The Cost of Robot-assisted Total Hip Arthroplasty

Comparing Safety and Hospital Charges to Conventional Total Hip Arthroplasty

Gregory J. Kirchner, MD, MPH; Alexander M. Lieber, MD; Brett Haislup, MD; Yehuda E. Kerbel, MD; Vincent M. Moretti, MD


J Am Acad Orthop Surg. 2021;29(14):609-615. 

In This Article


Our study used the National (Nationwide) Inpatient Sample, Healthcare Cost and Utilization Project (HCUP), and Agency for Healthcare Research and Quality.[14] The NIS comprises a 20% nationally representative sample of all inpatient discharges from community hospitals in the United States (excluding long-term acute care and rehabilitation hospitals). Data from patients with all insurance types including private, Medicare, and Medicaid are captured in the the NIS. We used the NIS between the years 2010 and 2014 based on the availability of the database at our institution. The HCUP provides trend weights that are commonly used to extrapolate national estimates from data within the NIS. However, for our cohort-matched study, weighting was not performed.

The International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) procedure codes were used to identify 292,836 patients who underwent C-THA (ICD 81.51) and 946 patients who underwent RA-THA (ICD 81.51 and ICD 17.41, 17.49). These patients represent only those who did not undergo additional orthopaedic procedures during the same hospital stay.

Case-control matching was performed using the fuzzy extension in Python Essentials, IBM SPSS Statistics for Macintosh, Version 24.0. The RA-THA cohort was statistically matched 1:1 to C-THA patients regarding patient age, sex, race, comorbidities, hospital type, and calendar year. Cases that were not matched were excluded, leaving two statistically matched groups containing 758 cases each. Before matching, the ages of the C-THA and RA-THA groups were 64.7 and 63.6 years, respectively (P < 0.001). After matching, the ages of the groups were statistically similar (C-THA: 64.8 years, RA-THA: 64.5 years; P = 0.826). Furthermore, subanalysis of the unmatched RA-THA patients demonstrated that the group was demographically similar to the matched RA-THA patients and that neither major nor minor complications occurred at disproportionately higher rates in the unmatched RA-THA patients (Appendix, Supplemental Digital Content 1,

Demographic characteristics of patients were abstracted from the database. Patient mortality was determined using the Uniform Bill patient disposition. The rates of major and minor complications and mortality were recorded. ICD-9-CM diagnosis codes were used to identify perioperative complications. Major complications included deep vein thrombosis, pulmonary embolism, respiratory complication, acute renal failure, stroke, myocardial infarction, intraoperative hemorrhage, pneumonia, sepsis, shock, retained surgical item, wound complications, and prosthetic complications. Minor complications included blood transfusion, superficial thrombophlebitis, urinary tract infection, peripheral nerve injury, and superficial surgical site infection. Specific ICD-9-CM diagnosis codes used to identify complications are listed in the Appendix (Supplemental Digital Content 1,

Hospital costs were calculated using hospital-specific cost-to-charge ratios provided by the HCUP. Cost was adjusted to the 2016 level of inflation using the consumer price index for medical care from the Bureau of Labor Statistics. Mean cost and LOS for each cohort were calculated and compared using the Kruskal-Wallis H test. Univariate and multivariate logistic regression were used to compare the risks of major and minor complications between the cohorts.