Does pelvic incidence tell us the risk of proximal junctional kyphosis in adult spinal deformity surgery?

PURPOSE: To investigate the relationship between pelvic incidence (PI) and proximal junctional kyphosis (PJK) in patients treated surgically for adult spinal deformity (ASD) with fusion from thoracolumbar junction to sacrum. METHODS: A consecutive series of ASD patients who underwent fusion from the thoracolumbar junction to the sacrum with a minimum of 2-year follow-up was studied. Patients were divided into low PI (≤ 50°) and high PI (> 50°) groups. We compared radiographic parameters and the rates of PJK, between the two groups. A sub-analysis was performed on patients with a postoperative PI minus lumbar lordosis mismatch between - 10° and 10° (i.e., ideally corrected). RESULTS: Sixty-three patients were included: 19 low PI and 44 high PI. Median follow-up was 34 months (range 24-103). Overall PJK rate was 38%. PJK was observed in 16% of low PI and 48% of high PI patients (p = 0.02). The odds ratio for developing PJK with a high PI compared to a low PI was 4.9 (p = 0.03). There were 32 ideally corrected patients. Eleven of these were in the low PI group, and 21 patients were in the high PI group. The incidence of PJK was 25% for ideally corrected patients. PJK occurred in none of these patients in the low PI group and 38% of patients in the high PI group (p = 0.03). CONCLUSION: When the upper-instrumented vertebra includes the thoracolumbar junction, patients with a PI > 50° are at a significantly higher risk of developing PJK compared to patients with a PI ≤ 50°.

Radiographic outcomes and complications after L4 or L5 pedicle subtraction osteotomy for fixed sagittal malalignment in 102 adult spinal deformity patients with a minimum 2-year follow-up.

PURPOSE: The objective of this retrospective study was to provide the radiographic outcomes and complications for pedicle subtraction osteotomy (PSO) performed at the low lumbar spine, i.e., L4 or L5 for ASD patients with fixed sagittal malalignment. METHODS: ASD patients who underwent L4 or L5 PSO with a minimum 2-year follow-up were included. Preoperative and postoperative radiographs, and complications were collected. Radiographic analysis included lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), thoracic kyphosis (TK), sagittal vertical axis (SVA), spinal lordosis (SL) ratio and global tilt (GT) on standing long-cassette radiographs. RESULTS: A total of 102 patients from 2 spinal centers were analyzed. 66 patients underwent PSO at L4 and 36 patients at L5. From preoperatively to the final follow-up, significant improvements occurred in LL (from - 31° to - 52°), SVA (from 13 to 5 cm), and GT (from 44° to 27°) (all, p < 0.05). 12 patients had transient neurological deficits, and 8 patients had persistent neurological deficit. 23 patients underwent revision for PJK (2), pseudarthrosis (10), neurological deficit (2), epidural hematoma (1), or deep surgical site infection (8). No PJK was observed in any of the patients with L5 PSO. CONCLUSIONS: PSO at the level of L4 or L5 remains a challenging technique but with an acceptable rate of complications and revisions. It enables correction of fixed sagittal malalignment in ASD patients with a globally satisfactory outcome. In comparison with L4 PSO, L5 PSO patients did not show PJK as a mechanical complication. Distal lumbar PSO at the level of L5 may represent one of the factors that may help preventing the proximal junctional kyphosis complication.

Revisiting thoracic kyphosis: a normative description of the thoracic sagittal curve in an asymptomatic population.

PURPOSE: Thoracic kyphosis (TK) remained in the shadow of lumbar lordosis. Based on Berthonnaud and Roussouly segmentation, TK is divided into two arches: upper TK (UTK) and lower TK (LTK). The purpose of this study is to propose a normative description of the TK arches in an asymptomatic adults' population and their correlation with spinal and pelvic parameters. METHODS: This is an observational study performed on asymptomatic healthy Caucasians volunteers aged between 18 and 45 years. Each patient had a standardized standing biplanar full spine X-rays. Using KEOPS®, sacropelvic parameters and global spinal parameters (LL, TK) as well as the inflexion point location were measured. The upper lumbar lordosis angle (ULL) as well as LTK and UTK was calculated. Patients were classified according to Roussouly morphotypes of normal spine. RESULTS: A total of 373 adults (F/M = 1.4/1) were enrolled with mean age of 27 years. Mean UTK averaged 25.8°, while mean LTK averaged 19.8° (p < 0.001). UTK angle values were statistically the same in the five different Roussouly spinal shapes (p > 0.05), while LTK values were variable among different Roussouly spine subtypes (p < 0.05). Finally, TK showed the highest correlation with the LL mainly with the ULL (Pearson = 0.66). CONCLUSION: In asymptomatic young adults, thoracic kyphosis is composed by two unequal arches, a stable UTK and a variable LTK, with an apex around T8 and T9 vertebra, depending on the spinal morphotype according to Roussouly classification. This should be taken into consideration when analyzing spine sagittal compensation and preparing corrections to minimize risk of mechanical complications.

