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.     

Sagittal morphology and equilibrium of pelvis and spine

A prospective analysis of the sagittal profile of 100 healthy young adult volunteers was carried out in order to evaluate the relationship between the shape of the pelvis and lumbar lordosis and to create a databank of the morphologic and positional parameters of the pelvis and spine in a normal healthy population. Inclusion criteria were as follows: no previous spinal surgery, no low back pain, no lower limb length inequality, no scoliotic deviation. For each subject, a 30 x 90-cm sagittal radiograph including spine, pelvis and proximal femurs in standing position on a force plate was performed. The global axis of gravity was determined with the force plate. Each radiograph was digitized using dedicated software. The spinal parameters registered were values for thoracic kyphosis and lumbar lordosis. The pelvic angles measured were: pelvic incidence, sacral slope and pelvic tilt. The global axis of gravity was on average 9 mm anterior of the center of the femoral heads. The anatomic parameter of pelvic incidence angle varied from 33 degrees to 85 degrees (mean: 51.7 degrees, SD: 11 degrees). The average lumbar lordosis was 46.5 degrees. The average thoracic kyphosis was 47 degrees. We found a statistical correlation between incidence angle and lumbar lordosis (r=0.69, P<0.001) and between sacral slope angle and lumbar lordosis (r=0.75, P<0.001). Spine and pelvis balance around the hip axis in order to position the gravity line over the femoral heads. We propose a scheme of sagittal balance of the standing human body.     

Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves

This paper proposes an anatomical parameter, the pelvic incidence, as the key factor for managing the spinal balance. Pelvic and spinal sagittal parameters were investigated for normal and scoliotic adult subjects. The relation between pelvic orientation, and spinal sagittal balance was examined by statistical analysis. A close relationship was observed, for both normal and scoliotic subjects, between the anatomical parameter of pelvic incidence and the sacral slope, which strongly determines lumbar lordosis. Taking into account the Cobb angle and the apical vertebral rotation confers a three-dimensional aspect to this chain of relations between pelvis and spine. A predictive equation of lordosis is postulated. The pelvic incidence appears to be the main axis of the sagittal balance of the spine. It controls spinal curves in accordance with the adaptability of the other parameters. Received: 17 January 1997 Revised: 30 September 1997 Accepted: 21 October 1997     

The sagittal anatomy of the sacrum among young adults,infants, and spondylolisthesis patients

The anatomic pelvic parameter "incidence" - the angle between the line perpendicular to the middle of the sacral plate and the line joining the middle of the sacral plate to the center of the bicoxo-femoral axis - has been shown to be strongly correlated with the sacral slope and lumbar lordosis, and ensures the individual an economical standing position. It is important for determining the sagittal curve of the spine. The angle of incidence has also been shown to depend partly on the sagittal anatomy of sacrum, which is established in childhood while learning to stand and walk. The purpose of this study was (1) to define the relationship between the sacrum and the angle of incidence, and (2) to compare these parameters in three populations: young adults, infants before walking, and patients with spondylolisthesis. Forty-four normal young adults, 32 infants not yet walking and 39 patients with spondylolisthesis due to isthmic spondylolysis underwent a sagittal full-spine radiography. A graphic table and the software for bidimensional study of the sacrum developed by J. Hecquet were used to determine various anatomic and positional parameters. Comparison tests of means, and multiple and partial correlation tests were used. A study of the reliability of the measurements using factorial plan methods was performed. The sagittal anatomic parameters of the sacrum were found to have a close relationship with the pelvic parameter of incidence angle, and therefore with the sagittal balance of the spine. The anatomy of the sacrum in spondylolisthesis patients is particular in that some features are much like those of young infants, but it is more curved and the incidence angle is significantly larger. There is a close relationship between angle of incidence and the slip of spondylolisthesis. All the parameters of young infants are significantly smaller than those of adults. It can be concluded that the sagittal anatomy of the sacrum plays a key role in spinal sagittal balance. The sacral bone is an integral a part of the pelvis and constitutes the undistorted part of the spinal curves. Organization of sagittal curves during growth can be followed up by looking at the sacrum. The sacrum in the spondylolisthesis group differs from the normal, and the greater angle of incidence and sacral slope in this group could predispose to vertebral slip.     

