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Load displacement behavior of the human lumbo-sacral joint
K M McGlashen1, J A Miller, A B Schultz
1Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor 48109.
Summary
This study analyzed the biomechanics of the L5-S1 spinal motion segment. Removing posterior elements significantly increased spinal segment motion, indicating their crucial role in stability.
Area of Science:
- Biomechanics
- Spinal Anatomy
- Orthopedic Research
Background:
- The L5-S1 spinal motion segment is critical for load-bearing and movement in the lower back.
- Understanding its mechanical behavior is essential for diagnosing and treating spinal disorders.
Purpose of the Study:
- To investigate the three-dimensional load-displacement characteristics of the L5-S1 spinal motion segment.
- To quantify the effect of posterior element excision on spinal segment stability and motion.
Main Methods:
- Tested nine fresh adult L5-S1 spine motion segments under various static loads and moments.
- Measured displacements and rotations of the inferior L5 endplate.
- Retested specimens after posterior element excision to assess stability changes.
Main Results:
- Intact L5-S1 segments exhibited displacements up to 2.21 mm in posterior shear and rotations up to 7.19 degrees in flexion.
- Posterior element excision increased shear translations by an average of 1.66-fold.
- Excision led to greater increases in bending (2.09-fold) and torsional (2.74-fold) rotations.
Conclusions:
- The L5-S1 spinal motion segment demonstrated significant stability, particularly in flexion, extension, and lateral bending.
- Posterior elements are vital for maintaining L5-S1 spinal stability.
- The L5-S1 segment is stiffer in bending but less stiff in torsion compared to more cranial lumbar segments.