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Impact of age within younger populations on outcomes following cervical surgery in the ambulatory setting

Published:September 16, 2022DOI:https://doi.org/10.1016/j.jcot.2022.102016

      Abstract

      Objective

      To determine the effect of age within the younger population seen at ambulatory surgical centers on patient-reported outcome measures (PROMs) after cervical spine surgery.

      Methods

      Patients of age <65 years undergoing single-level anterior cervical discectomy and fusion (ACDF) or cervical disc replacement (CDR) were included. Patients were divided by mean age of initial population (46 years). PROMs included Patient-reported Outcome Measurement Information System Physical Function (PROMIS-PF), 12-Item Short-Form Physical Component Survey (SF-12 PCS), Visual Analog Scale (VAS) neck, VAS arm, Neck Disability Index (NDI) collected preoperatively and at postoperative time points up to 2 years.

      Results

      138 patients were included, with 66 patients <46 years. Both cohorts demonstrated improvement from preoperative baseline with regard to all studied PROMs at multiple time points postoperatively (p ≤ 0.042, all). Between groups, the older cohort demonstrated greater mean PROMIS-PF scores preoperatively and at 6 weeks (p ≤ 0.011, both), while VAS arm scores were lower in the older group at 1 year (p = 0.002), and NDI scores were lower in the older group at 6 weeks and 1 year (p < 0.027, both). Minimal Clinically Important Difference (MCID) achievement rates were greater in the younger group in PROMIS PF at 2 years (p = 0.002), and in the older group in VAS arm score at 1 year (p = 0.007).

      Conclusion

      Both cohorts showed significant improvement at multiple postoperative time points for all PROMs. Between groups, the older group reported more favorable physical function, VAS arm, and NDI scores at several time points. However, MCID achievement rates only significantly differed in two PROMs at singular time points. Difference in age in patients <65 years likely does not significantly affect long-term outcomes after cervical spine surgery.

      Keywords

      Abbreviations:

      ACDF (anterior cervical discectomy and fusion), CDR (cervical disc replacement), PROM (patient-reported outcome measure), MCID (minimum clinically important difference)

      1. Introduction

      The rate of spine procedures performed on an annual basis has seen steady increase over the past several decades.
      • Gray D.T.
      • Deyo R.A.
      • Kreuter W.
      • et al.
      Population-based trends in volumes and rates of ambulatory lumbar spine surgery.
      • Wang M.C.
      • Kreuter W.
      • Wolfla C.E.
      • Maiman D.J.
      • Deyo R.A.
      Trends and variations in cervical spine surgery in the United States: medicare beneficiaries, 1992 to 2005.
      • Lad S.P.
      • Patil C.G.
      • Berta S.
      • Santarelli J.G.
      • Ho C.
      • Boakye M.
      National trends in spinal fusion for cervical spondylotic myelopathy.
      • Baird E.O.
      • Egorova N.N.
      • McAnany S.J.
      • Qureshi S.A.
      • Hecht A.C.
      • Cho S.K.
      National trends in outpatient surgical treatment of degenerative cervical spine disease.
      Regarding cervical spine surgery alone, multiple studies have cited drastic increase in procedure rates, with one study reporting an almost 7-fold increase in spinal fusions as indicated for degenerative cervical spine disease from the 1993 to 2002 period.
      • Wang M.C.
      • Kreuter W.
      • Wolfla C.E.
      • Maiman D.J.
      • Deyo R.A.
      Trends and variations in cervical spine surgery in the United States: medicare beneficiaries, 1992 to 2005.
      ,
      • Lad S.P.
      • Patil C.G.
      • Berta S.
      • Santarelli J.G.
      • Ho C.
      • Boakye M.
      National trends in spinal fusion for cervical spondylotic myelopathy.
      While cervical spine procedures have increased, utilization of ambulatory surgical centers (ASCs) for these procedures has escalated even more dramatically.
      • Wang M.C.
      • Kreuter W.
      • Wolfla C.E.
      • Maiman D.J.
      • Deyo R.A.
      Trends and variations in cervical spine surgery in the United States: medicare beneficiaries, 1992 to 2005.
      ,
      • Baird E.O.
      • Egorova N.N.
      • McAnany S.J.
      • Qureshi S.A.
      • Hecht A.C.
      • Cho S.K.
      National trends in outpatient surgical treatment of degenerative cervical spine disease.
      In a retrospective study of the management of patients with degenerative cervical spine disease across four states, there was a 60.5% increase in cervical procedures performed at an ASC per capita from 2005 to 2009, while the same procedures only increased by 8.7% per capita in the inpatient setting during the same period.
      • Baird E.O.
      • Egorova N.N.
      • McAnany S.J.
      • Qureshi S.A.
      • Hecht A.C.
      • Cho S.K.
      National trends in outpatient surgical treatment of degenerative cervical spine disease.
      While the increase in ASC utilization may be attributed to a variety of factors, including cost-benefit and productivity, such a dramatic increase in popularity demands further study of the patient population encountered in the ASC setting.
      • Baird E.O.
      • Egorova N.N.
      • McAnany S.J.
      • Qureshi S.A.
      • Hecht A.C.
      • Cho S.K.
      National trends in outpatient surgical treatment of degenerative cervical spine disease.
      ,
      • Mundell B.F.
      • Gates M.J.
      • Kerezoudis P.
      • et al.
      Does patient selection account for the perceived cost savings in outpatient spine surgery? A meta-analysis of current evidence and analysis from an administrative database: presented at the 2018 AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves.
      Age is a commonly studied demographic in surgical populations, in which its use as a prognostic factor has been extensively studied in a variety of surgical fields, including spine surgery. However, there is inherent selection bias regarding age in populations selected for ambulatory surgical care, also known as outpatient care, in which we see a significantly younger population on average compared to traditional inpatient care.
      • Mundell B.F.
      • Gates M.J.
      • Kerezoudis P.
      • et al.
      Does patient selection account for the perceived cost savings in outpatient spine surgery? A meta-analysis of current evidence and analysis from an administrative database: presented at the 2018 AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves.
      In 2006, 79.3% of patients receiving outpatient surgical care for musculoskeletal conditions presented between the ages of 15–64, while only 17.0% of patients presented older than the age of 65.
      • Cullen K.A.
      • Hall M.J.
      • Golosinskiy A.
      Ambulatory surgery in the United States, 2006.
      With this younger population comprising a greater than 4-fold portion of the ASC setting compared to those above 65 years of age, it is imperative to investigate how outcomes differ with further stratification of age in this younger population.
      • Cullen K.A.
      • Hall M.J.
      • Golosinskiy A.
      Ambulatory surgery in the United States, 2006.
      The goal of this study is to evaluate the potential relationship that age may play in this younger demographic in regard to commonly evaluated outcome measures to allow surgeons to more effectively manage expectations in the preoperative stage.

