Bilateral Pedicle Screw Research Articles

Correction of adolescent idiopathic scoliosis using a convex pedicle screw technique with low implant density.

The aim of this retrospective study was to compare the correction achieved using a convex pedicle screw technique and a low implant density achieved using periapical concave-sided screws and a high implant density. We hypothesized that there would be no difference in outcome between the two techniques. We retrospectively analyzed a series of 51 patients with a thoracic adolescent idiopathic scoliosis. There were 26 patients in the convex pedicle screw group who had screws implanted periapically (Group 2) and a control group of 25 patients with bilateral pedicle screws (Group 1). The patients' charts were reviewed and pre- and postoperative radiographs evaluated. Postoperative patient-reported outcome measures (PROMs) were recorded. The number of implants (14.5 vs 17.1) and the implant density (1.5 vs 1.9) were significantly lower in Group 2 (p < 0.001). Operating time was 27 minutes shorter in Group 2 than in Group 1, with a mean of 217 minutes (SD 50.5; 120 to 346). The duration of surgery per instrumented vertebra was reduced by 19% in Group 2 (p = 0.011). No statistical difference was found in the postoperative Cobb angle, vertebral rotation, the relative correction achieved, or postoperative PROMs. Despite a lower implant density and achieving correction through a convex rod, surgical correction of the Cobb angle and vertebral body rotation was similar in both groups. Periapical pedicle screws and primary correction on the concave side do not seem to be mandatory in order to achieve good surgical results in idiopathic thoracic scoliosis. The operating time was shorter in the group with lower implant density. In conclusion, the technique provided good results and has the potential to reduce complications and costs. Cite this article: Bone Joint J2021;103-B(3):536-541.

Posterior Lumbar Interbody Fusion Versus Transforaminal Lumbar Interbody Fusion: Finite Element Analysis of the Vibration Characteristics of Fused Lumbar Spine

Previous studies have investigated biomechanical characteristics of the lumbar spine after different types of lumbar interbody fusion surgery under static loadings. However, very few have dealt with the whole-body vibration (WBV) condition that is typically present in vehicles. The aim of this study was to compare the influence of posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) on dynamic responses of the fused lumbar spine to vertical WBV. The PLIF and TLIF procedures with bilateral pedicle screw fixation at L4-L5 level were simulated by modifying a previously validated intact lumbar L1-S1 finite element model. The PLIF and TLIF models were subjected to a sinusoidal vertical load with a compressive follower preload, and computed for transient dynamic analysis. The obtained dynamic responses for the models at the fused and adjacent levels were collected and compared. The results showed that the contact force between endplate and cage was higher in the PLIF model than in the TLIF model, indicating that PLIF allowed for higher compressive load across the anterior structure. At fused L4-L5 level, the TLIF led to a higher stress in the endplate and posterior BPSF system than the PLIF. At adjacent L3-L4 level and L5-S1 level, the computed dynamic responses, in terms of stress and deformation, for the PLIF and TLIF models showed very few differences. This study may be helpful to quantify dynamic mechanical properties of the fused lumbar spine, and better understand biomechanical differences between the PLIF and TLIF procedures during vibration.

Biomechanical Evaluation of Oblique Lumbar Interbody Fusion with Various Fixation Options: A Finite Element Analysis.

ObjectiveThe aim of the present study was to clarify the biomechanical properties of oblique lumbar interbody fusion (OLIF) using different fixation methods in normal and osteoporosis spines.MethodsNormal and osteoporosis intact finite element models of L1–S1 were established based on CT images of a healthy male volunteer. Group A was the normal models and group B was the osteoporosis model. Each group included four subgroups: (i) intact; (ii) stand‐alone cage (Cage); (iii) cage with lateral plate and two lateral screws (LP); and (iv) cage with bilateral pedicle screws and rods (BPSR). The L3–L4 level was defined as the surgical segment. After validating the normal intact model, compressive load of 400 N and torsional moment of 10 Nm were applied to the superior surface of L2 to simulate flexion, extension, left bending, right bending, left rotation, and right rotation motions. Surgical segmental range of motion (ROM), cage stress, endplate stress, supplemental fixation stress, and stress distribution were analyzed in each group.ResultsCage provided the minimal reduction of ROM among all motions (normal, 82.30%–98.81%; osteoporosis, 92.04%–97.29% of intact model). BPSR demonstrated the maximum reduction of ROM (normal, 43.94%–61.13%; osteoporosis, 45.61%–62.27% of intact model). The ROM of LP was between that of Cage and BPSR (normal, 63.25%–79.72%; osteoporosis, 70%–87.15% of intact model). Cage had the minimal cage stress and endplate stress. With the help of LP and BPSR fixation, cage stress and endplate stress were significantly reduced in all motions, both in normal and osteoporosis finite element models. However, BPSR had more advantages. For cage stress, BPSR was at least 75.73% less than that of Cage in the normal model, and it was at least 80.10% less than that of Cage in the osteoporosis model. For endplate stress, BPSR was at least 75.98% less than that of Cage in the normal model, and it was at least 78.06% less than that of Cage in the osteoporosis model. For supplemental fixation stress, BPSR and LP were much less than the yield strength in all motions in the two groups. In addition, the comparison between the two groups showed that the ROM, cage stress, endplate stress, and supplemental fixation stress in the normal model were less than in the osteoporosis model when using the same fixation option of OLIF.ConclusionOblique lumbar interbody fusion with BPSR provided the best biomechanical stability both in normal and osteoporosis spines. The biomechanical properties of the normal spine were better than those of the osteoporosis spine when using the same fixation option of OLIF.

