Electronic angular position and range of motion measuring device and method

An electronic device for measuring relative angular positional displacement and angular range of motion for body segments and articulating joints of the human skeleton is disclosed. The device has a hand-held interface unit which is placed against the body segment or joint to be tested. Mounted within the housing of the interface unit is a shaft with a pendulum at one end and an optical encoder at the other. As the body segment rotates or the joint articulates, the pendulum swings in the direction of gravity, causing the shaft to rotate. The optical encoder generates an electrical signal representative of the amount of rotation of the shaft. The generated signal is fed to a microprocessor which processes the information and can produce on a display the change in angular position relative to initial angular position or the angular range of motion of the body segment or articulating joint.

FIELD OF THE INVENTION 
This invention relates to an electronic device and method for accurately 
and quickly measuring the relative angular positional displacement and the 
angular range of motion for body segments and articulating joints of the 
human skeleton. 
BACKGROUND OF THE INVENTION 
Measuring relative angular positional displacement and the angular range of 
motion for body segments and articulating joints of the human skeleton is 
of value in the medical and rehabilitation fields. For example, with 
reference to the human spine, the primary spinal range-of-motion 
measurements, postural zero (straight up) to full flexion, postural zero 
to hyper-extension, postural zero to full left lateral bend, and postural 
zero to full right lateral bend, are used as part of the diagnosis of 
various spine and back-muscle disorders and diseases. As a patient engages 
in physical therapy or receives other treatment, the angular range of 
motion should increase, resulting in a changed measured value. However, 
prior instruments for measuring relative angular position and angular 
range of motion have not been found to be effective or accurate. 
In the past, doctors, clinicians and other medical professionals and 
paraprofessionals have measured the relative angular position and the 
angular range of motion for body segments and articulating joints of the 
human skeleton using mechanical inclinometers. These prior instruments 
were designed for use by plumbers and carpenters and therefore lack 
necessary features for use on the human skeleton. Such instruments are 
accurate only within plus or minus 1.degree. over a 360.degree. range, an 
accuracy which is not sufficient, for example, for the measurements made 
of the angular range of motion of the human spine, where an accuracy 
within plus or minus 0.5.degree. is desired. Mechanical inclinometers are 
often large and bulky and cannot be easily stabilized against the body 
segment or articulating joint, making it impossible to duplicate test 
conditions for two different measurements. Also, such instruments, because 
they do not have computational ability built into them, lack the ability 
to compute differential angles between two body segments. Further, such 
instruments are unsuitable for measurements in the lateral plane, as when 
a person bends from side to side at the waist. 
There has been a need for an easy to use, hand-held device which avoids the 
above-described problems. 
SUMMARY OF THE INVENTION 
This invention is directed to a hand-held electronic device for measuring 
relative angular positional displacement for body segments and 
articulating joints of the human skeleton. 
The device comprises a hand-held interface unit adapted for placement 
against the body segment or articulating joint. Generating means in the 
unit generates an electrical signal representative of a second angular 
position relative to a first angular position. 
In one embodiment, the generating means comprises an optical encoder 
mounted on a first end of a shaft and a pendulum mounted on a second end 
of the shaft, whereby the pendulum swings in the direction of the force of 
gravity as the body segment moves or the joint articulates, thereby 
causing the shaft to rotate, the encoder measuring the rotational motion 
of the shaft. The optical encoder generates an electrical signal in the 
form of electrical pulses representative of the rotational motion of the 
shaft. 
A microprocessor, electrically connected to the interface unit, processess 
the generated electrical signal and provides a measurement of the second 
angular position relative to the first angular position, or a measurement 
of angular range of motion. 
This invention is also directed to a related method for measuring relative 
angular positional displacement.

DETAILED DESCRIPTION OF THE INVENTION 
The device of the present invention allows for accurate and fast 
measurement of relative angular positional displacement and angular range 
of motion for body segments and articulating joints of the human skeleton. 
The preferred embodiment of the device of the present invention includes a 
control unit 10 and a hand-held interface unit 20, connected to one 
another by a flexible electrical cord 30, as shown in FIG. 1. As described 
below, there are also two attachments, one a lateral plane attachment 40 
for measurement of relative angular positional displacement and angular 
range of motion in a lateral plane (the side-to-side movement shown in 
FIG. 10), and the other an x-ray attachment 50 for measurement of angular 
differences on an x-ray film. 