      2. Methods

      2.1 Patient population

      Informed consent was obtained for all patients following Institutional Review Board approval (ORA #14051301) for this study. Data was obtained through search of a prospectively-maintained, retrospective database of spine surgery patients from a single-surgeon in association with a single academic institution. Patients were included if they were under the age of 65 years at time of surgery and had undergone either a single-level ACDF or CDR indicated due to herniated nucleus pulposus. Patients with other indications for surgery, specifically acute trauma, infection, or malignancy, were excluded. The resulting population was then divided into two cohorts by the mean age of the total population, 46 years. The younger cohort was defined as those less than 46 years of age at time of surgery, while the older cohort was defined as those greater than or equal to 46 years of age at time of surgery.

      2.2 Data collection

      Demographics collected for both cohorts included age, female or male gender, ethnicity (Caucasian, African-American, Hispanic, Asian, or other), comorbidities (diabetic status, body mass index [BMI], smoking status, hypertension status, American Society for Anesthesiologists [ASA] classification, Charlson Comorbidity Index [CCI] score) and insurance provider (Medicare/Medicaid, Workers' Comp versus Private). Both cohorts’ perioperative characteristics were collected and analyzed, including prevalence of central and foraminal stenosis, operative time in minutes (min), estimated blood loss in milliliters (mL), length of stay in hours, postoperative visual analog scale (VAS) reported pain, and postoperative narcotic consumption in oral morphine equivalents (OME). Patient-reported outcome measures (PROMs) were collected during the preoperative period and at several postoperative time points, including 6 weeks, 12 weeks, 6 months, and 1 year, and 2 years after surgery. Outcome measures studied included Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS PF) and 12-item Short Form Physical Component Score (SF-12 PCS) to evaluate physical function, Neck Disability Index (NDI) scores to evaluate disability, and VAS neck and VAS arm pain scores to evaluate pain.

      2.3 Statistical analysis

      All analysis of observed findings was conducted utilizing Stata 16.0 (StataCorp LP, College Station, TX) software. Demographic and perioperative characteristics were compared between cohorts utilizing chi-square tests and independent sample t-tests for categorical and continuous variables respectively. Paired t-tests were used for comparison of preoperative and postoperative mean PROM scores within each cohort. Independent t-tests were used to compare mean PROM scores between cohorts at each time point. Achievement rate of minimum clinically important difference (MCID) was determined by comparison of the degree of change between preoperative and postoperative mean PROM scores within each cohort to predetermined threshold values established within the literature, noted as: 4.5 for PROMIS PF, 8.1 for SF-12 PCS, 8.5 for NDI, 2.6 for VAS neck pain, and 4.1 for VAS arm pain.
      • Steinhaus M.E.
      • Iyer S.
      • Lovecchio F.
      • et al.
      Minimal clinically important difference and substantial clinical benefit using PROMIS CAT in cervical spine surgery.
      ,
      • Parker S.L.
      • Mendenhall S.K.
      • Shau D.N.
      • et al.
      Minimum clinically important difference in pain, disability, and quality of life after neural decompression and fusion for same-level recurrent lumbar stenosis: understanding clinical versus statistical significance.
      Comparison of rate of MCID achievement between cohorts was conducted with chi-square analyses. For all analyses performed, a p-value cutoff of less than 0.05 was utilized as the threshold to denote significance.