Clasped position for measurement of sagittal spinal alignment

Lateral whole-spine radiography is a useful tool in the management of spinal deformity, but the most appropriate arm position during radiography has yet to be determined. In this prospective study, we evaluated 26 adult volunteers and 22 patients with lumbar spinal canal stenosis. Lateral whole-spine radiographs were acquired in the most stable and relaxed position while the subjects were standing with their arms extended and their hand gently clasped in front of the trunk (clasped position). The following parameters were measured: sagittal vertical axis (SVA), lumbar lordotic angle (LLA), pelvic angle (PA), pelvic lordosis angle (PRS1), pelvic tilt (PT), and pelvic incidence (PI). The reliability of measurements was assessed by interclass correlation coefficients. The SVA was slightly positive in volunteers. LLA, PA, PRS1, PT, and PI were compatible with standard normal values. The results showed “almost perfect agreement” with regard to intra- and interobserver reliability. The clasped position can be used effectively and reliably for measurement of sagittal spinal alignment for the lumbar region in adults.     

成人特发性脊柱侧凸患者脊柱-骨盆矢状位平衡分析

目的:分析不同类型成人特发性脊柱侧凸(IS)患者的脊柱-骨盆矢状位平衡情况。方法:回顾分析2002年4月~2009年4月收治的83例成人IS患者,男16例,女67例,年龄20~84岁,平均43岁。在全脊柱站立位X线正侧位片(包括双侧髋关节)上测量侧凸Cobb角、胸椎后凸角(TK)、胸腰段后凸角(TLJ)、腰椎前凸角(LL)、骨盆入射角(PI)、骶骨倾斜角(SS)、骨盆倾斜角(PT)以及C7铅垂线与S1后上缘的水平距离(SVA)。将患者分为胸弯组和腰弯组,比较两组患者的脊柱-骨盆矢状位参数,分析各参数间的相关性及各参数与年龄的相关性。结果:胸弯组共39例,平均年龄40.9岁,主弯角度平均45.8°;腰弯组共44例,平均年龄44.8岁,主弯角度平均39.5°。两组患者的年龄无统计学差异(P>0.05)。两组的TK、TLJ、LL、PI、SS、PT均无统计学差异(P>0.05),但腰弯组的SVA明显大于胸弯组(P<0.05)。在≤40岁患者中,胸弯组和腰弯组患者的脊柱-骨盆矢状位序列无统计学差异(P>0.05);在>40岁患者中,腰弯组患者SVA和PT大于胸弯组(P<0.05),余参数两组间无统计学差异(P>0.05)。胸弯组9例(23.1%)出现脊柱失平衡,其中7例为负向失平衡;腰弯组12例(27.3%)出现脊柱失平衡,其中8例为正向失平衡。两组的LL与TK、SS有相关性,PI与PT、SS有相关性,SVA与LL、SS、PT有相关性,年龄与SVA、PT有相关性。与胸弯组不同,腰弯组患者的PI与LL无相关性,而年龄与LL、SS有相关性,PT与LL、SS有相关性。结论:成人IS中,胸弯和腰弯患者的骨盆形态无差别,骨盆与脊柱的矢状位序列密切相关,年龄与躯干平衡相关。胸弯患者易出现脊柱负向失平衡,而腰弯患者更易出现脊柱正向失平衡。     

Sagittal spinopelvic alignment and body mass index in patients with degenerative spondylolisthesis

The sagittal orientation and osteoarthritis of facet joints, paravertebral muscular dystrophy and loss of ligament strength represent mechanical factors leading to degenerative spondylolisthesis. The importance of sagittal spinopelvic imbalance has been described for the developmental spondylolisthesis with isthmic lysis. However, it remains unclear if these mechanisms play a role in the pathogenesis of degenerative spondylolisthesis. The purpose of this study was to analyze the sagittal spinopelvic alignment, the body mass index (BMI) and facet joint degeneration in degenerative spondylolisthesis. A group of 49 patients with L4–L5 degenerative spondylolisthesis (12 males, 37 females, average age 65.9 years) was compared to a reference group of 77 patients with low back pain without spondylolisthesis (41 males, 36 females, average age 65.5 years). The patient’s height and weight were assessed to calculate the BMI. The following parameters were measured on lateral lumbar radiographs in standing position: L1–S1 lordosis, segmental lordosis from L1–L2 to L5–S1, pelvic tilt, pelvic incidence and sacral slope. The sagittal orientation and the presence of osteoarthritis of the facet joints were determined from transversal plane computed tomography (CT). The average BMI was significantly higher (P = 0.030) in the spondylolisthesis group compared to the reference group (28.2 vs. 24.8) and 71.4% of the spondylolisthesis patients had a BMI > 25. The radiographic analysis showed a significant increase of the following parameters in spondylolisthesis: pelvic tilt (25.6° vs. 21.0°; P = 0.046), sacral slope (42.3° vs. 33.4°; P = 0.002), pelvic incidence (66.2° vs. 54.2°; P = 0.001), L1–S1 lordosis (57.2° vs. 49.6°; P = 0.045). The segmental lumbar lordosis was significantly higher (P < 0.05) at L1–L2 and L2–L3 in spondylolisthesis. The CT analysis of L4–L5 facet joints showed a sagittal orientation in the spondylolisthesis group (36.5° vs. 44.4°; P = 0.001). The anatomic orientation of the pelvis with a high incidence and sacral slope seems to represent a predisposing factor for degenerative spondylolisthesis. Although the L1–S1 lordosis keeps comparable to the reference group, the increase of pelvic tilt suggests a posterior tilt of the pelvis as a compensation mechanism in patients with high pelvic incidence. The detailed analysis of segmental lordosis revealed that the lordosis increased at the levels above the spondylolisthesis, which might subsequently increase posterior stress on facet joints. The association of overweight and a relatively vertical inclination of the S1 endplate is predisposing for an anterior translation of L4 on L5. Furthermore, the sagittally oriented facet joints do not retain this anterior vertebral displacement.     

