Influence of complete uncinate process removal on 2-year assessment of radiologic outcomes: subsidence and sagittal balance in patients receiving one-level anterior cervical discectomy and fusion

DOI: https://doi.org/10.21203/rs.2.12547/v1

Abstract

Background: Many patients who appealed cervical radiculopathy have stenosis of neural foramens because of cumulative osteophyte or uncovertebral joint hypertrophy. For cervical foraminal stenosis, complete UPR conducted concurrently with ACDF. The aim of this study was to evaluate the clinical and radiological consequences of complete uncinate process resection (UPR) during anterior discectomy and fusion (ACDF) versus those seen with ACDF without UPR. Methods: In total, 105 patients who underwent one-level ACDF with a cage-and-plate construct between 2011 and 2015 were retrospectively reviewed. Among them, 37 underwent ACDF with complete UPR, and 68 underwent ACDF without UPR. Radiographic parameters of disc height, C2–C7 lordosis, T1 slope, C2–C7 sagittal vertical axis (SVA), center of the sellar turcica–C7 SVA (St-SVA), spinocranial angle (SCA), and fusion rate were measured on plain radiographs at pre-operation, immediately post-operation, and during the follow-up period (median follow-up duration: 37.7 ± 10.5 months). Results: Improvement in Visual analogue scale (VAS) score for arm pain was significantly better in the ACDF with complete UPR group immediately post-operation. Fusion rates, C2–C7 lordosis, T1 slope, and C2–C7 SVA after single-level ACDF were not significantly different between the two groups (p>0.05). Subsidence occurred in 23 patients (ACDF with complete UPR: 14 cases [37%] versus ACDF without UPR: 9 cases [13%]; p < 0.05). Conclusions: Cervical sagittal alignment after ACDF with complete UPR is not significantly different from that achieved with ACDF without UPR. However, subsidence occurred more frequently after ACDF with complete UPR than after ACDF without UPR, although there was no clinical impact. More precise and careful selection of patients is needed when deciding on additional complete UPR.

Background

Anterior cervical discectomy and fusion (ACDF), which improves the stability of the vertebra by decompression of neural elements and fusion, is regarded as the gold-standard procedure for symptomatic cervical spondylosis in patients in whom non-operative care has failed [1]. Clinical and radiologic results after ACDF appear to be good [2]. Many patients who undergo cervical radiculopathy experience stenosis of neural foramens because of cumulative osteophyte or uncovertebral joint hypertrophy. Although most anterior cervical discectomy and fusion procedures include cervical uncosectomy or uncoforaminotomy to decompress nerve roots in patients with cervical radiculopathy, Lee DH et al. reported that complete uncinate process resection (UPR) in ACDF improves pain in a patient's arm more rapidly than conventional ACDF without UPR and provides similar fusion rates [3, 5]. Meanwhile, SH Lee et al. reported that complete UPR over 38% during ACDF increases the risk of subsidence during follow up [4].

At present, there is little evidence of whether this surgical technique provides good clinical and radiologic outcomes after complete unilateral or bilateral UPR, especially in regards to subsidence and cervical sagittal alignment. Accordingly, this study was undertaken to evaluate the influence of complete UPR on subsidence and regional cervical sagittal balance by comparing the clinical and radiologic outcomes after ACDF with complete UPR versus ACDF without UPR.

