Lumbar Foraminal Stenosis Classification That Guides Surgical Treatment

(a) Type I stable foraminal stenosis. The disc has completely degenerated; the root is squeezed between the upper and lower pedicles. (b) Type II stable foraminal stenosis. The disc has completely degenerated at the base of degenerative spondylolisthesis. The root is squeezed between the upper pedicles and lower vertebral corpus. (c) Type III stable foraminal stenosis. The disc has completely degenerated; the root is squeezed between the calcified facet joint and the corner of the upper pedicles and posterior wall of upper vertebrae. (d) Type IV stable foraminal stenosis. The disc is calcified in some areas and fused in some areas to the upper and lower vertebral corpus, with bulging of the posterior annulus. The root is squeezed between the calcified bulging of the posterior annulus, calcified facet joint, and upper pedicles. For all images, the red areas on the nerve root indicate dense areas where the nerve is squeezed.

(a) Type I unstable foraminal stenosis. There is a mobile degenerative bulged disc, and the root is squeezed mainly between the bulging of the disc and upper pedicles. (b) Type II unstable foraminal stenosis. The disc is degenerative and mobile, but there are degenerative spondylolisthesis and pseudobulging. The root is squeezed between the pseudobulbed disc and the superior pedicle. (c) Type III unstable foraminal stenosis. The disc is degenerative and mobile, and there is no bulging. The root is squeezed between the posterior degenerative facet joint, the corner between the pedicle and the posterior wall, and the vertebral corpus of upper vertebrae. (d) Type IV unstable foraminal stenosis. The disc is degenerative and mobile; the root is squeezed between the posterior degenerative facet joint and synovial cyst of the facet joint, and the only difference from unstable type III is bulging of the disc, which can be related to compression over the nerve root. For all images, the red areas on the nerve root indicate dense areas where the nerve is squeezed.