Patient Characteristics and Medical Provider Factors Are Associated With Length of Stay in Total Hip Arthroplasty Patients: a Retrospective Chinese Cohort Study

Total hip arthroplasty (THA) is a successful treatment in the improvement of quality of life. Diagnosis-related groups (DRGs) payment has a signicant impact on the hospital market in China and length of stay (LOS) is one of its crucial manifestations. Patient characteristics and medical provider factors can affect LOS but the relationship is uncertain. We intent to explore the relationship between patient characteristics and medical provider factors and LOS of primary THA patients. Methods We reviewed the database containing 461 patients who underwent primary THA between January 2014 to 2019 and regressed the LOS against a variety of perioperative factors. A multivariable linear regression model was performed to assess the difference. The study explores risk factors and illustrates the role of predicting the occurrence of prolonging and shortening the LOS in primary THA patients. For patient characteristics, comorbidities, pre-operation Alb < 30 g/L, and pre-operation CRP ≥ 5 mg/L may prolong LOS. For provider variables, duration and schedule of surgery, urinary catheter, and incision drainage may prolong LOS. Our study is useful for identifying risk factors of both patients and providers, which can help shorten the LOS, make better perioperative plans and improve the quality of medical care.


Introduction
Total hip arthroplasty (THA) is seen as a successful and effective treatment for part of improving quality of life (QOL), especially in increasing survival rates and reducing pain, for patients with hip diseases [1].
As the aged population keeps increasing, the volume of patients with hip diseases has increased substantially [2,3]. As a result, the demand for THA will also increase. In light of the success of THA, new protocols imply that the focus of research has shifted to reduction in LOS as one of the primary outcomes of success. LOS of patients who have undergone THA can also be interpreted as an outcome measure for surgical quality. Diagnosis-related groups (DRGs) based payment is increasingly used in China to control hospital costs but the standards of evaluations vary. Previous review suggested that a substantial rise in the burden of osteoarthritis (OA) is expected and should be addressed in health policies and DRGs payment had potential cost-saving implications by lowering LOS [4,5]. Extended LOS remains a paramount unsolved problem and how these different factors contribute to prolonging LOS is poorly characterized [6]. Moreover, the association between patient factors and provider factors is unclear.
Perioperative hospital adverse outcomes represent a signi cant origin, which were often overlooked. Even minor events such as fever or tachycardia may lead to prolonging LOS. Identifying risk factors that lengthen LOS and predicting high-risk patients before surgery is a crucial step in searching for strategies that might shorten LOS [7]. There is little literature concerning LOS after primary THA, and the speci c data is insu cient.

Methods
All of the surgeries were conducted by professors who were experienced and skilled in the Department of Bone & Joint Surgery at Peking University Shenzhen Hospital. Approaches such as direct anterior approaches, lateral, and posterior approaches were based on the general standard. The investigation of the LOS was performed carefully to ensure the validity of the study.

Patients selection
We built a dataset which contains 611 primary THA patients in our department. The mean age at surgery was 57.2 years (22 -96 years). Data were sourced retrospectively from the discharged abstract records.
Each discharged abstract involved a multitude of variables including demographic information and medical provider factors.
Patients who were lost to follow-up, refused to be discharged, underwent bilateral THA in the same period, femoral head arthroplasty, or renovation were excluded from the study. This study was a single-center, retrospective cohort study. We identi ed patients who met inclusion and exclusion criteria undergone primary THA by using the International Classi cation of Diseases 10th (ICD-10) codes. Finally, 461 patients who underwent primary THA were enrolled in this study (Fig. 1).
Discharge criteria Previous studies emphasize that discharge criteria vary worldwide and suggest that patients discharged quickly tend to display a decrease in early complications following primary THA when clinically appropriate [9,10]. The discharge criteria in our department are as follows. (1) Patients who are willing to be discharged, (2) patients' vital signs such as appetite and sleep are normal and stable, (3) incision has healed well without any signs of infection, (4) hematological results are in normal range, (5) visual analogue scale ≤ 3, and (6) patients who have satis ed the standard that they can walk alone with the help of aids and muscle strength grade ≥ 4.
Statistical analysisAll statistical analyses were carried out using Stata software (version 14.0) and SPSS software (version 23.0). Continuous variables were summarized using mean ± standard error (SE). Categorical variables were summarized using number and percent. Chi-square or Student's t test were applied in univariate analysis. A linear regression model was applied to assess the difference in LOS with patient characteristics and provider variables, controlling for confounding factors in the multivariable analysis. We also reported 95% con dence interval (CI) for each parameter estimate. An alpha level of 0.05 is considered statistically signi cant.

