Comparative analysis of changes in spinal dimensions following different correction methods in adult spinal deformity surgery

Background: Adult spinal deformity (ASD) surgery has gained popularity, with significant improvements in patient-reported outcomes. Posterior lumbar interbody fusion with multiple grade II osteotomies (PLIF + MOs) and lateral lumbar interbody fusion (LLIF) have been utilized to correct ASD; however, no studies have compared these methods with regard to the pre- and postoperative changes in length and volume of the spinal canal. This study aimed to investigate the 3-dimensional changes in the anterior vertical column length (AVCL), spinal canal length (SCL), and spinal canal volume (SCV) in patients with ASD after surgery, employing LLIF and PLIF + MOs. Methods: This retrospective study examined 44 patients with ASD who underwent surgery between 2010 and 2021 using two corrective surgical methods, LLIF and PLIF + MOs. Radiographic parameters and clinical outcomes were assessed, and three-dimensional models were created from computed tomography images to analyze changes in AVCL, SCL, and SCV. Results: We compared the effects of LLIF and PLIF + MOs on spinal canal dimensions during ASD surgery. LLIF demonstrated an increase in lumbar segment (L1-S1) AVCL and whole spine (T1-S1) SCL by 6.5 +/- 8.0 mm and 13.8 +/- 7.6 mm, respectively, compared with PLIF + MOs. However, PLIF + MOs exhibited a reduction in the lengths of the lumbar segment AVCL. Postoperative differences were significant for AVCL (L1-S1), SCL fusion level, and first-standing lumbar lordosis between the groups (p < 0.0001, 0.002, and 0.016, respectively). LLIF significantly increased the SCV at the fusion level and whole spine T1-S1 by 14.5% and 10.6%, respectively, outperforming PLIF + MOs. Despite changes in dimensions, the postoperative Oswestry disability index scores showed no significant difference between the two groups. Conclusions: Our study suggests that LLIF can increase spinal canal space, lumbar lordosis, and anterior column length in the lumbar spinal segment. Knowledge of these variations may be critical for enhancing surgical outcomes and preventing neurological complications.