Does Ending a Posterior Construct Proximally at C2 Versus C3 Impact Patient Reported Outcomes in Degenerative Cervical Myelopathy Patients up to 24 months After the Surgery?

Abstract

Study Design

Retrospective cohort study.

Objective

The primary objective was to evaluate the impact of the upper instrumented level (UIV) being at C2 vs C3 in posterior cervical construct on patient reported outcomes (PROs) up to 24 months after surgery for cervical degenerative myelopathy (DCM). Secondary objectives were to compare operative time, intra-operative blood loss (IOBL), length of stay (LOS), adverse events (AEs) and re-operation.

Methods

Patients who underwent a posterior cervical instrumented fusion (3 and + levels) with a C2 or C3 UIV, with 24 months follow-up were analyzed. PROs (NDI, EQ5D, SF-12 PCS/MCS, NRS arm/neck pain) were compared using ANCOVA. Operative duration, IOBL, AEs, and re-operation were compared. Subgroup analysis was performed on patient presenting with pre-operative malalignment (cervical sagittal vertical axis ≥40 mm and/or T1slope- cervical lordosis >15°).

Results

173 patients were included, of which 41 (24%) had a C2 UIV and 132 (76%) a C3 UIV. There was no statistically significant difference between the groups for the changes in PROs up to 24 months. Subgroup analysis of patients with pre-operative malalignment showed a trend towards greater improvement in the NDI at 12 months with a C2 UIV (P = .054). Operative time, IOBL and peri-operative AEs were more in C2 group (P < .05). There was no significant difference in LOS and re-operation (P > .05).

Conclusion

In this observational study, up to 24 months after surgery for posterior cervical fusion in DCM greater than 3 levels, PROs appear to evolve similarly.

Keywords

Patient reported outcomes cervical myelopathy posterior cervical spine surgery length of stay upper instrumented vertebra upper instrumentation C2 C3

Introduction

Degenerative cervical myelopathy (DCM) is 1 of the most common causes of nontraumatic spinal cord impairment.^1-5 Multiple prospective studies have reported that spinal cord decompression in DCM improves patient’s functional and neurological outcomes.^6-8 Cervical spine posterior decompression and instrumented fusion plays a major role in the treatment of DCM. The goal of the surgery is adequate spinal cord decompression while maintaining or obtaining satisfactory alignment. Despite the high number of posterior cervical decompression and fusion surgeries performed every year, questions regarding the optimal surgical technique remain, especially surrounding the choice of upper and lower instrumented levels.

Multiple factors are considered when selecting the cephalad and caudad fixation levels in a posterior cervical fusion. These include levels of spinal cord compression, degenerative changes, bone quality, the presence of a mal-alignment and patient-specific anatomy. Most of the literature has focused on the impact of the lower instrumented vertebra (LIV) in posterior cervical fusion.^9-12 Recent studies have shown that ending the construct in the cervico-thoracic junction does not negatively impact the Patient-reported outcomes (PROs).^9,10 Proponents of thoracic LIV report a lower rate of distal adjacent level disease.¹² Conversely, little has been reported on the upper instrumented level. Ending the proximal construct at C2 has the advantage of 3 column stability and substantial segmental control in both cadaveric and clinical studies.¹³ On the other hand, fixation in the subaxial cervical spine is technically simple, associated with less bleeding and risk to the vertebral artery, and does not require sophisticated image guidance.

There is a lack of consensus in the existing literature regarding the choice of the upper instrumented level. Using the DCM prospective multicentric Canadian observational cohort, the primary objective of this study was to evaluate the impact of ending the construct proximally at C2 vs C3 on PROs (NDI, EQ-5D, PCS-12, MCS-12) for patients undergoing multilevel posterior instrumented fusion (≥3 levels) up to 24 months after surgery (3-12 and 24 months). Secondary objectives were to evaluate change in modified Japanese Orthopaedic Association (mJOA) rating, to compare operative time, length of stay (LOS), satisfaction, adverse-event occurrence, and re-operation between the 2 groups. Lastly, we sought to compare the percentage of patients reaching minimally clinical importance difference in PROS and mJOA up to 24 months.

Methods

Study Design

In this retrospective analysis, the data used was collected prospectively from an on-going multicenter observational cohort study of patients with DCM. Since January 2015, nine participating centers from the Canadian Spine Outcomes and Research Network (CSORN) have been enrolling consecutive patients with a clinical diagnosis of DCM and confirmed evidence of compressive pathology on imaging. CSORN is a Canadian Research Network that monitors the outcomes of spine surgery across 22 centers and includes over 75 Neurosurgeons and Orthopaedic spine surgeons. Standardized data collection pre-operatively and at specific post-surgical time points was performed by trained research assistants. Local research ethics board was obtained at each center prior to data collection (IRB approval number H22-00699). Informed consent was not required as per IRB for CSORN.

Patient Sample

Patients enrolled in the CSORN-DCM observational cohort between January 2015 and October 2020 who were greater than 18 years old, who underwent a multilevel posterior cervical decompression and fusion (≥3 levels) with the UIV being either C2 or C3 and who have reached the 24 months post-operatively were included. Patients who underwent a fusion of less than 3 levels, had a UIV other than C2 or C3, a non-fusion procedure (decompression alone or laminoplasty), a revision surgery, a major deformity correction surgery requiring either a combined approach or a cervical osteotomy, and patients who had not yet reached 24 months post-operatively were excluded from this study. Enrolled patients were divided according to the UIV of their construct in two groups, 1) C2 UIV and 2) C3 UIV.

