Impact of Nordic Arthroplasty Register Association (NARA) collaboration on demographics, methods and revision rates in knee arthroplasty: a register-based study from NARA 2000-2017.

BACKGROUND AND PURPOSE: We have previously observed differences in treatment and outcome of knee arthroplasties in the Nordic countries. To evaluate the impact of Nordic collaboration in the last 15 years we aimed to compare patient demographics, methods, and revision rates in primary knee arthroplasties among the 4 Nordic countries. PATIENTS AND METHODS: We included 535,051 primary knee arthroplasties reported 2000-2017 from the Nordic Arthroplasty Register Association (NARA) database. Kaplan-Meier analysis (KM) and restricted mean survival time (RMST) analysis were used to evaluate the cumulative revision rate (CRR) and RMST estimates with 95% confidence intervals (CI) and to compare countries in relation to risk of revision for any reason. RESULTS: After 2010, the increase in incidence of knee arthroplasty plateaued in Sweden and Denmark but continued to increase in Finland and Norway. In 2017 the incidence was highest in Finland with 226 per 105 person-years, while it was less than 150 per 105 in the 3 other Nordic countries. In total knee arthroplasties performed for osteoarthritis (OA), overall CRR at 15 years for revision due to any reason was higher in Denmark (CRR 9.6%, 95% CI 9.2-10), Norway (CRR 9.1%, CI 8.7-9.5), and Finland (CRR 7.0%, CI 6.8-7.3) compared with Sweden (CRR 6.6%, CI 6.4-6.8). There were differences among the countries in use of implant brand and type, fixation, patellar component, and use of unicompartmental knee arthroplasty. INTERPRETATION: We evinced a slowing growth of incidence of knee arthroplasties in the Nordic countries after 2010 with Finland having the highest incidence. We also noted substantial differences among the 4 Nordic countries, with Sweden having a lower risk of revision than the other countries. No impact of NARA could be demonstrated and CRR did not improve over time.

Impact of patient and prosthesis characteristics on common reasons for total knee replacement revision: a registry study of 36,626 revision cases from Australia, Sweden, and USA.

BACKGROUND AND PURPOSE: Total knee replacement (TKR) studies usually analyze all-cause revision when considering relationships with patient and prosthesis factors. We studied how these factors impact different revision diagnoses. PATIENTS AND METHODS: We used data from 2003 to 2019 of TKR for osteoarthritis from the arthroplasty registries of Sweden, Australia, and Kaiser Permanente, USA to study patient and prosthesis characteristics for specific revision diagnoses. There were 1,072,924 primary TKR included and 36,626 were revised. Factors studied included age, sex, prosthesis constraint, fixation method, bearing mobility, polyethylene type, and patellar component use. Revision diagnoses were arthrofibrosis, fracture, infection, instability, loosening, pain, patellar reasons, and wear. Odds ratios (ORs) for revision were estimated and summary effects were calculated using a meta-analytic approach. RESULTS: We found between-registry consistency in 15 factor/reason analyses. Risk factors for revision for arthrofibrosis were age < 65 years (OR 2.0; 95% CI 1.4-2.7) and mobile bearing designs (MB) (OR 1.7; CI 1.1-2.5), for fracture were female sex (OR 3.2; CI 2.2-4.8), age ≥ 65 years (OR 2.8; CI 1.9-4) and posterior stabilized prostheses (PS) (OR 2.1; CI 1.3-3.5), for infection were male sex (OR 1.9; CI 1.7-2.0) and PS (OR 1.5; CI 1.2-1.8), for instability were age < 65 years (OR 1.5; CI 1.3-1.8) and MB (OR 1.5; CI 1.1-2.2), for loosening were PS (OR 1.5; CI 1.4-1.6), MB (OR 2.2; CI 1.6-3.0) and use of ultra-high molecular weight polyethylene (OR 2.3; CI 1.8-2.9), for patellar reasons were not resurfacing the patella (OR 13.6; CI 2.1-87.2) and MB (OR 2.0; CI 1.2-3.3) and for wear was cementless fixation (OR 4.9; CI 4.3-5.5). INTERPRETATION: Patients could be counselled regarding specific age and sex risks. Use of minimally stabilized, fixed bearing, cemented prostheses, and patellar components is encouraged to minimize revision risk.

The effect of patient and prosthesis factors on revision rates after total knee replacement using a multi-registry meta-analytic approach.

