General Session: Biomechanics
Presented by: A. Newcomb - View Audio/Video Presentation (Members Only)
A. Newcomb(1), J. Lehrman(1), B. Kelly(1), N. Crawford(1)
(1) Barrow Neurological Institute, Spinal Biomechanics Lab, Phoenix, AZ, United States
Background: Kinematic data from in vitro flexibility tests involving cadaveric spines are often used to validate finite element models of human spine segments. Despite a relatively wide range of kinematic data available in the literature, data describing the relationships between motion segments´ distinct features (i.e. general size of vertebral body and disc, subject's height, BMD, etc.) and its flexibility are lacking.
Purpose: To retrospectively study the relationships between cadaveric lumbar spinal motion segments and their biomechanical characteristics.
Study Design: Standard nondestructive flexibility tests were performed on intact lumbar spine segments. Relationships between donor spine features and in vitro range of motion (ROM) were studied using Pearson correlation analyses.
Patient Sample: 282 cadaveric lumbar motion segments (from L1 to S) from 85 donor spines [47 M/38 F, range: 21-73 yrs, mean age 54.1+/-10.9 yrs, BMD 0.819+/-0.169 g/cm2, mean subject height 1.73+/-0.09 m].
Outcome Measures: Spinal flexibility of intact motion segments was assessed using intervertebral mean range of motion (ROM) during flexion-extension, lateral bending, and axial rotation.
Methods: General spine tissue donor information (age, gender, height) was obtained from medical histories provided by tissue banks. Vertebral body heights, disc heights, and bone mineral densities (BMD) were obtained from x-rays and DEXA scans of the dissected spines. Kinematic data was retrieved from studies involving intact testing of the fresh frozen lumbar spine segments (L1 through S), with all tests performed in the same lab and using the same methods. Loads of 7.5 Nm were applied while measuring intervertebral flexion-extension (FL-EX), lateral bending (Lat Bend, average right and left), and axial rotation (Ax Rot, average right and left), optoelectronically. Relationships between donor information (subject height), spine segment features (BMD, vertebral body height, disc height) and ROM were studied using Pearson correlation analysis (p< 0.05).
Results: There were significant negative correlations between ROM and subject height (Figure 1), and ROM and disc height (Figure 2). Other significant correlations with ROM include: donor age [Ax Rot: R=0.243, P< 0.001], BMD [all directions: R< -0.16, P< 0.007], and vertebral body height [FL-EX: R=0.186, P=0.006, and Lat Bend: R=0.136, P=0.046]. There were no relationships between ROM and donor age during FL-EX (R=-0.016, P=0.791) or Lat Bend (R=0.023, P=0.700). Similarly, there was no correlation between ROM and body height during Ax Rot (R=0.094, P=0.170).
Discussion: Significant relationships exist between lumbar spine segments' geometric, material and biomechanical properties. These factors need to be considered during the validation process of finite element models involving human lumbar spine segments.
Figure 1 ROM vs. Subject Height
Figure 2 ROM vs. Disc Height