Two column lesions in the thoracolumbar junction: anterior, posterior or combined approach? A comparative biomechanical in vitro investigation

Which spinal fixation technique achieves which degree of stability after thoracolumbar trauma? A systematic quantitative review

BACKGROUND CONTEXT

Unstable traumatic spinal injuries require surgical fixation to restore biomechanical stability.

PURPOSE

The purpose of this review was to summarize and quantify three-dimensional spinal stability after surgical fixation of traumatic thoracolumbar spinal injuries using different treatment strategies derived from experimental studies.

STUDY DESIGN/SETTING

Systematic literature review.

METHODS

Keyword-based search was performed in PubMed and Web of Science databases to identify all in vitro studies investigating stabilizing effects of different surgical fixation strategies for the treatment of traumatic spinal injuries of the thoracolumbar spine. Biomechanical stability parameters such as range of motion, neutral zone, and translation, as well as the experimental design were extracted, collected, and evaluated with respect to the type and level of injury and treatment strategy.

RESULTS

A total of 66 studies with human specimens were included in this review, of which 16 studies examined the treatment of incomplete (AOSpine A3) and 34 studies the treatment of complete burst fractures (AOSpine A4). Fixations of wedge fractures (AOSpine A1, n=5 studies), ligament injuries (AOSpine B, n=7 studies), and three-column injuries (AOSpine C, n=7 studies) were investigated less frequently. Treatment approaches could be divided into five subgroups: Posterior fixation, e.g. posterior pedicle screw systems, anterior fixation, e.g. anterolateral plate fixation, combined anterior-posterior fixation, vertebral body replacement with additional instrumentation, and augmentation techniques, e.g. vertebroplasty and kyphoplasty. Minor injuries were generally treated with less invasive surgical methods such as augmentative and posterior approaches. Bisegmental posterior pedicle screw fixation led to stabilization of minor compression injuries, whereas in more severe injuries, e.g. AOSpine A4 or AOSpine C, instability remained in at least one motion plane. More invasive fixation techniques such as long segment posterior fixation, circumferential fixation, or vertebral body replacements with circumferential fixation provided total stabilization in terms of range of motion reduction even in more severe injuries. Pure augmentative treatment did not restore multidirectional stability. Neutral zone, which was reported in 25 studies, generally exhibited higher remaining increase than range of motion, which was reported in all 66 studies. Instability characteristics after treatment differed with respect to the spinal region, as thoracic injuries were more likely to remain unstable in flexion/extension, while thoracolumbar and lumbar injuries exhibited remaining instability primarily in axial rotation.

CONCLUSIONS

The stabilizing effect of surgical treatment depends on the type, severity, and location of injury, as well as the fixation strategy. There is an enormous range of surgical approaches and instrumentation strategies available. Pure augmentative techniques have not been able to restore complex multidimensional stability in traumatic spinal injuries. More invasive fixation approaches such as circumferential instrumentation or vertebral body replacement constructs together with posterior or anterior-posterior fixation offer more stability even in severe spinal injuries. Future studies are required to expand the knowledge especially regarding the stabilization of minor compression injuries, ligament injuries, and rotational injuries.

Injury of the thoracolumbar posterior ligamentous complex : a bibliometric literature review

OBJECTIVE

This bibliometric review of literature on posterior ligamentous complex (PLC) injury in thoracolumbar (TL) trauma aims to guide future research.

METHODS

We conducted a keyword-based search from January 2000 to September 2021 using the Scopus database. Relevant publications were analyzed for the year of publication, authorship, publishing journals, institution and country of origin, subject matter, and article type. In addition, content analysis of clinical articles was performed, analyzing for sample size, study design (retrospective vs. prospective), single vs. multicenter, and level of evidence.

RESULTS

262 publications have been published in 61 journals by 537 authors, 162 institutions, and 29 countries. Thomas Jefferson University, the University of Calgary, and the University of Toronto have the largest number of publications related to PLC injury. The United States, Canada, and China were the most frequent contributors in terms of the number of publications. Spine was the most prolific and top-cited Journal, while Vaccaro A.R. was the most prolific author. The most cited publication was the Thoracolumbar Injury Classification and Severity Score (TLICS) classification by Vaccaro et al. in 2005. Most of the publications have been case studies, with diagnostic accuracy being the most frequently discussed topic. The sample size for a large portion of the case series was less than 50. The majority of case series were retrospective studies conducted at a single center.

CONCLUSION

Our review provides an extensive list of the most historically significant spinal imaging articles, acknowledging the key contributions made to the advancement of this research area.

Monosegmental anterior column reconstruction using an expandable vertebral body replacement device in combined posterior-anterior stabilization of thoracolumbar burst fractures

INTRODUCTION

In combined posterior-anterior stabilization of thoracolumbar burst fractures, the expandable vertebral body replacement device (VBRD) is typically placed bisegmentally for anterior column reconstruction (ACR). The aim of this study, however, was to assess feasibility, outcome and potential pitfalls of monosegmental ACR using a VBRD. In addition, clinical and radiological outcome of monosegmental ACR was related to that of bisegmental ACR using the same thoracoscopic technique.

METHODS

Thirty-seven consecutive neurologically intact patients with burst fractures of the thoracolumbar junction (T11-L2) treated by combined posterior-anterior stabilization were included. Monosegmental ACR was performed in 18 and bisegmental ACR in 19 patients. Fracture type and extent of vertebral body comminution were determined on preoperative CT scans. Monosegmental and bisegmental kyphosis angles were analyzed preoperatively, postoperatively and at final radiological follow-up. Clinical outcome was assessed after a minimum of 2 years (74 ± 45 months; range 24-154; follow-up rate 89.2%) using VAS Spine Score, RMDQ, ODI and WHOQOL-BREF.

RESULTS

Monosegmental ACR resulted in a mean monosegmental and bisegmental surgical correction of - 15.6 ± 7.7° and - 14.7 ± 8.1°, respectively. Postoperative monosegmental and bisegmental loss of correction averaged 2.7 ± 2.7° and 5.2 ± 3.7°, respectively. Two surgical pitfalls of monosegmental ACR were identified: VBRD positioning (1) onto the weak cancellous bone (too far cranially to the inferior endplate of the fractured vertebra) and (2) onto a significantly compromised inferior endplate with at least two (even subtle) fracture lines. Ignoring these pitfalls resulted in VBRD subsidence in five cases. When relating the clinical and radiological outcome of monosegmental ACR to that of bisegmental ACR, no significant differences were found, except for frequency of VBRD subsidence (5 vs. 0, P = 0.02) and bisegmental loss of correction (5.2 ± 3.7° vs. 2.6 ± 2.5°, P = 0.022). After exclusion of cases with VBRD subsidence, the latter did not reach significance anymore (4.9 ± 4.0° vs. 2.6 ± 2.5°, P = 0.084).

