A Pilot Project: Mechanical Damping and the Spine

Todd Dodge1, Mina Wanis1, Hiroki Yokota1, 2 (PI), Liming Zhao1, Simon Shim1

1Department of Biomedical Engineering,

Indiana University - Purdue University Indianapolis

2Department of Anatomy and Cell Biology Indiana University School of Medicine

Supported by Pilot Research Project Training Program (PRP) Education and Research Center (ERC) Department of Environmental Health

University of Cincinnati

October 11, 2013

Title

Purpose: A knee loading modality is reported to stimulate bone formation in the loaded tibia and femur, but its potential effect on a bone remote to the loaded bone has not been examined. A question addressed herein was: does knee loading strengthen mechanical properties of trabecular bone in the spine? Design: Using ovariectomized (OVX) and sham OVX control mice, knee loading was applied daily for 4 weeks. Administration of salubrinal was employed as a positive control for systemic effects.

Purpose and Design

Approach: Mechanical properties of L5 vertebral body was characterized, focusing on:

•  stiffness (Young’s modulus) •  damping (dissipation energy) •  fracture behaviors (yield and ultimate strengths)

Approach

-3

-2

-1

0 0 1 2 3 4 5

forc

e (N

)

time (s)

A

C

knee

B

D

-3

-2

-1

0 0 0.1 0.2 0.3

forc

e (N

)

time (s)

L5 vertebral

body

Intervertebral disk

Sample I Sample II

Removal of the disk

Methods

0 50

100 150 200 250 300 350 400 450 500

sham OVX

Youn

g's

mod

ulus

(MP

a)

non-treated +load +sal

* * **

G

-7

-6

-5

-4

-3

-2 0.16 0.18 0.2

-7

-6

-5

-4

-3

-2 0.28 0.3 0.32

B

-7

-6

-5

-4

-3

-2 0.46 0.48 0.5

-7

-6

-5

-4

-3

-2 0.27 0.29 0.31

-7

-6

-5

-4

-3

-2 0.41 0.43 0.45

-7

-6

-5

-4

-3

-2 0.5 0.52 0.54

displacement (mm) displacement (mm)

A

C D

F E

forc

e (N

) fo

rce

(N)

forc

e (N

)

Young’s Modulus (rigidity)

-5

-4

-3

-2 0.63 0.65 0.67 0.69

forc

e (N

)

-5

-4

-3

-2 0.81 0.83 0.85 0.87

forc

e (N

)

-5

-4

-3

-2 0.16 0.18 0.2 0.22

-5

-4

-3

-2 0.3 0.32 0.34 0.36

A B

C D

displacement (mm) displacement (mm)

*

0 0.02 0.04 0.06 0.08

0.1 0.12 0.14 0.16 0.18

0.2

0.5 2 4 6 12

diss

ipat

ed e

nerg

y/cy

cle

(mJ)

frequency (Hz)

sham sample I sham sample II OVX sample I OVX sample II

E

**

** **

**

* **

**

**

**

**

*

* *

Dissipation Energy (Sham and OVX)

0 0.02 0.04 0.06 0.08

0.1 0.12 0.14 0.16 0.18

0.2

0.5 2 4 6 12

diss

ipat

ed e

nerg

y/cy

cle

(mJ)

frequency (Hz)

sham sham+load sham+sal A

B

*

* ** **

**

** **

** **

0 0.02 0.04 0.06 0.08

0.1 0.12 0.14 0.16 0.18

0.2

0.5 2 4 6 12

diss

ipat

ed e

nerg

y/cy

cle

(mJ)

frequency (Hz)

OVX OVX+load OVX+sal

Dissipation Energy (with disk)

A

B

* *

*

* *

*

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

0.1

0.5 2 4 6 12

diss

ipat

ed e

nerg

y/cy

cle

(mJ)

frequency (Hz)

sham sham+load sham+sal

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

0.1

0.5 2 4 6 12

diss

ipat

ed e

nerg

y/cy

cle

(mJ)

frequency (Hz)

OVX OVX+load OVX+sal

Dissipation Energy (without disk)

0

5

10

15

20

25

30

sham OVX

ultim

ate

stre

ngth

(MP

a)

non-treated +load +sal

0

5

10

15

20

25

30

sham OVX yi

eld

stre

ngth

(MP

a)

non-treated +load +sal

** *

*

** *

C

D

B

0 0.2 0.4 0.6 0 10 20 30 40 50

displacement (mm)

OVX

OVX+sal OVX+load

forc

e (N

) A

0 0.2 0.4 0.6 0 10 20 30 40 50

forc

e (N

)

displacement (mm)

sham

sham+sal

sham+load

Mechanical Strength

Summary: The results showed that knee loading increased Young’s modulus of the L5 vertebral body of OVX mice by 80% as compared to sham loaded controls. Knee loading reduced dissipation energy by 40-45%, in which bone contributed a significant portion (50-70%) to the damping capacity of the spine in a frequency dependent manner. In a compressive failure test, OVX animals treated with knee loading exhibited an increase in yield strength (60%) and ultimate strength (33%).

Summary

Conclusion: Both knee loading and administration of salubrinal increased stiffness and strength, and decreased damping of trabecular bone in the L5 vertebral body. The results provide supporting evidence that knee loading is capable of inducing loading effects in not only the loaded but also non-loaded bones. Impact: Back pain is a major problem in the Occupational Safety and Health field. This pilot project contributes to our basic understanding of the role of mechanical loading to the spine.

Conclsion and Impact

Supported by Pilot Research Project Training Program (PRP)

Education and Research Center (ERC) Department of Environmental Health

University of Cincinnati

Thank you!

Acknowledgement