Pedicle screws are essential implants in spinal fusion and fracture stabilization surgeries. Two common types — Polyaxial Pedicle Screws and Monoaxial Pedicle Screws — differ significantly in design, ease of use, and biomechanical performance.

Polyaxial Pedicle Screws feature a movable head that allows multi-planar angulation (up to 25–30 degrees or more). This flexibility makes rod insertion easier, especially in minimally invasive or complex anatomies with variable pedicle alignment. Surgeons appreciate the reduced stress at the screw-bone interface during placement and the convenience in contouring rods. However, the mobile head can lead to slightly lower construct stiffness and potential loss of correction over time due to possible slippage at the head-shaft interface.

Monoaxial Pedicle Screws have a fixed head-shaft relationship, creating a rigid, angular-stable construct. This design provides stronger leverage, enabling better restoration of vertebral height, improved correction of kyphotic deformity, and superior maintenance of reduction in thoracolumbar fractures. Biomechanical studies show monoaxial screws offer greater stability in flexion-extension and higher resistance to correction loss, making them particularly effective for short-segment fixation in trauma cases.