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Purpose To compare radiographic parameters, and functional and surgical outcomes between lumbar adolescent idiopathic scoliosis (AIS) and lumbar adult idiopathic scoliosis (AdIS). Methods A retrospective study was performed to identify Lenke 5c type AIS and AdIS patients from our scoliosis database who had undergone posterior surgical treatment for scoliosis. Preoperative and postoperative radiographic and clinical outcomes were compared between the two groups. Results A total of 22 patients were included in AdIS group, and 44 matched patients in AIS group. AdIS group had significantly larger L3 and L4 tilt and translation than AIS group (P P P P r = 0.492, P P P P P P Conclusion Lenke 5c AdIS patients had greater preoperative and postoperative L3 and L4 tilt and translation, as well as less correction of major curve and vertebral body derotation than AIS patients. However, the incidence of adding-on was similar between the two groups.

The global alignment and proportion (GAP) score was established based on American and European subjects, which might limit its applicability to the Chinese population due to ethnicity-related difference of sagittal alignment.To analyze the applicability of GAP score in the Chinese population and to investigate the age- and gender-associated differences of spinopelvic and GAP score parameters.A prospective cross-sectional radiographic study.Of 692 asymptomatic Chinese volunteers aged between 20 and 79 prospectively recruited between January 2017 and June 2019, 490 subjects were eventually included in this study.The pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), L1-S1 lordosis, L4-S1 lordosis, sagittal vertical axis (SVA), T1 pelvic angle (TPA) and global tilt (GT) were measured on lateral X-rays. The GAP scores and its parameters including relative pelvic version (RPV), relative lumbar lordosis (RLL), lordosis distribution index (LDI) and relative spinopelvic alignment (RSA) were calculated for each subject.Subjects were divided into four groups: Group 1M: male subjects60 years old; Group 1F: female subjects60 years old; Group 2M: male subjects ≥60 years old and Group 2F: female subjects ≥60 years old. The GAP scores and categories were determined and compared between groups. The results of sagittal alignment were compared with the previous studies evaluating the normative sagittal alignment in other populations. Univariate linear regression analysis was carried out between pelvic incidence (PI) and sacral slope (SS), lumbar lordosis (LL) and global tilt (GT) in each group.The distributions of GAP categories and the updated Roussouly classification were statistically different from other populations. Significantly different distribution of GAP categories was observed between Group 1M and Group 2M, Group 1F and Group 2F, and Group 1M and Group 1F. Radiographic measurements and GAP parameters were significantly different between Group 1M and Group 2M, and Group 1F and Group 2F. Gender-related difference of parameters was more prominent between Group 1M and Group 1F. Linear relationship of PI with SS, LL and GT were different from the regression models of "ideal" sagittal alignment in GAP score.The GAP score might be inappropriate in Chinese population due to ethnicity-related alignment difference. Worse feasibility of GAP score was observed in female and old subjects.

OBJECTIVE The aim of this study was to compare the radiographic and clinical outcomes in patients with degenerative scoliosis (DS) with type C coronal imbalance who underwent either a sequential correction technique or a traditional 2-rod technique with a minimum of 2 years of follow-up. METHODS DS patients with type C coronal imbalance undergoing posterior correction surgery from February 2014 to January 2018 were divided into groups by technique: the sequential correction technique (SC group) and the traditional 2-rod technique (TT group). Radiographic parameters, including Cobb angle, coronal balance distance (CBD), global kyphosis (GK), thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI), pelvic tilt (PT), and sacral slope, were assessed pre- and postoperatively. The SF-36 questionnaire was used to assess quality of life. RESULTS A total of 34 patients were included. Significant postoperative improvement in the Cobb angle of the main curve, CBD, GK, TK, LL, SVA, and PT was found in both groups (p < 0.05). Postoperatively, the coronal balance was type A in 13 patients (92.9%) in the SC group and in 16 patients (80.0%) in the TT group (p = 0.298). In the TT group, 1 patient had deteriorative coronal imbalance immediately postoperatively, and coronal imbalance deteriorated from type A to type C in 2 patients during follow-up. The scores of Physical Functioning, Role-Physical, Bodily Pain, Vitality, Social Functioning, Role-Emotional, and Mental Health were statistically improved postoperatively (p < 0.05) in both groups. Type C coronal imbalance at the last follow-up was associated with a relatively worse quality of life. There were no implant failures during follow-up in the SC group, whereas rod fracture was observed in 3 patients in the TT group. CONCLUSIONS Compared with the traditional 2-rod technique, the sequential correction technique can simplify rod installation procedure, enhance internal instrumentation, and reduce risk of implant failures. The sequential correction technique could be routinely recommended for DS patients with type C coronal imbalance.

A 3-column osteotomy is sometimes challenging in congenital kyphosis (CK) with many anterior unsegmented vertebrae (AUVs). This study compared surgical outcomes of single-level 3-column osteotomy and associated complications in CK with increasing number of AUVs.We retrospectively reviewed 25 consecutive patients with AUVs in CK who underwent surgery at a mean age of 16.2 ± 10.3 years. Patients were stratified into 2 groups according to the number of AUVs: 3 AUVs and ≥4 AUVs. Osteotomy types, surgical outcomes, and related complications were analyzed and compared between groups.The 3 AUVs group comprised 13 patients, and the ≥4 AUVs group comprised 12 patients. Pedicle subtraction osteotomy, grade 4 osteotomy, vertebral column resection, and vertebral column decancellation accounted for 15.4%, 38.5%, 46.1%, and 0% of procedures in the 3 AUVs group and 8.3%, 0%, 83.3%, and 8.3% of procedures in the ≥4 AUVs group. Preoperative focal kyphosis, which was significantly higher in the ≥4 AUVs group (82.9° ± 28° vs. 59.7° ± 9.4°, P = 0.010), was corrected in both groups postoperatively. The ≥4 AUVs group had significantly higher remaining kyphosis (33.6° ± 13.4° vs. 15.1° ± 9.1°, P0.001) with a significantly lower correction rate (61.2% ± 13.6% vs. 75.0% ± 15.6%, P = 0.001). The complication rate, mainly involving vertebral subluxation and proximal junctional kyphosis, was significantly higher in the ≥4 AUVs group than the 3 AUVs group (8/12 vs. 1/13, P = 0.004).Posterior single-level 3-column osteotomy can achieve satisfactory kyphosis correction in CK with 3 AUVs. Decreasing kyphosis correction and increasing surgery-related complications are prone to develop when treating CK with ≥4 AUVs.