Results
Univariate-factor Chi-square analysis For parts of patient demographic characteristics, the univariate-factor chi-square analysis showed no signi cant correlation between LOS and gender, age, BMI, or marriage (p > 0.05) ( Table 1). For parts of patient pre-operation characteristics, the univariate-factor chi-square analysis implies that comorbidities were associated with LOS (p < 0.05), while primary disease, pre-operative Alb, pre-operative ESR, pre-operative CRP, or pre-operative Hb had no signi cant correlation with LOS (p > 0.05) ( Table 2). For parts of provider pre-operation factors, the univariate-factor chi-square analysis implies that ASA class, anesthesia, and date of surgery were associated with LOS (p < 0.05), while the date of admission had no signi cant correlation with LOS (p > 0.05) ( Table 3). For parts of provider surgery factors, the univariate-factor chi-square analysis showed that duration and transfusion were associated with LOS (p < 0.05), while urinary catheter, incision drainage, or blood loss had no signi cant correlations with LOS (p > 0.05) ( Table 4). Here are the regression curves of factors that can in uence LOS in THA patients including comorbidities, ASA class, anesthesia, date of surgery, duration, and transfusion (Fig. 2).
Obviously, the results of univariate-factor analysis in this study suggest that some factors including comorbidities, ASA class, anesthesia, date of surgery, duration, and transfusion are signi cantly associated with LOS (p < 0.05), while some of the factors are not signi cantly statistically (p 0.05). However, when it pertains to the literature and clinical practice, factors that are not statistically signi cant in the univariate-factor analysis are also included in the multivariable linear regression analysis.

