Biomechanical Effect of the C2 Laminar Decortication on the Stability of C2 Intralaminar Screw Construct and Biomechanical Comparison of C2 Intralaminar Screw and C2 Pars Screw

2011 ◽  
Vol 69 (suppl_1) ◽  
pp. ons1-ons7 ◽  
Author(s):  
Jae Taek Hong ◽  
Tomoyuki Takigawa ◽  
Ranjith Udayakunmar ◽  
Hun Kyu Shin ◽  
Peter Simon ◽  
...  
Keyword(s):  
Axial Rotation ◽  
Insertion Torque ◽  
Lateral Mass ◽  
Pullout Strength ◽  
Lateral Bending ◽  
Biomechanical Stability ◽  
Laminar Screw ◽  
Flexion Extension ◽  
The Stability ◽  
C2 Laminar Screw

Abstract BACKGROUND: There have been no reports of biomechanical stability of C1-2 constructs after decortication of the C2 lamina. In addition, few studies have compared the stability of C2 laminar screw and pars screw constructs. OBJECTIVE: To compare the biomechanical stability of 3 different C1-2 construct conditions (C2 pars screw, C2 intralaminar screw, C2 intralaminar construct with C2 laminar decortication). METHODS: Fourteen fresh-frozen cadaveric cervical specimens (C1-3) were used. In 7 specimens, pure moments of 1.5 Nm were applied in flexion/extension, lateral bending, and axial rotation. Each specimen was tested in the normal state, in the destabilized state (after odontoidectomy and resection of transverse atlantal ligament), and after application of constructs. After kinematic study, these 7 specimens underwent axial pullout strength testing of pars screw and 50% decorticated C2 intralaminar screws. In another 7 specimens, insertion torque and pullout strength were measured to compare the pars screw and intact C2 intralaminar screw. RESULTS: There were no statistically significant differences between the intact C2 intralaminar and 50% decorticated C2 intralaminar screw constructs in terms of range-of-motion limitations. The C2 pars screw construct was significantly superior to the C2 laminar screw construct in lateral bending (P < .01) and axial rotation (P < .01) and equivalent to the C2 laminar screw construct in flexion/extension (P = .42). There was no significant pullout strength difference between the 3 kinds of C2 screw. CONCLUSION: The C1 lateral mass-C2 pars screws construct was stronger than the C1 lateral mass-C2 intralaminar screw construct. Decortication of C2 laminar (up to 50%) did not affect the immediate stability of the C1-2 construct.

Biomechanical analysis of screw constructs for atlantoaxial fixation in cadavers: a systematic review and meta-analysis

2015 ◽  
Vol 22 (2) ◽  
pp. 151-161 ◽  
Author(s):  
Jerry Y. Du ◽  
Alexander Aichmair ◽  
Janina Kueper ◽  
Timothy Wright ◽  
Darren R. Lebl
Keyword(s):  
Meta Analysis ◽  
Axial Rotation ◽  
Significant Heterogeneity ◽  
Lateral Mass ◽  
Lateral Bending ◽  
Biomechanical Stability ◽  
Spinal Motion ◽  
Flexion Extension ◽  
Atlantoaxial Fixation ◽  
Injury Models