      3. Results

      3.1 Descriptive analysis

      A total of 138 patients were identified that met the parameters of this study. After division of the cohorts, 66 patients were found to be less than 46 years of age at the time of operation with 72 patients greater than or equal to 46 years of age at time of surgery. The majority of patients were male (64.5%), Caucasian (73.1%), and had private insurance (62.2%) (Table 1). Of the demographic data collected, the cohorts only significantly differed in ASA classification, with a majority of the older cohort reporting a score greater than or equal to two (80.7%, compared to 44.0% in the younger cohort; p < 0.001), and CCI score, with the older cohort reporting an elevated mean score (1.1) when compared to the younger cohort (0.5) (p = 0.005) (Table 1). Per study design, all patients presented with an indication of herniated nucleus pulposus. The older cohort was observed to experience a higher prevalence of central stenosis (47.1% compared to 23.1% in the younger cohort; p = 0.004) (Table 2). Sixty-five and 73 patients underwent ACDF and CDR, respectively. No significant differences were noted between cohorts for the type of procedure (Table 2). No other perioperative characteristics observed differed significantly between the two cohorts.
      Table 1Patient demographics.
      CharacteristicTotal(n = 138)Age <46(n = 66)Age ≥46(n = 72)∗p-value
      Age (mean ± SD, years)45.2 ± 9.337.0 ± 5.352.7 ± 4.8<0.001
      Gender0.139
       Female35.5% (49)29.2% (19)41.4% (29)
       Male64.5% (89)70.8% (46)58.6% (41)
      Ethnicity0.942
       Caucasian73.1% (98)72.3% (47)73.9% (51)
       African-American9.0% (12)7.3% (5)10.8% (7)
       Hispanic12.7% (17)12.3% (8)13.0% (9)
       Asian2.2% (3)1.5% (1)2.9% (2)
       Other3.0% (4)3.1% (2)2.9% (2)
      Diabetic Status0.940
       Non-Diabetic97.0% (131)96.9% (63)97.1% (68)
       Diabetic3.0% (4)3.1% (2)2.9% (2)
      BMI (mean ± SD, kg/m2)28.6 ± 4.7828.2 ± 5.128.9 ± 4.50.374
      Smoking Status0.377
       Non-Smoker85.8% (115)83.1% (54)88.4% (61)
       Smoker14.2% (19)16.9% (11)11.6% (8)
      Hypertension Status0.272
       Non-hypertensive85.8% (115)89.2% (58)82.6% (57)
       Hypertensive14.2% (19)10.8% (7)17.4% (12)
      ASA Classification<0.001
       <236.5% (39)56.0% (28)19.3% (11)
       ≥263.5% (68)44.0% (22)80.7% (46)
      CCI Score (Mean ± SD)0.73 ± 0.60.5 ± 0.61.1 ± 1.130.005
      Insurance Type0.075
       Medicare/Medicaid1.5% (2)0.0% (0)2.9% (2)
       Workers' Comp36.3% (49)44.6% (29)28.6% (20)
       Private62.2% (84)55.4% (36)68.6% (48)
      BMI = body mass index; CCI = Charlson Comorbidity Index; ASA = American Society of Anesthesiologists; SD = standard deviation; Workers' Comp = workers' compensation.
      Boldface indicates significance.
      ∗p-values calculated using Student's t-test for continuous variables and chi-square analysis for categorical variables.
      Table 2Perioperative characteristics.
      CharacteristicTotal(n = 138)Age <46(n = 66)Age ≥46(n = 72)∗p-value
      Spinal Pathology
       Herniated Nucleus Pulposus100% (135)100% (60)100% (70)
       Central Stenosis35.6% (48)23.1% (15)47.1% (33)0.004
       Foraminal Stenosis20.7% (28)20.0% (13)21.4% (15)0.608
      Myeloradiculopathy87.5% (119)89.1% (57)86.1% (62)0.603
      Surgical Procedure0.320
       ACDF47.1% (65)51.5% (34)43.1% (31)
       CDR52.9% (73)48.5% (32)56.9% (41)
      Operative Time(Mean ± SD; min)48.7 ± 10.247.9 ± 7.449.6 ± 12.40.344
      Estimated Blood Loss(Mean ± SD; mL)27.0 ± 7.027.2 ± 7.626.7 ± 6.30.678
      Length of Stay (Mean ± SD; hours)6.0 ± 2.85.7 ± 1.76.4 ± 3.60.220
      Postoperative Vas pain POD 04.5 ± 2.34.5 ± 2.14.6 ± 2.40.922
      Postoperative Narcotic Consumption POD 020.4 ± 16.618.6 ± 14.922.1 ± 18.00.227
      ACDF = anterior cervical discectomy and fusion; CDR = cervical disc replacement; POD = postoperative day; mL = milliliters; SD = standard deviation.
      Boldface indicates significance.
      ∗p-values calculated using Student's t-test for continuous variables and chi-square analysis for categorical variables.

