Acute thoracolumbar burst fractures: a new view of loading mechanisms

How does vertical laminar fracture impact the decision-making in thoracolumbar fractures? A systematic scoping review and meta-analysis

OBJECTIVE

Although vertical laminar fracture (VLF) is generally considered a severity marker for thoracolumbar fractures (TLFs), its exact role in decision-making has never been established. This scoping review aims to synthesize the research on VLF's role in the decision-making of TLFs.

METHODS

A systematic review was conducted following PRISMA guidelines. We searched PubMed, Scopus, and Web of Science from inception to  June 11, 2023, for studies examining the association of VLF in thoracolumbar fractures with dural lacerations, neurological deficits, radiographic parameters, or treatment outcomes. Additionally, experimental studies that analyze the biomechanics of burst fractures with VLF were included. The studies extracted key findings, objectives, and patient population. A meta-analysis was performed for the association of VLF with dural laceration and neurological deficit, and ORs were pooled with a 95% confidence interval (CI).

RESULTS

Twenty-eight studies were included in this systematic review, encompassing 2021 patients, and twelve were included in the meta-analysis. According to the main subject of the study, the association of VLF with a dural laceration (n = 14), neurological deficit (n = 4), radiographic parameters (n = 3), thoracolumbar fracture classification (n = 2), and treatment outcome (n = 2). Seven studies with a total of 1010 patients reported a significant association between VLF and neurological deficit (OR = 7.35, 95% CI [3.97, 14.25]; P < 0.001). The pooled OR estimates for VLF predicting dural lacerations were 7.75, 95% CI [2.41, 24.87]; P < 0.001).

CONCLUSION

VLF may have several important diagnostic and therapeutic implications in managing TLFs. VLF may help to distinguish AO type A3 from A4 fractures. VLF may help to predict preoperatively the occurrence of dural laceration, thereby choosing the optimal surgical strategy. Clinical and biomechanical data suggest VLF may be a valuable modifier to guide the decision-making in burst fractures; however, more studies are needed to confirm its prognostic importance regarding treatment outcomes.

A comparison of fracture response in female and male lumbar spine in simulated under body blast component tests

Underbody blasts (UBB) from mines and improvised explosive devices in military combat can cause debilitating spine injuries to vehicle mounted soldiers. Due to the exclusion of females in combat roles in prior US Department of Defense policy, UBB exposure and injury have predominantly affected male soldiers. Recent policy changes have opened many combat roles to women serving in the US Military (Carter, 2015) and have increased the need to understand the injury potential for female Warfighters. The goal of this study was to investigate the fracture response of adult female lumbar spines compared to adult male spines in UBB relevant loading to identify potential differences in either fracture mechanism or force. Results are presented for 15 simulated UBB spine compression tests using three small female (SF), five large female (LF), and seven mid-sized male (MM) post-mortem human subjects (PMHS). These PMHS groups align to 5th- and 75th-percentile female and 50th-percentile males, based on height and weight from the 2012 Anthropometric Survey of U.S. Army Personnel (Gordon et al., 2014). Both small females and large females (similar in size to the males) were included to assess the role of size and/or sex in the response. Tests were conducted at Virginia Tech on a cam-driven linear compression rig, which included a 6-axis load cell and ram accelerometer to evaluate the fracture. Fracture was visualized through high-speed x-ray video. All female and male spines exhibited similar fracture initiation at the end plates and progression through the vertebral body. The resulting severe compression and burst fractures were representative of reported theatre injuries (Freedman et al., 2014). Mean axial fracture forces were -4182 ± 940 N (SF), -6225 ± 1180 N (LF), -5459 ± 1472 N (All Females) and -7993 ± 2445 N (MM). The SF group was found to have statistically significant differences in mean fracture force compared to both LF and MM groups, while no significant difference was found between LF and MM groups, although the mean force at initial fracture was lower for the LF group. The All-Females group Fz mean was significantly different from the MM group. These data suggest that the significant difference in weight between the SF and LF groups, did have an influence on the Fz outcome, when controlling for sex. Conversely, controlling for size in the LF and MM comparison, sex did influence the mean Fz, but was not statistically significant. Groups with combined sex and size differences, however, did show significant differences in mean Fz. Further study is warranted to understand whether sex or size has a larger effect on fracture force. Mean ram displacement (spine compression) values at fracture initiation were -6.0 ± 5.3 mm (SF), -4.4 ± 0.8 mm (LF), -5.0 ± 3.0 mm (All Females), -6.2 ± 4.5 mm (MM). Spine compression did not seem to be largely influenced by either sex or size, and none of the groups was found to have significant differences in mean displacement values.

The association between vertical laminar fracture and recurrent kyphosis after implant removal of Thoracolumbar burst fracture: a retrospective study

BACKGROUND

Surgeons often encounter recurrent kyphosis of Cobb angle following thoracolumbar burst fracture surgery. Some factors affecting postoperative correction loss have been studied in previous studies, but few have examined the relationship between laminar fractures and postoperative loss of correction.

METHODS

The clinical data of 86 patients with thoracolumbar burst fracture who met the inclusion criteria and were admitted to our Department of Spine Surgery between 2013 and 2020 was retrospectively analyzed. To examine the association between laminar fracturs and postoperative correction loss, demographic and radiographic characteristics of the two groups were analyzed.

RESULTS

The presence or absence of laminar fractures was statistically different between the two groups (P < 0.05). Binary logistic regression analysis showed that laminar fractures and preoperative Cobb were statistically significant in the two groups. There were statistically significant differences in the degree of injury of laminar fractures in the coronal plane between the two groups (P < 0.05).

CONCLUSION

This study investigated that the presence or absence of laminar fractures and preoperative Cobb contribute to loss of correction after thoracolumbar burst fracture surgery. There was a statistically significant difference between full-length and partial-length laminar fractures on the loss of postoperative correction of thoracolumbar burst fractures with laminar fractures.

Stress analysis of the thoracolumbar junction in the process of backward fall: An experimental study and finite element analysis

The aim of the present study was to evaluate the biomechanical mechanism of injuries of the thoracolumbar junction by the methods of a backward fall simulation experiment and finite element (FE) analysis (FEA). In the backward fall simulation experiment, one volunteer was selected to obtain the contact force data of the sacrococcygeal region during a fall. Utilizing the fall data, the FEA simulation of the backward fall process was given to the trunk FE model to obtain the stress status of local bone structures of the thoracolumbar junction during the fall process. In the fall simulation test, the sacrococcygeal region of the volunteer landed first; the total impact time was 1.14±0.58 sec, and the impact force was up to 4,056±263 N. The stress of thoracic (T)11 was as high as 42 MPa, that of the posterior margin and the junction of T11 was as high as 70.67 MPa, and that of the inferior articular process and the superior articular process was as high as 128 MPa. The average stress of T12 and the anterior margin of lumbar 1 was 25 MPa, and that of the endplate was as high as 21.7 MPa, which was mostly distributed in the back of the endplate and the surrounding cortex. According to the data obtained from the fall experiment as the loading condition of the FE model, the backward fall process can be simulated to improve the accuracy of FEA results. In the process of backward fall, the front edge of the vertebral body and the root of vertebral arch in the thoracolumbar junction are stress concentration areas, which have a greater risk of injury.

Specimen-specific fracture risk curves of lumbar vertebrae under dynamic axial compression

Underbody blast attacks of military vehicles by improvised explosives have resulted in high incidence of lumbar spine fractures below the thorocolumbar junction in military combatants. Fracture risk curves related to vertical loading at individual lumbar spinal levels can be used to assess the protective ability of new injury mitigation equipment. The objectives of this study were to derive fracture risk curves for the lumbar spine under high rate compression and identify how specimen-specific attributes and lumbar spinal level may influence fracture risk. In this study, we tested a sample of three-vertebra specimens encompassing all spinal levels between T12 to S1 in high-rate axial compression. Each specimen was tested with a non-injurious load, followed by a compressive force sufficient to induce vertebral body fracture. During testing, bone fracture was identified using measurements from acoustic emission sensors and changes in load cell readings. Following testing, the fractures were assessed using computed tomographic (CT) imaging. The CT images showed isolated fractures of trabecular bone, or fractures involving both cortical and trabecular bone. Results from the compressive force measurements in conjunction with a survival analysis demonstrated that the compressive force corresponding to fracture increased inferiorly as a function of lumbar spinal level. The axial rigidity (EA) measured at the mid-plane of the centre vertebra or the volumetric bone mineral density (vBMD) of the vertebral body trabecular bone most greatly influenced fracture risk. By including these covariates in the fracture risk curves, no other variables significantly affected fracture risk, including the lumbar spinal level. The fracture risk curves presented in this study may be used to assess the risk of injury at individual lumbar vertebra when exposed to dynamic axial compression.

