Best timing of bilateral knee arthroplasty – an analysis of revision and mortality rates from the German Arthroplasty Registry (EPRD)

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For patients with bilateral knee OA there is no clear recommendation when to time the second surgery. The purpose of this study was therefore to compare revision and mortality rate in bilateral unicondylar and bicondylar knee arthroplasties after different strategies of surgical timing in bilateral knee OA from the German Arthroplasty Registry (EPRD). Methods: Data from the German Arthroplasty Registry (EPRD) was used. Since 2012 a total of 15,154 patients had bilateral knee arthroplasty within one year. Patellofemoral arthroplasties and constraint total knee arthroplasties (TKA) were excluded. 1,144 TKA and 682 unicondylar arthroplasties (UKA) were simultaneously performed, 772 TKA and 292 UKA between 1 and 90 days (short interval) and 24,496 TKA and 2,922 UKA between 91 and 365 days (intermediate interval). Revision and mortality rates were analyzed up to 7 years after surgery. Cox regression was performed to evaluate the influence of different patient characteristics on these outcomes. Results: The highest cumulative revision rate for any of the bilateral TKA was found for simultaneous surgery with 3.4% (95% CI 2.1 – 5.5). Lower risk for revision was seen in two-staged surgery in short interval (HR 0.42; 95% CI 0.20 – 0.90) and intermediate interval (HR 0.58; 95% CI 0.39 – 0.85). The cumulative one year mortality rate for TKA was comparable in all three groups with 0.8% for simultaneous TKA, 1.3% for short interval two-staged and 0.7% for intermediate interval. In UKA there were no differences between the groups regarding cumulative revision rate and mortality rate. Conclusion: TKA should be performed simultaneously in selected patients only, the two-staged procedure demonstrated lower revision risks. For UKA we found no differences in timing, simultaneous surgery seems to be a safe option. Trial registration: Clinical trial number not applicable. Total knee arthroplasty Unicondylar knee arthroplasty Bilateral Same day Simultaneous Mortality Revision Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Background Osteoarthritis (OA) of the knee is a frequent cause of functional impairment. The FDA has recently categorized knee OA as a serious disease [15, 16]. Total knee arthroplasty (TKA) is a very effective treatment option for advanced OA of the knee, which decreases pain and improves function [18]. Evans et al. reported about an expected survival time (time to revision or death) of TKA up to 20 years in around 90.1% of patients [6]. Bilateral OA of the knee ranges from 60-90.4% [4, 5, 12, 25]. The burden of OA in multiple joints is high [5] and multiple surgeries and anesthesia procedures need a prolonged rehabilitation and recovery. In cases of bilateral knee OA there is always the question whether TKA is necessary bilateral and if so, how it should be performed (one stage, two stages, time between stages). Most patients get bilateral TKA as a staged procedure after a convalescence of several months. The one-staged, same day bilateral TKA is rather reserved for younger patients with less comorbidities [3] and risks and benefits are discussed controversially. Multiple single-center and retrospective studies concluded bilateral TKA as safe procedures in specialized high-volume center [22], but reserved for selected patients [ 1 ] and considering higher complications rates [2, 3, 9, 11, 19, 20, 24, 27]. In an older systematic review of retrospective studies Fu et al. reported about significant higher 30-days-mortality as well as pulmonary embolism and blood transfusion rate following same day bilateral TKA, but lower rates of deep infection and revision [9]. An recent meta-analysis showed significantly over twofold increased 90-day-mortality for same day bilateral TKA compared to staged bilateral TKA with equivocal revision rate within the first year and different trends of separate complication rates [20]. Another systematic review with contemporary studies demonstrated no differences if the baseline characteristics of the patients were similar [8, 21]. Aim of this study was therefore 1) to investigate the frequency and timing of bilateral TKA in Germany and 2) to determine revision and mortality rates associated with simultaneous versus two-staged TKA in the German Arthroplasty Registry (EPRD). Methods In this retrospective registry study data acquisition started in November 2012 and includes currently a total number of more than 3 million hip and knee replacements in its database. The EPRD covers primary and revision arthroplasty surgeries. Although participation is voluntarily, it covers about 70% of all hip and knee arthroplasties in Germany [10]. Once entered into the registry, the follow-up of an arthroplasty is nearly complete because data on revisions is obtained not only by hospitals, but additionally by health insurance companies. Demographic data such as age, sex, body mass index as well as comorbidities (weighted Elixhauser Score), length of stay and readmission rates are documented. Death and revision data are obtained from health insurance companies on a regular basis [14]. Revisions and mortality were analysed up to 7 years after the second of the bilateral knee arthroplasties. Annual hospital volume is documented as well. High-volume center for TKA/UKA surgeries were defined as performing at least 500 TKA/150 UKA per year. From a total number of 377,897 patients with knee arthroplasty in cases of OA (ICD-10 code diagnoses of M17.-) which were registered in the EPRD from 2012, 40,535 could be identified as having a bilateral primary knee arthroplasty and 15,154 within one year. Patients with a second knee arthroplasty due to other diagnosis than OA (M17), unknown implant types, patellofemoral arthroplasty and constraint TKA were not included. TKA and UKA were separately analyzed. Three different time intervals between both knee arthroplasties were chosen: 1) both procedures on exactly the same day (simultaneous) with 1,144 TKA and 682 UKA, 2) staged surgery with an interval of one to 90 days between index surgery and second knee arthroplasty (short interval) with 772 TKA and 292 UKA and 3) staged surgery with an interval of 91 to 365 days between both procedures (intermediate interval) with 24,496 TKA and 2,922 UKA, see flowchart, Fig. 1 . Between the groups there were significant differences regarding age, sex, BMI in categories and comorbidities (weighted Elixhauser Index). The endpoints were revision surgeries and death of the patients. The characteristics of the study cases are summarized in Table 1 , and Figs. 2 and 3 . table 1: characteristics of study cases TKA UKA same day 1-90 d 91-365 d p-value same day 1-90 d 91-365 d p-value (n=1,144) (n=772) (n=24,496) (n=682) (n=292) (n=2,922) Sex Female 630 (55%) 372 (48%) 15,361 (63%) <0.001 324 (48%) 120 (41%) 1,486 (51%) 0.003 Male 514 (45%) 400 (52%) 9,135 (37%) 358 (52%) 172 (59%) 1,436 (49%) Age <65 386 (34%) 345 (45%) 8,638 (35%) 0.063 352 (52%) 184 (63%) 1,675 (57%) <0.001 65-74 476 (42%) 232 (30%) 8,547 (35%) 238 (35%) 84 (29%) 819 (28%) 75-84 262 (23%) 177 (23%) 6,774 (28%) 90 (13%) 24 (8.2%) 414 (14%) 85+ 20 (1.7%) 18 (2.3%) 537 (2.2%) 2 (0.3%) 0 14 (0.5%) BMI mean (SD) 30.0 (5.6) 31.6 (6.2) 31.9 (6.3) <0.001 30.5 (5.1) 31.3 (5.2) 30.9 (5.5) 0.15 weighted Elixhauser Score by VW mean (SD) 0.6 (3.7) 0.4 (4.0) 0.5 (4.0) <0.001 -0.24 (2.93) -0.30 (3.24) -0.04 (3.21) 0.2 Annual hospital volume [TKA/UKA] < 250/50 294 (26%) 314 (41%) 13,255 (55%) <0.001 78 (12%) 57 (20%) 1,163 (41%) 500/150 224 (20%) 322 (42%) 5,302 (22%) 454 (67%) 196 (70%) 1,037 (37%) missing 4 12 536 6 13 112 *One-way ANOVA for continuous variables (e.g. age at admission), Chi-squared