Hyper-Selective Posterior Fusion is Recommended When the Modified S-Line is Positive in Lenke 5C Adolescent Idiopathic Scoliosis.

OBJECTIVE: Postoperative coronal decompensation and less fusion level are dilemmas and the proper selective posterior fusion (SPF) strategy should be investigated. We proposed a parameter, modified S-line, and aimed to investigate if the modified S-line could predict postoperative coronal decompensation in patients with Lenke 5C adolescent idiopathic scoliosis (AIS). METHODS: This is a retrospective radiographic study and Lenke 5C AIS patients undergoing SPF during the period from September 2017 to June 2021 were included. The modified S-line was defined as the line linking the centers of the concave-side pedicles of the upper end vertebra (UEV) and lower end vertebra (LEV) at baseline. A modified S-line tilt to the right is established as modified S-line+ (UEV being to the right of the LEV). The patients were further categorized into two groups: the Cobb to Cobb fusion group and the Cobb-1 to Cobb fusion group. Outcomes including thoracic Cobb angle, TL/L Cobb angle, coronal balance, upper instrumented vertebra (UIV) translation, lower instrumented vertebra (LIV) translation, UIV tilt, LIV tilt, LIV disc angle, thoracic apical vertebral translation, lumbar apical vertebral translation (L-AVT), L-T AVT ratio, L-T Cobb were measured at baseline, immediately after surgery, and the last follow-up. Radiographic parameters and the incidence of both proximal and distal decompensation between the two groups were compared by chi-square test. RESULTS: Among 92 patients, 48 were modified S-line+ and 44 were modified S-line-. Modified S-line+ status was identified as a risk factor for postoperative proximal decompensation (p = 0.005) during follow-up. In Cobb to Cobb group, a higher occurrence of proximal decompensation in individuals with modified S-line+ status (p = 0.001) was confirmed. Also, in the Cobb to Cobb group with baseline modified S-line+ status, patients presenting decompensation showed a significantly larger baseline of the UIV tilt and postoperative disc angle below the lower instrumented vertebra. However, In Cobb-1 group, the incidence of decompensation after surgery showed no association with baseline modified S-line tilt status (p = 0.815 and 0.540, respectively). CONCLUSION: The modified S-line could serve as an important parameter in surgical decision-making for Lenke 5C AIS patients. Cobb to Cobb SPF is not recommended with a modified S-line+ status, and the Cobb-1 to Cobb fusion may serve as a potential alternative.

Distance between the C2 vertical line and the femoral heads: a quasi-invariant global sagittal alignment parameter in both standing and sitting positions for asymptomatic adults.

Background: This study aimed to investigate whether the distance between the C2 vertical line and the femoral heads (C2-FH) is quasi-invariant for the sitting position. Methods: A cross-sectional, prospective study was conducted. A cohort of 59 asymptomatic volunteers was prospectively recruited between February 1, 2020, and February 31, 2020, at Nanjing Drum Tower Hospital of Nanjing University Medical School. The following radiographical parameters were evaluated: T4-T12 thoracic kyphosis (TK), cervical lordosis (CL), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), sagittal vertical axis (SVA), T1-pelvic angle (TPA), and the C2-FH. The inclusion criteria were as follows: age between 18 and 35 years and no symptoms related to neck or back pain. The exclusion criteria were as follows: a history of any prior lower extremity or spine surgery; and a history of inflammatory arthritis, neuromuscular disorders, or congenital anomalies. Individuals were divided into the following 3 groups according to the percentile of ΔPT (PT difference between standing position and sitting position): group A (1-25% ΔPT, n=14), group B (25-75% ΔPT, n=30), and group C (75-100% ΔPT, n=15). Summary statistics calculated using analysis of variance (ANOVA) were used to provide 95% confidence intervals for measurement errors. The significance level of all statistical analyses was set as P < 0.05. Results: There was no significant difference in any of the parameters among the 3 groups in the standing position. In the sitting position, for different degrees of pelvic retroversion, there were significant differences between the 3 groups in the other parameters except for C2-FH (P=0.80; 95% CI: -20.486 to -3.893), CL (P=0.47; 95% CI: -5.645 to 4.964), TK (P=0.54; 95% CI: 17.058-25.1), and PI (P=0.44; 95% CI: 40.747-49.087). Surprisingly, C2-FH changed slightly among the 3 groups in both the standing (P=0.87) and sitting (P=0.80) positions. As ΔPT gradually increased, ΔSS, ΔLL, ΔSVA, ΔL1-L4, ΔL4-S1, ΔTPA, ΔPT/PI, and ΔPI-LL showed corresponding gradual changes (all P values <0.05). However, there was no significant difference in PI (P=0.39), CL (P=0.46), C2-FH (P=0.51), or TK (P=0.51). Conclusion: C2-FH is a quasi-invariant parameter in both the standing and sitting positions for asymptomatic adults. The mean value of C2-FH was -11.95 mm in the standing position and -1.01 mm in the sitting position. Stable C2-FH could serve as a reference during the surgical decision-making process in adult patients with spinal deformity and sagittal malalignment.

