Outpatient Spine Surgery: Defining the Outcomes, Value, and Barriers to Implementation

Arjun Vivek Pendharkar, MD; Maryam Nour Shahin, BS; Allen Lin Ho, MD; Eric Scott Sussman, MD; David Arnold Purger, MD, PhD; Anand Veeravagu, MD; John Kevin Ratliff, MD; Atman Mukesh Desai, MD

Disclosures

Neurosurg Focus. 2018;44(5):e11

Abstract and Introduction

Abstract

Spine surgery is a key target for cost reduction within the United States health care system. One possible strategy involves the transition of inpatient surgeries to the ambulatory setting. Lumbar laminectomy with or without discectomy, lumbar fusion, anterior cervical discectomy and fusion, and cervical disc arthroplasty all represent promising candidates for outpatient surgeries in select populations. In this focused review, the authors clarify the different definitions used in studies describing outpatient spine surgery. They also discuss the body of evidence supporting each of these procedures and summarize the proposed cost savings. Finally, they examine several patient- and surgeon-specific considerations to highlight the barriers in translating outpatient spine surgery into actual practice.

Introduction

Spine surgery is one of the most impactful targets for reducing costs within the United States health care system.^[32] An estimated $90 billion is spent each year on the diagnosis and management of low-back pain alone.^[28] As summarized by Resnick et al., spinal disorders are an ideal target for cost reduction because of their high prevalence and significant contribution to morbidity- and disability-related costs.^[36] Furthermore, there is significant variability in the treatment paradigms for spinal disorders—representing the entire spectrum of pain medications, acupuncture, massage therapy, steroid injections, surgical decompression and fusion, and beyond. It is the enormous clinical burden of spinal disease paired with treatment heterogeneity that creates an opportunity to empirically define real value and produce savings for the health care system.

One promising but controversial cost reduction strategy involves transitioning surgical procedures to an outpatient setting. More than 54 million outpatient procedures are performed annually in the United States. Among Medicare beneficiaries, rates of outpatient surgery have increased by 40% in the last 10 years. And the number of ambulatory surgery centers has grown by 60% within the same time period.^[21] Although eye surgeries, arthroscopic procedures, peripheral nerve cases, and soft tissue cases represent the majority of ambulatory operations, an increasing proportion of spine surgeries has transitioned to the outpatient setting.^[2,5,7] Lumbar laminectomy with or without discectomy, lumbar fusion, anterior cervical discectomy and fusion, and cervical disc arthroplasty all represent promising candidates for outpatient surgeries in select populations.

In this focused review, we clarify the different definitions used in studies describing outpatient spine surgery. We also discuss the body of evidence supporting the transition of each of these procedures to an outpatient setting and summarize the proposed cost savings. Finally, we examine several patient- and surgeon-specific considerations to highlight the barriers in translating outpatient spine surgery into actual practice.

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Next Section

Abstract and Introduction
Definitions
Outcomes
Cost
Patient Selection and Discharge Criteria
Surgeon Preference
Conclusions
References

