Impact of Ankylosing Spondylitis/Diffuse Idiopathic Skeletal Hyperostosis on Postoperative and Patient-Reported Outcomes Following Elective Cervical and Lumbar Surgery

Abstract

Study Design

Retrospective cohort.

Objective

Limited evidence exists for outcomes after elective cervical and lumbar fusion in patients with ankylosing spondylitis (AS) or diffuse idiopathic skeletal hyperostosis (DISH). This study aimed to compare perioperative and patient-reported outcomes between patients with AS/DISH and matched control patients.

Methods

Adults with AS/DISH undergoing primary elective ACDF, PCDF, PLDF, or TLIF from 2004-2023 were identified. AS/DISH patients were propensity score matched (1:3) to controls without ankylosing disorders. Outcomes included readmission rates, discharge disposition, revision/reoperation, and patient-reported outcome measures at baseline and follow-up. Chi-square and t-tests were used, with P < 0.05 as significant.

Results

66 AS/DISH patients (42 cervical, 24 lumbar) were matched to 198 controls. AS/DISH patients had higher Charlson Comorbidity Index scores and greater 0-30 day readmission rates for both cervical (9.5% vs 1.6%, P = 0.035) and lumbar (20.8% vs 2.8%, P = 0.010) fusions. Cervical AS/DISH patients demonstrated superior VAS Neck, VAS Arm, and mJOA scores at several postoperative timepoints. Lumbar AS/DISH patients showed greater early VAS Back improvement (Δ6-month −4.00 vs −2.91, P = 0.010) but smaller VAS Leg gains (Δ6-month −1.50 vs −4.13, P = 0.021). Multivariable regression controlling for CCI score, male sex, and AS/DISH diagnosis identified that a diagnosis of AS/DISH was independently associated with greater odds of 30-day readmissions (OR: 6.04, 95% CI: 1.84-23.38, P = 0.004).

Conclusion

AS/DISH is associated with increased short-term readmissions after elective spinal fusion, despite some superior functional outcomes in cervical procedures. Future studies should evaluate whether targeted perioperative optimization can reduce these risks.

Keywords

III ankylosing spondylitis diffuse idiopathic hyperostosis AS DISH spinal fusion patient reported outcome measures

Introduction

Ankylosing spondylitis (AS) is common seronegative inflammatory spondyloarthropathy involving the sacroiliac (SI) joint and axial skeleton that has an estimated global prevalence of up to 0.3%.^1,2 The pathophysiology of AS typically involves osteoproliferation which can cause progressive, excess ossification, fusion of vertebral bodies via syndesmophytes, and facet joint ankylosis.³ Diffuse idiopathic skeletal hyperostosis (DISH) is a condition characterized by calcification and contiguous ossification of at least 4 anterolateral vertebral bodies with an estimated prevalence of up to 25%.^4,5 However, unlike AS, DISH typically does not involve the SI joint and is thought to have an etiology related to metabolic processes rather than inflammatory causes.⁴ Clinically, both AS and DISH are considered ankylosing spinal disorders and can present as axial back/neck pain, spinal rigidity, and symptomatology related to nerve root compression such as radiculopathy and myelopathy.^6,7 Furthermore, while both AS and DISH most commonly involve the thoracic or lumbar region in early stages, both diseases can progress to involve the cervical spine.^8-12

Patients with DISH are more susceptible to fractures of the vertebra due to a lack of appropriate distribution of forces in trauma, secondary to spinal rigidity which functionally results in an extended lever arm of the spine.¹³ Similarly, patients with AS are also susceptible to fractures not only due to spinal rigidity, but also because of poor bone mineral density (BMD) that results from chronic inflammation associated with AS.¹⁴ These patients consequently undergo relatively frequent rates of operative management to treat these fractures.^15,16 However, several studies have shown that patients with AS and DISH have worse outcomes compared to healthy patients when undergoing spinal fusion for treatment of vertebral fractures.^16,17

Patients with AS/DISH are also more likely to develop symptoms of nerve compression, in part due to ossification of the soft tissue structures such as the posterior longitudinal ligament (PLL), hypertrophy of the ligamentum flavum, and disc degeneration.^18,19 Subsequently, such patients often undergo spine surgery more frequently relative to the general population.^20,21 Some studies have shown that patients with DISH are more likely to undergo reoperation after spinal decompression with and without fusion.^21,22 Other studies have reported good outcomes in patients with AS undergoing elective spine surgeries in the cervical and thoracolumbar spine.^23-25 To this end, there is a lack of consensus and overall paucity of studies investigating the impact that AS/DISH diagnoses have on postoperative outcomes and complication rates after elective spinal fusion.

To the authors’ knowledge, the present work is the first to use a large, single institution to investigate postoperative outcomes and complication rates in patients undergoing elective lumbar and cervical fusion procedures in patients with AS/DISH. Specifically, we aimed to: (1) compare perioperative and patient-reported outcomes between AS/DISH patients and matched controls undergoing elective cervical or lumbar fusion, (2) evaluate differences in short-term complication and readmission rates, and (3) determine whether AS/DISH status influences postoperative functional improvement. We hypothesized that patients with AS/DISH undergoing fusion procedures would have worse postoperative outcomes compared to matched controls, given their higher medical comorbidity, altered spinal biomechanics, and greater baseline disability.

Methods

Study Design and Patient Selection

After obtaining Institutional Review Board (IRB) approval, a retrospective study was conducted at a tertiary care institution. A structured query language (SQL) was used to identify all adult patients with a diagnosis of AS or DISH who underwent a primary elective anterior cervical discectomy and fusion (ACDF), posterior cervical discectomy and fusion (PCDF), posterior lumbar decompression and fusion (PLDF), and transforaminal lumbar interbody fusion (TLIF) from 2004-2023. Diagnosis of AS was manually confirmed via chart review. Diagnosis of DISH was similarly manually confirmed via chart review via the Resnick criteria.¹⁹ Patients were excluded if they underwent these surgeries for malignancy, infection, or trauma. A total of 264 patients met the inclusion criteria. 66 patients with history of AS/DISH who underwent a spinal fusion procedure were further stratified into groups based on whether they received a primary elective fusion for the cervical and lumbar spine. The AS/DISH patients were then propensity score matched to 198 patients without history of AS/DISH who also underwent similar procedures in a 1:3 ratio.

SQL was used to collect demographic variables such as age, race, sex, body mass index (BMI), Charlson Comorbidity Index (CCI) score, Distressed Communities Index (DCI) score, and DCI quintile which were confirmed via manual chart review. Similarly, SQL was used to collect surgical variables such as surgery performed, number of levels fused, estimated blood loss (EBL), length of stay (LOS), operating room (OR) time, and cut to close time which were also confirmed via manual chart review.