Effects of a cervical disc prosthesis on maintaining sagittal alignment of the functional spinal unit and overall sagittal balance of the cervical spine

The object of this study is to review the early clinical results and radiographic outcomes following insertion of the Bryan Cervical Disc Prosthesis (Medtronic Sofamor Danek, Memphis, TN), together with its effect on maintaining sagittal alignment of the functional spinal unit (FSU) and overall sagittal balance of the cervical spine for the treatment of single-level or two-level symptomatic disc disease. Forty-seven patients with symptomatic single or two-level cervical disc disease who received the Bryan Cervical Artificial Disc were reviewed prospectively. A total of 55 Bryan disc were placed in 47 patients. A single-level procedure was performed in 39 patients and a two-level procedure in the other eight. Radiographic and clinical assessments were made preoperatively and at 1.5, 3, 6, 9, 12, and 18 and up to 33 months postoperatively. Mean follow-up duration was 24 months, ranging from 13 to 33 months. Periods were categorized as early follow up (1.5–3 months) and late follow up (6–33 months). The visual analogue scale (VAS), neck disability index(NDI), Odom’s criteria were used to assess pain and clinical outcomes. Static and dynamic radiographs were measured by hand and computer to determine the range of motion (ROM), the angle of the functional segmental unit (FSU), and the overall cervical alignment (C2–7 Cobb angle). With all of these data, we evaluated the change of the preoperative lordosis (or kyphosis) of the FSU and Overall sagittal balance of the cervical spine during the follow-up period. There was a statistically significant improvement in the VAS score from 7.0 ± 2.6 to 2.0 ± 1.5 (paired-t test, P = 0.000), and in the NDI from 21.5 ± 5.5 to 4.5 ± 3.9 (paired-t test P = 0.000). All of the patients were satisfied with the surgical results by Odom’s criteria. The postoperative ROM of the implanted level was preserved without significant difference from preoperative ROM of the operated level. Only 36% of patients with a preoperative lordotic sagittal orientation of the FSU were able to maintain lordosis following surgery. However, the overall sagittal alignment of the cervical spine was preserved in 86% of cases at the final follow up. Interestingly, preoperatively kyphotic FSU resulted in lordotic FSU in 13% of patients during the late follow-up, and preoperatively kyphotic overall cervical alignment resulted in lordosis in 33% of the patients postoperatively. Clinical results are encouraging, with significant improvement seen in the Bryan Cervical Artificial disc. The Bryan disc preserves motion of the FSU. Although the preoperative lordosis (or kyphosis) of the FSU could not always be maintained during the follow-up period, the overall sagittal balance of the cervical spine was usually preserved.     

