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OBJECTIVE: To investigate the reliability of a radiographic measurement procedure that uses a computer and sonic digitizer to determine projected spinal displacements from an ideal, normal position. DESIGN: A blind, repeated-measure design was used. Anteroposterior cervicothoracic spine radiographs were presented in random order to each of 3 examiners. Each film was digitized, and the films were randomized for a second examination. SETTING: Private, primary care chiropractic clinic. MAIN OUTCOME MEASURES: Intraclass correlation coefficients for intraexaminer and interexaminer reliability for measures on radiographs comparing the perpendicular distance (T(x)) from a vertical axis line drawn through the center of T4 and the center of C2, the linear distance (vertebra(apex)) from the center of the vertebra most displaced from a line connecting the centers of C2 and T4, the angle (Rz) formed by the intersection of the vertical axis line and the upper thoracic line, and the angle of intersection (CDA) between the upper thoracic line and the cervical line. RESULTS: Intraexaminer reliability for T(x) distance was 0.99 to 1.00, with confidence intervals from 0.98-1.00; for vertebra(apex) was 0.96 to 0.97, with confidence intervals from 0.92-0.98; for Rz was 0.94 to 0.98, with confidence intervals from 0. 89-0.99; and for CDA was 0.92 to 0.95, with confidence intervals from 0.84-0.97. Interexaminer reliabilities for the 3 examiners ranged from 0.97 to 0.99. CONCLUSIONS: Measures similar to those described in this study are commonly used to quantify and categorize spinal displacements from true vertical alignment (i.e., scoliosis measurements). Intraclass correlation coefficient values >0.70 are considered accurate enough for use in clinical and research applications. The measures tested here would fit within these guidelines of reliability. Establishing reliability is an important first step in evaluating these measures so that future studies of validity may be undertaken.

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STUDY DESIGN: Thirty lateral cervical radiographs were digitized twice by three examiners to compare reliability of the Cobb and posterior tangent methods. OBJECTIVES: To determine the reliability of the Cobb and Harrison posterior tangent methods and to compare and contrast these two methods. SUMMARY OF BACKGROUND DATA: Cobb's method is commonly used on both anteroposterior and lateral radiographs, whereas the posterior tangent method is not widely used. METHODS: A blind, repeated-measures design was used. Thirty lateral cervical radiographs were digitized twice by each of three examiners. To evaluate reliability of determining global and segmental alignment, vertebral bodies of C1-T1 were digitized. Angles created were two global two-line Cobb angles (C1-C7 and C2-C7), segmental Cobb angles from C2 to C7, and posterior tangents drawn at each posterior vertebral body margin. Cobb's method and the posterior tangent method are compared and contrasted with these data. RESULTS: Of 34 intraclass and interclass correlation coefficients, 28 were in the high range (>0.7), and 6 were in the good range (0.6-0.7). The Cobb method at C1-C7 overestimated the cervical curvature (-54 degrees ) and, at C2-C7 it underestimated the cervical curve (-17 degrees ), whereas the posterior tangents were the slopes along the curve (-26 degrees from C2 to C7). The inferior vertebral endplates and posterior body margins did not meet at 90 degrees (C2: 105 degrees +/- 5.2 degrees, C3: 99.7 degrees +/- 5.2 degrees, C4: 99.9 degrees +/- 5.8 degrees, C5: 96.1 degrees +/- 4.5 degrees, C6: 97.0 degrees +/- 3.8 degrees, C7: 95.4 degrees +/- 4.1 degrees ), which caused the segmental Cobb angles to underestimate lordosis at C2-C3, C4-C5, and C6-C7. CONCLUSIONS: Although both methods are reliable with the majority of correlation coefficients in the high range (ICC > 0.7), from the literature, the posterior tangent method has a smaller standard error of measurement than four-line Cobb methods. Global Cobb angles compare only the ends of the cervical curve and cannot delineate what happens to the curve internally. Posterior tangents are the slopes along the curve and can provide an analysis of any buckled areas of the cervical curve. The posterior tangent method is part of an engineering analysis (first derivative) and more accurately depicts cervical curvature than the Cobb method.

