Effect of compressive follower preload on the flexion–extension response of the human lumbar spine

Abstract

Traditional experimental methods are unable to study the kinematics of whole lumbar spine specimens under physiologic compressive preloads because the spine without active musculature buckles under just 120 N of vertical load. However, the lumbar spine can support a compressive load of physiologic magnitude (up to 1200 N) without collapsing if the load is applied along a follower load path. This study tested the hypothesis that the load–displacement response of the lumbar spine in flexion–extension is affected by the magnitude of the follower preload and the follower preload path. Twenty‐one fresh human cadaveric lumbar spines were tested in flexion–extension under increasing compressive follower preload applied along two distinctly different optimized preload paths. The first (neutral) preload path was considered optimum if the specimen underwent the least angular change in its lordosis when the full range of preload (0–1200 N) was applied in its neutral posture. The second (flexed) preload path was optimized for an intermediate specimen posture between neutral and full flexion. A twofold increase in flexion stiffness occurred around the neutral posture as the preload was increased from 0 to 1200 N. The preload magnitude (400 N and larger) significantly affected the range of motion (ROM), with a 25% decrease at 1200 N preload applied along the neutral path. When the preload was applied along a path optimized for an intermediate forward‐flexed posture, only a 15% decrease in ROM occurred at 1200 N. The results demonstrate that whole lumbar spine specimens can be subjected to compressive follower preloads of in vivo magnitudes while allowing physiologic mobility under flexion–extension moments. The optimized follower preload provides a method to simulate the resultant vector of the muscles that allow the spine to support physiologic compressive loads induced during flexion–extension activities. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.

Dynamics of an Intervertebral Disc Prosthesis in Human Cadaveric Spines

“…Comparatively, the stiffness values in the TDRimplanted spinal segments increased with increased compressive load in flexion/extension by 31% and by 7% in lateral bending. This finding is supported by other studies in which an increase in compressive load across the joint space decreased ROM [24] and increased stiffness during flexion/ extension [14,[25][26][27] and lateral bending [14,25,26].…”

En bloc spondylectomy reconstructions in a biomechanical in-vitro study

“…In contrast to the present study, different publications investigated the effect of compressive preload [41,42,45,55] on biomechanical testing of spinal specimens. Inducing preloads higher (500-1200 N) than the physiologic 350 N [3] in upright standing resulted in ROM reductions between 15 and 25% [41]. The present study used preloads of 100 N for implantation while motion analysis was performed without.…”

“…However, using pure moments for implant testing is a widely accepted method to imitate in vivo circumstances [39,66,67]. In contrast to the present study, different publications investigated the effect of compressive preload [41,42,45,55] on biomechanical testing of spinal specimens. Inducing preloads higher (500-1200 N) than the physiologic 350 N [3] in upright standing resulted in ROM reductions between 15 and 25% [41].…”

Role of intra-abdominal pressure in the unloading and stabilization of the human spine during static lifting tasks

“…1). The nonlinear load-displacement response under single and combined axial/shear forces and moments along with the flexion versus extension differences were represented in this model based on numerical and measured results of previous single-and multi-motion segment studies [59,60,66,67,75]. In all cases, based on the mean body weight of our subjects and percentage of body weight at each motion segment level reported elsewhere [62,70], a gravity load of 387 N was distributed eccentrically at different segmental levels.…”