test for categorical variables (e.g. sex of patient). Statisticcal analysis Data description was based on means and standard deviation (SD) for continuous variables and absolute and relative frequencies for categorical variables. To evaluate the influence of different patient characteristics on revision and mortality, a Cox regression model was applied. Cumulative incidences for the endpoints death of the patient and revision of each arthroplasty separately were calculated with the Kaplan-Meier survival function. A pairwise Log-Rank test with Holm´s correction for multiple testing was applied to identify intergroup differences. A p-value threshold of 0.05 was considered statistically significant. All data analyses were carried out using R statistical software, Version R-4.2.0 (R Foundation for Statistical Computing, Vienna, Austria). Results A total of 10.7% of patients with primary knee arthroplastyhave had both knee joints replaced, 4.0% in the same year and 0.2% simultaneously. The analysis demonstrated significantly higher cumulative revision rates for any of the bilateral TKA within 7 years for simultaneous (3.4%) vs. short (1.4%, HR 0.42; 95% CI 0.20–0.90) and intermediate interval (2.5%, HR 0.58; 95% CI 0.39–0.85), see Table 2 and Fig. 4 . Lower risk for revision was recognized if the surgery was performed in a high-volume center with more than 500 knee arthroplasties per year (HR 0.77; 95% CI 0.64–1.02) and for patients between 65–74 years (HR 0.61; 95% CI 0.49–0.77) Higher risk for revision was found for higher weighted Elixhauser Index (HR 1.03 per point; 95% CI 1.01–1.06). No significant association was found with sex and BMI. For TKA, there was no significant difference between the cumulative mortality rate in every group, see Table 3 and Fig. 6 . Higher risk for mortality in bilateral TKA was seen in men (HR 1.81; 95% CI 1.56–2.11), BMI > 40kg/m 2 (HR 2.1 compared to normal weight; 95% CI 1.34–3.29) and higher Elixhauser Index (HR 1.06 per point; 95%CI 1.04–1.87). Lower risk for mortality in bilateral TKA was seen in high-volume centers with > 500/y (HR 0.73; 95% CI 0.59–0.90). Table 2 Cumulative events for revision (95% Confidence Interval) in TKA and UKA TKA 1 year 3 years 5 years 7 years same day (%) 1.8 (1.2–2.8) 2.6 (1.8–3.8) 2.8 (1.9–4.2) 3.4 (2.1–5.5) 1–90 days (%) 0.8 (0.4–1.8) 1.4 (0.7–2.7) 1.4 (0.7–2.7) 1.4 (0.7–2.7) 91–365 days (%) 0.9 (0.8–1.1) 1.6 (1.4–1.8) 2 (1.8–2.2) 2.5 (2.2–2.9) UKA 1 year 3 years 5 years 7 years same day (%) 1.8 (1.0-3.2) 3.4 (2.2–6.2) 4.2 (2.7–6.4) 5.8 (3.1–10.7) 1–90 days (%) 1.1 (0.4–3.5) 2.8 (1.2–6.2) 4.2 (2.1–8.5) 4.2 (2.1–8.5) 91–365 days (%) 1.5 (1.1.-2.0) 2.3 (1.8-3.0) 3.0 (2.3–3.8) 3.1 (2.4–4.1) Table 3 Cumulative events for death of patient after second TKA and UKA (95% Confidence Interval). TKA 1 year 3 years 5 years 7 years same day (%) 0.9 (0.4–2.3) 1.8 (0.9–3.6) 8.0 (4.9–12.8) 11.6 (7.2–18.6) 1–90 days (%) 1.5 (0.6–3.6) 2.8 (1.4–5.5) 5.5 (3.0-9.9) 13.5 (6.6–26.6) 91–365 days (%) 0.7 (0.5–0.8) 3.5 (3.1–3.9) 7.9 (7.2–8.6) 13.5 (12.1–14.9) UKA 1 year 3 years 5 years 7 years same day (%) 0.3 (0.0-2.2) 0.3 (0.0-2.2) 2.7 (1.0-7.6) 2.7 (1.0-7.6) 1–90 days (%) 0.0 (0.0.) 1.0 (0.1–6.6) 3.2 (0.7–13.3) 8.5 (2.3–29.5) 91–365 days (%) 0.3 (0.1–0.8) 1.2 (0.7–2.1) 2.7 (1.7–4.3) 4.0 (2.3–6.9) Overall, UKA patients were younger and had less comorbidities. The cumulative revision rates within 7 years for UKA were not significantly different between simultaneous UKA (5.8%) compared to short (4.2%) and intermediate interval (3.1%), see Table 2 and Fig. 5 . There was no significant association between revision rates and cofactors. The cumulative mortality rates within 7 years for UKA were not significantly different between the three groups, s. Table 3 and Fig. 7 . Higher risk for mortality in bilateral UKA was seen in men (HR 2.24; 95% CI 1.02–4.93) and higher weighted Elixhauser Index (HR 1.14; 95% CI 1.04–1.26). Discussion In this large registry cohort, revision rate was lower in two-staged bilateral TKA compared to simultaneous surgery. In several studies benefits as well as risks of simultaneous TKA compared to two-staged surgeries at different intervals have been compared. Different advantages and disadvantages are consistently reported: On the one hand there is a reduction of cumulated operating time [26] and length of stay [20] with lower costs [19, 24]. But higher complication rates like thromboembolic and neurological complications [1, 2, 19, 20, 28], and revision rates [1, 19] as well as higher blood transfusion rates [2, 9, 26] were reported. Patients undergoing same day TKA were often younger [1, 13, 27, 28] and had less comorbidities [1, 26, 28], which was not confirmed in this large German cohort. While the registry data used for this study contained only major complications (revision and death), different studies reported about heterogenous results regarding risk for complications. Previous studies with different study designs and control groups reported conflicting results, including lower rates of deep infection and revision in simultaneous TKA [9], no difference in complication rates after six months in the data of the New Zealand National Joint Registry [13] or higher rates of complications [1–3, 19]. The conclusion in these studies was, that simultaneous TKA may be an option for healthy individuals. The mortality up to one year was low in all groups, but higher in TKA than UKA. Male sex, morbid obesity and higher Elixhauser Index were associated with higher mortality rates in TKA and UKA which should be taken into consideration by surgeons planning bilateral knee arthroplasty. A few studies demonstrated no significant difference in mortality between simultaneous and staged TKA in single-center-studies [2, 11, 22] or matched case-control studies [19]. In meta-analysis higher mmortality rates after 30 or 90 days were reported [9, 20]. That might be an expression for the specialized setting of those reporting single-centers, in which all healthcare professionals will be familiar with the whole treatment processs of a same day bilateral surgery. Especially for total hip arthroplasties (THA) Partridge et al. recommended a threshold of at least five same day THA per year [23] for a safe procedure. This might be applicable to TKA as well. No difference was found in revision rates for UKA. We found slightly higher proportion of male patients in simultaneous UKA, what could be an expression of patients who are more likely to be willing to take the higher risks and challenge of the strenuous rehabilitation. Another finding is the high proportion of simultaneous UKA (18% of all bilateral UKA, compared to 4% of all bilateral TKA). This could be explained by the less invasive procedure of UKA, which makes it easier for surgeons to tend to same day surgery. Actually, there are no recommendations from the large worldwide joint registries about one- or two-staged UKA. Two meta-analyses demonstrated no significant differences in all-cause complications between simultaneous and staged bilateral UKA. The authors recommend simultaneous UKA as a suitable option for bilateral uni-compartimental knee OA due to its superior cost-effectiveness without affecting the quality of outcome [7, 17] . Just 26.1% of all observed simultaneous bilateral surgeries were performed in a high-volume center with more than 500 TKA resp. 150 UKA per year. As there was a lower risk for revision in TKA in high-volume centers, the specialization and routinely performance of these procedures seems beneficial. Limitations The strength of the current study is its sample size, which is higher than all published meta-analysis and registry studies. Furthermore, the nearly complete follow-up allows for valid data on major complications. The registry setting covers real-world data