BACKGROUND AND PURPOSE: Characteristics of patients receiving total knee arthroplasty (TKA) and prostheses used vary between regions and change with time. How these practice variations influence revision remains unclear. We combined registry data for better understanding of the impact of variation, which could potentially improve revision rates. PATIENTS AND METHODS: We used data from 2003 to 2019 for primary TKA from arthroplasty registries of Sweden (SKAR), Australia (AOANJRR), and Kaiser Permanente (KPJRR). We included 1,072,924 TKA procedures for osteoarthritis. Factors studied included age, sex, ASA class, BMI category, prosthesis constraint, fixation, bearing mobility, patellar resurfacing, and polyethylene type. Cumulative percentage revision (CPR) was calculated using Kaplan-Meier estimates, and unadjusted Cox hazard ratios were used for comparisons. Random-effects generic inverse-variance meta-analytic methods were used to determine summary effects. RESULTS: We found similarities in age and sex, but between-registry differences occurred in the other 7 factors studied. Patients from Sweden had lower BMI and ASA scores compared with other registries. Use of cement fixation was similar in the SKAR and KPJRR, but there were marked differences in patellar resurfacing and posterior stabilized component use. Meta-analysis results regarding survivorship favored patients aged ≥ 65 years and minimally stabilized components. There were inconsistent results with time for sex, fixation, and bearing mobility, and no differences for the patellar resurfacing or polyethylene type comparisons. INTERPRETATION: Marked practice variation was found. Use of minimally stabilized and possibly also cemented and fixed bearing prostheses is supported.

Similar periprosthetic joint infection rates after and before a national infection control program: a study of 45,438 primary total knee arthroplasties.

Background and purpose - Strenuous efforts to minimize postoperative infection rates have been made, including the Swedish nationwide initiative Prosthesis Related Infections Shall be Stopped (PRISS). This study calculated the incidence rate of periprosthetic joint infection (PJI) following primary total knee arthroplasty (TKA) before and after PRISS. Patients and methods - All 45,438 primary TKAs registered in the Swedish Knee Arthroplasty Register (SKAR) during 2007-2008 and 2012-2013 were included. Matched data on antibiotic prescriptions were obtained from the Swedish Prescribed Drug Register (SPDR). All patients with ≥ 28 days of continuous antibiotic treatment within 2 years of primary surgery had their medical charts reviewed to identify cases of PJI. The incidence rate was calculated by dividing the number of PJIs by the total time at risk during each time period and presented as percentages with 95% confidence interval (CI). Results - 644 PJIs were identified, equaling a 2-year incidence rate of 1.45% (CI 1.34-1.57). The incidence rate was 1.44% (CI 1.27-1.61) before PRISS and 1.46% (CI 1.31-1.61) after. Diagnosis was made within 30 days of primary TKA in 52%, and within 90 days in 73% of cases. 603 cases were reoperated on or revised. Median time from operation to diagnosis was 29 days (1-716), for both time periods. Debridement with exchange of the insert was performed in 32% and 63% of cases before and after PRISS, respectively. Interpretation - We found similar incidence rates before and after the PRISS initiative without any statistically significant difference. Time to diagnosis was similar during both time periods. The project may have contributed to increased compliance with treatment protocols.

Primary Total Knee Arthroplasty Revised for Instability: A Detailed Registry Analysis.

BACKGROUND: Instability after total knee arthroplasty is a common but poorly understood complication. METHODS: Data from a large national registry was used to study patient and prosthesis characteristics of 2605 total knee arthroplasty revisions for instability. The cumulative percent revision was calculated using Kaplan-Meier estimates, and Cox proportional models used to compare revision rates. The rate of further revision was analyzed with regard to prostheses used in the first revision. RESULTS: Instability increased from 6% of all first revision procedures in 2003 to 13% in 2019. The revision risk was lower for minimally stabilized prostheses, males, and patients aged ≥65 years. Polyethylene insert exchange was used for 55% of revision procedures, using a thicker insert in 93% and a change in insert conformity in 24% of cruciate-retaining knees. The increase in either thickness or conformity had no effect on the rate of further revision. After a revision for instability, 24% had a second revision by 14 years. Recurrent instability accounted for 32% of further revisions. A lower second revision rate was seen after revision of both femoral and tibial components, and where constrained components were used. CONCLUSION: Revision for instability is increasing. Revising both femoral and tibial components led to a lower rate of second revision compared to a change in insert alone. Recurrent instability was common.