CONCLUSIONS

This study indicates that monosegmental ACR using a VBRD is feasible in thoracolumbar burst fractures if the inferior endplate is intact (incomplete burst fractures) or features only a single simple split fracture line (burst-split fractures). If the two identified pitfalls are avoided, monosegmental ACR may be a viable alternative to bisegmental ACR in selected thoracolumbar burst fractures to spare a motion segment and to reduce the distance for bony fusion.

Combined anteroposterior fixation using a titanium cage versus solely posterior fixation for traumatic thoracolumbar fractures: A systematic review and meta-analysis

Study Design:

Systematic review with meta-analysis.

Objective:

Additional anterior stabilization might prevent posterior implant failure, but over time, the disadvantageous of bone grafts have become evident. The objective of this systematic review was to compare risks and advantages of additional anterior stabilization with a titanium cage to solely posterior fixation for traumatic thoracolumbar fractures.

Methods:

An electronic search was performed in the literature from 1980 to March 2016. Studies comparing only posterior with anteroposterior fixation by means of a titanium cage were included in this study. Data extraction and Cochrane risk of bias assessment were done by two independent authors. In addition, the PRISMA statement was followed, and the GRADE approach was used to present results.

Results:

Of the 1584 studies, two randomized controlled trials (RCTs) and one retrospective cohort study were included in the meta-analysis. The RCTs reported evidence of high quality that anteroposterior stabilization maintained better kyphosis correction than posterior stabilization alone. However, these results were neutralized in the meta-analysis by the cohort study. Implant failure was reported by one study, in the posterior group. No differences in follow-up visual analog scale scores, neurologic improvement, and complications were found. Operation time, blood loss, and hospital stay all increased in the anteroposterior group.

Conclusions:

Patients with a highly comminuted or unstable fracture could benefit from combined anteroposterior stabilization with a titanium cage, for some evidence suggests this prevents loss of correction. However, large randomized studies still lack. There is a risk of cage subsidence, and increased perioperative risks have to be considered when choosing the optimal treatment.

Biomechanical analysis of the thoracolumbar spine under physiological loadings: Experimental motion data corridors for validation of finite element models

Biomechanical studies that involve normal, injured or stabilized human spines are sometimes difficult to perform on large samples due to limited access to cadaveric human spines and biological variability. Finite element models alleviate these limitations due to the possibility of reusing the same model, whereas cadaveric spines can be damaged during testing, or have their mechanicals behaviour modified by fatigue, permanent deformation or structural failure. Finite element models need to be validated with experimental data to make sure that they represent the complex mechanical and physiological behaviour of normal, injured and stabilized spinal segments. The purpose of this study is to characterize the mechanical response of thoracolumbar spine segments with an analytical approach drawn from experimental measurements. A total of 24 normal and fresh cadaveric thoracolumbar spine segments (T11-L3), aged between 53 and 91 years, were tested in pure flexion/extension, lateral bending and axial torsion using a specific experimental setup. Measurements of global and intervertebral angle variations were performed using three-dimensional mark tracking methods. Load/angle curves for each loading were fitted by a logarithmic approach with two coefficients. The coefficients for the functions describing the response of the spinal segments are given and constitute predictive models from experimental data. This work provides data corridors of human thoracolumbar spine motion segments subjected to pure bending in the three physiological planes. These data could be very useful to validate finite element models of the human spine.

Treatment of Lumbar Split Fracture-Dislocation With Short-Segment or Long-Segment Posterior Fixation and Anterior Fusion

STUDY DESIGN

Retrospective analysis of 16 patients.

SUMMARY OF BACKGROUND DATA

The lumbar split fracture-dislocation is a rare but severe injury, which is type C1.2.1 fracture in the Association for the Study of Internal Fixation spine fracture classification. The axial compressive and torsional force shattered the vertebral body into 2 halves and displaced them rotationally. This kind of fracture is so highly unstable that the treatment is very challenging.

PURPOSE

The purpose of this study was to report and compare on clinical outcome and complications of patients with lumbar split fracture-dislocation which had been treated either short-segment or long-segment posterior fixation and anterior fusion.

MATERIALS AND METHODS

A total of 16 patients with acute, split fracture-dislocation of the lumbar spine from March 2000 to May 2009 in our department were recruited. Seven patients (group I) treated by long-segment posterior fixation (2 levels above and 2 below the fracture) and anterior corpectomy and strut grafting. With the improvement of surgical technique and instrument, 9 patients after August 2004 were treated by short-segment posterior fixation (1 level above and 1 below, and included the fractured vertebrae itself) and anterior discectomy and strut grafting. The intraoperative blood loss, operation time, complications of operation, time to achieve bony fusion, Frankel scale, Oswestry Disability index, and Visual Analogue Pain Scale the Cobb angle were collected and compared.

RESULTS

The mean follow-up was 33.4 months for group I and 36.2 months for group II. The operation time was 457.1 minutes in group I which was significantly longer than 240.0 minutes in group II. The total blood loss was for group I was 2001.4 mL (range, 1580-2500 mL) and for group II was 730.6 mL (range, 430-950 mL). There was no neurological deterioration after surgery in both group and no difference in neurological outcome between the 2 groups. The loss of correction in Cobb angle averaged at the final evaluation was 2 and 5 degrees for groups I and II, respectively. There was no radiologically visible pseudarthrosis. The postoperative Visual Analogue Pain Scale score was 3.3 and 2.7 for groups I and II, respectively. In the SF-36 survey, after surgery the domains Role physical and Bodily pain improved significantly only in group B (P<0.05 and P=0.06, respectively). Time to achieve bony fusion in group I was 7.9 months which was significantly longer than 3.8 months in group II. Complications included 3 urinary infections, 1 decubitus ulcer, and 1 superficial infection that were cured by antibiotics. Screw breakage was found in 1 patient in the group II.

