Minor lateral pedicle wall breach patterns reduce construct stiffness without substantial stress amplification in posterior pedicle screw fixation

Pedicle screw fixation is widely used to restore spinal stability. However, breaching of the lateral pedicle wall remains a clinically relevant complication associated with screw malposition. Using finite element analysis, this study aimed to evaluate the biomechanical effects of different lateral pedicle wall breach patterns following placement of pedicle screw fixation constructs. A three-dimensional finite element model of the L1–L5 lumbar spine was established and used to simulate one-level posterior fixation at L3–L4. Eleven models were analyzed, including an intact model, a correctly instrumented fixation model, and nine malposition models with different distributions of pedicle screws breaching the lateral pedicle wall. All fixation constructs used titanium alloy pedicle screws and rods. Biomechanical responses were assessed under flexion, extension, lateral bending, and axial rotation. The maximum von Mises stress in the pedicle and screw, together with the construct stiffness, was compared among the models. Breaching the lateral pedicle wall did not result in a substantial increase in peak stress in the pedicle or screw in most malposition models. In contrast, the construct stiffness was reduced in nearly all breach configurations relative to the correctly instrumented model. The magnitude of stiffness reduction was influenced by both the number and distribution of breached pedicles. Nevertheless, even the least stable malposition model retained over 45% of the stiffness of the correctly instrumented construct. In healthy bone, minor lateral pedicle wall breaches (< 2 mm) did not substantially increase peak pedicle or screw stress under the simulated static loading conditions but could reduce construct stiffness. The magnitude of stiffness reduction depended on both the spatial distribution of the breached screws and the loading direction, with the greatest reductions occurring during lateral bending and axial rotation in selected malposition configurations. These findings indicate that minor lateral breach may preserve substantial residual fixation stiffness, although the results should not be extrapolated to long-term implant failure or clinical stability thresholds.