Geographical Socioeconomic Disadvantage is Associated with Adverse Outcomes Following Major Amputation in Diabetic Patients

Abstract

Objective

Socioeconomic disadvantage is a known predictor of adverse outcomes and amputation in patients with diabetes. However, its association with outcomes following major amputation has not been described. Here, we aimed to determine the association of geographic socioeconomic disadvantage with 30-day readmission and 1-year reamputation among diabetic patients undergoing major amputation.

Methods

Patients from the Maryland Health Services Cost Review Commission Database who underwent major lower extremity amputation with a concurrent diagnosis of diabetes mellitus between 2015–2017 were stratified by socioeconomic disadvantage as determined by the Area Deprivation Index (ADI) (ADI1: least deprived - ADI4: most deprived). The primary outcomes were rates of 30-day readmission and 1-year reamputation, evaluated using multivariable logistic regression models and Kaplan-Meier survival analyses.

Results

A total of 910 patients were evaluated (66.0% male, 49.2% Black race), including 30.9% ADI1 (least deprived), 28.6% ADI2, 19.1% ADI3, and 21.2% ADI4 (most deprived). After adjusting for differences in baseline demographic and clinical factors, the odds of 30-day readmission was similar among ADI groups (P>0.05 for all). Independent predictors of 30-day readmission included female sex (OR=1.45), Medicare insurance (vs. private insurance, OR=1.76), and peripheral artery disease (OR=1.49) (P<0.05 for all). Odds of 1-year reamputation was significantly greater among ADI4 (vs. ADI1, OR=1.74), those with a readmission for stump complication or infection/sepsis (OR=2.65), and those with CHF (OR=1.53) or PAD (OR=1.59) (P<0.05 for all).

Conclusions

Geographic socioeconomic disadvantage is independently associated with 1-year reamputation, but not 30-day readmission among Maryland patients undergoing major amputation for diabetes. A directed approach at improving postoperative management of chronic disease progression in socioeconomically deprived patients may be beneficial to reducing long-term morbidity in this high-risk group.

Table of Contents Summary

Geographic socioeconomic disadvantage, measured by the area deprivation index, is associated with reamputation, but not hospital readmission in this study of 910 diabetic patients undergoing major amputation. Targeted approaches to optimize management for deprived patients with major amputation are needed.

Introduction

Diabetic foot ulcers (DFUs) are a common complication among individuals with diabetes mellitus that are associated with high mortality and morbidity, including infection, hospitalizations, and lower extremity amputations.¹ Up to 20% of patients who develop a DFU will ultimately require a minor or major lower extremity amputation,² which are associated with poor post-operative prognoses.^3,4 Previous studies report 30-day readmission rates between 11% and 29% following major amputations.^5–7 The risk of reamputation following index amputation is also relatively high, occurring in 4.7% and 13.3% of patients at one and five years, respectively.⁸

Identification of the factors associated with readmission and reamputation following lower extremity procedures is critical for devising strategies to minimize post-operative morbidity. The impact of individual social factors including race, income, and payer status on diabetic lower extremity amputation have been previously described.⁹ However, the relationship between neighborhood disadvantage and health outcomes is often multifactorial and cannot be assessed by a single metric.¹⁰ The Area Deprivation Index (ADI)¹¹ is a comprehensive metric that encompasses the domains of household income, education, employment, and housing quality at the 9-digit zip code level.¹² By incorporating several socioeconomic measures into a single metric, the ADI possesses the distinct advantage of providing a holistic assessment of an individual’s socioeconomic deprivation that individual factors cannot. ADI has been previously associated with outcomes such as postoperative discharge destination following elective hip surgery, minor foot amputations, all-cause hospital readmissions, and mortality.^13–17 Arya et al. previously demonstrated that the risk of major amputation is higher with increasing ADI (i.e. more deprivation) in a cohort of patients with incident peripheral artery disease (PAD).¹⁸ Additionally, work from the state of California has demonstrated clustering of diabetic lower extremity amputations among areas of lower household income.¹⁹ However, there are no known studies to date assessing the relationship between neighborhood disadvantage and outcomes following major lower extremity amputation.

In this study, we aimed to determine the association of ADI with 30-day readmission and 1-year reamputation in a cohort of diabetic patients in Maryland who underwent major lower extremity amputation. We hypothesized that diabetic patients in higher ADI groups would have higher odds of 30-day readmission and 1-year reamputation after major amputation.