CONCLUSIONS

The lumbar sagittal split fracture-dislocation is a rare but severe injury, which can be treated either with short-segment or long-segment posterior fixation and anterior fusion. The short construct with pedicle screws in the fractured vertebrae followed by the maneuver of rod derotation can obtain anatomic reduction, restoration of 3-column alignment, and decompress the affected neural elements by restoration of the normal canal dimension. It may be a better therapeutic option for the highly unstable lumbar fracture of C1.2.1.

Use of baited remote underwater video (BRUV) and motion analysis for studying the impacts of underwater noise upon free ranging fish and implications for marine energy management

Free-ranging individual fish were observed using a baited remote underwater video (BRUV) system during sound playback experiments. This paper reports on test trials exploring BRUV design parameters, image analysis and practical experimental designs. Three marine species were exposed to playback noise, provided as examples of behavioural responses to impulsive sound at 163-171dB re 1μPa (peak-to-peak SPL) and continuous sound of 142.7dB re 1μPa (RMS, SPL), exhibiting directional changes and accelerations. The methods described here indicate the efficacy of BRUV to examine behaviour of free-ranging species to noise playback, rather than using confinement. Given the increasing concern about the effects of water-borne noise, for example its inclusion within the EU Marine Strategy Framework Directive, and the lack of empirical evidence in setting thresholds, this paper discusses the use of BRUV, and short term behavioural changes, in supporting population level marine noise management.

Comparison Between Posterior Short-segment Instrumentation Combined With Lateral-approach Interbody Fusion and Traditional Wide-open Anterior-Posterior Surgery for the Treatment of Thoracolumbar Fractures

The aim of the study was to compare the radiographic and clinical outcomes between posterior short-segment pedicle instrumentation combined with lateral-approach interbody fusion and traditional anterior-posterior (AP) surgery for the treatment of thoracolumbar fractures.Lateral-approach interbody fusion has achieved satisfactory results for thoracic and lumbar degenerative disease. However, few studies have focused on the use of this technique for the treatment of thoracolumbar fractures.Inclusion and exclusion criteria were established. All patients who meet the above criteria were prospectively treated by posterior short-segment instrumentation and secondary-staged minimally invasive lateral-approach interbody fusion, and classified as group A. A historical group of patients who were treated by traditional wide-open AP approach was used as a control group and classified as group B. The radiological and clinical outcomes were compared between the 2 groups.There were 12 patients in group A and 18 patients in group B. The mean operative time and intraoperative blood loss of anterior reconstruction were significantly higher in group B than those in group A (127.1 ± 21.7 vs 197.5 ± 47.7 min, P < 0.01; 185.8 ± 62.3 vs 495 ± 347.4 mL, P < 0.01). Two of the 12 (16.7%) patients in group A experienced 2 surgical complications: 1 (8.3%) major and 1 (8.3%) minor. Six of the 18 (33%) patients in group B experienced 9 surgical complications: 3 (16.7%) major and 6 (33.3%) minor. There was no significant difference between the 2 groups regarding loss of correction (4.3 ± 2.1 vs 4.2 ± 2.4, P = 0.89) and neurological function at final follow-up (P = 0.77). In both groups, no case of instrumentation failure, pseudarthrosis, or nonunion was noted.Compared with the wide-open AP surgery, posterior short-segment pedicle instrumentation, combined with minimally invasive lateral-approach interbody fusion, can achieve similar clinical results with significant less operative time, blood loss, and surgical complication. This procedure seems to be a reasonable treatment option for selective patients with thoracolumbar fractures.

Contribution of Round vs. Rectangular Expandable Cage Endcaps to Spinal Stability in a Cadaveric Corpectomy Model

BACKGROUND

Expandable cages are gaining popularity in anterior reconstruction of the thoracolumbar spine following corpectomy as they can provide adjustable distraction and deformity correction. Rectangular, rather than circular, endcaps provide increased resistance to subsidence by spanning the apophyseal ring; however their impact on construct stability is not known. The objective of this study was to investigate the contribution of expandable corpectomy cage endcap shape (round vs. rectangular) and fixation method (anterior plate vs. posterior pedicle screws) to the stability of an L1 sub-total corpectomy construct.

METHODS

Eight fresh-frozen cadaveric specimens (T11-L3) were subjected to multi-directional flexibility testing to 6 N·m with a custom spine simulator. Test conditions were: intact, L1 sub-total corpectomy defect, expandable cage (round endcap) alone, expandable cage (round endcap) with anterior plate, expandable cage (round endcap) with bilateral pedicle screws, expandable cage (rectangular endcap) alone, expandable cage (rectangular endcap) with anterior plate, expandable cage (rectangular endcap) with bilateral pedicle screws. Range-of-motion across T12-L2 was measured with an optoelectronic system.

RESULTS

The expandable cage alone with either endcap provided significant stability to the corpectomy defect, reducing motion to intact levels in flexion-extension with both endcap types, and in lateral bending with rectangular endcaps. Round endcaps allowed greater motion than intact in lateral bending, and axial rotation ROM was greater than intact for both endcaps. Supplemental fixation provided the most rigid constructs, although there were no significant differences between instrumentation or endcap types.

CONCLUSIONS

These results suggest anterior-only fixation may be adequate when using an expandable cage in a sub-total corpectomy application and choice of endcap type may be driven by other factors such as subsidence resistance.

Impact of constrained dual-screw anchorage on holding strength and the resistance to cyclic loading in anterior spinal deformity surgery: a comparative biomechanical study

STUDY DESIGN

Biomechanical in vitro laboratory study.

OBJECTIVE

To compare the biomechanical performance of 3 fixation concepts used for anterior instrumented scoliosis correction and fusion (AISF).

SUMMARY OF BACKGROUND DATA

AISF is an ideal estimate for selective fusion in adolescent idiopathic scoliosis. Correction is mediated using rods and screws anchored in the vertebral bodies. Application of large correction forces can promote early weakening of the implant-vertebra interfaces, with potential postoperative loss of correction, implant dislodgment, and nonunion. Therefore, improvement of screw-rod anchorage characteristics with AISF is valuable.