Objective. To analyze the performance of intra-operative neurophysiological monitoring (IONM) including somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) in patients with pre-operative neurological deficit and to identify the high-risk factors for failed IONM. Methods. Patients with pre-operative neurological deficit undergoing spinal surgery between October 2010 and August 2019 were retrospectively reviewed. The presence or absence of SEP and MEP of target muscles were separately recorded and the high-risk factors for failed IONM results were investigated. Results. A total of 136 patients (86 males, 50 females) with an average age of 43.0±17.7 years were included. The muscle strength of recorded muscles in 272 lower extremities included grade 1 in 25 muscles, grade 2 in 15, grade 3 in 41, grade 4 in 134 and grade 5 in 57. The SEP records were available in 177 (65.1%) lower extremities while MEP records were available in 199 (73.2%) lower extremities. Significantly higher success rates of SEP and MEP were obtained in lower extremities with muscle strength of grade 4-5 than those of grade 1-3 (PConclusions. The overall success rates of SEP and MEP were 65.1% and 73.2%, respectively. The high-risk indicators for failed IONM results included muscle strength lower than grade 4, spinal trauma and cervical spinal stenosis.

OBJECTIVE The aim of this paper was to compare the radiographic and clinical outcomes between the sequential correction (SC) technique and the traditional 2-rod correction (TC) technique in patients with severe thoracic idiopathic scoliosis (STIS) undergoing posterior-only correction surgery. METHODS Records of a consecutive series of STIS patients undergoing posterior-only correction surgery between October 2013 and October 2017 with more than 2 years of follow-up were reviewed. The radiographic parameters were assessed preoperatively, postoperatively, and at the last follow-up. Radiographic parameters, operative time, blood loss, and complications were compared between the two groups. RESULTS A total of 33 patients were included in the SC group, and 21 patients were included in the TC group. There was no significant difference in age, sex, or deformity magnitude (93.6° ± 7.8° vs 89.8° ± 6.6°, p = 0.070) preoperatively between groups. The operation time was shorter in the SC group than in the TC group (251.5 ± 42.8 minutes vs 275.4 ± 39.8 minutes, p = 0.020), while both blood loss (1284.6 ± 483.3 vs 1398.0 ± 558.4 ml, p = 0.432) and number of fused levels (13.1 ± 2.8 vs 13.6 ± 2.4, p = 0.503) were similar between the groups. Compared with the TC group, patients in the SC group had a higher correction rate (55.8% ± 9.2% vs 45.7% ± 8.8%, p < 0.001), less coronal (1.1° ± 0.81° vs 2.9° ± 0.93°, p < 0.001) and sagittal (1.5° ± 0.96° vs 2.1° ± 0.64°, p = 0.015) correction loss at the 2-year follow-up, and a lower incidence of intraoperative pedicle screw pullout (14.3% vs 23.8%, p = 0.026). CONCLUSIONS The SC technique could significantly and practically reduce the difficulty of rod installation with better deformity correction outcomes than the traditional TC technique. The SC technique was an effective alternative for patients with STIS.

To analyse the intra-operative neurophysiological monitoring (IONM) data in patients with dystrophic neurofibromatosis type 1 (NF1) associated scoliosis, and to investigate the possible risk factors for failed IONM monitoring.Patients undergoing posterior spinal fusion from September 2015 to December 2019 were retrospectively reviewed. The latency (P37, N50) and amplitude of somatosensory evoked potentials (SEP) in bilateral lower extremities, latency and amplitude of motor evoked potentials (MEP) in bilateral lower extremities and unilateral upper extremity were recorded. The neurological status, curve pattern, Cobb angle of main curve, vertebral rotatory subluxation and dystrophic features at pre-operation were assessed for each patient. The failed IONM monitoring was defined as no reliable SEP or MEP waveforms of all monitored muscles.A total of 92 patients (53 M, 39 F) with an average age of 14.1 ± 2.7 years were included. Failed IONM monitoring was identified in 17 patients with overall success rates being 87.0 and 94.6% for SEP and MEP. The average P37 latency, N50 latency, SEP amplitude and MEP latency showed no significant difference between concave and convex sides (The overall success rates were 87.0% for SEP and 94.6% for MEP in patients with NF1-associated scoliosis. Neurological deficit and more dystrophic features at pre-operation indicated higher risk of failed IONM monitoring.

STUDY DESIGN Retrospective review. OBJECTIVE To evaluate the effect of preoperative Halo-gravity traction (HGT) in the treatment of severe focal kyphosis in the upper thoracic spine (UTS), and to propose the indications that HGT could serve as an alternative for three-column osteotomy (3CO) among these patients. SUMMARY OF BACKGROUND DATA The HGT has been proven to be effective for severe kyphoscoliosis secondary to multiple etiologies. However, the safety and efficacy of HGT in severe focal kyphosis in UTS was still unclear. METHODS Patients with focal kyphosis in UTS undergoing HGT and without 3CO operation were reviewed. The sagittal focal kyphosis was measured at pre-, posttraction, and postoperation. The neurologic function at pretraction, posttraction, and postoperation were assessed according to the American Spinal Injury Association (ASIA) grading. The complications during HGT, operation, and follow-up were recorded. The comparison between pretraction and posttraction was performed using paired samples t test. RESULTS A total of 19 patients were included in this study, with a mean age of 13.2 ± 5.8 years. The average duration of HGT was 62.6 ± 8.4 days, during which the average kyphosis decreased from 95.3 ± 16.4° to 64.1 ± 19.2° (P

Modern development of flexible electronics has made use of bioelectronic materials as artificial tissue in vivo. As hydrogels are more similar to nerve tissue, functional hydrogels have become a promising candidate for bioelectronics. Meanwhile, interfacing functional hydrogels and living tissues is at the forefront of bioelectronics. The peripheral nerve injury often leads to paralysis, chronic pain, neurologic disorders, and even disability, because it has affected the bioelectrical signal transmission between the brain and the rest of body. Here, a kind of light-stimuli-responsive and stretchable conducting polymer hydrogel (CPH) is developed to explore artificial nerve. The conductivity of CPH can be enhanced when illuminated by near-infrared light, which can promote the conduction of the bioelectrical signal. When CPH is mechanically elongated, it still has high durability of conductivity and, thus, can accommodate unexpected strain of nerve tissues in motion. Thereby, CPH can better serve as an implant of the serious peripheral nerve injury in vivo, especially in the case that the length of the missing nerve exceeds 10 mm.