The anterior and traverse cage can provide optimal biomechanical performance for both traditional and percutaneous endoscopic transforaminal lumbar interbody fusion

BackgroundTransforaminal lumbar interbody fusion (TLIF) is a well-established surgical treatment for patients with lumbar degenerative disc disease; however, the optimal position for the interbody fusion cage in TLIF procedures for reducing cage-related complications remains uncertain. The present study aims to compare the biomechanical effects between different cage positions in TLIF and percutaneous endoscopic-TLIF (PE-TLIF). MethodAn intact finite element model of L3-L5 from computed tomography images of a 25-year-old healthy male without any lumbar disease was reconstructed and validated. TLIF and PE-TLIF were performed on L4-L5 with bilateral pedicle screws fixation. Two surgical finite element models were subjected to loads with six degrees of freedom. The range of motion (ROM) and von Mises stress of the implantations and endplates were measured for the anterior, middle, and posterior district and the traverse or oblique direction of the cage respectively. ResultsAs the cage was implanted forward, the ROMs in the fused L4-L5 segments and the von Mises stress of the cage and endplates decreased while the von Mises stress of the screws increased; this was also shown in the traverse cage when compared with the oblique cage (A-90—compared with A-45— had a 31.3%, 1.7%, 12.6%, and 5.7% decrease in FL, EX, LB and AR). The ROMs (TLIF A-45 increase of 80.8%, 23.8%, and 12.2% in FL, EX, and LB when compared with PE-TLIF), cage stress, and endplate stress of PE-TLIF were lower than those of TLIF. ConclusionsConsidering the ROM of the fusion segments, implanting the cage in the anterior district in the traverse direction can effectively enhance the fusion segment stiffness, thus contributing to the stability of the lumbar spine after fusion. It can also cause less cage stress and endplate stress, which indicates its beneficial effect in avoiding cage injury or subsidence. However, the higher stress of the pedicle screws and rods indicates higher failure risk. PE-TLIF had better biomechanical performance than TLIF. Therefore, it is recommended that the surgeon implant the cage in the anterior district of the L5 vertebra's upper endplate in the traverse direction using the PE-TLIF technique.

A biomechanical comparison of crossed and parallel rod configurations in atlantoaxial internal fixation.

Posterior atlantoaxial fixation with screw rod forms an approximate "II" shape or "H" increasing transverse link for better stability. In order to improve stability and in consideration of difficult placement of transverse connecting rod, possibility of inadequate bone graft, some scholars have preliminarily researched biomechanics of a novel crossed rod as an approximate "X" configuration of screw rod. The aim of this study was to evaluate and compare the biomechanics of the crossed and parallel rod configurations in the screw rod system for posterior atlantoaxial fixation on a cadaveric model. Six fresh cervical specimens were used to complete the range of motion (ROM) testing by applying pure moments of ± 2.0nm. Following intactstate and under destabilization testing, screws were implanted. The specimens were then tested in the following sequence: Group BLS + PR (C2 bilateral laminar screws + parallel rod), Group BLS + CR (C2 bilateral laminar screws + crossed rod), LPRLS + PR (C2 left pedicle screw and right laminar screw + parallel rod), LPRLS + CR (C2 left pedicle screw and right laminar screw + crossed rod), BPS + PR (C2 bilateral pedicle screws + parallel rod) and BPS + CR (C2 bilateral pedicle screws + crossed rod). The ROM of the C1-2 segments was measured in flexion-extension, lateral bending and axial rotation. Six surgical constructs were compared between the groupsand with intact condition, respectively. The six fixed modes significantly increased stability compared with both the intact and destabilization group in flexion-extension, lateral bending and axial rotation (p < .05). In extension, BPS + CR and BLS + CR showed greater stability than BLS + PR (p < .05). During flexion, the six fixation methods showed no statistical significance (p > .05). In left lateral bending, stability of the other five screw rod fixation techniques significantly increased when compared with BLS + PR (p < .05). In the right lateral bending direction, the stability of BLS + PR was worse than that of BPS + CR and BPS + PR (p < .05). In the left axial rotation, stability of BLS + CR, LPRLS + CR and BPS + CR was greater than that of BLS + PR, LPRLS + PR and BPS + PR (p < .05). In the right axial rotation, the stability of BPS + CR and BLS + CR was greater than that of BLS + PR (p < .05). The six investigated fixation methods provide sufficient biomechanical stability. The crossed rod configuration can further enhance the axial rotation stability of the screw rod system, which consists of C1 bilateral pedicle and C2 pedicle, or C2 lamina screws. The crossed rod can also improve the stability of the screw rod system made up of C1 bilateral pedicle and C2 lamina screws in lateral bending and extension. The crossed rod configuration is reliable and provides superior stability for clinical application.

