Published at : 19 Oct 2022
Volume : IJtech
Vol 13, No 5 (2022)
DOI : https://doi.org/10.14716/ijtech.v13i5.5824
Lau, L.W., Kok, C.K., Chen, G.M., Tso, C.P., 2022. Modelling HumanStructure Interaction in Sideways Fall for Hip Impact Force Estimation. International Journal of Technology. Volume 13(5), pp. 11491158
Lin Wei Lau  Pixel Automation Pte Ltd, 10 Admiralty Street #0413 North Link Building Singapore, Singapore 757695 
Chee Kuang Kok  Center for Advanced Mechanical and Green Technology, Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450 Bukit Beruang, Melaka, Malaysia 
Gooi Mee Chen  Center for Advanced Mechanical and Green Technology, Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450 Bukit Beruang, Melaka, Malaysia 
ChihPing Tso  Center for Advanced Mechanical and Green Technology, Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450 Bukit Beruang, Melaka, Malaysia 
Sideways fallinduced hip fracture is a primary
global health concern among the elderly. Existing impact models for predicting
peak hip impact force mostly consider the human bodyrelated parameters rather
than impact surface parameters. This study proposed improving existing
springmassdamper models by accounting for the humanstructure dynamic
interaction during sideways fall for better predicting peak impact force on the
hip. Information required to construct the models was extracted from the
literature. Different peak hip impact forces were estimated by considering
differences in gender, body height, body mass, stiffness, damping
coefficients of body tissue over the greater trochanter, and the impact surface
stiffness. The predicted peak hip impact forces were compared to measured or
simulated results in the literature and found to agree reasonably. Simulation
results show that interactions with impact surfaces with lower stiffness can
reduce the value of peak impact force applied on the hip by at least 16%.
Flooring material; Hip fracture; Impact force attenuation; Springmassdamper; Trochanteric tissue stiffness
Sideway fall often results in osteoporotic hip
fracture, which is a major health care issue over the world that leads to
immobility or even death (NorIzmin et
al., 2020). According
to statistics (Burns
& Kakara, 2018), 55% of unintentional injuries among Americans over
the age of 65 were caused by falls. Major clinical risk assessment tools
available today includinge
bone densitometry based on hip Dualenergy Xray absorptiometry (DXA), hip
structural analysis (HSA), and fracture risk assessment tool (FRAX) (Sarvi & Luo, 2015) could provide hip fracture risk assessment due to
sideways fall with reasonable accuracy
Biomechanics models (Kroonenberg
et al., 1995) have shown that effective
mass can vary from 25% to 75% of the overall
mass depending on different kinematic configurations right before the fall
impact. Sarvi and Luo
Previous research
2.1. Model Development
Sarvi and
Luo’s framework (2015) was adopted in
developing our peak hip force model. The authors' model is made up of two
submodels that work sequentially. First, a dynamic submodel determines the
effective mass and the impact velocity of the fallen body. Second, an impact
submodel predicts the peak hip force based on two springmassdamper stacked
in series. For the dynamic submodel, a twolink model with a 45degree
inclined torso (a.k.a. jackknife) (Kroonenberg et
al., 1995) was used for simulating sideways fall from a standing position,
and a point mass dynamic model for simulating very shortdistance sideways hip
release experiment (Laing et al., 2006).
Therefore, the impact velocity, v (m/s), and effective mass, m_{eff}
(kg), reduce to:

where h is the height (in unit m) of the
falling person, and H is the effective mass drop height. The selection
of the twolink model was based on the fact that this model exhibited the
lowest error (i.e., 22% to 36%) among the nonsubject specific models
The stiffness and damping coefficients of the
trochanteric tissue are key parameters in the impact submodel. Recent findings
on these coefficients will first be presented first, followed by
the justification of the current model. There are contradicting views on how
age and soft tissue thickness (STT) affect trochanteric tissue stiffness and
damping coefficients. Sarvi and Luo
It is also very likely that the stiffness of the tissue
is nonlinear (Choi et al.,
2015; Laing & Robinovitch, 2010; Makhsous et al., 2008). For an individual with average weight, it could be
induced from Makhsous et
al.’s
To model the effect of the impact surface, two
springmassdampers are stacked to form a twodegreeoffreedom vibration
system, as illustrated in Figure 1. In this figure, M is the mass, K
is the spring stiffness, and C is the damping coefficient. The subscripts
h and f represent the falling human and the impacted floor,
respectively