Methods

Patient recruitment and inclusion criteria

 Between January 2011 and December 2015, 578 patients who underwent ACDF for cervical spondylotic disease at our institution were collected. Among them, we excluded 473 patients whose follow-up period was less than 2 years or the surgery level was two levels or more. In this retrospective study, 105 consecutive patients with single-level cervical spondylotic disease who underwent primary ACDF with a cage-and-plate construct between January 2011 and December 2015 at the author’s institution (Fig. 1). This study was approved by the Institutional Review Board of our hospital. The uncinate process was randomly removed totally according to the technical preference of the single surgeon (Fig. 2). Thus, we defined ACDF with UPR as complete unilateral or bilateral removal of the uncinate process, while ACDF without UPR was defined as the conventional removal of only the anterior and posterior parts of the uncinate process or no removal of the uncinate process. This was confirmed with postoperative computed tomography (CT) scans. The patients were divided into two groups: 37 patients underwent ACDF with complete UPR and 68 patients were treated with ACDF without UPR. The inclusion criteria included the following: 1) patients with symptoms of degenerative cervical disease; 2) patients who received primary only one-level ACDF with UPR; and 3) a follow-up period greater than 24 months. The exclusion criteria were as follows: 1) patients who had previous cervical spine surgery due to ossification of posterior longitudinal ligaments, fractures, tumors, etc.; 2) patients who underwent ACDF for more than two levels; and 3) a follow-up period less than 24 months.

 

Surgical procedure

 The patients were positioned under general anesthesia in the supine position. The surgical technique was chosen using a standard Smith–Robinson technique. After confirmation and exposure of the proper vertebral levels according to the compressive materials, a discectomy was performed, and a high-speed burr was applied to remove the anterior and posterior bony spurs and the endplate cartilage. The endplate cartilage was eliminated with a curette carefully to preserve the bony endplate as much as possible to prevent cage subsidence. Discs, endplate cartilaginous, and other compressive materials were subducted to achieve appropriate dural and neural decompression. Using a osteotome, a high-speed electric drill and a Kerrison punch, the nerve roots were decompressed by completely removing the uncinate process. If the patient had unilateral symptoms and radiologic results were consistent, we performed removal of the uncinate process unilaterally. We used a plate (Atlantis; Medtronic, Minneapolis, MN, USA) and allograft cage (Cornerstone®-SR; Medtronic, Minneapolis, MN, USA) with local autologous bone. We did not use autologous iliac bone or growth factors, such as demineralized bone matrix (DBM) and recombinant bone morphogenetic proteins (rhBMP), as graft material. The proper size for the allobone cage was decided by both preoperative evaluation and intraoperative formatting using a trial cage. The cage was placed into the disc space as described above. Fixed type screws were utilized to fix the anterior cervical plate. If there was no complication during operation, all patients were able to sit upright and walk with a neck collar on the first day after surgery. The patients wore a cervical collar for 1 month after surgery. Clinical and radiographic results were obtained by an independent observer for five days post-operatively. In the outpatient clinic, patients were continuously followed up post-operation.

 

Clinical outcome assessment

 Intraoperative blood loss, operative time, days of hospitalization, and clinical outcomes were evaluated using the neck disability index (NDI), neck visual analog scale (VAS), and arm-VAS preoperatively, immediately after operation, and at 2 years follow up. During the last follow up, the patient was assessed according to Odom’s criteria, from poor to excellent [6].

 

Radiological evaluation

 Preoperative radiologic examination evaluated plain radiographs, CT scans, and magnetic resonance imaging (MRI). Plain radiological examinations of the cervical spine were also conducted immediately after surgery and at 2 years follow up for all patients. Cervical alignment was evaluated using the Cobb angle of C2–C7, working the process described by Borden [7]: this angle was made by the lines along the inferior endplate of C2 to the inferior endplate of C7 in the neutral position. Subsidence was decided by measuring the distance from the upper endplate of the upper vertebral body to the lower endplate of the lower vertebral body at the level of the operation. The segmental angle was calculated using the Cobb angle of the vertebral bodies adjacent to the involved disc. The total intervertebral height was decided as the distance from the upper endplate of the cephalad vertebral body to the inferior endplate of the caudal vertebral body of the fused segment, which was measured as the mean value of the height of the anterior and posterior borders [8]. Subsidence was described as a decline in the height of the operative segment greater than 3 mm between immediate images after the operation and those acquired at the last follow up (Fig. 3A). Spino-cranial angle (SCA) was defined as the angle between the C7 line and the line joining the center of the sellar turcica and the center of the inferior endplate of the C7 body. Center of sellar turcica – C7 sagittal vertical axis (St-SVA) was defined as the distance between a plumb line declined from the center of the sellar turcica and the center of the C7 body (Fig. 3B). The C2–C7 sagittal vertical axis (SVA) was decided as the length from the postero-superior corner of C7 and the vertical line form the center of the C2 body. The T1 slope was defined as the angle between the upper endplate of T1 and the horizontal line (Fig. 3C). Because keeping the horizontal gaze is the most important function of the cervical vertebrae, patients maintained a horizontal gaze position during radiologic examination. Occipital slope (O-s) is a postural variable reflecting the position of the skull, it can reflect the degree of horizontal gaze. O-s represents the angle between the McGregor line and horizontal line (Fig. 3D). We decided the maximum difference in the O-s value at each examination as 2 degrees. Radiological fusion was decided to have occurred when there was ≤ 2° movement on flexion–extension and/or ≤ 2 mm of movement of the interspinous distance on flexion–extension across the fusion segment [9].

