Existing data sources for clinical epidemiology: The Danish Knee Arthroplasty Register

Metabolic syndrome increases the length of stay and medical complications after hip and knee arthroplasty: results from a prospective cohort study of 2,901 patients

BACKGROUND AND PURPOSE

 Metabolic syndrome (MetS) affects more than 60% of the patients having a hip or knee arthroplasty due to osteoarthritis. As it is debated whether metabolic syndrome increases the risk of complications, we aimed to investigate the length of stay (LOS) and risk of readmission at 30 and 90 days after surgery, including causes of readmission.

METHODS

 We conducted a prospective cohort study of 2,901 patients undergoing hip and knee arthroplasty from May 2017 to November 2019. Physical examination, blood samples, and medical history from national registries determined the diagnosis of metabolic syndrome from the International Diabetes Federation definition. We used multivariate linear regression to investigate differences in LOS according to MetS, and binary regression to investigate the risk and causes of readmission within 30 and 90 days, including 95% confidence intervals (CI) and P values.

RESULTS

 Patients with MetS showed a slightly longer LOS (0.20 days, CI 0.10-0.29) and had an increased risk of readmission within 90 days (adjusted relative risk [RR] 1.2, CI 1.0-1.4; P = 0.02), but not within 30 days (adjusted RR 1.1, CI 0.9-1.4; P = 0.3) after surgery. Cardiovascular disease was the dominant cause of readmission.

CONCLUSION

Although patients with MetS do not experience a clinically relevant longer LOS after hip and knee arthroplasty, they have an increased risk of 90-day readmission mainly due to cardiovascular complications, which should be considered when planning surgical care in this group of patients.

Risk and Epidemiology of Periprosthetic Knee Fractures After Primary Total Knee Arthroplasty: A Nationwide Cohort Study

BACKGROUND

Periprosthetic knee fractures (PPKFs) following total knee arthroplasty (TKA) are uncommon, but potentially serious injuries. We analyze the risk and risk factors for a PPKF in standard primary TKA patients who have osteoarthritis and a minimally (cruciate-retaining TKAs without a femoral box cut) or posterior-stabilized TKA. In addition, we report the risk for patients who have other underlying knee disorders and/or a higher level of TKA constraint.

METHODS

All primary TKAs were identified from the Danish National Patient Register and the Danish Knee Arthroplasty Register using data between 1997 and 2022. Subsequent fractures were identified through the International Classification of Diseases diagnosis code, Nordic Medico-Statistical Committee procedure code, or indication for revision TKA.

RESULTS

We included 120,642 standard primary TKA patients who had 1,659 PPKFs. The cumulated proportions were 0.4% (95% confidence interval (CI) 0.3 to 0.4) at 2 years 0.8% (0.7 to 0.8) at 5 years. At 10 years, the cumulated proportion was 1.7% (1.6 to 1.8), with 1.3% in the femur, 0.2% in the patella, and 0.2% in the tibia. Significant risk factors were (hazard ratio [HR] [95% CI]); ipsilateral hip arthroplasty (2.3 [2.0 to 2.6]); women (2.1 [1.8 to 2.4]), osteoporosis (1.4 [1.2 to 1.7]); age 80+ (1.4 [1.3 to 1.6]), uncemented TKA (1.3 (1.1 to 1.5) and Charlson Comorbidity Index score 3+ (1.4 [1.1 to 1.8]). An additional 22,624 primary TKA patients who had other underlying knee disorders and/or a higher level of implant constraint were included with 633 PPKFs. The 10-year cumulated proportions were 8.3% (95% CI 6.9 to 9.8) when the underlying disorder was a previous fracture, 2.8% (2.2 to 3.5) for rheumatic disorders, and 5.2% (2.6 to 10.6) for osteonecrosis. In patients who had condylar constrained knees, it was 6.9% (5.1 to 9.4), and 12.4% (8.0 to 16.04) for hinges.

CONCLUSIONS

In standard primary TKA patients, the 10-year cumulated proportion of PPKFs was 1.7%, and ipsilateral hip arthroplasty, women, osteoporosis, advanced age, uncemented TKA and higher Charlson Comorbidity Index increased the risk. Higher risks were observed in non-osteoarthritis patients and/or patients who had a higher level of TKA constraint.

Metabolic syndrome and patient-reported outcome two years after hip and knee arthroplasty

Aims

The influence of metabolic syndrome (MetS) on the outcome after hip and knee arthroplasty is debated. We aimed to investigate the change in patient-reported outcome measure (PROM) scores after hip and knee arthroplasty, comparing patients with and without MetS.

Methods

From 1 May 2017 to 30 November 2019, a prospective cohort of 2,586 patients undergoing elective unilateral hip and knee arthroplasty was established in Denmark. Data from national registries and a local database were used to determine the presence of MetS. Patients' scores on Oxford Hip Score (OHS) or Oxford Knee Score (OKS), EuroQol five-dimension five-level questionnaire (EQ-5D-5L), University of California, Los Angeles (UCLA) Activity Scale, and Forgotten Joint Score (FJS) at baseline, three, 12, and 24 months after surgery were collected. Primary outcome was the difference between groups from baseline to 12 months in OHS and OKS. Secondary outcomes were scores of OHS and OKS at three and 24 months and EQ-5D-5L, UCLA Activity Scale, and FJS at three, 12, and 24 months after surgery. Generalized linear mixed model was applied, adjusting for age, sex, Charlson Comorbidity Index, and smoking to present marginal mean and associated 95% CIs.

Results

A total of 62.3% (1,611/2,586) of the cohort met the criteria for MetS. Both groups showed similar increase in mean OHS (MetS group 22.5 (95% CI 21.8 to 23.1), non-MetS group 22.1 (21.3 to 22.8); p = 0.477) and mean OKS (MetS group 18.0 (17.4 to 18.6), non-MetS group 17.8 (17.0 to 18.7); p = 0.722) at 12 months' follow-up. Between groups, similar improvements were seen for OHS and OKS at three and 24 months postoperatively and for the mean EQ-5D-5L, EuroQol-visual analogue scale (EQ-VAS), UCLA Activity Scale, and FJS at every timepoint.

Conclusion

Patients meeting the criteria for MetS obtain the same improvement in PROM scores as individuals without MetS up to 24 months after hip and knee arthroplasty. This is important for the clinician to take into account when assessing and advising patients with MetS.

Metabolic Syndrome and Morbid Obesity are Not Risk Factors for Revision Surgery in Patients Undergoing Hip and Knee Arthroplasty

BACKGROUND

The effect of metabolic syndrome (MetS) on the risk of revision after hip and knee arthroplasty is debated. The aim of our study was to investigate the risk of short-term (minimum 2.7 years) revision due to periprosthetic joint infection (PJI) after hip and knee arthroplasty. Secondly, we aimed to investigate the risk of revision due to any cause and mortality.

METHODS

During May 2017 to November 2019, a cohort of 2,901 patients undergoing a total of 3,024 hip and knee arthroplasties was established. In the cohort, 62.1% met the criteria for MetS. Data from national registries and a local database were used to determine the presence of MetS and revision surgeries, with a follow-up of at least two years and eight months. Cox regression was applied to the present hazard ratio (HR), associated 95% confidence intervals, and P values. Survival analyses were presented in a Kaplan-Meier plot.

RESULTS

The risk of PJI (HR 1.6 (0.5 to 4.9), P = .380), any revision (HR 0.8 (0.4 to 1.3), P = .295), and death (HR 1.3 (0.8 to 2.1), P = .282) was not increased in patients suffering from MetS compared with patients who did not have MetS. There was no PJI in patients not having MetS and receiving a knee arthroplasty. The risk of death was increased in the MetS group receiving a knee arthroplasty (HR 2.7 (1.3 to 5.9), P = .010), but not different from the MetS group receiving a hip arthroplasty. There was no elevated risk of PJI when analyzing morbid obesity (body mass index over 40), men, or diabetes as the exposures.

CONCLUSIONS

Patients suffering from MetS do not have an increased risk of revision caused by PJI. In general, performing hip and knee arthroplasty in patients suffering from MetS is without increased risk of revision surgery.

Knee arthroplasty: an international systemic review of epidemiological trends

BACKGROUND

In response to various socio-economic factors and technological advancements, knee arthroplasty procedures have steadily increased. To date, epidemiological analyses have been conducted on a single-country basis. The aims of this article are: (1) to identify arthroplasty databases by country, (2) to verify the international comparability of coding, (3) to study retrospective epidemiological trends, and (4) to analyze projections by country. The hypothesis is that countries will follow similar trends, though with varying time lags.

MATERIALS AND METHODS

A literature review from 2005 to 2023 was conducted following PRISMA recommendations on PubMed, Web of Science, and Cochrane, using the keywords: "Knee + Arthroplasty + Trends + Replacement + Epidemiology." Only articles featuring national analyses, based on references recognized by healthcare systems, were included.

RESULTS

Forty-eight articles, representing 16 countries, were selected. Europe was the most represented (47% of occurrences), followed by the USA (22%), Asia (20%), Oceania (8%), and Chile (2%). The data came from national databases or representative extrapolated samples. Extraction methods used precise national codes or specific definitions. Growth rates in volume and incidence were positive but varied between countries, with distinct dynamics and different phases of growth. Females had higher volumes and incidence rates (sex ratio 2/3), but growth was faster in males. Future forecasts, based on regression models (Poisson, linear, or logistic), predicted an increase in volumes of between +30% by 2030 and +805% by 2050.

CONCLUSION

The analysis of census systems revealed growth in knee arthroplasties in all countries, but with varying intensities depending on the period. These multifactorial disparities appeared to follow a similar pattern, staggered over time based on the countries' economic development.

LEVEL OF EVIDENCE

IV; epidemiological review.

Incidence and survival of multiply revised knee arthroplasties in Denmark 1998-2021: a nationwide register-based study

PURPOSE

The primary aim of our study was to identify the absolute incidence and implant survival of multiply revised knee arthroplasties based on nationwide register data. The secondary aim was to determine the change in the absolute incidence and implant survival of multiply revised knee arthroplasties Methods: We performed a retrospective observational study of primary knee arthroplasties using several nationwide Danish registers. All primary knee arthroplasties performed in Denmark from 1998 to 2021 were identified. From these primary arthroplasties, revision procedures were identified. Kaplan-Meier plots were used in survival analysis to estimate the likelihood of implant survival.

