Higher modified frailty index score is associated with 30-day postoperative complications following revision total shoulder arthroplasty

Abstract

Background

Previous studies have shown that increased 5-item modified frailty index (mFI-5) scores are associated with poor surgical outcomes. This study seeks to determine whether the comorbidities comprising the mFI-5 were correlated with poor outcomes following revision total shoulder arthroplasty (TSA).

Methods

Utilizing the National Surgical Quality Improvement Program database, a mFI-5 score was calculated for all patients 50 years and older who underwent revision TSA between 2013 and 2019. Pearson's Chi-squared tests and multivariable regression analysis were used to evaluate the association of the mFI score with various postoperative complications.

Results

Patients with a mFI-5 score of 2+ had significantly increased risk of readmission (OR 2.58), bleeding requiring transfusion (OR 3.66), extended length of stay (OR 2.43), and discharge to a non-home destination (OR 3.22) compared to patients with a mFI-5 score of 0. Relative to patients with a score of 1, those with a mFI-5 score of 2+ had an increased risk of postoperative transfusion (OR 2.46), extended length of stay (OR 2.16), and discharge to a non-home location (OR 2.84).

Discussion

The mFI-5 is a valuable tool that can stratify patients based on risk for postoperative complications following revision TSA.

Introduction

Revision total shoulder arthroplasty (TSA) is a complex procedure resulting in complication rates as high as 69%, which is significantly higher than complication rates following primary TSA. ¹ In order to assess and predict complication rates following surgery, previous studies have utilized the 5-item modified frailty index (mFI-5) which is an abbreviated version of the already established 11-item modified frailty index. The mFI-5 has served as a reliable indicator of frailty and has been associated with orthopedic postoperative complications such as 6-month mortality, length of hospital stay, discharge to a non-home location, and urinary tract infection. Despite the lack of a universal definition or assessment for frailty, many studies have validated the use of the modified frailty index and shown that as patients scores on the mFI-5 increases, their propensity for adverse surgical outcomes also increases.^2–8

Prior studies have sought to employ the mFI-5 to stratify patients based on risk of complication following TSA. Amongst patients undergoing TSA, Traven et al. found a correlation between mFI-5 scores and increasing risk of postoperative complications such as mortality, discharge to a non-home facility, readmission, increased length of stay, pulmonary embolism, cardiac arrest, myocardial infarction, septic shock, postoperative dialysis, reintubation, and prolonged ventilator requirement. ⁹ Given the increasing rates of TSA and revision TSA, and their impact on patient morbidity and economic burden,^10,11 there is a growing emphasis on risk-stratifying patients and reducing rates of complications. However, no studies have examined the role of the mFI-5 in predicting postoperative complications following revision TSA.

Therefore, the purpose of this study was to determine whether the comorbidities comprising the mFI-5 were associated with postoperative complications following revision TSA. We hypothesized that a higher mFI-5 score would be associated with increased complication rates in patients undergoing revision TSA.

Methods

The data for the patients included in this study were collected from the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database. The ACS-NSQIP and the hospitals participating in the ACS-NSQIP have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors of this study. The ACS-NSQIP is a national database that prospectively gathers information on surgical patients. Collected information include preoperative demographics, comorbidities, intraoperative variables, and 30-day postoperative complications. ¹² Data is entered and verified by trained surgical clinical reviewers with regular audits to ensure accuracy. All data in the database are deidentified, ¹³ therefore institutional review board approval was not required for this study.

Patient selection

Patients who underwent revision TSA from the years 2013 to 2019 were identified using Current Procedural Terminology codes 23473 and 23474. Similar to previous studies and due to the association between frailty and aging, only patients 50 years old or older were included in the study.^14,15 Patients were also excluded if they had missing demographics data, such as their gender or race, or if they were missing data for any of the variables needed to calculate the mFI-5.

Baseline patient characteristics

Patients’ baseline characteristics collected from the database included gender, age, body mass index (BMI), race, and American Society of Anesthesiologists (ASA) class. The breakdown of BMI was as follows: underweight (<18.5), normal weight (18.5–24.9), overweight (25.0–29.9), obese (30.0–34.9), severely obese (35.0–39.9), and morbidly obese (≥40.0).

