Current Directions in Biomedical Engineering 2019;5(1):347-350

Martin Weidling*, Christian Voigt, Toni Wendler, Martin Heilemann, Michael Werner,
Jan-Sven Jarvers and Christoph-E. Heyde

Kinematics of the Lumbo–Pelvic Complex
under Different Loading Conditions
Abstract: The lumbo-pelvic complex is a highly complex

structural system. The current investigation aims to identify
the kinematics between interacting bone segments under
different loading conditions. A specimen of the lumbo-pelvic
complex was obtained from a human body donor and tested
in a self-developed test rig. The experimental setup wasdesigned to imitate extension, flexion, right and left lateral
bending and axial rotation to the left and to the right,respectively. The vertebra L3 was firmly embedded and load
was introduced via hip joints. Using a digital image
correlation (DIC) system, the 3D motions of 15 markers at
different landmarks were measured for each loadcase undercyclic loading. For each loadcase, the kinematics wereanalyzed in terms of three-dimensional relative movements
between L3 and the sacrum. The usefulness of theexperimental technique was demonstrated. It may serve forfurther biomechanical investigations of relative motion ofsacroiliac and vertebral joints and deformation of bonystructures.
Keywords: range of motion, pelvis, spine, bone kinematics,

experimental biomechanics.

successful in the thoracic and lumbar spine. In the region of
lumbo-sacral transition, however, high loosening rates andimplant fractures occur frequently with these systems [3].
The lumbo-pelvic complex is comprised of the lumbosacral transition and the pelvic ring, including various bones,
ligaments and intervertebral discs. Further improvement ofimplant fixation requires knowledge about the load transferfrom the spine to the hip region, which is, therefore, a major
field of biomechanical investigation. However, studies in theliterature usually investigated only single directionalloadcases [2, 4]. To deepen our understanding how thesecomponents interact during load transfer, the current study
aims for identification the kinematics of the interacting bonesegments under different loading conditions.
This requires the development of an experimental setupthat can imitate near-realistic movements of the lumbo-pelvic
complex while maintaining simple and well definedboundary conditions. Measurement equipment has to becustomized, to capture the 3D motion of the individual bonesegments with high accuracy. Knowledge of the kinematics
and load situation is substantial for advancement of implantdesign.

https://doi.org/10.1515/cdbme-2019-0087

1

Introduction

With growing numbers of elderly patients, the number ofcases with degenerative diseases is also increasing.
Osteoporotic fractures of the spine and pelvis are a majorarea of concern [1]. Screw-rod systems have proven______*Corresponding author: Martin Weidling: Center for Researchon Musculoskeletal Systems (ZESBO), Faculty of Medicine,
University of Leipzig, Semmelweisstrasse 14, Leipzig, Germany,e-mail: martin.weidling@medizin.uni-leipzig.de
Christian Voigt, Toni Wendler, Martin Heilemann: Center for
Research on Musculoskeletal Systems (ZESBO), Faculty ofMedicine, University of Leipzig, Leipzig, Michael Werner:
Fraunhofer Institute for Machine Tools and Forming Technology
IWU, Dresden, Germany, Jan-Sven Jarvers and Christoph-E.
Heyde: Department of Orthopaedic, Trauma and Plastic Surgery,
University Hospital Leipzig, Leipzig, Germany
Open Access. © 2019 Martin Weidling et al., published by De Gruyter.
NoDerivatives 4.0 License.

2Materials and Methods

Preparation of specimen
From a male body donor (67 years at death) the compound oflumbar vertebrae L3-5 and pelvis was dissected and muscle
tissue was removed from the specimen, while preserving
intervertebral discs, facet joints and ligament structures. Afterdissection the specimen was fresh frozen. On the day of theexperiment the specimen was thawed under time andtemperature control. Pathologies were excluded by CT
examination. Furthermore, osteoporosis could be excluded bybone density scan (T-score: -0.4).