Comparison of different strategies on three-dimensional correction of AIS: which plane will suffer?

PURPOSE: There are distinct differences in strategy amongst experienced surgeons from different 'scoliosis schools' around the world. This study aims to test the hypothesis that, due to the 3-D nature of AIS, different strategies can lead to different coronal, axial and sagittal curve correction. METHODS: Consecutive patients who underwent posterior scoliosis surgery for primary thoracic AIS were compared between three major scoliosis centres (n = 193). Patients were treated according to the local surgical expertise: Two centres perform primarily an axial apical derotation manoeuvre (centre 1: high implant density, convex rod first, centre 2: low implant density, concave rod first), whereas centre 3 performs posteromedial apical translation without active derotation. Pre- and postoperative shape of the main thoracic curve was analyzed using coronal curve angle, apical rotation and sagittal alignment parameters (pelvic incidence and tilt, T1-T12, T4-T12 and T10-L2 regional kyphosis angles, C7 slope and the level of the inflection point). In addition, the proximal junctional angle at follow-up was compared. RESULTS: Pre-operative coronal curve magnitudes were similar between the 3 cohorts and improved 75%, 70% and 59%, from pre- to postoperative, respectively (P < 0.001). The strategy of centres 1 and 2 leads to significantly more apical derotation. Despite similar postoperative T4-T12 kyphosis, the strategy in centre 1 led to more thoracolumbar lordosis and in centre 2 to a higher inflection point as compared to centre 3. Proximal junctional angle was higher in centres 1 and 2 (P < 0.001) at final follow-up. CONCLUSION: Curve correction by derotation may lead to thoracolumbar lordosis and therefore higher risk for proximal junctional kyphosis. Focus on sagittal plane by posteromedial translation, however, results in more residual coronal and axial deformity.

Mechanical complications in adult spinal deformity and the effect of restoring the spinal shapes according to the Roussouly classification: a multicentric study.

PURPOSE: To evaluate the incidence of mechanical complications in patients with adult spine deformity (ASD) treated by restoring the normal shape according to the Roussouly classification. METHODS: This is a retrospective multicentric study with a minimum follow-up of 2 years. Patients operated on with fusion for ASD (minimum performed fusion: L2 to sacrum) were included. Patients with a history of previous spinal fusion of more than three levels were excluded. Spinal and pelvic parameters were measured on the preoperative and the immediate postoperative follow-up. All mechanical complications were recorded. RESULTS: A total of 290 patients met the criteria of inclusion with a minimum follow-up of 2 years. Mechanical complications occurred in 30.4% of the cohort. The most common complication was PJK with an incidence of 18% while nonunion or instrumentation failure (rod breakage, implant failure) occurred in 12.4%. 66% of the patients were restored to the normal shape according to the Roussouly classification based on their PI and had a mechanical complication rate of 22.5%, whereas the remaining 34% of patients had a complication rate of 46.8% (p < 0.001). The relative risk for developing a mechanical complication if the algorithm was not met was 3 (CI 1.5-4.3; p < 0.001) CONCLUSION: In the recent literature, there are no clear guidelines for ASD correction. Restoring the sagittal spinal contour to the normal shapes of Roussouly according to the PI could serve as a guideline for ASD treatment. Ignoring this algorithm has a threefold risk of increased mechanical complications. We recommend this algorithm for treatment of ASD. LEVEL OF EVIDENCE: IV cross-sectional observational study. These slides can be retrieved under Electronic Supplementary Material.

New sagittal classification of AIS: validation by 3D characterization.

