Compared to an inpatient group with similar age, sex, BMI, laterality, approach, Charlson Comorbidity Index (CCI), and smoking status, the outpatient group demonstrated superior outcomes at minimum 2 years postoperatively. There were significant differences in mHHS (91.5 vs. 86.2), HHS (92.3 vs. 87.4), and pain (1.0 vs. 1.5) at latest follow-up. In addition, although not statistically significant, the outpatient group exhibited higher FJS at latest follow-up (80.0 vs. 71.2, P = 0.17). Existing literature on outpatient THA focuses on perioperative patient safety as manifested in 90-day complication rates and readmissions. To date, there is only one study that directly compares inpatient and outpatient THA outcomes, and PROs were analyzed at 4-weeks postoperatively. To our knowledge, this is the first study to compare two-year PROs between an outpatient and inpatient THA group.
As the patient populations were matched for multiple variables, the reason for the improved outcomes in the outpatient population warrants discussion. One possibility that needs to be considered is the socioeconomic background of the patients. It is possible that despite the matching process, the inpatient population may have had a less robust home-based support system or been of lower socioeconomic status. Social support, including having someone to discuss concerns, reinforce goals, and provide daily care, can increase a patient’s self-efficacy during the sensitive postoperative period.[19, 20] In addition, socioeconomic status has been shown to influence both immediate and long term outcomes following THA[21–23]. Another possibility may be satisfaction with the surgical experience as this has been shown to influence post-surgical PROs . Lastly, length of stay was significantly longer in the inpatient group, at nearly two days. This may influence the immediate postoperative course, including sleep quality, nutrition, and comfort levels, which may in turn impact long term outcomes.
There were no significant differences in ASA scores, length of surgery, and blood loss between the two groups. The reduction in length of hospital stay in the outpatient group was very significant (6.8 hours vs. 43.2 hours, P < 0.001). Based on the 2017 American Hospital Association (AHA) Annual Survey, the average expense per inpatient day in the United States is $2,424 . Applying this data to our study, performing THA on an outpatient basis represents a savings of $3,676 per patient.
Several studies have reported a > 90% same day discharge rate in patients undergoing outpatient THA [5, 26, 27]. A systematic review on 955 patients undergoing outpatient total joint arthroplasty (TJA) found that 94.7% of patients were discharged the same day. In this study, all patients in the outpatient group met the discharge criteria and were discharged home the day of surgery, as planned. Same day discharge has been facilitated by a number of factors, including proper patient selection for outpatient surgery, comprehensive preoperative patient education, and an optimized perioperative rapid recovery protocol.
In addition, we evaluated readmissions, visits to the emergency room, and unplanned clinic visits. We did not detect any statistically significant differences in these measures, although this study may have been underpowered in this respect. There were no 90-day readmissions in the outpatient group and there was one readmission for wound revision in the inpatient group. In a study on 250,000 THAs using the Nationwide Readmissions Database, the rates of 30- and 90-day readmissions after THA were 4% and 8%, respectively. The authors found that a patient’s length of stay had the greatest influence on the cost of 90-day readmissions . In studies on outpatient TJA, rates of 90-day readmission are very low, at approximately 0.5%-1%[28, 30].
There are mixed findings on whether performing TJA on an outpatient basis increases the burden on the surgeon. Shah et al. found that outpatient TJA shifts the burden of care from the hospital to the surgeon, as outpatient surgery requires increased preoperative patient education and results in more patient phone calls the week following surgery. Conversely, in a multi-center, prospective, randomized study, Goyal et al. found no significant difference in the outpatient and inpatient THA group with regard to calls between the office staff and patients.
The primary concern in performing outpatient THA has been patient safety and complications. Based on the findings in this study, the outpatient group experienced fewer and less severe complications, although not statistically significant. In several studies, in appropriately selected patients, complications have been shown to be equal or lower in patients undergoing outpatient THA. Courtney et al. analyzed the American College of Surgeons-National Surgical Quality Improvement Program (ACS-NSQIP) database and found an 8% complication rate in the outpatient setting compared to a 16% complication rate in the inpatient setting. Arshi et al, performed a registry-based study on 2,184 patients undergoing outpatient THA, and found comparable rates of surgical and medical complications.
There are multiple notable strengths in the present study. First, outpatient cases were matched to a contemporary group of inpatient cases with similar age, sex, BMI, laterality, approach, Charlson Comorbidity Index (CCI), and smoking status. Second, the patients included in the outpatient cohort were a prospectively selected, consecutive series of patients which enabled consistent data acquisition, and reduced selection bias. Third, this study analyzed multiple outcomes, including several PROs, readmissions, 90-day complications, unplanned office visits, and 2-year revision rate. Fourth, by analyzing a single surgeon’s patient population, performance bias may be minimized enabling direct comparison between the inpatient and outpatient setting. This consistency is evident in the almost identical radiographic outcomes following surgery.
This study is not without limitations. Our study population included a younger than average cohort, with the average age being 53 and 55 for the outpatient and inpatient groups, respectively. Studies on outpatient THA have tended to consist of patients that are younger than the general population undergoing THA. In a multi-national study on nearly 500,000 THA procedures, more than 60% of patients were aged 60–79, with only 13–20% belonging to the 50–59 age group. This discrepancy is multifactorial, stemming from the senior author’s practice, which includes a younger, more active patient population, and the inherently younger cohort of inpatient THA cases needed to match the age of the outpatient THA group. Therefore, conclusions from this study may not be applicable to an older, more morbid patient population.
Second, the choice to undergo an inpatient or an outpatient procedure is determined by multiple factors, several of which depend on patient comorbidities. For the purpose of this study we utilized a propensity-score matching process that consisted of several variables including medical comorbidities, smoking status, age, and BMI. Despite this matching process, the inpatient group had more patient graded ASA 3, although this was not statistically significant.
Additionally, this study consists of a mixed group of anterior and posterior THAs. However, in both groups, the patients undergoing posterior THA represented a small minority (4.4% and 5.5% for inpatient and outpatient cohorts, respectively).
Fourth, although we addressed postoperative follow-up in readmissions, emergency room visits, and unplanned office visits, we did not account for additional phone calls between the office staff and patients. This was inconsistently recorded and therefore was omitted from our analysis.
Lastly, this study was based on a single surgeon’s practice, which may limit the generalizability of our results. This practice is a high-volume practice, with extensive experience operating in the outpatient setting, including arthroscopic and arthroplasty procedures. The workflow developed by the surgeon and the office staff to optimize outpatient management may be difficult to apply to smaller practices.