Three-dimensional morphology study of surgical adolescent idiopathic scoliosis patient from encoded geometric models

Purpose

The classification of three-dimensional (3D) spinal deformities remains an open question in adolescent idiopathic scoliosis. Recent studies have investigated pattern classification based on explicit clinical parameters. An emerging trend however seeks to simplify complex spine geometries and capture the predominant modes of variability of the deformation. The objective of this study is to perform a 3D characterization and morphology analysis of the thoracic and thoraco/lumbar scoliotic spines (cross-sectional study). The presence of subgroups within all Lenke types will be investigated by analyzing a simplified representation of the geometric 3D reconstruction of a patient’s spine, and to establish the basis for a new classification approach based on a machine learning algorithm.

Methods

Three-dimensional reconstructions of coronal and sagittal standing radiographs of 663 patients, for a total of 915 visits, covering all types of deformities in adolescent idiopathic scoliosis (single, double and triple curves) and reviewed by the 3D Classification Committee of the Scoliosis Research Society, were analyzed using a machine learning algorithm based on stacked auto-encoders. The codes produced for each 3D reconstruction would be then grouped together using an unsupervised clustering method. For each identified cluster, Cobb angle and orientation of the plane of maximum curvature in the thoracic and lumbar curves, axial rotation of the apical vertebrae, kyphosis (T4–T12), lordosis (L1–S1) and pelvic incidence were obtained. No assumptions were made regarding grouping tendencies in the data nor were the number of clusters predefined.

Results

Eleven groups were revealed from the 915 visits, wherein the location of the main curve, kyphosis and lordosis were the three major discriminating factors with slight overlap between groups. Two main groups emerge among the eleven different clusters of patients: a first with small thoracic deformities and large lumbar deformities, while the other with large thoracic deformities and small lumbar curvature. The main factor that allowed identifying eleven distinct subgroups within the surgical patients (major curves) from Lenke type-1 to type-6 curves, was the location of the apical vertebra as identified by the planes of maximum curvature obtained in both thoracic and thoraco/lumbar segments. Both hypokyphotic and hyperkypothic clusters were primarily composed of Lenke 1–4 curve type patients, while a hyperlordotic cluster was composed of Lenke 5 and 6 curve type patients.

Conclusion

The stacked auto-encoder analysis technique helped to simplify the complex nature of 3D spine models, while preserving the intrinsic properties that are typically measured with explicit parameters derived from the 3D reconstruction.

     

Clinical validation of coronal and sagittal spinal curve measurements based on three-dimensional vertebra vector parameters

Background context

For many decades, visualization and evaluation of three-dimensional (3D) spinal deformities have only been possible by two-dimensional (2D) radiodiagnostic methods, and as a result, characterization and classification were based on 2D terminologies. Recent developments in medical digital imaging and 3D visualization techniques including surface 3D reconstructions opened a chance for a long-sought change in this field. Supported by a 3D Terminology on Spinal Deformities of the Scoliosis Research Society, an approach for 3D measurements and a new 3D classification of scoliosis yielded several compelling concepts on 3D visualization and new proposals for 3D classification in recent years. More recently, a new proposal for visualization and complete 3D evaluation of the spine by 3D vertebra vectors has been introduced by our workgroup, a concept, based on EOS 2D/3D, a groundbreaking new ultralow radiation dose integrated orthopedic imaging device with sterEOS 3D spine reconstruction software.

Purpose

Comparison of accuracy, correlation of measurement values, intraobserver and interrater reliability of methods by conventional manual 2D and vertebra vector–based 3D measurements in a routine clinical setting.

Study design

Retrospective, nonrandomized study of diagnostic X-ray images created as part of a routine clinical protocol of eligible patients examined at our clinic during a 30-month period between July 2007 and December 2009.

Patient sample

In total, 201 individuals (170 females, 31 males; mean age, 19.88 years) including 10 healthy athletes with normal spine and patients with adolescent idiopathic scoliosis (175 cases), adult degenerative scoliosis (11 cases), and Scheuermann hyperkyphosis (5 cases). Overall range of coronal curves was between 2.4 and 117.5°. Analysis of accuracy and reliability of measurements was carried out on a group of all patients and in subgroups based on coronal plane deviation: 0 to 10° (Group 1; n=36), 10 to 25° (Group 2; n=25), 25 to 50° (Group 3; n=69), 50 to 75° (Group 4; n=49), and above 75° (Group 5; n=22).