Patient, Clinical, and Surgical Variables Considered

Patient variables (age, gender, number of comorbidities, tobacco use, education level, marital status, body mass index (BMI), pain medication use, symptom duration, working status, province of surgery, and active worker or insurance claim information) were collected prospectively. These variables were self-reported by the patient at baseline. Surgical variables considered were the UIV and LIV, the number of levels instrumented and/or decompressed. Presence of pre-operative T1 and/or T2 cord signal change on the magnetic resonance imaging was recorded. At baseline, the C2-C7 angle (negative values indicate lordosis and positive values, kyphosis), T1 Slope and the cervical sagittal vertical axis (cSVA) were measured on upright cervical radiographs (Figure 1). Malalignment was defined by a pre-operative cSVA ≥40 mm and/or T1 slope- cervical lordosis >15°.¹⁴

Figure 1.

Lateral cervical spine radiograph illustrating radiologic measurements of malalignment.

Outcome Measures

Patient reported outcomes included Neck Disability Index (NDI), EuroQol-5D (EQ-5D), the Short Form (SF-12) Survey Physical Component Score (PCS) and Mental Component Score (MCS) and the neck and arm pain numeric rating scale (NRS neck and arm). Analyses were focused on change in PROs between pre-op to 12 months post-op with secondary outcome endpoints of 3 and 24 months post-op also considered.

Additional outcomes considered included operative time duration, intra-operative blood loss, LOS, intra-operative and peri-operative (AEs), satisfaction and re-operation up to 24 months after surgery. Adverse events were collected prospectively using The Spine Adverse Event Severity System (SAVES).¹⁵ Neurological impairment at baseline was assessed using the modified Japanese Orthopaedic Association (mJOA) score and classified based on its severity (severe: mJOA 0-11, moderate: mJOA 12-14, mild: mJOA15-17).¹⁶

To determine the percentage of patient achieving the minimum clinically important difference (MCID), the threshold used were: 7.5 points for the NDI,¹⁷ 2.5 points for the NRS neck and arm pain,¹⁷ 4 points for the SF-12 PCS and MCS¹⁸ and .0485 points for the EQ-5D.¹⁹ The MCID for the mJOA score changes based on the baseline disease severity: 3, 2 and 1 point changes were required in patients with severe disease, moderate disease, and mild disease, respectively.¹⁶

Statistical Methods

Baseline demographics, radiologic measurement, surgical details, pre-operative PROs and mJOA were compared between the 2 groups using chi-square test for categorical variables and independent samples t-tests for continuous variables.

Mean values for each outcome measure were calculated for the entire cohort and for each group (C2 UIV and C3 UIV) at baseline, 3,12 and 24-months post operatively. Within group mean values at each of these time points were compared to baseline using paired sample t-tests; between group mean values were assessed using analysis of covariance (ANCOVA), adjusting for baseline significant differences between the 2 groups (province of surgery and symptoms duration). A subgroup analysis was performed for patients presenting with pre-operative malalignment.

Assessment of a clinically significant improvement at each time point was measured on the selected MCID for each outcome measures. Responder analysis for each group was performed by calculating the proportion of patients who met the MCID for each outcome measure. These proportions were compared between the 2 groups using chi-square tests. A subgroup analysis was performed for patients presenting with pre-operative malalignment. A multivariable logistic regression analysis was performed for predictors of reaching MCID of 7.5 point for the NDI at 12 months. Variable included in the model were: age, presence of malalignment, baseline NDI, symptom duration and the UIV. The variables included in the model were assessed for collinearity.

A P-value <.05 (2 tailed) was considered statistically significant for all tests. Analyses were conducted with IBM SPSS for Windows release 28.

Results

A total of 173 patients were included in this study (Figure 2). Of these, 41 patients (24%) had a UIV at C2 and 132 (76%) had the UIV at C3. The follow-up rate was 83% and 70% at 12 and 24 months. The baseline characteristics did not differ between those who were lost to follow-up and those who completed the 24 months follow-up.

Figure 2.

Flowchart of patient enrollment. UIV, Upper Instrumented Vertebra.

Mean age was 64 (SD 9.9) and most patients were male (71%). Symptoms duration >2 year (P < .024) and surgery done in western provinces (P < .001) were significantly more prevalent in the group with C3 UIV. Other baseline demographic variables were not statistically different between the groups. There was no significant difference between the groups in the baseline PROs and mJOA (P > .05).

Radiologic baseline data was available for 101 patients (28 C2 UIV and 73 C3 UIV). Eighty-two percent of the patients presented with malalignment (cSVA ≥40 mm and/or T1 slope – cervical lordosis >15°). Of these, 81% presented with a baseline cSVA ≥40 mm and 37% with T1 slope – cervical lordosis >15°. Eighty-six percent of the C2 UIV patients had malalignment compared to 81% in the C3 UIV group (P = .565). Specifically, in the C2 UIV cohort, 60% had cSVA ≥40 mm compared to 29% in the C3 UIV cohort (P = .05) while roughly 80% of the patients in each cohort had T1 slope- cervical lordosis >15° (P = .917) (Table 1).

Table 1.

Cohort Characteristics.

