1 Introduction

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by a wide range of clinical manifestations that can affect nearly any organ of the body and is seen more prevalently in young women.^1–3 Patients often present with variable clinical features ranging from mild joint and skin involvement to life-threatening kidney, hematologic, or central nervous system involvement. Advances in medical treatments have significantly improved the survival rates for patients with SLE, with 10-year survival rates now exceeding 85 %.^4–6 Despite this, patients with SLE frequently experience joint complications due to persistent inflammatation or osteonecrosis secondary to vascular or medication complications leading to joint damage which occurs in about 10–15 % of SLE patients.^7–14 Total hip or knee arthroplasty (THA/TKA) is often needed to alleviate pain and restore function for patients with these symptoms, and may be frequently indicated in patients with ongoing severe joint infection.^15–17

A growing concern in managing SLE patients readmitted following THA and TKA is the reimbursement challenges posed by the Centers for Medicare and Medicaid Services (CMS). The Hospital Readmissions Reduction Program (HRRP), introduced in 2012 under the CMS and expanded to include joint arthroplasties in 2014, place a significant financial burden on hospitals due to the implementation of readmission penalties.^18,19 Williams et al. (2022) highlighted that readmissions cost hospitals an average of $38,953 per TKA and $36,038 per THA, with over 55 % of orthopedic readmissions being unplanned.¹⁸ As a result, patients with chronic disease such as SLE may be placed at a greater disadvantage. As current policies penalize hospitals with high readmission rates, hospitals may become increasingly disincentivized to perform necessary THA/TKA procedures in patients with complex diseases such as SLE. This inadverdantly leaves large, urban teaching centers performing majority of the comprehensive care involved in this patient population. Understanding the causes of readmissions and identifying which patient characteristics increase this risk is critical to mitigating financial losses under CMS's current bundled payment models and ultimately optimize the medical care for patients with SLE undergoing THA/TKA.^19,20

Understanding the rate and causes of readmission after THA and TKA is necessary to help clinicians and policy makers develop approaches to minimize the burden or readmission for SLE patients and the hospitals where these patients receive care. To this end, several studies have examined complications after THA and TKA in SLE patients, but they have been limited in scope. Recently, Najjar et al. queried the rates and causes of 30-day readmission using the National Readmission Database (NRD) in patients with SLE after all hospitalizations, but not specific for TKA/THA. While this provides an insightful and more generalizable picture, this was limited to only one year of data (2016–2017).²¹ In this study, we used NRD data from 2017 to 2020 to establish the most comprehensive and current picture of the rates and causes of 30-day readmission after THA and TKA in patients with SLE.

2 Methods

3 Results

3.2

3.2 Yearly trends in readmission after THA and TKA in SLE patients

From 2017 to 2020, THA readmission rates were 6.5 % in 2017, 7.1 in 2018, 5.7 % in 2019, and 9.2 % in 2020. For TKA readmissions, the overall readmission rate by year was 5.5 % in 2017, 4.8 % in 2018, 5.4 % in 2019, and 5.5 % in 2020 (Fig. 1).

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Fig. 1 Yearly rate of readmission for SLE patients who underwent THA or TKA from 2017 to 2020.

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3.3

3.3 Causes of readmission after THA and TKA in SLE patients

The most frequent causes for readmission after THA and TKA were assessed from 2017 to 2020. Compared to TKA patients, THA patients were more frequently admitted for sepsis (14.6 % vs 10.4 %), nonseptic infection (14.8 % vs 5.5 %), cardiovascular (11.2 % vs 8.2 %), pulmonary (8.4 % vs 3.4 %), and renal complications (5.6 % vs 3.1 %) compared to TKA patients (Fig. 2).

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Fig. 2 Most frequent causes of readmission for SLE patients who underwent THA or TKA from 2017 to 2020.

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3.4

3.4 Risk of 30-day readmission after THA in patients SLE

Adjusted analysis revealed that younger SLE patients (>18-<45 years) had greater odds of readmission after THA compared to older patients (≥85) (OR 8.19, 95 % CI [5.36,12.48], p < 0.001) (Fig. 3). Compared to females, males had reduced odds of readmission (OR: 0.71 95 % CI [0.60, 0.85], p < 0.001). Additionally, a CCI score of 3 or greater was associated with higher odds of 30-day readmission (1.33 95 % CI [1.17, 1.49], p < 0.001).

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Fig. 3 Forest plot of multivariable logistic regression analysis showing individual study demographic and clinical characteristics and their odds of causing 30-day readmission after THA in SLE patients (adjusted for the following: age, sex, CCI score, primary payer, discharge destination, and median household income). Blue bars indicate significant odds ratios, and black bars represent insignificant odds ratios (p > 0.05).