Methods

All study subjects were examined by EOS 2D imaging, resulting in anteroposterior (AP) and lateral (LAT) full spine, orthogonal digital X-ray images, in standing position. Conventional coronal and sagittal curvature measurements including sagittal L5 vertebra wedges were determined by 3 experienced examiners, using traditional Cobb methods on EOS 2D AP and LAT images. Vertebra vector–based measurements were performed as published earlier, based on computer-assisted calculations of corresponding spinal curvature. Vertebra vectors were generated by dedicated software from sterEOS 3D spine models reconstructed from EOS 2D images by the same three examiners. Manual measurements were performed by each examiner, thrice for sterEOS 3D reconstructions and twice for vertebra vector–based measurements. Means comparison t test, Pearson bivariate correlation analysis, reliability analysis by intraclass correlation coefficients for intraobserver reproducibility and interrater reliability were performed using SPSS v16.0 software.

Results

In comparison with manual 2D methods, only small and nonsignificant differences were detectable in vertebra vector–based curvature data for coronal curves and thoracic kyphosis, whereas the found difference in L1–L5 lordosis values was shown to be strongly related to the magnitude of corresponding L5 wedge. Intraobserver reliability was excellent for both methods, and interrater reproducibility was consistently higher for vertebra vector–based methods that was also found to be unaffected by the magnitude of coronal curves or sagittal plane deviations.

Conclusions

Vertebra vector–based angulation measurements could fully substitute conventional manual 2D measurements, with similar accuracy and higher intraobserver reliability and interrater reproducibility. Vertebra vectors represent a truly 3D solution for clear and comprehensible 3D visualization of spinal deformities while preserving crucial parametric information for vertebral size, 3D position, orientation, and rotation. The concept of vertebra vectors may serve as a starting point to a valid and clinically useful alternative for a new 3D classification of scoliosis.     

Analysis of the relationship between coronal and sagittal deformities in adolescent idiopathic scoliosis

Purpose

To characterize the sagittal alignment of each Lenke type and investigate the relationship between coronal and sagittal deformities in adolescent idiopathic scoliotic (AIS) patients.

Methods

A cohort of 184 subjects with AIS was retrospectively recruited. Radiographic data were measured and collected, including the Lenke types, Cobb angles of structural curves, and sagittal spino-pelvic parameters. Subjects were grouped according to their genders, Lenke curve types, lumbar modifiers and the amount of coronal structural curves. The sagittal alignment was then compared between the different groups, and correlation analysis was also taken between coronal and sagittal parameters. Besides, each subject’s Roussouly type was decided and its distribution was compared among different Lenke types.

Results

The cohort included 59 males and 125 females, averagely aged at 15.5 ± 3.3 years old. Most sagittal parameters except thoracic kyphosis (TK) and pelvic tilt (PT) were similar among different Lenke types, while all the sagittal parameters were similar between males and females. The groups with different lumbar modifiers had similar sagittal parameters except TK, which was also true for the groups with different amounts of coronal curves. 42.4 % of the cohort belonged to Roussouly type 3, and the distribution of Roussouly types was comparable among all Lenke types. All sagittal parameters except C7 translation ratio were significantly different among Roussouly types (P < 0.05). Correlation analysis showed that main thoracic (MT) was negatively correlated with lumbar lordosis (LL, r = ?0.324), sacral slope (r = ?0.321) and spino-sacral angle (r = ?0.363). Partial correlation analysis found that thoracolumbar/lumbar was negatively correlated with TK (r = ?0.464) and LL (r = ?0.422) when MT was controlled.

Conclusions

The influence of coronal deformity on sagittal parameters was limited and mainly reflected in the deviation of TK. Most coronal and sagittal parameters were not significantly correlated, and the coronal deformity types did not change the global sagittal postural patterns.

     

Thoraco-lumbar selective fusion in adolescent idiopathic scoliosis with Lenke C modifier curves: clinical and radiographic analysis at 10-year follow-up

Purpose

To examine the radiological and clinical outcomes of a single-center case series of selective thoracic fusions (STF) in adolescent idiopathic scoliosis with Lenke C modifier curves, with a long-term follow-up.

Methods

We evaluated at 6 months and 10 years different radiological parameters on both thoracic and lumbar districts: coronal curves, sagittal curves, apical vertebral translation (AVT), and apical vertebral rotation (AVR). The clinical outcome was determined using the SRS 22 score. Data were also analyzed dividing the patients by their Risser and Lenke scores.

