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European Spine Journal

, Volume 27, Issue 6, pp 1440–1446 | Cite as

Spondylolisthesis adjacent to a cervical disc arthroplasty does not increase the risk of adjacent level degeneration

  • David Christopher Kieser
  • Derek Thomas Cawley
  • Cecile Roscop
  • Simon Mazas
  • Pierre Coudert
  • Louis Boissiere
  • Ibrahim Obeid
  • Jean-Marc Vital
  • Vincent Pointillart
  • Olivier Gille
Original Article
  • 126 Downloads

Abstract

Purpose

To understand whether a spondylolisthesis in the sub-axial spine cranial to a cervical disc arthroplasty (CDA) construes a risk of adjacent level disease (ALD).

Methods

A retrospective review of 164 patients with a minimum 5-year follow-up of a cervical disc arthroplasty was performed. Multi-level surgeries, including hybrid procedures, were included. Multiple implant types were included. The two inter-vertebral discs (IVD) cranial of the CDA were monitored for evidence of radiologic degeneration using the Kettler criteria.

Results

The rate of ALD in CDA found in this series was 17.8%, with most affecting the immediately adjacent IVD (27.4 and 7.6%, respectively p = 0.000). Pre-operative mild spondylolisthesis adjacent to a planned CDA was not found to be a risk factor for ALD within 5 years. Those with a degenerative spondylolisthesis are at higher risk of ALD (33%) than those with a non-degenerative cause for their spondylolisthesis (11%). Post-operative CDA alignment, ROM or induced spondylolisthesis do not affect the rate of ALD in those with an adjacent spondylolisthesis. Patients with ALD experience significantly worse 5-year pain and functional outcomes than those unaffected by ALD.

Conclusions

A pre-operatively identified mild spondylolisthesis in the sub-axial spine cranially adjacent to a planned CDA is not a risk factor for ALD within 5 years.

Graphical abstract

These slides can be retrieved under Electronic Supplementary Material.

Keywords

Adjacent level disease Proximal junctional failure Junctional kyphosis Cervical disc arthroplasty Spondylolisthesis 

Introduction

Spondylolisthesis is defined as an anterior (anterolisthesis) or posterior (retrolisthesis) translation of the superior vertebra on its inferior counterpart. It is commonly recognised in the lumbar spine and is widely classified according to the Meyerding criteria, which divides the antero-posterior length of the inferior vertebral body into quarters and defines each quarter as a grade of slippage [1]. Grade 1 is less than 25% anterior translation of the superior vertebra; grade 2 is 25–50% and so on.

There remains a paucity of the literature on spondylolisthesis of the cervical spine. Most previous publications mention it as a part of the spectrum of spondylosis or degeneration of the inter-vertebral disc (IVD), which may cause spondylolisthesis [2, 3, 4, 5, 6]. Others have described spondylolisthesis in younger patients with congenital abnormalities [7, 8, 9, 10]. However, most cervical spondylolisthesis is mild (grade 1), asymptomatic and incidentally recognised during the workup for another cervical pathology. To date, no knowledge on the natural history of such a low grade, asymptomatic cervical spondylolisthesis exists and, importantly, whether it construes an increased risk of degeneration. Furthermore, its role in surgical outcomes, and therefore, pre-operative decision-making, remains unknown.

Cervical disc arthroplasty (CDA) was first introduced in 1964 [11]. Its use has continued to increase, supported by its clinical success [12, 13, 14, 15, 16]. It is also believed that, in contrast to a fusing procedure, the maintenance of motion preserves the adjacent levels by reducing the relative forces on this area [17, 18, 19]. However, adjacent level degeneration (ALD) is poorly understood and multi-factorial with adjacent stiffness being only one of many risk factors. Other likely risk factors include patient age, sex, genetic predisposition to inter-vertebral disc (IVD) degeneration, alignment and instability.

The incidence of radiological ALD in CDA is reported to be 8.3% and that of symptomatic ALD is 0.9% [20]. While this may relate to predisposing factors unrelated to the CDA, these implants change the kinematics of the motion segment operated on, and may therefore adversely affect adjacent levels [21]. Furthermore, the clinical outcomes between anterior cervical decompression and fusion (ACDF) and CDA are similar, despite the increased costs associated with CDAs [22]. Thus, an accurate understanding of the long-term benefits and risks construed by CDA needs to be validated.

