Jacques A. de Guise

3D/2D registration and segmentation of scoliotic vertebrae using statistical models

We propose a new 3D/2D registration method for vertebrae of the scoliotic spine, using two conventional radiographic views (postero-anterior and lateral), and a priori global knowledge of the geometric structure of each vertebra. This geometric knowledge is efficiently captured by a statistical deformable template integrating a set of admissible deformations, expressed by the first modes of variation in Karhunen-Loeve expansion, of the pathological deformations observed on a representative scoliotic vertebra population. The proposed registration method consists of fitting the projections of this deformable template with the preliminary segmented contours of the corresponding vertebra on the two radiographic views. The 3D/2D registration problem is stated as the minimization of a cost function for each vertebra and solved with a gradient descent technique. Registration of the spine is then done vertebra by vertebra. The proposed method efficiently provides accurate 3D reconstruction of each scoliotic vertebra and, consequently, it also provides accurate knowledge of the 3D structure of the whole scoliotic spine. This registration method has been successfully tested on several biplanar radiographic images and validated on 57 scoliotic vertebrae. The validation results reported in this paper demonstrate that the proposed statistical scheme performs better than other conventional 3D reconstruction methods.

Sagittal plane analysis of the spine and pelvis in adolescent idiopathic scoliosis according to the coronal curve type

Study Design. A retrospective study investigated the sagittal alignment in adolescent idiopathic scoliosis (AIS). Objective. To evaluate the sagittal alignment of the spine and pelvis in adolescent idiopathic scoliosis on the basis of curve type. Summary of Background Data. The relation between the spine and pelvis highly influences the sagittal balance in adults. However, the sagittal alignment of the spine and pelvis in adolescent idiopathic scoliosis is poorly defined in the literature. Methods. Five sagittal parameters were evaluated on lateral radiographs of 160 patients with adolescent idiopathic scoliosis: thoracic kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence. The patients were classified according to their coronal curve type. Analysis of variance was used to compare the parameters between the curve types, and Pearson coefficients were used to investigate the relation between all parameters (&agr; = 0.05). Results. The thoracic kyphosis was significantly lower for King I, II, and III curves than for lumbar curves. The lumbar lordosis was higher for lumbar curves, although not significantly. No significant change between the groups was observed for the sacral slope, pelvic tilt, or pelvic incidence. The pelvic incidence was significantly correlated with the lumbar lordosis, sacral slope, and pelvic tilt for all the groups. The lumbar lordosis was strongly related to the sacral slope in all cases, but not with the thoracic kyphosis, except in the case of thoracolumbar curves. Conclusions. Thoracic kyphosis depended mostly on the spinal deformity, whereas lumbar lordosis was influenced mainly by the pelvic configuration. The scoliotic curve type was not associated with a specific pattern of sagittal pelvic morphology and balance. The pelvic incidence found in this study was significantly higher than that reported in the literature for normal adolescents. The role of the pelvic incidence in the pathogenesis of adolescent idiopathic scoliosis needs to be explored in a longitudinal study involving patients with adolescent idiopathic scoliosis and normal adolescents.

Peroperative three-dimensional correction of idiopathic scoliosis with the Cotrel-Dubousset procedure