	Whole Cohort (n = 173)	C2 UIV (n = 41)	C3 UIV (n = 132)	P value
Working n (%)	39 (23.6)	6 (15.8)	20 (15.7)	.204
Male n (%)	123 (71.1)	31 (75.6)	92 (69.7)	.466
Age mean (SD)	64.04 (9.98)	65.82 (10.63)	63.51 (9.77)	.212
BMI Mean (SD)	29.06 (5.63)	28.35 (5.99)	29.23 (5.55)	.404
Number of comorbidities mean (SD)	3.25 (2.07)	3.18 (2.15)	3.28 (2.05)	.796
Tobacco use n (%)	40 (24.7)	9 (24.3)	31 (24.8)	.953
Education > high school n (%)	75 (46.3)	15 (40.5)	60 (48)	.424
Living alone n (%)	35 (21.6)	7 (18.9)	28 (22.4)	.651
Married n (%)	113 (68.9)	28 (73.7)	85 (67.5)	.468
Pain medications use n (%)	102 (61.8)	21 (55.3)	81 (63.8)	.343
Symptom duration >2 years n (%)	70 (43.2)	10 (27.0)	60 (48.0)	.024
Surgery in a Western Province n (%)	132 (76.3)	20 (48.8)	112 (84.8)	<.001
Presence of T1 or T2 cord signal change n (%)	148 (87.6)	36 (94.7)	112 (85.5)	.128
Pre-operative PROS
NRS neck pain Mean (SD)	5.76 (2.95)	5.66 (3.05)	5.79 (2.93)	.806
NRS arm pain Mean (SD)	5.74 (3.00)	5.58 (3.29)	5.79 (2.92)	.708
NDI Mean (SD)	43.01 (21.00)	45.40 (21.75)	42.27 (20.78)	.407
SF-12 MCS Mean (SD)	42.15 (12.90)	42.92 (13.57)	41.92 (12.73)	.686
SF-12 PCS Mean (SD)	30.27 (9.49)	30.62 (10.28)	30.17 (9.28)	.802
EQ5D Mean (SD) mJOA Mean (SD)	.52 (.23)	.47 (.26)	.55 (.21)	.080
mJOA n (%)	11.6 (2.5)	11.2 (2.6)	11.8 (2.5)	.239
- Mild	26 (15.3)	5 (12.2)	21 (16.3)	.527
- Moderate	61 (35.9)	12 (29.3)	49 (38.0)	.311
- Severe	83 (48.8)	24 (58.5)	59 (45.7)	.153
Pre-operative alignment measures
Malalignment* n (%)	83 (82.2)	24 (85.7)	59 (80.8)	.773
cSVA ≥40 mm n (%)	37 (37.0)	16 (59.3)	21 (28.8)	.05
T1 slope- cervical lordosis >15° n (%)	80 (80.8)	22 (81.5)	58 (80.6)	.917

*Malalignment = cSVA ≥40 mm and/or T1 slope – cervical lordosis >15°.

UIV, Upper instrumented vertebra; PROs, Patient Reported Outcomes; NRS, numeric rating scale; NDI, Neck disability index; SF-12 MCS, Short Form-12 mental component score; SF-12 PCS, Short-Form-12 physical component score; EQ5D, EuroQol 5D; MJOA, Modified Japanese Orthopaedic Association score; cSVA, Cervical Sagittal Vertical Axis.

The most common construct for the C2 UIV group was C2-T1/T2 (49%) followed by C2-C7 (22%). Patients with UIV at C3 underwent most commonly a C3-T1/T2 (39%) followed by C3-C6 (34%) (Table 2). The upper level instrumented was also the upper level decompressed in 17 (42.5%) C2 UIV patients (42.5%) and 106 C3 UIV patients (83.5%) (P < .001). The lower instrumented vertebra was also the lower decompressed level in 12 (30.0%) and 71 (55.9%) patients for the C2 and C3 UIV groups, respectively (P < .004). The mean number of instrumented levels was 6.2 (1.3 SD) and 4.8 (1.2 SD) for the C2 and C3 UIV groups (P < .001). The mean number of decompressed levels was 4.5 (1.9 SD) and 3.6 (1.6 SD) for the C2 and C3 UIV groups (P < .007).

Table 2.

Descriptive table of the proximal and distal Instrumentation vertebra.

N, %	C4 LIV	C5 LIV	C6 LIV	C7 LIV	T1-T2 LIV
C2 UIV	1 (2)	5 (12)	6 (15)	9 (22)	20 (49)
C3 UIV	0	17 (13)	45 (34)	19 (14)	51 (39)

UIV, Upper instrumented vertebra; LIV, Lower instrumented vertebra.

Primary Outcome

Within groups, PROs (NRS neck pain, arm pain, NDI, EQ5D, SF-12 MCS and PCS) improved significantly from baseline to 3, 12 and 24 months post-operatively (P < .001). At 12 months, the mean change in the NDI was −17.26 (SD 3.74) for the C2 UIV group vs −9.44 (SD 2.36) for the C3 UIV group (P < .079). The PCS improved by a mean of 6.58 points (SD 2.77) in the C2 UIV cohort compared to 3.56 (SD 1.48) for the C3 UIV cohort at 12 months (P = .343). Up to 24 months after surgery, no significant difference in PROs was observed between the 2 groups (Figure 3).

Figure 3.

Patient Reported Outcomes and modified Japanese Orthopaedic Association scores at baseline, 3, 12, and 24 months. cSVA, Cervical Sagittal Vertical Axis; UIV, Upper Instrumented Vertebra.

