A method to simulate in vivo cervical spine kinematics using in vitro compressive preload

Area of Science:

• Biomechanics
• Spinal research
• Orthopedics

Background:

• Previous 3D in vitro cervical spine studies often used equal moments, which may not accurately reflect in vivo conditions.
• Recent advancements allow for physiologic compressive preload application in vitro.
• Optimal moment application for preloaded cervical spine segments to mimic in vivo kinematics remains unclear.

Purpose of the Study:

• To determine the specific three-dimensional (3D) flexibility test moments required for in vitro cervical spine (C2-T1) kinematics that accurately represent in vivo data.
• To compare two different moment application protocols under compressive preload.

Main Methods:

• Six fresh human cadaveric cervical spine specimens (C2-T1) were tested.
• A 100 N compressive preload was applied using flexible cables.
• Flexibility tests included flexion-extension, axial torsion, and lateral bending.
• Two protocols were compared: 1:1:1 (equal moments) and 2:4:2 (differential moments).

Main Results:

• The 2:4:2 protocol demonstrated significantly better agreement with in vivo data compared to the 1:1:1 protocol.
• For flexion-extension, the 2 Nm moment in the 2:4:2 protocol was within 17% of in vivo values.
• For axial torsion, the 4 Nm moment was within 22% of in vivo values.
• For lateral bending, the 2 Nm moment was within 15% of in vivo values.

Conclusions:

• The 2:4:2 moment protocol is recommended for in vitro testing of the human cervical spine (C2-T1) with a 100 N preload.
• This protocol yields spinal kinematics that closely represent in vivo conditions.