One Year Later: The Lasting Effect of the COVID-19 Pandemic on Elective Hip and Knee Arthroplasty

The novel severe acute respiratory syndrome coronavirus 2 (COVID-19) pandemic has created an enormous strain on the global healthcare system and has affected orthopaedic services and surgeons around the world.1 In the United States, strong recommendations were put forth by the Centers for Medicare and Medicaid Services,2 the Surgeon General, and the American College of Surgeons3 to curtail elective procedures to prevent spread of the virus and to preserve the supply of personal protective equipment and ventilators.4-6 Although definitions of “elective” or “nonessential” surgery vary across guidelines and state mandates, almost all primary hip and knee arthroplasty procedures (total hip arthroplasty [THA] and total knee arthroplasty [TKA]) and most revision hip and knee arthroplasty procedures (revision total hip arthroplasty [rTHA] and revision total knee arthroplasty [rTKA]) fall within the nonessential definition.4,7 Given that hip and knee arthroplasty comprise a substantial share of the elective surgical volume in the United States,8 the moratorium on these procedures was challenging for patients, healthcare providers, and institutions conducting these procedures. It is thought that the elective, nonfracture arthroplasty procedures experienced the largest percentage decline in volumes of all elective orthopaedic procedures.9

A report on the effect of COVID-19 on the arthroplasty practice among Medicare fee-for-service patients in the last 2 weeks of March 2020 by Barnes et al8 showed a steep decline in arthroplasty volumes, increase in trends of home discharge, and a substantial revenue loss for hospitals and surgeons. There was an initial estimation, based on data from the American Joint Replacement Registry (AJRR), of weekly cancellations of approximately 30,000 primary and 3,000 rTHA and rTKA procedures in the United States because of the restriction imposed because of the pandemic.11 After the peak of the COVID-19 pandemic began to fall by the summer of 2020, there had been a gradual return of elective arthroplasty services.2 However, the constraints on the delivery of elective procedures continued to exist driven by the strict safety precautions that became necessary to conduct these surgeries.6 Studies from around the world reported on the total joint arthroplasty (TJA) practice changes caused by the pandemic through sharing of their personal experiences, cross-sectional studies, and expert recommendations. However, most of these studies were based on the initial effect of the COVID-19 pandemic and were published while the pandemic was ongoing and guidelines were still evolving.7,10 Limited data are available on the longitudinal effect of the pandemic on TJA in the United States.

The purpose of this study was to report and evaluate the effect of the COVID-19 pandemic on a THA and TKA practice one year later and evaluate patient characteristics, surgical trends, and 90-day adverse postoperative events of those who underwent THA and TKA procedures during this period. We also evaluated the financial effect from hip and knee arthroplasty case volume decline in a large musculoskeletal group on surgeons and their affiliated hospitals. We hypothesize that there would be a difference in patient characteristics and their adverse events, an expedited shift of surgical trends to outpatient, and a reduction in revenue for TJA in the year of the pandemic compared with the previous historical period.

Methods

Patients undergoing primary THA or TKA and rTHA or rTKA in our institution were identified from a prospectively maintained arthroplasty database. All procedures were done by one of 48 surgeons in hospitals located across three states in the Northeastern region of the United States (Pennsylvania, New Jersey, and New York). Tracking the trends of COVID-19 infection in the aforementioned states revealed an early spike in the number of newly reported cases between March and May 2020. This was followed by a relative decrease in the number of daily cases and hospitalizations over the months of June to October 2020, and as a result, elective procedures were resumed. Then, in November 2020, there was a second spike of COVID-19 cases and hospitalizations, which lasted all the way through February 2021, when vaccination was being implemented on a wider scale.11 We examined the effect of the pandemic year on TJA by comparing TJA cases conducted during the 1-year period from March 1, 2020, through February 28, 2021, (pandemic cohort) with a control group of patients operated during the same historical period of the previous year, March 1, 2019, through February 29, 2020 (prepandemic cohort). We calculated the changes in average monthly cases of primary THA and TKA as well as rTHA and rTKA during the pandemic period. Patients undergoing urgent procedures for fracture or an oncology indication were excluded from this study. We included all surgeons and hospitals that were part of the group throughout the entire period of this study. We evaluated the variation in age, sex, race, and medical comorbidities (using the Charlson Comorbidity Index [CCI]) of patients operated during and before the pandemic. We also compared outcomes such as hospital length of stay, outpatient facility, discharge disposition, and adverse postoperative events, including complications and readmissions within 90 days, between the groups. For the cost analysis, we tabulated the charges and collections of surgeons between the prepandemic and pandemic cohorts. A subgroup analysis was also conducted to evaluate the effect of the pandemic on a population of people operated at an age older than 65 years because they were expected to be the most vulnerable to obtain serious complications from COVID-19 infection. We compared the patient demographics, medical comorbidities, volume trends, and 90-day complications and readmissions of this group with those of the same age group operated before the pandemic.