INTRODUCTION AND AIM: In order to improve surgical planning of sagittal correction in AIS, we proposed a new sagittal classification-Abelin-Genevois et al. Eur Spine J (27(9):2192-2202, 2018. https://doi.org/10.1007/s00586-018-5613-1 ). The main criticism is related to the fact that 2D lateral view results from the projection of the 3D deformity. The aim of this study is to show that the new sagittal classification system is a reliable system to describe the different sagittal scenarios that AIS could create both in 2D and 3D. METHODS: We performed retrospective radiograph analysis of prospectively collected data from 93 consecutive AIS patients who underwent an examination of the whole spine using the EOS® imaging system. 2D (Keops®) and 3D analyses (sterEOS®) provided frontal and sagittal spinal and spinopelvic parameters. In addition, 3D analysis provided apical vertebra rotation (AVR). RESULTS: Comparing 2D and 3D measurements for the general cohort, excellent correlation can be found for all parameters, but only fairly good for T10L2 and L1S1 angles. The highest variability was observed for T10L2, differences between 2D and 3D measurements being greater when the Cobb angle increased. AVR did not influence concordance between 2D and 3D measurements. Eighty-two percent were similarly classified in 2D and 3D according to the new classification. Misclassified patients were all AIS sagittal type 3 in 3D analysis, thoracolumbar junction (TLJ) lordosis being underestimated on 2D view. DISCUSSION: In conclusion, for the majority of cases (82%), 2D analysis may provide enough information for decision making when using a semi-automated 2D measurement system. However, in severe cases, especially when Cobb angle exceeds 55°, 3D analysis should be used to get a more accurate view on the thoracolumbar junction behavior. These slides can be retrieved under Electronic Supplementary Material.

Description of the sagittal alignment of the degenerative human spine.

PURPOSE: To present the description of sagittal alignment of the degenerative human spine and its possible evolution. MATERIALS AND METHODS: This is a retrospective observational study of degenerative evolution in spinal alignment in low back pain patients. Full spine EOS® sagittal X-rays were analyzed, and pelvic and spinal parameters were measured. Spinal shapes were classified on the hypothesis that the possible sagittal shapes of degenerative spine would be divided into four categories: "classical" Roussouly types 1-4, anteverted types (PT ≤ 5), retroverted types (PT ≥ 25) and kyphotic types. RESULTS: A total of 331 patients (280 women and 51 men) were included. "Classic" types 1-4 represented the majority in this cohort (71.9%). Retroverted types made the second most common category with 20.8% of the cohort. Kyphosis group (lumbar and global) make only 5.8% of this cohort, while anteverted group make the lowest incidence (1.5%). Retroverted type 2 with thoracic kyphosis should be considered a separate type and made 1.5% of this cohort. Two theoretical subtypes, retroverted type 1 and type 4 were not found. CONCLUSIONS: This is the first description of degenerative spine disease based on its shape and based on the classification of the normal variation in the sagittal alignment of the human lumbar spine described by Roussouly. Eleven types, divided into classical types, anteverted types, false shapes (retroverted) and kyphotic shapes, are described and an evolution pathway is proposed. An evaluation of surgical results in order to propose a treatment algorithm based on this classification should follow. LEVEL OF EVIDENCE: Level IV cross sectional observational study.

Classification of normal sagittal spine alignment: refounding the Roussouly classification.