and not only results from specialized centers. This study design has some limitations. Only mortality and revision rates could be analyzed, which do not give an overall picture of all peri- and post-operative complications. Patients with bilateral OA, who died after their first and before the second TKA, were not included. There is an inevitable time bias like in all studies about this topic. As the EPRD is a voluntary registry, not all TKA performed in Germany are included. However, data can be considered representative as it covers about 70% of all arthroplasties performed in Germany. Conclusion The lowest risk for revision in bilateral TKA was seen for high-volume centers, patients younger than 75 years and two-staged surgery. No differences were found in timing of UKA. Therefore, simultaneous UKA seems to be a safe option in bilateral unicondylar OA, whereas simultaneous TKA should be performed simultaneously only in selected patients in experienced centers. Abbreviations CI: Confidence interval; ICD-10: International classification of disease; OA: Osteoarthritis; HR: Hazard Ratio; THA: Total Hip Arthroplasty; TKA: Total Knee Arthroplasty; TJA: Total Joint Arthroplasty Declarations Ethics approval and consent to participate The EPRD received a general institutional review board approval from the University of Kiel (ID 473/11). A written consent was obtained from all patients. Clinical trial number: not applicable. Consent for publication Not applicable. Availability of data and materials All data generated or analyzed during this study are included in this published article. Competing interests The authors declare no competing interest to this work. Funding This study was funded by the EPRD. Authors’ contributions Conception and design: AP, JL, KPG, PK, YW, OM and AS. Analysis and interpretation of data: AP, JL, KPG, PK, YW, OM and AS. Drafting the manuscript: AP, JL, PK, YW and KPG. Critical revisions for important intellectual content: all authors. Final approval of the version to be submitted: all authors. Acknowledgements The authors thank all hospitals for providing the data and all members of the EPRD working groups for their voluntary activities. References Abdelaal MS, Calem D, Sherman MB, Sharkey PF. Short Interval Staged Bilateral Total Knee Arthroplasty: Safety Compared to Simultaneous and Later Staged Bilateral Total Knee Arthroplasty. The Journal of Arthroplasty. 2021;36:3901-3908. Agarwala S, Menon A. 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Bilateral simultaneous total knee arthroplasty may not be safe even in the healthiest patients. JBJS. 2021;103:303-311. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 31 Mar, 2025 Read the published version in BMC Musculoskeletal Disorders → Version 1 posted Editorial decision: Revision requested 05 Feb, 2025 Reviews received at journal 04 Feb, 2025 Reviews received at journal 19 Jan, 2025 Reviewers agreed at journal 13 Jan, 2025 Reviewers agreed at journal 08 Jan, 2025 Reviewers invited by journal 07 Jan, 2025 Editor invited by journal 30 Dec, 2024 Editor assigned by journal 30 Dec, 2024 Submission checks completed at journal 30 Dec, 2024 First submitted to journal 22 Dec, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Postler","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5klEQVRIiWNgGAWjYFADdiD+wJDA2HCAwYA4HTzMDAyMM0jWwsxDjBb+2b0HHzDusLG3Z2Y+9tm2LU227wDzxgf4tEjcOZdswHgmLbGHmS15dm5bjvHMA2zF+K25kWMmwdh2OIGHmceYObetInHDAR4zCXw65G/kmP8AarHnYeb/zGwJ0WL+A58WA6AtDEAtjD3MPMzMjG05YFvwusvwRo6xRCLIL4fZjBl7zqUZzzzMVozXYXI3cgw/fASGGHt782OGH2XJsn3Hmzd+wGsNCCQ2IPOYCaoHAsYGgkpGwSgYBaNgJAMABRxIKHYXuqIAAAAASUVORK5CYII=","orcid":"","institution":"University Hospital Carl Gustav Carus","correspondingAuthor":true,"prefix":"","firstName":"Anne","middleName":"Elisabeth","lastName":"Postler","suffix":""},{"id":396293225,"identity":"80adad69-d662-463e-b80c-3d8fb10a0845","order_by":1,"name":"Paula Krull","email":"","orcid":"","institution":"German Arthroplasty Registry 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(EPRD)","correspondingAuthor":false,"prefix":"","firstName":"Oliver","middleName":"","lastName":"Melsheimer","suffix":""},{"id":396293229,"identity":"79cbd46f-0756-43d5-8ea3-55aeaf53c5a5","order_by":5,"name":"Arnd Steinbrück","email":"","orcid":"","institution":"German Arthroplasty Registry (EPRD)","correspondingAuthor":false,"prefix":"","firstName":"Arnd","middleName":"","lastName":"Steinbrück","suffix":""},{"id":396293230,"identity":"d9fe9978-a066-4dee-9e42-25d17406d94c","order_by":6,"name":"Jörg Lützner","email":"","orcid":"","institution":"University Hospital Carl Gustav Carus","correspondingAuthor":false,"prefix":"","firstName":"Jörg","middleName":"","lastName":"Lützner","suffix":""}],"badges":[],"createdAt":"2024-12-22 16:38:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5694770/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5694770/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s12891-025-08548-5","type":"published","date":"2025-03-31T15:57:44+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":72755673,"identity":"40df40cd-da2a-4da0-84ef-81c0779a0963","added_by":"auto","created_at":"2025-01-01 16:54:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":182651,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart\u003c/p\u003e","description":"","filename":"figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-5694770/v1/63370847cda25764b86a0bda.png"},{"id":72755668,"identity":"b1f4a471-1e31-4972-8eec-94d3e85612d8","added_by":"auto","created_at":"2025-01-01 16:54:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":79155,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of second surgery\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-5694770/v1/197b5321eff51b087e31c9d4.png"},{"id":72756073,"identity":"c89ab271-e021-4a1d-91b9-2c6fe04d301b","added_by":"auto","created_at":"2025-01-01 17:02:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":152702,"visible":true,"origin":"","legend":"\u003cp\u003eFrequency of surgeries in hospital grouped by annual volume\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-5694770/v1/be126cd99ea25695af29e556.png"},{"id":72755675,"identity":"ac5c4be2-3928-46c2-901d-c5932cc91807","added_by":"auto","created_at":"2025-01-01 16:54:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":429791,"visible":true,"origin":"","legend":"\u003cp\u003eRevision rate in TKA\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-5694770/v1/3879456807cb8a92be8fc76d.png"},{"id":72756075,"identity":"6725f574-7660-4fdd-a2cf-c405bf71d00b","added_by":"auto","created_at":"2025-01-01 17:02:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":390983,"visible":true,"origin":"","legend":"\u003cp\u003eRevision rate in UKA\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-5694770/v1/77207d9e4eb82dd28e4f567d.png"},{"id":72755689,"identity":"f3fefd34-0321-4457-978d-c405866e0001","added_by":"auto","created_at":"2025-01-01 16:54:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":413898,"visible":true,"origin":"","legend":"\u003cp\u003eMortality rate in TKA\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-5694770/v1/c7a4b3b86ac24dc7bf9c871e.png"},{"id":72755677,"identity":"6f09ce6f-d186-454b-8ac5-2fc5ec48ea7d","added_by":"auto","created_at":"2025-01-01 16:54:23","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":385635,"visible":true,"origin":"","legend":"\u003cp\u003eMortality rate in UKA\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-5694770/v1/15e58ae7de55f20b1ef451fa.png"},{"id":80082073,"identity":"ca29f831-000f-4ae8-a470-b975b4fc3f77","added_by":"auto","created_at":"2025-04-07 16:06:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2772227,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5694770/v1/85e664af-7c7b-4823-81ee-3f76de386644.