Microtubule stabilization promotes the synthesis of type 2 collagen in nucleus pulposus cell by activating hippo-yap pathway.

Intervertebral disc degeneration (IDD) is the cardinal pathological mechanism that underlies low back pain. Mechanical stress of the intervertebral disc may result in a change in nucleus pulposus cells state, matrix degradation, and degeneration of the disc. Microtubules, which are components of the cytoskeleton, are involved in driving or regulating signal pathways, which sense and transmit mechano-transduction. Microtubule and the related proteins play an important role in the development of many diseases, while little is known about the role of microtubules in nucleus pulposus cells. Researchers have found that type II collagen (COL2) expression is promoted by microtubule stabilization in synovial mesenchymal stem cells. In this study, we demonstrated that microtubule stabilization promotes the expression of COL2 in nucleus pulposus cells. Stabilized microtubules stimulating Hippo signaling pathway, inhibiting YAP protein expression and activity. In addition, microtubules stabilization promotes the expression of COL2 and alleviates disc degeneration in rats. In summary, our study for the first time, identifies microtubule as a promising therapeutic target for IDD, up-regulating the synthesis of COL2 via Hippo-Yap pathway. Our findings may provide new insights into the etiologies and pathology for IDD, further, targeting of microtubule acetylation may be an effective strategy for the treatment of IDD.

Remodeling morphology of the subluxated osteotomy vertebra in closing-opening wedge osteotomy in ankylosing spondylitis: would the anterior bony beak blunt?

INTRODUCTION: To investigate the remodeling morphology of subluxated osteotomy vertebra in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis after single-level closing-opening wedge osteotomy (COWO). MATERIALS AND METHODS: Standing lateral radiographs were taken to evaluate sagittal parameters including lumbar lordosis (LL), C7 sagittal vertical axis (SVA), global kyphosis (GK), sacral slope (SS), and pelvic tilt (PT). Radiographic parameters of the osteotomy vertebra included osteotomized vertebra angle (OVA), sagittal translation (ST), anterior height (AH), posterior height (PH), and middle height (MH) of the osteotomy vertebrae. Furthermore, lateral projection area of the vertebral body was also measured to evaluate the remodeling of the osteotomy vertebrae. RESULTS: Sixty AS patients who underwent single-level lumbar COWO with a minimal 2-year follow-up were included. The cohort consisted of 54 males and 6 females with an average age of 36.6 years. All patients were divided into two groups according to the development of vertebral subluxation (VS): 15 in VS group (ST ≥ 5 mm), 45 in non-VS group (ST < 5 mm). There was significant difference in the correction of GK, SVA, and the loss of correction of SVA between AS patients with and without VS. Significant difference in vertebra-related parameters regarding AH and OVA was found between VS group and non-VS group (P < 0.05). CONCLUSIONS: After COWO, new bone formation narrowing the gap and adaptive resorption of the anterior bony beak at the osteotomy level during follow-up was surprisingly favorable. However, the ability of spinal canal remodeling is limited in patients complicated with VS.

Proximal junctional kyphosis is a compensation for post-operative negative C2-FH in ASD patients: a cross-sectional study.

BACKGROUND: Recent studies have found that C2-FH is close to 0 cm in both standing and sitting position for asymptomatic adults. We hypothesize that the thoracic spine may compensate with PJK when the immediate post-operative C2-FH was not ideally restored in adult spinal deformity (ASD). METHODS: The inclusion criteria were as follows: ASD patients over 45 years old; Cobb angle > 30°; with posterior spinal correction surgery; at least 2 years follow-up. C2-FH was defined as the distance between the femoral heads to the C2 vertical line. All participants were divided into two groups according to the occurrence of PJK at the last follow-up: PJK group and non-PJK group. RESULTS: 68 ASD patients, with a minimum follow-up of 2.5 years, were included. PJK was found in 24 patients (35.3%) while the rest 44 patients remained no sagittal malalignment. Immediately post-operative C2-FH showed significant difference between PJK group and non-PJK group (p = 0.015). However, at the last follow-up, C2-FH showed no significant difference between PJK and non-PJK group and the mean value of C2-FH in both groups was approximately - 1 cm, indicating that ASD patients could develop various compensatory mechanisms to maintain sagittal global balance. The AUC was 0.84 (95%CI 0.68-0.97), indicating the well effectiveness of ROC curve and cut-off value in predicting occurrence of PJK in ASD patients. Based on the ROC curve, the optimal cut-off value of C2-FH as indicators for occurrence of PJK was - 42.3 mm. CONCLUSION: Immediate postoperative negative global malalignment (C2-FH < - 42.3 mm) may predict proximal junctional kyphosis in ASD patients. The normal value of C2-FH, - 1 cm, may be the target of global sagittal compensation, and PJK is a compensatory mechanism. TRIAL REGISTRATION: 2021-LCYJ-DBZ-05, 2021.07, Retrospective study.