OBJECT The unique and complex biomechanics of the atlantoaxial junction make the treatment of C1–2 instability a challenge. Several screw-based constructs have been developed for atlantoaxial fixation. The biomechanical properties of these constructs have been assessed in numerous cadaver studies. The purpose of this study was to systematically review the literature on the biomechanical stability achieved using various C1–2 screw constructs and to perform a meta-analysis of the available data. METHODS A systematic search of PubMed through July 1, 2013, was conducted using the following key words and Boolean operators: “atlanto [all fields]” AND “axial [all fields]” OR “C1–C2” AND “biomechanic.” Cadaveric studies on atlantoaxial fixation using screw constructs were included. Data were collected on instability models, fixation techniques, and range of motion (ROM). Forest plots were constructed to summarize the data and compare the biomechanical stability achieved. RESULTS Fifteen articles met the inclusion criteria. An average (± SD) of 7.4 ± 1.8 cadaveric specimens were used in each study (range 5–12). The most common injury models were odontoidectomy (53.3%) and cervical ligament transection (26.7%). The most common spinal motion segments potted for motion analysis were occiput–C4 (46.7%) and occiput–C3 (33.3%). Four screw constructs (C1 lateral mass–C2 pedicle screw [C1LM–C2PS], C1–2 transarticular screw [C1–C2TA], C1 lateral mass–C2 translaminar screw [C1LM-C2TL], and C1 lateral mass–C2 pars screw [C1LM–C2 pars]) were assessed for biomechanical stability in axial rotation, flexion/extension, and lateral bending, for a total of 12 analyses. The C1LM–C2TL construct did not achieve significant lateral bending stabilization (p = 0.70). All the other analyses showed significant stabilization (p < 0.001 for each analysis). Significant heterogeneity was found among the reported stabilities achieved in the analyses (p < 0.001; I2 > 80% for all significant analyses). The C1LM–C2 pars construct achieved significantly less axial rotation stability (average ROM 36.27° [95% CI 34.22°–38.33°]) than the 3 other constructs (p < 0.001; C1LM–C2PS average ROM 49.26° [95% CI 47.66°–50.87°], C1–C2TA average ROM 47.63° [95% CI 45.22°–50.04°], and C1LM–C2TL average ROM 53.26° [95% CI 49.91°–56.61°]) and significantly more flexion/extension stability (average ROM 13.45° [95% CI 10.53°–16.37°]) than the 3 other constructs (p < 0.001; C1LM–C2PS average ROM 9.02° [95% CI 8.25°–9.80°], C1–C2TA average ROM 7.39° [95% CI 5.60°–9.17°], and C1LM–C2TL average ROM 7.81° [95% CI 6.93°–8.69°]). The C1–C2TA (average ROM 5.49° [95% CI 3.89°–7.09°]) and C1LM–C2 pars (average ROM 4.21° [95% CI 2.19°–6.24°]) constructs achieved significantly more lateral bending stability than the other constructs (p < 0.001; C1LM–C2PS average ROM 1.51° [95% CI 1.23°–1.78°]; C1LM–C2TL average ROM −0.07° [95% CI −0.44° to 0.29°]). CONCLUSIONS Meta-analysis of the existing literature showed that all constructs provided significant stabilization in all axes of rotation, except for the C1LM–C2TL construct in lateral bending. There were significant differences in stabilization achieved in each axis of motion by the various screw constructs. These results underline the various strengths and weaknesses in biomechanical stabilization of different screw constructs. There was significant heterogeneity in the data reported across the studies. Standardized spinal motion segment configuration and injury models may provide more consistent and reliable results.

The cervical end of an occipitocervical fusion: a biomechanical evaluation of 3 constructs

2008 ◽  
Vol 9 (3) ◽  
pp. 296-300 ◽  
Author(s):  
Michael A. Finn ◽  
Daniel R. Fassett ◽  
Todd D. Mccall ◽  
Randy Clark ◽  
Andrew T. Dailey ◽  
...  
Keyword(s):  
Tracking System ◽  
Plate Fixation ◽  
Axial Rotation ◽  
Lateral Mass ◽  
Lateral Bending ◽  
Cross Link ◽  
3D Tracking ◽  
Flexion Extension ◽  
Biomechanical Evaluation ◽  
Rotation Motion