 

Statistical analysis

The findings are presented as mean values ± standard deviation (SD) or counts, as indicated. The independent t-test and chi-squared test results were used to compare both groups. The multivariable logistic regression test was used to determine the influencing factor of subsidence. All P values <0.05 were considered to indicate statistical significance. All statistical analyses were performed using SPSS (version 23.0, SPSS, Chicago, IL, USA).

Results

  1. Patient demographics (Table 1)

In total, 105 patients underwent ACDF at the authors’ institution. Table 1 shows the detailed demographics of the two groups of patients, which were comparable. The patients’ ages ranged from 46 to 77 years (average age, 57.9±11.83 years old). The patients were followed for an average of 37.7±10.5 months. The operation level was primarily the C5/6 level (60 cases, 57%), followed by the C4/5 level (23cases, 22%).

 

  1. Comparison of intraoperative blood loss, operative time, days of hospitalization, and clinical parameters (Table 2)

Intraoperative blood loss, operative time, days of hospitalization, Arm-VAS, Neck-VAS, NDI, and Odom’s criteria of the two groups are shown in Table 2. All of the clinical parameters improved at the 2 years follow up (P<0.0001). Regarding Odom’s criteria, most of the surgical results were excellent and good in both groups. Also, there was no complication in either group. Between the ACDF with UPR and ACDF without UPR groups, clinical outcomes were not significantly different.

 

  1. Comparisons of radiologic parameters (Table 3)

Cervical lordosis, segmental angle, disc height, C2-C7 SVA, St-SVA, T1 slope, SCA, incidence of subsidence, and fusion rate of the two groups are shown in Table 3. Regarding cervical alignment in the two groups, segmental angles at 2 years follow up were markedly better than those preoperatively (p<0.05). All cervical sagittal parameters, such as cervical lordosis, segmental angle, disc height, C2-C7 SVA, St-SVA, T1 slope, and SCA, were similar between the ACDF with UPR and ACDF without UPR groups, although the differences in segmental angle, disc height, C2-C7 SVA, St-SVA, and SVA at 2 years follow up and preoperative examination were statistically significant (p<0.05). Subsidence occurred in 23 patients (ACDF with complete UPR: 14 cases [37%] versus ACDF without UPR: 9 cases [13%]; p < 0.05). Radiological images for representative patients in each group are displayed in Figures 4 and 5. There was no statistical significance because there were few cases of removal of uncinate on both sides. However, the subsidence occurred more frequently in the case of removing both sides than in the case of removing only one side.

 

  1. Multivariate analysis of the five measurements as significant parameters on subsidence (Table 4)

Radiologic factors that may potentially influence subsidence were analyzed using logistic regression test; the results are shown in Table 4. As a influencing factor of subsidence, preoperative C2-7 SVA, St-SVA, and SCA values were significant (P<0.05). In opposition to our hypothesis, complete UPR was not a significant factor affecting subsidence.