Outcome Measures

The primary outcomes of interest were patient reported outcome measures (PROMs) which were collected preoperatively and at 3 months, 6 months, 1 year, and 2 years postoperatively. The delta PROM values for each postoperative score relative to the preoperative score were calculated. Specific PROMs collected included Visual Analog Scale (VAS) neck and arm, VAS back and leg, Neck Disability Index (NDI), Oswestry Disability Index (ODI), Modified Japanese Orthopaedic Association (mJOA), Short Form-12 Physical Component Summary (PCS), and Short Form-12 Mental Component Summary (MCS). Secondary outcomes of interest included discharge disposition, 0-30 day readmission rates, 31-90 days readmission rates, 1 year revision rates, and 1 year reoperation rates.

Statistical Analysis

Descriptive statistics were used to characterize baseline and surgical variables which were reported as counts with standard deviations and percentages when appropriate. Surgical outcomes were reported as percentages. PROMS were reported as means with standard deviations. Bivariate analysis was conducted which consisted of Pearson Chi-Square tests for categorical variables and Analysis of Variance (ANOVA) and t-tests for continuous variables. A multivariable regression was conducted to identify independent predictors of 30-days readmissions after lumbar and cervical fusion. Statistical significance was set at P-value <0.05. Statistical analysis was performed using R software, Rstudio version 4.2 (RStudio, Boston, MA).

Results

Patient Demographics

Among all patients, the AS/DISH cohort had a smaller proportion of females (31.8 vs 47.5%; P = 0.038) and greater CCI scores (3.09 vs 2.27; P = 0.002) relative to the control cohort (Table 1). All other demographic variables were similar between the groups.

Table 1.

Patient Demographics – All Patients

	No ankylosis	Ankylosis	P value
	N = 198	N = 66	P value
Age	62.4 (11.2)	62.1 (11.0)	0.707
Race			0.653
White	173 (87.4%)	57 (86.4%)
Black	20 (10.1%)	6 (9.09%)
Other	5 (2.53%)	3 (4.55%)
Sex (female)	94 (47.5%)	21 (31.8%)	0.038
BMI	31.3 (6.70)	31.3 (6.57)	0.872
CCI	2.27 (2.00)	3.09 (1.63)	0.002
DCI	32.9 (24.4)	33.3 (21.8)	0.597
DCI quintile			0.208
Prosperous	83 (41.9%)	20 (30.8%)
Comfortable	42 (21.2%)	22 (33.8%)
Mid-Tier	42 (21.2%)	16 (24.6%)
At Risk	17 (8.59%)	3 (4.62%)
Distressed	14 (7.07%)	4 (6.15%)

Bold denotes statistical significance.

Abbreviations: BMI: Body Mass Index, CCI: Charlson Comorbidity Index, DCI: Distressed Communities Index.

Among patients who underwent ACDF or PCDF, there were 42 patients with a history of AS/DISH and 126 patients in the control group. The AS/DISH cohort had greater CCI scores (3.02 vs 1.92, P < 0.001) (Table 2). All other demographic variables were similar between the groups (P > 0.05 for all).

Table 2.

Patient Demographics – Cervical Only

	No ankylosis	Ankylosis	P value
	N = 126	N = 42	P value
Age	61.1 (11.6)	61.1 (12.0)	0.991
Race			0.738
White	112 (88.9%)	37 (88.1%)
Black	11 (8.73%)	3 (7.14%)
Other	3 (2.38%)	2 (4.76%)
Sex (female)	55 (43.7%)	14 (33.3%)	0.319
BMI	30.8 (6.97)	31.0 (7.53)	0.892
CCI	1.92 (2.07)	3.02 (1.65)	<0.001
DCI	31.2 (23.8)	33.5 (23.1)	0.384
DCI quintile			0.544
Prosperous	55 (43.7%)	14 (34.1%)
Comfortable	27 (21.4%)	13 (31.7%)
Mid-Tier	29 (23.0%)	8 (19.5%)
At Risk	5 (3.97%)	3 (7.32%)
Distressed	10 (7.94%)	3 (7.32%)

Bold denotes statistical significance.

Abbreviations: BMI: Body Mass Index, CCI: Charlson Comorbidity Index, DCI: Distressed Communities Index.

Among patients who underwent TLIF or PLDF, the AS/DISH cohort had a greater proportion of patients in the comfortable (37.5 vs 20.8%) and mid-tier (33.3 vs 18.1%) DCI quintiles but a smaller proportion of patients in the prosperous (25.0 vs 38.9%), at risk (0.00 vs 16.7%), and distressed (4.17 vs 5.56%) DCI quintiles (P = 0.043 for all) (Table 3).

Table 3.

Patient Demographics – Lumbar Only

	No ankylosis	Ankylosis	P value
	N = 72	N = 24	P value
Age	64.7 (10.3)	63.9 (9.05)	0.482
Race			1.000
White	61 (84.7%)	20 (83.3%)
Black	9 (12.5%)	3 (12.5%)
Other	2 (2.78%)	1 (4.17%)
Sex (female)	39 (54.2%)	7 (29.2%)	0.059
BMI	32.2 (6.14)	31.8 (4.54)	0.939
CCI	2.89 (1.73)	3.21 (1.64)	0.567
DCI	35.9 (25.2)	33.0 (19.8)	0.627
DCI quintile			0.043
Prosperous	28 (38.9%)	6 (25.0%)
Comfortable	15 (20.8%)	9 (37.5%)
Mid-Tier	13 (18.1%)	8 (33.3%)
At Risk	12 (16.7%)	0 (0.00%)
Distressed	4 (5.56%)	1 (4.17%)

Bold denotes statistical significance.

Abbreviations: BMI: Body Mass Index, CCI: Charlson Comorbidity Index, DCI: Distressed Communities Index.

Perioperative Outcomes

There were no differences in surgical characteristics between the cohorts in aggregate, cervical fusion, and lumbar fusion analysis (Tables 4-6).

Table 4.

Surgical Characteristics – All Patients

	N	No ankylosis	Ankylosis	P value
	N	N = 198	N = 66	P value
Surgery performed	264			1.000
ACDF		75 (37.9%)	25 (37.9%)
PCDF		51 (25.8%)	17 (25.8%)
PLDF		51 (25.8%)	17 (25.8%)
TLIF		21 (10.6%)	7 (10.6%)
Number of levels fused	264	2.81 (1.97)	2.83 (2.03)	0.940
EBL	57	196 (221)	416 (715)	0.158
LOS	223	2.84 (1.82)	4.00 (6.59)	0.433
OR time	183	260 (110)	267 (109)	0.564
Cut to close	184	185 (98.7)	184 (95.0)	0.931

Bold denotes statistical significance.