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Best timing of bilateral knee arthroplasty – an analysis of revision and mortality rates from the German Arthroplasty Registry (EPRD)","fulltext":[{"header":"Background","content":"\u003cp\u003eOsteoarthritis (OA) of the knee is a frequent cause of functional impairment. The FDA has recently categorized knee OA as a serious disease [15, 16]. Total knee arthroplasty (TKA) is a very effective treatment option for advanced OA of the knee, which decreases pain and improves function [18]. Evans et al. reported about an expected survival time (time to revision or death) of TKA up to 20 years in around 90.1% of patients [6]. Bilateral OA of the knee ranges from 60-90.4% [4, 5, 12, 25]. The burden of OA in multiple joints is high [5] and multiple surgeries and anesthesia procedures need a prolonged rehabilitation and recovery. In cases of bilateral knee OA there is always the question whether TKA is necessary bilateral and if so, how it should be performed (one stage, two stages, time between stages). Most patients get bilateral TKA as a staged procedure after a convalescence of several months. The one-staged, same day bilateral TKA is rather reserved for younger patients with less comorbidities [3] and risks and benefits are discussed controversially. Multiple single-center and retrospective studies concluded bilateral TKA as safe procedures in specialized high-volume center [22], but reserved for selected patients [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] and considering higher complications rates [2, 3, 9, 11, 19, 20, 24, 27]. In an older systematic review of retrospective studies Fu et al. reported about significant higher 30-days-mortality as well as pulmonary embolism and blood transfusion rate following same day bilateral TKA, but lower rates of deep infection and revision [9]. An recent meta-analysis showed significantly over twofold increased 90-day-mortality for same day bilateral TKA compared to staged bilateral TKA with equivocal revision rate within the first year and different trends of separate complication rates [20]. Another systematic review with contemporary studies demonstrated no differences if the baseline characteristics of the patients were similar [8, 21].\u003c/p\u003e \u003cp\u003eAim of this study was therefore 1) to investigate the frequency and timing of bilateral TKA in Germany and 2) to determine revision and mortality rates associated with simultaneous versus two-staged TKA in the German Arthroplasty Registry (EPRD).\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eIn this retrospective registry study data acquisition started in November 2012 and includes currently a total number of more than 3\u0026nbsp;million hip and knee replacements in its database. The EPRD covers primary and revision arthroplasty surgeries. Although participation is voluntarily, it covers about 70% of all hip and knee arthroplasties in Germany [10]. Once entered into the registry, the follow-up of an arthroplasty is nearly complete because data on revisions is obtained not only by hospitals, but additionally by health insurance companies. Demographic data such as age, sex, body mass index as well as comorbidities (weighted Elixhauser Score), length of stay and readmission rates are documented. Death and revision data are obtained from health insurance companies on a regular basis [14]. Revisions and mortality were analysed up to 7 years after the second of the bilateral knee arthroplasties. Annual hospital volume is documented as well. High-volume center for TKA/UKA surgeries were defined as performing at least 500 TKA/150 UKA per year.\u003c/p\u003e\n\u003cp\u003eFrom a total number of 377,897 patients with knee arthroplasty in cases of OA (ICD-10 code diagnoses of M17.-) which were registered in the EPRD from 2012, 40,535 could be identified as having a bilateral primary knee arthroplasty and 15,154 within one year. Patients with a second knee arthroplasty due to other diagnosis than OA (M17), unknown implant types, patellofemoral arthroplasty and constraint TKA were not included. TKA and UKA were separately analyzed.\u003c/p\u003e\n\u003cp\u003eThree different time intervals between both knee arthroplasties were chosen: 1) both procedures on exactly the same day (simultaneous) with 1,144 TKA and 682 UKA, 2) staged surgery with an interval of one to 90 days between index surgery and second knee arthroplasty (short interval) with 772 TKA and 292 UKA and 3) staged surgery with an interval of 91 to 365 days between both procedures (intermediate interval) with 24,496 TKA and 2,922 UKA, see flowchart, Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eBetween the groups there were significant differences regarding age, sex, BMI in categories and comorbidities (weighted Elixhauser Index). The endpoints were revision surgeries and death of the patients.\u003c/p\u003e\n\u003cp\u003eThe characteristics of the study cases are summarized in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, and Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003etable 1: characteristics of study cases\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"691\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 279px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTKA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 279px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUKA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003esame day\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1-90 d\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e91-365 d\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003esame day\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1-90 d\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e91-365 d\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e(n=1,144)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e(n=772)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e(n=24,496)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e(n=682)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e(n=292)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e(n=2,922)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSex\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"8\" style=\"width: 557px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003eFemale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e630 (55%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e372 (48%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e15,361 (63%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e324 (48%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e120 (41%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1,486 (51%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.003\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003eMale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e514 (45%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e400 (52%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e9,135 (37%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e358 (52%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e172 (59%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1,436 (49%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"8\" style=\"width: 557px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u0026lt;65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e386 (34%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e345 (45%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e8,638 (35%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 51px;\"\u003e\n \u003cp\u003e0.063\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e352 (52%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e184 (63%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1,675 (57%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e65-74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e476 (42%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e232 (30%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e8,547 (35%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e238 (35%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e84 (29%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e819 (28%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e75-84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e262 (23%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e177 (23%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e6,774 (28%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e90 (13%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e24 (8.