PURPOSE: Although the Roussouly classification of common variants in spinal sagittal alignment is well accepted, no studies have implemented it in an asymptomatic adult population. In addition, no study investigated the radiographic features of asymptomatic patients with an anteverted pelvis. The aim of this prospective radiographic study of 296 asymptomatic adults without spinal pathology was to investigate how the Roussouly classification could include the anteverted pelvis concept. METHODS: Pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), and the lumbar parameters lumbar lordosis (Global LL), lordosis tilt angle (LTA), total number of lordotic vertebra (LL verteb), and C7 plumbline/sacrofemoral distance ratio (C7PL ratio) were evaluated in 296 healthy volunteers (126 males, 170 females; mean age, 27 years; range 18-48 years). Comparison between the five types of the Roussouly classification used Student, ANOVA, and Tukey tests for quantitative variables and χ 2, Fischer, and Holm tests for qualitative variables. RESULTS: Mean PI and PT were, respectively, (39°, 10°) for type 1, (41°, 10°) for type 2, (53°, 13°) for type 3, and (62°, 12°) for type 4 (p < 0.0001 and p < 0.01). A sizable portion (16%) of the population (type 3 AP) showed low-grade PI (mean, 48° ± 6°) despite having SS > 35°. PT was low or negative (mean 4° ± 3°). C7PL ratio was >1 (in front of the hip axis) in 13% of all cases, and between 0 and 1 (between sacrum and hip axis) in 49%. CONCLUSION: Although asymptomatic adults stood with stable global balance, the sagittal spinal alignment of healthy subjects, newly divided in 5 sagittal types, varied significantly. Type 3 AP appears as a new and unusual sagittal shape with low-grade PI, very low or negative PT, and hyperlordosis. Whereas most asymptomatic adults stood with C7PL behind the hip axis, a sizeable portion had C7 in front of the hip axis. This could be a new controversial aspect of ideal spinal balance.

Proximal junctional kyphosis in adult scoliosis: comparison of four radiological predictor models.

OBJECTIVE: The objective of this retrospective study is to identify the best immediate postoperative radiological predictors for the occurrence of proximal junctional kyphosis (PJK). Four proposed methods will be explored. METHODS: A homogeneous database of adult scoliosis from multiple centers was used. Patients with whole spine X-rays at the required follow-up (FU) periods were included. Spinal and pelvic parameters were measured and calculated to compare four predictive methods: Method 1: assessment of the global sagittal alignment (GSA); Method 2: restoration of the theoretical values of lumbar lordosis (LL) and thoracic kyphosis (TK) according to pelvic incidence (PI); Method 3: evaluation of TK + LL, and Method 4: restoration of the apex of sagittal LL to its theoretical values according to various spine shapes in Roussouly Classification. PJK occurrence was assessed at the last FU radiograph. RESULTS: 250 patients were included; mean age was 56.67 years and mean FU was 2.5 years. PJK occurred in 25.6% of cases. PJK occurred in 19.9% in patients with a GSA <45° and in 29.9% where GSA >45° (p = 0.04, OR = 1.71). Restoring the sagittal apex of the LL to its theoretical values according to PI deceased PJK to 13.5% compared to 38.9% in the other cases (p = 0.01, OR = 4.6). The two other described methods (2 and 3) were not significant predictors. DISCUSSION: The comparison between the four predictive methods showed that a GSA >45° and restoration of sagittal apex of lordosis according to PI, were the most predictive methods for PJK in ASD. The latter had a higher predictive value. Our findings could prove useful in effective preoperative planning in ASD surgery to reduce PJK rates. LEVEL OF EVIDENCE: Level IV.

Posterior-only versus combined anterior/posterior fusion in Scheuermann disease: a large retrospective study.

PURPOSE: The literature shows controversies concerning surgical treatment of Scheuermann's kyphosis between posterior-only fixation and combined anterior/posterior fusion. The aim of this study is to compare the clinical and radiological results and the rate of complications between these two techniques. METHODS: We performed a multicentric retrospective review of 131 patients who underwent primary fusion for Scheuermann's kyphosis divided into two groups: 67 patients operated via posterior approach only and 64 operated via combined anterior/posterior approach. Classical clinical, surgical and radiological data were collected. A descriptive and statistical analysis was performed between the two groups to evaluate the influence of the surgical procedure on the rate of complications, the functional results and radiological correction. RESULTS: The average age was 23 and the average kyphosis was 77 degrees. The mean follow-up was 4.2 years (range 0.1-27.3). There was no difference regarding demographic data, preoperative radiographic data and length of fusion between the two groups. Functional results were good in 81% of cases. Kyphosis correction was on average 15° and the correction of the compensatory lumbar lordosis was 20°. The correction was stable at final follow-up. There was no difference between the two groups in terms of functional results, the complications rate and radiological correction. CONCLUSION: Surgery for Scheuermann's kyphosis gives good and stable functional and radiological results. Given the fact that the two surgical strategies give the same results, it appears that the anterior/posterior fusion technique to treat Scheuermann's kyphosis should be reserved for major deformations. These slides can be retrieved under Electronic Supplementary Material.

Differences in lumbar and pelvic parameters among African American, Caucasian and Asian populations.

