Stability potential of spinal instrumentations in tumor vertebral body replacement surgery

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.

Thoracic Spinal Stability and Motion Behavior Are Affected by the Length of Posterior Instrumentation After Vertebral Body Replacement, but Not by the Surgical Approach Type: An in vitro Study With Entire Rib Cage Specimens

Spinal tumors and unstable vertebral body fractures usually require surgical treatment including vertebral body replacement. Regarding primary stability, however, the best possible treatment depends on the spinal region. The purpose of this in vitro study was to evaluate the effects of instrumentation length and approach size on thoracic spinal stability including the entire rib cage. Six fresh frozen human thoracic spine specimens with intact rib cages (C7-L1) were loaded with pure moments of 5 Nm in flexion/extension, lateral bending, and axial rotation, while monitoring the relative motions of all spinal segments using optical motion tracking. The specimens were tested (1) in the intact condition, followed by testing after vertebral body replacement at T6 level using a unilateral approach combined with (2) long instrumentation (T4-T8) and (3) short instrumentation (T5-T7) as well as a bilateral approach combined with (4) long and (5) short instrumentation. Significant increases of the range of motion (p < 0.05) were found in the entire thoracic spine (T1-T12) using the bilateral approach and short instrumentation in primary flexion/extension and in secondary axial rotation during primary lateral bending compared to both conditions with long instrumentation, as well as in secondary lateral bending during primary axial rotation compared to unilateral approach and long instrumentation. Compared to the intact condition, the range of motion was significantly decreased using unilateral approach and long instrumentation in flexion extension and secondary lateral bending during primary axial rotation, as well as using bilateral approach and long instrumentation in lateral bending. On the segmental level, the range of motion was significantly increased at T4-T5 level in lateral bending using unilateral approach and short instrumentation and significantly decreased using bilateral approach and long instrumentation compared to their respective previous conditions. Regardless of the approach type, which did not affect thoracic spinal stability in the present study, short instrumentation overall shows sufficient primary stability in the mid-thoracic spine with intact rib cage, while creating considerably more instability compared to long instrumentation, potentially being of importance regarding long-term implant failure. Moreover, short instrumentation could affect adjacent segment disease due to increased motion at the upper segmental level.

Biomechanical Study of a Novel, Expandable, Non-Metallic and Radiolucent CF/PEEK Vertebral Body Replacement (VBR)

Vertebral body replacement is well-established to stabilize vertebral injuries due to trauma or cancer. Spinal implants are mainly manufactured by metallic alloys; which leads to artifacts in radiological diagnostics; as well as in radiotherapy. The purpose of this study was to evaluate the biomechanical data of a novel carbon fiber reinforced polyetheretherketone (CF/PEEK) vertebral body replacement (VBR). Six thoracolumbar specimens were tested in a six degrees of freedom spine tester. In all tested specimens CF/PEEK pedicle screws were used. Two different rods (CF/PEEK versus titanium) with/without cross connectors and two different VBRs (CF/PEEK prototype versus titanium) were tested. In lateral bending and flexion/extension; range of motion (ROM) was significantly reduced in all instrumented states. In axial rotation; the CF/PEEK combination (rods and VBR) resulted in the highest ROM; whereas titanium rods with titanium VBR resulted in the lowest ROM. Two cross connectors reduced ROM in axial rotation for all instrumentations independently of VBR or rod material. All instrumented states in all planes of motion showed a significantly reduced ROM. No significant differences were detected between the VBR materials in all planes of motion. Less rigid CF/PEEK rods in combination with the CF/PEEK VBR without cross connectors showed the smallest reduction in ROM. Independently of VBR and rod material; two cross connectors significantly reduced ROM in axial rotation. Compared to titanium rods; the use of CF/PEEK rods results in higher ROM. The stiffness of rod material has more influence on the ROM than the stiffness of VBR material.

Analysis of the spinal nerve roots in relation to the adjacent vertebral bodies with respect to a posterolateral vertebral body replacement procedure

OBJECTIVE

This study aims to improve the understanding of the anatomic variations along the thoracic and lumbar spine encountered during an all-posterior vertebrectomy, and reconstruction procedure. This information will help improve our understanding of human spine anatomy and will allow better planning for a vertebral body replacement (VBR) through either a transpedicular or costotransversectomy approach.

