Development Of Adjacent Segment Disease Research Articles

Lumbar Apex Position as an Independent Risk Factor for Adjacent Segment Diseases in Patients Undergoing Short-level Transforaminal Lumbar Interbody Fusion.

Retrospective study. To investigate whether lumbar apex position had an impact on the development of adjacent segment disease (ASD) following transforaminal lumbar interbody fusion (TLIF). Previous studies have demonstrated that solely concentrating on lumbar lordosis value is not suitable and neglecting the significance of lumbar apex can lead to mechanical complications. However, the relationship between lumbar apex and ASD is still not well understood. In this retrospective study, 234 consecutive patients who underwent L3-5 or L4-5 TLIF for degenerative diseases were reviewed. The study evaluated the associations between sagittal parameters and pelvic incidence (PI). Patients were labeled "matched" when lumbar apex position aligned with the theoretical target, and "mismatched" when it did not. Multivariate analysis was applied to find the independent risk factors of ASD. Additionally, a focused sub-analysis was performed based on the lumbar apex position (ideal match, cranial from ideal, and caudal from ideal). After an average follow-up period of 70.6 months, 68 cases were identified as having ASD. Postoperatively, 64.7% (44 out of 68) of the patients with ASD exhibited a mismatched lumbar apex, compared to 41% (68 out of 166) of those without ASD (p < 0.001). PI correlated significantly with proximal lordosis (PL) and lordosis distribution index (LDI), but not with distal lordosis (DL). Multivariate analysis identified age, L3-5 fusion, postoperative DL, and postoperative mismatched lumbar apex as independent risk factors of ASD. Upon the sub-analysis, it was discovered that there were unique compensatory strategies in the cranial and caudal groups, with notable variations in postoperative DL, PL, and LDI among three groups (all p value<0.05). Lumbar apex position significantly influenced the risk of ASD. To restore the lumbar apex to its ideal position, a proper value and distribution of DL should be attained.

Validation of Roussouly classification in predicting the occurrence of adjacent segment disease after short-level lumbar fusion surgery

BackgroundRecent studies demonstrated that restoring sagittal alignment to the original Roussouly type can remarkably reduce complication rates after adult spinal deformity surgery. However, there is still no data proving the benefit of maintaining ideal Roussouly shape in the lumbar degenerative diseases and its association with the development of adjacent segment disease (ASD). Thus, this study was performed to validate the usefulness of Roussouly classification to predict the occurrence of ASD after lumbar fusion surgery.Materials and MethodsThis study retrospectively reviewed 234 consecutive patients with lumbar degenerative diseases who underwent 1- or 2-level fusion surgery. Demographic and radiographic data were compared between ASD and non-ASD groups. The patients were classified by both “theoretical” [based on pelvic incidence (PI)] and “current” (based on sacral slope) Roussouly types. The patients were defined as “matched” if their “current” shapes matched the “theoretical” types and otherwise as “mismatched”. The logistic regression analysis was performed to identify the factors associated with ASD. Finally, clinical data and spinopelvic parameters of “theoretical” and “current” types were compared.ResultsWith a mean follow-up duration of 70.6 months, evidence of ASD was found in the 68 cases. Postoperatively, ASD group had more “current” shapes classified as type 1 or 2 and fewer as type 3 than the non-ASD group (p < 0.001), but the distribution of “theoretical” types was similar between groups. Moreover, 80.9% (55/68) of patients with ASD were mismatched, while 48.2% (80/166) of patients without ASD were mismatched (p < 0.001). A multivariate analysis identified age [odds ratio (OR) = 1.058)], 2-level fusion (OR = 2.9830), postoperative distal lordosis (DL, OR = 0.949) and mismatched Roussouly type (OR = 4.629) as independent risk factors of ASD. Among the four "theoretical" types, type 2 had the lowest lumbar lordosis, DL, and segmental lordosis. When considering the "current" types, current type 2 was associated with higher rates of 2-level fusion, worse DL, and greater pelvic tilt compared with other current types.ConclusionsDL loss and mismatched Roussouly type were significant risk factors of ASD. To decrease the incidence of ASD, an appropriate value of DL should be achieved to restore sagittal alignment back to the ideal Roussouly type.Level of Evidence: Level 4.

Letter to the Editor: Postoperative Sagittal Balance Has Only a Limited Role in the Development of Adjacent Segment Disease After Lumbar Spine Fusion for Degenerative Lumbar Spine Disorders A Subanalysis of the 10-Year Follow-up Study.