This study, aims to determine the minimum 5-year radiographic outcome of a cranial spondylolisthesis adjacent to a CDA to determine whether it construes an increased risk of ALD.

Methods

We hypothesised that the increased motion, evidenced by spondylolisthesis, in an adjacent level predisposed to adjacent level disease.

A retrospective review of 164 patients with prospectively collected standardised AP, standing lateral and flexion/extension radiographs of CDAs performed within our institution with a minimum 5-year follow-up was performed. Only patients with pre-operative, early post-operative (< 3 months from procedure) and late post-operative (> 5 years from procedure) radiographs were included. Patients with rigid ankylosing conditions and severe malalignment requiring corrective osteotomies (chin-on-chest deformity and loss of horizontal gaze) were excluded. Multi-level surgery was included, as well as hybrid procedures (multi-level surgery with CDA and ACDF) provided the most cranial level, which was a CDA.

Pre-operative cervical spondylolisthesis within two adjacent cranial vertebra of the CDA level were identified as a break in the posterior vertebral line (Fig. 1) and graded according to the Meyerding classification [1]. Only sub-axial articulations were included, and therefore, the C1/2 articulation was excluded.
Fig. 1

Pre-operative combined anterolisthesis and retrolisthesis of C4/5

The early post-operative standing lateral x-ray was used to determine sagittal alignment of the operated levels based on the posterior vertebral cortex as described by Harrison and colleagues [23]. In addition, the early post-operative flexion/extension views were analysed to determine the initial range of movement (ROM) and the mid-flexion point, defined as the mid-point between maximal flexion and maximal extension of the operated levels. These measurements were based on the relative angles between the upper and lower components of each implant, with extension defined as posterior convergence and flexion defined as anterior convergence (Fig. 2).
Fig. 2

Post-operative flexion and extension views illustrating the angular measurement of flexion (a) and extension (b)

Post-operatively these levels were monitored for spondylolisthesis progression, defined by a change in the Meyerding score, and progressive degeneration (ALD). Progressive degeneration was defined using the x-ray criteria of Kettler and colleagues on the AP and lateral standing profile views and included any of: loss of disc height, increased subchondral sclerosis and development or enlargement of osteophytes [24]. An increase in Kettler grade was required to identify progressive degeneration/ALD.

The ROM was reassessed on the most recent radiographs and compared to the initial films. The relationship between post-operative auto-fusion of the CDA, defined as 0° ROM, and ALD was analysed.

The clinical notes were reviewed for revision procedures, including adjacent level procedures. Visual Analogue Scores (VAS) for neck and arm pain were recorded pre-operatively, early post-operatively and at 5 years post-operatively. The Neck Disability Index (NDI) was recorded at 5 year post-operatively.

Statistics

A series of descriptive statistics were conducted to describe this sample of respondents. Following this, Chi-square analyses were conducted to determine the association between ALD and age, sex, implant type, level and direction of spondylolisthesis. Mann–Whitney tests assessed the relationship between ALD and the various post-operative parameters (alignment, ROM, flexion, extension, the mid-flexion point, VAS and NDI scores). Fisher exact tests were conducted to determine the association between auto-fusion of the upper CDA and CDA spondylolisthesis on ALD.

Statistical analysis was performed using SPSS software. Statistical significance was defined as a p value of less than 0.05.

Results

Of the 164 patients reviewed, the average age was 44 years (range 23–65 years), 52% female (85 female, 79 male) and average follow-up was 6.5 years (range 5–10 years). The CDA implants used were the Bryan® disc from Medtronic (43 patients), the Discocerv® from Alphatech Spine (38 patients), Mobi-C® from LDR (29 patients) and the Baguera-C® from Spineart (54 patients). There were 164 adjacent IVDs assessed immediately cranial to the CDA. In addition, there were 157 IVDs two levels cranial to the CDA assessed. Of the total 321 IVDs assessed, 80 (24.9%) had a pre-operative spondylolisthesis.

