Biomechanical Problems Related to the Pedicle Screw System

Area of Science:

• Spinal biomechanics
• Orthopedic surgery
• Biomedical engineering

Background:

• Pedicle screw (PS) systems are widely used in spinal fusion.
• Understanding the biomechanical limitations of PS systems is crucial for improving surgical outcomes.
• Adjacent segment disease and instrumentation failure are common complications.

Purpose of the Study:

• To assess the biomechanical problems associated with pedicle screw (PS) systems.
• To compare the stability of PS systems with and without crosslinks.
• To identify potential causes of adjacent segment disease and instrumentation failure.

Main Methods:

• Functional spinal units (L3-L4) from deer were tested using a 6-axis material testing machine.
• Specimen models included intact, damaged, PS, and crosslink configurations.
• Range of motion (ROM) was measured during bending and rotation tests in multiple directions.

Main Results:

• PS systems demonstrated reduced ROM compared to intact models in all tested directions.
• PS systems showed increased ROM during rotation compared to damaged models but less than intact models.
• Crosslink models offered greater stability during bending than PS models but increased ROM during rotation.

Conclusions:

• Excessive bending rigidity and rotational instability are identified biomechanical problems of PS systems.
• Excessive bending rigidity may contribute to adjacent segment disease.
• Rotational instability is a potential cause of instrumentation failure in PS systems.