Biomechanical role of osteoporosis in the vibration characteristics of human spine after lumbar interbody fusion.

Lumbar vertebrae osteoporosis is the most common challenge for lumbar interbody fusion, and this challenge has been widely concerned by scholars for many years. However, under whole-body vibration, osteoporosis how to affect the vibration characteristics of the fusion lumbar spine, complications, and fusion outcomes is urgent to know. The L1-L5 finite element model of lumbar spine was modified to simulate the transforaminal lumbar interbody fusion model with the bilateral pedicle screw fixator at L4-L5 level. A 5 Hz, 40 N sinusoidal vertical load supplemented with a 400 N preload was used to simulate the vertical vibration of human body. The results showed that under whole-body vibration, osteoporosis of fused vertebrae may cause the adjacent segments more unstable and increase the risk of adjacent segment diseases, subsidence, cage failure, rod failure, and lumbar instability. Osteoporosis of the fused vertebrae may cause the vertebral cells an unstable, inhibited growth and lead to poorer fusion outcomes. The findings may assist us in understanding the effect of osteoporosis on the vibration characteristics of lumbar spine fusion and provide references to clinical treatments for lumbar interbody fusion and lumbar vertebrae osteoporosis.

3D cone-beam tomosynthesis provides axial imaging of the spine with lower radiation compared to computed tomography

Three imaging techniques were compared using porcine spines. To compare image acquisition time, radiation exposure, pedicle width measurement, assessment of screw breach, and image artifact between cone-beam tomosynthesis (CBT) single mode, CBT dual mode (stereotactic CBT), and computed tomography (CT) imaging with and without spinal implants. CT is the standard for axial imaging of orthopedic procedures. CBT technology is being developed, allowing real-time intraoperative imaging and 3D surgical guidance. CBT may deliver useful axial imaging quicker with less radiation than current technologies. Six porcine spines were instrumented with bilateral pedicle screws at six levels connected with 5.5mm rods. Dosimeters were attached to four surfaces of spines. CT, CBT single and CBT dual images were acquired pre-implant and post-implant. Image acquisition and 3D reconstruction times were recorded. Pedicle widths were measured before and after instrumentation. Screw medial breaches were graded (0: no breach, 1: < 2mm, 2: 2-4mm, 3: > 4mm). Artifact and/or distortion of each image was ranked (0 = none, 1 = mild, 2 = moderate, 3 = large). Image acquisition and reconstruction times, radiation dose, pedicle width, screw breach and artifact were compared between techniques. Total image acquisition and reconstruction times of CBT was significantly less (single: 9.9 ± 0.2s, p < 0.001; dual: 60.0 ± 8.7 s, p < 0.001) than CT (250.3 ± 36.7s). CBT had significantly less radiation exposure than CT (CT: 0.7 ± 0.1rad, single: 0.03 ± 0.02rad, dual: 0.07 ± 0.03rad; p < 0.001). No difference in pedicle width change pre-implant to post-implant was found (CT: p = 0.449, single: p = 0.430, dual: p = 0.528). Pedicle width (pre-implant: p > 0.5, post-implant: p > 0.9) and pedicle width change (p > 0.4) was similar amongst all techniques. Breach assessment was not different between groups (p = 0.257). CBT images had consistently lower artifact grades than CT. Although CBT axial image quality appeared subjectively inferior to CT, it enabled consistent assessment of pedicle width and screw breach, at half time and 10× lower radiation exposure. With continued refinements, CBT technology may allow for adequate intra-operative axial imaging using low radiation exposure.

Biomechanical Analysis of an Interspinous Process Fixation Device with In Situ Shortening Capabilities: Does Spinous Process Compression Improve Segmental Stability?

The objective of this study was to characterize the biomechanical implications of spinous process compression, via in situ shortening of a next-generation interspinous process fixation (ISPF) device, in the context of segmental fusion. Seven lumbar cadaveric spines (L1-L4) were tested. Specimens were first tested in an intact state, followed by iterative instrumentation at L2-3 and subsequent testing. The order followed was 1) stand-alone ISPF (neutral height); 2) stand-alone ISPF (shortened in situ from neutral height; shortened); 3) lateral lumbar interbody fusion (LLIF)+ ISPF (neutral); 4) LLIF+ ISPF (shortened); 5) LLIF+ unilateral pedicle screw fixation; 6) LLIF+ bilateral pedicle screw fixation. A 7.5-Nm moment was applied in flexion/extension, lateral bending, and axial rotation via a kinematic test frame. Segmental range of motion (ROM) and lordosis were measured for all constructs. Comparative analysis was performed. Statistically significant flexion/extension ROM reductions: all constructs versus intact condition (P < 0.01); LLIF+ ISPF (neutral and shortened) versus stand-alone ISPF (neutral and shortened) (P < 0.01); LLIF+ USPF versus ISPF (neutral) (P= 0.049); bilateral pedicle screw fixation (BPSF) versus stand-alone ISPF (neutral and shortened) (P < 0.01); LLIF+ BPSF versus LLIF+ unilateral pedicle screw fixation (UPSF) (P < 0.01). Significant lateral bending ROM reductions: LLIF+ ISPF (neutral and shortened) versus intact condition and stand-alone ISPF (neutral) (P < 0.01); LLIF+ UPSF versus intact condition and stand-alone ISPF (neutral and shortened) (P < 0.01); LLIF+ BPSF versus intact condition and all constructs (P < 0.01). Significant axial rotation ROM reductions: LLIF+ ISPF (shortened) and LLIF+ UPSF versus intact condition and stand-alone ISPF (neutral) (P ≤ 0.01); LLIF+ BPSF versus intact condition and all constructs (P ≤ 0.04). In situ shortening of an adjustable ISPF device may support increased segmental stabilization compared with static ISPF.