SUMMARY OF BACKGROUND DATA

The major challenge to a total posterior approach vertebrectomy and VBR in the thoracolumbar spine lies in the preservation of important neural structures.

METHODS

This was a retrospective analysis. Hundred normal magnetic resonance imaging (MRI) spinal studies (T1-L5) on sagittal T2-weighted MRI images were studied to quantify: (1) mid-sagittal vertebral body (VB) dimensions (anterior, midline, and posterior VB height), (2) midline VB and associated intervertebral discs height, (3) mean distance between adjacent spinal nerve roots (DNN) and mean distance between the inferior endplate of the superior vertebrae to its respective spinal nerve root (DNE), and (4) posterior approach expansion ratio (PAER).

RESULTS

(1) The mean anterior VB height gradually increased craniocaudally from T1 to L5. The mean midline and posterior VB height showed a similar pattern up to L2. Mean posterior VB height was larger than the mean anterior VB height from T1 to L2, consistent with anterior wedging, and then measured less than the mean anterior VB height, indicating posterior wedging. (2) Midline VB and intervertebral disc height gradually increased from T1 to L4. (3) DNN and DNE were similar, whereby they gradually increased from T1 to L3. (5) Mean PAER varied between 1.69 (T12) and 2.27 (L5) depending on anatomic level.

CONCLUSIONS

The dimensions of the thoracic and lumbar vertebrae and discs vary greatly. Thus, any attempt at carrying out a VBR from a posterior approach should take into account the specifications at each spinal level.

Single-Stage Posterolateral Transpedicular Approach With 360-Degree Stabilization and Vertebrectomy in Primary and Metastatic Tumors of the Spine

OBJECTIVE

Currently, anterior, posterior, or combined approaches are used in various spinal disorders; however, a single-stage posterolateral transpedicular approach with 360° stabilization and vertebrectomy provides better results for spinal tumors.

METHODS

We evaluated the age, sex distribution, presenting symptoms, neurologic examination findings according to the pre- and postoperative Frankel classification, pre- and postoperative VAS pain scores, preoperatively administered medical therapies, pre- and postoperative corset use, level of the lesion, levels of previous surgical interventions, root ligation (if performed), results of the primary disease, hospitalization duration (after the operation), postoperative complications (if any), postoperative follow-up duration, and postoperative survival duration of 22 patients.

RESULTS

We observed that primary bone tumors were localized in the lumbar (75%) and thoracic regions (25%) and that metastatic tumors were localized in the thoracic (77.78%) and lumbar regions (22.22%). The VAS and Frankel scores of the 22 patients who were included in the study revealed that this surgical treatment modality was associated with statistically significant improvements in test scores (P < 0.001). No ribcage dislocation was observed. In 1 patient (4.54%), a neurologic deficit developed. Two patients (9.09%) required revision because of screw malposition.

CONCLUSIONS

In spinal tumors, 360° fusion performed via a posterolateral approach is a less risky, relatively safe, and less invasive method. This method, which reduces the risks of anesthesia and internal problems and decreases cost, is an essential technique for decreasing hospitalization duration, improving pain levels, and achieving faster mobilization and faster initiation of radiotherapy and chemotherapy.

Efficacy of Titanium Mesh Cages for Anterior Column Reconstruction after Thoracolumbar Corpectomy

STUDY DESIGN

This retrospective study was conducted to determine the safety and efficacy of titanium cage reconstruction and anterior plating after thoracolumbar corpectomy.

PURPOSE

To study the clinical and radiological outcome of anterior column reconstruction after thoracolumbar corpectomy.

OVERVIEW OF LITERATURE

Anterior column reconstruction aims to optimize neural decompression with adequate stabilization.

METHODS

A series of 16 patients underwent reconstruction after thoracolumbar corpectomy to treat injury due to trauma (n=10), tuberculosis (n=3), and tumor (n=3). The average duration of follow-up was 18 months (range, 8-58 months). The degree of kyphosis, construct height, and the subsidence of the cage in relation to the vertebral endplates were measured. The approach was thoracoabdominal in 10 cases and retroperitoneal in 6 cases.