Sethy, Siddharth S. MBBS, MS (Orthopaedics); Goyal, Nikhil MBBS, MS (Orthopaedics); Kandwal, Pankaj MBBS, MS (Orthopaedics) Author Information

Reply to Letter to the Editor Regarding the Article "Postoperative Sagittal Balance has Only a Limited Role in the Development of Adjacent Segment Disease after Lumbar Spine Fusion for Degenerative Lumbar Spine Disorders: A Subanalysis of the 10-year Follow-up Study".

Toivonen, Leevi A. MD, PhDa; Mäntymäki, Heikki MD, PhDa; Häkkinen, Arja PhDb; Kautiainen, Hannu PhDc; Neva, Marko H. MD, PhDa Author Information

Comparison of Oblique Lumbar Interbody Fusion Combined with Posterior Decompression (OLIF-PD) and Posterior Lumbar Interbody Fusion (PLIF) in the Treatment of Adjacent Segmental Disease(ASD)

An unintended consequence following lumbar fusion is the development of adjacent segment disease (ASD). Oblique lumbar interbody fusion combined with posterior decompression (OLIF-PD) is another feasible option for ASD, and there is no literature report on this combined surgical strategy. A retrospective analysis was performed on 18 ASD patients requiring direct decompression in our hospital between September 2017 and January 2022. Among them, eight patients underwent OLIF-PD revision and ten underwent PLIF revision. There were no significant differences in the baseline data between the two groups. The clinical outcomes and complications were compared between the two groups. The operation time, operative blood loss and postoperative hospital stay in the OLIF-PD group were significantly lower than those in the PLIF group. The VAS of low back pain in the OLIF-PD group was significantly better than that in the PLIF group during the postoperative follow-up. The ODI at the last follow-up in the OLIF-PD group and the PLIF group were significantly relieved compared with those before operation. The excellent and good rate of the modified MacNab standard at the last follow-up was 87.5% in the OLIF-PD group and 70% in the PLIF group. There was a statistically significant difference in the incidence of complications between the two groups. For ASD requiring direct decompression after posterior lumbar fusion, compared with traditional PLIF revision surgery, OLIF-PD has a similar clinical effect, but has a reduced operation time, blood loss, hospital stay and complications. OLIF-PD may be an alternative revision strategy for ASD.

Additional operation rates after surgery for degenerative spine diseases: minimum 10 years follow-up of 4705 patients in the national Swedish spine register

ObjectivesTo identify rates of additional operation after the index operation for degenerative lumbar spine diseases.DesignRetrospective register study.SettingNational outcome data from Swespine, the National Swedish spine register.ParticipantsA total of 4705 patients...

Intervertebral kinematics during neck motion 6.5 years after fusion and artificial disc replacement

BackgroundArthroplasty with artificial disc replacement for surgical treatment of cervical spine degeneration was introduced with the notion that motion-preserving approaches would prevent development of adjacent segment disease. Though clinical outcomes favor arthroplasty over the commonly used anterior cervical discectomy with fusion approach, clinical studies confirming the biomechanical basis of these results are lacking. The aim of this study was to compare intervertebral kinematics between arthroplasty and fusion patients 6.5 years post-surgery during physiological motion of the neck. MethodsUsing a biplane dynamic X-ray system, computed tomography imaging and model based tracking algorithms, three dimensional intervertebral kinematics were measured during neck axial rotation and extension in 14 patients treated for cervical radiculopathy with fusion (n = 8) or arthroplasty (n = 6). The measurements were performed at 2-year (baseline) and 6.5 year post-surgical time points, with the main interest being in the interaction between surgery types and time points. 3 translations and 3 rotations were investigated for the index (C5C6), and upper- (C4C5) and lower adjacent levels (C6C7). FindingsSurgery-time interaction was significant for axial rotation (P < 0.04) and flexion-extension rotation (P < 0.005) in C4C5 during neck axial rotation, left-right translation (P < 0.04) in C5C6 and anterior-posterior translation in C6C7 (P < 0.04) during neck extension. In contrast with the expectations, axial rotation and flexion-extension decreased in C4C5 during neck rotation and anterior-posterior translation decreased in C6C7 during neck extension for fusion. InterpretationThe findings do not support the notion that adjacent segment motion increases after fusion.

