Apical Axial Vertebral Rotation Research Articles

Validity of a fast automated 3d spine reconstruction measurements for biplanar radiographs: SOSORT 2024 award winner.

To validate a fast 3D biplanar spinal radiograph reconstruction method with automatic extract curvature parameters using artificial intelligence (AI). Three-hundred eighty paired, posteroanterior and lateral, radiographs from the EOS X-ray system of children with adolescent idiopathic scoliosis were randomly selected from the database. For the AI model development, 304 paired images were used for training; 76 pairs were employed for testing. The validation was evaluated by comparing curvature parameters, including Cobb angles (CA), apical axial vertebral rotation (AVR), kyphotic angle (T1-T12 KA), and lordotic angle (L1-L5 LA), to manual measurements from a rater with 8years of scoliosis experience. The mean absolute differences ± standard deviation (MAD ± SD), the percentage of measurements within the clinically acceptable errors, the standard error of measurement (SEM), and the inter-method intraclass correlation coefficient ICC[2,1] were calculated. The average reconstruction speed of the 76 test images was recorded. Among the 76 test images, 134 and 128 CA were exported automatically and measured manually, respectively. The MAD ± SD for CA, AVR at apex, KA, and LA were 3.3° ± 3.5°, 1.5° ± 1.5°, 3.3° ± 2.6° and 3.5° ± 2.5°, respectively, and 98% of these measurements were within the clinical acceptance errors. The SEMs and the ICC[2,1] for the compared parameters were all less than 0.7° and > 0.94, respectively. The average time to display the 3D spine and report the measurements was 5.2 ± 1.3s. The developed AI algorithm could reconstruct a 3D scoliotic spine within 6s, and the automatic curvature parameters were accurately and reliably extracted from the reconstructed images.

Maximal Axial Vertebral Rotation in Adolescent Idiopathic Scoliosis: Is the Apical Vertebra the Most Rotated?

Study Design:Retrospective cross-sectional study.Objectives:It is generally believed that the apical vertebra has the largest axial rotation in adolescent idiopathic scoliosis. We investigated the relationship between apical axial vertebral rotation (apicalAVR) and maximal axial vertebral rotation (maxAVR) in both major and minor curves using biplanar stereo-imaging.Methods:EOS 2D/3D biplanar radiograph images were collected from 332 patients with adolescent idiopathic scoliosis (Cobb angle range 10°-122°, mean age 14.7 years). Based on the X-ray images, with the help of 3D full spine reconstructions Cobb angle, curvature level, apicalAVR and maxAVR were determined. These parameters were also determined for minor curves in Lenke 2, 3, 4, 6 type patients. Maximal thoracic rotation and maximal thoracolumbar/lumbar rotation were calculated. Statistical analysis was performed with descriptive statistics, Shapiro-Wilk test, and Wilcoxon signed-rank test.Results:The apical vertebrae were the most rotated vertebra in only 40.4% of the major curves, and 31.7% in minor curves. MaxAVR significantly exceeded apicalAVR values in the major curves (P < .001) as well as in minor curves (P < .001). The 2 parameters differed significantly in each severity group and Lenke type.Conclusions:The apical vertebrae were not the most rotated vertebra in more than half of cases investigated indicating that apicalAVR and maxAVR should be considered as 2 distinct parameters, of which maxAVR fully describes the axial dimension of scoliosis. Furthermore, the substitution of maxAVR for the apicalAVR should be especially avoided in double and triple curves, as the apical vertebra was even less commonly the most rotated in minor curves.

Axial plane characteristics of thoracic scoliosis and their usefulness for determining the fusion levels and the correction technique.