PURPOSE: Ethnic differences in spino-pelvic parameters among a healthy population are poorly defined in the literature. The purpose of this study was to document sagittal spino-pelvic parameters in a sample of African Americans and to compare them with previously reported data for Caucasians and Asians. METHODS: African American individuals without spine pathology who had standing lateral radiographs were identified. Radiographs were measured to determine the following parameters: lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT) and sacral slope (SS). Data of adult subjects were compared with those previously published for Caucasians (n = 709) and Asians (n = 312). RESULTS: These measurements (LL, PI, PT, and SS) obtained for the 36 African American subjects aged 18 years or older [15 men and 21 women; mean age 26.6 ± 8.7 range (18-53)] The mean LL, PI, PT and SS values were 57.2°, 57.7°, 15.9° and 41.4°, respectively. A comparative analysis showed the means values for PI was greater in the African American than in Caucasian (57.7° vs. 52.6°, p = 0.007), and than in Asian (57.7° vs. 48.7°, p < 0.001). The linear regression model for the LL as a function of PI were "predict LL = 0.41 × PI + 33.7" in African American, "predict LL = 0.58 × PI + 24.3" in Caucasian, and "predict LL = 0.54 × PI + 22.0" in Asian, respectively. CONCLUSION: Significant differences in sagittal spino-pelvic parameters among races were seen. These differences should be considered when planning surgical reconstruction for spinal surgery. These slides can be retrieved under Electronic Supplementary Material.

Proximal junctional kyphosis in thoracic adolescent idiopathic scoliosis: risk factors and compensatory mechanisms in a multicenter national cohort.

INTRODUCTION: Proximal junctional kyphosis (PJK) is a frequent complication, up to 46%, in adolescent idiopathic scoliosis surgical treatment (AIS). Several risk factors have been evoked but remain controversial. The purpose of this study was to analyze the incidence of PJK in a multicenter cohort of AIS patient and to determine risk factor for PJK. MATERIALS AND METHODS: Lenke I and II AIS patients operated between 2011 and 2015 (minimum of 2-years follow-up) were included. On fullspine X-rays, coronal and sagittal radiographic parameters were measured preoperatively, postoperatively and at final follow-up. Occurrence of radiological PJK corresponding to a 10° increase in the sagittal Cobb angle, measured between the upper instrumented vertebra (UIV) and UIV + 2, between postoperative and 2-years follow-up X-rays, was reported. RESULTS: Among the 365 patients included, 15.6% (n = 57) developed a PJK and only 10 patients required a revision surgery. Preoperatively, PJK patients had significantly larger pelvic incidence (57° ± 13° vs. 51° ± 12°), larger lumbar lordosis (LL) (63° ± 12° vs. 57° ± 11°) and bigger C7 slope. Postoperatively (3 months), in the non-PJK group, thoracic kyphosis (TK) was increased and LL was not significantly different. However, postoperatively, in the PJK group, no significant change was observed in TK, whereas C7 slope decreased and LL significantly increased. There was also a postoperative change in inflection point which was located at a more proximal level in the PJK group. Between postoperative time and final follow-up, TK and LL significantly increased in the PJK group. CONCLUSION: PJK is a frequent complication in thoracic AIS, occurring 16%, but remains often asymptomatic (less than 3% of revisions in the entire cohort). An interesting finding is that patients with high pelvic incidence and consequently large LL and TK were more at risk of PJK. As demonstrated in ASD, one of the causes of PJK might be postoperative posterior imbalance that can be due to increased LL, insufficient TK or inflection point shift during surgery. These slides can be retrieved under Electronic Supplementary Material.

Normal sagittal parameters of global spinal balance in children and adolescents: a prospective study of 646 asymptomatic subjects.

PURPOSE: To document values for parameters of global spinal balance in asymptomatic children and adolescents. METHODS: Multicenter prospective study of normal sagittal global spinal balance in Caucasian children and adolescents. Spinosacral angle (SSA), spinal tilt (ST), and C7 translation ratio were evaluated in 646 asymptomatic children and adolescents (276 males and 370 females). RESULTS: Mean and standard deviation for SSA, ST, and C7 translation ratio were, respectively 132.1° ± 8.3°, 93.2° ± 4.6° and -0.7 ± 8.3. Mean ± 2 standard deviations were, respectively 116°-149° for SSA and 84°-102° for ST. C7 plumbline was behind the HA (hip axis) in 78 % of subjects. Correlations between global balance and age were small (-0.17 ≤ r ≤ 0.19). CONCLUSION: Asymptomatic children and adolescents tend to stand with a stable global balance, and 95 % have an SSA and ST between 116° and 149° and 85°-102°, respectively. C7 plumbline in front of the HA is not necessarily associated with a spinal pathology.