RESULTS

Four patients were neurologically intact with Frankel grade E on admission, and all remained intact postoperatively. Of the 6 patients with Frankel grade D, all fully recovered full motor and sensory functions. Of the 6 patients with Frankel grade C, three improved one grade and the other three improved two grades. The mean height of the vertebra before surgery was 41 mm and the mean construct height immediately after surgery and at follow-up was 47 mm and 44 mm, respectively. Solid fusion was observed in all patients. The sagittal alignment of the fractured segment was restored immediately after surgery as a significant decrease in the local kyphotic angle.

CONCLUSIONS

Anterior instrumentation is an effective and safe treatment for thoracolumbar instability with satisfactory clinical and radiological outcomes.

A novel approach for biomechanical spine analysis: Mechanical response of vertebral bone augmentation by kyphoplasty to stabilise thoracolumbar burst fractures

Kyphoplasty has been shown as a well-established technique for spinal injuries. This technique allows a vertebral bone augmentation with a reduction of morbidity and does not involve any adjacent segment immobilisation. There is a lack of biomechanical information resulting in major gaps of knowledge such as: the evaluation of the "quality" of stabilisation provided by kyphoplasty as a standalone procedure in case of unstable fracture. Our objective is to analyse biomechanical response of spine segments stabilised by Kyphoplasty and PMMA cement after experiencing burst fractures. Six fresh-frozen cadaveric spine specimens constituted by five vertebra (T11-L3) and four disks were tested. A specific loading setup has been developed to impose pure moments corresponding to loadings of flexion-extension, lateral bending and axial rotation. Tests were performed on each specimen in an intact state and post kyphoplasty following a burst fracture. Strain measurements and motion variations of spinal unit are measured by a 3D optical method. Strain measurements on vertebral bodies after kyphoplasty shows a great primary stabilisation. Comparisons of mobility and angles variations between the intact and post kyphoplasty states do not highlight significant difference. Percutaneous kyphoplasty offers a good primary stability in case of burst fracture. Kinematics analysis during physiological movements shows that this stabilisation solution preserve disk mobility in each adjacent spinal unit.

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.

Is lateral stabilization enough in thoracolumbar burst fracture reconstruction? A biomechanical investigation

BACKGROUND CONTEXT

Traditional reconstruction for burst fractures involves columnar support with posterior fixation at one or two levels cephalad/caudad; however, some surgeons choose to only stabilize the vertebral column.

PURPOSE

The aim was to distinguish biomechanical differences in stability between a burst fracture stabilized through a lateral approach using corpectomy spacers of different end plate sizes with and without integrated screws and with and without posterior fixation.

STUDY DESIGN/SETTING

This was an in vitro biomechanical study assessing thoracolumbar burst fracture stabilization.

METHODS

Six human spines (T11-L3) were tested on a six-degrees-of-freedom simulator enabling unconstrained range of motion (ROM) at ±6 N·m in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) after a simulated burst fracture at L1. Expandable corpectomy spacers with/without integrated screws (Fi/F; FORTIFY Integrated/FORTIFY; Globus Medical, Inc., Audubon, PA, USA) were tested with different end plate sizes (21×23 mm, 22×40-50 mm). Posterior instrumentation (PI) via bilateral pedicle screws and rods was used one level above and one level below the burst fracture. Lateral plate (LP) fixation was tested. Devices were tested in the following order: intact; Fi21×23; Fi21×23+PI; F21×23+PI+LP; F21×23+LP; F22×40-50+LP; F22×40-50+PI+LP; Fi22×40-50+PI; Fi22×40-50.

RESULTS

In FE and AR, constructs without PI showed no significant difference (p<.05) in stability compared with intact. In LB, F22×40-50+LP showed a significant increase in stability relative to intact, but no other construct without PI reached significance. In FE and LB, circumferential constructs were significantly more stable than intact. In AR, no construct showed significant differences in motion when compared with the intact condition.