Abbreviations: ACDF: Anterior Cervical Discectomy and Fusion, PCDF: Posterior Cervical Decompression and Fusion, PLDF: Posterior Lumbar Decompression and Fusion, TLIF: Transforaminal Lumbar Interbody Fusion, EBL: Estimated Blood Loss, LOS: Length of Stay, OR: Operating Room.

Table 5.

Surgical Characteristics – Cervical Only

	N	No ankylosis	Ankylosis	P value
	N	N = 126	N = 42	P value
Surgery performed	168			1.000
ACDF		75 (59.5%)	25 (59.5%)
PCDF		51 (40.5%)	17 (40.5%)
Number of levels fused	168	3.19 (1.88)	3.24 (2.09)	0.894
EBL	49	196 (221)	170 (189)	0.925
LOS	133	2.53 (1.68)	3.93 (7.97)	0.561
OR time	113	246 (91.6)	248 (89.9)	0.930
Cut to close	114	164 (77.6)	163 (73.3)	0.965

Bold denotes statistical significance.

Abbreviations: ACDF: Anterior Cervical Discectomy and Fusion, PCDF: Posterior Cervical Decompression and Fusion, EBL: Estimated Blood Loss, LOS: Length of Stay, OR: Operating Room.

Table 6.

Surgical Characteristics – Lumbar Only

	N	No ankylosis	Ankylosis	P value
	N	N = 72	N = 24	P value
Surgery performed	96			1.000
PLDF		51 (70.8%)	17 (70.8%)
TLIF		21 (29.2%)	7 (29.2%)
Number of levels fused	96	2.14 (1.94)	2.12 (1.73)	0.823
EBL	8	. (.)	969 (1111)	.
LOS	90	3.26 (1.92)	4.10 (3.11)	0.336
OR time	70	280 (129)	313 (139)	0.294
Cut to close	70	214 (118)	234 (123)	0.513

Bold denotes statistical significance.

Abbreviations: PLDF: Posterior Lumbar Decompression and Fusion, TLIF: Transforaminal Lumbar Interbody Fusion, EBL: Estimated Blood Loss, LOS: Length of Stay, OR: Operating Room.

Among all patients, the AS/DISH cohort had a greater proportion of patients with 0-30 days readmissions (13.6 vs 2.02%; P = 0.001), 31-90 days readmissions (4.55 vs 0.51%; P = 0.049), 1 total readmission (13.6 vs 1.01%; P < 0.001), and 2 total readmissions (3.03 vs 1.01%; P < 0.001) (Table 7).

Table 7.

Surgical Outcomes – All Patients

	No ankylosis	Ankylosis	P value
	N = 198	N = 66	P value
Discharge disposition			0.155
Home	102 (65.0%)	35 (59.3%)
Home Health Care	35 (22.3%)	15 (25.4%)
Inpatient Rehab	13 (8.28%)	2 (3.39%)
Skilled Nursing Facility	7 (4.46%)	7 (11.9%)
0-30 Day readmission	4 (2.02%)	9 (13.6%)	0.001
31-90 Day readmission	1 (0.51%)	3 (4.55%)	0.049
Number of readmissions			<0.001
0	194 (98.0%)	55 (83.3%)
1	2 (1.01%)	9 (13.6%)
2	2 (1.01%)	2 (3.03%)
1 Year revision	12 (6.06%)	1 (1.52%)	0.195
1 Year reoperation	13 (6.57%)	4 (6.06%)	1.000

Bold denotes statistical significance.

Among patients who underwent ACDF or PCDF, the AS/DISH cohort had a greater proportion of patients who had 0-30 days readmissions (9.52 vs 1.59%; P = 0.035), 31-90 days readmissions (7.14 vs 0.79%; P = 0.049), 1 total readmission (9.52 vs 0.79%; P. = 0.004), and 2 total readmissions (4.76 vs 0.79%; P = 0.004) (Table 8).

Table 8.

Surgical Outcomes – Cervical Only

	No ankylosis	Ankylosis	P value
	N = 126	N = 42	P value
Discharge disposition			0.373
Home	57 (62.6%)	28 (73.7%)
Home Health Care	23 (25.3%)	5 (13.2%)
Inpatient Rehab	7 (7.69%)	2 (5.26%)
Skilled Nursing Facility	4 (4.40%)	3 (7.89%)
0-30 Day readmission	2 (1.59%)	4 (9.52%)	0.035
31-90 Day readmission	1 (0.79%)	3 (7.14%)	0.049
Number of readmissions			0.004
0	124 (98.4%)	36 (85.7%)
1	1 (0.79%)	4 (9.52%)
2	1 (0.79%)	2 (4.76%)
1 Year revision	6 (4.76%)	0 (0.00%)	0.338
1 Year reoperation	6 (4.76%)	2 (4.76%)	1.000

Bold denotes statistical significance.

Among patients who underwent TLIF or PLDF, the AS/DISH cohort had a greater proportion of patients who were discharged to home health care (47.6 vs 18.2%) and a skilled nursing facility (19.0 vs 4.55%) and a smaller proportion of patients who were discharged home (33.3 vs 68.2%) (P = 0.002 for all). The AS/DISH cohort also had a greater proportion of 0-30 days readmissions (20.8 vs 2.78%; P = 0.010) and 1 total readmission (20.8 vs 1.39%; P = 0.003). The control group had a greater proportion of patients with 2 total readmissions (1.39 vs 0.00%; P = 0.003) (Table 9).

Table 9.

Surgical Outcomes – Lumbar Only

	No ankylosis	Ankylosis	P value
	N = 72	N = 24	P value
Discharge disposition			0.002
Home	45 (68.2%)	7 (33.3%)
Home Health Care	12 (18.2%)	10 (47.6%)
Inpatient Rehab	6 (9.09%)	0 (0.00%)
Skilled Nursing Facility	3 (4.55%)	4 (19.0%)
0-30 Day readmission	2 (2.78%)	5 (20.8%)	0.010
31-90 Day readmission	0 (0%)	0 (0%)	.
Number of readmissions			0.003
0	70 (97.2%)	19 (79.2%)
1	1 (1.39%)	5 (20.8%)
2	1 (1.39%)	0 (0.00%)
1 Year revision	6 (8.33%)	1 (4.17%)	0.676
1 Year reoperation	7 (9.72%)	2 (8.33%)	1.000

Bold denotes statistical significance.

Patient Reported Outcome Measures

Among all patients, the AS/DISH cohort had a lower preoperative NDI score (27.6 vs 37.6; P = 0.033), 12-month postoperative VAS Arm (0.57 vs 2.64; P = 0.029), 12-months delta VAS Leg (−0.33 vs −3.62; P = 0.039). The AS/DISH cohort also had a greater delta 6-months VAS Back (−4.00 vs −2.70; P = 0.002) (Table 10).