239. Comparison of single-position robot-assisted surgery vs conventional minimally invasive surgery following LLIF: an in vitro assessment

BACKGROUND CONTEXT Lateral lumbar interbody fusion (LLIF) provides indirect decompression of the neural elements while minimizing the potential vascular complications associated with anterior lumbar interbody fusion (ALIF). Posterior fixation may be applied through various techniques such as conventional minimally invasive surgery (CMIS), requiring the patient to be repositioned prone to provide access to both pedicles. Conversely, robot-assisted navigation (RAN) of pedicle screws can be utilized from a single position without flipping the patient. RAN is theorized to reduce patient surgical time, radiation, and blood loss due to positioning and workflow effects. PURPOSE To evaluate the effect of robot-assisted navigation in comparison to CMIS methods in terms of surgical time, radiation exposure, and pedicle screw accuracy. STUDY DESIGN/SETTING Cadaveric study. PATIENT SAMPLE N/A OUTCOME MEASURES N/A METHODS Twelve unembalmed human torsos were implanted with 2-level static LLIF cages, followed by posterior bilateral pedicle screw fixation using either CMIS (n=6) or RAN (n=6). Preoperative computed tomography (CT) RAN workflow utilized CT scans of the specimen taken offsite and transferred to the robotic system during setup. Screw planning was performed using these CT scans, and then was merged with intraoperative fluoroscopy. Surgical times, surgeon radiation exposure, and screw accuracy were measured. Patient flip time from a consecutive patient series was included. RESULTS Significant differences in surgical times and radiation dosages were found between groups. Surgical time for preoperative RAN and CMIS was 64.7 min±4.1 min and 123.0 min±13.7 min, respectively. Time per screw for RAN and CMIS workflows was 2.7±0.6 min and 4.3±1.3 min, respectively. RAN was significantly different for total operative time and time per screw in comparison to CMIS (p CONCLUSIONS Significant differences were found in both surgical time and radiation exposure between CMIS and RAN, with RAN resulting in shorter surgical times and less radiation exposure to the surgeon than CMIS. Consideration should be given to single-position LLIF procedures that utilize RAN to instrument the spine with bilateral pedicle screws. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

58. Benefits of macroscale topography features on and within interbody cages

BACKGROUND CONTEXT Implant design, material, surfaces, graft and surgical techniques play important roles in the success of interbody fusions and the ability to radiographically assess. PEEK's positive attributes of mechanical properties and radiolucency are maintained using a molecularly bonded submicron deposition of titanium to improve bone on-growth. Novel macroscale topography features on the endplate surfaces and inside the aperture were hypothesized to allow early bone integration and mechanical stability. PURPOSE To evaluate the effect of macroscale topography on a PEEK/Titanium composite cage in a large animal model of interbody fusion. STUDY DESIGN/SETTING Preclinical large animal model. PATIENT SAMPLE Not applicable. OUTCOME MEASURES Not applicable METHODS Lateral L45 interbody fusions were performed in 4-5-year-old ewes using a PEEK/titanium composite cage (Control group) compared to the same cage with macro 3D features on the endplate and inside the aperture (Test group). Iliac crest autograft was placed in the aperture and bilateral pedicle screws and rods for posterior stabilisation. Fusion assessment at 6 and 12 weeks (n=10 per group) included manual palpation, X-rays, mCT, tensile testing and pmMA histology. RESULTS The Test group's manual palpation was 9/10 and 10/10 at 6 and 12 weeks while the control was 4/10 and 7/10 at 6 and 12 weeks. Radiographs and mCT confirmed new bone formation in the aperture of the Control group cages with time while some areas of aperture radiolucency were present. Radiographs and mCT of the Test group cages revealed new bone formation and integration within the topography features on the endplates and inside the aperture which progressed with time. Histology confirmed the radiographic findings in the control group and integration with the host endplates and remodeled bone within the apertures in the Test group. Tensile testing demonstrated nearly a 3-fold statistically significant increase in mechanical properties at both time points for the Test group vs the control group. CONCLUSIONS The macroscale features in the Test group provided multiple opportunities for bone integration between the host endplates and graft within the aperture. Early bony integration translated to a statistically significant increase in mechanical strength compared to the control cage which did not include the same geometric features. Promising data in this clinically relevant animal model warrants further study in humans. FDA DEVICE/DRUG STATUS Shoreline RT (Approved for this indication).

