Misagh Mansouri Departments of Mechanical, Aerospace, and Biomedical Engineering

University of Tennessee

THE USE OF A PLATFORM FOR DYNAMIC

SIMULATION OF MOVEMENT: APPLICATION TO BALANCE RECOVERY

BME 599

Spring 2012

Why Do We Care About Posture Balance?

Why Do We Care About Balance?

• Treat Movement Disorders • Kids with Cerebral Palsy

• Stiff-knee gait

swing phase

What Is Considered the Cause of Stiff Knees?

Clinical observations

• Rectus femoris activity in swing

• Small peak knee flexion

• Late peak knee flexion

Common treatment

• Rectus femoris transfer surgery

Rectus femoris activity in swing

Excessive knee extension moment in swing

60

0

40

20

0 60 100

percent of gait cycle

knee

flexio

n ang

le (o )

40 20 80

swing phase

• Rectus transfer: • Altered Biarticular function

Treatment for Stiff-Knee Gait

Why Are Biarticular Muscles Unique?

• Act across 2 joints

• Energy transfer between muscles

• Control of external forces

• Biarticular muscles may influence posture control

• Does rectus femoris transfer compromise balance?

Hip Flexor

Knee Extensor

Implementation Steps

Musculoskeletal Model

• Pre / Post operative

• Foot contact model

• Support-Surface Translation

Forward Dynamic Simulation

• OpenSim and MATLAB Interface

Closed-loop Controller

• Stretch Reflex Controller

3D Musculoskeletal Model

q6 q7

q8

q3 q4

q5

q9

q11

q10

q12 q2

q1 q13

Delp et al. (1990, 2007), IEEE Trans Biomed Eng

• 10 body segments • 92 muscle-tendon actuators • 19 degrees of freedom • Scaled to patient data

• Height: 1.45 m • Mass: 35.76 kg

Rectus Femoris Transfer Surgery

Fox et al. (2009), J Biomech

Preoperative Unilateral Transfer

Vastus Medialis

Foot-Platform Interface

Elastic foundation Cadaver geometry

Erdemir et al. (2009), J Biomech Eng

6 cm

0.35 s

Support Surface Translation

Woolacott et al. (2005), Dev Med & Child Neur

0 0.5 1

0

2

4

6

time (s)

supp

ort s

urfa

ce

disp

lace

men

t (cm

)

6 cm

.5

Linking OpenSim Forward Dynamics with MATLAB/Simulink

1) Developing an interface (S-function) based on OpenSim and MATLAB

2) Designing an example closed-loop Simulink® model by adding a proportional-integral-derivative (PID) feedback controller to extend the open-loop model.

OpenSim MATLAB/ Simulink® Interface

Generic Open-Loop Model Verification

Closed-Loop Model Application

MATLAB

λL – resting length λV – velocity λG – control

Motor nerve

Sensory nerve

Muscle spindle

Monosynaptic Reflex Afferent Mechanisms

� ���� ����

0

)/()()/()()( 0 MAXVRLG VTLLLTLtu

�

Stretch-Reflex Controller

Results (Anterior Perturbation)

preoperative unilateral bilateral

Results (Posterior Perturbation)

preoperative unilateral bilateral

Results (Anterior Perturbation)

-5

0

5

10

15

0 1 2 3 4

CoM

disp

lacem

ent (

cm)

time(s)

biarticularuniarticularpreoperative

Ante

rior

Results ( Perturbation)

-15

-10

-5

0

5

0 1 2 3 4

CoM

disp

lacem

ent (

cm)

biarticularuniarticularpreoperative

Post

erio

r

Discussion

Initial Knee Flexion due to AnteriorPlatform Shift

Initial Knee Extension due to Posterior Platform Shift

Conclusion and Future Work

• Biarticular muscles play an important role in postural control.

• Multi-directional perturbation may need to investigate the stability on all directions.

• Alternative treatments need to be analyzed before preferring an intervention to the other one.

• Stretch-reflex controller can be replaced by more advanced controller.

Thank You