The preferred embodiment of the device of the present invention is intended 
to measure relative angular positional displacement and angular range of 
motion for the following motions of the human skeleton: postural zero 
(straight up) to full flexion; postural zero to hyper-extension; postural 
zero to full left lateral bend; and postural zero to full right lateral 
bend. The invention may be used, however, to measure any relative angular 
positional displacement and any angular range of motion of the human 
skeleton. 
The control unit 10, shown in FIGS. 1, 2, 3 and 4, is made, for example, 
from injection molded polycarbonate, which is chemically stable against 
any and all cleaning solutions used in hospital and clinical environments. 
The control unit 10 contains a conventional microprocessor (not shown), 
for example, an NEC 78C10. Also within the control unit 10 is a display 
12, for example a liquid crystal display, and a power source (not shown), 
for example, six size AA rechargeable batteries. In the embodiment shown 
in FIGS. 1 and 2, five membrane switches 13-17 are located below the 
display 12. Switch 16 turns the control unit 10 on and off. Switches 13-15 
are so-called protocol switches, and set the mode in which the device will 
operate. The description of exemplary protocols is set forth below in the 
section entitled "Protocol Selection". The final switch is labeled "Reset" 
and is used to reset the control unit 10 for a new measurement. 
For ease of use, the control unit 10 has a bracket (not shown) so that the 
control unit 10 can be mounted on a wall perpendicular to the line of 
sight, for easy reading of the display 12, as shown in FIG. 4. The control 
unit 10 may also be tilted, as shown in FIG. 3, for example 10.degree., 
for use on a flat surface such as a desk, to facilitate reading. 
As seen in FIG. 2, the hand-held interface unit 20 is stored in a back 
recess of the control unit 10 when not in use. 
The flexible electrical cord 30 is used as a path for the transmission of 
electrical signals in the form of electrical pulses from the hand-held 
interface unit 20 to the control unit 10. The cord 30 is connected to the 
control unit 10 and the interface unit 20 by conventional jacks 32. 
The hand-held interface unit 20 is shown in detail in FIGS. 5-7 and 13-15. 
The interface unit 20, for example, is a two-piece, injection molded 
polycarbonate plastic. The interface unit 20 in the present embodiment is 
adapted for use on the spine and is 37/8" long by 5" high and 1 5/16" at 
its widest point. The profile of the interface unit 20, best seen in FIG. 
3, is designed to optimize stabilization against the four regions of the 
spine; cervical, thoracic, lumbar and sacrum. A front end 21 of the 
interface unit 20 which makes contact with the body segment or 
articulating joint is 7/8" wide to facilitate stabilization against the 
body segment or joint. A flat surface 22a on the top end 22 of the 
interface unit 20 and a flat surface 22b on a bottom end 22' of the 
interface unit 20 allow the operator to hold the interface unit 20 in his 
or her hand when placing the front end 21 of the unit 20 against the body 
segment or articulating joint. A set button 23 is placed on a top end 22 
of the interface unit 20 for use by either right-handed or left-handed 
persons. The set button 23 is activated in most cases in order to take 
reference points, in the manner described below in the section entitled 
"Protocol Selection". The interface unit 20 is also designed to fit 
comfortably in the hand of the physician or clinician. 
Included within the interface unit 20 are a pendulum 24, a pendulum housing 
25, a shaft 26 and an optical encoder 27. The shaft 26 runs through a 
central bore in the housing 25. Ball bearing 28, shown in FIG. 14, which 
is fixed on its outside to the housing 25 and is fixed on its inside to 
the shaft 26, permits the shaft 26 to rotate within the housing 25. 
Retaining ring 28a keeps the bearing 28 on the shaft 26 in a conventional 
manner. 
The pendulum 24 is secured to a first end 26a of the shaft 26 by spring pin 
24a. Spring pin 24a passes through pendulum bore 24b, shown in FIG. 15. 
Any swinging motion of the pendulum 24 will therefore cause the shaft 26 
to rotate. 
Attached to a second end 26b of the shaft 26 is the optical encoder 27, 
which, for example, is a Hewlett Packard model HEDS 5300 or any other 
Hewlett Packard optical encoder in the model HEDS 5000 series. The encoder 
27 operates in a conventional manner to translate the amount of rotation 
of the shaft 26, up to 360.degree., into a digital electrical signal, in 
the form of electrical pulses, indicative of the degrees of rotation of 
the shaft 26. 
As previously described, the shaft 26 rotates in response to the movement 
of the pendulum 24. The pendulum 24 will swing in the direction of the 
force of gravity as the interface unit 20 changes its angular position in 
response to the angular movement of the body segment or articulating joint 
being tested, for example as the patient moves from a postural zero 
(straight up) position to a flexion position shown in FIG. 8, or to a 
hyper-extension position shown in FIG. 9. Therefore, the digital 
electrical signal generated by the encoder 27 is representative of the 
degrees of angular motion of the body segment or articulating joint being 
tested. 
