Range Of Motion Of Adjacent Segments Research Articles

Biomechanical Effect of Different Posterior Fixation Techniques on Stability and Adjacent Segment Degeneration in Treating Thoracolumbar Burst Fracture With Osteoporosis: A Finite Element Analysis.

Finite element analysis. To investigate the biomechanical effect of four posterior fixation tcehniques on stability and adjacent segment degeneration in treating thoracolumbar burst fractures with osteoporosis. In terms of stability and adjacent segment degeneration, there remains no consensus or guidelines on the optimal technique for the treatment of thoracolumbar burst fractures in patients with osteoporosis. Images of CT scans were imported into MIMICS and further processed by Geomagic to build 3-dimensional models of the T10-L5 region. A v-shaped osteotomy was performed on the L1 vertebral body to simulate a burst fracture in the setting of osteoporosis. Subsequently, four fixation techniques were designed using SolidWorks software. Range of motion (ROM) of the global spine, ROM distribution, ROM of adjacent segment, Von Mises stress on adjacent intervertebral discs and facet joints were analyzed. Among the four groups, the cortical bone screw fixation (CBT) showed the highest global ROM at 1.86°, while long-segmented pedicle screw fixation (LSPS) had the lowest global ROM at 1.25°. The LSPS had the smallest percentage of ROM of fractured vertebral body to fixed segment at 75.04%, suggesting the highest stability after fixation. The maximum ROM of the adjacent segment was observed in the CBT at 1.32°, while the LSPS exhibited the smallest at 0.89°. However, the LSPS group experienced larger maximum stress on the adjacent intervertebral discs (9.60MPa) and facet joints (3.36MPa), indicating an increasing risk of adjacent segment disease. LSPS provided the greatest stability, while CBT provided the smallest amount of stability. However, the elevated stress on adjacent intervertebral discs and facet joints after LSPS fixation increased the possibility of adjacent segment degeneration. Cement-augmented pedicle screw fixation (CAS) and combined cortical bone screw and pedicle screw fixation (CBT-PS) demonstrated significant biomechanical advantages in providing moderate fixation strength while reducing stress on the intervertebral discs and facet joints.

Determining a relative total lumbar range of motion to alleviate adjacent segment degeneration after transforaminal lumbar interbody fusion: a finite element analysis

BackgroundA reduction in total lumbar range of motion (ROM) after lumbar fusion may offset the increase in intradiscal pressure (IDP) and facet joint force (FJF) caused by the abnormally increased ROM at adjacent segments. This study aimed to determine a relative total lumbar ROM rather than an ideal adjacent segment ROM to guide postoperative waist activities and further delay adjacent segment degeneration (ASD).MethodsAn intact L1-S1 finite element model was constructed and validated. Based on this, a surgical model was created to allow the simulation of L4/5 transforaminal lumbar interbody fusion (TLIF). Under the maximum total L1-S1 ROM, the ROM, IDP, and FJF of each adjacent segment between the intact and TLIF models were compared to explore the biomechanical influence of lumbar fusion on adjacent segments. Subsequently, the functional relationship between total L1-S1 ROM and IDP or total L1-S1 ROM and FJF was fitted in the TLIF model to calculate the relative total L1-S1 ROMs without an increase in IDP and FJF.ResultsCompared with those of the intact model, the ROM, IDP, and FJF of the adjacent segments in the TLIF model increased by 12.6-28.9%, 0.1-6.8%, and 0-134.2%, respectively. As the total L1-S1 ROM increased, the IDP and FJF of each adjacent segment increased by varying degrees. The relative total L1-S1 ROMs in the TLIF model were 11.03°, 12.50°, 12.14°, and 9.82° in flexion, extension, lateral bending, and axial rotation, respectively.ConclusionsThe relative total L1-S1 ROMs after TLIF were determined, which decreased by 19.6-29.3% compared to the preoperative ones. Guiding the patients to perform postoperative waist activities within these specific ROMs, an increase in the IDP and FJF of adjacent segments may be effectively offset, thereby alleviating ASD.

Preoperative and Postoperative Segmental and Overall Range of Motion in Patients Undergoing Lumbar Spinal Fusion Using HA-Infused PEEK and HA-Treated Titanium Alloy Interbody Cages.

Retrospective observational radiographic analysis. Determine how single level lumbar interbody fusion (LIF) alters segmental range of motion (ROM) at adjacent levels and decreases overall ROM. This study included 54 patients who underwent single-level anterior (ALIF, 39%), thoraco-LIF (TLIF, 26%), posterior LIF (PLIF, 22%), or lateral LIF (LLIF, 13%) (L2-3/L3-4/L4-5/L5-S1: 4%/13%/35%/48%). Segmental ROM from L1-2 to L5-S1 and the overall lumbar ROM (L1-S1) were assessed from preoperative and postoperative flexion-extension radiographs. K-means cluster analysis was used to identify ROM subgroups. The overall L1-S1 ROM decreased 14% (25.5 ± 20.4° to 22.0 ± 17.2°, P = .104) postoperatively. ROM at the fusion level decreased 77% (4.8 ± 5.0° to 1.1 ± 1.1°, P < .001). Caudal adjacent segment ROM decreased 12% (5.2 ± 5.7° to 4.6 ± 4.4°, P = .345) and cranially ROM increased 34% (4.3 ± 5.0° to 5.7 ± 5.7°, P = .05). K-cluster analysis identified 3 distinct clusters (P < .05). Cluster 1 lost more ROM and had less improvement in patient-reported outcomes measures (PROMs) than average. Cluster 2 had less ROM loss than average with worse PROMs improvement. Cluster 3 did not have changes in ROM and better improvement in PROMs than average. Successful fusion was verified in 96% of all instrumented segments with >6months follow-up (ROM <4°). Following single-level L IF, patients should expect a loss of 3.3°, or 14% of overall lumbar motion with increases in ROM of the cranial segment. However, specific clusters of patients exist that experience different relative changes in ROM and PROMs.

