issue. Compliance is the percentage of all TARs that have been entered into the NJR within a month period. Compliance for completion of primary TAR in the NJR has risen from % in 0 to % in 0.[] Conclusion TAR has -day readmission of.%, which is similar to knee replacement but lower than total hip replacement..% of patients undergoing primary TAR require a reoperation within months of the primary procedure, of which.% will require a revision procedure. The leading patient factors that increase the risk of reoperation & revision are rheumatoid arthritis, preoperative deformity and high ASA-grade. In terms of hospital/surgeons factors, early revision rates are significantly higher in low volume centres. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

20 Page of BMJ Open Acknowledgements We thank the patients and staff of all the hospitals in England, Wales and Northern Ireland who have contributed data to the National Joint Registry. We are grateful to the Healthcare Quality Improvement Partnership (HQIP), the NJR Research Sub-Committee and staff at the NJR Centre 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 or the Health Quality Improvement Partnership (HQIP) who do not vouch for how the information is presented. The Healthcare Quality Improvement Partnership ( HQIP ) and/or the National Joint Registry ( NJR ) take no responsibility for the accuracy, currency, reliability and correctness of any data used or referred to in this report, nor for the accuracy, currency, reliability and correctness of links or references to other information sources and disclaims all warranties in relation to such data, links and references to the maximum extent permitted by legislation. We would also like to acknowledge Suzie Cro (MRC biostatistician) for her input with NJR data application. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

21 Page 0 of References No Authors Listed. Data and statistics Arthritis Research UK. (accessed Jan0). Briggs TW. Improving the Quality of Orthopaedic Care within the National Health Service in England. Get it Right First Time, Br Orthop Assoc News 0;0:. Fitzpatrick R, Shortall E, Sculpher M, et al. Primary total hip replacement surgery: a systematic review of outcomes and modelling of cost-effectiveness associated with different prostheses. Heal Technol Assess ;:. Hunt LP, Ben-Shlomo Y, Clark EM, et al. 0-day mortality after 0 total hip replacements for osteoarthritis, from the National Joint Registry for England and Wales: a retrospective analysis. Lancet 0;:0 0. doi:0.0/s00-()- Green M, Wishart N, Beaumont R, et al. th Annual Report. NJR. 0. Goldberg AJ, Macgregor A, Dawson J, et al. The demand incidence of symptomatic ankle osteoarthritis presenting to foot & ankle surgeons in the United Kingdom. Foot 0;:. doi:s0-()000- [pii] 0.0/j.foot No Authors Listed, Listed NA Zaidi R, Cro S, Gurusamy K, et al. The outcome of total ankle replacement: A systematic review and meta-analysis. Bone Joint J 0;-B:00. doi:0./0-0x.b. Nwachukwu BU, McLawhorn AS, Simon MS, et al. Management of End-Stage Ankle Arthritis: Cost-Utility Analysis Using Direct and Indirect Costs. J Bone Joint Surg Am 0;:. doi:0.0/jbjs.n.0 0 Zaidi R, Pfeil M, Macgregor AJ, et al. How do patients with end-stage ankle arthritis decide between two surgical treatments? A qualitative study. BMJ Open 0;:. doi:0./bmjopen-0-00 Rumball-Smith J, Hider P. The validity of readmission rate as a marker of the quality of hospital care, and a recommendation for its definition. N Z Med J 00;: 0. (accessed Jan0). Health and Social Care Information Centre, Trevelyan Square, Boar Lane, Leeds, LS AE UK. Health and Social Care Information Centre website: Home page. (accessed May0). Zhu Y, Matsuyama Y, Ohashi Y, et al. When to conduct probabilistic linkage vs. deterministic linkage? A simulation study. J Biomed Inform 0;:0. doi:0.0/j.jbi Kelman CW, Bass AJ, Holman CDJ. Research use of linked health data--a best practice 0 BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

