DOCUMENTATION OF COMPLIANCE MEASUREMENT USED IN THE FORCE RECORDING AND ANALYSIS SYSTEM
J. M. Evans, C. L. Evans
Sense Technology, Inc.

BACKGROUND

Shortly after the introduction of the Model SHLCP-5 Precision Adjustor, reports were received from clinicians that the sound of the impulse changed during use. Some clinicians began using the change in sound as an indicator that the adjustment phase should be terminated.4 Another group of clinicians5 began to use the instrument as a percussor to help locate points on the spine as candidates for adjustment.

The use of percussive techniques as an aid to diagnosis is well known in the medical arts. The image of the physician tapping our body with a small hammer is a vivid childhood memory for most.

As commonly practiced, this technique is subject to wide variability in both the application of the percussive force (was the last impulse the same as the current impulse?) and the interpretation of the results (you can hear the difference, can't you?). This variability and the total subjectivity of the interpretation of the results require a certain minimum training and individual aptitude to make the technique useful and the results transferable across patients and examiners.

The development of the Force Recording and Analysis System presents an opportunity to improve the percussive technique since:


With these potential benefits in mind, it was decided to investigate the potential for improving the use of the Model SHLCP-5 Precision Adjustor by incorporating an objective method of measuring substrate compliance in the Force Recording and Analysis System Model 01.
PURPOSE

Development of a reliable objective method of assessing differences in the response of the body to the application of a light impulse loading.

THEORETICAL ANALYSIS

Impulse techniques are commonly used in engineering analysis to examine the response characteristics of structures or electrical circuits.6 7 These techniques employ the use of instrumented impulse hammers to excite a structure and appropriate sensors to measure the response of the structure. Of particular interest is the single point vibration analysis in which the excitation and response of the structure occur at the same point.

The adjusting head of the Force Recording and Analysis System may be used in a manner consistent with single point impulse-response testing. In this case the excitation of the "structure" is achieved by the armature within the solenoid body being brought into contact with the anvil of the adjusting head. To achieve this excitation, the adjusting head must first be pressed against the patient until a pre-defined preload is achieved. This assures that the initial conditions for the impulse are the same each time.

At a given force level the energy imparted to the solenoid armature is the same each time the head is activated. Since the mass of the armature is also constant, the velocity of impact of the armature with the anvil is essentially constant. The energy of excitation imparted to the anvil by the armature will thus be constant each time the head is activated at a given force level.

After the anvil has been excited by the armature, it is free to move with respect to the adjusting head. The movement of the anvil against the resistance of the substrate (patient simulator or patient body) determines the force between the anvil and the patient's body as measured by the force transducer attached to the front of the anvil. Under these conditions, "the stiffness of the contacting surfaces affects the shape of the force pulse..."8



Illustration of Pulse Shapes Obtained From Different Substrates


Illustration Using a Simple Discrete Parameter Model

The patient's body is represented by the spring with spring constant K and the damper C. In the equation of motion for this system, the mass used would include the mass of the anvil as well as a virtual mass of tissue. Assuming that the damping and virtual mass are essentially constant, the frequency response of the system and, therefore, the shape of the impulse would be determined primarily by the spring constant or stiffness of the substrate.

If this simple analysis is fundamentally sound, the peak force of each impulse would be expected to vary with the stiffness (or inversely with the compliance) of the substrate and would be expected to be constant at a point on a substrate.

OBJECTIVE

Document rationale and performance of assessment techniques.

MATERIALS

Sense Technology Force Recording and Analysis System Model 01.

Patient simulators of various density and elasticity.

Patient volunteer.

METHOD

The adjusting head of the Force Recording and Analysis System was placed on a substrate simulating a point on the body of a patient and activated twenty times. The peak force for each impulse was recorded. The mean peak force and standard deviation of the observation was calculated. This test was repeated twenty times and the standard deviation of the total data set was calculated. This is a measure of the variability in the peak force measurements. Two peak force measurements many standard deviations apart indicate a change in the physical system.

This test was repeated on simulator materials of different compliance.

