The use of tourniquet in primary total knee arthroplasty does not increase the risk of venous thromboembolism within 90 days of surgery: a Danish nationwide cohort study of 19,804 patients.

PURPOSE: Existing evidence estimates a twofold risk of venous thromboembolisms (VTEs) if tourniquet is applied during total knee arthroplasties (TKAs). However, this estimate relies on multiple trials with a low number of patients analyzing VTEs as a secondary outcome. We hypothesized that tourniquet-use increases the risk of symptomatic VTE within 90 days of contemporary primary TKA and aimed to use the extensive Danish healthcare registries to quantify this risk. METHODS: Prospectively collected registry data from Danish patients receiving primary TKAs between 2014 and 2018 were included in the study. Patients were divided by tourniquet-use during surgery. By merging information from four nationwide registries, the study included 44 baseline characteristics with the potential to confound the association between tourniquet-use and VTE. Incidence rate and odds ratios were used to compare the risk of VTE within 90 days of surgery. RESULTS: 19,804 patients of whom 10,111 (51%) were operated with tourniquet and 9693 (49%) without were included. The mean age (SD) was 70 (9) in both groups and 62% were females in the tourniquet group compared with 61% in the no tourniquet group. The groups were similarly comparable across all other baseline characteristics except type of post-operative thromboprophylaxis, type of anaesthesia, implant fixation, and year of surgery. The 90-days incidence of VTE was 0.77% (95% CI 0.60-0.94) in the tourniquet group compared with 1.10% (95% CI 0.90-1.31) in the no tourniquet group. Following adjustment for the unbalanced confounders, the odds ratio for VTE was 0.77 (95% CI 0.54-1.10) associated with tourniquet-use. CONCLUSION: In contemporary TKAs the rate of VTE within 90 days is low and not significant altered by tourniquet-use. Thus, tourniquet can safely be applied during primary TKA-surgery without jeopardizing the risk of postoperative VTE. LEVEL OF EVIDENCE: II-prospective cohort study.

Projection of primary and revision hip arthroplasty surgery in Denmark from 2020 to 2050.

BACKGROUND AND PURPOSE: The incidence of primary and revision total hip arthroplasty (THA) has increased over the last decades. Previous forecasts from different healthcare systems have predicted a continuous increase. We present a forecast of both primary and revision surgery from 2020 to 2050 based on 25 years data from the healthcare system in Denmark. PATIENTS AND METHODS: We retrieved data from the Danish Hip Arthroplasty Register on 198,835 primary and 29,456 revision surgeries. Historical censuses and population forecasts were retrieved from Statistics Denmark. Logistic and Gompertz regression analysis was used to forecast incidence rates (IR) and total numbers in the next 30 years. RESULTS: Our forecast predicts an increase in IR of 3-9% and an increase in total numbers of primary THA of between 12% and 19% in 2050. For revision THA the IRs have reached a plateau but total numbers are predicted to increase by 19% in 2050. CONCLUSION: Our forecast shows that both primary and revision THA will increase in total numbers in the next decades, but the IR for primary THA is near its plateau and for revision THA the plateau has already been reached. The forecast may aid in healthcare resource planning for the decades to come.

Patient-Reported Outcomes for Function and Pain in Total Knee Arthroplasty Patients.

BACKGROUND: Some patients undergoing total knee arthroplasty successfully manage their condition postoperatively, whereas others encounter challenges in regaining function and controlling pain during recovery at home. OBJECTIVE: The aim of this study was to use traditional statistics and machine learning to develop prediction models that identify patients likely to have increased care needs related to managing function and pain following total knee arthroplasty. METHODS: This study included 201 patients. Outcomes were changes between baseline and follow-up in the functional and pain subcomponents of the Oxford Knee Score. Both classification and regression modeling were applied. Twenty-one predictors were included. Tenfold cross-validation was used, and the regression models were evaluated based on root-mean-square error, mean absolute error, and coefficient of determination. Classification models were evaluated based on the area under the receiver operating curve, sensitivity, and specificity. RESULTS: In classification modeling, random forest and stochastic gradient boosting provided the best overall metrics for model performance. A support vector machine and a stochastic gradient boosting machine in regression modeling provided the best predictive performance. The models performed better in predicting challenges related to function compared to challenges related to pain. DISCUSSION: There is valuable predictive information in the data routinely collected for patients undergoing total knee arthroplasty. The developed models may predict patients who are likely to have enhanced care needs regarding function and pain management. Improvements are needed before the models can be implemented in routine clinical practice.

The potential of dividing the oxford knee score into subscales for predicting clinically meaningful improvements in pain and function of patients undergoing total knee arthroplasty.

BACKGROUND: Subdividing the Oxford Knee Score (OKS) into a pain component scale (OKS-PCS) and a function component scale (OKS-FCS) for predicting clinically meaningful improvements may provide a basis for identifying patients in need of enhanced support from health care professionals to manage pain and functional challenges following total knee arthroplasty. AIM: To assess the potential of dividing the OKS into subscales for predicting clinically meaningful improvements in pre- and postoperative pain and function by comparing two different versions of extracting pain and function derived from the OKS. METHODS: This retrospective observational cohort study included 201 patients undergoing total knee arthroplasty. Multiple logistic regression analysis was applied for binary classification of whether patients achieved clinically meaningful improvements in pain and function. RESULTS: The best overall version for predicting clinically meaningful improvements had an area under the receiver operating characteristic curve of 0.79 for both pain and function, whereas Nagelkerke's R2 was 0.322 and 0.334, respectively. CONCLUSION: The findings indicate that it is reasonable to subdivide the OKS into subscales for predicting clinically meaningful improvements in pain and function. However, more studies are needed to compare various types of classification algorithms in larger patient populations.

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.

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.

High Completeness and Accurate Reporting of Key Variables Make Data from the Danish Shoulder Arthroplasty Registry a Valuable Source of Information.

PURPOSE: The Danish Shoulder Arthroplasty Registry (DSR) is a nationwide database providing data for research and health care monitoring. The aim of this study was to validate the DSR by (1) assessing registration completeness, (2) comparing key variables with information from medical records, (3) assessing the number and proportion of missing data for key variables. MATERIALS AND METHODS: The completeness of registration in the DSR from 2006-2015 was assessed for primary arthroplasties by comparing the number of arthroplasties reported to the DSR with the number of arthroplasties recorded by the Danish National Patient Register which is an administrative database used by the Danish healthcare authorities to monitor all hospitalizations including shoulder arthroplasty surgery. Positive predictive values (PPV) were used to estimate the accuracy of the reporting in a randomly selected population. Information retrieved from medical records were used as gold standard. The number of missing values for each variable was evaluated to depict if these registrations were missing at random. RESULTS: The completeness of reporting was 94.4. The PPV for the three major indications: osteoarthritis, fracture and rotator cuff arthropathy was 92%, 97%, and 94%, respectively. PPV was high for resurfacing arthroplasty (93%) and reverse shoulder arthroplasty (93%), but low for total shoulder arthroplasty (79%) and hemiarthroplasty (83%). The proportion of missing data in DSR was less than 1% for age, gender, previous surgery, indication and arthroplasty type and these can be regarded as missing at random. CONCLUSION: The study showed that data from the DSR are sufficiently valid to be used for research and quality monitoring. Lower PPV's for total shoulder arthroplasty and hemiarthroplasty are possibly related to inadequate definitions and mutually nonexclusive items in the reporting form. Regular validation is necessary since the data reported to the registry continuously evolve because of changes in clinical practice.

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.

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.

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.

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.