The Influence of Pedicle Screw Compression Direction on Lumbar Lordosis in Fusion Surgery

Study Design: A prospective, crossover clinical study. Objective: To evaluate whether the direction of pedicle screw compression influences segmental lordosis in lumbar fusion surgery and validate previous in vitro biomechanical findings in a clinical setting. Summary of Background Data: Restoring sagittal balance is crucial in lumbar fusion surgery to prevent adjacent segment degeneration and mechanical complications. Previous biomechanical studies have suggested that the sequence of screw locking and compression may significantly impact the degree of lordosis achieved. However, these findings have not been systematically tested in a clinical setting. Methods: A total of 20 patients undergoing 1-level or 2-level lumbar fusion at 2 institutions were enrolled. Each patient was subjected to 2 different compression techniques in a randomized order. In Method A (conventional technique), the caudal screw was locked first, and compression proceeded cranially. In Method B, the cranial screw was locked first, and compression proceeded caudally. Intraoperative fluoroscopic images were analyzed to measure the change in lordotic angle before and after compression. A Wilcoxon signed-rank test was used to compare the lordotic gain between the 2 methods. Results: The mean lordotic gain with Method A was 3.85 degrees (range: 1–7 degrees), while Method B resulted in a significantly greater mean gain of 6.02 degrees (range: 3–12 degrees), representing a 56.3% increase ( P <0.001). Method B produced greater lordosis in 18 of 20 cases, with no difference observed in 2 cases. Conclusions: This study confirms that the sequence of pedicle screw compression significantly influences lordosis gained during lumbar fusion surgery. Locking the cranial screw first and compressing caudally (Method B) resulted in superior lordotic restoration. These findings provide a simple, intraoperative technique to enhance sagittal alignment, potentially improving long-term surgical outcomes.