Clinical Biomechanics of Posture — Chapter 1: Evidence for CBP® Clinical Practice

The Final Written Piece from Dr. Donald Harrison

Dr Don Harrison

Editors Note: This chapter is the last, complete, written document that my father produced when he was still healthy and had all his faculties. Presented here is the introductory chapter to our new, upcoming, CBP Technique Text book that my father, my step-mother, and I were collaborating on. It is the Harrison family’s sincere wish that you will see Dr. Don’s purpose, passion, and his love for the truth of Chiropractic in this, his final work.

Donald D. Harrison, Ph.D., DC, MSE — Evanston, WY
Deed E. Harrison, DC — Elko, Nevada
Sanghak O. Harrison, DC — Evanston, W

© 2004-2011 Harrison CBP Seminars, Inc. All rights reserved
Published by: © Harrison Chiropractic BioPhysics Seminars, Inc., 2004, 2011
First Published as CBP: The Physics of Spinal Correction 1986, 1988, 1992, revised in 1994, revised in 2002
Printed in United States of America

Library of Congress Cataloguing-in-Publication Data
Harrison, D.D., 1946; Harrison, S.O., 1953; Harrison, D.E., 1972.
Clinical Biomechanics of Posture/ D.D. Harrison, S.O. Harrison, D.E. Harrison
Includes bibliographical references and index.
ISBN 0-9721314-1-8

Introduction, History & Original Ideas

Clinical Biomechanics of Posture® or Chiropractic BioPhysics® (CBP®) is a conservative approach to patient rehabilitation with its roots in Linear Algebra,1 as evidenced by the uses of rotations and translations to describe the spine and posture parts during both displacement analysis and correction. CBP is composed of unique approaches to applying forces to and positioning of the human body to restore normal posture and normal spinal alignment. These original Harrison approaches include Mirror Image® postural adjusting with a drop table and/or an instrument, Mirror Image postural exercises, Mirror Image postural traction, and sagittal curve traction. It is the purpose of this chapter to (a) briefly provide the foundations of CBP care from the principles of Linear Algebra applied to posture, (b) define Mirror Image methods, and (c) provide the published clinical evidence for utilization of CBP Technique as of 2008.

Since approximately 1985, most Biomechanics courses in Chiropractic Colleges include an analysis of the spine as rotations of the vertebrae and translations of the vertebrae, but without any of the mathematical analyses behind this notation (Figure 1). While after memorization, this system of analysis of vertebral movement as rotations (Rx, Ry, Rz) and translations (Tx, Ty, Tz) may seem straight forward, there is considerable underlying mathematics, of which health care providers are totally unaware. At the risk of being confusing, we provide a brief paragraph of details before confining our discussions to applications.

The mathematical field of Linear Algebra can be quite abstract, but its practical applications in mathematics and engineering concern vectors, vector spaces, and finite dimensional matrix theory.2 A matrix is an array of numbers expressed in its number of rows and columns (eg., 2×2 or 3×3). While high school and college students are familiar with polynomial functions (x2 +2x +1) and trigonometric functions (sine, cosine, tangent), few are familiar with matrices as functions. It is little appreciated in health sciences that rotations are matrix functions (3×3 array) and translations are vectors (3×1 array). Avoiding mathematical calculations, we will discuss human upright posture as rotations around an axis and translations (straight line or linear movements) along an axis. However, at times some surprising conclusions can be drawn from Linear Algebra theory, such as rotations and translations have unique inverses. This knowledge enabled Harrison,1,4,6 a mathematician and mechanical engineer, to originate the CBP Technique principle of “Mirror Image” postural positions. As to the insight that Linear Algebra provided to Harrison, we lead the reader through some details of coordinate systems, possible movements in 3-dimensions, unique inverses, and the concept of degrees of freedom.

In 1974, Panjabi et al. suggested the directions (x,y,z) of a right-handed coordinate systems for biomechanics and medical research.3 This system had the positive x-axis to the left, positive y-axis to the vertical, and the positive z-axis to the anterior (Figure 1). Subsequently, this coordinate system became the most commonly used system in the biomedical literature to the dismay of many engineers, who preferred the system suggested by NASA researchers many years before 1974 (Figure 2). Engineers and mathematicians prefer to denote the vertical axis as the last letter of the alphabet (which would be the z-axis in 3-Dimensions).