After the tests were concluded on substrates of constant but different compliance, the test was repeated on a volunteer. The first test point was chosen to be the heel of the subject's hand, the second test point was the palm of the subject's hand and the third was the tip of the index finger.

All tests were run at a force setting of fifteen pounds and the peak force was recorded with the Force Recording and Analysis System.

Results of the patient simulator tests are summarized in Table 1.


ANALYSIS

The results of the tests indicate that the peak force of the impulse produced by the adjusting head of the Force Recording and Analysis System can be reliably reproduced when the impulse is applied to a single point on a unchanging substrate such as a patient simulator. The results also indicate that the peak force of the impulse is repeatable when applied on one point of the body. An estimation of the measurement error at each force level is shown in the graph.

In addition, the mean force varies in a predictable and expected manner when the impulse is applied to surfaces of differing compliance; that is, low compliance substrates (high resistance) result in a higher peak impulse with higher compliance substrates (lower resistance) substrates resulting in lower peak forces. Furthermore, the variability of the data indicate that differences in peak force of greater than ten percent (fifteen pounds at full scale) have a ninety-five percent chance of representing valid differences in the underlying substrate.

CONCLUSIONS

The results of the testing and analysis indicate that fundamental engineering analysis methodologies may be productively applied to the problem of quantifying the analysis of the compliance of the human body. In particular, single point vibration analysis techniques utilizing impulse loading are useful in explaining and analyzing the force output of the adjusting head of the Sense Technology Force Recording and Analysis System. The peak force has been shown to be related to the compliance of the substrate to which the adjusting head is applied. The peak force has been shown to be essentially constant for a single substrate. Variations of greater than ten percent in the peak force indicate a high probability that the output was derived from two different substrates.
APPENDIX II Intra- and Inter-Examiner Reliability Studies


DOCUMENTATION OF INTRA- AND INTER-EXAMINER RELIABILITY OF
DIFFERENTIAL COMPLIANCE METHODOLOGY
(a pilot study)
K. Allen D.C., R. Crisman, D.C., R. Keeler, D.C.,
J. Pesce, D.C. S. Saleeby, D.C., J. M. Evans, Ph.D.

The compliance of the human spine may be thought of as the ease of movement of each individual vertebra. For the purposes of this paper, compliance is defined as the displacement response of a structure when subjected to a unit force. It is the inverse of stiffness and intuitively can be thought of as the flexibility of a structure. This paper describes reliability studies on an instrument which measures the compliance of the human spine, before, during and after adjustment.

Sense Technology, Inc. has developed a unique chiropractic adjusting system which incorporates a percussive adjusting head. This percussor is instrumented with a force transducer that supplies data to a computer system. The computer stores and displays the force data for clinical evaluation. This system, referred to as the Force Recording and Analysis System (FRAS), is an extension of previous adjustors which are marketed without the force instrumentation.9 The clinician uses the Force Recording and Analysis System to challenge each vertebra with a low energy impulse. The system records and displays the peak force measured at each vertebra. The compliance of the vertebra is inversely proportional to the peak force. The results of the compliance assessment are used by the clinician, in conjunction with other diagnostic techniques (such as palpation, X-ray examination, thermal analysis, and analysis of patient complaint and history) to determine appropriate adjustment locations.

BACKGROUND

Sigler and Howe [20] and Jackson et al. [10] have pointed out that when measurement systems are used as the basis for diagnostic techniques, the reliability of the measurement system directly influences the reliability of the diagnostic system. Sigler and Howe found that the errors involved in measuring very small changes in atlas position on X-ray films were of such magnitude that the validity of the entire diagnostic and therapeutic regime was open to question. Jackson et. al. found using a somewhat different measurement system that changes in angles between vertebrae could be reliably obtained from X-ray films. A series of studies has been conducted examining the reliability of palpation and motion palpation for the detection of "somatic dysfunction" with mixed results [4,14,15,17,25,27]. Where statistical significance has been achieved, the level or strength of the findings has been relatively low. DeBoer et. al. [4] points out that such findings are not surprising since even well-established procedures such as reading X-rays, E K G's or blood pressure give maximum intra-examiner correlation in the range of .40 to .60. Others [19,21-24] have attempted to assess the reliability of simple instrumentation (inclinometers, temperature measurement instruments and penetration devices) as aids to diagnosis, again with mixed results. Several authors [7,8,16] have critiqued the methodology used in intra- and inter- examiner reliability studies. Their critiques may be useful as general guides and to raise questions regarding statistical methodology.