A subgroup analysis of 83 patients presenting with pre-operative malalignment showed that the EQ-5D at 3 months was worse in the C2 UIV cohort (−.09 vs .12, P = .043). This association was lost at further follow-up. At 12 and 24 months, patients with a C2 UIV had a trend towards greater improvement in the NDI compared to the patient with a C3 UIV: −20.21 (5.51) vs −6.49 (3.67), P = .054 and −18.25 (6.13) vs −6.52 (3.73), P = .134. Similar trends were observed with the NRS neck pain, PCS and the EQ5D (P > .05) (Figure 4).

Figure 4.

Subgroup analysis of patients presenting with malalignment (cSVA ≥40 mm and/or T1 slope – cervical lordosis >15°): Patient Reported Outcomes and modified Japanese Orthopaedic Association scores at baseline, 3, 12, and 24 months. cSVA, Cervical Sagittal Vertical Axis; UIV, Upper Instrumented Vertebra.

Secondary Outcomes

Operative time was significantly longer in the C2 UIV group (203.6 min (SD 72.8) vs 159.3 (58.9), P < .001). Intraoperative blood loss was almost twice in the C2 UIV group (479.6 mL (SD 398.2) vs 278 (SD 216.9), P < .001). There were 11 intra-operative AEs, with dural tear being most common (n = 9). There was no significant difference in the intra-operative AEs between the groups (P > .05). There were 34 peri-operative AEs which were significantly more prevalent in the C2 UIV group (P < .008). There was no significant difference between the groups in LOS and discharge disposition (P = .66 and .803, respectively). Patient’s satisfaction with surgery was high for both groups at 3, 12 and 24 months and did not differ significantly (P > .05) (Table 3).

Table 3.

Secondary outcomes.

	Cohort	C2 UIV	C3 UIV	P-value
Operative duration (min) mean (SD)	169.8 (65.10)	203.56 (72.82)	159.23 (58.95)	<.001
Intra-operative blood loss (ml) mean (SD)	323.28 (279.51)	479.59 (398.17)	278.45 (216.86)	.005
Number of instrumented levels mean (SD)	5.14 (1.34)	6.17 (1.34)	4.82 (1.16)	<.001
Number of decompressed levels mean (SD)	3.8 (1.7)	4.5 (1.9)	3.6 (1.6)	.007
UIV = upper decompressed level n (%)	123 (71.1)	17 (42.5)	106 (83.5)	<.001
LIV = Lower decompressed level n (%)	83 (48)	12 (30)	71 (55.9)	.004
Total Intra-operative adverse events, n (%)	11 (6.4)	3 (7.3)	8 (6.1)	.723
- Vascular injury	0 (0)	0 (0)	0 (0)	1.000
- Instrumentation/Fixation requiring revision	1 (.6)	1 (2.4)	0 (0)	1.000
- Dural tear	9 (5.2)	2 (4.9)	7 (5.3)	1.000
- Cutaneous	1 (.6)	0 (0)	1 (.8)	1.000
- Massive blood loss	0 (0)	0 (0)	0 (0)	1.000
Total Peri-operative adverse events n (%)
5 most encountered adverse event	34 (19.7)	14 (34.1)	20 (15.2)	.008
- Cardiac Event	4 (2.3)	1 (2.4)	3 (2.3)	1.000
- Delirium	7 (4.0)	5 (12.2)	2 (1.5)	.009
- Hematoma	4 (2.3)	3 (7.3)	1 (.8)	.042
- Urinary retention	12 (6.9)	2 (4.9)	10 (7.6)	.734
- Peri-operative wound infection	6 (3.5)	3 (7.3)	3 (2.3)	.146
Re-operation n (%)
- Total	15 (8.7)	6 (14.6)	9 (6.8)	.270
- For wound complication	11 (6.4)	5 (12.2)	6 (4.5)	.212
- For anterior decompression within 3 months from index surgery	2 (1.2)	1 (2.4)	1 (.8)	1.000
- UIV extension	1 (.6)	0	1 (.8)	1.000
- LIV extension	1 (.6)	0	1 (.8)	1.000
Length of stay (days) mean (SD) *	6.01 (4.67)	7.68 (7.06)	5.49 (3.50)	.066
Discharge disposition home n (%)	125 (72.3)	29 (70.7)	96 (72.7)	.803
Patient satisfied or very satisfied at 3 months n (%)	134 (85.4)	31 (83.8)	103 (85.8)	.893
Patient satisfied or very satisfied at 12 months n (%)	100 (73.0)	21 (77.8)	79 (71.8)	.414
Patient satisfied or very satisfied at 24 months n (%)	87 (75.0)	18 (85.7)	69 (72.6)	.452

*Adjusted for baseline difference (symptoms duration, province of surgery).

UIV, Upper instrumented vertebra; LIV, Lower instrumented vertebra.

Up to 24 months after surgery, there were 15 re-operations: 6 in the C2 UIV group and 9 in the C3 UIV group (P = .270). Ten patients had a wound complication requiring 11 returns to the operative room (5 in C2 UIV and 6 C3 UIV, P = .212). One patient in each group underwent an anterior decompression within 3 months of the initial surgery. Two patients with a C3 UIV underwent an extension within 2 years (1 proximal and 1 distal). No patients in the C2 UIV group required an extension.

Within groups, mJOA improved significantly from baseline to 3, 12 and 24 months post-operatively (P < .001). When adjusted for baseline difference (symptoms duration, province of surgery), there was a significant difference in the mJOA score at 3 months, favoring the C3 UIV group (P < .019) (Figure 2).