Radiographic study of peak velocity of pelvic incidence in adolescent idiopathic scoliosis.

BACKGROUND: Pelvic incidence (PI), a parameter related to the ideal spinopelvic alignment, is a morphological parameter that is usually considered fixed, but the PI's growth during adolescence has been reported. We investigated the peak PI velocity during adolescence and describe the relationship between increasing PI and changes in the morphology of the pelvis and sacrum. METHODS: We measured standing height (SH) and radiological anatomical parameters including pelvic height (PH), pelvic width (PW), sacral width (SW), femoral head-sacrum (FH-S), sacrum-coccyx (S-C) length, and S-C distance at each follow-up of 76 adolescent idiopathic scoliosis (AIS) patients. ΔParameter was the difference between the next measurement and the previous one. Growth velocity was ΔParameter divided by time interval. All ΔParameters were compared between different Risser stages using repeated-measures analysis of variance (ANOVA). The Pearson coefficients of correlation were calculated to assess the relationships between PI and ΔParameters. RESULTS: PI reached peak growth with a 1.6°/year growth in females and 1.8°/year in males at Risser stage 1. PI tended to grow rapidly with Risser 0 and closed triradiate cartilage (female: 1.3°/year and male: 1.4°/year) and to slow down at Risser 2 (female: 1.2°/year and male: 1.3°/year). ΔPI strongly correlated with ΔFH-S (R>0.508, P<0.05) and also correlated with ΔSH, ΔPH, ΔPW, ΔSW, and ΔS-C length (R>0.192, P<0.05) but not correlated with ΔS-C distance and ΔS-C ratio. CONCLUSIONS: In patients with AIS, the peak PI velocity is at Risser 1, and it is still increasing at Risser 5. Our result suggested that the growth of the PI may be associated with SH and changing pelvic morphology during skeletal growth of adolescence.

Risk factors for postoperative coronal decompensation in adult lumbar scoliosis after posterior correction with osteotomy.

INTRODUCTION: To determine potential risk factors for postoperative coronal imbalance following posterior osteotomy for adult scoliosis. MATERIALS AND METHODS: A total of 74 patients underwent osteotomy for rigid adult lumbar scoliosis. A group of 20 patients with postoperative coronal imbalance was identified. Clinical data and surgical strategies were compared to determine the risk factors, including age, gender, etiology, Cobb angle, preoperative coronal balance distance, direction of preoperative imbalance, T1 tilt, tilt of upper instrumented vertebra (UIV), UIV translation, location of UIV (T6 above or below), fusion to L5 or S1, lower instrumented vertebra (LIV) tilt, LIV rotation, screw density, osteotomy procedure (PSO or SPOs) and use of iliac screws. RESULTS: Comparison between patients with and without postoperative coronal imbalance showed that postoperative coronal imbalance occurred in older patients and those with degenerative scoliosis as the etiology, UIV above T6, preoperative LIV rotation, preoperative LIV tilt and preoperative coronal imbalance towards the convex side and who underwent Smith-Petersen osteotomy. All seven parameters were included in the logistic regression analysis. UIV above T6 (P = 0.010), LIV rotation (P = 0.012) and preoperative coronal imbalance towards the convex side (P = 0.005) were identified as risk factors for postoperative coronal imbalance after osteotomy. CONCLUSIONS: Patients with preoperative coronal imbalance towards the convex side (UIV above T6) and LIV rotation were more likely to develop coronal imbalance than those without risk factors. Older patients and those with degenerative scoliosis were also at a relatively higher risk of postoperative coronal imbalance.

Sacral Agenesis: A Neglected Deformity That Increases the Incidence of Postoperative Coronal Imbalance in Congenital Lumbosacral Deformities.