Results

In examining 90 patients we reported a radiological benefit from STF on both thoracic and lumbar districts. The corrections in the values of both coronal curves, AVT, and AVR are relevant at 6 months and do not significantly vary at the latest follow-up. Sagittal curves are not relevantly affected at any time point. All the SRS 22 score evaluations showed significant improvement at 6 months, in particular, the self-image analysis. A further improvement was also reported at 10 years, in particular in pain and function scores. At no time point were significant differences retrieved by comparing SRS 22 results as divided by Risser or Lenke grading systems.

Conclusions

STF is an effective treatment option both in clinical and radiographical terms. The results at 10-year follow-up confirm both the stability of the correction and the improvement of the clinical outcome scores. Risser and Lenke grading systems are not relevant variables predictive of clinical efficacy.

     

Preoperative computer-based simulations for the correction of kyphotic deformities in ankylosing spondylitis patients

Background context

A preoperative plan is important to obtain appropriate balance of the sagittal plane in patients with kyphotic deformity. Previous methods to calculate the correction angle are inconvenient and complicated, whereas the method using computer simulations may be very effective and much simpler than existing methods.

Purpose

To evaluate the efficacy of preoperative measurements using a computer simulation for corrective osteotomy for the surgical treatment of kyphosis caused by ankylosing spondylitis (AS).

Study design

Retrospective clinical data analysis.

Patient sample

The sample comprises 18 AS patients with fixed kyphotic deformity who underwent corrective osteotomies at our hospital between October 2007 and January 2010.

Outcome measures

Thoracic kyphosis, lumbar lordosis, and the sagittal vertical axis (SVA) of the spine were evaluated by preoperative computer simulation and radiologic measurement. Clinical assessments were performed according to the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Short Form-36 (SF-36), and EuroQol-5 dimension (EQ-5D) before and after the surgery.

Methods

The coincidence between the preoperative computer simulation and postoperative radiologic parameters was evaluated. We also analyzed the changes derived from each clinical and radiologic measurement before and after the surgery.

Results

Mean thoracic kyphosis changed from 32.4° to 31.9°, mean lumbar lordosis was corrected from 11.5° to 26.9°, and the SVA was improved from 125.7 to 65.1 mm after surgery (p<.001). The correlation coefficients within groups between the computer simulations and radiologic parameters were 0.9, 0.6, and 0.7, showing significant congruency. Although BASDAI and BASFI did not significantly differ (p=.53 and p=.45, respectively), SF-36 and EQ-5D were significantly increased (p<.05 and p<.001, respectively).

Conclusions

Comparisons of preoperative simulations and actual surgical outcomes showed significant coincidences; thus, evaluations through computer simulations before surgery are expected to help predict the level of correction possible after surgery and improve surgical planning.     

Computerized tomography imaging in adolescent idiopathic scoliosis: prone versus supine

Background

The aim of the present study was to assess the degree of apical vertebral rotation values in Adolescent Idiopathic Scoliosis (AIS) that were obtained on CT scans, and to analyze the influence of patient position (supine versus prone) on the degree of rotation.

Methods

The study included 50 apical vertebra rotation measurements of 34 patients with Type 1A and Type 3C curvature according to the Lenke classification. CT imaging was applied to the patients in supine and prone positions to measure the apical vertebral rotation (AVR). The average AVR angles were measured using the Aaro–Dahlborn method and the results were compared.

Results

No significant differences were found between the vertebral rotation measured in the prone and supine positions for the Lenke 1A subgroup and the Lenke 3C thoracic group (p = 0.848; p = 0.659, respectively). In the Lenke 3C lumbar group, however, the vertebral rotation in the supine position was found to be significantly lesser than that in the prone position (difference ?1.40° ± 1.79°, p = 0.007).

Conclusion

The assessment of the apical vertebra rotation is crucial in AIS. Even though the vertebral rotation in the supine position was found to be significantly lesser than that in the prone position, CT imaging in a prone position could not be considered clinically more relevant than the CT images in a supine position as there was less than 3° difference.

     

Risk factor analysis of proximal junctional kyphosis after posterior fusion in patients with idiopathic scoliosis

Study design

A retrospective analysis of 150 adolescents who underwent spinal fusion for idiopathic scoliosis.

Objective

To analyse the incidence of the postoperative proximal junctional kyphosis after posterior fusion to the upper thoracic vertebra in adolescents with idiopathic scoliosis and to explore its risk factors.

Summary of background data

The reported incidence of the proximal junctional kyphosis after the posterior fusion in patients with idiopathic scoliosis varies depending on surgical methods and strategies adopted by the institution.