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M. Weidling et al., Kinematics of the Lumbo–Pelvic Complex under Different Loading Conditions — 348

Figure 1: Experimental setup: a – CAD-concept of theexperimental setup; b – Human bone and soft tissue specimen
including measurement markers at anatomical landmarks,evaluated markers of the current study are indicated with a green
dot.

The specimen was embedded with the L3 inside a
mounting socket using polyurethane casting resin RenCast®
(Huntsman Int. LLC, USA), while aligning the intervertebral
joint L3/L4 parallel with the rim and the base plate of themounting socket. Prior alignment of the specimen in themounting socket allows for positioning the specimen
corresponding to an upright body posture, when the socket ismounted horizontally [6]. Care was taken to ensure that themobility of the L3/L4 joint, especially at the facet joints andthe intervertebral disc, remained undisturbed by theembedding material.

Experimental setup
The self-developed test rig was set up in a DYNA-MESS
testing machine (Type 2082/000, built-in test modes: tensile,compression, torsion, DYNA-MESS, Aachen, Germany).
The working axis of the testing machine is its central verticalaxis, specified as Y-axis in the experimental coordinate
system (Figure 1a). A locking hinge, which can be pre-set todifferent angular positions, was incorporated to fix themounting socket with the specimen to the upper frame of thetesting machine. Congruent spheres, made of aluminium,
were inserted into the acetabula of the pelvis and checked forsmooth mobility to represent intact physiological hip joints.
The spheres were installed on posts which were sitting
upright on a cross slide, which allowed them to freely movein the horizontal plane. The cross slide was mounted to theactuator driven base plate of the testing machine. Insummary, the specimen was suspended with boundary
conditions of rigid fixation at the upper end (L3) and of low
friction sliding and vertical loading on the lower end(acetabula) while the Y-axis was the axis of all loadapplications.
Pins were inserted into the specimen at anatomicallandmarks. Measurement markers in the shape of small plateswith black and white speckle patterns were attached to thesepins (Figure 1b). The markers were captured during
movement in 3D space using a digital image correlation(DIC) system with a three-camera-setup (Q400, LIMESS
Messtechnik und Software GmbH, Krefeld, Germany).

Figure 2: Tested loadcases: a – pictograms of loading scenario; b – evaluated cyclic force-displacement diagrams of complete
specimen during each loadcase.

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M. Weidling et al., Kinematics of the Lumbo–Pelvic Complex under Different Loading Conditions — 349

Figure 3: Kinematic results of relative motion between L3 und sacrum for all tested loadcases. Above – Loadcase specific main
components of relative motion are shown in anatomical body coordinate system and indicated in red; Middle – Rotational components of
3D relative motion; Below - Translational components of 3D relative motion.

Experimental procedure
The loading scenarios are shown in Figure 2a. Extension,flexion, right and left lateral bending motion are each tested
individually. To examine extension and flexion, the locking
hinge was pre-set to 20° anterior/posterior tilt with regard to
the horizontal plane (XZ), respectively (Figure 2a). In rightand left lateral bending, the locking hinge was pre-set to 45°
right/left lateral tilt with regard to the horizontal plane (XZ),
respectively (Figure 2a), while the cross slide (XZ) waslocked in the Z-direction to allow only lateral movement.
Thereby, only one acetabulum was engaged, which iscorresponding to the body posture of one-legged stance. Thespecimen was loaded at a rate of 1 mm/s along the Y-axis.
Ten cycles with a maximum compression force of 56.25 N
were recorded.
During axial rotation, the specimen was fixed in neutral
position so that the mounting socket and, thereby, theintervertebral joint L3/L4 were orientated parallel to thehorizontal plane. The torque actuator of the testing machine
is located at the upper fixture of the machine. Therefore, theload was introduced into the specimen via the L3 as arotation around the Y-axis. Five cycles of rotation from left
to right and reverse were tested at a rate of 1°/s with amaximum torque of 5.625 Nm, respectively. To balance out
the weight of the hanging specimen, the base plate actuator