The number of patients reaching MCID for the PROS at 3, 12 and 24 months was similar in both groups except for the mJOA and EQ5D. Patient in the C3 UIV cohort with baseline severe myelopathy were more likely to reach MCID for the mJOA at 3 and 12 months (P < .05) and for the EQ5D at 24 months (P = .041) (Table 4). A subgroup analysis of those with malignment showed that the number of patients reaching MCID for the NDI was 20% higher at 12 and 24 months in the C2 UIV but this did not reach statistical significance (P = .124 and P = .083) (Table 4). A multivariable logistic regression analysis showed that baseline NDI was the only predictive factor associated with reaching MCID for NDI at 12 months. Other variables included in the model were C2 vs C3 UIV, presence of malalignment, age and symptom duration (Table 5).

Table 4.

Patients reaching the minimally clinically important difference in Patient Reported Outcomes and Modified Japanese Orthopaedic association scores.

	C2 UIV n (%)	C3 UIV n (%)	P value
Whole Cohort
At 3 months
NRS neck pain	18 (51.2)	42 (26.8)	.124
NRS arm pain	16 (45.7)	53 (45.3)	.965
NDI	21 (58.3)	54 (43.2)	.109
SF-12 MCS	14 (45.2)	57 (53.8)	.399
SF-12 PCS	16 (51.6)	53 (50.0)	.874
EQ5D	21 (61.8)	58 (49.6)	.210
MJOA
- Mild	2 (40.0)	12 (60.0)	.623
- Moderate	6 (54.5)	26 (56.5)	.906
- Severe	6 (31.6)	41 (77.4)	<.001
At 12 months
NRS neck pain	10 (37.0)	47 (44.8)	.470
NRS arm pain	14 (51.9)	47 (43.9)	.460
NDI	20 (66.7)	66 (57.9)	.383
SF-12 MCS	11 (42.3)	42 (44.2)	.862
SF-12 PCS	16 (61.5)	48 (50.5)	.319
EQ5D	16 (59.3)	59 (56.2)	.774
MJOA
- Mild	1 (33.3)	7 (53.8)	1.000
- Moderate	3 (37.5)	20 (55.6)	.448
- Severe	9 (45.0)	27 (79.4)	.01
24 months
NRS neck pain	12 (54.5)	38 (42.7)	.317
NRS arm pain	13 (59.1)	35 (38.9)	.086
NDI	17 (68.0)	56 (54.9)	.235
SF-12 MCS	11 (50.0)	39 (47.0)	.801
SF-12 PCS	13 (59.1)	44 (53.0)	.611
EQ5D	15 (68.2)	40 (44.0)	.041
MJOA
- Mild	2 (100)	8 (53.3)	.208
- Moderate	4 (66.7)	12 (66.7)	1.000
- Severe	3 (30.0)	18 (72.0)	.053
Subgroup analysis of patients with malalignment *
At 3 months
NRS neck pain	9 (40.9)	21 (38.9)	.870
NRS arm pain	9 (40.9)	23 (41.8)	.942
NDI	13 (56.5)	23 (40.4)	.188
SF-12 MCS	9 (42.9)	23 (51.1)	.532
SF-12 PCS	12 (57.1)	20 (44.4)	.336
EQ5D	13 (59.1)	23 (41.1)	.151
MJOA
- Mild	1 (33.3)	5 (62.5)	.545
- Moderate	3 (60.0)	14 (53.8)	1.000
- Severe	4 (28.6)	14 (66.7)	.041
At 12 months
NRS neck pain	6 (33.3)	22 (44.0)	.430
NRS arm pain	9 (50.0)	21 (41.2)	.516
NDI	15 (71.4)	28 (51.9)	.124
SF-12 MCS	6 (35.3)	19 (42.2)	.620
SF-12 PCS	13 (76.5)	22 (48.9)	.084
EQ5D	11 (61.1)	27 (55.1)	.660
MJOA
- Mild	1 (50.0)	5 (71.4)	1.000
- Moderate	2 (50.0)	14 (63.6)	.625
- Severe	7 (46.7)	14 (82.4)	.062
At 24 months
NRS neck pain	7 (53.8)	21 (48.8)	.752
NRS arm pain	7 (50.0)	17 (39.5)	.491
NDI	12 (75.0)	23 (47.9)	.083
SF-12 MCS	6 (46.2)	16 (43.2)	.856
SF-12 PCS	9 (69.2)	18 (48.6)	.332
EQ5D	8 (61.5)	14 (32.6)	.061
MJOA
- Mild	2 (100.0)	2 (40.0)	.429
- Moderate	3 (75.0)	9 (64.3)	1.000
- Severe	2 (28.6)	12 (75.0)	.066

*Malalignment = cSVA ≥40 mm and/or T1 slope – cervical lordosis >15°.

UIV, Upper instrumented vertebra; LIV, Lower instrumented vertebra; PROs, Patient Reported Outcomes; NRS, numeric rating scale; NDI, Neck disability index; SF-12 MCS, Short Form-12 mental component score; SF-12 PCS, Short-Form-12 physical component score; EQ5D, EuroQol 5D; MJOA, Modified Japanese Orthopaedic Association score; cSVA, Cervical Sagittal Vertical Axis.

Table 5.

Multivariable logistic regression model for predictive factors of reaching the minimally clinical important difference of 7.5 points for the Neck Disability Index at 12 months.

