Anatomical study of the lumbar isthmus / 中华骨科杂志

ABSTRACT

Objective To provide an anatomic data of the lumbar isthmus, and to increase the fusion rate of the graft bone for spondylolisthesis treated with posterolateral spinal fusion and Steffee plate fixation. Methods The area and volume of the bone graft bed for posterolateral spinal fusion in the lumbar isthmus were studied on 30 dried specimens of adult lumbar spines from L 1 to L 5(a total of 150 lumbar vertebrae) with a vernier calipers, a goniometer and a graduate. Results The length of the superior edge of the isthmus gradually increased from L 1[(7.34? 1.15) mm] to L 5[(10.31? 1.89) mm], and that of its inferior edge progressively decreased from L 1[(6.63? 1.24) mm] to L 5 [( 4.73? 1.21) mm]. The superior edge of the isthmus was the thinnest at L 1[(1.85? 0.64)mm], and the thickness increased inferiorly from L 1[(6.57? 1.24) mm] to L 5[(7.57? 1.16) mm]. The medial and caudal inclination of the isthmus with respect to the pedicle gradually increased from L 1 (113.9?? 13.3? ) to L 5(119.1?? 13.5? ) medial inclination and from (101.2?? 9.5? ) at L 1 to (117.6?? 13.4? ) at L 5 caudal inclination, respectively. The length of the superior edge of the isthmus and the transverse diameter of the pedicle were positively correlated to the vertebral levels. The length of the inferior edge of the isthmus were negatively correlated to the vertebral levels. The dimensions of the graft bed area were postively correlated to dimensions of the graft bone volume. Conclusion The application of firm spinal internal fixation system with adequate graft bed area and adequate graft volume, the maintenance of close contact between the graft bed and the graft bone, and adequate period of postoperative stable contact of the graft in bed were the keys to enable reduction of the spondylolisthesis and to increase the fusion rate of posterolateral bone graft.