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OBJECTIVE: To determine cervical coupling during the posture of lateral head translation relative to a fixed thoracic cage. DESIGN: Digitized measurements from anteroposterior cervical radiographs of 20 volunteers were obtained in neutral, left, and right lateral translation posture of the head compared to a fixed thorax. BACKGROUND DATA: Clinically, lateral translation of the head is a common posture. Ranges of motion and spinal coupling have not been reported for this movement. METHODS: Vertebral body corners, mid-lateral articular pillars and the superior spinous-lamina junction of C3-T4 were digitized on 60 radiographs. Using the orthogonal axis of positive x-direction to the left, vertical as positive y and anterior as positive z, digitized points were used to measure projected segmental z-axis rotation, y-axis rotation, and segmental lateral translations of each vertebra. RESULTS: Subjects translated their heads laterally a mean of 51 mm. The major coupled motion was lateral bending (z-axis rotation), which changed direction at the C4-C5 disc space creating an S-shape. Upper cervical (C3-C4) lateral bending was contralateral to the main motion of head translation direction. Lower cervical and upper thoracic lateral bending were ipsilateral. Other segmental motions averaged less than 1 mm and 1 degrees. CONCLUSIONS: Lateral head translations (x-axis) compared to a fixed thoracic cage can be large with a mean of 51 mm to one side. The major spinal coupling was lateral bending which changed direction at C4-C5 resulting in an S-configuration. This might have application in side impacts. All other segmental movements were small, less than 1 mm and 1 degrees. RELEVANCE: The clinically common posture of lateral head translation results in an S-shaped cervical spine and may occur in side impact trauma. This posture has not been studied for cervical coupling patterns or range of motion (ROM).

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BACKGROUND: Driving has been associated with signs and symptoms caused by vibrations. Sitting causes the pelvis to rotate backwards and the lumbar lordosis to reduce. Lumbar support and armrests reduce disc pressure and electromyographically recorded values. However, the ideal driver's seat and an optimal seated spinal model have not been described. OBJECTIVE: To determine an optimal automobile seat and an ideal spinal model of a driver. DATA SOURCES: Information was obtained from peer-reviewed scientific journals and texts, automotive engineering reports, and the National Library of Medicine. CONCLUSION: Driving predisposes vehicle operators to low-back pain and degeneration. The optimal seat would have an adjustable seat back incline of 100 degrees from horizontal, a changeable depth of seat back to front edge of seat bottom, adjustable height, an adjustable seat bottom incline, firm (dense) foam in the seat bottom cushion, horizontally and vertically adjustable lumbar support, adjustable bilateral arm rests, adjustable head restraint with lordosis pad, seat shock absorbers to dampen frequencies in the 1 to 20 Hz range, and linear front-back travel of the seat enabling drivers of all sizes to reach the pedals. The lumbar support should be pulsating in depth to reduce static load. The seat back should be damped to reduce rebounding of the torso in rear-end impacts. The optimal driver's spinal model would be the average Harrison model in a 10 degrees posterior inclining seat back angle.

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OBJECTIVE: To determine lumbar coupling during lateral postural translations (lumbosacral list) of the thoracic cage relative to a fixed pelvis. DESIGN: Digitized measurements from anteroposterior lumbar radiographs of 17 volunteers were obtained in neutral, maximal left lateral translation and maximal right lateral translation posture of the thoracic cage compared to a fixed pelvis. Subjects were constrained with two sets of clamps at the lateral borders of the pelvis and lower ribs. BACKGROUND: Data. Clinically, lumbosacral list is a common posture. Range of motion and spinal coupling results have not been reported for the lumbosacral list movement. METHODS: Four vertebral body corners, mid narrow-waisted body margins, superior and inferior pedicle margins, and spinous-lamina junction of T12-L5 were digitized on 51 anterior-posterior lumbar radiographs. Using the orthogonal axes of positive x-direction to the left, vertical as positive y, and anterior as positive z, digitized points were used to measure projected segmental z-axis rotation, y-axis rotation, and segmental lateral translations of each vertebra. RESULTS: Using the displacement of T12, subjects could translate 35-70 mm left or right along the x-axis with an average of 53.2 mm to the left and 52.1 mm to the right. Using superior endplates to superior sacral base, lateral flexion was largest at L1 and decreased from L1 to L5, but the segmental rotation angles for lateral flexion were largest at L2-L3 (3.9 degrees ), L3-L4 (6.2 degrees ) and L4-L5 (5.7 degrees ) and were in the same direction as the main motion translation. The relative z-axis rotation of T12 was opposite to the direction of L1-L5. The coupled y-axis rotations were less than 1 degrees and coupled segmental lateral translations were averaging less than 1 mm. CONCLUSIONS: Thoracic cage x-axis translations compared to a fixed pelvis are significant, between 35 and 70 mm. The z-axis lumbar coupled rotation was largest at L2-L3, L3-L4 and L4-L5 and to the same side of the main motion translation in L1-L5, but opposite the main motion direction for T12. All other movements were small, averaging less than 1 degrees or 1 mm. RELEVANCE: The clinically common posture of lateral translation of the thoracic cage (lumbosacral list) is often associated with disc herniation. Yet normal lumbar coupling patterns and total range of motion of this movement have not been established in the literature. Normal values for lumbar segmental coupling on anterior-posterior lumbo-pelvic radiographs during trunk list might be important for an analysis of segmental instability since segmental translations were determined to be 1 mm or less.