Continuous data were presented as mean ± SD for parametric data, and categorical data were presented as percentage with the numerator and denominator in parentheses. An independent samples Student t-test was used for parametric data to calculate the P values. Chi square or Fisher exact tests were used for categorical data depending on the cell counts. Several subgroup analyses were performed to have a better understanding of certain trends in the data. Financial comparisons were also done to see how the intake of money changed from before COVID-19 to after COVID-19. All statistical analyses were conducted using R Studio (Version 3.6.3, Vienna, Austria). A P-value of < 0.05 was defined as statistically significant.

Results

We included a consecutive series of 26,493 primary and revision THA and TKA procedures. We found a 20.0% decline in the total volume of cases of primary and revision TJA procedures after the start of the pandemic in March 2020 (11,778 versus 14,715, P < 0.001). Primary TKAs and primary THAs account for the major decrease in case volume between both periods (10,641 versus 13,425, P = 0.014) (Figure 1) compared with revision procedures (Figure 2). In the prepandemic period, there was a range of 6.78% to 10.30% of procedure volume conducted per month (median: 8.11%). We noticed two striking periods related to the COVID-19 pandemic year. The first started in March 2020 and resulted in a notable drop in volume during March 2020 (6.17% versus 7.16%), April 2020 (0.31% versus 9.04%), and May 2020 (4.07% versus 8.11%) compared with the same months of 2019 (P < 0.001). However, an increase in the volume of primary and revision TJA was noted from June 2020 to November 2020 compared with the previous year. After this gradual improvement, the second hit occurred by December 2020 because of the surge of COVID-19 cases in our area; however, the effect was smaller compared with that in the beginning of the pandemic (Table 1).

F1Figure 1:

Graph showing the rates of monthly procedural volume of “primary total hip arthroplasty and total knee arthroplasty” from March 2019 to February 2021. The shaded areas demonstrate the effect of the first and second hits (waves) of the COVID-19 pandemic on the case volume.

F2Figure 2:

Graph showing the rates of monthly procedural volume of “revision total hip arthroplasty and total knee arthroplasty” from March 2019 to February 2021. The shaded areas demonstrate the effect of the first and second hits (waves) of the COVID-19 pandemic on the case volume.