Sacral and pelvic osteotomies for correction of spinal deformities.

INTRODUCTION: Restoring a physiological sagittal spine balance is one of the main goals in spine surgery. Several technics have been described previously, as pedicle subtraction osteotomy. In more complicated cases involving spino-pelvic disorders, three authors proposed sacral osteotomy to restore sagittal balance of the spine. The authors describe the use of pelvic osteotomies for the correction of lumbo-sacral kyphosis, for decreasing pelvic incidence and for achieving sagittal balance correction in cases of lumbo-sacral sagittal deformity as an alternative of pedicle subtraction osteotomies (PSO). MATERIALS AND METHODS: We simulate four types of pelvic osteotomies previously described for hip pathology (Salter, modified Salter, Chiari and posterior sacral osteotomy) on drawing software, and calculate during these osteotomies the variation of pelvic incidence (PI). Then, we compare the behaviour in this simulation to a cadaveric model where we perform the same four pelvic osteotomies. Via X-rays made the study, we calculate also the PI. Then, we analyse 11 patients who underwent pelvic osteotomies for sagittal unbalance, analysing operative and clinical data. RESULTS: We find a mathematical law governing the PI during anterior opening and posterior closing osteotomies (respectively Salter and sacral osteotomy):[Formula: see text]These laws are confirmed in the cadaveric model which retrieves the same behaviour. In the clinical series, Salter osteotomy is easy and efficient on sagittal rebalancing; sacral osteotomy is more powerful. DISCUSSION: The Salter osteotomy is efficient for restoring sagittal balance of the spine. The posterior sacral osteotomy is more powerful but technically demanding. The indications of such special osteotomies are fixed lumbo-sacral kyphosis, especially high-grade spondylolisthesis, previously operated or not. CONCLUSION: A study of a more substantial series would be considered.

Sacral doming progression in developmental spondylolisthesis: a demonstrative case report with two different evolutions.

STUDY DESIGN: Demonstrative case report of two different evolutions in developmental spondylolisthesis. To our knowledge spontaneous sacral doming reconstruction and healing has never been previously reported. METHODS: Presentation of two cases with developmental spondylolisthesis and no sacral dome that had at the beginning a similar presentation and finally evolved in different ways. RESULTS: Initially, both cases were without sacral dome. In the first case, sacral dome appeared and completely healed in presence of a stable elongata pars and stable spondylolisthesis. In the second case, apparition, progression of sacral dome, rolling up of L5 and spondylolisthesis occurred in the presence of lytic defect in the pars. CONCLUSION: Sacral doming is secondary to L5 abnormal position regarding to S1. The mechanism of sacral doming looks like as an osteochondritis phenomena. Loss of support of the sacral plateau by sacral rounding may induce high grade spondylolisthesis.

Pre- and post-operative sagittal balance in idiopathic scoliosis: a comparison over the ages of two cohorts of 132 adolescents and 52 adults.