This model is very similar to
Shahabpoor and Pavic’s
The variables M, K, C, and P
in Equations (8) to (10) are to be substituted with corresponding mass, spring
stiffness, damping coefficients, and residual force of the human or the floor,
according to Equations (6) and (7), respectively.
The initial stiffness (K_{1}) damping
coefficients and estimated thickness of human tissues (STT) over the greater
trochanter used in this study were as reported in (Nasiri & Luo, 2016). Table 1 shows the mean stiffness data reduced to
simple regressions with correlation coefficients greater than 0.94. Damping
coefficients were treated as categorical data corresponding to BMI and gender
categories (Nasiri &
Luo, 2016). Furthermore,
the trochanteric tissue stiffness was represented by a trilinear nestedspring
design in Fig 2, and K_{1} is the tissue stiffness according to
Equations (12b) and (13b). It should be noted that the stiffness and damping
coefficients of the greater trochanter tissue reported in (Nasiri & Luo, 2016) were originally obtained by Robinovitch et al.
Table
1 Simple
regressions between BMI, STT, and mean stiffness
Gender 
Variable 
Expression 

Male 
STT
(mm) 
STT
= 3.8429*BMI  45.254 
(12a) 

K
(kN/m) 
K
= 395.6*(BMI)^{0.755} 
(12b) 
Female 
STT
(mm) 
STT
= 2.4991*BMI  14.189 
(13a) 

K
(kN/m) 
K
= 1935.6*(BMI)^{1.4} 
(13b) 
The effective stiffness and effective damping
coefficient of an impact surface used in the current study were taken from Ref.
(Laing et al., 2006). Table 2 depicts the range of effective stiffness of
compliant flooring as reported by Laing et al.
Figure 2 (a) Trilinear approximation (i.e., three red lines to approximate the blue curve); (b) Nested spring representation of trilinear tissue stiffness.
Table 2 Effective stiffness of compliant flooring (Laing et al., 2006)
Floor Type 
Floor Thickness (cm) 
Flooring Stiffness, k (kN/m) 
Rigid 
NIL 
~? 
Firm 
1.5 
263 
Semifirm 
4.5 
95 
Semisoft 
7.5 
67 
Soft 
10.5 
59 
3.1. Fall on Rigid Flooring
The predictions of impact forces using the proposed
model will be verified using four different cases of sideways fall or
smalldistance hip release on rigid flooring from the literature. The input
parameters and predicted impact force are summarized in Table 3. Case 1 is a
simulated sideways fall from standing height on a rigid impact surface on
nonsubjectspecific individuals. Case 2, a protected fall experiment by Sarvi et. al
In estimating peak impact force due to a sideways fall
from standing height in Case 1, the interaction between a human body with a
rigid flooring was simulated. The mean values of human body parameters (as in
Table 4) were taken from the Centrers
for Disease Control and Prevention
Figure 3 Predicted
peak impact force for (a) male and (b) female with mean heights and mass
Table
3 Input
parameters and predicted impact force for four different cases on rigid
flooring

Input 
Output: Hip Peak Impact force (N) 

Case/ Input 
Gender 
Height (m) 
Weight (kg) 
Impact Velocity (m/s) 
Effective Mass (kg) 
Experiment 
Model 
Percent Error

Case 1 
Male 
1.757 
88.8 
Eq (1a) 
Eq (2a) 
From 4050 to 6420 
4777 
Within Range 
Female 
1.616 
76.4 
Eq (1a) 
Eq (2a) 
3245 
19.9% 

Case 2 (Sarvi, et al., 2014) 
Male 
1.73 
77 
1.063 
35.56 
1900.8 
1722 
9.4% 
Male 
1.72 
72 
1.236 
29.75 
1714.4 
1905 
11.1% 