In previous work[6] we have documented the reliability and applicability of force measurement techniques for measuring differences in compliance of various substrates including the human body. That study concluded that the peak force of the impulse of the adjusting head varies directly with the stiffness of the substrate ( inversely with the compliance). The measures obtained showed that the system produced a repeatable result and that differences of greater than ten percent in peak force were significant.

Clinicians are currently using the Model SHLCP-5 Precision Adjustor to percussively test the spine both before and after adjustment [3]. The force levels used are generally higher (twenty-five pounds) than used for the initial assessment of the Force Recording and Analysis System (fifteen pounds). The proposal to apply these techniques to the analysis of compliance along the human spine raises some fundamental questions. This study examined the following:




In order to provide preliminary answers to these questions, the following trials were conducted:

Trial One- Examine the variability of compliance measurements in the cervical spine

Trial Two- Determine the reproducibility of repeated compliance readings taken by the same examiner.

Trial Three- Determine the reproducibility of repeated compliance measures taken by two different examiners.

TRIAL ONE
Determine the variability of compliance measurements
of the human spine using the Force Recording and Analysis System.

Method: A 30mm dual prong attachment was used to straddle the
spinous of the patient's vertebrae. The examining chiropractor
stabilized the head of the seated patient in flexion, chose the line
of drive and positioned the tips of the attachment on the
appropriate vertebra. Measurements were taken in the cervical
area of the spine of ten patients.

Results: Variations of peak force of up to 55% were found along the cervical
spine of individual patients.

Analysis: Some variation in measured peak force along the spine would be
expected from measurement variability alone. The commonly
observed differences in peak force of over ten percent between
adjacent vertebrae suggest that there is information in the
measurements that cannot be explained by measurement
variability [6]. This is suggestive of clinical significance.

Occasional differences in the mean of the cervical measurements
between patients were observed during the initial testing phase.
These differences were eliminated by normalizing each set of
measurements against the highest reading before display. The
normalized display showed the peak force readings as a percent of
the highest peak force reading for each patient. These normalized
displays allow the clinician to focus on the difference between
peak force readings rather than their absolute value.




Illustration of Normalized Display

TRIAL TWO
Determine the reproducibility of repeated compliance readings
taken by the same examiner.

Method: Using the 30mm dual prong attachment to straddle the
spinous of the patient's cervical vertebrae, the examining
chiropractor stabilized the head and neck of the seated patient
in flexion. The examining chiropractor chose the line of drive
and positioned the tips of the instrument on the occiput, and
vertebrae C1-7 and T1-3. Twenty patients participated in the study.
The examiner obtained a second set of readings on each patient
immediately after the first set. There were no markings on the
patient to serve as position references.

Research
Hypothesis: The patterns of compliance measurements obtained using the
Force Recording and Analysis System in consecutive measure-
ments of the human cervical spine by the same examiner show
no significant differences from one trial to the next.

Statistical
Analysis: Each set of consecutive readings was examined for similarity
using the following statistical techniques. First, the probability that
the two sets of data were different was computed using a c2
statistic. This method was chosen since an estimate of the
measurement error at each force level was available.[6] The c2
statistic was computed using the formula:


where: xi = the first set of data collected from the patient
yi = the second set of data
= the standard deviation at the force level
= the standard deviation at the force level
and are calculated using the empirical relationship
developed in [6]:

where: = .14
= .035


The probability of obtaining a c2 value at least as large as that
observed, assuming the measurements were drawn from the same
distribution, was computed from an incomplete gamma function.10
If this probability is smaller than .05, then the hypothesis that the
data sets are the same may be rejected with a confidence of 95%.