Competing Risks Methods Are Recommended for Estimating the Cumulative Incidence of Revision Arthroplasty for Health Care Planning Purposes.

Cumulative incidence of revision provides a measure of the failure rate of joint replacements and can be used to project demand for revisions. The most commonly applied survival analysis method (Kaplan-Meier [KM]) does not account for competing risks (eg, death). The authors compared the cumulative incidence function (CIF), a competing risks method, with the KM method through application to population-based cohorts. They measured time to revision, death, or censoring for unilateral total hip arthroplasty (THA; n=12,496) and total knee arthroplasty (TKA; n=19,172) cohorts in administrative databases in Alberta and TKAs (n=80,177) in the Swedish Knee Arthroplasty Register. The authors compared relative differences between the KM and CIF. They fitted Cox, Fine and Gray, and Royston and Parmar regression models and compared coefficients, standard errors, and P values. On sensitivity analysis, the authors included staged bilateral operations. Kaplan-Meier estimates exceeded the CIF at each time point. The magnitude of overestimation increased with follow-up time and was greatest for the Swedish cohort. At 5 years, relative differences between KM and CIF estimates for the Alberta THA and TKA and Swedish TKA cohorts were 1.8%, 2.3%, and 3.8%, respectively. These differences increased to 3.1%, 5.8%, and 8.2%, respectively, at 9 years, reaching 39.1% at 20 years (Swedish cohort). On sensitivity analysis (including staged bilateral operations), the Fine and Gray subdistribution hazard ratio differed from the Cox and Royston and Parmar hazard ratios. When the frequency of competing risks is high, competing risks methods are recommended to obtain accurate cumulative incidence estimates for informing health care planning and decision making. [Orthopedics. 2021;44(4):e549-e555.].

Bipolar hemiarthroplasty versus total hip arthroplasty in femoral neck fracture patients: results from Lithuanian Arthroplasty Register.

INTRODUCTION: Elderly patients with displaced femoral neck fractures (FNF) are usually operated with arthroplasty but with various combinations of implants and approaches. Thus, the optimal treatment is still controversial. We aimed to compare the results between the cemented bipolar hemiarthroplasty (HA) and total hip arthroplasty (THA) patients operated for FNF regarding revision rate at 1 year postoperatively. METHODS: The data were derived from the Lithuanian Arthroplasty Register. We included patients operated with cemented bipolar HA and compared them to the most frequently used cemented THA with 28-mm head during 2011-2016. For survival analysis, we used both revision for all reasons and for dislocations as an endpoint. Cox proportional hazards models were used to analyse the influence of covariates (age groups, gender, surgical approaches and arthroplasty groups). RESULTS: There were 1177 bipolar HA and 514 THA included in our study. 26 (2.2%) revisions had occurred among the bipolar HAs as compared to 25 (4.9%) among the THAs 1 year after surgery. The main reason for revision was dislocation. The unadjusted cumulative revision rate for any reason at 1 year after surgery was 2.4% for the bipolar HA group and 5.1% for the THA group (p = 0.0054). Cox regression analysis showed that the use of bipolar HA, anterolateral approach and younger age groups had lower risk of revision for all reasons. CONCLUSION: Bipolar HA and anterolateral approach had a significantly lower overall 1-year risk of revision in femoral neck fracture patients as compared to THA with 28-mm femoral heads.

Variation and trends in reasons for knee replacement revision: a multi-registry study of revision burden.

Background and purpose - Studies describing time-related change in reasons for knee replacement revision have been limited to single regions or institutions, commonly analyze only 1st revisions, and may not reflect true caseloads or findings from other areas. We used revision procedure data from 3 arthroplasty registries to determine trends and differences in knee replacement revision diagnoses.Patients and methods - We obtained aggregated data for 78,151 revision knee replacement procedures recorded by the Swedish Knee Arthroplasty Register (SKAR), the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), and the Kaiser Permanente Joint Replacement Registry (KPJRR) for the period 2003-2017. Equivalent diagnosis groups were created. We calculated the annual proportions of the most common reasons for revision.Results - Infection, loosening, and instability were among the 5 most common reasons for revision but magnitude and ranking varied between registries. Over time there were increases in proportions of revisions for infection and decreases in revisions for wear. There were inconsistent proportions and trends for the other reasons for revision. The incidence of revision for infection showed a uniform increase.Interpretation - Despite some differences in terminology, comparison of registry-recorded revision diagnoses is possible, but defining a single reason for revision is not always clear-cut. There were common increases in revision for infection and decreases in revision for wear, but variable changes in other categories. This may reflect regional practice differences and therefore generalizability of studies regarding reasons for revision is unwise.