Biomechanical properties of a novel cervical spine implant with elastic deformation: a cadaveric study.

Introduction: Anterior cervical discectomy and fusion (ACDF) is a most frequently used surgical procedure for treating cervical radiculopathy and myelopathy. However, there is concern about the high adjacent segment degeneration (ASD) rate after ACDF surgery. We creatively designed an elastically deformable cervical implant to reduce the postoperative stress concentration. In this study, we aimed to investigate the biomechanical performance of this novel cervical implant and compare it with the commonly used cervical devices. Methods: Biomechanical test was conducted on twelve fresh-frozen human cadaveric cervical spines (C2-C7) and randomly divided into four groups according to implant types: intact group, Zero-P VA fusion (ACDF) group, the novel cervical implant group and Pretic-I artificial cervical disc (ACDR) group. An optical tracking system was used to evaluate the segmental range of motion (ROM) of the C4/C5, C5/C6, and C6/C7 segments and micro pressure sensor was used to record the maximum facet joint pressure (FJP), maximum intradiscal pressure (IDP) at the C4-5 and C6-7 segments. Results: There were no significant differences in the ROM of adjacent segments between the groups. Compared with the intact group, the ACDR group essentially retained the ROM of the operated segment. The novel cervical implant decrease some ROM of the operated segment, but it was still significantly higher than in the fusion group; The maximum FJP and IDP at the adjacent segments in the ACDF group were significantly higher than those values in the other groups, and there were no differences in the other groups. Conclusion: While the newly developed elastically deformable cervical implant does not completely maintain ROM like the artificial cervical disc, it surpasses the fusion device with regards to biomechanical attributes. After further refinement, this novel implant may be suitable for patients who are prone to severe adjacent segment degeneration after fusion surgery but no indication for artificial cervical disc surgery.

Biomechanical Comparison of Different Surgical Approaches for the Treatment of Adjacent Segment Diseases after Primary Transforaminal Lumbar Interbody Fusion: A Finite Element Analysis.

Adjacent segment disease (ASD) is a well-known complication after interbody fusion. Revision surgery is necessary for symptomatic ASD to further decompress and fix the affected segment. However, no optimal construct is accepted as a standard in treating ASD. The purpose of this study was to compare the biomechanical effects of different surgical approaches for the treatment of ASD after primary transforaminal lumbar interbody fusion (TLIF). A finite element model of the L1-S1 was conducted based on computed tomography scan images. The primary surgery model was developed with a single-level TLIF at L4-L5 segment. The revision surgical models were developed with anterior lumbar interbody fusion (ALIF), lateral lumbar interbody fusion (LLIF), or TLIF at L3-L4 segment. The range of motion (ROM), intradiscal pressure (IDP), and the stress in cages were compared to investigate the biomechanical influences of different surgical approaches. The results indicated that all the three surgical approaches can stabilize the spinal segment by reducing the ROM at revision level. The ROM and IDP at adjacent segments of revision model of TLIF was greater than those of other revision models. While revision surgery with ALIF and LLIF had similar effects on the ROM and IDP of adjacent segments. Compared among all the surgical models, cage stress in revision model of TLIF was the maximum in extension and axial rotation. The IDP at adjacent segments and stress in cages of revision model of TLIF was greater than those of ALIF and LLIF. This may be that direct extension of the surgical segment in the same direction results in stress concentration.

Comparative study of outcomes between allograft intervertebral disc transplantation and anterior cervical discectomy and fusion: a retrospective cohort study at least 5 years of follow-up