In addition, the Pearson product moment correlation (r ) was
computed on the data sets using the formula:



where: xi = the first set of data collected from the patient
yi = the second set of data

Finally, the intra-class correlation coefficient (ICC) was computed
by performing a one way analysis of variance and formulating the
ICC according to:



where = the variance within the data
= the variance between the data sets
m = the number of levels of the analysis

The chi square metric computes the square of the difference between each paired observation (the value obtained at level C1 on the first observation is subtracted from the value obtained at C1 on the second observation and the difference squared) and then compares that value to an estimate of the measurement, determined through empirical repetitive testing on known substrates of constant compliance[6].

If the measurements are exactly the same, the chi square returns a value of zero and the probability of obtaining a poorer (larger) result is necessarily equal to one. The larger the chi square the less likely that the two sets of measurements are "the same" or that the measurement is repeatable within an acceptable degree of error.

The chi square is a good measure of the significance of the difference between two sets of measures. Because its numeric values are not subject to direct interpretation, it does not provide a measure of the strength of the association. Some form of correlation coefficient is generally used as a measure of the strength of a significant association. The most widely used is the linear correlation (also referred to as the product-moment correlation or Pearson's r). The use of this statistic has been criticized [7,8,16], primarily because of artifacts such as obtaining a high correlation even though the two sets of measures differed by some constant value (i.e., a correlation equal to one would be obtained from two data sets even though each value in the second data set were twice the value of its mate in the first data set). In our case, where the pattern of data within the set may be more important than the exact values, this limitation may not be important.

The intra-class correlation coefficient (ICC) has been proposed, [7,16] as a more reliable indicator of the strength of a significant association for reliability studies involving continuous measurements. This coefficient can be constructed from the results of a one way analysis of variance. The formulation is:



where = the variance within the data
= the variance between the data sets
m = the number of levels of the analysis

If the data sets are exactly the same then MSB equals zero and the ICC equals one. If the variance between the data sets is greater than the variance within the data set then the ICC will be negative (no agreement between levels). If the variance between the data sets is less than the variance within the data then the ICC will be positive and there is said to be some agreement between levels. The results are summarized in TABLE 1.

Examiner Patient p r
1 1 10.52 .484 .98
1 2 41.23 <.0000 .86
1 3 12.01 .363 .85
1 4 11.94 .368 .80
1 5 12.62 .319 .85
1 6 9.47 .579 .80
1 7 10.89 .452 .82
1 8 12.11 .355 .74
1 9 3.73 .977 .97
1 10 15.56 .158 .82
1 11 14.82 .191 .80
1 12 11.5 .402 .84
1 13 20.61 .038 .91
1 14 15.68 .153 .82
1 15 15.35 .167 .86

Linear Correlation Across Patients for Examiner One =.88
ICC Across Patients for Examiner One =.90

2 1 18.58 .069 .89
2 2 9.21 .602 .95
2 3 14.43 .210 .91
2 4 49.91 <0000 .72
2 5 19.94 .046 .86

Linear Correlation Across Patients for Examiner Two =.85
ICC Across Patients for Examiner Two =.93

Linear Correlation Across Patients for Examiner One and Two =.96
ICC Across Patients for Examiner One and Two =.96

TABLE 1- INTRA-EXAMINER RELIABILITY


Example of results judged to be "different" according to the c2 criterion.


Example of results judged to be "the same" according to the c2 criterion.

Analysis: The two consecutive readings taken in the cervical area
were highly correlated for each chiropractor. In addition,
the c2 probability indicates that the null hypothesis (the
measurements are the same) could be rejected in only three
cases. It appears that the intra-examiner reliability
of the tests is high, by any of the metrics. The chi-squared and
ICC metrics sometimes disagree since chi-squared normalizes the
observed variability against an empirical estimate of the
measurement error, and the ICC normalizes against the variability
in the patient's measurements. If the ICC is calculated for all of the
data, a very high value is returned. This is done in the
overall ICC measurements reported in TABLE 1 above.

Sources of Variability:
There are two obvious sources of variability which may influence
the outcome of this intra-examiner reliability study. The first is
the error introduced due to imperfect placement. By placement,
we mean the position of the dual prong tips used for contacting
the patient during the examination as well as the line of drive
chosen by the examiner. Even with markings on the cervical area
(which were not used in this study), the angle of the instrument
and the positioning of the tips would be impossible to duplicate
exactly from the first examination to the second.

