Orthopedics

Feature Article 

The July Effect for Total Joint Arthroplasty Procedures

Zachary A. Rockov, MD; David A. Etzioni, MD; Adam J. Schwartz, MD, MBA

Abstract

The “July effect” refers to the assumed increased risk of complications during the months when medical school graduates transition to residency programs. The actual existence of a July effect is controversial. With this study, the authors sought to determine whether evidence exists for the presence of a July effect among total joint arthroplasty (TJA) procedures. The 2013 and 2014 Nationwide Readmission Databases were combined and all index primary and revision arthroplasty procedures were identified, and then patients from December were excluded. Thirty-day readmission rates, time to readmission, and readmission costs were analyzed by index procedure month and index procedure type. A total of 1,193,034 procedures (index primary: n=1,107,657; revision arthroplasty: n=85,377) were identified. Among all procedure types, 46,674 (3.9%) 30-day readmissions were observed. Among all procedures, an index procedure with a discharge in July resulted in the highest monthly readmission rate of the year (4.2%), which was significantly higher than the mean annual readmission rate (P<.0001). This effect was most pronounced for primary total knee arthroplasty (3.9% vs 3.6%, P<.0001). When stratifying results into teaching vs nonteaching hospitals, the highest readmission rate occurred if the index procedure occurred at a nonteaching hospital in July (4.5%, P<.0001). These data provide evidence that a July effect appears to exist for TJA procedures and is most pronounced at nonteaching institutions. Based on published mean readmission costs, the total annualized cost variation attributable to the higher readmission rate for primary TJA procedures in July is approximately $18.6 million. [Orthopedics. 2020;43(6):e543–e548.]

Abstract

The “July effect” refers to the assumed increased risk of complications during the months when medical school graduates transition to residency programs. The actual existence of a July effect is controversial. With this study, the authors sought to determine whether evidence exists for the presence of a July effect among total joint arthroplasty (TJA) procedures. The 2013 and 2014 Nationwide Readmission Databases were combined and all index primary and revision arthroplasty procedures were identified, and then patients from December were excluded. Thirty-day readmission rates, time to readmission, and readmission costs were analyzed by index procedure month and index procedure type. A total of 1,193,034 procedures (index primary: n=1,107,657; revision arthroplasty: n=85,377) were identified. Among all procedure types, 46,674 (3.9%) 30-day readmissions were observed. Among all procedures, an index procedure with a discharge in July resulted in the highest monthly readmission rate of the year (4.2%), which was significantly higher than the mean annual readmission rate (P<.0001). This effect was most pronounced for primary total knee arthroplasty (3.9% vs 3.6%, P<.0001). When stratifying results into teaching vs nonteaching hospitals, the highest readmission rate occurred if the index procedure occurred at a nonteaching hospital in July (4.5%, P<.0001). These data provide evidence that a July effect appears to exist for TJA procedures and is most pronounced at nonteaching institutions. Based on published mean readmission costs, the total annualized cost variation attributable to the higher readmission rate for primary TJA procedures in July is approximately $18.6 million. [Orthopedics. 2020;43(6):e543–e548.]

Total hip arthroplasties (THAs) and total knee arthroplasties (TKAs) are successful procedures, and a large proportion of patients who elect to have these procedures are satisfied with their outcomes.1 As the patient population in the United States continues to age, the demand for TKA and THA can be expected to increase.2 Despite the typically successful outcomes of total joint arthroplasty (TJA) procedures, complications and read-missions after TKA and THA can be disastrous for the patient, the provider, and the entire health care system. Although medical diagnoses represent a large proportion of readmissions following TJA, the most common reasons for readmission within 30 days of surgery are typically procedure related, most notably infection and dislocation.3

The “July effect” refers to the assumed increased risk of complications during July, when medical school graduates within the United States transition to residency programs. The actual existence of a July effect is controversial in the literature, both in orthopedics as well as other medical specialties.4–19 Several studies have reported an increased risk of medical errors, patient morbidity, and patient mortality in the months of July and August when residents are transitioning into their new roles for the year.4,9,10,15,17,20,21

Although these findings do not point to causation, they do show that the beginning of the academic year for residents within academic institutions can be a burden to patient care.4,9,10,15,17,20,21 Conversely, several studies have reported no evidence of a July effect and that the time of the year does not affect patient care outcomes.6,7,12–14,22–24 There is limited evidence of increased surgical time, complications, and cost in teaching hospitals vs nonteaching hospitals,24–26 but the current authors are unaware of any prior studies examining the role of teaching hospital status and the July effect for TJA procedures.