PurposeAdjacent segment degeneration (ASDeg) after anterior cervical discectomy and fusion (ACDF) seriously affects the long-term efficacy of the operation. Therefore, our team has done a lot of research on allograft intervertebral disc transplantation (AIDT) to prove its feasibility and safety. This study will compare the efficacy between AIDT and ACDF in the treatment of cervical spondylosis.MethodsAll patients who received ACDF or AIDT in our hospital from 2000 to 2016 and followed up for at least 5 years were recruited and divided into ACDF and AIDT groups. The clinical outcomes including functional scores and radiological data of both groups were collected and compared preoperatively and postoperatively at 1 week, 3 months, 6 months, 12 months, 24 months, 60 months and last follow-up. Functional scores included Japanese Orthopedic Association score (JOA), Neck Disability Index (NDI), Visual Analog Scale of Neck (N-VAS) and Arms (A-VAS) pain, the Short Form Health Survey-36 (SF-36) and imaging dates including digital radiographs in the lateral, hyperextension and flexion positions to assess the stability, sagittal balance and mobility of the cervical spine and magnetic resonance imaging (MRI) scans to assess the degeneration of adjacent segment.ResultsThere were 68 patients with 25 in AIDT group and 43 in ACDF group. Satisfactory clinical results were obtained in both groups, but the long-term NDI score and N-VAS score in the AIDT group were better. The AIDT obtained the same stability and sagittal balance of the cervical spine as fusion surgery. The range of motion of adjacent segments can be restored to the preoperative level after transplantation, but this increases significantly after ACDF. There were significant differences in the superior adjacent segment range of motion (SROM) between two groups at 12 months (P = 0.039), 24 months (P = 0.035), 60 months (P = 0.039) and the last follow-up (P = 0.011). The inferior adjacent segment range of motion (IROM) and SROM had a similar trend in the two groups. The ratio value of the greyscale (RVG) of adjacent segments showed a downward trend. At the last follow-up, the RVG decreased more significantly in the ACDF group. At the last follow-up, there was a significant difference in the incidence of ASDeg between the two groups (P = 0.000). And the incidence of adjacent segment disease (ASDis) is 22.86% in the ACDF group.ConclusionThe allograft intervertebral disc transplantation may be as an alternative technique to traditional anterior cervical discectomy and fusion for the management of cervical degenerative diseases. For the more, the results showed it would improve cervical kinematics and reduce the incidence of adjacent segment degeneration.

Biomechanical effect of endplate defects on the intermediate vertebral bone in consecutive two-level anterior cervical discectomy and fusion: a finite element analysis

BackgroundIntermediate vertebral collapse is a newly discovered complication of consecutive two-level anterior cervical discectomy and fusion (ACDF). There have been no analytical studies related to the effects of endplate defects on the biomechanics of the intermediate vertebral bone after ACDF. This study aimed to compare the effects of endplate defects on the intermediate vertebral bone biomechanics in the zero-profile (ZP) and cage-and-plate (CP) methods of consecutive 2-level ACDF and to determine whether collapse of the intermediate vertebra is more likely to occur using ZP.MethodsA three-dimensional finite element (FE) model of the intact cervical spine (C2–T1) was constructed and validated. The intact FE model was then modified to build ACDF models and imitate the situation of endplate injury, establishing two groups of models (ZP, IM-ZP and CP, IM-ZP). We simulated cervical motion, such as flexion, extension, lateral bending and axial rotation, and compared the range of motion (ROM), upper and lower endplate stress, fusion fixation device stress, C5 vertebral body stress, intervertebral disc internal pressure (intradiscal pressure, or IDP) and the ROM of adjacent segments in the models.ResultsThere was no significant difference between the IM-CP model and the CP model in the ROM of the surgical segment, upper and lower endplate stress, fusion fixation device stress, C5 vertebral body stress, IDP, or ROM of the adjacent segments. Compared with the CP model, the endplate stress of the ZP model is significantly higher in the flexion, extension, lateral bending and axial rotation conditions. Compared with the ZP model, endplate stress, screw stress, C5 vertebral stress and IDP in IM-ZP were significantly increased under flexion, extension, lateral bending and axial rotation conditions.ConclusionsCompared to consecutive 2-level ACDF using CP, collapse of the intermediate vertebra is more likely to occur using ZP due to its mechanical characteristics. Intraoperative endplate defects of the anterior lower margin of the middle vertebra are a risk factor leading to collapse of the middle vertebra after consecutive 2-level ACDF using ZP.

Comparative analysis of the biomechanics of anterior cervical discectomy and fusion with multiple segmental plates fixation versus single multilevel plate fixation: a finite element study

BackgroundThis study aimed to compare the biomechanical differences between anterior cervical discectomy and fusion (ACDF) with multiple-level separate plates and conventional long plates by using finite element analysis.MethodsThe following four finite element models were created to simulate various fixations: (1) C4–6 ACDF with multiple plates, (2) C4–6 ACDF with a single plate, (3) C3–6 ACDF with multiple plates, and (4) C3–6 ACDF with a single plate. The maximum Von-mises stress of the cage and fixation, compressive force of the adjacent intervertebral discs and range of motion (ROM) of different segments in the four models were calculated and analyzed.ResultsFor C4–6 ACDF, the maximum Von-mises stress of the cage and fixation was lower in the multiple plate fixation model in all motion states. Similarly, for the C3–6 ACDF models, the peak stress of the C3–4 and C5–6 cages was lower with multiple plates fixation in all motions but the stress of the C4–5 cage in the multiple plates model was slightly higher in flexion, bending and rotation. Besides, applying multiple plates in C3–6 ACDF models resulted in a decreased maximum stress of the fixation under different motions except for bending. In both the C4–6 ACDF and C3–6 ACDF models, the ROM values of the adjacent motion segments were lower in the multiple plates models in extension, bending and rotation. In the C4–6 ACDF models, the peak stress on the adjacent intervertebral discs in the multiple plates models was slightly smaller. In C3–6 ACDF models, the maximum stress on the adjacent intervertebral discs was larger in the single-plate model under flexion, bending and rotation movements.ConclusionMultiple plates fixation has a positive effect on increasing stiffness and maintaining the ROM of adjacent segments, indicating lower risk of construct failure and adjacent segment degeneration. Further studies are required to confirm its efficacy in clinical practice.