There is insufficient information regarding axial plane characteristics of scoliosis despite its 3D nature. The posterior-anterior vertebral vector (VV) has been proposed to characterize the axial plane appearances of the thoracic scoliosis. This study aimed to highlight the importance of knowledge of axial plane features when determining fusion levels and correction techniques of thoracic curves. Altogether, 233 thoracic curves were analyzed using the VV after proving its usability instead of 3D angles to determine axial plane parameters such as apical vertebral (APV) axial rotations, APV lateral displacement, and intervertebral rotations (IVR). K-means clustering and regression analysis were used to identify axial plane curve patterns and determine the relationship between the coronal angles and axial plane characteristics, respectively. A close correlation was found between 3D angles and VV projected angles. Eight axial plane clusters were distinct, exhibiting different lateral APV displacement toward the interacetabular axis with relatively small axial rotations and a simultaneous decrease in sagittal curves. The regression analysis showed that the correlation of coronal curve magnitude was significantly stronger (r = 0.78) with APV lateral translation than with APV axial rotation (r = 0.65). Based on these findings, the primary goal of scoliosis correction should focus on minimizing lateral translation rather than eliminating axial rotation. Knowing the IVR in the axial plane helps accurately determine the limits of the structural curves. VV-based axial views can facilitate the accurate determination of the end vertebrae and selection of the appropriate correction technique of the curve. These slides can be retrieved under Electronic Supplementary Material.

How to Optimize Axial Correction Without Altering Thoracic Sagittal Alignment in Hybrid Constructs With Sublaminar Bands: Description of the “Frame” Technique

Study DesignRetrospective monocentric database study. ObjectivesTo describe the “frame” reduction technique and report the 3D quantitative analysis of postoperative corrections in a consecutive series of thoracic adolescent idiopathic scoliosis (AIS) patients. Summary of Background DataPosteromedial translation technique using sublaminar bands have been proved to be efficient and safe for 3D correction of the deformity and overall cosmetic aspect of the trunk. However, the ability to correct the axial plane may tend to rotate the vertebra clockwise instead of counterclockwise, thus increasing apical vertebra axial rotation (AVR) and the rib hump. A technical improvement was developed to emphasize axial correction. Methods60 thoracic AIS patients consecutively operated by posteromedial translation using the “frame” reduction technique were included with a minimum 2-year follow-up. Precontoured rods were connected with fixed transverse connectors according to a personalized preoperative planning. Rods were first inserted distally in the pedicle screws to achieve lumbar correction, and then in the upper anchors, and finally sublaminar bands were connected to their corresponding rods to progressively bring the concave lamina to the concave rod to correct the thoracic deformity. Sagittal and coronal 3D measures were performed preoperatively and at the latest follow-up using SterEOS (EOS Imaging, Paris, France) to assess the efficiency of the technique. ResultsThe distance from the center of the apical vertebra to the reference axis in the frontal plane was reduced from 4.7 to 1.1 cm, traducing the efficient medial translation of the spine during correction. T1–T12 kyphosis significantly increased after surgery (28°–35°). 3D location of the upper instrumented vertebra (UIV) was not affected. The apical rotation was significantly reduced after surgery (19°–11°), and the AVR correction rate averaged 42.2%. ConclusionThe “frame” technique is an innovative way of using polyester bands, optimizing axial correction while respecting sagittal alignment. Level of EvidenceLevel IV.

Radiographic Axial Malalignment is Associated With Pretreatment Patient-Reported Health-Related Quality of Life Measures in Adult Degenerative Scoliosis: Implementation of a Novel Radiographic Software Tool