In vitro assessment of the role of the nucleus pulposus in the mechanism of vertebral body fracture under dynamic compressive loading using high-speed cineradiography

Traumatic Spinal Cord Injuries (TSCI) have a disastrous effect on the physical and mental health of both the patients and their relatives. Around 15 % of these injuries are caused by burst fractures, a sub-type of compressive fractures of the vertebral body. The transient dynamics of these fracture have been studied through in vitro experiments coupled with numerical simulations, but no direct observation have ever been made of their genesis and evolution and the behaviour of the nucleus pulposus under compressive loading has only been hypothesized. The purpose of this study was to evaluate the interactions between the vertebral body and the nucleus pulposus under dynamic compressive loading using high-speed cineradiography. A radiopaque agent was injected into the nuclei pulposi of 4 young porcine thoraco-lumbar and lumbar cadaveric segments, and a dynamic compressive load was applied to them using a servo-hydraulic bench-test. The compression process was filmed with a custom high-speed fluoroscope. The nucleus pulposus loaded the vertebral endplate up to 14,142 ± 486 N, before fracturing it and diffusing into the vertebral body. Then, internal pressure seemingly built up until an outward projection of the nucleus pulposus, at an antero-posterior velocity up to 2.9 m.s^-1, or until retroprojection of bony fragments into the spinal canal. These results directly corroborate the hypotheses previously made by other studies and stress the unprecedented advantages of using high-speed cineradiography for the study of complex fractures genesis and evolution.Clinical Relevance- Methodology and results from this study would provide an unprecedented insight on the genesis and transient evolution of complex spinal fractures.

Influence of different postures under vertical impact load on thoracolumbar burst fracture

Clinical studies have extensively shown that burst fractures can cause severe and long-term neurological deficits. However, the mechanism of burst fracture is not clear, and the influence of different spinal postures on burst fracture is still unidentified. The study aimed at investigating the influence of different postures under vertical impact load on thoracolumbar burst fracture. A detailed nonlinear finite element model of T12-L2 segment was developed to investigate these problems. In this work, a rigid ball was used to vertically impact the finite element spinal segment, which emulated the process of burst fracture as in experimental condition. During the process, amounting to 9 different postures (normal, flexion, extension, right/left lateral bending of 8°, right/left axial rotation of 4° and 8°) were studied. Totally five failure modes were observed. Six different parameters, including vertebral height, vertebral bulge, interpedicular widening, vertebral kyphotic angle, posterior vertebral body angle, and joint facet contact force, were observed to evaluate the corresponding severity of burst fracture. Burst fracture in extension was the severest, and the loss of vertebral height in flexion was the most. The different postures in these simulations changed the morphology of intervertebral disc and facet joints force, resulting in different types of fracture.

A biomechanical investigation of thoracolumbar burst fracture under vertical impact loads using finite element method

BACKGROUND

A sudden vertical impact load on spine can cause spinal burst fracture, especially in the thoracolumbar junction region. This study aimed at investigating the mechanism of spinal burst fracture under different energy vertical impact loads, producing the failure risk region to understand burst fracture, reducing nervous system damage and guiding clinical treatment.

METHODS

A nonlinear finite element model of T12-L1 motion segment was created to analyze the response of the vertical impact load. A rigid ball was used to impact the segment vertically to simulate the vertical impact load in practice. There were three different mass balls to represent the different loads: low energy, intermediate energy and high energy (respectively 13 J, 30 J and 56 J). The results of impact force, vertical displacement, stress, intradiscal pressure and contact force were obtained during the process.

FINDINGS

At low energy condition, the rigid ball rebounded rapidly. At intermediate energy condition, fractures were initiated in vertebral foramen and left rear regions on the superior cortical bone near the superior endplate of L1. At high energy condition, burst fracture occurred and a part of L1 was isolated from the model.

INTERPRETATION

The fracture occurred on the L1 segment only at the intermediate energy and high energy. The strength of vertebral body under low and intermediate energy was enough to support the impact. The burst fracture pattern at high energy was also observed in clinical practice. The findings may explain the mechanism of burst fracture.

Risk Factor of Failed Reduction of Posterior Ligamentatoxis Reduction Instrumentation in Managing Thoracolumbar Burst Fractures: A Retrospective Study

OBJECTIVE

To determine whether radiographic findings associated with thoracolumbar burst fractures could be predictors of failure of short-segment posterior instrumentation with insertion screw at the fracture level (SSPI-f).

METHODS

Seventy-five patients with thoracolumbar burst fracture surgically treated by SSPI-f were enrolled in the study and divided into 2 groups: a reduction group (n = 46) and a failed-reduction group (n = 29). Radiographic data including local kyphosis, Cobb angle, anterior vertebral height, posterior vertebral height (PVH), anterior/posterior vertebral height ratio, interpedicle distance (IPD), bony compress area, bony fracture area, and compress-fracture area of the fractured vertebra and clinical data including age and neurologic function were also analyzed. t test, Pearson χ² test, and binary logistic regression were performed to compare the values.

RESULTS

The PVH in the failed-reduction group was smaller than that of the reduction group (83.5% ± 7.2% and 89.1% ± 5.4%, respectively) (P = 0.001). The IPD differed between the reduction and failed-reduction group (18.0% ± 4.1% and 25.8% ± 7.1%, respectively) (P < 0.001). There was a statistical difference between the 2 groups in delayed time before surgery (P = 0.008). There was a significant difference of bony fracture area and compress-fracture area of the fractured vertebra between the failed-reduction and reduction group (both P < 0.001). Binary logistic regression showed that IPD was a risk factor of reduction failure of SSPI-f (P = 0.001).

CONCLUSIONS

These results showed that increased IPD was a risk factor of failed-reduction of SSPI-f in managing thoracolumbar burst fractures, particularly for patients with neurologic deficit, whereas local kyphosis, Cobb angle, anterior vertebral height, PVH, anterior/posterior vertebral height ratio, bony compress area, bony fracture area, and compress-fracture area of the fractured vertebra were not.

Biomechanical tolerance of whole lumbar spines in straightened posture subjected to axial acceleration

Quantification of biomechanical tolerance is necessary for injury prediction and protection of vehicular occupants. This study experimentally quantified lumbar spine axial tolerance during accelerative environments simulating a variety of military and civilian scenarios. Intact human lumbar spines (T12-L5) were dynamically loaded using a custom-built drop tower. Twenty-three specimens were tested at sub-failure and failure levels consisting of peak axial forces between 2.6 and 7.9 kN and corresponding peak accelerations between 7 and 57 g. Military aircraft ejection and helicopter crashes fall within these high axial acceleration ranges. Testing was stopped following injury detection. Both peak force and acceleration were significant (p < 0.0001) injury predictors. Injury probability curves using parametric survival analysis were created for peak acceleration and peak force. Fifty-percent probability of injury (95%CI) for force and acceleration were 4.5 (3.9-5.2 kN), and 16 (13-19 g). A majority of injuries affected the L1 spinal level. Peak axial forces and accelerations were greater for specimens that sustained multiple injuries or injuries at L2-L5 spinal levels. In general, force-based tolerance was consistent with previous shorter-segment lumbar spine testing (3-5 vertebrae), although studies incorporating isolated vertebral bodies reported higher tolerance attributable to a different injury mechanism involving structural failure of the cortical shell. This study identified novel outcomes with regard to injury patterns, wherein more violent exposures produced more injuries in the caudal lumbar spine. This caudal migration was likely attributable to increased injury tolerance at lower lumbar spinal levels and a faster inertial mass recruitment process for high rate load application. Published 2017. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 36:1747-1756, 2018.