RESULTS

161,384 primary knee arthroplasties and their revisions performed between 1998 and 2021 were identified; of 13,786 (8.5%) revisions there were 10,638 1st revisions, 2,148 2nd revisions, 624 3rd revisions, 223 4th revisions, and 153 procedures that had been revised more than 4 times. The 10-year revision-free survival of primary arthroplasties was 92.3% (95% confidence interval [CI] 92.2-92.5). First-time revisions had a 10-year revision-free survival of 75.9% (CI 74.9-76.9). The 10-year survival of second- and third-time revisions was 65.1% (CI 62.6-67.6) and 57.8% (CI 53.4-62.5), respectively. The 10-year implant survival probabilities of primary knee arthroplasties were 91.4% in 1998-2009 and 93.3% in 2010-2021 (difference 2.2%). The 10-year implant survival probabilities of 1st revisions were 77% in 1998-2009 and 75% in 2010-2021 (difference -2.4%).

CONCLUSION

We found that 0.3% of all primary knee arthroplasties resulted in 3 or more revisions. The implant survival decreased for each consecutive revision, with almost half of the 3rd revisions being re-revised within 10 years. The 10-survival of the primary implant was higher in 2010-2021, and the 10-year survival of the 1st revision was higher in 1998-2009.

Risks of major bleeding and venous thromboembolism in patients undergoing total hip or total knee arthroplasty using therapeutic dosages of DOACs

About 1.5% of patients undergoing total hip (THA) or total knee arthroplasty (TKA) still develop postoperative venous thromboembolism (VTE), indicating that the current thromboprophylaxis strategy is not optimal. To evaluate the feasibility of therapeutic dosages of direct oral anticoagulants (DOACs) as thromboprophylaxis for high VTE risk patients, we determined the risks of major bleeding and VTE in patients who underwent THA/TKA and were treated with DOACs in therapeutic dosages for atrial fibrillation (AF). We conducted a registry-based cohort study from 2010 to 2018 in Denmark and included AF patients on therapeutic DOACs dose who underwent THA/TKA. AF patients were utilized as proxy since they have a life-long indication for therapeutic anticoagulant medication. The 49-days cumulative incidence (with death as competing risk) of major bleeding was assessed. The same was done for VTE at 49- and 90-days. 1,354 THA and TKA procedures were included. The 49-days cumulative incidence of major bleeding was 1.40% (95%Confidence Interval[CI] 0.88-2.14%). Most bleeding events occurred at the surgical site. The cumulative incidence of VTE at 49-days was 0.59% (95%CI 0.28-1.13%) and 0.74% (95%CI 0.38-1.32%) at 90-days. The incidence of major bleeding in THA/TKA patients on DOACs in therapeutic dosages was in line with previously reported incidences among THA/TKA patients on thromboprophylaxis dosages, while the incidence of VTE was relatively low. These data provide a solid basis for the design of randomized controlled trials to establish the safety and efficacy of therapeutic dosages of DOACs to prevent VTE in high-risk patients.

The impact of comorbidity status on knee function 1 year after total knee arthroplasty: a population-based cohort study

BACKGROUND AND PURPOSE

Few studies have examined the impact of comorbidity on functional and clinical knee scores after primary total knee arthroplasty (TKA). We compared the effect of having a high Charlson Comorbidity Index (CCI), relative to a low CCI, on changes in the American Knee Society Score (AKSS) functional and clinical scores from baseline to week 52 after TKA in patients with knee osteoarthritis (OA).

METHODS

This population-based cohort study included 22,533 patients identified in the Danish Knee Arthroplasty Register from 1997 to 2021. Patients were classified as having low, medium, or high comorbidity based on CCI. The outcome was defined as the mean change (from preoperative to 1-year post-TKA) in functional and clinical knee scores measured by the AKSS (0-100). The association was analyzed using multiple linear regression by calculating mean change scores adjusting for sex, age, weight, cohabiting status, and baseline AKSS.

RESULTS

The prevalence of patients with low, medium, and high comorbidity was 75%, 21%, and 4%, respectively. The mean change score in functional AKSS for patients with high comorbidity was -6 points (95% confidence interval [CI] -7 to -5) compared with low comorbidity. The mean change score in clinical AKSS for patients with high comorbidity was -1 point (CI -2 to 0) compared with low comorbidity.

CONCLUSION

Patients with knee OA and medium or high comorbidity can expect similar improvements in functional and clinical AKSS after TKA to patients with low comorbidity.

Enhancing the data capture of periprosthetic joint infections in the Danish Knee Arthroplasty Registry: validity assessment and incidence estimation

BACKGROUND AND PURPOSE

Revisions due to periprosthetic joint infection (PJI) are underestimated in national arthroplasty registries. Our primary objective was to assess the validity in the Danish Knee Arthroplasty Register (DKR) of revisions performed due to PJI against the Healthcare-Associated Infections Database (HAIBA). The secondary aim was to describe the cumulative incidences of revision due to PJI within 1 year of primary total knee arthroplasty (TKA) according to the DKR, HAIBA, and DKR/HAIBA combined.

METHODS

This longitudinal observational cohort study included 56,305 primary TKAs (2010-2018), reported in both the DKR and HAIBA. In the DKR, revision performed due to PJI was based on pre- and intraoperative assessment disclosed by the surgeon immediately after surgery. In HAIBA, PJI was identified from knee-related revision procedures coinciding with 2 biopsies with identical microbiological pathogens. We calculated the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of revision due to PJI in the DKR (vs. HAIBA, within 1 year of TKA) with 95% confidence intervals (CI). Cumulative incidences were calculated using the Kaplan-Meier method.

RESULTS

The DKR's sensitivity for PJI revision was 58% (CI 53-62) and varied by TKA year (41%-68%) and prosthetic type (31% for monoblock; 63% for modular). The specificity was 99.8% (CI 99.7-99.8), PPV 64% (CI 62-72), and NPV 99.6% (CI 99.6-99.7). 80% of PJI cases not captured by the DKR were caused by non-reporting rather than misclassification. 33% of PJI cases in the DKR or HAIBA were culture-negative. Considering potential misclassifications, the best-case sensitivity was 64%. The cumulative incidences of PJI were 0.8% in the DKR, 0.9% in HAIBA, and 1.1% when combining data.

CONCLUSION

The sensitivity of revision due to PJI in the DKR was 58%. The cumulative incidence of PJI within 1 year after TKA was highest (1.1%) when combining the DKR and HAIBA, showing that incorporating microbiology data into arthroplasty registries can enhance PJI validity.

Temporal trends in revision rate due to knee periprosthetic joint infection: a study of 115,120 cases from the Danish Knee Arthroplasty Register

BACKGROUND AND PURPOSE

We aimed to examine the temporal trends in periprosthetic joint infection (PJI) revision incidence after knee arthroplasty (KA) from 1997 through 2019.

PATIENTS AND METHODS

115,120 primary KA cases from the Danish Knee Arthroplasty Register were followed until the first PJI revision. We computed cumulative incidences and adjusted hazard ratios (aHRs) of PJI revision by calendar periods and several patient- and surgical-related risk factors. Results were analyzed from 0-3 months and from 3-12 months after KA.

RESULTS

The overall 1-year PJI revision incidence was 0.7%, increasing from 0.5% to 0.7% (1997 through 2019). The incidence of PJI revision within 3 months increased from 0.1% to 0.5% (1997 through 2019). The adjusted hazard ratio (aHR) within 1 year of primary KA was 5.1 comparing 2017-2019 with 2001-2004. The PJI revision incidence from 3-12 months of KA decreased from 0.4% to 0.2%, with an aHR of 0.5 for 2017-2019 vs. 2001-2004. Male sex, age 75-84 (vs. 65-74), and extreme obesity (vs. normal weight) were positively associated with the risk of PJI revision within 3 months, whereas only male sex was associated from 3-12 months. Partial knee arthroplasty (PKA) vs. total KA was associated with a lower risk of PJI revision both within 3 months and 3-12 months of KA.

CONCLUSION

We observed an increase in PJI revision within 3 months of KA, and a decrease in PJI revision incidence from 3-12 months from 1997 through 2019. The reasons for this observed time-trend are thought to be multifactorial. PKA was associated with a lower risk of PJI revision.

Usage of guideline-adherent core treatments for knee osteoarthritis before and after consulting an orthopaedic surgeon: A prospective cohort study

Objective

To describe 1) the proportion of patients with knee osteoarthritis (OA) undergoing guideline-adherent core treatments until six months after primary referral to an orthopaedic surgeon, 2) which specific treatment pathways these patients undertake and 3) the characteristics of patients choosing different treatment pathways.

Design

This prospective cohort study consecutively invited patients referred to an orthopaedic surgeon due to knee OA at two Danish hospitals from October 2018 to December 2020. Before and six months after consulting the surgeon, patients answered a questionnaire reporting which treatments they had received for knee OA. The proportion receiving the combination of guideline-adherent treatments (i.e., exercise, education, and dietary weight management if needed) was determined. We evaluated the specific treatment usage before and until six months after the consultation and investigated characteristics of patients undertaking different pathways.

Results

Out of 5251 eligible patients, 2574 (49%) had complete data and were included in analyses. 23% received guideline-adherent treatments, 10% had no treatment. Patients underwent 1143 unique treatment pathways, 62% including treatments not recommended/recommended against. Those who underwent guideline-adherent pathways had similar characteristics to those who did not but tended to be females, retired, had longer-lasting knee problems, have comorbidities, and higher education levels.

Conclusions

Only one in four patients with knee OA received treatment adhering to clinical guidelines before and six months after consulting the surgeon. Patients used many different treatment pathways. There is a need for a structured effort to increase the use of guideline-adherent core treatments.

Trial Identifiers

Registration: NCT03746184, Protocol: PMID: 34233992.

Patient-reported outcomes and satisfaction after revisions of medial unicompartmental knee arthroplasties for unexplained pain vs aseptic loosening

PURPOSE

Does patients revised for unexplained pain after mUKA present the same PROM and satisfaction scores 1-3 years after revision as patients revised for aseptic loosening?".