Table 10.

PROMs – All Patients

	N	No ankylosis	Ankylosis	P value
	N	N = 198	N = 66	P value
Pre Op VAS neck	120	4.93 (3.05)	5.44 (3.11)	0.416
Post Op 3 month VAS neck	81	3.21 (2.64)	2.12 (2.47)	0.227
Delta 3 month VAS neck	73	−1.70 (2.91)	−2.83 (4.02)	0.412
Post Op 6 month VAS neck	81	2.93 (2.80)	2.50 (2.17)	0.935
Delta 6 month VAS neck	70	−1.78 (2.97)	−3.20 (2.59)	0.226
Post Op 12 month VAS neck	106	2.72 (2.67)	0.86 (0.90)	0.075
Delta 12 month VAS neck	89	−2.32 (3.09)	−3.75 (2.63)	0.309
Post Op 24 month VAS neck	66	2.65 (2.64)	2.83 (1.72)	0.549
Delta 24 month VAS neck	59	−2.19 (3.58)	−4.40 (2.70)	0.146
Pre Op VAS arm	119	5.03 (2.93)	4.61 (3.26)	0.625
Post Op 3 month VAS arm	81	2.79 (2.53)	1.62 (1.92)	0.228
Delta 3 month VAS arm	72	−2.00 (3.31)	−2.00 (4.15)	1.000
Post Op 6 month VAS arm	81	2.67 (2.70)	1.00 (2.00)	0.111
Delta 6 month VAS arm	70	−2.06 (3.33)	−4.20 (3.77)	0.278
Post Op 12 month VAS arm	105	2.64 (2.62)	0.57 (1.13)	0.029
Delta 12 month VAS arm	88	−2.42 (3.42)	−3.75 (2.99)	0.443
Post Op 24 month VAS arm	66	2.53 (2.98)	0.83 (1.33)	0.159
Delta 24 month VAS arm	59	−2.80 (4.06)	−4.40 (3.71)	0.485
Pre Op NDI	107	37.6 (21.5)	27.6 (14.3)	0.033
Post Op 3 month NDI	46	26.5 (22.4)	21.0 (16.8)	0.571
Delta 3 month NDI	40	−10.94 (19.0)	−6.00 (16.3)	0.525
Post Op 6 month NDI	41	24.9 (22.8)	20.0 (10.6)	1.000
Delta 6 month NDI	35	−13.88 (17.7)	−19.00 (21.2)	0.791
Post Op 12 month NDI	57	23.7 (17.6)	18.3 (15.9)	0.490
Delta 12 month NDI	34	−15.27 (17.3)	−16.00 (.)	.
Post Op 24 month NDI	23	26.6 (22.8)	16.5 (2.52)	0.839
Delta 24 month NDI	14	−20.00 (22.0)	−6.00 (14.1)	0.362
Pre Op VAS back	76	6.30 (2.67)	7.89 (1.17)	0.133
Post Op 3 month VAS back	57	3.53 (2.52)	5.50 (3.51)	0.232
Delta 3 month VAS back	53	−2.84 (2.87)	−3.00 (4.08)	0.973
Post Op 6 month VAS back	65	3.53 (2.42)	5.33 (2.31)	0.185
Delta 6 month VAS back	58	−2.70 (3.05)	−4.00 (0.00)	0.002
Post Op 12 month VAS back	71	3.48 (2.62)	4.40 (3.05)	0.427
Delta 12 month VAS back	59	−2.88 (3.02)	−3.67 (3.51)	0.742
Post Op 24 month VAS back	42	4.21 (3.01)	6.67 (2.31)	0.153
Delta 24 month VAS back	33	−2.28 (2.85)	0.00 (.)	.
Pre Op VAS leg	76	6.46 (2.99)	5.11 (3.14)	0.160
Post Op 3 month VAS leg	57	3.08 (2.85)	2.25 (1.50)	0.702
Delta 3 month VAS leg	53	−3.76 (3.52)	−0.50 (3.00)	0.114
Post Op 6 month VAS leg	65	2.95 (2.55)	4.33 (4.04)	0.497
Delta 6 month VAS leg	58	−3.96 (3.78)	−1.50 (0.71)	0.170
Post Op 12 month VAS leg	71	3.17 (2.79)	3.20 (3.56)	0.847
Delta 12 month VAS leg	59	−3.62 (3.70)	−0.33 (1.53)	0.039
Post Op 24 month VAS leg	42	3.31 (3.29)	4.33 (3.21)	0.471
Delta 24 month VAS leg	33	−4.25 (3.79)	1.00 (.)	.
Pre Op ODI	75	47.7 (17.3)	51.2 (16.5)	0.577
Post Op 3 month ODI	56	30.2 (20.3)	45.3 (21.6)	0.152
Delta 3 month ODI	50	−18.10 (16.7)	−8.00 (7.21)	0.112
Post Op 6 month ODI	65	26.6 (17.3)	43.3 (19.2)	0.150
Delta 6 month ODI	59	−23.01 (18.8)	−9.00 (7.07)	0.216
Post Op 12 Month ODI	72	26.7 (18.9)	31.4 (21.7)	0.557
Delta 12 Month ODI	59	−24.05 (21.2)	−8.30 (19.5)	0.294
Post Op 24 month ODI	44	29.9 (21.6)	44.4 (10.4)	0.177
Delta 24 month ODI	35	−19.26 (17.2)	6.00 (.)	.
Pre Op mJOA	123	14.0 (3.23)	14.9 (2.68)	0.291
Post Op 3 month mJOA	91	15.0 (3.00)	16.6 (1.74)	0.144
Delta 3 month mJOA	84	1.04 (3.67)	1.71 (2.56)	0.447
Post Op 6 month mJOA	84	15.3 (2.53)	16.0 (1.55)	0.672
Delta 6 month mJOA	78	1.34 (2.56)	1.60 (1.34)	0.542
Post Op 12 month mJOA	112	15.0 (3.17)	16.9 (1.55)	0.085
Delta 12 month mJOA	99	1.17 (3.61)	1.40 (2.51)	0.923
Post Op 24 month mJOA	69	14.9 (2.86)	16.5 (1.38)	0.216
Delta 24 month mJOA	61	1.09 (3.71)	1.80 (1.30)	0.259
Pre Op PCS	207	32.3 (8.79)	30.9 (8.94)	0.432
Post Op 3 month PCS	132	34.4 (9.48)	37.0 (9.66)	0.392
Delta 3 month PCS	129	2.66 (9.57)	8.13 (11.9)	0.149
Post Op 6 month PCS	145	36.9 (11.2)	32.8 (12.1)	0.236
Delta 6 month PCS	139	5.35 (11.1)	4.32 (8.91)	0.748
Post Op 12 month PCS	185	37.5 (10.6)	37.9 (12.5)	0.966
Delta 12 month PCS	171	5.56 (10.5)	6.51 (9.17)	0.738
Post Op 24 month PCS	120	36.3 (10.7)	35.2 (11.6)	0.657
Delta 24 month PCS	112	4.38 (10.7)	6.66 (11.9)	0.717
Pre Op MCS	207	45.3 (12.8)	47.2 (13.0)	0.467
Post Op 3 month MCS	132	49.5 (11.4)	51.1 (13.9)	0.484
Delta 3 month MCS	129	4.06 (11.0)	3.67 (11.0)	0.909
Post Op 6 month MCS	145	49.9 (11.7)	51.7 (14.8)	0.378
Delta 6 month MCS	139	4.27 (12.3)	4.88 (13.8)	0.956
Post Op 12 month MCS	185	49.9 (12.6)	56.5 (9.22)	0.072
Delta 12 month MCS	171	5.26 (13.6)	6.80 (8.58)	0.527
Post Op 24 month MCS	120	50.9 (10.9)	56.2 (8.36)	0.091
Delta 24 month MCS	112	4.90 (13.3)	4.74 (11.7)	0.858