CONCLUSIONS

Constructs without posterior fixation were the least stable of all tested constructs. Circumferential fixation provided greater stability in FE and LB than lateral fixation and intact. Axial rotation showed no significant differences in any construct compared with the intact state.

Single posterior approach for circumferential decompression and anterior reconstruction using cervical trabecular metal mesh cage in patients with metastatic spinal tumour

Background

The goal of surgical management of metastatic spinal tumours is to remove the tumour mass, restore spinal stability and alignment, and provide a better quality of life. A single posterior transpedicular approach, with circumferential decompression, for anterior reconstruction has been advocated to reduce the risk of complication and morbidity associated with a combined anterior-posterior approach. The purpose of our study was to evaluate the clinical outcomes of patients who underwent a single posterior approach for anterior reconstruction at our institution to determine the feasibility and effectiveness of the approach, including the use of a cervical trabecular metal (TM) mesh cage as a vertebral body replacer. As a secondary aim, we evaluated the effect of accumulated experience with the surgical approach on clinical outcomes.

Methods

Twenty consecutive cases of single posterior approach were identified from a retrospective review of spinal surgeries performed at our institution between January 2009 and December 2012. Information on the following clinical outcomes was retrieved from the medical charts for analysis: visual analogue pain score (VAS); neurological status, classified on the Frankel scale; vertebral body reconstruction; spinal alignment, using Cobb’s angle; operative time; volume of blood loss; complications; and the modified Brodsky criteria score, which was used to classify functional recovery as excellent, good, fair, or poor.

Results

Pre- to post-surgical evaluation of outcomes demonstrated a significant decrease in pain (p < 0.001), improved spinal alignment, with a mean correction angle of 12° (range, 3°–29°), and higher Frankel score (p < 0.001). No severe complications were identified, including deep surgical infection or neurologic deterioration. Eighteen patients achieved good to excellent outcomes, based on the modified Brodsky criteria (p < 0.001), with two patients dying within 9 and 11 months of their surgery. Accumulated surgical experience reduced operative time and intraoperative blood loss (p ≤ 0.007).

Conclusions

A single posterior approach provided good to excellent clinical and functional outcomes. Based on this evidence, we propose that a posterior approach provides a feasible alternative to the combined posterior-anterior approach for managing patients with metastatic spinal tumours.

Properties of an interspinous fixation device (ISD) in lumbar fusion constructs: a biomechanical study

BACKGROUND

Segmental fixation improves fusion rates and promotes patient mobility by controlling instability after lumbar surgery. Efforts to obtain stability using less invasive techniques have lead to the advent of new implants and constructs. A new interspinous fixation device (ISD) has been introduced as a minimally invasive method of stabilizing two adjacent interspinous processes by augmenting an interbody cage in transforaminal interbody fusion. The ISD is intended to replace the standard pedicle screw instrumentation used for posterior fixation.

PURPOSE

The purpose of this study is to compare the rigidity of these implant systems when supplementing an interbody cage as used in transforaminal lumbar interbody fusion.

STUDY DESIGN

An in vitro human cadaveric biomechanical study.

METHODS

Seven human cadaver spines (T12 to the sacrum) were mounted in a custom-designed testing apparatus, for biomechanical testing using a multiaxial robotic system. A comparison of segmental stiffness was carried out among five conditions: intact spine control; interbody spacer (IBS), alone; interbody cage with ISD; IBS, ISD, and unilateral pedicle screws (unilat); and IBS, with bilateral pedicle screws (bilat). An industrial robot (KUKA, GmbH, Augsburg, Germany) applied a pure moment (±5 Nm) in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) through an anchor to the T12 vertebral body. The relative vertebral motion was captured using an optoelectronic camera system (Optotrak; Northern Digital, Inc., Waterloo, Ontario, Canada). The load sensor and the camera were synchronized. Maximum rotation was measured at each level and compared with the intact control. Implant constructs were compared with the control and with each other. A statistical analysis was performed using analysis of variance.