Study DesignRetrospective study of prospectively collected data. ObjectivesThe purpose of this study was to evaluate the relationship between apical vertebral axial rotation and pretreatment patient-reported health-related quality of life (HRQOL), disability, and pain in patients with adult degenerative scoliosis (ADS) using a novel radiographic software tool. Summary of Background DataRecent studies have demonstrated that in ADS, sagittal and coronal plane deformity are weakly to moderately associated with HRQOL, disability, and pain. However, as ADS is a three-dimensional spinal deformity, the impact of axial malalignment on HRQOL is yet to be determined. MethodsA total of 74 ADS patients were enrolled. HRQOL measures included the Short Form-36v2 (SF-36v2) and Scoliosis Research Society questionnaire (SRS-22r). Disability and pain measures included the Oswestry Disability Index (ODI) and numeric rating scale back and leg pain. Radiographic measures included Cobb angle (CA), sagittal spinopelvic parameters, lateral and anteroposterior (AP) translation of the apical vertebra. The amount of apical vertebral axial rotation was measured on digital AP radiograph images using a novel software technology. Subjects were stratified into four clinical groups based on the degree of apical vertebral axial rotation. ResultsApical vertebral axial rotation showed no association with lateral (r = 0.21; p = .15) and AP (r = 0.08, p = .80) translation of the apical vertebra. A significant moderate association was found between apical vertebral axial rotation and Cobb angle (r = 0.57; p < .05). Patients in the group with the highest degree of apical vertebral axial rotation reported significantly worse ODI and SRS-22r Subtotal and Pain scores (p < .05), irrespective of sagittal spinopelvic parameters. ConclusionsThis is the first study that reports on the association between apical vertebral axial rotation and pretreatment HRQOL, disability, and pain in ADS. This study suggests that increased apical vertebral axial rotation is associated with suboptimal pretreatment health status scores. Level of EvidenceLevel III.

Tridimensional Analysis of Rotatory Subluxation and Sagittal Spinopelvic Alignment in the Setting of Adult Spinal Deformity

Study DesignRetrospective single-center. ObjectiveTo investigate rotatory subluxation (RS) in adult spinal deformity (ASD) with three-dimensional (3D) stereoradiographic images and analyze relationships between RS, transverse plane parameters, spinopelvic parameters, and clinical outcomes. BackgroundRecent research has demonstrated that sagittal plane malalignment and listhesis correlate with ASD patient-reported outcomes. However, there is still a lack of knowledge regarding the clinical impact of 3D evaluation and rotatory subluxation. Recent developments in stereoradiography allow clinicians to obtain full-body standing radiographs with low-dose radiation and 3D reconstruction. MethodsOne hundred thirty lumbar ASD patients underwent full-spine biplanar radiographs (EOS Imaging, Paris, France). Clinical outcomes were recorded. Using sterEOS software, spinopelvic parameters and lateral listhesis were measured. 3D transverse plane parameters included apical axial vertebral rotation, axial intervertebral rotation (AIR), and torsion index (sum of AIR in the curve). ASD patients were divided in three groups: AIR <5°, 5°< AIR <10°, AIR >10°. Groups were compared with respect to radiographic and clinical data. Correlations were performed between the transverse and sagittal plane parameters and clinical outcomes. ResultsPatients with AIR >10° were significantly older, with larger Cobb angle (39.5°) and greater sagittal plane deformity (pelvic incidence–lumbar lordosis mismatch 11.7° and pelvic tilt 22.6°). The AIR >10° group had significantly greater apical vertebra axial rotation apex (24.8°), torsion index (45°), and upper-level AIR (21.5°) than the two other groups. Overall, 27% of AIR patients did not have two-dimensional (2D) lateral listhesis. Patients with AIR >10° had significantly worse Oswestry Disability Index and more low back pain. ConclusionFor patients in which lateral listhesis was unreadable in 2D imaging, rotatory subluxation was revealed using stereoradiography and at an earlier disease stage. Moreover, different 3D transverse plane parameters are related to different patient-reported outcomes. Therefore, axial rotation can be considered in evaluation of lumbar degenerative scoliosis severity and prognosis. Level of EvidenceLevel III.