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e414 (14%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e85+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e20 (1.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e18 (2.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e537 (2.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e2 (0.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e14 (0.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"8\" style=\"width: 557px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003emean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e30.0 (5.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e31.6 (6.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e31.9 (6.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e30.5 (5.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e31.3 (5.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e30.9 (5.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eweighted Elixhauser Score by VW\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"8\" style=\"width: 557px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 133px;\"\u003e\n \u003cp\u003emean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e0.6 (3.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e0.4 (4.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e0.5 (4.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e-0.24 (2.93)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e-0.30 (3.24)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e-0.04 (3.21)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 51px;\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"9\" style=\"width: 691px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAnnual hospital volume [TKA/UKA]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u0026lt; 250/50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e294 (26%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e314 (41%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e13,255 (55%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e78 (12%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e57 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1,163 (41%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e251/51 - 500/150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e622 (55%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e124 (16%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e5,403 (23%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e144 (21%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e26 (9.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e610 (22%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003e\u0026gt; 500/150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e224 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e322 (42%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e5,302 (22%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e454 (67%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e196 (70%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1,037 (37%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 133px;\"\u003e\n \u003cp\u003emissing\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e536\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e112\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e*One-way ANOVA for continuous variables (e.g. age at admission), Chi-squared test for categorical variables (e.g. sex of patient).\u003cstrong\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003ch2\u003eStatisticcal analysis\u003c/h2\u003e\n\u003cp\u003eData description was based on means and standard deviation (SD) for continuous variables and absolute and relative frequencies for categorical variables. To evaluate the influence of different patient characteristics on revision and mortality, a Cox regression model was applied.\u003c/p\u003e\n\u003cp\u003eCumulative incidences for the endpoints death of the patient and revision of each arthroplasty separately were calculated with the Kaplan-Meier survival function. A pairwise Log-Rank test with Holm\u0026acute;s correction for multiple testing was applied to identify intergroup differences.\u003c/p\u003e\n\u003cp\u003eA p-value threshold of 0.05 was considered statistically significant. All data analyses were carried out using R statistical software, Version R-4.2.0 (R Foundation for Statistical Computing, Vienna, Austria).\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 10.7% of patients with primary knee arthroplastyhave had both knee joints replaced, 4.0% in the same year and 0.2% simultaneously. The analysis demonstrated significantly higher cumulative revision rates for any of the bilateral TKA within 7 years for simultaneous (3.4%) vs. short (1.4%, HR 0.42; 95% CI 0.20\u0026ndash;0.90) and intermediate interval (2.5%, HR 0.58; 95% CI 0.39\u0026ndash;0.85), see Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Lower risk for revision was recognized if the surgery was performed in a high-volume center with more than 500 knee arthroplasties per year (HR 0.77; 95% CI 0.64\u0026ndash;1.02) and for patients between 65\u0026ndash;74 years (HR 0.61; 95% CI 0.49\u0026ndash;0.77) Higher risk for revision was found for higher weighted Elixhauser Index (HR 1.03 per point; 95% CI 1.01\u0026ndash;1.06). No significant association was found with sex and BMI. For TKA, there was no significant difference between the cumulative mortality rate in every group, see Table \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Higher risk for mortality in bilateral TKA was seen in men (HR 1.81; 95% CI 1.56\u0026ndash;2.11), BMI\u0026thinsp;\u0026gt;\u0026thinsp;40kg/m\u003csup\u003e2\u003c/sup\u003e (HR 2.1 compared to normal weight; 95% CI 1.34\u0026ndash;3.29) and higher Elixhauser Index (HR 1.06 per point; 95%CI 1.04\u0026ndash;1.87). Lower risk for mortality in bilateral TKA was seen in high-volume centers with \u0026gt;\u0026thinsp;500/y (HR 0.73; 95% CI 0.59\u0026ndash;0.90).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCumulative events for revision (95% Confidence Interval) in \u003cem\u003eTKA\u003c/em\u003e and \u003cem\u003eUKA\u003c/em\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTKA\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 year\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3 years\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5 years\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7 years\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003esame day (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.8 (1.2\u0026ndash;2.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.6 (1.8\u0026ndash;3.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.8 (1.9\u0026ndash;4.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.4 (2.1\u0026ndash;5.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e1\u0026ndash;90 days (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.8 (0.4\u0026ndash;1.