The mechanism of thoracolumbar burst fracture may be related to the basivertebral foramen

BACKGROUND CONTEXT

The basivertebral foramen (BF), located in the middle posterior wall of the vertebral body, may induce local weakness and contribute to the formation of a retropulsed bone fragment (RBF) in thoracolumbar burst fracture (TLBF). We hypothesize that the mechanism of TLBF is related to the BF.

PURPOSE

This study aimed to clarify the relationship between RBFs and the BF in TLBFs, and to explain the results using biomechanical experiments and micro-computed tomography (micro-CT).

STUDY DESIGN

A comprehensive research involving clinical radiology, micro-CT, and biomechanical experiments on cadaveric spines was carried out.

PATIENT SAMPLE

A total of 162 consecutive patients diagnosed with TLBF with RBFs, drawn from 256 patients who had reported accidents or injuries to their thoracolumbar spine, comprised the patient sample.

OUTCOME MEASURES

Dimensions and location of the RBFs in relation to the BF were the outcome measures.

MATERIALS AND METHODS

Computed tomography reconstruction imaging was used to measure the dimensions and location of RBFs in 162 patients (length, height, width of RBF and vertebral body). Furthermore, micro-CT scans were obtained of 10 cadaveric spines. Each vertebral body was divided into three layers (superior, middle, and inferior), and each layer was divided further into nine regions (R1-R9). Microarchitecture parameters were calculated from micro-CT scans, including bone volume fraction (BV/TV), connectivity (Conn.D), trabecular number (Tb.N), trabecular thickness (Tb.Th), and bone mineral density (BMD). Differences were analyzed between regions and layers. Burst fractures were simulated on cadaveric spines to explore the fracture line location and test the relationship between RBFs and BF.

RESULTS

Retropulsed bone fragment width was usually one-third of the width of the vertebral body, whereas RBF length and height were approximately half of the corresponding vertebral body dimensions. Measures of trabecular bone quality were generally lowest in those central and superior regions of the vertebral body which are adjacent to the BF and which are most affected by burst fracture. In simulated TLBFs, the fracture line went across the vertex or upper surface of the BF.

CONCLUSIONS

The most vulnerable regions in the vertebral body lie within or just superior to the BF. The central MR2 region in particular is at risk of fracture and RBF formation.

Development of an experimental model of burst fracture with damage characterization of the vertebral bodies under dynamic conditions

BACKGROUND

Burst fractures represent a significant proportion of fractures of the thoracolumbar junction. The recent advent of minimally invasive techniques has revolutionized the surgical treatment of this type of fracture. However mechanical behaviour and primary stability offered by these solutions have to be proved from experimental validation tests on cadaveric specimens. Therefore, the aim of this study was to develop an original and reproducible model of burst fracture under dynamic impact.

METHODS

Experimental tests were performed on 24 cadaveric spine segments (T11-L3). A system of dynamic loading was developed using a modified Charpy pendulum. The mechanical response of the segments (strain measurement on vertebrae and discs) was obtained during the impact by using an optical method with a high-speed camera. The production of burst fracture was validated by an analysis of the segments by X-ray tomography.

FINDINGS

Burst fracture was systematically produced on L1 for each specimen. Strain analysis during impact highlighted the large deformation of L1 due to the fracture and small strains in adjacent vertebrae. The mean reduction of the vertebral body of L1 assessed for all the specimens was around 15%. No damage was observed in adjacent discs or vertebrae.

INTERPRETATION

With this new, reliable and replicable procedure for production and biomechanical analysis of burst fractures, comparison of different types of stabilization systems can be envisaged. The loading system was designed so as to be able to produce loads leading to other types of fractures and to provide data to validate finite element modelling.

Additional vertebral augmentation with posterior instrumentation for unstable thoracolumbar burst fractures

BACKGROUND

To investigate the role of vertebral augmentation in kyphosis reduction, vertebral fracture union, and correction loss after surgical management of thoracolumbar burst fracture.

DESIGN

Retrospective chart and radiographic review.

SETTING

Level 1 trauma center.

METHODS

The analysis included patients treated between April 2007 and June 2015, who received pedicle-screw-rod distraction and reduction within two days following acute traumatic thoracolumbar burst fracture with a load sharing score >6. Medical records were retrospectively reviewed for data regarding operative details, imaging and laboratory findings, neurological function, and functional outcomes.

INTERVENTION

Not applicable.

MAIN OUTCOME MEASURES

Sagittal index, pain score, loss of correction, and implant failure rate.

RESULTS

Nineteen patients were enrolled in this study (mean age, 37.2±13years; age range, 17-62 years; female/male ratio: 10/9). Of the five patients who received only reduction (no augmentation), one underwent revision surgery because of implant failure and pedicle screw backing out. Compared to patients who received only reduction, those who received both reduction and augmentation showed better sagittal alignment after the operation, with better sagittal index immediately postoperatively and during the follow-up (p<0.05).

CONCLUSIONS

Transpedicular vertebral augmentation with calcium sulfate/phosphate-based bone cement may reinforce thoracolumbar burst fracture stability, partially restore vertebral body height, and reduce pedicle screw bending and movement, thereby preventing early implant failure and late loss of correction, especially in patients with excellent fracture reduction.

LEVEL OF EVIDENCE

Therapeutic level III, retrospective chart review.

[Percutaneous pedicle screw fixation and minimally invasive decompression in the same incision for type A3 thoracolumbar burst fracture]

Objective

To assess the effectiveness of percutaneous pedicle screw fixation and minimally invasive decompression in the same incision for type A3 thoracolumbar burst fracture.

Methods

Between May 2014 and February 2016, 43 cases of type A3 thoracolumbar burst fracture with or without nerve symptoms were treated with pedicle screw fixation and neural decompression. Of them, 21 patients underwent percutaneous pedicle screw fixation and minimally invasive decompression in the same incision (percutaneous group), and the other 22 patients underwent traditional open surgery (open group). There was no significant difference in gender, age, cause of injury, fractures level, preoperative American Spinal Injury Association (ASIA) grade, thoracolumbar injury classification and severity (TLICS) score, load-sharing classification, height of injury vertebrae, kyphotic Cobb angle, and spinal canal encroachment between 2 groups ( P>0.05). The length of soft tissue dissection, operation time, intraoperative blood loss, postoperative drainage, X-ray exposure times, and incision visual analogue scale (VAS) score at 1 day after operation were recorded and compared. At last follow-up, Japanese Orthopaedic Association (JOA) score and low back pain VAS score were recorded and compared respectively. The ASIA grade recovery was evaluated; the height of injury vertebrae, kyphotic Cobb angle, and spinal canal encroachment were assessed postoperatively.

Results

Percutaneous group was significantly better than open group in the length of soft tissue dissection, intraoperative blood loss, postoperative drainage, and incision VAS at 1 day after operation ( P<0.05), but no significant difference was found in operation time between 2 groups ( P>0.05); however, X-ray exposure times of open group were significantly better than that of percutaneous group ( P<0.01). The patients were followed up 12 to 19 months (mean, 15.1 months) in 2 groups. All patients achieved effective decompression. No complications of iatrogenic neurological injury and internal fixation failure occurred. The height of injury vertebrae, kyphotic Cobb angle, and spinal canal encroachment of the fractured vertebral body were significantly improved at 3 days after operation when compared with preoperative ones ( P<0.05), but no significant difference was found between 2 groups ( P>0.05). At last follow-up, JOA score and low back pain VAS score of percutaneous group were significantly better than those of open group ( P<0.05). The neurological function under grade E was improved at least one ASIA grade in 2 groups, but no significant difference was shown between 2 groups ( Z=0.480, P=0.961).

Conclusion

Percutaneous pedicle screw fixation and minimally invasive decompression in the same incision for type A3 thoracolumbar burst fracture has satisfactory effectiveness. And it has the advantages of minimal trauma, quick recovery, safeness, and reliableness.