STUDY DESIGN: A retrospective study. OBJECTIVES: To identify if there is a link between sacral agenesis (SA) and post-operative coronal imbalance in patients with congenital lumbosacral deformities. METHODS: This study reviewed a consecutive series of patients with congenital lumbosacral deformities. They had a minimum follow-up of 2 years. According to different diagnosis, they were divided into SA and non-SA group. Comparison analysis was performed between patients with and without post-operative coronal imbalance and risk factors were identified. RESULTS: A total of 45 patients (18 in SA group and 27 in non-SA group) were recruited into this study, among whom 33 patients maintained coronal balance while 12 demonstrated postoperative coronal imbalance at last follow-up (14.32 ± 7.67 mm vs 35.53 ± 3.91 mm, P < 0.001). Univariate analysis showed that preoperative lumbar Cobb angle, immediate postoperative coronal balance distance and diagnosis of SA were significantly different between patients with and without post-operative coronal imbalance (P < 0.05). Binary logistic regression analysis showed that SA was an independent risk factor for postoperative coronal imbalance. CONCLUSIONS: As an independent risk factor for postoperative coronal imbalance, high level of suspicion of SA should be aware in children with congenital lumbosacral deformities. Sufficient bone grafts at sacroiliac joint are recommended for SA patients to prevent postoperative coronal imbalance.

Brace treatment for scoliosis secondary to chiari malformation type 1 or syringomyelia without neurosurgical intervention: A matched comparison with idiopathic scoliosis.

PURPOSE: To evaluate the effectiveness of brace treatment in patients with Chiari malformation type 1 (CM-1) or syringomyelia associated scoliosis without neurosurgical intervention. METHODS: This was a retrospective case-control study. 34 CM-1 or syringomyelia (CMS) patients who received brace treatment without neurosurgical intervention were recruited. Another 68 matched patients with idiopathic scoliosis who received bracing served as the control group. The matching criteria included gender, age (± 1 years), Risser sign (± 1 grade), initial curve magnitude (± 5°), curve patterns and follow-up time (± 6 months). Patients who encountered curve progression and scoliosis surgery were compared between different groups. RESULTS: Until the last visit, 16 (47%) patients in CMS group and 18 (26%) patients in IS group occurred curve progression; 9 (26%) patients and 15 (22%) patients underwent scoliosis surgery, respectively. Compared to idiopathic scoliosis, patients with CMS-associated scoliosis had a significantly higher rate of curve progression (P = 0.038). However, no significant difference was observed between two groups regarding to the rate of surgery (P = 0.867). Patients with combined CM-1 and syringomyelia had a higher rate of surgery than patients with isolated CM-1 or syringomyelia (P = 0.049). The double major curve pattern was identified as the risk factor for curve progression. CONCLUSION: Brace treatment is effective for CMS-associated scoliosis without neurosurgical intervention. Compared to idiopathic scoliosis, brace can provide similar prevention for scoliosis surgery in CMS patients, but slight or moderate curve progression may occur. Specifically, patients with combined CM-1 and syringomyelia should be followed closely with a higher expectation of curve progression.

Optimizing the fusion level for lenke 5C adolescent idiopathic scoliosis: is the S-line a validated and reproducible tool to predict coronal decompensation?

PURPOSE: To validate the predictability of S-line in Lenke 5C patients. METHODS: Lenke 5C patients with a minimum 2-year follow-up and with the lowest instrumented vertebra (LIV) at lower end vertebra were included. The S-line was defined as a line connecting the centers of concave-side pedicles of upper instrumented vertebra (UIV) and LIV on baseline films. The S-line tilt to right was defined as positive S-line status (S-line +) and tilt to left as S-line - status. Statistical analysis was performed between different subgroups. RESULTS: Among the 92 patients, 69 patients had a left lumbar curve and 23 patients had a right lumbar curve. For left curves, the S-line + status had a significantly higher incidence of both proximal and distal decompensation. However, for right curves, the S-line - status was the risk factor. Thus, we modified the definition of S-line: The value of S-line tilt for right curves was opposite to that for left curves. Patients with modified S-line + showed a significantly higher incidence of both proximal and distal decompensation in Lenke 5C patients with both left and right curves (p < 0.001 and p = 0.010). In UEV group, patients with modified S-line + showed significantly higher incidence of proximal decompensation (P = 0.001). However, in UEV-1 group, the incidence of proximal decompensation was not statistically affected by modified S-line + (P = 0.281). CONCLUSION: Modified S-line + is a validated risk factor that predisposed to post-operative coronal decompensation in Lenke 5C AIS patients. Selecting UIV at one level caudal to UEV could be a possible solution if the modified S-line was positive.

Different distal fixation anchors in lumbosacral spinal deformities associated with sacral agenesis: which one is better?

