Biomechanical characteristics of osteotomy correction for kyphosis secondary to ankylosing spondylitis: a finite...

This study comparatively analyzed the biomechanical performance of different vertebral level osteotomies in patients with severe kyphosis secondary to ankylosing spondylitis (ASK) using finite element analysis.

The hilus pulmonis-hip axis (HP-HA) method was employed to determine osteotomy angles. Posterior vertebral column resection (PVCR) was simulated at four distinct vertebral levels (T12, L1, L2, and L3), followed by pedicle screw-rod fixation combined with interbody fusion cages. Total displacement, von Mises stress distribution in the pedicle screw-rod construct, titanium cage, and cage-vertebral interface were evaluated and compared across models.

Four finite element models (A-D, corresponding to T12, L1, L2, and L3 osteotomies) were successfully established and validated. Total displacement decreased progressively from model A to model D, measuring 6.88 mm, 5.44 mm, 3.90 mm, and 2.26 mm, respectively. Peak von Mises stresses in the pedicle screw-rod systems were 115.58 MPa, 139.53 MPa, 191.35 MPa, and 184.14 MPa, respectively. Model D (L3 osteotomy) demonstrated the smallest displacement and well-dispersed stress distribution, while model A (T12 osteotomy) exhibited the largest displacement despite having the lowest screw-rod stress. All stresses remained below the yield strength of the internal fixation devices.

This finite element study demonstrates that L3 osteotomy yields superior stability compared to T12 osteotomy, though the conclusion is based on a single-case model and requires further validation through multicase studies. These findings underscore the importance of considering segment-specific biomechanical factors in surgical planning for ASK patients.