It has been suggested that the utilization of total joint arthroplasty (TJA) in patients with rheumatoid arthritis (RA) is decreasing over time;1 however, this observation is largely based upon evidence pertaining to lower extremity TJA.2 It remains unknown if these observed trends also hold true for shoulder arthroplasty, whereby the utilization of shoulder arthroplasty in RA patients is not limited to the management of end-stage inflammatory arthropathy. In this study, we used a nationally representative population database in the US to identify trends in the utilization of shoulder arthroplasty among patients with RA. As a secondary objective, we sought to determine the rate of early adverse events, length of stay, and hospitalization costs associated with RA patients undergoing shoulder arthroplasty and compare these outcomes to those of patients without a diagnosis of RA undergoing shoulder arthroplasty. We hypothesize that the utilization of shoulder arthroplasty in RA patients would be decreasing, but adverse events, length of stay, and hospitalization costs would not differ between patients with and without RA undergoing shoulder arthroplasty.
METHODS
We conducted a retrospective cohort study using the Healthcare Cost and Utilization Project (HCUP) Nationwide Inpatient Sample (NIS) from 2002 to 2011.3 The NIS comprises a 20% stratified sample of all hospital discharges in the US. The NIS includes information about patient characteristics (age, sex, insurance status, and medical comorbidities) and hospitalization outcomes (adverse events, costs, and length of stay). The NIS allows identification of hospitalizations according to procedures and diagnoses using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes. Given the anonymity of this study, it was exempt from Institutional Review Board ethics approval.
Hospitalizations were selected for the study based on ICD-9-CM procedural codes for hemiarthroplasty (81.81), anatomic total shoulder arthroplasty (TSA) (81.80), and reverse TSA (81.88). These patients were then stratified by an ICD-9-CM diagnosis of RA (714.X). We also utilized ICD-9-CM diagnosis codes to determine the presence of rotator cuff pathology at the time of shoulder arthroplasty (726.13, 727.61, 840.4) and to exclude patients with a history of trauma (812.X, 716.11, 733.8X). In a separate analysis, all patients in the NIS database with an ICD-9-CM diagnosis of RA were identified for each calendar year of the study, and a national estimate of RA patients was generated annually to assess overall and individual utilization rates of shoulder arthroplasty in this population (the national estimate served as the denominator).
Preoperative patient data withdrawn from the NIS included age, sex, insurance status, and medical comorbidities. An Elixhauser Comorbidity Index (ECI) was generated for each patient based on the presence of 29 comorbid conditions. The ECI was chosen because of its capacity to accurately predict mortality and represent the patient burden of comorbidities in similar administrative database studies.4-6
Early adverse events were also chosen based on ICD-9-CM diagnosis codes (Appendix A), and included the following: death, acute kidney injury, cardiac arrest, thromboembolic event, myocardial infarction, peripheral nerve injury, pneumonia, sepsis, stroke, surgical site infection, urinary tract infection, and wound dehiscence. The overall adverse event rate was defined as the occurrence of ≥1 of the above adverse events in a patient.
Appendix A. ICD-9-CM Codes Corresponding to Postoperative Adverse Events
Event | ICD-9-CM |
Acute kidney injury | 584.5-584.9 |
Cardiac arrest | 427.41, 427.5 |
Thromboembolic event | 453.2-453.4, 453.82-453.86, 415.1 |
Myocardial Infarction | 410.00-410.92 |
Peripheral nerve injury | 953.0-953.9 954.0-954.9, 955.0-955.9, 956.0-956.9 |
Pneumonia | 480.0-480.9, 481, 482.0-482.9, 483.0-483.8, 484.1-484.8, 485, 486 |
Sepsis | 038.0-038.9, 112.5, 785.52, 995.91, 995.92 |
Stroke | 430, 432, 433.01-434.91, 997.02 |
Surgical site infection | 998.51, 998.59, 996.67 |
Urinary tract infection | 599 |
Wound dehiscence | 998.30-998.33 |
Abbreviation: ICD-9-CM, International Classification of Diseases, Ninth Revision, Clinical Modification
Length of stay and total hospital charges were available for each patient. Length of stay represents the number of calendar days a patient stayed in the hospital. All hospital charges were converted to hospitalization costs using the HCUP Cost-to-Charge Ratio Files. All hospitalization costs were adjusted for inflation using the US Bureau of Labor statistics yearly inflation calculator to represent charges in the year 2011, which was the final and most recent year in this study.
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