Methods

Data Source

This study was a retrospective cohort analysis of nonconfidential patient records from the Maryland Health Services Cost and Review Commission (HSCRC) database between Quarter 3 of 2015 to Quarter 3 of 2017. The HSCRC is a prospectively maintained database of all inpatient and outpatient hospital visits to 53 non-federal hospitals in the state of Maryland that contains patient-level demographic, clinical, and billing data.²⁰ Eligible patients were linked to a unique identifier that allowed for identification of future inpatient admissions and procedures. The study design and methods for data collection were approved by the Johns Hopkins University School of Medicine Institutional Review Board. Informed consent was waived because the data was deidentified and publicly available.

Inclusion and Exclusion Criteria

All clinical diagnoses and comorbidities were identified using codes from the International Classification of Disease, ninth and tenth edition, Clinical Modification (ICD-CM). Major amputations were identified using the ICD Procedure Coding System (ICD-PCS). All adult patients with a diagnosis of diabetes who underwent an initial major amputation in an inpatient setting were included in our study. Major amputation was defined as any amputation at the level of the leg (0Y6C0Zx, 0Y6D0Zx, 0Y6J0Zx, 0Y6H0Zx), knee (0Y6F0ZZ, 0Y6G0ZZ), or femur (0Y670ZZ, 0Y680ZZ). Patients who underwent an index minor amputation (i.e. below the level of the ankle) were excluded (n=2,499). Patients who died during their postoperative inpatient stay (n=43; 3.8% ADI1, 6.1% ADI2, 3.8% ADI3, 4.0% ADI4) were also excluded.

ADI percentiles for the state of Maryland were retrieved from the University of Wisconsin Department of Medicine’s Neighborhood Atlas.¹² ADI was then calculated for each patient based on their 9-digit residential zip code as previously described.²¹ Patients were subsequently stratified into nationally-defined ADI quartiles [ADI1 (least deprived): 0–25; ADI2: 26–50; ADI3: 51–75; ADI4 (most deprived): 76–100]. ADI1 is designed to contain 85% of the general population, whereas ADI2-4 are designed to capture the remaining 15% in 5% increments.²¹

Other patient sociodemographic factors assessed included age (18–39 years, 40–64 years, ≥65 years), sex, race (white, black, other/unknown), geographic status (rural, urban), payer status (private, Medicare, Medicaid, other/uninsured), and smoking status (never, current, former). Geographic rurality was determined using the Missouri Census Data Center’s Census geographic crosswalk²⁰ and matched using each patient’s 5-digit residential zip code. Amputation level was categorized as below-knee amputation (BKA) or above-knee amputation (AKA). Discharge destination was classified as skilled nursing facility or subacute rehabilitation (SNF/SAR) facility or home. Clinical comorbidities assessed included hypertension (HTN), dyslipidemia (DLD), congestive heart failure (CHF), coronary artery disease (CAD), peripheral artery disease (PAD), chronic kidney disease (CKD), peripheral neuropathy (PN), and chronic obstructive respiratory disease (COPD).

Outcomes

The primary outcomes of this study were 30-day readmission and 1-year reamputation. 30-day readmission was defined as the presence of a documented inpatient event at any hospital within the state of Maryland within 30 days of discharge from the index major amputation. For those patients discharged to a SNF/SAR, admissions occurring on the same day of discharge from the index procedure were assumed to be due to facility transfer and thus not included as a readmission. For patients with a 30-day readmission, the principal diagnosis at time of readmission was retrieved and categorized as previously described in Kayssi et al.⁶ Similarly, 1-year reamputation was defined as the presence of a documented inpatient event containing an ICD procedure code for major lower extremity amputation within one year from the index amputation. Selected procedure codes were limited to ones in which a major amputation was performed, in order to exclude stump revisions from being counted as reamputation. Of note, stump revisions within 30 days of the index amputation were captured in the 30-day readmission outcome, and were classified as having a stump complication in Supplementary Table I.

