3-D back surface analysis of severe idiopathic scoliosis by rasterstereography: comparison of rasterstereographic and digitized radiometric data.

Rasterstereography has been shown to be a reliable method for three-dimensional surface measurement of idiopathic scoliosis with Cobb angles up to 50 degrees. In this study, 25 patients with severe idiopathic scolioses (Cobb angles 47 degrees-92 degrees) were examined before and after operation (VDS instrumentation). The a.p. radiographs were digitized according to the Drerup method. The similarity of rasterstereographic and radiometric data was quantified by the rms. differences between the rasterstereographic and radiographic curves of lateral deviation and vertebral or surface rotation. The average rms. differences were 5.8 mm for lateral deviation and 4.4 degrees for vertebral and surface rotation, which is about 40% higher than for mild to medium scolioses.

[Functional rasterstereographic images. A new method for biomechanical analysis of skeletal geometry]. / Rasterstereographische Funktionsaufnahmen. Eine neue Methode zur biomechanischen Analyse der Skelettgeometrie.

Video rasterstereography has been developed for optical back shape measurement and for biomechanical analysis of spinal and pelvic geometry. Analysis of one single measurement permits 3-dimensional reconstruction of the back surface and calculation of shape parameters including pelvis tilt and torsion. In addition, estimates of the lateral deviation of the spinal midline and of vertebral rotation are provided. Its extended analytic potential makes rasterstereography a very appropriate tool for functional examinations. The term "functional examinations" refers in this context to biomechanical analysis of functional movements of the spine and pelvis caused by quasi-continuous changes of posture, if these can be observed as changes in back shape. Two examples are given to illustrate the aim and performance of functional examinations. Shoe elevation is used to correct leg-length discrepancy and is therefore prescribed for prevention and correction of scoliosis produced by pelvic obliquity. In a previous study it was shown that simulating leg-length discrepancy by raising a foot causes the pelvis to perform a torsional movement about the transverse axis. In effect, this movement reduces to some extent the effect of shoe elevation; thus a larger elevation might give better results. 42 scoliotic patients underwent functional examination. Leg-length discrepancies were simulated in 7 steps, and the resulting back shape was analysed by rasterstereography. The measurements were corrected for pelvic torsion. This method provided satisfactory correspondence with radiographically recorded leg-length discrepancies, i.e. 0.7 mm +/- 11.2 mm. One specific advantage of this procedure is that it covers aspects relating to spinal lateral deviation and vertebral rotation. It is concluded, however, that the 7 measurements used are hardly sufficient for this application and that better results are therefore to be expected from extended series. Kyphosis and lordosis clearly depend on posture. This is confirmed in a functional examination where these angles are measured under voluntary changes of posture. In forward bending, the trunk straightens and kyphosis and lordosis angles decrease. The reverse case applies to backward bending. If this effect is taken into quantitative consideration, an improved accuracy of measurements is obtained by reference to a standardised, mathematically defined posture. The resulting rms-error of kyphosis/lordosis measurement is then reduced from 3.10 degrees/2.95 degrees to 1.65 degrees/1.40 degrees. These figures open up new applications in the follow-up of kyphotic and lordotic deformities.

[Scanning stereographic surface measurement in idiopathic scoliosis after VDS (ventral derotation spondylodesis)]. / Rasterstereografische Oberflächenvermessung idiopathischer Skoliosen nach VDS.