Object Stabilization with rigid screw/rod fixation is the treatment of choice for craniocervical disorders requiring operative stabilization. The authors compare the relative immediate stiffness for occipital plate fixation in concordance with transarticular screw fixation (TASF), C-1 lateral mass and C-2 pars screw (C1L-C2P), and C-1 lateral mass and C-2 laminar screw (C1L-C2L) constructs, with and without a cross-link. Methods Ten intact human cadaveric spines (Oc–C4) were prepared and mounted in a 7-axis spine simulator. Each specimen was precycled and then tested in the intact state for flexion/extension, lateral bending, and axial rotation. Motion was tracked using the OptoTRAK 3D tracking system. The specimens were then destabilized and instrumented with an occipital plate and TASF. The spine was tested with and without the addition of a cross-link. The C1L-C2P and C1L-C2L constructs were similarly tested. Results All constructs demonstrated a significant increase in stiffness after instrumentation. The C1L-C2P construct was equivalent to the TASF in all moments. The C1L-C2L was significantly weaker than the C1L-C2P construct in all moments and significantly weaker than the TASF in lateral bending. The addition of a cross-link made no difference in the stiffness of any construct. Conclusions All constructs provide significant immediate stability in the destabilized occipitocervical junction. Although the C1L-C2P construct performed best overall, the TASF was similar, and either one can be recommended. Decreased stiffness of the C1L-C2L construct might affect the success of clinical fusion. This construct should be reserved for cases in which anatomy precludes the use of the other two.

scholarly journals Biomechanical Comparison of Posterior Fixation Combinations with an Allograft Spacer between the Lateral Mass and Pedicle Screws

2020 ◽  
Vol 10 (20) ◽  
pp. 7291
Author(s):  
Soo-Bin Lee ◽  
Hwan-Mo Lee ◽  
Tae-Hyun Park ◽  
Sung Lee ◽  
Young-Woo Kwon ◽  
...  
Keyword(s):  
Pedicle Screws ◽  
Element Model ◽  
Axial Rotation ◽  
Posterior Fixation ◽  
Hybrid Technique ◽  
Lateral Mass ◽  
Lateral Bending ◽  
Flexion Extension ◽  
Hybrid Motion ◽  
Biomechanical Comparison

Background: There are a few biomechanical studies that describe posterior fixation methods with pedicle screws (PS) and lateral mass screws (LMS); the combination of both screw types and their effect on an allograft spacer in a surgically treated cervical segment is unknown. Methods: Finite element model (FEM) analyses were used to investigate the effects of a hybrid technique using posterior PS and LMS. Stress distribution and subsidence risk from a combination of screws under hybrid motion control conditions, including flexion, extension, axial rotation, and lateral bending, were investigated to evaluate the biomechanical characteristics of different six-screw combinations. Findings: The load sharing on the allograft spacer in flexion mode was highest in the LMS model (74.6%) and lowest in the PS model (35.1%). The likelihood of subsidence of allograft spacer on C6 was highest in the screws from the distal LMS (type 5) model during flexion and extension (4.902 MPa, 30.1% and 2.189 MPa, 13.4%). In lateral bending, the left unilateral LMS (type 4) model screws on C5 (3.726 MPa, 22.9%) and C6 (2.994 MPa, 18.4%) yielded the greatest subsidence risks, because the lateral bending forces were supported by the LMS. In counterclockwise axial rotation, the left unilateral LMS (type 4) model screws on C5 (3.092 MPa, 19.0%) and C6 (3.076 MPa, 18.9%) demonstrated the highest subsidence risks. Conclusion: The asymmetrical ipsilateral use of LMS and posterior PS in lateral bending and axial rotation demonstrated the lowest stability and greatest subsidence risk. We recommend bilateral symmetrical insertion of LMS or posterior PS and posterior PS on distal vertebrae for increased stability and reduced risk of allograft spacer subsidence.

