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Effects of Strain Distribution in the Intervertebral Discs on the Progression of Ossification of the Posterior Longitudinal Ligaments

Matsunaga, Shunji, MD*; Sakou, Takashi, MD*; Taketomi, Eiji, MD*; Nakanisi, Kenji, DrEng

Biomechanic
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Study Design Strain distribution in the intervertebral discs was evaluated biomechanically using an engineering true strain calculation formula.

Objectives This study was performed to clarify the involvement of dynamic factors in the progression of ossification of the posterior longitudinal ligament.

Summary of Background Data In patients with ossification of the posterior longitudinal ligament of the cervical spine, ossification frequently progresses after laminectomy. This suggests the involvement of dynamic factors in the progression of ossification. However, these factors have not yet been clarified.

Methods The analysis was performed on 101 patients with ossification of the posterior longitudinal ligament by employing dynamic lateral x-ray films of the cervical spine. The x-ray films were digitized and used as computer data for calculating the strain distribution. x-ray films were obtained again 5 years later, and the strain distribution and the presence or absence of progression of ossification were evaluated.

Results The progression of ossification of the posterior longitudinal ligament was highly correlated with abnormal strain distribution in the intervertebral discs. Progression of ossification was frequently observed in areas having disc distortion in tension and extension on the posterior longitudinal ligament.

Conclusions In this study, the area of progression of ossification corresponded to the area showing uneven strain distribution and resultant concentration of dynamic stress. These results suggest an important role for dynamic factors in the progression of ossification of the posterior longitudinal ligament.

From the *Department of Orthopaedic Surgery, Faculty of Medicine, Kagoshima University, Kagoshima, Japan, and Department of Mechanical Engineering, Faculty of Engineering, Kagoshima University.

This study was carried out with the aid of the Investigation Committee on the Ossification of Spinal Ligaments, Ministry of Public Health and Welfare, Japan.

Acknowledgment date: September 21, 1994.

First revision date: March 7, 1995.

Second revision date: June 5, 1995.

Acceptance date: June 23, 1995.

Device status category: 1.

Address reprint requests to: Shunji Matsunaga, MD; Department of Orthopaedic Surgery; Faculty of Medicine; Kagoshima University; 8-35-1, Sakuragaoka, Kagoshima; Japan

© Lippincott-Raven Publishers.