Biomechanics of lumbar pedicle subtraction osteotomies and associated reconstructive instrumentation strategies: a comprehensive narrative review

PURPOSE: To perform a narrative review of the biomechanics of lumbar pedicle subtraction osteotomies (L-PSO) and associated surgical constructs. METHODS: A non-systematic literature search was performed. PubMed was queried for investigations published between 2010 and 2025 with the following search terms: "lumbar", "PSO", "biomechanics, "finite element analysis", "cadaver". Studies evaluating biomechanical properties of L-PSO (L1-L5) constructs were included. Clinical studies and non-lumbar level (cervical/thoracic) PSOs were excluded. RESULTS: L-PSOs create a highly destabilized environment, particularly in axial rotation. Two-rod constructs significantly reduce range of motion (ROM) relative to the uninstrumented spine but are associated with high rod stresses. Multi-rod constructs (satellite and accessory rods) consistently reduce ROM and primary rod stresses, although the magnitude of benefit varies across studies and configurations. Rod material (cobalt chrome) and increased rod diameter further enhance construct rigidity but may increase stress shielding. Cross-links may increase rod stress when placed near a L-PSO site, while monoaxial screws increase construct stiffness compared to polyaxial screws. Interbody cages placed adjacent to L-PSOs improve load sharing and reduce posterior rod strains, particularly when used in a "sandwich" configuration. Biomechanical improvements, such as reduced rod strain and ROM, have not been directly linked to clinical outcomes, including fusion rates or rod fractures. CONCLUSIONS: While biomechanical studies demonstrate multi-rod constructs and adjunct techniques improve construct stability, the relationship between these biomechanical advantages and clinical outcomes, including osseous healing and rod fractures, remains unclear. In L-PSOs, increasing construct rigidity alone is not the primary goal; instead, optimal load sharing across the osteotomy site is a critical biomechanical consideration. As such, future work should focus on elucidating the optimal balance between protecting posterior instrumentation through construct rigidity and preserving adequate compressive forces across L-PSOs, integrating biomechanical findings with clinical data, and developing patient-specific biomechanical modeling to further refine L-PSO instrumentation techniques.