Primary Creep Characterization in Porcine Lumbar Spine Subject to Repeated Loading

Area of Science:

• Biomechanics
• Orthopedics
• Spine Research

Background:

• Low back pain (LBP) is a prevalent global condition with often unknown injury causes.
• Lumbar spine injury risk is elevated by flexion and repeated compression, yet its complex viscoelastic behavior under such loading is poorly understood.
• Characterizing non-injurious primary creep is crucial for understanding the biomechanical response preceding lumbar spine injury.

Purpose of the Study:

• To characterize the primary creep behavior of the lumbar spine under repeated flexion-compression loading.
• To model the viscoelastic response of porcine lumbar spinal units using generalized Kelvin-Voigt and quasilinear viscoelastic (QLV) models.
• To determine biomechanical parameters including creep time constants, creep coefficients, and elastic constants.

Main Methods:

• Fifteen porcine lumbar spinal units were subjected to repeated flexion-compression loading, simulating high-speed watercraft occupant exposures.
• Strain response in the primary creep region was modeled using a generalized Kelvin-Voigt model.
• A quasilinear viscoelastic (QLV) approach was employed to differentiate time-dependent creep from stress-dependent elastic responses.

Main Results:

• The generalized Kelvin-Voigt and QLV models accurately represented the experimental data (average R² = 0.997).
• Optimized creep time constants of 24 s and 580 s contributed 20% ± 3% and 30% ± 3% to the overall strain, respectively.
• Non-transient and elastic behaviors accounted for 50% ± 0% and an average standard deviation of 24.5% strain, respectively.

Conclusions:

• The study successfully characterized primary creep in porcine lumbar spines under simulated occupational loading.
• These findings provide essential biomechanical data on the response preceding lumbar spine injury.
• The results can enhance lumbar injury prediction models and kinematic simulations for improved safety measures.