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.4 (0.7\u0026ndash;2.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.4 (0.7\u0026ndash;2.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.4 (0.7\u0026ndash;2.7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e91\u0026ndash;365 days (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.9 (0.8\u0026ndash;1.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.6 (1.4\u0026ndash;1.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2 (1.8\u0026ndash;2.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.5 (2.2\u0026ndash;2.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eUKA\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e1 year\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e3 years\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e5 years\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e7 years\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003esame day (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.8 (1.0-3.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.4 (2.2\u0026ndash;6.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.2 (2.7\u0026ndash;6.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.8 (3.1\u0026ndash;10.7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e1\u0026ndash;90 days (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.1 (0.4\u0026ndash;3.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.8 (1.2\u0026ndash;6.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.2 (2.1\u0026ndash;8.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.2 (2.1\u0026ndash;8.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e91\u0026ndash;365 days (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.5 (1.1.-2.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.3 (1.8-3.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.0 (2.3\u0026ndash;3.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.1 (2.4\u0026ndash;4.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCumulative events for death of patient after second \u003cem\u003eTKA\u003c/em\u003e and \u003cem\u003eUKA\u003c/em\u003e (95% Confidence Interval).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTKA\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 year\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3 years\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5 years\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7 years\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003esame day (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.9 (0.4\u0026ndash;2.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.8 (0.9\u0026ndash;3.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.0 (4.9\u0026ndash;12.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11.6 (7.2\u0026ndash;18.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e1\u0026ndash;90 days (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.5 (0.6\u0026ndash;3.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.8 (1.4\u0026ndash;5.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.5 (3.0-9.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13.5 (6.6\u0026ndash;26.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e91\u0026ndash;365 days (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.7 (0.5\u0026ndash;0.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.5 (3.1\u0026ndash;3.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.9 (7.2\u0026ndash;8.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13.5 (12.1\u0026ndash;14.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eUKA\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e1 year\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e3 years\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e5 years\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e7 years\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003esame day (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.3 (0.0-2.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.3 (0.0-2.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.7 (1.0-7.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.7 (1.0-7.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e1\u0026ndash;90 days (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0 (0.0.)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.0 (0.1\u0026ndash;6.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.2 (0.7\u0026ndash;13.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8.5 (2.3\u0026ndash;29.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e91\u0026ndash;365 days (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.3 (0.1\u0026ndash;0.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.2 (0.7\u0026ndash;2.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.7 (1.7\u0026ndash;4.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.0 (2.3\u0026ndash;6.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOverall, UKA patients were younger and had less comorbidities. The cumulative revision rates within 7 years for UKA were not significantly different between simultaneous UKA (5.8%) compared to short (4.2%) and intermediate interval (3.1%), see Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003e. There was no significant association between revision rates and cofactors. The cumulative mortality rates within 7 years for UKA were not significantly different between the three groups, s. Table \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Higher risk for mortality in bilateral UKA was seen in men (HR 2.24; 95% CI 1.02\u0026ndash;4.93) and higher weighted Elixhauser Index (HR 1.14; 95% CI 1.04\u0026ndash;1.26).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this large registry cohort, revision rate was lower in two-staged bilateral TKA compared to simultaneous surgery. In several studies benefits as well as risks of simultaneous TKA compared to two-staged surgeries at different intervals have been compared. Different advantages and disadvantages are consistently reported: On the one hand there is a reduction of cumulated operating time [26] and length of stay [20] with lower costs [19, 24]. But higher complication rates like thromboembolic and neurological complications [1, 2, 19, 20, 28], and revision rates [1, 19] as well as higher blood transfusion rates [2, 9, 26] were reported. Patients undergoing same day TKA were often younger [1, 13, 27, 28] and had less comorbidities [1, 26, 28], which was not confirmed in this large German cohort.\u003c/p\u003e \u003cp\u003eWhile the registry data used for this study contained only major complications (revision and death), different studies reported about heterogenous results regarding risk for complications. Previous studies with different study designs and control groups reported conflicting results, including lower rates of deep infection and revision in simultaneous TKA [9], no difference in complication rates after six months in the data of the New Zealand National Joint Registry [13] or higher rates of complications [1\u0026ndash;3, 19]. The conclusion in these studies was, that simultaneous TKA may be an option for healthy individuals. The mortality up to one year was low in all groups, but higher in TKA than UKA. Male sex, morbid obesity and higher Elixhauser Index were associated with higher mortality rates in TKA and UKA which should be taken into consideration by surgeons planning bilateral knee arthroplasty. A few studies demonstrated no significant difference in mortality between simultaneous and staged TKA in single-center-studies [2, 11, 22] or matched case-control studies [19]. In meta-analysis higher mmortality rates after 30 or 90 days were reported [9, 20]. That might be an expression for the specialized setting of those reporting single-centers, in which all healthcare professionals will be familiar with the whole treatment processs of a same day bilateral surgery. Especially for total hip arthroplasties (THA) Partridge et al. recommended a threshold of at least five same day THA per year [23] for a safe procedure. This might be applicable to TKA as well.