Another source of error is a result of the measurement itself.
In our case, it is not difficult to understand that the second
set of measurements may differ from the first due to the act of
measuring because the energy used in the measurement may
well be sufficient to cause changes in the underlying structure
of the spine. Such changes would be expected to result in
differences in response to the energy of the test impulse. That
these changes are relatively small is attested to by the excellent
agreement found. This agreement may well be improved by
training and/or lowering the energy of the impulse.

Conclusions:
The intra-examiner reliability of compliance measurements
obtained in the cervical spine with the Force Recording and
Analysis System is consistently high.

TRIAL THREE
Determine the reproducibility of repeated compliance readings
taken by two different examiners.

Method: Using the 30mm dual prong attachment to straddle the spinous
of the patient's cervical vertebrae, an examining chiropractor
stabilized the head and neck of the seated patient in flexion.
The first examining chiropractor chose the line of drive and
positioned the tips of the instrument on the occiput and
vertebrae C1-7 and T1-3. Three patients participated in the study.
A second examiner obtained a second set of readings on each patient
immediately after the first set. There were no markings on the
patient to serve as position references.

Research
Hypothesis: The patterns of compliance measurements obtained using
the Force Recording and Analysis System in consecutive
measurements of the human cervical spine by two different
examiners show no significant differences from one trial to
the next.

Statistical
Analysis: This analysis was conducted in the same manner as the
previous analysis for the intra-examiner reliability.


Examiner Patient p r
1-3 21 10.95 .447 .80
1-3 22 8.45 .673 .87
1-3 23 11.4 .432 .75


Linear Correlation Across Patients for Examiner One and Three =.89
ICC Across Patients for Examiner One and Three =.65


Analysis: The two consecutive readings taken in the cervical area
were highly correlated for each chiropractor. In addition,
the c2 probability indicates that the null hypothesis (the
measurements are the same) could not be rejected in any
of the cases. It appears that the intra-examiner repeatability
of the tests is high.


Discussion: The purpose of this trial is to determine whether
or not the compliance measurements obtained by two different
clinicians on a single patient are the same. The statistics suggest
that the measurements are quite reproducible across clinicians.


CONCLUSION

This study suggests that the measurements of the FRAS system reflect the actual compliance of the patient's spine. Further, the intra- and inter- examiner reproducibility of these measurements is good. A subsequent study will quantify our observations that these compliance measurements change after chiropractic adjustment with the instrument. Clinicians are just beginning to develop diagnostic and treatment rules to use the information provided by this new instrument.

Sense Technology Inc.
12/15/94

NOTES ON THE VALIDITY OF COMPLIANCE MEASUREMENTS OBTAINED WITH THE FORCE RECORDING AND ANALYSIS SYSTEM

Rob Crisman DC

ABSTRACT


OBJECTIVE
To verify that striated muscle contraction reduces the response of the skeletal structure to a low energy impulse when compared to the relaxed state. In addition, to verify that joints of different mobility will have predictable outcomes, i.e., when tested with a low energy impulse, skeletal joints with low mobility will elicit a higher response than skeletal joints with higher mobility.

DESIGN
Four normal volunteers were recruited to investigate the effects of muscle spasm on the readings obtained with the Force Recording and Analysis System (FRAS). Additionally a series of joints with known and different gross compliance were tested.

SETTING
Private clinical practice.

INTERVENTIONS
None.

MAIN OUTCOME MEASURES
Differential Compliance readings obtained with the Force Recording and Analysis System.

RESULTS
The results verified that the measurements taken with the FRAS on human subjects confirmed the hypotheses postulated by the investigator that muscle spasm may produce lower readings and that measurements taken on joints of low compliance versus joints of high compliance in human volunteers varied in the manner expected.

CONCLUSION
Both hypotheses were confirmed by the tests. It appears that the compliance measurements obtained using the FRAS vary predictably in the expected manner and may be useful in the clinical setting.