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OBJECTIVE: To review literature pertaining to neurologic disorders stemming from abnormal postures of the spine. DATA COLLECTION: A hand search of available reference texts and a computer search of literature from Index Medicus sources was performed, with special emphasis placed on spinal cord stresses and strains caused by various postural rotations and translations of the skull, thorax, and pelvis. RESULTS: Spinal postures will often deform the neural elements within the spinal canal. Spinal postures can be broken down into four types of loading: axial, pure bending, torsion, and transverse, which cause normal and shear stresses and strains in the neural tissues and blood vessels. Prolonged stresses and strains in the neural elements cause a multitude of disease processes. CONCLUSION: Four types of postural loads create a variety of stresses and strains in the neural tissue, depending on the exact magnitude and direction of the forces. Transverse loading is the most complex load. The stresses and strains in the neural elements and vascular supply are directly related to the function of the sensory, motor, and autonomic nervous systems. The literature indicates that prolonged loading of the neural tissue may lead to a wide variety of degenerative disorders or symptoms. The most offensive postural loading of the central nervous system and related structures occurs in any procedure or position requiring spinal flexion. Thus flexion traction, rehabilitation positions, exercises, spinal manipulation, and surgical fusions in any position other than lordosis for the cervical and lumbar spines should be questioned.

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OBJECTIVE: To review spinal cord strains arising from postural loads. DATA COLLECTION: A hand search of available reference texts and a computer search of literature from the Indexed Medicus sources were collected, with special emphasis placed on spinal cord strains caused by various postural rotations and translations of the skull, thorax, and pelvis RESULTS: All spinal postures will deform the neural elements within the spinal canal. Flexion causes the largest canal length changes and, hence, the largest nervous system deformations. Neural tissue strains depend on the spinal level, the spinal movement generated, and the sequence of movements when more than one spinal area is moved. CONCLUSIONS: Rotations of the global postural components (head, thoracic cage, pelvis, and legs) cause stresses and strains in the central nervous system and peripheral nervous system. Translations of the skull, thorax, and pelvis, as well as combined postural loads, need to be studied for their effects on the spinal canal and neural tissue deformations. Flexion of any part of the spinal column may generate axial tension in the entire cord and nerve roots. Slight extension is the preferred position of the spine as far as reducing the magnitude of mechanical stresses and strains in the central nervous system is concerned.

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OBJECTIVE: To investigate the reliability of a radiographic measurement procedure that uses a computer and sonic digitizer to determine projected spinal displacements from an ideal normal position. DESIGN: A blind, repeated-measure design was used. Anteroposterior lumbopelvic radiographs were presented to each of 3 examiners in random order. Each film was digitized, and the films were randomized for a second run. SETTING: Private, primary-care chiropractic clinic. MAIN OUTCOME MEASURES: The angle of the sacral base in comparison to a true horizontal line (horizontal base angle), lumbodorsal angle, lumbosacral angle, and the thoracic translational displacement from true vertical determined as the perpendicular distance from the center of T12 to a vertical axis line drawn from the center of the S1 spinous process cephalad and parallel to the lateral edge of the x-ray film. RESULTS: Intraexaminer reliability for the (a) horizontal base angle was .72 to .94, with confidence intervals included in the range of .52 to .97; (b) lumbodorsal angle was .90 to .96, with confidence intervals in the range of .82 to .98; (c) lumbosacral angle was .84 to .96, with confidence intervals in the range of .72 to .98, and (d) thoracic translational displacement from vertical was .95 to.97, with confidence intervals included in the range of .91 to .99. Interexaminer reliability for the three examiners ranged from .71 to .97. CONCLUSIONS: Measures similar to those described in this study are commonly used to measure and categorize spinal displacements from true vertical alignment (ie, scoliosis measurements). Most patient assessment methods used in chiropractic have poor or unknown reliability. The one possible exception to this rule is spinal displacement analysis performed on radiographs. In chiropractic, intraclass correlation coefficients values greater than .70 are considered accurate enough for use in clinical and research applications. The measures tested here would fit within these guidelines of reliability. Establishing reliability is an important first step in evaluating these measures so that future studies of validity may be undertaken.