Evaluating the Change in Axial Vertebral Rotation Following Thoracoscopic Anterior Scoliosis Surgery Using Low-Dose Computed Tomography

Background ContextIn recent years, there has been increasing appreciation of the need to treat scoliosis as a three-dimensional deformity. PurposeAssessment of surgical strategies and outcomes should consider not only the coronal plane correction but also derotation of the transverse plane deformity that can affect trunk appearance. Study DesignThis study included a cohort of 29 female adolescent idiopathic scoliosis patients who received thoracoscopic single rod anterior fusion (TASF) surgery. This study used pre- and postoperative low-dose computed tomographic (CT) scans to accurately measure apical axial vertebral rotation (AVR). MethodsThe pre- and postoperative values for clinically measured coronal Cobb correction and rib hump correction as well as AVR were compared to determine whether these values improved postoperatively. There are no conflicts of interest to report for authors of this investigation. ResultsAs expected, statistically significant reductions in coronal Cobb angle (mean preoperative Cobb 51°, reducing to 24° at the two-year follow-up) and rib hump (mean preoperative rib hump 15°, reducing to 7° at two-year follow-up) were achieved. The mean reduction in apical AVR measured using CT was only 3° (mean preoperative AVR 16°, reducing to 13° at two-year follow-up), which was statistically but not clinically significant. Significant correlations were found between Cobb angle and rib hump, between Cobb angle and AVR, and between AVR and rib hump, suggesting that patients with greater coronal Cobb correction also achieve better derotation with this surgical procedure. ConclusionsThe historical low-dose CT data set permitted detailed three-dimensional assessment of the deformity correction that is achieved using thoracoscopic anterior spinal fusion for progressive adolescent idiopathic scoliosis.

The impact of direct vertebral rotation (DVR) on radiographic outcome in surgical correction of idiopathic scoliosis

IntroductionRecent developments of spinal instruments allow to address nearly all components of idiopathic scoliosis. Direct vertebral rotation (DVR) maneuver was introduced to correct apical axial vertebral rotation. It is however still not well established how efficiently DVR affects results of scoliosis correction. The object of the study was to evaluate en bloc apical vertebral rotation (DVR) and its impact on coronal and sagittal correction of the spine in patients undergoing surgical scoliosis treatment.Materials and methodsThirty-six consecutive patients who underwent posterior spinal fusion with pedicle screws only constructs for idiopathic scoliosis. Fifteen patients (20 curves) were corrected by rod derotation only and 21 patients (26 curves) had both rod derotation and DVR. Curve measurements were performed on x-rays obtained before and postoperatively—coronal curves, kyphosis (T2–T12, T5–T12). Spine flexibility was assessed on prone bending x-rays. Apical axial rotation was determined on CT scans obtained intraoperatively and postoperatively. Rotation angle (RAsag) was measured according to Aaro and Dahlborn.ResultsWe observed reduction of RAsag in all patients; however, in DVR group, decrease was greater, by 31.8% comparing to non-DVR group, by 8.6% (p = 0.0003). Mean coronal correction in DVR group was 68.8% and in rod derotation group without DVR 55% (p = 0.002). No significant correlation was found between degree of derotation obtained and coronal correction. In DVR group T2–T12 kyphosis has increased in 28 (65%) patients whereas in non-DVR group in 31 (69%) cases. Mean value of T2–T12 kyphosis growth was 16.7% in DVR and 22.1% in non-DVR group. These differences however did not occur statistically significant.ConclusionsDirect vertebral rotation (DVR) maneuver reduces significantly apical rotation of the spine, enhances ability of coronal correction, and it does not reduce thoracic kyphosis.

The Impact of Direct Vertebral Rotation (DVR) on Radiographic Outcome in Surgical Correction of Idiopathic Scoliosis