KEY INDEXING TERMS
CFI, Computer, Fixation, Medical Imaging, Compliance.

INTRODUCTION


The Force Recording and Analysis System (FRAS) manufactured by Sense Technology Inc. is used to perform a Computerized Fixation Imaging Scan (CFI Scan) of a patient's skeletal structure. The Differential Compliance Methodology implemented with the FRAS enables the examiner to objectively determine the relative compliance of two or more vertebral segments or to evaluate the mobility of a single spinal segment in any of its degrees of freedom.

The first step in obtaining a CFI Scan is to obtain a measure of the compliance of each vertebra or segment of the spine under evaluation. This measure is obtained by applying a low energy mechanical impulse to each segment of the spine sequentially and recording the response of the segment. After all segments of interest have been challenged in this way, the responses are displayed visually for the examiner as a bar graph. Low bar graph readings indicate a segment with high compliance (low resistance) and high bar graph readings indicate a segment of low compliance (high resistance). The clinical interpretation of these results is that a joint segment with a much lower compliance than its neighbors may be fixated and a candidate for adjustment.

Previous work1 has demonstrated that the FRAS instrument gives reliable and predictable results when applied to surfaces of known and constant compliance and to parts of the body with different compliance. Clinical use of the instrument, while supporting the general conclusions drawn from these tests, raises questions regarding the role of the musculature surrounding and attached to skeletal segments. In particular, striated muscle contraction surrounding a joint segment commonly found in soft tissue injury2.may influence the results of the scan. If the muscle contraction reduces the normal response of the segment, a joint segment that is in fact fixated may be judged normal or of high compliance.

The purpose of this study is to examine the hypothesis that muscle contraction reduces the response of a skeletal segment to the mechanical impulse used to challenge the segment. In addition, a series of joints of different compliance were tested to examine the hypothesis that joints of low compliance produce higher readings when compared to joints of high compliance.

METHODS


SUBJECTS
Four normal, pain free volunteers (two females: the first, 26 years of age, 170 cm in height, 66 kg in weight; the second, 33 years of age, 165 cm in height, 65.8 kg in weight; and two males: the first, 27 years of age, 180 cm in height; 86 kg in weight; the second, 32 years of age, 183 cm in height, 88.4 kg in weight) were recruited for the study. Each subject was required to read an information sheet describing the study and give written informed consent before being included in the study.

PROCEDURE


EFFECT OF MUSCLE SPASMS
In order to test the effect of muscle spasm or tetanus on the compliance readings obtained with the Force Recording and Analysis System, one site on each subject was tested. The site chosen was the anterior midpoint of the diaphysis of the right humerus. The midpoint was visually determined after palpation of both ends of the bone. This point, coincident with the belly of the bicep muscle, is the thickest part of the muscle when in full contraction. Tests were made with the elbow bent at approximately 35 degrees, 90 degrees and 150 degrees with the bicep muscle in full isotonic contraction. The same point was tested three times at 35 degrees, three times at 90 degrees, twice at 150 degrees and three times with no contraction.





For convenience, the tests were conducted using an eleven point data collection and analysis algorithm. In general, the first eight readings were obtained with the muscle under examination in a contracted state. Then, without leaving the data collection routine, the last three readings were obtained with the muscle in a relaxed normal state of tetany. After all eleven data points were collected, the algorithm normalized the results and displayed all the data points as a series of eleven bars in graph format.

COMPARISON OF JOINTS OF DIFFERENT COMPLIANCE
In order to compare compliance measurements obtained on joints of known and different compliance, a series of tests were made on sutura, condyloid and ginglymus joints. These tests were conducted on the male subjects The tests were conducted in the presumed order of lowest compliance to the highest compliance, i.e. the sutura was tested first followed by the condyloid and ginglymus joints. The specific joints chosen were:



Again, for convenience, an eleven point algorithm was used for data collection and analysis. Each joint with the exception of the last was challenged four times with the low force impulse and the response recorded. The last joint was challenged three times.