While the paper, containing the coordinate system suggested by Panjabi et al,1 featured a mathematical description that could be applied to every joint, no one applied this analysis to human posture as an analysis of the head, rib cage, and pelvis until Harrison in 1980.4 For an example in 1975 by the originators of this system, White et al,5 in their Table 1, discussed how to describe anatomical movements as rotation around the x-axis (Rx), rotation around the y-axis (Ry), and rotation around the z-axis (Rz) of nearly every human joint (“shoulders, elbow, wrist, fingers and thumb, hip, knee, ankle, subtalar, toes, and spine”5), but not posture using the head, rib cage or pelvis. Note also the translations were mainly ignored/neglected (Tx, Ty, Tz).

Dr. Don Harrison was the first to categorize human posture as rotations and/or translations in 3-D (three dimensions) in 1980.4 By 1981, the CBP Instrument Adjusting text and the 1981 CBP videos, featuring Dr. Kathryn Riley and Dr. Marc Delgadillo as models, illustrated set-ups (Mirror Image postural positions) of all the single and double combinations of postural rotations and translations in the head and rib cage.

For his postural analysis of the head, rib cage, and pelvis, Harrison made a similar analysis of the possible degrees of freedom (DoF) of the top vertebra in an FSU (Functional Spinal Unit), which are shown in Figure 3.6 Degrees of Freedom can be defined as the number of axes (total = 6) that a vertebra can rotate around (3) added to the number of axes that a vertebra can translate along (3). Thus, analogous to Figure 3, for each of the head, rib cage, and pelvis, Harrison described their 6 DoF in the coordinate system suggested by Panjabi et al (Figure 4).


When the positive and negative directions of movement/displacement of each vertebra in Figure 3 are drawn, one observes that there are 12 simple movements in 6 DoF in 3-dimensions (Figure 5). Using a completely analogous analysis, the 12 simple postural positions (movements) of the head, rib cage, and pelvis can be determined from Figure 4. Thus, there are 12 single postural positions in 6 DoF in 3-D for each of the head, rib cage, and pelvis (Figure 6-8).


Logically, when looking at each DoF, one notices that the movements of the head, rib cage, and pelvis come in pairs, which are the positive and negative directions of movement around or along any axis, i.e., ±Rx, ±Ry, ±Rz, ±Tx, ±Ty, and ±Tz are pairs. Note that to distinguish what axis the movement has occurred around or along, we have used subscripts. To indicate direction, the symbols “+” and “-” will be used. To distinguish regions (head or rib cage or pelvis), we will use superscripts, e.g. –RyH = right axial head rotation. For an example using ±TxH, which is the pair of lateral head translations in Figure 6, we note that these head positions are equally spaced to the right (-TxH) and left (-TxH) of the median-sagittal plane emanating from the thoracic cage. Using a mirror as the median-sagittal plane, one might classify these movements as reflections of each other.

Interestingly, in Linear Algebra, there is a matrix function termed “Reflection”. In our case (±TxH), we are using the vertical median-sagittal plane and the x-axis is perpendicular to this plane. In this situation, Reflection is defined as the function that moves an object across a vertical line (in 2-D) or across a vertical plane (in 3-D) such that the y and z-coordinates remain the same, while the x-coordinates are just a sign change from negative to positive or vice-versa. This matrix function, Reflection, has a matrix formula:


Additionally, it is known that Reflections have unique inverses and you may have guessed that +TxH and -TxH are the unique inverses of each other. This is exactly what Dr. Don Harrison realized in 1980. He adapted Linear Algebra theory concerning Reflections to human head postures. Since the pairs ±Rx (flexion-extension), ±Ty (vertical translations), and ±Tz (forward-backward translations) do not exactly fit the precise definitions of Reflection as well as the pairs of ±Tx, ±Ry, and ±Rz, do, in order to include all DoF in his CBP methods, he termed his clinical methods of postural reversal as “Mirror Image” postural adjusting, “Mirror Image” exercising, and “Mirror Image” traction. In healthcare, traction is commonly assumed to be flexion-longitudinal stretching (+Rx & +Ty). However, to an engineer, traction can be stretching on any DoF (Rx, Ry, Rz, Tx, Ty, or Tz). During the 1980’s, Dr. Sang Harrison, an artists, illustrated all the CBP texts with her detailed skeletal drawings, which helped convey the principles of rotations and translations of the head, rib cage, and pelvis applied to Chiropractic methods.