Modified frailty index

The mFI-5 was utilized for this study. The mFI-5 was adapted from the original mFI-11 and it has been validated against the mFI-11 for use in orthopedic surgery and has been successfully used to predict complications following orthopedic procedures and other surgical procedures.^2–7,16,17 The benefit of using the mFI-5 rather than the 11-item index is that it translates more easily into clinical practice and still retains predictive power.^3,16,18,19 The mFI-5 includes the following: (1) history of diabetes mellitus, (2) congestive heart failure (CHF) within 30 days of surgery, (3) hypertension requiring medication, (4) history of chronic obstructive pulmonary disease or pneumonia, and (5) dependent functional status (partially or totally dependent on another person for activities of daily living within 30 days of surgery). The mFI-5 score (possible score of 0–5) was calculated for all patients by adding the number of items present in each patient (Table 1). Patients who scored 0 out of 5 were defined as non-frail while patients who scored 1 were pre-frail, 2 were frail, and 3+ were severely frail.

Table 1.

Items included in the mFI-5.

Items
1. Diabetes mellitus: non-insulin or insulin dependent
2. CHF within 30 days before surgery
3. Hypertension requiring medication
4. History of COPD or pneumonia
5. Partially or totally dependent functional health status before surgery

mFI-5: 5-item modified frailty index; CHF: congestive heart failure; COPD: chronic obstructive pulmonary disease.

Postoperative complications

The 30-day outcomes assessed in this study included mortality, readmission, reoperation, urinary tract infection, postoperative transfusion requirement, extended length of hospital stay, and discharge to a non-home destination. Based on previous studies, extended length of stay was defined as more than 3 days. ²⁰ Complications were further classified into clinically relevant groups, including wound (superficial or deep surgical site infections, organ/space infections, or wound dehiscence), pulmonary (pneumonia, reintubation, or failure to wean off ventilator for more than 48 h), renal (renal failure or insufficiency), cardiac (cardiac arrest or myocardial infarction), thromboembolic (deep vein thrombosis, pulmonary embolism, or stroke), and sepsis (sepsis or septic shock).

Statistical analysis

Pearson's Chi-squared tests were used to compare the incidence of complications between patients with varying mFI scores. Complications with a p-value <0.05 were analyzed with multivariable regression analysis. Multivariable regression models, controlling for age, gender, race, BMI, and total operative time, were used to further evaluate the complication rates between patients with different mFI scores. Multivariate analysis results were reported as odds ratios with 95% confidence intervals. Statistical Package for the Social Sciences (SPSS; Version 28; Armonk, NY) software was used to conduct the analyses in this study. A p-value of <0.05 was considered statistically significant.

Results

Demographics

In total, 1393 patients who underwent revision TSA were included in the analysis after the exclusion criteria were applied (Table 2). The average patient was 69 years old (±8.96 years), and there was a slight female predominance noted (53.7%). The average BMI for the patients was 31.1 kg/m² (±6.85), with most patients being overweight (31.1%) or obese (26.2%). The majority of the patients were white (87.1%) and had an ASA class of III (60.0%).

Table 2.

Baseline patient characteristics.

Variable	Overall
Total patients, n	1393
Gender, %
Female	53.7
Male	46.3
Age, mean (SD), years	68.56 (8.96)
BMI, mean (SD), kg/m2	31.13 (6.85)
BMI category, %
Underweight (<18.5)	0.4
Normal weight (18.5–24.9)	16.6
Overweight (25.0–29.9)	31.1
Obese (30.0–34.9)	26.2
Severely obese (35.0–39.9)	13.8
Morbidly obese (≥40.0)	9.9
Race, %
White	87.1
Black or African American	7.1
Hispanic	4.4
Native American or Alaska Native	0.3
Asian	1.0
Native Hawaiian or Pacific Islander	0.1
ASA class, %
I (normal healthy)	0.8
II (mild systemic disease)	35.4
III (severe systemic disease)	60.0
IV (severe systemic disease with threat to life)	3.8
mFI score, %
0	27.4
1	47.1
2	22.5
3	2.9
4	0.1
5	0.0