Discussion

ACDF is the treatment of choice for symptomatic cervical spondylosis in patients when conservative treatments, such as medication or physiotherapy, have failed [10]. Patients with arm pain with neural foramen stenosis due to osteophytes or hypertrophy of the uncovertebral joint should be treated with ACDF, as well as UPR. ACDF with complete UPR is known to improve pain in the arm better and faster [11]. However, inadequate removal of the uncinate process has been reported to contribute to poor outcomes in cervical spondylosis cases [12]. In our study, the ACDF with UPR group had better arm pain in the immediate post-operation period than the ACDF without UPR group. As the uncinate process is an important structure to maintaining the stability of adjacent vertebral bodies in the spinal axis, we investigated whether sagittal alignment or subsidence is affected by removing the uncinate process.

Subsidence occurs as a natural process during the course of an interbody fusion procedure and is described as settlement of a body with a higher elasticity modulus (e.g., graft, cage, spacer) into a body with lower elasticity modulus (e.g., vertebral body), leading to a change in spine structure [13]. However, upon excessive subsidence, interbody spaces are narrowed and kyphosis of the spine occurs. This introduces instability of the screw-plate and screw-bone (e.g., pull-out, change of angulation, breakage of the instrumentation) [13]. To the best of our knowledge, end-plate preparation, type of cage and size, multilevel fusion, recombinant human bone morphogenetic protein-2 (rhBMP-2), process of instrumentation, and bone quality are significant factors of subsidence [14]. In our study, when the ACDF with complete UPR and ACDF without UPR were compared under the same conditions, subsidence was significantly higher when complete UPR was performed after 3 years on average. Considering these reasons, it would seem that end-plate preparations would be performed more in the process of UPR in the ACDF with UPR group. However, between the ACDF with UPR and ACDF without UPR groups, clinical outcomes were not significantly different. This is because the foramen is widened due to the UPR, such that, even if subsidence occurs, radiculopathy due to pressing of the root does not occur. Overall, in the case of one-level ACDF, it is difficult to find a significant adverse effect of subsidence. However, caution against subsidence is needed, and a large-scale and long-term follow-up study of multiple-level ACDF with UPR is necessary.

 Sagittal balance has been suggested for cervical spine treatment. T1 slope determines the sagittal balance of the cervical spine, and this parameter is related with C2–C7 angle [15]. Previous studies have reported that C2-C7 lordosis is closely related to the other cervical and thoracic parameters (cervical lordosis, thoracic kyphosis) [16]. Cervical sagittal imbalance influences health-related quality of life patient (HRQOL) [17]. St-SVA and C2–C7 SVA are closely associated with the clinical results of neck pain and HRQOL [18]. The
A study by Tang et al. suggested that increasing cervical SVA is a cause for
clinical concern of cervical malalignment as reflected by poor HRQOL scores [19]. In our study, C2-C7 lordosis, segmental angle, disc height, C2-C7 SVA, St-SVA, T1 slope, and SCA were not different between ACDF with UPR and ACDF without UPR group, although the differences significant in segmental angle, disc height, C2-C7 SVA, St-SVA, and SVA at last follow-up and preoperatively were statistically between the two surgery groups (p<0.05). Accordingly, there were no differences in clinical outcomes between the two groups.

Global cervical spine lordosis was not influenced by single-level ACDF [20]. This is the natural mechanism of the human body, which keeps the head on a neutral axis in the optimal horizontal plane for the visiovestibular system and re-establishes sagittal balance [20]. In our study, single-level ACDF with UPR did not affect sagittal balance, although parameters of segmental angle, disc height, C2-C7 SVA, St-SVA, and SVA were worse. Thus, long-term follow-up and a large scale study of multiple-level ACDF with UPR or ACDF in kyphotic cervical spine are necessary.

 

Limitations of this study

Our study had a few limitations. The number of patients who underwent removal of the uncinate process was small. Also, cases with a bilaterally UPR were rare. Also, because our study did not have a randomized controlled design, we could not completely control the possibility of selection bias. Additionally, because our study size was small, we were limited in our ability to make comparisons between the groups for several factors known to affect prognosis. Failure to indicate the extent to which the uncinate process was removed as an objective indicator was also a limitation. However, the results of this study suggest that when performing ACDF with complete UPR, the risk of subsidence should be considered. Prospective studies will be conducted using well-guided evidence-based protocols with adequate controls.

