Anatomical study of correlation between lumbar disc heights and intervertebral foramen and nerve roots

Objective:To observe the morphological changes and the result of disc height vertical loss in lumbar spine and provide the anatomy basis for clinical diagnosis and treatment of stenosis of intervertebral foramina and compression of nerve roots.Methods:Six adult cadaveric lumbar spine of L_1 to S_1 were measured to dynamicly evaluate the anatomic relations of the vertical and sagittal dimensions of the intervertebral foramens to the adjacent neural structures.There were 6 cadavers with normal disc space height in the control group (group A).As test groups (group B,C,D,E),the same cadavers were used after disc removal,4,3,2 and 1 mm silicone rubber discs were inserted and pressured in axial respectively. Results:For group A,the nerve roots were located in the upper part of the foramina,and pass across the foramina obliquely.The diameter of the ventral root gradually increased from L_1(1.1±0.3) mm to L_5 (2.0±0.9) mm.The diameter of the dorsal root gradually increased from L_1 (2.0±1.1) mm to L_5 (3.8±0.4) mm.The major dorsal root ganglion gradually increased from L_1(3.9±0.8) mm to L_5 (7.1±0.9) mm.On the sagittal aspect of the foramina,the ventral root were located in 5:00 or 7:00 of the dorsal root ganglion.For group B,the vertical dimensions of all the foramina were reducted,but the nerve root were not oppressed.For group C,the foramina of L_ 3,4 ,L_ 4,5 and L_5S_1 became narrower vertically,the nerve root and nerve root ganglion were oppressed between the protrudent disc and the inferior border of the foramen.For group D,sagittal oppression occurred in the nerve root of L_4 and L_5.Compared with group A in group E,the frontal angle of the nerve root of L_3 from(33.6°±6.5°) aggrandized to (39.7°±7.1°),L_4 from (29.3°±7.5°)aggrandized to (40.1°±5.2°) and L_5 from (20.1°±5.3°) aggrandized to (46.2°±7.3°).Conclusion:Disc height ≤3 mm may be used as reference standard for the diagnosis of the foraminal stenosis in lower lumbar spine.Key surgical treatment of the foraminal stenosis includes decompressing the foramen,recovering the height of the disc,and spinal fusion using pedicle screw instrumentation.Such surgical treatmet is recommended for failed nonsurgery cases.