Deed E. Harrison

Cobb method or Harrison posterior tangent method: which to choose for lateral cervical radiographic analysis.

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°) 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. 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.—

Sitting biomechanics part I: review of the literature.

OBJECTIVE To develop a new sitting spinal model and an optimal drivers 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.

Radiographic analysis of lumbar lordosis: centroid, Cobb, TRALL, and Harrison posterior tangent methods.

Study Design. Delayed, repeated measures, with three examiners each twice digitizing thirty lateral lumbar radiographs. Objectives. 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. Background Data. 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. Methods. 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. Results. 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. Conclusions. 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.

Elliptical modeling of the sagittal lumbar lordosis and segmental rotation angles as a method to discriminate between normal and low back pain subjects.

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, Fergusons 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 groups 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 Fergusons angle, and largest pelvic tilt angle.

Modeling of the Sagittal Cervical Spine as a Method to Discriminate Hypolordosis: Results of Elliptical and Circular Modeling in 72 Asymptomatic Subjects, 52 Acute Neck Pain Subjects, and 70 Chronic Neck Pain Subjects

Study Design. Computer analysis of digitized vertebral body corners on lateral cervical radiographs. Objectives. 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. Summary of Background Data. 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. Methods. 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. Results. 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. Conclusions. 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.

Reliability of Centroid, Cobb, and Harrison Posterior Tangent Methods: Which to Choose for Analysis of Thoracic Kyphosis

Study Design. Thirty lateral thoracic radiographs were digitized twice by each of the three examiners. Objectives. To determine the reliability of the centroid, Cobb, and Harrison posterior tangent methods when applied to analysis of thoracic kyphosis. Background Data. Reliability studies on measurements of thoracic kyphosis are rare. Methods. Blind, repeated-measures design was used. Thirty lateral thoracic radiographs were digitized twice by each of three examiners. To evaluate reliability of determining global and segmental alignment, vertebral bodies of T1–T12 were digitized. Centroids at the intersection of vertebral body diagonals and tangents to posterior vertebral bodies were constructed by computer. Also the computer constructed global and segmental centroid angles, Cobb angles (two-line method), and posterior tangent intersection angles from T1 to T12. Interclass and Intraclass correlation coefficients for these data were calculated and interpreted. Results. From the points selected by examiners, all three methods have similar high ICC values for the global angles (> 0.94). For the segmental angles, the interobserver and intraobserver reliability is also very similar for all three methods, with ICCs in the good and excellent ranges (0.59–0.75 and 0.75–1.0, respectively). The mean absolute differences of observers’ measurements are low, similar, and in the range of 0.9° to 2.5°. Conclusions. The centroid, two-line Cobb, and Harrison posterior tangent methods, when applied to measurements of kyphosis, are all reliable and have similar small error ranges. The centroid method does not give an accurate segmental analysis, uses more points and more time in clinical applications, and results in smaller angles of total kyphosis than the Cobb or posterior tangent methods. The posterior tangents are the slopes along the curve.

Prediction of osteoporotic spinal deformity

Study Design. A biomechanical model was developed from full-spine lateral radiographs to predict osteoporotic spinal deformity in elderly subjects. Objective. To investigate the biomechanics of age-related spinal deformity and concomitant height loss associated with vertebral osteoporosis. Summary of Background Data. Vertebral bone loss and disc degeneration associated with aging causes bone and disc structures to weaken and deform as a result of gravity and postural stresses. Methods. An anatomically accurate sagittal-plane, upright-posture biomechanical model of the anterior spinal column (C2–S1) was created by digitizing lateral full-spine radiographs of 20 human subjects with a mean height of 176.8 cm and a mean body weight of 76.6 kg. Body weight loads were applied to the model, after which intervertebral disc and vertebral body forces and deformation were computed and the new spine geometry was calculated. The strength and stiffness of the vertebral bodies were reduced according to an osteopenic aging model and modulus reduction algorithm, respectively. Results. The most osteopenic model (L3 Fult = 750 N) produced gross deformities of the spine, including anterior wedge-like fracture deformities at T7 and T8. In this model, increases in thoracic kyphosis and decreases in vertebral body height resulted in a 25.2% decrease in spinal height (C2-S1), an 8.6% decrease in total body height, and a 15.1-cm anterior translation of the C2 spine segment centroid. The resulting deformity qualitatively resembled deformities observed in elderly individuals with osteoporotic compression fractures. Conclusions. These predictions suggest that postural forces are responsible for initiation of osteoporotic spinal deformity in elderly subjects. Vertebral deformities are exacerbated by anterior translation of the upper spinal column, which increases compressive loads in the thoracolumbar region of the spine.