Biomechanical comparative analysis of effects of dynamic and rigid fusion on lumbar motion with different sagittal parameters: An in vitro study

Background: Although the management of the lumbar disease is highly dependent on the severity of the patient’s condition, optimal surgical techniques to reduce the risk of adjacent degeneration disease (ADS) remain elusive. Based on in vitro biomechanical tests of the cadaver spine, this study aimed to comparatively analyze the kinematic responses of the spine with dynamic and rigid fixations (i.e., Coflex fixation and posterolateral fusion) after single-or double-level lumbar fusion in daily activities. Methods: Six human lumbar specimens (L1-S1) were selected for this experiment, and the sagittal parameters of each lumbar specimen were measured in the 3D model. The specimens were successively reconstructed into five groups of models: intact model, single-level L4-5 Coflex fixation model, single-level L4-5 Fusion (posterior pedicle screw fixation) model, double-level L4-5 Coflex + L5-S1 Fusion model; and double-level L4-5 Fusion + L5-S1 Fusion model. The pure moment was applied to the specimen model to simulate physiological activities in daily life through a custom-built robot testing device with an optical tracking system. Results: For single-level lumbar fusion, compared to the traditional Fusion fixation, the Coflex dynamic fixation mainly restricted the extension of L4-L5, partially retained the range of motion (ROM) of the L4-L5 segment, and reduced the motion compensation of the upper adjacent segment. For the double-level lumbar fixation, the ROM of adjacent segments in the Coflex + Fusion was significantly decreased compared to the Fusion + Fusion fixation, but there was no significant difference. In addition, PT was the only sagittal parameter of the preoperative lumbar associated with the ROM under extension loading. The Coflex fixation had little effect on the original sagittal alignment of the lumbar spine. Conclusion: The Coflex was an effective lumbar surgical technique with a less altering kinematic motion of the lumbar both at the index segment and adjacent segments. However, when the Coflex was combined with the fusion fixation, this ability to protect adjacent segments remained elusive in slowing the accelerated degradation of adjacent segments.

In Vivo Evidence of Early Instability and Late Stabilization in Motion Segments Immediately Superior to Anterior Cervical Arthrodesis.

Prospective cohort study. The aim was to identify patient factors that affect adjacent segment kinematics after anterior cervical discectomy and fusion (ACDF) as measured by biplane radiography. The etiology of adjacent segment disease (ASD) may be multifactorial. Previous studies have investigated associations between patient factors and ASD, although few attempted to link patient factors with mechanical changes in the spine that may explain ASD development. Previous studies manually measured intervertebral motion from static flexion/extension radiographs, however, manual measurements are unreliable, and those studies failed to measure intervertebral motion during rotation. Patients had continuous cervical spine flexion/extension and axial rotation movements captured at 30 images per second in a dynamic biplane radiography system preoperatively and 1 year after ACDF. Digitally reconstructed radiographs generated from subject-specific computed tomography scans were matched to the biplane radiographs using a validated tracking process. Dynamic kinematics and preoperative disc height were calculated from this tracking process. Preoperative magnetic resonance imagings were evaluated for disc bulge. Patient age, sex, body mass index, smoking status, diabetes, psychiatric history, presence of an inciting event, and length of symptoms were collected. Multivariate linear regression was performed to identify patient factors associated with 1-year postoperative changes in adjacent segment kinematics. Sixty-three patients completed preoperative and postoperative testing. Superior adjacent segment disc height and disc bulge predicted the change in superior adjacent segment range of motion after surgery. Inferior adjacent segment disc bulge, smoking history, and the use of psychiatric medications predicted the change in inferior adjacent segment flexion/extension range of motion after surgery. Preexisting adjacent segment disc degeneration, as indicated by disc height and disc bulge, was associated with reduced adjacent segment motion after ACDF, while lack of preexisting adjacent disc degeneration was associated with increased adjacent segment motion after ACDF. These findings provide in vivo evidence supporting early instability and late stabilization in the pathophysiology of disc degeneration.

Biomechanical effects of interbody cage height on adjacent segments in patients with lumbar degeneration: a 3D finite element study