Conclusions

Cervical sagittal alignment after ACDF with complete UPR is not significantly different from that achieved with ACDF without UPR. However, subsidence occurs more frequently after ACDF with complete UPR than after ACDF without UPR, although this appears to have no clinical impact. More precise and careful selection of patients is needed when deciding on additional complete UPR

Abbreviations

ACDF: Anterior cervical discectomy and fusion

UPR: Uncinate process resection

VAS: Visual analog scale

NDI: Neck disability index

BMD: Bone mineral density

BMI: Body mass index

DM: Diabetes mellitus

SVA: Sagittal vertical axis

St-SVA: Sellar turcica- Sagittal vertical axis

SCA: Spinocranial angle

CT: Computed tomography

MRI: Magnetic resonance imaging

O-s: Occipital slope

RhBMP-2: Recombinant human bone morphogenetic protein-2

HRQOL: Health-related quality of life

Declarations

Ethics approval and consent to participate

This study had been approved by the Internal review boeard (IRB) of the Gangnam Severance Hospital.

Consent for publication

Not applicable

Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.

Funding

No funding

Authors’ contributions

All authors made substantive intellectual contributions to this study to qualify as authors. Noh and KH Kim contributed to study design, acquisition of data, analysis of data, and interpretation of results. Park, Kuh, Chin, KS Kim, Cho contributed to discuss the article. All authors read and approved the final manuscript.

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Tables

Table 1. Patient demographics

 

ACDF without UPR

(n = 68)

ACDF with complete  UPR (n = 37)

p-value

Sex

 

 

 

Female

24

16

 

Male

44

21

0.423

Mean age (years)

57.5 ± 11.34

58.6 ± 9.91

0.628

BMD (g/cm2)

T-score

-0.66 ± 0.68

-0.69 ± 0.58

0.866

BMI (kg/m2)

23.9 ± 7.65

23.2 ± 6.95

0.852

DM

12

9

0.248

Smoking

15

10

0.629

Operation level

 

 

 

C2/3

C3/4

0

3

1

0

 

C4/5

C5/6

C6/7

16

36

13

7

24

5

 

 

0.404

Resection side

 

 

 

Unilateral

 

30

 

Bilateral

 

7

 

BMD; bone mineral density, BMI; body mass index, DM, diabetes mellitus;

ACDF; anterior cervical discectomy and fusion

UPR; uncinate process removal

*p < 0.05 comparing ACDF without UPR and ACDF with complete UPR 

 

Table 2. Comparison of intraoperative blood loss, operative time, days of hospitalization, and clinical parameters

 

ACDF without UPR

(n = 68)

ACDF with complete UPR (n = 37)

p-value

Intraoperative blood loss (ml)

69.51±22.91

74.44±17.15

0.453

Operation time (min)

107.81±17.96

113.33±19.12

0.364

Duration of hospitalization (day)

6.35±1.14

6.47±2.55

0.673

Arm VAS

Preoperation

Postoperation

2 years follow-up

 

8.6 ± 0.65

4.2 ± 0.56

1.8 ± 0.96

 

8.4 ± 0.77

2.9 ± 0.12

1.7 ± 0.45

 

0.116

< 0.001

0.101

Neck VAS

Preoperation

Postoperation

2 years follow-up

 

8.1 ± 0.73

2.7 ± 0.89

1.4 ± 0.96

 

8.4 ± 0.75

2.6 ± 0.95

1.3 ± 0.95

 

0.116

0.214

0.134

NDI

Preoperation

Postoperation

2 years follow-up

 

38.7 ± 1.89

22.1 ± 1.87

14.5 ± 1.56

 

39.7 ± 2.15

21.5 ± 1.56

13.6 ± 2.35

 

0.346

0.213

0.156

Odom’s criteria

Excellent

Good

Fair

Poor

 

28

38

2

0

 

14

22

1

0

 

 

 

 