METHODS

104 patients undergoing revision of mUKA's for the indications unexplained pain and aseptic loosening were included in the period January 1, 2018 to December 31, 2020. from the Danish Knee Arthroplasty Register. 52 patients were revised for unexplained pain and 52 for aseptic loosening. Patient demographics did not differ between the two groups. PROMs [Oxford Knee Score (OKS), EQ-5D-5L, Forgotten Joint Score (FJS)] and questions about satisfaction with the surgery were sent to digitally secured mailboxes. Pearson's Chi-square test and Wilcoxon Rank Sum test were used to test for statistical differences between groups.

RESULTS

The median OKS 1-3 years after revision was 26 (IQR 22) for unexplained pain vs 34 (IQR 12) for aseptic loosening, p = 0.033. The median EQ-5D-5L Index after revision was 0.7 (IQR 0.6) for unexplained vs 0.8 (IQR 0.1) for aseptic loosening, p = 0.014. The median FJS after revision was 48 (IQR 10) for unexplained pain vs 52 (IQR 14) for aseptic loosening, p = 0.1. The mean satisfaction with the surgery on a 0-100 scale (100 = not satisfied; 0 = very satisfied) was 55 (IQR 60) for unexplained pain vs 50 (IQR 67) for aseptic loosening, p = 0.087, and patients revised for unexplained pain were less likely to find their knee problem importantly improved (p = 0.032).

CONCLUSION

Patients undergoing revision of mUKAs for unexplained pain presented poor postoperative PROM scores, and PROM scores were worse compared to those of patients revised for aseptic loosening. Patients revised for unexplained pain were less likely to find their knee problem importantly improved. This study support the evidence against revisions for unexplained pain.

LEVEL OF EVIDENCE

Level III.

Use of a tourniquet is not associated with increased risk of venous thromboembolism after fast-track total knee arthroplasty: a prospective multicenter cohort study of 16,250 procedures

BACKGROUND AND PURPOSE

Venous thromboembolism (VTE) is a serious postoperative complication after total knee arthroplasty (TKA). Use of a tourniquet has shown conflicting results for risk of VTE after TKA. We aimed to investigate the associated risk of VTE after TKA using tourniquet in a fast-track set-up as no previous data exists.

PATIENTS AND METHODS

We performed an observational cohort study from 9 fast-track centers including unilateral primary TKA from 2010-2017 with prospective collection of preoperative risk-factors and complete 90-day follow-up. Use of a tourniquet was registered in the Danish Knee Arthroplasty Register. Postoperative VTE was identified from health records. We performed risk analyses using a mixed-effects logistic regression model adjusting for previously identified risk factors.

RESULTS

Of the 16,250 procedures (39% males, mean age 67.9 [SD 10.0] years, median LOS 2 [interquartile range 2-3]) 12,518 (77%) were performed with a tourniquet. The annual tourniquet usage varied greatly between departments from 0% to 100%, but also within departments from 0% to 99%. There was no significant difference between the 2 groups with 52 (0.42%) VTEs in the tourniquet group vs. 25 (0.67%) in the no-tourniquet group (p = 0.06 for cumulative 90-day incidence of VTE). This association remained statistically insignificant for VTE using tourniquet after adjustment for previously identified risk factors.

CONCLUSION

We found no association between the use of a tourniquet and increased risk of 90-day VTE after primary fast-track TKA, irrespective of the length of time for which the tourniquet was applied.

Long-term survivorship and results in lower limb arthroplasty: a registry-based comparison study

INTRODUCTION

Popularity of joint replacement surgery due to ever aging population surges the demand for a proper national joint registry. Our Chinese University of Hong Kong - Prince of Wales Hospital (CUHK-PWH) joint registry has passed the 30^th year. The aims of this study are 1) summarize our territory-wide joint registry which has passed the 30th year since establishment and 2) compare our statistics with other major joint registries.

METHODS

Part 1 was to review the CUHK-PWH registry. Demographic characteristics of our patients who underwent knee and hip replacements had been summarized. Part 2 was a series of comparisons with registries from Sweden, UK, Australia and New Zealand.

RESULTS

CUHK-PWH registry captured 2889 primary total knee replacements (TKR) (110 (3.81%) revision) and 879 primary total hip replacements (THR) (107 (12.17%) revision). Median Surgery time of TKR was shorter than THR. Clinical outcome scores were much improved after surgery in both. Uncemented of hybrid in TKR were most popular in Australia (33.4%) and 40% in Sweden and UK. More than half of TKR and THR patients showed the highest percentage with ASA grade 2. New Zealand reflected the best cumulative percentage survival 20 years after surgery of 92.2%, 76.0%, 84.2% survivorship 20 years after TKR, unicompartmental knee replacement (UKR) and Hip.

CONCLUSION

A worldwide accepted patient-reported outcome measure (PROM) is recommended to develop to make comparisons among registries and studies feasible. Completeness of registry data is important and useful to improve surgical performance through data comparisons from different regions. Funding from government on sustaining registries is reflected. Registries from Asian countries have yet to be grown and reported.

Patient-Reported Outcomes and Satisfaction 1 to 3 Years After Revisions of Total Knee Arthroplasties for Unexplained Pain Versus Aseptic Loosening

BACKGROUND

It is unknown if patients are relieved of pain after knee arthroplasty revision for unexplained pain. The aim of this cross-sectional case-control study was to compare patient-reported outcome measures (PROMs) and satisfaction 1 to 3 years after revision of total knee arthroplasties (TKAs) for the indications of unexplained pain versus aseptic loosening.

METHODS

We included 384 patients undergoing TKA revision for the indications of unexplained pain and aseptic loosening from January 1, 2018 to December 31, 2020 from the Danish Knee Arthroplasty Register. A total of 81 patients were revised for unexplained pain and 303 for aseptic loosening. Questionnaires including PROMs (Oxford Knee Score, EQ-5D-5L, and Forgotten Joint Score) and satisfaction with the surgery on a 0-100 scale (100 = not satisfied; 0 = very satisfied) were sent to digitally secured mailboxes. Time from revision to data collection was a median 3.1 years (range, 1.4-4.4 years).

RESULTS

Median Oxford Knee Score was 25 (interquartile range [IQR] 15) versus 31 (IQR 18) 1-3 years after revisions for unexplained pain versus aseptic loosening, P = .009. Median EQ-5D-5L was 0.6 (IQR 0.4) versus 0.8 (IQR 0.3) for unexplained pain versus aseptic loosening, P = .009. Median Forgotten Joint Score was 50 (IQR 7) versus 50 (IQR 16) for unexplained pain versus aseptic loosening, P = .905. Satisfaction was 75 (IQR 38) for unexplained pain and 50 (IQR 73) for aseptic loosening, P < .001.

CONCLUSION

Patients undergoing TKA revision for the indication of unexplained pain had worse results on PROMs than those revised for aseptic loosening. Likewise, patients revised for unexplained pain were less satisfied compared to patients revised for aseptic loosening. This information is valuable to both surgeons and patients when candidates for revision surgery are selected, to obtain the best possible outcomes.

Prosthesis survival after revision knee arthroplasty for "pain without loosening" versus "aseptic loosening": a Danish nationwide study

Background and purpose - Patients having a knee arthroplasty revision for the indication "pain without loosening" may have a higher risk of re-revisions than patients revised for other indications. The primary aim of this study was to compare the survival of knee arthroplasties revised for "pain without loosening" compared with "aseptic loosening." The second was to investigate the prosthesis survival rates in 3 surgical subgroups (total knee arthroplasty (TKA)-TKA; partial revision (revision of tibial or femoral component); unicompartmental knee arthroplasty-TKA) and to compare the prosthesis survival rates for 1997-2009 and 2010-2018. Patients and methods - 4,299 revisions were identified in the period 1997-2018 from the Danish Knee Arthroplasty Register. Of these, 1,111 (26%) were performed due to "pain without loosening" without any other indications, 674 (16%) due to "pain without loosening" combined with other indications, and 2,514 (59%) due to "aseptic loosening". Survival analysis was performed by a Cox multivariate analysis and Kaplan-Meier curves were presented. Results - The cumulated proportions of re-revision after 2, 5, and 20 years were 12% (95% CI 10-14), 18% (CI 16-20), and 23% (CI 20-25) for "pain without loosening" versus 11% (CI 9.3-12), 16% (CI 14-17), and 19% (CI 18-21) for "aseptic loosening." There were no statistically significant differences between the 2 indications in repeated analyses for each of the surgical subgroups. The hazard ratio for re-revision comparing "pain without loosening" with "aseptic loosening" was 1.03 (CI 0.87-1.2). The 8-year risk of re-revision for "pain without loosening" was 22% (CI 19-26) versus 22% (CI 20-25) for "aseptic loosening" in the period from 1997-2009, and 18% (CI 15-22) versus 14% (CI 13-16) in the period from 2010-2018. Interpretation - The risk of re-revision was similar for patients having a knee arthroplasty revision for the indication "pain without loosening" compared with "aseptic loosening." However, we observed a slight improvement of prosthesis survival rates after revisions for both indications from 1997-2009 to 2010-2018. We cannot recommend for or against revision in cases with "pain without loosening" based on these data alone.

Eighty Percent Survival of Resurfacing Implants in the Knee After 10 Years: A Nationwide Cohort Study on 379 Procedures from the Danish Knee Arthroplasty Registry

OBJECTIVE

Focal cartilage injuries are debilitating and difficult to treat. Biological cartilage repair procedures are used for patients younger than 40 years, and knee arthroplasties are generally reserved for patients older than 60 years. Resurfacing implants are well suited for patients in this treatment gap. The objective was to investigate the 10-year survival of resurfacing implants in the Danish Knee Arthroplasty Registry.

DESIGN

In this retrospective cohort study, patients treated with resurfacing implants were followed longitudinally in the Danish Knee Arthroplasty Registry from 1997 to 2020. The primary endpoint was revision surgery. The survival of the resurfacing implants was analyzed by Kaplan-Meier method.