Table 1. Summary on the safety of and outcomes for outpatient lumbar laminectomy and discectomy
Authors & Year	Study Information	Type of Surgery	Observations/Conclusions	Outcomes
Asch et al., 2002	Single institution, prospective, 212 outpatients	Lumbar microdiscectomy	Workers' comp & age had negative impact on outcome	Success rate 75%–80% at 2 yrs, 1 patient (0.5%) admitted to inpatient service after surgery
Best & Sasso, 2007	2 surgeons, patient age ≥65 yrs, study dates 1992–2001	Lumbar decompression: 1377	Lumbar spine surgical decompression safe as outpatient procedure in elderly patients	Required hospital stay: 30 (11.4%), converted to inpatient due to complication: 10 (4.1%), any complication: 4 (7.1%), 72.5% patients who completed questionnaire said they would repeat outpatient procedure; 69.1% said surgical outcome produced good or better function than preop level
Walid et al., 2010	Reviewed patients who went through common process of surgery venue selection: 97 outpatients, 578 inpatients	ACDF (levels unspecified), lumbar microdiscectomy, lumbar decompression w/or w/o fusion	Mean age older in inpatients (p <0.001); prevalence of DM, CHF, heart disease, CABG/stent/balloon angioplasty, knee problems, & depression higher in inpatients (p <0.05); prevalence of COPD & history of stroke higher in outpatient cervical surgery cohort (p <0.05)	Outpatients: any complication 1 (1.0%), postop infection 1 (1.0%); inpatients: any complication 16 (2.8%), postop infection 16 (2.8%); all patients w/complications obese
Pugely et al., 2013	NSQIP, study dates 2005–2010, 1652 (38.3%) outpatients, 2658 (61.7%) inpatients	Single-level lumbar discectomy	Complication rate higher in inpatients (p <0.0001); age, DM, preop wound infection, blood transfusion, op time, & inpatient hospital stay all independent risk factors for short-term complication; surgeons should consider outpatient surgery in appropriate candidates	Complication rates: 3.5% outpatients, 6.5% inpatients
Lang et al., 2014	Two academic hospitals, study dates 2008–2012, 368 after outpatient protocol, 643 before outpatient protocol	Lumbar discectomy	w/implementation of outpatient protocol, outpatient lumbar discectomy safe & effective; improving periop pain management & ensuring cases scheduled early in the day may decrease admissions	Before outpatient protocol: admission rate 96.4%, 30-day readmission 2.3%, ED visit w/o admission 1.1%; after outpatient protocol: admission rate 50.3%, 30-day readmission 4.6%, ED visit w/o admission 2.2%; most common reasons for admission after protocol implemented: uncontrolled pain 18.9%, late op start times 14.1%, comorbidities 13%, intraop complications (almost all dural tears) 11.9%
Best et al., 2015	National Survey of Ambulatory Surgery	Discectomy, laminectomy, fusion	Ambulatory surgeries for intervertebral disc disorders & spinal stenosis increased btwn 1994 & 2006