Augmentation of Anterior Lumbar Interbody Fusion with Anterior Pedicle Screw Fixation: Demonstration of Novel Constructs and Evaluation of Biomechanical Stability in Cadaveric Specimens

Neurosurgery ◽  
2006 ◽  
Vol 58 (3) ◽  
pp. 522-527 ◽  
Author(s):  
Aftab Karim ◽  
Debi Mukherjee ◽  
Murali Ankem ◽  
Jorge Gonzalez-Cruz ◽  
Donald Smith ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Interbody Fusion ◽  
Axial Rotation ◽  
The Novel ◽  
Lumbar Interbody Fusion ◽  
Lateral Bending ◽  
Biomechanical Stability ◽  
Current Standard ◽  
Computed Tomographic ◽  
Flexion Extension

Abstract OBJECTIVE: Anterior lumbar interbody fusion (ALIF) has proven effective for indications including discogenic back pain, nonunion, and instability. Current practice involves posterior pedicle screw augmentation of the ALIF procedure (ALIF-PPS). This approach requires intraoperative repositioning of the patient for percutaneous posterior pedicle screw placement. We have developed a novel technique in which the ALIF procedure is augmented with anterior pedicle screws (APS; ALIF-APS). In this study, we introduce this new technique and compare the biomechanical stability of the novel ALIF-APS with the current standard ALIF-PPS. METHODS: The technique was demonstrated in a cadaveric L4–S1 specimen using neuronavigation and fluoroscopy. Plain radiographs and computed tomographic scans of the construct were obtained. Twelve cadaveric spines (7 men and 5 women) from donors with an average age of 81 years (range, 64–93 yr) were then harvested from L4–S1. Six specimens were dedicated to ALIF-APS constructs, and the remaining six were dedicated to ALIF-PPS constructs. The specimens were then studied at L5–S1 in the following steps: 1) intact form, 2) after anterior discectomy, 3) after implantation of titanium cages (ALIF), and 4) after APS or PPS fixation in conjunction with the ALIF. Measurements were obtained in axial rotation and left and right lateral bending flexion-extension. Data were normalized by calculating the ratio of the stiffness of the instrumented to the intact spine. Statistical analyses were then performed on the data. RESULTS: Radiographs and computed tomographic scans of the construct showed accurate placement of the APS at L5 and S1. The normalized data showed that ALIF-APS and ALIF-PPS had approximately equal stability in axial rotation (1.17 ± 0.43 versus 0.85 ± 0.14), lateral bending (0.93 ± 0.22 versus 0.95 ± 0.16), and flexion- extension (0.77 ± 0.13 versus 0.84 ± 0.2). Paired t test analysis did not show a significant difference between the biomechanical stiffness of ALIF-APS and ALIF-PPS in axial rotation, lateral bending, and flexion-extension. CONCLUSION: We demonstrate a new technique in a cadaveric specimen whereby the ALIF procedure is augmented with APS fixation using neuronavigation and fluoroscopy. Biomechanical evaluation of the constructs suggests that the ALIF-APS has comparable stability with ALIF-PPS. APS augmentation of ALIF has potential advantages over the current standard ALIF-PPS because it can 1) eliminate the patient repositioning step, 2) minimize the total number of incisions and the total operative time, and 3) protect against dislocation of the ALIF interbody graft or cage. Work is in progress to develop a low-profile system for the novel APS constructs described here.

scholarly journals Biomechanics of transvertebral screw fixation in the thoracic spine: an in vitro study

2016 ◽  
Vol 25 (2) ◽  
pp. 187-192 ◽  
Author(s):  
Nestor G. Rodriguez-Martinez ◽  
Amey Savardekar ◽  
Eric W. Nottmeier ◽  
Stephen Pirris ◽  
Phillip M. Reyes ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Thoracic Spine ◽  
Axial Rotation ◽  
Lateral Bending ◽  
Motion Segment ◽  
Thoracic Spinal ◽  
Flexion Extension ◽  
Intact Condition ◽  
The Mean ◽  
The Stability

