Analysis of radiological factors promoting degeneration in adjacent disc levels after anterior cervical discectomy and fusion(acdf)

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1 Analysis of radiological factors promoting degeneration in adjacent disc levels after anterior cervical discectomy and fusion(acdf) Dept. of neurosurgery, Sapporo Azabu Neurosurgical Hospital*, Sapporo, Japan Dept. of neurosurgery, Hokkaido University**, Sapporo, Japan Shunsuke Yano*, Kazutoshi Hida**, Toshitaka Seki**, Takeshi Aoyama**, Toru Sasamori**, Hisatoshi Saitou *

2 Past reports (Incidence of ASD) Introductions Although anterior cervical discectomy and fusion (ACDF) is a commonly applied procedure for cervical spondylosis, adjacent segment disease (ASD) is considered as one of the important factors affecting long-term results. Radiological ASD =25~89 %, Clinical ASD = 1.8~36 %, Surgical revision = 3~8 % Hilibrand (1999), Goffin(2004), Mummaneni(2007), Elsawaf(2009), Carrier CS, (2013), Litrico S, (2014), Song JS. (2014) Past reports / The risk factors for ASD Positive factors for ASD Decrease in disc intensity (MRI) Pre-existing degeneration ROM at adjacent disc level (pre-op.) Number of ACDF Canal diameter Segmental angle at op. level (post-op.) C2-7 angle (post-op.) Gender(Male), Age (< 60yrs) ASD level (C5/6, C6/7) Osteopenia Lumbar degenerative disc disease Negative factors for ASD Degeneration (MRI)= Natural history ROM at fusion level (pre-op.) C2-7 angle (pre- and post-op. ) ROM of C2-7 (pre-op.) Number of ACDF Canal diameter Age, Gender, Tobacco, alcohol, sports Lundine KM. (2014) Song JS. (2014) Litrico S, (2014) Carrier CS, (2013) Matsumoto M. (2009) Elsawaf A. (2009) Goffin J. (2004) Higashino O.(2004) Katsuura A. (2001) A factor evaluated as a positive for ASD has been reported as a negative in another report. The purpose of this study is to clarify the radiological factors affecting ASD after ACDF.

3 Objectives & Methods Patients who underwent ACDF and observed radiologically for more than 5 years after surgery. 72 patients, 145 disc levels One patient performed ACDF at C4/5 and C6/7 had 3 adjacent disc levels. Male: 49, Female: 23 Age at the operation: 31 ~ 82 yo (Mean age : 54.3 yo) F/U: 60 ~ 143 months (Mean F/U : 87.2 months ) Surgical procedure: Modified Smith-Robinson s method using titanium cages Radiological assessments Dynamic X-ray, MRI At pre-op., 1 or 2 weeks after op., and final follow-up time Retrospective analysis Frequency of ASD (Freq-ASD) was calculated on each factors ASD criteria No pre-op. radiological degeneration Appearance of any radiological degeneration at F/U time Some pre-op. radiological degeneration Progression of the degeneration at F/U time

4 General factors Age, Gender Evaluating factors Number of operated levels, Rostral or caudal to operated level Radiological factors Adjacent to the operated levels Disc height, Disc intensity on MRI, Focal ROM (pre-op.) Operated levels Focal disc angle (pre-op.), Changes in value of focal angle (pre-op. post-op.), Solid fusion Overall cervical alignment (C2-7 angle) ROM of C2-7 (pre-op.), C2-7 angle (pre-op.) Changes in value of C2-7 angle (pre-op. post-op.)

5 Results Overall incidence of ASD Person Level 81.9%(59/72 cases) 52.4%(76/145 disc levels) Average time of ASD appearance 30.9 months Secondary surgery due to ASD 11.1 % (8/72cases) C4 C6 Pre-op. MRI C4/5,5/6 ACDF C4 C6 4 yrs after the op.

6 General factors Age, Gender: No statistical significance Rostral or caudal to op. level Number of operated level Freq.-ASD (%) Freq.-ASD (%) Rostral Caudal 41.1% 65.8% 57.1% 50.0% 91.7% 84.6% 1 level 2 levels 3 levels 4 levels p= Chi-square test No statistical significance Rostral side to the operation level is more frequently in ASD developing

7 Factors on the adjacent levels Disc status Disc intensity on MRI Decrease in intensity on T2WI Freq.-ASD (%) Decrease intensity(+) 44.6% Decrease intensity(-) 80.0% Disc intensity P= Chi-square test Disc height Corrected by disc height of Th1/2 level = (Disc height of adjacent level) (Disc height of T1/2 level) x 100 Disc height Freq.-ASD (%) ACDF level ~ ~ ~ 44.9% 55.6% 59.5% No statistical significance Mild degenerative disc at adjacent segment which with decrease in intensity on MRI but without collapse of disc space is one of the risk factors for ASD developing.

8 Focal ROM (pre-op.) at adjacent level (Ext angle)-(flex angle) 10 or <10 Freq.-ASD (%) % 10 < 47.3% Flex. Xp. Ext. Xp. ACDF level p= Chi-square test Canal diameter More than 12mm Less than 12mm Freq.-ASD (%) 12mm < 65.7% A-P diameter 12mm 41.3% p= Chi-square test The risk of developing ASD is significantly higher in cases with preoperative larger ROM of the adjacent level, and/or with smaller canal diameter.

9 Factors on the operated levels Focal angle at operated levels Pre-op. focal angle: Lordosis or Kyphosis Changes in value angle between pre- and post-op. Solid fusion Focal angle Lordosis or Kyphosis 5 or 5 < Changes in value of angle ~4.9 or 5.0~ Pre-op. Neut. Xp. Post-op Neut. Xp. Freq.-ASD (%) Freq.-ASD (%) Freq.-ASD (%) Solid fusion or not lordosis 82.6% 5 ~ 89.5% Fusion(-) 55.6% kyphosis 84.0% ~ % Fusion(+) 85.7% p=0.856 p=0.639 p= Chi-square test Factors on the operated level are not related to ASD developing.

10 Pre-op. C2-7 angle Lordosis or kyphosis Factors on C2-7 angle Pre-op. ROM (Ext-Flex) ~39 or 40 ~ Changes in value of angle (pre-post) ~4.9 or 5.0 ~ C2 C2 C2 C7 C7 C7 Pre-op. Neut. Xp. Pre-op. Flex. Xp. Pre-op. Ext. Xp. Pre-op. Neut. Xp. Post-op. Neut. Xp. Freq.-ASD (%) Freq.-ASD (%) Freq.-ASD (%) lordosis 85.2% 40 ~ 72.7% 5 ~ 85.7% kyphosis 70.6% ~ % ~ % p=0.319 p=0.108 p=0.577 Chi-square test Factors on the C2-7 angle have no affect on ASD developing.

11 Rostral adjacent level p= Summary Positive factors for ASD Decrease in disc intensity on MRI at adjacent level p= Flex. Xp. ACDF level Ext. Xp. Larger focal ROM at adjacent level p= (more than 10 degree) Canal stenosis p= (less than 12 mm) ASD is related mainly to the factors on adjacent disc level, not on operated level or cervical alignment.

12 Conclusions In this study, radiological factors for ASD after ACDF were evaluated. ASD may be related to the factors on the adjacent disc levels, not on the operated level or cervical alignment, radiologically. Although ACDF is an useful and widely accepted method for cervical degenerative disease, careful observation is needed post-operatively, especially in the case with positive factors of ASD. Disclosure declaration None of the authors have any conflicts of interest associated with this study.