Single-Side Iatrogenic Pedicle Injury May Trigger an Increased Risk of Contralateral Screw Loosening: An In Silico Study

Abstract

Background

Screw loosening is a frequently reported complication following pedicle screw fixation, resulting in various adverse outcomes. The primary trigger for screw loosening is biomechanical deterioration. Iatrogenic injury to the pedicle is a commonly observed scenario. This alteration can lead to an increased risk of pedicle screw loosening. Bilateral pedicle screws distribute load during the patient's daily activities and can be regarded as an integrated structure from a biomechanical perspective. Consequently, biomechanical interactions are prevalent between the two sides of the pedicle screws. This study aimed to determine whether unilateral pedicle injury influences contralateral screw loosening by deteriorating the local biomechanical environment.

Methods

The numerical model of the L5 vertebral body, developed in our previous studies, was employed in this investigation. Bilateral pedicle screws were inserted following the standard trajectory. Simulations of both half and complete ventral and dorsal side pedicle injuries were performed on the right-side pedicle. Stress and strain values of the screw trajectory, along with screw displacement values on the contralateral side, were recorded to assess the potential risk of screw loosening.

Results

Compared to the model without pedicle injury, models with pedicle injuries exhibited higher interfacial stress and strain, as well as greater screw displacement. This effect was particularly pronounced when the pedicle on the side of torque restriction (e.g., caudal side pedicle injury under the flexion loading condition) was considered. Furthermore, unilateral iatrogenic injury to the pedicle can trigger multi-degree-of-freedom coupled motion under a single-direction torque.

Conclusions

Single-side iatrogenic pedicle injury can lead to multi-degree-of-freedom coupled motion of the screw-fixed vertebral body, and biomechanical deterioration of the contralateral screw trajectory, thereby increasing the risk of contralateral pedicle screw loosening.