Helseth et al., 2015	Private clinic, single institution, prospectively recorded complications, study dates 2008–2013, 1449 outpatients	Microsurgical decompression: lumbar 1073, cervical 376	In favor of outpatient spinal surgery for properly selected patients	Surgical mortality: 0 (0%), any complication: 51 (3.5%), same-day admission: 3 (0.2%), admission w/in 3 mos: 22 (1.5%), hematoma: 9 (0.6%), neurological deterioration: 4 (0.3%), deep wound infection: 13 (0.9%), dural lesion & CSF leakage: 15 (1.0%), persistent dysphagia: 2 (0.1%), persistent hoarseness: 2 (0.1%), severe pain/headache: 6 (0.4%), reoperation: 67 (4.6%), all life-threatening hematomas detected w/in hrs after cervical (6 hrs) & lumbar (3 hrs) surgery
Emami et al., 2016	Single institution, study dates Jan–Dec 2012, 32 outpatients, 64 inpatients	1- or 2-level MI TLIFs	Outpatients significantly younger, had lower ASA physical status scores & lower CCIs than inpatients; no statistical difference in overall postop complication rate, readmission rate, final ODI or VAS scores	Outpatients: neurological (allograft malposition or persistent nerve root compression) 2, postop hematoma 0, incidental durotomy 0, SSI 0, instrumentation (pedicle screw malposition, hardware prominence, rod disengagement) 1; inpatients: neurological (allograft malposition or persistent nerve root compression) 3, postop hematoma 2, incidental durotomy 1, SSI 3, instrumentation (pedicle screw malposition, hardware prominence, rod disengagement) 1
Chin et al., 2016	Multiple institutions, 30 outpatients, 40 inpatients	Single-level LLIF w/supplemental pst fixation at each lumbar level from L-1 to L-5; LLIF performed at ASC or as inpatient procedure	LLIF as outpatient procedure has significant improvement in ODI scores compared to scores for inpatient procedure (p = 0.013); outpatient LLIF improves patient outcome w/similar safety as inpatient procedure	Complication rate for inpatient > that for ASC; ASC dermatome numbness: 2 (7%); inpatient dermatome numbness: 4 (10%); weakness: 3 (7.5%); inability to walk: 1 (2.5%)
Chin et al., 2017¹³	Single surgeon, ASC, study dates 2008–2014, 557 ASC, 210 inpatients	Inpatient: decompression 71, fusion 138; outpatient: decompression 150, fusion/disc replacement 197	Majority of spine surgery can be done as outpatient procedure after meeting certain eligibility criteria	Overall revision surgery 14%, overall complication rate 5%
Idowu et al., 2017	Truven Health Marketscan Research Databases, study dates 2003–2014, inpatient hospital, outpatient hospital, ASC	Lumbar fusion, lumbar decompression, ant cervical fusion, pst cervical decompression, pst cervical fusion	True ambulatory surgeries (defined as at ASC) not increasing at same rate as outpatient procedures
Yen & Albargi, 2017	Single institution, 2 18-mo periods, pre- & postimplementation of ambulatory outpatient protocol	Lumbar laminectomy	1 readmission in inpatient cohort, outpatient & overnight laminectomy safe, out of town patients also safe	No patients required postop admission to hospital or readmission in 30 days; inpatient readmission: 1

