Conversion THA With Concomitant Removal of Orthopaedic Hardware Should Be Reclassified as a Revision Surgery in the Medicare Severity Diagnosis-Related Group Coding Scheme: An Analysis of Cost and Resource Use
Authors: Blackburn Collin W. , Chen Kallie J. , Du Jerry Y. , Marcus Randall E. 
Published: October 2023

Abstract

Background
Conversion THA, which we defined for this study as THA with concomitant removal of preexisting orthopaedic hardware, has been associated with increased hospital costs and perioperative complications compared with primary THA. Yet, conversion THA is classified as a primary procedure under the Medicare Severity Diagnosis-Related Group coding scheme, and hospitals are reimbursed based on the resource use expected for a routine primary surgery. Prior authors have argued for conversion THA to be reclassified as a revision procedure. Although prior research has focused on comparisons between conversion THAs and primary arthroplasties, little is known about the resource use of conversion THA compared with that of revision THA.

Questions/purposes
(1) Do inpatient hospital costs, estimated using cost-to-charge ratios, differ between conversion THA and revision THA? (2) Do the median length of stay, intensive care unit use, and likelihood of discharge to home differ between conversion and revision THA?

Methods
This was a retrospective study of the Medicare Provider Analysis and Review Limited Data Set for 2019. A total of 713,535 primary and 74,791 revision THAs and TKAs were identified initially. Exclusion criteria then were applied; these included non–fee-for-service hospitalizations, nonelective admissions, and patients with missing data. Approximately 37% (263,545 of 713,535) of primary and 34% (25,530 of 74,791) of revision arthroplasties were excluded as non–fee-for-service hospitalizations. Two percent (13,159 of 713,535) of primaries and 11% (8159 of 74,791) of revisions were excluded because they were nonelective procedures. Among the remaining 436,831 primary and 41,102 revision procedures, 31% (136,748 of 436,831) were primary THAs and 36% (14,774 of 41,102) were revision THAs. Two percent (2761 of 136,748) of primary THAs involved intraoperative removal of hardware and were classified as conversion THAs. After claims with missing data were excluded, there were 2759 conversion THAs and 14,764 revision THAs available for analysis. Propensity scores were generated using a multivariate logistic regression model using the following variables as covariates: gender, age, race, van Walraven index, hospital setting, geography, hospital size, resident-to-bed ratio, and wage index. After matching, 2734 conversion THAs and 5294 revision THAs were available for analysis. The van Walraven index, which is a weighted score of patient preoperative comorbidities, was used to measure patient health status. Hospital costs were estimated by multiplying cost-to-charge ratios obtained from the 2019 Impact File by total hospital charges. This methodology enabled the use of a large national database to mitigate the random effects of individual hospitals’ unique practices and patient populations. Multivariable regression was performed after matching to determine the independent effects of surgery type (that is, conversion versus revision THA) on hospital cost, length of stay greater than 2 days, intensive care unit use, and discharge to home.

Results
There was no difference in the estimated hospital cost between conversion THA and revision THA (β = 0.96 [95% confidence interval 0.90 to 1.01]; p = 0.13). Patients undergoing conversion THA had increased odds of staying in the hospital for more than 2 days (odds ratio 1.12 [95% CI 1.03 to 1.23]; p = 0.01), increased odds of using the intensive care unit (OR 1.24 [95% CI 1.03 to 1.48]; p = 0.02), and decreased odds of being discharged to home (OR 0.74 [95% CI 0.67 to 0.80]; p < 0.001).

Conclusion
The inpatient hospital cost of conversion THA is no different from that of revision THA, although patients undergoing conversion surgery have modestly increased odds of prolonged length of stay, intensive care unit use, and discharge to a nonhome location. These findings support the conclusion that reclassification of conversion THA is warranted. Orthopaedic surgeons must advocate for the reclassification of conversion THA using data-backed evidence or run the risk that orthopaedic procedures will be given decreased reimbursement.

Level of Evidence
Level III, economic and decision analysis.