Statistical analysis

Baseline characteristics for patients, stratified by ADI quartile, were reported using percentages. 30-day readmission and 1-year reamputation events were reported as binary outcomes and compared among ADI quartiles using Pearson’s chi-square tests. A nonparametric test for trend was also performed to assess whether there was correlation between increasing ADI quartile and the primary outcomes. Kaplan-Meier analysis with log-rank test was used to compare reamputation rates between ADI groups. Univariable and multivariable logistic models were then used to assess risk factors associated with 30-day readmission and 1-year reamputation. Factors that yielded P≤0.25 on univariable analysis were subsequently included in the multivariable model.²² Statistical significance was considered at P<0.05. Statistical analysis was performed with Stata/MP version 15.1 (StataCorp, College Station, TX, USA).

Results

Study Cohort

Overall, 910 patients with diabetes underwent a major amputation during the study period (Table II). 281 (30.9%) patients were classified as ADI1 (least deprived), 260 (28.6%) as ADI2, 175 (19.2%) as ADI3, and 194 (21.3%) as ADI4 (most deprived) Compared to the ADI distribution of the general population, major amputations were more prevalent in the more deprived (Figure 1). 46.5% (N=423) of patients underwent AKA as their index operation, and 84.4% (N=768) were discharged to a SNF/SAR. Approximately half of patients were age ≥65 (50.1%, N=456), 66.0% (N=601) were male, and 49.2% (N=448) were Black. The majority (90.9%, N=827) of patients were classified as residing in an urban environment, 66.6% (N=606) utilized Medicare as their primary insurer, and 57.8% (N=526) were never smokers. Comorbid conditions, including PAD (52.4%, N=477), CKD (49.2%, N=448), DLD (48.0%, N=437), HTN (45.6%, N=415), CAD (44.3%, N=403), and CHF (30.2%, N=275), were common.

Table 2.

30-day readmission and 1-year reamputation events following diabetic major lower extremity amputation in Maryland (2013–2019), stratified by ADI quartile.

	ADI1	ADI2	ADI3	ADI4
Event Rate, n (%)	(Least Deprived)		(Most Deprived)		P	P-trend
30-day readmission	47 (16.73)	54 (20.77)	25 (14.29)	46 (23.71)	0.078	0.208
1-year reamputation	31 (11.03)	40 (15.38)	22 (12.57)	38 (19.59)	0.057	0.026

Abbreviations: ADI; Area Deprivation Index.

Figure 1.

Overview of study cohort, by ADI quartile. Proportion of index major amputations by ADI quartile (green bars) compared to the expected distribution of ADI quartile (blue bars).

Crude Outcomes

The overall frequency of 30-day readmission across all ADI groups was 18.9% (N=172) and did not significantly change with increasing ADI quartile (P-trend=0.208; Table II). The most common reason for 30-day readmission was amputation stump complication (23% overall), followed by infection or sepsis (20% overall) and diabetic complications (13% overall; Supplementary Table I). Readmissions related to cardiovascular disease were more common among ADI4 compared to the other ADI categories (P = 0.025; Supplementary Table I).

One-year reamputation events occurred in 14.4% (N=131) of patients, and significantly increased with increasing ADI quartile (P-trend=0.026; Table II). Kaplan-Meier analysis confirmed that higher ADI quartile was associated with an increased risk of reamputation by one-year postoperatively (P=0.043; Figure 1).

Risk Factors for 30-Day Readmission

Based on univariate logistic regression analysis, factors associated with increased an odds of 30-day readmission included female sex, having Medicare (vs. private) insurance, and comorbid DLD and PAD (P≤0.05 for all; Table III). ADI4 (most deprived) had a slightly elevated odds of 30-day readmission compared to ADI1 (least deprived), but this was not statistically significant [OR=1.55, 95% CI (0.98, 2.44); Table III].

Table 3.

Risk factors associated with 30-day readmission among diabetic patients undergoing major lower extremity amputation in Maryland (2013–2019).