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OBJECTIVE: To discuss how the spinal cord deforms as a result of changes in posture or biomechanical alterations of the spine. DATA COLLECTION: A hand search of available reference texts and a computer search of literature from the Index Medicus sources were collected, with special emphasis placed on spinal canal changes caused by various postural rotations and translations of the skull, thorax, and pelvis. RESULTS: All spinal postures will deform the spinal canal. Flexion causes a small increase in canal diameter and volume as the vertebral lamina are separated. Extension causes a small decrease in canal diameter and volume as the vertebral lamina are approximated. Lateral bending and axial rotation cause insignificant changes in spinal canal diameter and volume in cases without stenosis. CONCLUSIONS: Rotations of the global postural components, head, thoracic cage, and pelvis cause changes in the diameter of the spinal canal and intervertebral foramen. These changes are generally a reduction of less than 1.5 mm in extension, compared with a small increase in flexion of approximately 1 mm. These small changes do not account for the clinical observation of patients having increased neurologic signs and symptoms in flexion.

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BACKGROUND: Low back pain exists in epidemic proportions in the United States. Studies that demonstrate innervation to the intervertebral disk provide evidence that may account for instances of discogenic low back pain encountered in general medical and chiropractic practice. Many patients and health care practitioners believe that intervertebral disk lesions require surgery as the only method of treatment that will result in satisfactory outcome. Surgery rates vary widely across geographic regions. Only one randomized prospective study exists that compares surgical and nonsurgical treatment; it demonstrated essentially equal outcomes in the long run. OBJECTIVE: To review specific aspects of the examination, history, imaging, and treatment of patients with suspected intervertebral disk lesions and to provide guidelines for conservative management, imaging, and relative and absolute indications for surgical referral. DATA SOURCES: Review articles, texts, and original articles from indexed refereed sources that discuss the lumbar intervertebral disk in regard to patient history, physical examination, imaging, treatment, and referral for surgery. RESULTS: Patients with low back pain who do not present with so-called red flags (fever, history of cancer, unexplained weight loss, urinary tract infection, intravenous drug use, saddle anesthesia, or prolonged use of corticosteroids) may be treated initially with conservative methods. Imaging studies are helpful in determining the patient's diagnosis, and computed tomography, magnetic resonance imaging, or other special imaging studies should be ordered judiciously. The only prospective, randomized study of conservative versus surgical management of herniated lumbar intervertebral disk lesions indicates both methods provide adequate outcome in the long run. Little consensus exists on the best method of management for patients with intervertebral disk lesions without absolute indications for surgery. CONCLUSION: Patients should be screened for "red flags" to determine whether they are candidates for conservative treatment. Magnetic resonance imaging is perhaps the most practical imaging study for evaluation of lumbar disk lesions because it involves no use of ionizing radiation and because magnetic resonance imaging has other advantages over computed tomographic scanning such as excellent delineation of soft tissue structures, direct multiplanar imaging, and excellent characterization of medullary bone. Provocation computed tomography-diskography is an invasive procedure and should be reserved for patients with normal magnetic resonance imaging findings and continuing severe pain who have not been helped by conservative treatment attempts and for whom surgical intervention is contemplated. Both conservative and surgical interventions have been shown to be effective in the treatment of discogenic and radicular pain syndromes.