22 Page of BMJ Open protocol. Aust N Z J Public Health 00;:. (accessed Oct0). No Authors Listed. Data collection forms orms/tabid/0/default.aspx (accessed Dec0). No Authors Listed. NJR A Form. ;:. A.pdf No Authors Listed. NJR A form. collection forms/mdsv.0_a_v00.pdf Henricson A, Carlsson A, Rydholm U. What is a revision of total ankle replacement? Foot Ankle Surg 0;: 0. doi:0.0/j.fas Akaike H. A new look at the statistical model identification. IEEE Trans Automat Contr ;:. doi:0.0/tac Burnham KP, Anderson DR, Edition S. Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach [Hardcover]. Springer; nd ed. 00. Corr. rd printing 00 edition Inference-Information-Theoretic/dp/0 (accessed Feb0). Armitage JN, van der Meulen JH. Identifying co-morbidity in surgical patients using administrative data with the Royal College of Surgeons Charlson Score. Br J Surg 00;:. doi:0.00/bjs. No Authors Listed. OPCS- Classification Health and Social Care Information Centre. (accessed Oct0). Issa K, Cherian JJ, Kapadia BH, et al. Readmission Rates for Cruciate-Retaining Total Knee Arthroplasty. J Knee Surg Published Online First: May 0. doi:0.0/s- 00- No Authors Listed. Hospital Episode Statistics. Garellick, Karrholm, Lindahl, et al. Swedish arthroplasty registry report doi:0./epp.0 No Authors Listed. Norwegian Register Annual Report Wishart N, Beaumont R, Young E, et al. NJR th Annual Report. 0. Spirt AA, Assal M, Hansen ST. Complications and failure after total ankle arthroplasty. J Bone Jt Surg Am 00;-A:. Raikin SM, Kane J, Ciminiello ME. Risk factors for incision-healing complications following total ankle arthroplasty. J Bone Joint Surg Am 00;:0. doi:0.0/jbjs.i.000 Fevang B-TS, Lie S a, Havelin LI, et al. ankle arthroplasties performed in Norway between and 00. Acta Orthop 00;:. doi:0.00/00 Spencer A. Hospital Episode Statistics (HES): Improving the quality and value of hospital BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

23 Page of data. 0. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

24 Page of BMJ Open Figure Legends Figure. A flowchart to illustrate the linkage process BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

25 Page of Figure. The Frequency of use of ankle prosthesis brands in the UK BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

26 Page of BMJ Open Figure Frequency of concurrent procedures performed with primary TAR BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

27 Page of Figure Frequency of concurrent procedures performed with revision TAR BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

28 Page of BMJ Open Tables Re-operation Type Arthroscopy Bone debridement Calcaneal osteotomy Soft tissue operations Wound/Infection related Removal of metalwork Subtalar fusion OPCS (Office of Population Censuses and Surveys) codes Y, Y, W, W, W, W, W W, W0, W, W0, W0, Y0, W W, X T, Z, O, T0, A, W, T, W, T, W, T0, T, T S, S, S, S, S, S, T W W0, W0 Revision W, W, W, W, W, W, W, W, W, W0, W0, Y0, W, W, W, W Table OPCS codes used to identify re-operation for the HES dataset BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

29 Page of Operation n Rate within months Mean time to re-op (days, SD) Primary TAR Bone debridement 0.% (% CI 0.-0.) () Calcaneal osteotomy 0.% (% CI 0.-0.) 00 (.) Ligamentous 0.% (% CI 0.-0.). () Wound/Infection related 0.% (% CI 0.-0.). (.) Removal of metalwork 0 0.% (% CI 0.-0.) 00 (.) Revision.% (% CI.-.). (.) Arthroscopy.% (% CI -.) 0. (.) Subtalar fusion 0.% (% CI 0.-0.) (.) Other.% (% CI.-.). () Total. (% CI.-.) Revision TAR Ankle fusion.% (% CI.-.). () Removal of metalwork.% (% CI.-.). () Total.% (% CI.-0.) Table rate and mean time to re-operation following primary and revision ankle replacement. SD = Standard Deviation n = Number of patients BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