Analysis of hip dysplasia and spinopelvic alignment in cerebral palsy

Background contextKnowledge of sagittal spinopelvic parameters and hip dysplasia is important in cerebral palsy (CP) patients because these parameters differ from those found in the general population and can be related to symptoms.PurposeThe purpose of this study was to analyze sagittal spinopelvic alignment and determine its relation to hip dysplasia in CP patients.Study designRadiological analysis was conducted on patients with CP.Patient sampleFifty-four patients with CP and 24 normal controls were included in this study.Outcome measuresParticipants underwent radiographs of the whole spine.MethodsThe patient and control groups comprised 54 CP patients and 24 volunteers, respectively. All underwent lateral radiography of the whole spine and hip joint anteroposterior radiography. The radiographic parameters examined were sacral slope, pelvic tilt, pelvic incidence, S1 overhang, thoracic kyphosis, thoracolumbar kyphosis, lumbar lordosis, sagittal balance, center edge angle, acetabular angle, and migration index. Statistical analysis was performed to identify significant differences and correlations between the two groups.ResultsSacral slope, thoracolumbar kyphosis, lumbar lordosis, sagittal balance, acetabular angle, and migration index were significantly higher in CP patients, whereas pelvic tilt, S1 overhang, and center edge angle were significantly lower (p<.05). Correlation analysis revealed that pelvic incidence, sacral slope, pelvic tilt, and S1 overhang were related to each other and that thoracolumbar kyphosis was related to the thoracic kyphosis and lumbar lordosis (p<.05). For spinal and pelvic parameters, lumbar lordosis was related to sacral slope, pelvic incidence, pelvic tilt, and S1 overhang; for hip dysplasia parameters, center edge angle and acetabular angle were found to be interrelated (p<.05). Regarding symptoms, pelvic tilt, S1 overhang, and thoracolumbar kyphosis were found to be correlated with symptom severity in patients. However, no hip dysplasia parameters were found to be related to hip or spinal symptoms.ConclusionsThis study found significant differences between CP patients and normal controls in terms of spinopelvic alignment and hip dysplasia. Furthermore, relationships were found between the sagittal spinopelvic parameters and hip dysplasia, and correlations were found between sagittal spinopelvic parameters and pain.     

Sagittal plane deformity: an overview of interpretation and management

The impact of sagittal plane alignment on the treatment of spinal disorders is of critical importance. A failure to recognise malalignment in this plane can have significant consequences for the patient not only in terms of pain and deformity, but also social interaction due to deficient forward gaze. A good understanding of the principles of sagittal balance is vital to achieve optimum outcomes when treating spinal disorders. Even when addressing problems in the coronal plane, an awareness of sagittal balance is necessary to avoid future complications. The normal spine has lordotic curves in the cephalad and caudal regions with a kyphotic curve in between. Overall, there is a positive correlation between thoracic kyphosis and lumbar lordosis. There are variations on the degree of normal curvature but nevertheless this shape allows equal distribution of forces across the spinal column. It is the disruption of this equilibrium by pathological processes or, as in most cases, ageing that results in deformity. This leads to adaptive changes in the pelvis and lower limbs. The effects of limb alignment on spinal posture are well documented. We now also know that changes in pelvic posture also affect spinal alignment. Sagittal malalignment presents as an exaggeration or deficiency of normal lordosis or kyphosis. Most cases seen in clinical practise are due to kyphotic deformity secondary to inflammatory, degenerative or post-traumatic disorders. They may also be secondary to infection or tumours. There is usually pain and functional disability along with concerns about self-image and social interaction due to inability to maintain a horizontal gaze. The resultant pelvic and lower limb posture is an attempt to restore normal alignment. Addressing this complex problem requires detailed expertise and awareness of the potential pitfalls surrounding its treatment.     

Lumbopelvic alignment on standing lateral radiograph of adult volunteers and the classification in the sagittal alignment of lumbar spine

The analysis of the sagittal balance is important for the understanding of the lumbopelvic biomechanics. Results from previous studies documented the correlation between sacro-pelvic orientation and lumbar lordosis and a uniqueness of spino-pelvic alignment in an individual person. This study was subjected to determine the lumbopelvic orientation using pelvic radius measurement technique. The standing lateral radiographs in a standardized standing position were taken from 100 healthy volunteers. The measurements which included hip axis (HA), pelvic radius (PR), pelvic angle (PA), pelvic morphology (PR-S1), sacral translation distance (HA-S1), total lumbosacral lordosis (T12-S1), total lumbopelvic lordosis (PR-T12) and regional lumbopelvic lordosis angles (PR-L2, PR-L4 and PR-L5) were carried out with two independent observers. The relationships between the parameters were as follows. PR-S1 demonstrated positive correlation to regional lumbopelvic lordosis and revealed negative correlation to T12-S1. PA showed negative correlation to PR-S1 and regional lumbopelvic lordosis, but revealed positive correlation to HA-S1. T12-S1 was significantly increased when PR-S1 was lesser than average (35°–45°) and was significantly decreased when PR-S1 was above the average. PR-L4 and PR-L5 were significantly reduced when PR-S1 was smaller than average and only PR-L5 was significantly increased when PR-S1 was above the average. In conclusion, this present study supports that lumbar spine and pelvis work together in order to maintain lumbopelvic balance.     

