Unfused Segments Research Articles

Changes in the Position of the Junctional Vertebrae After Posterior Spinal Fusion in Adolescent Idiopathic Scoliosis: Implication in Risk Assessment of Proximal Junctional Kyphosis Development.

The development of proximal junctional kyphosis (PJK) after posterior spinal fusion in adolescent idiopathic scoliosis is a major problem. Changes in the global sagittal parameters as they relate to PJK have been reported after surgery, however, the relationships between the changes in the upper-instrumented vertebra (UIV) during and after surgery as they relate to development of PJK have not been quantified. We hypothesize that the compensatory changes in the unfused segments of the spine over time are correlated with the surgically induced changes in the UIV position. Sixty adolescent idiopathic scoliosis patients (with at least 1-year follow-up) who underwent posterior spinal surgery were included retrospectively. Global spinal parameters were calculated using 3-dimensional models of the spine, additional parameters [proximal junctional kyphosis angle (PJKA), cervical lordosis angle] were measured manually before surgery and at 3 postoperative follow-ups. The 3-dimensional position of the vertebral body centroids was calculated for T1, UIV, and lower-instrumented vertebra at all timepoints. The sagittal position of T1, UIV, and lower-instrumented vertebra were correlated to the cervical lordosis, PJKA, lumbar lordosis, and pelvic tilt. The position of T1 and UIV were significantly more anterior at first erect for patients who developed PJK. The posterior shift of UIV at the most recent follow-up as compared with the preoperative position was significant in both the PJK and non-PJK cohort. A larger anterior shift in UIV at first erect correlated with a larger T1 and UIV posterior shift at the most recent follow-up. At the most recent follow-up, a more posterior position of the UIV correlated with a larger angle of PJKA (P<0.05). Both a larger anterior shift of UIV between preoperative and first erect and a more posterior position of UIV at the most recent follow-up was correlated with a higher PJKA. A larger anterior shift in the position of the UIV after surgery was associated with a higher posterior shift of UIV at the last follow-up. The surgically induced changes in the UIV are an important parameter associated with the development of PJK. Level IV.

176. Degenerative cervical spondylolisthesis: does adjacent level surgical stabilization result in progressive listhesis?

BACKGROUND CONTEXT Patients with CSM often present with multilevel disease and may experience spondylolisthesis within or adjacent to the levels of clinical pathology. The progression of an unfused DCS segment remains unclear when it is not included within the surgical construct. PURPOSE We sought to evaluate if unfused DCS segments, adjacent to the fusion, develop worsening instability that requires surgery. STUDY DESIGN/SETTING Retrospective case series. PATIENT SAMPLE Twenty-three consecutive patients who presented with cervical spondylotic myelopathy (CSM), had radiographs revealing degenerative cervical spondylolisthesis (DCS) at one or more levels, and underwent surgical intervention, were reviewed. All patients showed no evidence of clinical symptoms present at the DCS level and had surgery performed at adjacent levels. OUTCOME MEASURES Radiographic measurements were obtained on preoperative and final follow-up radiographs to assess the amount of listhesis, cervical lordosis, sagittal vertebral axis, and T1 slope at the pathologic level. METHODS Multivariate analysis was used to find independent risk factors for progression of disease. RESULTS DCS was present at C2-3 in three cases (13%), C3-4 nine cases (39.5%), C4-5 seven cases (30.4%), C5-6 two cases (8.7%), C6-7 no cases (0%), C7-T1 two cases (8.7%). The average preoperative slip was 2.7 mm±0.5 mm. At final follow-up, five (21.7%) demonstrated progression (>0.5 mm) of their slip, 18 (78%) remained stable (within 0.5 mm) or improved. Older age and male sex were associated with progression, but did not increase the risk of reoperation. Two patients (8.7%) with DCS underwent revision surgery, one for symptomatic pseudoarthrosis, and one for myeloradiculopathy due to progression of the adjacent DCS. CONCLUSIONS Despite the presence of altered stress at the DCS level with the adjacent surgical intervention, the majority of patients did not experience DCS progression at final follow-up nor require further surgical intervention. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