STUDY DESIGN An experiment was conducted to investigate the effect of wearing a weight lifting belt on the endurance and fatigue characteristics of the extensor muscles of the spine. OBJECTIVE To evaluate the effectiveness of back belts in preserving the endurance characteristics of the spinal musculature. SUMMARY OF BACKGROUND DATA Previous studies have investigated the use of back belts in increasing intra-abdominal pressure and thus increasing the stabilization of the spine. Other studies have looked at the association of low back disability and wearing back belts. No study has examined the relationship between wearing back belts and measures of spinal muscle fatigue and endurance. METHODS Thirteen male industrial workers performed a lifting and lowering task from the floor to a 76.2 cm height at 4.3 min-1 2 days a week for 4 weeks. The load was psychophysically determined and averaged 28.1 kg for a total of 28.9 metric tons moved in 4 hours. Subjects lifted for 1, 2, 3, and 4 hours, respectively, for the first 4 days of the experiment. These were considered training days. During the last 4 days, subjects lifted for 4 hours per day; 2 days with a back belt, and 2 days without a back belt. Maximum isokinetic endurance of the extensors was measured for 50 repetitions (5 sets of 10 repetitions) at the end of 4 hours of lifting. Median frequencies of the electromyographic signal from six locations over the back extensors were measured for 30 seconds at 80% of maximum isometric voluntary contraction after 4 hours of lifting. RESULTS There were no significant differences in maximum isokinetic endurance, or in the slope of median frequency, between lifting with a back belt and lifting without a back belt. Similarly, a modified Borg scale and a postexperiment survey question were unable to distinguish between wearing a back belt and not wearing a back belt. CONCLUSION There were no significant differences in maximum isokinetic endurance and electromyographic spectral parameters of the back extensor muscles as a result of wearing a back belt during heavy lifting and lowering tasks.Study Design. A peroperative measurement technique based on magnetic fields was used to document the thoracic and lumbar vertebral changes induced by derotation of the concave rod during corrective surgery of idiopathic scoliotic deformities with Cotrel‐Dubousset instrumentation. Objectives. Objective was to accurately document the immediate changes induced by the derotation maneuver to gain a better understanding of its effect on curve correction during a surgical procedure. Summary of Background Data. Accurate peroperative documentation of these three‐dimensional changes was very limited, and the exact contribution of the derotation maneuver in the entire process of correction of a scoliotic deformity was still poorly understood. Methods. A digitizer using magnetic fields was used to record the three‐dimensional orientation and x, y, and z coordinates of the tip of every spinous process exposed at surgery before and after derotation of the concave rod in a group of 22 female patients with idiopathic scoliosis. Results. A significant improvement of the scoliotic deformity was noted in the frontal plane, and improvement of thoracic hypokyphosis and lumbar hypolordosis in the sagittal plane was seen. Vertebral axial rotation remained unchanged. Conclusions. The derotation maneuver is effective in achieving three‐dimensional correction of idiopathic scoliosis, but vertebral axial derotation is not an important component of this correction.

Comparison between preoperative and postoperative three-dimensional reconstructions of idiopathic scoliosis with the Cotrel-Dubousset procedure.

Study Design Pre-and postoperative three-dimensioned reconstructions of the spine and rib cage were done and compared in a group of adolescents with idiopathic scoliosis. Objectiv Changes in the shape of the thoracic spine and rib cage induced by the cotrel-Dubousset instrumentation and procedure were documented. Summary of Background Data Although many authors have reported significant curve improvament in the frontal plane, attempts to document derotation of the spine have shown only limited correction of apical vertabral rotation. Methods Three-dimensional reconstructions were obtained pre-and postoperatively using a stereoradio graphic technique in a group of 37 adolescents with idiopathic scoliosis. Several geometrical indices of the spine and rib cage were compared using Student tests. Results The curve correction averaged 50% in the frontal plane and 24% in the plane of maximum curvature, while normal thoracic kyphosis was maintained in the saginal plane. the orientation of the plane of maximum curvature was shifted very significantly toward the sagaital plane, indicating en bloc movement of the thoracic spine and three-dimensional correction of the deformity. A small but significant change in vertebral axial rotation and rib hump was found and improvement in the overal orientation of the ribs was documented. Conclusions The cotre-Dubousset instrumentation and procedure are effective in producing thre-dimensional improvement of the thoracic spine by en location of the instrumented spine rather than by vertebral axial derotation.

Postural model of sagittal spino-pelvic alignment and its relevance for lumbosacral developmental spondylolisthesis.

Study Design. Comparative study of sagittal spino-pelvic alignment in children and adolescents with developmental lumbosacral spondylolisthesis compared with asymptomatic subjects. Objective. To develop a global postural model of sagittal spino-pelvic alignment. Summary of Background Data. The relationships between parameters of sagittal spino-pelvic alignment in developmental spondylolisthesis are still unclear. Methods. Radiographs of 120 control subjects and 131 subjects with developmental spondylolisthesis (91 low-grade, 40 high-grade) were reviewed. Subjects with high-grade spondylolisthesis were divided according to their sacro-pelvic alignment: balanced versus retroverted sacro-pelvis. Parameters of the sacro-pelvis (pelvic incidence, pelvic tilt, sacral slope), lumbosacral region (lumbosacral angle, slip percentage), lumbar spine (lumbar lordosis, lumbar tilt), thoracic spine (thoracic kyphosis, thoracic tilt), and global balance (spinal tilt, sagittal offset between C7 and femoral heads) were assessed. Parameters were compared between all groups and a correlation study was performed between all parameters. A postural model that includes the measured parameters was used to analyze the obtained correlations. Results. Significant differences in all parameters are found between all groups, except for sagittal offset. The pattern and strength of correlations is similar between normal and low-grade subjects, showing interdependence between sacro-pelvic, lumbosacral, lumbar, and thoracic regions. The pattern of relationships was altered in high-grade spondylolisthesis, especially for subjects with a retroverted sacro-pelvis for which correlations between pelvic incidence and pelvic tilt, and between the sacro-pelvic unit and lumbar spine geometry are lost. Conclusion. Children and adolescents stand with a relatively constant global sagittal spino-pelvic alignment, regardless of the local lumbosacral deformity. A normalposture is maintained in low-grade spondylolisthesis and in high-grade spondylolisthesis with a balanced sacro-pelvis. Posture is abnormal in high-grade spondylolisthesis associated with a retroverted sacro-pelvis, suggesting that surgical reduction of the local lumbosacral deformity in these patients could be attempted to restore a normal posture.