ant = anterior; ASA = American Society of Anesthesiologists; ASC = ambulatory surgery center; CABG = coronary artery bypass grafting; CCI = Charlson Comorbidity Index; CHF = congestive heart failure; COPD = chronic obstructive pulmonary disease; DM = diabetes mellitus; ED = emergency department; LLIF = lateral lumbar interbody fusion; MI = minimally invasive; NSQIP = National Surgical Quality Improvement Program; ODI = Oswestry Disability Index; pst = posterior; SSI = surgical site infection; TLIF = transforaminal lumbar interbody fusion; VAS = visual analog scale.

Table 2. Summary on the safety of and outcomes for outpatient lumbar fusion
Authors & Year	Study Information	Type of Surgery	Observations/Conclusions	Outcomes
Walid et al., 2010	Reviewed patients who went through common process of surgery venue selection: 97 outpatients, 578 inpatients	ACDF (levels unspecified), lumbar microdiscectomy, lumbar decompression w/or w/o fusion	Mean age older in inpatients (p <0.001); prevalence of DM, CHF, heart disease, CABG/stent/balloon angioplasty, knee problems, & depression higher in inpatients (p <0.05); prevalence of COPD & history of stroke higher in outpatient cervical surgery cohort (p <0.05)	Outpatients: any complication 1 (1.0%), postop infection 1 (1.0%); inpatients: any complication 16 (2.8%), postop infection 16 (2.8%); all patients w/complications obese
Best et al., 2015	National Survey of Ambulatory Surgery	Discectomy, laminectomy, fusion	Ambulatory surgeries for intervertebral disc disorders & spinal stenosis increased btwn 1994 & 2006
Chin et al., 2017¹²	ASC, single surgeon, 16 outpatients	1-level PLIF or TLIF (direct open, single-level PLIF)	Direct open PLIF done safely w/significant reduction in average pain & ODI scores	Worsened back pain & possible aseptic discitis: 1 (6.3%)
Chin et al., 2016	Multiple institutions, 30 outpatients, 40 inpatients	Single-level LLIF w/supplemental pst fixation at each lumbar level from L-1 to L-5; LLIF performed at ASC or as inpatient procedure	LLIF as outpatient procedure has significant improvement in ODI scores compared to scores for inpatient procedure (p = 0.013); outpatient LLIF improves patient outcome w/similar safety as inpatient procedure	Complication rate for inpatients > that for outpatients; ASC dermatome numbness: 2 (7%); inpatient dermatome numbness: 4 (10%), weakness: 3 (7.5%), inability to walk: 1 (2.5%)
Emami et al., 2016	Single institution, study dates Jan–Dec 2012, 32 outpatients, 64 inpatients	1- or 2-level MI TLIFs	Outpatients significantly younger, had lower ASA physical status scores & lower CCIs than inpatients; no statistical difference in overall postop complication rate, readmission rate, final ODI or VAS scores	Outpatients: neurological 2, postop hematoma 0, incidental durotomy 0, SSI 0, instrumentation (pedicle screw malposition, hardware prominence, rod disengagement) 1; inpatients: neurological 3, postop hematoma 2, incidental durotomy 1, SSI 3, instrumentation (pedicle screw malposition, hardware prominence, rod disengagement) 1
Smith et al., 2016	ASC, predictive arm: 873 d/c <24 hrs (outpatients), 160 d/c >23 hrs (inpatients); clinical study: 54 consecutive XLIF & 18 consecutive MI pst fusion	Lumbar fusion (1–4 levels), XLIF, MI pst fusion	Select patients can be treated as outpatients w/XLIF & other MI surgical approaches; based on predictive study: younger age, higher preop hemoglobin, fewer levels, lower BMI, & less advanced disease may predict early d/c	Clinical study (72): no intraop or postop complications in either XLIF or MI pst fusion cohort; no transfers to inpatient facility
Idowu et al., 2017	Truven Health Marketscan Research Databases, study dates 2003–2014, inpatient hospital, outpatient hospital, ASC	Lumbar fusion, lumbar decompression, ant cervical fusion, pst cervical decompression, pst cervical fusion	True ambulatory surgery (defined as at ASC) not increasing at same rate as outpatient procedures
Chin et al., 2017¹²	Prospective, single institution, 30 CBT pedicle screws OSC, 30 traditional pedicle screws inpatient	Pst lumbar fixation	Successful lumbar fusions in OSC using midline CBT pedicle screw; traditional method may still work as outpatient procedure, but authors claim midline technique is more advantageous; OSC led to significant improvement in VAS back pain (p = 0.004) and ODI (p = 0.027) scores; similar fusion rate at 2 yrs
Chin et al., 2017¹³	Single surgeon, ASC, study dates 2008–2014, 557 ASC, 210 inpatients	Inpatient: decompression 71, fusion 138; outpatient: decompression 150, fusion/disc replacement 197	Majority of spine surgery can be done as outpatient procedure after meeting certain eligibility criteria	Overall revision surgery 14%, overall complication rate 5%

BMI = body mass index; d/c = discharge; LLIF or XLIF = lateral lumbar interbody fusion; CBT = cortical bone trajectory; OSC = outpatient surgery center; PLIF = posterior lumbar interbody fusion.