P4. In vitro assessment of adjustable lordotic expandable lateral interbody spacers on endplate loading and lordosis correction

BACKGROUND CONTEXT Anterior column realignment is a minimally invasive technique that uses a lateral transpsoas interbody approach with anterior longitudinal ligament (ALL) release, which aims to restore sagittal alignment. Resection of the ALL enables use of expandable lateral lumbar interbody fusion (LLIF) spacers with larger implant heights and lordosis, increasing focal lordosis correction and minimizing endplate mismatch. The relationship between implant height and lordosis selection, and their effect on segmental lordosis correction and anterior-posterior endplate loading, is poorly understood. PURPOSE The aim of this study is to quantify lordosis correction and endplate force distribution using an adjustable-lordosis expandable LLIF spacer. STUDY DESIGN/SETTING In vitro human cadaveric study. PATIENT SAMPLE A total of seven cadaveric specimens. OUTCOME MEASURES Lordosis and anterior-posterior endplate forces. METHODS Seven L4–L5 cadaveric segments were used. A 55 lb axial load was applied to L4 to simulate intraoperative loads. Segments were instrumented with bilateral pedicle screws and a sequence of expandable spacers with anterior fixation at varied heights and implant lordosis (ten constructs), including (A) 0°, 6°, and 20° lordosis with intact ALL; B) 20° and 30° lordosis following ALL resection. Segmental lordosis and endplate force-maps were collected. An equivalent loading ratio (ELR=anterior load/total load*100%) was calculated; ELR=80% refers to 80% anterior and 20% posterior edge loading. ELR was statistically compared to 50%, which is equivalent anterior-posterior loading. RESULTS The mean intact L4–L5 lordosis was 11.5°±3.0°. With the ALL intact, the 20° spacer without expansion increased lordosis to 11.9°±3.6° (p>0.05). Following ALL resection, use of 20° spacer with largest expansions (14.7 and 17.4 mm) significantly increased lordosis to 19.4°±4.5° (p=0.036 and 22.5°±4.9° (p CONCLUSIONS This study suggests that expandable spacers may help to balance anterior-posterior endplate loading while maximizing lordosis correction. Following ALL release, hyperlordotic spacers do not increase anterior loading, therefore, spacers may be selected for maximum lordosis. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

P5. In vitro comparison of novel adjustable-lordotic expandable and static hyperlordotic lateral interbody spacers on endplate loading and lordosis correction

BACKGROUND CONTEXT For restoration of sagittal alignment, hyperlordotic lateral lumbar interbody fusion (LLIF) spacers are available as expandable or static spacers with many sizes, and possess up to 30° of implant lordosis to maximize lumbar lordosis when used in combination with anterior longitudinal ligament (ALL) resection. However, angular mismatch between the implant and vertebral endplates may play a role in subsidence due to asymmetric loading of the anterior implant edge. The relationship between implant size and their effect on segmental lordosis correction and anterior-posterior endplate loading is poorly understood. PURPOSE The aim of this study is to compare adjustable-lordosis expandable and static LLIF spacers in regards to lordosis correction and endplate force distribution. STUDY DESIGN/SETTING In vitro human cadaveric study. PATIENT SAMPLE A total of 14 cadaveric specimens. OUTCOME MEASURES Lordosis and anterior-posterior endplate forces. METHODS Fourteen L4–L5 cadaveric segments were used. A 55 lb axial load was applied to L4 to simulate intraoperative loads. Segments were instrumented with bilateral pedicle screws and a sequence of expandable spacers with anterior fixation (n=7) or static spacers (n=7) at varied heights and implant lordosis matched between spacers (nine constructs per spacer), including (A three height and lordosis combinations with intact ALL; and B) six height and lordosis combinations following ALL resection. Segmental lordosis and endplate force-maps were collected and compared between the two spacers. An equivalent loading ratio (ELR=anterior load/total load*100%) was calculated; ELR=80% refers to 80% anterior and 20% posterior edge loading. An ELR of 50% is equivalent anterior-posterior loading. RESULTS No significant differences in lordosis was observed between spacers except at between the 20° expandable spacer (17.4mm) and the 13mm 20° static spacer (22.5°±4.9° and 16.7°±2.3°, respectively, p=0.020). Equivalent anterior-posterior loading ratios were also quantified. Prior to ALL resection, the 9mm 10° static spacer had a significantly larger ELR than the 20° expandable spacer (11.5mm, p=0.016), indicating more anterior loading with the static spacer (91.5% ± 7.6 versus 70.5% ± 18.8%). Following ALL resection, the 11mm 10°, 11mm 20°, and 13mm 20° static spacers (85.1%, 99.2%, and 94.8%, respectively) all had significantly larger ELRs than the 20° expandable at 11.5mm, 14.7mm, and 17.4mm heights (52.0%, 70.0%, and 76.2%), respectively (p CONCLUSIONS This study suggests that expandable and static spacers have comparable lordosis correction; however, greater anterior endplate loading was observed with static spacers. Increased anterior endplate loading may lead to subsidence. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

238. Interbody spacers and instability: is there a difference in subsidence and range of motion between various cages for osteotomy techniques?