STUDY DESIGN A retrospective study. OBJECTIVE To determine the significance of postoperative upper instrumented vertebra (UIV) horizontalization on the evolution of proximal compensatory curve after hemivertebra resection and short fusion in young patients with lumbosacral hemivertebra (LSHV). SUMMARY OF BACKGROUND DATA Postoperative compensatory curve progression (CCP) is an undesired complication in patients undergoing spinal fusion. Posterior-only hemivertebra resection and short fusion has gradually become a preferred treatment for young patients with LSHV. Postoperative UIV horizontalization might play an important role in the behavior of compensatory curve after surgery. METHODS This study reviewed a consecutive series of patients undergoing posterior-only LSHV resection and short fusion from August 2006 to June 2016. The radiographic parameters were measured at preoperation, immediately postoperation, and the last follow-up. Based on the immediately postoperative UIV tilt, patients were divided into horizontal group (UIV tilt

BACKGROUND For some patients with severe congenital angular kyphoscoliosis (SCAK), 1-level vertebral column resection is insufficient and the Scoliosis Research Society (SRS)-Schwab Grade 6 osteotomy may be necessary. However, the indications and clinical outcomes of SRS-Schwab Grade 6 osteotomy in patients with SCAK have not been investigated in depth. OBJECTIVE To investigate the middle-term radiographic and clinical outcomes, and to evaluate the safety of this high technique-demanding procedure. METHODS Patients with SCAK undergoing SRS-Schwab Grade 6 osteotomy from 2005 to 2016 followed up at least 2 yr were retrospectively reviewed. The potential indications of SRS-Schwab Grade 6 osteotomy were analyzed. The coronal Cobb angle, segmental kyphosis (SK), deformity angular ratio (DAR), coronal balance, and sagittal vertical axis (SVA) were measured in the preoperative, postoperative, and final follow-up. The intraoperative and postoperative complications were recorded. RESULTS A total of 17 patients with SCAK (10 M and 7F) were included, and the mean follow-up was 30.8 ± 16.4 mo. The indications of SRS-Schwab Grade 6 osteotomy were as follows: multiple "pushed-out" hemivertebrae (13, 76.5%) and multilevel anterior block (4, 23.5%). Compared with preoperation, the coronal Cobb angle, SK and SVA at postoperation were significantly improved (P

STUDY DESIGN A retrospective and comparative study. OBJECTIVE To evaluate the difference of DNA methylation in protocadherin10 (PCDH10) genes between adolescent idiopathic scoliosis (AIS) and normal controls, and to assess the association between DNA methylation and the etiology of AIS. SUMMARY OF BACKGROUND DATA The PCDH10 gene showed abnormal expression in AIS. However, the mechanism was still unclear. DNA methylation was an important epigenetic mechanism at the interface between genetics and environmental phenotype, seeming to be a suitable epigenetic mark for the abnormal expression of PCDH10 in AIS. METHODS There were 50 AIS patients and 50 healthy controls included in the study. The peripheral blood sample of each participant was taken. The pyrosequencing assay was used to assess the methylation status of PCDH10 promoter and real time PCR (RT-PCR) was used to detect the PCDH10 gene expression. The comparison analysis was performed using independent t test and 2-tailed Pearson coefficients was calculated for the correlation analysis. RESULTS The average methylation level was 4.32 ± 0.73 in AIS patients and 3.14 ± 0.97 in healthy controls (P

Background: Scoliosis behavior after curettage of spinal osteoid osteoma has been not clarified as most studies regarding scoliosis secondary to osteoid osteoma (OO) were case reports. The aims of this study were to investigate (1) clinical and radiographic features of scoliosis secondary to OO; (2) scoliosis behavior after Curettage of OO. Methods: A retrospective study was performed at patients who were diagnosed as OO clinically or pathologically from July 1998 to December 2019 in a single institution. Age, gender, location of pain, location of lesion and curve pattern of scoliosis were collected preoperatively. Intraoperative blood loss, operation time and surgical complications were documented. VAS scores and curve magnitude were collected pre- and postoperatively and at last follow-up.Results: The mean operation time was 124±32 min and the average intraoperative blood loss was 274±134 ml. The mean preoperative VAS score was 6.2±2.7 , and the mean postoperative VAS score was 2.1±1.8 . Thoracic scoliosis was improved from 22.7±10.6°to 6.2±4.3°after operation，and to 4.1±4.3° at last follow-up. Lumbar scoliosis was improved from 18.1±7.4° to 6.7±5.2°after operation，and to 5.3±3.9°at last follow-up. Trunk shift was improved from 34.7±12.4mm to 10.5±7.2mm after operation，and to 8.4±5.6mm at last follow-up. There was no significant differences as to sagittal radiographic parameters (P＞0.05).Conclusion: Patients with spinal OO had a significantly high incidence of scoliosis. Patients could get rapid relief of pain and scoliosis with low occurrence. Night pain, pain at the concave side of curve, normal sagittal alignment could help differentiate it from scoliosis associated with lumbar disc herniation.

Background. Rib head dislocation (RHD) in dystrophic scoliosis of type 1 neurofibromatosis (DS-NF1) is a unique disorder caused by skeletal dystrophy and scoliotic instability. No particular surgical manipulation is mentioned in the literature to instruct the spine surgeons to effectively obtain more migration of the dislocated rib head without resection. The present study aimed to investigate the effectiveness of screw/hook insertion at vertebrae with RHDs on the retraction of penetrated rib head from spinal canal.Methods. 37 neurologically intact patients with DS-NF1 and concomitant 53 RHDs undergoing scoliosis surgery without rib head excision were retrospectively reviewed. We used pre and postoperative whole-spine radiographs to determine the Cobb angle and the vertebral translation (VT), and the CT scans to evaluate the intraspinal rib length (IRL) and rib-vertebral angle (RVA). The dislocated ribs were stratified into two groups according to the presence of screw/hook insertion at vertebrae with RHD: screw/hook group and non-screw/hook group. Results. 37 dislocated ribs with screws/hooks insertion at corresponding vertebrae were assigned into the screw/hook group and the remaining 16 dislocated ribs consisted of the non-screw/hook group. In the screw/hook group, the correction rates of Cobb angle and VT were significantly higher than the non-screw/hook group after surgery (58.7±16.0% vs. 30.9±12.4%, p=0.003; 61.8±18.8% vs. 35.1±16.6%, p=0.001; respectively). Similarly, more correction rates of IRL and RVA were found in the screw/hook group than the non-screw/hook group (63.1±31.3% vs. 30.1±20.7%, p=0.008; 17.6±9.7% vs. 7.2±3.6%, p=0.006; respectively). Multiple linear regression analysis revealed that the correction rates of Cobb angle, VT and RVA contributed significantly to correction of IRL (β=0.389, 0.939 and 1.869, respectively; p=0.019, 0.001 and 0.002, respectively).Conclusion. Screw/hook insertion at dystrophic vertebrae with RHDs contributed significantly to the degree of retraction of penetrated rib head from spinal canal. This effectiveness is mediated by more corrections of VT and RVA.

