Electronic medical record was retrospectively reviewed for all subjects with MCs at a single institution from September 2018 to October 2022. This study included a total of 263 subjects who met the following inclusion criteria: 1) adult subjects (≥ 18 years of age) on admission; 2) underwent lumbar X-ray examination in the neutral (0°), flexion (40°), and extension positions (-20°) and lumbar magnetic resonance imaging (MRI) scanning in the supine position; 3) MRI scanning revealed at least one of the three types of MCs at lumbar level; 4) available and clear images.
Subjects with spinal scoliosis more severe than 15 degrees, or a prior history of lumbar spine, or lumbar specific and/or nonspecific infectious, spinal trauma, and spinal tumor were excluded in this study. Subjects with hip or knee disorders, were also excluded due to substantial impact on gait and posture, which may lead to compensatory changes in lumbar spine.
The selection of the study population and the measurement of imaging parameters were carried out independently by two groups of this study’s authors. The study subjects were sequentially coded and their personal information was covered before measurement. The present work was implemented under the guide of the principles of the Declaration of Helsinki. Patients who participated in this study signed the informed consent provided, declaring they were aware of the study details. The ethical committee of the People’s Hospital of Guangxi Zhuang Autonomous Region, Nanning, People’s Republic of China, reviewed and approved the study protocol (No. 2016–12).
Radiographic evaluation and measurement
The types of MCs, the involvement extents of MCs, and lumbar segmental motions were independently evaluated and measured by two experienced authors. Two spinal surgeons with more than three-year clinical experience independently evaluated the patients’ MRI.
Measurement of lumbar segmental motions
We assessed the segmental angular and translation motions in the flexion and extension positions on X-ray images (Fig. 1). Lumbar vertebral bodies of the subject from the subjects were marked with four points (anterosuperior, anteroinferior, posterosuperior, and posteroinferior). The angular motion was counted as an absolute value of the difference between the intervertebral angles from flexion to extension. The translation motion was measured as an absolute value of the difference in the horizontal movement of the superior endplates on their adjacent inferior endplates from flexion and extension.
MRI equipment parameters
All patients who met our inclusion criteria were examined with 1.5 Tesla magnetic resonance units (Espree, Siemens, Germany). The scanning range was settled from T12 to sacrum 1.
The following parameters were applied: the sagittal T1-weighted imaging (T1WI) [slice thickness (ST): 4 mm, time of repetition (TR): 400 ms, time to echo (TE): 8 ms, field of view (FOV): 280 mm], the sagittal T2-weighted images (T2WI) [ST: 4 mm, TR: 3000 ms, TE: 100 ms, FOV: 280 mm]; and the axial T2WI (ST: 4 mm, TR: 5000 ms, TE: 97 ms, FOV: 250 mm).
Evaluation of the three types of MCs
Modic et al. [4, 5] classified MCs into three types according to their imaging appearance on T1WI and T2WI (Fig. 2). MC1 shows a decreased signal intensity on T1WI but an increased signal intensity on T2WI. MC2 demonstrates the increased signal intensity both on T1-and T2WIs. In contrast, MC3 reflects the decreased signal intensity both on T1- and T2WIs.
Definition of the sizes of MCs
According to the classification proposed by Hanımoğlu et al. , the vertebral body and endplate are equally divided into 4 parts horizontally and vertically, comprising of 16 small cells. Each small cell involved by MCs is recorded and summed up to calculate the total involvement area of MCs for this subject. I, II, III, and IV represent < 25%, 25%-50%, 50%-75%, and > 75% of the endplate involved by MCs in the horizontal plane, respectively. 1, 2, 3, and 4 represent < 25%, 25%-50%, 50%-75%, and > 75% of the vertebral body involved by MCs in the vertical plane, respectively. Therefore, I1 indicates that MCs invade a small cell, which involve less than 25% of vertebral body and endplate both in horizontal and vertical directions; I2 means that two small grids were involved by MCs, which invade less than 25% of vertebral endplate in the horizontal plane but 25%-50% of the vertebral body in the vertical plane and so on. We define the involvement area of MCs < 25% of the vertebral body in the horizontal or vertical plane as slight, 25%-75% as moderate, > 75% as severe.
Inter- and intra-observer reliability
We randomly selected 15 of all included subjects to independently evaluate the types of MCs, the extent of MCs lesion involvement, and lumbar segmental motions by two authors (M.X.P. and X.D.W.). The above-mentioned radiographic evaluation and parameters were requested to be repeated 10 days after their first evaluation. The inter- and intra-observer reliability was calculated after they evaluation. An intraclass correlation coefficient (ICC) value > 0.80 represented perfect agreement, 0.61–0.80 substantial agreement. It should be considered unreliable if an ICC value less than 0.60 .
We performed the data analysis using IBM SPSS 22.0 (SPSS Inc., Armonk, New York) in the present work. Mean ± standard deviation (SD) was calculated to manifest the continuous variables. We adopted one-way variance analysis or Kruskal–Wallis test to analyze the differences in subjects’ age, BMI and their lumbar segmental motions between the groups. For dichotomous variables such as subjects’ gender, chi-square test was used in this study. A p ≤ 0.05 was considered as a significant difference. Intra-class correlation coefficient (ICC) was employed to calculate the inter- and intra-observer reliability in the extent of MCs lesion involvement, lumbar angular and translation motions. Cohen’s coefficient kappa was used to identify the inter- and intra-observer reliability in the types of MCs,