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Additional Data

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In addition to the in vivo measured joint loads, further kinetic and kinematic data are published at OrthoLoad.com. Short descriptions of these additional measures are given in this chapter.

Instrumented Crutches

Instrumentes Crutches
Instrumentes Crutches

Fcont - Contralateral Crutch Force

Fipsi - Ipsilateral Crutch Force

2kN Force Transducer (KM 30z)

Instrumentes Crutches
Technical data:
Bridge resistance: 350 Ohm
Linearity error: 0.1%
Hysteresis error: 0.1%
Measurement amplifier BA660
Sensitivity: 0.5mV/V
Bridge Voltage: 5V
Output Voltage: +/- 5V
Linearity error: 0.02%
fc output filter: 250Hz

Bending Moment

The resultant bending moment Mbend , acts in the middle of the femoral neck and perpendicular to the neck axis, and is calculated with the following formula:

Bending formula01.png

with Bending formula02.png

Bending formula03.png

The forces (Fx’, Fy’, Fz’) and moments (Mx’, My’, Mz’) are measured in the “implant coordinate system” x’, y’, z’ centered in the middle of the implant head. The force component Fx’ acts laterally, Fy’ anteriorly, and –Fz’ distally along the femur axis. The measured moment components Mx’, My’, and Mz’ turn right around the x’, y’, and z’ axes. N is the distance between the head center and the middle of the femoral neck and is equal to ½ L.

Mtne acts around the neck axis of the femur and represents the torsional loading of the neck. It is calculated by α = -45° rotation of the "bone coordinate system” around the y-axis.

Bending Moment

Ground reaction forces

Ground reaction forces were measured using two 6 degrees of freedom force plates (AMTI, Watertown, MA). The coordinate system is a right-handed system.

Raw data:

Fx,y,z 1/2 Ground reaction forces, forceplate 1 and 2 N 960 Hz
Mx,y,z 1/2 Moments relative to the original forceplate coordinate system, forceplate 1 and 2 Nmm 960 Hz

For the calculation of the center of pressure the following offsets were used. The true origins of the coordinate systems are located below the top surfaces, with a distance (zo).

GroundReactionForces 01.png GroundReactionForces 02.png

Processed data

(see Comprehensive Data Sample):

Fgrx,y,zi Ground reaction forces, ipsilateral leg N 90-110 Hz
COP_x,yi Center of pressure, relative to forceplate center, ipsilateral leg mm 90-110 Hz
Tz_i Torque around z-axis at CoP, ipsilateral leg Nm 90-110 Hz
GroundReactionForces 03.png

grf2f.eof data:

(Downsampled Ground Reaction Forces)

Fgrxi,yi,zi Ground reaction forces, ipsilateral leg N 90-110 Hz
Fgrxc,yc,zc Ground reaction forces, contralateral leg N 90-110 Hz
F Resultant joint contact force (implant) N 90-110 Hz
GroundReactionForces 03.png