      3.2 Primary outcome measures

      PROMs chosen for this study were collected and analyzed in Table 3. Both cohorts showed significant improvement in postoperative PROMIS PF scores when compared to their mean preoperative scores at all time points at and after 12 weeks up to 2 years (p ≤ 0.029, all) (Table 3). The older cohort did have significantly higher PROMIS PF scores at the preoperative and 6-week time points compared to the younger cohort (p ≤ 0.011, both) (Table 3). Regarding mean SF-12 PCS scores, both cohorts showed significant improvement at two postoperative time points when compared to their preoperative scores, 12-week and 6-month marks for the younger cohort, and 6-week and 1-year marks for the older cohort (p ≤ 0.042, all) (Table 3). Regarding VAS neck scores, the younger cohort showed significant improvement in mean scores for all postoperative time points prior to the 2-year mark when compared to the preoperative mean score (p ≤ 0.025, all) (Table 3). The older cohort showed significant improvement in mean scores for VAS neck pain for all postoperative time points measured when compared to their preoperative baseline score (p ≤ 0.015, all) (Table 3). No significant difference between mean VAS neck pain scores was found between groups at any time point studied. For the younger population, mean VAS arm pain scores were significantly improved from the preoperative period up to and including the 6-month time point, after which time significance was no longer seen (p < 0.001, all) (Table 3). The older cohort saw significant improvement in mean VAS arm pain scores extending to the 1-year mark but did not see significance at the 2-year time point (p ≤ 0.007, all) (Table 3). When compared to the younger cohort, the older cohort had significantly lower VAS arm pain scores at the 1-year period (p = 0.002) (Table 3). Both cohorts saw significant improvement in mean NDI scores at all postoperative time points measured when compared to their baseline measures in the preoperative period (p ≤ 0.013, all) (Table 3). The older cohort noted significantly lower mean NDI scores at the 6-week and 1-year time points when compared to the younger population (p ≤ 0.027, both) (Table 3). Overall MCID achievement rates for each PROM studied were greater than or equal to 44.4% (Table 4). The younger cohort saw significantly greater MCID achievement for PROMIS PF score at the 2-year time point; however, the older cohort had significantly greater MCID achievement for VAS arm pain scores at the 1-year time point (p ≤ 0.007, both) (Table 4). No other significance was found between groups for MCID achievement at any other time point.
      Table 3Mean patient reported outcomes.
      PROMAge <46 Mean ± SD∗p-valueAge ≥46 Mean ± SD∗p-value†p-value
      PROMIS PF
       Preoperative38.3 ± 6.341.9 ± 7.00.011
       6-week38.6 ± 7.00.92445.3 ± 8.20.2120.001
       12-week46.4 ± 8.3<0.00147.4 ± 12.30.0090.687
       6-month46.2 ± 10.7<0.00150.2 ± 11.7<0.0010.237
       1-year47.2 ± 9.40.02952.8 ± 6.40.0040.083
       2-year49.1 ± 12.60.00141.4 ± 4.30.0240.956
      SF-12 PCS
       Preoperative34.2 ± 8.435.0 ± 9.10.664
       6-week34.3 ± 7.70.82237.5 ± 8.50.0370.091
       12-week40.9 ± 10.90.01040.1 ± 12.00.2040.755
       6-month43.5 ± 10.1<0.00140.8 ± 9.70.0740.366
       1-year43.2 ± 12.50.08344.9 ± 10.30.0420.674
       2-year42.8 ± 12.20.11838.0 ± 13.70.2220.406
      VAS neck
       Preoperative6.5 ± 2.16.1 ± 2.30.238
       6-week3.9 ± 2.3<0.0013.2 ± 2.8<0.0010.197
       12-week2.6 ± 2.2<0.0012.4 ± 2.6<0.0010.765
       6-month2.8 ± 2.3<0.0012.4 ± 2.7<0.0010.458
       1-year3.9 ± 2.60.0253.2 ± 3.40.0140.481
       2-year3.8 ± 3.50.2114.0 ± 2.70.0150.901
      VAS arm
       Preoperative5.9 ± 2.56.0 ± 2.60.850
       6-week2.8 ± 2.6<0.0012.3 ± 2.6<0.0010.389
       12-week2.5 ± 3.0<0.0013.1 ± 3.3<0.0010.372
       6-month3.0 ± 2.8<0.0013.1 ± 3.1<0.0010.891
       1-year4.6 ± 2.60.4431.8 ± 1.90.0070.002
       2-year2.5 ± 3.40.3383.8 ± 3.90.2080.518
      NDI
       Preoperative45.0 ± 19.240.2 ± 16.50.147
       6-week36.9 ± 18.60.01327.5 ± 21.2<0.0010.027
       12-week25.6 ± 19.1<0.00122.7 ± 23.0<0.0010.527
       6-month23.8 ± 17.8<0.00121.9 ± 22.2<0.0010.679
       1-year27.4 ± 19.60.00211.2 ± 14.2<0.0010.016
       2-year24.2 ± 28.60.01222.2 ± 20.30.0080.881
      Boldface indicates significance.
      ∗p-values calculated using paired sample t-test to determine preoperative to postoperative improvement.
      †p-values calculated using Student's t-test to compare mean PROMs between both cohorts.
      Table 4Minimum clinically important difference.
      PROMAge <46%, (n)Age ≥46%, (n)∗p-value
      NDI
       6-week37.8% (14)54.2% (26)0.135
       12-week100.0% (55)100.0% (58)
       6-month71.8% (28)72.7% (24)0.930
       1-year55.6% (10)69.2% (9)0.440
       2-year85.7% (6)100.0% (6)0.335
       Overall48.7% (55)51.8% (59)0.332
      PROMIS PF
       6-week35.7% (10)33.3% (8)0.857
       12-week60.7% (17)50.0% (12)0.438
       6-month63.6% (14)72.2% (13)0.564
       1-year60.0% (9)60.0% (6)1.000
       2-year75.0% (9)0.0% (0)0.002
       Overall55.6% (30)44.4% (24)0.257
      SF-12 PCS
       6-week18.8% (6)30.3% (10)0.280
       12-week31.3% (10)28.0% (7)0.790
       6-month50.0% (13)41.2% (7)0.571
       1-year35.3% (6)36.4% (4)0.954
       2-year40.0% (4)50.0% (4)0.671
       Overall57.5% (23)42.5 (17)0.483
      VAS neck
       6-week41.5% (17)49.0% (24)0.476
       12-week70.2% (33)62.8% (27)0.456
       6-month65.1% (28)66.7% (22)0.888
       1-year31.6% (6)53.9% (7)0.208
       2-year62.5% (5)50.0% (3)0.640
       Overall54.4% (43)45.6%0.129
      VAS arm
       6-week35.0% (14)44.7% (21)0.359
       12-week43.2% (19)40.0% (16)0.768
       6-month30.8% (12)40.0% (12)0.425
       1-year10.5% (2)53.9% (7)0.007
       2-year42.7% (3)20.0% (1)0.408
       Overall52.7% (29)47.3% (26)0.782
      Boldface indicates significance.
      ∗p-values calculated using chi-square analysis.