50. Sagittal parameters poorly predict clinical outcomes following anterior cervical discectomy and fusion

BACKGROUND CONTEXT While attention to sagittal parameters in the cervical spine is increasing, the relationship between these radiographic measurements and clinical outcomes is less clear. PURPOSE The aim of the present study was to characterize independent associations between cervical spine radiographic parameters and clinical outcomes following anterior cervical discectomy and fusion (ACDF). STUDY DESIGN/SETTING Retrospective cohort analysis. PATIENT SAMPLE Analysis of consecutive patients who underwent a single-level ACDF at an academic institution between 2008 and 2015 for cervical radiculopathy and/or myelopathy, with a minimum of 6 months of clinical and radiographic follow-up. OUTCOME MEASURES Disc height was measured as the anterior vertebral distance (AVD), mid-vertebral distance (MVD), and posterior vertebral distance (PVD) on preoperative and immediate postoperative radiographs. Sagittal parameters were also measured, and included C2-C7 lordosis, T1 angle, fusion segment lordosis, sagittal vertical axis (SVA), proximal and distal adjacent segment lordosis. Preoperative and final visual analog scale (VAS) neck, VAS arm, and Neck Disability Index (NDI) scores were collected. The rates of reoperation, successful fusion, and subsidence (postoperative disc space collapse >2 mm) were determined. METHODS Preoperative, postoperative, and final radiographs were reviewed. Radiographic parameters were tested for association with patient-reported outcomes, reoperation, fusion, and subsidence using multivariate linear regression and multivariate logistic regression for continuous and binary outcomes, respectively. Multivariate regressions controlled for potential confounding variables in order to identify independent risk factors for each outcome. The Sidak-Holm method was used to adjust p-values in order to correct for multiple statistical comparisons. The threshold for statistical significance was set at p RESULTS A total of 381 patients met inclusion criteria. Average follow-up length was 28 months, average age was 50.2 years, average body mass index was 28.7, and 49.2% of patients were female. Of these patients, 93.7% achieved successful fusion, 6.6% had graft subsidence, and 4.99% had a reoperation. Preoperative and postoperative radiographic measurements and patient-reported outcomes were collected. Preoperative radiographic measurements poorly predicted clinical outcomes. Increased preoperative lordosis at the adjacent unfused segment proximal to the eventual fusion mass was found to be associated with increased final NDI (corrected p=0.018), and increased final proximal lordosis was associated with increased final NDI (corrected p=0.049). However, no other radiographic parameters were associated with any patient-reported clinical outcomes. Subsidence rates were increased with greater change in proximal lordosis from preoperative to postoperative (OR 1.30, corrected p=0.007) and from preoperative to final follow-up (OR 1.17, corrected p=0.044). Subsidence was negatively associated with increased change in lordosis across the fused segments from preoperative to postoperative (OR 0.88, corrected p=0.032) and from preoperative to final follow-up (OR 0.86, corrected p=0.017). CONCLUSIONS The present study found that sagittal parameters were poorly predictive of clinical outcomes. Increased preoperative lordosis at the adjacent segment proximal to the fusion mass was associated with worse final NDI scores, and was the only preoperative radiographic parameter associated with clinical outcomes. Further research should attempt to identify other preoperative factors or radiographic parameters that are more closely associated with clinical outcomes. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

294. Coupled rotation patterns in cervical axial rotation can change when the head is kept level

BACKGROUND CONTEXT Axial rotation of the cervical spine with the cranium held level occurs during certain daily activities such as looking over one's shoulder when walking or driving. These activities require rotation from the suboccipital and subaxial cervical spine. The literature on cervical spine axial rotation and coupled rotations has been obtained from experiments where the segmental axis of rotation is aligned with the global axis of rotation. In looking over one's shoulder, the segmental rotation axes may not be aligned with the global and primarily vertical rotation axis due to curvature of the spine. Furthermore, fusion may limit the amount of rotation that can be obtained from the subaxial spine and reduce the facility with which the daily activities are performed. PURPOSE (1) To define the rotation of the intact subaxial spine during horizontal axial rotation of the cranium, and (2) To measure the effect of C5-C7 fusion on the rotation of the subaxial spine during horizontal axial rotation of the cranium. STUDY DESIGN/SETTING Biomechanical experiment. PATIENT SAMPLE Five C0-T1 cadaveric spine specimens (38-54 years old, 3 female and 2 male). OUTCOME MEASURES Rotation of the subaxial cervical spine in response to applied axial rotation moment. METHODS A left and right axial rotation moment of 1Nm was applied to specimens mounted in an apparatus that held the cranium in an orientation consistent with horizontal gaze (horizontal Frankfort line). The axial rotation axis passed through the midpoint between the two external auditory meatuses. Rotations of the individual vertebrae before and after C5-C7 fusion using lateral mass screws and posterior rods were measured using an optoelectronic motion measurement system. RESULTS C5-C7 fusion reduced the C3-T1 axial rotation range of motion from a mean of 31±5° to 22±5°. In the nonfused levels, the axial rotation range of motion changed less than half a degree. Holding the cranium level (horizontal gaze) changes the segmental and overall coupled rotation behavior of the cervical spine during axial rotation. In 3 specimens, left axial rotation induced both right lateral bending in the lower segments and left lateral bending in upper segments, and vice versa with right axial rotation. In the three specimens in which both left and right lateral bending was induced by axial rotation, there was a 0.1° to 3.7° reduction in the coupled C3-C4 lateral bending range of motion. In the other two specimen, C3-C4 lateral bending range of motion increased by 0.8° to 1.8°. C5-C7 fusion changed the amount but not the direction of coupled lateral bending of unfused segments. CONCLUSIONS Without the horizontal gaze constraint, right axial rotation has been shown to induce right lateral bending in the cervical spine. There are various activities of daily living, such as looking over one's shoulder, that involve holding the gaze horizontal while axially rotating the cervical spine. In this biomechanical experiment, a constrained horizontal axial rotation resulted in specimen-specific coupled rotation of the subaxial cervical spine. In three of the specimen, axial rotation induced left and right segmental lateral bending regardless of the axial rotation direction.This specimen-specific difference in the coupled lateral bending and in the ability to perform constrained axial rotation after C5-C7 fusion leads us to wonder whether there may also be a patient-specific difference. This difference would have clinical implications for patients who are candidates for C5-C7 fusion. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

The Impact of Adult Thoracolumbar Spinal Deformities on Standing to Sitting Regional and Segmental Reciprocal Alignment.