Introduction: Recent developments of spinal instruments allow to address nearly all components of idiopathic scoliosis. Direct vertebral rotation (DVR) maneuver was introduced to correct apical axial vertebral rotation. It is however still not well established how efficiently DVR affects results of scoliosis correction. The object of the study was to evaluate en bloc apical vertebral rotation (DVR) and its impact on coronal and sagittal correction of the spine in patients undergoing surgical scoliosis treatment. Material and methods: 36 consecutive patients who underwent posterior fusion with pedicle screws only constructs for idiopathic scoliosis. 15 patients (20 curves) were corrected by rod derotation only and 21 patients (26 curves) had both rod derotation and DVR. Curve measurements were performed on x-rays obtained before and post operatively - coronal curves, kyphosis (T2-T12, T5-T12). Spine flexibility was assessed on prone bending x-rays. Apical axial rotation was determined on CT scans obtained intraoperatively and postoperatively. Rotation angle (RAsag) was measured according to Aaro and Dahlborn. Results: We observed reduction of RAsag in all patients, however in DVR group decrease was greater, by 31.8% comparing to non-DVR group, by 8.6% (p=0.0003). Mean coronal correction in DVR group was 68.8% and in rod derotation group without DVR 55% (p=0.002). No significant correlation was found between degree of derotation obtained and coronal correction. In DVR group T2-T12 kyphosis has increased in 28 (65%) patients whereas in non DVR group in 31 (69%) cases. Mean value of T2-T12 kyphosis growth was 16.7% in DVR and 22.1% in non DVR group. These differences however did not occur statistically significant. Conclusions: Direct vertebral rotation (DVR) manoeuvre reduces significantly apical rotation of the spine, enhances ability of coronal correction and it does not reduce thoracic kyphosis.

The change on vertebral axial rotation after posterior instrumentation of idiopathic scoliosis.

Agreement between the correction objectives and the instrumentation strategies remains controversial in idiopathic scoliosis. Most studies have focus on the frontal and sagittal plane. The goal of this study was to evaluate the change on vertebral axial rotation after posterior instrumentation in fused and unfused segments. Fourteen patients operated on for idiopathic scoliosis were prospectively included. Fusion and instrumentation were done by posterior approach. All patients had a pre-operative and a 10-day post-operative radiological evaluation with the EOS system. Axial orientation of the vertebrae with special interest to the apical, junctional, and unfused areas was obtained thanks to the reconstruction software. Mean apical vertebra axial rotation statistically decreased from 21° pre-operatively to 13° post-operatively. But, there were no statistically significant differences between pre-operative and post-operative mean axial intervertebral rotations in the main curve and axial rotation of the non-instrumented lower counter curve. 3D analysis of the spine in standing position is a great advancement for post-operative analysis of adolescent idiopathic scoliosis (AIS) corrections. This study confirmed that actual instrumentations are able to achieve "en bloc" 3D correction of the spine but not intervertebral axial rotation correction.

Clinical and stereoradiographic analysis of adult spinal deformity with and without rotatory subluxation

IntroductionIn degenerative adult spinal deformity (ASD), sagittal malalignment and rotatory subluxation (RS) correlate with clinical symptomatology. RS is defined as axial rotation with lateral listhesis. Stereoradiography, recently developed for medical applications, provides full-body standing radiographs and 3D reconstruction of the spine, with low radiation dose. Hypothesis3D stereoradiography improves analysis of RS and of its relations with transverse plane and spinopelvic parameters and clinical impact. Material and methodsOne hundred and thirty adults with lumbar ASD and full-spine EOS® radiographs (EOS Imaging, Paris, France) were included. Spinopelvic sagittal parameters and lateral listhesis in the coronal plane were measured. The transverse plane study parameters were: apical axial vertebral rotation (apex AVR), axial intervertebral rotation (AIR) and torsion index (TI). Two groups were compared: with RS (lateral listhesis>5mm) and without RS (without lateral listhesis exceeding 5mm: non-RS). Correlations between radiologic and clinical data were assessed. ResultsRS patients were significantly older, with larger Cobb angle (37.4° vs. 26.6°, P=0.0001), more severe sagittal deformity, and greater apex AVR and TI (respectively: 22.9° vs. 11.3°, P<0.001; and 41.0° vs. 19.9°, P<0.001). Ten percent of patients had AIR>10° without visible RS on 2D radiographs. RS patients reported significantly more frequent low back pain and radiculalgia. DiscussionIn this EOS® study, ASD patients with RS had greater coronal curvature and sagittal and transverse deformity, as well as greater pain. Further transverse plane analysis could allow earlier diagnosis and prognosis to guide management. Level of evidence4, retrospective study.