Table 1 - Study Characteristics of Total Primary and Revision THA and TKA Including Monthly Procedure Volume, Age, Sex, Joint, LOS, Discharge Destination, Location of Surgery, 90-day Readmission, and 90-day Complication Rates Variable Primary THA and TKA rTHA and rTKA Prepandemic Pandemic P Prepandemic Pandemic P Total number 13,425 (100%) 10,641 (100%) <0.001* 1,290 (100%) 1,137 (100%) <0.001* Months  January 1,387 (10.3%) 861 (8.09%) 118 (9.15%) 87 (7.65%)  February 1,228 (9.15%) 900 (8.46%) 116 (8.99%) 115 (10.1%)  March 962 (7.17%) 637 (5.99%) 92 (7.13%) 90 (7.92%)  April 1,199 (8.93%) 8 (0.08%) 131 (10.2%) 27 (2.37%)  May 1,100 (8.19%) 424 (3.98%) 94 (7.29%) 55 (4.84%)  June 1,059 (7.89%) 1,228 (11.5%) 105 (8.14%) 109 (9.59%)  July 1,036 (7.72%) 1,126 (10.6%) 96 (7.44%) 119 (10.5%)  August 910 (6.78%) 1,065 (10.0%) 103 (7.98%) 116 (10.2%)  September 1,054 (7.85%) 1,157 (10.9%) 105 (8.14%) 106 (9.32%)  October 1,256 (9.36%) 1,211 (11.4%) 103 (7.98%) 136 (12.0%)  November 1,071 (7.98%) 1,142 (10.7%) 112 (8.68%) 90 (7.92%)  December 1,163 (8.66%) 882 (8.29%) 115 (8.91%) 87 (7.65%) Age 66.7 (9.85) 65.9 (9.54) <0.001* 68.2 (10.0) 68.4 (10.5) 0.772 Sex <0.001* 0.830  Female 7,692 (57.3%) 5,731 (53.9%) 682 (52.9%) 607 (53.4%)  Male 5,733 (42.7%) 4,910 (46.1%) 608 (47.1%) 530 (46.6%) Joint <0.001* 0.455  Hip 5,627 (41.9%) 4,745 (44.6%) 581 (45.0%) 494 (43.4%)  Knee 7,798 (58.1%) 5,896 (55.4%) 709 (55.0%) 643 (56.6%) Days of hospital stay (SD) 1.56 (1.56) 1.49 (1.18) 0.050 3.63 (3.26) 2.98 (2.52) 0.035* Discharge destination <0.001* <0.001*  Home 7,094 (91.6%) 2,273 (98.2%) 229 (80.4%) 167 (92.8%)  Inpatient/Rehab 648 (8.37%) 42 (1.81%) 56 (19.6%) 13 (7.22%) Location <0.001* <0.001*  Inpatient 12,328 (91.8%) 8,220 (77.3%) 1,278 (99.1%) 1,095 (96.3%)  Outpatient + ambulatory 1,096 (8.16%) 2,412 (22.7%) 11 (0.85%) 42 (3.69%) Readmission 159 (1.18%) 149 (1.40%) 0.155 0 (0.00%) 0 (0.00%) Complication 344 (2.56%) 222 (2.09%) 0.017* 0 (0.00%) 1 (0.09%) 0.468

*Statistically significant (p < 0.05).

rTHA = revision total hip arthroplasty, rTKA = revision total knee arthroplasty, THA = total hip arthroplasty, TKA = total knee arthroplasty

The average age of patients operated for primary THA and TKA during the pandemic year was lower than that before the pandemic (65.9 ± 9.54 years versus 66.7 ± 9.85 years, P < 0.001). Regarding medical comorbidities, age-adjusted CCI scores were similar among patients undergoing primary and revision TJA before and after the pandemic (Table 1). No notable difference was observed in the rates of 90-day readmissions before and during the pandemic year, regardless of the conducted procedure. However, the percentage of 90-day complications were significantly lower during the pandemic year (2.09% versus 2.56%, P = 0.017). There was a significant decline in the hospital length of stay (LOS) after primary THA and TKA cases in the pandemic group, decreasing from 1.70 ± 1.79 days to 1.58 ± 1.35 days (P = 0.007). LOS was also reduced after revision cases from 3.63 (±3.26) days to 2.98 (±2.52) days (P = 0.035) during the pandemic. The percentage of procedures conducted in an outpatient setting was significantly higher in the pandemic group (21% versus 7.5%, P < 0.001). There was also a higher percentage of cases being discharged home during the pandemic, rising from 91.6% to 98.2% of primary THAs and primary TKAs (P < 0.001) and from 80.4% to 92.8% of rTHAs and rTKAs (P < 0.001).

In the older-than-65-years cohort, we found a 26% drop in the volume of primary THAs and TKAs (5,606 versus 7,567 cases, P < 0.001) during the pandemic. More volume drop was seen among women (30.0% versus 19.1%, P < 0.001) compared with men. This older pandemic group was relatively healthier with a lower age-adjusted CCI score (4.07 ± 1.19 versus 4.20 ± 1.19, P = 0.006) than their prepandemic counterparts. This group had shorter LOS (1.56 ± 2.03 versus 1.71 ± 1.06, P = 0.014), more home discharges (97.1% versus 87.4%, P < 0.001), and more outpatient procedures (18.6% versus 6.65%, P < 0.001). There were similar 90-day complications (2.97% versus 2.64%, P = 0.277) and 90-day readmissions (1.61% versus 1.57%, P = 0.903) among the prepandemic and pandemic cohorts (Table 2).