Regional and segmental changes of the lumbar spine have previously been described as patients transition from standing to sitting; however, alignment changes in the cervical and thoracic spine have yet to be investigated. So, the aim of this study was to assess cervical and thoracic regional and segmental changes in patients with thoracolumbar deformity versus a nondeformed thoracolumbar spine population. This study was a retrospective cohort study of a single center's database of full-body stereoradiographic imaging and clinical data. Patients were ≥ 18 years old with nondeformed spines (nondegenerative, nondeformity spinal pathologies) or thoracolumbar deformity (ASD: PI-LL > 10°). Patients were propensity-score matched for age and maximum hip osteoarthritis grade and were stratified by Scoliosis Research Society (SRS)-Schwab classification by PI-LL, SVA, and PT. Patients with lumbar transitional anatomy or fusions were excluded. Outcome measures included changes between standing and sitting in global alignment parameters: sagittal vertical axis (SVA), pelvic incidence minus lumbar lordosis (PI-LL), pelivc tilt (PT), thoracic kyphosis, cervical alignment, cervical SVA, C2-C7 lordosis (CL), T1 slop minus CL (TS-CL), and segmental alignment from C2 to T12. Another analysis was performed using patients with cervical and thoracic segmental measurements. A total of 338 patients were included (202 nondeformity, 136 ASD). After propensity-score matching, 162 patients were included (81 nondeformity, 81 ASD). When categorized by SRS-Schwab classification, all nondeformity patients were nonpathologically grouped for PI-LL, SVA, and PT, whereas ASD patients had mix of moderately and markedly deformed modifiers. There were significant differences in pelvic and global spinal alignment changes from standing to sitting between nondeformity and ASD patients, particularly for SVA (nondeformed: 49.5 mm versus ASD: 27.4 mm; P&thinsp;< .001) and PI-LL (20.12° versus 13.01°, P < .001). With application of the Schwab classification system upon the cohort, PI-LL (P = .040) and SVA (P = .007) for severely classified deformity patients had significantly less positional alignment change. In an additional analysis of patients with segmental measurements from C2 to T12, nondeformity patients showed significant mobility of T2-T3 (-0.99° to -0.54°, P = .023), T6-T7 (-3.39° to -2.89°, P = .032), T7-T8 (-2.68° to -2.23°, P = .048), and T10-T11 (0.31° to 0.097°, P = .006) segments from standing to sitting. ASD patients showed mobility of the C6-C7 (1.76° to 3.45°, P < .001) and T11-T12 (0.98° to 0.54°, P = 0.014) from standing to sitting. The degree of mobility between nondeformity and ASD patients was significantly different in C6-C7 (-0.18° versus 1.69°, P = .003), T2-T3 (0.45° versus -0.27°, P = .034), and T10-T11 (0.45° versus -0.30°, P = .001) segments. With application of the Schwab modifier system upon the cohort, mobility was significant in the C6-C7 (nondeformed: 0.18° versus moderately deformed: 2.12° versus markedly deformed: 0.92°, P = .039), T2-T3 (0.45° versus -0.08° versus -0.63°, P = .020), T6-T7 (0.48° versus 0.36° versus -1.85°, P = .007), and T10-T11 (0.45° versus -0.21° versus -0.23°, P = .009) segments. Nondeformity patients and ASD patients have significant differences in mobility of global spinopelvic parameters as well as segmental regions in the cervical and thoracic spine between sitting and standing. This study aids in our understanding of flexibility and compensatory mechanisms in deformity patients, as well as the possible impact on unfused segments when considering deformity corrective surgery.

Biomechanical effects on the intermediate segment of noncontiguous hybrid surgery with cervical disc arthroplasty and anterior cervical discectomy and fusion: a finite element analysis

Background contextSurgery for cervical degenerative disc disorder (CDDD) at two noncontiguous segments is infrequent. Few studies have explored the biomechanical effects on the intermediate adjacent segment of anterior cervical discectomy and fusion (ACDF) or cervical disc arthroplasty (CDA) in this situation. No study has examined biomechanical differences between ACDF and hybrid surgery (HS) constructs for noncontiguous CDDD. Differences in the biomechanical changes between the intermediate and adjacent segments are unknown. PurposeThis study was conducted to compare the biomechanical changes resulting from noncontiguous ACDFs and HS. Study designA finite element analysis study. MethodsA finite element model of a healthy cervical spine (C2–C7) was constructed. Three surgical models were developed: (1) ACDF at C3/4 and C5/6 (FF), (2) ACDF at C3/4 and CDA at C5/6 (FA) and (3) CDA at C3/4 and ACDF at C5/6 (AF). A 75-N follower load with 1.0 N·m moments was applied to the top of the C2 vertebra in the intact model to simulate flexion, extension, lateral bending, and axial rotation. Surgical models achieved identical motion angles of the intact model in each direction following the displacement-control protocols. ResultsThe FF model required much higher moments than did the AF and FA models to achieve the same amount of motion. In the FF model, the motion contributions of the unfused segments were unevenly increased. The magnitude of the increased motion in the intermediate segment was larger than those in the supra- or infra-adjacent segments. The facet contact force (FCF) and intradiscal pressure (IDP) at the intermediate segment were also more susceptible to impact. In the FA and AF models, the motion contributions of the untreated levels were evenly changed, and the intermediate segment did not experience additive motion, FCF, or IDP. The segment adjacent to the level of ACDF had greater FCF and IDP than did the segment adjacent to the level of CDA in the two HS constructs. ConclusionsHS constructs resulted in less altered biomechanics and kinematics of the untreated levels and showed no additive biomechanical effects on the intermediate segments compared with ACDF at noncontiguous levels. However, the effects were associated with the relative location of the ACDF and CDA levels. Clinical significanceThis study provides a biomechanical rationale for the use of HS to treat patients with noncontiguous CDDD.