The electrical signal from the encoder 27, which is in the form of 
electrical pulses, is transmitted along cable 27a and then along cord 30 
to the microprocessor in the control unit 10, which acts as a processing 
means to process the electrical signal from the encoder 27 in a manner 
determined by the programming of the microprocessor. 
An improvement to the present invention is a device which includes the use 
of damping means, for example precision ball 29 made of stainless steel 
located in a groove 24c of the pendulum 24, to dampen the oscillations of 
the pendulum 24 as the pendulum 21 swings. This prevents inaccurate 
readings of angular position due to rotation of shaft 26 in response to 
the oscillations of pendulum 24. 
The pendulum 24 has a natural frequency of oscillation at which it will 
swing as the shaft 26 turns. This frequency is dependent on the distance 
from the center of the mass of the pendulum 24 to the center of rotation 
of the shaft 26. The ball 29 also has a natural frequency of oscillation 
which is dependent on the diameter of the ball 29 and the diameter of the 
counterbore in the housing 25. The natural frequency of oscillation of the 
pendulum 24 is different from the natural frequency of oscillation of the 
ball 29. As the pendulum 24 swings in response to movement of the shaft, 
the differing natural frequencies of oscillation of the pendulum 24 and 
the ball 29 cause interference of relative motion between the ball 29 and 
the pendulum 24, resulting in a resistance between the pendulum 24 and the 
ball 29 and a damping of the pendulum's oscillations. In a preferred 
embodiment of the improved device, for improved damping, there is a second 
identical precision ball directly behind the ball 29 in the groove 24c. 
Rapid motion of the device can also cause extreme unwanted acceleration of 
the pendulum. To prevent such extreme acceleration, the groove 24c has 
tapered walls. During rapid motion, the ball 29 gets driven between the 
tapered walls of the groove 24c and the counterbore of the housing 25. 
This causes a wedging effect which quickly reduces the oscillations of the 
pendulum 24. 
This improvement which includes the damping means is not our invention but 
rather is the invention of Arthur Sammartano and is the subject of a 
patent application filed on even date herewith entitled "Improved 
Electronic Angular Position and Angular Range of Motion Measuring Device 
with Damping Means". The present application contains a description of the 
improvement invented by Mr. Sammartano solely to avoid any question 
regarding the best mode, pursuant to 35 U.S.C. Sec. 112, contemplated by 
us for carrying out our invention. The inclusion of a description of the 
improvement in this application should not be construed as an assertion by 
us that we invented the improvement claimed in Mr. Sammartano's 
application. 
The optical encoder 27 operates in a conventional manner to translate the 
rotation of the shaft 26 into interruptions of a light beam which are then 
output as electrical pulses along cable 27a and then along cord 30 to the 
microprocessor in the control unit 10. A code wheel 27c in the encoder 27, 
shown in FIG. 14, has, for example, 720 equally spaced apertures around 
its circumference, permitting measurement of angular rotation within 
0.5.degree.. 
Also shown in FIG. 14 is the stationary phase plate 27d of the encoder 27 
which has apertures such that the light beam from the encoder 27 is 
transmitted only when the apertures in the code wheel 27c and the 
apertures in the phase plate 27d line up. In the present embodiment, 
during one complete revolution of the shaft 26, there will be 720 
alternating light and dark periods. The optical information is then 
translated into generated electrical signals, in the form of electrical 
pulses, and transmitted to the microprocessor in the control unit 10 for 
processing. 
The device of the present invention may also be used to determine angular 
position or angular range of motion in the lateral plane, for example, 
when a person bends side to side, as shown in FIG. 10. Lateral attachment 
40, shown in FIG. 11, is adapted to be attached to the interface unit 20, 
for example, for snap-fitting into the interface unit 20, so that a 
lateral plane measurement can be made. The interface unit 20 with attached 
lateral attachment 40 is placed against the body segment or articulating 
joint in the direction of the arrow of FIG. 11. 
The device of the present invention, using the x-ray attachment 50 shown in 
FIGS. 12, 16 and 17, may be used to measure angular displacement on an 
x-ray film in several ways. As described below in the Protocol Section, 
the device with x-ray attachment 50 may be used to verify the results of 
external measurements such as those shown in FIGS. 8-9, and may also be 
used to measure subtle angular displacements such as interarticular 
changes, or to quantify the degree of deformity, such as in scoliosis. 