Association between fixation type and revision risk in total knee arthroplasty patients aged 65 years and older: a cohort study of 265,877 patients from the Nordic Arthroplasty Register Association 2000-2016.

Background and purpose - The population of the Nordic countries is aging and the number of elderly patients undergoing total knee arthroplasty (TKA) is also expected to increase. Reliable fixation methods are essential to avoid revisions. We compared the survival of different TKA fixation concepts with cemented fixation as the gold standard.Patients and methods - We used data from the Nordic Arthroplasty Register Association (NARA) database of 265,877 unconstrained TKAs performed for patients aged ≥ 65 years with primary knee osteoarthritis between 2000 and 2016. Kaplan-Meier (KM) survival analysis with 95% confidence intervals (CI) and the Cox multiple-regression model were used to compare the revision risk of the fixation methods.Results - Cemented fixation was used in 243,166 cases, uncemented in 8,000, hybrid (uncemented femur with cemented tibia) in 14,248, and inverse hybrid (cemented femur with uncemented tibia) fixation in 463 cases. The 10-year KM survivorship (95% CI) of cemented TKAs was 96% (96 - 97), uncemented 94% (94 - 95), hybrid 96% (96 - 96), and inverse hybrid 96% (94 - 99), respectively. Uncemented TKA was associated with increased risk of revision compared with the cemented TKA; the adjusted hazard ratio was 1.3 (95% CI 1.1 - 1.4).Interpretation - Cemented, hybrid, and inverse hybrid TKAs showed 10-year survival rates exceeding 95%. Uncemented fixation was associated with an increased risk of revision in comparison with cemented fixation. As both hybrid and inverse hybrid fixation were used in only a limited number of TKAs, indicating possibility of selection bias in their favor, cemented TKA still remains the gold standard, as it works reliably in the hands of many.

Bariatric surgery prior to total knee arthroplasty is not associated with lower risk of revision: a register-based study of 441 patients.

Background and purpose - Obesity is a considerable medical challenge in society. We investigated the risk of revision for any reasons and for infection in patients having total knee arthroplasty (TKA) for osteoarthritis (OA) within 2 years after bariatric surgery (BS) and compared them with TKAs without BS.Patients and methods - We used the Scandinavian Obesity Surgery Registry (SOReg) and the Swedish Knee Arthroplasty Register (SKAR) to identify patients operated on in 2009-2019 with BS who had had primary TKA for OA within 2 years after the BS (BS group) and compared them with TKAs without prior BS (noBS group). We determined adjusted hazard ratio (HR) for the BS group and noBS group using Cox proportional hazard regression for revision due to any reasons and for infection. Adjustments were made for sex, age groups, and BMI categories preoperatively.Results - 441 patients were included in the BS group. The risk of revision for infection was higher for the BS group with HR 2.2 (95% CI 1.1-4.7) adjusting for BMI before the TKA, while the risk of revision for any reasons was not statistically significant different for the BS group with HR 1.3 (CI 0.9-2.1). Corresponding figures when adjusting for BMI before the BS were HR 0.9 (CI 0.4-2) and HR 1.2 (CI 0.7-2).Interpretation - Our findings did not indicate that BS prior to TKA was associated with lower risk of revision.

The implications of an aging population and increased obesity for knee arthroplasty rates in Sweden: a register-based study.

