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).

Biomechanics of lateral lumbar interbody fusion constructs with lateral and posterior plate fixation

2014 ◽  
Vol 20 (3) ◽  
pp. 291-297 ◽  
Author(s):  
Guy R. Fogel ◽  
Rachit D. Parikh ◽  
Stephen I. Ryu ◽  
Alexander W. L. Turner
Keyword(s):  
Interbody Fusion ◽  
Plate Fixation ◽  
Spinous Process ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Interbody Cage ◽  
Lateral Bending ◽  
Lateral Plate ◽  
Flexion Extension ◽  
Supplemental Fixation

Object Lumbar interbody fusion is indicated in the treatment of degenerative conditions. Laterally inserted interbody cages significantly decrease range of motion (ROM) compared with other cages. Supplemental fixation options such as lateral plates or spinous process plates have been shown to provide stability and to reduce morbidity. The authors of the current study investigate the in vitro stability of the interbody cage with a combination of lateral and spinous process plate fixation and compare this method to the established bilateral pedicle screw fixation technique. Methods Ten L1–5 specimens were evaluated using multidirectional nondestructive moments (± 7.5 N·m), with a custom 6 degrees-of-freedom spine simulator. Intervertebral motions (ROM) were measured optoelectronically. Each spine was evaluated under the following conditions at the L3–4 level: intact; interbody cage alone (stand-alone); cage supplemented with lateral plate; cage supplemented with ipsilateral pedicle screws; cage supplemented with bilateral pedicle screws; cage supplemented with spinous process plate; and cage supplemented with a combination of lateral plate and spinous process plate. Intervertebral rotations were calculated, and ROM data were normalized to the intact ROM data. Results The stand-alone laterally inserted interbody cage significantly reduced ROM with respect to the intact state in flexion-extension (31.6% intact ROM, p < 0.001), lateral bending (32.5%, p < 0.001), and axial rotation (69.4%, p = 0.002). Compared with the stand-alone condition, addition of a lateral plate to the interbody cage did not significantly alter the ROM in flexion-extension (p = 0.904); however, it was significantly decreased in lateral bending and axial rotation (p < 0.001). The cage supplemented with a lateral plate was not statistically different from bilateral pedicle screws in lateral bending (p = 0.579). Supplemental fixation using a spinous process plate was not significantly different from bilateral pedicle screws in flexion-extension (p = 0.476). The combination of lateral plate and spinous process plate was not statistically different from the cage supplemented with bilateral pedicle screws in all the loading modes (p ≥ 0.365). Conclusions A combination of lateral and spinous process plate fixation to supplement a laterally inserted interbody cage helps achieve rigidity in all motion planes similar to that achieved with bilateral pedicle screws.

Assessment of L5–S1 anterior lumbar interbody fusion stability in the setting of lengthening posterior instrumentation constructs: a cadaveric biomechanical study

2021 ◽  
pp. 1-9
Keyword(s):  
Interbody Fusion ◽  
Posterior Instrumentation ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Anterior Lumbar Interbody Fusion ◽  
Posterior Fusion ◽  
Lumbar Interbody Fusion ◽  
Lateral Bending ◽  
Fusion Construct ◽  
Flexion Extension

OBJECTIVE Excessive stress and motion at the L5–S1 level can lead to degenerative changes, especially in patients with posterior instrumentation suprajacent to L5. Attention has turned to utilization of L5–S1 anterior lumbar interbody fusion (ALIF) to stabilize the lumbosacral junction. However, questions remain regarding the effectiveness of stand-alone ALIF in the setting of prior posterior instrumented fusions terminating at L5. The purpose of this study was to assess the biomechanical stability of an L5–S1 ALIF with increasing lengths of posterior thoracolumbar constructs. METHODS Seven human cadaveric spines (T9–sacrum) were instrumented with pedicle screws from T10 to L5 and mounted to a 6 degrees-of-freedom robot. Posterior fusion construct lengths (T10–L5, T12–L5, L2–5, and L4–5) were instrumented to each specimen, and torque-fusion level relationships were determined for each construct in flexion-extension, axial rotation, and lateral bending. A stand-alone L5–S1 ALIF was then instrumented, and L5–S1 motion was measured as increasing pure moments (2 to 12 Nm) were applied. Motion reduction was calculated by comparing L5–S1 motion across the ALIF and non-ALIF states. RESULTS The average motion at L5–S1 in axial rotation, flexion-extension, and lateral bending was assessed for each fusion construct with and without ALIF. After adding ALIF to a posterior fusion, L5–S1 motion was significantly reduced relative to the non-ALIF state in all but one fused surgical condition (p < 0.05). Longer fusions with ALIF produced larger L5–S1 motions, and in some cases resulted in motions higher than native state motion. CONCLUSIONS Posterior fusion constructs up to L4–5 could be appropriately stabilized by a stand-alone L5–S1 ALIF when using a nominal threshold of 80% reduction in native motion as a potential positive indicator of fusion. The results of this study allow conclusions to be drawn from a biomechanical standpoint; however, the clinical implications of these data are not well defined. These findings, when taken in appropriate clinical context, can be used to better guide clinicians seeking to treat L5–S1 pathology in patients with prior posterior thoracolumbar constructs.