Background. There was a paucity of valid information on how to discriminate between different patterns of convex coronal imbalance (CCI>3cm) in dystrophic scoliosis secondary to Type I neurofibromatosis (DS-NF1), while aggravated postoperative CCI occurred regularly with the causes being insufficiently investigated. We aimed to develop a new classification of CCI in DS-NF1, and to optimize the coronal rebalancing strategies.Methods. NF1-related scoliosis database was reviewed and different types of CCI were identified, and the outcomes of coronal rebalance were analyzed. Results. Two main CCI patterns were defined: thoracic CCI (Type 1) and thoracolumbar/lumbar CCI (Type 2), and were further subtyped by the compensatory behavior of the upper hemi-curve (straight or curved morphology). The incidence of immediate post-op CCI was 0.0% and 63.6% for Type1 and Type 2 groups, respectively. Mismatch of both translation and inclination correction between the upper and lower hemi-curve was significant in the post-op coronal imbalanced group (△Upper Arc Translation/△Lower Arc Translation: 109.6±60.0% vs. 31.8±34.4%, p=0.008; △Upper Arc Inclination/△Lower Arc Inclination: 89.8±36.6% vs. 33.5±37.3%, p=0.012). Multiple linear regression analysis revealed that △UAT/△LAT significantly correlated with the correction of coronal balance distance (β=-21.567; p=0.018). A surgical rebalancing algorithm was proposed to treat each subtype.Conclusion. Thoracolumbar/lumbar CCI in dystrophic scoliosis was prone to suffer high risk of persistent post-op CCI. Satisfying coronal rebalance should rely on maximal translational correction of lower hemi-curve, while the upper hemi-curve played the role of fine-tuning for coronal realignment rather than radical Cobb correction, straight morphology in particular.

It is well-documented that melatonin deficiency has been linked to the etiopathogenesis of adolescent idiopathic scoliosis. In this study, we intended to apply melatonin in melatonin-deficient mice to ascertain whether melatonin could reduce the incidence/severity of scoliosis, and investigate the role of melatonin on bone mineral density in scoliosis. A total of 80 mice were divided into 4 groups: 20 quadrupedal mice and 20 bipedal mice served as controls; 20 quadrupedal and 20 bipedal mice received oral melatonin (8 mg/kg BW) daily. After 5th, 10th, 15th and 20th weeks of treatment, radiographs and in vivo micro-CT were used to determine the incidence of scoliosis and bone qualities, respectively. Upon sacrifice, the levels of melatonin were measured in each group. At 20th week, the occurrence of scoliosis was 80%, 30%, 22% and 5% in bipedal, quadrupedal, bipedal + melatonin and quadrupedal + melatonin group, respectively. The trabecular bone quality of the vertebral body was significantly ameliorated in the melatonin-treated bipedal models. Likewise, the number of osteoclasts was significantly less in those treated with melatonin. Our results indicated that melatonin deficiency may be crucial for scoliotic development, and restoration of melatonin levels can prevent scoliotic development with the improvement in bone density.

STUDY DESIGN A retrospective study. OBJECTIVE The aim of this study was to compare the long-term outcomes of correction surgery for Lenke 1 A/B scoliosis among those with symmetric fusion (SF), upper-dominant fusion (UF), and lower-dominant fusion (LF) in adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA Symmetric fusion, defined as equal number of vertebral levels included in instrumented fusion above and below the apical vertebra or disc of the primary curve, was a new concept raised in AIS selective fusion. Previous study showed that similar correction the effect on clinical outcomes of this fusion style. METHODS Preoperative, postoperative, and last follow-up radiographs of 117 consecutive patients with Lenke type 1A/B curves who underwent posterior selective thoracic instrumentation surgery were analyzed. Patients were divided into two groups (SF and nonsymmetric fusion [NSF]). Patients in NSF was further divided into two groups UF (more vertebrate was fused above the apex) and LF (more vertebrate was fused below the apex). Clinical outcomes and coronal decompensation including adding-on and trunk shift were analyzed and compared among three groups. RESULTS There was no significant difference between SF and NSF in magnitude of preoperative main thoracic curve (P = 0.69) and correction rate (P = 0.50). Distal adding-on was observed in 21 patients (17.9%), and coronal decompensation was observed in eight patients (6.8%) in all at final follow up. No significant differences were found between the two groups regarding adding-on phenomenon (P = 0.64) and coronal imbalance (P = 0.72). Significantly higher rates of adding-on were found in UF compared with SF and LF (P