RESULTS

A total of 379 resurfacing implant procedures were retrieved from the Danish Knee Arthroplasty Registry. The mean age and weight of patients were 50 years (SD = 11) and 84 kg (SD = 17), respectively. The indications for surgery were as follows: secondary osteoarthritis (42%), primary osteoarthritis (32%), and osteochondral lesions (20%). Within the follow-up period, 70 (19%) of the implants were revised to arthroplasties. The 1-, 5-, and 10-year revision-free survival estimation was 0.95 (95% CI 0.93-0.97), 0.84 (95% CI 0.80-0.88), and 0.80 (95% CI 0.75-0.84), respectively. The median time to revision was 2 years.

CONCLUSION

The 10-year revision-free survival rate for resurfacing implants was 80%. Based on the revision rates, this treatment offers a viable alternative to biological cartilage repair methods in patients aged 40 to 60 years with focal cartilage pathology. Improved patient selection could further improve the implant survival rate. Further studies are needed to investigate this treatment method.

Thromboembolic and bleeding complications following primary total knee arthroplasty : a Danish nationwide cohort study

AIMS

The aim of this study is to compare the effectiveness and safety of thromboprophylactic treatments in patients undergoing primary total knee arthroplasty (TKA).

METHODS

Using nationwide medical registries, we identified patients with a primary TKA performed in Denmark between 1 January 2013 and 31 December 2018 who received thromboprophylactic treatment. We examined the 90-day risk of venous thromboembolism (VTE), major bleeding, and all-cause mortality following surgery. We used a Cox regression model to compute hazard ratios (HRs) with 95% confidence intervals (CIs) for each outcome, pairwise comparing treatment with dalteparin or dabigatran with rivaroxaban as the reference. The HRs were both computed using a multivariable and a propensity score matched analysis.

RESULTS

We identified 27,736 primary TKA patients who received thromboprophylactic treatment (rivaroxaban (n = 18,846); dalteparin (n = 5,767); dabigatran (n = 1,443); tinzaparin (n = 1,372); and enoxaparin (n = 308)). In the adjusted multivariable analysis and compared with rivaroxaban, treatment with dalteparin (HR 0.68 (95% CI 0.49 to 0.92)) or dabigatran (HR 0.31 (95% CI 0.13 to 0.70)) was associated with a decreased risk of VTE. No statistically significant differences were observed for major bleeding or all-cause mortality. The propensity score matched analysis yielded similar results.

CONCLUSION

Treatment with dalteparin or dabigatran was associated with a decreased 90-day risk of VTE following primary TKA surgery compared with treatment with rivaroxaban. Cite this article: Bone Joint J 2021;103-B(10):1571-1577.

A projection of primary knee replacement in Denmark from 2020 to 2050

Background and purpose - The incidence of knee replacements (KRs) has increased in the past decades. Previous studies have forecast a continuous and almost exponential rise in the use of KRs, but this rise must cease at some point. We estimated when and at what incidence the use of KRs will plateau in Denmark.Patients and methods - We retrieved 138,223 primary KRs conducted from 1997 to 2019 from the Danish Knee Arthroplasty Registry. Censuses from 1997 to 2019 as well as population projections from 2020 through 2050 were collected from Statistics Denmark. We applied logistic and Gompertz regression analysis to the data to estimate the future incidence until 2050 with root mean squared error (RMSE) as a quantitative measurement of the models' fit.Results - The Danish incidence of KRs from 1997 to 2009 increased by more than 300%, but has stalled since 2009. Logistic and Gompertz regression had an RMSE of 14 and 15 indicating that these models fitted the data well. Logistic and Gompertz regressions estimated that the maximum incidence will be reached in 2030 at 250 (95% prediction interval [PI]) 159-316) KRs per 10⁵ or in 2035 at 260 (PI 182-336) KRs per 10⁵, respectively.Interpretation - The Danish incidence of KRs seems set to plateau within the coming decades. Countries experiencing a current exponential rise at a lower incidence may benefit from this study's projection when forecasting their future demand for KRs.

Revision for periprosthetic joint infection rate stratified by seasonality of operation in a national population of total and unicompartmental knee arthroplasty patients: a register-based analysis

Aim: The aim of this study was to investigate whether the revision rate for periprosthetic joint infection (PJI) depends on the season of the primary procedure using a national population of knee arthroplasty (KA) patients. Seasonal variation of some surgical procedures has been observed to impact subsequent infection risks, with a higher risk of revision for surgeries performed during summer, but an analysis of PJI rates based on a national arthroplasty register has yet to be completed. We hypothesized that an increased risk of revision due to PJI could be demonstrated in a national population when primary surgery was performed during the summer. Methods: The Danish Knee Arthroplasty Registry (DKR) was used to determine the risk of revision due to PJI within 2 years after primary surgery. All primary KA procedures between 1 January 1997 and 31 December 2014 and revisions until 31 December 2016 were identified. Smoothing spline regression was used to identify possible seasonal pattern effects of the primary procedure on revision risk, and logistic regression was used to calculate risk of infection differences between seasons. Results: A total number of 124 809 primary procedures was registered in the study period. After excluding duplicates and matching primary procedures with the first revisions within 2 years after the primary procedure, 3391 were identified. Of these, 348 cases were recorded with an indication of deep infection requiring revision. Spline regression analyses did not demonstrate any clear seasonal pattern of the primary procedure regarding the risk of revision for infection or any other cause. Logistic regression found a decreased risk of revision for infection when the primary procedure was performed during the summer in the years 1997 to 2005, no influence on the risk of revision for infection in 2005 to 2012, and an increased risk of revision for infection following summer procedures during the years 2013 to 2014. Conclusion: It was not possible to demonstrate a consistent seasonal variation of the risk of revision for PJI following primary KA. This is most likely because the underlying etiologies for PJI are not subject to seasonal variation.

Development of a multivariable prediction model for early revision of total knee arthroplasty - The effect of including patient-reported outcome measures

BACKGROUND

Revision TKA is a serious adverse event with substantial consequences for the patient. As revision is becoming increasingly common in patients under 65 years, the need for improved preoperative patient selection is imminently needed. Therefore, this study aimed to identify the most important factors of early revision and to develop a prediction model of early revision including assessment of the effect of incorporating data on patient-reported outcome measures (PROMs).

MATERIAL AND METHODS

A cohort of 538 patients undergoing primary TKA was included. Multiple logistic regression using forward selection of variables was applied to identify the best predictors of early revision and to develop a prediction model. The model was internally validated with stratified 5-fold cross-validation. This procedure was repeated without including data on PROMs to develop a model for comparison. The models were evaluated on their discriminative capacity using area under the receiver operating characteristic curve (AUC).

RESULTS

The most important factors of early revision were age (OR 0.63 [0.42, 0.95]; P = 0.03), preoperative EQ-5D (OR 0.07 [0.01, 0.51]; P = 0.01), and number of comorbidities (OR 1.01 [0.97, 1.25]; P = 0.15). The AUCs of the models with and without PROMs were 0.65 and 0.61, respectively. The difference between the AUCs was not statistically significant (P = 0.32).

CONCLUSIONS

Although more work is needed in order to reach a clinically meaningful quality of the predictions, our results show that the inclusion of PROMs seems to improve the quality of the prediction model.

Venous thromboembolism after fast-track elective revision hip and knee arthroplasty - A multicentre cohort study of 2814 unselected consecutive procedures

BACKGROUND

Venous thromboembolism (VTE) prophylaxis is much debated within total hip and knee arthroplasty (THA/TKA). Revision hip and knee arthroplasty (rTHA/rTKA) are more extensive procedures, but data on the risk of postoperative VTE is conflicting and there are no specific guidelines for thromboprophylaxis. Furthermore, data on rTHA/rTKA within a fast-track protocol is sparse. Thus, we aimed at evaluating the incidence and time course of VTE in unselected elective rTHA/rTKA within our established multicentre fast-track collaboration with in-hospital only thromboprophylaxis if length of stay (LOS) ≤ 5 days.

METHODS

We used an observational study design of unselected consecutive fast-track elective major component rTHA/rTKA from 6 dedicated fast-track centres between 2010 and 2018. We obtained information on revisions through Danish hip and knee arthroplasty registers and complete (>99%) 90 days follow-up through the Danish National Patient Registry in combination with chart review.

RESULTS

We included 2814 procedures with median LOS 3 days [2-5] and 21% had LOS >5 days. The 90-day incidence of VTE was 0.42% (n = 12), with 8 (0.28%) DVT and 4 (0.14%) PE, after median 14 days [IQR: 11-23] with the latest on day 31.

CONCLUSION

The 90-day incidence of VTE after elective fast-track rTHA and rTKA was about 0.4% which is comparable to the 90-day VTE incidence after primary fast-track THA, TKA and unicompartmental knee arthroplasty. Future investigations should focus on identification of high-risk patients while the surgical trauma per se may be less important.

Revision total knee arthroplasty longer term outcome and comparison between infection and aseptic loosening at mean follow-up of 10 years

Background:

Although the majority of total knee arthroplasty cases have good outcome and survival, some arthroplasty eventually required revision. While early outcomes of revision knee arthroplasty are well reported, there is relatively fewer literatures reporting on the longer term outcome of revision knee arthroplasty. This study aims to review the outcome of revision knee arthroplasty for a longer term, and also make comparison between the two common indications for revision arthroplasty of infection and aseptic loosening.

Methods:

This study reviews all total knee arthroplasty revision performed at a single center over a 11 year period. Of the 48 cases found, 35 cases not lost to follow-up had a mean follow-up duration of 10.6 years (SD 2.9) for aseptic loosening, and 10.1 years (SD 2.6) for infection. Data of initial arthroplasty, revision arthroplasty, demographics, follow-up outcome were obtained, analyzed and compared.

Results:

Revision arthroplasty due to infection had more cases that required use of varus/valgus constraints (p ∼ 0.008) and extensile surgical exposure of quadriceps snip (p ∼ 0.005) compared to aseptic loosening. The survival at 10 years for this study is 91% overall (aseptic loosening 93.3%, infection 89.3%). Infection cases had significant initial improvement for range of motion (p ∼ 0.001) and use of walking aid (p ∼ 0.04) at post-operation 1 year, but no significant differences between the infection and aseptic loosening cases at 5 years and 10 years follow-up. Comparison between the two groups on other factors including initial arthroplasty, operative details, demographics, post-operative details and X-rays showed no statistically significant difference.