Table 3. Summary on the safety of and outcomes for outpatient anterior cervical spine surgeries
Authors & Year	Study Information	Type of Surgery	Observations/Conclusions	Outcomes
Silvers et al., 1996	Single institution, study dates May–Dec 1994, 50 prospectively analyzed outpatients, 53 retrospectively analyzed inpatient controls	1- to 2-level ACDF	No statistically significant difference btwn inpatient & outpatient groups on any parameters; ambulatory surgery does not compromise safety or efficacy of ACDF	Mortality: 0%, complication rate for each group: 2%; outpatients: dysphagia (partially recovered) & vocal cord paralysis (not fully resolved at >1 yr): 1 (2%); inpatients: superficial wound infection: 1 (1.9%)
Trahan et al., 2011	One physician's practice, study dates Nov 2005–Apr 2009, 59 outpatients, 58 inpatients	1- to 2-level ACDF: 1-level 68, 2-level 49	1- to 2-level ACDF can be done on an outpatient basis; complication rates low, critical postop complications including respiratory compromise occur very infrequently & in the immediate postop period	Outpatients: any complication 1 (1.4%), neck swelling & difficulty breathing & anxiety requiring readmission 1 (1.4%)
Stieber et al., 2005	Two senior authors, freestanding ASC, study dates 1998–2002, 30 ASC, 60 inpatients	1- to 2-level ACDF+P at C4–5 or below as adjunct to autogenous iliac crest bone graft or structural allograft: 1-level: 40, 2-level: 50	Outpatient group had lower complication rate than controls (likely due to selection bias); transient dysphagia most common complication in outpatients	ASC: any complication 3 (10%), dysphagia 3 (10%), readmission 0 (0%); inpatients: any complication 7 (13%), transient dysphagia 3 (5%), graft donor site pain 4 (14%), increased LOS due to complication 4 (7%), readmitted for early complication 4 (7%)
Lied et al., 2008	Single institution, 390 outpatients	ACDF: 278 fused w/autologous iliac crest, 112 fused w/PEEK graft	6-hr postop observation, then discharge is safe	Mortality: 0 (0%); any complication: 37 (9%), immediate complication (0–6 hrs): 17, early complication (6–72 hrs): 1, late complication (>72 hrs): 19; all life-threatening neck hematomas detected w/in first 6 hrs
Villavicencio et al., 2007	Single institution, study dates Apr 2003–Apr 2005, 103 outpatients, d/c <15 hrs postop: 99 (96.1%), d/c after 23 hrs observation after 3-level ACDF: 4 (3.9%)	1- to 3-level ACDF	ACDF w/instrumentation as outpatient is safe & feasible & not associated w/increased complications	Overall complication rate: 4 (3.8%), major complications (vertebral fracture & dehydration resulting in readmission): 2 (1.9%), minor complications (allergic reaction to medications that did not require hospitalization, transient [≤3 mos] neurological deficit): 2 (1.9%)
Garringer & Sasso, 2010	Single surgeon, prospective, study dates Nov 1993–May 2006, 645 outpatients	1-level ACDF	1-level ACDF safe in outpatient setting w/4-hr observation; using postop drain is questionable	Mortality: 0 (0%), any complication: 2 (0.3%), both epidural hematomas, both occurred w/in 4-hr observation period, both resolved w/o permanent deficit; unplanned admission: 24 (6%), >80% due to pain or nausea
Sheperd & Young, 2012	ASC dedicated to spine surgery, study dates 2007–2009, 152 ASC	1- to 2-level ACDF	75 patients completed self-reported survey w/in 6 mos, reporting 100% satisfaction rate; ACDF safe in selected patients as outpatient procedure w/high patient satisfaction	ED visit 6 (3.9%): neck pain 2 (1.3%), dysphagia 1 (0.7%), vocal cord paralysis & dysphagia 1 (0.7%), nausea 1 (0.7%), cervical swelling 1 (0.7%); required readmission: 1 (0.7%); long-term sequelae: 0 (0%); complication rate: 3.9%