Characteristic	Unadjusted		Adjusted
	OR (95% CI)	P	OR (95% CI)	P
ADI quartile
1	Ref		Ref
2	1.31 (0.84, 2.01)	0.229	1.31 (0.84, 2.06)	0.226
3	0.83 (0.49, 1.41)	0.487	0.79 (0.46, 1.35)	0.384
4	1.55 (0.98, 2.44)	0.060	1.32 (0.82, 2.14)	0.254
Age, years
18–39	Ref		-
40–64	1.48 (0.43, 5.07)	0.534	-
≥65	1.98 (0.58, 6.76)	0.275	-
Sex
Male	Ref		Ref
Female	1.52 (1.08, 2.13)	0.015	1.45 (1.01, 2.06)	0.042
Race
White	Ref		Ref
Black	1.34 (0.96, 1.88)	0.088	1.18 (0.82, 1.70)	0.380
Other/unknown	0.17 (0.02, 1.29)	0.087	0.21 (0.03, 1.58)	0.129
Geographic status
Rural	Ref		-
Urban	0.85 (0.48, 1.49)	0.566	-
Insurance
Private	Ref		Ref
Medicare	1.96 (1.15, 3.23)	0.013	1.76 (1.01, 3.06)	0.046
Medicaid	1.10 (0.56, 2.18)	0.780	1.12 (0.55, 2.29)	0.751
Other/uninsured	-	-	-	-
Smoking status
Never	Ref		Ref
Current	1.01 (0.67, 1.53)	0.971	1.07 (0.67, 1.70)	0.772
Former	0.75 (0.48, 1.16)	0.198	0.73 (0.46, 1.15)	0.176
Amputation level
BKA	Ref		Ref
AKA	1.37 (0.99, 1.92)	0.061	1.22 (0.85, 1.74)	0.276
Discharge
SNF/SAR	Ref		-
Home	1.07 (0.68, 1.69)	0.758	-
Comorbidities
HTN	1.05 (0.75, 1.46)	0.791	-	-
DLD	1.43 (1.02, 1.99)	0.036	1.40 (0.99, 2.00)	0.060
CHF	1.18 (0.83, 1.69)	0.355	-	-
CAD	1.22 (0.87, 1.70)	0.245	0.96 (0.66, 1.38)	0.810
PAD	1.59 (1.13, 2.23)	0.008	1.49 (1.04, 2.12)	0.030
CKD	1.27 (0.91, 1.77)	0.159	1.17 (0.82, 1.69)	0.388
PN	0.54 (0.23, 1.29)	0.169	0.48 (0.20, 1.18)	0.112
COPD	1.39 (0.91, 2.13)	0.128	1.23 (0.77, 1.95)	0.392

Abbreviations: ADI, Area Deprivation Index; BKA, Below knee amputation; AKA, Above knee amputation; SNF, Skilled nursing facility; SAR, Subacute rehabilitation facility; HTN, Hypertension; DLD, Dyslipidemia; CHF, Congestive heart failure; CAD, Coronary artery disease; PAD, Peripheral artery disease; CKD, Chronic kidney disease; PN, Peripheral neuropathy; COPD, Chronic obstructive pulmonary disease.

After adjusting for baseline demographic and clinical factors, ADI quartile was not associated with an increased odds of 30-day readmission (P≥0.22; Table 3). Female sex [OR=1.45, 95% CI (1.01, 2.06)], having Medicare insurance [vs. private; OR=1.76, 95% CI (1.01, 3.06)], and PAD [OR=1.49, 95% CI (1.04, 2.12); Table III] remained significant risk factors for 30-day readmission.

Risk Factors for 1-Year Reamputation

Unadjusted analyses demonstrated that ADI4 [vs. ADI1; OR=1.96, 95% CI (1.17, 3.29); Table IV] was associated with the highest odds of 1-year reamputation. Black race was also associated with greater 1-year reamputation [vs. White race; OR=1.46, 95% CI (1.00, 2.14)]; however, other socioeconomic factors including age, sex, geographic status, and payer status did not demonstrate statistical significance (all P>0.05; Table IV). Having a readmission for stump complication or infection/sepsis within 30 days after the index amputation was also associated with 1-year reamputation [OR=2.82, 95% CI (1.65, 4.83); Table IV]. Clinical comorbidities associated with reamputation within one year included CHF [OR=1.58, 95% CI (1.08, 1.73)] and PAD [OR=1.82, 95% CI (1.24, 2.68); Table IV]. Level of amputation was not significantly associated with reamputation [AKA vs. BKA; OR 1.00, 95% CI (0.69, 1.45); Table IV].

Table 4.

Risk factors associated with 1-year reamputation among diabetic patients undergoing major lower extremity amputation in Maryland (2013–2019).