17. Seven-year outcomes of ACDF vs minimally invasive posterior cervical foraminotomy in the treatment of cervical radiculopathy

<h3>BACKGROUND CONTEXT</h3> Minimally invasive posterior cervical foraminotomy (MI-PCF) is a motion sparing technique that has been shown in several studies to be similarly effective as ACDF in treating cervical radiculopathy due to foraminal stenosis and other related degenerative pathologies. MI-PCF also has several advantages over ACDF as it is associated with fewer hardware complications, shortened hospital stay, reduced blood loss and cost. It has been hypothesized that preserving motion may reduce the risk of the development of adjacent segment disease (ASD) in MI-PCF vs ACDF. Recent studies have shown a similar revision rate between MI-PCF and ACDF at 2-year follow-up; however, long-term follow-up data comparing MI-PCF vs ACDF are scarce. <h3>PURPOSE</h3> The purpose of this study is to compare outcomes of MI-PCF and ACDF in the treatment of unilateral cervical radiculopathy over long-term (>7 years) follow-up. <h3>STUDY DESIGN/SETTING</h3> Retrospective comparative study. <h3>PATIENT SAMPLE</h3> A total of 177 consecutive patients at a single institution who underwent ACDF or MI-PCF between 2009-2013 with a minimum follow-up of 7 years. <h3>OUTCOME MEASURES</h3> (1) Patient demographics; (2) complication rate; (3) revision rate; (4) patient-reported outcome scores Neck Disability Index (NDI), Visual Analog Score for neck (VAS-n) and arm (VAS-a). <h3>METHODS</h3> A retrospective review was performed to identify all patients between 2009-2013 who underwent either ACDF or MI-PCF with a minimum follow-up of 7 years. Demographic data were recorded and compared between both cohorts. Revision rates and complication rates between ACDF and MI-PCF were also compared. Patient-reported outcome scores were assessed with NDI, VAS-n, and VAS-a measurements at follow-up visits. Standard binomial and categorical comparative analysis were performed. <h3>RESULTS</h3> A total of 177 consecutive patients were included–143 in the ACDF cohort and 34 in the MI-PCF cohort. There were 60 males and 83 females in the ACDF cohort compared to 29 males and 9 females in the MI-PCF cohort, a statistically significant difference (p <0.001). Mean follow-up of the ACDF and MI-PCF cohorts were 96.8 and 94.5 months, respectively. Complication rates were 4.9% and 2.9% for the ACDF and MI-PCF cohorts, respectively (p =1.0). The overall revision rates were 9.1% for the ACDF cohort and 11.8% for the MI-PCF cohort (p=0.745). All MI-PCF patients were revised to a fusion. Both cohorts experienced significant improvements in their functional outcome scores compared to their preoperative values; however, the magnitude of improvement was not statistically significant between the ACDF and MI-PCF cohorts. <h3>CONCLUSIONS</h3> MI-PCF is a safe and effective alternative to ACDF in the treatment of unilateral cervical radiculopathy without myelopathy, demonstrating benefit at a minimum of 7-year follow up. MI-PCF demonstrated similar improvements in functional outcome scores, without increased complication or revision rates. Further studies should consist of cost analysis to evaluate how utilizing MI-PCF would impact overall health care spending. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Postoperative Sagittal Balance Has Only a Limited Role in the Development of Adjacent Segment Disease After Lumbar Spine Fusion for Degenerative Lumbar Spine Disorders: A Subanalysis of the 10-year Follow-up Study.

Study Design.Retrospective additional analysis of a prospective follow-up study.Objectives.We aimed to find out whether poor postoperative sagittal alignment increases revisions for adjacent segment disease (ASD) after lumbar spine fusion (LSF) performed for degenerative lumbar spine disease.Summary of Background Data.Revisions for ASD accumulate over time after LSF for degenerative lumbar spine disease. The etiology of ASD is considered multifactorial. Yet, the role of postoperative sagittal balance in this process remains controversial.Materials and Methods.A total of 215 consecutive patients who had undergone an elective LSF surgery for spinal stenosis with (80%) or without (20%) spondylolisthesis were analyzed. Spinal reoperations were collected from the hospital records. Preoperative and postoperative sagittal alignment were evaluated from standing radiographs. The risk of revisions for ASD was evaluated by Cox proportional hazards regression models.Results.We did not find the poor postoperative balance [pelvic incidence−lumbar lordosis (LL) >9°] to significantly increase the risk of revisions for ASD: crude hazard ratio (HR)=1.5 [95% confidence interval (CI): 0.8–2.7], adjusted (by age, sex, pelvic incidence, fusion length, and the level of the caudal end of fusion): HR=1.7 (95% CI: 0.9–3.3). We found higher LL outside the fusion segment (LL−segmental lordosis) to decrease the risk of revisions for ASD: HR=0.9 (95% CI: 0.9–1.0).Conclusion.Poor sagittal balance has only a limited role as a risk factor for the revisions for ASD among patients with degenerative spinal disease. However, the risk for ASD might be the greatest among patients with reduced spinal mobility.