METHODS

A total of 111 thoracolumbar vertebrae harvested from 7 human spines completed a testing protocol. Age of specimens was 62.9 ± 8.2 years. Vertebrae were potted in polymethylmethacrylate and instrumented using 3 different devices with identical screw length and unicortical fixation: single constrained screw fixation (SC fixation), nonconstrained dual-screw fixation (DNS fixation), and constrained dual-screw fixation (DC fixation) resembling a novel implant type. Mechanical testing of each implant-vertebra unit using cyclic loading and pullout tests were performed after stress tests were applied mimicking surgical maneuvers during AISF. Test order was as follows: (1) preload test 1 simulating screw-rod locking and cantilever forces; (2) preload test 2 simulating compression/distraction maneuver; (3) cyclic loading tests with implant-vertebra unit subjected to stepwise increased cyclic loading (maximum: 200 N) protocol with 1000 cycles at 2 Hz, tests were aborted if displacement greater than 2 mm occurred before reaching 1000 cycles; and (4) coaxial pullout tests at a pullout rate of 5 mm/min. With each test, the mode of failure, that is, shear versus fracture, was noted as well as the ultimate load to failure (N), number of implant-vertebra units surpassing 1000 cycles, and number of cycles and related loads applied.

RESULTS

Thirty-three percent of vertebrae surpassed 1000 cycles, 38% in the SC group, 19% in the DNS group, and 43% in the DC group. The difference between the DC group and the DNS group yielded significance (P = 0.04). For vertebrae not surpassing 1000 cycles, the number of cycles at implant displacement greater than 2 mm in the SC group was 648.7 ± 280.2 cycles, in the DNS group was 478.8 ± 219.0 cycles, and in the DC group was 699.5 ± 150.6 cycles. Differences between the SC group and the DNS group were significant (P = 0.008) as between the DC group and the DNS group (P = 0.0009). Load to failure in the SC group was 444.3 ± 302 N, in the DNS group was 527.7 ± 273 N, and in the DC group was 664.4 ± 371.5 N. The DC group outperformed the other constructs. The difference between the SC group and the DNS group failed significance (P = 0.25), whereas there was a significant difference between the SC group and the DC group (P = 0.003). The DC group showed a strong trend toward increased load to failure compared with the DNS group but without significance (P = 0.067). Surpassing 1000 cycles had a significant impact on the maximum load to failure in the SC group (P = 0.0001) and in the DNS group (P = 0.01) but not in the DC group (P = 0.2), which had the highest number of vertebrae surpassing 1000 cycles.

CONCLUSION

Constrained dual-screw fixation characteristics in modern AISF implants can improve resistance to cyclic loading and pullout forces. DC constructs bear the potential to reduce the mechanical shortcomings of AISF.

Six-year outcome of thoracoscopic ventral spondylodesis after unstable incomplete cranial burst fractures of the thoracolumbar junction: ventral versus dorso-ventral strategy

PURPOSE

The purpose of this study is to determine the long term-results after thoracoscopic spondylodesis particularly with respect to a ventral versus dorso-ventral treatment strategy.

METHODS

In this prospective cohort study, a follow-up examination was performed in 19 patients (seven men, 12 women, average age: 37.7 years, follow-up rate: 79 %), six years after ventral thoracoscopic spondylodesis of unstable, incomplete burst fractures. Nine patients received a ventral monosegmental spondylodesis with iliac crest bone graft. The other ten cases were treated dorso-ventrally, five undergoing a ventral monosegmental treatment with iliac crest bone graft; the other five a ventral bisegmental treatment with expandable titanium cage.

RESULTS

The complication rate was 15.7 %, the rate of revision of 10.5 %. No complication was related to the ventral thoracoscopic approach, whereas all of them were related to the iliac crest bone graft. The operative bisegmental kyphotic reduction was higher in the dorso-ventrally treated group. Afterwards, the loss of reduction was similar in both study groups. The mean VAS spine score summed up to more than 80 in both groups. The mean PCS scores were comparable to a normal healthy collective of the same age.

CONCLUSIONS

The ventral thoracoscopic approach to the spine seems to be a safe therapeutic strategy. A dorso-ventral treatment concept goes along with a higher operative reduction potential.

An in vitro biomechanical comparison of single-rod, dual-rod, and dual-rod with transverse connector in anterior thoracolumbar instrumentation

BACKGROUND

After thoracolumbar corpectomy, standard anterolateral instrumentation may consist of dual rods with cross-connectors. However, when the vertebral bodies are small or involved with disease, only 1 rod may be possible.

OBJECTIVE

To compare the biomechanics of an in vitro L1 corpectomy model using 1 rod, 2 rods, or 2 rods with 2 cross-connectors.

METHODS

Eight fresh frozen human cadaveric spines were potted from T9 to L3. Pure moments of 1.5, 3, and 4.5 Nm were applied, and the motion of the spine was measured using 3 infrared cameras. Loads were applied in flexion and extension, right and left lateral bending, and right and left axial rotation. Each spine was first tested in the intact state. After performing an L1 corpectomy and replacement with a carbon fiber reinforced polymer cage, 3 constructs were tested: single rod (1R), dual rod (2R), and dual rod with 2 transverse connectors (CC).

RESULTS

Analysis of variance suggests significant main effects of load (P < .0001), axis (P = .022), construct (P =.0019), and individual spine (P < .0001). Overall, the single-rod construct is significantly less rigid than the intact spine in axial rotation. There is no significant difference between the intact spine and either the dual-rod construct or the dual-rod cross-connector construct.

CONCLUSION

In our in vitro model of anterior spinal stabilization after corpectomy and grafting, a single-rod construct is significantly less rigid than the intact spine. Addition of a second rod returns the rigidity of the spine to the intact state. A dual-rod cross-connector construct is significantly more rigid than a single-rod construct.

Outcome after thoracoscopic ventral stabilisation of thoracic and lumbar spine fractures

BACKGROUND AND PURPOSE

Thoracoscopic-assisted ventral stabilisation for thoracolumbar fractures has been shown to be associated with decreased recovery time and less morbidity when compared with open procedures. However, there are a limited number of studies evaluating late clinical and radiological results after thoracoscopic spinal surgery.