Characteristic	OR (95% CI)	P	OR (95% CI)	P
ADI quartile
1	Ref		Ref
2	1.47 (0.89, 2.42)	0.136	1.49 (0.89, 2.49)	0.129
3	1.16 (0.65, 2.08)	0.618	1.17 (0.65, 2.13)	0.595
4	1.96 (1.17, 3.29)	0.010	1.74 (1.02, 2.97)	0.042
Age, years
18–39	Ref		-
40–64	0.85 (0.28, 2.57)	0.779	-
≥65	0.90 (0.30, 2.72)	0.858	-
Sex
Male	Ref		Ref
Female	1.44 (0.99, 2.10)	0.059	1.31 (0.89, 1.94)	0.176
Race
White	Ref		Ref
Black	1.46 (1.00, 2.14)	0.048	1.30 (0.87, 1.93)	0.201
Other/unknown	0.53 (0.12, 2.30)	0.397	0.63 (0.14, 2.80)	0.545
Geographic status
Rural	Ref		-
Urban	1.19 (0.59, 2.37)	0.625	-
Insurance
Private	Ref		Ref
Medicare	1.72 (0.95, 3.11)	0.073	1.36 (0.74, 2.51)	0.322
Medicaid	1.38 (0.66, 2.87)	0.390	1.24 (0.58, 2.64)	0.582
Other/uninsured	1.22 (0.25, 5.89)	0.805	1.27 (0.26, 6.24)	0.772
Smoking status
Never	Ref		-
Current	1.15 (0.72, 1.83)	0.472	-
Former	1.23 (0.78, 1.94)	0.383	-
Amputation level
BKA	Ref		-
AKA	1.00 (0.69, 1.45)	0.984	-
Discharge
SNF/SAR	Ref		-
Home	0.73 (0.42, 1.27)	0.261	-
Readmission for infection	2.82 (1.65, 4.83)	<0.001	2.65 (1.52, 4.63)	0.001
Comorbidities
HTN	1.05 (0.72, 1.52)	0.811	-
DLD	1.08 (0.74, 1.56)	0.693	-
CHF	1.58 (1.08, 2.32)	0.020	1.53 (1.03, 2.29)	0.037
CAD	1.20 (0.83, 1.73)	0.344	-
PAD	1.82 (1.24, 2.68)	0.002	1.59 (1.07, 2.37)	0.010
CKD	1.13 (0.78, 1.64)	0.507	-
PN	1.09 (0.50, 2.36)	0.834	-
COPD	1.22 (0.75, 1.98)	0.420	-

Abbreviations: ADI, Area Deprivation Index; BKA, Below knee amputation; AKA, Above knee amputation; SNF, Skilled nursing facility; SAR, Subacute rehabilitation facility; HTN, Hypertension; DLD, Dyslipidemia; CHF, Congestive heart failure; CAD, Coronary artery disease; PAD, Peripheral artery disease; CKD, Chronic kidney disease; PN, Peripheral neuropathy; COPD, Chronic obstructive pulmonary disease.

Multivariable logistic regression confirmed that ADI4 was persistently associated with an increased odds of 1-year reamputation [vs. ADI1; OR=1.74, 95% CI (1.02, 2.97); Table IV] after adjusting for baseline demographic and clinical characteristics. 30-day readmission for stump complication or infection/sepsis was associated with a 2.65-increased odds of 1-year reamputation [95% CI (1.52, 4.63); Table IV]. CHF [OR=1.53, 95% CI (1.03, 2.29)] and PAD [OR=1.59, 95% CI (1.07, 2.37); Table IV] were also independent predictors of 1-year reamputation.

Discussion

Despite continued advancements in the management of DFUs and techniques for limb salvage, major amputation remains a commonly performed and highly morbid procedure among the diabetic population.² Individual socioeconomic factors have been associated with poor outcomes following diabetic amputation in the past.^9,18 However, no studies to date have examined the association of ADI, an aggregate measure of geographic deprivation, with outcomes following major lower extremity amputation in patients with diabetes. Here, we demonstrate that increasing ADI quartile (i.e., increased deprivation) is independently associated with 1-year reamputation, but not 30-day readmission in a cohort of 910 diabetic patients who underwent major amputation. This finding has important implications for the long-term postoperative management of deprived populations undergoing major amputation.