Methods

The changes in the Cobb angle of the proximal junctional kyphosis on the lateral spine X-ray were measured and the presence of PJK was recorded. The risk factors were screened using statistical analysis.

Results

PJK occurred in 35 out of 123 patients with an overall incidence of 28%. Among them, 28 patients (80%) experienced PJK within 1.5 years after surgery. The PJK-inducing factors included greater than 10° intraoperative decrease in thoracic kyphosis, thoracoplasty, the use of a pedicle screw at the top vertebra, autogenous bone graft and fusion to the lower lumbar vertebra (below L2).

Conclusions

There is a high incidence of postoperative proximal junctional kyphosis after posterior fusion to the upper thoracic vertebra within 1.5 years after surgery in adolescents with idiopathic scoliosis. In order to reduce its incidence, the risk factors for PJK should be carefully evaluated before surgery.     

Cervical sagittal alignment in adolescent idiopathic scoliosis patients (Lenke type 1–6)

Objective

We collected the radiographic and clinical data of 129 AIS patients (Lenke type 1–6) to analyze the characteristics of cervical sagittal alignment in adolescent idiopathic scoliosis patients and the correlations between cervical sagittal alignment and global sagittal alignment, and clinical symptoms.

Radiological and clinical outcome of selective thoracic fusion for patients with Lenke 1C and 2C adolescent idiopathic scoliosis with a minimum follow-up of 2 years

Background Context

In Lenke 1C and 2C curves, the choice between selective thoracic fusion (STF) versus non-selective thoracic fusion as the optimal surgical treatment is controversial.

Flexibility assessment of the unfused thoracic segments above the “potential upper instrumented vertebrae” using the supine side bending radiographs in Lenke 5 and 6 curves for adolescent idiopathic scoliosis patients

Background Context

Selection of upper instrumented vertebra for Lenke 5 and 6 curves remains debatable, and several authors have described different selection strategies.

Transverse plane pelvic rotation in adolescent idiopathic scoliosis: primary or compensatory?

Several studies have suggested that the pelvis is involved in the etiology or pathogenesis of adolescent idiopathic scoliosis (AIS). The purpose of this retrospective, cross-sectional radiographic study is to identify any correlation between the transverse plane rotational position of the pelvis in stance and operative-size idiopathic or congenital scoliosis deformities, using Scheuermann’s kyphosis and isthmic spondylolisthesis patients for comparison. The hypothesis tested was that the direction of transverse pelvic rotation is the same as that for a thoracic scoliosis. As a group, AIS patients had a significant transverse plane pelvic rotation in the same direction as the thoracic curve. When subdivided into the six Lenke curve patterns, this was true for the groups with a major thoracic curve: thoracic (1), double thoracic (2) and double curve patterns (3). It was not true for patterns with a major thoracolumbar/lumbar curve: single thoracolumbar/lumbar (5) and double thoracic-thoracolumbar/lumbar (6). Nor was it true for triple (4) curves. The Lenke 1 and 2 major thoracic curves without compensatory thoracolumbar/lumbar curves did not have the predicted pelvic rotation. All congenital scoliosis patients studied had main thoracic curves and significant transverse plane pelvic rotation in the same direction as the thoracic curve. There was no transverse plane pelvic rotation in the Scheuermann’s kyphosis or isthmic spondylolisthesis patients. We interpret these findings as consistent with a compensatory rotation of the pelvis in the same direction as the main thoracic curve in most patients with a compensatory thoracolumbar/lumbar curve as well as in patients with main thoracic congenital scoliosis.     

The use of the T1 sagittal angle in predicting overall sagittal balance of the spine

Background context

A balanced sagittal alignment of the spine has been shown to strongly correlate with less pain, less disability, and greater health status scores. To restore proper sagittal balance, one must assess the position of the occiput relative to the sacrum. The assessment of spinal balance preoperatively can be challenging, whereas predicting postoperative balance is even more difficult.

Purpose

This study was designed to evaluate and quantify multiple factors that influence sagittal balance.

Study design

Retrospective analysis of existing spinal radiographs.

Methods

A retrospective review of 52 adult spine patient records was performed. All patients had full-column digital radiographs that showed all the important skeletal landmarks necessary for accurate measurement. The average age of the patient was 53 years. Both genders were equally represented. The radiographs were measured using standard techniques to obtain the following parameters: scoliosis in the coronal plane; lordosis or kyphosis of the cervical, thoracic, and lumbar spine; the T1 sagittal angle (angle between a horizontal line and the superior end plate of T1); the angle of the dens in the sagittal plane; the angle of the dens in relation to the occiput; the sacral slope; the pelvic incidence; the femoral-sacral angle; and finally, the sagittal vertical axis (SVA) measured from both the dens of C2 and from C7.