BACKGROUND CONTEXT Several types of spine osteotomy techniques have been described to maintain sagittal alignment, varying regarding degree of deformity correction and invasiveness. Intradiscal osteotomy (IDO) is an alternative osteotomy technique for correcting thoracolumbar deformity. Lordotic interbody spacers provide anterior column support and act as a fulcrum around which an osteotomy can be reduced. Partial removal of the posterior endplate during IDO may increase subsidence risk. PURPOSE The purpose of this cadaveric study was to compare the biomechanical stability of bilateral IDO with static and expandable oblique interbody spacers to that of standard Smith-Petersen osteotomy (SPO) with transforaminal lateral interbody fusion (TLIF) using a static, banana-shaped spacer, pre- and postsubsidence. STUDY DESIGN/SETTING Biomechanical cadaveric study PATIENT SAMPLE N/A OUTCOME MEASURES N/A METHODS Eighteen cadaveric functional spine units (FSU) were divided into three equal groups (n=6): SPO-TLIF, bilateral IDO and static cage (sIDO), or bilateral IDO and expandable cage (eIDO). Bilateral pedicle screws were placed proximally and distally for all specimens. Subsidence was created by cyclically loading between 400N and 1200N compression for 20000 cycles at 2Hz, and was defined as the amount of implant settling between the first 1200N cycle and last 1200N cycle. Range of motion (ROM) was captured for flexion/extension (FE), lateral bending (LB), and axial rotation (AR), pre- and postsubsidence. RESULTS ROM in FE, LB, and AR was similar for all three groups, with no significant differences in motion pre- or post-subsidence (p>.05). The eIDO group had the largest loss of stability following subsidence, with motion increasing by 111.9±50.7% in FE, 91.4±42.6% in LB, and 65.5±29.9% in AR. Motion following subsidence was significantly higher than pre-subsidence for eIDO for all three bending planes (p=.003). sIDO motion increased by 103.0±104.3% in FE, 70.3±71.4% in LB, and 73.9±72.8% in AR. SPO-TLIF motion increased by 42.0±33.9% in FE, 27.7±20.1% in LB, and 19.4±17.8% in AR. Motion following subsidence was significantly higher than pre-subsidence for SPO-TLIF for LB (p=.037). CONCLUSIONS In this cadaveric model of a single FSU, IDO with both static and expandable interbodies showed similar biomechanical stability to SPO-TLIF both pre- and postsubsidence. Motion in the eIDO group significantly increased following subsidence in all three bending modes, while sIDO did so in none, and SPO-TLIF did so in only LB. This may be due to larger amounts of subsidence in the eIDO group. Expandable spacers in the eIDO group may have been overexpanded, causing endplate damage upon reducing the osteotomy. Further studies are required to elucidate clinical significance. FDA DEVICE/DRUG STATUS RISE (Globus Medical Inc.) (Not approved for this indication), SUSTAIN (Globus Medical Inc.) (Not approved for this indication), SIGNATURE (Globus Medical Inc.) (Not approved for this indication)

Rate of failure of indirect decompression in lateral single-position surgery: clinical results.

Lateral single-position surgery (LSPS) of the lumbar spine generally involves anterior lumbar interbody fusion (ALIF) performed in the lateral position (LALIF) at L5-S1 with or without lateral lumbar interbody fusion (LLIF) at L4-5 and above, followed by bilateral pedicle screw fixation (PSF) without repositioning the patient. One obstacle to more widespread adoption of LSPS is the perceived need for direct decompression of the neural elements, which typically requires flipping the patient to the prone position. The purpose of this study was to examine the rate of failure of indirect decompression in a cohort of patients undergoing LSPS from L4 to S1. A multicenter, post hoc analysis was undertaken from prospectively collected data of patients at 3 institutions who underwent LALIF at L5-S1 with or without LLIF at L4-5 with bilateral PSF in the lateral decubitus position between March 2018 and March 2020. Inclusion criteria were symptoms of radiculopathy or neurogenic claudication, central or foraminal stenosis (regardless of degree or etiology), and indication for interbody fusion at L5-S1 or L4-S1. Patients with back pain only; those who were younger than 18 years; those with tumor, trauma, or suspicion of infection; those needing revision surgery; and patients who required greater than 2 levels of fusion were excluded. Baseline patient demographic information and surgical data were collected and analyzed. The number of patients in whom indirect decompression failed was recorded and each individual case of failure was analyzed. A total of 178 consecutive patients underwent LSPS during the time period (105 patients underwent LALIF at L5-S1 and 73 patients underwent LALIF at L5-S1 with LLIF at L4-5). The mean follow-up duration was 10.9 ± 6.5 months. Bilateral PSF was placed with the patient in the lateral decubitus position in 149 patients, and there were 29 stand-alone cases. The mean case time was 101.9 ± 41.5 minutes: 79.3 minutes for single-level cases and 134.5 minutes for 2-level cases. Three patients (1.7%) required reoperation for failure of indirect decompression. The rate of failure of indirect decompression in LSPS from L4 to S1 is exceedingly low. This low risk of failure should be weighed against the risks associated with direct decompression as well as the risks of the extra operative time needed to perform this decompression.