      4. Discussion

      4.1 Literature cross-analysis

      Utilization of ASCs for elective surgery has greatly affected the landscape of elective surgery over the past two decades. Spine surgery alone saw a greater than 5-fold increased rate of ASC use from 1994 to 2006, with prevalence of cervical spine surgery in ASC increasing 7-fold compared to the rate of inpatient cases.
      • Baird E.O.
      • Egorova N.N.
      • McAnany S.J.
      • Qureshi S.A.
      • Hecht A.C.
      • Cho S.K.
      National trends in outpatient surgical treatment of degenerative cervical spine disease.
      ,
      • Mundell B.F.
      • Gates M.J.
      • Kerezoudis P.
      • et al.
      Does patient selection account for the perceived cost savings in outpatient spine surgery? A meta-analysis of current evidence and analysis from an administrative database: presented at the 2018 AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves.
      While cost-benefit analyses are routinely cited, one of the factors contributing to this shift is likely the multitude of data demonstrating the safety of common cervical spine procedures, most notably the anterior cervical discectomy and fusion (ACDF).
      • Mullins J.
      • Pojskić M.
      • Boop F.A.
      • Arnautović K.I.
      Retrospective single-surgeon study of 1123 consecutive cases of anterior cervical discectomy and fusion: a comparison of clinical outcome parameters, complication rates, and costs between outpatient and inpatient surgery groups, with a literature review.
      • Yerneni K.
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      • Chunduru P.
      • et al.
      Safety of outpatient Anterior cervical discectomy and fusion: a systematic review and meta-analysis.
      • McGirt M.J.
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      • Devin C.J.
      Quality analysis of anterior cervical discectomy and fusion in the outpatient versus inpatient setting: analysis of 7288 patients from the NSQIP database.
      Many prior studies have established the safety and efficacy of ACDF performed at an ASC, even in cases of three- or four-level fusions, finding no increased complication or readmission rates in these cohorts.
      • Mullins J.
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      • Arnautović K.I.
      Retrospective single-surgeon study of 1123 consecutive cases of anterior cervical discectomy and fusion: a comparison of clinical outcome parameters, complication rates, and costs between outpatient and inpatient surgery groups, with a literature review.
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      Safety of outpatient Anterior cervical discectomy and fusion: a systematic review and meta-analysis.
      • McGirt M.J.
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      • Devin C.J.
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      Outpatient surgery in the cervical spine: is it safe?.
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      • Mendoza-Lattes S.
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      • et al.
      Are outpatient three- and four-level anterior cervical discectomies and fusion safe?.
      Cervical disc replacement (CDR) has garnered attraction recently as an alternative to ACDF due to the preservation of motion with comparable outcomes.
      • Uschold T.D.
      • Fusco D.
      • Germain R.
      • Tumialan L.M.
      • Chang S.W.
      Cervical and lumbar spinal arthroplasty: clinical review.
      Several studies have found CDR to be equivalent to, if not superior to, ACDF for single-level disease due to motion preservation, improved disability scores, and decreased risk of adjacent segment disease in long-term follow-up.
      • Uschold T.D.
      • Fusco D.
      • Germain R.
      • Tumialan L.M.
      • Chang S.W.
      Cervical and lumbar spinal arthroplasty: clinical review.
      • Heller J.G.
      • Sasso R.C.
      • Papadopoulos S.M.
      • et al.
      Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial.
      • Phillips F.M.
      • Lee J.Y.B.
      • Geisler F.H.
      • et al.
      A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion. 2-year results from the US FDA IDE clinical trial.
      • Findlay C.
      • Ayis S.
      • Demetriades A.K.
      Total disc replacement versus anterior cervical discectomy and fusion: a systematic review with meta-analysis of data from a total of 3160 patients across 14 randomized controlled trials with both short- and medium- to long-term outcomes.
      While additional studies may be beneficial to continue demonstrating the efficacy of CDR in comparison to ACDF, especially in the ambulatory setting, the rising prominence of CDR necessitated its inclusion within this study.
      With increased ASC utilization for many orthopaedic surgical procedures, there has been a shift in demographics compared to traditional inpatient care. One of the most notable demographic changes seen in the outpatient setting is a decreased mean age, with Crawford et al. (2015) reporting the largest demographic of individuals undergoing orthopaedic surgery at an ASC to be between 45 and 64 years of age.
      • Crawford D.C.
      • Li C.S.
      • Sprague S.
      • Bhandari M.
      Clinical and cost implications of inpatient versus outpatient orthopedic surgeries: a systematic review of the published literature.
      Cullen at al. (2009) reported patients undergoing any orthopaedic surgery at an ASC to be four times as likely to be younger than 65 years of age instead of older.
      • Cullen K.A.
      • Hall M.J.
      • Golosinskiy A.
      Ambulatory surgery in the United States, 2006.
      Similarly, in several studies of ACDF safety in ASC discussed prior, the authors routinely reported that the inpatient cohorts were significantly older compared to their ASC counterparts, with Baird et al. (2014) reporting patients greater than 70 years of age to account for only 2.5% of all cases in the outpatient setting.
      • Baird E.O.
      • Egorova N.N.
      • McAnany S.J.
      • Qureshi S.A.
      • Hecht A.C.
      • Cho S.K.