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3.4.1

3.4.1 Risk of 30-day readmission after TKA in patients SLE

For TKA readmissions, adjusted analyses showed that older age (65–75 years) was associated with lower odds of readmission (OR 0.66, 95 % CI [0.50, 0.87] p = 0.003). Similar to THA patients, having a CCI score of 3 or greater was positively associated with greater odds of readmission (OR 1.21 95 % CI [1.06, 1.39], p = 0.005). Additionally, a length of stay greater than 5 days showed significantly greater odds of readmission in TKA patients (OR: 1.35 95 % CI [1.16, 1.57], p < 0.001) (Fig. 4).

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Fig. 4 Forest plot of multivariable logistic regression analysis showing individual study demographic and clinical characteristics and their odds of causing 30-day readmission after THA in SLE patients (adjusted for the following: age, sex, CCI score, primary payer, discharge destination, and median household income). Blue bars indicate significant odds ratios, and black bars represent insignificant odds ratios (p > 0.05).

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4 Discussion

This is the first and largest study to date using national estimates across U.S. hospitals reporting rates and causes for 30-day readmission following THA and TKA in patients with SLE. We observed a slightly higher rate of readmission among THA (6 %) and TKA patients (5 %), with sepsis being the most common cause of readmission for both procedures. THA patients who were readmitted were younger on average than non-readmitted patients (57.3 vs. 61.7 years), and a CCI score of 3 or greater was significantly associated with increased readmission odds for both THA and TKA. These findings suggest that refining perioperative strategies in infection control and comorbidity management may mitigate readmission risks, improving outcomes and decreasing the financial burden for SLE patients undergoing THA and TKA.

Our findings on readmission characteristics for SLE patients undergoing THA and TKA differ from the trends observed by others in osteoarthritis (OA) patients. Both Ricciardi et al. (2017) and Williams et al. (2022) observed lower overall 30-day readmission rates for OA patients with THA/TKA (around 3–4.5 %), while we in contrast found higher rates in SLE patients.^18,24 In Ricciardi et al.’s (2017) cohort of 21,864 patients, only 60 total individuals with THA and TKA were readmitted within 30 days, with fracture, infection, and dislocation being the most common causes.²⁴ Similarly, Williams et al. (2022) reported that only 4.4 % of 6065 patients experienced 30-day readmissions, with heart failure, COPD, and dialysis as key contributors ¹⁸. In contrast, our study showed that 30-day readmission rates were higher in SLE patients, driven primarily by infection, cardio-pulmonary complications, and renal issues, pointing to a more complex interaction between the underlying disease process in SLE and postoperative outcomes.

The difference in readmission rates and causes between OA and SLE patients can be largely attributed to the underlying pathophysiology. OA is a localized joint disease, typically associated with age-related wear and tear, leading to fewer systemic comorbidities and a more straightforward postoperative recovery. In Ricciardi et al. (2017), readmissions were driven by mechanical factors—fracture, dislocation, and infection—closely tied to surgical and perioperative issues, such as procedure time and discharge to skilled nursing facilities.²⁴ Similarly, Williams et al. (2022) identified underweight status and comorbidities like heart failure and COPD as key risk factors, but these are generally more easily characterized and potentially more manageable compared to the systemic inflammation of SLE.¹⁸ The complexity in managing SLE is driven by the potential multiorgan involvement of the kidneys, lungs, and heart, explaining why our study found infection, renal, and pulmonary complications to be leading causes of readmission. The higher disease burden in SLE, compounded by immunosuppressive medications, predisposes these patients to infections and delayed healing, leading to higher readmission rates. This was further clarified by Yazdany et al. (2024) who found a 16.5 % all-cause readmission rate in SLE patients (not just those admitted for TKA/THA), driven by lupus-specific complications like nephritis and thrombocytopenia, which are rarely seen in OA patients, highlighting the systemic nature of lupus and its impact on surgical intervention.²⁵ Interestingly, Aziz et al.’s (2020) findings also suggest that SLE patients undergoing TKA may be slightly less prone to major complications than THA patients, a pattern that was mirrored in our study where TKA had lower readmission rates compared to THA.¹⁵ One potential explanation for this discrepancy is that THA involves greater manipulation of larger joints, potentially increasing the inflammatory response and risk of infection, especially in patients with active autoimmune disease. This aligns with both the mechanical and systemic demands placed on the body postoperatively in THA, which seem to disproportionately affect SLE patients compared to those with OA. Alternatively, the hips in patients with SLE may be far deteriorated with concomitant occurrence of avascular necrosis compared to the hips presenting with OA.