After March 1980, with his new “Mirror Image” postural methods, Harrison began to make routine postural corrections as evidenced by using pre- and post-Polaroid photographs and pre- and post-postural measurements with Dr. Larry Allen’s GSA (Gravity Stress Analyzer). However, Harrison noticed that his sagittal Mirror Image postural work (±Rx, ±Ty, and ±Tz) did not often result in satisfactory changes in the sagittal cervical lordosis, thoracic kyphosis, or lumbar lordosis. Thus, he began originating different types of extension cervical traction (-Rx). Not-with-standing the personal satisfaction derived from normalizing patients’ postures and spinal alignment on pre- and post-x-ray, this is not the clinical proof of new methods that others are expecting. Thus, in 1990, CBP Nonprofit, through Harrison’s direction, began to investigate, with formal-proper research studies, the new clinical methods that Harrison had originated.

In the mid 1990’s, Dr. Deed Harrison began to help his father with biomedical research. He advanced CBP with some of his own original ideas. He invented sagittal lumbar traction for the lumbar lordosis, the matching of different cervical traction methods to his typing of cervical displacements by posture and buckled mode, full spine standing and thoracic kyphosis traction for large postural displacements and different scoliotic configurations.7-10 Over the years since 1990, Dr. Deed Harrison and Dr. Don Harrison attracted many clinicians (Dr. Jason Haas, Dr. Joe Betz, Dr. Paul Oakley, Dr. Joe Ferrantelli, Dr. Jennifer Brandon, Dr. Curtis Fedorchuk, to name a few) who were also interested in research. From 1993-2011, together this CBP team of researchers has published over 140 studies in the Index Medicus, CINAHL (Cumulative Index for Nursing and Allied Health), and ICL (Index for Chiropractic Literature).

Clinical evidence of successful care/treatment requires published clinical studies (randomized trials, non-randomized trials, and observational studies) utilizing valid and reliable methods of collecting clinical data. The clinical goals in CBP Technique include, but are not limited to, improving the outcomes of posture, x-ray analysis, range of motion (ROM), pain (NRS = numerical rating scale, VAS = visual analogue scale), and health status questionnaires (RAND 36 or SF-36). However, before clinical outcomes studies can be performed, the measurements methods must be studied for reliability and validity. To perform reliability, validity, clinical, and biomechanical research, a research organization, with nonprofit status, was formed in 1982 by the Harrisons (CBP Nonprofit, Inc). CBP Nonprofit researchers spent many years establishing posture analysis and x-ray analysis as valid, reliable, desirable, and measurable clinical outcomes.

At present, the supporting “evidence” for utilizing CBP Technique has reached a substantial level, and is still ongoing. However, the term “evidence” in the clinical setting has some specific definitions in the literature for the past 30 years. Next, we discuss “Levels of evidence” and evaluate the Levels of Evidence for the utility of CBP Technique.

Levels of Evidence in CBP Research

In the later 1990’s, the buzz words “Evidence-Based” became a common way to condemn patient care methods that did not have published research evaluating all possible aspects of treatment.11-19 The goals of evidence-based medicine (EBM) was to improve patient outcomes and quality of care. Systematic reviews of available published evidence are required, however, these literature reviews depend on the quality of the review (selection bias) and the quality of the publications.20 To have “evidence” on all aspects of a certain treatment method is nearly impossible in any healthcare discipline, including medicine, dentistry, physical therapy, chiropractic, nutrition, naturopathy, homeopathy, or massage therapy. The highest form of “evidence” would seem to be reliability studies, validity studies, and randomized clinical control trials (RCTs).

However, without consideration of the importance of other clinical and basic science studies, critics of a certain healthcare method often condemn that method if reliability studies, validity studies, and RCTs have not been published. This is not reasonable since there are numerous other types of clinical and basic science studies that provide “evidence” that a certain type or method of care might be reasonable, sufficient, or standard.