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OBJECTIVE: To develop a new sitting spinal model and an optimal driver's seat by using review of the literature of seated positions of the head. spine, pelvis, and lower extremities. DATA SELECTION: Searches included MEDLINE for scientific journals, engineering standards, and textbooks. Key terms included sitting ergonomics, sitting posture, spine model, seat design, sitting lordosis, sitting electromyography, seated vibration, and sitting and biomechanics. DATA SYNTHESIS: In part I, papers were selected if (1) they contained a first occurrence of a sitting topic, (2) were reviews of the literature, (3) corrected errors in previous studies, or (4) had improved study designs compared with previous papers. In part II, we separated information pertaining to sitting dynamics and drivers of automobiles from part 1. RESULTS: Sitting causes the pelvis to rotate backward and causes reduction in lumbar lordosis, trunk-thigh angle, and knee angle and an increase in muscle effort and disc pressure. Seated posture is affected by seat-back angle, seat-bottom angle and foam density, height above floor, and presence of armrests. CONCLUSION: The configuration of the spine, postural position, and weight transfer is different in the 3 types of sitting: anterior, middle, and posterior. Lumbar lordosis is affected by the trunk-thigh angle and the knee angle. Subjects in seats with backrest inclinations of 110 to 130 degrees, with concomitant lumbar support, have the lowest disc pressures and lowest electromyography recordings from spinal muscles. A seat-bottom posterior inclination of 5 degrees and armrests can further reduce lumbar disc pressures and electromyography readings while seated. To reduce forward translated head postures, a seat-back inclination of 110 degrees is preferable over higher inclinations. Work objects, such as video monitors, are optimum at eye level. Forward-tilting, seat-bottom inclines can increase lordosis, but subjects give high comfort ratings to adjustable chairs, which allow changes in position.

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Clinical significance of lumbar lordosis has not been agreed on. Our purpose is to compare lordotic measurements of normal and pain subjects and to test the validity of a new anthropometric model of lumbar curvatures. Digitized radiographic points (body corners) from standing lateral lumbar radiographs were modeled with ellipses in a least-squares method and were used to create segmental angles, a global angle at L1-L5, a Cobb angle from T12 to S1, Ferguson's sacral base angle, and an angle of pelvic tilt. Fifty normal subjects were matched in age, sex, weight, and height with 50 acute pain subjects, 50 chronic pain subjects, and 24 pain subjects with radiographic abnormalities. Of 11 angles, 2 distances, and 2 ratios, statistical analysis was significantly different across groups for 12 of these measurements, with the alternative hypotheses accepted for the other 3 measurements. The lordosis of both normal and low back pain subjects can be successfully modeled with a portion (approximately 86 degrees) of an ellipse, but with different major and minor axis ratios. The normal group's average elliptic lordosis has the smallest least-squares error, approximately 1 mm per digitized point, with (minor axis)/(major axis) ratio = 0.39, L1-L5 global angle = 40 degrees, and Cobb angle = 65 degrees. The chronic and radiographic abnormalities pain groups have an elongated ellipse with hypolordosis, reduced L1-L5 global angle = 29.6-35 degrees, reduced Cobb angle = 57-58 degrees, and elliptic axis ratio = 0.27-0.30. The acute pain group is hyperlordotic with the largest L1-L5 global angle, largest Cobb angle = 70 degrees, largest Ferguson's angle, and largest pelvic tilt angle.

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OBJECTIVE: To investigate the reliability of a specific method of radiographic analysis of the geometric configuration of the lumbopelvic spine in the sagittal plane, and to investigate the concurrent validity of a computer-aided digitization procedure designed to replace the more tedious and time-consuming manual measurement process. DESIGN: A blind, repeated-measures design was used. The results of radiographic measures derived through the traditional manual marking method were compared with measures derived by computer-aided digitization of lateral lumbopelvic radiographs. SETTING: Private chiropractic clinic. MAIN OUTCOME MEASURES: Pearson's product-moment correlation coefficients, paired sample t tests and intraclass correlation co-efficients (ICC) were used to examine intraexaminer reliability, and repeated measures of analysis of variance were used to examine interexaminer reliability for relative rotation angles for T12-L1, L1-L2, L2-L3, L3-L4, L4-L5, L5-S1, overall lordosis measurement [absolute rotation angle (ARA)] from L1-L5 and Cobb angle of overall lordosis measured from the inferior surface of T12 to the superior surface of S1, Ferguson's sacral base angle to horizontal, angle of pelvic tilt (arcuate angle) to horizontal and anteroposterior thoracic translation (Sz) in millimeters. RESULTS: ICC estimates for intraexaminer reliability were in the range of 0.96-0.98 for the L1-L5 ARA, a range of 0.87-0.99 for the arcuate angle measurement, 0.83-0.94 for the Ferguson's angle measurement, 0.88-0.95 for the Cobb angle measurement from the inferior surface of T12 compared with the superior surface of S1 and 0.98-1.00 for the translation measurement of the lower thoracic spine to S1 (Sz). The intersegmental measurement's (T12-L1, L1-L2, L2-L3, L3-L4, L4-L5, L5-S1) correlations ranged from a low of 0.55 to a high of 0.97. Examination of these findings suggests that the reliability for the three doctors is acceptable with only the T12-L1 intersegmental measure falling below 0.70 for the least experienced examiner. Average ICC of interexaminer reliability for manual and computer-aided digitizing examiners were the following: 0.96 for the L1-L5 ARA; 0.84 for the arcuate angle measurement; 0.82 for the Ferguson's angle measurement; 0.88 for the Cobb angle measurement; 1.00 for the Sz translation measurement; and values of 0.65, 0.73, 0.74, 0.75, 0.89 and 0.81 for relative rotation angle measurements T12-L1, L1-L2, L2-L3, L3-L4, L4-L5 and L5-S1, respectively. CONCLUSION: The data tend to support the reliability of this method of radiographic analysis of the geometric configuration of the lumbopelvic spine as viewed on lateral lumbopelvic radiographs. The additional data presented here tend to support the concurrent validity of the computer-aided digitization method of analysis inasmuch as the measures determined by the digitizing examiners are essentially identical to those determined by the manual method plus or minus the average standard error of measure of each value.