      National trends in outpatient surgical treatment of degenerative cervical spine disease.
      ,
      • Mullins J.
      • Pojskić M.
      • Boop F.A.
      • Arnautović K.I.
      Retrospective single-surgeon study of 1123 consecutive cases of anterior cervical discectomy and fusion: a comparison of clinical outcome parameters, complication rates, and costs between outpatient and inpatient surgery groups, with a literature review.
      ,
      • McGirt M.J.
      • Godil S.S.
      • Asher A.L.
      • Parker S.L.
      • Devin C.J.
      Quality analysis of anterior cervical discectomy and fusion in the outpatient versus inpatient setting: analysis of 7288 patients from the NSQIP database.
      While the general effect of age on surgical outcomes has been studied extensively, the selection bias for younger patients for outpatient surgery warrants further evaluation of the effect that age plays within this new demographic to guide surgeons in patient selection as well as management of patient expectations.
      Prior studies have evaluated age in cervical surgery in both inpatient and outpatient settings, with the majority finding age greater than 65 years to be an independent risk factor for worse postoperative outcomes along with greater complication rates.
      • Wang M.C.
      • Kreuter W.
      • Wolfla C.E.
      • Maiman D.J.
      • Deyo R.A.
      Trends and variations in cervical spine surgery in the United States: medicare beneficiaries, 1992 to 2005.
      ,
      • Martin C.T.
      • Pugely A.J.
      • Gao Y.
      • Mendoza-Lattes S.
      Thirty-day morbidity after single-level anterior cervical discectomy and fusion: identification of risk factors and emphasis on the safety of outpatient procedures.
      ,
      • Boddapati V.
      • Mathew J.
      • Lee N.J.
      • et al.
      Are outpatient three- and four-level anterior cervical discectomies and fusion safe?.
      ,
      • Archer K.R.
      • Bydon M.
      • Khan I.
      • et al.
      Development and validation of cervical prediction models for patient-reported outcomes at 1 Year after cervical spine surgery for radiculopathy and myelopathy.
      ,
      • Nakashima H.
      • Tetreault L.A.
      • Nagoshi N.
      • et al.
      Does age affect surgical outcomes in patients with degenerative cervical myelopathy? Results from the prospective multicenter AOSpine International study on 479 patients.
      Two studies contrasted this data, with Chotai et al. (2017) reporting equivalent outcomes for both cohorts divided by age at 65 years and Scerrati (2021) finding age to not be an independent risk factor for functional outcomes specifically after ACDF.
      • Chotai S.
      • Parker S.L.
      • Sielatycki J.A.
      • et al.
      Impact of old age on patient-report outcomes and cost utility for anterior cervical discectomy and fusion surgery for degenerative spine disease.
      ,
      • Scerrati A.
      • Germano’ A.
      • Montano N.
      • et al.
      Factors affecting functional outcome after anterior cervical discectomy and fusion: a multicenter study.
      One study conducted by Hirvonen et al. (2020) studied a younger population, adults age 18–40 years, and reported high rates of long-term, greater than 90% patient follow-up at 12 years, satisfaction after ACDF with persistently improved NDI scores.
      • Hirvonen T.
      • Siironen J.
      • Marjamaa J.
      • Niemelä M.
      • Koski-Palkén A.
      Anterior cervical discectomy and fusion in young adults leads to favorable outcome in long-term follow-up.
      However, this study did not have an older cohort to which the younger patients were compared. During review of the literature in recent years, only three studies regarding cervical spine surgery were identified that stratified patients by age beyond a single cut-off of 65 years. Lee et al. (2020) studied differences in elderly patients with cohorts separated into those 65–74 years of age and those age 75 or older, finding no difference between groups after ACDF regarding VAS pain scores, NDI score, or Odom's criteria.
      • Lee C.H.
      • Son D.W.
      • Lee S.H.
      • et al.
      Radiological and clinical outcomes of anterior cervical discectomy and fusion in older patients: a comparative analysis of young-old patients (ages 65-74 Years) and middle-old patients (over 75 Years).
      Croci et al. (2022) separated their patients into three groups: young (<65 years), early elderly (65–74 years), and late elderly (≥75 years) and found the young patients to have worse significantly worse VAS pain and NDI scores preoperatively and at three and twelve months postoperative compared to the two older cohorts.
      • Croci D.M.
      • Sherrod B.
      • Alvi M.A.
      • et al.
      Differences in postoperative quality of life in young, early elderly, and late elderly patients undergoing surgical treatment for degenerative cervical myelopathy.
      Further, NDI and VAS arm pain scores improved significantly more in the two older groups at the three-month period; however, overall MCID achievement was greater in VAS arm and NDI for younger patients.
      • Croci D.M.
      • Sherrod B.
      • Alvi M.A.
      • et al.
      Differences in postoperative quality of life in young, early elderly, and late elderly patients undergoing surgical treatment for degenerative cervical myelopathy.
      These mixed findings appear to indicate that while younger patients may present in a poorer preoperative state regarding outcome measures, the younger cohort saw greater effect overall from surgical intervention compared to their older cohorts, while the older cohorts still saw significant improvement as well in the short-term. However, this study is still limited in application to ambulatory surgical center demographics as no stratification of patient age occurred beneath 65 years of age.
      Only one study regarding cervical surgery, conducted by Omidi-Kashani et al. (2014), was found to stratify this younger population, separating patients into two groups by those younger than 45 years of age and those 45 years of age or older.
      • Omidi-Kashani F.
      • Ghayem Hasankhani E.