ObjectiveTo investigate the biomechanical effects of interbody cage height on adjacent segments in patients with lumbar degeneration undergoing transforaminal lumbar interbody fusion (TLIF) surgery, so as to provide references for selection of interbody cage.MethodsThe finite element model of normal lower lumbar spine (L3–S1) was built and validated, then constructed three different degenerative segments in L3–L4, and the cages with different height (8, 10, 12, 14 mm) were implanted into L4–L5 disc. All the twelve models were loaded with pure moment of 7.5 N m to produce flexion, extension, lateral bending and axial rotation motions on lumbar spine, and the effects of cage height on range of motion (RoM) and intervertebral pressure in lumbar spine were investigated.ResultsThe RoM of adjacent segments and the maximum stress of intervertebral discs increased with the increase in cage height, but this trend was not obvious in mild and moderate degeneration groups. After implantation of four different height cages (8, 10, 12, 14 mm), the RoM of L3/L4 segment reached the maximum during extension. The RoM of mild degeneration group was 2.07°, 2.45°, 2.48°, 2.54°, that of moderate degeneration group was 1.79°, 1.97°, 2.05°, 2.05°, and that of severe degeneration group was 1.43°, 1.66°, 1.74°, 1.74°. The stress of L3–L4 intervertebral disc reached the maximum during flexion. The maximum stress of L3–L4 intervertebral disc was 20.16 MPa, 20.28 MPa, 20.31 MPa and 20.33 MPa in the mild group, 20.58 MPa, 20.66 MPa, 20.71 MPa and 20.75 MPa in the moderate group, and 21.27 MPa, 21.40 MPa, 21.50 MPa and 21.60 MPa in the severe group.ConclusionFor patients with mild-to-moderate lumbar degenerative disease who need to undergo TLIF surgery, it is recommended that the height of fusion cage should not exceed the original intervertebral space height by 2 mm, while for patients with severe degeneration, a fusion cage close to the original intervertebral height should be selected as far as possible, and the intervertebral space should not be overstretched.

Biomechanical Analysis of the Reasonable Cervical Range of Motion to Prevent Non-Fusion Segmental Degeneration After Single-Level ACDF

The compensatory increase in intervertebral range of motion (ROM) after cervical fusion can increase facet joint force (FJF) and intradiscal pressure (IDP) in non-fusion segments. Guiding the post-ACDF patient cervical exercise within a specific ROM (defined as reasonable ROM) to offset the increase in FJF and IDP may help prevent segmental degeneration. This study aimed to determine the reasonable total C0–C7 ROM without an increase in FJF and IDP in non-fusion segments after anterior cervical discectomy and fusion (ACDF). A three-dimensional intact finite element model of C0–C7 generated healthy cervical conditions. This was modified to the ACDF model by simulating the actual surgery at C5–C6. A 1.0 Nm moment and 73.6 N follower load were applied to the intact model to determine the ROMs. A displacement load was applied to the ACDF model under the same follower load, resulting in a total C0–C7 ROM similar to that of the intact model. The reasonable ROMs in the ACDF model were calculated using the fitting function. The results indicated that the intervertebral ROM of all non-fusion levels was increased in the ACDF model in all motion directions. The compensatory increase in ROM in adjacent segments (C4/5 and C6/7) was more significant than that in non-adjacent segments, except for C3/4 during lateral bending. The intervertebral FJF and IDP of C0–C7 increased with increasing ROM. The reasonable ROMs in the ACDF model were 42.4°, 52.6°, 28.4°, and 42.25° in flexion, extension, lateral bending, and axial rotation, respectively, with a decreased ROM of 4.4–7.2%. The postoperative increase in FJF and IDP in non-fusion segments can be canceled out by reducing the intervertebral ROM within reasonable ROMs. This study provided a new method to estimate the reasonable ROMs after ACDF from a biomechanical perspective, and further in vitro and clinical studies are needed to confirm this.

Classification of three-level hybrid surgery for the treatment of cervical degenerative disc disease: a retrospective study of 108 patients

IntroductionAccording to the different numbers and locations of cervical disc arthroplasty (CDA) and anterior cervical discectomy and fusion (ACDF), three-level hybrid surgery (HS) has many constructs. The purpose of the present study was to introduce a classification system for three-level HS and compare the two types with each other and with ACDF.MethodsA retrospective study was conducted involving patients with three-level cervical degenerative disc disease (CDDD) who underwent ACDF or HS in our hospital between June 2012 and May 2019. According to the different numbers and locations of ACDFs and CDAs, we classified the three-level HS into two types (type I: one-level CDA and two-level ACDF, and type II: two-level CDA and one-level ACDF). The differences of clinical and radiological outcomes were compared with each other and with three-level ACDF.ResultsA total of 108 patients were analyzed. The Neck Disability Index (NDI) of the ACDF group at 3 months postoperatively was significantly higher than that in the type I and type II groups (p < 0.05). The cervical lordosis was significantly lower in the ACDF group than that in the type I and II groups at 3 days, 6, 12 months postoperatively and the final follow-up (p < 0.05). The range of motion (ROM) of the total cervical spine decreased significantly in all three groups at 3, 6, and 12 months postoperatively and at the final follow-up (p < 0.05). The ACDF group was observed with the most severe loss of ROM of the total cervical spine, followed by the type I group. The type II group could preserve the most ROM of the total cervical spine. The ROM of adjacent segments increased most in the ACDF group, followed by the type I group.ConclusionsCompared with ACDF, three-level HS may yield a faster recovery rate and superior radiological outcomes, such as a superiority in maintaining the cervical curvature and ROM of the total cervical spine and a smaller increase in the ROM of adjacent segments. The advantages were most remarkable in the type II group.

Adjacent-segment effects of lumbar cortical screw-rod fixation versus pedicle screw-rod fixation with and without interbody support.