scholarly journals Biomechanical Analysis of Cortical Versus Pedicle Screw Fixation Stability in TLIF, PLIF, and XLIF Applications

2018 ◽  
Vol 9 (2) ◽  
pp. 162-168 ◽  
Author(s):  
Edward K. Nomoto ◽  
Guy R. Fogel ◽  
Alexandre Rasouli ◽  
Justin V. Bundy ◽  
Alexander W. Turner
Keyword(s):  
Pedicle Screw ◽  
Interbody Fusion ◽  
Screw Fixation ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Biomechanical Analysis ◽  
Lumbar Interbody Fusion ◽  
Lateral Bending ◽  
Cortical Screw ◽  
Flexion Extension

Study Design: Cadaveric biomechanical study. Objectives: Medial-to-lateral trajectory cortical screws are of clinical interest due to the ability to place them through a less disruptive, medialized exposure compared with conventional pedicle screws. In this study, cortical and pedicle screw trajectory stability was investigated in single-level transforaminal lumbar interbody fusion (TLIF), posterior lumbar interbody fusion (PLIF), and extreme lateral interbody fusion (XLIF) constructs. Methods: Eight lumbar spinal units were used for each interbody/screw trajectory combination. The following constructs were tested: TLIF + unilateral facetectomy (UF) + bilateral pedicle screws (BPS), TLIF + UF + bilateral cortical screws (BCS), PLIF + medial facetectomy (MF) + BPS, PLIF + bilateral facetectomy (BF) + BPS, PLIF + MF + BCS, PLIF + BF + BCS, XLIF + BPS, XLIF + BCS, and XLIF + bilateral laminotomy + BCS. Range of motion (ROM) in flexion-extension, lateral bending, and axial rotation was assessed using pure moments. Results: All instrumented constructs were significantly more rigid than intact ( P < .05) in all test directions except TLIF + UF + BCS, PLIF + MF + BCS, and PLIF + BF + BCS in axial rotation. In general, XLIF and PLIF + MF constructs were more rigid (lowest ROM) than TLIF + UF and PLIF + BF constructs. In the presence of substantial iatrogenic destabilization (TLIF + UF and PLIF + BF), cortical screw constructs tended to be less rigid (higher ROM) than the same pedicle screw constructs in lateral bending and axial rotation; however, no statistically significant differences were found when comparing pedicle and cortical fixation for the same interbody procedures. Conclusions: Both cortical and pedicle trajectory screw fixation provided stability to the 1-level interbody constructs. Constructs with the least iatrogenic destabilization were most rigid. The more destabilized constructs showed less lateral bending and axial rotation rigidity with cortical screws compared with pedicle screws. Further investigation is warranted to understand the clinical implications of differences between constructs.

Biomechanics of a lumbar interspinous anchor with anterior lumbar interbody fusion

2010 ◽  
Vol 12 (4) ◽  
pp. 372-380 ◽  
Author(s):  
Dean G. Karahalios ◽  
Taro Kaibara ◽  
Randall W. Porter ◽  
Udaya K. Kakarla ◽  
Phillip M. Reyes ◽  
...  
Keyword(s):  
Interbody Fusion ◽  
Plate Fixation ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Anterior Lumbar Interbody Fusion ◽  
Lumbar Interbody Fusion ◽  
Lateral Bending ◽  
Anterior Plate ◽  
Foraminal Height ◽  
Flexion And Extension

Object An interspinous anchor (ISA) provides fixation to the lumbar spine to facilitate fusion. The biomechanical stability provided by the Aspen ISA was studied in applications utilizing an anterior lumbar interbody fusion (ALIF) construct. Methods Seven human cadaveric L3–S1 specimens were tested in the following states: 1) intact; 2) after placing an ISA at L4–5; 3) after ALIF with an ISA; 4) after ALIF with an ISA and anterior screw/plate fixation system; 5) after removing the ISA (ALIF with plate only); 6) after removing the plate (ALIF only); and 7) after applying bilateral pedicle screws and rods. Pure moments (7.5 Nm maximum) were applied in flexion and extension, lateral bending, and axial rotation while recording angular motion optoelectronically. Changes in angulation as well as foraminal height were also measured. Results All instrumentation variances except ALIF alone reduced angular range of motion (ROM) significantly from normal in all directions of loading. The ISA was most effective in limiting flexion and extension (25% of normal) and less effective in reducing lateral bending (71% of normal) and axial rotation (71% of normal). Overall, ALIF with an ISA provided stability that was statistically equivalent to ALIF with bilateral pedicle screws and rods. An ISA-augmented ALIF allowed less ROM than plate-augmented ALIF during flexion, extension, and lateral bending. Use of the ISA resulted in flexion at the index level, with a resultant increase in foraminal height. Compensatory extension at the adjacent levels prevented any significant change in overall sagittal balance. Conclusions When used with ALIF at L4–5, the ISA provides immediate rigid immobilization of the lumbar spine, allowing equivalent ROM to that of a pedicle screw/rod system, and smaller ROM than an anterior plate. When used with ALIF, the ISA may offer an alternative to anterior plate fixation or bilateral pedicle screw/rod constructs.