The effects of pathology and one-level versus two-level arthrodesis on cervical spine intervertebral helical axis of motion

The etiology of adjacent segment disease after anterior cervical discectomy and fusion (ACDF) remains controversial. Range of motion (ROM) is typically used to infer the effects of arthrodesis on adjacent segment motion following ACDF, however, ROM only measures the total amount of motion. In contrast, the helical axis of motion (HAM) quantifies how the motion occurs and may provide additional insight into the etiology of adjacent segment pathology. Synchronized biplane radiographs of the cervical spine were acquired at 30 images per second while 62 ACDF patients and 38 control participants performed dynamic neck flexion/extension. A validated tracking process matched digitally reconstructed radiographs created from subject-specific bone models to the radiographs with sub-millimeter accuracy. The intervertebral HAM was then calculated and compared between pre and 1 year post surgery in patients, and between patients and controls at corresponding motion segments using linear mixed-effects analysis. Small differences in the anterior/posterior location of the HAM were found between the symptomatic motion segments before surgery and corresponding motion segments in controls. No changes in the HAM of motion segments adjacent to the arthrodesis were observed from pre to 1-year post-surgery. No differences in adjacent segment HAM were found between patients with one- versus two-level arthrodesis. Neither symptomatic pathology nor arthrodesis appear to change the way motion occurs in the cervical spine during flexion/extension one year after one or two-level arthrodesis. These results suggest ACDF does not alter short-term adjacent segment kinematics in a way that would contribute to the development of adjacent segment disease.

Musculoskeletal biomechanics of patients with or without adjacent segment degeneration after spinal fusion

Study designA retrospective, single center, case-control study was performed.ObjectiveThe present study employed patient-specific biomechanical modeling to find potential biomechanical differences after spinal fusion at L4/5 in patients with and without subsequent development of adjacent segment disease (ASD).MethodsThe study population comprised patients who underwent primary spinal fusion at L4/5 and were either asymptomatic during > 4 years of follow-up (CTRL; n = 18) or underwent revision surgery for ASD at L3/4 (n = 20). Landmarks were annotated on preoperative and follow-up lateral radiographs, and specific musculoskeletal models were created using a custom-built modeling pipeline. Simulated spinal muscle activation and lumbar intervertebral shear loads in unfused segments were analyzed in upright standing and forward flexion. Differences between the pre- and postoperative conditions were computed for each patient.ResultsThe average postoperative muscle activity in the upright standing posture was 88.4% of the preoperative activity in the CTRL group (p < 0.0001), but did not significantly change from pre- to postoperatively in the ASD group (98.0%). The average shear load magnitude at the epifusional joint L3/4 during upright standing increased from pre- to postoperatively in the ASD group (+ 3.9 N, +/− 17.4 (n = 18)), but decreased in the CTRL group (− 4.6 N, +/− 23.3 (n = 20); p < 0.001).ConclusionPatient-specific biomechanical simulation revealed that spinal fusion surgery resulted in greater shear load magnitude and muscle activation and therefore greater forces at the epifusional segment in those with ASD compared with those without ASD. This is a first report of patient-specific disc load and muscle force calculation with predictive merits for ASD.

32. DJK and revision rates in multilevel posterior cervical fusions terminating at the cervicothoracic junction

<h3>BACKGROUND CONTEXT</h3> Despite the consensus that posterior cervical fusion can be used to treat multiple cervical pathologies, questions remain as to if crossing the cervicothoracic junction (CTJ) influences the rate of revision and how radiographic outcomes may differ. Even less is known about how crossing the CTJ may predict the development of adjacent segment disease. A retrospective review of 91 posterior cervical fusion patients was performed comparing long constructs (≥3 levels) terminating at C7 vs T1-3. Revision and DJK rates were compared between the two groups. Mean change in cervical lordosis, T1 slope, cervical SVA, and T1 slope-cervical lordosis mismatch (T1S-CL) were also compared. Distal segment kyphosis at final follow up was significantly greater in the thoracic group, but no other statistically significant differences were identified. <h3>PURPOSE</h3> Compare revision rates and radiographic outcomes in patients receiving posterior cervical fusion of ≥3 levels that terminate at C7 vs T1, 2 or 3. Our hypothesis is patients with multilevel posterior cervical fusion constructs terminating at C7 will have similar rates of revision, DJK and cervicothoracic radiographic outcomes compared to patients whose constructs crossed the CTJ to T1, T2, or T3. <h3>STUDY DESIGN/SETTING</h3> Single center retrospective analysis. <h3>PATIENT SAMPLE</h3> Consecutive posterior cervical fusion patients with greater than or equal to 3 levels fused from January 2010 until December 31, 2019 at a single institution. <h3>OUTCOME MEASURES</h3> Primary outcome: 1. Need for revision. Secondary outcomes: 2. Distal junctional kyphosis; 3. Mean change in cervical lordosis (CL); 4. Mean change in T1 slope (T1S); 5. T1S - CL mismatch; 6. cervical SVA. <h3>METHODS</h3> A retrospective review of medical records identified posterior cervical fusion cases with at least one year of radiographic follow-up and fusion greater than or equal to 3 segments. Identified cases were divided into 2 groups based on location of lowest instrumented vertebra. Group 1 included fusions terminating at C7 and group 2 included fusions terminating at T1, 2, or 3. At multiple intervals, cervical lordosis (CL), T1 slope, cervical sagittal vertical axis (cSVA), distal segment kyphosis, and T1 slope-cervical lordosis mismatch (T1S-CL) were measured. Any need for revision surgery was also documented. <h3>RESULTS</h3> A total of 91 patients were included, 53 in Group 1 (mean age 58.9 years, 56.6% women) and 38 in Group 2 (mean age 64.4 yrs, 55% women). Revision rate did not reveal statistical difference between the two groups (Group 1: 9.4% vs Group 2: 2.6% P=0.39). There was no statistical difference in patients meeting criteria for DJK at final follow up (Group 1: 5.6% vs Group 2: 5.2% P=0.9). However, within each group, a statistically significant increase in mean distal segment kyphosis at final follow-up was identified in Group 2 (Group 1: 0.82°, P=0.31 vs Group 2: 2.5°, P=0.0001). Mean change in CL, T1 Slope, cSVA and T1S-CL mismatch were not statistically different between the groups at final follow up. <h3>CONCLUSIONS</h3> Our study demonstrated that revision rates, cervicothoracic radiographic parameters, and DJK were not significantly different when comparing multilevel posterior cervical fusions terminating at C7 vs the upper thoracic spine. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

165. Risk of revision surgery following cervical disc replacement vs anterior cervical discectomy and fusion: population based cohort study

<h3>BACKGROUND CONTEXT</h3> In recent years, cervical disc replacement (CDR) has gained popularity for cervical degenerative disorders. The rationale for CDR over anterior cervical discectomy and fusion (ACDF) is preservation of segmental motion and physiological spinal kinematics, which is hoped to delay development of adjacent segment disease and reoperation rates. Superiority of CDR over ACDF in rates of secondary surgeries has not been demonstrated in long-term follow-up. <h3>PURPOSE</h3> This study compares rate of reoperation in CDR and ACDF for treatment of cervical degenerative disc disease using population-based data for the province of Ontario. <h3>STUDY DESIGN/SETTING</h3> A population-based cohort study was conducted using health administrative databases including patients undergoing ACDF or CDR between October 2005 to March 2018. <h3>PATIENT SAMPLE</h3> Patients receiving CDR vs ACDF were identified using physician service claims and hospital discharge abstracts. <h3>OUTCOME MEASURES</h3> The primary outcome was revision surgery in the cervical spine defined as an operation more than 30 days after the index procedure. Secondary outcomes were immediate/acute complications within the first 30 days after the index operation, readmissions and length of hospital stay. <b>METHODS:</b> Cox proportional hazard models were used to identify predictors of time to revision surgery. Predictors of the binary outcome of an immediate complication within 30 days were estimated using logistic regression. <h3>Results</h3> A total of 5,207 patients were included. Mean follow-up was 2,728 days for CDR and 2,542 days for ACDF. Among 4,937 ACDF procedures, 7.5% underwent subsequent revision surgery and among 270 CDR procedures, 8.9% had revision surgery. While the study groups did not differ in their risk of revision surgery (adjusted HR 1.20, 95% CI 0.78-1.85), CDR was associated with a lower probability of an acute complication (adjusted OR 0.41, 95% CI 0.21-0.80). Among other factors, multi-level surgery was an independent predictor of acute complication [OR= 1.33 (95% CI 1.06 – 1.66)]. CDR patients experienced shorter mean (±SD) length of hospital stay [1.42 (±0.87) vs. 2.00 ± (3.08) d for ACDF]. <h3>Conclusions</h3> This study does not demonstrate superiority of CDR over ACDF in revision surgery at the index and/or adjacent level of the cervical spine for single and multi-level procedures. CDR may have an advantage over ACDF in the acute postoperative phase, with a shorter length of hospital stay and lower probability of acute complication. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Assessment of Rod Material Types in Spine Surgery Outcomes: A Systematic Review

Lumbar spine fusion surgery is traditionally performed with rigid fixation. Because the rigidity is often supraphysiologic, semirigid rods were developed. To the best of our knowledge, a comprehensive evaluation of rod material type on surgical outcomes has yet to be conducted. A systematic review based on PRISMA guidelines was conducted across 3 electronic databases. After examination for inclusion and exclusion criteria, data were extracted from the studies. Seventeen studies, including 1399 patients, were included in this review. The mean rigid rod fusion rate is 92.2% and 95.5% for semirigid rods (P= 0.129). The mean improvement in back pain was 60.6% in rigid rods and 71.6% in semirigid rods. The improvement in leg pain was 81.9% and 77.2%, respectively. There were no differences in visual analog scale back pain score (P= 0.098), visual analog scale leg pain score (P= 0.136), or in functional improvement between rigid and semirigid rods (P= 0.143). There was no difference (P= 0.209) in the reoperation rate between rigid rods (13.1%) and semirigid rods (6.5%). There was a comparable incidence of adjacent segment disease (3%), screw fracture (1.7%), and wound infection (1.9%) between rod material types. There is a moderate level of evidence supporting that surgical intervention results in high fusion rates regardless of rod material type. Surgical intervention improves back pain, leg pain, and function, with neither material type showing clear superiority. There are comparable rates of reoperation, development of adjacent segment disease, development of mechanical complications, and incidence of infection in both rigid and semirigid rods. Further studies regarding rod material type are warranted.

Biomechanical effects of laminectomies in the human lumbar spine: a finite element study

Previous studies have analyzed the effect of laminectomy on intervertebral disc (IVD), facet-joint-forces (FJF), and range of motion (ROM), while only two have specifically reported stresses at the pars interarticularis (PI) with posterior element resection. These studies have been performed utilizing a single subject, questioning their applications to a broader population. We investigate the effect of graded PI resection in a three-dimensional manner on PI stress to provide surgical guidelines for avoidance of iatrogenic instability following lumbar laminectomy. Additionally, quantified FJF and IVD stresses can provide further insight into the development of adjacent segment disease. Biomechanical finite element (FE) method investigation of the lumbar spine. FE models of the lumbar spine of three subjects were created using the open-source finite element software, FEBio. Single-level laminectomy, two-level laminectomy, and ventral-to-dorsal PI resection simulations were performed with varying degrees of PI resection from 0% to 75% of the native PI. These models were taken through cardinal ROM under standard loading conditions and PI stresses, FJF, IVD stresses, and ROM were analyzed. The three types of laminectomy simulated in this study showed a nonlinear increase in PI stress with increased bone resection. Axial rotation generated the most stress at the PI followed by flexion, extension and lateral bending. At 75% bone resection all three types of laminectomy produced PI stresses that were near the ultimate strength of human cortical bone during axial rotation. FJF decreased with increased bone resection for the three laminectomies simulated. This was most notable in axial rotation followed by extension and lateral bending. IVD stresses varied greatly between the nonsurgical models and likewise the effect of laminectomy on IVD stresses varied between subjects. ROM was mostly unaffected by the laminectomies performed in this study. Regarding the risk of iatrogenic spondylolisthesis, the combined results are sufficient evidence to suggest surgeons should be particularly cautious when PI resection exceeds 50% bone resection for all laminectomies included in this study. Lastly, the effects seen in FJF and IVD stresses indicate the degree to which the remainder of the spine must experience compensatory biomechanical changes as a result of the surgical intervention.

Comparing Oblique Lumbar Interbody Fusion with Lateral Screw Fixation and Transforaminal Full-Endoscopic Lumbar Discectomy (OLIF-TELD) and Posterior Lumbar Interbody Fusion (PLIF) for the Treatment of Adjacent Segment Disease.

Background A potential long-term complication of lumbar fusion is the development of adjacent segment disease (ASD), which may require surgical intervention and adversely affect outcomes. A high incidence of recurrent ASD was reported in patients who underwent the second (repeat) PLIF for symptomatic ASD. Herein, a feasible method, oblique lumbar interbody fusion combined with transforaminal endoscopic lumbar discectomy (OLIF-TELD) for dealing with adjacent lumbar disc herniation with upward or downward migration after lumbar spinal fusion, was proposed. Methods A total of 19 patients who underwent revision surgery at ASD were consecutively enrolled. Clinical efficacy analysis included operative time, intraoperative bleeding, visual analogue scale (VAS) score, Oswestry dysfunction index (ODI) score, and Japanese orthopaedic association (JOA) assessment treatment score. Results Among them, 11 patients were treated in a new surgical strategy, which is OLIF-TELD, and 8 patients underwent PLIF. There was no statistically significant difference between the two groups in terms of age, gender, and preoperative scores of VAS, ODI, and JOA. The operative duration was shorter, and intraoperative bleeding was less in the OLIF-TELD group compared with the PLIF group. PLIF had the greatest blood loss, and the OLIF-TELD group had lower VAS scores than the PLIF group postoperatively. The symptoms of all patients improved postoperatively with statistical significance. Conclusion OLIF with lateral screw fixation combined with TELD may be an alternative surgical method for the treatment of adjacent lumbar disc herniation with upward or downward migration after lumbar fusion surgery.

Finite Element Analysis of Short- Versus Long-Segment Posterior Fixation for Thoracolumbar Burst Fracture

The thoracolumbar (TL) area marks the transition of the rigid thoracic spine into the mobile lumbar spine, and it is considered to be the weakest part of the spine. This study was designed to develop a finite element (FE) model of the TL junction (T9-L3) to provide data that could help the clinician and researcher to answer the question of whether short-segment posterior fixation is sufficient for biomechanical performance. In addition, the aim was to examine whether long-segment posterior fixation carries a greater risk of the development of adjacent segment disease. This was a biomechanical finite element model analysis. FE analysis of the spine was conducted with posterior instrumentation under multidirectional loading conditions in order to evaluate the kinematics of the instrumented lumbar spine, as well as stresses in the posterior spinal instrumentation. We analyzed the following: 1) the range of motion of the T9-L3 region; and 2) the von Mises stress nephograms of the pedicle screws, rods, vertebrae, endplates, and intervertebral discs of 2 fixation FE models. Long-segment stabilization was found to be beneficial in terms of reducing total stress on the spine. However, it is possible to reduce the stress on the system by incorporating the spinal fracture into the stabilization system. Therefore, short-segment stabilization is sufficient to create a safe and robust stabilization system and to maintain neighboring intact vertebrae. Short-segment posterior fixation is sufficient to stabilize fractures at the TL junction, where the spinal fracture is included in the stabilization system.

Adjacent segment disease after instrumented fusion for adult lumbar spondylolisthesis: Incidence and risk factors

ObjectiveA potential long-term complication of lumbar fusion is the development of adjacent segment disease (ASD), which may necessitate second surgery and adversely affect outcomes. The objective of this is to determine the incidence of ASD following instrumented fusion in adult patients with lumbar spondylolisthesis and to identify the risk factors for this complication. Patients and methodsWe retrospectively assessed adult patients who had undergone decompression and instrumented fusion for lumbar spondylolisthesis between January 2006 and December 2012. The incidence of ASD was analyzed. Potential risk factors included the patient-related factors, surgery-related factors, and radiographic variables such as sagittal alignment, preexisting disc degeneration and spinal stenosis at the adjacent segment. ResultsA total of 154 patients (mean age, 58.4 years) were included. Mean duration of follow-up was 28.6 months. Eighteen patients (11.7%) underwent a reoperation for ASD; 15 patients had reoperation at cranial ASD and 3 at caudal ASD. The simultaneous decompression at adjacent segment (p=0.002) and preexisting spinal stenosis at cranial adjacent segment (p=0.01) were identified as risk factors for ASD. The occurrence of ASD was not affected by patient-related factors, the types, grades and levels of spondylolisthesis, surgical approach, fusion procedures, levels of fusion, number of levels fused, types of bone graft, use of bone morphogenetic proteins, sagittal alignment, preexisting adjacent disc degeneration and preexisting spinal stenosis at caudal adjacent segments. ConclusionOur findings suggest the overall incidence of ASD is 11.7% in adult patients with lumbar spondylolisthesis after decompression and instrumented fusion at a mean follow-up of 28.6 months, the simultaneous decompression at the adjacent segment and preexisting spinal stenosis at cranial adjacent segment are risk factors for ASD.

Predisposing Characteristics of Adjacent Segment Disease After Lumbar Fusion.

Retrospective Review. The aim of this study was to determine medical, radiographic, and surgical risk factors for the development of adjacent segment disease (ASD) after lumbar fusion. ASD is a recognized outcome of spinal fusion that leads to increased costs and debilitating symptoms for patients. However, a comprehensive understanding of risk factors for the development of this surgical outcome does not exist. The medical records of patients who received their first lumbar fusion for any indication were retrospectively examined for preoperative medical comorbidities and medications, as well as surgical approach and perioperative complications. A blinded reviewer assessed radiographs for each patient to examine sagittal alignment after fusion. Multivariable logistic regression was used to model the risk of developing ASD on the basis of one or more predictors. A total of 137 patients fit the inclusion criteria; 9% required a follow-up operation for degeneration at segments adjacent to the fusion. The ASD group had a mean follow-up of 21.1 months prior to revision surgery and an overall follow-up of 41.0 months. The average follow-up in the control group was 14.0 months. Statistically significant independent predictors of developing ASD included antidepressant use [odds ratio (OR) = 5.4], diagnosis of degenerative scoliosis (OR = 34.2), fusion of L4-S1 (OR = 56.5), having no decompressions adjacent to the fusion, and low sacral slope (OR = 0.9). No patient who developed ASD received a decompression adjacent to the fusion such that an OR could not be generated for this independent predictor. This study is the first to use a combination of medical, surgical, and postoperative sagittal balance as risk factors for the development of adjacent segment disease after lumbar fusion. The awareness of these risk factors may allow for better patient selection and surgical technique to decrease the probability of acquiring this adverse outcome. 4.

Nonfusion Does Not Prevent Adjacent Segment Disease

Case series. The aim of this study was to determine the relationship between fusion and adjacent segment disease via Dynesys long-term outcomes. Dynesys is a dynamic stabilization system meant to improve symptoms by stabilizing the spine without fusion and avoiding the development of adjacent segment disease. However, few studies have evaluated long-term outcomes. All patients were operated on with Dynesys from 2006 to 2009 by a single surgeon at a single institution. We prospectively collected 18 variables among the following categories: patient characteristics, comorbidities, surgical indications, and OR variables. We analyzed two primary endpoints: solid fusion on X-ray and clinical adjacent segment disease (ASD) both at 5 years. Secondary endpoints were time to fusion, time to ASD, reoperation, Oswestry disability index (ODI), and visual analogue scale (VAS) leg pain. We conducted a multivariate analysis via the random forest method. Mann-Whitney U test and Fisher exact test were then used to qualify relationship between variables. We had 52 patients to review in the database. Eight had preexisting ASD. Mean follow-up was 92 months (median 87 months). Fifteen had ASD (29%) during follow-up at a mean 45 months (Median 35 months). Nine had a solid fusion (17%), 2 of which also had ASD. Mean time to fusion was 65 months (median 71 months). Differences in improvement of ODI (P = 0.005) and VAS leg pain (P = 0.002) were significant favoring patients without ASD. The multivariate analysis revealed four variables associated with ASD: prior ASD (OR 11.3, P = 0.005), neurological deficit (OR 8.5, P = 0.018), revision OR (OR 8.5, P = 0.018), and multilevel degeneration (OR 0.184, P = 0.026). No variable was associated with fusion. Dynesys was associated with a high rate of ASD over long-term follow-up despite maintaining a low fusion rate. Prior ASD was the strongest predictor of progressive ASD. 3.