The sagittal profile of the cervical and lumbosacral spine in Scheuermann thoracic kyphosis

The sagittal profiles of the cervical and lumbar spine have not been studied in Scheuermann kyphosis. The purpose of this study was to investigate these profiles. Standing lateral radiographs of the spine in 34 children with Scheuermann kyphosis were reviewed. Cervical lordosis, lumbar lordosis, thoracic kyphosis, sagittal vertebral axis, and sacral inclination were measured. The relations between these variables were explored using the Pearson correlation. The average patient age was 15.5 +/- 1.8 years, thoracic kyphosis was 65 degrees +/- 12 degrees, lumbar lordosis 71 degrees +/- 13 degrees, and cervical lordosis 4 degrees +/- 15 degrees (Cobb angle), and 9 degrees +/- 14 degrees (posterior vertebral body angle [PVBA]). No correlations were noted between cervical lordosis and thoracic kyphosis. Correlations were noted between cervical lordosis and lumbar lordosis (r2 = 0.17, Cobb angle; r2 = 0.16, PVBA) and between cervical lordosis and the residual sagittal difference (thoracic kyphosis minus lumbar lordosis; r2 = 0.32, p = 0.001 [Cobb angle], and r2 = 0.19, p = 0.01 [PVBA]). In Scheuermann kyphosis, the flexible cervical and lumbar spine is linked by the intermediate rigid thoracic segment. As the residual sagittal difference becomes more kyphotic, lordosis of the cervical spine increases as the patient strives to maintain a forward visual gaze.     

Lumbosacral lordosis in fetal spine: genetic or mechanic parameter

Many believe that the fetus spine had only one curvature from cranial to caudal which is a global kyphosis and that the lumbosacral lordosis appears with the erect posture. They agree that the sacrum of Homo sapiens is not positioned posteriorly at birth and that it is during the first few years that the sacrum, in humans, moves dorsally in relation with the progressive acquisition of erect posture and the ontogeny of bipedal locomotion. Nevertheless, there is no biometric study assessing these parameters in vivo in utero during the fetal life. Cross-sectional biometric study of the lumbosacral junction of the spine in in utero fetuses was to document the presence of a lumbosacral lordosis in the fetal population in utero long before standing and walking and its change during growth. Forty-five MRIs (magnetic resonance imaging) of fetuses aged of 23–40 weeks of gestation were analyzed. The measurements were performed on computerized MRI DICOM images using a professional software to calculate the curvature and radius of the lumbosacral junction. The presence or absence of visual lumbosacral lordosis was noted for each case. Correlation tests were performed in order to disclose a correlation between the gestational age and the curvature calculated. A test was considered significant for P < 0.01. There were 14 males, 17 females and 14 undetermined. All the curves (100%) showed mathematically the presence of a lordosis in the lumbosacral region. The visual lumbosacral lordosis was present in 60% of cases. The measurement of the lumbosacral curvature varies between −0.133 and −0.033 mm⁻¹ and a mean of −0.054 mm⁻¹ with a corresponding radius ranging from −7 to −303 mm with a mean of −18.7 mm. The statistical analysis showed no correlation between the gestational age and the lumbosacral curvature (R ² = 0.11). The hypothesis of increased lumbosacral lordosis with gestational age is rejected. It is difficult to accurately determine the role played separately by genetics and by erect posture. A visual lumbosacral lordosis was noted in 60% of cases with mean radius of −18.6691 mm. This lordosis was not correlated statistically to gestational age which means that it is not related to growth and might be genetically determined. Mechanical factors may play a major role in the determination of the shape of the growing pelvis. One can ask if the pelvis morphology is genetically determined or if it is mechanically determined under muscular and ligamentous stresses. This study shows that the sacrum of human fetuses is oriented posteriorly mathematically in 100% of cases, and in 60% of cases based on the morphologic appearance of the lumbosacral junction. So beside the effect of progressive acquisition of erect posture and bipedalism in determining the formation of lumbosacral angle, we believe that genetics play an important role in the formation of the lumbosacral angle.     