Study design Retrospective radiographical clinical study. Objective To investigate the incidence and risk factors of coronal imbalance (CI) after three-column osteotomy (3-CO) in patients with thoracolumbar congenital kyphoscoliosis (CKS). Summary of background data The incidence and risk factors of postoperative CI have been reported in adolescent idiopathic and degenerative lumbar scoliosis. However, limited data exists for patients with CKS after 3-CO. Methods We reviewed a consecutive series of patients with CKS who underwent posterior-only 3-CO. Coronal curve patterns were classified according to absolute C7 translation values into: Type A, C7 translation is less than 30 mm; Type B, C7 translation more than or equal to 30 mm and C7 plumb line (C7PL) shifted to the concave side of the main curve; and Type C, C7 translation more than or equal to 30 mm and C7PL shifted to the convex side. CI was defined as C7 translation on either side more than or equal to 30 mm. According to C7 translation at the latest follow-up, patients was subdivided into an imbalanced group and a balanced group. Results One-hundred-thirty patients (mean age, 17.7 ± 5.2 yr) were recruited. The mean follow-up was 41.3 ± 18.5 months. Twenty-six patients (20%) were identified as having CI at the latest follow-up. Compared with the balanced group, the imbalanced group had a larger proportion of preoperative Type C pattern, higher main curve correction, and greater lowest instrumented vertebra (LIV) tilt before and after surgery. Multiple logistic regression showed that risk factors for CI were preoperative type C pattern, preoperative LIV tilt more than or equal to 23.5° and immediate postoperative LIV tilt more than or equal to 12.3°. Conclusion The incidence of CI in patients with CKS after 3-CO was 20%. A preoperative type C pattern, preoperative LIV tilt more than or equal to 23.5°, and immediate postoperative LIV tilt more than or equal to 12.3° were found to be associated with CI at the latest follow-up. Level of evidence 3.

BACKGROUND: The relationship between structural damage and inflammation of the spine and the sagittal imbalance in ankylosing spondylitis (AS) is not well understood. The present study aimed to investigate the correlation between structural damage and inflammation of the lumbar spine and the sagittal imbalance in AS patients with thoracolumbar kyphosis. METHODS: Forty-five AS patients with thoracolumbar kyphosis were retrospectively reviewed. Six sagittal spinal parameters, including the C7 tilt (C7T), spino-sacral angle (SSA), global kyphosis (GK), the sagittal vertical axis (SVA), thoracic kyphosis (TK), and lumbar lordosis (LL), were measured. Structural damage of the lumbar spine was assessed by the modified Stoke AS Spine Score (mSASSS) on radiographs. Lumbar spinal inflammation was evaluated by the AS spinal magnetic resonance imaging (MRI) activity (ASspiMRI-a) on MRI. Correlation analysis was performed using the paired sample t-test. Multivariable linear regression models were constructed to analyze the contributions of mSASSS and ASspiMRI-a to the sagittal parameters. RESULTS: The average values of the sagittal parameters C7T, SSA, GK, SVA, TK, and LL were 68.1°, 80.1°, 77.3°, 168.7 mm, 47.7°, and −0.7°, respectively. The average mSASSS and ASspiMRI-a scores were 9.8 and 10.8, respectively. Correlation analysis showed that the mSASSS and ASspiMRI-a were correlated with C7T, SSA, SVA, and LL (the Spearman correlation coefficients were −0.439, −0.390, 0.424, and 0.530 for mSASSS; −0.406, −0.402, 0.378, and 0.486 for ASspiMRI-a; P

A retrospective study.The aim of this study was to investigate the incidence and risk factors for distal adding-on (AO) phenomenon after posterior spinal fusion (PSF) in scoliosis secondary to Chiari malformation type I (CMS) patients with right major thoracic curve.Distal AO phenomenon is a common complication observed in adolescent idiopathic scoliosis (AIS), which is significantly associated with unsatisfactory outcomes. However, few studies specifically focused on the incidence and risk factors of distal AO in CMS.Seventy-eight CMS adolescents were included with a minimum of 2-year follow-up after PSF. patients with distal AO at the final follow-up were divided into AO group and those without were No-AO group. The coronal and sagittal parameters were evaluated preoperatively, immediately after surgery, and at the last follow-up. Clinical outcome was analyzed using the Chicago Chiari Outcome Scale (CCOS).Distal AO was observed in 18 of 78 patients (23.1%). Compared with No-AO group, patients with distal AO had significantly lower Risser sign (P = 0.001), more flexibility of lumbar curve (P = 0.021), higher incidence of lowest instrumented vertebra-last substantially touched vertebra (LIV-LSTV) ≤0 (P = 0.001), smaller postoperative Cobb angle of lumbar curve (P0.001), and greater correction rate of lumbar curve (P = 0.001). Logistic regression analysis revealed that low Risser sign (Grade 1-2, odds ratio [OR] = 5.7, P = 0.029) and LIV-LSTV ≤0 (OR = 6.4, P = 0.019) were independent risk factors for distal AO. There was no significant difference of CCOS scores between two groups at the final follow-up (P 0.05 for all).The incidence of distal AO was 23.1% in CMS patients after PSF. Patients with low Risser sign and LIV-LSTV ≤0 were high risk factors for distal AO.Level of Evidence: 3.