OBJECTIVE: Sacral agenesis (SA) is a rare congenital malformation of the spine. There has been a paucity of clinical research to investigate the surgical outcome of spinopelvic fixation in these patients. In this study, the authors aimed to evaluate the outcome of different distal fixation anchors in lumbosacral spinal deformities associated with SA and to determine the optimal distal fixation anchor. METHODS: Patients with diagnoses of SA and lumbosacral scoliosis undergoing spinopelvic fixation with S1 screws, iliac screws, or S2-alar-iliac (S2AI) screws were analyzed. The main curve, coronal balance distance, and pelvic obliquity were compared at baseline, postoperatively, and during follow-up in three groups. The complications were also recorded. RESULTS: A total of 24 patients were included: 8 patients were stratified into group 1 (S1 screws), 9 into group 2 (iliac screws), and 7 into group 3 (S2AI screws). The main curves were well corrected postoperatively (p < 0.05) in all groups. Coronal balance showed a tendency of deterioration during follow-up in patients with S1 screws (from 18.8 mm to 27.0 mm). Regarding pelvic obliquity, patients with both iliac and S2AI screws showed significant correction (from 3.7° to 2.3° and from 3.3° to 1.6°). Implant-related complications were rod breakage in 3 patients and infection in 1 patient in group 2, and no implant-related complications were observed in group 3. There were 3 cases of unilateral S1 pedicle screw misplacement in group 1. CONCLUSIONS: Spinopelvic fixation is a safe and effective procedure that can achieve coronal correction in lumbosacral scoliosis associated with SA. Compared with S1 and iliac screws, S2AI screws as distal fixation anchors can achieve a more satisfactory correction with fewer implant-related complications.

Fractional Curve in Adult Spinal Deformity: Is it a Driver of or a Compensation for Coronal Malalignment?

STUDY DESIGN: This was a retrospective review of the multicenter adult spine deformity database. OBJECTIVE: The objective of this study was to investigate the role of the fractional curve (FC) on global coronal malalignment. SUMMARY OF BACKGROUND DATA: Despite being very common, the role of the coronal FC as either a driver or compensation for global coronal malalignment is not well documented. MATERIALS AND METHODS: Patients with the following characteristics were extracted from a prospective multicenter database: lumbar/thoracolumbar (TL) major coronal curve >15 degrees, apex at T11-L3, lower end vertebra at L3 or L4, above 45 years old, and FC >5 degrees. In addition to the classic radiographic parameters, baseline analysis included Cobb angle, pelvic obliquity (PO), fractional ratio (fractional Cobb/main Cobb), the sum of PO and FC, as well as the coronal Qiu classification. Curves distribution (TL vs. FC) were compared across the 3 Qui types, and the role of the FC was investigated. RESULTS: A total of 404 patients (63 y old, 83.3% female) were included: 43 patients were classified as type B, 120 as type C, and 241 were coronally balanced (type A). Compared with the balanced patients, type C patients had similar major TL Cobb angles but significantly larger fractional Cobb angles (17.5 vs. 22.3 degrees, P<0.001). By opposition, type B patients had significantly larger major TL Cobb angles (49 vs. 41 degrees, P=0.001) but smaller fractional Cobb angles (P<0.001). PO>5 degrees in the same direction as FC was more common in type B patients (20%) than in type C patients (7.5%), which suggests the preferential role of pelvic compensation. CONCLUSIONS: Our findings challenge the idea that FC is only a compensatory curve below a main lumbar or TL curve. In type B patients, FC acts as a compensation mechanism but fails to maintain coronal alignment despite the presence of PO. In type C patients, however, the lumbosacral FC acts as a primary driver of coronal malalignment. LEVEL OF EVIDENCE: Level III.

Position-related Change of Pelvic Incidence Depends on the Nonfused Sacroiliac Joint in Patients with Degenerative Spinal Diseases.

STUDY DESIGN: A retrospective cross-sectional study. OBJECTIVE: This study aims to determine whether the sacroiliac (SI) joint motion correlated to pelvic incidence (PI) change from standing to supine position in patients with degenerative spinal diseases. SUMMARY OF BACKGROUND DATA: PI was found an unstable parameter after adolescence as the fixed nature of PI was challenged by several studies. The SI joint has been shown to have some motion, age-related degenerative changes of cartilage and SI ligaments contribute to SI joint instability. METHODS: The study contains both specimen study and radiographic study. One human specimen was acquired, on which PI was measured with different sacrum-ilium positions. In radiographic study, patients with old thoracolumbar fracture, lumbar disc herniation, stenosis, and spondylolisthesis were included. Ankylosing spondylitis (AS) patients were also included as control group. PI was measured on standing x-rays and scanogram of computed tomography images in supine position. RESULTS: Specimen study result revealed that SI motion would lead to the change of PI with fixed pelvic thickness. In radiographic study, 101 patients with different etiology and 30 AS patients were included. After stratifying into different age groups, standing PI was significantly larger than supine PI in each age groups (P = 0.002, <0.001, and <0.001, respectively). In patients with degenerative diseases, PI was significantly larger on standing position than that on supine position. ΔPI showed no significant difference across etiologies. However, in AS patients, standing PI and supine PI revealed no significant difference (P = 0.528). CONCLUSION: Mobile SI joint may be the cause of increased PI in the aging spine. The dynamic change of PI is etiology-independent if the SI joint was not fused. Older patients have greater position-related change of PI.Level of Evidence: 4.