Sagittal balance of the pelvis-spine complex and lumbar degenerative diseases. A comparative study about 85 cases

Retrospective analysis of the spino-pelvic alignment in a population of 85 patients with a lumbar degenerative disease. Several previous publications reported the analysis of spino-pelvic alignment in the normal and low back pain population. Data suggested that patients with lumbar diseases have variations of sagittal alignment such as less distal lordosis, more proximal lumbar lordosis and a more vertical sacrum. Nevertheless most of these variations have been reported without reference to the pelvis shape which is well-known to strongly influence spino-pelvic alignment. The objective of this study was to analyse spino-pelvic parameters, including pelvis shape, in a population of 85 patients with a lumbar degenerative disease and compare these patients with a control group of normal volunteers. We analysed three different lumbar degenerative diseases: disc herniation (DH), n = 25; degenerative disc disease (DDD), n = 32; degenerative spondylolisthesis (DSPL), n = 28. Spino-pelvic alignment was analysed pre-operatively on full spine radiographs. Spino-pelvic parameters were measured as following: pelvic incidence, sacral slope, pelvic tilt, lumbar lordosis, thoracic kyphosis, spino-sacral angle and positioning of C7 plumb line. For each group of patients the sagittal profile was compared with a control population of 154 asymptomatic adults that was the subject of a previous study. In order to understand variations of spino-pelvic parameters in the patients’ population a stratification (matching) according to the pelvic incidence was done between the control group and each group of patients. Concerning first the pelvis shape, patients with DH and those with DDD demonstrated to have a mean pelvic incidence equal to 49.8° and 51.6°, respectively, versus 52° for the control group (no significant difference). Only young patients, less than 45 years old, with a disc disease (DH or DDD) demonstrated to have a pelvic incidence significantly lower (48.3°) than the control group, P < 0.05. On the contrary, in the DSPL group the pelvic incidence was significantly greater (60°) than the control group (52°), P < 0.0005. Secondly the three groups of patients were characterized by significant variations in spino-pelvic alignment: anterior translation of the C7 plumb line (P < 0.005 for DH, P < 0.05 for DDD and P < 0.05 for DSPL); loss of lumbar lordosis after matching according to pelvic incidence (P < 0.0005 for DH, DDD and DSPL); decrease of sacral slope after matching according to pelvic incidence (P = 0.001 for DH, P < 0.0005 for DDD and P < 0.0005 for DSPL). Measurement of the pelvic incidence and matching according to this parameter between each group of patients and the control group permitted to understand variations of spino-pelvic parameters in a population of patients.     

胸椎及胸腰段角状后凸畸形对骨盆矢状位形态及序列的影响

目的 分析胸椎及胸腰段角状后凸畸形对骨盆形态及序列的影响.方法 2002年5月至2010年6月收治的胸腰椎角状后凸患者32例,年龄13～56岁,平均29.6岁.详细记录患者病史以及病因.患者发生后凸畸形的年龄为1～17岁,平均6.1岁,陈旧结核性后凸畸形20例,先天性后凸畸形12例.全部患者接受后路截骨矫形手术.术前术后行全脊柱负重位X线侧位片检查(包括双侧髋关节),测量后凸畸形Cobb角、腰椎前凸(LL)、骨盆入射角(PI)、骶骨倾斜角(SS)、骨盆倾斜角(PT)以及脊柱的矢状位平衡(C7铅垂线与S1后上缘的水平距离,SVA).将测量结果与既往报道的正常值进行比较.比较中上胸椎后凸和下胸椎或胸腰段后凸的PI值.比较术前术后的各测量参数.分析PI的独立影响因素.结果 32例患者中,后凸角度平均为90.1°(31°～138°).术前PI平均为34.8°,SS为35.8°,PT为-0.7°,其中PI和PT明显小于对照组(P＜0.001).术后后凸角度改善至27.9°.术后PI平均为37.5°±9.4°,与术前比较差异无统计学意义(P＞0.05).12例患者后凸畸形位于中上胸椎(T1～8),20例位于下胸椎(T8以下)及胸腰段.两组相比,前者的PI值(40.5°)明显大于后者(31.5°,P＜0.05),前者SS(45.1°)亦明显大于后者(30.3°,P＜0.05).后凸角度和后凸部位是PI的独立影响因素,而年龄和LL对PI无影响.结论 胸腰椎角状后凸畸形若发生在儿童少年时期,将影响骨盆的形态发育(PI明显减小).后凸部位越低、后凸角度越大对骨盆形态的影响越大.手术可改变脊柱的序列,但骨盆的矢状位形态一旦形成将无法改变.早期治疗不仅可恢复脊柱的序列,亦有益于骨盆的正常形态的形成以及骨盆的正常矢状位序列.