Background and purpose - Total knee arthroplasty (TKA) has increased substantially in Sweden. We quantified the relative risk for TKA in the Swedish population for different BMI categories and age groups to investigate whether the continued increase in TKA is attributable to increased prevalence of obesity and elderly people in the population, and to put forward model predictions for coming needs for TKA. Patients and methods - We used the Swedish Nationwide Health Survey (SNHS) and the Swedish Knee Arthroplasty Register (SKAR) 2009-2015 to calculate the relative risk (RR) of TKA by age (middle-aged 45-64 years and elderly 65-84 years) and BMI (BMI 18.5-24.9 normal weight; BMI 25.0-29.9 overweight; BMI > 30 obese). The RR for TKA was applied to the demographic forecasts for the Swedish population as a forecasting model. Results - Population size increased 5.2% from 2009 to 2015 to 40,000 middle-aged and 250,000 elderly, and the prevalence of obesity increased from 16% to 18% in these 2 age categories. Compared with those of normal weight, the RR for TKA was 2.7 (95% CI 2.5-3.0) higher for the overweight and 7.3 (6.7-8.0) higher for the obese, aged 45-64. The corresponding figures for individuals aged 65-84 were 2.1 (2.0-2.2) and 4.0 (3.8-4.3) higher, respectively. The changes in the prevalence of obesity and an increase in the elderly population accounted for an estimated increase of 1,700 TKAs over the 7 years. Interpretation - The increase in obesity frequency and the rise in the population of middle-aged and elderly may, to some extent, explain the rise in TKA utilization in Sweden.

Increases in the rates of primary and revision knee replacement are reducing: a 15-year registry study across 3 continents.

Background and purpose - Rates of knee replacement (KR) are increasing worldwide. Based on population and practice changes, there are forecasts of a further exponential increase in primary knee replacement through to 2030, and a corresponding increase in revision knee replacement. We used registry data to document changes in KR over the past 15 years, comparing practice changes across Sweden, Australia, and the United States. This may improve accuracy of future predictions.Patients and methods - Aggregated data from the Swedish Knee Arthroplasty Register (SKAR), the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), and the Kaiser Permanente Joint Replacement Registry (KPJRR) were used to compare surgical volume of primary and revision KR from 2003 to 2017. Incidence was calculated using population census statistics from Statistics Sweden and the Australian Bureau of Statistics, as well as the yearly active membership numbers from Kaiser Permanente. Further analysis of KR by age < 65 and ≥ 65 years was carried out.Results - All registries recorded an increase in primary and revision KR, with a greater increase seen in the KPJRR. The rate of increase slowed during the study period. In Sweden and Australia, there was a smaller increase in revision surgery compared with primary procedures. There was consistency in the mean age at surgery, with a steady small decrease in the proportion of women having primary KR. The incidence of KR in the younger age group remained low in all 3 registries, but the proportional increases were greater than those seen in the ≥ 65 years of age group.Interpretation - There has been a generalized deceleration in the rate of increase of primary and revision KR. While there are regional differences in KR incidence, and rates of change, the rate of increase does not seem to be as great as previously predicted.

Short-term Revision Risk of Patellofemoral Arthroplasty Is High: An Analysis from Eight Large Arthroplasty Registries.

BACKGROUND: Patellofemoral arthroplasty (PFA) is one option for the treatment of isolated patellofemoral osteoarthritis, but there are limited data regarding the procedure and results. Because isolated patellofemoral arthritis is relatively uncommon, available case series generally are small, and even within national registries, sample sizes are limited. Combining data from multiple registries may aid in assessing worldwide PFA usage and survivorship. QUESTIONS/PURPOSES: We combined and compared data from multiple large arthroplasty registries worldwide to ask: (1) What proportion of patients undergoing primary knee arthroplasty have PFA? (2) What are the patient and prosthesis characteristics associated with PFA in common practice, as reflected in registries? (3) What is the survivorship free from revision of PFA and what are the reasons for and types of revisions? METHODS: Data were provided by eight registries that are members of the International Society of Arthroplasty Registries (ISAR) who agreed to share aggregate data: Australia, New Zealand, Canada, Sweden, Finland, Norway, the Netherlands, and the United States. De-identified data were obtained for PFA performed from either the beginning of year 2000, or the earliest recorded implantation date after that in each individual registry when PFA data collection commenced, up to December 31, 2016. This included patient demographics, implant use, all-cause revision rate (determined by cumulative percent revision [CPR]), and reasons for and type of revision. RESULTS: During the data collection period, 6784 PFAs were performed in the eight countries. PFAs comprised less than 1% of primary knee replacements in all registries. Patient demographics were comparable in all countries. Patients were generally more likely to be women than men, and the mean age ranged from 50 years to 60 years. All registries showed a high rate of revision for PFA. The 5-year CPR for any reason ranged from 8.0% (95% CI 4.5 to 11.5) in Norway to 18.1% (95% CI 15.5 to 20.7) in the Netherlands. The most common reason for revision across all countries was disease progression (42%, 434 of 1034). Most PFAs (83%, 810 of 980) were revised to a TKA. CONCLUSIONS: The revision risk of PFA in all registries surveyed was more than three times higher than the reported revision risk of TKA at the same times. The survivorship of PFA is similar to that of the no-longer-used procedure of metal-on-metal conventional hip replacement. Although there may be potential functional benefits from PFA, these findings of consistent and alarmingly high rates of revision should create concern, particularly as this procedure is often used in younger patients. LEVEL OF EVIDENCE: Level III, therapeutic study.