STUDY DESIGN: Retrospective study of a prospective clinical and radiological database of subjects with adolescent (AIS) and adult (AS) idiopathic scoliosis undergoing surgical correction by posterior approach. OBJECTIVES: To evaluate the differences in sagittal alignment of the spine and pelvis in AIS and AS before surgery and changes after surgery in both populations. The relationship between the spine and pelvis highly influences the sagittal balance in adults and adolescents. However, the sagittal alignment of the spine and pelvis before and after surgery in idiopathic scoliosis, whatever the age, is poorly defined in the literature. METHODS: Clinical and radiological data were extracted from a prospective database of 132 AIS patients and 52 AS before and at last follow-up after surgical correction. Sagittal parameters were evaluated on AP and lateral radiographs using a custom software: pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis (LL), thoracic kyphosis (TK), C7 Barrey's ratio, spino-sacral angle (SSA). A new algorithm of combination of balance parameters was proposed to characterize and compare the various pathological spino-pelvic settings. Based on PI subdivision in high (<55°) and low values (>55°), then on a range of PT indexed on PI giving the pelvis positioning (anteverted, normal or retroverted), the population was finally characterized by the C7 plumbline position with regard to the posterior edge of the sacrum and the center of the femoral heads, in balanced, slightly unbalanced and unbalanced. More specifically, the AIS study included the cervical shape alignment with cervical lordosis (CL) and sagittal thoracic profile assessment (hypo vs. normokyphotic). In AS, the study focused on thoraco-lumbar kyphosis (TLK) occurrence (LL length). Paired Student t tests were used for comparison (α = 0.02). RESULTS: Pre-operatively, in AIS there was a prevalence of lower PI (57 %). Whatever the PI, PT remained anteverted or normal. Positioning of C7 was much more unbalanced, forward of the femoral heads (50 %), than in asymptomatic population (17 %). There was a notable loss and reversal of cervical lordosis in the majority of subjects, with an average cervical kyphosis measurement of 10 ± 18°. Thoracic kyphosis values were lower than average, while lumbar lordosis values were within normal limits. After surgery, in the entire group, a slight but significant increase of PT coupled to a decrease of SS and LL was noted, while no changes could be documented in thoracic kyphosis and cervical lordosis. However, when sub-classified according to thoracic hypo versus normokyphosis pre-op, there was a significant decrease of TK coupled to a decrease of LL and CL in the normokyphotic group, while TK and CL were improved in the hypokyphotic group. A significant number of patients improved their global balance. Changes in sagittal profile between Lenke curve types were minimal. In AS there were significant differences between low and high PI populations. Severity of unbalance increased in high PI population with association of retroverted pelvis and forward unbalance. In lower PI, increasing PT was generally sufficient to balance the patients. The occurrence of TLK was strongly increased in the entire population and became the rule in those with lower PI (76 %). Post-operatively, in those with high PI, PT did not change while global balance improved slightly. The strategy of correction in higher PI was to maintain TLK. In those with low PI, PT improved while C7 did not change. Correction of TLK was obtained in eight cases. CONCLUSIONS: A decrease of cervical lordosis and thoracic kyphosis is commonly associated with AIS. The anterior unbalance frequently found in AIS does not seem to have the same significance of severity as in AS. In AIS PI does not change the balance criterions, while in AS the severity of unbalance is increased with higher PI. TLK seems to be a way of worsening the balance in elderly, mainly in lumbar and thoraco-lumbar scoliosis with low PI. Surgical correction of the thoracic and lumbar spine in AIS induces significant changes in the sagittal spino-pelvic profile. Changes in the cervical sagittal profile vary according to the pre-op sagittal profile of the thoracic kyphosis. Cervical lordosis and thoracic kyphosis are improved by surgical correction in subjects with pre-operative hypokyphosis, but a reverse effect is noted in those with normal pre-operative kyphosis. The clinical significance of these changes in sagittal shape remains to be determined. In AS, it appears easier to restore a good balance in the lower PI population than in those with less pre-operative unbalance.

Analysis of the cervical spine sagittal alignment in young idiopathic scoliosis: a morphological classification of 120 cases.

PURPOSE: To analyze the relationship between the cervical spine and global spinal-pelvic alignment in young patients with idiopathic scoliosis based on a morphological classification, and to postulate the hypothesis that cervical kyphosis is a part of cervico-thoracic kyphosis in them. METHODS: 120 young patients with idiopathic scoliosis were recruited retrospectively between 2006 and 2011. The following values were measured and calculated: cervical angles (CA), cervico-thoracic angles (CTA), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), spinal sacral angle (SSA), hip to C7/hip to sacrum, thoracic kyphosis (TK), lumbar lordosis (LL), Roussouly sagittal classification, Lenke Type Curve and Lumbar Modifier. The cervical curves were classified as lordosis, straight, sigmoid and kyphosis. They were categorized into four groups as cervical non-kyphosis group (CNK Group), cervical kyphosis group (CK Group), cervical-middle-thoracic kyphosis group (CMTK Group), and cervical-lower-thoracic kyphosis group (CLTK Group) according to their morphological characters of sagittal alignments. All parameters were compared and analyzed among groups. RESULTS: The incidence of cervical kyphosis was 40 % (48/120). The CA and the CTA were in significant correlation (r = 0.854, P = 0.00). The cervical spine alignments were revealed to be significantly different among groups (r = 85.04, P = 0.00). Significant differences among groups in CA, CTA and TK were also detected. A strong correlation between the group type and Lenke Lumbar Modifier was still seen (P < 0.05). Fisher's exact test revealed that the individual vertebral body kyphosis and wedging were directly related to the overall cervical kyphosis (P = 0.00, respectively). CONCLUSION: The cervical kyphosis is correlated with global sagittal alignment, and is a part of cervico-thoracic sagittal deformity in young patients with idiopathic scoliosis. Despite the deformity in cervical alignment, the global spine could still be well-balanced with spontaneous adjustment. The correlation between our grouping based on the morphological characteristics of the sagittal alignments and Lenke Lumbar Modifier suggests that the coupled motion principle be appropriate to explain the modifications both in coronal and sagittal planes.

