Biomechanical study on the interaction between the extent of lumbar vertebral lamina and facet joint removal and segmental stability: a finite element analysis

This study aimed to establish a finite element model of the lumbar spine, evaluating the impact of lamina and facet joint removal on lumbar stability and stress distribution in posterior structures. A healthy volunteer was randomly selected for developing a preoperative model (M0) through finite element analysis. Depending on the extent of the lateral articular facet joint resection, five intraoperative models M1(A)-M1(E) were built. as five subgroups, and all subgroups underwent the same degree of unilateral laminectomy (with a resection ratio of 50%). Under six different conditions, the models were evaluated for lumbar range of motion and maximum von Mises stress in the intervertebral disc, in the facet joints and in the isthmus. As the extent of surgical resection increased, the maximum stress within the L4-5 intervertebral disc exhibited a progressive upward trend. Compared with M0, M1(A)-M1(E) showed only modest increases in maximum disc stress; in contrast, the extensive resection model demonstrated a more pronounced elevation. In the L4-5 segment, M1(A), M1(B), and M1(C) exhibited slight increases in maximum stress at the left facet joint relative to M0; M1(D) and M1(E) showed progressively greater increases. Under all six loading conditions, the maximum stress at the right L4-5 facet joint increased in M1(A), M1(B), and M1(C) compared with M0. Specifically, during right lateral bending, left rotation, and right rotation, the maximum stress at the right facet joint rose by 12.46–63.27%, 25.67-181.57%, and 18.86-185.09%, respectively. Stress distribution analyses indicated that progressive resection of posterior bony and ligamentous structures elevates mechanical loading on the facet joints and the isthmus—particularly during rotational motions. Extensive posterior resection may induce abnormal stress redistribution and thereby exacerbate segmental instability. Through finite element analysis, this study confirmed that when the partial resection of the unilateral lamina and facet joint was ≤ 50%, the relative biomechanical stability of the L4-5 segment can be maintained; however, when the resection exceeds 50%, it will lead to excessive increase in segmental mobility, abnormal redistribution of stress in the intervertebral disc, facet joint and pedicle, and may cause iatrogenic instability. These findings provide direct biomechanical evidence for defining the safe bone resection threshold in minimally invasive transforaminal lumbar surgery.