Abstract：

Objective To analyze the impact of thoracic and thoracolumbar angular kyphosis on pelvic shape and sagittal alignment. Methods From May 2002 to June 2010, the sagittal spinopelvic parameters were analyzed in lateral standing radiographs of 32 patients (mean age 29.6 years ) with thoracolumbar angular kyphosis. The parameters included Cobb angle of kyphosis, lumbar lordosis ( LL),pelvic incidence ( PI ), sacrum slope ( SS), pelvic tilt ( PT ) and sagittal vertical axis ( SVA ). All pelvic parameters in the patients were compared with those reported in historical normal subjects. All patients were treated by using kyphotic correction and fusion. The preoperative and postoperative parameters were compared. The pelvic parameters were also compared between the patients with kyphotic apex located at T1-8 and those located at T9-12 and thoracolumbar junction. The linear regression analysis was used to investigate the independent factors of PI. Results The mean kyphosis was 90. 1 ° (31°-138°). The mean age of kyphosis occurrence was 6. 1 years. The mean PI, SS and PT were 34. 8° ,35.8° and -0. 7° respectively. The PI and PT were significantly smaller( P ＜ 0. 001 ) in the patients than those in normal subjects while the SS was similar. The kyphosis was improved to 27.9° post-operatively. There was no difference in PI values between preoperation and postoperation ( P ＞ 0. 05 ). The PI and SS in patients whose kyphosis located at thoracic spine(T1-8) were significantly higher than those at T9-L2. Instead of patients' age and LL, the preoperative Cobb angle of kyphosis and the levels where kyphosis located were two independent impact factors of PI. Conclusions The kyphosis occurred at childhood may influence pelvic shape and alignment significantly. The lower kyphotic apex located and the bigger kyphosis, the greater impact on the pelvic morphology. The surgery can improve the kyphosis, but can not change the sagittal pelvic morphology. Early treatment of thoracolumbar angular kyphosis is beneficial not only to reconstruction of spine alignment but also to the formation of sagittal pelvic morphology.     

正常脊柱-骨盆矢状位参数的影像学研究

目的 描述正常成人的骨盆矢状位形态,分析正常成人脊柱-骨盆矢状位序列类型.方法 采用前瞻性影像学分析对139名志愿者进行研究,男94名,女45名;年龄21～28岁,平均(23.5±1.5)岁.所有志愿者行全脊柱正、侧位X线检查,利用院内影像归档与通信系统(picture archiving and communication systems,PACS)测量骨盆入射角(pelvic incidence,PI)、骨盆倾斜角(pelvic tilt,PT)、骶骨倾斜角(sacral slope,SS).按照脊柱矢状面解剖定义和形态特点描述脊柱各矢状面形态参数,分析各参数间相关性,并根据腰椎前凸顶点位置不同分析国人腰椎-骨盆矢状位序列类型.结果 PI平均值为45.1°±9.6°,明显小于西方成人,并明显小于韩国成人;女性PI值明显高于男性.骨盆各参数间密切相关,脊柱相邻前凸节段、后凸节段间密切相关,腰弯前凸还与颈弯前凸、矢状位平衡(sagittal vertical axis,SVA)密切相关;依据腰弯前凸顶点位置,将腰椎-骨盆矢状位序列分为四型:Ⅰ型,顶点位于L5椎体或L4,5椎间隙,共11名(占7.8％);Ⅱ型,顶点位于L4底部或中部,共61名(占43.3％);Ⅲ型,顶点位于L4上部或L34椎间隙,共33名(占23.4％);Ⅳ型,顶点位于L3椎体及其以上,共34名(占24.5％).所有志愿者的胸弯后凸顶点为T6.7,颈弯胸弯拐点为C7.各类型间骨盆矢状位形态、腰弯倾斜程度存在明显差异.结论 中国正常成人骨盆矢状位形态与西方和韩国人群存在明显差异.腰椎通过骨盆的调节后,在维持脊柱整体矢状位平衡方面起到核心作用;随着腰弯前凸顶点提高,脊柱-骨盆序列将出现骶骨增加倾斜、下腰弯前凸角度增加、下腰弯组成椎体数量增加、腰弯倾斜减小等变化.     