Wohns, 2010	Single institution, study dates Feb 2009–May 2010, 14 ASC, 12 hospital-based outpatients	Cervical disc arthroplasty	100% patients reported improvement; outpatient cervical disc arthroplasty costs: 62% < 1-level outpatient ACDF, 84% < 1-level inpatient cervical disc arthroplasty; outpatient: 1-level cervical disc arthroplasty: $11,144.83, 1-level ACDF: $29,313.43; inpatient: 1-level cervical disc arthroplasty: $68,000, 1-level ACDF: $61,095.49	No mortality, complications, cases requiring hospital transfer, postop ED visit
Walid et al., 2010	Reviewed patients who went through common process of surgery venue selection, 97 outpatients, 578 inpatients	ACDF (levels unspecified), lumbar microdiscectomy, lumbar decompression w/or w/o fusion	Mean age older in inpatients (p <0.001); prevalence of DM, CHF, heart disease, CABG/stent/balloon angioplasty, knee problems, & depression higher in inpatients (p <0.05); prevalence of COPD & history of stroke higher in outpatient cervical surgery cohort (p <0.05)	Outpatients: any complication 1 (1.0%), postop infection 1 (1.0%); inpatients: any complication 16 (2.8%), postop infection 16 (2.8%); all patients w/complications obese
Lied et al., 2013	Single institution, 96 outpatients	1- or 2-level ACDF: 1-level: 60, 2-level: 36	91% patient satisfaction using NASSQ; ACDF in select patients w/cervical disc degeneration appears safe as outpatient procedure w/sufficient postop observation; clinical outcomes & patient satisfaction comparable w/those for inpatient procedure	Mortality: 0%; surgical morbidity: 5.2%, hematoma 2 (2.1%), dysphagia 2 (2.1%), neurological deterioration 1 (1%)
Baird et al., 2014	US HCUP SID & SASD for CA, NY, FL, & MD; study dates 2005–2009	Cervical spine surgery in outpatient setting	Increase in cervical spine surgeries in ambulatory setting during study period: ACDF 68%, pst decompression 21%; majority (>99%) d/c home after ambulatory surgery
Martin et al., 2008	NSQIP, 597 outpatients, 2317 inpatients	1-level ACDF	Age >65 yrs, ASA score III or IV, current dialysis, current steroid use, recent sepsis, & op times >120 mins all independent risk factors for complications; no significant differences in complication rate btwn groups; reasonable to consider inpatient 1-level ACDF in patients w/aforementioned risk factors	Mortality: 5 (0.2%), any complication: 92 (3.2%), reoperation: 34 (1.2%); outpatients: mortality 1 (0.2%), any complication (1.3%), reoperation (0.2%); inpatients: mortality 4 (0.2%), any complication (3.6%), reoperation (1.4%)
Best et al., 2015	National Survey of Ambulatory Surgery	Discectomy, laminectomy, fusion	Ambulatory surgeries for intervertebral disc disorders & spinal stenosis increased btwn 1994 & 2006
Helseth et al., 2015	Private clinic, single institution, prospectively recorded complications, study dates 2008–2013, 1449 outpatients	Microsurgical decompression: lumbar 1073, cervical 376	In favor of outpatient spinal surgery for properly selected patients	Surgical mortality: 0 (0%), any complication: 51 (3.5%), same-day admission: 3 (0.2%), admission w/in 3 mos: 22 (1.5%), hematoma: 9 (0.6%), neurological deterioration: 4 (0.3%), deep wound infection 13 (0.9%), dural lesion & CSF leakage: 15 (1.0%), persistent dysphagia: 2 (0.1%), persistent hoarseness: 2 (0.1%), severe pain/headache: 6 (0.4%), reoperation: 67 (4.6%); all life-threatening hematomas detected w/in hrs after cervical (6 hrs) & lumbar (3 hrs) surgery
McGirt et al., 2015	NSQIP, study dates 2005–2011, 1168 outpatients, 6120 inpatients	1- to 2-level ACDF	Return to OR w/in 30 days & major morbidity lower in outpatients	Outpatients: major morbidity 0.94%, return to OR w/in 30 days 1.4%; inpatients: major morbidity 4.5%, return to OR w/in 30 days 2%
Adamson et al., 2016	Single institution, ASC, study dates 2006–2013, 1000 ASC, 484 inpatients	1-, 2-, >2-level ACDF; ASC: 1-level 629, 2-level 365, >2-level 6; inpatient: 1-level 274, 2-level 210	Surgical complications low & can be diagnosed in 4-hr ASC PACU window; similar results compared to those for inpatient ACDF; can perform ACDF safely as outpatient ASC procedure; 90-day morbidity similar btwn cohorts for 1- & 2-level ACDF	Transfer from ASC to inpatient: 8 (0.8%), pain control: 3, chest pain & EEG changes: 2, intraop CSF leak: 1, postop hematoma: 1, profound postop weakness & surgical re-exploration: 1; mortality: 0%; 30-day hospital readmission: 2.2%