OBJECTIVE Transvertebral screws provide stability in thoracic spinal fixation surgeries, with their use mainly limited to patients who require a pedicle screw salvage technique. However, the biomechanical impact of transvertebral screws alone, when they are inserted across 2 vertebral bodies, has not been studied. In this study, the authors assessed the stability offered by a transvertebral screw construct for posterior instrumentation and compared its biomechanical performance to that of standard bilateral pedicle screw and rod (PSR) fixation. METHODS Fourteen fresh human cadaveric thoracic spine segments from T-6 to T-11 were divided into 2 groups with similar ages and bone quality. Group 1 received transvertebral screws across 2 levels without rods and subsequently with interconnecting bilateral rods at 3 levels (T8–10). Group 2 received bilateral PSR fixation and were sequentially tested with interconnecting rods at T7–8 and T9–10, at T8–9, and at T8–10. Flexibility tests were performed on intact and instrumented specimens in both groups. Presurgical and postsurgical O-arm 3D images were obtained to verify screw placement. RESULTS The mean range of motion (ROM) per motion segment with transvertebral screws spanning 2 levels compared with the intact condition was 66% of the mean intact ROM during flexion-extension (p = 0.013), 69% during lateral bending (p = 0.015), and 47% during axial rotation (p < 0.001). The mean ROM per motion segment with PSR spanning 2 levels compared with the intact condition was 38% of the mean intact ROM during flexion-extension (p < 0.001), 57% during lateral bending (p = 0.007), and 27% during axial rotation (p < 0.001). Adding bilateral rods to the 3 levels with transvertebral screws decreased the mean ROM per motion segment to 28% of intact ROM during flexion-extension (p < 0.001), 37% during lateral bending (p < 0.001), and 30% during axial rotation (p < 0.001). The mean ROM per motion segment for PSR spanning 3 levels was 21% of intact ROM during flexion-extension (p < 0.001), 33% during lateral bending (p < 0.001), and 22% during axial rotation (p < 0.001). CONCLUSIONS Biomechanically, fixation with a novel technique in the thoracic spine involving transvertebral screws showed restoration of stability to well within the stability provided by PSR fixation.

scholarly journals Atlantoaxial fixation using C1 posterior arch screws: feasibility study, morphometric data, and biomechanical analysis

2019 ◽  
Vol 30 (3) ◽  
pp. 314-322 ◽  
Author(s):  
Gilbert Cadena ◽  
Huy T. Duong ◽  
Jonathan J. Liu ◽  
Kee D. Kim
Keyword(s):  
Biomechanical Testing ◽  
Axial Rotation ◽  
Biomechanical Analysis ◽  
Posterior Arch ◽  
Lateral Mass ◽  
Morphometric Data ◽  
Lateral Bending ◽  
Freehand Technique ◽  
Flexion Extension ◽  
Low Incidence

OBJECTIVEC1–2 is a highly mobile complex that presents unique surgical challenges to achieving biomechanical rigidity and fusion. Posterior wiring methods have been largely replaced with segmental constructs using the C1 lateral mass, C1 pedicle, C2 pars, and C2 pedicle. Modifications to reduce surgical morbidity led to the development of C2 laminar screws. The C1 posterior arch has been utilized mostly as a salvage technique, but recent data indicate that this method provides significant rigidity in flexion-extension and axial rotation. The authors performed biomechanical testing of a C1 posterior arch screw (PAS)/C2 pars screw construct, collected morphometric data from a population of 150 CT scans, and performed a feasibility study of a freehand C1 PAS technique in 45 cadaveric specimens.METHODSCervical spine CT scans from 150 patients were analyzed to determine the average C1 posterior tubercle thickness and size of C1 posterior arches. Eight cadavers were used to compare biomechanical stability of intact specimens, C1 lateral mass/C2 pars screw, and C1 PAS/C2 pars screw constructs. Paired comparisons were made using repeated-measures ANOVA and Holm-Sidak tests. Forty-five cadaveric specimens were used to demonstrate the feasibility and safety of the C1 PAS freehand technique.RESULTSMorphometric data showed the average craniocaudal thickness of the C1 posterior tubercle was 12.3 ± 1.94 mm. Eight percent (12/150) of cases showed thin posterior tubercles or midline defects. Average posterior arch thickness was 6.1 ± 1.1 mm and right and left average posterior arch length was 28.7 mm ± 2.53 mm and 28.9 ± 2.29 mm, respectively. Biomechanical testing demonstrated C1 lateral mass/C2 pars and C1 PAS/C2 pars constructs significantly reduced motion in flexion-extension and axial rotation compared with intact specimens (p < 0.05). The C1 lateral mass/C2 pars screw construct provided significant rigidity in lateral bending (p < 0.05). There was no statistically significant difference between the two constructs in flexion-extension, lateral bending, or axial rotation. Of the C1 posterior arches, 91.3% were successfully cannulated using a freehand technique with a low incidence of cortical breach (4.4%).CONCLUSIONSThis biomechanical analysis indicates equivalent stability of the C1 PAS/C2 pars screw construct compared with a traditional C1 lateral mass/C2 pars screw construct. Both provide significant rigidity in flexion-extension and axial rotation. Feasibility testing in 45 cadaveric specimens indicates a high degree of accuracy with low incidence of cortical breach. These findings are supported by a separate radiographic morphometric analysis.

