Three-dimensional measurement of intervertebral range of motion in ossification of the posterior longitudinal ligament: are there mobile segments in the continuous type?

Clinical article

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Object

In this paper, the authors' goals were to determine the extent of the effect of continuous-type ossification of the posterior longitudinal ligament (OPLL) of the cervical spine on intervertebral range of motion (ROM) and to examine the relationship between the 3D morphology of OPLL and intervertebral ROM.

Methods

The authors evaluated 5 intervertebral segments in each of 20 patients (11 men and 9 women) with continuous-type OPLL, for a total of 100 intervertebral segments, using functional CT in anteroposterior (AP) flexion and right and left axial rotation. Three-dimensional kinematics were evaluated using the voxel-based registration method. Ossification was classified on the basis of 3D kinematics and morphology.

Results

The authors found 49 ossifications that were obviously of the continuous type. They were divided into 2 types: 1) bridging (13 instances), with thick, continuous ossification of the anterior or posterior longitudinal ligament bridging intervertebral segments and with an ROM of 0.3° in AP flexion and 0.2° in rotation; and 2) nonbridging (36 instances), with a minute gap in the ossification itself or between the ossification and vertebra and with an ROM of 4.9° in AP flexion and 4.0° in rotation. There were 8 stalagmite-type ossifications in the nonbridging group that had the unique kinematics of restricted AP flexion and normal axial rotation.

Conclusions

The authors' findings indicate that most continuous-type ossifications that are categorized using the conventional radiographic classification system have mobile segments. The discrimination between bridging and nonbridging on CT scans can be a useful predictive index for dynamic factors.

Abbreviations used in this paper:AP = anteroposterior; JOA = Japanese Orthopaedic Association; OPLL = ossification of the posterior longitudinal ligament; ROM = range of motion.

Article Information

Address correspondence to: Takahito Fujimori, M.D., Department of Orthopedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. email: takahito-f@hotmail.co.jp.

Please include this information when citing this paper: published online April 27, 2012; DOI: 10.3171/2012.3.SPINE111083.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    The morphology of ossification based on lateral radiographs.

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    Acquisition of CT scans of maximum AP flexion and maximum axial rotation. The examiner was instructed to help participants bend their necks until they could rest their chin on their chest with the use of a supportive device in anterior flexion without pain or discomfort, and to have participants rotate their head perpendicular to the axis of their body trunk.

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    Computed tomography scans showing the bridging (A), nonbridging (B), and stalagmite (C) types of ossification.

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    Case 1. Radiograph (A) and CT scans (B and C) of ossifications. The radiograph shows a continuous-type OPLL at the C3–6 level; however, the reconstructed scans reveal the discontinuity (arrows) of ossifications of the nonbridging type.

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    Case 1. Three-dimensional model, viewed from behind, of ossifications of the nonbridging type. The vertebral arches are removed for better visualization.

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    Case 2. Computed tomography scan (left) and MRI study (right) of the cervical spine. The MRI study shows a T2 high-intensity area in the spinal cord at the C3–4 level.

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