Statistics in Brief: Instrumental Variable Analysis: An Underutilized Method in Orthopaedic Research

Tranexamic Acid Is Safe in Arthroplasty Patients Who Have a History of Venous Thromboembolism: An Analysis Accounting for Surgeon Selection Bias

BACKGROUND

Retrospective data supporting the use of tranexamic acid (TXA) among high-risk total joint arthroplasty (TJA) patients are limited by surgeon selection bias. This study sought to evaluate the thromboembolic risk associated with TXA administration among elective arthroplasty patients who have history of venous thromboembolism while accounting for surgeon selection.

METHODS

A healthcare database was retrospectively queried from 2015 to 2021 to identify all patients who had a history of deep vein thrombosis or pulmonary embolism who underwent elective TJA. Patients were categorized into two cohorts: (1) patients treated by a surgeon who used TXA in 0 to 30% of cases; and (2) patients treated by a surgeon who used TXA in 90 to 100% of cases. Patients were assessed based on the surgeon who treated them rather than their exposure to TXA. Demographics, comorbidities, and the incidence of 90-day postoperative complications were compared between the two groups. Multivariable and instrumental variable analysis using surgeon as an instrument were conducted to account for confounding factors.

RESULTS

In total, 70,759 high-risk elective TJA patients were identified, of which 7,190 (10.2%) were performed by surgeons in the infrequent-TXA cohort and 9,478 (13.4%) were performed by surgeons in the frequent-TXA cohort. On instrumental variable analysis, patients treated by surgeons in the frequent-TXA cohort had a lower risk of aggregate bleeding complications (instrumental variable odds ratio 0.94, 95% confidence interval: 0.89 to 0.98, P = 0.005), including transfusion (instrumental variable odds ratio 0.60, 95% confidence interval: 0.54 to 0.66, P < 0.001). However, no significant differences were observed in postoperative deep vein thrombosis, pulmonary embolism, stroke, and myocardial infarction between the two cohorts (P > 0.05).

CONCLUSIONS

After accounting for surgeon selection, TXA administration was associated with a significant reduction in early postoperative bleeding complications with no observed increase in thromboembolic risk. Given the favorable safety profile, surgeons should consider TXA among high-risk arthroplasty patients.

Aspirin for Venous Thromboembolic Prophylaxis Following Total Hip and Total Knee Arthroplasty: An Analysis of Safety and Efficacy Accounting for Surgeon Selection Bias

BACKGROUND

Aspirin may be effective at preventing venous thromboembolism following total knee arthroplasty (TKA) or total hip arthroplasty (THA). Current evidence is limited by bias as many surgeons who use aspirin prescribe for high-risk patients alternative chemoprophylactic agents. Therefore, this study aimed to evaluate the risk of pulmonary embolism (PE) and deep vein thrombosis (DVT) in patients who received aspirin and warfarin while accounting for surgeon selection bias.

METHODS

A national database was queried for patients undergoing primary elective TKA or THA from 2015 to 2020. Patients whose surgeon used aspirin in >90% of their patients were compared to patients whose surgeon used warfarin in >90% of cases. Instrumental variable analyses were performed to assess for PE, DVT, and transfusion while accounting for selection bias. Among TKA patients, 26,657 (18.8%) were in the warfarin cohort and 115,005 (81.2%) were in the aspirin cohort. Among THA patients, 13,035 (17.7%) were in the warfarin cohort and 60,726 (82.3%) were in the aspirin cohort.

RESULTS

Analyses were unable to identify a difference in the risk of PE (TKA: adjusted odds ratio [aOR]: 0.98, P = .659; THA: aOR = 0.93, P = .310) and DVT (TKA: aOR = 1.05, P = .188; THA: aOR = 0.96, P = .493) between the aspirin and warfarin cohorts. However, the aspirin cohort was associated with a lower risk of transfusion (TKA: aOR = 0.58, P < .001, THA: 0.84, P < .001).

DISCUSSION

After accounting for surgeon selection bias, aspirin was as effective as warfarin at preventing PE and DVT following TKA and THA. Furthermore, aspirin was associated with a lower risk of transfusion compared to warfarin.

Tranexamic Acid and Prothrombotic Complications Following Total Hip and Total Knee Arthroplasty: A Population-Wide Safety Analysis Accounting for Surgeon Selection Bias

BACKGROUND

Tranexamic acid (TXA) utilization during total joint arthroplasty (TJA) has become ubiquitous. However, concerns remain regarding the risk of thrombotic complications. The goal of this study was to examine the risk of prothrombotic complications in patients who received TXA during total knee (TKA) and total hip arthroplasty (THA).