Interlaminar stabilization for spinal stenosis in the Medicare population

The number of complex fusions performed on Medicare beneficiaries, defined as ≥age 65, with lumbar spinal stenosis with or without spondylolisthesis has been increasing. Typically, these procedures are longer, more invasive and pose a greater risk for complications. Interlaminar stabilization (ILS) serves as an intermediary between decompression alone and decompression with fusion. The purpose of this study was to prospectively examine the efficacy of ILS in patients ≥age 65 through comparison to fusion in the same age group and ILS in younger patients. A prospective, multicentered, randomized controlled trial comparing decompression with ILS to decompression with posterolateral fusion with bilateral pedicle screw instrumentation. Patients from 21 sites in the United States underwent surgery for moderate stenosis with up to a grade 1 degenerative spondylolisthesis and failure of conservative treatment with low back pain at 1 or 2 contiguous levels from L1-L5. Preoperatively, patient-reported assessment had to meet the criteria of significant pain and disability (Visual Analog Scale [VAS back pain] ≥50 mm on a 100 mm scale; Oswestry Disability Index [ODI] of ≥20/50). The primary outcome was overall Composite Clinical Success (CCS) as determined by ODI scores, incidence of postoperative epidural injections and/or reoperations, incidence of device-related complications, and persistent or progressive neurological deficit. Secondary outcomes included patient satisfaction as measured by VAS for back and worse leg pain and Zurich Claudication Questionnaire scores. Narcotic usage data and radiographic assessment of changes in postoperative posterior disc height and foraminal height were also evaluated. At 1- or 2-levels, 84 patients ≥age 65 underwent decompression with ILS, 57 patients ≥age 65 underwent decompression with fusion, and 131 patients <age 65 underwent decompression with ILS. Comparisons were made between ≥age 65 ILS patients and ≥age 65 fusion patients and between <age 65 and ≥age 65 ILS patients. The patients were assessed before and after surgery at 6 weeks and 3, 6, 12, 18, 24, 48, and 60 months. At 24 and 60 months, there were no statistically significant differences in CCS or any of the individual components of CCS between the ≥ age 65 ILS and fusion groups or between the < age 65 and ≥ age 65 ILS groups. ILS Medicare patients experienced significantly shorter surgeries (p<.001), less blood loss (p<.001), and a shorter hospital stay (p<.001) than fusion patients. There were no significant differences radiographically or with regards to postoperative narcotic usage. Clinically, ILS patients ≥age 65 performed as well as both those receiving fusion and those <age 65 who received ILS. Importantly, however, for this older population, ILS Medicare patients experienced less blood loss, a shorter operation and shorter hospital stay than fusion Medicare patients.

Undercut macrostructure topography on and within an interbody cage improves biomechanical stability and interbody fusion

BACKGROUND CONTEXTThe interface and interactions between an interbody cage, graft material, and host bone can all participate in the fusion. Shortcomings of Poly(aryl-ether-ether-ketone) interbody cages have been addressed with novel titanium surfaces. Titanium surfaces paired with macroscale topography features on the endplates and within the aperture may provide additional benefits. PURPOSETo evaluate the influence of cage design parameters on interbody fusion in a large animal preclinical model. STUDY DESIGN/SETTINGA comparative preclinical large animal model was performed to evaluate how macroscale topography features of an interbody cage can facilitate early integration between the host bone, graft material, and interbody cage and these effects on biomechanical stability and fusion. METHODSForty single level interbody fusions (L4–L5) using iliac crest autograft and bilateral pedicle screw fixation were performed in adult sheep to evaluate the effect of undercut macrostructure topography features of an interbody cage on the endplates and within the aperture. Fusions were evaluated at 6 and 12 weeks (n=10 per group) using radiography, microcomputed tomography, biomechanical integrity, and histology endpoints. RESULTSThe presence of the undercut macrostructures present on the endplates and within the aperture statistically improved biomechanical integrity at 6 and 12 weeks compared with controls. Microcomputed tomography and histology demonstrated bony interdigitation within the endplate and aperture features contributing to the improvement in properties. CONCLUSIONSThe present study demonstrates that Poly(aryl-ether-ether-ketone) implants with titanium surfaces can be augmented by undercut macrostructures present on the endplates and within the aperture to provide opportunities for a series of anchoring points that, with new bone formation and remodelling, result in earlier and improved biomechanical integrity of the treated level. CLINICAL SIGNIFICANCEThis preclinical study showed that bone interdigitation with the undercut macrostructures present on the endplates and within the aperture resulted in improved fusion and biomechanical stability in a clinically relevant spinal fusion model. Future clinical study is warranted to evaluate such implants’ performance in humans.

Safety Profile, Surgical Technique, and Early Clinical Results for Simultaneous Lateral Lumbar Interbody Fusion and Anterior Lumbar Interbody Fusion in a Lateral Position.

