Loading of pedicle screws within the vertebra

Area of Science:

• Spine Biomechanics
• Orthopedic Surgery
• Biomedical Engineering

Background:

• Pedicle screws are crucial for spinal instrumentation, but their loading characteristics are not fully understood.
• Previous methods for estimating pedicle screw loading include finite element analysis and external strain measurements.
• A precise understanding of in-situ bending moments is needed to optimize spinal construct design and prevent failure.

Purpose of the Study:

• To hypothesize and test if pedicle screw bending moments can be accurately characterized using a mathematical model.
• To experimentally measure bending moments at multiple locations along the pedicle screw shaft.
• To develop and validate a mathematical model for predicting pedicle screw loading within a vertebra.

Main Methods:

• Utilized cadaveric lumbar spine (L4) motion segments instrumented with unique pedicle screw transducers.
• Loaded the instrumented vertebrae axially in a corpectomy model.
• Measured bending moments at three distinct locations along the threaded shaft of the pedicle screws.

Main Results:

• Pedicle screw bending moments were highest near the screw hub and decreased non-linearly towards the tip.
• A mathematical model was successfully fitted to the experimental bending moment data.
• The developed model accurately described the loading response of pedicle screws within the vertebral body.

Conclusions:

• The study successfully characterized pedicle screw bending moments using a novel mathematical model.
• This model validates prior analytical approaches and offers a predictive tool for spinal construct design.
• The experimental model serves as a valuable resource for validating finite element analyses of pedicle screw loading.