Male 
1.74 
64 
2.493 
24.62 
2961.8 
3406 
15.0% 

Case 3 
Female 
1.70 
59.6 
Eq (1b) 
Eq (2b) 
1059±42 
1273 
16% 
Case 4 (Fleps, et al., 2019) 
Female 
1.63 
40.8 
3.1 
Eq (2b) 
2910 
5145 
76.8% 
Female 
1.78 
49.0 
3.1 
Eq (2b) 
6131 
5627 
8.2% 

Female 
1.65 
59.0 
3.1 
Eq (2b) 
5641 
4797 
15.0% 

Female 
1.68 
61.3 
3.1 
Eq (2b) 
4907 
4869 
0.8% 

Female 
1.63 
84.0 
3.1 
Eq (2b) 
4958 
4305 
13.2% 

Female 
1.58 
99.8 
3.1 
Eq (2b) 
4910 
3950 
19.6% 

Male 
1.75 
45.4 
3.1 
Eq (2a) 
5242 
5840 
11.4% 

Male 
1.83 
63.5 
3.1 
Eq (2a) 
5043 
6193 
22.8% 

Male 
1.75 
68.1 
3.1 
Eq (2a) 
7601 
6105 
19.7% 
Using the current impact model in Case 2, experimental
peak hip impact forces and the predictions agree with experiments to within 15%
of error, although the drop configurations and subsequent kinematics were
subjectspecific in the experiment. Unlike the work of Laing and Robinovitch
Similarly, when benchmarked against Fleps et al.
3.2. Fall on Nonrigid Flooring
Laing et al.
Table 4 Hip impact force attenuation
Floor Type 
% attenuation 
% attenuation (Current study) 
Firm 
610 
16 
Semifirm 
1416 
23 
Semisoft 
1518 
25 
Soft 
1619 
27 
Although the current model slightly overpredicted the
percent attenuation in the simulated fall experiments by an extra 68%, the
trend of decreasing gain in the attenuation rate from semifirm to soft
flooring material matches the observation in Ref. (Laing et al., 2006) well. The 68% extra attenuation could be taken as
the percent error of the model, and the error may have come from the
uncertainty related to the prediction of trochanteric tissue stiffness based on
BMI and gender.
The authors demonstrated that factors such as body
height, body weight (and thence BMI), gender of the individuals, and impact
velocity alone appear sufficient in a nonsubjectspecific model for estimating
the peak hip impact force. In contrast, age and actual trochanteric tissue
thickness may be less significant. Except for one scenario, the proposed model
could predict the mean peak hip impact force of a sideways fall from standing
height with 77% accuracy. The amount of attenuation indicated in the hip impact
force (i.e., 16%27%) due to compliant flooring also agrees with previous work
(i.e., 6%19%). Regressions were made
on the trochanteric tissue stiffness in published literature. The predictions were
made using a trilinear springmassdamper stacked model, and no individual
measurements of trochanteric tissue stiffness and damping coefficients were
required. To be sure, the inclusion of a third spring in the trilinear spring
model is not entirely justified. More testing may be required to validate its
use.
This
research work has not received any grant from any funding agency. The authors
are grateful to Multimedia University for granting them access to a MATLAB
license to produce this work.
Filename  Description 