RESULTS

A comparison between the intact spine and the IBS group showed no significant difference in the range of motion (ROM) in FE, LB, or AR for the operated level, L3-L4. After implantation of the ISD to augment the IBS, there was a significant decrease in the ROM of 74% in FE (p<.001) but no significant change in the ROM in LB and AR. The unilat construct significantly reduced the ROM by 77% compared with FE control (p<.001) and by 55% (p=.002) and 42% (p=.04) in LB and AR, respectively, compared with control. The bilat construct reduced the ROM in FE by 77% (p<.001), LB by 77% (p=.001), and AR by 65% (p=.001) when compared with the control spine. There was no statistically significant difference in the ROM in FE among the stand-alone ISD, unilat, and bilat constructs. However, in both LB and AR, the unilat and the bilat constructs were significantly stiffer (reduction in the ROM) than the ISD and the IBS combination. The ISD stability in LB and AR was not different from the intact control with no instrumentation at all. There was no statistical difference between the stability of the unilat and the bilat constructs in any direction. However, LB and AR in the unilat group produced a mean rotation of 3.83°±3.30° and 2.33°±1.33°, respectively, compared with the bilat construct that limited motion to 1.96°±1.46° and 1.39°±0.73°. There was a trend suggesting that the bilat construct was the most rigid construct.

CONCLUSIONS

In FE, the ISD can provide lumbar stability comparable with Bilat instrumentation. It provides minimal rigidity in LB and AR when used alone to stabilize the segment after an IBS placement. The unilat and the more typical bilat screw constructs were shown to provide similar levels of stability in all directions after an IBS placement, though the bilat construct showed a trend toward improved stiffness overall.

Comparison of expandable and fixed interbody cages in a human cadaver corpectomy model, Part I: endplate force characteristics

Object

Expandable cages are becoming more popular due in large part to their versatility, but subsidence and catastrophic failure remain a concern. One of the proposed reasons of failure is edge loading of the endplate caused by a mismatch between the sagittal alignment of the motion segment and cage. This in vitro analysis investigates the endplate forces characteristic of expandable and fixed interbody cages in a single-level human cadaver corpectomy model.

Methods

Ten human thoracolumbar spines (T10–L2, L3–5) were biomechanically evaluated following a single-level corpectomy that was reconstructed with an expandable or fixed cage. Fixed cages were deployed with the best-fitting end cap combination, whereas expandable cages were deployed in normal, hypolordotic, and hyperlordotic alignment scenarios. The endplate forces and contact area were measured with a pressure measurement system, and the expansion torque applied by the surgeon was measured with a custom-made insertion device.

Results

The contact areas of the expandable cages were, in general, higher than those of the fixed cages. The endplate forces of the expandable cages were similar to those of the fixed cages in the normal alignment scenario. Higher endplate forces were observed in the hyperlordotic scenario, whereas the endplate forces in the hypolordotic and normal alignment scenarios were similar. There was no correlation with the expansion torque and the final endplate forces.

Conclusions

Expandable cages resulted in consistently higher contact area and endplate forces when compared with the fixed cages. Because the expansion torque does not correlate with the final endplate forces, surgeons should not rely solely on tactile feedback during deployment of these cages.

The posterior transpedicular approach for circumferential decompression and instrumented stabilization with titanium cage vertebrectomy reconstruction for spinal tumors: consecutive case series of 50 patients

STUDY DESIGN

A retrospective case series.

OBJECTIVE

To demonstrate the feasibility, safety, and results of the posterior transpedicular approach for circumferential decompression and instrumented reconstruction of thoracolumbar spinal tumors.

SUMMARY OF BACKGROUND DATA

Patients presenting with spinal tumor disease requiring 3-column instrumented stabilization are typically treated with a combined anterior and posterior surgical approach. However, circumferential decompression and instrumented stabilization may also be achieved through a single-stage, midline posterior transpedicular approach.

METHODS

Fifty consecutive patients (27 women and 23 men) underwent surgery between 2003 and 2010 at a single institution by the senior author. Mean age was 55.9 years (range, 25-79 yr).Single or multilevel, contiguous subtotal vertebrectomy was performed ranging from T1 to L4 (38 thoracic and 12 lumbar). Three-column spinal stabilization was achieved using posterior pedicle screw fixation and vertebral body reconstruction, with a titanium cage introduced through the posterior transpedicular route. The mean follow-up period was 17 months (range, 1-54 mo).

