Sid E. Williams, B.S., D.C.,
Edward F. Owens, M.S.
Lawrence B. Steinle, D.C.
Ronald S. Hosek, Ph.D

Life Chiropractic College, Marietta, Ga

Presented at: The 15th Annual Biomechanics of the Spine Conference
Seoul, Korea, October, 1984


One of the virtues of instrument adjusting is that it eliminates the variations inherent in any doctor's adjusting skill. Because of this, the adjusting instrument would appear to be the ideal tool for researching the effectiveness of different adjusting strategies. Unfortunately, most instruments are not capable of monitoring and repeating the many factors which constitute an adjustment. Such factors would include the six spatial variables which determine stylus position and orientation, stylus force, excursion and speed, headpiece force and stressbar force. Because of the documentation and repeatability requirements necessary in controlled research, a knowledge of the characteristics of the adjustment is mandatory if the adjustment is truly to be an independent variables.

To meet this need, we have developed an instrument at Life College which senses the positional, force and velocity parameters of an adjustment and makes them available to a computer for monitoring, storage, analysis and display. With this device, (described in another paper in these proceedings) known as the Sid Williams Research Instrument, it is possible to study a wide variety of questions about precision adjusting and material properties.

Although a number of different upper cervical specific techniques exist, most agree on the fact that atlas should be the focus of the adjustment and that the direction of the adjustment is extremely important. There is little agreement, however, on the amount of force to use for the adjustive thrust. Both light and heavy force techniques are in use today. Because we are interested in the role played by force, we have undertaken a study of the degree to which stylus preload and excursion affect the outcome of a single adjustment in a mixed population. This report presents preliminary results of a study which is still underway.

For purposes of this study, we have broken the force of adjustment into two parts. The first is preload; it is defined as the reaction force between the stylus and the tissue of the neck prior to delivery of the thrust. It is a reaction force because the harder the tissue pushes back of it, the greater will be the measured stylus force. The second part is the force between the stylus and the neck tissues during the thrust. This variable is more complicated, as the force applied is really a function of the tissue into which the stylus is moving. Its value is continually changing during the thrust as the stylus encounters increasing tissue resistance. Stylus force becomes therefore a function of stylus excursion, i.e., location. The greater the excursion, the greater the force. For this reason, we have opted to control excursion in this experiment while monitoring the stylus force. This is appropriate in light of the fact that we are studying rapid thrusts (25-50 ms duration); in these cases the stylus encounters more reaction force from the neck tissues but is seldom felt by the subject/patient. Most adjusting techniques, both hand and instrument, use rapid thrusts such as this with comparable durations.


Subjects for this experiment are volunteers obtained from the patient population of the Life College Clinic. Participation is contingent upon passage of the clinic physical and signing an informed consent. The experiment itself basically involves assessing each subject by x-ray, leg check, and palpation, adjusting and then reassessing. A flowchart of this process is shown in figure 1. Upon acceptance, each subject is assigned randomly to one of four possible study groups. The subject is blinded to his group assignment but is aware that group differences exist. The groups reflect the combination of excursion and preload used: Group 0 has Zero preload and Zero excursion; Group 1 has 0 preload and 1/8 inch excursion; Group 2 has 1/4 lb preload and 0 excursion; Group 3 has 1/4 lb preload and 1/8 inch excursion. Note that in the Zero preload groups, the stylus is moved back far enough that it never contacts the skin. These group characteristics are shown in Figure 2.

After assignment, subjects are given a standard set of three upper cervical x-rays: the lateral, nasium and vertex. In taking these films, placement is critical and is carefully monitored by two doctors. Following development, the x-rays are analyzed using the Life Cervical method, resulting in a side of laterality, line of drive, rotational couple and formula for placing a stress bar to prestress the cervical spine. The analysis also yields variables which describe the atlas position and the cervical curve. These are used together as measures of structure in this study, in a way that will be described in detail later.

A pre-adjustment supine leg check is performed according to a typical upper cervical protocol. This involves having the subject start from a standing position, push up onto the table and recline as straight as possible. The assessor provides a small amount of headward pressure, gently removes inversion or eversion and then reads the length difference at the heel-last line. The leg check is always monitored and checked by a second assessor. Leg check results are scored as integers representing the number of 16ths of an inch short; a short left leg would be scored as a minus number, short right would be positive while even would be scored as 0.

A subjective assessment is obtained by palpating bilaterally at the levels of the C1 and C2 vertebrae for pain, tenderness or spasm. Earlier work has demonstrated the reliability of this measure. Palpation is scored as a number which consists of the sum of qualities at each site. For example, a subject reporting pain and tenderness at C1 left and spasm at C2 right would be scored as a 3. The presence of no pain, tenderness or spasm would be scored as a zero, while having all three qualities at all four sites would be scored as a 12.

The results of the palpation, leg check and x-ray analysis are recorded on a data collection sheet coded for group membership.

Next, the adjustment is given. With the Sid Williams Research Instrument, the numbers from the x-ray analysis are given to the computer which determines the direction factors. These are set by the adjustor using a readout on the computer monitor. At the same time, the experimental excursion is set. The subject is placed with the side of atlas laterality up and the opposite mastoid or temple is supported on the headpiece according to the side of atlas listing. Headpiece, shoulderpiece and stressbar heights are set according to the results of the analysis of the lower cervical curve. The adjusting head is moved into place and the appropriate preload, either 0 or 1/4 lb, is applied. Delivery of the thrust is accomplished by activating a foot switch. Following the delivery of one thrust, the computer begins to plot the force and excursion data sampled during the actual thrust. At this time, the subject is given a post leg check and palpation assessment, followed by a set of post x-rays. The force excursion curves, as well as all of the adjusting directional parameters, the preload and the stressbar and headpiece force profiles are printed out for a permanent record.