Bold denotes statistical significance.

Abbreviations: VAS: Visual Analog Scale, NDI: Neck Disability Index, ODI: Oswestry Disability Index, mJOA: Modified Japanese Orthopaedic Association, PCS: Physical Component Summary, MCS: Mental Component Summary.

Among patients who underwent ACDF or PCDF, the AS/DISH cohort had a lower preoperative NDI (27.1 vs 37.6; P. = 0.036), 12-months postoperative VAS Neck (1.00 vs 2.72; P = 0.003), 12-months postoperative VAS Arm (0.67 vs 2.64; P = 0.007), 24-months postoperative VAS Arm (0.83 vs 2.53; P = 0.027). The AS/DISH cohort also had a higher 3 months postoperative (16.6 vs 15.0; P = 0.035), 12-months postoperative (17.1 vs 15.0; P = 0.007), and 24-months postoperative (16.5 vs 14.9; P = 0.039) mJOA scores and 12-months postoperative MCS (56.8 vs 49.4; P = 0.009) and 24-months postoperative (56.1 vs 50.5; P = 0.032) MCS scores (Table 11).

Table 11.

PROMs – Cervical Only

	N	No ankylosis	Ankylosis	P value
	N	N = 126	N = 42	P value
Pre Op VAS neck	117	4.99 (3.04)	5.24 (3.07)	0.763
Post Op 3 month VAS neck	79	3.24 (2.66)	2.12 (2.47)	0.262
Delta 3 month VAS neck	71	−1.75 (2.94)	−2.83 (4.02)	0.547
Post Op 6 month VAS neck	80	2.97 (2.80)	2.50 (2.17)	0.633
Delta 6 month VAS neck	69	−1.81 (2.99)	−3.20 (2.59)	0.307
Post Op 12 month VAS neck	105	2.72 (2.67)	1.00 (0.89)	0.003
Delta 12 month VAS neck	89	−2.32 (3.09)	−3.75 (2.63)	0.360
Post Op 24 month VAS neck	66	2.65 (2.64)	2.83 (1.72)	0.821
Delta 24 month VAS neck	59	−2.19 (3.58)	−4.40 (2.70)	0.146
Pre Op VAS arm	116	5.11 (2.90)	4.88 (3.14)	0.782
Post Op 3 month VAS arm	79	2.87 (2.52)	1.62 (1.92)	0.124
Delta 3 month VAS arm	70	−2.03 (3.35)	−2.00 (4.15)	0.986
Post Op 6 month VAS arm	80	2.70 (2.70)	1.00 (2.00)	0.095
Delta 6 month VAS arm	69	−2.09 (3.35)	−4.20 (3.77)	0.285
Post Op 12 month VAS arm	104	2.64 (2.62)	0.67 (1.21)	0.007
Delta 12 month VAS arm	88	−2.42 (3.42)	−3.75 (2.99)	0.443
Post Op 24 month VAS arm	66	2.53 (2.98)	0.83 (1.33)	0.027
Delta 24 month VAS arm	59	−2.80 (4.06)	−4.40 (3.71)	0.402
Pre Op NDI	103	37.6 (21.3)	27.1 (14.8)	0.036
Post Op 3 month NDI	46	26.5 (22.4)	21.0 (16.8)	0.442
Delta 3 month NDI	40	−10.94 (19.0)	−6.00 (16.3)	0.525
Post Op 6 month NDI	41	24.9 (22.8)	20.0 (10.6)	0.530
Delta 6 month NDI	35	−13.88 (17.7)	−19.00 (21.2)	0.791
Post Op 12 month NDI	56	23.7 (17.6)	14.0 (13.3)	0.185
Delta 12 month NDI	34	−15.27 (17.3)	−16.00 (.)	.
Post Op 24 month NDI	23	26.6 (22.8)	16.5 (2.52)	0.075
Delta 24 month NDI	14	−20.00 (22.0)	−6.00 (14.1)	0.362
Pre Op mJOA	120	13.9 (3.24)	14.9 (2.75)	0.177
Post Op 3 month mJOA	89	15.0 (3.02)	16.6 (1.74)	0.035
Delta 3 month mJOA	82	1.07 (3.71)	1.71 (2.56)	0.557
Post Op 6 month mJOA	83	15.3 (2.54)	16.0 (1.55)	0.329
Delta 6 month mJOA	77	1.39 (2.54)	1.60 (1.34)	0.763
Post Op 12 month mJOA	111	15.0 (3.17)	17.1 (1.46)	0.007
Delta 12 month mJOA	99	1.17 (3.61)	1.40 (2.51)	0.854
Post Op 24 month mJOA	69	14.9 (2.86)	16.5 (1.38)	0.039
Delta 24 month mJOA	61	1.09 (3.71)	1.80 (1.30)	0.372
Pre Op PCS	132	34.0 (9.12)	33.5 (8.93)	0.827
Post Op 3 month PCS	80	35.5 (9.89)	39.5 (9.31)	0.276
Delta 3 month PCS	79	1.54 (10.3)	9.06 (14.1)	0.183
Post Op 6 month PCS	86	37.1 (11.8)	32.4 (13.6)	0.401
Delta 6 month PCS	81	3.91 (11.5)	2.63 (9.41)	0.745
Post Op 12 month PCS	125	37.5 (11.1)	40.1 (13.7)	0.574
Delta 12 month PCS	114	4.25 (9.90)	4.26 (8.19)	0.997
Post Op 24 month PCS	80	36.5 (11.2)	36.9 (12.5)	0.922
Delta 24 month PCS	76	3.08 (11.0)	6.81 (13.2)	0.464
Pre Op MCS	132	44.7 (13.4)	46.8 (12.7)	0.498
Post Op 3 month MCS	80	48.8 (11.0)	52.8 (13.3)	0.444
Delta 3 month MCS	79	4.55 (11.7)	7.23 (11.0)	0.533
Post Op 6 month MCS	86	48.7 (12.1)	54.1 (11.1)	0.262
Delta 6 month MCS	81	4.11 (13.4)	8.14 (14.1)	0.490
Post Op 12 month MCS	125	49.4 (12.7)	56.8 (6.79)	0.009
Delta 12 month MCS	114	5.54 (14.5)	10.5 (7.72)	0.131
Post Op 24 month MCS	80	50.5 (11.5)	56.1 (6.67)	0.032
Delta 24 month MCS	76	5.16 (14.7)	6.48 (12.5)	0.788

Bold denotes statistical significance.