This study is the first to describe the relationship between socioeconomic factors and reamputation among patients with diabetes who undergo major amputation. While previous studies have focused on demographic characteristics and clinical risk factors,^8,23,24 we demonstrate that neighborhood socioeconomic disadvantage is an independent predictor of reamputation even after adjusting for these factors. Notably, perioperative readmissions for stump complications occurred with similar frequency across ADI quartiles, suggesting that reamputation is a long-term issue rather than a difference in perioperative outcomes. Consistent with this notion, we found no differences in 30-day readmission rates between ADI groups, and our Kaplan-Meier analysis suggests that reamputations are a longitudinal problem among deprived patients. Previous studies have demonstrated that low socioeconomic status is a barrier to proper access and utilization of cardiovascular disease and diabetes care services,^25,26 both clinical factors that are known contributors to amputation risk.^24,27 Here, we also demonstrate that readmission secondary to cardiovascular disease is more common among individuals within ADI4. Thus, it seems that the factors predisposing the socioeconomically disadvantaged to greater rates of major amputation are also placing them at higher risk of reamputation postoperatively.

It is important to note the skewness of our cohort towards the disadvantaged. Based on the 85-5-5-5% population distribution of the national ADI as originally described by Kind et al.,²¹ it is expected that the vast majority of individuals undergoing major amputation would be classified as ADI1. However, our sample is relatively evenly distributed across all ADI quartiles, with only 30.9% of individuals falling under ADI1 (Figure 1). These data suggest that, in a sample of patients with diabetes from Maryland, the distribution of major amputees is disproportionately skewed toward the socioeconomically deprived. Furthermore, only about 50% of patients in our study had PAD, suggesting that a large proportion of amputations were performed for wounds and/or infection, which are largely avoidable with the use of regular foot exams and early referral to a multidisciplinary limb salvage service.²⁸

Notably, 46.5% of patients in our cohort underwent an AKA. Previous studies have demonstrated greater likelihood of successful rehabilitation and quality of life with a lower level of amputation.^29,30 Thus, there are efforts among clinicians to maximize utilization of BKA whenever major amputation is indicated.^31,32 However, in an epidemiological study of lower extremity operations in England, AKA still comprised 46.7% of all major amputations performed.³³ Our findings, representing a longitudinal series of all major amputations from the state of Maryland between 2015–2017, are similar. It is somewhat surprising that patients with diabetes but without PAD are undergoing such high AKA rates. Unfortunately, the administrative nature of the dataset precludes our ability to understand the precise indication for amputation and amputation level. Additional population-based studies are needed to further delineate patterns of usage of BKA and AKA among individuals who require major amputation.

There is some variation among studies that report 1-year reamputation outcomes after major amputation in diabetic patients, with reported rates ranging from 5–19%.^8,23,24 Our overall 1-year reamputation rate of 14.4% is consistent with these findings. Aside from ADI, we found that PAD was associated with higher odds of reamputation. This was an expected finding given that PAD has been associated with higher risks of lower extremity amputation and reamputation in the past.^34–36 Importantly, we did not find a significant difference in odds of reamputation between patients that underwent BKA versus AKA. Major perioperative complications, including reoperation, have been reported to occur in approximately 10% of BKA patients and 12% of AKA patients.^37,38 However, longer-term data comparing major reamputation following BKA vs. AKA is limited. In a study of 116 patients undergoing non-traumatic amputation, Schmiegelow et al. reported 90-day reamputation rates of 19.1% vs. 2.1% for BKA vs. AKA, respectively.³⁹ In a small cohort of patients who underwent lower extremity amputations in Greece, Skoutas et al. demonstrated that 20% (4 of 20) of BKA patients and 0% (0 of 5) of AKA patients underwent reamputation within 18 months of index operation.²⁴ Contrary to these data, our findings suggest that, based on data from nearly 1,000 major amputations, major reamputation rates following BKA vs. AKA may actually be more similar in patients with diabetes than previously thought. It is unclear whether the difference in our study findings compared to those of the previous studies is due to differences in patient populations, our inability to distinguish between proximal ipsilateral reamputation and index contralateral major amputation, or other factors currently unaccounted for. Further work is needed to elucidate differences in reamputation rates between patients undergoing BKA versus AKA.