In this study, we have observed leg length difference, palpation and cervical x-rays before and after a single adjustment of one of four types. For each variable, the thing of interest is how it has changed with the adjustment. To display such changes we performed the following transformation on all pre-post data:

                              (PRE - POST)
          CHANGE VARIABLE = (_____________)  X  100

The numbers generated by this transformation we call CHANGE VARIABLES. They let us see how close we have come to correcting or reducing a variable to its normal state. For instance, if the pre-palpation score is 6 and the post-palpation score is 0, this transformation yields a result of 100. This value means the adjustment has changed the variable to its normal or optimally correct value. Numbers less than 100 but greater than 0 mean a less than perfect correction. Greater than 100 means overcorrection. Numbers less than 0 mean changes in the wrong direction or a worsening.

Looking across a population of 20 subjects representing five individuals in each group, we see that there appears to be a relatively uneven distribution of the change variable for leg length across groups (fig. 3). If, however, we look at the group averages, we see that there are really no significant differences (fig. 4). If anything, Groups 0 and 1, the "light adjusting" groups, show the greatest changes. Note that no one experienced a worsened leg check.

The scanning palpation results show no apparent trends by group averages (fig. 6). Although groups 0 and 3, the lightest and heaviest adjustment respectively, show the greatest average change, the differences are not significant. It may be seen that, in the main, all subjects experienced a relative improvement in their palpation findings.

The most objective of the assessments used in this study is the x-ray. To obtain a measure of pre to post structural change, an index is used which is envolved from angles obtained during the analysis. This index consists of the average of the following four change variables: ATOCC, ATAX, CCL and SSL. These variables represent changes in atlas position relative to occiput, atlas position relative to axis, the upper angle and the lower cervical angle, respectively.

Examining this index by group, it appears as though there is an uneven distribution with no pattern (fig. 7). In three cases, a movement away from normal, i.e., a worsening of structure is note. No significant differences exist in the group averages (fig. 8); no group is distinctly different from any other group, implying that outcome is not affected by adjustive force.


While the foregoing results are preliminary, they suggest an interesting possibility--namely that low force, even off-the-skin adjusting has some effect on structural and functional variables. This observation is not new; in fact, some adherents of at least one upper cervical technique group routinely adjust with an instrument off the skin with excellent results.

It is appropriate to question the degree to which these results are skewed by x-ray placement and analysis errors. Some of these errors may be considered as relatively constant, such as those due to x-ray misalignment, placement biases and the methods of point choice. We have endeavored to eliminate these by maintaining aligned x-rays and using more than one individual for placement and analysis decisions. Errors of these types would tend to show up on x-rays as laterality biases or persistent distortions. We have not seen this. Another type of error, that due to random processes, should average itself out across a group of films. While we have attempted to reduce x-ray artifacts to a minimum, we acknowledge that no system is perfect.

We are in fact working even now on ways to improve our placement and analysis techniques, and expect to utilize a 3-D system of the Suh type soon. When this is in place we expect to participate in the Suh research studies using controlled adjustments delivered by the Sid Williams Research Instrument.


The present results, while interesting, only serve to provide us with a number of new questions to answer. If the stylus does not need to touch the skin, how do adjustive forces reach the cervical complex to cause structural changes which reduce derangements? To answer this question, a number of issues have to be addressed. The first issue that needs to be resolved is the degree to which subject placement on the adjusting table affects the outcome. This can be studied by repeating the present work but performing no adjustment. The position of the subject can be documented by using the stylus position sensors to monitor landmarks on the head and body and then recording the measured headpiece and stressbar forces. In this fashion, the effects of different setups as determined by different headpiece, shoulderpiece and stressbar combinations can be studied.

Even though the present work suggests that low force or no-force adjusting can cause positive changes, it remains still to determine how much force might be transmitted to the cervical complex through other means. One way this might happen is be vibration set up by the adjusting cam which could be transmitted through the headpiece to the cervical complex. Another possibility would be forces generated by neck muscles reflexively responding to vibration or to the sound of the cam and motor. To evaluate these possibilities, it will be necessary to analyze the force curves generated by the headpiece and stressbar transducers. We have these curves from the present study and are currently performing such an analysis.

Beyond these issues, it will be fruitful to examine the effects of stylus orientation and velocity on outcome. Stylus orientation or line of drive is often mentioned as being the single most important variable. It is the variable yielded by most analyses, even ones not specific to the cervical spine. The appropriate speed of adjustment is widely debated as well; it can only be studied effectively with an instrument such as ours which provides speed control and monitors speed.

As we embark on studies of these and other factors of the adjustment, we will need more sensitive, objective, and reliable outcome measures. Candidates for these would include neurological and thermal profiles and perhaps scanning for microwave radiation. The goal of the work ultimately is to achieve a complete understanding of the behavior of the cervical complex and how to remove its subluxations in acute and chronically ill patients. This of course implies a thorough understanding of the adjustment as well. Ideally, the adjustment should be delivered as specifically as possible, both in terms of where and how it's given and when. It should not be delivered haphazardly as is the case with plain manipulation. Before this can happen, all of the work outlined above and more must be completed. The technology to accomplish it, such as the Sid Williams Research Instrument, is becoming more available. Being able to control and monitor the adjustment is a big part of it. To the best of our knowledge, no other instrument can provide this. We invite other investigators to share with us in this work.