Abbreviations: VAS: Visual Analog Scale, NDI: Neck Disability Index, mJOA: Modified Japanese Orthopaedic Association, PCS: Physical Component Summary, MCS: Mental Component Summary.

Among patients who underwent PLDF and TLIF, the AS/DISH cohort had greater preoperative (7.89 vs 6.59; P = 0.018), 6-month postoperative (4.00 vs 3.33; P = 0.045), and delta 6-months (−4.00 vs −2.91; P = 0.010) VAS Back scores. The AS/DISH cohort had lower delta 6-months (−1.50 vs −4.13; P = 0.021) and 12-months (−0.33 vs −3.70; P = 0.037) VAS Leg scores. Finally, this cohort also had greater 6-months (−6.52 vs 4.48; P. = 0.047) and 24 months (−2.25 vs 4.37; P = 0.001) MCS scores (Table 12).

Table 12.

PROMs – Lumbar Only

	N	No ankylosis	Ankylosis	P value
	N	N = 72	N = 24	P value
Pre Op VAS back	70	6.59 (2.53)	7.89 (1.17)	0.018
Post Op 3 month VAS back	52	3.52 (2.41)	5.50 (3.51)	0.344
Delta 3 month VAS back	50	−2.83 (2.94)	−3.00 (4.08)	0.938
Post Op 6 month VAS back	57	3.33 (2.43)	4.00 (0.00)	0.045
Delta 6 month VAS back	55	−2.91 (2.98)	−4.00 (0.00)	0.010
Post Op 12 month VAS back	60	3.36 (2.62)	5.00 (3.16)	0.379
Delta 12 month VAS back	57	−2.93 (3.06)	−3.67 (3.51)	0.752
Post Op 24 month VAS back	35	3.97 (2.97)	8.00 (.)	.
Delta 24 month VAS back	33	−2.28 (2.85)	0.00 (.)	.
Pre Op VAS leg	70	6.87 (2.72)	5.11 (3.14)	0.143
Post Op 3 month VAS leg	52	2.96 (2.90)	2.25 (1.50)	0.446
Delta 3 month VAS leg	50	−4.02 (3.37)	−0.50 (3.00)	0.095
Post Op 6 month VAS leg	57	2.93 (2.62)	2.50 (3.54)	0.892
Delta 6 month VAS leg	55	−4.13 (3.70)	−1.50 (0.71)	0.021
Post Op 12 month VAS leg	60	3.30 (2.83)	4.00 (3.56)	0.725
Delta 12 month VAS leg	57	−3.70 (3.59)	−0.33 (1.53)	0.037
Post Op 24 month VAS leg	35	3.09 (3.40)	8.00 (.)	.
Delta 24 month VAS leg	33	−4.25 (3.79)	1.00 (.)	.
Pre Op ODI	68	49.8 (15.7)	51.2 (16.5)	0.818
Post Op 3 month ODI	51	29.6 (20.6)	45.3 (21.6)	0.244
Delta 3 month ODI	47	−18.73 (16.8)	−8.00 (7.21)	0.097
Post Op 6 month ODI	57	24.7 (16.6)	45.0 (26.9)	0.477
Delta 6 month ODI	56	−24.06 (18.5)	−9.00 (7.07)	0.148
Post Op 12 month ODI	60	25.2 (18.3)	35.3 (23.0)	0.452
Delta 12 month ODI	56	−24.86 (21.4)	−8.30 (19.5)	0.276
Post Op 24 month ODI	37	28.6 (21.3)	46.0 (.)	.
Delta 24 month ODI	34	−19.24 (17.5)	6.00 (.)	.
Pre Op PCS	75	29.3 (7.34)	26.4 (7.28)	0.243
Post Op 3 month PCS	52	32.8 (8.70)	31.9 (9.42)	0.865
Delta 3 month PCS	50	4.39 (8.15)	6.25 (6.93)	0.640
Post Op 6 month PCS	59	36.6 (10.3)	34.2 (8.23)	0.746
Delta 6 month PCS	58	7.26 (10.3)	10.2 (3.87)	0.458
Post Op 12 month PCS	60	37.4 (9.71)	33.4 (9.22)	0.403
Delta 12 month PCS	57	8.18 (11.2)	11.0 (10.6)	0.639
Post Op 24 month PCS	40	36.0 (10.0)	30.6 (8.72)	0.315
Delta 24 month PCS	36	6.97 (9.59)	6.08 (7.61)	0.898
Pre Op MCS	75	46.4 (11.5)	47.9 (14.2)	0.751
Post Op 3 month MCS	52	50.5 (11.9)	47.9 (16.6)	0.771
Delta 3 month MCS	50	3.29 (9.90)	−3.45 (7.60)	0.174
Post Op 6 month MCS	59	51.5 (11.0)	43.4 (28.7)	0.759
Delta 6 month MCS	58	4.48 (10.8)	−6.52 (3.04)	0.047
Post Op 12 month MCS	60	50.7 (12.4)	55.9 (13.9)	0.464
Delta 12 month MCS	57	4.70 (11.6)	−0.68 (4.33)	0.085
Post Op 24 month MCS	40	51.7 (9.86)	56.6 (13.3)	0.523
Delta 24 month MCS	36	4.37 (10.2)	−2.25 (0.14)	0.001

Bold denotes statistical significance.

Abbreviations: VAS: Visual Analog Scale, ODI: Oswestry Disability Index, PCS: Physical Component Summary, MCS: Mental Component Summary.

Multivariable regression controlling for CCI score, male sex, and AS/DISH diagnosis identified that a diagnosis of AS/DISH was independently associated with greater odds of 30-day readmissions after cervical and lumbar fusion (OR: 6.04, 95% CI: 1.84-23.38, P = 0.004) (Table 13).

Table 13.