METHODS

We performed an analysis of the late outcomes of thoracolumbar fractures after minimally invasive thoracoscopic ventral instrumentation. Between August 2003 and December 2008, 70 patients with thoracolumbar fractures (T5-L2) underwent ventral thoracoscopic stabilisation. Tricortical bone grafts, anterior plating systems (MACS-System), and cage implants were used for stabilisation. Outcomes measured include radiologic images (superior inferior endplate angle), Visual Analogue Scale (VAS), VAS Spine Score, quality of life scores SF-36 and Oswestry Disability Index (ODI).

RESULTS

Forty seven patients (67%, 47 out of 70) were recruited for the follow up evaluation (2.2 ± 1.5 years). Lower VAS Spine scores were calculated in patients with intra- or postoperative complications (44.7 (± 16.7) vs. 65.8 (± 24.5), p=0.0447). There was no difference in outcome between patients treated with bone graft vs. cage implants. Loss of correction was observed in both bone graft and titanium cage groups.

INTERPRETATION

The present study demonstrates diminished long-term quality of life in patients treated with thoracoscopic ventral spine when compared with the outcome of german reference population. In contrast to the other patients, those patients without intra-operative or post-operative complications were associated with improved outcome. The stabilisation method (bone graft versus spinal cage) did not affect the long-term clinical or radiographic results in this series.

6-Year follow-up of ventral monosegmental spondylodesis of incomplete burst fractures of the thoracolumbar spine using three cortical iliac crest bone grafts

INTRODUCTION

Autologous bone graft is the gold standard for vertebral body replacement. Currently, after modern implants for vertebral body replacement are available, controversies exist regarding the optimal implant strategy.

PATIENTS AND METHODS

Between 2002 and 2003, 17 patients were included in this study, all suffering from incomplete burst fractures of the thoracolumbar spine. All of them were treated by ventral monosegmental spondylodesis using iliac crest bone graft. The individual treatment strategy depended on the fracture situation and patient's condition. After an average of 74 months (range 66-84) a clinical and computer tomographic follow-up examination was performed in 14 patients (average age, 35.2 years) including VAS spine score and SF 36 score. Nine patients were treated ventral only five patients dorsoventrally.

RESULTS

Complete osseous consolidation was visible in nine, partial consolidation (>30 %) in four, and lysis in one patient, without any significant differences between ventral only or dorsoventral approach. After removal of the fixateur interne the level of consolidation improved in all patients, treated dorsoventrally. There was no significant correlation between percentage of osseous consolidation and the clinical follow-up parameters. After 6 years, 71 % of the patients suffered from persistent pain associated with the approach to the iliac crest. Two revision surgeries have been necessary.

CONCLUSION

High rates of osseous consolidation are visible 6 years after ventral spondylodesis by iliac crest bone grafts. A further improvement of consolidation can be expected after dorsal implant removal. But the surgical approach to the iliac crest is accompanied with a relevant complication rate.

Implications of the center of rotation concept for the reconstruction of anterior column lordosis and axial preloads in spinal deformity surgery

OBJECT

In thoracolumbar deformity surgery, anterior-only approaches are used for reconstruction of anterior column failures. It is generally advised that vertebral body replacements (VBRs) should be preloaded by compression. However, little is known regarding the impact of different techniques for generation of preloads and which surgical principle is best for restoration of lordosis. Therefore, the authors analyzed the effect of different surgical techniques to restore spinal alignment and lordosis as well as the ability to generate axial preloads on VBRs in anterior column reconstructions.

METHODS

The authors performed a laboratory study using 7 fresh-frozen specimens (from T-3 to S-1) to assess the ability for lordosis reconstruction of 5 techniques and their potential for increasing preloads on a modified distractable VBR in a 1-level thoracolumbar corpectomy. The testing protocol was as follows: 1) Radiographs of specimens were obtained. 2) A 1-level corpectomy was performed. 3) In alternating order, lordosis was applied using 1 of the 5 techniques. Then, preloads during insertion and after relaxation using the modified distractable VBR were assessed using a miniature load-cell incorporated in the modified distractable VBR. The modified distractable VBR was inserted into the corpectomy defect after lordosis was applied using 1) a lamina spreader; 2) the modified distractable VBR only; 3) the ArcoFix System (an angular stable plate system enabling in situ reduction); 4) a lordosizer (a customized instrument enabling reduction while replicating the intervertebral center of rotation [COR] according to the COR method); and 5) a lordosizer and top-loading screws ([LZ+TLS], distraction with the lordosizer applied on a 5.5-mm rod linked to 2 top-loading pedicle screws inserted laterally into the vertebra). Changes in the regional kyphosis angle were assessed radiographically using the Cobb method.

RESULTS

The bone mineral density of specimens was 0.72 ± 22.6 g/cm(2). The maximum regional kyphosis angle reconstructed among the 5 techniques averaged 9.7°-16.1°, and maximum axial preloads averaged 123.7-179.7 N. Concerning correction, in decreasing order the LZ+TLS, lordosizer, and ArcoFix System outperformed the lamina spreader and modified distractable VBR. The order of median values for insertion peak load, from highest to lowest, were lordosizer, LZ+TLS, and ArcoFix, which outperformed the lamina spreader and modified distractable VBR. In decreasing order, the axial preload was highest with the lordosizer and LZ+TLS, which both outperformed the lamina spreader and the modified distractable VBR. The technique enabling the greatest lordosis achieved the highest preloads. With the ArcoFix System and LZ+TLS, compression loads could be applied and were 247.8 and 190.6 N, respectively, which is significantly higher than the insertion peak load and axial preload (p < 0.05).

CONCLUSIONS

Including the ability for replication of the COR in instruments designed for anterior column reconstructions, the ability for lordosis restoration of the anterior column and axial preloads can increase, which in turn might foster fusion.

Biomechanical comparison of the end plate design of three vertebral body replacement systems

INTRODUCTION

Compression fractures at the thoracolumbar junction are frequently treated by reconstruction with vertebral body replacement systems. Modern cage implants have been developed which respect the anatomy and angulation of the adjacent bony endplates. The objective of this study was to investigate the biomechanical performance of anatomic endplate design and variable endplate angulation.

MATERIALS AND METHODS

Three cage systems [Hydrolift (HYL), Aesculap; Synex II (SYN), Synthes; Obelisc (OBC), Ulrich] were compared employing a composite bone substitute material at two levels of endplate angulation (0°, 3°). Their load-bearing capacity was assessed in a physiologic test with human vertebral specimens in a misalignment situation (3°). The HYL and SYN offered anatomically shaped endplates. The endplates of the HYL had variable angulation during insertion and were then mechanically fixated. The OBC had fixed and circular endplates. The load to failure and system stiffness were evaluated by an axial compression test. The bone mineral density (BMD) and the area of the bony endplates were measured via CT.