INTRODUCTION: So far only radiometric and clinical methods have been available for the evaluation of results after anterior scoliosis surgery. Rasterstereography has proved to be a reliable method for three-dimensional surface measurement of conservatively treated idiopathic scoliosis patients. Therefore, patients treated operatively with anterior instrumentation were examined using rasterstereography to determine the three-dimensional correction of the spinal deformity. The aim was to measure back shape deformity, in particular derotation, and thus cosmetic improvements. METHODS: 31 patients with idiopathic thoracic, thoracolumbar and lumbar scoliosis (Cobb angle 57.2 degrees) were examined with raster stereography preoperatively, postoperatively and after follow-up (25.2 months) in a standardized standing posture. Standing radiographs were compared with raster stereography. RESULTS: The mean Cobb angle was reduced from 57.2 degrees to 17.2 degrees, the rasterstereographic maximal surface rotation from 16.5 degrees to 10.8 degrees, and the vertebral rotation according to Perdriolle from 29.2 degrees to 16.7 degrees. During follow-up the Cobb angle increased to 20.8 degrees, and surface rotation to 11.3 degrees. Vertebral rotation remained constant. Lordosis and kyphosis angles changed only slightly. CONCLUSION: Rasterstereography is a suitable tool for analyzing the three-dimensional correction of spinal deformities after anterior scoliosis surgery. In particular, the cosmetic improvement is clearly demonstrated. The measurement of surface rotation allows objective quantification of the obtained derotation.

[3-dimensional surface measurement of spinal deformities with video rasterstereography]. / Die dreidimensionale Oberflächenvermessung von Wirbelsäulendeformitäten anhand der Videorasterstereographie.

QUESTION: Video rasterstereography is a method for back surface measurement comprising automatic back surface reconstruction and shape analysis. Aim of this prospective study was to determine the accuracy of this method in comparison to the conventional frontal and lateral standing radiographs. METHOD: 95 patients with idiopathic scoliosis or scoliotic postural abnormalities and 18 patients with thoracic hyperkyphosis and Scheuermann's disease were investigated. The Cobb angles, the sagittal profile and apical vertebral rotation as well as pelvic obliquity and trunk decompensation were measured. The analysis was carried out by two independent observers. RESULTS: The root mean square (r.m.s.) deviation of the Cobb angle in the cases of idiopathic scoliosis ranged between 7 degrees and 8 degrees. In video rasterstereography there were no false negative results and two false positive results concerning differentiation between structural scoliosis and scoliotic postural abnormality. The r.m.s. deviation of apical vertebral rotation averaged 7.9 degrees and for pelvic obliquity respectively trunk imbalance 0.65 cm respectively 1.07 cm. The thoracic hyperkyphosis in Scheuermann's disease showed a r.m.s. deviation of 5.6 degrees. CONCLUSIONS: Video rasterstereography is a reliable method in the three-dimensional evaluation of spinal deformities and constitutes a valuable additional tool to the clinical examination and can reduce the number of radiographs.

Assessment of scoliotic deformity from back shape asymmetry using an improved mathematical model.

OBJECTIVE: The objective of the study was to improve with respect to accuracy and smoothness the three-dimensional model of the spinal midline which has been calculated from rasterstereographic back surface data. DESIGN: A new mathematical model using frequency-modulated sine curves has been applied to existing rasterstereographic and radiographic data in an in vivo study. BACKGROUND: Analysis of back shape (measured by rasterstereography) enables a three-dimensional model of the spinal midline to be calculated. The model is based on the so-called symmetry line which coincides approximately with the line of the spinous processes. In addition the surface rotation on the symmetry line is taken as an estimate for vertebral axial rotation in scoliosis. METHODS: Four hundred and seventy-eight pairs of radiographs and rasterstereographs of scoliotic patients have been evaluated and compared using the new model. The radiographs were digitized manually, delivering curves of lateral deviation and vertebral rotation. Analysis of back shape from the rasterstereographs delivers a three-dimensional model of the spinal midline, the frontal projection of which is to be compared with the radiographic curve. Likewise, vertebral rotation and surface rotation are compared. RESULTS: The use of frequency-modulated sine curves improved the results as compared to the existing procedure with respect to prediction accuracy of lateral deviation (typically from sigma(x) = 4.6 mm to sigma(x) = 4.0 mm, P < 10(-10)). The prediction of axial rotation was not significantly improved (sigma(varrho) thick approximate 3.8 degrees ). In addition, the smoothness of the curves is considerably improved. The prediction accuracy proved to be independent of the scoliosis type as represented by apex height (r = -0.09 ellipsis + 0.03). CONCLUSION: The use of frequency-modulated sine curves improves significantly the accuracy and smoothness of the spinal model curves.

