Variations Among Human Lumbar Spine Segments and Their Relationships to In Vitro Biomechanics: A Retrospective Analysis of 281 Motion Segments From 85 Cadaveric Spines

Background: Biomechanical properties of intact spinal motion segments are used to establish baseline values during in vitro studies evaluating spinal surgical techniques and implants. These properties are also used to validate computational models (ie, patient-specific finite element models) of human lumbar spine segments. Our laboratory has performed a large number of in vitro mechanical studies of lumbar spinal segments, using a consistent methodology. This provides extensive biomechanical data for a large number of intact motion segments, along with donor demographic variables, bone mineral density (BMD) measurements, and geometric properties. The objective of this study was to analyze how donor demographics, BMD, and geometric properties of cadaveric lumbar spine segments affect motion segment flexibility, including the range of motion (ROM), lax zone (LZ), and stiff zone (SZ), to help improve our understanding of spinal biomechanics.

Methods: A retrospective study examined the relationships between the biomechanical properties of 281 lumbar motion segments from 85 human cadaveric spines, donor demographic variables (age, sex, weight, height, and body mass index), and specimen measurements (vertebral body height, intervertebral disc height, and BMD).

Results: Statistical correlation and regression analyses showed that the flexibility of a lumbar motion segment is affected by lumbar level, donor age, sex, and weight as well as the intervertebral disc height, vertebral body height, and bone quality. Increased disc height was associated with decreased ROM (axial rotation), decreased LZ (flexion-extension and axial rotation), and increased SZ (flexion-extension and lateral bending) in the male group, but increased ROM (lateral bending) in the female group. Increased vertebral body height correlated with increased LZ (lateral bending) in the female group. Increased BMD correlated with decreased ROM overall.

Conclusions: Biomechanical measurements from flexibility testing of cadaveric lumbar spine segments are significantly correlated with donor demographics and specimen measurements. Many of these correlations are sex-dependent.