In the current study, the authors sought to determine whether evidence exists for the presence of a July effect among TJA procedures. They hypothesized that 30-day readmission rates following primary and revision THA and TKA would be higher for procedures in July compared with other months of the year. The specific aims of the study were to (1) determine whether readmission rates for TKA and THA are higher in certain months of the year; (2) evaluate the added cost of readmissions in months that have higher readmission rates; and (3) evaluate the re-admission rates at teaching vs nonteaching hospitals to assess the presence of a July effect in both facilities.

Materials and Methods

To investigate whether evidence exists for a July effect among TJA procedures, the authors used a large nationwide administrative claims-based database. The Nationwide Readmission Database (NRD) is part of the Healthcare Costs and Utilization Project. The NRD is created using the State Inpatient Database, with data obtained from 22 states, representing 51.2% of the total US resident population and 49.3% of all US hospitalizations. Unweighted, the NRD contains data from approximately 15 million discharges from US health care institutions per year; weighted, this number is approximately 35 million.27

All index primary and revision arthroplasty procedures were identified using the 2013 and 2014 NRD databases during a 22-month period using International Classification of Diseases, 9th Revision procedure codes 81.51 (primary THA), 81.54 (primary TKA), 00.70 (revision THA, both components), 00.71 (revision THA, acetabular component), 00.72 (revision THA, femoral component), 00.73 (revision THA, head and liner), 81.53 (revision THA, not otherwise specified), 00.80 (revision TKA, all components), 00.81 (revision TKA, tibial component), 00.82 (revision TKA, femoral component), 00.84 (revision TKA, tibial insert), and 81.55 (revision TKA, not otherwise specified). Cases were excluded if length of stay or admission day was missing, if the patient was younger than 18 years, if the patient died on the index admission, or if the patient was discharged in December (because the NRD does not capture read-missions across calendar years).

Readmissions for any reason within 30 days were identified, and outcome data for the first readmission were merged back to the original NRD data set to allow for analysis of readmission data by the index admission discharge month. In addition to the presence or absence of readmission for each index procedure, outcome data included index and readmissions costs (calculated from charges using the NRD hospital cost-to-charge ratio file), index and readmission length of stay, and days to readmission. A working data set including only those cases with an index arthroplasty procedure (using the International Classification of Diseases, 9th Revision procedure codes listed above) was created from the full merged NRD data set.

Statistical Analysis

Descriptive statistics were determined from the full data set. Patient sex, age, procedure type, index and readmission length of stay, overall hospital costs, primary payer type, and hospital type were determined. The groups were compared using the Student's t test for continuous, normally distributed variables, and the chi-square test for categorical variables.

A weighted bivariate logistic regression model was created using readmission as the dependent variable and discharge month as the predictor variable. The chi-square test was used to compare proportions across all months and, in the case of significant differences in proportions, was followed with an analysis of means for proportions to compare each month's specific readmission rate to the overall mean, with an alpha set to 0.05. Modeling was performed for all patients and then controlled for hospital type (teaching vs non-teaching), as well as procedure type (primary vs revision, and revision subtype).

Mean annualized cost of readmission for primary TKA and THA to the US health care system was determined by multiplying the mean readmission rate by the annualized incidence of primary hip and knee replacement, and then multiplying this number by the average cost for a single readmission as previously reported in the literature.28 This cost was then subtracted from the month-specific annualized readmission cost to determine the annualized additional (lower) cost due to excessive (reduced) readmission rates. Statistical analysis was performed using SAS and JMP Pro, version 14.1 (SAS Institute, Cary, North Carolina).

Results

A total of 1,193,034 index primary (1,107,657) and revision (85,377) arthroplasty procedures were identified (Table 1). Among all procedure types, 46,674 (3.9%) 30-day readmissions were observed. Among all procedures, an index procedure associated with a discharge in July resulted in the highest monthly read-mission rate of the year (4.2%), which was significantly higher than the mean annual readmission rate (P<.0001; Figure 1). The weighted readmission frequency and rate by primary procedure type and month were determined. For primary THA, a total of 275,255 procedures had 10,668 total 30-day readmissions. The highest 30-day readmission months for primary THA were associated with an index procedure occurring in July (4.1%) and September (4.1%), but were not significantly higher than the mean annual readmission rate. For primary TKA there were a total of 832,402 procedures with 30,173 total 30-day readmissions. The highest 30-day re-admission months for primary TKA were associated with an index procedure occurring in July (3.9%) and August (3.9%), which were significantly higher than the mean annual readmission rate (P<.05).

Weighted Readmission Frequency and Rate by Month

Table 1:

Weighted Readmission Frequency and Rate by Month

Monthly readmission rates for all primary total hip and knee arthroplasty procedures from 2013 to 2014. Shaded area represents 95% confidence interval (CI). Horizontal line represents mean readmission rate. Red dots indicate a statistical outlier (alpha less than 0.05); green dots fall within the expected decision limits, and are not statistically different from the overall proportion.