The sagittal balance of the spine in children and adolescents with osteogenesis imperfecta

In severe forms of osteogenesis imperfecta, multiple compression fractures of the spine, as well as vertebral height shortening could be responsible for an increased thoracic kyphosis or a diminished lumbar lordosis. Theses progressive changes in sagittal shapes of the trunk could be responsible for a global sagittal trunk imbalance. We compare the parameters of sagittal spinopelvic balance in young patients with OI to those parameters in a control group of healthy volunteers. Eighteen patients with osteogenesis imperfecta were compared to a cohort of 300 healthy volunteers. A standing lateral radiograph of the spine was obtained in a standardized fashion. The sacral slope, pelvic tilt, pelvic incidence, lumbar lordosis, thoracic kyphosis, T1 and T9 sagittal offset were measured using a computer-assisted method. The variations and reciprocal correlations of all parameters in both groups according to each other were studied. Comparison of angular parameters between OI patients and control group showed an increased T1T12 kyphosis in OI patients. T1 and T9 sagittal offset was positive in OI patients and negative in control group. This statistically significant difference among sagittal offsets in both groups indicated that OI patients had a global sagittal balance of the trunk displaced anteriorly when compared to the normal population. Reciprocal correlations between angular parameters in OI patients showed a strong correlation between lumbar lordosis (L1L5 and L1S1) and sacral slope. The T9 sagittal offset was also strongly correlated with pelvic tilt. Pelvic incidence was correlated with L1S1 lordosis, T1 sagittal offset and pelvic tilt. In OI patients, the T1T12 thoracic kyphosis was statistically higher than in control group and was not correlated with other shape (LL) or pelvic (SS, PT or PI) parameters. Because isolated T1T12 kyphosis increase without T4T12 significant modification, we suggest that vertebral deformations worsen in OI patients at the upper part of thoracic spine. Further studies are needed to precise the exact location of most frequent vertebral deformities.     

Sagittal alignment of spine and pelvis regulated by pelvic incidence: standard values and prediction of lordosis

Pelvis and spinal curves were studied with an angular parameter typical of pelvis morphology: pelvic incidence. A significant chain of correlations between positional pelvic and spinal parameters and incidence is known. This study investigated standards of incidence and a predictive equation of lordosis from selective pelvic and spinal individual parameters. One hundred and forty nine (78 men and 71 women) healthy adults, aged 19–50 years, with no spinal disorders, were included and had a full-spine lateral X-ray in a standardised upright position. Computerised technology was used for the measurement of angular parameters. Mean-deviation section of each parameter and Pearson correlation test were calculated. A multivariate selection algorithm was running with the lordosis (predicted variable) and the other spinal and pelvic parameters (predictor variables), to determine the best sets of predictors to include in the model. A low incidence (<44°) decreased sacral-slope and the lordosis is flattened. A high incidence (>62°) increased sacral-slope and the lordosis is more pronounced. Lordosis predictive equation is based on incidence, kyphosis, sacral-slope and ±T9 tilt. The confidence limits and the residuals (the difference between measured and predicted lordosis) assessed the predicted lordosis accuracy of the model: respectively, ±1.65 and 2.41° with the 4-item model; ±1.73 and 3.62° with the 3-item model. The ability of the functional spine-pelvis unit to search for a sagittal balance depended both on the incidence and on the variation section of the other positional parameters. Incidence gave an adaptation potential at two levels of positional compensation: overlying state (kyphosis, T9 tilt), underlying state (sacral slope, pelvic tilt). The biomechanical and clinical conditions of the standing posture (as in scoliosis, low back pain, spondylisthesis, spine surgery, obesity and postural impairments) can be studied by comparing the measured lordosis with the predicted lordosis.     

A new MRI technique for imaging scoliosis in the sagittal plane

The purpose of the present study was to introduce a new magnetic resonance imaging (MRI) procedure showing the whole spine in a coronal and sagittal plane, and to study the assessment of sagittal Cobb angle measurements using this technique. Prospectively we studied 32 patients (average age 14.8 years) with idiopathic scoliosis (mean thoracic Cobb angle 33 degrees on radiograph) and 18 patients (average age 14.5 years) without scoliosis. The MRI investigation was carried out in a standard supine position. The cervical and upper thoracic spine and the lower thoracic and lumbar spine were measured on a 1.5-T Gyroscan ACS-NT Powertrak 6000 system. An algorithm was developed to combine the results of the cranial and caudal scans into a coronal and a sagittal image of the whole spine (MR total spine imaging). Measurement of the sagittal Cobb angle conducted ten times by four independent investigators revealed an intraobserver variance of 1.6 degrees and an interobserver variance of 1.8 degrees. In the group with scoliosis the mean sagittal Cobb angle from T4 to T12 was 12 degrees (range -3 degrees to 24 degrees) and in the group without scoliosis 22 degrees (range 16 degrees to 30 degrees), which was a significant difference. MR total spine imaging makes it possible to image scoliosis in the sagittal plane. On these MR projections, idiopathic thoracic scoliosis was identified by a reduced sagittal Cobb angle. MR total spine imaging would allow monitoring of scoliosis in the sagittal plane, which can reveal relevant clinical data without radiation exposure.