Compensatory mechanisms contributing to keep the sagittal balance of the spine.

INTRODUCTION: Aging spine is characterized by facet joints arthritis, degenerative disc disease, bone remodeling and atrophy of extensor muscles resulting in a progressive kyphosis of the lumbar spine. OBJECTIVE: The aim of this paper is to describe the different compensatory mechanisms for patients with severe degenerative lumbar spine. MATERIAL AND METHODS: According to the severity of the imbalance, three stages are observed: balanced, balanced with compensatory mechanisms and imbalanced. For the two last stages, the compensatory mechanisms permit to limit the consequences of loss of lumbar lordosis on global sagittal alignment and therefore contribute to keep the sagittal balance of the spine. RESULTS: The basic concept is to extend adjacent segments of the kyphotic spine allowing for compensation of the sagittal unbalance but potentially inducing adverse effects. CONCLUSION: Finally, we propose a three-step algorithm to analyze the global balance status and take into consideration the presence of the compensatory mechanisms in the spinal, pelvic and lower limb areas.

Early Revision Surgery for Distal Adding-On Correction in Lenke 1 and 2 Adolescent Idiopathic Scoliosis.

Objective To evaluate the outcome of an early revision strategy for postoperative distal adding-on (DAO) after Lenke 1 and 2 adolescent idiopathic scoliosis (AIS) surgery. Summary of background data Improper choice of the lowest instrumented vertebra (LIV) is a major cause of postoperative imbalance and unsatisfactory results in AIS surgery. The long-term consequences of such imbalance remain unclear. Early corrective surgery has not been described. Methods We retrieved the records of operated AIS patients at the former institution of the senior author. There were 18 cases of early revision by one-level distal extension of instrumentation and fusion. Patients were reoperated based on progressive distal local imbalance and clinical lumbar asymmetry. Several local and global balance parameters were compared on serial long-standing radiographs before and after the index surgery, before and after the revision surgery, and at the last follow-up. The Kruskal-Wallis test was used for the comparison of the results. A value of p<0.05 was considered significant. Results All patients were female with a mean age of 13.9 years. The mean delay between the two surgeries was 8.4 months and the last follow-up was at 32.5 months after the revision surgery. Unsatisfactory results after the index surgery were reflected by a progressive increase in disc angulation below the lowest instrumented vertebra (LIV) and an increased tilt and rotation of the LIV+1. The clinical lumbar shift was also accentuated from 19 mm to 25 mm. Revision surgery significantly reduced local and global balance parameters. There was a decrease in the LIV translation (from 26 mm to 19 mm) and of the wedging below it (from 7.9° to 1.3°) and a better positioning of the LIV+1 with less tilt (from 14.6° to 3.6°), translation (from 22.2 mm to 13.8 mm) and rotation (from 20° to 15°). The clinical lumbar shift was reduced from 25 mm to 3.6 mm. Global coronal and sagittal balance were also ameliorated. All results were maintained at a mean follow-up of 32.5 months from the revision surgery. No complications were noted and there was no need for a blood transfusion. Conclusion The revision surgery proposed in this paper is simple with low morbidity and may be considered as a fine-tuning of the failed index surgery. Further studies are needed to evaluate the long-term consequences of treated and untreated postoperative distal adding-on in AIS surgery.