Mini‐open Pedicle Subtraction Osteotomy versus Standard Posterior Approach for Ankylosing Spondylitis‐related Spinal Kyphosis: A Comparative Study

OBJECTIVE: Surgical strategy for spinal kyphosis in patients with ankylosing spondylitis (AS) has been challenging. Pedicle subtraction osteotomy (PSO) through a minimally invasive (MI) approach has been developed with promising clinical outcomes. We aimed to compare the effectiveness and safety of PSO via an MI approach and a standard posterior approach (SPA) for treating AS‐related spinal kyphosis. METHODS: A total of 41 patients with AS‐related spinal kyphosis who underwent PSO through an MI approach (MI surgery [MIS] group: n = 25) or SPA (SPA group: n = 16) between January 2015 and July 2020 were retrospectively included. Spinopelvic parameters were evaluated before the surgery, immediately after the surgery, and at the 2‐year follow‐up. Clinical data including operative time, estimated blood loss, blood transfusion, level of fusion, incision length, bed rest period, length of hospitalization, and surgical complications were compared between the two groups. The Scoliosis Research Society outcomes instrument‐22 (SRS‐22) was administered to assess patients' quality of life at the latest follow‐up. Comparisons between the two groups were performed using independent sample t‐test or Chi‐square test. RESULTS: Characteristics and baseline kyphosis of the two groups were matched. At the 2‐year follow‐up, in the MIS group, the average correction values of the sagittal vertical axis and global kyphosis (GK) were 9.5 cm and 44.3°, respectively. Compared with the SPA group, the MIS group had similar correction values and correction losses after surgery. No obvious differences were observed in any radiographic parameters, except for GK, immediately after surgery and at the 2‐year follow‐up between the two groups (p > 0.05). The MIS group had a significantly shorter operative time, lesser blood loss, lesser transfusion volume, shorter fusion level, and lesser time to mobilization than did the SPA group. Higher average functional activity scores of SRS‐22 were obtained in the MIS group than in the SPA group. CONCLUSION: Mini‐open PSO may be an effective alternative to the SPA for treating AS‐related spinal kyphosis, with comparable correction effect, lesser surgical trauma and faster recovery. This comparative study may provide valuable guidance for surgical decision‐making and patient counseling.