Sitting biomechanics, part II: optimal car driver's seat and optimal driver's spinal model

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 drivers 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 drivers spinal model would be the average Harrison model in a 10 degrees posterior inclining seat back angle.

Postural development in school children: a cross-sectional study.

BackgroundLittle information on quantitative sagittal plane postural alignment and evolution in children exists. The objectives of this study are to document the evolution of upright, static, sagittal posture in children and to identify possible critical phases of postural evolution (maturation).MethodsA total of 1084 children (aged 4–12 years) received a sagittal postural evaluation with the Biotonix postural analysis system. Data were retrieved from the Biotonix internet database. Children were stratified and analyzed by years of age with n = 36 in the youngest age group (4 years) and n = 184 in the oldest age group (12 years). Children were analyzed in the neutral upright posture. Variables measured were sagittal translation distances in millimeters of: the knee relative to the tarsal joint, pelvis relative to the tarsal joint, shoulder relative to the tarsal joint, and head relative to the tarsal joint. A two-way factorial ANOVA was used to test for age and gender effects on posture, while polynomial trend analyses were used to test for increased postural displacements with years of age.ResultsTwo-way ANOVA yielded a significant main effect of age for all 4 sagittal postural variables and gender for all variables except head translation. No age × gender interaction was found. Polynomial trend analyses showed a significant linear association between child age and all four postural variables: anterior head translation (p < 0.001), anterior shoulder translation (p < 0.001), anterior pelvic translation (p < 0.001), anterior knee translation (p < 0.001). Between the ages of 11 and 12 years, for anterior knee translation, T-test post hoc analysis revealed only one significant rough break in the continuity of the age related trend.ConclusionA significant linear trend for increasing sagittal plane postural translations of the head, thorax, pelvis, and knee was found as children age from 4 years to 12 years. These postural translations provide preliminary normative data for the alignment of a childs sagittal plane posture.

Radiographic Mensuration Characteristics of the Sagittal Lumbar Spine from a Normal Population with a Method to Synthesize Prior Studies of Lordosis

Standing lateral lumbar radiographs of 50 normal healthy subjects were retrospectively selected for evaluation of lumbar lordosis. The objective was to evaluate, in a normal population, global and segmental contributions to lordosis in the standing position, and to devise a method to compare the seemingly unrelated multitude of lordotic values in the literature. Because of a variety of positioning and measurement methods of lordosis in live subjects and cadavers, correlation of results is difficult. While often relying on simple pain questionnaires, studies of normal subjects rarely have complete medical history, physical, neurological, and orthopedic examinations. Standing lateral lumbar radiographs of 50 subjects, who had complete histories and normal examinations, were analyzed to determine overall lordosis, segmental contributions, and vertical sagittal alignment. Using posterior body tangents, the mean L1-L5 angle was -39.7 degrees, CobbT12-S1 = -65 degrees, Fergusons sacral angle = 39 degrees, pelvic tilt angle was 49 degrees, and average RRAs (segmental angles) were RRAT12-L1 = -3.6 degrees, RRAL1-L2 = -4.1 degrees, RRAL2-L3 = -7.6 degrees, RRAL3-L4 = -11.7 degrees, RRAL4-L5 = -16.8 degrees, and RRAL5-S1 = -32.4 degrees. Using segmental rotation angles as a method to compare past and current literature, a normal standing lumbar lordosis of CobbT12-S1 = -61 degrees, range -55 degrees to -65 degrees, was determined with specific segmental angles.