METHODS

The Premier Healthcare Database was queried for patients who underwent elective TJA. TXA utilization trends were described from 2008 to 2020. Two analyses were performed using ICD-10 codes from 2016 to 2020: (1) patients who received TXA compared to patients who did not receive TXA and, (2) to account for surgeon selection bias, patients whose surgeon utilized TXA consistently (≥90% of cases) compared to patients whose surgeons used TXA infrequently (≤30% of cases). Multivariate and instrumental variable analyses (IVA) were performed to assess outcomes while accounting for confounding factors. TXA utilization increased from 0.1% of cases in 2008 to 89.2% in 2020. From 2016 to 2020, 1,120,858 TJAs were identified (62.1% TKA, 27.9% THA), of which 874,627 (78.0%) received TXA.

RESULTS

Patients who received TXA were at lower risk of prothrombotic (adjusted Odds Ratio (aOR) 0.82, P < .001), bleeding (aOR 0.75, P < .001), and infectious complications (aOR 0.91, P < 0.001). Furthermore, patients who underwent surgery from surgeons who utilized TXA consistently were at lower risk for prothrombotic (aOR 0.90, P < .001) and bleeding (aOR 0.72, P < .001) complications.

CONCLUSION

The widespread utilization of TXA during elective TJA was not associated with increased rates of prothrombotic complications. These findings persisted after accounting for surgeon selection bias.

LEVEL OF EVIDENCE

Level III.

Association of Drain Use in Ankle Arthrodesis With Increased Blood Transfusion Risk: A National Observational Study

Background:

Closed wound drainage has been extensively studied in the hip and knee arthroplasty literature with equivocal results on its clinical benefits. Although also used in orthopaedic surgeries like ankle arthrodesis and ankle arthroplasty, large-scale data are currently lacking on utilization patterns and real-world effectiveness. We, therefore, aimed to address this research gap in this distinct surgical cohort using national claims data.

Methods:

Using the Premier Healthcare claims database from 2006 to 2016, ankle arthrodesis (n=10,085) and ankle arthroplasty (n=4,977) procedures were included. The main effect was drain use, defined by detailed billing descriptions. Outcomes included blood transfusion, 90-day readmission, and length and cost of hospitalization. Mixed-effects models measured associations between drain use and outcomes. Odds ratios (OR, or % change), 95% CIs, and P values are reported.

Results:

Overall, drains were used in 11% (n=1,074) and 15% (n=755) of ankle arthrodesis and ankle arthroplasty procedures, respectively. Drain use dramatically decreased over the years in both surgery types: from 14% to 6% and 24% to 7% between 2006 and 2016, for arthrodesis and ankle arthroplasty procedures, respectively. After adjustment for relevant covariates, drain use was associated with increased odds of blood transfusion in ankle arthrodesis surgery (OR 1.4, CI 1.1-1.8, P = .0168), whereas differences that were statistically but not clinically significant were seen in cost and length of stay. In total ankle arthroplasty, no statistically significant associations were observed between drain use and the selected outcomes.

Conclusion:

This is the first national study on drain use in ankle surgery. We found a decrease in use over time. Drain use was associated with higher odds of blood transfusion in ankle arthrodesis patients. Although this negative effect may be mitigated by the rapidly decreasing use of drains, future studies are needed to discern drivers of drain use in this distinct surgical population.

Level of Evidence:

Level III, retrospective cohort study

Health Services Research in Anesthesia: A Brief Overview of Common Methodologies

The use of large data sources such as registries and claims-based data sets to perform health services research in anesthesia has increased considerably, ultimately informing clinical decisions, supporting evaluation of policy or intervention changes, and guiding further research. These observational data sources come with limitations that must be addressed to effectively examine all aspects of health care services and generate new individual- and population-level knowledge. Several statistical methods are growing in popularity to address these limitations, with the goal of mitigating confounding and other biases. In this article, we provide a brief overview of common statistical methods used in health services research when using observational data sources, guidance on their interpretation, and examples of how they have been applied to anesthesia-related health services research. Methods described involve regression, propensity scoring, instrumental variables, difference-in-differences, interrupted time series, and machine learning.