A Three-Dimensional Radiographic Comparison of Cotrel-Dubousset and Colorado Instrumentations for the Correction of Idiopathic Scoliosis

Study Design. A prospective clinical study comparing two instrumentation systems for the correction of idiopathic scoliosis. Objectives. To measure the short-term three-dimensional changes in the shape of the spine after corrective surgery and compare the Cotrel–Dubousset instrumentation to the more recent Colorado instrumentation to determine whether one system provides better three-dimensional correction. Summary of Background Data. Adequate three-dimensional correction of scoliotic deformities has been reported with the Cotrel–Dubousset instrumentation system. During the past decade, a new generation of more versatile and user-friendly spinal implants has appeared, but there are no reports available to indicate whether similar or better correction can be obtained with these newer systems. Methods. The three-dimensional geometry of the thoracic and lumbar spine was documented in the standing position using a three-dimensional reconstruction technique based on multiplanar radiography in 67 adolescents with idiopathic scoliosis undergoing correction by a posterior approach. Changes in spinal shape were measured 3 days before and 1 month after the surgery in 31 patients with Cotrel–Dubousset instrumentation and 36 patients with Colorado instrumentation. Results. In both groups, adequate three-dimensional correction of the scoliotic deformities was documented for thoracic and lumbar curves, with significant changes in the frontal plane, in the plane of maximum curvature, and in its orientation. When comparing both groups, better correction was obtained in the frontal plane with the Colorado instrumentation (65%vs. 48% with Cotrel–Dubousset), a finding that may be explained by the significantly greater proportion of pedicle screws used in this group. Conclusion. Both instrumentation techniques achieve an effective and comparable three-dimensional correction of the scoliotic deformities.

Rib cage-spine coupling patterns involved in brace treatment of adolescent idiopathic scoliosis.

Study Design. The three‐dimensional (3‐D) interrelations in the correction of the spine and rib cage produced by the Boston brace were analyzed in a group of adolescents with idiopathic scoliosis. Objectives. To investigate the coupling movements between the spine and rib cage initiated by brace wear (i.e., the displacements of the spine that take place in other directions than the ones generated by brace pressures on the thorax). Summary of Background Data. The effects of thoraco‐lumbo‐sacral orthosis in the frontal plane have been well documented, but they have never been studied in terms of 3‐D coupled movements between the spine and rib cage. Methods. The spine and rib cage of 36 adolescents with idiopathic scoliosis with and without their Boston brace were reconstructed in 3‐D using a stereo‐radiographic technique. Several geometric indices were evaluated on the trunk, and the relative motions of the spine and rib cage resulting from brace wearing were compared by means of Student t tests, Pearson correlation matrices, and linear regressions. Results. Rib cage transverse plane translations resulting from brace pressures are related to those of the spine. Coupled movements between the spine and rib cage were found to alter substantially the expected 3‐D correction of the trunk. Significant anterior displacements of the thorax were observed and were statistically associated with lateral displacements of the spine and with an increase of spinal thoracic curvatures in the frontal and sagittal planes. Conclusion. Brace loads are not applied in an optimal way to correct the 3‐D deformities associated with thoracic idiopathic scoliosis. Loads applied on the posterior rib hump should be reequilibrated to reduce anterior displacement of the trunk.

Intraoperative comparison of two instrumentation techniques for the correction of adolescent idiopathic scoliosis. Rod rotation and translation.

