What are the optimal disc height changes for successful indirect decompression with OLIF? Analysis of pre- and postoperative parameter changes up to 1 year

Study design : Retrospective study. Objective : To evaluate the associated factors for successful indirect decompression by assessing the changes in disc height and spinal canal width. Methods : This study included 63 patients and 104 involved surgical levels. The efficacy of OLIF for lumbar spinal stenosis on spinal canal and foramen before and after surgery was analyzed up to 1 year. Radiologic parameters were anterior disc height (ADH), posterior disc height (PDH), lumbar lordotic angle (LL), segmental lordotic angle (SL), foraminal height (FH), cross-sectional area (CSA) of the spinal canal, cross-sectional foraminal area (CSF), and subsidence (SD). Results : Comparing pre- and postoperative values, the mean CSA and CSF were significantly increased (p < 0.001). FH increased from 15.23 ± 3.48 mm to 18.78 ± 2.93 mm and was stable for up to 1 year (p < 0.0001). The VAS leg and ODI scores significantly improved after surgery (P < 0.05). Changes of immediate postoperative and 1-year FH were significantly related to 1 year ADH, PDH, and VAS leg changes (P < 0.05). The group showing 1-year FH improvement (positive(+) group) demonstrated significantly larger immediate postoperative ADH and PDH changes compared with the FH negative(-) group (6.46 mm vs. 4.52 mm, p = 0.038; 3.59 vs. 2.40, P < 0.001, respectively). The CSF positive(+) group also showed significantly higher immediate postoperative ADH and PDH changes (6.24 mm vs. 4.55 mm, p = 0.043; 3.00 vs. 1.57, P = 0.010, respectively). Conclusions OLIF provided satisfactory indirect decompression up to 1 year. Considering the increase of foraminal height, we recommend more than 3.0 mm of immediate postoperative PDH increase, avoiding over-distraction of disc space.