Modeling the index finger of a clinician duringthe course of physical examthe course of physical exam

By:

Yasser Ashraf GandomiApril 26, 2012University of Tennessee

Motivation:

To model the force applied by index finger of a clinician duringthe course of physical examthe course of physical exam

Denniz Zolnoun, MD, MPH

In particular:

Denniz Zolnoun, MD, MPHAssociate Professor; Director, Vulvar Clinic

Department of Obstetrics and Gynecology, UNCDivision of Advanced Laparoscopy and Pelvic Pain

To investigate the contact forces being applied by the index fingerof the clinician during different postures.

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What other researchers have done before?Table1: Prior studies regarding index finger modeling

Model Year Method Equilibrium equations

K. S. Fok et al.  2008 Minimize tendon forces based  Ten (10) force and 

Table1: Prior studies regarding index finger modeling

(2008)  on muscle PCSA cost function , non‐linear optimization

moment equations based on four DOF 

Vigouroux et 2007 Minimize tendon forces based Four (4) momentVigouroux et al. (2007) 

2007 Minimize tendon forces based on muscle PCSA cost function, non‐linear optimization 

Four (4) moment equations based on four DOF 

Sancho‐Bru et al. (2001) 

2001 Minimize tendon forces based on muscle PCSA cost function, non‐linear optimization, 

d l

Four (4) moment equations based on four DOF 

excursion model 

Li et al. (2001)  2001 Direct solution to simultaneous equations

Three (3) moment equations based on

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equations  equations based on three DOF 

The Musculoskeletal Model:

Skeletal Modeling:1‐ 3D2‐ Four segments (Metacarpal Bone, Proximal Phalanx, Middle Phalanx, Distal Phalanx) 3‐ Three joints

Fig 1: Index finger schematic model

Muscular Modeling:Flexor and Extensor muscles

Fig. 1: Index finger schematic model 

Fig. 2: Index finger including muscles4/30/2012

The SIMM Model:

Upper‐extremity right‐side model

Fig. 3: The imported SIMMmodelFig. 3: The imported SIMM model

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Two‐dimensional equations of motion tol l t fi j i t tcalculate finger joint torques:

Newton‐Euler inverse dynamic approach:dynamic approach:Index finger segments wereapproximated by cylinderswith circular cross sections.

Fig. 4: Simplified index model with joints and segments

Torque of each joint is expressed in terms of mass M, centrifuge R, coriolis C, gravity G and external force F

(1)

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G, and external force F

Joint equations:Table 2: Geometrical and mass properties of the segments

Secondmc 8.3e‐6 0.016 3.9e‐7 4.1e‐6

2proxph 2.8e‐6 0.0054 6.7e‐8 2.4e‐6

2midph 6e‐7 0.0011 5e‐9 1.6e‐7p

2distph 2e‐7 0.0004 8e‐10 3.5e‐8

(2)

(3)(3)

(4)

(5)

4/30/2012Fig. 5: Simplified index model with joints and segments

(6)

Contact model:To achieve the desired normal force, since the index finger is covered by soft‐viscoelastic layer, the dynamic model of the contact was modeled based on the Hunt‐Crossley model.

The Hunt‐Crossley model : This model incorporates a spring in parallel with a nonlinear damper to model the viscoelastic dynamics.

(7)(8)

(9)

(10)

4/30/2012Fig. 6: The Hunt‐Crossley model

Experimental set‐up:

Fig 7: Real time data acquisition was conducted via a computer interface calibrated to A) Wegner Digitalalgometer® custom fitted with a cotton swab for the purposes of mucosal sensitivity assessment, B) ForceSensing Resistor (FSR) affixed on plastic thimble to examine pelvic muscles.Sensing Resistor (FSR) affixed on plastic thimble to examine pelvic muscles.

Experimental findings:‐ The average calculated contact forces from sensory 18‐25 N

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‐ The maximum applied force 30N

Results:

Fig. 8: Normal contact forces variation with contact layer’s distance

4/30/2012Fig. 9: Frictional contact forces variation with contact layer’s distance

Fig. 10: Normal contact force for different contact surfaces

4/30/2012Fig. 11: Frictional contact force for different contact surfaces

Fig. 12: Flexor muscle forces for different contact surfaces

4/30/2012Fig. 13: Extensor muscle forces for different contact surfaces

Fig. 14: A schematic review of fingers’ joints

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Fig. 15: Proximal interphalangeal joint flexion for different contact surfaces

Fig. 16: Metacarpal phalangeal joint flexion for different contact surfaces

4/30/2012 Fig. 17: Distal interphalangeal joint flexion for different contact surfaces

Discussion:

Findings:

1‐ The study revealed that the contact forces predicted by the model based on theC l ’ i l i d l i d d i h h i lHunt‐Crossley’s viscoelastic contact model are in good accord with the experimental

data.

2‐ It was shown that by increasing the contact surface’s distance from the clinician’sy gindex finger through the process of pressure sensing; both the normal and frictionalcontact forces increase to a specific level then by further increasing; these loadsdecrease.

3‐ The findings indicated that by decreasing the stiffness of the contact surface (shiftingfrom muscular body to fatty one), the normal and frictional contact forces decrease. Inaddition, by decreasing the stiffness, the contact forces reach their optimummagnitudes later.

4‐ It was concluded that the flexor muscle forces first increase by increased contactsurface’s stiffness then further increasing the stiffness yield to decreased musclesurface s stiffness then, further increasing the stiffness, yield to decreased muscleforces.

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Acknowledgement:Acknowledgement:

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Thank You:Thank You

Q ?4/30/2012

Questions?