Study Design. A prospective and controlled comparative study of two instrumentation techniques used for the correction of adolescent idiopathic scoliosis. Objective. To measure the three‐dimensional intraoperative correction obtained with a rotation maneuver as compared with that obtained with a translation maneuver of the first instrumentation rod inserted to determine the difference, if any, in the two techniques for achieving three‐dimensional correction. Summary of Background Data. Adequate three‐dimensional correction of scoliotic deformities has been reported with the Cotrel‐Dubousset instrumentation using the rod‐rotation maneuver. More recently, however, authors of studies with newer instrumentation systems have claimed that better correction can be obtained using a translation technique. So far, no report has clearly demonstrated the three‐dimensional changes obtained with this more recent instrumentation technique. Methods. The changes in position of thoracic and lumbar vertebrae exposed during surgery were documented using a three‐dimensional magnetic digitizer in 70 adolescents with idiopathic scoliosis undergoing correction by a posterior approach. Vertebral positions were measured intraoperatively before and after the surgical maneuver in 39 patients with the Cotrel‐Dubousset instrumentation (rod rotation) and in 31 patients with the Colorado instrumentation (translation). Results. In both groups, adequate three‐dimensional correction of the scoliotic deformities was documented, with significant changes in the frontal and sagittal planes and in the orientation of the plane of maximum deformity for thoracic and lumbar curves. On the other hand, no significant differences were documented between the two procedures except in the frontal plane where a tendency for greater correction was observed for thoracic curves with the translation technique. Conclusions. The two instrumentation techniques are equally able to achieve a comparable and effective three‐dimensional correction of the scoliotic deformities. The use of either a rotation maneuver or a translation technique during surgery does not result in any significant measurable difference in three‐dimensional correction.

Feature selection using a principal component analysis of the kinematics of the pivot shift phenomenon

The pivot shift test reproduces a complex instability of the knee joint following rupture of the anterior cruciate ligament. The grade of the pivot shift test has been shown to correlate to subjective criteria of knee joint function, return to physical activity and long-term outcome. This severity is represented by a grade that is attributed by a clinician in a subjective manner, rendering the pivot shift test poorly reliable. The purpose of this study was to unveil the kinematic parameters that are evaluated by clinicians when they establish a pivot shift grade. To do so, eight orthopaedic surgeons performed a total of 127 pivot shift examinations on 70 subjects presenting various degrees of knee joint instability. The knee joint kinematics were recorded using electromagnetic sensors and principal component analysis was used to determine which features explain most of the variability between recordings. Four principal components were found to account for most of this variability (69%), with only the first showing a correlation to the pivot shift grade (r = 0.55). Acceleration and velocity of tibial translation were found to be the features that best correlate to the first principal component, meaning they are the most useful for distinguishing different recordings. The magnitudes of the tibial translation and rotation were amongst those that accounted for the least variability. These results indicate that future efforts to quantify the pivot shift should focus more on the velocity and acceleration of tibial translation and less on the traditionally accepted parameters that are the magnitudes of posterior translation and external tibial rotation.

Idiopathic scoliosis in three dimensions : a succession of two-dimensional deformities?

Study Design. A geometric analysis of computerized three-dimensional (3-D) reconstructions of the spine of adolescents with idiopathic scoliosis. Objectives. To analyze and describe the 3-D location of scoliotic curves with respect to the global frontal, sagittal, and transverse planes of each subject. Summary of Background Data. Clinical two-dimensional (2-D) measurements cannot fully describe the 3-D deformity of a scoliotic spine because they are done in the 2-D frontal or sagittal plane projection of a subject and do not correspond to the actual deformity. Methods. The spinal deformity from T1 to L5 of 50 adolescents with thoracic idiopathic scoliosis was reconstructed in 3-D using a multiplanar digital radiographic technique allowing the visualization of the vertebral line of the spine in any projection using auto CAD software. The curvature was segmented in three distinct curves for each subject: a high thoracic, a thoracic, and a lumbar. A regional plane passing through the two end-vertebrae and the apical vertebra was defined, and a series of geometric manipulations were performed to realign each regional plane with the global axis system of each subject. Results. A total of 91% of the 147 curves studied were found to be entirely contained within its 2-D regional plane, and all scoliotic curves were found to be oriented in a 3-D location different from the classic frontal, sagittal, and transverse orthogonal planes of each subject. Conclusion. In thoracic idiopathic scoliosis the deformity of the spine is 3-D, but the regional deformity of each high thoracic, thoracic, or lumbar curve is almost always 2-D. The orientation in space of each 2-D plane is such that it cannot be seen in its true frontal or sagittal projection using standard frontal or sagittal radiologic views of the subject.