Stabilizing effect of posterior lumbar interbody fusion cages before and after cyclic loading

2000 ◽  
Vol 92 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Annette Kettler ◽  
Hans-Joachim Wilke ◽  
Rupert Dietl ◽  
Matthias Krammer ◽  
Christianto Lumenta ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Interbody Fusion ◽  
Posterior Lumbar Interbody Fusion ◽  
Axial Rotation ◽  
Lumbar Interbody Fusion ◽  
Lateral Bending ◽  
Content Type ◽  
Flexion Extension ◽  
Stabilizing Effect ◽  
Fine Print

Object. The function of interbody fusion cages is to stabilize spinal segments primarily by distracting them as well as by allowing bone ingrowth and fusion. An important condition for efficient formation of bone tissue is achieving adequate spinal stability. However, the initial stability may be reduced due to repeated movements of the spine during everyday activity. Therefore, in addition to immediate stability, stability after cyclic loading is of remarkable relevance; however, this has not yet been investigated. The object of this study was to investigate the immediate stabilizing effect of three different posterior lumbar interbody fusion cages and to clarify the effect of cyclic loading on the stabilization. Methods. Before and directly after implantation of a Zientek, Stryker, or Ray posterior lumbar interbody fusion cage, 24 lumbar spine segment specimens were each evaluated in a spine tester. Pure lateral bending, flexion—extension, and axial rotation moments (± 7.5 Nm) were applied continuously. The motion in each specimen was measured simultaneously. The specimens were then loaded cyclically (40,000 cycles, 5 Hz) with an axial compression force ranging from 200 to 1000 N. Finally, they were tested once again in the spine tester. Conclusions. In general, a decrease of movement in all loading directions was noted after insertion of the Zientek and Ray cages and an increase of movement after implantation of a Stryker cage. In all three cage groups greater stability was demonstrated in lateral bending and flexion than in extension and axial rotation. Reduced stability during cyclic loading was observed in all three cage groups; however, loss of stability was most pronounced when the Ray cage was used.

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 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 analysis of an expandable lateral cage and a static transforaminal lumbar interbody fusion cage with posterior instrumentation in an in vitro spondylolisthesis model

2016 ◽  
Vol 24 (1) ◽  
pp. 32-38 ◽  
Author(s):  
Matthew Mantell ◽  
Mathew Cyriac ◽  
Colin M. Haines ◽  
Manasa Gudipally ◽  
Joseph R. O’Brien
Keyword(s):  
Interbody Fusion ◽  
Facet Joint ◽  
Posterior Instrumentation ◽  
Degenerative Spondylolisthesis ◽  
Pedicle Screws ◽  
Transforaminal Lumbar Interbody Fusion ◽  
Biomechanical Analysis ◽  
Lumbar Interbody Fusion ◽  
Significant Difference ◽  
Flexion Extension

OBJECT Insufficient biomechanical data exist from comparisons of the stability of expandable lateral cages with that of static transforaminal lumbar interbody fusion (TLIF) cages. The purpose of this biomechanical study was to compare the relative rigidity of L4–5 expandable lateral interbody constructs with or without additive pedicle screw fixation with that of L4–5 static TLIF cages in a novel cadaveric spondylolisthesis model. METHODS Eight human cadaver spines were used in this study. A spondylolisthesis model was created at the L4–5 level by creating 2 injuries. First, in each cadaver, a nucleotomy from 2 channels through the anterior side was created. Second, the cartilage of the facet joint was burred down to create a gap of 4 mm. Light-emitting-diode tracking markers were placed at L-3, L-4, L-5, and S-1. Specimens were tested in the following scenarios: intact model, bilateral pedicle screws, expandable lateral 18-mm-wide cage (alone, with unilateral pedicle screws [UPSs], and with bilateral pedicle screws [BPSs]), expandable lateral 22-mm-wide cage (alone, with UPSs, and with BPSs), and TLIF (alone, with UPSs, and with BPSs). Four of the spines were tested with the expandable lateral cages (18-mm cage followed by the 22-mm cage), and 4 of the spines were tested with the TLIF construct. All these constructs were tested in flexion-extension, axial rotation, and lateral bending. RESULTS The TLIF-alone construct was significantly less stable than the 18- and 22-mm-wide lateral lumbar interbody fusion (LLIF) constructs and the TLIF constructs with either UPSs or BPSs. The LLIF constructs alone were significantly less stable than the TLIF construct with BPSs. However, there was no significant difference between the 18-mm LLIF construct with UPSs and the TLIF construct with BPSs in any of the loading modes. CONCLUSIONS Expandable lateral cages with UPSs provide stability equivalent to that of a TLIF construct with BPSs in a degenerative spondylolisthesis model.