BACKGROUND: The distraction-based growth-friendly technique has become a mainstay of treatment for young children with long-spanned congenital scoliosis. However, in patients who are 9 years to 11 years old, the choice is much less clear, and posterior spinal fusion is also a potential option. QUESTIONS/PURPOSES: Comparing growth-friendly scoliosis surgery and posterior spinal fusion, which technique (1) provides greater correction of spinal deformity, (2) is associated with more surgical complications, and (3) results in greater improvement in pulmonary function tests, health-related quality of life scores, other patient-reported outcomes? METHODS: Between 2009 and 2017, one spinal center performed 212 spinal interventions for scoliosis in patients aged between 9 years and 11 years old and who had open triradiate cartilage, including 40 patients with growth-friendly approaches (34 with growing-rod technique and six with a vertical expandable prosthetic titanium rib) and 172 with one-stage posterior spinal fusion, respectively. During this period, our general indications for using growth-friendly surgery were patients with open triradiate cartilage, major curve higher than 40°, and upper and lower end vertebrae involving at least eight segments. Twelve patients with a median (range) age of 9.3 years (9 to 11) treated with growth-friendly surgery met the following inclusion criteria: (1) had at least two lengthening procedures before definitive spinal fusion along with 2 years of follow-up after definitive spinal fusion; (2) had been followed until skeletal maturity (Risser grade ≥ 4); and (3) with complete radiographic and clinical data (health-related quality of life (HRQoL) and pulmonary function test results) preoperatively and at the latest follow-up. A group of patients between 9 years and 11 years old and underwent one-stage posterior spinal fusion was selected from our database of patients with congenital scoliosis. Our general indications for using one-stage posterior spinal fusion were patients with a major curve greater than 40°, and with thoracic height higher than 18 cm. Sixty-two patients who had open triradiate cartilage and had been followed until skeletal maturity (Risser grade ≥ 4) were accounted for. In this retrospective, controlled study, we matched patients in the posterior spinal fusion group to those 12 patients who had growth-friendly surgery by age, sex, pathologic findings, major curve size, and location of the apex of the major curve (2:1 matching provided 24 patients in the control group). The median (range) age was 9.8 years (9 to 11). We then compared the groups in terms of magnitude of correction and postoperative complications. Surgical complications, including infection, implant-related complications, and alignment-related complications were evaluated and classified using the surgical complications grading system. Pulmonary function tests and HRQoL were also compared between groups. Pulmonary function tests were performed at the same center with a spirometer. HRQoL were assessed by questionnaire, including the 24-item Early-onset Scoliosis questionnaire for parent-reported outcomes and the Scoliosis Research Society-22 questionnaire for patient-reported outcomes. All patients involved in this study gave their informed consent. RESULTS: The posterior spinal fusion group achieved a greater correction magnitude at the latest follow-up (median [range] 46% [28 to 70] versus median 34% [9 to 58], difference of medians = 11%; p < 0.001) than the growth-friendly group. A higher proportion of patients in the growth-friendly group had complications than in the posterior spinal fusion group (7 of 12 versus 4 of 24; p = 0.03). There were no between-group differences in terms of pulmonary function tests. Few differences were found between the groups in terms of 24-item Early-onset Scoliosis parental impact (median [range] 60 [44 to 83] for the growth-friendly group versus median 71 [55 to 87] for the posterior spinal fusion group, difference of medians = 13; p = 0.001), financial burden (median 44 [30 to 55] for the growth-friendly group versus median 62 [53 to 75] for the posterior spinal fusion group, difference of medians = 16; p < 0.001) and the Scoliosis Research Society-22 self-image scores (median 3.8 [3.2 to 4.3] for the growth-friendly group versus median 4.4 [4.1 to 4.6] for the posterior spinal fusion group, difference of medians = 0.5; p = 0.006) at the latest follow-up, and those differences that were observed all favored the posterior spinal fusion group. CONCLUSIONS: In light of the superior deformity correction and fewer observed complications with posterior spinal fusion, and the absence of important differences in validated outcomes scores or pulmonary function tests, posterior spinal fusion might be a better choice for 9- to 11-year-old children with long-spanned congenital scoliosis and limited growth potential in the intended instrumentation area. LEVEL OF EVIDENCE: Level III, therapeutic study.

OBJECTIVEDystrophic lumbar scoliosis secondary to neurofibromatosis type 1 (DLS-NF1) may present an atypical, unique curve pattern associated with a high incidence of coronal imbalance and regional kyphosis. Early surgical intervention is complicated and risky but necessary. The present study aimed to assess the unique characteristics associated with the surgical treatment of DLS-NF1.METHODSThirty-nine consecutive patients with DLS-NF1 treated surgically at a mean age of 14.4 ± 3.9 years were retrospectively reviewed. Patients were stratified into three types according to the coronal balance classification: type A (C7 translation < 30 mm), 22 patients; type B (concave C7 translation ≥ 30 mm), 0 patients; and type C (convex C7 translation ≥ 30 mm), 17 patients. Types B and C were considered to be coronal imbalance. The diversity of surgical strategies, the outcomes, and the related complications were analyzed.RESULTSThe posterior-only approach accounted for 79.5% in total; the remaining 20.5% of patients received either additional anterior supplemental bone grafting (12.8%) to strengthen the fixation or convex growth arrest (7.7%) to reduce growth asymmetry. The lower instrumented vertebra (LIV) being L5 accounted for the largest share (41%), followed by L4 and above (35.9%), the sacrum (15.4%), and the pelvis (7.7%). Type C coronal imbalance was found in 23 patients (59%) postoperatively, and the incidence was significantly higher in the preoperative type C group (14/17 type C vs 9/22 type A, p = 0.020). All the patients with postoperative coronal imbalance showed ameliorative transition to type A at the last visit. The rate of screw malposition was 30.5%, including 9.9% breached medially and 20.6% breached laterally, although no serious neurological impairment occurred. The incidence of rod breakage was 16.1% (5/31) and 0% in patients with the posterior-only and combined approaches, respectively. Four revisions with satellite rods and 1 revision with removal of iliac screw for penetration into the hip joint were performed.CONCLUSIONSSurgical strategies for DLS-NF1 were diverse across a range of arthrodesis and surgical approaches, being crucially determined by the location and the severity of dystrophic changes. The LIV being L5 or lower involving the lumbosacral region and pelvis was not rare. Additional posterior satellite rods or supplementary anterior fusion is necessary in cases with insufficient apical screw density. Despite a high incidence of postoperative coronal imbalance, improvement of coronal balance was frequently confirmed during follow-up. Neurological impairment was scarce despite the higher rate of screw malposition.

OBJECTIVE The aim of this study was to compare the radiological and clinical outcomes of early-onset scoliosis (EOS) patients with or without intraspinal anomalies (IAs) managed with growing rods (GRs), and to evaluate the safety of the GR technique in EOS patients with untreated IAs. METHODS EOS patients undergoing GR placement between August 2008 and July 2017 were retrospectively reviewed. Patients with untreated IAs were classified into the EOS+IA group, and those without IAs into the EOS−IA group. The radiographic parameters including Cobb angle of the major curve, T1–S1 height, and apical vertebral translation were measured, and a detailed assessment of the neurological status was performed at each visit. RESULTS Seventy-six patients with EOS (32 boys, 44 girls) with an average age of 6.5 ± 2.3 years at initial surgery satisfied the inclusion and exclusion criteria, including 28 patients in the EOS+IA group and 48 patients in the EOS−IA group. The radiographic measurements were comparable between groups preoperatively, postoperatively, and at the latest follow-up. One patient in the EOS+IA group experienced sensory deficit in a unilateral lower extremity after initial surgery, and an intraoperative neurophysiological monitoring event was observed in a patient in the EOS−IA group. No permanent neurological deficit was observed in either group. CONCLUSIONS EOS patients with and those without IAs had comparable clinical and radiological outcomes of the GR technique. Repeated lengthening procedures may be safe for EOS patients with untreated IAs.