\u003c/p\u003e \u003cp\u003eNo difference was found in revision rates for UKA. We found slightly higher proportion of male patients in simultaneous UKA, what could be an expression of patients who are more likely to be willing to take the higher risks and challenge of the strenuous rehabilitation. Another finding is the high proportion of simultaneous UKA (18% of all bilateral UKA, compared to 4% of all bilateral TKA). This could be explained by the less invasive procedure of UKA, which makes it easier for surgeons to tend to same day surgery. Actually, there are no recommendations from the large worldwide joint registries about one- or two-staged UKA. Two meta-analyses demonstrated no significant differences in all-cause complications between simultaneous and staged bilateral UKA. The authors recommend simultaneous UKA as a suitable option for bilateral uni-compartimental knee OA due to its superior cost-effectiveness without affecting the quality of outcome [7, 17] .\u003c/p\u003e \u003cp\u003eJust 26.1% of all observed simultaneous bilateral surgeries were performed in a high-volume center with more than 500 TKA resp. 150 UKA per year. As there was a lower risk for revision in TKA in high-volume centers, the specialization and routinely performance of these procedures seems beneficial.\u003c/p\u003e"},{"header":"Limitations","content":"\u003cp\u003eThe strength of the current study is its sample size, which is higher than all published meta-analysis and registry studies. Furthermore, the nearly complete follow-up allows for valid data on major complications. The registry setting covers real-world data and not only results from specialized centers. This study design has some limitations. Only mortality and revision rates could be analyzed, which do not give an overall picture of all peri- and post-operative complications. Patients with bilateral OA, who died after their first and before the second TKA, were not included. There is an inevitable time bias like in all studies about this topic. As the EPRD is a voluntary registry, not all TKA performed in Germany are included. However, data can be considered representative as it covers about 70% of all arthroplasties performed in Germany.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe lowest risk for revision in bilateral TKA was seen for high-volume centers, patients younger than 75 years and two-staged surgery. No differences were found in timing of UKA. Therefore, simultaneous UKA seems to be a safe option in bilateral unicondylar OA, whereas simultaneous TKA should be performed simultaneously only in selected patients in experienced centers.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCI: Confidence interval; ICD-10: International classification of disease; OA: Osteoarthritis; HR: Hazard Ratio; THA: Total Hip Arthroplasty; TKA: Total Knee Arthroplasty; TJA: Total Joint Arthroplasty\u003c/p\u003e\n"},{"header":"Declarations","content":"\u003cp\u003e\u003cu\u003eEthics approval and consent to participate\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe EPRD received a general institutional review board approval from the University of Kiel (ID 473/11). A written consent was obtained from all patients.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eClinical trial number: not applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eConsent for publication\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAvailability of data and materials\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated or analyzed during this study are included in this published article.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cu\u003eCompeting interests\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interest to this work.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cu\u003eFunding\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by the EPRD.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAuthors\u0026rsquo; contributions\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eConception and design: AP, JL, KPG, PK, YW, OM and AS. Analysis and interpretation of data: AP, JL, KPG, PK, YW, OM and AS. Drafting the manuscript: AP, JL, PK, YW and KPG. Critical revisions for important intellectual content: all authors.\u003c/p\u003e\n\u003cp\u003eFinal approval of the version to be submitted: all authors.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAcknowledgements\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank all hospitals for providing the data and all members of the EPRD working groups for their voluntary activities.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbdelaal MS, Calem D, Sherman MB, Sharkey PF. Short Interval Staged Bilateral Total Knee Arthroplasty: Safety Compared to Simultaneous and Later Staged Bilateral Total Knee Arthroplasty. The Journal of Arthroplasty. 2021;36:3901-3908. \u003c/li\u003e\n\u003cli\u003eAgarwala S, Menon A. Safety and efficacy of sequential simultaneous bilateral total knee arthroplasty: A single centre retrospective cohort study. Journal of Clinical Orthopaedics and Trauma. 2020;11:S636-S644. \u003c/li\u003e\n\u003cli\u003eAlmaguer A, Cichos K, McGwin Jr G, Pearson J, Wilson B, Ghanem E. Combined total hip and knee arthroplasty during the same hospital admission: is it safe? The Bone \u0026amp; Joint Journal. 2019;101:573-581.\u003c/li\u003e\n\u003cli\u003eBischoff-Ferrari HA, Orav EJ, Egli A, Dawson-Hughes B, Fischer K, Staehelin HB, Rizzoli R, Hodler J, Von Eckardstein A, Freystaetter G. Recovery after unilateral knee replacement due to severe osteoarthritis and progression in the contralateral knee: a randomised clinical trial comparing daily 2000 IU versus 800 IU vitamin D. RMD open. 2018;4:e000678. \u003c/li\u003e\n\u003cli\u003eCallhoff J, Albrecht K, Redeker I, Lange T, Goronzy J, G\u0026uuml;nther KP, Zink A, Schmitt J, Saam J, Postler A. Disease burden of patients with osteoarthritis: Results of a cross‐sectional survey linked to claims data. Arthritis Care \u0026amp; Research. 2020;72:193-200. \u003c/li\u003e\n\u003cli\u003eEvans JT, Evans JP, Walker RW, Blom AW, Whitehouse MR, Sayers A. How long does a hip replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up. The Lancet. 2019;393:647-654. \u003c/li\u003e\n\u003cli\u003eFeltri P, da Lodi CMT, Grassi A, Zaffagnini S, Candrian C, Filardo G. One-stage bilateral unicompartmental knee arthroplasty is a suitable option vs. the two-stage approach: a meta-analysis. EFORT Open Reviews. 2021;6:1063-1072. \u003c/li\u003e\n\u003cli\u003eFlick TR, Ofa SA, Patel AH, Ross BJ, Sanchez FL, Sherman WF. Complication rates of bilateral total hip versus unilateral total hip arthroplasty are similar. Journal of Orthopaedics. 2020;22:571-578.\u003c/li\u003e\n\u003cli\u003eFu D, Li G, Chen K, Zeng H, Zhang X, Cai Z. Comparison of clinical outcome between simultaneous-bilateral and staged-bilateral total knee arthroplasty: a systematic review of retrospective studies. The Journal of arthroplasty. 2013;28:1141-1147. \u003c/li\u003e\n\u003cli\u003eGrimberg A, Jansson V, L\u0026uuml;tzner J, Melsheimer O, Morlock M, Steinbr\u0026uuml;ck A. EPRD Jahresbericht 2021; 2021. \u003c/li\u003e\n\u003cli\u003eGromov K, Troelsen A, Stahl Otte K, \u0026Oslash;rsnes T, Husted H. Morbidity and mortality after bilateral simultaneous total knee arthroplasty in a fast-track setting. Acta orthopaedica. 2016;87:286-290.