RESULTS

The mean operating time was 4.2 hours. The mean estimated blood loss for a subgroup of 9 patients with hypervascular tumor pathology was 3933 mL (range, 2700-5800 mL). The mean blood loss in the remaining 41 patients was 1262 mL (range, 250-2500 mL).Postoperative neurological status was maintained or improved in all patients. Mean postoperative stay was 7.7 days (range, 3-12 d). At last review, 14 patients were alive, with a mean survival of 36 months (range, 13-71 mo). The mean survival for the 36 patients who died was 19 months (range, 2 weeks to 54 mo).

CONCLUSION

This is the largest reported series of patients with spinal tumor disease undergoing circumferential decompression and 3-column instrumented stabilization through the posterior transpedicular approach.This surgical approach provides sufficient access for safe and effective circumferential decompression and stabilization, with reduced complications compared with costotransversectomy or combined anterior transcavitary and posterior approaches.

Biomechanical analysis of a new expandable vertebral body replacement combined with a new polyaxial antero-lateral plate and/or pedicle screws and rods

PURPOSE

Restoration of the anterior spinal profile and regular load-bearing is the main goal treating anterior spinal defects in case of fracture. Over the past years, development and clinical usage of cages for vertebral body replacement have increased rapidly. For an enhanced stabilization of rotationally unstable fractures, additional antero-lateral implants are common. The purpose of this study was the evaluation of the biomechanical behaviour of a recently modified, in situ distractible vertebral body replacement (VBR) combined with a newly developed antero-lateral polyaxial plate and/or pedicle screws and rods using a full corpectomy model as fracture simulation.

METHODS

Twelve human spinal specimens (Th12-L4) were tested in a six-degree-of-freedom spine tester applying pure moments of 7.5 Nm to evaluate the stiffness of three different test instrumentations using a total corpectomy L2 model: (1) VBR+antero-lateral plate; (2) VBR, antero-lateral plate+pedicle screws and rods and (3) VBR+pedicle screws and rods.

RESULTS

In the presented total corpectomy defect model, only the combined antero-posterior instrumentation (VBR, antero-lateral plate+pedicle screws and rods) could achieve higher stiffness in all three-movement planes than the intact specimen. In axial rotation, neither isolated anterior instrumentation (VBR+antero-lateral plate) nor isolated posterior instrumentation (VBR+pedicle screws and rods) could stabilize the total corpectomy compared to the intact state.

CONCLUSIONS

For rotationally unstable vertebral body fractures, only combined antero-posterior instrumentation could significantly decrease the range of motion (ROM) in all motion planes compared to the intact state.

Mechanical stability analysis of reference clamp fixation in computer-assisted spine surgery

BACKGROUND

Pedicle screw misplacement is a common complication, while 7% may result in neurological complications. Computer-assisted navigation improves the rate of ideally placed screws. Inappropriate reference marker attachment can cause major problems in the outcome and duration of surgery.

OBJECTIVE

To improve fixation of reference bases by comparing different designs of spine clamps and measuring their stability against the relevant thoracic and lumbar anatomy.

METHODS

Force needed to dislocate the clamp from the processus spinosus using defined fixation of 0.79, 0.90 and 1.02 Nm torque was evaluated. Force transmission from clamp to the processus spinosus was also examined. Artificial thoracic and lumbar vertebral bodies were used for attaching spine clamps of three different designs. An instrument transmitted linear force onto the reference clamp and recorded the force when dislocation occurred. Another device determined transmitted force for each clamp utilizing 0.79, 0.90, 1.02, 1.13 and 1.24 Nm torque.

RESULTS

L-clamp had the most stable fixation in lumbar section for every torque and developed the greatest forces. These transmitted forces were similar to the less stable Y-design. I-design created the smallest forces and had the most stable fixation for thoracic spine. The Y- and the L-design caused a notably high number of fractures.

CONCLUSION

Great force leads to great stability, but also creates more fractures, favoring the use of smaller forces. Specific anatomy adaptation is important. Different clamp designs create different forces, while still differing in stability depending on their application in the thoracic or the lumbar spine.