Validation of registration of pharmacological treatment in the Danish Hip and Knee Arthroplasty Registers

The aim of this study was to validate registration of pharmacological treatment in the Danish Hip Arthroplasty Register (DHR) and Danish Knee Arthroplasty Register (DKR). We conducted a population-based study in the Capital Region of Denmark, January 2012 to April 2016. Positive predictive value (PPV) and sensitivity were calculated with 95% confidence intervals (CI) for antithrombotic, antihemorrhagic and antibiotic treatment registered in the DHR and DKR using electronic health records as the reference standard. For the DHR, the PPV and sensitivity were 77.9% (95% CI: 77.2-78.6) and 99.6% (95% CI: 99.4-99.7) for antithrombotic treatment, 70.9% (95% CI: 70.1-71.7) and 97.4% (95% CI: 97.1-97.7) for antihemorrhagic treatment, and 82.9% (95% CI: 82.2-83.5) and 99.4% (95% CI: 99.3-99.5) for antibiotic treatment, respectively. For the DKR, the PPV and sensitivity were 80.6% (95% CI: 79.8-81.4) and 99.6% (95% CI: 99.4-99.7) for antithrombotic treatment, and 84.4% (95% CI: 83.7-85.1) and 100.0% (95% CI: 99.9-100.0) for antibiotic treatment, respectively. The PPV and sensitivity for overall pharmacological treatment registered in the DHR and DKR were generally high and acceptable for use in research.

Perceived facilitators and barriers among physical therapists and orthopedic surgeons to pre-operative home-based exercise with one exercise-only in patients eligible for knee replacement: A qualitative interview study nested in the QUADX-1 trial

AIM

Clinical guidelines recommend non-surgical treatment before surgery is considered in patients eligible for knee replacement. Surgical treatment is provided by orthopedic surgeons and exercise therapy is provided by physical therapists. The aim of this study was to identify perceived facilitators and barriers-among orthopedic surgeons and physical therapists-towards coordinated non-surgical and surgical treatment of patients eligible for knee replacement using pre-operative home-based exercise therapy with one exercise.

METHODS

This qualitative study is embedded within the QUADX-1 randomized trial that investigates a model of coordinated non-surgical and surgical treatment for patients eligible for knee replacement. Physical therapists and orthopedic surgeons working with patients with knee osteoarthritis in their daily clinical work were interviewed (one focus group and four single interviews) to explore their perceived facilitators and barriers related to pre-operative home-based exercise therapy with one exercise-only in patients eligible for knee replacement. Interviews were analyzed using thematic analysis.

RESULTS

From the thematic analysis three main themes emerged: 1) Physical therapists' dilemma with one home-based exercise, 2) Orthopedic surgeons' dilemma with exercise, and 3) Coordinated non-surgical and surgical care.

CONCLUSION

We found that the pre-operative exercise intervention created ambivalence in the professional role of both the physical therapists and orthopedic surgeons. The physical therapists were skeptical towards over-simplified exercise therapy. The orthopedic surgeons were skeptical towards the potential lack of (long-term) effect of exercise therapy in patients eligible for knee replacement. The consequence of these barriers and ambivalence in the professional role is important to consider when planning implementation of the model of coordinated non-surgical and surgical treatment.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT02931058.

Can Machine-learning Algorithms Predict Early Revision TKA in the Danish Knee Arthroplasty Registry?

BACKGROUND

Revision TKA is a serious adverse event with substantial consequences for the patient. As the demand for TKA rises, reducing the risk of revision TKA is becoming increasingly important. Predictive tools based on machine-learning algorithms could reform clinical practice. Few attempts have been made to combine machine-learning algorithms with data from nationwide arthroplasty registries and, to the authors' knowledge, none have tried to predict the likelihood of early revision TKA.

QUESTION/PURPOSES

We used the Danish Knee Arthroplasty Registry to build models to predict the likelihood of revision TKA within 2 years of primary TKA and asked: (1) Which preoperative factors were the most important features behind these models' predictions of revision? (2) Can a clinically meaningful model be built on the preoperative factors included in the Danish Knee Arthroplasty Registry?

METHODS

The Danish Knee Arthroplasty Registry collects patients' characteristics and surgical information from all arthroplasties conducted in Denmark and thus provides a large nationwide cohort of patients undergoing TKA. As training dataset, we retrieved all preoperative variables of 25,104 primary TKAs from 2012 to 2015. The same variables were retrieved from 6170 TKAs conducted in 2016, which were used as a hold-out year for temporal external validation. If a patient received bilateral TKA, only the first knee to receive surgery was included. All patients were followed for 2 years, with removal, exchange, or addition of an implant defined as TKA revision. We created four different predictive models to find the best performing model, including a regression-based model using logistic regression with least shrinkage and selection operator (LASSO), two classification tree models (random forest and gradient boosting model) and a supervised neural network. For comparison, we created a noninformative model predicting that all observations were unrevised. The four machine learning models were trained using 10-fold cross-validation on the training dataset after adjusting for the low percentage of revisions by over-sampling revised observations and undersampling unrevised observations. In the validation dataset, the models' performance was evaluated and compared by density plot, calibration plot, accuracy, Brier score, receiver operator characteristic (ROC) curve and area under the curve (AUC). The density plot depicts the distribution of probabilities and the calibration plot graphically depicts whether the predicted probability resembled the observed probability. The accuracy indicates how often the models' predictions were correct and the Brier score is the mean distance from the predicted probability to the observed outcome. The ROC curve is a graphical output of the models' sensitivity and specificity from which the AUC is calculated. The AUC can be interpreted as the likelihood that a model correctly classified an observation and thus, a priori, an AUC of 0.7 was chosen as threshold for a clinically meaningful model.

RESULTS

Based the model training, age, postfracture osteoarthritis and weight were deemed as important preoperative factors within the machine learning models. During validation, the models' performance was not different from the noninformative models, and with AUCs ranging from 0.57 to 0.60, no models reached the predetermined AUC threshold for a clinical useful discriminative capacity.

CONCLUSION

Although several well-known presurgical risk factors for revision were coupled with four different machine learning methods, we could not develop a clinically useful model capable of predicting early TKA revisions in the Danish Knee Arthroplasty Registry based on preoperative data.

CLINICAL RELEVANCE

The inability to predict early TKA revision highlights that predicting revision based on preoperative information alone is difficult. Future models might benefit from including medical comorbidities and an anonymous surgeon identifier variable or may attempt to build a postoperative predictive model including intra- and postoperative factors as these may have a stronger association with early TKA revisions.

Differences in patient characteristics and external validity of randomized clinical trials on pain management following total hip and knee arthroplasty: a systematic review

Background

The external validity of randomized controlled trials (RCTs) is critical for the relevance of trial results in a clinical setting. We aimed to assess the external validity of RCTs investigating postoperative pain treatment after total hip and knee arthroplasty (THA and TKA) by comparing patient characteristics in these trials with a clinical cohort. Further, we assessed the use of exclusion criteria of the included RCTs.

Methods

We searched PubMed, Embase, and Cochrane Central Register of Controlled Trials for relevant RCTs up to June 2019. Data on patient characteristics from this research population were compared with an unselected clinical cohort from the Danish Hip and Knee Arthroplasty Registries in the period 2005–2019. Trends in patient characteristics and the use of exclusion criteria were assessed with control charts.

Results

In total, 550 RCTs with 48 962 participants were included in the research cohort. The clinical cohort included 101 439 THA patients and 90 505 TKA patients. Patient characteristics (age, body mass index (BMI), American Society of Anesthesiologists (ASA) score and sex distribution) in the research cohort resembled those of the clinical cohort. Age, BMI and ASA scores did not change over time in the research cohort. In the clinical cohort, age increased among both THA and TKA patients, and BMI and ASA scores increased among TKA patients. Most commonly used exclusion criteria in the RCTs were high ASA score (62%), older age (45%), obesity (32%) and chronic opioid use (41%). Exclusion of chronic opioid users and individuals with obesity increased over time.

Conclusion

Patient characteristics in research trials investigating postoperative pain management after THA and TKA currently resemble those of a clinical cohort. However, individuals in the clinical cohort are getting older, and TKA patients more obese with increasing ASA scores. Concomitantly, RCTs increase the tendency to exclude patients with older age, obesity, chronic pain and/or opioid use. This trending discrepancy can hinder the generalizability of future research results, and therefore increased focus on pragmatic trials resembling real-world conditions are needed.

PROSPERO registration number

CRD42019125691

Reduced survival of total knee arthroplasty after previous unicompartmental knee arthroplasty compared with previous high tibial osteotomy: a propensity-score weighted mid-term cohort study based on 2,133 observations from the Danish Knee Arthroplasty Registry

Background and purpose - Both medial unicompartmental knee arthroplasties (UKA) and high tibial osteotomies (HTO) are reliable treatments for isolated medial knee osteoarthritis. However, both may with time need conversion to a total knee arthroplasty (TKA). We conducted the largest nationwide registry comparison of the survival of TKA following UKA with TKA following HTO.Patients and methods - From the Danish Knee Arthroplasty Registry, aseptic conversions to TKA from UKA and TKA converted from HTO within the period of 1997-2018 were retrieved. The Kaplan-Meier method and the Cox proportional hazards regression were used to estimate the survival and hazard ratio (HR) for revision, considering confounding by indication utilizing propensity-score based inverse probability of treatment weighting (PS-IPTW).Results - PS-IPTW yielded a well-balanced pseudo-cohort (standard mean difference (SMD) < 0.1 for all covariates, except implant supplementation) of 963.8 TKAs following UKA and 1139.1 TKAs following HTO. The survival of TKA following UKA was significantly less than that of TKA following HTO with a 5-year estimated survival of 0.88 (95% confidence interval (CI) 0.85-0.90) and 0.94 (CI 0.93-0.96), respectively. The differences in survival corresponded to an implant-supplementation adjusted HR of 2.7 (CI 2.4-3.1) for TKA following UKA compared with TKA following HTO.Interpretation - Previous UKA more than doubled the revision risk of a subsequent TKA compared with previous HTO. This potential risk should be considered in the shared treatment decision of patients who are candidates for both UKA and HTO.

