Investigation of Symptomatic Unstable Changes of Non-Fused Component in the Mixed-Type Cervical Ossification of Posterior Longitudinal Ligament Using Dynamic Magnetic Resonance Imaging: A Case Report

A 43-year-old man was transferred to our hospital with recurring myelopathic symptoms after previous anterior and posterior surgical decompressions for mixed-type cervical ossification of the posterior longitudinal ligament (OPLL). Conventional magnetic resonance imaging (MRI) showed a preserved cervical curve and the achievement of successful decompression after the previous surgeries. The patient's symptoms were aggravated when he was in the extended neck posture. Dynamic MRI performed with the patient in an extended neck position revealed cord compression by OPLL from C3 to C4 with newly developed retrolisthesis of the C4–5 segment. We recommend the use of dynamic MRI to investigate motion-dependent cord compression caused by instability of the non-fused OPLL component.