R1ME582420220811114120.JPG  Revised Figure 1 
R1ME582420220811114143.JPG  Revised Figure 2 
R1ME582420220811114201.JPG  Revised Figure 3 
Abe,
S., Kouhia, R., Nikander, R., Narra, N., Hyttinen, J., Sievanen, H., 2022.
Effect of Fall Direction on the Lower Hip Fracture Risk in Athletes with
Different Loading Histories: A Finite Element Modeling Study in Multiple
Sideways Fall Configurations. Bone, Volume 158, p. 116351
Ahmad,
M.A., Zulkifli, N.N.M.E., Shuib, S., Sulaiman, S.H., Abdullah, A.H., 2020.
Finite Element Analysis of Proximal Cement Fixation in Total Hip Arthroplasty. International
Journal of Technology, Volume 11(5), pp. 1046–1055
Burns,
E., Kakara. R., 2018. Deaths from Falls Among Persons Aged ?65 Years — the
United States, 2007–2016. MMWR. Morbidity and Mortality Weekly Report,
Volume 67(18), pp. 509–514
Choi,
W., Russell, C., Tsai, C., Arzanpour, S., Robinovitch, S., 2015. Agerelated Changes in Dynamic Compressive
Properties of Trochanteric Soft Tissues Over the Hip. Journal of
Biomechanics, Volume 48(4), pp. 695–700
Choi,
W.J., 2013. Biomechanics of Falls and Hip Fractures in Older Adults.
Master’s Dissertation, Graduate Program, Simon Fraser University, Burnaby,
British Colombia, Canada
Chopra,
A.K. 2017. Dynamics of Structures: Theory and Applications to Earthquake
Engineering. Hoboken, NJ: Pearson
Farrer,
A.I., Odeen, H., Christensen, D.A., 2015. Characterization and Evaluation of
Tissuemimicking Gelatin Phantoms for Use with MRgFUS. Journal of
Therapeutic Ultrasound Volume
3(9), pp. 1–11
Fleps,
I., Guy, P., Ferguson, S.J., Cripton, P.A., Helgason, B.,
2019. Explicit Finite Element Models Accurately Predict SubjectSpecific and
VelocityDependent Kinetics of Sideways Fall Impact. Journal of Bone and Mineral Research, Volume 34(10), pp. 1837–1850
Fung,
A., Fleps, I., Cripton, P.A., Guy, P., Ferguson, S.J., Helgason. B., 2022.
Prophylactic Augmentation Implants in the Proximal Femur for Hip Fracture. Journal
of the Mechanical Behaviour of Biomedical Materials, Volume 126, p. 104957
Groen,
B., Weerdesteyn, V., Duysens, J., 2008. The Relation between Hip Impact
Velocity and Hip Impact Force Differs between Sideways Fall Techniques. Journal
of Electromyography and Kinesiology, Volume 18(2), pp. 228–234
Kani,
K., Porrino, J., Dahiya, M., Taljanovic, M., Mulcahy, H., Chew, F., 2016. A
Visualization of the Greater Trochanter and Peritrochanteric Soft Tissues. The
American Academy of Physical Medicine and Rehabilitation, Volume 9(3), pp.
318–324
Khakpour,
S., Tanska, P., Esrafilian, A., Mononen, M.E., Saarakkala, S., Korhonen, R.K.,
Jämsä, T., 2021. Effect of Impact Velocity, Flooring Material, and Trochanteric
SoftTissue Quality on Acetabular Fracture during a Sideways Fall: A Parametric
Finite Element Approach. Applied Sciences, Volume 11(365), pp. 1–35
Kok,
J., Grassi, L., Gustafsson, A., Isaksson, H., 2021. Femoral Strength and
Strains in Sideways Fall: Validation of Finite Element Models Against Bilateral
Strain Measurements. Journal of Biomechanics, Volume 122, p. 110445
Kroonenberg,
V.D.A.J., Hayes, W.C., McMahon, T.A., 1995. Dynamic Models for Sideways Falls
from Standing Height. Journal of Biomedical Engineering, Volume 117, pp.
309–318
Laing,
A.C., Robinovitch, S.N., 2008. The Force Attenuation Provided by Hip Protectors
Depends on Impact Velocity, Pelvic Size, and Soft Tissue Thickness. Journal
of Biomechanical Engineering, Volume 130, pp. 1–9
Laing,