was set to apply a constant counter-acting support force in Ydirection during the test procedure, equal to the previously
measured weight of the specimen.
Experimental procedures lasted not more than 20 hours
at room temperature (23°C, 50% humidity), during which thespecimen was kept moist at all times [6].
Evaluation
Image data were recorded over the entire motion sequence
and analysed with the image correlation software Istra 4D
V4.4.4, Dantec Dynamics, Skovlunde, Denmark. 3D
coordinates analysed at measurement points on each marker
had to be translated to the underlying landmark on the bone
surface. Therefore, coordinates were shifted by the freestanding length of the attached pin, respectively. The relative
motion between two bony landmarks was then evaluated inall six degrees of freedom (Matlab R2015b, MathWorks,
Natick, MA, USA).
For more intuitive readability, the final results weretransferred to the anatomical body coordinate system (xyz),
which is commonly used to describe an orientation withregard to an upright body posture. Hence, the xy-plane iscongruent with the frontal plane and the xz-plane iscongruent with the transverse plane (Figure 3).

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M. Weidling et al., Kinematics of the Lumbo–Pelvic Complex under Different Loading Conditions — 350

3Results

The loads applied by the testing machine and the analysed
kinematic reactions of the complete specimen are shown for
all investigated loading cycles in Figure 2b in theexperimental coordinate system (XYZ). After a few cycles analmost constant hysteresis curve is obtained. Only one cycle
was chosen for further consideration (3rd cycle for axialrotation, 7th cycle for all other loadcases).
The relative motion between L3 and sacrum wasevaluated for all tested loadcases which is shown in Figure 3
in the anatomical body coordinate system (xyz). In Figure 1b,
the segments whose relative kinematics were evaluated aremarked with a green dot. In the upper part of Figure 3, theaxes that make up the characteristic components of relative
motion are highlighted in red. The three components of therotational motion and the three components of thetranslational motion are shown in the diagrams below.

4Discussion and Conclusion

In the literature in vitro studies of the lumbo-pelvic complex
under near-realistic loading conditions are rare. In mostcases, loads are applied in only one direction of motion [4,5]. These movements are often measured on the surface ofthe specimen using only few tactile displacement meters [4]or glued-on markers [2]. The underlying soft tissue caninduce inaccuracies of measurement. In the present study, anexperimental technique is proposed as a solution for theseproblems. Thus, the lumbo-pelvic complex is loaded indifferent directions in a simple and defined way,corresponding to common body postures and movements ofextension, flexion, lateral bending and axial rotation. The
kinematics of bone segments can be determined by a full setof markers. Moreover, the markers are connected to the boneby pins to account for bone movement rather than soft tissuemovement.
The analysed relative movements between L3 andsacrum comply with the expected directions of movement foreach loadcase. In addition, they can be precisely quantified asa function of the load.
With the presented method, biomechanical investigationsof the relative motion of individual intersegmental joints aswell as the overall deformation of bones can be conducted for

different loading scenarios. A better understanding of thebiomechanical behaviour of the lumbo-pelvic complex can beuseful for development of advanced implant fixation
techniques.
Acknowledgements

The authors wish to thank Christoph Oefner for his support
during the experiments and Florian Metzner for his
segmentation of the CT scan.
Author Statement

Research funding: Federal Ministry for Economic Affairs andEnergy of Germany within “Zentrales Innovationsprogramm
Mittelstand” (KF2036726AK4). Conflict of interest: Authors
state no conflict of interest. Informed consent: Informed
consent was not required as no individuals were involved inthis study. Ethical approval: The research related to humanuse complies with all the relevant national regulations,institutional policies and was performed in accordance withthe tenets of the Helsinki Declaration, and has been approvedby the authors' institutional review board.

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