Creating reproducible thoracolumbar burst fractures in human specimens: an in vitro experiment

OBJECT

The treatment of traumatic burst fractures unaccompanied by neurological impairment remains controversial and ranges from conservative management to 360° fusion. Because of the heterogeneity of fracture types, classification systems, and treatment options, comparative biomechanical studies might help to improve our knowledge. The aim of the current study was to create a standardized fracture model to investigate burst fractures in a multisegmental setting.

METHODS

A total of 28 thoracolumbar fresh-frozen human cadaveric spines were used. The spines were dissected into segments (T11–L3). The T-11 and L-3 vertebral bodies were embedded in Technovit 3040 (cold-curing resin for surface testing and impressions). To simulate high energy, a metallic drop tower was designed. Stress risers were used to ensure comparable fractures. CT scans were acquired before and after fracture. All fractures were classified using the AO/OTA classification.

RESULTS

The preparation and embedding of the spine segments worked well. No repositioning or second embedding of the specimen, even after fracture, was required. It was possible to create single burst fractures at the L-1 level in all 28 spine segments. Among the 28 fractures there were 16 incomplete burst fractures (Type A3.1), 8 burst-split fractures (Type A3.2), and 4 complete burst fractures (Type A3.3). The differences before and after fracture for stiffness and for anterior, posterior, and central heights were all significant (p < 0.05).

CONCLUSIONS

The ability to create reproducible burst fractures of a single vertebral body in a thoracolumbar spine segment may serve as a basis for future biomechanical studies that will provide better understanding of mechanical properties or fixation techniques.

The effect of laminae lesion on thoraco-lumbar fracture reduction

INTRODUCTION

The treatment of fractures involving the lumbar spine has been controversial. Laminae lesion may be complete or of the greenstick type (incomplete). Dural tears and nerve root entrapment may accompany these laminae fractures. The aim of this study is twofold, to assess the effect of different types of laminae fractures on the anteriorvertebral height restoration in upper lumbar burst fractures and to determine the incidences of the intraoperatively detected dural tear and neural entrapment in complete and incomplete laminae fractures to choose the optimal treatment.

MATERIALS AND METHODS

A retrospective review was conducted on 112 patients with 114 lumbar burst fractures treated operatively, age ranged from 17 to 55 years (mean age 32). Male to female ratio was (93%/7%), 8 females. Patients were divided into three groups, group 1 patients without lamina fracture, group 2 patients with complete type lamina fracture and group 3 patients with (percutaneous) incomplete type lamina fractures. All clinical charts and radiologic data of these groups were analyzed for their association with dural tears, neural entrapment and the impact of lamina fracture (complete and incomplete types) on the efficacy of anterior vertebral height restoration. The severity of injury was determined using the ASIA (Modified Frankel scale).

RESULTS

Out of 114 upper lumbar burst fractures, lamina fracture occurred in 34 patients (29.8%), complete lamina fracture occurred in 21 patients (61.7%), whereas incomplete lamina fracture occurred in 13 patients (38.3%). Dural tear was detected in 16 patients (47%) and was predominantly higher in complete type lamina fracture 12 patients (57%) when compared to 4 dural tears (30%) in incomplete lamina fractures. Analysis of the data revealed no significant difference in the preoperative anterior vertebral height loss and local kyphotic angle between the three groups. However the anterior vertebral height and local kyhpotic angle restoration were found to be affected by the presence of complete lamina fracture when compared to other groups with incomplete lamina fracture and without lamina fracture (P=0.001).

CONCLUSION

In upper lumbar burst fractures, complete lamina fracture is an indicator of injury severity. When detected preoperatively on CT or MRI scanning, it should be operated by open book laminectomy even if the patient is neurologically intact since it carries a high risk of neural entrapment, and its presence affects the intraoperative postural and instrumental trials for anterior vertebral height restoration.

Transverse fracture of the stapes anterior crus caused by the blast pressure from a land mine explosion

Stapes fractures without other ossicle problems are rare and ossicle problems due to explosion pressure are also rare. We describe a very rare case of stapes anterior crural fracture resulting from a land mine explosion. As this case suggests, a close examination of the ossicles is necessary during an exploration tympanotomy.

Dynamics of interpedicular widening in spinal burst fractures: an in vitro investigation

BACKGROUND CONTEXT

Spinal burst fractures are a significant cause of spinal instability and neurologic impairment. Although evidence suggests that the neurologic trauma arises during the dynamic phase of fracture, the biomechanics underpinning the phenomenon has yet to be fully explained. Interpedicular widening (IPW) is a distinctive feature of the fracture but, despite the association with the occurrence of neurologic deficit, little is known about its biomechanics.

PURPOSE

To provide a comprehensive in vitro study on spinal burst fracture, with special attention on the dynamics of IPW.

STUDY DESIGN

Experimental measurements in combination with computed tomography scanning were used to quantitatively investigate the biomechanics of burst fracture in a cadaveric model.

METHODS

Twelve human three-adjacent-vertebra segments were tested to induce burst fracture. Impact was delivered through a drop-weight tower, whereas IPW was continuously recorded by two displacement transducers. Computed tomography scanning aided quantifying canal occlusion (CO) and evaluating sample anatomy and fracture appearance. Two levels of energy were delivered to two groups: high energy (HE) and low energy (LE).

RESULTS

No difference was found between HE and LE in terms of the residual IPW (ie, post-fracture), maximum IPW, or CO (median 20.2%). Whereas IPW was not found to be correlated with CO, a moderate correlation was found between the maximum and the residual IPW. At the fracture onset, IPW reached a maximum median value of 15.8% in approximately 20 to 25 milliseconds. After the transient phase, the pedicles were recoiled to a median residual IPW of 4.9%.

CONCLUSIONS

Our study provides for the first time insight on how IPW actually evolves during the fracture onset. In addition, our results may help shedding more light on the mechanical initiation of the fracture.

Biomechanics of Thoracolumbar Burst and Chance-Type Fractures during Fall from Height

Study Design In vitro biomechanical study. Objective To investigate the biomechanics of thoracolumbar burst and Chance-type fractures during fall from height. Methods Our model consisted of a three-vertebra human thoracolumbar specimen (n = 4) stabilized with muscle force replication and mounted within an impact dummy. Each specimen was subjected to a single fall from an average height of 2.1 m with average velocity at impact of 6.4 m/s. Biomechanical responses were determined using impact load data combined with high-speed movie analyses. Injuries to the middle vertebra of each spinal segment were evaluated using imaging and dissection. Results Average peak compressive forces occurred within 10 milliseconds of impact and reached 40.3 kN at the ground, 7.1 kN at the lower vertebra, and 3.6 kN at the upper vertebra. Subsequently, average peak flexion (55.0 degrees) and tensile forces (0.7 kN upper vertebra, 0.3 kN lower vertebra) occurred between 43.0 and 60.0 milliseconds. The middle vertebra of all specimens sustained pedicle and endplate fractures with comminution, bursting, and reduced height of its vertebral body. Chance-type fractures were observed consisting of a horizontal split fracture through the laminae and pedicles extending anteriorly through the vertebral body. Conclusions We hypothesize that the compression fractures of the pedicles and vertebral body together with burst fracture occurred at the time of peak spinal compression, 10 milliseconds. Subsequently, the onset of Chance-type fracture occurred at 20 milliseconds through the already fractured and weakened pedicles and vertebral body due to flexion-distraction and a forward shifting spinal axis of rotation.

Experimental and computational approach investigating burst fracture augmentation using PMMA and calcium phosphate cements

The aim of the study was to use a computational and experimental approach to evaluate, compare and predict the ability of calcium phosphate (CaP) and poly (methyl methacrylate) (PMMA) augmentation cements to restore mechanical stability to traumatically fractured vertebrae, following a vertebroplasty procedure. Traumatic fractures (n = 17) were generated in a series of porcine vertebrae using a drop-weight method. The fractured vertebrae were imaged using μCT and tested under axial compression. Twelve of the fractured vertebrae were randomly selected to undergo a vertebroplasty procedure using either a PMMA (n = 6) or a CaP cement variation (n = 6). The specimens were imaged using μCT and re-tested. Finite element models of the fractured and augmented vertebrae were generated from the μCT data and used to compare the effect of fracture void fill with augmented specimen stiffness. Significant increases (p < 0.05) in failure load were found for both of the augmented specimen groups compared to the fractured group. The experimental and computational results indicated that neither the CaP cement nor PMMA cement could completely restore the vertebral mechanical behavior to the intact level. The effectiveness of the procedure appeared to be more influenced by the volume of fracture filled rather than by the mechanical properties of the cement itself.