Protocol Selection 
The microprocessor in the control unit 10 may be programmed for any number 
of protocol operations. "Protocol" in the context of this invention means 
the calculations incorporated in the software by which the specific 
angular positional displacements are reported to the user. Below are 
described some protocol procedures which can be programmed in a 
conventional manner into the microprocessor of the control unit 10. FIG. 
19 shows the steps for one such representative protocol in flow chart 
form, the so-called compound mode protocol. It is understood that any 
number of protocol operations are possible and may be programmed into the 
microprocessor. 
Single Reference Mode Protocol 
This protocol, which is activated by depressing the Continuous switch 13, 
offers the ability to test total angular range of motion of one body 
segment or articulating joint at one location on the body segment or 
articulating joint while the patient is moved from a first anatomical 
angular position to a second anatomical position, for instance from the 
straight-up position to the flexion position (FIG. 8) or the 
hyper-extension position (FIG. 9). 
The interface unit 20 is placed by the physician or clinician (hereafter 
"the operator") on the body segment or articulating joint to be tested. 
The patient is then positioned into the first anatomical angular position 
and set button 23 is depressed, providing a reference point. The set 
button 23 is electrically connected to the microprocessor in the control 
unit 10 and acts in most cases to provide reference points. 
With the interface unit 20 stabilized by the operator against the body 
segment or articulating joint the patient is allowed to move. The control 
unit 10 will provide a continuous readout on the display 12 of angular 
displacement from the first angular position point during the movement. 
At the end of the anatomical range of motion of the patient or at the point 
of pain, or at any other defined point in the angular motion, the set 
button 23 is again depressed and the last displayed relative angle will 
remain on the display 12. When the reset button 17 on the control unit 10 
is depressed, the display 12 will clear and another test can begin. 
The Single Reference Mode Protocol can also be used to measure the relative 
angle between two body segments or articulating joints at two locations 
for one anatomical position. To accomplish this, the operator places the 
interface unit 20 device in location on the first body segment or 
articulating joint to be tested. The patient is then positioned to the 
desired initial anatomical angular position. The operator depresses the 
set button 23, providing a reference point. 
Making sure to keep the patient in the same anatomical position, the 
operator places the interface unit 20 on the second body segment or 
articulating joint to be tested. The operator depresses the set button 23. 
The last displayed angle will remain on the display 12. This will be the 
relative angle between the two locations chosen on the first and second 
body segments or articulating joints. 
To verify the results of external measurements, i.e. measurements taken on 
the body segments such as those shown in FIGS. 8 and 9, the x-ray 
attachment 50 of FIG. 12 is used. The attachment 50 is adapted to be 
attached to the interface unit 20, for example, by securing the attachment 
50 to the interface unit 20 by the tongue and groove method. As shown in 
FIG. 16, the device is placed flat on the x-ray film with the attachment 
50 pressed against one edge of the image of the spine on the film. Set 
button 23 is depressed to provide a reference point. The device is then 
moved to another x-ray film showing the spine in a different angular 
position, such as that shown in FIG. 17, and the angular displacement from 
FIG. 16 to FIG. 17 is shown on the display 12. This allows the operator to 
verify the external angular displacement measurements previously made. 
In order to measure interarticular changes, the displacement of specific 
segments (such as the lumbar vertebrae) can be measured by aligning the 
x-ray attachment 50 with the segments to be measured. A similar technique 
can be used to quantify degree of displacement in conditions such as 
scoliosis. 
The function of the Continuous switch 13 is to measure angular displacement 
in a continuous fashion. Once the Continuous switch 13 is depressed, the 
unit will continue to collect displacement data regardless of ending 
position. This mode may be used for general assessment purposes. For 
example, the operator may instruct the patient to move through a range of 
motion and note where the patient feels some tightness or discomfort, but 
not restriction of motion. The operator can note the angle at which this 
tightness or discomfort occurs, and instruct the patient to continue 
moving until motion is restricted by pain or other physiologic factors. It 
is imperative, however, that the operator note the final angle of 
displacement, as the device will not lock in the value but will simply 
continue to collect data. 
The Compound Mode Protocol 
This protocol, which is activated by depressing the Compound switch 15, 
offers the ability to test total range of motion of two body segments 
(connected either directly or indirectly) from their own set reference 
points. For example, the operator can measure the combined range of the 
scapula and humerus which are directly connected via the glenoid fossa. 
One can also measure the total range of the hip and entire spine by using 
the sacrum and base of the occiput as reference points. These two 
anatomical landmarks are indirectly connected via the lumbar, thoracic, 
and cervical spine. The microprocessor in the control unit 10 will then 
calculate the differential range of motion between the two body segments. 