Multivariable Regression Identifying Predictors of 30-Days Readmissions

Variable	Odds Ratio	Lower 95	Upper 95	P Value
Spine AS/DISH	6.04	1.84	23.39	0.004
CCI	1.17	0.84	1.62	0.339
Male	0.29	0.04	1.14	0.115

Bold denotes statistical significance.

Abbreviations: AS/DISH: Ankylosing Spondylitis/Diffuse Idiopathic Skeletal Hyperostosis, CCI: Charlson Comorbidity Index.

Discussion

AS and DISH are two of the most common ankylosing disorders of the axial skeleton.^2,4 Although these two diseases have unique etiologies, they are both ankylosing spinal disorders characterized by ossification of the vertebral bodies and subsequent stiffness of the spine.^13,14 Patients with AS/DISH are consequentially more susceptible to sustaining vertebral fractures from minor trauma, and therefore undergo spine surgery at relatively frequent rates.^15,16 Furthermore, patients with AS/DISH are more prone to nerve compression due to ossification of the posterior longitudinal ligament (PLL), hypertrophy of the ligamentum flavum, and disc degeneration.^18,19 While several studies have shown worse outcomes in patients with AS/DISH undergoing operative management for vertebral fractures compared to controls, there is an overall paucity of studies investigating postoperative outcomes after elective spine fusion in these patients.^16,17 Our study aimed to investigate the impact that AS/DISH has on postoperative outcomes after primary, elective lumbar and cervical fusion. We identified several differences in postoperative outcomes between patients with AS/DISH and healthy controls who underwent spinal fusion procedures. Patients with AS/DISH tended to have more frequent readmission rates after surgery. Regarding PROMs, interestingly the AS/DISH cohort tended to have superior outcomes with some metrics and inferior outcomes with others.

There were several baseline demographic differences in patients with and without AS/DISH in the present work, largely consistent with existing literature. Patients with AS/DISH were less likely to be female and more likely to have greater CCI scores. Historically, AS has been thought to be a disease that overwhelmingly affected more males than females with several studies demonstrating the male: female ratio of AS prevalence to be as high as 2.7:1.^26,27 However, other sources have reported a more even distribution of AS prevalence between genders, attributing the historical under-diagnosis of AS in women to the tendency of females to have less severe radiographic manifestations of AS compared to males.^28,29 Similarly, Le et al reported a 2:1 distribution of males to females diagnosed with DISH.¹⁹ Several studies have also corroborated our findings regarding greater CCI score in our AS/DISH cohort compared to controls. A Korean population study performed by Lee et al matched 1111 patients with AS to 5555 controls and found that the AS cohort had 2.18 greater odds of having a CCI score of greater than or equal to 3.³⁰ In addition, several studies have reported metabolic syndrome to be a risk factor developing DISH which likely contributed to the greater CCI scores seen in our AS/DISH cohort.³¹

Interestingly, there were no significant differences in surgical characteristics between our AS/DISH and control cohorts. This is somewhat contradictory with the current literature. There is a theoretical supposition that spine surgeries in patients with AS are overall more complex and more prone to complications, potentially due to the poor bone quality and increased comorbidity burden that are characteristic of AS.^24,32 Furthermore, a retrospective database study demonstrated that patients with AS have a 1.5 times greater odds of requiring blood transfusions relative to controls in patients undergoing thoracolumbar fusion for treatment of vertebral fractures.³³ Regarding the impact that DISH has on postoperative outcomes, Shimizu et al demonstrated that patients with DISH had greater numbers of levels fused (4.2 vs 1.8; P < 0.001), greater length of surgery (200 vs 136 minutes; P < 0.001), and EBL (438 vs 169 mL; P = 0.008) relative to non-DISH patients when treated for cervical spinal cord injuries. In our present work, the AS/DISH cohort had greater, albeit not statistically significant, EBL, LOS, and OR time in aggregate analysis.³⁴ We postulate that this may partially be explained by our small sample size, which may have been underpowered to detect differences between our cohorts. In addition, many of the studies that investigate surgical characteristics in fusion procedures in patients with AS/DISH focus on lumbar and/or cervical fusion that is indicated for traumatic fractures, rather than on elective surgeries. This highlights a need for future studies with larger sample sizes comparing outcomes after primary, elective fusions in patients with and without ankylosing disorders.

Patients with AS/DISH were found to generally have more frequent readmissions and non-home discharge dispositions in the current work. While there is limited literature directly investigating the impact that these diagnoses have on readmission rates and non-home discharge dispositions, several studies have demonstrated that greater comorbidity burden can influence these factors in spine surgery.^35,36 Within our AS/DISH cohort, it is possible that the increased readmission rates and non-home discharges in are partially explained by the increased comorbidity burden of the cohort. However, our multivariable regression controlling for baseline differences in sex and CCI score identified AS/DISH diagnoses to be independently predictive of 30-days readmissions, indicating that patients with ankylosing disorders of the lumbar and cervical spine tend to experience greater readmission rates after spinal fusion independent of comorbidity burden. However, further studies are needed to contextualize these findings. While there were no differences in 1 year revision or reoperation rates between the AS/DISH and control cohorts in the current study, several studies have reported discordant findings. Otsuki et al first investigated outcomes after short-segment lumbar interbody fusion in patients with DISH and found that patients with DISH were significantly more likely to undergo reoperation (25.6% vs 6.5%).³⁷ Otsuki et al conducted a similar study investigating reoperation rates after lumbar decompression procedures without fusion, and found that patients with DISH were more likely to undergo revision surgery (19% vs 6.9%) compared to healthy controls.²² However, it is difficult to contextualize the findings of the present work due to a paucity of studies investigating this topic, also highlighting a need for future research.

Patients undergoing cervical spine surgery demonstrated superior outcomes regarding VAS Neck, VAS Arm, and mJOA at certain postoperative timepoints relative to the control cohort. These findings are somewhat concordant with those from a study by Alam et al, demonstrating that VAS scores significantly improved from 6.1 preoperatively to 3.1 postoperatively in AS patients undergoing operative management of vertebral fractures.³⁸ Similarly, Kato et al demonstrated that there was no difference in the degree of improvement after operative management of vertebral fractures between DISH and non-DISH patients.³⁹ Chen et al investigated outcomes after cervical fixation for treating cervical fractures in patients with AS and demonstrated that VAS score improved from 6.88 preoperatively to 1.47 3-months postoperatively. Regarding mJOA scores, our AS/DISH cohort demonstrated superior metrics at various postoperative time points compared to our controls, indicating that they had superior clinical status in terms of myelopathic symptoms. Overall, these findings suggest that AS/DISH diagnosis does not prevent a patient from experiencing clinical benefit after elective cervical fusion.