Hybrid cadaveric/surrogate model of thoracolumbar spine injury due to simulated fall from height

A fall from high height can cause thoracolumbar spine fracture with retropulsion of endplate fragments into the canal leading to neurological deficit. Our objectives were to develop a hybrid cadaveric/surrogate model for producing thoracolumbar spine injury during simulated fall from height, evaluate the feasibility and performance of the model, and compare injuries with those observed clinically. Our model consisted of a 3-vertebra human lumbar specimen (L3-L4-L5) stabilized with muscle force replication and mounted within an impact dummy. The model was subjected to a fall from height of 2.2 m with impact velocity of 6.6 m/s. Kinetic and kinematic time-history responses were determined using spinal and pelvis load cell data and analyses of high-speed video. Injuries to the L4 vertebra were evaluated by fluoroscopy, radiography, and detailed anatomical dissection. Peak compression forces during the fall from height occurred at 7 ms and reached 44.7 kN at the ground, 9.1 kN at the pelvis, and 4.5 kN at the spine. Pelvis acceleration peaks reached 209.9 g at 8 ms for vertical and 62.8 g at 12 ms for rearward. Tensile load peaks were then observed (spine: 657.0 N at 47 ms; pelvis: 569.4 N at 61 ms). T1/pelvis peak flexion of 68.3° occurred at 38 ms as the upper torso translated forward while the pelvis translated rearward. Complete axial burst fracture of the L4 vertebra was observed including endplate comminution, retropulsion of bony fragments into the canal, loss of vertebral body height, and increased interpedicular distance due to fractures anterior to the pedicles and a vertical split fracture of the left lamina. Our dynamic injury model closely replicated the biomechanics of real-life fall from height and produced realistic, clinically relevant burst fracture of the lumbar spine. Our model may be used for further study of thoracolumbar spine injury mechanisms and injury prevention strategies.

Simultaneous combined anterior and posterior surgery for severe thoracolumbar fracture dislocations

OBJECTIVE

To analyze the clinical results of simultaneously combined anterior and posterior surgery for severe thoracolumbar fracture dislocations, and to clarify the surgical indications for these high-energy injuries.

METHODS

Thirty-four patients with severe thoracolumbar fracture dislocations were managed with simultaneously combined anterior and posterior surgery. The injured segments included the following: T11 (2 patients), T12 (5), L1 (1), L2 (8), L3 (5), L4 (2) and L4 and L5 (1). When classified according to the Magerl Classification, the breakdown was as follows: 12 A3 injuries, 2 B1, 2 B2, 12 C1 injuries, 4 C2, and 2 C3. Clinical data, including operative procedures, neurological changes, postoperative CT scans and sequential radiographs, was collected and analyzed. Thirty-two patients were followed up for an average of 13 months (range, 6-60).

RESULTS

Operative time ranged from 180 to 320 min with a mean of 230 min. Intraoperative blood loss ranged from 900 to 2400 ml with a mean of 1200 ml. According to the classification of the American Spinal Injury Association (ASIA), neurological status improved at least 1 grade in all of the 24 patients who had an incomplete paralysis preoperatively. Satisfactory decompressions, reductions and reconstructions were obtained and well maintained in all patients at all intervals of follow-up.

CONCLUSION

For severe thoracolumbar fracture dislocations that cannot be effectively treated with either an anterior or posterior approach alone, simultaneously combined anterior and posterior surgery is a reliable method that can achieve a sufficient decompression, reduction and reconstruction.

Calibration of hyperelastic material properties of the human lumbar intervertebral disc under fast dynamic compressive loads

Under fast dynamic loading conditions (e.g. high-energy impact), the load rate dependency of the intervertebral disc (IVD) material properties may play a crucial role in the biomechanics of spinal trauma. However, most finite element models (FEM) of dynamic spinal trauma uses material properties derived from quasi-static experiments, thus neglecting this load rate dependency. The aim of this study was to identify hyperelastic material properties that ensure a more biofidelic simulation of the IVD under a fast dynamic compressive load. A hyperelastic material law based on a first-order Mooney-Rivlin formulation was implemented in a detailed FEM of a L2-L3 functional spinal unit (FSU) to represent the mechanical behavior of the IVD. Bony structures were modeled using an elasto-plastic Johnson-Cook material law that simulates bone fracture while ligaments were governed by a viscoelastic material law. To mimic experimental studies performed in fast dynamic compression, a compressive loading velocity of 1 m/s was applied to the superior half of L2, while the inferior half of L3 was fixed. An exploratory technique was used to simulate dynamic compression of the FSU using 34 sets of hyperelastic material constants randomly selected using an optimal Latin hypercube algorithm and a set of material constants derived from quasi-static experiments. Selection or rejection of the sets of material constants was based on compressive stiffness and failure parameters criteria measured experimentally. The two simulations performed with calibrated hyperelastic constants resulted in nonlinear load-displacement curves with compressive stiffness (7335 and 7079 N/mm), load (12,488 and 12,473 N), displacement (1.95 and 2.09 mm) and energy at failure (13.5 and 14.7 J) in agreement with experimental results (6551 ± 2017 N/mm, 12,411 ± 829 N, 2.1 ± 0.2 mm and 13.0 ± 1.5 J respectively). The fracture pattern and location also agreed with experimental results. The simulation performed with constants derived from quasi-static experiments showed a failure energy (13.2 J) and a fracture pattern and location in agreement with experimental results, but a compressive stiffness (1580 N/mm), a failure load (5976 N) and a displacement to failure (4.8 mm) outside the experimental corridors. The proposed method offers an innovative way to calibrate the hyperelastic material properties of the IVD and to offer a more realistic simulation of the FSU in fast dynamic compression.

Can the interpedicular distance reliably assess the severity of thoracolumbar burst fractures?

STUDY DESIGN

Retrospective analysis of 260 patients with acute spine fractures treated at a tertiary trauma center from 1989 to 2009.

OBJECTIVE

To correlate the Interpedicular distance (IPD) to the percentage of narrowing of the spinal canal and to the presence of neurological deficit and laminar fracture in thoracolumbar burst fractures.

SUMMARY OF BACKGROUND DATA

Several reports use radiographic findings such as severity of vertebrae collapse, comminution of the vertebral body, and grade of localized kyphosis to determine the severity of spinal traumas and establish appropriate management. However, the importance of the IPD in burst fractures has rarely been mentioned, and no report specifically describes the correlation between an increased IPD and the severity of the lesion or a higher occurrence of lamina fractures.

METHODS

Plain radiographs of 260 patients with acute thoracolumbar burst fractures were studied. The percentage of widening between the pedicles of the fractured vertebra (IPD) was established by comparing this distance with that of the vertebrae immediately above and below. Data concerning neurological status, percentage of narrowing of the spinal canal, and the presence of laminar fracture were correlated to the IPD.

RESULTS

A significant correlation between IPD and the percentage of narrowing of the spinal canal was found (r = 0.39; t = 6.78; P = 0.00). IPD was significantly increased in patients with neurological deficit (24.7% ± 12.6%) and in patients with lamina fractures (24.6% ± 16.2%).

CONCLUSION

IPD measured from plain radiographs proved to be a reliable instrument to assess narrowing of the spinal canal, neurological deficits, and laminar fractures.

Retrospective comparison of H-graft and posterior vertebral graft procedures for the treatment of thoracolumbar burst fractures

A retrospective cohort study was conducted to compare fusion rates achieved by H-grafts, posterior vertebral grafts, and no graft for the surgical treatment of thoracolumbar fractures. Ninety-two patients were included in this study. The patients fell into 1 of 3 groups: those who received H-grafts (n=36), posterior vertebral grafts (n=30), and no graft (n=26). Mean follow-up was 38 months (range, 24-51 months). All operations were performed by a single senior surgeon. All patients underwent operative treatment with posterior reduction and instrumentation. Radiographic parameters, estimated blood loss, operative time, and length of hospital stay were compared among patients in the 3 graft groups. Differences were assessed using unpaired t tests. P values <.05 were considered significant. We found no significant difference among groups in age, fracture location, or type of fracture. Patients who received H-grafts or posterior vertebral grafts achieved solid fusion, but spontaneous fusion occurred in only 2 patients who received no bone graft. Most patients with neurological deficits showed significant neurological improvement. Operative time and estimated blood loss were significantly lower in the no-graft group than in the H-graft and posterior vertebral graft groups (P<.05). Mean loss of correction, operative time, and estimated blood loss were lower for patients who received H-grafts than for those who received posterior vertebral grafts (P<.05). The use of an atlas fixation system in combination with a posterior H-graft for the treatment of thoracolumbar fracture is a stable and reliable method that effectively prevents inner fixation failure and reduces bone loss and anisotropy.

A New PMHS Model for Lumbar Spine Injuries During Vertical Acceleration

Ejection from military aircraft exerts substantial loads on the lumbar spine. Fractures remain common, although the overall survivability of the event has considerably increased over recent decades. The present study was performed to develop and validate a biomechanically accurate experimental model for the high vertical acceleration loading to the lumbar spine that occurs during the catapult phase of aircraft ejection. The model consisted of a vertical drop tower with two horizontal platforms attached to a monorail using low friction linear bearings. A total of four human cadaveric spine specimens (T12-L5) were tested. Each lumbar column was attached to the lower platform through a load cell. Weights were added to the upper platform to match the thorax, head-neck, and upper extremity mass of a 50th percentile male. Both platforms were raised to the drop height and released in unison. Deceleration characteristics of the lower platform were modulated by foam at the bottom of the drop tower. The upper platform applied compressive inertial loads to the top of the specimen during deceleration. All specimens demonstrated complex bending during ejection simulations, with the pattern dependent upon the anterior-posterior location of load application. The model demonstrated adequate inter-specimen kinematic repeatability on a spinal level-by-level basis under different subfailure loading scenarios. One specimen was then exposed to additional tests of increasing acceleration to induce identifiable injury and validate the model as an injury-producing system. Multiple noncontiguous vertebral fractures were obtained at an acceleration of 21 g with 488 g/s rate of onset. This clinically relevant trauma consisted of burst fracture at L1 and wedge fracture at L4. Compression of the vertebral body approached 60% during the failure test, with -6,106 N axial force and 168 Nm flexion moment. Future applications of this model include developing a better understanding of the vertebral injury mechanism during pilot ejection and developing tolerance limits for injuries sustained under a variety of different vertical acceleration scenarios.

Traumatic canal stenosis should not be an indication for surgical decompression in thoracolumbar burst fracture

Thoracolumbar burst fracture (TLBF) is a common type of spinal injuries and frequently causes spinal cord injury. The frequency of neurological deficits in all TLBF can reach up to 50-60%. The typical TLBF images seen on axial computerized tomography are the bone fragment projected into the spinal canal, which always persuade surgeons that the narrowed canal must compress the neural content and therefore is responsible for neurological deficits, with the corollary that surgical decompression of spinal canal is an essential therapeutic strategy for functional recovery. We hypothesize that in TLBF, traumatic canal stenosis is a predictive factor for neurological dysfunction and the surgical decompression is vital to the recovery of neurological function. After a review of the available evidences, we conclude that spinal canal stenosis is poorly correlated with neurological dysfunction in TLBF, and surgical decompression is not vital to the neurological recovery. Therefore, traumatic canal stenosis should not be an isolated indication for surgical decompression in TLBF.

Thoracolumbar burst fractures: a systematic review of management

The management of thoracolumbar burst fractures remains challenging. Ideally, it should effectively correct the deformity, induce neurological recovery, allow early mobilization and return to work, and be associated with minimal risk of complication. This article reviews the related studies reporting their clinical data for the management of thoracolumbar burst fractures, discusses the most suitable approach in cases such as these, highlights specific treatment recommendations, and proposes a treatment algorithm. Using PubMed and Scopus databases to search the term thoracolumbar burst fractures, abstracts and original articles in English investigating the treatment of thoracolumbar burst fractures were searched and analyzed.

Comparison of radiography and computed tomography in evaluating posterior indirect reduction of spinal canal bone fragment

This article describes a retrospective study of patients who underwent posterior indirect reduction procedures for thoracolumbar burst fractures. The goal of this study was to explore a simple and effective method for evaluating the reduction of spinal canal fragments during posterior indirect reduction procedures.Sixty-four burst fractures with retropulsed bone fragments encroaching the spinal canal at the thoracolumbar junction were performed. C-arm fluoroscopy was used to evaluate the spinal canal fragments' reduction. A standard lateral view of the thoracolumbar spine was set up. When a continuous and smooth posterior vertebral body line of the injured vertebrae appeared, similar to below and above the vertebrae, the spinal canal bone fragment was considered to be satisfactorily reduced. The midsagittal diameter of the injured segment was measured on preoperative and postoperative computed tomography (CT) scans. Narrowing of the midsagittal diameter of the injured segment was improved from 41.4%+/-15.9% to 13.7%+/-9.7%. The correction value was 27.6%+/-15.6%. All pre- and postoperative outcome variables had statistical significance (P<.01). Forty-two patients experienced a restored posterior vertebral body line with a continuous and smooth vertical line, indicating that the fragment reduction was satisfactory. Post-operative CT showed that the spinal canal compromise was <10% (range, 0%-9.8%; mean, 6.1%+/-2.9%).Continuous and smooth posterior vertebral body line imaging is a simple and effective method to judge the reduction of a bone fragment retropulsed into the spinal canal. It can provide evidence as to whether a laminotomy and pushing the bone fragment are necessary during posterior surgery.

Anterior versus modified combined instrumentation for burst fractures of the thoracolumbar spine: a biomechanical study in calves

PURPOSE

To compare stability after anterior instrumentation alone versus modified combined anterior and posterior instrumentation for burst fractures of the thoracolumbar spine in calves.

METHODS

Thoracolumbar spines of 10 calves were used. An axial compression force was applied on each specimen using a material-testing machine, until there was a burst fracture at T12 or L1. Five specimens were fixed with anterior instrumentation alone, using 2 rods connected by 2 screws above and 2 screws below the fractured vertebra plus one tranverse connector. Another 5 were fixed with our modified technique of combined anterior and posterior instrumentation. This entailed one rod connected with one screw above and one screw below the fractured vertebra anteriorly, and another rod connected with one transpedicular screw above and one transpedicular screw below the fractured vertebra posteriorly. After instrumentation, the experiment was conducted again on each specimen and the compressive stiffness and vertebral height loss between the 2 groups compared.

RESULTS

The mean compressive stiffness was significantly greater after modified combined anterior and posterior instrumentation than anterior instrumentation alone (5508 vs 2888 N, p=0.0256), whereas the respective vertebral height losses were 37 and 33 mm (p=0.3808).

CONCLUSION

Our modified technique of combined anterior and posterior instrumentation provides greater stability than traditional anterior instrumentation alone.

Preventing fall-related vertebral fractures: effect of floor stiffness on peak impact forces during backward falls

STUDY DESIGN

In vivo biomechanical study of 11 male volunteers.

OBJECTIVE

To measure the peak forces applied to the buttocks in a backward fall from standing, and to determine whether this force is lowered by reductions in floor stiffness.

SUMMARY OF BACKGROUND DATA

Fall-related vertebral fractures are common and backward falls result in impact to the buttocks. Compliant flooring may reduce impact force and risk for vertebral fracture during a fall. However, we have little knowledge of the peak forces applied to the body during a backward fall, or how floor stiffness affects this force.