Quality of Life During Pregnancy, Caesarean Section Rate, and Anesthesia in Women with a History of Anterior Correction Surgery for Lumbar Scoliosis: A Case-Control Study.

BACKGROUND This study investigated the prevalence and severity of low back pain (LBP), caesarean section (C-section) rate, and the anesthesia approaches among lumbar scoliosis patients undergoing anterior correction surgery, and compared them with a healthy control cohort. MATERIAL AND METHODS The inclusion criteria for adolescent idiopathic scoliosis (AIS) patients were: presence of lumbar scoliosis, history of 1 or more pregnancies after surgery, and underwent anterior-only surgery. Healthy women with a history of 1 pregnancy were included as the control group. We recorded the type of delivery, neonatal birth weight, and perinatal complications. The quality of life was also evaluated. RESULTS New-onset LBP was reported in 65.6% of AIS patients, significantly higher than in the control group (p<0.001). C-section was performed in 11 scoliosis patients (34.4%) and 25 healthy controls (31.25%), and the rates were not significantly different between groups (P=0.75). No serious perinatal complications were reported in either group. General anesthesia was used for all C-section AIS patients. The rate of successful neuraxial anesthesia in the control group was significantly higher (P<0.001). CONCLUSIONS Compared with the healthy control group, lumbar AIS patients did not experience a higher risk of perinatal complications or C-section rate after anterior surgical correction, but general anesthesia was more commonly used than neuraxial regional anesthesia. LBP was more frequently observed in the post-operative AIS patients.

An analysis of the interactions between the spine, pelvis, and lower limbs in asymptomatic adults with limited pelvic compensation.

BACKGROUND: The interactions between the spine, pelvis, and lower limbs are dynamic based on the "cone of economy" concept; thus, different global radiographic parameters could be regarded as reflections of different centers of gravity. We conducted this retrospective study to evaluate the offsets of different centers of gravity in asymptomatic populations and to investigate how the global sagittal alignment is supported. METHODS: The following parameters were measured: cervical lordosis, thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), the ratio between PT and PI (PT/PI), sacral slope, PI minus LL (PI-LL), the sagittal vertical axis (SVA), cranial SVA to ankle center (Cr-A), CrSVA to the femoral head center (Cr-FH), C2SVA to the femoral head center (C2-FH), pelvic translation (P. Shift), and knee angle (KA). Participants were divided into subgroups based on the PT/PI ratio. Mean values were compared using the t-test, and correlations were assessed using Pearson's coefficient. RESULTS: A total of 82 asymptomatic adults were enrolled. The average PT/PI in subgroup 1 was the smallest, showing that individuals in this group may have limited pelvic retroversion. No significant differences in Cr-FH, Cr-A, or C2-FH were found between subgroups (all P>0.1), implying that global alignment was well supported in each group. Specifically, C2-FH showed minor changes between subgroups (P=0.998), showing that C2-FH may be a target for sagittal compensation. There were positive correlations between PT/PI and both P. Shift and SVA (r=0.930 and r=0.606, respectively). However, Cr-FH, Cr-A, and C2-FH were not significantly correlated with P. Shift or PT/PI (all P>0.05). Weak correlations existed between Cr-A, Cr-FH, and age (all P>0.2). CONCLUSIONS: This study revealed that the Cr-FH and C2-FH offsets are stable across the population and could be maintained by regulating only the sagittal spinal curvature when pelvic compensation is limited. Cr-FH is not affected by age in the asymptomatic population. Thus, the stable Cr-FH and C2-FH could provide references for surgeons during the surgical decision-making process in patients with adult spinal deformity with sagittal malalignment.

Spino-femoral muscles affect sagittal alignment and compensatory recruitment: a new look into soft tissues in adult spinal deformity.