The primary goal of this protocol is to be able to obtain the relative 
range of motion between two body segments minus the effect of any other 
body position changes. 
In this protocol, the angular range of motion of the second body segment 
selected should be related to the total angular range of motion of the 
first body segment selected; that is, the two body segments selected 
should be combined components of the total range of motion to be tested. 
For example, trunk forward flexion is a combination of hip flexion and 
spine flexion. In order to assess the contribution of hip motion versus 
lumbar spine motion, the total motion of the hip and lumbar regions must 
be measured together, with total hip motion subtracted from total combined 
motion to calculate lumbar motion. 
The operator places the interface unit 20 at the first location on the body 
segment to be tested. The operator then positions the patient at the 
anatomical starting position and depresses the set button 23, providing a 
first reference point. 
Making sure to keep the patient in the same anatomical position, the 
operator places the interface unit 20 at a second location on the body 
segment to be tested. The operator then depresses the set button 23, 
providing a second reference point. 
With the interface unit 20 at the second location on the body segment, the 
patient is allowed to move. The display 12 will provide a continuous 
readout of angular displacement from the second reference point during the 
movement. 
At the end of the anatomical range of motion of the patient or at a point 
of pain, or at any other defined point in the angular motion, the set 
button 23 is depressed again and the last displayed angle will remain on 
the display 12. This angle is the total angular displacement of the body 
segment at the second location during the test. 
Making sure to keep the patient in the same anatomical position, the 
operator places the interface unit 20 back at the first location on the 
body segment and depresses the set button 23. This will lock in the total 
range of motion for the first location of the body segment. The display 12 
will now show the total angular displacement of the body segment at the 
first location during the test. 
The interface unit 20 can now be removed from the patient. The operator 
depresses the set button 23 one more time and the microprocessor in the 
control unit 10 will calculate the differential angle between the first 
location and the second location on the body segment. 
Since the control unit 10 is locked in a "display only" mode, the control 
unit 10 on the display 12 will redisplay the results previously shown in 
the following order each time the set button 23 is depressed: 
total range of motion for the first location; 
total range of motion for the second location; and 
differential range of motion between the total range of motion for the 
first location and the total range of motion for the second location. 
This will continue until the Reset button 17 is depressed. 
FIG. 18 is a software flow chart showing the basic system operation of the 
preferred embodiment of the device of the present invention. Referring to 
FIG. 18, after the operator turns on the device by depressing the On-Off 
switch 16 on the control unit 10, the system tests the liquid crystal 
display 12 and the random access memory in the microprocessor. The 
operator then selects an operating mode by depressing one of switches 13, 
14 or 15. This step is represented by the block labelled "Mode Select" in 
FIG. 18. After the mode is chosen, the operator initializes the protocol 
by depressing the Reset switch 12 and, when the interface unit 20 is in 
the first or initial position on the body segment or joint, depressing the 
set button 23. 
As the device is moved to a different angular position, the system 
registers a start of the test (the block labelled "Test Start" in FIG. 18) 
and executes the desired protocol. If the device is moved too quickly such 
that the microprocessor is unable to read all of the electrical pulses 
from the encoder 27 ("Missed State" on FIG. 18), an error is displayed on 
the display 12 and the device will not execute another test until the 
Reset switch 17 is depressed. If there is no missed state, and the encoder 
27 is generating electrical pulses, the microprocessor processes the 
pulses from the encoder 27 ("Process Changes" in FIG. 17) and displays on 
the display 12 information regarding angular position. 
If at any time the device is inactive for five minutes or more, the device 
is automatically shut off to conserve battery power. 
An advantage of the present invention is that at a later time, for example, 
after the patient undergoes physical therapy or other treatment, the 
procedures described above relating to any of the specified protocols or 
any other programmed protocols can be repeated and further measurements 
taken. The operator can determine if the patient's angular motion 
capabilities have improved or deteriorated. This is possible because at 
the later time the interface unit 20 can be stabilized against the body 
segment or articulating joint in exactly the same fashion as the first 
measurement, permitting absolute repeatability of the measurement 
parameters. 
It is readily seen that the device of the present invention provides an 
accurate and fast method for measuring relative angular positional 
displacement and angular range of motion for body segments and 
articulating joints of the human skeleton. The interface unit 20 is 
compact and easy to hold, and the display 10 provides all information 
required and can be programmed for any number of different testing 
procedures. 
Applicants' invention is not limited to the embodiment of the device or the 
method described above. It is further understood that applicants, 
invention is as set forth in the following claims: