Biomechanical Evaluation of Short-Segment Posterior Instrumentation With and Without Crosslinks in a Human Cadaveric Unstable Thoracolumbar Burst Fracture Model

Wahba, George; Bhatia, Nitin; Bui, Christopher; Lee, Kenneth H.; Lee, Thay Q.

doi:10.1097/brs.0b013e3181bda4e6

Cited by 53 publications

(49 citation statements)

References 28 publications

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“…The addition of crosslinks is one strategy, and previous studies have shown increased stiffness in lateral bending and axial rotation upon such an addition. 2,17,26 In addition, construct stiffness is also dependent on the grade of facetectomy, 1,29 and the type, size, and orientation of the intervertebral cage. 7,14,25 Tsitsopoulos et al performed a biomechanical analysis on a lumbar interbody fusion technique using cadaveric spines, and concluded that the greater stability of the TLIF construct was due to more anterior placement of the cage and preservation of the contralateral facet joint.…”

Section: Discussionmentioning

confidence: 99%

Biomechanical evaluation of the fixation strength of lumbar pedicle screws using cortical bone trajectory: a finite element study

Matsukawa

Yato

Imabayashi

et al. 2015

SPI

105

107

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OBJECT Cortical bone trajectory (CBT) maximizes thread contact with the cortical bone surface and provides increased fixation strength. Even though the superior stability of axial screw fixation has been demonstrated, little is known about the biomechanical stiffness against multidirectional loading or its characteristics within a unit construct. The purpose of the present study was to quantitatively evaluate the anchorage performance of CBT by the finite element (FE) method. METHODS Thirty FE models of L-4 vertebrae from human spines (mean age [± SD] 60.9 ± 18.7 years, 14 men and 16 women) were computationally created and pedicle screws were placed using the traditional trajectory (TT) and CBT. The TT screw was 6.5 mm in diameter and 40 mm in length, and the CBT screw was 5.5 mm in diameter and 35 mm in length. To make a valid comparison, the same shape of screw was inserted into the same pedicle in each subject. First, the fixation strength of a single pedicle screw was compared by axial pullout and multidirectional loading tests. Next, vertebral fixation strength within a construct was examined by simulating the motions of flexion, extension, lateral bending, and axial rotation. RESULTS CBT demonstrated a 26.4% greater mean pullout strength (POS; p = 0.003) than TT, and also showed a mean 27.8% stronger stiffness (p < 0.05) during cephalocaudal loading and 140.2% stronger stiffness (p < 0.001) during mediolateral loading. The CBT construct had superior resistance to flexion and extension loading and inferior resistance to lateral bending and axial rotation. The vertebral fixation strength of the construct was significantly correlated with bone mineral density of the femoral neck and the POS of a single screw. CONCLUSIONS CBT demonstrated superior fixation strength for each individual screw and sufficient stiffness in flexion and extension within a construct. The TT construct was superior to the CBT construct during lateral bending and axial rotation.

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Section: Discussionmentioning

confidence: 99%

Biomechanical evaluation of the fixation strength of lumbar pedicle screws using cortical bone trajectory: a finite element study

Matsukawa

Yato

Imabayashi

et al. 2015

SPI

105

107

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“…3,4,8,9,13,14,16, 22 An et al conducted a biomechanical study on L-2 burst fracture and found no significant difference in construct stiffness between short constructs and long constructs (2 above and 2 below). 3 Baaj et al in their study compared the biomechanical characteristics of short constructs (1 above and 1 below, with additional screws placed at fracture level) to long extended constructs (2 above and 2 below with index-level screws) for an L-1 burst fracture model.…”

Section: Discussionmentioning

confidence: 99%

“…4 Wahba et al in their biomechanical study on T-12 burst fracture showed that short-segment posterior instrumentation with cross-links significantly improved construct stiffness. 22 Mahar et al in their study compared short segmental fixation (additional short screws placed at fracture level) with traditional nonsegmental fixation for an L-2 burst fracture cadaveric model. These investigators found that stability significantly increased with segmental fixation.…”

Section: Discussionmentioning

confidence: 99%

Biomechanical evaluation of a simulated T-9 burst fracture of the thoracic spine with an intact rib cage

Perry

Mageswaran

Colbrunn

et al. 2014

SPI

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Object Classic biomechanical models have used thoracic spines disarticulated from the rib cage, but the biomechanical influence of the rib cage on fracture biomechanics has not been investigated. The well-accepted construct for stabilizing midthoracic fractures is posterior instrumentation 3 levels above and 2 levels below the injury. Short-segment fixation failure in thoracolumbar burst fractures has led to kyphosis and implant failure when anterior column support is lacking. Whether shorter constructs are viable in the midthoracic spine is a point of controversy. The objective of this study was the biomechanical evaluation of a burst fracture at T-9 with an intact rib cage using different fixation constructs for stabilizing the spine. Methods A total of 8 human cadaveric spines (C7–L1) with intact rib cages were used in this study. The range of motion (ROM) between T-8 and T-10 was the outcome measure. A robotic spine testing system was programmed to apply pure moment loads (± 5 Nm) in lateral bending, flexion-extension, and axial rotation to whole thoracic specimens. Intersegmental rotations were measured using an optoelectronic system. Flexibility tests were conducted on intact specimens, then sequentially after surgically induced fracture at T-9, and after each of 4 fixation construct patterns. The 4 construct patterns were sequentially tested in a nondestructive protocol, as follows: 1) 3 above/2 below (3A/2B); 2) 1 above/1 below (1A/1B); 3) 1 above/1 below with vertebral body augmentation (1A/1B w/VA); and 4) vertebral body augmentation with no posterior instrumentation (VA). A repeated-measures ANOVA was used to compare the segmental motion between T-8 and T-10 vertebrae. Results Mean ROM increased by 86%, 151%, and 31% after fracture in lateral bending, flexion-extension, and axial rotation, respectively. In lateral bending, there was significant reduction compared with intact controls for all 3 instrumented constructs: 3A/2B (−92%, p = 0.0004), 1A/1B (−63%, p = 0.0132), and 1A/1B w/VA (−66%, p = 0.0150). In flexion-extension, only the 3A/2B pattern showed a significant reduction (−90%, p = 0.011). In axial rotation, motion was significantly reduced for the 3 instrumented constructs: 3A/2B (−66%, p = 0.0001), 1A/1B (−53%, p = 0.0001), and 1A/1B w/VA (−51%, p = 0.0002). Between the 4 construct patterns, the 3 instrumented constructs (3A/2B, 1A/1B, and 1A/1B w/VA) showed comparable stability in all 3 motion planes. Conclusions This study showed no significant difference in the stability of the 3 instrumented constructs tested when the rib cage is intact. Fractures that might appear more grossly unstable when tested in the disarticulated spine may be bolstered by the ribs. This may affect the extent of segmental spinal instrumentation needed to restore stability in some spine injuries. While these initial findings suggest that shorter constructs may adequately stabilize the spine in this fracture model, further study is needed before these results can be extrapolated to clinical application.

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“…To improve the vertebral stability against lateral bending and axial rotation, the following two points are advocated: 1) to enhance each screw's anchoring ability within a construct as much as possible by selecting the optimal screw trajectory and screw size 18,28) , and 2) to take countermeasures against torsional motion for the screw-rod construct by preservation of the facet joint 30) , large interbody grafting to reconstruct anterior column support 31) , and the addition of a crosslink connector 32) .…”

Section: Fixation Strength Of Cbt Constructmentioning

confidence: 99%

Lumbar pedicle screw fixation with cortical bone trajectory: A review from anatomical and biomechanical standpoints

Matsukawa

Yato

2017

Spine Surg Relat Res

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Abstract:Over the past few decades, many attempts to enhance the integrity of the bone-screw interface have been made to prevent pedicle screw failure and to achieve a better clinical outcome when treating a variety of spinal disorders. Cortical bone trajectory (CBT) has been developed as an alternative to the traditional lumbar pedicle screw trajectory. Contrary to the traditional trajectory, which follows the anatomical axis of the pedicle from a lateral starting point, CBT starts at the lateral part of the pars interarticularis and follows a mediolateral and caudocranial screw path through the pedicle. By markedly altering the screw path, CBT has the advantage of achieving a higher level of thread contact with the cortical bone from the dorsal entry point to the vertebral body. Biomechanical studies demonstrated the superior anchoring ability of CBT over the traditional trajectory, even with a shorter and smaller CBT screw. Furthermore, screw insertion from a more medial and caudal starting point requires less exposure and minimizes the procedure-related morbidity, such as reducing damage to the paraspinal muscles, avoiding iatrogenic injury to the cranial facet joint, and maintaining neurovascular supply to the fused segment. Thus, the features of CBT, which enhance screw fixation with limited surgical exposure, have attracted the interest of surgeons as a new minimally invasive method for spinal fusion.The purpose of this study was: 1) to identify the features of the CBT technique by reviewing previous anatomical and biomechanical literature, and 2) to describe its clinical application with a focus on the indications, limitations, surgical technique, and clinical evidence.

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Biomechanical Evaluation of Short-Segment Posterior Instrumentation With and Without Crosslinks in a Human Cadaveric Unstable Thoracolumbar Burst Fracture Model

Cited by 53 publications

References 28 publications

Biomechanical evaluation of the fixation strength of lumbar pedicle screws using cortical bone trajectory: a finite element study

Biomechanical evaluation of the fixation strength of lumbar pedicle screws using cortical bone trajectory: a finite element study

Biomechanical evaluation of a simulated T-9 burst fracture of the thoracic spine with an intact rib cage

Lumbar pedicle screw fixation with cortical bone trajectory: A review from anatomical and biomechanical standpoints

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