Revision Risk for Total Knee Arthroplasty Converted from Medial Unicompartmental Knee Arthroplasty: Comparison with Primary and Revision Arthroplasties, Based on Mid-Term Results from the Danish Knee Arthroplasty Registry

BACKGROUND

Medial unicompartmental knee arthroplasties (UKAs) have good clinical outcomes but implant survival is inferior to that of total knee arthroplasties (TKAs). Conversion to a TKA is a reliable option when UKA fails. However, there is controversy regarding these conversions. The aim of this study was to analyze the survival of TKAs converted from UKAs when compared with both primary and revision TKAs.

METHODS

On the basis of registrations in the Danish Knee Arthroplasty Registry from 1997 to 2017, 1,012 TKAs converted from UKAs were compared with 73,819 primary TKAs and 2,572 revision TKAs. The primary outcome was the risk of revision. Secondarily, the study analyzed the influence of different implants, the indication for the UKA conversion, and surgical volume on the survival of TKA converted from UKA. Third, the study compared the indications for revision.

RESULTS

The converted UKAs were mainly mobile-bearing (85%) and, at the time of conversion, the patients were younger (mean [standard deviation], 66 ± 10 years) and more were Charnley class A (55%) compared with patients with primary TKA (70 ± 9 years and 35% class A) or revision TKA (70 ± 10 years and 42% class A) (all p < 0.001). The survival of TKAs converted from UKAs was comparable with that of revision TKAs (p = 0.42) and significantly inferior to the survival of primary TKAs (p < 0.001). This relationship was unaffected by differences between the groups, with an adjusted hazard ratio of 0.94 (95% confidence interval [CI]: 0.74 to 1.19) compared with revision TKAs and 3.00 (95% CI: 2.47 to 3.66) compared with primary TKAs. The survival of TKA converted from UKA was unaffected by differences in the conversion implants (all p ≥ 0.47), experience with revision surgery (all p ≥ 0.06), and the indications for the UKA-to-TKA conversion (all p ≥ 0.27). Instability (26%) and unexplained pain (13%) were more frequent indications for revisions of TKA converted from UKA (p < 0.001).

CONCLUSIONS

TKA converted from medial UKA has a 3-fold higher risk of revision when compared with primary TKA. The implant survival resembled that of revision TKA but with a higher prevalence of unexplained pain and instability.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Medial unicompartmental knee arthroplasty: increasingly uniform patient demographics despite differences in surgical volume and usage-a descriptive study of 8,501 cases from the Danish Knee Arthroplasty Registry

Background and purpose - Using contemporary indications, up to 50% of patients undergoing knee arthroplasty are eligible for unicompartmental knee arthroplasty (UKA), and lower UKA use likely reflects a restrictive approach to patient selection. Since broader indications have been successfully introduced, and low surgical volume and UKA percentage (usage) are associated with higher revision rates, it is of interest whether the actual use of UKA has changed accordingly. We explored this by assessing time trends in patient demographics and whether these are associated with center UKA volume and usage. Patients and methods - From the Danish Knee Arthroplasty Registry, we included 8,501 medial UKAs performed for primary osteoarthritis during 2002-2016. Using locally weighted regression, we examined changes-both overall and by center volume and usage (low vs high)-in sex distribution, age, weight, and preoperative American Knee Society Score (AKSS-O). Results - Over the last 20 years, UKA use in Denmark has been increasing steadily. Age, weight, and proportion of men all increased regardless of volume and usage. AKSS-O showed an initial increase followed by a decrease. In low-usage and low-volume centers, the proportion of women was higher, patients were younger, weighed less, and had higher AKSS-O scores; however, for age and AKSS-O, the groups were converging during the last part of the period. Interpretation - Characteristics of UKA patients have changed in the last 15 years irrespective of center volume and usage. We found between-group differences for both volume and usage, though with convergence for age and AKSS-O, which suggests an increasingly uniform approach to patient selection.

The Danish health care system and epidemiological research: from health care contacts to database records

Denmark has a large network of population-based medical databases, which routinely collect high-quality data as a by-product of health care provision. The Danish medical databases include administrative, health, and clinical quality databases. Understanding the full research potential of these data sources requires insight into the underlying health care system. This review describes key elements of the Danish health care system from planning and delivery to record generation. First, it presents the history of the health care system, its overall organization and financing. Second, it details delivery of primary, hospital, psychiatric, and elderly care. Third, the path from a health care contact to a database record is followed. Finally, an overview of the available data sources is presented. This review discusses the data quality of each type of medical database and describes the relative technical ease and cost-effectiveness of exact individual-level linkage among them. It is shown, from an epidemiological point of view, how Denmark’s population represents an open dynamic cohort with complete long-term follow-up, censored only at emigration or death. It is concluded that Denmark’s constellation of universal health care, long-standing routine registration of most health and life events, and the possibility of exact individual-level data linkage provides unlimited possibilities for epidemiological research.

Prior High Tibial Osteotomy Does Not Affect the Survival of Total Knee Arthroplasties: Results From the Danish Knee Arthroplasty Registry

BACKGROUND

High tibial osteotomy (HTO) is a joint preserving treatment of unicompartmental osteoarthritis in the knee. In cases with insufficient or deteriorating clinical results patients may undergo a total knee arthroplasty (TKA). The influence of prior HTO on TKA survival is debated.

METHODS

We conducted a population-based registry study comparing 1044 primary TKAs in patients with prior HTO to 63,763 de novo TKAs inserted from 1997 to 2015. Implant survival was estimated by Kaplan-Meier analysis with revision of any kind as endpoint. Patient and surgery characteristics, including choice of implant design, were compared and their influence on TKA survival was estimated by Cox regression. Finally, indications of revision were compared between the groups.

RESULTS

TKA following HTO had an inferior survival with a 10-year estimated survival of 91% compared to 94% for de novo TKA, corresponding to a crude hazard ratio (HR) of 1.73 (P < .001). However, after adjustment for differences in gender and age this risk diminished (HR 1.19, P = .09). The choice of implant constraint was similar between the groups and in both groups posterior stabilized TKA was associated with inferior survival with an adjusted HR of 1.46 (P = .03) in post-HTO TKA when compared to cruciate-retaining TKA.

CONCLUSION

TKA following HTO had a crude inferior survival when compared to TKA without prior surgery of any kind. The inferior survival was explainable by patient characteristics, defined by male gender and lower age, rather than the prior HTO. However, when the prior HTO resulted in the use of posterior stabilized TKA the survival decreased.

Arthroplasty knee registry of Catalonia: What scientific evidence supports the implantation of our prosthesis?

INTRODUCTION

In our environment, it is increasingly necessary to perform an activity based on scientific evidence and the field of prosthetic surgery should be governed by the same principles. The national arthroplasty registries allow us to obtain a large amount of data in order to evaluate this technique. The aim of our study is to analyse the scientific evidence that supports the primary total knee arthroplasties implanted in Catalonian public hospitals, based on the Arthoplasty Registry of Catalonia (RACat) MATERIAL AND METHODS: A review of the literature was carried out on knee prostheses (cruciate retaining, posterior stabilized, constricted and rotational) recorded in RACat between the period 2005-2013 in the following databases: Orthopedic Data Evaluation Panel, PubMed, TripDatabase and Google Scholar. The prostheses implanted in fewer than 10 units (1,358 prostheses corresponding to 62 models) were excluded.

RESULTS

41,947 prostheses (96.86%) were analysed out of 43,305 implanted, corresponding to 74 different models. In 13 models (n = 4,715) (11.24%) no clinical evidence to support their use was found. In the remaining 36 models (n = 13,609) (32.45%), level iv studies were the most predominant evidence.

CONCLUSIONS

There was a significant number of implanted prostheses (11.24%) for which no clinical evidence was found. The number of models should be noted, 36 out of 110, with fewer than 10 units implanted. The use of arthroplasty registries has proved an extremely useful tool that allows us to analyse and draw conclusions in order to improve the efficiency of this surgical technique.

Micrometer-Sized Titanium Particles Induce Aseptic Loosening in Rabbit Knee

Wear debris induced aseptic loosening is the leading cause of total knee arthroplasty (TKA) failure. The complex mechanism of aseptic loosening has been a major issue for introducing effective prevention and treatment methods, so a simplified yet efficient rabbit model was established to address this concern with the use of micrometer-sized titanium particles. 20 New Zealand white rabbits were selected and divided into two groups (control = 10, study = 10). A TKA surgery was then performed for each of them, with implantation of a titanium rod prosthesis which was coated evenly with micrometer-sized titanium in the study group and nothing in the control group, into right femoral medullary cavity. After 12 weeks, all the animals were euthanized and X-ray analyses, H&E staining, Goldner Masson trichrome staining, Von Kossa staining, PCR, and Western blotting of some specific mRNAs and proteins in the interface membrane tissues around the prosthesis were carried out. The implantation of a titanium rod prosthesis coated with 20 μm titanium particles into the femoral medullary cavity of rabbits caused continuous titanium particle stimulation around the prosthesis, effectively inducing osteolysis and aseptic loosening. Titanium particle-induced macrophages produce multiple inflammatory factors able to activate osteoclast differentiation through the OPG/RANKL/RANK signaling pathway, resulting in osteolysis while suppressing the function of osteoblasts and reducing bone ingrowth around the prosthesis. This model simulated the implantation and loosening process of an artificial prosthesis, which is an ideal etiological model to study the aseptic prosthetic loosening.

Efficacy of pre-operative quadriceps strength training on knee-extensor strength before and shortly following total knee arthroplasty: protocol for a randomized, dose-response trial (The QUADX-1 trial)

BACKGROUND

Patients with knee osteoarthritis (OA) report knee pain, limitation in physical activities and low quality of life. The two primary treatments for knee OA are non-surgical treatment (e.g., exercise) and surgery (total knee arthroplasty (TKA)); however, national guidelines recommend non-surgical treatment to be tried prior to surgical procedures. Patients with knee OA are characterized by decreased muscle strength, particularly in the knee-extensor muscles. Correspondingly, decreased knee-extensor strength is found to be associated with an increased risk of development, progression and severity of knee OA symptoms. Recent trials suggest a positive effect of pre-operative exercise on pre- and post-operative outcome; however, the most effective pre-operative knee-extensor strength exercise dosage is not known. The purpose of the present trial is to investigate the efficacy of three different exercise dosages of pre-operative, home-based, knee-extensor strength exercise on knee-extensor strength before and shortly after surgery in patients eligible for TKA due to end-stage knee OA.