      • Ghandehari R.
      Impact of age and duration of symptoms on surgical outcome of single-level microscopic anterior cervical discectomy and fusion in the patients with cervical spondylotic radiculopathy.
      While not statistically significant, the younger group was reported to have lower VAS pain and NDI scores preoperatively compared to the older cohort.
      • Omidi-Kashani F.
      • Ghayem Hasankhani E.
      • Ghandehari R.
      Impact of age and duration of symptoms on surgical outcome of single-level microscopic anterior cervical discectomy and fusion in the patients with cervical spondylotic radiculopathy.
      Both groups reported significant improvement in VAS pain and NDI scores at time of last postoperative follow-up, time not specified; however, the older cohort demonstrated significantly greater improvement in NDI scores compared to the younger cohort and additionally, while not significant, did show greater improvement in VAS pain score.
      • Omidi-Kashani F.
      • Ghayem Hasankhani E.
      • Ghandehari R.
      Impact of age and duration of symptoms on surgical outcome of single-level microscopic anterior cervical discectomy and fusion in the patients with cervical spondylotic radiculopathy.
      While this study did not directly report changes in physical function, improvement in NDI score has been strongly correlated with improvement in PROMIS PF score.
      • Moses M.J.
      • Tishelman J.C.
      • Stekas N.
      • et al.
      Comparison of patient reported outcome measurement information system with neck disability index and visual analog scale in patients with neck pain.
      In our study, we found both cohorts to have significant improvement in all outcome measures evaluated when compared to their preoperative baseline scores at least two or more postoperative time points. Regarding physical function, the younger cohort (age <46 years) showed significant improvement in mean PROMIS PF scores from preoperative baseline at all time points after and including 12 weeks. The older cohort (age ≥46 years) was observed to have similar findings, with significant improvement in mean PROMIS PF scores from the 12-week time point onward, continuing to the 2-year mark. Utilizing the correlation between NDI score and PROMIS PF, these results are similar to those seen in the study conducted by Omidi-Kashani et al. (2014).
      • Omidi-Kashani F.
      • Ghayem Hasankhani E.
      • Ghandehari R.
      Impact of age and duration of symptoms on surgical outcome of single-level microscopic anterior cervical discectomy and fusion in the patients with cervical spondylotic radiculopathy.
      In contrast to their study, our younger cohort was observed to have significantly lower PROMIS PF scores at the preoperative and 6-week postoperative periods compared to the older cohort. While both cohorts showed improvement in SF-12 PCS score in all postoperative time points, significance was only found at two-time points for each cohort: 12-week and 6-month periods for the younger cohort, 6-week and 1-year time points for the older cohort. In light of the diffuse significance seen in PROMIS PF score improvement, the lack of significance seen in SF-12 PCS score may be due to lack of power from loss to follow-up. MCID achievement in PROMIS PF significantly differed between cohorts at the 2-year time point in favor of the younger cohort; however, no significant differences were noted at any other time points in PROMIS PF or any time points regarding SF-12 PCS.
      Regarding pain, both groups showed significant improvement in VAS neck and arm scores at many postoperative time points compared to their preoperative baseline scores. The younger cohort saw significant improvement at all postoperative time points, excluding the 2-year mark. Significance was not noted at the 2-year mark; however, the score reported was still lower than those seen in the preoperative, 6-week, and 1-year periods, leading us to conclude that lack of significance was primarily due to loss to follow-up. Similarly, the older cohort showed significant improvement in VAS neck score at all postoperative time points including the 2-year mark. Correlating results were found for VAS arm scores for both cohorts, showing significant improvement up to 6 months in the younger cohort and up to 1 year in the older cohort. In contrast to the study by Omidi-Kashani et al. (2014), the older cohort showed significantly lower mean VAS arm score at the 1-year time point compared to the younger cohort.
      • Omidi-Kashani F.
      • Ghayem Hasankhani E.
      • Ghandehari R.
      Impact of age and duration of symptoms on surgical outcome of single-level microscopic anterior cervical discectomy and fusion in the patients with cervical spondylotic radiculopathy.
      MCID achievement differed significantly in VAS arm scores in favor of the older group at the 1-year time point, but no significant difference in achievement rate was noted at any other time point for either VAS pain score.
      Regarding disability, similar to the Omidi-Kashani et al. (2014) study, both cohorts showed significant improvement in NDI score at all postoperative time points continuing to final follow-up at 2 years.
      • Omidi-Kashani F.
      • Ghayem Hasankhani E.
      • Ghandehari R.
      Impact of age and duration of symptoms on surgical outcome of single-level microscopic anterior cervical discectomy and fusion in the patients with cervical spondylotic radiculopathy.
      Additionally, the older cohort showed significantly lower mean NDI scores than the younger cohort at the 6-week and 1-year time points, concurring with the Omidi-Kashani et al. (2014) description of significantly greater improvement in NDI score seen in the older population in their study.
      • Omidi-Kashani F.
      • Ghayem Hasankhani E.
      • Ghandehari R.
      Impact of age and duration of symptoms on surgical outcome of single-level microscopic anterior cervical discectomy and fusion in the patients with cervical spondylotic radiculopathy.
      MCID did not significantly differ at any time point regarding NDI between groups.