A.C., Robinovitch, S.N., 2010. Characterizing the Effective Stiffness of the
Pelvis During Sideways Falls on the Hip. Journal of Biomechanics, Volume
43, pp. 1898–1904
Laing,
A.C., Tootoonchi, I., Hulme, P.A., Robinovitch, S.N., 2006. Effect of Compliant
Flooring on Impact Force during Falls on the Hip. Journal of Orthopaedic
Research, Volume 24(7), pp. 1405–1411
Li,
N., Tsushima, E., Tsushima, H., 2013. Comparison of Impact Force Attenuation by
Various Combinations of Hip Protector and Flooring Material using A Simplified
FallImpact Simulation Device. Journal of Biomechanics, Volume 46, pp.
1140–1146
Lim,
K.T., Choi. W.J., 2019. Soft Tissue Stiffness Over the Hip Increases with Age
and Its Implication in Hip Fracture Risk in Older Adults. Journal of
Biomechanics, Volume 93, pp. 28–33
Makhsous,
M., Venkatasubraminian, G., Chawla, A., Pathak, Y., Priebe, M., Rymer, W.Z.,
Lin, F., 2008. Investigation of SoftTissue Stiffness Alteration in Denervated
Human Tissue Using an Ultrasound Indentation System. The Journal of Spinal
Cord Medicine, Volume 31(1), pp. 88–96
Nasiri,
M., Luo, Y., 2016. Study of Sex Differences in the Association between Hip
Fracture Risk and Body Parameters by DXABased Biomechanical Modeling. Bone,
Volume 90, pp. 90–98
NorIzmin,
N.A., Hazwani, F., Todo, M., Abdullah, A.H., 2020. Risk of Bone Fracture in
Resurfacing Hip Arthroplasty at Varus and Valgus Implant Placements. International
Journal of Technology, Volume 11(5), pp. 1025–1035
Radzevi?ien?,
L., Ostrauskas, R., 2013. Body Mass Index, Waist Circumference, WaistHip
Ratio, WaistHeight Ratio and Risk for Type 2 Diabetes in Women: A CaseControl
Study. Public Health, Volume 127(3), pp. 241–246
Robinovitch,
S.N., Hayes, W.C., McMahon, T.A., 1991. Prediction of Femoral Impact Forces in
Falls on the Hip. Journal of Biomechanical Engineering, Volume 113, pp.
366–374
Robinovitch,
S.N., Hayes, W.C., McMahon, T.A., 1995. EnergyShunting Hip Padding System
Attenuates Femoral Impact Force in a Simulated Fall. Journal of
Biomechanical Engineering, Volume 117, pp. 409–413
Sarvi,
M. N., Luo, Y., Sun, P., Ouyang J., 2014. Experimental Validation of
SubjectSpecific Dynamics Model for Predicting Impact Force in Sideways Fall. Journal
of Biomedical Science and Engineering, Volume 07(07), pp. 405–418
Sarvi,
M.N., Luo, Y., 2015. A TwoLevel SubjectSpecific Biomechanical Model for
Improving Prediction of Hip Fracture Risk. Clinical Biomechanics, Volume
30(8), pp. 881–887
Sarvi,
M.N., Luo, Y., 2017. Sideways FallInduced Impact Force and Its Effect on Hip
Fracture Risk: A Review. Osteoporosis International, Volume 28(10), pp.
2759–2780
Sarvi,
M.N., Luo. Y., 2019. Improving the Prediction of Sideways FallInduced Impact
Force for Women by Developing a FemaleSpecific Equation. Journal of
Biomechanics, Volume 88, pp. 64–71
Shaabpoor,
E., Pavic, A., 2016. Humanstructure Dynamic Interactions during ShortDistance
Free Fall. Shock and Vibration, Volume 2016, pp. 1–12
Triwardono,
K., Supriadi, S., Whulanza, Y., Saragih, A.S., Novalianita, D.A., Utomo, M.S.,
Kartika, I. 2021. Evaluation of the
Contact Area in Total Knee Arthroplasty Designed for Deep Knee Flexion. International
Journal of Technology, Volume 12(6), pp. 1312–1322
Zijden,
V.D.A.M., Groen, B.E., Tanck, E., Nienhuis, B., Verdonschot, N., Weerdesteyn,
V., 2017. Estimating Severity of Sideways Fall using a Generic MultiLinear
Regression Model Based on Kinematic Input Variables. Journal of Biomechanics,
Volume 54, pp. 19–25