Measurement of a spinal motion segment stiffness matrix

Area of Science:

• Biomechanics
• Spinal Mechanics
• Orthopedics

Background:

• Spinal motion segments exhibit complex six-degrees-of-freedom elastic behavior.
• This behavior can be characterized by a stiffness matrix.
• Understanding spinal mechanics is crucial for diagnosing and treating spinal disorders.

Purpose of the Study:

• To develop and validate a direct method for measuring the stiffness matrix of spinal motion segments.
• To investigate the effect of axial preload on spinal motion segment stiffness under physiological conditions.

Main Methods:

• A novel method was employed to measure the stiffness matrix directly.
• Measurements were conducted on a pig lumbar spinal motion segment in an isotonic fluid bath.
• Forces and moments were recorded for six orthogonal translations and rotations under varying axial preload (0 N and 500 N).
• Linear least squares analysis assuming a symmetric matrix was used to derive the stiffness matrix from load-displacement data.

Main Results:

• The study successfully measured the stiffness matrix of the spinal motion segment.
• A significant stiffening effect was observed when a 500 N axial preload was applied.
• Axial preload substantially altered the elastic behavior of the spinal motion segment.

Conclusions:

• The described method enables direct measurement of spinal motion segment stiffness matrices under physiological conditions.
• Axial preload plays a critical role in modulating spinal stiffness.
• These findings contribute to a better understanding of spinal biomechanics and may inform clinical interventions.