Cortical screw-rod (CSR) fixation has emerged as an alternative to the traditional pedicle screw-rod (PSR) fixation for posterior lumbar fixation. Previous studies have concluded that CSR provides the same stability in cadaveric specimens as PSR and is comparable in clinical outcomes. However, recent clinical studies reported a lower incidence of radiographic and symptomatic adjacent-segment degeneration with CSR. No biomechanical study to date has focused on how the adjacent-segment mobility of these two constructs compares. This study aimed to investigate adjacent-segment mobility of CSR and PSR fixation, with and without interbody support (lateral lumbar interbody fusion [LLIF] or transforaminal lumbar interbody fusion [TLIF]). A retroactive analysis was done using normalized range of motion (ROM) data at levels adjacent to single-level (L3-4) bilateral screw-rod fixation using pedicle or cortical screws, with and without LLIF or TLIF. Intact and instrumented specimens (n = 28, all L2-5) were tested using pure moment loads (7.5 Nm) in flexion, extension, lateral bending, and axial rotation. Adjacent-segment ROM data were normalized to intact ROM data. Statistical comparisons of adjacent-segment normalized ROM between two of the groups (PSR followed by PSR+TLIF [n = 7] and CSR followed by CSR+TLIF [n = 7]) were performed using 2-way ANOVA with replication. Statistical comparisons among four of the groups (PSR+TLIF [n = 7], PSR+LLIF [n = 7], CSR+TLIF [n = 7], and CSR+LLIF [n = 7]) were made using 2-way ANOVA without replication. Statistical significance was set at p < 0.05. Proximal adjacent-segment normalized ROM was significantly larger with PSR than CSR during flexion-extension regardless of TLIF (p = 0.02), or with either TLIF or LLIF (p = 0.04). During lateral bending with TLIF, the distal adjacent-segment normalized ROM was significantly larger with PSR than CSR (p < 0.001). Moreover, regardless of the types of screw-rod fixations (CSR or PSR), TLIF had a significantly larger normalized ROM than LLIF in all directions at both proximal and distal adjacent segments (p ≤ 0.04). The use of PSR versus CSR during single-level lumbar fusion can significantly affect mobility at the adjacent segment, regardless of the presence of TLIF or with either TLIF or LLIF. Moreover, the type of interbody support also had a significant effect on adjacent-segment mobility.

Efficacy of Hybrid anterior cervical spine surgery on range of motion and curvature in the treatment of cervical degenerative diseases

To observe the change of cervical curvature and range of motion (ROM) on imaging at 6 months after Hybrid surgery. A total of 29 patients with cervical degenerative disease who underwent Hybrid surgery from January 2017 to July 2018 were retrospectively analyzed. Also, they all met the inclusion criteria and had complete preoperative and 6 months postoperative imaging data. There were 11 males and 18 females, aged from 34 to 76 (55.86±10.69) years, and the operation time was from 2 to 4(3.03±0.51) hours. The Cobb angle method was used to measure the changes of cervical curvature and ROM of C2-C7, replacement segments, fusion segments, and upper adjacent segments on cervical lateral X-rays before and 6 months after surgery. There was no statistically significant difference in C2-C7 curvature and ROM between 6 months after operation and before operation (P>0.05). The degree of curvature and ROM of the replacement segment increased compared with that before operation (P<0.05). The curvatureof the fusion segment was increased than that before operation (P<0.05). There was no statistically significant difference in ROM of the fusion segment compared with that before operation (P>0.05). There was no statistically significant difference in the curvature and ROM of the upper adjacent segments compared with those before operation (P>0.05). There was no significant difference in the curvature between the replacement and fusion segments before and 6 months after operation (P>0.05);the ROM of the replacement segment was higher than that of the fusion segment at 6 months after operation (P<0.05). Hybrid surgery reconstructs the lordotic curvature of the entire cervical spine and the responsible segment, retains the ROM of the cervical replacement segment, and restores the biomechanical function of cervical spine.

P12. Does posterior ligamentous complex disruption following lumbar pedicle screw and rod instrumentation affect the upper adjacent level?