Biomechanics following skip-level cervical disc arthroplasty versus skip-level cervical discectomy and fusion: a finite element-based study

BackgroundModerately increased motion at the intermediate segment (IS) after skip-level fusion may accelerate disc degeneration. However, limited biomechanical data are available that examine the effects on the IS following cervical disc arthroplasty (CDA). The purpose of this study is to investigate the biomechanical changes in the IS of the cervical spine after skip-level fusion or skip-level arthroplasty.MethodsA finite element model of a healthy cervical spine (C2-C7) was constructed. Two surgical models were developed: (1) skip-level fusion at C3/4 and C5/6 and (2) skip-level arthroplasty at C3/4 and C5/6. A 75-N follower load and 1.0-N·m moments were applied to the top of the C2 vertebra to produce flexion, extension, lateral bending and axial rotation in the intact model. The end-points in each direction corresponding to the intact model were applied to the surgical models under displacement-control protocols.ResultsThe ranges of motion (ROMs) of the fusion model were markedly decreased at the operated levels, while the corresponding ROMs of the arthroplasty model were similar to those of the intact spine in all directions. In the fusion model, the ROMs of the IS (C4/5) were markedly increased in all directions. The ROMs in the arthroplasty model were similar to those in the intact spine, and the ROMs of untreated segments were evenly increased. In the fusion model, the intradiscal pressure and facet contact force at were C4/5 remarkably increased and unevenly distributed among the unfused segments. In the arthroplasty model, the IS did not experience additive stress.ConclusionThe IS does not experience additive ROM or stress in the intervertebral disc or facet joints after skip-level arthroplasty, which has fewer biomechanical effects on the IS than does skip-level fusion. This study provides a biomechanical rationale for arthroplasty in treating patients with skip-level cervical degenerative disc disease.

Measurement of Spinopelvic Angles on Prone Intraoperative Long-Cassette Lateral Radiographs Predicts Postoperative Standing Global Alignment in Adult Spinal Deformity Surgery

Retrospective review from a single institution. To evaluate intraoperative T1-pelvic angle (TPA), T4PA, and T9PA as predictors of postoperative global alignment after adult spinal deformity (ASD) surgery. Malalignment following adult spinal surgery is associated with disability and correlates with health-related quality of life. Preoperative planning and intraoperative verification are crucial for optimal postoperative outcomes. Currently, only pelvic incidence minus lumbar lordosis (PI-LL) mismatch has been used to assess intraoperative correction. Patients undergoing ≥4-level spinal fusion with full-length pre-, intra-, and first postoperative calibrated radiographs were included from a single institution. Alignment measurements were obtained for sagittal vertical axis (SVA), PI-LL, TPA, T4PA, and T9PA. The whole cohort was divided into upper thoracic (UT: UIV > T7) and lower thoracic fusions (LT: UIV < T7). Change was assessed between phases, and a subanalysis was included for UT and LT groups to compare alignment changes for differing extent of proximal fusion in the sagittal plane. Eighty patients (mean 63.4 years, 70% female, mean levels fused 11.9) underwent significant ASD correction (ΔPI-LL = 22.1°; ΔTPA = 13.8°). For all, intraoperative TPA, T4PA, and T9PA correlated with postoperative SVA (range, r = 0.41-0.59), whereas intraoperative PI-LL correlated less (r = 0.38). For UT (n = 49), all spinopelvic angles and LL were similar intraoperative to postoperatively (p > .09). For LT (n=31), intraoperative and postoperative T9PA and LL were similar (p > .10) but TPA and T4PA differed (p < .02). For UT, all intraoperative and postoperative spinopelvic angles strongly correlated (r = 0.8-0.9). For LT, intraoperative to postoperative T9PA strongly correlated (r = 0.83) and TPA, T4PA, and LL correlated moderately (r = 0.65-0.70). LT trended toward more reciprocal kyphosis postoperatively (8.1° vs. 2.6°; p = .059). Intraoperative measurements of TPA, T4PA, and T9PA correlated better with postoperative global alignment than PI-LL, demonstrating their utility in confirming alignment goals. When comparing intraoperative to postoperative films, only T9PA was similar in LT whereas all spinopelvic angles were similar in UT. Reciprocal kyphosis in unfused segments of LT fusions may account for difference in TPA and T4PA from intraoperative to postoperative films. Level III.