RESULTS

None of the mechanical properties differed between 0° and 3° for the HYL cage using bone substitute material, while the OBC lost 19% of the failure load (p = 0.001) and 55% of stiffness (p = 0.001) in case of misalignment. In human bone specimens, failure loads were comparable among all implants (p > 0.1) with the HYL showing the largest system stiffness (p < 0.05). Furthermore, a strong correlation between stiffness and BMD (R(2) = 0.82) and failure load and BMD (R(2) = 0.87) was found.

CONCLUSION

Anatomically shaped and continuously variable endplates provide mechanical advantages under imperfect alignment and may thus reduce secondary dislocation and the loss of correction. This is achieved by retaining an optimal contact area between the implant and the bony endplates. Conventional cage design with circular endplates offer adequate stability in optimal contact situations.

Anterior construct location following vertebral body metastasis reconstruction through a posterolateral transpedicular approach: does it matter?

Object

The posterolateral transpedicular approach (PTA) is a widely used method for the surgical treatment of vertebral body metastases. It is crucial to understand the optimal location of the anterior graft in terms of sound and durable reconstruction following PTA. The purpose of this study was to investigate whether postoperative construct stability is related to the location of anterior grafts.

Methods

The authors conducted a retrospective review of 45 cases of metastatic spine disease with epidural tumor extension in which patients underwent circumferential decompression and fusion by means of PTA. Mechanical (anterior construct stability), pain (visual analog scale score), and neurological (American Spinal Injury Association scale) outcomes were evaluated and correlated with the anterior graft location (lateral or central) and surgical approach (unilateral or bilateral), number of decompressed levels, types of anterior graft, screw density of posterior fixation (number of screws used divided by the number of pedicles spanned), and kyphotic angle change from the immediate postoperative period to the most recent follow-up.

Results

Seven of 45 constructs were judged unstable—5 with a lateral location of the anterior graft and 2 with a central location.

The anterior graft was located laterally in 31 cases (69%), centrally in 11 (24%), and bilaterally in 3 (7%). A unilateral approach was used in 33 cases and a bilateral approach in 12. Neither the location of the anterior graft nor the approach had a significant effect on the stability of the reconstructed spine (p > 0.05). There was a significant difference in construct stability between the single-level decompression group (33 patients) and the multiple-level decompression group (12 patients) (p = 0.0001). The types of anterior graft, screw density, and kyphotic angle change were not correlated to the mechanical outcome.

Conclusions

The anterior graft location showed no significant relationship to the final mechanical, pain, and neurological outcomes.

Quantifying intervertebral disc mechanics: a new definition of the neutral zone

Background

The neutral zone (NZ) is the range over which a spinal motion segment (SMS) moves with minimal resistance. Clear as this may seem, the various methods to quantify NZ described in the literature depend on rather arbitrary criteria. Here we present a stricter, more objective definition.

Methods

To mathematically represent load-deflection of a SMS, the asymmetric curve was fitted by a summed sigmoid function. The first derivative of this curve represents the SMS compliance and the region with the highest compliance (minimal stiffness) is the NZ. To determine the boundaries of this region, the inflection points of compliance can be used as unique points. These are defined by the maximum and the minimum in the second derivative of the fitted curve, respectively. The merits of the model were investigated experimentally: eight porcine lumbar SMS's were bent in flexion-extension, before and after seven hours of axial compression.

Results

The summed sigmoid function provided an excellent fit to the measured data (r² > 0.976). The NZ by the new definition was on average 2.4 (range 0.82-7.4) times the NZ as determined by the more commonly used angulation difference at zero loading. Interestingly, NZ consistently and significantly decreased after seven hours of axial compression when determined by the new definition. On the other hand, NZ increased when defined as angulation difference, probably reflecting the increase of hysteresis. The methods thus address different aspects of the load-deflection curve.

Conclusions

A strict mathematical definition of the NZ is proposed, based on the compliance of the SMS. This operational definition is objective, conceptually correct, and does not depend on arbitrarily chosen criteria.

Resultados do tratamento de fraturas crônicas pela via anterior em pacientes com osteoporose

OBJETIVO: Analisar os resultados da cirurgia de corpectomia e artrodese por via anterior nos pacientes com fratura tipo explosão da coluna toracolombar e com osteoporose, que foram submetidos a tratamento conservador prévio por no mínimo sete meses, sem melhora importante do quadro doloroso. MÉTODOS: Foram tratadas seis pacientes idosas com fratura-explosão da coluna toracolombar em um único nível, depois de, no mínimo, sete meses do trauma, pela via anterior, com corpectomia, uso de enxerto autólogo de costela e fixação com parafusos pediculares nos níveis adjacentes. A dor foi avaliada pela EVA no pré-operatório, três semanas, três meses, seis meses e um anos após a cirurgia. RESULTADO: As pacientes apresentaram melhora significativa da dor pós-operatória, com diminuição substancial do uso de medicação analgésica. CONCLUSÕES: Os autores recomendam a via anterior isolada como método de tratamento para fraturas tipo explosão crônicas em pacientes com osteoporose pela baixa taxa de complicações e pelos resultados satisfatórios encontrados.

In vitro biomechanics of an expandable vertebral body replacement with self-adjusting end plates

BACKGROUND CONTEXT

Unstable burst fractures of the thoracolumbar spine may be treated surgically. Vertebral body replacements (VBRs) give anterior column support and, when used with supplemental fixation, impart rigidity to the injured segments. Although some VBRs are expandable, device congruity to the vertebral end plates is imprecise and may lead to stress risers and device subsidence.

PURPOSE

The objective of this study was to compare the rigidity of a VBR that self-adjusts to the adjacent vertebral end plates versus structural bone allograft and with an unsupported anterior column in a traumatic burst fracture reconstruction model.

STUDY DESIGN

Biomechanical flexibility testing with rod strain measurement.

PATIENT SAMPLE

Twelve T11-L3 human spine segments.

OUTCOME MEASURES

Range of motion, neutral zone, and posterior fixation rod stress (moments).