0.739

VAS; Visual analog scale, NDI; Neck Disability Index

*p < 0.05 comparing ACDF without UPR and ACDF with UPRp < 0.05 compared with the preoperative value

 

Table 3. Comparison of radiologic parameters

 

ACDF without UPR

(n = 68)

ACDF with complete UPR (n = 37)

p-value

C2–C7 lordosis (°)

Preoperation

Postoperation

2 years follow-up

2 years follow-up - Preoperation

 

12.9 ± 7.53

14.5 ± 6.96

17.6 ± 8.71

5.1 ± 2.23

 

12.6 ± 7.31

14.2 ± 8.25

17.6 ± 7.98

 5.4 ± 2.77

 

0.271

0.259

0.321

0.605

Segmental angle (°)

Preoperation

Postoperation

2 years follow-up

2 years follow-up - Preoperation

 

5.8 ± 3.8

6.1 ± 4.49

6.6 ± 6.17

1.5 ± 2.03

 

4.9 ± 3.89

5.3 ± 3.15

5.3 ± 3.69

0.4 ± 1.31

 

0.471

0.687

0.269

0.002*

Disc height (mm)

Preoperation

Postoperation

2 years follow-up

2 years follow-up – Preoperation

 

 

5.5 ± 1.48

7.8 ± 1.31

6.6 ± 6.17

1.1 ± 1.47

 

5.9 ± 1.01

7.6 ± 1.01

5.3 ± 3.69

-0.6 ± 1.91

 

0.541

0.358

0.256

0.046*

C2–C7 SVA (mm)

Preoperation

Postoperation

2 years follow-up

2 years follow-up - Preoperation

 

20.1 ± 6.02

18.5 ± 6.51

17.2 ± 1.28

-3.3 ± 3.83

 

19.2 ± 5.97

20.9 ± 9.03

21.1 ± 11.47

2.1 ± 3.92

 

0.461

0.103

0.063

0.001*

St-SVA (mm)

Preoperation

Postoperation

2 years follow-up

2 years follow-up - Preoperation

 

29.1 ± 7.31

24.5 ± 9.33

23.3 ± 8.28

-6.1 ± 3.02

 

27.4 ± 9.41

28.7 ± 12.33

30.5 ± 16.67

2.9 ± 2.68

 

0.294

0.058

0.051

0.001*

T1 slope (°)

Preoperation

Postoperation

Last follow-up

Last follow-up - Preoperation

 

23.5 ± 6.43

22.7 ± 6.08

22.6 ± 6.28

-1.1 ± 1.14

 

24.4 ± 5.01

23.9 ± 4.35

24.4 ± 5.67

0.2 ± 1.68

 

0.135

0.825

0.433

0.139

SCA (°)

Preoperation

Postoperation

2 years follow-up

2 years follow-up - Preoperation

 

105.9 ± 7.03

106.6 ± 5.21

107.3 ± 5.28

2.7 ± 4.64

 

111.2 ± 5.01

107.5 ± 6.01

105.4 ± 5.67

-6.7 ± 5.95

 

0.056

0.825

0.303

0.001*

Subsidence

9 (13%)

14 (37%)

0.004*

Fusion

65 (95%)

35 (94%)

0.898

SVA; sagittal vertical axis, St-SVA; sellar turcicasagittal vertical axis,

SCA; spinocranial angle

* Statistically significant  

 

Table 4. Multivariate analysis of the five measurements as significant parameters on subsidence

Factor

Odds Ratio

95% CI

p-value

Preoperative C2–C7 SVA

1.362

1.144 – 1.62

0.001*

Preoperative St-SVA

1.154

1.028 – 1.295

0.015*

Preoperative SCA

1.806

1.346 – 2.425

0.001*

Preoperative CL

0.909

0.819 – 1.008

0.071

Preoperative T1-slope

0.997

0.842 –1.13

0.959

SVA; sagittal vertical axis, St-SVA; sellar turcicasagittal vertical axis,

SCA; spinocranial angle, CL; cervical lordosis, CI: confidence interval

* Statistically significant