Results

It was found that the SVA when measured from the dens was on average 16 mm farther forward than the SVA measured from C7 (p<.0001). The dens plumb line (SVA_dens) was then used in the study. An analysis was done to examine the relationship between SVA_dens and each of the other measurements. The T1 sagittal angle was found to have a moderate positive correlation (r=0.65) with SVA_dens, p<.0001, indicating that the amount of sagittal T1 tilt can be used as a good predictor of overall sagittal balance.When examining the other variables, it was found that cervical lordosis had a weak correlation (r=0.37) with SVA_dens that was unexpected, given that cervical lordosis determines head position. Thoracic kyphosis also had a weak correlation (r=0.26) with SVA_C1, which was equally surprising. Lumbar lordosis had a slightly higher correlation (r=0.38), p=.006, than the cervical or thoracic spine.A multiple regression was run on the data to examine the relationship that all these independent variables have on SVA_dens. SPSS (SPSS, Inc., Chicago, IL, USA) was used to create a regression equation using the independent variables of T1 sagittal angle, cervical lordosis, thoracic kyphosis, lumbar lordosis, sacral slope, pelvic incidence, and femoral-sacral angle and the dependent variable of SVA_dens. The model had a strong correlation (r=0.80, r²=0.64) and was statistically significant (p<.0001).The T1 sagittal angle was the variable that had the strongest correlation with the SVA_dens Spearman r=0.65, p<.0001, followed by pelvic incidence, p=.002, and lumbar lordosis, p=.006. We also observed that when the T1 tilt was higher than 25°, all patients had at least 10 cm of positive sagittal imbalance. In addition, patients with negative sagittal balance had mostly low T1 tilt values, usually lower than 13°. The other variables were not shown to have a statically significant influence on SVA.

Conclusions

This analysis shows that many factors influence the overall sagittal balance of the patient, but it may be the position of the pelvis and lower spine that have a stronger influence than the position of the upper back and neck. Unfortunately, to our knowledge, there are no studies to date that have established a normal sagittal T1 tilt angle. However, our analysis has shown that when the T1 tilt was higher than 25°, all patients had at least 10 cm of positive sagittal imbalance. It also showed that patients with negative sagittal balance had mostly low T1 tilt values, usually below 13° of angulation.The T1 sagittal angle is a measurement that may be very useful in evaluating sagittal balance, as it was the measure that most strongly correlated with SVA_dens. It has its great utility where long films cannot be obtained. Patients whose T1 tilt falls outside the range 13° to 25° should be sent for full-column radiographs for a complete evaluation of their sagittal balance. On the other hand, a T1 tilt within the above range does not guarantee a normal sagittal balance, and further investigation should be performed at the surgeon’s discretion.     

Accuracy and reliability of coronal and sagittal spinal curvature data based on patient-specific three-dimensional models created by the EOS 2D/3D imaging system

Background context

Three-dimensional (3D) deformations of the spine are predominantly characterized by two-dimensional (2D) angulation measurements in coronal and sagittal planes, using anteroposterior and lateral X-ray images. For coronal curves, a method originally described by Cobb and for sagittal curves a modified Cobb method are most widely used in practice, and these methods have been shown to exhibit good-to-excellent reliability and reproducibility, carried out either manually or by computer-based tools. Recently, an ultralow radiation dose–integrated radioimaging solution was introduced with special software for realistic 3D visualization and parametric characterization of the spinal column.

Purpose

Comparison of accuracy, correlation of measurement values, intraobserver and interrater reliability of methods by conventional manual 2D and sterEOS 3D measurements in a routine clinical setting.

Study design/setting

Retrospective nonrandomized study of diagnostic X-ray images created as part of a routine clinical protocol of eligible patients examined at our clinic during a 30-month period between July 2007 and December 2009.

Patient sample

In total, 201 individuals (170 females, 31 males; mean age, 19.88 years) including 10 healthy athletes with normal spine and patients with adolescent idiopathic scoliosis (175 cases), adult degenerative scoliosis (11 cases), and Scheuermann hyperkyphosis (5 cases). Overall range of coronal curves was between 2.4° and 117.5°. Analysis of accuracy and reliability of measurements were carried out on a group of all patients and in subgroups based on coronal plane deviation: 0° to 10° (Group 1, n=36), 10° to 25° (Group 2, n=25), 25° to 50° (Group 3, n=69), 50° to 75° (Group 4, n=49), and more than 75° (Group 5, n=22).