Stabilizing effect of posterior lumbar interbody fusion cages before and after cyclic loading

1999 ◽  
Vol 7 (6) ◽  
pp. E7 ◽  
Author(s):  
Annette Kettler ◽  
Hans-Joachim Wilke ◽  
Rupert Dietl ◽  
Matthias Krammer ◽  
Christianto Lumenta ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Interbody Fusion ◽  
Bone Ingrowth ◽  
Posterior Lumbar Interbody Fusion ◽  
Axial Rotation ◽  
Lumbar Interbody Fusion ◽  
Lateral Bending ◽  
Everyday Activity ◽  
Flexion Extension ◽  
Stabilizing Effect

The function of interbody fusion cages is to stabilize spinal segments primarily by distracting them as well as by allowing bone ingrowth and fusion. An important condition for efficient formation of bone tissue is achieving adequate spinal stability. However, the initial stability may be reduced due to repeated movements of the spine during everyday activity. Therefore, in addition to immediate stability, stability after cyclic loading is of remarkable relevance; however, this has not yet been investigated. The object of this study was to investigate the immediate stabilizing effect of three different posterior lumbar interbody fusion cages and to clarify the effect of cyclic loading on the stabilization. Before and directly after implantation of a Zientek, Stryker, or Ray posterior lumbar interbody fusion cage, 24 lumbar spine segment specimens were each evaluated in a spine tester. Pure lateral bending, flexion-extension, and axial rotation moments (± 7.5 Nm) were applied continuously. The motion in each specimen was measured simultaneously. The specimens were then loaded cyclically (40,000 cycles, 5 Hz) with an axial compression force ranging from 200 to 1000 N. Finally, they were tested once again in the spine tester. In general, a decrease of movement in all loading directions was noted after insertion of the Zientek and Ray cages and an increase of movement after implantation of a Stryker cage. In all three cage groups greater stability was demonstrated in lateral bending and flexion than in extension and axial rotation. Reduced stability during cyclic loading was observed in all three cage groups; however, loss of stability was most pronounced when the Ray cage was used.

Biomechanics of C-7 transfacet screw fixation

2009 ◽  
Vol 11 (3) ◽  
pp. 338-343 ◽  
Author(s):  
Eric M. Horn ◽  
Phillip M. Reyes ◽  
Seungwon Baek ◽  
Mehmet Senoglu ◽  
Nicholas Theodore ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Normal Condition ◽  
Small Diameter ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Lateral Bending ◽  
Screw Insertion ◽  
Loading Mode ◽  
Significant Difference ◽  
Flexion Extension

Object The small diameter of the pedicle can make C-7 pedicle screw insertion dangerous. Although transfacet screws have been studied biomechanically when used in pinning joints, they have not been well studied when used as part of a C7–T1 screw/rod construct. The authors therefore compared C7–T1 fixation using a C-7 transfacet screw/T-1 pedicle screw construct with a construct composed of pedicle screws at both levels. Methods Each rigid posterior screw/rod construct was placed in 7 human cadaveric C6–T2 specimens (14 total). Specimens were tested in normal condition, after 2-column instability, and once fixated. Nondestructive, nonconstraining pure moments (maximum 1.5 Nm) were applied to induce flexion, extension, lateral bending, and axial rotation while recording 3D motion optoelectronically. The entire construct was then loaded to failure by dorsal linear force. Results There was no significant difference in angular range of motion between the 2 instrumented groups during any loading mode (p > 0.11, nonpaired t-tests). Both constructs reduced motion to < 2° in any direction and allowed significantly less motion than in the normal condition. The C-7 facet screw/T-1 pedicle screw construct allowed a small but significantly greater lax zone than the pedicle screw/rod construct during lateral bending, and it failed under significantly less load than the pedicle screw/rod construct (p < 0.001). Conclusions When C-7 transfacet screws are connected to T-1 pedicle screws, they provide equivalent stability of constructs formed by pedicle screws at both levels. Although less resistant to failure, the transfacet screw construct should be a viable alternative in patients with healthy bone.

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