Description of surgical technique and retrospective review. To describe a novel surgical technique for multilevel lumbar fusion and describe early clinical results. Patients with multilevel lumbar spinal stenosis and adult degenerative scoliosis often require multilevel interbody placement to achieve indirect decompression and lordosis. We describe a case series of patients treated with simultaneous lateral lumbar interbody fusion (LLIF) and anterior lumbar interbody fusion (ALIF) at L5-S1. We retrospectively reviewed a consecutive series of patients treated for multilevel lumbar spinal stenosis with simultaneous ALIF and LLIF with at least 3-month follow-up. All patients received supplemental percutaneous bilateral pedicle screw placement as well. We measured on preoperative radiographs their lumbar lordosis, pelvic incidence, and L5-S1 lordosis. Intraoperative factors such as operative time, estimated blood loss, fluids provided, number of levels fused, and whether a trainee was present during the procedure were all recorded. There were 15 patients included within our case series (69.5, 4 F). There were no reported intraoperative vascular or neurological complications in 15 cases. The operative time for the cases ranged from 2.7 to 8.4 hours (average=5.2±1.9 h). The average lordosis gained at L5-S1 was 8.6±3.0 degrees and the average lumbar lordosis gained was 14.7±6.4 degrees. The average PI-LL mismatch went from 22.4±13.3 degrees preoperative to 7.8±10.2 degrees postoperative. One patient had a postoperative complication of a sacral fracture requiring placement of a pelvic screw for a L2-pelvis fusion. There were 8 patients with 4+ levels of fusion. For this cohort of patients, the average lumbar lordosis gained was 16.0±7.5 degrees and the average PI-LL mismatch went from 24.7±16.3 degrees preoperative to 8.8±12.9 degrees postoperative. For the patients with 4+ levels of fusion, the average operative time was 5.9±1.8 hours. We have described our early positive results with simultaneous LLIF/ALIF surgery for treatment of lumbar degenerative conditions.

Biomechanical Comparison of Stand-Alone and Bilateral Pedicle Screw Fixation for Oblique Lumbar Interbody Fusion Surgery—A Finite Element Analysis

The most common complication of oblique lumbar interbody fusion (OLIF) is endplate fracture/subsidence. The mechanics of endplate fracture in OLIF surgery are still unclear. The aim of the present study was to evaluate the biomechanical stability in patients undergoing OLIF surgery with stand-alone (SA) and bilateral pedicle screw fixation (BPSF) methods. A finite element model of the L1-L5 spinal unit was established and validated. Using the validated model technique, L4-L5 functional surgical models corresponding to the SA and BPSF methods were created. Simulations using the models were performed to investigate OLIF surgery. A 500-N compression force was applied to the superior surface of the model to represent the upper body weight, and a 7.5-Nm moment was applied to simulate the 6 movement directions of the lumbar spinal model: flexion and extension, right and left lateral bending, and right and left axial rotation. Finite element models were developed to compare the biomechanics of the SA and BPSF groups. Compared with the range of motion of the intact lumbar model, that of the SA model was decreased by 79.6% in flexion, 54.5% in extension, 57.2% in lateral bending, and 50.0% in axial rotation. The BPSF model was decreased by 86.7% in flexion, 77.3% in extension, 76.2% in lateral bending, and 75.0% in axial rotation. Compared with the BPSF model, the maximum stresses of the L4 inferior endplate and L5 superior endplate were greatly increased in the SA model. The L4 inferior endplate stress was increased to 49.7 MPa in extension, and the L5 superior endplate stress was increased to 47.7 MPa in flexion, close to the yield stress of the lamellar bone (60 MPa). OLIF surgery with BPSF could reduce the maximum stresses on the endplate, which might reduce the incidence of cage subsidence. OLIF surgery with the SA method produced more stress compared with BPSF, especially in extension and flexion, which might be a potential risk factor for cage subsidence.

Short fixation with a 3-rod technique for posterior hemivertebra resection in children younger than 5 years old.

ABSTRACTImportanceCongenital hemivertebra is commonly treated with posterior hemivertebra resection with bilateral transpedicular fixation. However, implant‐related complications are common in children younger than 5 years old who undergo this surgical procedure.ObjectiveTo present the preliminary clinical and radiological outcomes of children younger than 5 years old treated by posterior hemivertebra resection and 3‐rod fixation technique.MethodsFrom January 2016 to December 2017, 14 consecutive patients of congenital scoliosis with 16 hemivertebrae were retrospectively reviewed, including 5 girls and 9 boys, aged between 25 and 55 months old (average, 37.6 months). All patients underwent posterior hemivertebra resection with short fixation with bilateral pedicle screws and a convex lamina hook. Surgical complications and corrective outcomes were assessed based on the clinical charts and spinal radiographs with a minimum 24‐month follow‐up.ResultsThe mean Cobb angle of the main curve was 38.4° before surgery, 8.5° after surgery, and 8.7° at final follow‐up. In the compensatory cranial curve, the preoperative Cobb angle of 16.8° was corrected to 8.1° postoperatively and was 10.3° at final follow‐up. In the compensatory caudal curve, the preoperative Cobb angle of 15.9° improved to 5.3° postoperatively and was 7.8° at final follow‐up. The segmental kyphosis was corrected from 13.5° to 0.5° and was 1.1° at final follow‐up. There were no crankshaft phenomena, no proximal kyphosis, and no complications related to the instrumentation.InterpretationPosterior hemivertebra resection with instrumentation with bilateral pedicle screws and a convex lamina hook can achieve rigid fixation and deformity correction.

WITHDRAWN: Biomechanical comparison of unilateral and bilateral pedicle screws fixation for oblique lumbar inter-body fusion surgery – a finite element analysis

WITHDRAWN: Biomechanical comparison of unilateral and bilateral pedicle screws fixation for oblique lumbar inter-body fusion surgery – a finite element analysis