Methods

Coronal and sagittal curvature measurements were determined by three experienced examiners, using either traditional 2D methods or automatic measurements based on sterEOS 3D reconstructions. Manual measurements were performed three times, and sterEOS 3D reconstructions and automatic measurements were performed two times by each examiner. Means comparison t test, Pearson bivariate correlation analysis, reliability analysis by intraclass correlation coefficients for intraobserver reproducibility and interrater reliability were performed using SPSS v16.0 software (IBM Corp., Armonk, NY, USA). No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this article.

Results

In comparison with manual 2D methods, only small and nonsignificant differences were detectable in sterEOS 3D–based curvature data. Intraobserver reliability was excellent for both methods, and interrater reproducibility was consistently higher for sterEOS 3D methods that was found to be unaffected by the magnitude of coronal curves or sagittal plane deviations.

Conclusions

This is the first clinical report on EOS 2D/3D system (EOS Imaging, Paris, France) and its sterEOS 3D software, documenting an excellent capability for accurate, reliable, and reproducible spinal curvature measurements.     

Mid-term effects of Cotrel-Dubousset instrumentation on the configuration of the spine and the thoracic cage in thoracic idiopathic scoliosis

Summary The effect of Cotrel-Dubousset instrumentation (CDI) on the three-dimensional spinal deformity in 24 consecutive patients with idiopathic scoliosis was investigated by posteroanterior and lateral radiographs and by computed tomography preoperatively, postoperatively, and at a mean follow-up of 3.2 years (range 2.0–5.3 years). At follow-up the mean Cobb angle was decreased by 73%, and the translation of the apical vertebra was significantly decreased by 33%. The sagittal contour was significantly improved with thoracic kyphosis T5–12 increased by 46% (6.9°) and lumbar lordosis L1–5 increased by 28% (10.3°) at follow-up. The sagittal diameter was significantly improved by 5 mm at follow-up. Although the vertebral rotation and the size of rib hump was improved postoperatively, this was followed by significant loss of correction, and at follow-up the vertebral rotation and the size of rib hump were not significantly better than preoperatively. The study indicates that while CDI improves the coronal and sagittal plane deformity permanently, the effect on vertetebral rotation and the rib hump deteriorates with time.     

Sagittal balance correction of idiopathic scoliosis using the in situ contouring technique

Purpose

Idiopathic scoliosis can lead to sagittal imbalance. The relationship between thoracic hyper- and hypo-kyphotic segments, vertebral rotation and coronal curve was determined. The effect of segmental sagittal correction by in situ contouring was analyzed.

Methods

Pre- and post-operative radiographs of 54 scoliosis patients (Lenke 1 and 3) were analyzed at 8 years follow-up. Cobb angles and vertebral rotation were determined. Sagittal measurements were: kyphosis T4–T12, T4–T8 and T9–T12, lordosis L1–S1, T12–L2 and L3–S1, pelvic incidence, pelvic tilt, sacral slope, T1 and T9 tilt.

Results

Thoracic and lumbar curves were significantly reduced (p = 0.0001). Spino-pelvic parameters, T1 and T9 tilt were not modified. The global T4–T12 kyphosis decreased by 2.1° on average (p = 0.066). Segmental analysis evidenced a significant decrease of T4–T8 hyperkyphosis by 6.6° (p = 0.0001) and an increase of segmental hypokyphosis T9–T12 by 5.0° (p = 0.0001). Maximal vertebral rotation was located at T7, T8 or T9 and correlated (r = 0.422) with the cranial level of the hypokyphotic zone (p = 0.003). This vertebra or its adjacent levels corresponded to the coronal apex in 79.6 % of thoracic curves.

Conclusions

Lenke 1 and 3 curves can show normal global kyphosis, divided in cranial hyperkyphosis and caudal hypokyphosis. The cranial end of hypokyphosis corresponds to maximal rotation. These vertebrae have most migrated anteriorly and laterally. The sagittal apex between segmental hypo- and hyper-kyphosis corresponds to the coronal thoracic apex. A segmental sagittal imbalance correction is achieved by in situ contouring. The concept of segmental imbalance is useful when determining the levels on which surgical detorsion may be focused.     