METHODS

In this randomized dose-response trial with a three-arm parallel design, 140 patients with end-stage knee OA (candidates for TKA) are randomized to one of three exercise dosages (two, four or six session/week) of knee-extensor strength exercise (three sets, 12 repetitions at 12 RM, per exercise session) for 12 weeks. The knee-extensor strength exercise is home-based (unsupervised) and performed with an elastic exercise band following an initial exercise instruction. Adherence is objectively quantified using a sensor attached to the exercise band. The primary outcome will be the change in knee-extensor strength. Following the 12-week exercise period, the need for TKA surgery is re-assessed by an orthopedic surgeon.

DISCUSSION

Decreased knee-extensor strength is a major challenge in patients with knee OA. Exercise programs focusing on knee-extensor strength are found to be more effective in relieving knee OA pain and symptoms compared to more general exercise programs. However, the optimal exercise dosage for knee-extensor strength deficits in patients with knee OA is inconclusive. Knowledge on the dose-response relationship for knee-extensor strength exercise in patients with knee OA will help guide future non-surgical treatment in this patient population.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT02931058 . Pre-registered on 10 October 2016.

Predictors of revision, prosthetic joint infection and mortality following total hip or total knee arthroplasty in patients with rheumatoid arthritis: a nationwide cohort study using Danish healthcare registers

OBJECTIVES

To investigate predictors of 10-year risk of revision and 1-year risk of prosthetic joint infection (PJI) and death following total hip/total knee arthroplasty (THA/TKA) in (1) patients with rheumatoid arthritis (RA) compared with patients with osteoarthritis (OA); and (2) patients with RA treated with biological disease-modifying antirheumatic drugs (bDMARD) within 90 days preceding surgery compared with non-treated.

METHODS

Register-based cohort study using the Danish National Patient Register, the DANBIO rheumatology register (RA-specific confounders and treatment episodes) and the Danish Hip and Knee Arthroplasty Registers. Survival analyses were used to calculate confounder-adjusted sub-HRs (SHR) and HRs.

RESULTS

In total, 3913 patients with RA with THA/TKA were compared with 120 499 patients with OA. Patients with RA had decreased risk of revision (SHR 0.71 (0.57-0.89)), but increased risk of PJI (SHR=1.46 (1.13-1.88)) and death (HR=1.25 (1.01-1.55)). In DANBIO, 345 of 1946 patients with RA with THA/TKA had received bDMARD treatment within 90 days preceding surgery. bDMARD-treated patients did not have a statistically significant increased risk of revision (SHR=1.49 (0.65-3.40)), PJI (SHR=1.61 (0.70-3.69)) nor death (HR=0.75 (0.24-2.33)) compared with non-treated. Glucocorticoid exposure (HR=2.87 (1.12-7.34)) and increasing DAS28 (HR=1.49 (1.01-2.20)) were risk factors for mortality.

CONCLUSION

Patients with RA had a decreased 10-year risk of revision while the risk of death and PJI was increased compared with patients with OA following THA/TKA. bDMARD exposure was not associated with statistically significant increased risk of neither PJI nor death in this study. Glucocorticoid exposure and increased disease activity were associated with an increased risk of death.

Is decreasing mortality in total hip and knee arthroplasty patients dependent on patients' comorbidity?

Background and purpose - Mortality after primary total hip and knee arthroplasty (THA and TKA) has declined, and the proportion of THA and TKA patients with comorbid conditions has increased. We therefore wanted to examine changes in comorbidity burden over time and the impact of comorbid on mortality following primary total hip and knee arthroplasty in patients with osteoarthritis. Patients and methods - We used the Danish arthroplasty registers to identify THA and TKA patients from 1996 through 2013. From administrative databases, we collected data on pre-surgery hospital history for all patients, which were used to calculate the Charlson comorbidity index (CCI). Patients were divided into 4 groups: CCI-none, CCI-low, CCI-moderate, and CCI-high. We calculated the relative risk (RR) of mortality within 90 days after surgery with a 95% confidence interval (CI), with stratification according to CCI group and year of surgery. Results - 99,962 THAs and 63,718 TKAs were included. The proportion of THAs with comorbidity increased by 3-4% in CCI-low, CCI-moderate, and CCI-high patients, from 1996-1999 to 2010-2013. The overall 90-day mortality risk declined for both procedures. Compared to CCI-none, THA patients with low, moderate, and high comorbidity burdens had an RR of 90-day mortality of 1.9 (95% CI: 1.6-2.4), 1.9 (CI: 1.5-2.5), and 3.3 (CI: 2.6-4.2), respectively. Similar increases in proportions and RRs were observed in TKAs. Interpretation - Despite the fact that the proportion of THA and TKA patients with comorbidities has increased over the past 18 years, the overall mortality has declined. The mortality risk depended on the comorbidity burden and did not decline during the study period for THA and TKA patients with a moderate or high comorbidity burden at the time of surgery.

Increased risk of early and medium-term revision after post-fracture total knee arthroplasty

Background and purpose - Total knee arthroplasty (TKA) due to posttraumatic fracture osteoarthritis (PTFA) may be associated with inferior prosthesis survival. This study is the first registry-based study solely addressing this issue. Both indications and predictors for revision were identified. Patients and methods - 52,518 primary TKAs performed between 1997 and 2013 were retrieved from the Danish Knee Arthroplasty Register (DKR). 1,421 TKAs were inserted due to PTFA and 51,097 due to primary osteoarthritis (OA). Short-term (< 1 year), medium-term (1-5 years), and long-term (> 5 years) implant survival were analyzed using Kaplan-Meier analysis and Cox regression after age stratification (< 50, 50-70, and >70 years). In addition, indications for revision and characteristics of TKA patients with subsequent revision were determined. Results - During the first 5 years, TKAs inserted due to PTFA had a higher risk of revision than OA (with adjusted hazard ratio ranging from 1.5 to 2.4 between age categories). After 5 years, no significant differences in the risk of revision were seen between the groups. Infection and aseptic loosening were the most common causes of revision in both groups, but TKA instability was a more frequent indication for revision in the PTFA group. In both groups, the revision rates were higher with younger age and extended duration of primary surgery. Interpretation - We found an increased risk of early and medium-term revision of TKAs inserted due to previous fractures in the distal femur and/or proximal tibia. Predictors of revision such as age <50 years and extended duration of primary surgery were identified, and revision due to instability occurred more frequently in TKAs performed due to previous fractures.

Transfemoral Amputation After Failure of Knee Arthroplasty: A Nationwide Register-Based Study

BACKGROUND

Transfemoral amputation is considered the last treatment option for failed knee arthroplasty. The extent to which this procedure is performed is not well known. The purpose of this study was to identify the incidence and causes of amputation following failure of knee arthroplasty in a nationwide population.

METHODS

Data were extracted from the Danish Civil Registration System, the Danish National Patient Register, and the Danish Knee Arthroplasty Register. With use of individual data linkage, 92,785 primary knee arthroplasties performed from 1997 to 2013 were identified. Of these, 258 were followed by amputation. Hospital records of all identified cases were reviewed. A competing-risk model was used to estimate the cumulative incidence of amputation. Differences in cumulative incidences were analyzed with use of the Gray test.

RESULTS

A total of 115 amputations were performed for causes related to failed knee arthroplasty. The 15-year cumulative incidence of amputation was 0.32% (95% confidence interval [CI], 0.23% to 0.48%). The annual incidence of amputation following arthroplasties performed from 1997 to 2002 was 0.025% compared with 0.018% following arthroplasties performed from 2008 to 2013 (p = 0.06). The causes of the amputation were periprosthetic infection in 95 cases (83%), soft-tissue deficiency in 26 (23%), severe bone loss in 21 (18%), extensor mechanism disruption in 11 (10%), intractable pain in 11 (10%), periprosthetic fracture in 10 (9%), and vascular complications in 9 (8%). In 92 (80%) of the cases, there were ≥2 indications for amputation.

CONCLUSIONS

The cumulative incidence of amputation within 15 years after primary knee arthroplasty was 0.32%, with a tendency toward a decreasing incidence in the last part of the study period.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Primary total hip arthroplasty in Catalonia: What is the clinical evidence that supports our prosthesis?

INTRODUCTION

The implementation of National Prostheses Registries allows us to obtain a large amount of data and make conclusions in order to improve the use of them. Sweden was the first country to implement a National Prostheses Registry in 1979. Catalonia has been doing this since 2005. The aim of our study is to analyse the evidence that supports primary total hip replacement in Catalonia in the last 9 years, based on the Arthroplasty Registry of Catalonia (RACat).

MATERIAL AND METHODS

A review of the literature was carried out of the prosthesis (acetabular cups/stems) reported in the RACat between the period 2005 to 2013 in the following databases: ODEP (Orthopaedic Data Evaluation Panel), TRIP database, PubMed, and Google Scholar. Those prostheses implanted in less than 10 units (182 acetabular components corresponding to 49 models/228 stems corresponding to 63 models) were excluded.

RESULTS

A total of 18,634 (99%) implanted acetabular cups were analysed out of a total number of 18,816, corresponding to 74 different models. In 18 models (2527 acetabular cups) no clinical evidence to support its use was found. An analysis was performed on 19,367 (98.84%) out of a total number of 19,595 implanted stems, corresponding to 75 different models. In 16 models (1845 stems) no clinical evidence was found to support their use. Variable evidence was found in the 56 models of acetabular cups (16,107) and 59 models of stems (17,522), most of it corresponding to level iv clinical evidence.

CONCLUSIONS

There was a significant number implanted prostheses evaluated (13.56% acetabular cups/9.5% stems) for which no clinical evidence was found. The elevated number of models is highlighted (49 types for acetabular cups/63 types for stems) with less than 10 units implanted, which corresponds to only 1% of the total implants. The use of arthroplasty registers is shown to be an extremely helpful tool that allows analyses and conclusions to be made for the follow-up and post-marketing surveillance period.

No Increased Risk for Primary Osteoarthritis in Liver Cirrhosis - A Danish Nationwide Cohort Study

Objective

Chronic synovial inflammation causes primary osteoarthritis, but it is unknown whether chronic systemic inflammation does, too. Patients with cirrhosis have chronic systemic inflammation and therefore we examined the association between cirrhosis and primary osteoarthritis of the hip and knee.