While the rating of evidence seems useful, the exclusion of all other forms of evidence other than RCTs is unreasonable. Some of the clinical studies that should be considered as providing “evidence” are Single Case Study, Case-Control Study, Case Referent Study, Case-Comparison Study, Case Series, Case Series-Control, Cohort-Control, Cohort, Inception Cohort, Cohort Analytical, Survey, Cost Benefit Analysis, Cost Effectiveness Analysis, Crossover Trial, Before-After Trial, Nonrandomized Control Trial, and Randomized Control Trial.

Additionally, often authors of Guidelines and “Evidence” publications omit basic Science Studies. In fact, Chiropractic education is often broken down into the components of (a) Clinical Sciences and (b) Basic Sciences. Some of the basic science studies providing “evidence” would include, but not be limited to, anatomical, spinal modeling, evaluations of loads, evaluation of stresses and strains, comparisons of alignment in patients and controls (spine or posture), posture and spinal coupling (main motion and coupled motion), and spinal buckling.

CBP has multiple types of Index Medicus publications as “evidence” for its patient treatment methods, i.e., reliability of posture evaluation,21-33 validity and reliability of CBP Postural analysis,34-37 reliability of radiographic positioning,38 reliability of radiographic line drawing analysis,39-48 Linear Algebra basis of CBP,1 normal spinal model as a goal of care,49-56 evaluations of loads & stress,57-60 posture and coupling,61-64 and efficacy studies including two Randomized Clinical Control Trial (RCT),65,66 7 non-randomized clinical control trials,67-73 and over 80 case reports.74-157

The studies just cited are mostly studies funded by CBP Nonprofit, Inc. that are published in the peer-reviewed literature, some are peer-reviewed studies self-funded by private practitioners, and some of the case reports are published in non-peer-reviewed Chiropractic trade journals.

Primary Outcome Measures of CBP Technique

Now, it should be pointed out that a CBP analysis of a patient is dependent on a postural evaluation and a radiographic evaluation.

It is the responsibility of the individual doctor to do a thorough patient evaluation and chiropractic analysis/diagnosis. These evaluation procedures are taught in all health care colleges and are not the responsibility of a rehabilitation method. After evaluating the patient’s condition from history, orthopedic examination, ranges of motion, and neurological examination, a CBP standing posture examination and CBP radiographic examination are provided. The precise applications of forces used in CBP Technique are dependent on the individual results of these CBP standing posture and radiographic examinations.

The CBP postural examination determines rotations and translations of the head, rib cage, and pelvis in 3-dimensions. The CBP radiographic examination determines the state of the sagittal curves, sagittal balance, pelvic tilt, and deviations from vertical in the AP view. Since postural movements (main motion) have well known associated spinal coupled motions, the posture and radiographic images are compared for main motions and coupled motions. As in the patient evaluation procedures, it is the individual doctor’s responsibility to perform a radiographic evaluation for pathologies and disease processes, and not the responsibility of a rehabilitation method. Pertaining to radiographic information, in the CBP procedures, alignment or mal-alignment is measured on the radiographs and this knowledge is used for determining part of the rehabilitation approach that will be unique to each individual.

In order for the reader to rate the Evidence published by CBP Nonprofit, a discussion of Levels of Evidence is required.

Levels of Evidence

When reviewing a volume of evidence on a particular topic, it is important to understand there are different levels of evidence. Not all forms of evidence can be considered of equal value. However, of equal importance, it also needs to be stated that all levels of evidence are important and have their respective value. It is widely accepted in the scientific and health care community that there are four levels of clinical treatment evidence.158-161 Depending on which organisation’s guideline we look at, there are subtle variations however the basic categorisations are the same:

Clinical Sciences

  • Level 1. Randomized controlled trials—includes quasi-randomized processes such as alternate allocation.
  • Level 2. Non-randomized controlled trial—a prospective (pre-planned) study, with predetermined eligibility criteria and outcome measures.
  • Level 3. Observational studies with controls—includes retrospective, interrupted time series (a change in trend attributable to the intervention), case-control studies, cohort studies with controls, and health services research that includes adjustment for likely confounding variables.
  • Level 4. Observational studies without controls (e.g., cohort studies without controls, case series without controls, and case studies without controls).

