J Korean Neurosurg Soc.  2016 Sep;59(5):471-477. 10.3340/jkns.2016.59.5.471.

Compression Angle of Ossification of the Posterior Longitudinal Ligament and Its Clinical Significance in Cervical Myelopathy

• Lee N
• Yoon DH
• Kim KN
• Shin HC
• Shin DA
• Ha Y

• KMID: 2351715
• DOI: http://doi.org/10.3340/jkns.2016.59.5.471

Abstract

OBJECTIVES
The correction of clinical and radiologic abnormalities in patients with symptomatic ossification of the posterior longitudinal ligament (OPLL) is the current mainstay of treatment. This study aimed to identify radiographic predictors of severity of myelopathy in patients with symptomatic OPLL.
METHODS
Fifty patients with symptomatic cervical OPLL were enrolled. Based on Japanese Orthopedic Association (JOA) scores, patients were divided into either the mild myelopathy (n=31) or severe myelopathy (n=19) group. All subjects underwent preoperative plain cervical roentgenogram, computed tomography (CT), and MR imaging (MRI). Radiological parameters (C2-7 sagittal vertical axis, SVA; C2-7 Cobb angle; C2-7 range of motion, ROM; OPLL occupying ratio; and compression angle) were compared. Compression angle of OPLL was defined as the angle between the cranial and caudal surfaces of OPLL at the maximum level of cord compression
RESULTS
The occupying ratio of the spinal canal, C2-7 Cobb angle, C2-7 SVA, types of OPLL, and C2-7 ROM of the cervical spine were not statistically different between the two groups. However, the OPLL compression angle was significantly greater (p=0.003) in the severe myelopathy group than in the mild myelopathy group and was inversely correlated with JOA score (r=-0.533, p<0.01). Furthermore, multivariate regression analysis demonstrated that the compression angle (B=-0.069, p<0.001) was significantly associated with JOA scores (R=0.647, p<0.005).
CONCLUSION
Higher compression angles of OPLL have deleterious effects on the spinal cord and decrease preoperative JOA scores.

Keyword

Ossification of the posterior longitudinal ligament; Cervical myelopathy; Compression angle

MeSH Terms

Asian Continental Ancestry Group
Humans
Longitudinal Ligaments*
Magnetic Resonance Imaging
Orthopedics
Range of Motion, Articular
Spinal Canal
Spinal Cord
Spinal Cord Diseases*
Spine

Figure

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  Fig. 1 A : Measurement of C2–7 SVA interval between C2 body plumb line and posterior superior endplate of C7. B : Sagittal alignment by C2–7 Cobb angle method : angle between two lines parallel to the endplate of C2 and C7 on lateral plain radiographs.

• 

  Fig. 2 Compression angle of OPLL. Special kyphotic angle at most compressed level. In this study, the angle was measured by sagittal T2 weighted preoperative MRI image. A : C3/4 is the most compressed level on T2WI. B : We measured the compression angle at C3/4 level. α : compression angle.

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  Fig. 3 Regression analysis shows negative correlation for compression angle and JOA score. JOA : Japanese Orthopedic Association.

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