METHODS

Eleven males, mean age 25 +/- 5 (SD) years, were suddenly released from a backward lean of 15 degrees , falling backward onto the ground which was covered with 4.5, 7.5, or 10.5 cm of ethylene vinyl acetate foam rubber. We measured 3-dimensional impact forces applied to the buttocks at 960 Hz with a force plate. We used repeated measures analysis of variance and post hoc t tests to compare peak forces between conditions. We also modeled peak vertical force for falls onto a bare floor. RESULTS.: There was a significant difference in peak vertical force between falls onto the 10.5 cm foam condition compared with the 7.5 cm (P = 0.002) and 4.5 cm (P < 0.001) conditions. Peak vertical force (N) was (mean +/- SD) 5099 +/- 868, 4788 +/- 702, and 4544 +/- 672 for the 4.5, 7.5, and 10.5 cm foam conditions, respectively, and estimated at 6027 +/- 988 for the rigid (bare floor) condition. Compared with the bare floor, these foam floors provided, on average, 24, 20, and 15% force attenuation respectively.

CONCLUSION

In a backward fall onto the buttocks, peak impact forces are 6.4 to 9.0 times body weight in a fall onto a bare floor. Reducing floor stiffness using even a thin (4.5 cm) layer of foam may provide 15% vertical force attenuation during a fall onto the buttocks.

Fluoroscopically-guided indirect posterior reduction and fixation of thoracolumbar burst fractures without fusion

This article presents an evaluation of fluoroscopy for indirect, posterior reduction and fixation of thoracolumbar burst fractures. A prospective study of 25 patients with thoracolumbar burst fractures who underwent C-arm machine-guided posterior indirect reduction and short segment fixation without fusion is described. No laminotomies were performed. All patients had a mean follow-up of 30.4 months. At postoperative review, the average anterior and posterior vertebral heights were corrected from 57.9% to 99.0% and 89.0% to 99.5%, respectively. The Cobb angle was corrected from 18.4 degrees to 0.17 degrees . The canal compromise ratio was improved from 35.2% to 8.6%. In all 25 cases, neurological status was intact at last follow-up. Fluoroscopy guidance is an effective method to accomplish indirect reduction and fixation. Reduction was confirmed on lateral fluoroscopic views by looking for a "one-line sign," which is the reconstitution of the posterior border of the vertebral body.

Translational constraint influences dynamic spinal canal occlusion of the thoracic spine: An in vitro experimental study

Mechanical constraints to spine motion can arise in a variety of real-world situations such as when shoulder belts prevent anterior translation of the thorax during automotive collisions. The effect of such constraint on spinal column-spinal cord interaction during injury remains unknown. The purpose of the present study was to compare maximal dynamic spinal canal occlusion, measured via a specialized transducer, in cadaveric upper thoracic spine specimens under a variety of anterior-posterior constraint conditions. Four injury models were produced using 24 cadaveric spine specimens (T1-T4). Incremental compressive trauma was applied under constrained (i.e. blocked anterior-posterior translation) flexion-compression, pure-compression and extension-compression, and under unconstrained (i.e. free anterior-posterior translation) flexion-compression. All displacements were applied at 500 mm/s. For all three constrained trauma groups, complete transducer occlusion occurred between 20 and 30 mm of compressive displacement. The extension-compression caused transducer occlusion significantly less than the other constrained models (p < 0.022) at 20 mm compression. For unconstrained flexion-compression, a compression of up to 50 mm resulted in a mean of 26% transducer occlusion. The constrained pure-compression tests led to burst fracture with significant body height loss at T2. The constrained flexion-compression and extension-compression tests caused fracture-dislocation injury at the T2-T3 level. Constrained trauma clearly led to more spinal canal occlusion than the unconstrained in these models, and more severe injury to the spinal column. The results add to our understanding of the effect of column injury pattern on spinal cord injury. This information has clear implications for the design of injury prevention devices.

Medical Screening for Red Flags in the Diagnosis and Management of Musculoskeletal Spine Pain

When a patient presents with pain in the different regions of the spine, the clinician executes a region-appropriate basic examination that includes appropriate historical cues and specific physical examination tests that can be used to identify red flags. The clinical tests include a specific examination of the sensory and motor systems. Test outcomes are best interpreted in context with the entire examination profile, where the sensitivity and specificity of these tests can influence their utility in uncovering red flags. These red flags can be categorized based on the nature and severity or the specific elements of the patient's presentation. Many general red flags can be observed in any region of the spine, while specific red flags must be categorized and discussed for each spinal region. This categorization can guide the clinician in the direction of management, whether that management is aimed at redirecting the patient's care to another specialist, reconsidering the presentation and observing for clusters of findings that may suggest red flags, or managing the patient within the clinician's specialty in context with the severity of the patient's presentation.

A review of the management of thoracolumbar burst fractures

BACKGROUND

Burst fractures account for more than half of all thoracolumbar fractures, which often cause a neurologic deficit and present a significant economic burden to the family and society. Accepted methods of treatment of thoracolumbar burst fractures include conservative therapy, posterior reduction and instrumentation, and anterior decompression and instrumentation. However, the management of thoracolumbar burst fractures has been the subject of much controversy.

METHODS

Publications reporting clinical data relating to the thoracolumbar burst fractures were reviewed. These articles were determined via review of the results of PubMed searches and articles gathered through compilation of references from those articles.

RESULTS

There exist different criteria for the choice of the management based on the severity of kyphotic deformity, canal compromise, vertebral height loss, and neurologic status. To our knowledge, none of the existing criteria for the treatment of thoracolumbar burst fractures are generally accepted.

CONCLUSIONS

In thoracolumbar burst fractures without a neurologic deficit, there is no superiority of conservative therapy over operative therapy. When the neurologic involvement is significant, the choice of operative management is advised. Also, there is no obvious superiority of one approach over the other.

Treatment of unstable thoracolumbar junction burst fractures with short- or long-segment posterior fixation in magerl type a fractures

The treatment of thoracolumbar fractures remains controversial. A review of the literature showed that short-segment posterior fixation (SSPF) alone led to a high incidence of implant failure and correction loss. The aim of this retrospective study was to compare the outcomes of the SS- and long-segment posterior fixation (LSPF) in unstable thoracolumbar junction burst fractures (T12-L2) in Magerl Type A fractures. The patients were divided into two groups according to the number of instrumented levels. Group I included 32 patients treated by SSPF (four screws: one level above and below the fracture), and Group II included 31 patients treated by LSPF (eight screws: two levels above and below the fracture). Clinical outcomes and radiological parameters (sagittal index, SI; and canal compromise, CC) were compared according to demographic features, localizations, load-sharing classification (LSC) and Magerl subgroups, statistically. The fractures with more than 10 degrees correction loss at sagittal plane were analyzed in each group. The groups were similar with regard to age, gender, LSC, SI, and CC preoperatively. The mean follow-ups were similar for both groups, 36 and 33 months, respectively. In Group II, the correction values of SI, and CC were more significant than in Group I. More than 10 degrees correction loss occurred in six of the 32 fractures in Group I and in two of the 31 patients in Group II. SSPF was found inadequate in patients with high load sharing scores. Although radiological outcomes (SI and CC remodeling) were better in Group II for all fracture types and localizations, the clinical outcomes (according to Denis functional scores) were similar except Magerl type A33 fractures. We recommend that, especially in patients, who need more mobility, with LSC point 7 or less with Magerl Type A31 and A32 fractures (LSC point 6 or less in Magerl Type A3.3) without neurological deficit, SSPF achieves adequate fixation, without implant failure and correction loss. In Magerl Type A33 fractures with LSC point 7 or more (LSC points 8-9 in Magerl Type A31 and A32) without severe neurologic deficit, LSPF is more beneficial.