SD: standard deviation; BMI: body mass index; ASA: American society of anesthesiologists; mFI: modified frailty index.

mFI-5 scores

Most patients had a mFI-5 score of 1 (47.1%), followed by a score of 0 (27.4%), and a score of 2 (22.5%) (Table 2). Given that 97% of the patients had a score of 0, 1, or 2, analyses were performed using the following groups: mFI-5 score of 0, mFI-5 score of 1, and mFI-5 score of 2 or greater. This is consistent with prior studies.^14,21

Postoperative outcomes

On bivariate analysis, relative to patients with a mFI-5 score of 0, patients with a mFI-5 score of 1 were more likely to undergo reoperation (3.8% vs 1.6%; p = 0.041). There were no differences in any other complications between patients with a mFI-5 score of 0 and those with a score of 1. Compared to patients with a mFI-5 score of 0, patients with a score of 2 or greater were more likely to require readmission to the hospital (8.6% vs 3.9%; p = 0.016), postoperative blood transfusion (6.2% vs 2.6%; p = 0.018), extended length of stay greater than 3 days (14.9% vs 5.8%; p < 0.001), and discharge to a non-home destination (18.3% vs 6.6%; p < 0.001). In comparison to patients with a mFI-5 score of 1, those with a score of 2 or greater were more likely to require postoperative transfusion (6.2% vs 2.9%; p = 0.011), extended length of stay greater than 3 days (14.9% vs 7.9%; p < 0.001), and discharge to a non-home destination (18.3% vs 7.9%; p < 0.001) (Table 3).

Table 3.

Bivariate analysis of postoperative complications.

Complications	mFI score = 0	mFI score = 1	p-value: mFI score = 1 vs mFI score = 0 a	mFI score ≥ 2	p-value: mFI score ≥ 2 vs mFI score = 0 a	p-value: mFI score ≥ 2 vs mFI score = 1 a
Total patients, n	381	656		356
Mortality, n (%)	1 (0.3)	2 (0.3)	0.902	1 (0.3)	0.962	0.947
Readmission, n (%)	12 (3.9)	33 (6.1)	0.152	25 (8.6)	0.016	0.188
Reoperation, n (%)	6 (1.6)	25 (3.8)	0.041	13 (3.7)	0.075	0.899
Wound complication, n (%)	12 (3.1)	24 (3.7)	0.666	7 (2.0)	0.311	0.136
Pulmonary complication, n (%)	1 (0.3)	3 (0.5)	0.626	2 (0.6)	0.524	0.821
Renal complication, n (%)	0 (0.0)	0 (0.0)	-	1 (0.3)	0.301	0.174
Cardiac complication, n (%)	0 (0.0)	4 (0.6)	0.127	2 (0.6)	0.143	0.924
Thromboembolic complication, n (%)	2 (0.5)	8 (1.2)	0.270	6 (1.7)	0.129	0.545
Sepsis complication, n (%)	2 (0.5)	9 (1.4)	0.199	6 (1.7)	0.129	0.694
Urinary tract infection, n (%)	3 (0.8)	8 (1.2)	0.513	3 (0.8)	0.933	0.581
Postoperative transfusion, n (%)	10 (2.6)	19 (2.9)	0.798	22 (6.2)	0.018	0.011
Extended length of stay (> 3 days), n (%)	22 (5.8)	52 (7.9)	0.198	53 (14.9)	< 0.001	< 0.001
Non-home discharge, n (%)	25 (6.6)	52 (7.9)	0.419	65 (18.3)	< 0.001	< 0.001

mFI: modified frailty index.

^a Pearson's chi-squared test.

Bold equals significance p < 0.05.