\u003c/li\u003e\n\u003cli\u003eG\u0026uuml;nther K, St\u0026uuml;rmer T, Sauerland S, Zeissig I, Sun Y, Kessler S, Scharf H, Brenner H, Puhl W. Prevalence of generalised osteoarthritis in patients with advanced hip and knee osteoarthritis: the Ulm Osteoarthritis Study. 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Elsevier: 2022:152070.\u003c/li\u003e\n\u003cli\u003eKwan H, To K, Bojanic C, Romain K, Khan W. A meta-analysis of clinical and radiological outcomes in simultaneous bilateral unicompartmental knee arthroplasty. Journal of Orthopaedics. 2021;23:128-137. \u003c/li\u003e\n\u003cli\u003eLearmonth ID, Young C, Rorabeck C. The operation of the century: total hip replacement. The Lancet. 2007;370:1508-1519. \u003c/li\u003e\n\u003cli\u003eLindberg-Larsen M, Pitter F, Husted H, Kehlet H, J\u0026oslash;rgensen C. Simultaneous vs staged bilateral total knee arthroplasty: a propensity-matched case\u0026ndash;control study from nine fast-track centres. Archives of Orthopaedic and Trauma Surgery. 2019;139:709-716. \u003c/li\u003e\n\u003cli\u003eMakaram NS, Roberts SB, Macpherson GJ. Simultaneous bilateral total knee arthroplasty is associated with shorter length of stay but increased mortality compared with staged bilateral total knee arthroplasty: a systematic review and meta-analysis. The Journal of Arthroplasty. 2021;36:2227-2238.\u003c/li\u003e\n\u003cli\u003eMalahias M-A, Gu A, Adriani M, Addona JL, Alexiades MM, Sculco PK. Comparing the safety and outcome of simultaneous and staged bilateral total knee arthroplasty in contemporary practice: a systematic review of the literature. The Journal of Arthroplasty. 2019;34:1531-1537.\u003c/li\u003e\n\u003cli\u003eNajfeld M, Kalteis T, Spiegler C, Ley C, Hube R. The Safety of Bilateral Simultaneous Hip and Knee Arthroplasty versus Staged Arthroplasty in a High-Volume Center Comparing Blood Loss, Peri-and Postoperative Complications, and Early Functional Outcome. Journal of Clinical Medicine. 2021;10:4507. \u003c/li\u003e\n\u003cli\u003ePartridge TC, Charity JA, Sandiford NA, Baker PN, Reed MR, Jameson SS. Simultaneous or staged bilateral total hip arthroplasty? An analysis of complications in 14,460 patients using national data. The Journal of Arthroplasty. 2020;35:166-171. \u003c/li\u003e\n\u003cli\u003ePfeil J, H\u0026ouml;hle P, Rehbein P. Bilateral endoprosthetic total hip or knee arthroplasty. Deutsches \u0026Auml;rzteblatt International. 2011;108:463. \u003c/li\u003e\n\u003cli\u003eRiddle DL. Prevalence of similar or worse symptom and osteoarthritis severity of index and contralateral knees prior to knee arthroplasty: A cross-sectional multicenter cohort study. The Knee. 2020;27:485-492. \u003c/li\u003e\n\u003cli\u003eSaini R, Powell J, Sharma R, Puloski S, Mahdavi S, Smith C, Johnston K. One-stage versus 2-stage bilateral total joint arthroplasty: a matched cohort study. Canadian Journal of Surgery. 2020;63:E167.\u003c/li\u003e\n\u003cli\u003eSheth DS, Cafri G, Paxton EW, Namba RS. Bilateral simultaneous vs staged total knee arthroplasty: a comparison of complications and mortality. The Journal of arthroplasty. 2016;31:212-216.\u003c/li\u003e\n\u003cli\u003eWarren JA, Siddiqi A, Krebs VE, Molloy R, Higuera CA, Piuzzi NS. Bilateral simultaneous total knee arthroplasty may not be safe even in the healthiest patients. JBJS. 2021;103:303-311.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Total knee arthroplasty, Unicondylar knee arthroplasty, Bilateral, Same day, Simultaneous, Mortality, Revision","lastPublishedDoi":"10.21203/rs.3.rs-5694770/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5694770/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground: \u003c/strong\u003eThe burden of osteoarthritis (OA) in multiple joints is high. For patients with bilateral knee OA there is no clear recommendation when to time the second surgery.\u003c/p\u003e\n\u003cp\u003eThe purpose of this study was therefore to compare revision and mortality rate in bilateral unicondylar and bicondylar knee arthroplasties after different strategies of surgical timing in bilateral knee OA from the German Arthroplasty Registry (EPRD).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods: \u003c/strong\u003eData from the German Arthroplasty Registry (EPRD) was used.\u003cem\u003e \u003c/em\u003eSince 2012 a total of 15,154 patients had bilateral knee arthroplasty within one year. Patellofemoral arthroplasties and constraint total knee arthroplasties (TKA) were excluded. 1,144 TKA and 682 unicondylar arthroplasties (UKA) were simultaneously performed, 772 TKA and 292 UKA between 1 and 90 days (short interval) and 24,496 TKA and 2,922 UKA between 91 and 365 days (intermediate interval). Revision and mortality rates were analyzed up to 7 years after surgery. Cox regression was performed to evaluate the influence of different patient characteristics on these outcomes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003eThe highest cumulative revision rate for any of the bilateral TKA was found for simultaneous surgery with 3.4% (95% CI 2.1 – 5.5). Lower risk for revision was seen in two-staged surgery in short interval (HR 0.42; 95% CI 0.20 – 0.90) and intermediate interval (HR 0.58; 95% CI 0.39 – 0.85). The cumulative one year mortality rate for TKA was comparable in all three groups with 0.8% for simultaneous TKA, 1.3% for short interval two-staged and 0.7% for intermediate interval. In UKA there were no differences between the groups regarding cumulative revision rate and mortality rate.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e TKA should be performed simultaneously in selected patients only, the two-staged procedure demonstrated lower revision risks. For UKA we found no differences in timing, simultaneous surgery seems to be a safe option.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTrial registration:\u003c/strong\u003e Clinical trial number not applicable.\u003c/p\u003e","manuscriptTitle":"Best timing of bilateral knee arthroplasty – an analysis of revision and mortality rates from the German Arthroplasty Registry (EPRD)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-01 16:54:17","doi":"10.21203/rs.3.rs-5694770/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-02-05T10:21:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-02-04T23:45:44+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-01-19T17:25:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"265900220832339413898122348740083791975","date":"2025-01-13T09:48:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"264180652129401524652199937315926813746","date":"2025-01-09T03:10:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-01-07T19:00:51+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-12-30T23:02:39+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-12-30T17:17:07+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-12-30T17:15:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Musculoskeletal Disorders","date":"2024-12-22T16:30:17+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0f6e1f62-b1ac-496f-8889-63f73d037586","owner":[],"postedDate":"January 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[{"value":"featured","date":"2025-01-02 18:38:51"}],"updatedAt":"2025-04-07T16:02:08+00:00","versionOfRecord":{"articleIdentity":"rs-5694770","link":"https://doi.org/10.1186/s12891-025-08548-5","journal":{"identity":"bmc-musculoskeletal-disorders","isVorOnly":false,"title":"BMC Musculoskeletal Disorders"},"publishedOn":"2025-03-31 15:57:44","publishedOnDateReadable":"March 31st, 2025"},"versionCreatedAt":"2025-01-01 16:54:17","video":"","vorDoi":"10.1186/s12891-025-08548-5","vorDoiUrl":"https://doi.org/10.1186/s12891-025-08548-5","workflowStages":[]},"version":"v1","identity":"rs-5694770","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5694770","identity":"rs-5694770","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}