	Odds Ratio	95% Confidence Interval	P-value
Baseline NDI score*	1.057	1.024-1.091	<.001
Symptom duration >2 year	.629	.205-1.930	.417
C3 upper Instrumented level	2.484	.677-9.116	.170
Presence of malignment **	1.829	.444-7.529	.403
Age ***	1.002	.950- 1.057	.948

*Odds ratio reported per 1 point NDI increase.

**Malalignment = cSVA ≥40 mm and/or T1 slope – cervical lordosis >15°.

***Odds ratio reported per 1 year of age increase.

cSVA, Cervical Sagittal Vertical Axis; NDI, Neck disability index.

Discussion

This study is the largest study in the current literature comparing C2 to C3 UIV in cervical posterior decompression and fusion in the setting of DCM. Up to 24 months after surgery, when adjusting for the baseline difference, there was no statistically significant difference in the PROs between the C2 and C3 UIV. At 3 months post-operatively, the patients with a C3 UIV had greater improvement in the mJOA, but that difference did not persist at 12 and 24 months. Operative time was longer and intra-operative blood loss was greater in the patients with a C2 UIV. This can be explained by the additional dissection required to instrument C2 and by the fact that patients who had a C2 UIV generally had more levels instrumented than patients who had a C3 UIV. The rate of intra-operative AEs did not differ but the C2 UIV group had a greater rate of peri-operative AES. Patients who presented with baseline malalignment showed a trend toward a greater improvement in the NDI score at 12 months when a C2 UIV was chosen.

While there is an abundant literature on the distal instrumented level in posterior instrumented fusion, there is a limited number of reports on the upper level of fixation, mainly focused on the biomechanical aspects.^13,20,21 The biomechanical superiority of C2 has been used to justify the additional surgical time and dissection. Recently, Roth et al compared C2 UIV to C3/C4 UIV in a cohort of one hundred and seventeen patients.²² Similar to our cohort, there was no difference in the PROs between the 2 groups at 1 year following surgery. Longer operative time but no difference in estimated blood loss was observed for the C2 UIV cohort. Our study adds to this literature by providing a larger cohort and adding pre-operative radiologic measures of malignment.

Traditionally, the focus of the literature in the DCM population has been around the neurologic outcomes but recently cervical alignment has been getting more attention.²³ High cSVA has been associated with worse NDI in the cervical deformity population.²⁴ Additional measures such as the T1 slope minus cervical lordosis has been added to the cervical deformity definition.¹⁴ Other measures like the chin brow angle are not captured in the CSORN-DCM study. Using the cSVA and the T1 slope-CL measures, we are reporting that cervical mal-alignment is prevalent in the DCM population. Patients with a combined antero-posterior approach were excluded of the analysis which is suggesting that patients with severe kyphotic deformity were excluded. Despite this, 80 out of 101 patients with available pre-operative radiologic measures had malalignment. In a cervical deformity population, Passias et al reported improved horizontal gaze at 1 year in patients with a C2 UIV compared to a subaxial 1.²⁵ Woodrofe et al reported increased post-operative cSVA and T1 slope in patients who had C2 UIV compared to a subaxial UIV.²⁶ Two limitations of this study were that the pre-operative radiologic measures were missing for a significant portion of the cohort and post-operative alignment measures were not available.

The subgroup analysis of patient with malalignment showed that the NDI improvement at 12 months was 3 times better if the UIV was C2 but this was not statistically significant (P = .054). Similar trends were observed with the PCS, NRS neck pain and EQ-5D, although these differences did not reach statistical significance. Considering the effect size difference, this may be explained by a lack of power related to the small sample size, rather than a true lack of significance. While preoperative surgical planning algorithms for cervical spine deformity correction surgery exist in the literature, little emphasis is placed on the optimal fusion length and upper instrumented vertebra UIV.^27-30

In surgeries where the C3 was the UIV, the lamina of C3 was removed in over 80% of the time whereas the C2 lamina was removed roughly 40% of the time in the C2 UIV group. The theorical advantage of preserving the upper lamina and superior ligament attachment is to prevent junctional kyphosis and decrease adjacent level disease. The impact of having the UIV and upper decompressed level the same yet remains to be determined. In this series, only 1 patient in the C3 UIV (.8%) had to be extended to C2 within 2 years of the surgery and in that case, the C3 lamina was removed during the index surgery. This rate of proximal re-operation with the C3 UIV compares favorably with the 5% re-operation for proximal junctional failure rate at a minimum of 12 months of follow-up.³¹

The impact of the spinal cord decompression on the neurologic outcomes has been the focus of many studies.^6,8 As expected, patients myelopathic symptoms (mJOA) improved with decompressive surgery. The C3 UIV patients had greater improvement in the mJOA at 3 months and were more likely to reach MCID at 3 and 12 months than the C2 UIV patients. Predictive factors of poor neurologic outcomes following surgery such as age, symptoms duration and the severity of the myelopathy were not different between the groups.³² There was no statistically significant difference in the number of patient presenting with T1 and/or T2 cord signal change between the groups. While T1 cord signal change on pre-operative MRI has been associated with poor outcomes, the registry does not differentiate between T1 or T2 associated changes and their grading.³³ Lastly, this study did not assess the quality of the decompression.