Patient characteristics influenced 30-day readmission rates among SLE patients undergoing THA and TKA. Younger SLE patients undergoing THA had higher risk of 30 day readmission and this is consistent with the previous report of Najjar et al. where they were not specifically focused on THA/TKA (2023) (ADD the actual ref). Younger patients often have more severe disease courses.^26,27 In the study by Najjar et al. (2023) readmissions were driven by aggressive disease manifestations like autoimmune hemolytic anemia and glomerular disease ²¹. Sex may also play a role, with male SLE patients, though fewer in number, often bearing a higher comorbidity burden, including heart failure and renal disease, which heightens readmission risk.²⁸

A large portion of the patients in our study were covered by Medicare (70–75 %) as well as those less than 65 (47.4 %), likely reflecting the inclusion of younger patients with SLE who are on Social Security Disability (SSD). In the context of SLE, many younger patients qualify for Medicare due to long-term disability related to severe disease manifestations, such as lupus nephritis or cardiovascular complications. This younger demographic adds complexity to postoperative outcomes, as these patients often have a higher burden of comorbidities and greater disease severity, increasing their likelihood of readmission. Insurance status plays a crucial role in access to healthcare resources, which can affect both postoperative care and readmission rates. As noted by Williams et al. (2022), the CMS enacted the HRRP, which penalizes hospitals for high readmission rates following procedures like THA and TKA.¹⁸ Despite the program, readmission rates remain high, and the financial burden associated with 30-day readmissions persists. The average cost per readmission for TKA and THA is $38,953 and $36,038, respectively, contributing billions annually to Medicare expenditures. In our study, the predominance of Medicare patients undergoing THA and TKA likely reflects the broader trends of higher financial risk faced by hospitals in managing vulnerable populations like SLE patients.¹⁸ As Bosco et al. (2014) highlighted, unplanned readmissions are financially cumbersome for hospitals, especially given the thin cost margins for Medicare-reimbursed total joint arthroplasty procedures.²⁰ Kurtz et al. (2017) further noted that bundled payment models shift financial risk to hospitals, placing additional pressure on institutions to manage complications and readmissions, despite limited success in reducing these rates.¹⁹ Addressing the drivers of readmission, particularly among younger, disabled patients with SLE, is essential for improving both patient outcomes and financial performance under CMS policies to maintain access to THA and TKA for patients with SLE.

This study has several key strengths, including the use of a large, nationally representative dataset to provide insights into 30-day readmission rates and causes in SLE patients undergoing THA and TKA. However, several limitations must be acknowledged. First, the retrospective design and reliance on database coding may introduce potential biases, particularly regarding the accuracy and completeness of clinical information as well as the diagnosis of SLE. The NRD does not include specific details on disease activity, medication use, or severity of SLE, which could be important confounding factors in readmission risk. Additionally, while our findings highlight important trends, the lack of long-term follow-up precludes an assessment of outcomes beyond the 30-day period, limiting the evaluation of long-term complications and readmission causes. Finally, given the complexity of SLE, the findings may not fully capture the nuances of patient management in different hospital settings. Future research should focus on prospective, multicenter studies with detailed clinical data to better understand the drivers of readmission and improve outcomes in this high-risk population.

5 Conclusion

We analyzed the 30-day readmission rates, causes, and patient characteristics in SLE patients undergoing THA and TKA based on a large US national database. Our findings suggest that SLE patients may experience a higher frequency of postoperative readmissions, with infections and cardiovascular complications being common causes. Younger age, higher comorbidity burden, and female sex were associated with increasing odds of readmission. For younger, disabled patients covered by Medicare, a greater emphasis on preoperative planning, infection prevention strategies, and comorbidity management of cardiovascular and renal disease may be of benefit to both patients and hospitals. Postoperative strategies, including more vigilant monitoring for infection and coordinated care with specialists, may help prevent progression of systemic complications leading to readmission. Given the financial burden of readmissions under CMS policies, hospitals should implement structured discharge planning and early follow-up protocols for patients with known risk factors that may contribute to complicating events during the postoperative period. Future research should focus on identifying specific perioperative interventions tailored for high-risk SLE patients and evaluating their long-term effectiveness in reducing readmissions and improving patient outcomes through multicenter, prospective studies.

CRediT authorship contribution statement

Omkar S. Anaspure: Formal analysis, Writing – original draft. Michael L. Parks: Writing – review & editing. Jason Blevins: Writing – review & editing. David Fernandez: Writing – review & editing. Chisa Hidaka: Writing – review & editing. Susan M. Goodman: Formal analysis, Writing – review & editing, Supervision. Bella Mehta: statistics, Writing – review & editing, Methodology, Funding acquisition.

Informed consent statement

Informed consent was not required to gather the data to publish this paper.

Institutional review board statement

Not applicable.

Ethical statement

This study did not require Institutional Review Board (IRB) approval as it involved data that was collected in a manner consistent with ethical research practices and did not involve human subjects or sensitive personal information. Informed consent was not required as the data used was publicly available or anonymized prior to analysis. All procedures followed applicable ethical guidelines to ensure the privacy and confidentiality of any individuals involved."

Funding information

Dr. Mehta is supported by the NIH/NIAMS 1K23AR082991-01A1 grant and the Anna Marie and Stephen Kellen Foundation TKIP Program Kellen Scholars Award.