Preload substantially influences the intervertebral disc stiffness in loading-unloading cycles of compression

Area of Science:

• Biomedical Engineering
• Biomechanics
• Spinal Research

Background:

• Intervertebral disc hydration influences load distribution and time-dependent mechanical properties.
• Understanding disc mechanics is crucial for diagnosing and treating spinal conditions.

Purpose of the Study:

• To investigate how varying compression preload magnitudes affect spinal disc axial cyclic compression stiffness.
• To evaluate the impact of preload on disc height and stiffness under physiological loading conditions.

Main Methods:

• Bovine disc-bone and isolated disc specimens were hydrated for 20 hours.
• Specimens were subjected to different preload magnitudes (0, 0.06, 0.28 MPa) for eight hours.
• Axial cyclic compression tests were performed to measure disc height changes and stiffness.

Main Results:

• A 0.06 MPa preload resulted in greater height loss than recovery, leading to progressive height reduction and increased stiffness.
• Higher preloads (0.28 MPa) showed significant differences in height loss and stiffness compared to lower preloads (0 and 0.06 MPa).
• Disc preload magnitude and history significantly influence disc stiffness and height loss during loading/unloading cycles.

Conclusions:

• Disc preload magnitude and hydration level are critical determinants of disc stiffness and height loss.
• Achieving proper preconditioning and hydration is essential for accurate simulation of in vivo disc height recovery.