Bone Turnover Markers in Patients With Ossification of the Posterior Longitudinal Ligament in the Thoracic Spine

Study Design. A prospective, single-center, observational study. Objective. To explore the association between serum levels of bone turnover markers and ossification of the posterior longitudinal ligament (OPLL) in the thoracic spine. Summary of Background Data. The relationship between bone turnover markers, such as N-terminal propeptide of type Ⅰ procollagen (PⅠNP) or tartrate-resistant acid phosphate 5b (TRACP-5b), and OPLL has previously been examined. However, the correlation between these markers and thoracic OPLL, which is more severe than cervical-only OPLL, remains unclear. Methods. This prospective study included 212 patients from a single institution with compressive spinal myelopathy and divided them into those without OPLL (Non-OPLL group, 73 patients) and those with OPLL (OPLL group, 139 patients). The OPLL group was further subdivided into cervical OPLL (C-OPLL, 92 patients) and thoracic OPLL (T-OPLL, 47 patients) groups. Patients’ characteristics and biomarkers related to bone metabolism, such as calcium, inorganic phosphate (Pi), 25-hydroxyvitamin D, 1α,25-dihydroxyvitamin D, PⅠNP, and TRACP-5b, were compared between the Non-OPLL and OPLL groups, as well as the C-OPLL and T-OPLL groups. Bone metabolism biomarkers were also compared after adjusting for age, sex, body mass index, and the presence of renal impairment using propensity score-matched analysis. Results. The OPLL group had significantly lower serum levels of Pi and higher levels of PⅠNP versus the Non-OPLL group as determined by propensity score-matched analysis. The comparison results between the C-OPLL and T-OPLL groups using a propensity score-matched analysis showed that T-OPLL patients had significantly higher concentrations of bone turnover markers, such as PⅠNP and TRACP-5b, compared to C-OPLL patients. Conclusion. Increased systemic bone turnover may be associated with the presence of OPLL in the thoracic spine and bone turnover markers such as PⅠNP and TRACP-5b can help screen for thoracic OPLL.