ADI quartile was not associated with 30-day readmissions in our study. We had hypothesized that patients with higher ADI (i.e. more deprivation) would have higher odds of 30-day readmission after major amputation based off of previous work demonstrating an association between ADI and readmission rates in other fields.^13,21,40 In one of the first studies to examine the impact of ADI on healthcare outcomes, Kind et al. demonstrated that the rate of 30-day rehospitalization for patients discharged with congestive heart failure, pneumonia, or myocardial infarction increased with greater geographic deprivation (i.e., ADI2 - ADI4) among Medicare patients.²¹ They attributed their findings to the notion that geographic areas of concentrated poverty results in burdens beyond those stemming from individual circumstances. The lack of an association of ADI with readmission in our study may be due to differences in readmission risk profiles. Readmission in the immediate postoperative period may be more contingent on wound care and rehabilitation in our cohort, versus social determinants of health that may play a greater role following hospitalization for medical (i.e., non-surgical) reasons.^6,41 This concept is supported by a higher frequency of readmissions for cardiovascular complications among ADI4 patients in our study, but similar frequencies of readmission for stump complications and infection. In addition, 84% of patients in our study were discharged to a SNF/SAR, which may have mitigated the social challenges that lead to readmissions in other cohorts.

In order to avoid significant morbidity after diabetic foot amputation, it is important to identify potential strategies to address the increased risk of reamputation among socioeconomically deprived patients. One consideration is to improve the postoperative management of chronic disease processes that contribute to DFUs and subsequent major amputation. Reamputation can occur from many etiologies, including as a sequela of poorly controlled diabetes,²⁴ and engagement in regular postoperative follow-up and chronic disease management is important for patients undergoing major amputation. This is particularly true among socially deprived individuals who tend to have reduced access to healthcare compared to non-deprived populations.⁴² Additionally, use of a multidisciplinary model for longitudinal care of diabetes has also been shown to reduce the rate of amputations and other complications.^43–45 We have previously demonstrated that the association of ADI with diabetic foot ulcer healing is mitigated with the use of a multidisciplinary care approach.²⁸ All patients at our institution are seen by a vascular surgeon, as well as surgical podiatrist, wound care nurse, physician assistant, prosthetist, and endocrinologist in order to optimize care prior to amputation and provide longitudinal support of chronic disease afterwards.²⁸ Future research is needed to assess the utility of a multidisciplinary team in the post-operative period for diabetic major amputation in order to facilitate potentially critical components of care, such as endocrinology, physical medicine, and rehabilitation, for these patients.

This study has some limitations. First, the HSCRC is a comprehensive and longitudinal database that contains information on all inpatient and outpatient hospital visits within Maryland. However, it is an administrative database, and all procedures and clinical features were defined using ICD-PCS and -CM codes. Other relevant factors, including indications for major amputation, PAD severity/anatomy, obesity status, and disability status could not be assessed due to lack of appropriate variables. Severity of underlying diabetes was also not directly measured. Another limitation of using administrative coding to define reamputation is the inability to distinguish between a proximal ipsilateral reamputation and an index contralateral major amputation. However, both represent a failure of postoperative convalescence and chronic disease management with significant morbidity. We were also unable to assess long-term survival of amputees due to the lack of longitudinal mortality data in the HSCRC. Additionally, since the HSCRC only captures hospital cases within Maryland, follow-up care that is sought outside of the state or in an ambulatory setting cannot be unaccounted for. Maryland is also the only state in the nation that reimburses providers and hospitals under an all-payer system, such that compensation for a given service is the same regardless of payer status.⁴⁶ The all-payer system aims to provide improved quality of care and lower expenditure for residents covered under Medicare and Medicaid, and thus our Maryland-specific reported outcomes may differ if expanded to a national cohort.

Conclusion

In this study, we demonstrate that neighborhood socioeconomic status, as defined by the ADI, is independently associated with 1-year reamputation, but not 30-day readmission, following major amputation for diabetes in a cohort of Maryland patients. Targeted initiatives directed at improving the postoperative management of chronic disease progression in highly deprived patients undergoing major amputation are needed to improve access to postoperative care and rehabilitation in this high-risk group.

Supplementary Material

1

Supplementary Table 1. Reasons for readmission to hospital within 30 days of major amputation, stratified by ADI quartile.

Figure 2.

Kaplan-Meier analysis for the association of ADI quartile with reamputation among diabetic patients undergoing major lower extremity amputation in Maryland (2013–2019).

Note: All standard error values were less than 10%. ADI1 = least deprived; ADI4 = most deprived.