A generalizable pattern of trends in PROMs was not as apparent among our AS/DISH patients undergoing lumbar fusion procedures. While our AS/DISH cohort had greater 6-month postoperative VAS Back scores, the delta value of VAS Back scores 6-months postoperatively was also superior in the AS/DISH cohort. This may partially be explained by the greater preoperative VAS Back scores observed in our AS/DISH cohort, which has been shown to be predictive of greater ability to achieve minimum clinically important difference after lumbar fusion.⁴⁰ In contrast, our AS/DISH cohort demonstrated inferior improvements in VAS Leg scores are multiple postoperative timepoints compared to the control. Furthermore, patients with AS/DISH undergoing both lumbar and cervical fusion had greater postoperative MCS scores, indicating that AS/DISH diagnosis can be associated with worse mental state even after successful decompression and fusion. However, it is difficult to contextualize these findings to determine the impact that AS/DISH diagnosis has on postoperative PROMs after elective lumbar fusion, indicating a need for future work investigating this topic.

This study has several limitations. First, due to the retrospective nature of this study, it is not possible to draw casual relationships from our findings. Therefore, while we were able to determine that AS/DISH diagnosis was associated with several postoperative outcomes after primary, elective lumbar and cervical fusion, it is not possible to discern that the AS/DISH diagnosis was the sole cause of these findings. In addition, since this study was conducted at a single, large institution, it is not possible to generalize the findings of this study to all clinical settings. Third, although this study is one of the largest scale investigations at a single institution that has investigated the impact of AS/DISH diagnosis on postoperative outcomes after primary elective fusions, the sample size of our AS/DISH diagnosis remained relatively small which potentially underpowered our study to detect true outcomes. Future, larger scale or multi-institution studies can therefore be considered in future work. Finally, patients with AS and DISH were combined into a single cohort which limited our ability to determine whether there were differences in postoperative profiles after elective fusion between patients with these diagnoses. This is especially important considering that patient demographics and pathophysiology of these disorders may differ considerably. However, given that these diagnoses are both ankylosing disorders of the spine that result in stiffness, the authors deemed it appropriate to combine such patients into a single cohort to determine the impact that spine stiffness has on outcomes after spine surgery, especially considering that the sample sizes of patients with AS and DISH separately would likely have resulted in an underpowered study. Future studies are needed to determine the independent impact that these diagnoses have on postoperative outcomes after elective fusion.

Conclusion

The current work is one of the largest single-institution studies that have investigated the impact that AS/DISH have on postoperative outcomes after primary, elective lumbar and cervical fusion. Overall, the present study demonstrated generally similar PROMs between our AS/DISH and control cohorts. However, our AS/DISH cohort demonstrated significantly higher readmission rates. Patients with AS/DISH undergoing primary, elective lumbar and cervical fusions may potentially benefit from medical optimization and multimodal postoperative management via early mobilization, pain expectation counseling, proactive pain control, and proper DMARD management to decrease readmission risk.

Footnotes

ORCID iDs

Adam Fano

Mitchell Ng

Chloe Herczeg

William Green

Ian D. Kaye

Jose Canseco

Alan Hilibrand

Ethical Consideration

This is an IRB-approved retrospective study (approval #19D.508).

Consent to Participate

All patient information was de-identified and patient consent was not required. Patient data will not be shared with third parties.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: AF: None. JB: None. MN: Stryker. Inc. – paid consultant, Johnson & Johnson Ethicon Inc. – paid consultant, CurvaFix Inc. – paid consultant, Pacira BioSciences Inc. – paid consultant, Sage Products Inc. – paid consultant, Alafair Biosciences Inc. – paid consultant, Next Science LLC – paid consultant, Bonutti Technologies Inc. – paid consultant, Hippocrates Opportunities Fund LLC – paid consultant, and Ferghana Partners Inc. – paid consultant.. GB: None. AG: None. JD: None. RN: None. RH: None. CH: None. RJO: None. JO: None. YE: None. WG: None. JM: None. MC: None. NP: None. MS: None. SF: None. RC: None. JAR: Cervical Spine Research Society- Board or committee member, Globus Medical- Paid consultant, The Spine Journal- Editorial or governing board, XTANT Medical- Stock or stock Options, IDK: Camber Spine – paid consultant; research support, Johnson & Johnson – paid consultant, North American Spine Society – board or committee member, Nuvasive – paid consultant, Spinal Cord and Case Series – editorial or governing board, Thieme – publishing royalties, financial or material support. JAC: Accelus – research support, Cervical Spine Research Society – board or committee member, PathKeeper Surgical – stock or stock options; unpaid consultant, Wolters Kluwer Health – Lippincott Williams & Wilkins – editorial or governing board. ASH: Biomet – IP royalties, CTL America – IP royalties, Paradigm spine – stock or stock options. ARV: Receives royalties from Stryker, Globus, Medtronic, Atlas Spine, Alphatech Spine, SpineWave, Spinal Elements, Curiteva, Elsevier, Jaypee, Stout Medical, Taylor Francis/Hodder and Stoughton, Wolters Kluwer, and Wheel House Medical, and Thieme; has stock or stock options in Accelus, Advanced Spinal Intellectual Properties, Atlas, Avaz Surgical, AVKN Patient Driven Care, Cytonics, Deep Health, Dimension Orthotics LLC, Electocore, Flagship Surgical, FlowPharma, Rothman Institute and Related Properties, Globus, Harvard MedTech, Innovative Surgical Design, Jushi (Haywood), Orthobullets, Parvizi Surgical Innovation, Progressive Spinal Technologies, Sentryx, Stout Medical, See All AI, and ViewFi Health; is a consultant for Curiteva, Medcura, Stryker, Globus, Spinal Elements, Accelus, Wheel House Medical, and Ferring Pharmaceutical; Serves on Scientific Advisory Board / Board of Directors / Committee for National Spine Health Foundation (NSHF), Sentryx, and Accelus; and is a member in good standing/independent contractor for AO Spine. CKK: Clinical Spine Surgery – editorial or governing board, Inion – IP royalties, Regeneration Technologies, Inc. – research support. GDS: Advance Medical – paid consultant, AOSpine – board or committee member, AOSpine – other financial or material support, Bioventus – paid consultant, Cerapedics – research support, Cervical Spine Research Society – board or committee member, DePuy, A Johnson & Johnson Company – research support, Medtronic Sofamor Danek – research support, Surgalign – paid consultant, Wolters Kluwer Health – Lippincott Williams & Wilkins – editorial or governing board.

Data Availability Statement

All relevant data are included in the manuscript draft, tables, and figures. The raw data are available upon reasonable request from the corresponding author.*

Data Source

All data utilized in this study were sourced from institutional records.

Drug Statement

The drug(s) mentioned in this study is FDA-approved or approved by corresponding national agency for this indication.

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