Risk factors related to adjacent segment degeneration: retrospective observational cohort study and survivorship analysis of adjacent unfused segments

Object: Adjacent segment disease (ASD) has been described as a frequent complication after a lumbar spinal fusion procedure, though its incidence and the factors related to its appearance are not well established. The radiographic signs that identify ASD in unfused segments may be a consequence of biomechanical changes induced by the fusion procedure. This study sought to analyse the incidence of radiographic changes (radiographic ASD) in all adjacent unfused segments, the clinical changes that require a second procedure (clinical ASD), and the risk factors of their appearance evaluated at different follow-up times.Methods: We conducted a retrospective cohort study of patients fused for degenerative spine disease and instability to analyse ASD risk factors using actuarial estimation, comparison of the Kaplan-Meier survival curves of each variable, and Cox proportional-hazards regression analysis.Results: Among the 263 patients included in the study, radiographic changes were observed in 57.4% and related clinical changes in 20.2%. The univariate analysis showed a higher risk of ASD in patients with smaller post- vs. pre-operative lumbar lordosis (p = .018), diagnosis of lumbar canal stenosis (p = .019), fusion of three or more vs. fewer levels (p = .009) and those fixed with top-loading screws vs. side-connecting screws (p = .001). Cox proportional-hazards regression analysis showed that the use of top-loading pedicle screws and three or more levels of fusion led to a 3- and 2-fold higher risk of degeneration in adjacent unfused segments respectively.Conclusions: Risk of a second surgical procedure due to clinical changes is 3-fold higher in patients with three or more levels of fusion, and 2.5-fold higher in patients intervened with top-loading pedicle screws.

Preservation of Spine Motion in the Surgical Treatment of Adolescent Idiopathic Scoliosis Using an Innovative Apical Fusion Technique: A 2-Year Follow-Up Pilot Study.

This trial reports the 2-year and immediate postremoval clinical outcomes of a novel posterior apical short-segment (PASS) correction technique allowing for correction and stabilization of adolescent idiopathic scoliosis (AIS) with limited fusion. Twenty-one consecutive female AIS patients were treated at 4 institutions with this novel technique. Arthrodesis was limited to the short apical curve after correction with translational and derotational forces applied to upper and lower instrumented levels. Instrumentation spanned fused and unfused segments with motion and flexibility of unfused segments maintained. The long concave rods were removed at maturity. Radiographic data collected included preoperative and postoperative data for up to 2 years as well as after long rod removal. All 21 patients are beyond 2 years postsurgery. Average age at surgery was 14.2 years (11-17 years). A mean of 10.5 ± 1 levels per patient were stabilized and 5.0 ± 0.5 levels (48%) were fused. Cobb angle improved from 56.1° ± 8.0° to 20.8° ± 7.8° (62.2% improvement) at 1 year and 20.9° ± 8.4°, (62.0% improvement) at 2 years postsurgery. In levels instrumented but not fused, motion was 26° ± 6° preoperatively compared to 10° ± 4° at 1 year postsurgery, demonstrating 38% maintenance of mobility in nonfused segments. There was no report of implant-related complications. PASS correction technique corrected the deformity profile in AIS patients with a lower implant density while sparing 52% of the instrumented levels from fusion through the 2-year follow-up.

Wednesday, September 26, 2018 3:35 PM – 5:05 PM How to Avoid Complications

BACKGROUND CONTEXT PJK is a frequent complication following adult spinal deformity (ASD) occurring in 80% of the patients within the first 6 weeks. PJK is a subject of numerous research projects, yet little is known regarding the risk factors for new onset PJK after 6 weeks. PURPOSE This study aims to bring to light radiographic risk factors associated with PJK development between 6 weeks and 2 years in patients with lower thoracic. STUDY DESIGN/SETTING Retrospective review of a prospective database. PATIENT SAMPLE A total of 116 ASD patients, who underwent a complete fusion of the lumbar spine down to the pelvis with a UIV between T8 and L1. OUTCOME MEASURES Classic spino pelvic parameters. Radiographic PJK at 6 weeks and 2 years: defined as a kyphotic angle greater than 10° between the upper instrumented vertebra (UIV) and 2 levels above it or a kyphotic change at the same level greater than 10° between preop and postop. Gravity line parameters at 6 weeks: bending moments, gravity line offsets from the UIV. METHODS Patients were categorized based on the presence of PJK (Glattes) at 6 weeks and 2 years FU. Only patients with no-PJK at 6 weeks and no revision surgery were retained for the analysis and were categorized as progress (PJK at 2 Years) versus maintain (no PJK at 2 years). Based on anthropometric data, the projection of the center of gravity of the trunk and head in the standing posture was modeled. This mechanical model was previously developed and validated on an external full-body database. Demographic, surgical, gravity line, and radiographic data were compared between progress and maintain. Linear correlations and regression were performed to predict change above the instrumentation. RESULTS Out of the 116 patients included; 82% are female with average BMI of 27 kg/m2 and average age 62 years. At 6 weeks, there were no differences in classic spino-pelvic parameters. The PJA angle was -3.8±6.3 (Progress) and. −6.2±7.3 (Maintain). Progress group had more posterior T9SPi (−13.3±3.5 vs. −11.5±4.9, p CONCLUSIONS As a crucial element of standing posture, unfused segments changed to maintain the GL over the feet. Onset of PJK after 6 weeks postop was associated with a more posterior UIV position relative to the center of mass of the trunk. This increase in distance may lead to increased stress and mechanical loading at the junction, favoring acute reciprocal change. Further investigation is needed to define optimal loading at the UIV to reduce PJK. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: innovation, surface technology and biomechanics: 179. Alignment targets, curve proportion and mechanical loading: preliminary analysis of an ideal shape toward reducing proximal junctional kyphosis

BACKGROUND CONTEXT PJK is a common problem following ASD surgery. When significant junctional pathology develops, patients commonly recruit compensatory mechanisms, and this can lead not only to suboptimal clinical outcome but also a distortion of how postoperative alignment is assessed. Recent articles have demonstrated the validity of a numerical model to remove PJK influence from postoperative alignment by combining postoperative alignment of fused segments with alignment of preoperative unfused segments PURPOSE Investigate the offset from alignment targets (radiographic and mechanical loading) in PJK patients using a validated model to remove PJK compensation. STUDY DESIGN/SETTING Retrospective review. PATIENT SAMPLE A total of 373 pts from 501 (74.5%) eligible with minimum 2 years follow-up. OUTCOME MEASURES Real and virtual postoperative alignment. METHODS Pts with a complete fusion of the lumbar spine and 2 years follow-up were included on this analysis. Patients were categorized into non-PJK, PJK or PJF group based on the Glattes criteria; PJF patients were those undergoing revision surgery. Alignment targets were derived from recent publications on age-alignment objectives (Spine, 2016), theoretical values of thoracic kyphosis based on lordosis, and normative mechanical loading at each vertebra (SRS, 2016). Using the virtual alignment, offsets from alignment targets were compared across PJK groups and a sub-stratification by UIV position was conducted (upper thoracic – UT versus Lower thoracic – LT). Multilinear logistic regression was conducted to identify independent predictor of PJK and/or PJF. RESULTS From 373 pts included (62.7 yo±9.9; 81%F), 172 (46.1%) were identified as PJK, and 21 (5.6%) as PJF 2 years after surgery. Significant difference were found in terms of PI-LL (5.7°, 1.6°, and −4.9) and TK (−47.8, −56.3, −65.0) and Bending moment at the UIV (all p CONCLUSIONS By removing the effect of PJK on compensatory mechanisms and global alignment, the analysis highlighted a significantly more posterior correction in PJK patients Analysis of offset from targets (age adjusted value, proportionality between curves, and mechanical loading) demonstrated an over correction versus age alignment, under correction of TK (smaller), and under loading of the UIV to reduce reciprocal change.

Posterior spinal surgery for adolescent idiopathic scoliosis does not induce compensatory increases in distal adjacent segment motion: a prospective gait analysis study

Background ContextPatients with adolescent idiopathic scoliosis (AIS) perform surprisingly well after spinal correction and fusion. It was previously hypothesized that, during gait, certain mechanisms compensate for the loss in spinal motion. Still, previous studies could not identify such compensatory mechanisms in the lower body. PurposeThis study aims to test the hypothesis of a compensatory increased motion of the distal unfused part of the spine during gait after posterior spinal correction and fusion. StudyThis is a prospective gait study. Patients and MethodsTwelve patients with AIS were included. Sets of three VICON skin markers were used to measure the 3D motion of the proximal part of the fusion in relation to the pelvis (PFP) and the distal part of the fusion in relation to the pelvis (DFP). By doing so, PFP represents the motion of the fused and unfused parts of the spine, and DFP represents the motion of the unfused part of the spine. Measurements were performed preoperatively and 3 and 12 months after posterior spinal correction and fusion. ResultsSurgery resulted in a decrease in PFP transversal plane range of motion (ROM) (8.3° vs. 5.9°, p=.006). No compensatory increase in the ROM of DFP could be identified. Actually, DFP transversal plane ROM also decreased (8.2° vs. 5.6°, p=.019). No improvement over time was observed when comparing the 3- and 12-month postoperative measurements. ConclusionsThe hypothesis of a compensatory increase in motion of the distal unfused segments after spinal fusion for AIS is a much researched and controversial topic. This study is the first to study this hypothesis in such detail during gait and could not demonstrate such increase.

Risk factors for non-fusion segment disease after anterior cervical spondylosis surgery: a retrospective study with long-term follow-up of 171 patients

BackgroundThe purpose of this study was to investigate the incidence and causes of non-fusion segment disease (NFSD), both adjacent and non-adjacent to a fused segment, after anterior cervical arthrodesis.MethodsThis is a single-center study. Between January 1998 and January 2011, two surgeons’ 171 patients who had an anterior cervical decompression and fusion were followed clinically for more than 5 years. The correlation between the incidence of symptomatic non-fusion segment disease and the following clinical parameters (age at operation, fusion levels,) and radiological parameters (number of patients who had a plate, anterior cervical decompression and fusion (ACDF) or corpectomies, preoperative and postoperative cervical spine alignment, Pavlov’s ratio at the C5 level, and preoperative existence of a non-fusion segment degeneration on magnetic resonance imaging) was evaluated.ResultsOf the 171 patients reviewed, 16 patients had non-fusion segment disease (9.36%), of which 12 had adjacent segment disease and 4 had non-adjacent segment disease. Postoperative cervical lordosis in the non-fusion segment disease group was significantly smaller than that of the disease-free group (P < 0.001). Fusion levels in the NFSD group were 1.69 whereas 2.26 in disease-free group (P = 0.005). The incidences of disc degeneration in unfused segments was more severe in the NFSD group than in the disease-free group (P = 0.004). The results of binary logistic regression showed that the major factor affecting NFSD is postoperative cervical lordosis (P = 0.000) followed by disc degeneration (P = 0.024). The other parameters did not show a statistically significant difference.ConclusionsThe incidence of symptomatic non-fusion segment disease after anterior cervical arthrodesis has multifactorial causes. Postoperative cervical lordosis and disc degeneration in non-fusion segments were major factors in the incidence of NFSD.

Virtual Modeling of Postoperative Alignment After Adult Spinal Deformity Surgery Helps Predict Associations Between Compensatory Spinopelvic Alignment Changes, Overcorrection, and Proximal Junctional Kyphosis.

Retrospective review of a prospective multicenter database. To develop a method to analyze sagittal alignment, free of the influence of proximal junctional kyphosis (PJK), and then compare PJK to non-PJK patients using this method. PJK after adult spinal deformity (ASD) surgery remains problematic as it alters sagittal alignment. The present study proposes a novel virtual modeling technique that attempts to eliminate the confounding effects of PJK on postoperative spinal alignment. A virtual spinal modeling technique was developed on a retrospective ASD cohort of patients with multilevel spinal fusions to the pelvis with at least 2-year postoperative follow-up. The virtual postoperative alignment (VIRTUAL) was created from the postoperative alignment of the instrumented segments and the preoperative alignment of the unfused segments. VIRTUAL was validated by comparisons to actual 2-year postoperative alignment (REAL) in non-PJK patients. Patients were then divided into two groups: PJK and non-PJK based on the presence/absence of PJK at 2 years postoperatively. PJK and non-PJK patients were compared using VIRTUAL and REAL. A total of 458 patients (78F, mean 57.9 yr) were analyzed. The validation of VIRTUAL versus REAL demonstrated correlation coefficients greater than 0.7 for all measures except sagittal vertical axis (SVA; r = 0.604). At 2 years, REAL alignment in PJK patients demonstrated a smaller pelvic incidence minus lumbar lordosis and a larger thoracic kyphosis than non-PJK patients, but similar SVA, T1 pelvic angle, and pelvic tilt. An analysis of VIRTUAL demonstrated that patients with PJK had a smaller pelvic incidence minus lumbar lordosis, pelvic tilt, SVA, and T1 pelvic angle than non-PJK patients (P < 0.05). This technique demonstrated strong correlations with actual postoperative alignment. Comparisons between REAL and VIRTUAL alignments revealed that postoperative PJK may develop partially as a compensatory mechanism to the overcorrection of sagittal deformities. Future research will evaluate the appropriate thresholds for deformity correction according to age and ASD severity. 3.

Artificial Cervical Disk Replacement for the Treatment of Adjacent Segment Disease After Anterior Cervical Decompression and Fusion.

Retrospective study. To evaluate the outcome of artificial cervical disk replacement (ACDR) for the treatment of adjacent segment disease (ASD) after anterior cervical decompression and fusion (ACDF). ACDF is the useful procedure for degenerative cervical diseases. However, studies have reported accelerated degeneration of functional spinal units adjacent to the fusion site after ACDF. Between January 2004 and January 2011, 32 inpatients (18 male, 14 female; age, 38-61 y; mean, 48 y) underwent ACDR for the treatment of ASD after previous ACDF (single-level: n=12; 2-level: n=15; 3-level: n=5). In 22 patients, ASD occurred above the fusion site, and in 10 it occurred below the site. After ACDR, the patients were followed up for 30-62 months (mean, 49 mo). Before and after ACDR, patients were evaluated using the pain visual analog scale (VAS), the Japanese Orthopedic Association (JOA) score, and neck disability index (NDI). In addition, the range of motion (ROM) of the replaced and adjacent unfused segments was measured by flexion/extension lateral radiography. Periprosthetic heterotopic ossification was detected using McAfee's classification. Degeneration of the adjacent unfused segment was evaluated using Goffin scale. All patients had successful surgery. Before ACDR, neck VAS, upper-limb VAS, JOA score, and NDI were 7.2±1.8, 6.9±1.1, 9.8±2.5, and 40.5±4.8, respectively. At the last follow-up, they were 1.2±0.3, 0.9±0.3, 14.5±1.1, and 9.0±2.5, respectively. Compared with presurgery, the improvements in VAS, JOA score, and NDI at the final follow-up were statistically significant (all P<0.05). During follow-up, prosthesis positioning was satisfactory without migration or downward movement. Preoperatively, the ROMs of the replaced and adjacent segments were 8.7±2.6 and 7.6±3.0, respectively. At the last follow-up, they were 8.5±2.2 and 7.2±2.6, respectively (both P>0.05). At the last follow-up, 2 patients had grade II heterotopic ossification; 3 patients had aggravated degeneration (vs. preoperative status) of the adjacent unfused segment. However, the reduction in Goffin grade was not statistically significant. Our follow-up shows that ACDR is an effective treatment for post-ACDF ASD. It can maintain the ROMs of the replaced segment as well as the adjacent unfused segment.

Reliability and scientific use of a surgical planning software for anterior cervical discectomy and fusion (ACDF).

Software-based planning of a spinal implant inheres in the promise of precision and superior results. The purpose of the study was to analyze the measurement reliability, prognostic value, and scientific use of a surgical planning software in patients receiving anterior cervical discectomy and fusion (ACDF). Lateral neutral, flexion, and extension radiographs of patients receiving tailored cages as suggested by the planning software were available for analysis. Differences of vertebral wedging angles and segmental height of all cervical segments were determined at different timepoints using intraclass correlation coefficients (ICC). Cervical lordosis (C2/C7), segmental heights, global, and segmental range of motion (ROM) were determined at different timepoints. Clinical and radiological variables were correlated 12 months after surgery. 282 radiographs of 35 patients with a mean age of 53.1±12.0years were analyzed. Measurement of segmental height was highly accurate with an ICC near to 1, but angle measurements showed low ICC values. Likewise, the ICCs of the prognosticated values were low. Postoperatively, there was a significant decrease of segmental height (p<0.0001) and loss of C2/C7 ROM (p=0.036). ROM of unfused segments also significantly decreased (p=0.016). High NDI was associated with low subsidence rates. The surgical planning software showed high accuracy in the measurement of height differences and lower accuracy values with angle measurements. Both the prognosticated height and angle values were arbitrary. Global ROM, ROM of the fused and intact segments, is restricted after ACDF.

From Goethe’s plant archetype via Haeckel’s biogenetic law to plant evo-devo 2016

In 1790, the German poet Johann W. v. Goethe (1749-1832) proposed the concept of a hypothetical sessile organism known as the 'Plant Archetype,' which was subsequently reconstructed and depicted by 19th-century botanists, such as Franz Unger (1800-1870) and Julius Sachs (1832-1897), and can be considered one of the first expressions of Evo-Devo thinking. Here, we present the history of this concept in the context of Ernst Haeckel's (1834-1919) biogenetic law espoused in his Generelle Morphologie der Organismen of 1866. We show that Haeckel's idea of biological recapitulation may help to explain why various phenomena, such as the ontogenetic transformations in the stellar anatomy of lycopods and ferns, the transition from primary to secondary anatomy of seed plants, the presence of unfused juvenile cone scale segments in the Japanese cedar (Cryptomeria japonica), and the transition of C3- to C4-photosynthesis in the ontogeny of maize (Zea mays), appear to support his theories. In addition, we outline the current status of plant evolutionary developmental biology (Evo-Devo), which can be traced back to Haeckel's (1866) biogenetic law, with a focus on the model plant thale cress (Arabidopsis thaliana).

Analysis of Segmental Mobility Following a Novel Posterior Apical Short-Segment Correction for Adolescent Idiopathic Scoliosis.

A prospective, nonrandomized, multicenter study. The purpose of this study was to evaluate the amount of motion present at instrumented but unfused segments and at motion segments adjacent to the instrumentation following application of a new posterior apical short-segment correction technique for correcting adolescent idiopathic scoliosis (AIS). High-density pedicle screw instrumentation and posterior arthrodesis of all instrumented levels is the most common surgical treatment for AIS stabilization. The consequence of long fusion is an abnormal load on adjacent levels with an increased risk of future adjacent segment degeneration. This new system applied translational and derotational forces over a short apical segment. The short apical region was prepared for fusion while maintaining motion of unfused vertebral segments. Radiographic data were collected pre-operatively, at surgery, and at 3, 6, and 12 months after surgery. Twenty-one female patients, mean age of 14.2 years (10.6-16.9 years) with Lenke 1A/1B curves, were enrolled. The range of motion in the unfused instrumented segment was significantly higher than the apical fused segment (11 vs. 0.9, P < 0.001). The range of motion of unfused vertebral levels distal to the construct at one year did not differ significantly from their respective pre-op values. When the analysis was extended to understand the impact of lower instrumented vertebra (LIV) on motion of unfused segments distal to the construct, it appeared that (1) the change in motion from pre-op to 12 months post-op as a function of LIV is not statistically significant; and (2) The motion of the unfused distal vertebral segments at 12 months does not statistically increase with a lower LIV. Through one year, this novel technique achieved and maintained similar AIS correction to current posterior fusion techniques while maintaining the mobility of unfused motion segments with less implant density. 4.

Sagittal Correction and Reciprocal Changes After Thoracic Pedicle Subtraction Osteotomy.

A retrospective clinical review. To evaluate the sagittal correction efficacy of a thoracic pedicle subtraction osteotomy (PSO), to determine and predict changes at both the cervical and lumbar mobile unfused segments after whether an upper or lower level thoracic PSO. Thoracic PSO is a technically challenging but increasingly valid procedure in the treatment of fixed thoracic deformities.Anatomical characteristics differentiate upper and lower segment thoracic PSOs and define its corrective ability. There is yet paucity in the literature concerning the causality between the osteotomy level and the reciprocal changes observed postoperatively at the adjacent unfused curves. Data collection from a single institutional database was carried out retrospectively by reviewing medical records and imaging of fixed thoracic kyphotic deformity patients submitted to a single level thoracic PSO. Seventeen patients (11M:6F), with a mean age of 44 years (range, 17-76). Fifty-nine percent had a previous spine surgery. The mean follow-up was of 55 months (range, 27-122). In six patients PSO was performed in the upper thoracic segment (T1-T6) and in 11 patients between T7 and T12 (lower thoracic segment), allowing a mean local kyphosis correction of 31° and 41° respectively. The mean cervical and lumbar lordosis globally improved. The upper thoracic PSO group had a significant improvement of the cervical lordosis with a mean C7 slope correction of 28° (P = 0.004), whereas in the lower thoracic PSO group a more pronounced correction of the maximal lumbar lordosis was observed (22°, P = 0.033). After a fixed sagittal thoracic deformity, the predominant lordotic compensation seems to occur at the nearest mobile curve from the deformity apex. The PSO-induced restoration of the thoracic kyphosis relieved the compensatory cervical and/or lumbar excessive lordosis, which were present preoperatively and are now no longer needed to achieve balance and maintain horizontal gaze. 4.