This study has several limitations. We are reporting that in carefully selected patient, PROS evolves similarly whether the UIV is C2 or C3. Because this is an observational study, the level of fixation and decompression were chosen by the attending surgeon. It is unknown whether the extent of the construct to C2 or to the cervico-thoracic junction was a result of cervical alignment, extent of spinal stenosis, or surgeon preference, for example. This study examined several clinical and radiological variables but other factors such as presence of pre-existing osteoporosis diagnosis or fragility fracture, extent of the degenerative changes and presence of instability are not captured in the database and might have impacted the choice of the upper fixation level. The type of fixation performed in C2 (pars, pedicle, laminar screws) was not recorded in our database. However, a recent study did not show difference in PROs associated with the choice of fixation.²² While this study is the largest in the literature to date, it has a small sample size and will need to be validated with larger cohort to improve statistical power. Longer term follow-up and post-operative radiologic measures will be required to determine the longevity of the construct and the ability to achieve optimization of the alignment.

Conclusion

Up to 24 months after surgery for posterior cervical fusion in DCM ≥3 levels, PROs change is similar in patients having a C2 or C3 UIV. Increased operative time, estimated blood loss and peri-operative adverse events were more common with a C2 UIV construct. Early mechanical failures were uncommon in either group. When malalignment was present, the C2 UIV patients showed a trend toward greater improvement in the NDI compared to the C3 UIV patients. These findings suggest that a C2 UIV should be considered in presence of malalignment, but this decision will need to be examined in a larger cohort.

Footnotes

Acknowledgments

The authors thank all of the subjects who participated in the study and the support staff, research coordinator staff, and investigators from the Canadian Spine Outcomes and Research Network (CSORN) contributing sites: Calgary Foothills Medical Centre, Winnipeg Health Sciences Centre, Vancouver General Hospital, Victoria Hospital - London Health Sciences Centre, Queen Elizabeth II – Halifax Sciences Centre, Quebec Hopital de L’Enfant Jesus, Edmonton University of Alberta Hospital, the Ottawa Hospital Civic Campus.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Correction (March 2024):

This article has been updated to correct the first author’s affiliation.

ORCID iDs

Nathan Evaniew

Greg McIntosh

Jérome Paquet

Alexandra Stratton

Raphaële Charest-Morin

References

Choi

Y-A

Kim

. Stenosis and neurologic level discrepancies in Cervical Spondylotic Myelopathy. Pharm Manag PM R. 2018;10(10):1051-1055. doi: 10.1016/j.pmrj.2018.04.003

Nouri

Tetreault

Singh

Karadimas

Fehlings

. Degenerative cervical myelopathy: Epidemiology, genetics, and pathogenesis. Spine. 2015;40(12):E675-E693. doi: 10.1097/BRS.0000000000000913

New

Cripps

Bonne Lee

. Global maps of non-traumatic spinal cord injury epidemiology: Towards a living data repository. Spinal Cord. 2014;52(2):97-109. doi: 10.1038/sc.2012.165

Moore

Blumhardt

. A prospective survey of the causes of non-traumatic spastic paraparesis and tetraparesis in 585 patients. Spinal Cord. 1997;35(6):361-367. doi: 10.1038/sj.sc.3100422

Yamaguchi

Mitsuhara

Abiko

Takeda

Kurisu

. Epidemiology and overview of the clinical spectrum of degenerative cervical Myelopathy. Neurosurg Clin. 2018;29(1):1-12. doi: 10.1016/j.nec.2017.09.001

Fehlings

Wilson

Kopjar

, et al. Efficacy and safety of surgical decompression in patients with cervical spondylotic myelopathy: Results of the AOSpine North America prospective multi-center study. J Bone Joint Surg Am Volume. 2013;95(18):1651-1658. doi: 10.2106/JBJS.L.00589

Badhiwala

Witiw

Nassiri

, et al. Efficacy and safety of surgery for mild degenerative cervical Myelopathy: Results of the AOSpine North America and International prospective multicenter studies. Neurosurgery. 2019;84(4):890-897. doi: 10.1093/neuros/nyy133

Karim

Cadotte

Wilson

, et al. Effectiveness of surgical decompression in patients with degenerative cervical myelopathy: Results of the Canadian prospective multicenter Study. Neurosurgery. 2021;89:844-851. doi: 10.1093/neuros/nyab295

Chan

Badiee

Rivera

, et al. Crossing the Cervicothoracic junction during posterior Cervical fusion for Myelopathy is associated with superior Radiographic parameters but similar clinical outcomes. Neurosurgery. 2020;87(5):1016-1024. doi: 10.1093/neuros/nyaa241

10.

Charest-Morin

Bailey

McIntosh

, et al.

Does extending a posterior cervical fusion construct into the upper thoracic spine impact patient-reported outcomes as long as 2 years after surgery in patients with degenerative cervical myelopathy?

J Neurosurg Spine. 2022;37:547-555. doi: 10.3171/2022.3.SPINE211529

11.

Truumees

Singh

Lavelle

, et al. Is it safe to stop at C7 during multilevel posterior cervical decompression and fusion? - multicenter analysis. Spine J. 2021;21(1):90-95. doi: 10.1016/j.spinee.2020.08.018

12.

Goyal

Akhras

Wahood

Alvi

Nassr

Bydon

. Should multilevel posterior cervical fusions involving C7 cross the Cervicothoracic junction? A systematic review and meta-analysis. World Neurosurg. 2019;127:588-595.e5. doi: 10.1016/j.wneu.2019.03.283

13.

Benke

O’Brien

Turner

AWL

. Biomechanical comparison of transpedicular versus intralaminar C2 fixation in C2-C6 subaxial constructs. Spine. 2011;36(1):E33-E37. doi: 10.1097/BRS.0b013e3181eea6e2

14.