Back shape measurement using video rasterstereography and three-dimensional reconstruction of spinal shape.

Video rasterstereography is a method for back surface measurement comprising automatic back surface reconstruction and shape analysis. It is particularly appropriate for the examination of scoliosis. In this application shape analysis includes model-based calculations of vertebral rotation (determined from surface rotation) and of the spinal midline in three dimensions. The results are delivered in quasi-real time (computing time < 5 min). The aim of the present study was to validate the method by comparison of rasterstereographic and radiographic data. Anteroposterior radiographs and rasterstereographs (478) of 113 scoliosis patients were analysed, each pair taken on the same day. Matching the radiographic midline of the spine to its rasterstereographic equivalent, the deviations between the two curves are properly expressed by their root mean square (r.m.s.) deviation. A r.m.s. deviation in the order of 4 mm was found. Similarly, the r.m.s. deviation of vertebral rotation from surface rotation was about 3°. No systematic difference of vertebral and surface rotation, as reported by other authors, could be found. This may be attributed to our method of data evaluation, consisting of a sophisticated analysis of surface curvature and shape asymmetry. These mathematical procedures are made possible by the high sampling density and resolution of video rasterstereography. Conventional scoliosis parameters (e.g. Cobb angle, apical rotation, apex height, etc.) can be estimated with limited accuracy from the reconstructed midline. The relevant standard deviations are given.

Evaluation of frontal radiographs of scoliotic spines--Part II. Relations between lateral deviation, lateral tilt and axial rotation of vertebrae.

The shape of scoliotic spines as measured from frontal radiographs (see Part I of this paper) is analysed with respect to interrelations between lateral deviation, lateral tilt and axial rotation of the vertebrae. These parameters are represented by sinusoidal functions of the longitudinal coordinate. The interrelations can, therefore, be expressed in terms of amplitude and phase relations. Two additional functions--'spinal tilt' and (local) curvature--are calculated from the first and second derivatives of lateral deviation. The method has been applied to three patient groups with different aetiology: 113 patients with idiopathic scoliosis (478 radiographs, partially follow-up examinations), 23 patients with scoliosis secondary to Wilms' tumour irradiation and 18 patients with scoliosis secondary to poliomyelitis. The amplitude and phase relations of all functions reveal a characteristic pattern which is apparently independent of the specific aetiology. The results show that the available biomechanic explanations of coupling of vertebral motions are questionable.

Evaluation of frontal radiographs of scoliotic spines--Part I. Measurement of position and orientation of vertebrae and assessment of clinical shape parameters.

A new method largely exploiting the shape information which may be obtained from frontal radiographs of scoliotic patients is presented. For a complete description of spinal deformity, six position parameters are needed for each vertebra. From a strictly mathematical point of view, none of them can be determined from a single standard radiograph. However, the four most important parameters can be measured if some reasonable assumptions are made. For a better interpretation, three of these parameters (lateral coordinate x, lateral tilt alpha and axial rotation rho) are plotted as a function of the fourth parameter, the longitudinal coordinate y. These functions may well be approximated by sinusoidal curves (or possibly by Fourier series). The data smoothing implied by this procedure improves the reliability of the data. The method has been tested with 478 radiographs of 113 patients (Cobb angles up to 52 degrees). The results are compared with scoliosis parameters which have been determined according to the conventional clinical rules. A particular advantage of approximation by a sinusoidal function lies in the direct relation of the curve parameters to common scoliosis parameters. Moreover, a mathematical analysis of the interrelations between different parameters--for example, between lateral deviation and axial rotation--is possible in this case.

Age-associated T-lymphocyte activation through mitogens in patients with multiple sclerosis and blood donors.

