gms | German Medical Science

Objective: Posterior longitudinal ligament (OPLL) is not a two-dimensional (2D) disease, but rather a three-dimensional (3D) disease. Therefore, conventional measurement of parameters using radiography may not be suitable for evaluating OPLL. However, there is no study investigated the correlation between 3D parameters of OPLL and clinical outcomes. Therefore, the aim of this study is to evaluate the usefulness of three-dimensional (3D) measurement of ossification of the posterior longitudinal ligament (OPLL), and identify the reliability of a novel 3D method of measurement.

Method: Fifty patients (40 males and 10 females; mean age 57.2 years) with symptomatic OPLL were enrolled. Neurological and clinical outcome scales were measured using the Japanese Orthopedic Association (JOA) score, visual analogue scale (VAS), short-form health survey (SF-36) and neck disability index (NDI). A 3D model was reconstructed with DICOM files from axial CT images using software (MIMICS^®; Materialise, Leuven, Belgium) to obtain the following parameters: 3D volume of OPLL (amount of whole volume of OPLL), 3D volume of the spinal canal (confined to the vertebral level involving OPLL), spinal canal diameter (anterior-posterior interval of spinal canal), thickness of OPLL (anterior-posterior interval of OPLL), and length of OPLL (longitudinal interval of OPLL). All patients were divided into two different groups, the mild myelopathy group (JOA score = 18, n = 11) and the severe myelopathy group (JOA score = 17, n = 23).

Results: The 3D OPLL volume itself did not correlate with clinical outcomes (r = -0.275, P = 0.116). 3D OPLL ratio and OPLL thickness had a significant negative relationship with JOA score (r = -0.502, P < 0.005 and r = -0.437, P < 0.05, respectively). In particular, 3D OPLL ratio was an independent risk factor for increased severity of myelopathy (B = -29.71, P < 0.05). On the other hand, conventional occupying ratio did not show statistical significance (r = -0.293, P = 0.093). The mild myelopathy group showed lower 3D OPLL ratio than the severe myelopathy group (0.092 vs. 0.148, P < 0.05).

Conclusions: 3D method of measurement is superior to the conventional method in terms of evaluating the clinical state of symptomatic OPLL patients. Higher 3D OPLL ratio has an adverse effect on the spinal cord and is associated with deteriorating JOA score.