Thirty lateral cervical radiographs were digitized twice by three examiners to compare reliability of the Cobb and posterior tangent methods. To determine the reliability of the Cobb and Harrison posterior tangent methods and to compare and contrast these two methods. Cobb’s method is commonly used on both anteroposterior and lateral radiographs, whereas the posterior tangent method is not widely used. 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. 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°) and, at C2–C7 it underestimated the cervical curve (−17°), whereas the posterior tangents were the slopes along the curve (−26° from C2 to C7). The inferior vertebral endplates and posterior body margins did not meet at 90° (C2: 105° ± 5.2°, C3: 99.7° ± 5.2°, C4: 99.9° ± 5.8°, C5: 96.1 ° ± 4.5°, C6: 97.0° ± 3.8°, C7: 95.4° ± 4.1°), which caused the segmental Cobb angles to underestimate lordosis at C2–C3, C4–C5, and C6–C7. 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.—

To investigate the presence of a "functionally normal" cervical lordosis and identify if this and the amount of forward head posture are related to neck complaints. Using the posterior tangent method, an angle of cervical lordosis was measured from C2 through C7 vertebrae on 277 lateral cervical x-rays. Anterior weight bearing was measured as the horizontal distance of the posterior superior body of the C2 vertebra compared to a vertical line drawn superiorly from the posterior inferior body of the C7 vertebra. The measurements were sorted into 2 groups, cervical complaint and noncervical complaint groups. The data were then partitioned into age by decades, sex, and angle categories. Patients with lordosis of 20 degrees or less were more likely to have cervicogenic symptoms (P < .001). The association between cervical pain and lordosis of 0 degrees or less was significant (P < .0001). The odds that a patient with cervical pain had a lordosis of 0 degrees or less was 18 times greater than for a patient with a noncervical complaint. Patients with cervical pain had less lordosis and this was consistent over all age ranges. Males had larger median cervical lordosis than females (20 degrees vs 14 degrees) (2-sided Mann-Whitney U test, P = .016). When partitioned by age grouping, this trend is significant only in the 40- to 49-year-old range (2-sided Mann-Whitney U test, P < .01). We found a statistically significant association between cervical pain and lordosis < 20 degrees and a "clinically normal" range for cervical lordosis of 31 degrees to 40 degrees. Maintenance of a lordosis in the range of 31 degrees to 40 degrees could be a clinical goal for chiropractic treatment.

Delayed, repeated measures, with three examiners each twice digitizing thirty lateral lumbar radiographs. To determine the reliability and clinical utility of the centroid, Cobb, tangential radiologic assessment of lumbar lordosis (TRALL), and Harrison posterior tangent line-drawing methods for analysis of lumbar lordosis. Cobb’s method is commonly used for curvature analysis on lateral lumbar radiographs, whereas the centroid, TRALL, and Harrison posterior tangent methods are not widely used. Thirty lateral lumbar radiographs were digitized twice by each of three examiners. To evaluate reliability of determining global and segmental alignment, all four vertebral body corners of T12–S1 and the superior margin of the femur head were digitized. Angles created were segmental and global centroid, (two-line) Cobb angles, and intersections of posterior tangents. A global TRALL angle was determined. Means, standard deviations, mean absolute differences, interclass and intraclass correlation coefficients (ICC), and confidence intervals were calculated. The interobserver and intraobserver reliabilities of measuring all segmental and global angles were in the high range (ICCs > 0.83). The mean absolute differences of observers’ measurements were small (0.6°–2.0°). Distal segmental (L4–S1) and global angles of lumbar curvature were dependent on the method of measurement. All four radiographic methods had high reliability and low mean absolute differences of observers’ measurements. Because it lacks a segmental analysis, the TRALL method is not recommended. The centroid, Cobb, and Harrison posterior tangent methods provide global and segmental angles. However, the centroid segmental method requires three segments and is less useful for a stability analysis.

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. 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. 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. 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. 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.

Computer analysis of digitized vertebral body corners on lateral cervical radiographs. Using elliptical and circular modeling, the geometric shape of the path of the posterior bodies of C2–C7 was sought in normal, acute pain, and chronic pain subjects. To determine the least squares error per point for paths of geometric shapes, minor axis to major axis elliptical ratios (b/a), Cobb angles, sagittal balance of C2 above C7, and posterior tangent segmental and global angles. When restricted to cervical lordotic configurations, normal, acute pain, and chronic pain subjects have not been compared for similarities or differences of these parameters. Conventional Cobb angles provide only a comparison of the endplates of the distal vertebrae, while geometric modeling provides the shape of the entire sagittal curves, the orientation of the spine, and segmental angles. Radiographs of 72 normal subjects, 52 acute neck pain subjects, and 70 chronic neck pain subjects were digitized. For normal subjects, the inclusion criteria were no kyphotic cervical segments, no cranial-cervical symptoms, and less than ± 10 mm horizontal displacement of C2 above C7. In pain subjects, inclusion criteria were no kyphotic cervical segments and less than 25 mm of horizontal displacement of C2 above C7. Measurements included segmental angles, global angles of lordosis (C1–C7 and C2–C7), height-to-length ratios, anterior weight bearing, and from modeling, circular center, and radius of curvature. In the normal group, a family of ellipses wasfound to closely approximate the posterior body margins of C2–C7 with a least squares error of less than 1 mm per vertebral body point. The only ellipse/circle found to include T1, with a least squares error of less than 1 mm, was a circle. Compared with the normal group, the pain group’s mean radiographic angles were reduced and the radius of curvature was larger. For normal, acute, and chronic pain groups, the mean angles between posterior tangents on C2–C7 were 34.5°, 28.6°, and 22.0°, C2–C7Cobb angles were 26.8°, 16.5°, and 12.7°, and radius of curvature were r = 132.8 mm, r = 179 mm, and r = 245.4 mm, respectively. The mean cervical lordosis for all groups could be closely modeled with a circle. Pain groups had hypolordosis and larger radiuses of curvature compared with the normal group. Circular modeling may be a valuable tool in the discrimination between normal lordosis and hypolordosis in normal and pain subjects.