Arshi et al., 2017	Humana-insured patients, study dates 2011–2016, 1215 outpatients, 10,964 inpatient	1- to 2-level ACDF	Adjusting for age, sex, & comorbidities: outpatients more likely to undergo revision surgery for pst fusion at 6 mos & 1 yr, ant fusion at 1 yr; outpatient more likely to have postop acute renal failure	Outpatients: acute renal failure 15 (1.23%), respiratory failure 16 (1.32%), CVA 12 (0.99%); inpatients: acute renal failure 164 (1.50%), respiratory failure 313 (2.85%), CVA 132 (1.20)
Chin et al., 2017¹⁴	Single center, ASC	TDR: 55; 1-level ACDF: 55	1-level TDR safe in ASC w/satisfactory clinical & patient-reported outcomes; comparable w/ACDF in outpatient setting	Dysphagia most common postop complaint in both groups (6 total), no intergroup significant differences
Chin et al., 2017¹³	Single surgeon, ASC, study dates 2008–2014, 557 ASC, 210 inpatients	Inpatient: decompression 71, fusion 138; outpatient: decompression 150, fusion/disc replacement 197	Majority of spine surgery can be done as outpatient procedure after meeting certain eligibility criteria	Overall revision surgery 14%, overall complication rate 5%
Idowu et al., 2017	Truven Health Marketscan Research Databases, study dates 2003–2014, inpatient hospital, outpatient hospital, ASC	Lumbar fusion, lumbar decompression, ant cervical fusion, pst cervical decompression, pst cervical fusion	True ambulatory surgery (defined as at ASC) not increasing at same rate as outpatient procedures
Fu et al., 2017	NSQIP database, study dates 2011–2014, 4759 outpatients, 17,211 inpatients	1- to 2-level ACDF: 2-level 6890 (20.7% outpatient)	Greater comorbidity burden (CCI), higher ASA class, chronic steroid use, HTN, & male sex independent risk factors for post-d/c complications; outpatient 2-level ACDF not associated w/increased postop morbidity relative to inpatient procedure	2-level ACDF complications: 1.47% outpatient, 3.94% inpatient (p<0.001)
Khanna et al., 2018	NSQIP, study dates 2011–2013, 1778 (25.6%) outpatients, 5162 (74.4%) inpatients	1-level ACDF 6940	Complication rate higher in inpatient group (p=0.003); outpatient surgery for 1-level ACDF safe & favorable for select patients	Overall complication rate: 4.2%; outpatient: complication rate 1.2%, 30-day readmission 1.8%, mortality 0.1%; inpatient: complication rate 2.5%, 30-day readmission 2.2%, mortality 0.1%
Purger et al., 2017	CA, FL, NY SID & SASD, 3135 ambulatory, 46,966 inpatients	ACDF	Ambulatory younger (48.0 vs 53.1 yrs), more likely white; higher CCI, increased rate of ED visits, & readmission in both groups; overall charges lower for ambulatory $33,362.51 vs inpatient $74,667.04	Ambulatory: mortality 0%, ED w/in 30 days 168 (5.4%), readmitted 51 (1.6%), reoperation 200 (0.4%); infection, hematoma, disruption of surgical site or complication from implant: 20, neck pain or injury, radiculopathy, DD: 52, laryngeal/airway: 0, dysphagia/esophageal: 7, other: 172; inpatient: infection, hematoma, disruption of surgical site or complication from implant: 397, neck pain or injury, radiculopathy, DD: 630, laryngeal/airway: 7, dysphagia/esophageal: 118, other: 3792

ACDF+P = ACDF with plating; CVA = cerebrovascular accident; DD = degenerative disease; EEG = electroencephalography; HCUP = United States Healthcare and Cost Utilization Project; HTN = hypertension; LOS = length of stay; NASSQ = North American Spine Society Questionnaire; OR = operating room; PACU = post-anesthesia care unit; PEEK = polyetheretherketone; SID = State Inpatient Databases; SASD = State Ambulatory Surgery and Services Databases; TDR = total disc replacement.