      4.2 Limitations

      While this study holds several strengths, including consistent technique due to data originating from a single-surgeon database, moderate follow-up time extending to 2 years, isolated spinal pathology of herniated nucleus pulposus, and use of thoroughly studied outcome measures in the form of PROMs and MCID achievement, there are several severe limitations. First, while single-level surgeries were utilized to compare more uniform data, generalization of these findings to multi-level surgeries is then limited. Further, while this study prioritized evaluation of PROMs, specifically analyzing physical function, pain, and disability, this study did not evaluate rates of postoperative complication between groups, which is likely the greatest limiting factor for surgeon recommendation regarding these two cohorts. Although we reported the number of patients with cervical myeloradiculopathy, the PROMs utilized within this study may not adequately address other myelopathic symptoms such as fine motor work or bowel and bladder issues. The PROMs used in this study merely assess the basics of physical function, pain, and neck disability. Usage of the modified Japanese Orthopaedic Association scoring system or Nurick grading system in future studies may mitigate this limitation and allow for further comparison of patients’ improvement in these more detailed myelopathic concerns. Patients with isolated myelopathic symptoms may have varying results as mentioned by the limitations of these PROMs; however, only two patients reported isolated myelopathic symptoms in this study, both within the older population, limiting our ability to analyze this subset of the population. Use of multiple surgeons or institutions may additionally allow for greater power to further study mid-to long-term outcomes in these patient groups, where in our case we found several outcomes to lack significance at our study endpoint likely due to lack of power. Notably, ASA classification and CCI scores were both significantly poorer in the older population, similar to prior studies.
      • Nakashima H.
      • Tetreault L.A.
      • Nagoshi N.
      • et al.
      Does age affect surgical outcomes in patients with degenerative cervical myelopathy? Results from the prospective multicenter AOSpine International study on 479 patients.
      Larger sample sizes may allow for propensity matching while maintaining power to account for these differences that inherently bias the study. Finally, while both ACDF and CDR procedures were included due to their overlap in indication with the goal of increasing generalizability of the study, surgeons who routinely perform one of these techniques may be limited in application of these findings due to the heterogeneous nature of the study.

      5. Conclusion

      There is a gross sparsity of data regarding the influence of age on cervical spine surgery outcomes as stratified in younger populations more commonly encountered in the ambulatory setting. While the younger group presented with poorer physical function status preoperatively, both younger (<46 years) and older (46–64 years) groups experienced significant improvement in many outcomes regarding function, pain, and disability postoperatively in short-to mid-term postoperative periods. Older patients may report significantly better scores than younger patients regarding function, pain, and disability in the postoperative period; however, younger patients may notice more tangible improvement in function at later postoperative time points, while older patients may report more tangible improvement in pain. The broad spectrum of improvement seen for both cohorts along with the mixed results noted indicate that cervical spine surgery is effective for both young and middle-aged populations and requires further study to elucidate differences that potentially exist between this younger demographic seen in the ambulatory setting.

      Disclosure of funding

      This research did not receive any specific grant from public, commercial or not-for-profit funding agencies.

      CRediT authorship contribution statement

      Timothy J. Hartman: Conceptualization, Methodology, Visualization, Formal analysis, Software, Investigation, Writing – original draft, Writing – review & editing. James W. Nie: Conceptualization, Methodology, Visualization, Formal analysis, Software, Investigation, Writing – original draft, Writing – review & editing. Hanna Pawlowski: Project administration, Data curation, Investigation, Writing – review & editing. Michael C. Prabhu: Project administration, Data curation, Investigation, Writing – review & editing. Nisheka N. Vanjani: Project administration, Data curation, Investigation, Writing – review & editing. Kern Singh: Conceptualization, Methodology, Supervision, Resources, Investigation, Writing – review & editing.

      Declaration of competing interest

      The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Kern Singh reports a relationship with Zimmer Biomet that includes: consulting or advisory. Kern Singh reports a relationship with Stryker that includes:. Kern Singh reports a relationship with RTI Surgical that includes:. Kern Singh reports a relationship with Lippincott Williams and Wilkins that includes:. Kern Singh reports a relationship with Thieme that includes:. Kern Singh reports a relationship with Jaycee Publishing that includes:. Kern Singh reports a relationship with Slack Publishing that includes:. Kern Singh reports a relationship with Avaz Surgical LLC that includes: equity or stocks. Kern Singh reports a relationship with Vital 5 LLC that includes: board membership and equity or stocks. Kern Singh reports a relationship with K2M that includes: consulting or advisory. Kern Singh reports a relationship with TDi LLC that includes: board membership. Kern Singh reports a relationship with Minimally Invasive Spine Study Group that includes: board membership. Kern Singh reports a relationship with Contemporary Spine Surgery that includes: board membership. Kern Singh reports a relationship with Orthopedics Today that includes: board membership. Kern Singh reports a relationship with Vertebral Columns that includes: board membership. Kern Singh reports a relationship with Cervical Spine Research Society that includes: board membership. Kern Singh reports a relationship with International Society for the Advancement of Spine Surgery that includes: board membership. Kern Singh reports a relationship with American Academy of Orthopaedic Surgeons that includes: board membership. Kern Singh reports a relationship with Cervical Spine Research Society that includes: funding grants.

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