The biomechanical contribution of varying posterior constructs following anterior thoracolumbar corpectomy and reconstruction

2010 ◽  
Vol 13 (2) ◽  
pp. 234-239 ◽  
Author(s):  
Frank S. Bishop ◽  
Mical M. Samuelson ◽  
Michael A. Finn ◽  
Kent N. Bachus ◽  
Darrel S. Brodke ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Screw Fixation ◽  
Posterior Instrumentation ◽  
Axial Rotation ◽  
Pedicle Screw Fixation ◽  
Bending Stiffness ◽  
Lateral Bending ◽  
Biomechanical Stability ◽  
Flexion Extension ◽  
Anterior Plating

Object Thoracolumbar corpectomy is a procedure commonly required for the treatment of various pathologies involving the vertebral body. Although the biomechanical stability of anterior reconstruction with plating has been studied, the biomechanical contribution of posterior instrumentation to anterior constructs remains unknown. The purpose of this study was to evaluate biomechanical stability after anterior thoracolumbar corpectomy and reconstruction with varying posterior constructs by measuring bending stiffness for the axes of flexion/extension, lateral bending, and axial rotation. Methods Seven fresh human cadaveric thoracolumbar spine specimens were tested intact and after L-1 corpectomy and strut grafting with 4 different fixation techniques: anterior plating with bilateral, ipsilateral, contralateral, or no posterior pedicle screw fixation. Bending stiffness was measured under pure moments of ± 5 Nm in flexion/extension, lateral bending, and axial rotation, while maintaining an axial preload of 100 N with a follower load. Results for each configuration were normalized to the intact condition and were compared using ANOVA. Results Spinal constructs with anterior-posterior spinal reconstruction and bilateral posterior pedicle screws were significantly stiffer in flexion/extension than intact spines or spines with anterior plating alone. Anterior plating without pedicle screw fixation was no different from the intact spine in flexion/extension and lateral bending. All constructs had reduced stiffness in axial rotation compared with intact spines. Conclusions The addition of bilateral posterior instrumentation provided significantly greater stability at the thoracolumbar junction after total corpectomy than anterior plating and should be considered in cases in which anterior column reconstruction alone may be insufficient. In cases precluding bilateral posterior fixation, unilateral posterior instrumentation may provide some additional stability.

scholarly journals Biomechanical evaluation of lumbar pedicle screws in spondylolytic vertebrae: comparison of fixation strength between the traditional trajectory and a cortical bone trajectory

2016 ◽  
Vol 24 (6) ◽  
pp. 910-915 ◽  
Author(s):  
Keitaro Matsukawa ◽  
Yoshiyuki Yato ◽  
Hideaki Imabayashi ◽  
Naobumi Hosogane ◽  
Takashi Asazuma ◽  
...  
Keyword(s):  
Cortical Bone ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Fixation Strength ◽  
Isthmic Spondylolisthesis ◽  
Pullout Strength ◽  
Lateral Bending ◽  
Cortical Bone Trajectory ◽  
Significant Difference ◽  
Flexion Extension