There was no significant difference of age (p = 0.083) or sex (p = 0.796) between those with or without a pre-operative spondylolisthesis. Furthermore, there was no significant relationship between age (p = 0.482) or sex (p = 0.208) and those with a pre-operative spondylolisthesis that progressed to ALD.

Pre-operative spondylolisthesis did not significantly increase the rate of post-operative degeneration (p = 0.315) (Fig. 3).
Fig. 3

Representative case of a single level C5/6 Baguera-C® CDA with flexion views showing adjacent level spondylolisthesis that did not progress to ALD

Table 1 shows the rate of ALD dependant on the direction of spondylolisthesis. Of the 80 patients with a spondylolisthesis, 64 had an anterolisthesis, 11 had a retrolisthesis and five had a combined anterolisthesis and retrolisthesis. Only grade 1 spondylolisthesis was identified, no cases of greater spondylolisthesis were found. There was no significant difference identified between the direction of spondylolisthesis, including no spondylolisthesis, and the risk of degeneration (p = 0.315).
Table 1

Direction of spondylolisthesis and risk of adjacent level degeneration (total, with percentage in brackets)

Group

Post-operative degeneration

Yes

No

Total

Spondylolisthesis

 All

11 (13.8%)

69 (86.3%)

80

 Anterolisthesis

8 (12.5%)

56 (87.5%)

64

 Retrolisthesis

2 (18.2%)

9 (81.8%)

11

 Both

1 (20.0%)

4 (80.0%)

5

No spondylolisthesis

46 (19.1%)

195 (80.9%)

241

Total

57 (17.8%)

264 (82.2%)

321

11.3% of IVDs with a spondylolisthesis had radiological evidence of pre-operative degeneration in contrast to 11.6% of IVD without spondylolisthesis (p = 0.940). There was no difference in the rate of progression to ALD in IVDs with pre-operative degeneration between those with a spondylolisthesis and those without (p = 0.583). However, in those with a pre-operative degenerative spondylolisthesis, 33.3% progressed their degeneration in contrast to 11.4% in those with a non-degenerative pre-operative spondylolisthesis (p = 0.041).

In patients with a pre-operative spondylolisthesis, there was no significant relationship between the most cranial CDA early alignment (p = 0.955), ROM (p = 0.663), maximal flexion (p = 0.892), maximal extension (p = 0.851) and mid-flexion point (p = 0.934) with progression to ALD (Table 2). Furthermore, in multi-level surgery, there was no significant difference between the early average alignments of each operated level (p = 0.580), or the total number of fused levels (p = 0.845), with progression to ALD.
Table 2

Analysis of variables associated with adjacent level degeneration

Location

Variable

No pre-op spondylolisthesis

Pre-op spondylolisthesis

Pre-op anterolisthesis

Pre-op retrolisthesis

Pre-op anterolisthesis and retrolisthesis

ALD

ALD

ALD

ALD

ALD

No

Yes

Sig.

No

Yes

Sig

No

Yes

Sig

No

Yes

Sig

No

Yes

Sig

Upper CDA

Alignment

− 0.3

− 0.0

0.31

− 1.1

− 0.6

0.96

− 1.3

− 0.4

0.95

0.3

− 2.5

0.40

− 0.3

2.0

1.00

Flexion

2.4

3.2

0.43

3.0

3.2

0.89

2.9

4.6

0.21

5.3

− 1.5

0.04

− 1.0

1.0

0.50

Extension

3.9

2.8

0.34

3.9

3.7

0.85

3.8

3.0

0.55

2.9

6.0

0.18

8.3

5.0

1.00

ROM

6.3

6.0

0.27

6.9

6.9

0.66

6.7

7.6

0.39

8.2

4.5

0.53

7.3

6.0

1.00

Mid-flexion

− 0.5

− 0.2

0.44

− 0.2

− 0.3

0.93

− 0.2

− 0.4

0.36

1.5

− 3.8

0.18

− 4.3

− 2.0

0.50

Total

Alignment

− 0.6

− 0.9

0.02

− 0.8

− 1.4

0.81

− 1.2

− 1.3

0.64

1.2

− 5.0

0.33

1.0

2.0

1.00

Fusion levels

0.16

0.11

0.56

0.2

0.3

0.85

0.2

0.4

0.34

0.3

0.0

0.73

0.75

0.0

0.80

Alignment is defined as a positive value for kyphosis and a negative value for lordosis. Statistically significant results are in bold