Radiological analysis of lumbar degenerative kyphosis in relation to pelvic incidence

Background context

Lumbar degenerative kyphosis (LDK) is characterized by sagittal imbalance resulting from a loss of lumbar lordosis (LL). The pelvic incidence (PI) regulates the sagittal alignment of the spine and pelvis.

Purpose

The purpose of this study is to evaluate the spinopelvic parameters in patients with LDK and to compare them with those of a normal population.

Study design/setting

A cross-sectional study.

Patient sample

The selected patients showed characteristic clinical features of LDK. As control group, asymptomatic volunteers without spinal pathology were recruited.

Outcome measures

Full-length radiographs of the spine in the anteroposterior and lateral planes were taken, extending from the base of the skull to the proximal femur. Pelvic incidence, sacral slope (SS), pelvic tilt (PT), main thoracic kyphosis (TK), thoracolumbar junction (TLJ), LL, and sagittal vertical axis (SVA) were evaluated.

Methods

In terms of PI, the patient and control groups were divided into three groups: low (PI≤45°), middle (45°<PI≤60°), and high PI groups (PI>60°). All the spinopelvic parameters were compared between each group and between the patient and control groups in each group. The correlations between each of the parameters were analyzed.

Results

We evaluated 172 patients with symptomatic LDK and 39 healthy volunteers. The number of LDK patients with low, middle, and high PI groups were 44 (25.6%), 72 (44.8%), and 51 (29.6%), respectively. In the control group, the number of low, average, and high PI patients were 18 (46.2%), 15 (38.5%), and 6 (15.4%), respectively. In the control group, PI determined all spinopelvic parameters except SVA. In the LDK group, PI also determined spinopelvic parameters except for TK and SVA. Lumbar degenerative kyphosis with low PI was associated with pronounced kyphosis in LL and TLJ; LDK with a high PI was associated with relatively preserved lordosis in LL with a flat or lordotic TLJ. In terms of pelvic parameters, low PI showed flattened SS and low PT, whereas high PI showed steep SS and high PT.

Conclusions

The results of this study suggest the importance of the key anatomical parameter, PI, in the determination of sagittal contour in symptomatic LDK patients and normal population. Spinopelvic parameters and pelvic compensatory mechanisms in LDK patients differ according to PI. Identifying the spinopelvic parameters is useful when correcting deformities.     

Selective thoracic fusion of a left decompensated main thoracic curve: proceed with caution?

Purpose

Previous research has shown that with certain idiopathic scoliosis curve types, performing a selective thoracic fusion (STF) is associated with an increased risk of coronal decompensation post-operatively. The purpose of the current study was to determine the influence of curve correction and fusion level on post-operative balance in STF for adolescent idiopathic scoliosis patients with pre-operative coronal decompensation.

Methods

A multicenter database was queried for subjects with right Lenke 1–4C curves, pre-operative left coronal imbalance, and 2-year follow-up who underwent STF (caudal fusion level of L1 or proximal). Rates of decompensation were compared between groups with different levels of fusion. Thoracic and lumbar curve correction as well as Scoliosis Research Society-22 outcome scores were compared between groups that were post-operatively balanced or persistently decompensated.

Results

121 patients were identified with average thoracic and lumbar curves of 53° and 41°. Mean pre- and post-operative decompensations were 2.4 ± 1.0 and 1.8 ± 1.1 cm, respectively. Eighteen patients were fused short, 62 to, and 41 were fused past the stable vertebra. Ten patients were fused short, 32 to, and 78 were fused past the neutral vertebra. Incidence of post-operative decompensation was 41%. No differences in post-operative decompensation relative to the stable or neutral vertebra were noted (p = 0.66, p = 0.74). Post-operatively, those patients who were balanced had similar thoracic curve correction (58%) to those decompensated (54%, p = 0.11); however, patients balanced post-operatively had greater SLCC (45 vs 40%, p = 0.04). No differences in SRS-22 outcome scores were noted between groups (p > 0.05).

Conclusions

There was a high rate of post-operative decompensation in patients with pre-operative coronal decompensation undergoing STF. Fusion to or past the stable or neutral vertebra did not affect the risk of persistent decompensation. Attempts to improve SLCC could reduce post-operative decompensation.

     

Facet joint contact pressure is not significantly affected by ProDisc cervical disc arthroplasty in sagittal bending: a single-level cadaveric study

Background context

Total disc arthroplasty is a motion-preserving spinal procedure that has been investigated for its impact on spinal motions and adjacent-level degeneration. However, the effects of disc arthroplasty on facet joint biomechanics remain undefined despite the critical role of these posterior elements on guiding and limiting spinal motion.

