Anterior direct decompression significantly relieves spinal cord high signal in patients with ossification of the posterior longitudinal ligament: a case-control study
Authors: Wu Zichuan , Zhang Zifan , Xu Aochen , Lu Shihao , Cui Cheng , Sun Baifeng , Liu Yang 
Published: November 2023

Abstract
Background
In patients with cervical spondylotic myelopathy caused by ossification of the posterior longitudinal ligament, high cord signal (HCS) is frequently observed. However, limited research has investigated the variations in HCS improvement resulting from different surgical approaches. This study aims to explore the potential relationship between the choice of surgical approach and the postoperative improvement of intramedullary high signal in ossification of the posterior longitudinal ligament (OPLL) patients.

Methods
We extensively reviewed the patients' medical records, based on which demographic information such as gender, age, and body mass index (BMI) were recorded, and assessed the severity of the patients' neurological status preoperatively and postoperatively by using the Japanese Orthopedic Association score (JOAs), focusing on consecutive preoperative and postoperative Magnetic resonance imaging (MRI) T2WI measurements, to study the statistical correlation between the improvement of HCS and the choice of surgical approach.

Results
There were no significant differences in demographic, imaging parameters, and clinical symptoms between patients undergoing anterior and posterior surgery (p > 0.05, Table 1). However, both improvement in JOAs (Recovery2) and improvement in HCS (CR2) were significantly better in the anterior surgery group two years after surgery (p < 0.05, Table 1). Multifactorial logistic regression analysis revealed that posterior surgery and higher preoperative signal change ratio (SCR) were identified as risk factors for poor HCS improvement at the two-year postoperative period (p < 0.05, Table 2).Table 1
Differences in demographic, imaging parameters, and clinical symptoms in patients with anterior and posterior approach

Anterior approach
Posterior approach
P-Values

Demographic data

Sex (male/female)
10/12
6/17
0.175

Age
58.59 ± 5.68
61.43 ± 9.04
0.215

Hypertension
14/8
14/9
0.848

Diabetes
16/6
19/4
0.425

BMI
25.58 ± 4.72
26.95 ± 4.58
0.331

Smoking history
19/3
16/7
0.175

Preoperative measured imaging parameters

Preoperative SCR
1.615 ± 0.369
1.668 ± 0.356
0.623

CR1
0.106 ± 0.125
0.011 ± 0.246
0.08

CNR
0.33 ± 0.073
0.368 ± 0.096
0.15

C2–7 Cobb angle
8.977 ± 10.818
13.862 ± 13.191
0.182

SVA
15.212 ± 8.024
17.46 ± 8.91
0.38

mK-line INT
3.694 ± 3.291
4.527 ± 2.227
0.323

Imaging follow-up

6 months postoperative SCR
1.45 ± 0.44
1.63 ± 0.397
0.149

2 years postoperative SCR
1.26 ± 0.19
1.65 ± 0.35
0.000**

CR2
0.219 ± 0.14
− 0.012 ± 0.237
0.000**

Clinical symptoms

Preoperative JOAs
10.64 ± 1.59
10.83 ± 1.47
0.679

6 months postoperative JOAs
11.82 ± 1.37
11.65 ± 1.4
0.69

2 years postoperative JOAs
14.18 ± 1.01
12.52 ± 2.06
0.001**

Recovery1
0.181 ± 0.109
0.128 ± 0.154
0.189

Recovery2
0.536 ± 0.178
0.278 ± 0.307
0.001**

*, statistical significance (p < 0.05). **, statistical significance (p < 0.01)
BMI = body mass index. SCR = the signal change ratio between the localized high signal and normal spinal cord signal at the C7-T1 levels. CR1 = the regression of high cord signals at 6 months postoperatively (i.e., CR1 = (Preoperative SCR—SCR at 6 months postoperatively)/ Preoperative SCR). CR2 = the regression of high cord signal at 2 years postoperatively (i.e., CR2 = (Preoperative SCR—SCR at 2 years postoperatively)/ Preoperative SCR). CNR = canal narrowing ratio. SVA = sagittal vertical axis. mK-line INT = modified K-line interval. JOAs = Japanese Orthopedic Association score. Recovery1 = degree of JOAs recovery at 6 months postoperatively (i.e., Recover1 = (JOAs at 6 months postoperatively—Preoperative JOAs)/ (17- Preoperative JOAs)). Recovery2 = degree of JOAs recovery at 2 years postoperatively (i.e., Recover2 = (JOAs at 2 years postoperatively−Preoperative JOAs)/ (17−Preoperative JOAs))
Table 2
Linear regression analyses for lower CR2 values

95% CI
P value

Uni-variable analyses

Demographic data

Sex (male/female)
− 0.01
0.221
0.924

Age
− 0.015
0.003
0.195

Hypertension
− 0.071
0.204
0.334

Diabetes
− 0.195
0.135
0.716

BMI
− 0.375
0.422
0.905

Smoking history
− 0.249
0.077
0.295

Surgical approach
− 0.349
− 0.113
0.000#

Preoperative measured imaging parameters

C2–7 Cobb angle
− 0.009
0.002
0.185

SVA
− 0.008
0.008
0.995

mK-line INT
− 0.043
0.005
0.122

Preoperative SCR
0.092
0.445
0.004#

CR1
0.156
0.784
0.004#

CNR
− 0.76
0.844
0.918

Multi-variable analyses

Surgical approach
− 0.321
− 0.118
0.000**

Preoperative SCR
0.127
0.41
0.000**

CR1
− 0.018
0.501
0.067

#, variables that achieved a significance level of p < 0.1 in the univariate analysis
*statistical significance (p < 0.05). **statistical significance (p < 0.01)
BMI = body mass index. SCR = the signal change ratio between the localized high signal and normal spinal cord signal at the C7-T1 levels. CR1 = the regression of high cord signals at 6 months postoperatively (i.e., CR1 = (Preoperative SCR—SCR at 6 months postoperatively)/ Preoperative SCR). CR2 = the regression of high cord signal at 2 years postoperatively (i.e., CR2 = (Preoperative SCR—SCR at 2 years postoperatively)/ Preoperative SCR). CNR = canal narrowing ratio. SVA = sagittal vertical axis. mK-line INT = modified K-line interval

Conclusions
For patients with OPLL-induced cervical spondylotic myelopathy and intramedullary high signal, anterior removal of the ossified posterior longitudinal ligament and direct decompression offer a greater potential for regression of intramedullary high signal. At the same time, this anterior surgical strategy improves clinical neurologic function better than indirect decompression in the posterior approach.