The effect of fixation type on the survivorship of contemporary total knee arthroplasty in patients younger than 65 years of age: a register-based study of 115,177 knees in the Nordic Arthroplasty Register Association (NARA) 2000-2016.

Background and purpose - Cemented fixation is regarded as the gold standard in total knee arthroplasty (TKA). Among working-age patients, there has been controversy regarding the optimal fixation method in TKA. To address this issue, we conducted a register-based study to assess the survivorship of cemented, uncemented, hybrid, and inverse hybrid TKAs in patients aged < 65 years.Patients and methods - We used the Nordic Arthroplasty Register Association data of 115,177 unconstrained TKAs performed for patients aged < 65 years with primary knee osteoarthritis over 2000-2016. Kaplan-Meier (KM) survival analysis with 95% confidence intervals (CI) and Cox multiple-regression model with adjustment for age, sex, and nation were used to compare fixation methods in relation to revision for any reason.Results - The 10-year KM survivorship of cemented TKAs was 93.6% (95% CI 93.4-93.8), uncemented 91.2% (CI 90.1-92.2), hybrid 93.0% (Cl 92.2-93.8), and inverse hybrid 96.0% (CI 94.1-98.1). In the Cox model, hybrid TKA showed decreased risk of revision after 6 years' follow-up compared with the reference group (cemented) (hazard ratio [HR] 0.5 [CI 0.4-0.8]), while uncemented TKAs showed increased risk of revision both < 1 year (HR 1.4 [1.1-1.7]) and > 6 years' (HR 1.3 [1.0-1.7]) follow-up compared to the reference.Interpretation - Both cemented and hybrid TKAs had 10-year survival rates exceeding 92->93% in patients aged < 65 years. Cemented TKA, however, was used in the vast majority (89%) of the operations in the current study. As it performs reliably in the hands of many, it still deserves the status of gold standard for TKA in working-age patients.

Higher Risk of Loosening for a Four-Pegged TKA Tibial Baseplate Than for a Stemmed One: A Register-based Study.

BACKGROUND: Modern modular implants allow surgeons to mix different combinations of components within the same brand. From 1999 to 2012, the NexGen®-CR Option femoral component, together with a NexGen® Option Stemmed tibial plate (stemmed baseplate), which uses a short central stem, was the most-frequently used NexGen® combination in the Swedish Knee Arthroplasty Register. However, from 1999 to 2012, the same femoral component was also used along with the NexGen® Precoat four-pegged tibial baseplate (pegged baseplate). Considering the difference in the fixation concepts for these two tibial baseplates, we wanted to study whether their revision rates differed. QUESTIONS/PURPOSES: To investigate the difference in (1) all-cause revision and (2) the risk of revision for aseptic loosening between the NexGen® pegged and stemmed baseplates when used with the NG-CR Option femoral component and the same two types of inserts. METHODS: The Swedish Knee Arthroplasty Register provided data. The register, which was started in 1975, has since 1999 registered part numbers for individual implant components, allowing it to assess the combinations of components used in each patient. It has been shown to have high completeness (97%) and validity [12, 15]. The inclusion period was 1999 to 2012; during that time, 137,143 primary knee arthroplasties were registered, of which 125,094 were TKAs. Only TKAs performed for osteoarthritis and without patellar resurfacing were included, since not resurfacing the patella is the standard procedure in Sweden. This left 15,287 knees with the stemmed baseplate and 2479 with the pegged baseplate, or 12% and 2% of the total number of TKAs, respectively. Two general hospitals used the pegged baseplate exclusively during that period. Thus, specific patients were not selected for having the pegged plate. The mean age, mortality, and length of followup were similar for the two groups.We used the Kaplan-Meier statistics to calculate the cumulative revision rate (CRR) and Cox regression to compare risk ratios after adjusting for age and sex. The end point was a knee revision for respective all causes or aseptic loosening. The study ended on December 31, 2016. Due to the free healthcare system in Sweden it is highly unusual for patients to seek elective revision abroad, and by use of the extensive Swedish census register, we estimate the level of followup approximately 97%. RESULTS: Knees with the pegged baseplate had a higher risk for all-cause revision than did those with the stemmed baseplate (5.8% [95% confidence interval {CI}, 4-8.3] and 3% [95% CI, 2.6-3.5] at 15 years; p = 0.003). After controlling for age and sex, the aseptic loosening risk in the pegged baseplate group was still higher than that in the stemmed group (relative risk, 5.40; 95% CI, 3.64-8.02; p < 0.001). CONCLUSIONS: In this Swedish registry study, we observed a higher loosening risk with the pegged baseplate than the stemmed one, even after controlling for age and sex. Because this was only a comparison of implants from one vendor, and because there may have been other between-group differences for which we could not fully control, this concerning finding should be explored using data from other registries. LEVEL OF EVIDENCE: Level III, therapeutic study.