Table 2 - Study Parameters of Primary and Revision Total Hip Arthroplasty and Total Knee Arthroplasty Above 65 Years of Age Including Sex, LOS, Discharge Destination, Location of Surgery, 90-day Readmission, and 90-day Complication Rates Cohort Prepandemic
N = 7,567 Pandemic
N = 5,606 P n (%) n (%) Sex <0.001*  Female 4,699 (62.1%) 3,286 (58.6%)  Male 2,868 (37.9%) 2,320 (41.4%) Days of hospital stay (SD) 1.71 (2.03) 1.56 (1.06) 0.014* Discharge destination <0.001*  Home 3,751 (87.4%) 1,137 (97.1%)  Inpatient/Rehab 540 (12.6%) 34 (2.90%) Location <0.001*  Inpatient 7,064 (93.4%) 4,560 (81.4%)  Outpatient + ambulatory 503 (6.65%) 1,041 (18.6%) Readmission 122 (1.61%) 88 (1.57%) 0.903 Complication 225 (2.97%) 148 (2.64%) 0.277

*Statistically significant (p < 0.05).

There was a 17.6% decrease in total surgeons' charges with an estimated loss of $24.4 million during the pandemic year. The average monthly charges for surgeons declined from $2,931,425 (SD = 1,776,755) to $2,397,207 (SD = 1,578,288) (P = 0.010). In addition, total surgeon payments declined by 16.3%, with an estimated loss of $9.7 million, from an average monthly amount of $1,261,086 (SD = 811,024.10) in the prepandemic period to $1,046,373 (SD = 717,910.60) in the pandemic year (P = 0.017). There was significant decrease in average monthly charges of hospitals located in Pennsylvania from $14,330,835 (SD = 5,640,108) in the prepandemic period to $11,305,530 (SD = 5,103,593) during the pandemic year (P = 0.005). In addition, the monthly hospital reimbursement declined from an average of $6,136,772 (SD = 2,471,386) in the prepandemic period to $4,855,621(SD = 2,243,857) in the pandemic year (P = 0.005). No significant differences were found in charges (P = 0.613) or payment (P = 0.696) in the affiliated hospitals located in New Jersey and New York between the two periods (Table 3).

Table 3 - Cost Data: Charges and Payments of Surgeons and Hospitals Variable Prepandemic
USD Cost (SD) Pandemic
USD Cost (SD) P Difference
USD Cost (SD) Surgeons  Charges 2,931,425 (1,776,755) 2,397,207 (1,578,288) 0.010* −534,217.50 (1,338,913)  Payment 1,261,086 (811,024.10) 1,046,373 (717,910.60) 0.017* −214,713.30 (582,859) Hospitals in PA  Charges 14,330,835 (5,640,108) 11,305,530 (5,103,593) 0.005* −3,025,305 (1,541,353)  Payment 6,136,772 (2,471,386) 4,855,621 (2,243,857) 0.005* −1,281,151 (651,640) Hospitals in NY/NJ  Charges 8,715,862 (6,428,287) 7,676,479 (3,978,710) 0.613 −1,039,384 (4,718,384)  Payment 3,756,251 (2,535,475) 3,428,426 (1,724,613) 0.696 −327,825 (1,937,911)

*Statistically significant (p < 0.05).

USD = US dollars


Discussion

In this study, we analyzed the extended effect of the COVID-19 pandemic on elective TJA by comparing the year after the start of the pandemic with the trends of the precedent year. Initial reductions of elective service allowed conservation of personal protective equipment, reduction of unnecessary hospital traffic, and preservation of staffing to afford deployment to COVID-19 wards.10 Reduction in elective hospital admissions also vacated hospital beds and equipment (including ventilators) for the care of COVID-19 patients.12 Patients may have delayed or opted not to have joint arthoplasty procedures for a number of reasons including fear of obtaining the COVID-19 viral infection and mindful consideration for an overwhelmed health system and healthcare workers. Another explanation is the financial constraints caused by the pandemic with a sizable share of the population becoming unemployed or underemployed, which influenced their ability to rely on private insurance to undergo elective arthroplasty procedures. Surgeons' thresholds for recommending elective surgeries during the pandemic may have become more stringent because they may not have wanted to expose this older, more at-risk population to a hospital stay and risk of contracting the virus.13 There was a greater decrease in the rates of primary TKA compared with primary THA. One possible explanation might be the fact that patients experience a higher severity of symptoms and more debilitation with arthritic hips.14 Notably, the decline in the volume of revision arthroplasty was less drastic than that of primary cases. This may be because many of these surgeries were justifiably considered essential, such as prosthetic joint infection or recurrent hip dislocation, with additional delay placing the patient at risk for increased morbidity.10