Figure 1:

Monthly readmission rates for all primary total hip and knee arthroplasty procedures from 2013 to 2014. Shaded area represents 95% confidence interval (CI). Horizontal line represents mean readmission rate. Red dots indicate a statistical outlier (alpha less than 0.05); green dots fall within the expected decision limits, and are not statistically different from the overall proportion.

The annualized monthly cost variation was also calculated for procedure type and month based on weighted readmission frequency and rate (Table 2). The annualized cost variation for each month was greatest in July for both THAs and TKAs. The annualized cost variation was $4,907,223.61 for THAs in July and $13,695,963.76 for TKAs in July. In July alone, this number equated to a total of $18,603,187.37 in additional costs.

Weighted Readmission Frequency and Rate by Procedure Type and Month, Along With Calculated Annualized Monthly Cost Variationa

Table 2:

Weighted Readmission Frequency and Rate by Procedure Type and Month, Along With Calculated Annualized Monthly Cost Variation

When controlling for teaching hospital status, the highest readmission rate occurred if the index procedure occurred at a teaching hospital in May (4.1%, P<.0001; Figure 2) and at a nonteaching hospital in July (4.5%, P<.0001; Figure 3).

Monthly readmission rates for all primary total hip and knee arthroplasty procedures performed at teaching institutions from 2013 to 2014. Shaded area represents 95% confidence interval (CI). Horizontal line represents mean readmission rate. Red dots indicate a statistical outlier (alpha less than 0.05); green dots fall within the expected decision limits, and are not statistically different from the overall proportion.

Figure 2:

Monthly readmission rates for all primary total hip and knee arthroplasty procedures performed at teaching institutions from 2013 to 2014. Shaded area represents 95% confidence interval (CI). Horizontal line represents mean readmission rate. Red dots indicate a statistical outlier (alpha less than 0.05); green dots fall within the expected decision limits, and are not statistically different from the overall proportion.

Monthly readmission rates for all primary total hip and knee arthroplasty procedures performed at nonteaching institutions from 2013 to 2014. Shaded area represents 95% confidence interval (CI). Horizontal line represents mean read-mission rate. Red dots indicate a statistical outlier (alpha less than 0.05); green dots fall within the expected decision limits, and are not statistically different from the overall proportion.

Figure 3:

Monthly readmission rates for all primary total hip and knee arthroplasty procedures performed at nonteaching institutions from 2013 to 2014. Shaded area represents 95% confidence interval (CI). Horizontal line represents mean read-mission rate. Red dots indicate a statistical outlier (alpha less than 0.05); green dots fall within the expected decision limits, and are not statistically different from the overall proportion.

Discussion

The July effect refers to the assumed increase in complication rates during July, when medical students are transitioning to residency programs within the United States and are assuming new roles and responsibilities as they advance in their training. The presence of the July effect across several subspecialties has been described, and its effects and existence have been debated.4–19 The current study is the first to provide evidence of a July effect for TKA and THA procedures, which equates to an estimated $18.6 million annually in additional cost to the health care system during July. Unique to this study is the finding that this effect seems to be predominantly driven by hospitals designated as nonteaching. Conversely, teaching institutions appear to have a statistically average readmission rate in July, which gradually decreases throughout the year and reaches its nadir in January, but then increases precipitously until it reaches its peak in May. This “May effect” has not previously been described.

The orthopedic and nonorthopedic literature demonstrate contradicting evidence regarding the July effect.6,12–17,21,23,24,26,29 A pediatric trainee study by Shah et al5 described an increase in reported medical errors in a teaching hospital during July, but no increase in adverse patient outcomes due to those errors. Similarly, Inaba et al10 showed an increase in reported errors at the beginning of the academic year, but they did not impact mortality.

The medical literature has shown increased mortality, fatal medication errors, longer length of stay, and increased costs in teaching hospitals in July.4,20,30 One study by Varma et al31 in the gynecologic literature examined 30-day readmission rates, similar to the current study, but did not find an increase in readmissions in July.

In the orthopedic literature, Bohl et al6 reviewed more than 21,000 THAs and TKAs using the National Surgical Quality Improvement Program (NSQIP) database and were unable to find evidence for a July effect. Unlike the data source used in the current study, the NSQIP does not provide institutional data or teaching hospital status, which could explain the discrepancy between their findings and the current findings. Conversely, Anderson et al,15 using the National Inpatient Sample, studied elderly patients with hip fractures and demonstrated a 12% greater relative risk of mortality among elderly patients with hip fractures in July and August.

Although several studies have debated the existence of a July effect among teaching hospitals, this is the first study to find a higher 30-day readmission rate at a nonteaching hospital if the index procedure occurred in July. Shah et al5 argued that teaching hospitals have an increase in reported medical errors in July, but an absence of increased adverse events due to hypervigilance of the staff to the new medical trainees. This may explain the protective effect seen in the current study among teaching hospitals that may be absent in July in nonteaching hospitals. Nonteaching hospitals experience work-force turnover during summer months, as do teaching institutions, because residents, fellows, and other professional graduates are transitioning to new roles and responsibilities.