The most common cranial CDA level was C5/6. There was no significantly increased risk of ALD relative to the specific IVD level (p = 0.575). However, irrespective of pre-operative spondylolisthesis, the rate of ALD was significantly higher for those IVDs immediately adjacent to a CDA than those two IVD spaces cranial of the CDA (27.4 and 7.6%, respectively p = 0.000). This was similar when specifically analysing those IVDs with a spondylolisthesis (20.9 and 5.4%, respectively p = 0.043).

A total of 96 patients had a single-level CDA, 56 had a double-level procedure (43 double CDA and 13 hybrid procedures), 11 had a triple-level (five single-level CDA with double-level ACDF; one double-level CDA with single-level ACDF) and one had a four-level (triple-level CDA and single-level ACDF) procedure. There was no increased risk of ALD, in IVDs with spondylolisthesis, with increased numbers of levels operated (p = 0.890), the number of levels fused (p = 0.699) or the total number of fused or replaced levels (including congenital fusions) (p = 0.883).

There was no significant difference between implant type and the rates of ALD in patients with a pre-operative spondylolisthesis (p = 0.223). Furthermore, in implants which themselves had a post-operative spondylolisthesis, there was no significant difference in the rate of post-operative ALD in IVDs with an adjacent spondylolisthesis (p = 0.477).

The ROM of the most cranial CDA did not differ between those with and without ALD (mean 6° for both p = 0.569). Auto-fusion of the most cranial CDA occurred in 30 patients (18.3%). Auto-fusion was associated with a significantly increased risk of ALD overall (27.8% with auto-fusion vs. 16.6% without auto-fusion p = 0.039) (Fig. 4). However, the rate of ALD in those with an auto-fusion did not significantly differ between those with or without an adjacent spondylolisthesis (p = 0.339).
Fig. 4

Representative case of auto-fusion of a Discocerv CDA without adjacent spondylolisthesis who progressed to ALD. Note the large anterior osteophyte that developed at the adjacent level

No patients required further surgery on their cervical spine during the timeframe of this study. This included reoperations or revisions of their implants and extension for ALD.

Patients with ALD had no significant difference in their pre-operative or early post-operative VAS scores (Table 3). However, they were affected by significantly worse 5-year pain scores for both neck and arm.
Table 3

VAS scores for patients with and without ALD

 

ALD

P value

No

Yes

Pre-operative

 Neck

5.9

6.4

0.198

 Arm

6.9

7.2

0.456

Early post-operative

 Neck

2.2

2.4

0.757

 Arm

1.5

2.0

0.300

Late post-operative

 Neck

1.5

2.7

0.024

 Arm

0.9

2.3

0.003

Patents with ALD experienced a significantly worse 5-year post-operative NDI score compared to those without ALD (20.1 versus 12.3 p = 0.011).

Discussion

This study has found that a pre-operatively identified mild spondylolisthesis, in the sub-axial spine, cranially adjacent to a planned CDA is not a risk factor for ALD within 5 years.

We used dynamic X-rays to identify a spondylolisthesis as a break in the posterior vertebral lines. All of our cases were mild (grade 1) spondylolisthesis. To date, the natural history of such a cervical spondylolisthesis is unknown, and therefore, comparison to published literature is not possible. However, because of our strict criteria, our rate of spondylolisthesis is higher than previous reports. Kopacz and colleagues assessed the prevalence of cervical spondylolisthesis in 174 patients undergoing scout lateral x-rays during barium swallows and found a prevalence of anterolisthesis of 5.2% and retrolisthesis of 0% [25]. But these were not dynamic views, which are designed to accentuate instability. Furthermore, our diagnostic criteria defined a spondylolisthesis as a break in the posterior vertebral lines, rather than a minimum two-millimetre translation in a standing profile film. Lastly, we had a selection bias as we pre-selected patients with IVD pathology.

Despite the variance in the literature of what defines a spondylolisthesis, we feel that our criterion offers a pragmatic interpretation, which is easily performed. We confirmed that the patient’s age, sex and implant type were similar between the groups and did not affect the rates of ALD. Therefore, we excluded these as confounders of our findings.