OBJECTIVE: To quantify muscle characteristics (volumes and fat infiltration) and identify their relationship to sagittal malalignment and compensatory mechanism recruitment. METHODS: Female adult spinal deformity patients underwent T1-weighted MRI with a 2-point Dixon protocol from the proximal tibia up to the T12 vertebra. 3D reconstructions of 17 muscles, including extensors and flexors of spine, hip and knee, were obtained. Muscle volume standardized by bone volume and percentage of fat infiltration (Pfat) were calculated. Correlations and regressions were performed. RESULTS: A total of 22 patients were included. Significant correlations were observed between sagittal alignment and muscle parameters. Fat infiltration of the hip and knee flexors and extensors correlated with larger C7-S1 SVA. Smaller spinal flexor/extensor volumes correlated with greater PI-LL mismatch (r = - 0.45 and - 0.51). Linear regression identified volume of biceps femoris as only predictor for PT (R2 = 0.34, p = 0.005) and Pfat of gluteus minimus as only predictor for SVA (R2 = 0.45, p = 0.001). Sagittally malaligned patients with larger PT (26.8° vs. 17.2°) had significantly smaller volume and larger Pfat of gluteus medius, gluteus minimus and biceps femoris, but similar values for gluteus maximus, the hip extensor. CONCLUSION: This study is the first to quantify the relationship between degeneration of spino-femoral muscles and sagittal malalignment. This pathoanatomical study identifies the close relationship between gluteal, hamstring muscles and PT, SVA, which deepens our understanding of the underlying etiology that contributes to adult spinal deformity.

Skeletal growth velocity of adolescent idiopathic scoliosis: abnormal in spine but normal in lower limbs.

BACKGROUND: Abnormal spinal overgrowth has been identified in patients with adolescent idiopathic scoliosis (AIS), which may be attributed to a secondary change. However, growth velocity in adolescents with different maturity statuses, and the final length of the lower extremities were not investigated in patients with AIS. Here, we compared the peak height velocity (PHV) time point of the lower limbs between AIS and healthy adolescents and analyzed whether abnormal growth of the lower limbs exists in patients with AIS. METHODS: Female AIS patients with a thoracic Cobb angle of 20° to 60° were enrolled in the current study. The major Cobb angle, length of the spine (LOS), length of the lower limbs (LLL), and height of the pelvis (HOP) were measured. In addition, RatioSL was defined as LOS/LLL; RatioSP was defined as LOS/HOP; and RatioPL was defined as HOP/LLL. All patients and healthy controls were classified into three groups according to skeleton maturity status: pre-PHV, defined as Risser 0, and open triradiate cartilage (TC); during-PHV (Risser 0, and closed TC); and post-PHV (Risser ranging from 1 to 5). RESULTS: RatioSL and RatioSP were significantly higher in scoliosis patients at Risser ≥4 compared to healthy controls (all, P<0.05). However, RatioPL was similar between patients with AIS and healthy controls in both the Risser 0 and Risser ≥4 groups. The change in ratio from pre-PHV to post-PHV showed similar trends between patients with AIS and healthy controls; both RatioSL and RatioPL were significantly lower in the during-PHV group (all, P<0.05). CONCLUSIONS: The final length of the lower extremities was similar between groups, while the peak growth of the lower extremities was earlier than that of pelvis and spine in both patients with AIS and healthy adolescents, indicating that lower limb growth pattern was not altered in AIS patients.

Hyper-Selective Posterior Fusion in Lenke 5C Adolescent Idiopathic Scoliosis: When Can We Stop Below the Upper End Vertebra?

STUDY DESIGN: A prospective analysis. OBJECTIVE: To investigate whether the hyper-selective posterior fusion (upper instrumented vertebra [UIV] as the vertebra one level below the upper end vertebra [UEV], lower instrumented vertebra [LIV] as the lower end vertebra [LEV]) was applicable in posterior fusion of Lenke 5C adolescent idiopathic scoliosis (AIS) patients and what could be the indication of hyper-selective fusion. SUMMARY OF BACKGROUND DATA: The improper UIV selection in selective fusion could lead to progressive thoracic compensatory curve, shoulder imbalance, and even coronal imbalance. However, few studies analyzed the clinical outcome of hyper-selective fusion. METHODS: A prospective analysis of 80 patients with Lenke 5C AIS who underwent selective fusion was performed. According to the relationship between UEV and UIV, the patients were divided into UEV group (UIV = UEV) and UEV-1 group (UIV = UEV-1). Radiographic parameters and the incidence of postoperative proximal decompensation were compared. The Scoliosis Research Society (SRS)-22 scores were used to evaluate clinical outcomes between two groups. RESULTS: Thirteen patients (27%) in UEV group and six (18.75%) in UEV-1 group showed proximal decompensation during follow-up, and the incidence was equivalent (P = 0.280). Within the UEV-1 group, the patients with proximal decompensation showed similar Risser grade, baseline thoracic Cobb angle, and main Cobb angle (P = 0.611, 0.435, 0.708, respectively). However, the baseline L-T apical vertebral translation (AVT) ratio was significantly larger in patients with proximal decompensation (P = 0.028). Meanwhile, patients with proximal decompensation in UEV group showed significantly smaller preoperative UIV translation and lumbar AVT but similar postoperative UIV tilt. CONCLUSION: Hyper-selective posterior fusion strategy could be performed in Lenke 5C patients with Risser more than grade 2 and with thoracic compensatory curve over 15°. The UIV in patients with small baseline thoracic curve, represented by larger baseline lumbar-thoracic AVT ratio, should be selected as UEV to prevent proximal decompensation. LEVEL OF EVIDENCE: 4.

