2008 年 22 巻 1 号 p. 17-22
Factors affecting titanium cage subsidence after anterior cervical fixation were evaluated in 31 patients who were radiologically followed-up for at least 1 year. Cage subsidence was defined as significant when the cage sank into the vertebral endplate to a depth of 2 mm or more. Subsidence occurred at 16 of 47 intervertebral spaces, and was invariably prominent at the antero-inferior side of the cages. Box-type cages (Syncage-C, Synthes) were more preventive against subsidence than cylindrical cages (Amslu, Eurosurgical) requiring reaming of the endplate. Box-type cage subsidence occurred exclusively at malaligned intervertebral spaces with a flexibility of 10 degrees or more, however, the contents (local bone fragment vs. hydroxyapatite plate) or position (between the anterior vertebral cortex vs. behind the cortical surface) of the box-type cage had no influence on the subsidence. The results imply that mechanical load is an essential factor causing cage subsidence. Prediction of subsidence seems to be possible by measuring segmental flexibility and an optimal operative procedure can thus be chosen to improve the architectural outcome after anterior fixation of the cervical spine.