Methods

In Danish healthcare databases we identified all residents over 60 years diagnosed with cirrhosis in 1994–2011, and for each of them we sampled five age- and gender-matched reference persons from the general population. We excluded everyone with risk factors for secondary osteoarthritis and computed incidence rates of primary osteoarthritis of the hip or knee. We used stratified Cox regression to estimate the hazard ratios of primary osteoarthritis for cirrhosis patients vs. reference persons in strata defined by gender, age, cirrhosis etiology, and ascites vs. no ascites. We also computed separate HRs for primary osteoarthritis of the hips or knees.

Results

We identified 10,049 cirrhosis patients. Their median age was 67 years, and 65% were men. Among the cirrhosis patients the crude incidence rate of primary osteoarthritis was 8.40 (95% CI: 7.30–9.63) per 1000 person-years. The rate was similar in the reference persons: 8.76 (95% CI: 8.43–9.12) per 1000 person-years. Accordingly, the hazard ratio for primary osteoarthritis for cirrhosis patients vs. reference persons was 0.99 (95% CI: 0.85–1.16), and we found the same null association in all patient strata and in both joints.

Conclusion

Cirrhosis, and thus chronic systemic inflammation, is not a risk factor for primary osteoarthritis.

Knee Arthrodesis After Failure of Knee Arthroplasty: A Nationwide Register-Based Study

BACKGROUND

Arthrodesis is considered a salvage procedure after failure of a knee arthroplasty. Data on the use of this procedure are limited. The purpose of this study was to identify the incidence, causes, surgical techniques, and outcomes of arthrodesis after failed knee arthroplasty in a nationwide population.

METHODS

Data were extracted from the Danish Civil Registration System, the Danish National Patient Register, and the Danish Knee Arthroplasty Register. A total of 92,785 primary knee arthroplasties performed in Denmark from 1997 to 2013 were identified by linking the data using the unique personal identification number assigned to each patient. Of these arthroplasties, 165 were followed by arthrodesis. Hospital records of all identified cases of arthrodesis were reviewed. A competing risk model was used to estimate the cumulative incidence of arthrodesis in the study period. Differences in cumulative incidence were compared with the Gray test.

RESULTS

A total of 164 of the 165 arthrodeses were performed for causes related to failed knee arthroplasty. The 15-year cumulative incidence of arthrodesis was 0.26% (95% confidence interval, 0.21% to 0.31%). The 5-year cumulative incidence decreased significantly (p < 0.0001) from 0.32% for arthroplasties performed from 1997 to 2002 to 0.09% for arthroplasties performed from 2008 to 2013. The most common causes of arthrodesis were periprosthetic infection in 152 patients (93%), extensor mechanism disruption in 46 (28%), soft-tissue deficiency in 25 (15%), and severe bone loss in 11 (7%). In 79 patients (48%), there were 2 or more indications for arthrodesis. Solid fusion was achieved in 65% of the patients. The fusion rate was significantly higher after intramedullary nail fixation compared with external fixation (p = 0.01). A total of 34 patients (21%) underwent repeat arthrodesis, and 23 patients (14%) eventually underwent transfemoral amputation.

CONCLUSIONS

The cumulative incidence of arthrodesis within 15 years after primary knee arthroplasty was 0.26%. There was a significant decrease in the 5-year cumulative incidence during the study period, suggesting an overall improvement in prevention of this adverse outcome of knee arthroplasty.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

New Zealand Joint Registry data underestimates the rate of prosthetic joint infection

Background and purpose - Recent studies have revealed deficiencies in the accuracy of data from joint registries when reoperations for prosthetic joint infections (PJIs) are reported, particularly when no components are changed. We compared the accuracy of data from the New Zealand Joint Registry (NZJR) to a multicenter audit of hospital records to establish the rate of capture for PJI reoperations. Methods - 4,009 cases undergoing total knee or hip arthroplasty performed at 3 tertiary referral hospitals over a 3-year period were audited using multiple hospital datasets and the NZJR. The number of reoperations for PJI that were performed within 2 years of the primary arthroplasty was obtained using both methods and the data were compared. Results - The NZJR reported a 2-year reoperation rate for PJI of 0.67%, as compared to 1.1% from the audit of hospital records, giving the NZJR a sensitivity of 63%. Only 4 of 11 debridement-in-situ-only procedures and 7 of 12 modular exchange procedures were captured in the NZJR. Interpretation - The national joint registry underestimated the rate of reoperation for PJI by one third. Strategies for improving the accuracy of data might include revising and clarifying the registry forms to include all reoperations for PJI and frequent validation of the registry data against other databases.

Particle Disease: A Current Review of the Biological Mechanisms in Periprosthetic Osteolysis After Hip Arthroplasty

Background:

Inflammatory responses to wear debris cause osteolysis that leads to aseptic prosthesis loosening and hip arthroplasty failure. Although osteolysis is usually associated with aseptic loosening, it is rarely seen around stable implants. Aseptic implant loosening is a simple radiologic phenomenon, but a complex immunological process. Particulate debris produced by implants most commonly causes osteolysis, and this is called particle-associated periprosthetic osteolysis (PPO).

Objective:

The objective of this review is to outline the features of particle-associated periprosthetic osteolysis to allow the physician to recognise this condition and commence early treatment, thereby optimizing patient outcome.

Methods:

A thorough literature search was performed using available databases, including Pubmed, to cover important research published covering particle-associated PPO.

Results:

Although osteolysis causes bone resorption, clinical, animal, and in vitro studies of particle bioreactivity suggest that particle-associated PPO represents the culmination of several biological reactions of many cell types, rather than being caused solely by the osteoclasts. The biological activity is highly dependent on the characteristics and quantity of the wear particles.

Conclusion:

Despite advances in total hip arthroplasty (THA), particle-associated PPO and aseptic loosening continue to be major factors that affect prosthetic joint longevity. Biomarkers could be exploited as easy and objective diagnostic and prognostic targets that would enable testing for osteolysis after THA. Further research is needed to identify new biomarkers in PPO. A comprehensive understanding of the underlying biological mechanisms is crucial for developing new therapeutic interventions to reverse or suppress biological responses to wear particles.

Sex differences in risk and heritability estimates on primary knee osteoarthritis leading to total knee arthroplasty: a nationwide population based follow up study in Danish twins

BACKGROUND

Symptomatic knee osteoarthritis is a highly age and sex associated complex disease. Little is known about the causes behind this age and sex associated increase, or if genetic and environmental factors impacts differently by gender. Our study examined the risk and heritability of primary knee osteoarthritis leading to total knee arthroplasty and whether these differences were attributable to sex and age differences in heritability.

METHODS

All twins of known zygosity from The Danish Twin Register alive in 1997 were examined in a nationwide population based follow-up study collecting information on all twins recorded in The Danish Knee Arthroplasty from 1997 to follow-up in 2010. Our main outcomes were the cumulative incidence, probandwise concordance rates, heritability, within pair correlations in monozygotic and dizygotic twin pairs and the genetic and environmental influence estimated in models taking into account that individuals may not have had a total knee arthroplasty at follow up.

RESULTS

92,748 twins were eligible for analyses and 576 twins had a record of primary knee osteoarthritis in The Danish Knee Arthroplasty Register at follow-up comprising 358 female and 218 male twin cases. The risk increased particular after the age of 50 years displaying significant sex differences in the elderly. In the sex stratified analyses a discrete genetic component was found in females, but in males no genetic component could be detected. In both genders common and unique environmental factors were highly significant. In the sex-adjusted analysis an additive genetic component of 18 % (0; 62), a shared environmental component of 61 % (25; 97) and an individual environmental component of 21 % (6; 36) accounted for the variation in liability to primary total knee arthroplasty.

CONCLUSION

The risk of primary total knee arthroplasty increases significantly after the age of 50 years, in particular in females, displaying significant sex differences in the elderly. After sex-adjustment 82 % of the variation in liability to primary total knee arthroplasty was attributable to common and unique environmental factors; the remaining 18 % of this variation was attributable to additive genetic factors indicating a pivotal impact of environmental factors on this disease.

How can the research potential of the clinical quality databases be maximized? The Danish experience

In Denmark, the need for monitoring of clinical quality and patient safety with feedback to the clinical, administrative and political systems has resulted in the establishment of a network of more than 60 publicly financed nationwide clinical quality databases. Although primarily devoted to monitoring and improving quality of care, the potential of these databases as data sources in clinical research is increasingly being recognized. In this review, we describe these databases focusing on their use as data sources for clinical research, including their strengths and weaknesses as well as future concerns and opportunities. The research potential of the clinical quality databases is substantial but has so far only been explored to a limited extent. Efforts related to technical, legal and financial challenges are needed in order to take full advantage of this potential.

Update on the etiology of revision TKA -- Evident trends in a retrospective survey of 1449 cases

BACKGROUND

A working and complete knowledge of the different causes of dysfunction and pain after TKA is essential for the ability to correctly determine the cause of failure and to address this problem specifically. The purpose of this study was to update the etiology of implant failure. New diagnosis and current trends should be displayed.

METHODS

All TKA revisions performed in our institution between 2001 and 2010 were reviewed retrospectively. Patient demographics and the precise indication for the surgery were documented. Descriptive statistical analyses and association analyses of both the diagnosis and patient demographics were performed.

RESULTS

Within our collective of 1449 revision TKA a total of 40 different pathologies leading to revision surgery were identified and categorized. Overall 68.5% of the revisions were categorized aseptic, 31.5% as septic implant failure. Some recently debated diagnoses like low-grade-infection showed a high increase in incidence whereas classic failure mechanisms like polyethylene wear showed a decrease over the time.

CONCLUSION

We believe that this study successfully updates the current knowledge of different failure mechanisms in revision TKA, which have to be considered on dysfunction or pain after surgery. We were able to evaluate the clinical relevance of each pathology and could shift from implant related problems like wear to more surgical problems like instability and or malalignment over the last years. With a higher alertness to chronic low-grade-infections the incidence of infection is even increasing.

LEVEL OF EVIDENCE

Level II, economic and decision analysis.