METHODS

Flexibility testing was performed to ± 6 Nm in flexion-extension, lateral bending, and axial rotation on 12 intact human T11-L3 specimens. Burst fractures were created in L1, and flexibility testing was repeated in three additional states: subtotal corpectomy with posterior instrumentation (PI) only from T12 to L2, reconstruction with a femoral strut allograft and PI, and reconstruction with a VBR (with self-adjusting end plates) and PI. The PI consisted of pedicle screws and strain gage instrumented rods that were calibrated to measure rod stress via flexion-extension bending moments.

RESULTS

There was no statistical difference in range of motion or neutral zone between the strut graft and VBR constructs, which both had less motion than the PI-only construct in flexion/extension and torsion and were both less than the intact values in flexion/extension and lateral bending (p < .05). Posterior rod moments were significantly greater for the PI-only construct in flexion/extension relative to the strut graft and VBR states (p = .03).

CONCLUSIONS

This study, which simulated the immediate postoperative state, suggests that a VBR with self-adjusting end plate components has rigidity similar to the standard strut graft when combined with PI. Posterior rod stress was not significantly increased with this type of VBR compared with the strut graft reconstruction. The benefits of burst fracture stabilization using a self-adjusting VBR ultimately will not be known until long-term clinical studies are performed.

Operative treatment of 733 patients with acute thoracolumbar spinal injuries: comprehensive results from the second, prospective, Internet-based multicenter study of the Spine Study Group of the German Association of Trauma Surgery

The second, internet-based multicenter study (MCSII) of the Spine Study Group of the German Association of Trauma Surgery (Deutsche Gesellschaft für Unfallchirurgie) is a representative patient collection of acute traumatic thoracolumbar (T1-L5) injuries. The MCSII results are an update of those obtained with the first multicenter study (MCSI) more than a decade ago. The aim of the study was to assess and bring into focus: the (1) epidemiologic data, (2) surgical and radiological outcome, and (3) 2-year follow-up (FU) results of these injuries. According to the Magerl/AO classification, there were 424 (57.8%) compression fractures (A type), 178 (24.3%) distractions injuries (B type), and 131 (17.9%) rotational injuries (C type). B and C type injuries carried a higher risk for neurological deficits, concomitant injuries, and multiple vertebral fractures. The level of injury was located at the thoracolumbar junction (T11-L2) in 67.0% of the case. 380 (51.8%) patients were operated on by posterior stabilization and instrumentation alone (POSTERIOR), 34 (4.6%) had an anterior procedure (ANTERIOR), and 319 (43.5%) patients were treated with combined posteroanterior surgery (COMBINED). 65% of patients with thoracic (T1-T10) and 57% with lumbar spinal (L3-L5) injuries were treated with a single posterior approach (POSTERIOR). 47% of the patients with thoracolumbar junction (T11-L2) injuries were either operated from posterior or with a combined posterior-anterior surgery (COMBINED) each. Short angular stable implant systems have replaced conventional non-angular stable instrumentation systems to a large extent. The posttraumatic deformity was restored best with COMBINED surgery. T-spine injuries were accompanied by a higher number and more severe neurologic deficits than TL junction or L-spine injuries. At the same time T-spine injuries showed less potential for neurologic recovery especially in paraplegic (Frankel/AISA A) patients. 5% of all patients required revision surgery for perioperative complications. Follow-up data of 558 (76.1%) patients were available and collected during a 30-month period from 1 January 2004 until 31 May 2006. On average, a posterior implant removal was carried out in a total of 382 COMBINED and POSTERIOR patients 12 months after the initial surgery. On average, the rehabilitation process required 3-4 weeks of inpatient treatment, followed by another 4 months of outpatient therapy and was significantly shorter when compared with MCSI in the mid-1990s. From the time of injury until FU, 80 (60.6%) of 132 patients with initial neurological deficits improved at least one grade on the Frankel/ASIA Scale; 8 (1.3%) patients deteriorated. A higher recovery rate was observed for incomplete neurological injuries (73%) than complete neurological injuries (44%). Different surgical approaches did not have a significant influence on the neurologic recovery until FU. Nevertheless, neurological deficits are the most important factors for the functional outcome and prognosis of TL spinal injuries. POSTERIOR patients had a better functional and subjective outcome at FU than COMBINED patients. However, the posttraumatic radiological deformity was best corrected in COMBINED patients and showed significantly less residual kyphotic deformity (biseg GDW -3.8° COMBINED vs. -6.1° POSTERIOR) at FU (p = 0.005). The sagittal spinal alignment was better maintained when using vertebral body replacement implants (cages) in comparison to iliac strut grafts. Additional anterior plate systems did not have a significant influence on the radiological FU results. In conclusion, comprehensive data of a large patient population with acute thoracolumbar spinal injuries has been obtained and analyzed with this prospective internet-based multicenter study. Thus, updated results and the clinical outcome of the current operative treatment strategies in participating German and Austrian trauma centers have been presented. Nevertheless, it was not possible to answer all remaining questions to contradictory findings of the subjective, clinical outcome and corresponding radiological findings between different surgical subgroups. Randomized-controlled long-term investigations seem mandatory and the next step in future clinical research of Spine Study Group of the German Trauma Society.

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

OBJECT

Thoracolumbar corpectomy is a procedure commonly required for the treatment of various pathologies involving the vertebral body. Although the biomechanical stability of anterior reconstruction with plating has been studied, the biomechanical contribution of posterior instrumentation to anterior constructs remains unknown. The purpose of this study was to evaluate biomechanical stability after anterior thoracolumbar corpectomy and reconstruction with varying posterior constructs by measuring bending stiffness for the axes of flexion/extension, lateral bending, and axial rotation.

METHODS

Seven fresh human cadaveric thoracolumbar spine specimens were tested intact and after L-1 corpectomy and strut grafting with 4 different fixation techniques: anterior plating with bilateral, ipsilateral, contralateral, or no posterior pedicle screw fixation. Bending stiffness was measured under pure moments of +/- 5 Nm in flexion/extension, lateral bending, and axial rotation, while maintaining an axial preload of 100 N with a follower load. Results for each configuration were normalized to the intact condition and were compared using ANOVA.