30 Page of BMJ Open months following primary total ankle replacement Reoperation No-Reoperation Age n (proportion) n (proportion) OR (% CI, p value) < (0.) (0.) ref - (0.) (0.) 0. (0.-., p=0.) > 0 (0.) (0.) 0. (0.-., p=0.) Length of stay mean (range) mean (range). (0-). (0-) P = 0. BMI n (proportion) n (proportion) OR (% CI, p value) underweight (0.0) (0.00) (0.-, p=0.) normal (0.) (0.) Ref overweight (0.) (0.). (0.-, p=0.) obese (0.) (0.) 0. (0.-., p=0.) Missing = Gender/F.%.% Indications n (proportion) n (proportion) OR (% CI, p value) osteoarthritis (0.) (0.) Ref rheumatoid arthritis (0.) (0.0). (.-., p= 0.00) inflammatory (0.0) 0 (0.0). (0.-, p= 0.) other (0.0) (0.0). (0.-., p= 0.) Operation n (proportion) n (proportion) OR (% CI, p value) uncemented (0.) 0 (0.) Ref cement (0.0) (0.0).(. -, p= 0.0) hybrid 0 (0) (0.00) - Approach n (proportion) n (proportion) OR (% CI, p value) anterior (0.) 000 (0.) Ref lateral (0.0) (0.0). (0.0, p= 0.) ant-lateral 0 (0) 0 (0.0) - Missing = Organisation n (proportion) n (proportion) OR (% CI, p value) NHS (0.) (0.) Ref Independent hospital (NHS funded) (0.0) (0.0) 0. (0. -., p= 0.) Independent treatment centre (NHS funded) (0.0) (0.0). (0.., p= 0.) Grade of surgeon n (proportion) n (proportion) OR (% CI, p value) consultant (0.) (0.) Ref other (0.0) (0.0) 0. (0.-., p= 0.) ASA n (proportion) n (proportion) OR (% CI, p value) (0.0) (0.) Ref (0.) (0.). (.-, p= 0.0) (0.) (0.). (., p= 0.0) 0 (0) (0.00) - Charlson n (proportion) n (proportion) 0 (.0) 00 (0.) 0 (0) (0.0) 0 (0) (0.00) BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

31 Page of Table Univariate analysis of comparing reoperation versus no-reoperation months following primary ankle replacement surgery. n, number of patients OR, odds ratio CI, confidence interval BMI, body mass index ASA, American Society of Anesthesiologists months following revision ankle replacement Reoperation No- Reoperation Age n (proportion) n (proportion) OR (% CI, p value) < (0.) (0.) Ref - (0.) (0.). (0.-, p= 0.) > (0.) (0.). (0.0-, p= 0.) Length of stay mean (range) mean (range). (-). (-) p= 0. BMI n (proportion) n (proportion) OR (% CI, p value) underweight (0.) 0 (0) - normal (0.) (0.) Ref overweight (0.) (0.) 0. (0.0-, p= 0.) Missing = Gender/F % % Operation n (proportion) n (proportion) OR (% CI, p value) Uncemented TAR (0.) (0.) Ref Hybrid (0.) (0.). (0.-, p= 0.) TTC nail (0.) (0.0). (0.-0, p= 0.) Missing = ASA n (proportion) n (proportion) OR (% CI, p value) - (0.) (0.) Ref - (0.) (0.) 0. (0.-, p= 0.) Charlson n (proportion) n (proportion) 0 (.0) (0.) 0 (0) (0.0) 0 (0) 0 (0) Table Univariate analysis of comparing reoperation versus no-reoperation months following revision ankle replacement surgery. n, number of patients OR, odds ratio CI, confidence interval BMI, body mass index ASA, American Society of Anesthesiologists BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

