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A New Concept for Making Decisions Regarding the Surgical Approach for Cervical Ossification of the Posterior Longitudinal Ligament: The K-Line

Fujiyoshi, Takayuki, MD*; Yamazaki, Masashi, MD, PhD*; Kawabe, Junko, MD*; Endo, Tomonori, MD*; Furuya, Takeo, MD*; Koda, Masao, MD, PhD*; Okawa, Akihiko, MD, PhD*; Takahashi, Kazuhisa, MD, PhD*; Konishi, Hiroaki, MD, PhD

doi: 10.1097/BRS.0b013e318188b300
Diagnostic Imaging
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Study Design. To report a new index, the K-line, for deciding the surgical approach for cervical ossification of the posterior longitudinal ligament (OPLL).

Objective. To analyze the correlation between the K–line-based classification of cervical OPLL patients and their surgical outcome.

Summary of Background Data. Previous studies showed that kyphotic alignment of the cervical spine and a large OPLL are major factors causing poor surgical outcome after laminoplasty for cervical OPLL patients. However, no report has evaluated these 2 factors in 1 parameter.

Methods. The K-line was defined as a line that connects the midpoints of the spinal canal at C2 and C7. Twenty-seven patients who had cervical OPLL and underwent posterior decompression surgery were classified into 2 groups according to their K-line classification. OPLL did not exceed the K-line in the K-line (+) group and did exceed it in the K-line (−) group. By intraoperative ultrasonography, we evaluated the posterior shift of the spinal cord after the posterior decompression procedure. The Japanese Orthopedic Association scores before surgery and 1 year after surgery were evaluated, and the recovery rate was calculated.

Results. Eight patients were classified as K-line (−), and 19 patients were classified as K-line (+). The mean recovery rate was 13.9% in the K-line (−) group and 66.0% in the K-line (+) group (P < 0.01). Ultrasonography showed that the posterior shift of the spinal cord was insufficient in the K-line (−) group.

Conclusion. The present results demonstrate that a sufficient posterior shift of the spinal cord and neurologic improvement will not be obtained after posterior decompression surgery in the K-line (−) group. Our new index, the K-line, is a simple and practical tool for making decisions regarding the surgical approach for cervical OPLL patients.

We proposed a new index, the K-line, which can evaluate cervical alignment and OPLL size in 1 parameter. The K-line is a simple and practical tool for predicting the surgical outcome after posterior decompression surgery and making decisions regarding the surgical approach for cervical OPLL patients.

From the *Spine Section, Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, Chiba; and †Department of Orthopaedic Surgery, Nagasaki Rosai Hospital, Nagasaki, Japan.

Acknowledgment date: February 11,2008. Revision date: July 3, 2008. Acceptance date: July 9, 2008.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Other funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Supported by a grant for Intractable Diseases from the Public Health Bureau, the Ministry of Health, Labour, and Welfare of Japan (Investigation Committee on Ossification of the Spinal Ligaments).

Address correspondence and reprint requests to Masashi Yamazaki, MD, PhD, Spine Section, Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8677, Japan; E-mail: masashiy@faculty.chiba-u.jp

© 2008 Lippincott Williams & Wilkins, Inc.