In 128 patients with multiple sclerosis (MS) and 204 blood donors (control persons) the in vitro activation of 'Ficoll-purified' peripheral blood T lymphocytes was measured using the 3H-thymidine incorporation rate without (spontaneous proliferation) and with mitogen addition (concanavalin A, phytohemagglutinin). Mitogen responsiveness in control persons and MS patients decreased with age, reflecting a T-lymphocyte inherent mechanism for the diminution of responsiveness. The MS patients, ranging in age between 20 and 30 years, showed decreased mitogen responsiveness and a tendency to increased spontaneous proliferation compared to the control persons. These results could be an expression of a viral infection.

Automatic localization of anatomical landmarks on the back surface and construction of a body-fixed coordinate system.

A method for automatic measurement of anatomical landmarks on the back surface is presented. The landmarks correspond to the verteba prominens, the dimples of the posterior superior iliac spines and the sacrum point (beginning of rima ani), which are characterized by distinct surface curvature. The surface curvatures are calculated from rasterstereographic surface measurements. The procedure of isolating a region of interest for each landmark (surface segmentation) and the calculation of the landmark coordinates are described in detail. The accuracy of landmark localization was tested with serial rasterstereographs of 28 patients (with moderate idiopathic scoliosis). From the results the intrinsic accuracy of the method is estimated to be little more than 1 mm (depending on the sampling density of the surface measurement). Therefore, the landmarks may well be used for the objective definition of a body-fixed reference coordinate system. The accuracy is, however, dependent on the specific landmark and a minor influence of posture variations is observed.

Movement of the human pelvis and displacement of related anatomical landmarks on the body surface.

Anatomical landmarks on the body surface can be measured with high accuracy by using rasterstereography and surface curvature analysis. The present study shows that the lumbar dimples can be localized with a statistical error of about 1 mm. It is generally assumed that the dimples are in close relation to the pelvis (in particular to the PSISs) and may thus be taken as indicators for pelvis movements. By introducing an artificial pelvis tilt of up to +/- 10 degrees this relation was examined. In fact, a nearly perfect correlation (r approximately equal to 0.99) between landmark and pelvis movements was observed. Asymmetries of pelvis motion due to scoliotic deformity were not observed. There was, however, a systematic lag of the dimple movements, resulting in a displacement of the dimples of up to +/- 1.5 mm relative to the pelvis (for +/- 10 degrees pelvis tilt). Either a soft tissue effect or a torsion of the pelvis may be responsible for this behaviour. The theory of pelvis torsion is confirmed by the fact that the orientation of the back surface at the locus of the dimples reveals a corresponding torsion of similar magnitude and sign. A torsion angle of about +/- 1.5 degrees in either sacro-iliac joint is sufficient to explain the observed dimple lag and the surface torsion. An independent measurement (e.g. using roentgenphotogrammetry) would be desirable to further validate this theory. According to our measurements the dimples of the PSISs cannot be taken as exact indicators for orientation and movement of the pelvis.(ABSTRACT TRUNCATED AT 250 WORDS)

Rasterstereography in the measurement and postoperative follow-up of anterior chest wall deformities.

Rasterstereography is a contact-free photogrammetric method for the measurement of body surfaces. As such it is particularly suited for the objective documentation of anterior chest wall deformities and the results of surgery. An example of its application and first results are presented. The possibilities of a thorough data analysis with regard to diagnosis and therapy control are outlined.

Objective determination of anatomical landmarks on the body surface: measurement of the vertebra prominens from surface curvature.

A method for the objective detection of anatomical landmarks on the body surface is presented. The method is based on an analysis of local surface shape which is described in terms of surface curvature. The curvature is calculated from the surface coordinates as measured by optical methods such as moiré topography or rasterstereography. As an example, the location of the vertebra prominens is determined. In order to assess the accuracy and reliability of the procedure, the results are compared with the conventional method of palpation and marking. The measured deviations are in the order of a few millimeters.