Several osteotomy techniques including pedicle subtraction osteotomy and vertebral column resection have been employed in the correction of congenital kyphosis (CK) and satisfying outcomes have been demonstrated. However, the Scoliosis Research Society (SRS)-Schwab Grade 4 osteotomy, defined as resection of posterior elements, partial vertebral body, and superior adjacent disc, is rarely reported in the treatment of CK.The present study aimed to evaluate the efficiency and safety of SRS-Schwab Grade 4 osteotomy in patients with CK, and to propose its optimal indication.This is a retrospective analysis of clinical and radiographic outcomes of patients with CK undergoing SRS-Schwab Grade 4 osteotomy.Patients with thoracolumbar CK undergoing SRS-Schwab Grade 4 osteotomy from January 2010 to May 2015 followed up for at least 2 years were retrospectively reviewed.The thoracic kyphosis, lumbar lordosis, segmental kyphosis (SK), sagittal vertical axis (SVA), pelvic incidence, pelvic tilt, and sacral slope were measured on lateral spinal x-rays. Patients were required to fulfill the SRS-22 questionnaire at preoperation and the last follow-up.The sagittal spinal-pelvic parameters were assessed at preoperation, postoperation, and last follow-up. The comparison between preoperation and postoperation was performed by paired samples t test.A total of 38 patients with CK (17 male and 21 female) with an average age of 16.5±9.9 years were included. The mean operating time was 242.7±88.1 minutes and blood loss was 634.5±177.8 mL. The mean follow-up was 38.8±20.3 months. The SK was 49.5±11.7° at preoperation, 6.8±7.4° at postoperation (p.001), and 8.0±8.1° at the last follow-up. No significant correction loss during follow-up was found in SK (p=.125). The SVA was improved from -36.0±18.3 mm at preoperation to 3.7±17.8 mm at postoperation (p.001), and the correction was well maintained during follow-up (p=.113). Compared with preoperation, the mean postoperative scores of each domains of SRS-22 questionnaire improved at different levels. Intraoperative complications included one case with incidental dural tear and another with transient root injury. Proximal junctional kyphosis occurred in three patients at 6 months after operation and remained stable during the follow-up. At the last follow-up, all patients were identified to have achieved solid bony fusion.The SRS-Schwab Grade 4 osteotomy, if selected appropriately, could provide satisfying correction of congenital kyphosis. The correction could be well maintained during the longitudinal follow-up.

OBJECTIVEThis study aimed to evaluate the correction results of traditional dual growing rods (DGRs) on axial rotation using CT scans and to further explore the relationships between axial and torso deformities in patients with early-onset scoliosis (EOS).METHODSPatients with EOS who were treated with traditional DGRs between January 2006 and December 2014 were retrospectively reviewed. Plain radiographs were used to assess the degree of coronal and sagittal deformity. The apical vertebral rotation (AVR) and rib hump (RH) were measured on CT scans at the apical vertebra. Pearson or Spearman rank correlation analyses were used to analyze the associations between spinal and torso deformities.RESULTSA total of 27 patients (10 boys and 17 girls, average age 6.5 ± 1.7 years) were enrolled in this study. The average number of lengthenings per patient was 5.0 ± 1.9, with a mean follow-up duration of 52.9 ± 18.2 months. The apical vertebral translation, apical vertebral body–rib ratio (AVB-R), AVR, and RH parameters were significantly decreased after the initial surgery (p < 0.05) but showed notable progression at the latest follow-up evaluation (p < 0.05). The preoperative AVR and its correction after index surgery were significantly correlated with the preoperative values as well as with the corrections of the major Cobb angle, AVB-R, and RH. During the follow-up period, significant correlations were found between the deterioration of AVR and the AVB-R and also between the deterioration of AVR and the RH from the initial surgery to the latest follow-up.CONCLUSIONSSignificant AVR correction can be achieved by DGR techniques after the initial surgery. However, this technique weakly prevents the deterioration of AVR during the follow-up period.

Background The gene of pituitary homeobox 1 (PITX1) has been reported to be down-regulated in adolescent idiopathic scoliosis (AIS), of which the cause has not been well addressed. The abnormal DNA methylation was recently assumed to be an important mechanism for the down-regulated genes expression. However, the association between PITX1 promoter methylation and the etiology of AIS was not clear. Methods The peripheral blood samples of 50 AIS patients and 50 healthy controls were collected and the genomic DNA was extracted. The pyrosequencing assay was used to assess the methylation status of PITX1 promoter and real-time quantitative polymerase chain reaction (PCR) was used to detect the PITX1 gene expression. Comparison analysis was performed using independent t test and Chi-square tests, while correlation analysis were performed with 2-tailed Pearson coefficients. Results The mean methylation level was (3.52 ± 0.96)% in AIS and (1.40 ± 0.81)% in healthy controls (P

Background Accurate skeletal maturity assessment is important to guide clinical evaluation of idiopathic scoliosis, but commonly used methods are inadequate or too complex for rapid clinical use. The objective of the study was to propose a new simplified staging method, called the thumb ossification composite index (TOCI), based on the ossification pattern of the 2 thumb epiphyses and the adductor sesamoid bone; to determine its accuracy in predicting skeletal maturation when compared with the Sanders simplified skeletal maturity system (SSMS); and to validate its interrater and intrarater reliability. Methods Hand radiographs of 125 girls, acquired when they were newly diagnosed with idiopathic scoliosis prior to menarche and during longitudinal follow-up until skeletal maturity (a minimum of 4 years), were scored with the TOCI and SSMS. These scores were compared with digital skeletal age (DSA) and radius, ulna, and small hand bones (RUS) scores; anthropometric data; peak height velocity; and growth-remaining profiles. Correlations were analyzed with the chi-square test, Spearman and Cramer V correlation methods, and receiver operating characteristic curve analysis. Reliability analysis using the intraclass correlation (ICC) was conducted. Results Six hundred and forty-five hand radiographs (average, 5 of each girl) were scored. The TOCI staging system was highly correlated with the DSA and RUS scores (r = 0.93 and 0.92, p 0.97. Conclusions The new proposed TOCI could provide a simplified staging system for the assessment of skeletal maturity of subjects with idiopathic scoliosis. The index needs to be subjected to further multicenter validation in different ethnic groups.