Weight and height separated provide better understanding than BMI on the risk of revision after total knee arthroplasty: report of 107,228 primary total knee arthroplasties from the Swedish Knee Arthroplasty Register 2009-2017.

Background and purpose - Obesity defined as increased BMI is commonly associated with higher revision rates following total knee arthroplasty (TKA). We examined the effect of BMI on the rate of revision after TKA, for both infection and other reasons, and analyzed weight and height separately to provide better understanding of the risk profile.Patients and methods - The Swedish national knee arthroplasty register was used to identify 107,228 patients operated with primary TKA for osteoarthritis between 2009 and 2017. Cox proportional hazards regression was used to calculate hazard ratios (HRs) with 95% confidence intervals (CIs) for BMI (categories: < 18.5, 18.5-24.9, 25-29.9, 30-34.9, 35-39.9, ≥ 40), weight (categories: < 65, 65-89, 90-114, ≥ 115 kg) and height (categories: < 160, 160-179, ≥ 180 cmResults - There were 2,503 revisions in the follow-up period; 1,036 for infection and 1,467 for other reasons. Higher BMI and weight categories were associated with a similar and statistically significantly increased risk of revision for all causes and for infection. The risk of revision for infection was almost twice in the highest BMI and highest weight group: HR = 3.4 (CI 2.3-4.7) and HR = 3.1 (CI 2.5-3.9) respectively. For BMI and weight categories there was no statistically significant association between revision for other reasons than infection, contrary to the tallest height category where it was statistically significant (HR = 1.3 [CI 1.1-1.5]).Interpretation - BMI, weight, and height may be associated with different types of risks for revision following TKA.

The benefits of collaboration: the Nordic Arthroplasty Register Association.

The Nordic Arthroplasty Register Association (NARA) was established in 2007 by arthroplasty register representatives from Sweden, Norway and Denmark with the overall aim to improve the quality of research and thereby enhance the possibility for quality improvement with arthroplasty surgery. Finland joined the NARA collaboration in 2010.NARA minimal hip, knee and shoulder datasets were created with variables that all countries can deliver. They are dynamic datasets, currently with 25 variables for hip arthroplasty, 20 for knee arthroplasty and 20 for shoulder arthroplasty.NARA has published statistical guidelines for the analysis of arthroplasty register data. The association is continuously working on the improvement of statistical methods and the application of new ones.There are 31 published peer-reviewed papers based on the NARA databases and 20 ongoing projects in different phases. Several NARA publications have significantly affected clinical practice. For example, metal-on-metal total hip arthroplasty and resurfacing arthroplasty have been abandoned due to increased revision risk based on i.a. NARA reports. Further, the use of uncemented total hip arthroplasty in elderly patients has decreased significantly, especially in Finland, based on the NARA data.The NARA collaboration has been successful because the countries were able to agree on a common dataset and variable definitions. The collaboration was also successful because the group was able to initiate a number of research projects and provide answers to clinically relevant questions. A number of specific goals, set up in 2007, have been achieved and new one has emerged in the process. Cite this article: EFORT Open Rev 2019;4 DOI: 10.1302/2058-5241.4.180058.

Sequence of 305,996 total hip and knee arthroplasties in patients undergoing operations on more than 1 joint.