Cervical vertebral maturation (CVM) stage as a supplementary indicator for the assessment of peak height velocity (PHV) in adolescent idiopathic scoliosis (AIS).

BACKGROUND: Radiographic methods in evaluating the skeletal maturity include Risser sign and Tanner-Whitehouse score. They are either inappropriate or too complex for a busy clinic setting. The cervical vertebral maturation (CVM) stage is commonly used in orthodontics but has been less acknowledged in studies of spinal growth. The purpose of this study was to evaluate whether the CVM stage could be used as an alternative to Risser sign in determining peak height velocity (PHV). METHODS: This was a two-stage study. Inclusion criteria for stage I study were adolescent female idiopathic scoliosis (AIS) patients, aged between 9-16 years old, who had undergone full spine imaging with clear visibility of the cervical spine. Patients in the stage II study had follow-up through CVM stage 2-4. The correlation between CVM and Risser was analyzed. The spinal growth parameters were measured at each follow-up, and the growth velocity of parameters (PaGVs) was calculated. The PaGVs at CVM stage 2-4 were further compared. RESULTS: A total of 170 AIS patients were included for stage I study (mean age 12.7 years). The CVM stages were found to correlate strongly with the Risser sign (r=0.85, P<0.01). For those patients with Risser stage 0 with closed TC, 71% were CVM stage 3. Fifty-one patients were included for stage II study. The stature growth velocity averaged 5.4 cm/year in CVM stage 2 patients and 6.3 cm/year in CVM stage 3 patients, which was significantly greater growth than that in CVM stage 4 patients (3.3 cm/year, both P<0.01); similarly, the growth velocity of arm span, trunk height, and spinal lengths were also significantly higher in CVM stage 3 patients compared to CVM stage 2 and 4 patients. CONCLUSIONS: The CVM stage could provide an alternative option for the assessment of skeletal maturity of subjects with idiopathic scoliosis. CVM stage 3 may be a new sign of PHV.

The clinical impact of global coronal malalignment is underestimated in adult patients with thoracolumbar scoliosis.

STUDY DESIGN: Retrospective review of multicenter adult spine deformity (ASD) database. OBJECTIVES: A recent publication demonstrated that the laterality of the coronal offset is a key parameter that directly impacts postoperative outcomes. The objective of this study is to analyze the relationship between global coronal malalignment (GCM) and functional outcomes in a North American population of ASD patients with no history of previous surgery. The clinical impact of GCM in patients with ASD remains controversial. METHODS: Primary patients were drawn from a multicenter database of ASD patients and categorized with the Qiu classification: Type A = GCM < 3 cm; Type B = GCM > 3 cm toward the concave side of the curve; and Type C = GCM > 3 cm toward the convex side. In addition to the classic radiographic parameter, the coronal truncal inclination was investigated in regard to the pelvic obliquity. Clinical outcomes, radiographic parameters, and demographics were compared across the three Qiu Types using analysis of variance. The analysis was repeated after propensity matching of the three types by age and sagittal alignment (PI-LL mismatch, pelvic tilt, and sagittal vertical axis). RESULTS: 576 ASD patients (mean age 58.8 years) were included. Type B patients had significantly worse functional scores (Oswestry Disability Index, 36-item Short Form Survey physical component summary, and Scoliosis Research Society-22) and a more severe coronal deformity in terms of maximum Cobb angle, global coronal deformity angle, and coronal malalignment; they were also older (65.4 vs. 58.8 years, p = 0.004) and displayed more severe sagittal malalignment. Similar findings were observed after propensity matching. CONCLUSIONS: This study is the first to establish an association between functional outcomes and the severity of the coronal plane deformity in the setting of a specific coronal curve pattern in patients without previous surgery. Coronal malalignment significantly affects the health status of patients when the offset is greater than 3 cm in the direction of curve concavity. LEVEL OF EVIDENCE: III.