BACKGROUND: Bone mineral density plays a key role in the assessment of operative instrumentation complications and clinical outcomes. The MRI-based vertebral bone quality (VBQ) score has been introduced as a novel marker of bone quality. However, few studies have investigated the relationship between VBQ score and patients associated with cervical ossification of the posterior longitudinal ligament (OPLL).
PURPOSE: The aims of the study were (1) to reveal bone mineral density between cervical OPLL and cervical spondylotic myelopathy (CSM) group by VBQ score, (2) to compare the VBQ score of cervical OPLL between male and female group, (3) to explore the relationship between segmental VBQ scores associated with OPLL.
STUDY DESIGN: Retrospective cohort study.
PATIENT SAMPLE: Consecutive series of 425 patients at a single academic institution.
OUTCOME MEASURES: MRI based measurements of C2-C7 VBQ scores.
METHODS: Preoperative noncontrast T1-weighted MRIs of the cervical spine was used to measure the VBQ score. The VBQ score was defined as the mean value of the signal intensity of the vertebrae divided by that of the cerebrospinal fluid (CSF) space at the cisterna magna. Patients with cervical OPLL and CSM were matched based on age, sex, body mass index (BMI), comorbidity, medication history, diet habit, smoking, alcohol consumption via propensity score matching (PSM). Normality of each VBQ score was tested by the Shapiro-Wilk test. Wilcoxon's rank-sum test was used to compare matched cohorts. Kruskal-Wallis test was performed to compare the VBQ scores between segments. Multivariate logistic regression analysis was used to evaluate factors associated with the development of cervical OPLL.
RESULTS: A total of 425 patients were assessed. For final analysis, 135 paired patients were compared between the cervical OPLL and CSM groups, and 22 paired patients were compared between male and female group associated with cervical OPLL. There were no statistically significant differences in age, sex, BMI, comorbidity, medication history, diet habit, smoking, alcohol between the matched cohorts. OPLL group was associated with lower VBQ score compared with CSM group at C3, while there were no differences in VBQ score for the other levels between the two groups. There were no differences between male and female group associated with OPLL in C2-C7 VBQ scores. VBQ scores of cervical OPLL are variable between segments, with significantly lower scores at C6, C7 compared with C1-C5. Multivariate logistic regression analysis showed that BMI was correlated with the development of OPLL (regression coefficient, 0.162; 95% confidence interval, 0.010-0.037). Additional risk factors included hypertension, calcium supple history and smoking.
CONCLUSIONS: This study demonstrates that cervical OPLL is associated with lower VBQ score at C3, with no differences for the other levels when compared with CSM derived from measurements on MRI. No differences were found between male and female group associated with OPLL in C2-C7 VBQ scores. Cervical OPLL were found to have smaller VBQ score at C6, C7 compared with C1-C5. Our findings provide new insight for bone density assessment in cervical OPLL patient.