Study Design: A prospective magnetic resonance imaging study. Objective: To quantitatively explore the differences in the anatomic position of the aorta relative to the spine between supine and prone positions in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis. Summary of Background Data: Aortic complications may occur during the lumbar spine osteotomy in correcting thoracolumbar kyphosis secondary to AS, and a clear understanding of the spatial relationship between the aorta and the vertebrae is essential to prevent these iatrogenic complications. However, previous anatomic study was performed with AS patients in the supine position, which was different from the prone position adopted in surgery. To date, no report has been published to investigate the mobility of the aorta relative to the vertebrae between supine and prone positions in AS patients with thoracolumbar kyphosis. Materials and Methods: From March 2013 to September 2014, 22 AS patients (21 males, 1 female) with thoracolumbar kyphosis with a mean age of 30.7 years (range, 19–46 y) were recruited. Magnetic resonance imaging examinations from T9 to L3 in both the supine and prone positions were performed, and the left pedicle-aorta (LtP-Ao) angle and LtP-Ao distance were measured at each level. The differences of these parameters between the 2 positions were compared by the paired sample t test, and the relationships between the shifting of the aorta and the change of global kyphosis and lumbar lordosis were evaluated by the Pearson correlation coefficient. The level of significance (α) was set at 0.05. Results: At T9–L3 levels, no significant difference was noted in LtP-Ao distances (43.78 vs. 44.42 mm; P=0.077) and LtP-Ao angles (0.82 vs. 0.22 degrees; P=0.053) between supine and prone positions. The correlation analysis also revealed no remarkable correlation between the change of LtP-Ao angle and increase of global kyphosis and lumbar lordosis in the prone position. Conclusions: There is no significant change of the relative positions between the aorta and the vertebrae at T9–L3 levels after the patient turned to a prone position, which implied that the mobility and range of motion of the aorta is limited in advanced stage of AS.

A retrospective radiographic study.To evaluate the asymmetry of breast volume (BV) and shape in female adolescent idiopathic scoliosis (AIS) patients and to define their relationship with deformed components of the anterior chest wall and curved spine.The higher incidence of asymmetric breast development in AIS was described by prior studies. However, the interplay between scoliosis curve magnitude and severity of breast asymmetry (BA) are unknown.A total of 73 surgically treated female right thoracic AIS patients classified as Lenke type I were enrolled in this study, with the average Cobb angle being 52.08±11.68 degrees. The Image J software was utilized to calculate BV. Both concave and convex radiographic parameters of breast shape were measured including the extraversion angle (EA), the coverage angle (CA), the axial breast height, the vertical breast height (VBH), and the nipple-to-sternum distance. The inclination angles of the concave and convex anterior chest wall were also assessed. BA was calculated according to the formula as follows: BA=(concave-convex)×BV/[(concave+convex)×BV]/2. The measurements of spinal deformity parameters included the Cobb angle, the RAsag angle, and the RAml angle. Paired t test was performed to analyze the asymmetry of breast shape, and Pearson correlation analysis was utilized to define the correlation between the breast shape, spinal deformity, and the inclination of anterior chest wall.The concave BV, EA, axial breast height, and vertical breast height were significantly larger than those of the convex side (P0.05), whereas the concave CA and the inclination angle of the anterior chest wall were significantly smaller than those of the convex side (P0.05). No difference was detected between the concave and the convex nipple-to-sternum distance (P0.05). The averaged BA was 11.4%, with the ratio of asymmetry beyond 10% being 52.1%. No statistically significant relationships between BA and Cobb angle, RAsag angle, RAml angle were detected (P0.05). The inclination angle of the anterior chest wall demonstrated significant correlation with EA (P0.001) and CA (P0.001), respectively.The incidence of BA in AIS is notable, with the concave breast being larger, more extroversive, and more concentrated than the convex breast. The discrepancy between concave and convex anterior chest wall inclination bound to scoliosis could have a major influence on breast orientation and profile, suggesting a synergistic role of anterior chest wall deformity and bilateral BV discrepancy in the formation of BA.

Background Previous studies have reported favorable short-term outcomes after posterior-only hemivertebra resection and short fusion in patients with LSHV. However, there is a paucity of data evaluating the long-term outcomes following this procedure. The aim of the study is to evaluate the radiological outcomes following posterior-only hemivertebra resection and short fusion for the treatment of congenital scoliosis (CS) secondary to lumbosacral hemivertebra (LSHV) with a minimum of a 5-year follow-up. Methods A total of 23 patients treated with one-stage posterior-only LSHV resection and short fusion with a minimum of a 5-year follow-up were reviewed. Radiographic parameters including the Cobb angles of the lumbosacral curve and compensatory curve, the upper instrumented vertebra (UIV) tilt, and trunk shift were measured. The complications were recorded accordingly. Results The mean duration of follow-up was 88.6 ± 28.5 months, and the average age at surgery was 7.8 ± 3.5 years. Fusion levels averaged 3.0 ± 0.7 segments. The lumbosacral curve was corrected from 30.7 ± 10.4° to 6.7 ± 7.1° after surgery (P P Conclusion One-stage posterior-only hemivertebra resection with short fusion is an effective procedure for LSHV, and the correction can be well maintained during longitudinal follow-up. Great attention should be paid to the restoration of lumbosacral horizontalization.

To analyze the somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in neurologically asymptomatic Chiari malformation-associated scoliosis (CMS) patients with and without syringomyelia as compared with those in idiopathic scoliosis (IS) ones, and to identify whether the deformities have impacts on the neurophysiological monitoring.This study included neurologically asymptomatic CMS patients undergoing posterior correction surgery between January 2010 and January 2016. IS patients were involved as control group and a subgroup of age- and height-matched IS patients were selected. The age, standing height and Cobb angles of main curve were measured. The SEPs latency and amplitude, MEPs amplitude, and the rate of abnormal SEPs pathologic change were compared between CMS and IS patients using independent-sample t-test and Chi-square test.Sixty CMS patients and 210 IS patients were included. There was no difference between CMS patients and IS or matched IS patients in SEPs latency and amplitude, MEPs amplitude or rate of abnormal SEPs (p 0.05). Forty-eight CMS patients concurrent with syringomyelia were associated with higher Cobb angle of main curve and lower SEPs amplitude than those without syringomyelia (p 0.05). No significant difference was found between CMS patients with and without syringomyelia in age, height, SEPs latency, MEPs amplitude or rate of abnormal SEPs (p 0.05).Neurologically asymptomatic CMS patients showed similar absolute values of neurophysiological monitoring with IS patients. The syringomyelia in CMS indicated more severe curvature and lower SEPs amplitude even after posterior fossa decompression.