Results
This study included a combined total of 3501 ATSAs and RTSAs performed between 2011 and 2013. The overall readmission rate was 2.7%. The associated diagnosis for readmission was available for 54% of the readmitted patients. Of the known readmission diagnoses, 33% were secondary to HACs.
Of the 51 readmissions, 34 (67%) were for medical complications, and 17 (33%) were for surgical complications. Pneumonia was the most common medical complication (11.8%), followed by UTI (7.8%), DVT (5.9%), PE (5.9%), and renal insufficiency (3.9%). Surgical-site infection was the most common surgical complication (13.7%), followed by prosthetic joint dislocation (9.8%) and hematoma (3.9%).
Other risk factors significantly (P < .05) associated with readmission were age over 75 years, dependent functional status, ASA score of 4 or higher, cardiac comorbidity, 2 or more comorbidities, postoperative CAUTI, extended LOS, and revision surgery (Table 3).
Discussion
Hospital readmissions are important because they represent quality of care and play a role in patient outcomes. Arthroplasty research has focused mainly on readmissions after primary knee and hip replacements.23-25
Historical rates of early readmission after SA14 are comparable to those found in our study. Previously identified risk factors have included increasing age, Medicaid insurance status, low-volume surgical centers, and SA type.3 Mahoney and colleagues14 reported a 90-day readmission rate of 5.9%, but, when they removed hemiarthroplasty replacement from the analysis and shortened the readmission timeline to 30 days, the readmission rate was identical to the 2.7% rate in the present study. In their series from a single high-volume institution, the highest 90-day readmission rate was found for hemiarthroplasty (8.8%), followed by RTSA (6.6%) and ATSA (4.5%). In a study by Schairer and colleagues,3 the readmission rate was also influenced by replacement type, but their results differed from those of Mahoney and colleagues.14 Schairer and colleagues3 analyzed data from 7 state inpatient databases and found that the highest readmission rate was associated with RTSA (11.2%), followed by hemiarthroplasty (8.2%) and ATSA (6.0%). In both series, RTSA readmission rates were higher than ATSA readmission rates—consistent with the complication profiles of these procedures, with RTSA often provided as a surgery of last resort, after failure of other procedures, including ATSA.26 The lower 30-day readmission rate in the present study may be attributable to the fact that some surgical and medical complications may not have developed within this short time. Nonetheless, the majority of readmissions typically present within the first 30 days after SA.14,15 Other factors, including hospital volume, surgeon volume, race, and hospital type, may also influence readmission rates but could not be compared between studies.27,28
The present study found that revision surgery, 3 or more comorbidities, and extended LOS (>4.3 days) more than doubled the risk of readmission. Published SA revision rates range from 5% to 42%, with most revisions performed for instability, dislocation, infection, and component loosening.6,29 Complication rates are higher for revision SA than for primary SA, which may explain why revisions predispose patients to readmission.30 Compared with primary SAs, revision SAs are also more likely to be RTSAs, and these salvage procedures have been found to have high complication rates.31 In the present study, the most common comorbidities were hypertension, diabetes, and COPD; the literature supports these as some of the most common comorbid medical conditions in patients who undergo ATSA or RTSA.5,26,32 Furthermore, all 3 of these comorbidities have been shown to be independent predictors of increased postoperative complications in patients who undergo SA, which ultimately would increase the risk of readmission.3,26,33,34 Last, extended LOS has also been shown to increase the risk of unplanned readmissions after orthopedic procedures.35 Risk factors associated with increased LOS after ATSA or RTSA include female sex, advanced age, multiple comorbidities, and postoperative complications.32Several other factors must be noted with respect to individual risk for readmission. In the present study, age over 75 years, dependent functional status, ASA score of 4 or higher, and cardiac comorbidity were found to have a significant association with readmission. Increased age is a risk factor for increased postoperative complications, more medical comorbidities, and increased LOS.34,36 Older people are at higher risk of developing osteoarthritis and rotator cuff tear arthropathy and are more likely to undergo SA.5,6 Older people also are more likely to be dependent, which itself is a risk factor for readmission.19 An ASA score of 3 or 4 has been found to be associated with increased LOS and complications after SA, and cardiac comorbidities predispose patients to a variety of complications.34,36,37In studies that have combined surgical and medical factors, rates of complications early after ATSA and RTSA have ranged from 3.6% to 17.8%.26,38,39 After SAs, medical complications (80%) are more common than surgical complications (20%).39 In the present cohort, many more readmissions were for medical complications (67%) than for surgical complications (33%). In addition, Schairer and colleagues3 found medical complications associated with more than 80% of readmissions after SA.3 Infection was the most common medical reason (pneumonia) and surgical reason (surgical-site infection) for readmission—consistent with findings of other studies.3,35,40 Infection has accounted for 9.4% to 41.4% of readmissions after ATSA and RTSA.3,14In joint arthroplasty, infection occurs more often in patients with coexisting medical comorbidities, leading to higher mortality and increased LOS.41 Prosthetic joint dislocation was common as well—similar to findings in other studies.3,10In the present study, 33% of known readmission diagnoses were secondary to HACs. Surgical-site infection was the most common, followed by CAUTI, DVT, and PE. In another study, of knee and hip arthroplasties, HACs accounted for more than 40% of all complications and were the strongest predictor of early readmission.16 In SA studies, HACs were responsible for 9.3% to 34.5% of readmissions after ATSA and RTSA.3,14 Our finding (33%) is more in line with Mahoney and colleagues14 (34.5%) than Schairer and colleagues3 (9.3%). One explanation for the large discrepancy with Schairer and colleagues3 is that UTI was not among the medical reasons for readmission in their study, but it was in ours. Another difference is that we used a database that included data from multiple institutions. Last, Schairer and colleagues3 excluded revision SAs from their analysis (complication rates are higher for revision SAs than for primary SAs30). They also excluded cases of SA used for fracture (shown to increase the risk for PE42). The US Department of Health and Human Services estimated that patients experienced 1.3 million fewer HACs during the period 2010-2013, corresponding to a 17% decline over the 3 years.43 This translates to an estimated 50,000 fewer mortalities, and $12 billion saved in healthcare costs, over the same period.43 Preventing HACs helps reduce readmission rates while improving patient outcomes and decreasing healthcare costs.
This study had several limitations. We could not differentiate between ATSA and RTSA readmission rates because, for the study period, these procedures are collectively organized under a common CPT code in the NSQIP database. Readmission and complication rates are higher for RTSAs than for ATSAs.3,14 In addition, our data were limited to hospitals that were participating in NSQIP, which could lead to selection bias. We studied rates of only those readmissions and complications that occurred within 30 days, but many complications develop after 30 days, and these increase the readmission rate. Last, reasons for readmission were not recorded for 2011, so this information was available only for the final 2 years of the study. Despite these limitations, NSQIP still allows for a powerful study, as it includes multiple institutions and a very large cohort.