<h3>BACKGROUND CONTEXT</h3> The lumbar level above the fusion segment is the most common level for the development of adjacent level instability. The posterior ligamentous complex (PLC), (eg, interspinous ligament, and supraspinous ligament) a posterior tension band that stabilizes the spine, is usually removed for laminectomy during lumbar fusion and decompression surgery. The removal of the posterior complex may jeopardize upper adjacent level stability. <h3>PURPOSE</h3> To compare mobility and principal disc strains at the upper adjacent level to L4-5 pedicel screw-rod fixation (PSR) between L4-5 PSR, L4-5 PSR+ bilateral laminotomy (PLC preservation), and L4-5 PSR+ conventional laminectomy, in cadaveric specimens. The disc strain was studied with a new optical technique of soft tissue strain analysis (3D digital image correlation (DIC) technique). <h3>STUDY DESIGN/SETTING</h3> Biomechanic testing in human cadaveric spine specimens. <h3>PATIENT SAMPLE</h3> Human cadaveric lumbar spine. <h3>OUTCOME MEASURES</h3> 1. Adjacent segment range of motion, 2. Disc surface strains. <h3>METHODS</h3> Seven human cadaveric L3-S1 specimens were instrumented with L4-5 PSR. All specimens were tested multi-directionally under pure moment loading (7.5Nm) following: 1) L4-5 PSR, 2) L4-5 PSR+bilateral L4 laminotomy while preserving PLC and 3) L4-5 PSR +L4 conventional laminectomy. DIC was performed with cameras positioned laterally (left side) to capture the change in disc principal strain (Pmax and Pmin) at upper adjacent level (L3-4) under peak load. Optical motion tracking was simultaneously performed on the right side. The disc region was divided into four similar sized quarters and included upper and lower endplates. Analysis of variance of upper adjacent level (L3-4) range of motion (ROM) and disc strain between the groups was performed. Statistically significant was set at p≤0.05. <h3>RESULTS</h3> ROM of the upper adjacent (L3-4) level was significantly greater with L4-5 PSR+laminectomy (6.26 degree) versus L4-5 PSR+ bilateral laminotomy (5.94 degree, p=0.006), and L4-5 PSR (5.20 degree, p<0.001) respectively, during flexion. During extension, left lateral bending, and axial rotation, upper adjacent level ROM was significantly greater with L4-5+ laminectomy and L4-5 PSR+ bilateral laminotomy versus L4-5 PSR (p≤0.046) but there were no significant differences between L4-5 PSR+ laminectomy and L4-5PSR+ bilateral laminotomy (p≥0.087). The intervertebral disc Pmax strains of the upper adjacent level were significantly greater with L4-5 PSR+laminectomy than L4-5 PSR during flexion (25,225 VS 18,007uE, p=0.031), extension (22,803 VS 19,356uE, p=0.020), left lateral bending (32,778 VS 24,100uE, p=0.027), right lateral bending (88,761 VS 62,869uE, p=0.024), and right axial rotation (24,747 VS 19,289uE, p=0.025). <h3>CONCLUSIONS</h3> The posterior ligamentous complex disruption during lumbar fusion surgery was associated with significant increases in upper adjacent level instability and principle (Pmax) intervertebral disc stress/strain. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

P11. Does the choice of spinal interbody fusion approach significantly affect adjacent segment mobility?

<h3>BACKGROUND CONTEXT</h3> Previous studies have concluded that LLIF, TLIF, and PLIF with posterior pedicle screw-rod fixation (PSR) provide equivalent stability in cadaveric specimens and are comparable in fusion rate and functional outcome. However, long-term complications, such as adjacent segment degeneration associated with each type of interbody device, are currently unclear. Little is known about the biomechanical effects of interbody fusion technique on the mobility of adjacent segments. <h3>PURPOSE</h3> To investigate the differences in adjacent segment mobility among three types of LIF: lateral lumbar interbody fusion (LLIF), transforaminal lumbar interbody fusion (TLIF) and posterior lumbar interbody fusion (PLIF). <h3>STUDY DESIGN/SETTING</h3> Biomechanical study of range of motion (ROM) at the vertebral levels adjacent to the construct of posterior pedicle screw-rod fixation with different types of lumbar interbody fusion techniques (LIF). <h3>PATIENT SAMPLE</h3> Human cadaveric lumbar spine. <h3>OUTCOME MEASURES</h3> Adjacent segment range of motion. <h3>METHODS</h3> Normalized ROM data at the levels adjacent to L3–L4 PSR fixation with 3 different types of lumbar interbody fusion approaches (LLIF, TLIF, and PLIF) were analyzed. Intact (n=21) and instrumented (n=7 per group) L2–L5 cadaveric specimens were tested multidirectionally under pure moment loading (7.5 Nm). Analysis of variance of adjacent segment ROM among the groups was performed. Statistical significance was set at p<0.05. <h3>RESULTS</h3> Normalized ROM was significantly greater with PLIF than with LLIF in all directions at both proximal and distal adjacent segments (p≤0.02) except for axial rotation at the distal adjacent segment (p=0.07). TLIF also had greater normalized ROM than LLIF during lateral bending at the proximal adjacent segment (p=0.008) and during flexion, extension, and lateral bending at the distal adjacent segment (p≤0.03). Normalized ROM was not significantly different between PLIF and TLIF. <h3>CONCLUSIONS</h3> The choice of lumbar interbody fusion approach influences adjacent segment motion in a cadaveric model. LLIF had the least adjacent segment motion. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

20. Biomechanical effect of facet joint violation on adjacent segment motion and disc strain following single level lumbar fusion with transpedicular screw and rod instrumentation