Loss of apical vertebral derotation in adolescent idiopathic scoliosis: 2-year follow-up using multi-planar reconstruction computed tomography

The objective of this study was to evaluate 2years post-surgical loss of three-dimensional correction in adolescent idiopathic scoliosis (AIS) patients using multi-planar reconstruction computed tomography (CT). Twenty-seven AIS patients treated by segmental pedicle screw (PS) constructs were included in this study. Correction in the axial plane was evaluated using the "relative apical vertebral rotation angle" (rAVR), defined as the difference between the axial rotation angles of the upper instrumented vertebra and the apical vertebra on reconstructed axial CT images. The Cobb angle of the main curve and apical vertebral translation was measured to evaluate the coronal correction. Thoracic kyphosis was also measured for the evaluation of sagittal profile. Measurements were performed before surgery, and 1week and 2years after surgery. The relationships between the correction losses and skeletal maturity, and variety of spinal constructs were also evaluated. The mean preoperative Cobb angle of the major curve was 59.1°±11.2° before and 13.0°±7.2° immediately after surgery. Two years later, the mean Cobb angle had increased significantly, to 15.5°±7.8°, with a mean correction loss of 2.5°±1.5° (p<0.001). The mean preoperative rAVR of 28.5°±8.4° was corrected to 15.8°±7.8° after surgery. It had increased significantly to 18.5±8.4 by 2years after surgery, with a mean correction loss of 2.7°±1.0° (p<0.001). The mean correction losses for both the Cobb angle and rAVR were significantly greater in the skeletally immature patients. The significant correlations were recognized between the correction losses and the proportion of multi-axial screws, and the materials of constructs. Statistically significant loss of correction in the Cobb angle and apical vertebral axial rotation angle (AVR) were recognized 2years after surgery using PS constructs. The correction losses, especially AVR, were more evident in the skeletally immature patients, and in patients treated with more multi-axial screws and with titanium constructs rather than with stainless constructs.

Biomechanical comparison of alternative densities of pedicle screws for the treatment of adolescent idiopathic scoliosis

The objective of this computational study was to compare the biomechanical effects of different implant densities in terms of curve reduction and the force levels at the implant-vertebra interface and on the intervertebral elements. Eight cases were randomly picked among patients who have undergone a posterior spinal instrumentation for adolescent idiopathic scoliosis (AIS). For each case, two computer simulations were performed, one with the actual surgery implant pattern and another with the same fusion levels but an alternative implant pattern proposed by an experienced surgeon. The two implant patterns for each case were respectively put into higher and lower implant density group. The spinal correction and the force levels at bone-implant interface and on the intervertebral elements were analyzed and compared between the two groups. There were on average 13% more pedicle screws and 30% more bilaterally placed pedicle screws in the higher versus lower density group. The difference in the density of screws (92% vs. 79%) did not lead to significant difference in terms of the resulting main thoracic (MT) Cobb angle, and the MT apical axial vertebral rotation. The average and maximum implant-vertebra force levels were about 50 and 65%, respectively higher in the higher versus lower density group, but without consistent distribution patterns. The average intervertebral forces did not significantly differ between the two groups. With the same fusion levels, lower density screws allowed achieving similar deformity correction and it was more likely to have lower screw-vertebra loads.

A three-dimensional retrospective analysis of the evolution of spinal instrumentation for the correction of adolescent idiopathic scoliosis

