Development of a multisegmental test body to calibrate and validate studies with spinal testing devices with follower load

Abstract

Spinal testing devices need a tool for calibration and comparison of accomplished studies. The objective of this study was the development of a polysegmental test body, which simulates several functional spinal motion units and provides a standard calibration. The test body consists of aluminum moldings simulating the vertebral bodies, rubber discs simulating the intervertebral discs and cylindrical guide elements with ball joints simulating the vertebral joints. The test body was tested multidirectional with a moment of 7.5 Nm and follower loads up to 800 N. The results showed sigmoid load-deformation curves of the test body similar to a human lumbar cadaver spine, but with a higher range of motion (ROM). The follower load had no influence during extension-flexion, but an increasing follower load during lateral bending and rotation caused increased friction and restoring forces with a decrea-sed ROM. The polysegmental test body does not show the same mechanical behavior like a polysegmental human cadaver spine in all directions of motion, but it provides reproducible values without requiring preconditioning as proposed for human specimen. This test body could improve the comparability of cadaver studies performed with different spinal testing devices by standardization of the test set-ups.