Background and purpose - Patient-specific data on multiple total arthroplasties (TA) of the lower limbs due to osteoarthritis (OA) are limited. We investigated the sequence of surgical procedures and risk factors for additional surgery in such patients. Patients and methods - 305,996 patients operated with a TA of the hip and/or knee due to OA were extracted from the Swedish National Hip (SHAR) and the Swedish Knee Arthroplasty Register (SKAR). 177,834 total hip arthroplasty (THA, 56% women, mean age 69 years) and 128,162 total knee arthroplasty (TKA, 60% women, mean age 69 years) procedures constituted the index operations. The mean, median, and maximum follow-up was 8, 6, and 23 years. Multivariable Cox regression analysis was used and Kaplan-Meier survival curves were constructed. Results - Right-sided primary TA (34%) was most frequent. Subsequent surgery was most frequent after primary left-sided TKA (33%). The time interval to a second TA procedure was 3.1 (SD 3.2) years after TKA and 4.0 (SD 3.9) years after THA. After the index TA the probability of no subsequent surgery amounted to 64% (SD 0.3) for THA and 58% (SD 0.4) for TKA over 20 years. Lower age, female sex, left side, and TKA at index operation were associated with a higher probability for subsequent TA. Interpretation - Delineation of factors that influence risk and the size of the risk for subsequent TA in 1 of the 3 major remaining joints is of value for clinicians and healthcare providers in the decision-making process for future resource allocation.

Manipulation under anesthesia after primary knee arthroplasty in Sweden: incidence, patient characteristics and risk of revision.

Background and purpose - The incidence of manipulation under anesthesia (MUA) after knee arthroplasty surgery has been reported to vary between 0.5% and 10%. We evaluated the incidence of MUA after primary knee arthroplasty in Sweden, the demographics of the patients and the risk of revision. Patients and methods - Between 2009 and 2013, 64,840 primary total and unicompartmental knee arthroplasties (TKA and UKA) were registered in the Swedish Knee Arthroplasty Register (SKAR). MUAs performed between 2009 and 2014 were identified through the in- and outpatient registers of the Swedish National Board of Health and Welfare. Pertinent data were verified through medical records and patient demographics and revisions were obtained from the SKAR. Results - 1,258 MUAs were identified. Of these, 1,078 were 1st-time MUAs, performed within 1 year after the primary knee arthroplasty. The incidence of MUA was 1.7% and the incidence varied between hospitals from 0% to 5%. The majority were performed after TKA (98%), in younger patients (65% < 65 years), women (64%), and relatively healthy persons (88% had ASA ≤ 2). The cumulative risk of revision at 10 years was 10% (95% CI 8.6-12), similar for men and women. Interpretation - In Sweden, MUA is a rather uncommon measure after knee arthroplasty, especially after UKA. The CRR at 10 years was doubled compared to the general knee arthroplasty population. The frequency of the procedure varies between hospitals but in general it is performed more frequently in healthier and younger patients.

Validation of Lithuanian Arthroplasty Register Telephone Survey of 2769 Patients Operated for Total Knee Replacement.

Background and objectives: The aim of our study is to validate the registration of knee arthroplasty revisions in the Lithuanian Arthroplasty Register (LAR) and thus give an indication of the accuracy of the published revision rates. Materials and methods: A total of 4269 primary total knee arthroplasties (TKAs) registered in the LAR between 2013 and 2015 were included. Two years after surgery the patients were contacted by phone in order to inquire if they had been subject to revision. The information from the patients was then cross checked against what had been registered in the LAR, and in case of a revision not having been registered hospital charts were investigated. Thus, the patients were followed up with regarding revision and/or death until 2017. A true revision was defined as an addition, exchange, or removal of one or all components. Results: Out of 4269 primary TKAs, we managed to contact and interview 2769 patients. Nine small hospitals were not able to provide contact details (telephone numbers) for 533 patients (549 knees). Sixty-seven patients (67 knees) were deceased (data from the Lithuanian National Census Register) and a further 438 patients (565 knees) appeared to have a wrong or non-valid telephone number, leaving 3031 (3091 knees) patients being contacted. Of those, 262 patients (266 knees) refused to participate in the study which left 2769 responders (2825 knees). Sixty-one patients said that reoperation had been performed on the index knee within two years of their primary surgery. After checking with the clinics, 10 were surgical procedures on the knee but not true revisions by our criteria. Out of the 51 true revisions we found that 46 were registered to the LAR as revised, while five (9.8%) revisions were missing. Conclusions: We conclude that the Lithuanian Arthroplasty Register has a good completeness of registered revision TKAs as only 9.8% of revisions were missing.