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BACKGROUND: Current medical, biomechanical, and chiropractic literature indicates that X-ray line drawing analysis for spinal displacement is reliable, with high Interclass Correlation Coefficients (ICCs) found in most studies. Normal sagittal spinal curvatures are being accepted as important clinical outcomes of care; however, just the opposite is taught in many chiropractic college radiology courses. OBJECTIVE: To review the current literature on X-ray line drawing reliability and abnormal static lateral positions. DATA SOURCES: Searches were performed on Medline, Chiro-LARS, MANTIS, and CINAHL on X-ray reliability, normal spinal position, and sagittal spinal curvatures as clinical outcomes. RESULTS: X-ray line drawing analysis for spinal displacement was found to have high reliability with a majority of ICCs in the .8-.9 range. The reliability for determining X-ray pathology was found to be only fair to good by both medical doctors and chiropractors and by both chiropractic and medical radiologists, with a majority of ICCs in the range .40-.75. Muscle spasms, facet hyperplasia, short pedicles and patient positioning errors have not been shown to alter sagittal plane alignment. The sagittal spinal curves are desirable clinical outcomes of care in surgery, physical therapy, rehabilitation and chiropractic. These results contradict common claims found in the indexed literature. CONCLUSION: X-ray line drawing is reliable. Normal values for the sagittal spinal curvatures exist in the literature. The normal sagittal spinal curvatures are important clinical outcomes of care. Patient positioning and postural radiographs are highly reproducible. When these standardized procedures are used, the pre-to-post alignment changes are a result of treatment procedures applied. Chiropractic radiology education and publications should reflect the recent literature, provide more support for X-ray line drawing analyses and applications of line drawing analyses for measuring spinal displacement on plain radiographs.

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OBJECTIVE: To compare the current knowledge of 3-D spinal mechanics and abnormal equilibrium states with chiropractic motion theories, chiropractic vertebral letter listing theories, and chiropractic technique theories. DATA COLLECTION: A manual search of available reference texts and a computer search of literature from Index Medicus were collected with an emphasis on 3-D studies of human spinal movements, segmental instability, Euler buckling of the spine, and chiropractic theories concerning vertebral movements. RESULTS: Previous spinal coupling results based upon two-dimensional radiographic studies are inadequate and inaccurate. Therefore, the validity of any chiropractic technique procedure, listing, motion analysis or adjusting style based on the two-dimensional radiograph and coupling studies must be questioned. We have identified four types of spinal subluxations (displacements) in the biomechanical literature: (a) posture main motion and associated segmental coupling, (b) Euler buckling viewed in the anteroposterior view, (c) snap through viewed in the lateral view and (d) segmental instability. CONCLUSIONS: Full three-dimensional investigations of spinal coupling patterns have shown that the vertebrae rotate and translate in all three axes and that previous theories of spinal coupling based upon two-dimensional studies are inaccurate and invalid. Previous chiropractic letter listings (e.g., PRI, PLS, etc.) of spinal displacements are inadequate and invalid. Only one of the four types of biomechanical displacements, segmental instability, is consistent with the traditional chiropractic theory of segmental spinal displacements; in general, this does not respond well to care. In general, vertebrae displacement must be viewed in the context of equilibrium configurations and one vertebra can not be displaced as an individual misalignment. Validity questions arise for any technique methods that use letter listings of displacement taken from motion palpation or two-dimensional radiographic analysis.

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