DATA ANALYSIS
Each skeletal segment of interest is challenged by a low energy impulse. This impulse contains a wide band of frequencies (from zero to approximately 20,000 Hertz). The segment resists the initial impulse and the amount of resistance is recorded with a force transducer. The peak force recorded is a simple measure of the resistance of the segment to the initial low energy impulse. More complex analysis of the response waveform would reveal the major frequency of the response of the segment. For our purposes, the maximum response was sufficient to characterize the compliance of each of the skeletal segments of interest.

After the segment has been challenged and the maximum response recorded, the analysis routine asks for the next segment. The investigator repeats the test on all segments of interest in turn. In this case the analysis routine was composed of eleven segments. After all eleven segments have been tested, the analysis routine selects the segment with the maximum response and sets its value to one. The values of the remaining segments are transformed to a value proportional to the maximum value by the following relationship:

fn = fi /fmax
where fn = the normalized maximum value for segment i
fi = the maximum value for segment i
fmax = the maximum value recorded for all segments

This yields a set of values for the segments tested that are normalized relative to the maximum value recorded. These values are then displayed for the investigator as a bar graph with eleven elements.

RESULTS

Typical results obtained from the humerus with the elbow bent at 35 degrees, 90 degrees, and 150 degrees and relaxed. First nine measurements with muscle in full isotonic contraction with the elbow at the three respective angles; first three measurements at 35 degrees, second three at 90 degrees, next three at 150 degrees, remaining measurements with muscle relaxed.

Typical results obtained from sequential testing of sutura joint, condyloid joint, and ginglymus joint. First four measurements obtained from the sutura joint; second four measurements from the condyloid; last three measurements from the ginglymus.

DISCUSSION


The results of the tests clearly indicate that contracted versus relaxed striated muscle gives lower readings when the muscle is contracted. The reason for this result appears to be the greater absorption of the energy of the test impulse when the test is conducted on contracted striated muscle. The greater absorption may be due to the actin and myosin filament crossing over each other in the sacromere, causing the muscle to be thicker at the belly of the muscle.3 Also, the tension of the muscle creates a spring board effect which, when combined with the damping properties of tissue, acts to shield the underlying structure much like a spring and shock absorber in an automobile. Conversely, when the muscle was relaxed, the impulse penetrates directly to the underlying bone which produces a higher response to the impulse.

When a low reading is obtained clinically with the FRAS, the clinician must determine whether the reading represents a highly mobile (hypermobile?) segment or whether the reading is due to muscular involvement. This determination is relatively straightforward and is made primarily through palpation of the segment in question to determine evidence of tenderness or muscle tightness.

CONCLUSION


Two hypothesis were postulated by the examiner. The first was that a joint surrounded by muscle in contraction would produce a low response to a low energy mechanical impulse when compared to the response to the same impulse when the muscle is not in contraction. The hypothesis was tested by challenging the skeletal body at one point where the contraction of the overlying muscle was easily controlled. The point was the belly of the bicep muscle over the midpoint of the humerus. The intensity of the contraction was controlled by varying the angle between the humerus and the forearm. Observation of the test results showed that the more intense the contraction at either site correlated with lower readings (higher apparent compliance). These results supported the hypothesis and confirmed instructions in the manufacturer's manuals as well as the clinical protocol co-authored by the author.

The second hypothesis was that joints with different compliance would produce different results when tested and that the results would vary predictably with known joint compliance when compared on the same scale. This hypothesis was also confirmed. The response obtained from the sutura was 40 percent higher than the responses obtained from the condyloid and approximately 500 percent greater than that obtained from the ginglymus.

Both hypotheses were confirmed by the tests. It appears that the compliance measurements obtained using the FRAS vary predictably in the expected manner and may be useful in the clinical setting.

REFERENCES

1. Evans, J M, Evans, C L. Documentation of Compliance Measurement Used in the Force Recording and Analysis System, Sense Technology Inc., 1994

2 Gordon, Huxley and Julian, "The Length-tension Diagram of Single Vertebrate Striate Muscle Fibers, "Journal of Physiology 171:28P, 1964.

3 Lan, N.C. et al., "Mechanisms of Glucocorticoid Hormone Action,"Journal of Steroid Biochemistry, 20:77, 1984.



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