Following adjustment to control for potential confounders on multivariable regression analysis, a higher mFI-5 score continued to show an association with an increased rate of postoperative complications. Relative to patients with a mFI-5 score of 0, patients with a score of 1 were found to have an increased risk of reoperation (OR 2.528; 95% CI 1.001 to 6.383; p = 0.050). Compared to patients with a score of 0, patients with a mFI-5 score of 2 or greater were at increased risk of readmission (OR 2.584; 95% CI 1.168 to 5.717; p = 0.019), bleeding requiring transfusion (OR 3.655; 95% CI 1.466 to 9.112; p = 0.005), extended length of stay (OR 2.434; 95% CI 1.366 to 4.337; p = 0.003), and discharge to a non-home destination (OR 3.215; 95% CI 1.827 to 5.658; p < 0.001). Compared to patients with a mFI-5 score of 1, those with a score of 2 or greater had an increased risk of postoperative transfusion (OR 2.461; 95% CI 1.261 to 4.804; p = 0.008), extended length of stay (OR 2.160; 95% CI 1.410 to 3.307; p < 0.001), and discharge to a non-home location (OR 2.837; 95% CI 1.841 to 4.372; p < 0.001) (Table 4).

Table 4.

Multivariable regression analysis of postoperative complications.

Complications	mFI score = 1 (reference group is mFI score = 0)		mFI score ≥ 2 (reference group is mFI score = 0)		mFI score ≥ 2 (reference group is mFI score = 1)
	p-value	Odds ratio (95% CI)	p-value	Odds ratio (95% CI)	p-value	Odds ratio (95% CI)
Readmission	0.234	1.531 (0.759 to 3.091)	0.019	2.584 (1.168 to 5.717)	0.287	1.354 (0.775 to 2.365)
Reoperation	0.050	2.528 (1.001 to 6.383)	0.104	2.505 (0.829 to 7.570)	0.791	0.909 (0.448 to 1.843)
Postoperative transfusion	0.590	1.256 (0.548 to 2.882)	0.005	3.655 (1.466 to 9.112)	0.008	2.461 (1.261 to 4.804)
Extended length of stay (> 3 days)	0.195	1.427 (0.833 to 2.443)	0.003	2.434 (1.366 to 4.337)	< 0.001	2.160 (1.410 to 3.307)
Non-home discharge	0.881	0.960 (0.564 to 1.634)	< 0.001	3.215 (1.827 to 5.658)	< 0.001	2.837 (1.841 to 4.372)

mFI: modified frailty index; CI: confidence interval.

Bold equals significance p < 0.05.

Discussion

Our study demonstrates that in comparison to patients with a mFI-5 score of 0, patients with a score of 1 were more likely to experience reoperation and patients who had a score of 2 or greater were more likely to be readmitted, require an unplanned blood transfusion, experience an extended length of stay, or be discharged to a non-home location. Notably, there was no significant difference in pulmonary, renal, cardiac, wound, thromboembolic, or sepsis complications between any of the cohorts. The majority of the 1393 patients who underwent revision TSA between the years 2013 and 2019 were found to have at least one comorbidity listed on the mFI-5 (72.6%). Only 27.4% of the patients who needed revision TSA had a score of 0 on the mFI-5.

The findings included in this study are clinically relevant because they demonstrate the increased economic burden of revision TSA patients with comorbidities listed on the mFI-5. Notably, the extended length of stay as well as increased risk of readmission, reoperation, and non-home discharge are all factors that can pose significant cost burdens on patients and the health care system. Various studies have looked into the costs incurred by the average patient recovering from total joint arthroplasty. Sibia et al. estimated that a single day in a US hospital costs between $1528 and $7272, ultimately yielding a total sum of $238 million for patients nationwide who experience an extended length of stay.^22,23 In addition to extended length of stay, studies have shown that patient readmission and reoperation for TSA incurs costs up to $15,000 ²⁴ and $10,100 ²⁵ respectively, which highlights how the presence of comorbidities can drastically increase overall cost of care. Our study shows that the mFI-5 can help stratify patients based on risk for postoperative complications in order to better inform and optimize high risk revision TSA patients prior to surgery. While we cannot state for certain whether risk stratification directly reduces complication rates, we believe that informing patients of their increased risk for surgery may lead them to opt out, thus reducing the overall rates of complication. As such, we recommend that all patients undergoing revision TSA with an mFI-5 score of 2 or greater should be informed of how their risk for the postoperative complications outlined in this study has increased. Additionally, patients should also be made aware of what the financial burden may look like in the case of poor postoperative outcomes, whether their insurance will likely cover the added expenditures, and what resources are available within the local community to support the patient in the case of a non-home discharge.