A notable backlog of cancelled arthroplasty procedures caused a significant rise in cases conducted from June 2020 through November 2020. The volume of recovery was faster than what was estimated by Jain et al who expected that it would take approximately 7 to 16 months until the healthcare systems would be able to revert to a 90% prepandemic expected volume.15 However, our findings may not be generalizable because the ability for healthcare systems to accommodate an increase in elective surgery volume vary by region, institutional capacity, and resource availability.

The results of this study demonstrated a notable shift toward outpatient surgeries for both primary and revision TJA without a notable increase in short-term complications. Outpatient arthroplasty has proved to be safe with favorable outcomes and cost-saving metrics for selected patients.15-17 The pandemic accelerated previous trends in TJA practice toward patient risk stratification to mitigate potential complications while allowing for the appropriate allocation of perioperative resources.18 Although the pandemic can partially explain the shift toward outpatient-based surgery, the substantial improvement in the surgical, medical, and anesthetic innovations of delivery of primary THAs and TKAs has made this transition safer and smoother.19 LOS after arthroplasty has dramatically reduced in the recent few years, especially with the introduction of fast-track pathways and improved perioperative pain management strategies.20 Our findings are consistent with the historical data from the AJRR, which demonstrate a steady increase in outpatient TJA surgeries and a tendency toward reduced LOS after TJA. The AJRR 2021 report21 showed that the volume of TJAs done in outpatient settings, such as ambulatory surgical centers, increased by 82% in 2020 compared with the previous year. In addition, when looking at the AJRR data from 2012 to 2020, the average LOS markedly decreased for both primary elective THA (2.7 days versus 1.8) and primary elective TKA (2.3 days versus 0.8). These trends are further driven by other considerations such as the removal of THA and TKA from the Centers for Medicare and Medicaid Services inpatient-only list and their authorization as qualified procedures for ambulatory surgery centers.22,23

Before the pandemic, there was a shift away from discharging patients to rehabilitation facilities and skilled nursing facilities after TJA procedures.24 This process was presumably expedited during the pandemic with a notable increase in home discharges compared with the prepandemic period, which reflected the desire to avoid skilled nursing facilities to prevent contracting COVID-19 viral infection. Similar shifts in TJA practice were observed in our subanalysis, which included patients older than 65 years, and there was no increase in short-term readmissions or complications. It was noticed that elderly patients who underwent surgery during the COVID-19 pandemic were relatively healthier compared with those operated on before the pandemic. Elderly patients with severe comorbidities might have self-selected out of surgery to avoid contracting the virus. In addition, it is likely that restrictions imposed resulted in less consistent office visits to avoid exposure, which might have led to underreporting of minor complications. Risk stratification remains critical when electing elderly patients to an expedited practice approach of TJA.

Financial viability is an important component of any healthcare system to be able to meet the needs of its patient population. In our study, the fiscal ramifications of the COVID-19 pandemic on both surgeons and hospitals because of the notable case volume decrease were profound. Our practice was affected not only by the lost revenue from cancelled procedures but also by the increased burden of rescheduling primary and revision TJA surgeries. The overall revenue losses to this group of surgeons from decreased operational capacities during the pandemic year have been estimated at $24.4 million in charges and $9.7 million in payments. This may be viewed similarly to the economic downturn during 2008 and 2009, when 30% of the American Association of Hip and Knee Surgeons (AAHKS) surgeons reported a surgical volume decrease.25 It is crucial to understand the financial effect of the pandemic to assess the magnitude of the loss, which is important for developing future budgets.7,26 Multiple studies reported notable financial and career consequences for arthroplasty surgeons during the pandemic.27,28 However, these studies reported the financial effect at the early period of the pandemic. This study reported the yearlong economic implications of the pandemic on a large group of arthroplasty surgeons and hospitals. Importantly, the notable variation in arthroplasty case volume creates enormous challenges for arthroplasty practices and institutions when trying to budget and determine staffing needs.