Purpose

The goal was to measure the pressure in the facet joint in cadaveric human cervical spines subjected to sagittal bending before and after implantation of the ProDisc-C (Synthes Spine Company, L.P, West Chester, PA, USA).

Study design

A biomechanical study was performed using cadaveric human cervical spines during sagittal bending in the intact and implanted conditions.

Methods

Seven C2–T1 osteoligamentous cadaveric cervical spines were instrumented with a transducer to measure the C5–C6 facet pressure profiles during physiological sagittal bending, before and after implantation of a ProDisc-C at that level. Rotations of the index segment and global cervical spine were also quantified.

Results

The mean C5–C6 range of motion significantly increased (p=.009) from 9.6°±5.1° in the intact condition to 16.2°±3.6° after implantation. However, despite such changes in rotation, there was no significant difference in the facet contact pressure during extension between the intact (64±30 kPa) and implanted (44±55 kPa) conditions. Similarly, there was no difference in facet pressure developed during flexion.

Conclusions

Although implantation of a ProDisc-C arthroplasty device at the C5–C6 level increases angular rotations, it does not significantly alter the local facet pressure at the index level in flexion or extension. Using a technique that preserves the capsular ligament, this study provides the first direct measurement of cervical facet pressure in a disc arthroplasty condition.     

Strain distribution in the lumbar vertebrae under different loading configurations

Background context

The stress/strain distribution in the human vertebrae has seldom been measured, and only for a limited number of loading scenarios, at few locations on the bone surface.

Purpose

This in vitro study aimed at measuring how strain varies on the surface of the lumbar vertebral body and how such strain pattern depends on the loading conditions.

Methods

Eight cadaveric specimens were instrumented with eight triaxial strain gauges each to measure the magnitude and direction of principal strains in the vertebral body. Each vertebra was tested in a three adjacent vertebrae segment fashion. The loading configurations included a compressive force aligned with the vertebral body but also tilted (15°) in each direction in the frontal and sagittal planes, a traction force, and torsion (both directions). Each loading configuration was tested six times on each specimen.

Results

The strain magnitude varied significantly between strain measurement locations. The strain distribution varied significantly when different loading conditions were applied (compression vs. torsion vs. traction). The strain distribution when the compressive force was tilted by 15° was also significantly different from the axial compression. Strains were minimal when the compressive force was applied coaxial with the vertebral body, compared with all other loading configurations. Also, strain was significantly more uniform for the axial compression, compared with all other loading configurations. Principal strains were aligned within 19° to the axis of the vertebral body for axial-compression and axial-traction. Conversely, when the applied force was tilted by 15°, the direction of principal strain varied by a much larger angle (15° to 28°).

Conclusions

This is the first time, to our knowledge, that the strain distribution in the vertebral body is measured for such a variety of loading configurations and a large number of strain sensors. The present findings suggest that the structure of the vertebral body is optimized to sustain compressive forces, whereas even a small tilt angle makes the vertebral structure work under suboptimal conditions.     

Characterizing the differences between the 2D and 3D measurements of spine in adolescent idiopathic scoliosis

Purpose

Although adolescent idiopathic scoliosis (AIS) is known to impact the 3D orientation of the spine and pelvis, the impact of the vertebral position relative to the X-ray scanner on the agreement between 2D and 3D measurements of a curve has not been evaluated. The purpose of this study was to investigate the agreement between 2D and 3D measurements of the scoliotic curve as a function of the 3D spinal parameters in AIS.

Methods

Three independent observers measured the thoracic and lumbar Cobb angles, Kyphosis, and lordosis on the posterior–anterior and lateral X-rays of AIS patients. The 3D reconstructions were created from bi-planar X-rays and the 3D spinal parameters were calculated in both radio and patient planes using SterEOS software. The degree of agreement between the 2D and 3D measurements was tested and its relationship with the curve axial rotation was determined.

Results

2D and 3D measurements of the sagittal plane spinal parameters were significantly different (p < 0.05). The differences between the 2D and 3D measurements were related to the apical vertebrae rotation, the orientation of the plane of maximum curvature, pelvic axial rotation, and the curve magnitude. Differences between the radio plane and patient plane measurements were related to the pelvic axial rotation, Cobb angles, and apical vertebrae rotation, p < 0.05.

Conclusion

Clinically and statistically significant differences were observed between the 2D and 3D measurements of the scoliotic spine. The differences between the 2D and 3D techniques were significant in sagittal plane and were related to the spinal curve and pelvic rotation in transverse plane.