Specific foraminal changes originate from degenerative spondylolisthesis on computed tomographic images

Purpose Operative treatment for degenerative spondylolisthesis (DS) is accompanied by the high incidence of nerve injury. Foraminal structures, especially the hypertrophied facet joints, have significant impacts on the adjacent nerve. This study aims to identify the specific foraminal changes relating to DS and nerve injury. Methods The CT images of 70 patients with DS and 50 patients without lumbar disease were collected. The length and height of the foraminal structure were measured horizontally and vertically on sagittally reconstructed images. Horizontal stenosis, meaning to pending compression to nerve root after complete reduction, was evaluated on the image located to the middle of the foramen. Chi-square test or T -test were carried out using SPSS 26.0. Results The hyperplasia of the superior articular process (SAP) and articular capsule (Ac) incidence rates in DS group was significantly more common than that of the control group (9.2 vs 0.0%, 42.9 vs 2.0%). The height and width of the SAP and Ac in vertical and horizontal directions were significantly greater than those in the control group (4.95 mm vs − 0.47 mm, P < 0.0001; 3.28 vs 0.02 mm, P < 0.0001; 5.27 vs3.44 mm, P < 0.0001; 2.60 vs 0.37 mm, P < 0.0001). In the DS group, hyperplasia of the SAP and Ac accounted for 9 and 43% respectively, 85 and 45% of which were accompanied by horizontal stenosis of the intervertebral foramen. Conclusion DS is usually characterized of excessive hyperplasia of the SAP and Ac, both of which are possible elements of nerve root injury after complete reduction in operation and should be focused on during surgery.