Limitations of this study include its retrospective nature, although all data were prospectively collected. Second, the assumption that the effects seen were related directly to COVID-19 when there are confounding factors to changes in clinical practice during this time to include the shift toward outpatient status and the ambulatory surgery center for arthroplasty that have trended before the pandemic. Furthermore, despite covering over 26,000 patient episodes in our study, it was limited by data capture from healthcare systems in a specific geographic region (Northeast United States), which might have different burden and effect of COVID-19 including backlog of cases and the exacerbation of healthcare disparities. Thus, conclusions might not be generalizable to all regions given the varying burden and effect of the pandemic. Nevertheless, to the best of our knowledge, this is the first quantitative study of the effect of the COVID-19 pandemic on hip and knee arthroplasty services over the year after the start of the pandemic. It is imperative that decisions made by administrators and hospital leadership be backed by clinical data to provide realistic projections and to better mold the deployment of staffing and resources. Decisions based on clinical data could avoid overestimating the effectiveness of emergency measures and jeopardizing the provision of healthcare services in future pandemic situations.

Conclusions

The results of this study highlight the profound effect that the COVID-19 pandemic had on the hip and knee arthroplasty volume, especially among patients older than 65 years. Weariness of the virus likely led to the shift of TJA patients to outpatient facilities, reduction of the LOS, and increased rates of home discharge, which was shown to be safe, even in an older population more vulnerable to COVID-19. These changes are foreseen to be long-lasting. Major financial losses occurred for the healthcare system and might have had profound effects on our patients who had to have their surgery postponed or cancelled. To maintain high-quality arthroplasty care, additional federal aids to hospitals and surgical practices may be required.

References

References printed in bold type are those published within the past 5 years.

1. WHO Characterizes COVID-19 as a Pandemic—PAHO/WHO. Pan American Health Organization. Available at: https://www.paho.org/en/news/11-3-2020-who-characterizes-covid-19-pandemic. Accessed January 26, 2021. 2. CMS Releases Recommendations on Adult Elective Surgeries, Non-Essential Medical, Surgical, and Dental Procedures During COVID-19 Response. CMS. Available at: https://www.cms.gov/newsroom/press-releases/cms-releases-recommendations-adult-elective-surgeries-non-essential-medical-surgical-and-dental. Accessed February 7, 2021. 3. Clinical Issues and Guidance. American College of Surgeons. Available at: https://www.facs.org/covid-19/clinical-guidance. Accessed January 26, 2021. 4. State Guidance on Elective Surgeries. Available at: https://www.ascassociation.org/covid-19-state. Accessed February 7, 2021. 5. Chen AZ, Shen TS, Bovonratwet P, Pain KJ, Murphy AI, Su EP: Total joint arthroplasty during the COVID-19 pandemic: A scoping review with implications for future practice. Arthroplast Today 2021;8:15-23. 6. Healthcare Cost and Utilization Project (HCUP). Available at: http://www.ahrq.gov/data/hcup/index.html. Accessed February 7, 2021. 7. O'Connor CM, Anoushiravani AA, DiCaprio MR, Healy WL, Iorio R: Economic recovery after the COVID-19 pandemic: Resuming elective orthopedic surgery and total joint arthroplasty. J Arthroplasty 2020;35:S32-S36. 8. Barnes CL, Zhang X, Stronach BM, Haas DA: The initial impact of COVID-19 on total hip and knee arthroplasty. J Arthroplasty 2021;36:S56-S61. 9. Bedard NA, Elkins JM, Brown TS: Effect of COVID-19 on hip and knee arthroplasty surgical volume in the United States. J Arthroplasty 2020;35:S45-S48. 10. Parvizi J, Gehrke T, Krueger CA, et al.: Resuming elective orthopaedic surgery during the COVID-19 pandemic: Guidelines developed by the International Consensus Group (ICM). J Bone Joint Surg Am 2020;102:1205-1212. 11. United States COVID-19 Cases and Deaths by State over Time|Data. Centers for Disease Control and Prevention. Available at: https://data.cdc.gov/Case-Surveillance/United-States-COVID-19-Cases-and-Deaths-by-State-o/9mfq-cb36. Accessed February 7, 2021. 12. Dillon MT, Chan PH, Prentice HA, et al.: The effect of a statewide COVID-19 shelter-in-place order on shoulder arthroplasty for proximal humerus fracture volume and length of stay. Semin Arthroplasty 2021;31:339-345.

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