Expanded Combined Loading Injury Criterion for the Human Lumbar Spine Under Dynamic Compression

Area of Science:

• Biomechanics
• Spine Injury Biomechanics
• Injury Risk Assessment

Background:

• Current lumbar spine injury tolerance models for under-body blast scenarios are limited to axial compression and bending moments.
• Injuries frequently involve a broader range of flexion/extension and greater moment contributions, necessitating expanded injury criteria.

Purpose of the Study:

• To expand a previously proposed combined loading injury criterion for the human lumbar spine.
• To incorporate eccentric loading data to augment the applicability of existing injury criteria.
• To propose a refined combined loading injury risk model using survival analysis.

Main Methods:

• Fifteen cadaveric lumbar spine failure tests with high eccentric loading magnitudes were analyzed.
• Survival analysis was employed to develop a loglogistic injury risk model.
• Optimized critical values for resultant sagittal force (F_r,crit) and bending moment (M_y,crit) were determined.

Main Results:

• Optimized critical values for the combined loading metric were F_r,crit = 6011 N and M_y,crit = 904 Nm.
• A combined loading metric value of 1 corresponded to a 50% probability of injury.
• Eccentric loading increased bending moment contribution and reduced resultant sagittal force contribution compared to previous models.

Conclusions:

• The refined injury criterion expands the applicability to a wider range of flexion/extension for the human lumbar spine under dynamic compression.
• The updated model provides a more comprehensive assessment of lumbar spine injury risk during blast events.
• These findings are critical for improving safety measures and protective equipment design.