Table 1.

Demographic and clinical characterics of diabetic patients who underwent major lower extremity amputation in Maryland (2013–2019), stratified by ADI quartile.

ADI Percentile:	ADI1	ADI2	ADI3	ADI4
	(Least Deprived)			(Most Deprived)
Characteristic, %	281 (30.88%)	260 (28.57%)	175 (19.23%)	194 (21.32%)
Age, years
18–39	4 (1.37)	7 (2.69)	5 (2.86)	9 (4.64)
40–64	117 (41.44)	132 (50.77)	89 (50.86)	91 (46.91)
≥65	160 (57.19)	121 (46.54)	81 (46.29)	94 (48.45)
Sex
Male	186 (66.19)	181 (69.62)	117 (66.86)	117 (60.13)
Female	95 (33.81)	79 (30.38)	58 (33.14)	77 (39.69)
Race
White	144 (51.25)	139 (53.46)	86 (49.14)	64 (32.99)
Black	121 (43.06)	116 (44.62)	85 (48.57)	126 (64.95)
Other/unknown	16 (5.69)	5 (1.92)	4 (2.29)	4 (2.06)
Geographic status
Rural	40 (14.29)	16 (6.15)	12 (6.86)	12 (6.25)
Urban	240 (85.71)	24 (93.85)	163 (93.14)	180 (93.75)
Insurance
Private	55 (19.57)	50 (19.23)	23 (13.14)	14 (7.22)
Medicare	188 (66.90)	162 (62.31)	118 (67.43)	138 (71.13)
Medicaid	36 (12.10)	42 (16.15)	30 (17.14)	39 (20.10)
Other/insured	4 (1.43)	6 (2.30)	4 (2.28)	3 (1.55)
Smoking status
Never	165 (58.72)	150 (57.69)	101 (57.71)	110 (56.70)
Current	44 (15.66)	59 (22.69)	39 (22.29)	49 (25.26)
Former	72 (25.62)	51 (19.62)	35 (20.00)	35 (18.04)
Amputation level
BKA	149 (53.02)	135 (51.92)	98 (56.00)	105 (54.12)
AKA	132 (46.98)	125 (48.08)	77 (44.00)	89 (45.88)
Discharge
SNF/SAR	239 (85.36)	216 (83.08)	145 (82.86)	168 (86.60)
Home	41 (14.64)	44 (16.92)	30 (17.14)	26 (13.40)
Comorbidities
HTN	130 (46.26)	119 (45.77)	72 (41.14)	94 (48.45)
DLD	140 (59.82)	117 (45.00)	84 (48.00)	96 (49.48)
CHF	88 (31.32)	75 (28.85)	56 (32.00)	56 (28.87)
CAD	132 (46.98)	118 (45.38)	77 (44.00)	76 (39.18)
PAD	147 (52.31)	135 (51.92)	84 (48.00)	111 (57.22)
CKD	151 (53.74)	120 (46.15)	90 (51.43)	87 (44.85)
PN	18 (6.41)	12 (4.62)	9 (5.14)	13 (6.70)
COPD	33 (11.74)	41 (15.77)	33 (18.86)	38 (19.59)

Abbreviations: ADI, Area Deprivation Index; BKA, Below knee amputation; AKA, Above knee amputation; SNF, Skilled nursing facility; SAR, Subacute rehabilitation facility; HTN, Hypertension; DLD, Dyslipidemia; CHF, Congestive heart failure; CAD, Coronary artery disease; PAD, Peripheral artery disease; CKD, Chronic kidney disease; PN, Peripheral neuropathy; COPD, Chronic obstructive pulmonary disease.

ARTICLE HIGHLIGHTS.

Type of Research:

Retrospective cohort study of registry data from the Maryland Health Services Cost Review Commission (HSCRC).

Key Findings:

Among 910 diabetic patients who underwent major amputation stratified by area deprivation index (ADI) quartile, socioeconomic disadvantage was not associated with 30-day hospital readmission. However, the odds of 1-year reamputation was significantly greater among the most deprived (ADI4; OR 1.74 vs. ADI1, least deprived).

Take Home Message:

Neighborhood socioeconomic status, as defined by ADI, is independently associated with 1-year reamputation, but not 30-day readmission, following major diabetic lower extremity amputation.