510 - Dynamic Biomechanical Examination of the Cervical Spine Using a Novel...

#510 Dynamic Biomechanical Examination of the Cervical Spine Using a Novel Pendulum System

Basic Sciences-Research

Poster Presented by: S. Esmende

Author(s):

S. Esmende (1)
A. Daniels (1)
S. Koruprolu (1)
D. Paller (1)
M. Palumbo (1)
J. Crisco (1)

(1) Brown University/Rhode Island Hospital, Orthopaedic Surgery, Providence, RI, USA

Abstract

Background: Previous protocols for biomechanical testing of the cervical spine were limited in their ability to apply high physiologic compressive loads or to apply dynamic bending moments while allowing unconstrained three-dimensional motion. To limit the aforementioned limitations, we developed a novel pendulum testing system as a means to study the complex kinematics and the dynamic nature of the cervical spine. The pendulum apparatus is capable of applying physiologic compressive loads dynamically without constraining the motion of the functional spinal unit (FSU). The number of cycles to equilibrium observed under pendulum testing is a marker of the energy absorbed by the FSU. To our knowledge, energy absorption of motion preserving spinal implants under simulated physiologic motion and loading conditions has not previously been described.

Methods: Thirteen unembalmed, frozen human cervical FSUs were tested on the pendulum system with axial compressive loads of 25N, 50N, 100N, chosen to represent physiologic loading (based on head weight in kg). Cervical spine FSUs used were Cervical C3-4 and C5-6. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5° resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was be recorded and bending stiffness (N-m/°) was calculated and compared for each testing mode. Each test was repeated 2X. 3D motion of the superior vertebra relative to the inferior vertebra was measured at 30 Hz using an Optotrak 3020 3D motion tracking system (resolution to 0.01 mm). 6 infrared-emitting diode markers were attached to the upper potting cup and pendulum arm, 6 to the lower FSU. Custom NDI 6D Architect software will be used to define the markers with respect to the coordinate system. A one factor repeated measures analysis of variance was performed (SigmaPlot version 12) to determine is statistical significance existed between bending stiffness under varying compressive load for each test condition (flexion, extension and lateral bending). In all instances, statistical significance was set to p < 0.05 a priori. A Tukey post hoc test was performed to identify statistical differences between load level.

Results: Increasing the compressive pendulum load correlated significantly with a linear increase in bending stiffness or the FSUs. For flexion, the 100N load was significantly stiffer than the 25N and 50N loads (p < 0.05). A Friedman repeated ANOVA on ranks was performed for flexion stiffness. Similarly for extension, the 100N load was also significantly stiffer than both the 25N and 50N loads. In both left and right lateral bending, 100N also were significantly stiffer compared to 25N and 50N.

Conclusion: Bending sitffness increased significantly in flexion, extension, and lateral bending as the compressive load increased. The pendulum apparatus is a simple approach used to determine the dynamic bending properties of the FSU, and potentially in disc arthroplasty studies. Current investigation in the energy absorption of the each the FSUs with increasing load is underway and will be reported upon acceptance of this abstract.