Investigation of thoracolumbar T12–L1 burst fracture mechanism using finite element method

A finite element model of the T12-L1 motion segment was subjected to dynamic vertical impact to investigate vertebral burst fracture mechanism at the thoracolumbar junction. A rigid ball was directed vertically towards a rigid plate fixed on top of the T12 vertebral body to simulate the axial impact. The results show that upon impact, the T12 vertebra exhibited a vibratory motion. At its maximum compression, the endplates bulged towards their vertebral bodies. The central parts of the endplates adjacent to the nucleus experienced the highest effective stress, and localized stress concentration developed correspondingly within the central parts of the cancellous bone adjacent to the endplates. This appears to confirm the hypothesis that nucleus material is forced to enter the vertebral body, pressurizing it further and squeezing the fat and marrow contents out of the cancellous bone. When the nucleus material enters the vertebral body faster than fat and marrow being expulsed, the vertebral body could burst through the anterior and posterior cortical shell. Upon sudden posterior cortex fracture, the transient fragment encroachment could be further into the spinal canal than the final observed locations, as the fragments are retropulsed to the vertebral body during the bursting process.

Bone mineral density of the thoracolumbar spine in relation to burst fractures: a quantitative computed tomography study

The most common pattern among thoracolumbar burst fractures involves failure of the superior vertebra end-plate. There have been many biomechanical studies of thoracolumbar burst fractures, but the biomechanics related to the internal architecture of thoracolumbar vertebrae has been rarely documented. The objective of this study was to test the hypotheses that distribution of the bone mineral density (BMD) of the thoracolumbar spine is related to the stress concentration in this region and therefore, supports the pattern of burst fractures that occur most commonly. We measured spinal BMD of the first lumbar vertebra in 22 individuals using quantitative computed tomography (QCT) in three levels. At each level, the BMD for the trabecular compartment was determined from each of six sites and from one site within each pedicle. Thus the trabecular density was measured at a total of 20 sites for each person. The highest average QCT BMD was in the pedicle (sites 13 and 14), whereas the BMD was abruptly decreased at the posterior part of the vertebral body near the pedicles. The results of the study indicate that stress concentration of the spine related to the regional variation in vertebral bone density may be implicated in the biomechanical mechanism underlying thoracolumbar burst fractures. This finding may be correlated with the injury mechanism of thoracolumbar burst fractures and of clinical significance.

Anterior spinal column augmentation with injectable bone cements

A vertebral fracture, whether originating from osteoporosis or trauma, can be the cause of pain, disability, deformation and neurological deficit. The treatment of vertebral compression fractures has, for many years until the advent of vertebroplasty, consisted of bedrest and analgesics. Vertebroplasty is a percutaneous technique during which bone cement is injected in a vertebral body to provide immediate pain relief by stabilization. Inflatable bone tamps can, prior to the injection of cement, be used to create a void in the vertebral body, in which case the technique is known as balloon vertebroplasty (or kyphoplasty). The chance of extracorporal cement leakage is smaller for balloon vertebroplasty than for vertebroplasty. Some authors also claim to have gained some correction in vertebral body height or angulation. Both interventions can be used for several indications, including osteoporotic compression fractures and osteolytic lesions of the vertebral body such as myeloma, hemangioma or metastasis, and also for traumatic burst fractures in combination with pedicle screw instrumentation. Polymethyl methacrylate cement is the bone void filler that is used most frequently, although the application of calcium phosphate cements has been studied widely in vitro, in vivo and also in small-scale clinical series. The clinical results of (balloon-) vertebroplasty are favorable with 85-95% of all patients experiencing immediate and long-lasting relief of pain. Serious complications are relatively rare but include neurological deficit and pulmonary embolism. In this paper, both vertebroplasty and balloon vertebroplasty and their respective indications, techniques and results are described in relation with the application and limitations of permanent and resorbable injectable bone cements.

Treatment of Thoracolumbar Burst Fractures with Variable Screw Placement or Isola Instrumentation and Arthrodesis

BACKGROUND

The controversy of burst fracture surgical management is addressed in this retrospective case study and literature review.

METHODS

The series consisted of 40 consecutive patients, index included, with 41 fractures treated with stiff, limited segment transpedicular bone-anchored instrumentation and arthrodesis from 1987 through 1994.

RESULTS

No major acute complications such as death, paralysis, or infection occurred. For the 30 fractures with pre- and postoperative computed tomography studies, spinal canal compromise was 61% and 32%, respectively. Neurologic function improved in 7 of 14 patients (50%) and did not worsen in any. The principal problem encountered was screw breakage, which occurred in 16 of the 41 (39%) instrumented fractures. As we have previously reported, transpedicular anterior bone graft augmentation significantly decreased variable screw placement (VSP) implant breakage. However, it did not prevent Isola implant breakage in two-motion segment constructs. Compared with VSP, Isola provided better sagittal plane realignment and constructs that have been found to be significantly stiffer. Unplanned reoperation was necessary in 9 of the 40 patients (23%). At 1- and 2-year follow-up, 95% and 79% of patients were available for study, and a satisfactory outcome was achieved in 84% and 79%, respectively. These satisfaction and reoperation rates are consistent with the literature of the time.

CONCLUSIONS

Based on these observations and the loads to which implant constructs are exposed following posterior realignment and stabilization of burst fractures, we recommend that three- or four-motion segment constructs, rather than two motion, be used. To save valuable motion segments, planned construct shortening can be used. An alternative is sequential or staged anterior corpectomy and structural grafting.

Treatment of Thoracolumbar Burst Fractures with Polymethyl Methacrylate Vertebroplasty and Short-segment Pedicle Screw Fixation

OBJECTIVES

We aimed to evaluate the efficacy of reinforcing short-segment pedicle screw fixation with polymethyl methacrylate (PMMA) vertebroplasty in patients with thoracolumbar burst fractures.

METHODS

We enrolled 70 patients with thoracolumbar burst fractures for treatment with short-segment pedicle screw fixation. Fractures in Group A (n = 20) were reinforced with PMMA vertebroplasty during surgery. Group B patients (n = 50) were not treated with PMMA vertebroplasty. Kyphotic deformity, anterior vertebral height, instrument failure rates, and neurological function outcomes were compared between the two groups.

RESULTS

Kyphosis correction was achieved in Group A (PMMA vertebroplasty) and Group B (Group A, 6.4 degrees; Group B, 5.4 degrees). At the end of the follow-up period, kyphosis correction was maintained in Group A but lost in Group B (Group A, 0.33-degree loss; Group B, 6.20-degree loss) (P = 0.0001). After surgery, greater anterior vertebral height was achieved in Group A than in Group B (Group A, 12.9%; Group B, 2.3%) (P &lt; 0.001). During follow-up, anterior vertebral height was maintained only in Group A (Group A, 0.13 ± 4.06%; Group B, −6.17 ± 1.21%) (P &lt; 0.001). Patients in both Groups A and B demonstrated good postoperative Denis Pain Scale grades (P1 and P2), but Group A had better results than Group B in terms of the control of severe and constant pain (P4 and P5) (P &lt; 0.001). The Frankel Performance Scale scores increased by nearly 1 in both Groups A and B. Group B was subdivided into Group B1 and B2. Group B1 consisted of patients who experienced instrument failure, including screw pullout, breakage, disconnection, and dislodgement (n = 11). Group B2 comprised patients from Group B who did not experience instrument failure (n = 39). There were no instrument failures among patients in Group A. Preoperative kyphotic deformity was greater in Group B1 (23.5 ± 7.9 degrees) than in Group B2 (16.8 ± 8.40 degrees), P &lt; 0.05. Severe and constant pain (P4 and P5) was noted in 36% of Group B1 patients (P &lt; 0.001), and three of these patients required removal of their implants.

CONCLUSION

Reinforcement of short-segment pedicle fixation with PMMA vertebroplasty for the treatment of patients with thoracolumbar burst fracture may achieve and maintain kyphosis correction, and it may also increase and maintain anterior vertebral height. Good Denis Pain Scale grades and improvement in Frankel Performance Scale scores were found in patients without instrument failure (Groups A and B2). Patients with greater preoperative kyphotic deformity had a higher risk of instrument failure if they did not undergo reinforcement with vertebroplasty. PMMA vertebroplasty offers immediate spinal stability in patients with thoracolumbar burst fractures, decreases the instrument failure rate, and provides better postoperative pain control than without vertebroplasty.