Basic Sciences

Since we did not locate any “Evidence Levels” for Basic Science studies, we have formulated our own:

  • Level 1. Spinal modeling, Evaluations of loads, Stresses, & Strains, Normal & abnormal anatomy, Physiology, Chemical composition of human tissues, Pathological processes; Biomechanics, Spinal alignment & Health studies (e.g., Correlation studies with spinal alignment & health), Population studies with Longitudinal Design & Control group, Reliability and validity studies on clinical devices/procedures with > 30 subjects.
  • Level 2. Population study of Cross-Section Design with Control group, Reliability and Validity studies on clinical devices/procedures with < 30 subjects.
  • Level 3. Population study with Longitudinal Design, but without control group
  • Level 4. Population study of Cross-Section Design, but without control group

While many Guidelines include “Expert Opinion” as “Evidence”, we have encountered opposition to our opinion as evidence.162-164 Never-the-less we shall include Expert Opinion as Level 5 Clinical Sciences evidence. Additionally, after defining Levels of Evidence, it is important to define how this evidence is rated. Tables 1 and 2 provide our Classes of Evidence and Ratings of Evidence.

While some might contest our classifications of “Population Studies” in our Basic Sciences category, we suggest that these studies do not have treatment interventions and thus do not fit in with the Levels of Evidence for RCTs, Cohorts, Case Series, and Case Studies, which have treatment interventions.


While CBP Practitioners and CBP Nonprofit have not published studies in all the categories in Table 1 above, they have published on a large variety of topics in a large variety of journals in ICL, CINAHL, and the Index Medicus. It is noted that a large number of CBP publications appeared in the Journal of Manipulative and Physiological Therapeutics (JMPT is one of only two chiropractic journals listed in the Index Medicus). Table 3 summarizes CBP published research.


Before presenting levels and rating of CBP® published evidence, it should be pointed out that CBP Methods are different from Spinal Manipulative Therapy (SMT). In agreement with this claim, Chiropractic adjustment is not the same as SMT according to the World Health Organization’s definitions:163

Chiropractic Adjustment: Any chiropractic therapeutic procedure that ultimately uses controlled force, leverage, direction, amplitude, and velocity, which is applied to specific joints and adjacent tissues. Chiropractors commonly use such procedures to influence joint and neurophysiological function.163,164

Spinal Manipulative Therapy: Includes all procedures where the hands or mechanical devices are used to mobilize, adjust, manipulate, apply traction, massage, stimulate or otherwise influence the spine and paraspinal tissues with the aim of influencing the patient’s health.163

Therefore, it is evident that most RCTs, preformed with SMT as the treatment, do not pertain to chiropractic practice, and in fact, few SMT-RCTs utilize DCs as the treating physician.164

Clinical Science Evidence by CBP

While more Level 1 clinical studies (RCTs), utilizing CBP methods, are being planned, to date there has only been one published Level 1 study and 1 in review utilizing CBP Technique.65,65a Thus, the majority of Clinical Science evidence for CBP® Technique exits as Levels 2, 3, and 4 studies.66-157

Basic Science Evidence by CBP

In order to identify abnormality (subluxation) of upright spinal and postural alignment, much of CBP’s research efforts focused on normal spinal modeling that would provide clinicians with ideal and average alignment values (Figure 9). This normal spinal model is based, in part, on average values from normal subjects and has been published in orthopedic and chiropractic journals.49-56 This research resulted in ideal and average subject geometric models for the sagittal plane curves of the cervical lordosis, thoracic kyphosis and lumbar lordosis. Additionally, average and ideal values were published for each sagittal vertebral segmental angle (RRA = relative rotation angle, e.g., T8-T9) and for sagittal regional global angles (ARA = absolute rotation angle, e.g., C2-C7, T3-T10, and L1-L5). This CBP spinal model is truly ‘evidence-based.’ In fact, the CBP sagittal lumbar model51 and the sagittal cervical model56 were found to have discriminative validity in as much as they can distinguish between normal subjects, acute pain subjects, and chronic pain subjects.51,56


Further validity for an optimum upright spinal position comes from an analysis of loads and stresses based on minimum energy expenditure. To this extent CBP researchers published a variety of spine modeling projects whose focus were to ascertain conditions for upright spine alignment where the loads acting on the spine components were either abnormal in magnitude, altered in type/direction, or both.57-61 These modeling projects predicted that cervical kyphosis, cervical straightening, anterior head translation, anterior thoracic translation postures, increased thoracic kyphosis, and loss of the distal lumbar lordosis were all abnormal upright static positions due to the increased and altered loads acting on the various spine structures. 57-61

