ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

and extension angles of up to 12.3° may be caused by the application of the follower
load [20].
6. RECOMMENDED LOADS FOR THE SIMULATION OF MOTION IN THE
MAIN ANATOMICAL PLANES
In everyday life, a great variety of spinal motions is possible. Among these numerous
possibilities, motions in the three main anatomical planes representing flexion –
extension, lateral bending and axial rotation are those which are usually investigated. In
these cases, a follower load and a pure moment are often applied. The advantage of a
pure moment is that each level encounters the same load and that the results are nearly
independent of the number of segments studied. The magnitudes of the force and
moment vary, however, strongly in different studies. Only few in vivo studies exist
where the intervertebral rotations in all lumbar segments were measured, for example,
during axial rotation. The intradiscal pressure during axial rotation has been measured
by Wilke et al. [3]. Using a validated finite element model of the lumbar spine,
Dreischarf et al. [21] optimized the magnitudes of the applied follower load and
torsional moment in order to achieve a good agreement with intervertebral rotations and
intradiscal pressure measured in vivo. They found the smallest differences when the
follower load of 720 N and a torsional moment of 5.5 Nm were applied. The following
Table provides recommended loads for simulating different activities.
Table: Recommended loads for simulating motion in the three main anatomical planes.
Activity Follower Bending moment Torsional moment References
load (N) (Nm)
(Nm)
Standing 500 [22]
Flexion 1175 7.5 [23]
Extension 500 7.5 [23]
Lateral bending 700 7.8 [24]
Axial rotation 720 5.5 [21]
The loads on the spine affect the intervertebral rotations, the contact forces in the facet
joints, the intradiscal pressures and the stresses and strains in various structures of the
trunk. Thus, they may also affect degenerative processes in the spine and are probably
one reason for the occurrence of low back pain. Therefore, it is necessary to improve
our knowledge about the spinal loads during activities of daily living and to apply
physiological and relevant loads in numerical studies.
REFERENCES
[1] Nachemson A. The load on lumbar disks in different positions of the body. Clin.
Orthop. 1966;45:107-22.
[2] Nachemson AL. Disc pressure measurements. Spine 1981;6:93-7.
[3] Wilke H-J, Neef P, Caimi M, Hoogland T, Claes LE. New in vivo measurements of
pressures in the intervertebral disc in daily life. Spine 1999;24:755-62.
[4] Wilke H-J, Neef P, Hinz B, Seidel H, Claes L. Intradiscal pressure together with