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Research Papers

An Integrated Musculoskeletal-Finite-Element Model to Evaluate Effects of Load Carriage on the Tibia During Walking

[+] Author and Article Information
Chun Xu, Ginu Unnikrishnan

Telemedicine and Advanced
Technology Research Center,
Department of Defense Biotechnology
High Performance Computing
Software Applications Institute,
U.S. Army Medical Research
and Materiel Command,
Fort Detrick, MD 21702-5012

Amy Silder

Department of Bioengineering,
Stanford University,
Stanford, CA 94305-6175

Ju Zhang

Auckland Bioengineering Institute,
University of Auckland,
Auckland 1010, New Zealand

Julie Hughes

U.S. Army Research Institute
of Environmental Medicine,
Natick, MA 01760-5007

Jaques Reifman

Telemedicine and Advanced
Technology Research Center,
Department of Defense Biotechnology
High Performance Computing
Software Applications Institute,
U.S. Army Medical Research
and Materiel Command,
MCMR-TT, 504 Scott Street,
Fort Detrick, MD 21702-5012
e-mail: jaques.reifman.civ@mail.mil

Vineet Rakesh

Telemedicine and Advanced
Technology Research Center,
Department of Defense Biotechnology
High Performance Computing
Software Applications Institute,
United States Army Medical Research
and Materiel Command,
Fort Detrick, MD 21702-5012

1Corresponding author.

Manuscript received January 12, 2016; final manuscript received July 12, 2016; published online August 8, 2016. Assoc. Editor: David Corr.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J Biomech Eng 138(10), 101001 (Aug 08, 2016) (11 pages) Paper No: BIO-16-1013; doi: 10.1115/1.4034216 History: Received January 12, 2016; Revised July 12, 2016

Prior studies have assessed the effects of load carriage on the tibia. Here, we expand on these studies and investigate the effects of load carriage on joint reaction forces (JRFs) and the resulting spatiotemporal stress/strain distributions in the tibia. Using full-body motion and ground reaction forces from a female subject, we computed joint and muscle forces during walking for four load carriage conditions. We applied these forces as physiological loading conditions in a finite-element (FE) analysis to compute strain and stress. We derived material properties from computed tomography (CT) images of a sex-, age-, and body mass index-matched subject using a mesh morphing and mapping algorithm, and used them within the FE model. Compared to walking with no load, the knee JRFs were the most sensitive to load carriage, increasing by as much as 26.2% when carrying a 30% of body weight (BW) load (ankle: 16.4% and hip: 19.0%). Moreover, our model revealed disproportionate increases in internal JRFs with increases in load carriage, suggesting a coordinated adjustment in the musculature functions in the lower extremity. FE results reflected the complex effects of spatially varying material properties distribution and muscular engagement on tibial biomechanics during walking. We observed high stresses on the anterior crest and the medial surface of the tibia at pushoff, whereas high cumulative stress during one walking cycle was more prominent in the medioposterior aspect of the tibia. Our findings reinforce the need to include: (1) physiologically accurate loading conditions when modeling healthy subjects undergoing short-term exercise training and (2) the duration of stress exposure when evaluating stress-fracture injury risk. As a fundamental step toward understanding the instantaneous effect of external loading, our study presents a means to assess the relationship between load carriage and bone biomechanics.

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References

Figures

Grahic Jump Location
Fig. 1

Flowchart of the methodology. EMG: electromyography; HU: Hounsfield unit; and MAP: Musculoskeletal Atlas Project.

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Fig. 9

Volume engagement histogram of (a) stress and (b) stress–time exposure under different load-carriage conditions. (c) Peak stress distribution at pushoff phase. (d) Cumulative stress–time exposure distribution over one gait cycle. BW: body weight.

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Fig. 8

Temporal evolution of principal stresses ((a)and (b)) and principal strains ((c)and (d)) averaged over the anterior crest (dashed lines) and the posterior aspects (solid lines) of the tibia for baseline (no load carriage) and 30% body weight (BW) load carriage conditions. Shaded region represents one standard deviation.

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Fig. 7

Spatiotemporal distribution of tibial stresses during one gait cycle without (a) and with 10% (b), 20% (c), and 30% (d) body weight (BW) load carriage at foot-flat (FF), midstance (MS), and pushoff (PO). We divided the cross section of the left tibia into six sectors. A: anterior; MA: medial anterior; MP: medial posterior; P: posterior; LP: lateral posterior; and LA: lateral anterior.

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Fig. 6

Joint kinematics and kinetics for different loads during one gait cycle. Positive angles and moments represent extension, and negative values represent flexion. Forces are shown as normalized dimensionless quantities. BW: body weight; deg: degree; DF: dorsiflexion; Ext: extension; Flex: flexion; JRF: joint reaction force; and PF: plantar flexion.

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Fig. 5

Temporal evolution of muscle activities with 30% of body weight (BW) load carriage at heel-strike (HS, (a)), foot-flat (FF, (b)), midstance (MS, (c)), and pushoff (PO, (d)). At each time point, both anterior–posterior (left) and medial–lateral (right) views are shown. Muscle activity is described as 0–100% of maximum activity. At HS, the tibialis anterior is activated until the foot is completely in contact with the floor. Gluteus medius is activated before HS to prepare for load bearing and continues to be active throughout the first half of the stance phase. At FF, the hip moves slowly into extension caused by a contraction of muscles, such as the gluteus maximus. Extension of the knee is caused by a contraction of the quadriceps, and flexion is caused by a contraction of the hamstrings. At MS, the hip moves from flexion to extension by the contraction of the gluteus medius muscle. During PO, gastrocnemius and soleus are activated to accelerate the body forward, reaching more than 60% of muscle strength.

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Fig. 4

Results from mesh morphing (a) and material mapping (b)–(f). In (a), the nodes of the deformed source mesh (blue) were overlaid onto the nodes of the target mesh (red). Mapped material properties superimposed on the tibial model are shown at anterior (b), posterior (c), lateral (d), medial (e), and a coronal cross section (f).

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Fig. 3

Comparison of the in vivo tibial strain measurements (dashed lines) and model predictions at the medial side of the midshaft. Solid lines denote the simulated axial-strain curves averaged over the (a) anterior and (b) posterior aspects of thetibia, with the shaded region representing one standard deviation.

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Fig. 2

Comparison of muscle activities predicted by the model (solid lines) and measured by electromyography (EMG, dashed lines) as a function of percent of stride. We normalized magnitudes to the maximum values for each curve.

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