RESULTS

Spinal constructs with anterior-posterior spinal reconstruction and bilateral posterior pedicle screws were significantly stiffer in flexion/extension than intact spines or spines with anterior plating alone. Anterior plating without pedicle screw fixation was no different from the intact spine in flexion/extension and lateral bending. All constructs had reduced stiffness in axial rotation compared with intact spines.

CONCLUSIONS

The addition of bilateral posterior instrumentation provided significantly greater stability at the thoracolumbar junction after total corpectomy than anterior plating and should be considered in cases in which anterior column reconstruction alone may be insufficient. In cases precluding bilateral posterior fixation, unilateral posterior instrumentation may provide some additional stability.

Anterior-only stabilization using plating with bone structural autograft versus titanium mesh cages for two- or three-column thoracolumbar burst fractures: a prospective randomized study

STUDY DESIGN

A randomized, controlled follow-up study to review patients with acute thoracolumbar burst fractures treated by anterior instrumentation and reconstruction.

OBJECTIVE

The objective of this study was to evaluate the results of anterior instrumentation in the treatment of thoracolumbar burst fractures and to determine whether anterior-only approach would be sufficient for highly unstable burst fractures. In this prospective follow-up study, we also compared the results of anterior reconstruction with structural grafting and with titanium mesh cage in a randomized fashion.

SUMMARY OF BACKGROUND DATA

Anterior decompression and reconstruction supplemented with instrumentation is generally believed to be superior to fixation with posterior pedicle screw instrumentation for a highly unstable burst fracture, but the indications and methods for anterior approach has not been fully documented.

METHODS

A total of 65 patients undergoing anterior plating for a thoracolumbar burst fracture with a load-sharing score of 7 or more between 2000 and 2003 were included this study. They were randomized to receive iliac crest autograft (group A, n = 32) or titanium mesh cages (group B, n = 33). The patients were similar in the distribution of 3-column injuries (n = 8 in group A vs. n = 9 in group B). During the minimum 4-year (range, 4-7 years) follow-up period, all patients were prospectively evaluated for clinical and radiologic outcomes. The Frankel scale, the ASIA motor score, and the Short Form 36 were used for clinical evaluation, whereas the fusion status and the loss of kyphosis correction for the local kyphosis angle were examined for radiologic outcome.

RESULTS

All patients in this study achieved solid fusion, with significant neurologic improvement and no significant correction loss as defined by loss of kyphosis correction. The clinical and radiologic results were not significantly different (P > 0.05) at all time points between the 2 groups A and B. Twenty-six of 32 patients in group A still complained of donor site pain to some degree at the final follow-up. No significant impact of 3-column injuries (P > 0.05) were identified on the results for all comparisons.

CONCLUSION

Anterior-only instrumentation and reconstruction with structural autograft or titanium mesh cages is sufficient for surgical treatment of thoracolumbar burst fractures with a load-sharing score of > or = 7 and even with 3-column injuries.

Long-term investigation of nonsurgical treatment for thoracolumbar and lumbar burst fractures: an outcome analysis in sight of spinopelvic balance

The nonsurgical treatment of thoracolumbar (TLB) and lumbar burst (LB) fractures remains to be of interest, though it is not costly and avoids surgical risks. However, a subset of distinct burst fracture patterns tend to go with a suboptimal radiographic and clinical long-term outcome. Detailed fracture pattern and treatment-related results in terms of validated outcome measures are still lacking. In addition, there are controversial data on the impact of local posttraumatic kyphosis that is associated, in particular, with nonsurgical treatment. The assessment of global spinal balance following burst fractures has not been assesed, yet. Therefore, the current study intended to investigate the radiographical and clinical long-term outcome in neurologically intact patients with special focus on the impact of regional posttraumatic kyphosis, adjacent-level compensatoric mechanisms, and global spine balance on the clinical outcome. For the purpose of a homogenous sample, strong in- and exclusion criteria were applied that resulted in a final study sample of 21 patients with a mean follow-up of 9.5 years. Overall, clinical outcome evaluated by validated measures was diminished, with 62% showing a good or excellent outcome and 38% a moderate or poor outcome in terms of the Greenough Low Back Outcome Scale. Notably, vertebral comminution in terms of the load-sharing classification, posttraumatic kyphosis, and an overall decreased lumbopelvic lordosis showed a significant effect on clinical outcome. A global and segmental curve analysis of the spine T9 to S1 revealed significant alterations as compared to normals. But, the interdependence of spinopelvic parameters was not disrupted. The patients' spinal adaptability to compensate for the posttraumatic kyphotic deformity varied in the ranges dictated by pelvic geometry, in particular the pelvic incidence. The study substantiates the concept that surgical reconstruction and maintenance of a physiologically shaped spinal curve might be the appropriate treatment in the more severely crushed TLB and LB fractures.

Endoscopy-assisted Approaches for Anterior Column Reconstruction after Pedicle Screw Fixation of Acute Traumatic Thoracic and Lumbar Fractures

Objective:

Surgical treatment of thoracic and lumbar vertebral body fractures combines instrumentation to stabilize the fracture and an anterior reconstruction to promote fusion of the fractured spine. The aim of the present study was to show that minimally invasive thoracoscopic or endoscopy-assisted approaches to the thoracic and lumbar spine are feasible for anterior column reconstruction.

Methods:

This prospective, single-center study included 83 consecutive patients harboring 100 acute thoracic and lumbar vertebral fractures. Patients' neurological status; preoperative, postoperative, and follow-up radiographic data; and surgical data were obtained.

Results:

Fractures ranged from T5 to L5. All fractures underwent posterior pedicle screw fixation followed by a thoracoscopic or endoscopy-assisted anterior approach for anterior column reconstruction to promote fusion. Ventral graft position was correct in 45 patients and acceptable in 37 patients; one patient required a surgical repositioning. Initial correction of kyphosis was 9 degrees; during follow-up (23 ± 11 mo), the mean loss of correction was 6 degrees. In 84 minimally invasive approaches, five conversions to an open approach were necessary. Complications included one case of L1 nerve root injury, two cases of transient neurological worsening, one case of posterior wound infection, and one case of pleural empyema.

Conclusion:

The minimally invasive endoscopic approach for anterior column reconstruction is a feasible strategy in the treatment of unstable thoracic and lumbar fractures. Fracture type and the material of the anterior graft can affect long-term maintenance of correction.