Discussion
Lots of relevant research has consistently identi ed THA as a successful treatment for patients' endstage hip diseases [11]. Over time, the implementation process of DRGs-based payment has developed rapidly and LOS has become one of the most critical manifestations of health policies [12,13]. Even though there has been rapid progress in THA surgery, there is little literature concerning factors that may affect LOS of THA patients. Peters et al believed that factors could be classi ed into two categories: patient characteristics and medical provider factors [14]. The concept of LOS was investigated quite intensively in recent years, but the reasons for extending LOS are currently unknown.
Although former researchers have spent much effort on shortening LOS and improving outcomes of THA. Unfortunately, most of the ndings are varied and uncertain and they have not developed an e cient and effective method yet. Accurate data, regarding risk factors for prolonging LOS after THA, are critical for improving health outcomes. Efforts to reduce LOS and minimize adverse outcomes are necessary.
Therefore, it is signi cant to explore the in uence of the factors.
Reports from international registries revealed that extended LOS was independently associated with a history of comorbidities such as diabetes, heart disease, and hypertension, which were correlated with improved selected outcomes [15,16]. Our ndings are in consistent with earlier reports that comorbidity is one of the risk factors. For future patient care, multiple disciplinary discussions and more speci cally perioperative evaluation are necessary for patients who were caught comorbidity if possible.
Previous papers demonstrated that several pre-operative variables were independently associated with extended LOS. Lower pre-operative Alb is one of the independent risk factors for predicting adverse outcomes following primary THA [17][18][19]. Our ndings are in line with earlier reports and con rm the strong association between LOS and hypoalbuminemia (Alb < 30 g/L). Pre-operative Alb could promote incision healing and re ect the nutrition status, while hypoalbuminemia would lead to a variety of complications or even death. Malnutrition is a modi able risk factor for poor outcomes and surgeons should pay close attention to patients' nutrition status. Accurate identi cation of patients' malnutrition will allow pre-operative nutrition interventions, which can help to improved post-operative outcomes.
Besides hypoalbuminemia, researchers demonstrated that abnormal pre-operative hematological tests are associated with prolonged LOS [20]. Lower pre-operative health status was associated with less satisfaction [21]. Our ndings are in consistent with earlier reports and con rm the strong association between pre-operation CRP and LOS. CRP is a sensitive indicator predicting the probability of infection and in ammation. Laboratory evaluation could help surgeons identify and take appropriate preventive measures for high-risk patients. They can also help guide preparation pre-operatively and determine the intervention of routine follow-up post-operatively.
For patient characteristics, comorbidity is a non-modi able risk factor but the status of nutrition and hematological results are modi able. Devoting more attention to selected patients emphasizes the importance of considering comorbidities and preparing positive interventions in the context of the speci c procedure.
Previous studies reported that surgical techniques could reduce adverse outcomes [22]. Acute nerve injury is rare but potentially devastating following THA due to the schedule of surgery [23]. Our results are consistent with earlier reports and con rm the strong associations linking LOS to date of surgery. These associations imply that schedule of operation is signi cant and crucial variables in improving outcomes.
Surgical techniques and proper schedule are needed to be improved in order to perform surgery accurately.
Routine use of urinary catheterization in fast-track THA may increase the risk of postoperative urinary retention and infection, which are potential sources of infection [24]. These ndings con ict against the routine use of perioperative indwelling catheterization [25,26]. However, our results imply that catheterization is a risk factor and con rm the strong association between catheterization and LOS.
Former research ndings are debatable and further study may be needed. Patients treated with indwelling catheterization, history of urinary retention, and high volumes of uid volume were signi cantly more likely to experience urinary retention and infection postoperatively. Intermittent catheterization, or removing it in the early stage, would be better choices for selected patients to prevent adverse outcomes if necessary.
Several papers have used administrative databases to evaluate drainage, which was associated with a prolonged LOS [27,28]. Drainage could result into heterotopic ossi cation, which may result in more complications due to restriction of early postoperative mobilization and exercise [29,30]. All of these ndings are in line with our results and we indicate that drainage is a risk factor of prolonged LOS. Furthermore, no-drainage for easy THA may be a better choice for surgeons but complicated THA should be evaluated in details.
Based on the current nding, we can draw the conclusion that schedule of surgery, urinary catheter, and drainage can extend LOS for THA patients for parts of medical care providers. This knowledge not only can help physicians guide patients' expectations before THA but also direct surgeons devoting more attention to these factors in case of bringing negative effect.
Additionally, previous analysis demonstrated that extended LOS was independently associated with gender and age, and obesity [31,32]. Some research believes that understanding current practice patterns in anesthesia may serve as a platform for future work aimed at maximizing effective postoperative pain control and minimizing the risks [33,34]. The former research ndings are not in line with ours but our data revealed the tendency about this, which may be due to the limitation of our dataset and the patient characteristics of our registration. We will consider increasing our sample size and performing a followup investigation in a future study.
Previous studies have emphasized potential advantages in reducing LOS. Evaluation of risk factors is bene cial in discussion of the perioperative risks of THA and patients' education in the different patient populations, and future studies should try to identify more precise factors. In order to shorten the LOS and improve THA outcomes, surgeons should pay more attention to selected patients during the perioperative management. Individualized treatment schedules and proper methods are needed to strengthen the intervention, which would be highly bene cial in shortening the LOS.
Furthermore, there are several limitations in our research study. First, we conducted this retrospective cohort study by using a database in our department several years ago, particularly with new generation constructs. Prospective studies are needed to validate these calculators and to re ne them over time. Moreover, the standard of discharge may not be consistent according to the surgeon. Last but not least, the database did not include information on long-term follow-up outcomes. We believe that future studies are necessary to de ne the risk factors clearly and use more robust experimental designs to con rm the results.

Conclusions
The study explores risk factors and illustrates the role of predicting the occurrence of prolonging and shortening the LOS in primary THA patients. For patient characteristics, comorbidities, pre-operation Alb < 30 g/L, and pre-operation CRP ≥ 5 mg/L may prolong LOS. For provider variables, duration and schedule of surgery, urinary catheter, and incision drainage may prolong LOS. Our study is useful for identifying risk factors of both patients and providers, which can help shorten the LOS, make better perioperative plans and improve the quality of medical care.

Declarations
Availability of data and materials Please contact the author for data requests.
Ethics approval and consent to participate Ethical review approval was obtained from the Human Subject Committee at Ethics Committee of Peking University Shenzhen Hospital (Ethics Committee of Peking University Shenzhen Hospital (research) [2020] 013th).

Con ict of interest statement:
All of the authors of this paper have disclosed potential or pertinent con icts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical eld which may be perceived to have potential con ict of interest with the submitted article. Each author certi es that his or her institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research. 34. Kuchalik, J., A. Magnuson, A. Lundin, and A. Gupta, Local in ltration analgesia or femoral nerve block for postoperative pain management in patients undergoing total hip arthroplasty. A randomized, double-blind study. Scand J Pain, 2017. 16: p. 223-230. Figure 1 Regression curves.