<h3>BACKGROUND CONTEXT</h3> Facet joint violation (FV) is a complication occurring while placing pedicle screws at the upper-most level using an entry point and trajectory too close to the superior facet joint. The incidence of FV has been reported up to be as high as 50%. However, little is known about how FV affects superior adjacent level spinal stability and especially intervertebral disc (IVD) strain after lumbar fusion. <h3>PURPOSE</h3> To investigate the biomechanical effects of FV in terms of mobility and disc surface strains at the upper level adjacent to L4-5 pedicle screw-rod fixation (PSR) in cadaveric specimens. The disc strain was studied with a new optical technique of soft tissue strain analysis (3D digital image correlation [DIC] technique). <h3>STUDY DESIGN/SETTING</h3> Biomechanic testing in human cadaveric spine specimens. <h3>PATIENT SAMPLE</h3> A total of 14 human cadaveric L3-S1 specimens. <h3>OUTCOME MEASURES</h3> 1. Upper adjacent segment range of motion. 2. Disc surface strain/stress. <h3>METHODS</h3> A total of 14 human cadaveric L3-S1 specimens were divided into two equal groups. L4-5 pedicle-rod fixation was performed in a different fashion in each group ie, facet joint preservation (FP) and facet joint violation (FV). The violation of the facet joint was defined by denuding the facet joint capsule and removing of the external cortical surface of the superior articular process with a 3 mm Leksell-rongeur. The entry point of these pedicle screws was located at the junction between the inferolateral aspect of the facet joint. All specimens were tested multi-directionally under pure moment loading (7.5Nm). DIC was performed with cameras positioned laterally (left side) to capture the change in principal disc strains (Pmax and Pmin) at the upper adjacent level (L3-4) under peak load. Optical motion tracking was simultaneously performed on the right side. The IVD region was divided into four similar sized quarters and included upper and lower endplates. Analysis of variance of upper adjacent level range of motion (ROM) and disc strain, normalized to intact, was performed between the groups. Statistical significant was set at P≤0.05. <h3>RESULTS</h3> Normalized ROM was significantly greater with FV than FP at upper adjacent level (L3-4) during right axial rotation (1.22 vs 0.99, 23% difference, p=0.047). Normalized IVD Pmax strains at the upper adjacent level (L3-4) were significantly greater with FV than FP in the anterior quadrant during right axial rotation (1.80 vs 0.83 (ratio to intact), 97% difference, p=0.003). However, there were no significant differences in ROM and disc Pmax or Pmin strains during flexion, extension and lateral bending. <h3>CONCLUSIONS</h3> Facet violations at the uppermost level of fusion construct during pedicle screw-rod fixation were associated with adjacent level torsional instability and the increase of IVD strain. This study suggested that the preservation of uppermost facet joint of fusion segment was helpful for alleviating adjacent segment mobility and stress concentrations of the IVD above the fusion segment. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Biomechanical Evaluation of a Novel S-Type, Dynamic Zero-Profile Cage Design for Anterior Cervical Discectomy and Fusion with Variations in Bone Graft Shape: A Finite Element Analysis

Variations in cage design, material, and graft shape can affect osteointegration and adjacent segment range of motion (ROM) and stress after anterior cervical discectomy and fusion (ACDF) surgery. This study aimed to evaluate the biomechanical properties of a novel dynamic cervical cage design in both titanium (Ti) and polyether ether ketone (PEEK) with variations in bone graft shape using a single level ACDF (FE) model. A 3-dimensional C3-C6 FE model was developed using computed tomography scan data from a healthy male subject. The novel S-shaped dynamic interbody fusion cage with a zero-profile fixation was inserted at the C4-C5 level with 4 different bone graft shapes (square, circular, rectangular, and elliptical). Changes in segmental ROM and maximum von Mises stresses at the fusion and adjacent segments were analyzed. Both Ti and PEEK cages showed decreased ROM at the fusion and adjacent levels for all shapes of bone graft when compared with the intact spine model. The elliptical graft, for both Ti and PEEK cages, showed a lower percentage of reduction in segmental ROM at the fusion and adjacent levels (0%-5.6%) when compared with other graft shapes (0%-12%). Maximum stresses at the fusion level were lowest in Ti cage with elliptical graft (229.8-347.6 MPa) when compared with other shapes (241.2-476.2 MPa) in flexion, extension, and lateral bending. For the bone graft, maximum stresses were highest on the elliptical-shaped bone graft in flexion and extension in the Ti cage, and in flexion and lateral bending in the PEEK cage. Both Ti and PEEK cages showed decreased ROM at the fusion and adjacent levels for all shapes of bone graft when compared with the intact spine model. In the Ti and PEEK dynamic cages, the elliptical shape bone graft showed decreased stress on the cage and increased stress on the bone graft. Further experimental and clinical studies are needed to confirm these encouraging biomechanical results of this novel dynamic, zero-profile fusion device with elliptical bone graft in ACDF surgery.

Upper and lower adjacent segment range of motion after fixation of different lumbar spine segments in the goat: an in vitro experiment.

ObjectivesThe purpose of this study was to examine the biomechanical effects of fixation on range of motion (ROM) in the upper and lower adjacent segments of different lumbar spine segments in a goat spine model.MethodsFifteen goat spine specimens (vertebrae T12–S1) were randomly divided into three groups: A (single-segment fixation), B (double-segment fixation), and C (triple-segment fixation). Motion in different directions was tested using a spinal motion simulation test system with five external loading forces. Transverse, forward–backward, and vertical displacement of the upper and lower adjacent segments were measured.ResultsAs the external load increased, the upper and lower adjacent segment ROM increased. A significantly greater ROM in group C compared with group A was found when the applied external force was greater than 75 N. The upper adjacent segment showed a significantly greater ROM than the lower adjacent segment ROM within each group.ConclusionsAdjacent segment ROM increased with an increasing number of fixed lumbar segments. The upper adjacent segment ROM was greater than that of the lower adjacent segments. Adjacent segment stability after lumbar internal fixation worsened with an increasing number of fixed segments.