Ames

Smith

Eastlack

, et al. Reliability assessment of a novel cervical spine deformity classification system. J Neurosurg Spine. 2015;23(6):673-683. doi: 10.3171/2014.12.SPINE14780

15.

Rampersaud

Anderson

Dimar

Fisher

Spine Trauma Study Group and Degenerative Spine Study Group . Spinal adverse events severity system, version 2 (SAVES-V2): Inter- and intra observer reliability assessment. J Neurosurg Spine. 2016;25(2):256-263. doi: 10.3171/2016.1.SPINE14808

16.

Tetreault

Nouri

Kopjar

Côté

Fehlings

. The minimum clinically important difference of the modified Japanese Orthopaedic association scale in patients with degenerative Cervical Myelopathy. Spine. 2015;40(21):1653-1659. doi: 10.1097/BRS.0000000000001127

17.

Carreon

Glassman

Campbell

Anderson

. Neck disability index, short form-36 physical component summary, and pain scales for neck and arm pain: the minimum clinically important difference and substantial clinical benefit after cervical spine fusion. Spine J. 2010;10(6):469-474. doi: 10.1016/j.spinee.2010.02.007

18.

Badhiwala

Witiw

Nassiri

, et al. Minimum clinically important difference in SF-36 scores for use in degenerative Cervical Myelopathy. Spine. 2018;43(21):E1260-E1266. doi: 10.1097/BRS.0000000000002684

19.

Kato

Oshima

Matsubayashi

Taniguchi

Tanaka

Takeshita

. Minimum clinically important difference in outcome scores among patients undergoing cervical laminoplasty. Eur Spine J. 2019;28(5):1234-1241. doi: 10.1007/s00586-019-05945-y

20.

Sanelli

Tong

Gonzalez

Eskey

. Normal variation of vertebral artery on CT angiography and its implications for diagnosis of acquired pathology. J Comput Assist Tomogr. 2002;26(3):462-470. doi: 10.1097/00004728-200205000-00027

21.

Karaikovic

Daubs

Madsen

Gaines

. Morphologic characteristics of human cervical pedicles. Spine. 1997;22(5):493-500. doi: 10.1097/00007632-199703010-00005

22.

Roth

Khan

Chotai

, et al.

Is it better to stop at C2 or C3/4 in elective posterior Cervical decompression and fusion?

Spine. 2022;47(7):565-573. doi: 10.1097/BRS.0000000000004273

23.

Evaniew

Charest-Morin

Jacobs

, et al. Cervical Sagittal alignment in patients with cervical Spondylotic Myelopathy: An observational study from the Canadian spine outcomes and research network. Spine. 2022;47(5):E177-E186. doi: 10.1097/BRS.0000000000004296

24.

Kato

Nouri

Nori

Tetreault

Fehlings

. Impact of cervical spine deformity on preoperative disease severity and postoperative outcomes following fusion surgery for degenerative cervical myelopathy: Sub-analysis of AOSpine North America and International Studies. Spine. 2018;43(4):248-254. doi: 10.1097/BRS.0000000000002307

25.

Passias

Bortz

Segreto

, et al. Limited morbidity and possible radiographic benefit of C2 vs. subaxial cervical upper-most instrumented vertebrae. J Spine Surg. 2019;5(2):236-244. doi: 10.21037/jss.2019.06.04

26.

Woodroffe

Helland

Hollatz

, et al. Impact of the inclusion of C2 in posterior cervical fusions for cervical Myelopathy on Sagittal cervical alignment. Clin Spine Surg. 2020;33(4):E141-E146. doi: 10.1097/BSD.0000000000000931

27.

Tan

Riew

Traynelis

. Cervical spine deformity-Part 2: Management algorithm and anterior techniques. Neurosurgery. 2017;81(4):561-567. doi: 10.1093/neuros/nyx388

28.

Ames

Blondel

Scheer

, et al. Cervical radiographical alignment: Comprehensive assessment techniques and potential importance in cervical myelopathy. Spine. 2013;38(22 suppl 1):S149-S160. doi: 10.1097/BRS.0b013e3182a7f449

29.

Lafage

Challier

Liabaud

, et al. Natural head posture in the setting of Sagittal Spinal Deformity: Validation of Chin-Brow vertical angle, slope of line of sight, and McGregor’s slope with health-related quality of life. Neurosurgery. 2016;79(1):108-115. doi: 10.1227/NEU.0000000000001193

30.

Hann

Chalouhi

Madineni

, et al. An algorithmic strategy for selecting a surgical approach in cervical deformity correction. Neurosurg Focus. 2014;36(5):E5. doi: 10.3171/2014.3.FOCUS1429

31.

Xia

Kosztowski

, et al. Reoperation for proximal adjacent segment pathology in posterior cervical fusion constructs that fuse to C2 vs C3. Neurosurgery. 2019;85(3):E520-E526. doi: 10.1093/neuros/nyz019

32.

Moradi

Bagheri

Saeidiborojeni

, et al. Predictors of poor clinical outcome in patients with cervical spondylotic myelopathy undergoing cervical laminectomy and fusion. Musculoskelet Surg. 2021:1-7. doi: 10.1007/s12306-021-00731-w

33.

Shakya

Sharma

Singh

Jaiswal

Marathe

Garje

. Preoperative T1 magnetic resonance imaging changes carry a poor postoperative prognosis in cervical myelopathy: A retrospective study of 182 patients. Surg Neurol Int. 2021;12:629. doi: 10.25259/SNI_1151_2021