OBJECTIVE In the management of isthmic spondylolisthesis, the pedicle screw system is widely accepted surgical strategy; however, there are few reports on the biomechanical behavior of pedicle screws in spondylolytic vertebrae. The purpose of the present study was to compare fixation strength between pedicle screws inserted through the traditional trajectory (TT) and those inserted through a cortical bone trajectory (CBT) in spondylolytic vertebrae by computational simulation. METHODS Finite element models of spondylolytic and normal vertebrae were created from CT scans of 17 patients with adult isthmic spondylolisthesis (mean age 54.6 years, 10 men and 7 women). Each vertebral model was implanted with pedicle screws using TT and CBT techniques and compared between two groups. First, fixation strength of a single screw was evaluated by measuring axial pullout strength. Next, vertebral fixation strength of a paired-screw construct was examined by applying forces simulating flexion, extension, lateral bending, and axial rotation to vertebrae. RESULTS Fixation strengths of TT screws showed a nonsignificant difference between the spondylolytic and the normal vertebrae (p = 0.31–0.81). Fixation strength of CBT screws in the spondylolytic vertebrae demonstrated a statistically significant decrease in pullout strength (21.4%, p < 0.01), flexion (44.1%, p < 0.01), extension (40.9%, p < 0.01), lateral bending (38.3%, p < 0.01), and axial rotation (28.1%, p < 0.05) compared with those in the normal vertebrae. In the spondylolytic vertebrae, no statistically significant difference was observed for pullout strength between TT and CBT (p = 0.90); however, the CBT construct showed lower vertebral fixation strength in flexion (39.0%, p < 0.01), extension (35.6%, p < 0.01), lateral bending (50.7%, p < 0.01), and axial rotation (59.3%, p < 0.01) compared with the TT construct. CONCLUSIONS CBT screws are less optimal for stabilizing the spondylolytic vertebra due to their lower fixation strength compared with TT screws.

scholarly journals Biomechanical evaluation of lateral lumbar interbody fusion with secondary augmentation

2016 ◽  
Vol 25 (6) ◽  
pp. 720-726 ◽  
Author(s):  
Marco T. Reis ◽  
Phillip M. Reyes ◽  
Idris Altun ◽  
Anna G. U. S. Newcomb ◽  
Vaneet Singh ◽  
...  
Keyword(s):  
Interbody Fusion ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Lumbar Interbody Fusion ◽  
Lateral Bending ◽  
Lateral Lumbar Interbody Fusion ◽  
Significant Difference ◽  
Flexion Extension ◽  
Supplemental Fixation ◽  
The Stability

