QUANTIFICATION OF TRAINING EFFECTS ON FEMORAL BONE QUALITY USING PATIENT-SPECIFIC FE ANALYSIS

Leen Lenaerts (1), Sabine Verschueren (2), An Bogaerts (2), Steven Boonen (3), Christophe Delecluse (4), Karl Fritscher (5), G. Harry van Lenthe (1)

1. Biomechanics Section; 2. Research Unit for Musculoskeletal Rehabilitation; 3. Division of Geriatric Medicine; 4. Research Center for Exercise and Health,

K.U.Leuven, Leuven, Belgium; 5. Institute for Biomedical Image Analysis, UMIT, Hall in Tirol, Austria

Introduction

Recently, Whole Body Vibration (WBV) training

received some attention as a training method to

prevent osteoporosis. In a previous study in

postmenopausal women it was shown that WBV

training can stop the decrease in bone mineral

density (BMD) in the proximal femur or even

slightly reverse it [Verschueren, 2004]. However,

bone quality does not depend on BMD alone; other

aspects such as bone geometry and internal

architecture are important too. Therefore, the aim of

this study was to quantify the effects of a one-year

training program in postmenopausal women on

total hip BMD as well as on bone quality (stiffness)

by means of patient-specific FE analysis.

Materials and methods

Eighty-one postmenopausal women (age=60-81

years) volunteered to participate. Subjects were

randomly assigned to one of three groups: a control

group (CON, n=23), a resistance training group

(RES, n=21) and a WBV training group (WBV,

n=37). The training groups participated in a one-

year training program as described by Bogaerts et

al (2007). The control group did not participate in

any training. At the start of the study (PRE) and

after one year of training (POST), DXA and CT

scans (resolution 0.98mm x 0.98mm x 1mm) were

made of the proximal femora of every volunteer.

To determine bone stiffness, the right femora were

segmented from the CT images [Fritscher, 2007]

and used to build patient-specific FE models with

linear hexahedral elements. PRE and POST femora

were registered such that identical loading

conditions could be applied. Linear elastic material

properties were assigned to every element, based on

the grayvalue of the corresponding voxel in the CT

images [Morgan, 2003]. The length of all models

was set to 150mm, their distal end was fixed and a

displacement of 0.2mm was applied to each femur

head, parallel to the shaft axis. The FE models were

solved using MARC (MSC Software, Santa Ana,

CA) and the stiffness of every proximal femur was

calculated. The average PRE-POST differences in

BMD and stiffness were calculated (ALL) for each

of the three groups. Results were analyzed by

repeated measures ANOVA. In a subsequent

analysis, groups were divided into two subgroups

based on the BMD T-score: healthy subjects (HEA,

T�-1, nCON=6, nRES=10, nWBV=15) and osteopenic/

osteoporotic subjects (OST, T<-1, nCON=17, nRES=

11, nWBV=22).

Results

BMD declined significantly in the three groups

(Table 1-ALL). These decreases reached

significance for OST but not for HEA. Stiffness

ALL showed a significant decrease in CON but was

unaffected in RES and WBV. WBV caused a

significant increase in femoral stiffness in healthy

subjects, whereas it preserved bone stiffness in

osteopenic subjects.

CON RES WBV

BMD ALL *-1.56 *-1.5 *-1.01

Stiffness ALL *-1.85 0.09 1.14

BMD HEA -1.39 -0.92 -0.53

Stiffness HEA -1.07 -0.92 *2.56

BMD OST *-1.61 *-2.04 *-1.33

Stiffness OST *-2.13 1.01 0.18

Table 1: Average change (%) in BMD and in

stiffness in 1 year for the control group (CON), the

resistance training group (RES) and the whole body

vibration training group (WBV). (* Significant

PRE-POST difference within group, p < 0.05)

Discussion

Our findings suggest that due to training bone

stiffness can increase even when BMD is

decreasing. Where BMD was lost in all three

groups, stiffness was unaffected in the training

groups; it even improved significantly in healthy

subjects. We conclude that bone stiffness appears to

be a sensitive parameter picking up bone adaptive

responses that go unnoticed with the analysis of

BMD.

References

Bogaerts et al, Gaitpost, 26:309-316, 2007.

Fritscher et al, Int J CARS, 1(6):341-350, 2007.

Morgan et al, J Biomech, 36:897-904, 2003.

Verschueren et al, JBMR, 19(3):352-359, 2004.

S542 Presentation 1517 − Topic 37. Osteoporosis and bone strength

Journal of Biomechanics 45(S1) ESB2012: 18th Congress of the European Society of Biomechanics