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

BACKGROUND AND PURPOSE

Characteristics of patients receiving total knee arthroplasty (TKA) and prostheses used vary between regions and change with time. How these practice variations influence revision remains unclear. We combined registry data for better understanding of the impact of variation, which could potentially improve revision rates.

PATIENTS AND METHODS

We used data from 2003 to 2019 for primary TKA from arthroplasty registries of Sweden (SKAR), Australia (AOANJRR), and Kaiser Permanente (KPJRR). We included 1,072,924 TKA procedures for osteoarthritis. Factors studied included age, sex, ASA class, BMI category, prosthesis constraint, fixation, bearing mobility, patellar resurfacing, and polyethylene type. Cumulative percentage revision (CPR) was calculated using Kaplan-Meier estimates, and unadjusted Cox hazard ratios were used for comparisons. Random-effects generic inverse-variance meta-analytic methods were used to determine summary effects.

RESULTS

We found similarities in age and sex, but between-registry differences occurred in the other 7 factors studied. Patients from Sweden had lower BMI and ASA scores compared with other registries. Use of cement fixation was similar in the SKAR and KPJRR, but there were marked differences in patellar resurfacing and posterior stabilized component use. Meta-analysis results regarding survivorship favored patients aged ≥ 65 years and minimally stabilized components. There were inconsistent results with time for sex, fixation, and bearing mobility, and no differences for the patellar resurfacing or polyethylene type comparisons.

INTERPRETATION

Marked practice variation was found. Use of minimally stabilized and possibly also cemented and fixed bearing prostheses is supported.

The Influence of Increasing Levels of Provider-Patient Discussion on Quit Behavior: An Instrumental Variable Analysis of a National Survey

Objective: We aimed to examine the influence of increasing levels of discussion (both asked and advised, either asked or advised but not both, and neither asked nor advised) on quit behavior. Methods: We included 4133 adult current smokers from the 2015 National Health Interview Survey. The primary outcomes were quit intent and quit attempt, and the secondary outcomes were methods used for quitting. We used an instrumental variable analysis, as well as propensity score weighted and multivariable logistic regressions. Results: Compared to no discussion, having both or only one discussion, respectively, increased quit intent (OR = 1.65, 95% CI = 1.63–1.66 and OR = 1.02, 95% CI = 0.99–1.05), quit attempt (OR = 1.76, 95% CI = 1.75–1.77 and OR = 1.60, 95% CI = 1.57–1.63). Among those who attempted to quit (n = 1536), having both or only one discussion increased the use of pharmacologic (OR = 1.99, 95% CI = 1.97–2.02 and OR = 1.56, 95% CI = 1.49–1.63) or behavioral (OR = 2.01, 95% CI = 1.94–2.08 and OR = 2.91, 95% CI = 2.74–3.08) quit methods. Conclusions: Increasing levels of provider–patient discussion encourages quit behavior, and should be an integral part of reducing the health and economic burden of smoking. Strategies that promote the adherence and compliance of providers to communicate with patients may help increase the success of smoking cessation.

Association Between Uncemented vs Cemented Hemiarthroplasty and Revision Surgery Among Patients With Hip Fracture

IMPORTANCE

Consensus guidelines and systematic reviews have suggested that cemented fixation is more effective than uncemented fixation in hemiarthroplasty for displaced femoral neck fractures. Given that these recommendations are based on research performed outside the United States, it is uncertain whether these findings also reflect the US experience.

OBJECTIVE

To compare the outcomes associated with cemented vs uncemented hemiarthroplasty in a large US integrated health care system.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective cohort study of 12 491 patients aged 60 years and older who underwent hemiarthroplasty treatment of a hip fracture between 2009 and 2017 at 1 of the 36 hospitals owned by Kaiser Permanente, a large US health maintenance organization. Patients were followed up until membership termination, death, or the study end date of December 31, 2017.

EXPOSURES

Hemiarthroplasty (prosthetic replacement of the femoral head) fixation via bony growth into a porous-coated implant (uncemented) or with cement.

MAIN OUTCOMES AND MEASURES

The primary outcome measure was aseptic revision, defined as any reoperation performed after the index procedure involving exchange of the existing implant for reasons other than infection. Secondary outcomes were mortality (in-hospital, postdischarge, and overall), 90-day medical complications, 90-day emergency department visits, and 90-day unplanned readmissions.