OBJECTIVE Lateral lumbar interbody fusion (LLIF) has emerged as a popular method for lumbar fusion. In this study the authors aimed to quantify the biomechanical stability of an interbody implant inserted using the LLIF approach with and without various supplemental fixation methods, including an interspinous plate (IP). METHODS Seven human cadaveric L2–5 specimens were tested intact and in 6 instrumented conditions. The interbody implant was intended to be used with supplemental fixation. In this study, however, the interbody was also tested without supplemental fixation for a relative comparison of these conditions. The instrumented conditions were as follows: 1) interbody implant without supplemental fixation (LLIF construct); and interbody implant with supplemental fixation performed using 2) unilateral pedicle screws (UPS) and rod (LLIF + UPS construct); 3) bilateral pedicle screws (BPS) and rods (LLIF + BPS construct); 4) lateral screws and lateral plate (LP) (LLIF + LP construct); 5) interbody LP and IP (LLIF + LP + IP construct); and 6) IP (LLIF + IP construct). Nondestructive, nonconstraining torque (7.5 Nm maximum) induced flexion, extension, lateral bending, and axial rotation, whereas 3D specimen range of motion (ROM) was determined optoelectronically. RESULTS The LLIF construct reduced ROM by 67% in flexion, 52% in extension, 51% in lateral bending, and 44% in axial rotation relative to intact specimens (p < 0.001). Adding BPS to the LLIF construct caused ROM to decrease by 91% in flexion, 82% in extension and lateral bending, and 74% in axial rotation compared with intact specimens (p < 0.001), providing the greatest stability among the constructs. Adding UPS to the LLIF construct imparted approximately one-half the stability provided by LLIF + BPS constructs, demonstrating significantly smaller ROM than the LLIF construct in all directions (flexion, p = 0.037; extension, p < 0.001; lateral bending, p = 0.012) except axial rotation (p = 0.07). Compared with the LLIF construct, the LLIF + LP had a significant reduction in lateral bending (p = 0.012), a moderate reduction in axial rotation (p = 0.18), and almost no benefit to stability in flexion-extension (p = 0.86). The LLIF + LP + IP construct provided stability comparable to that of the LLIF + BPS. The LLIF + IP construct provided a significant decrease in ROM compared with that of the LLIF construct alone in flexion and extension (p = 0.002), but not in lateral bending (p = 0.80) and axial rotation (p = 0.24). No significant difference was seen in flexion, extension, or axial rotation between LLIF + BPS and LLIF + IP constructs. CONCLUSIONS The LLIF construct that was tested significantly decreased ROM in all directions of loading, which indicated a measure of inherent stability. The LP significantly improved the stability of the LLIF construct in lateral bending only. Adding an IP device to the LLIF construct significantly improves stability in sagittal plane rotation. The LLIF + LP + IP construct demonstrated stability comparable to that of the gold standard 360° fixation (LLIF + BPS).

Biomechanical comparison of occipitoatlantal screw fixation techniques

2008 ◽  
Vol 8 (2) ◽  
pp. 143-152 ◽  
Author(s):  
Nicholas C. Bambakidis ◽  
Iman Feiz-Erfan ◽  
Eric M. Horn ◽  
L. Fernando Gonzalez ◽  
Seungwon Baek ◽  
...  
Keyword(s):  
Screw Fixation ◽  
Axial Rotation ◽  
Segmental Motion ◽  
Lateral Mass ◽  
Lateral Bending ◽  
Flexion Extension ◽  
Improved Stability ◽  
Fixation Techniques ◽  
Structural Graft ◽  
Lateral Mass Screws

Object The stability provided by 3 occipitoatlantal fixation techniques (occiput [Oc]–C1 transarticular screws, occipital keel screws rigidly interconnected with C-1 lateral mass screws, and suboccipital/sublaminar wired contoured rod) were compared. Methods Seven human cadaveric specimens received transarticular screws and 7 received occipital keel–C1 lateral mass screws. All specimens later underwent contoured rod fixation. All conditions were studied with and without placement of a structural graft wired between the skull base and C-1 lamina. Specimens were loaded quasistatically using pure moments to induce flexion, extension, lateral bending, and axial rotation while recording segmental motion optoelectronically. Flexibility was measured immediately postoperatively and after 10,000 cycles of fatigue. Results Application of Oc–C1 transarticular screws, with a wired graft, reduced the mean range of motion (ROM) to 3% of normal. Occipital keel–C1 lateral mass screws (also with graft) offered less stability than transarticular screws during extension and lateral bending (p < 0.02), reducing ROM to 17% of normal. The wired contoured rod reduced motion to 31% of normal, providing significantly less stability than either screw fixation technique. Fatigue increased motion in constructs fitted with transarticular screws, keel screws/lateral mass screw constructs, and contoured wired rods, by means of 19, 5, and 26%, respectively. In all constructs, adding a structural graft significantly improved stability, but the extent depended on the loading direction. Conclusions Assuming the presence of mild C1–2 instability, Oc–C1 transarticular screws and occipital keel–C1 lateral mass screws are approximately equivalent in performance for occipitoatlantal stabilization in promoting fusion. A posteriorly wired contoured rod is less likely to provide a good fusion environment because of less stabilizing potential and a greater likelihood of loosening with fatigue.

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