32 Page of BMJ Open 0 0 Revision Arthroscopy Bone Debridement Calcaneal osteotomy Ligamentous operation wound related removal of metal work subtalar fusion Indication OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p Osteoarthritis ref ref ref ref ref ref ref ref Rheumatoid. (0.-.) 0.. (0.-.) 0.. (0.-) (0.-na) (na) 0.. (.-.) 0.0. (.-.) (0.-.) 0. Inflammatory. (0.-) (0.00-.) (0.00-) 0.. (0.-na) (na) (na) 0.. (0.-.) (na) 0. other 0.0 (na) (0.0-.) 0.. (0.-.) 0.. (0.-na) (na) 0.. (0.-.) 0.0. (0.-) (na) 0. Operation OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p Type uncemented ref ref ref ref ref ref ref ref cemented 0.0 (na) 0.. (na) (na- ) 0.. (na) 0.. (.-) 0.0. (.-) (na) (na) 0. hybrid. (0.-.) 0.. (na) (na -) 0.. (na) (na) (na) (na) (na) 0. Approach to OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p Ankle anterior ref ref ref ref ref ref ref ref ant-lat 0.0 (na) 0..0 (0.0-.) (0.0-.) 0. (0.-na) (na) (na) (na) (na) 0. lateral 0.0(na) 0.. (na) (0.00-) 0.. (0.-na) (na) 0.. (.0-.) (na) (na) 0. Organisation OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p NHS ref ref ref ref ref ref ref ref ind.hosp.0 (0.-.) 0.. (0.-) 0.. (0.0-.) (0.-na) 0.. (0.-.) (na) (na) (na) 0. itc. (0.-.) 0. (.0-.) (0.00-) 0.. (0. -na) (0.00-) (na) (na) (na) 0. Unit volume OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p >0 ref ref ref ref ref ref ref ref <0. (.-.) 0.0. (0.-.) (0.-.) (0.0-.) (0.-.) 0.. (0.-.) (0.-0.) (na) 0. Pre-op OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p Deformity Neu ref ref ref ref ref ref ref ref Valgus 0.0 (na) (0.00-) (0.00-) 0.. (0.-na) (na) (na) 0.. (0.-.) 0.. (0.-.) 0. Varus. (0.-.) (0.-.) (0.00- ) 0. (0.-) (na) 0.. (0.-.) 0.. (0.-.) 0.. (0.-.) 0. Pre-op OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p Dorsiflexion to 0 ref ref ref ref ref ref ref ref Neu. (0.-.) 0..0 (0.-.) (0.00-) 0. (0.-) 0.. (0.-.) (0.-.) (0.-0.) (na) 0. Fixed Eq. (.-) 0.0. (.-.) 0.0. (0.-.) 0. (0.-) (0.-.) (0.-.) (0.-.) (0.-.) 0. Pre-op OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p Plantarflexio n to ref ref ref ref ref ref ref ref to.0 (0.-) 0.. (.-.) 0.0. (0.-) 0. (na) 0.. (0.-.) 0..0 (0.-0) (0.-.) (0.0-.) 0. No. of OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p associated procedures 0 ref ref ref ref ref ref ref ref 0. (0.-.) (0.0-.) (0.-). (0.-.) 0.. (0.-) (0.-.) 0.. (0.-) (0.0-) 0.. (0.-.) (0.-.) (0.- ). (0.-) 0.. (0.-.) 0.. (.-) 0.. (0.-) (0.-.) 0. on October 0 by guest. Protected by copyright. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from