Because we only assessed cranial ALD, we hypothesised that the most cranial CDAs alignment and mobility may influence the rate of ALD in those with an adjacent spondylolisthesis. However, we found no relationship between early post-operative alignment, ROM, maximal flexion (except in retrolisthesis), maximal extension or the mid-flexion point and ALD. In retrolisthesis, we found that if the most cranial CDA had reduced flexion (− 1.5° in those who develop ALD compared to 5.3o in those who do not develop ALD), that there was a significant increased rate of ALD (p = 0.04). This may be explained by the lack of flexion preventing the adjacent level from compensating for the retrolisthesis, and therefore degenerating.

We did not specifically assess the global cervical alignment as this study assessed an average population without severe malalignment requiring corrective osteotomies. However, we did assess the overall alignment of the operative levels and found no significant relation to ALD. This supports surgeons, in this patient population, not changing the implant sizings to influence the risk of ALD. We also found no relationship between the total number of levels operated or the number of fused levels, supporting surgeons’ decision-making into their optimal treatment for each level.

We found that the immediately adjacent IVD was at higher risk of ALD than its neighbouring IVD (27.4 and 7.6%, respectively p = 0.000) and that there was a significantly increased rate of ALD in patients with auto-fusion of the most cranial CDA irrespective of spondylolisthesis (27.8% with auto-fusion vs. 16.6% without auto-fusion p = 0.039). This confirms the concerns of neighbouring stiffness being a risk factor for ALD and may support the concept of avoiding upper level ACDF [26, 27]. However, with an overall auto-fusion rate of 18% identified in this study, CDA does not eliminate this concern. Furthermore, we have not assessed the effect of an ACDF on an adjacent CDA, therefore, extrapolation of these results should be guarded.

This study is limited by its radiological parameters of degeneration. Within the literature, there is no single system that can define the prognosis, and therefore, treatment of disc degeneration [28]. We used the Kettler criteria because it is specific to the cervical spine and is reportedly the most reliable when using x-rays [24, 28]. Patients who developed ALD experienced worse pain and functional outcomes at 5 years, but no patient required a revision or reoperation on their cervical spine within the timeframe of this study. Long-term follow-up is necessary to determine the reoperation rates of the radiologic evidence of degeneration identified in this study.

Conclusion

The rate of ALD in CDA found in this series was 17.8%, mostly affecting the immediately adjacent IVD (27.4 and 7.6%, respectively p = 0.000). Pre-operative mild spondylolisthesis, in the sub-axial spine, cranial and adjacent to a planned CDA was not found to be a risk factor for ALD within 5 years. Those with a degenerative spondylolisthesis are at higher risk of ALD (33%) than those with a non-degenerative cause for their spondylolisthesis (11%). Post-operative CDA alignment, ROM or induced spondylolisthesis do not affect the rate of ALD in those with an adjacent spondylolisthesis. Patients with ALD experience significantly worse 5-year pain and functional outcomes than those unaffected by ALD.

Notes

Acknowledgements

Glynny Kieser for her editorial input.

Compliance with ethical standards

Conflict of interest

All authors declare that they have no conflict of interest.

Supplementary material

586_2018_5574_MOESM1_ESM.pptx (186 kb)
Supplementary material 1 (PPTX 185 kb)

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • David Christopher Kieser
    • 1
    • 3
  • Derek Thomas Cawley
    • 2
  • Cecile Roscop
    • 2
  • Simon Mazas
    • 2
  • Pierre Coudert
    • 2
  • Louis Boissiere
    • 2
  • Ibrahim Obeid
    • 2
  • Jean-Marc Vital
    • 2
  • Vincent Pointillart
    • 2
  • Olivier Gille
    • 2
  1. 1.Department of Orthopaedic Surgery and Musculoskeletal Medicine, Canterbury School of MedicineUniversity of OtagoChristchurchNew Zealand
  2. 2.L’Institut de la Colonne Vertébrale, CHU PellegrinBordeauxFrance
  3. 3.Department of Orthopaedic Surgery and Musculoskeletal MedicineCanterbury District Health BoardChristchurchNew Zealand

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