This is a clinical radiographic study, spanning over three decades, analyzing the three-dimensional (3-D) changes in spine geometry after corrective surgery for adolescent idiopathic scoliosis (AIS) using four generations of instrumentation systems. The objective of this study was to retrospectively evaluate the evolution of spinal instrumentation over time by measuring the 3-D changes of spinal shape before and after surgical correction of subjects with AIS using Harrington/Harrington-Luque (H/HL) instrumentation, original and recent generations of Cotrel-Dubousset Instrumentation (CDI) with rod rotation maneuvers, as well as third generation systems using thoracic pedicle screws and direct vertebral derotation (DVD) manoeuver in order to determine if the claims for improved 3-D correction from generation to next generation could be substantiated. The 3-D shape of the thoracic and lumbar spine was recorded from a pair of standing radiographs using a novel 3-D reconstruction technique from uncalibrated radiographs in 128 adolescents with AIS undergoing surgery by a posterior approach. Changes in coronal Cobb angles, kyphosis, lordosis, as well as in a series of 3-D parameters computed from the spine reconstructions before and after surgery were used to compare the four groups. Results demonstrate statistically significant differences (P = 0.05) between generations with regards to the correction of the coronal Cobb angle, and different loss of physiological lordosis. More importantly, significant differences in the 3-D correction of the spine based on the orientation of the planes of maximal curvature were observed (20/-6% H/HL vs. 39/39% CDI vs. 42/18% DVD for the thoracic/lumbar regions, respectively), confirming that recent CDI and third generation instrumentations coupled with DVD can bring the deformity significantly closer to the sagittal plane. An increased correction in apical vertebra axial rotation was observed with the DVD manoeuver (74%), while fewer notable differences were found between DVD and recent CDI systems in terms of 3-D correction. This is the first quantitative study to clearly demonstrate that the rod derotation and DVD maneuvers can significantly improve 3-D correction of scoliotic deformities, thereby supporting the transition towards these more elaborate and costly instrumentation technologies in terms of 3-D assessment.

Three-dimensional simulations of the scoliosis derotation maneuver with Cotrel-Dubousset instrumentation

The derotation maneuver using Cotrel-Dubousset instrumentation (CDI) is intended to correct the counterdirectional transverse plane rotations of the spine and of the vertebrae in thoracic scoliosis. This was simulated in a finite element model of an idealized thoracic scoliosis with an initial 65° scoliosis angle and 0° kyphosis angle. After 90° of rod rotation the apical vertebra derotated 50° towards the sagittal plane but the apical vertebra axial rotation worsened by 8°. The scoliosis angle corrected to 29° and a 54° kyphosis was created. If the initial rod curvature was reduced by 9°, the model predicted only small changes in spinal curvature resulting from the forces required to connect the vertebrae to the hooks. Decreased kyphosis and scoliosis curvatures but increased vertebra axial rotation were produced by the derotation maneuver. The increase in apical vertebra axial rotation was reversed by modifying the representation of the motion segments by repositioning their effective axes 30 mm posteriorly.

Rib cage deformities in scoliosis: Spine morphology, rib cage stiffness, and tomography imaging

A computer-implemented biomechanical model of a thoracolumbar spine and deformable rib cage was used to investigate the influence of spine morphology and rib cage stiffness properties on the rib cage deformities that arise from scoliosis and to study the relationship of actual rib distortions with those seen on computed tomography (CT) scans. For the purposes of this study, it was assumed that rib cage deformities result from forces imposed on the ribs by the deforming spine. When a structurally normal rib cage was allowed to follow freely the imposition of scoliotic curves on the spine, different configurations of scoliosis led to substantial differences in the resulting rib cage deformities. Rib cage lateral offset correlated well with the Cobb angle of the scoliosis but not with the apical vertebral axial rotation, whereas rib cage axial rotation correlated well with apical vertebral axial rotation but not with the Cobb angle. These model-obtained findings mirror clinical findings that correction of the Cobb angle leads to correction of the lateral offset of the rib cage but does not correlate well with correction of the rib cage axial rotation. The stiffnesses of the ligamentous tissue connecting the sternum to the pelvis, of the costovertebral joints, and of the ribs themselves also influenced the rib deformities substantially. The influence of the sternopelvic ligamentous ties has not been recognized previously. The total rib cage volume remained essentially constant regardless of the severity of the resulting deformity, but the distribution of this volume between convex and concave sides varied somewhat.(ABSTRACT TRUNCATED AT 250 WORDS)