33 Page of 0. (na) (0.0-). (0.-). (0.-.) 0. (0.-.) 0.. (0.-.) 0.. (0.-.) 0.. (0.-.) 0. Type of OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p OR (% CI) p associated procedure none ref ref ref ref ref ref ref ref subtalar fusion talonavicular fusion calcaneal osteotomy lengthening 0 of achilles fusion distal tibiofibular fibula osteotomy medial malleolar osteotomy lateral 0. (0.-) (0.0- ) 0.. (0.0- na) (.-) 0.0 ligament recon medial 0 ligament recon Table Logistic regression of predictors of re-operation following primary total ankle replacement. Adjusted for age, gender, BMI (body mass index) and co-morbidity. OR, odds ratio CI, confidence interval 0. (0.-) (0.0 - ) 0.. (0.0-na) 0. (0.-.) (0.0-) 0. (.-.) 0.0. (0.-.) (na-) 0. (0.-.) (0.00- ) 0.. (0.0- ) (0.0-) (na-) 0.. (.-.) (na-.) (na-) (0.-) (0.00-) 0.. (0.-) 0.. (0.-) 0.. (0.-.) 0.. (0.-.) (na-) (na-) 0.. (0.-.) (0.0- ) (0.-na) (0.-) 0.. (0.-.) 0.. (0.-.) 0. 0.(0.-.) (na-) 0.. (0.-) 0.0 (na-) 0. (na) 0. (na) 0.0 (na-) (na- ) (na-) (na-) (0.0 -na) (0.00- ) (na) 0. (0.0-na) 0. (.-) (na-) (na-) (na-) (0.00-) (na-) (na) 0. (0.0-na) 0.. (0.-.) (0.00- ) (na-) (na-0) (0.0-) (0.0-) (na-) (na-) 0.. (0.-) (na-) (0.0- na) 0. (0.0-na) (na - ) (0.0-) (na-0) (na-) 0. on October 0 by guest. Protected by copyright. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from

34 Page of BMJ Open BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

35 Page of 0 0 Section/Topic Item # STROBE 00 (v) Statement Checklist of items that should be included in reports of cohort studies Recommendation Reported on page # Title and abstract (a) Indicate the study s design with a commonly used term in the title or the abstract and Introduction (b) Provide in the abstract an informative and balanced summary of what was done and what was found Background/rationale Explain the scientific background and rationale for the investigation being reported - Objectives State specific objectives, including any prespecified hypotheses - Methods Study design Present key elements of study design early in the paper Setting Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection Participants (a) Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up (b) For matched studies, give matching criteria and number of exposed and unexposed Variables Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if Data sources/ measurement applicable * For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group Bias Describe any efforts to address potential sources of bias Study size 0 Explain how the study size was arrived at - Quantitative variables Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why Statistical methods (a) Describe all statistical methods, including those used to control for confounding Results (b) Describe any methods used to examine subgroups and interactions (c) Explain how missing data were addressed and (d) If applicable, explain how loss to follow-up was addressed (e) Describe any sensitivity analyses on October 0 by guest. Protected by copyright. BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from na na

36 Page of BMJ Open 0 0 Participants * (a) Report numbers of individuals at each stage of study eg numbers potentially eligible, examined for eligibility, confirmed 0 eligible, included in the study, completing follow-up, and analysed (b) Give reasons for non-participation at each stage na Descriptive data (c) Consider use of a flow diagram * (a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential confounders (b) Indicate number of participants with missing data for each variable of interest - (c) Summarise follow-up time (eg, average and total amount) 0 Outcome data * Report numbers of outcome events or summary measures over time Main results (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, % confidence 0 interval). Make clear which confounders were adjusted for and why they were included (b) Report category boundaries when continuous variables were categorized - (c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period na Other analyses Report other analyses done eg analyses of subgroups and interactions, and sensitivity analyses Discussion Key results Summarise key results with reference to study objectives Limitations Interpretation 0 Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence Generalisability Discuss the generalisability (external validity) of the study results Other information Funding Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based *Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies. In figures - Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at Annals of Internal Medicine at and Epidemiology at Information on the STROBE Initiative is available at BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.

37 Quality Measures for Total Ankle Replacement, -day readmission and reoperation rates within year of surgery: a data linkage study using the NJR dataset Journal: BMJ Open Manuscript ID bmjopen-0-0.r Article Type: Research Date Submitted by the Author: -Apr-0 Complete List of Authors: Zaidi, Razi; UCL, Institute of Orthopaedics and Musculoskeletal Science MacGregor, Alex; University of East Anglia, Norwich Medical School Goldberg, Andrew; University College London, Institute of Orthopaedics and Musculoskeletal Science <b>primary Subject Heading</b>: Surgery Secondary Subject Heading: Health informatics Keywords: Foot & ankle < ORTHOPAEDIC & TRAUMA SURGERY, ankle replacement, national joint registry, data linkage BMJ Open: first published as 0./bmjopen-0-0 on May 0. Downloaded from on October 0 by guest. Protected by copyright.