Proximal Lower Extremity Weakness Following Pedicle Subtraction Osteotomy in Adult Spinal Deformity: Influence of Correction Level and Clinical Outcomes.

Background Neurological paralysis, particularly proximal lower extremity muscle weakness (PW) involving the iliopsoas and quadriceps, is a severe complication of surgery for adult spinal deformity (ASD) that significantly impairs ambulatory function and can delay postoperative rehabilitation and reduce quality of life. However, it remains unclear at which spinal level correction is most likely to induce PW. Therefore, this study aimed to identify the spinal level at which correction after ASD surgery is most likely to cause PW to help optimize surgical planning and postoperative recovery. Methodology To investigate the relationship between the pedicle subtraction osteotomy (PSO) correction level and the development of PW, we analyzed cases in which PSO was performed at a single vertebral level without changes to the alignment of other spinal segments. A total of 85 patients who underwent PSO for adult spinal deformity, including staged surgery or correction of iatrogenic kyphosis, were included. In staged cases, corrective procedures other than PSO were performed during the first stage without any weakness, and only PSO was performed during the second stage; patients who underwent PSO at the second stage were included in this analysis. Inclusion criteria were single-level PSO with complete pre- and postoperative radiographs and postoperative neurological assessment. Exclusion criteria were prior anterior/anterolateral spinal surgery and preoperative weakness of the iliopsoas or quadriceps. PW was defined as a manual muscle testing (MMT) score <3 for the iliopsoas and quadriceps muscles on postoperative day one. The incidence of PW was evaluated at each PSO level, and demographic characteristics and pre-/postoperative radiographic parameters were compared between the PW and non-PW groups. Results The vertebrae that underwent PSO were as follows: T8 (n = 1), T9 (n = 1), T11 (n = 1), T12 (n = 11), L1 (n = 6), L2 (n = 9), L3 (n = 15), L4 (n = 26), and L5 (n = 15). PW occurred in 20 patients (4 males, 16 females). PW occurred predominantly at the lower lumbar levels (L4-L5): 1/15 (6.7%) at L3, 12/26 (46.2%) at L4, and 7/15 (46.7%) at L5. PW resolved in all patients within one year of surgery, with the exception of one who was lost to follow-up. A significant difference was observed in the preoperative L4-S1 angle in the radiographic data (25.8° vs. 15.8°, p < 0.001). Conclusions PW occurred particularly frequently after the correction of kyphosis of the lower lumbar spine (L4 or L5), but the prognosis was favorable, with recovery in most cases within one year. Clinically, surgeons should anticipate this risk during lower lumbar correction and consider preventive strategies to reduce nerve root traction, such as minimizing prolonged hip extension intraoperatively and maintaining hip and knee flexion postoperatively in the early postoperative period.