Documentation provided by Healthcare Costs and Utilization Project defines a teaching hospital as one with one or more Accreditation Council for Graduate Medical Education (ACGME)–approved residency programs, one that is a member of the Council of Teaching Hospitals (COTH), or one that has a ratio of full-time equivalent interns and residents to beds of 0.25 or higher.27 With this limited definition, it is reasonable to assume that even nonteaching hospitals will accommodate a large number of new and transitioning residents and other trainees. Perhaps the lack of heightened awareness of “senior” staff over the trainees creates potential for increased errors in July.

Although a heightened awareness of the ancillary and senior staff in July helps to explain the lack of a July effect in teaching hospitals, it does not account for the increase in admissions given an index procedure occurring in May at these institutions. The authors hypothesize that there is a paradoxical decrease in vigilance at the end of the year with a concomitant decrease in resident attention to detail as other important deadlines approach and confidence in their training is at its peak. Upper-level residents in particular could be shifting their attention to board examinations, fellowship training, and job searches. In addition, there is the possibility of intensifying feelings of burnout for residents of all years as the academic year progresses. This hypothesis is further strengthened by the shape of the monthly readmission rates, which slowly decrease, reaching a nadir in January, and then increasing rapidly again over the following months as the academic year comes to an end.

There are notable limitations to this study. This study used administrative claims–based data that contains a large amount of retrospectively collected information dependent on the accuracy of coding. If coding is inaccurate, this would undermine the statistical analysis and conclusions of the study. Another limitation is that these data do not contain information related to resident involvement in each particular case. Because participation level will vary across institutions, attending physicians, residents, and cases, it is difficult to generalize the findings of this study to each individual teaching or non-teaching institution.

Conclusion

This study provides evidence that a July effect appears to exist for TJA procedures, particularly when the index procedure occurs at a nonteaching institution, resulting in a significant cost burden to the health care system. In addition, a separate but related May effect appears to exist at teaching institutions, a finding that has never been previously reported, to the authors' knowledge. Future research is needed to determine the causes of and possible solutions to these costly problems.

References

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Weighted Readmission Frequency and Rate by Month

MonthOverall (N=1,193,034)

Frequency%
January38023.6
February39853.9
March41073.9
April39974.0
May43054.0
Junea43664.0
Julya42984.2b
Augusta44794.1b
September40974.0
October47343.7
November45053.7
Total46,674c3.9

Weighted Readmission Frequency and Rate by Procedure Type and Month, Along With Calculated Annualized Monthly Cost Variationa

MonthPrimary THA (n=275,255)Primary TKA (n=832,402)Combined Annualized Cost Variation


Frequency%THA Annualized Cost VariationFrequency%TKA Annualized Cost Variation
January8723.7−$3,843,132.8424423.3−$16,165,625.59−$20,008,758.42
February8633.7−$3,843,132.8425983.6−$1,234,830.91−$5,077,963.75
March9233.9$532,045.3926823.7$3,742,100.65$4,274,146.03
April8973.9$532,045.3925393.7$3,742,100.65$4,274,146.03
May10204.0$2,719,634.5027943.7$3,742,100.65$6,461,735.15
Juneb10194.0$2,719,634.5027663.6−$1,234,830.91$1,484,803.59
Julyb10004.1$4,907,223.612736c3.9c$13,695,963.76c$18,603,187.37
Augustb10103.8−$1,655,543.722944c3.9c$13,695,963.76c$12,040,420.04
September9614.1$4,907,223.6126403.7$3,742,100.65$8,649,324.26
October10723.8−$1,655,543.7230973.5−$6,211,762.47−$7,867,306.19
November10303.6−$6,030,721.9529353.4−$11,188,694.03−$17,219,415.98
Total10,668d3.9NA30,1733.6−$1,234,830.91NA
Authors

The authors are from the University of Arizona College of Medicine (ZAR), Tucson, and the Department of Colon and Rectal Surgery (DAE) and the Department of Orthopaedic Surgery (AJS), Mayo Clinic Arizona, Phoenix, Arizona.

The authors have no relevant financial relationships to disclose.

This research was made possible in part by the Mayo Clinic Robert D. and Patricia E. Kern Center for the Science of Health Care Delivery, United States.

Correspondence should be addressed to: Adam J. Schwartz, MD, MBA, Department of Orthopaedic Surgery, Mayo Clinic Arizona, 5777 E Mayo Blvd, Phoenix, AZ 85054 ( schwartz.adam@mayo.edu).

Received: April 29, 2019
Accepted: September 24, 2019
Posted Online: August 20, 2020

10.3928/01477447-20200812-08

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