System of measurement provides indications of ulnar properties independent of characteristics of surrounding soft tissue and other bones. Mechanical modal approximated ulnar response so average bending rigidity could be determined to provide direct index of bone resistance to bending loading

Thompson, G.

Young, D. R.

English

NASA Technical Reports Server

DRIVING PROBE-11 FORCE .F 
IMPEDANCE HEADJ
log (F/a) 
GAIN	 DIGITAL METERS 
PHASE	 BCD 
METER	 ANALOG 
org (F/a) 
Dectmber 1974	 B74-10245 
NASA TECH BRIEF 
Ames Research Center 	
A 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
In Vivo Measurement of Mechanical Impedance of Bone 
During an investigation of the factors contributing 
to .the loss of bone strength, a method was developed 
for measuring the mechanical impedance of the ulnar 
bone in living human subjects in order to determine 
the response of the bone to lateral vibrations. A sys-
tem of measurement was designed to provide indica-
tions of ulnar properties independent of the character-
istics of surrounding soft tissue and other bones. A 
mechanical model made of discrete elements was 
constructed to approximate the ulnar response so 
that estimates of the static bending stiffness of the 
bone could be made. From the estimates of stiffness, 
an average bending rigidity can be determined which 
provides a direct index of the resistance of the bone 
to bending loading.
pedance head and probe are cancelled in the opera-
tional-amplifier circuit. The gain-phase meter is used 
to obtain both digital and analog presentations of the 
ratio of force to acceleration and the associated phase 
angle. Although the combined measuring system is 
capable of operating over the frequency range of 20 
Hz to 10 kHz, measurements are made only below 
1000 Hz because impedance above that frequency 
reflects largely the properties of the soft tissue lying 
between the probe and the bone. 
The subjects forearm is placed horizontally over 
the drive probe in a fixture that supports the wrist 
and elbow. At the elbow is a small pad cast from plas-
ter to conform to the bony prominences; it is posi-
tioned transverse to the ulna and centered under the 
HIGH 
PASS	 MASS CHARGE amPs
	 I—	 FILTERS	 .,CANCELL 
VOLTMETER 
ADJUSTABLE	 ELECTROMAGNETIC 
COUNTERWEIGHT	 SHAKER
AUDIO
AMPLIFIER 
AUDIO 
OSc 
As shown in the diagram of the equipment, an 
electromagnetic shaker is located at one end of a 
balance beam; a counterweight at the other end is 
used to apply a constant preload force to couple the 
vibrations through the drive-probe to the forearm. 
The driving force and acceleration are measured by 
an impedance head; the effective end mass of the im-
OSCILLOSCOPE 
greater sigmoid cavity so that the ulna is constrained 
from moving when a subject pushes down through 
the humerus. Motion of the ulna at the distal end is 
inhibited by placing a conforming plaster pad directly 
under the styloid process and applying downward 
pressure through the styloid end of the radius with a 
clamping fixture. By this method of positioning, 
measurements are relatively independent of the mag-
nitude of the constraining forces at the elbow and 
wrist.
(continued overleaf) 
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https://ntrs.nasa.gov/search.jsp?R=19740000245 2020-03-17T13:59:24+00:00Z
Vibrations of the ulna are excited by the electro-
magnetic shaker at approximately 60 percent of the 
distance from the olecranon end of the ulna to the 
styloid process. The transverse position of the drive 
probe is determined by scanning across the forearm 
at a fixed frequency of 100 Hz until a position is 
found where impedance is at a maximum. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP 74-10245
Patent status:	 0 
NASA has decided not to apply for a patent. 
Source: Donald R. Young 
Ames Research Center

with Gerald Thompson of

M. B. Associates
under contract to

Ames Research Center

(ARC-10857) 
[11 
B74-10245	 Category 05


In vivo measurement of mechanical impedance of bone

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