RESULTS

Among 12 491 patients in the study cohort who underwent hemiarthroplasty for hip fracture (median age, 83 years; 8660 women [69.3%]), 6042 (48.4%) had undergone uncemented fixation and 6449 (51.6%) had undergone cemented fixation, and the median length of follow-up was 3.8 years. In the multivariable regression analysis controlling for confounders, uncemented fixation was associated with a significantly higher risk of aseptic revision (cumulative incidence at 1 year after operation, 3.0% vs 1.3%; absolute difference, 1.7% [95% CI, 1.1%-2.2%]; hazard ratio [HR], 1.77 [95% CI, 1.43-2.19]; P < .001). Of the 6 prespecified secondary end points, none showed a statistically significant difference between groups, including in-hospital mortality (1.7% for uncemented fixation vs 2.0% for cemented fixation; HR, 0.94 [95% CI, 0.73-1.21]; P = .61) and overall mortality (cumulative incidence at 1 year after operation: 20.0% for uncemented fixation vs 22.8% for cemented fixation; HR, 0.95 [95% CI, 0.90-1.01]; P = .08).

CONCLUSIONS AND RELEVANCE

Among patients with hip fracture treated with hemiarthroplasty in a large US integrated health care system, uncemented fixation, compared with cemented fixation, was associated with a statistically significantly higher risk of aseptic revision. These findings suggest that US surgeons should consider cemented fixation in the hemiarthroplasty treatment of displaced femoral neck fractures in the absence of contraindications.

Drain Use is Associated with Increased Odds of Blood Transfusion in Total Shoulder Arthroplasty: A Population-Based Study

BACKGROUND

In the absence of evidence supporting its benefit, the American Academy of Orthopaedic Surgeons (AAOS) strongly recommends against closed wound drainage in TKA; however, drain usage remains common in other joints, including the shoulder. While an extensive body of research exists for drain use in lower extremity joint arthroplasty, large-scale data on drain use and its association with benefits and complications in shoulder arthroplasties is lacking. Such data may be particularly valuable given the rapidly increasing demand for shoulder arthroplasties.

QUESTION/PURPOSE

Using national claims data, we (1) evaluated the trends in frequency of drain usage in shoulder arthroplasty procedures over time, as well as the association between drain usage and (2) blood transfusion usage, (3) length of stay (LOS), and (4) readmission or early infection within 30 days.

METHODS

This retrospective study used data from the nationwide Premier Healthcare claims database (2006-2016; n = 105,116, including total, reverse, and partial shoulder arthroplasties, in which drains were used in 20% [20,886] and no drain was used in 80% [84,230]). Included hospitals were mainly concentrated in the South (approximately 40%) with equal distributions among the Northeast, West, and Midwest (approximately 20% each). The Premier database contains detailed inpatient billing data on approximately 20% to 25% of US hospital discharges, which allows the creation of a variable indicating drain use by evaluating inpatient billing for drains. Baseline demographics differed minimally between patients receiving a drain compared with those who did not, with a median age of 70 years in both groups. The potential for selection bias was addressed by adjusting for measured confounders in mixed-effects models that estimated associations between drain use and blood transfusion usage, LOS, and readmission or (early) infection within 30 days. In addition, alternative statistical approaches were applied to address confounding, including propensity score analysis and instrumental variable analysis where a so-called "instrumental variable" is applied that mimics the treatment assignment process similar to a randomized study. We report odds ratios (OR; or % change for continuous variables) and 95% confidence intervals (CIs).

RESULTS

The usage of drains decreased over time, from 1106 of 4503 (25%) in 2006 to 2278 of 14,501 (16%) in 2016. After adjusting for relevant covariates, drain use was associated with an increased usage of blood transfusions (OR, 1.49; 95% CI, 1.35-1.65; p < 0.001) while only associated with a small increase in LOS (+6%, 95% CI, +4% to +7%; p < 0.001). Drain use was not associated with increased odds for early postoperative infection or 30-day readmission. Propensity score analysis and instrumental variable analysis corroborated our main results.

CONCLUSIONS

Use of drains in patients undergoing shoulder arthroplasty is associated with an almost 50% increased odds for blood transfusions. Given that our findings parallel close to what is known in patients undergoing lower extremity joint arthroplasty, we believe that our results from a large national database are sufficient to discourage the routine use of drains in patients undergoing shoulder arthroplasty.

LEVEL OF EVIDENCE

Level III, therapeutic study.