There are several types of validity for health care practices and techniques. Construct and predictive validity can be applicable in clinical situations, while a second type, we term “Biomechanical validity”. For this, biomechanical validity, the clinician compares the spinal coupled motions on the different spinal radiographic views to the published results of “main motion coupled motion” performed on postural movements. If the usual coupled motion patterns on these radiographs are not present for a particular spine posture, the clinician is then alerted to the fact that either anomalies or spinal injuries are present. This requires basic science information of spinal kinematics due to specific postural movements.

CBP researchers had the foresight and timing to investigate several main postural motions for their specific-unique coupled motion interactions. This type of basic science research was done in a series of original publications, reviews and texts, by Harrison et al4-10, 62-65. This research outlined the cervical, thoracic, and lumbo-pelvic coupling movement for the postures of:

  • Head axial rotation on the nasium x-ray,
  • Head lateral bending on the nasium x-ray,
  • Lateral head translations on the AP cervico-thoracic,
  • Lateral thoracic translations on the AP thoraco-lumbar.
  • Sagittal plane thoracic translations on the full spine lateral.

General Evidence for CBP Technique Patient Evaluation Procedures

The CBP postural examination determines rotations and translations of the head, rib cage, and pelvis in 3-dimensions. The CBP radiographic examination determines the state of the sagittal curves, sagittal balance, pelvic tilt, and deviations from vertical in the AP view. Since postural movements (main motion) have well known associated spinal coupled motions, the posture and radiographic images are compared for main motions and coupled motions. As in the patient evaluation procedures, it is the individual doctor’s responsibility to perform a radiographic evaluation for pathologies and disease processes, and not the responsibility of a rehabilitation method. Pertaining to radiographic information, in the CBP procedures, alignment or mal-alignment is measured on the radiographs and this knowledge is used for determining part of the rehabilitation approach that will be unique to each individual.

Recently there has been interest in the radiographic alignment of the normal spine in the lateral view, termed sagittal balance.165-188 While some authors have suggested vertical alignment of C7 and S1,169-170 to minimizing loads and posterior muscle efforts, other authors have suggested vertical alignment of T1, T12, and S1.173 Vertical alignment of T1, T12, and S1 does not provide insight into what the normal geometric configurations of the thoracic kyphosis and lumbar lordosis might be.
Additionally, several authors have measured segmental and global angles from T1 to S1,180-188 however, angular measurements do not provide knowledge as to what geometric shape might be expressed by the normal sagittal spine. Clinicians need normal values and simple models to judge outcomes. Such models and values would include the geometric shape of thoracic kyphosis and cervical and lumbar lordosis, sagittal balance, global angles, and segmental angles.

Chapter Summary

Contrary to many academics’ and clinicians’ misconceptions, loss of the sagittal spinal curvatures (cervical lordosis, thoracic kyphosis, and lumbar lordosis) has been correlated to pain, poor outcomes after surgery, pathology, and disease. Therefore, besides sagittal spinal balance of posture, the sagittal spinal curvatures are important outcomes of rehabilitative care.

Standing posture in the “minimum energy” position is repeatable. The positioning for this “minimum energy” postural examination starts with the feet placed under the femur heads. With eyes closed, the subject walks in place a few steps, next he/she flexes and extends a couple of times, and then comes to what he/she perceives as a comfortable, neutral position. Using this “minimum energy” position, radiographic positioning is repeatable. Geometric line drawing on radiographs is reliable. Additionally, postural evaluation is one of the most valid measures of health.189-202

CBP technique is one of the most scientifically studied named techniques in chiropractic. Studies definitively linking reduction of specific subluxation models to improvement in patient specific conditions are in their infancy. With multiple clinical efficacy studies, providing preliminary patient outcomes with CBP technique, the foundation is available for studying patient specific improvements due to reduction of spinal subluxation using the ideal model as a reference frame. We have in our long-range research plans several studies to advance the state of knowledge with CBP technique interventions. However, research is terribly time/dollar consuming and many smaller studies were needed before progressing to more advanced study designs for outcome assessment following CBP Technique treatment methods and protocols of care.


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