Several studies have affirmed the utility of mFI-5 in various orthopedic procedures, including posterior lumbar fusion ²⁶ and corrective procedures for adult spinal deformity. ²⁷ They consistently found that higher mFI-5 scores correlated with increased risks of complications, readmission, and non-home discharge, thus coinciding with our study's findings. The main point of variation between these studies was in terms of the specific surgical procedures analyzed, the timeframes of data collection from NSQIP, and the specific types of complications investigated. Collectively, however, these studies work together to validate mFI-5's effectiveness in assessing frailty and predicting postoperative outcomes.

To date, a variety of studies have demonstrated that patients with more comorbidities are more likely to have complications following either revision TSA ²⁸ or TSA.^29,30 Given the increasing rates of TSA and revision TSA, and its impact on patient morbidity and financial burden,^22–25 understanding preoperative optimization of these patients is essential to reducing rates of further complications. Our study expands upon the limited literature on mFI-5 and TSA. Traven et al. found a correlation between mFI-5 scores and increased risk of postoperative complications among patients undergoing primary TSA. ⁹ We expanded upon the variables in Traven et al., including risk of reoperation, wound complications, pulmonary complications, cardiac complications, thromboembolic complications, urinary tract infection, and unplanned postoperative transfusion, because revision TSA patients tend to have more comorbidities and complications.

Jain et al. also showed that patients undergoing arthroplasty with multiple comorbidities had significantly greater odds of postoperative complications when compared to those with single or no comorbidities. ³¹ Of the comorbidities studied in the literature, some of the most common were CHF, steroid use, obesity, age, ASA class 4, low hematocrit, intraoperative blood loss, operative time greater than 2 h, smoking, hypertension, diabetes, and dependent status.^{20,28,30–33} While some of these variables make up the mFI-5, other variables are more complex and cannot be quantified as quickly. Despite not including all of the aforementioned variables, the mFI-5 has proven repeatedly its ability to predict postoperative complication risk.

This study should be interpreted with respect to its limitations. Due to minimal patients in our cohort having mFI-5 scores above 3, we were unable to determine the significance of postoperative complications as a patient increased to mFI-5 score threshold past 2. This imposes an artificial ceiling on our data that hinders our ability to understand how the highest mFI-5 scores correlate with postoperative complications. Additionally, the ACS-NSQIP database does not include complications that occur beyond 30 days of the completed procedure. While this is standard for all NSQIP studies, it is very likely that we are missing the occurrence of postoperative complications that occur outside of the 30-day window. NSQIP also is not able to identify what revision surgery validation process was used at each participating hospital nor does it include pertinent data such as living status on admission, hemoglobin levels, and renal function that would enhance the overall findings of this study. This study is limited by the quality and accuracy of data entered into NSQIP, and there is a potential for selection bias within the cohorts, especially in regard to potential underreporting of complications.^34,35 Also, this study does not include a population comparison between the patients included in this study and the general population. As such, our data has limited applicability to patients whose demographics vary from those studied. Finally, because ACS-NSQIP pulls from only participating hospitals, there is a subset of patients throughout the United States who underwent revision TSA but did not have their data included in our dataset. Unfortunately, we have no way to pull data from those hospitals who do not participate in ACS-NSQIP and are therefore unable to determine the proportion of patients outside of the database. Despite the weaknesses in the ACS-NSQIP database, there are also some key strengths. Because the ACS-NSQIP includes data from more than 600 hospitals throughout the United States, it serves to diversify and strengthen the external validity of the results from this study.

Conclusion

This study identified the mFI-5 to be a valuable tool to stratify patients based on risk for postoperative complications following revision TSA. As revision TSA patients tend to have more comorbidities and complications, it is essential that we examine preoperative risk stratification methods, like the mFI-5, to optimize patient outcomes. Identifying patients who have a high mFI-5 preoperatively may help reduce complications.