Single stage corpectomy and instrumentation in the treatment of pathological fractures in the lumbar spine

PURPOSE

Corpectomy and implantation of titanium cages is standard in pathological fracture treatment but additional single ventral instrumentation remains controversial with regard to rotational stability.

METHODS

This study included 45 patients suffering from vertebral metastases with spinal stenosis, instability and/or neurological deficits secondary to pathological lumbar spine fractures and bone mineral density (BMD) ≥ 1.20 g/cm(2). The clinical results of a single stage anterior decompression with corpectomy defect restoration with titanium cage and single double rod system in patients were evaluated at mean 36 months postoperatively with follow-up neurological and radiological exams at three months then every six months. Evaluation of neurological recovery included grading following a modified Frankel scale. Contentment, disability and actual pain were evaluated using the visual analogue scale (VAS) and Oswestry disability index (ODI). BMD was measured using dual-energy X-ray absorptiometry (DXA).

RESULTS

Postoperative neurological evaluations showed improvement in all patients. In the radiological follow-up in 40 patients (89%) findings were similar compared to the postoperative control. In five patients (11%) a loss of correction at a mean of 8° degrees (Cobb angle) secondary to cage subsidence occurred. No breakage of the device or displacement of the instrumentation was seen. Overall the Frankel scale improved 0.65 points (p < 0.05) and the ODI improved 40.69 points (p < 0.05).

CONCLUSIONS

In lumbar spine fractures of metastatic origin with stenosis, instability and/or neurological deficit, a single stage ventral decompression and instrumentation in patients with BMD ≥ 1.20 g/cm(2) should be considered.

Comparison of allograft bone and titanium cages for vertebral body replacement in the thoracolumbar spine: a biomechanical study

BACKGROUND

When an anterior approach to repair a burst fracture is indicated, several devices can be used to restore spinal stability (eg, bone graft, free-standing titanium cage, and expandable titanium cage).

OBJECTIVE

We compare the biomechanical stability and prices of each of these systems.

MATERIALS AND METHODS

Eight fresh human cadaver T11 through L3 vertebral specimens were harvested and cleaned of soft tissues. T11-T12 and L2-L3 were fixed by screws. The fixed ends were then set in automotive body filler (Bondo). The prepared specimens were tested in the Biaxial Instron tester (8874, Norwood, MA) after a sequence of the following: intact, after the creation of an anterior corpectomy at L1, and after insertion of both of the 2 different titanium cages and the fibular graft. A titanium screw-and-plate anterolateral system was used to secure the construct (VANTAGE, Medtronic Sofamor Danek, Memphis, TN). The conditions of displacement testing were as follows: rotation (+/- 3.5 degrees ), flexion and extension, and left and right bending (+/- 3.5 mm). For each mode of testing, the stiffness was calculated.

RESULTS

The stiffness data, when statistically analyzed by repeated-measures analysis of variance (at P = .05 and power > 0.9), indicated no significant differences among these devices.

CONCLUSION

On the basis of this biomechanical study, the stiffness of the fibular graft was similar to that of the other metallic devices in this cadaver model.

A customized modular reference array clamp for navigated spine surgery

INTRODUCTION

The current authors have developed a modular system of reference array fixation which is tailored specifically to the spinal level being operated upon. They believe that this system may further increase the precision and accuracy of pedicle screw placement.

MATERIALS AND METHODS

Two formalin-fixed whole body cadavers were used for this study. For cervical spine evaluation of the reference clamp, four odontoid screws (two per cadaver) for C1/C2-fusion and four lateral mass screws (two per cadaver) were implanted. Following navigated screw placement with 2D and 3D fluoroscopic verification, insertion of two lateral mass screws was performed. In the same way, lumbar and thoracic pedicle screws were implanted. Two pedicle screws were placed at two levels of the lumbar and two levels of the thoracic areas giving an overall of 16 screws implanted (8 cervical, 4 thoracic, and 4 lumbar). Postoperative evaluation involved comparison of postoperative 3D scans and preoperative planning images. A simple classification system was used for evaluation of any deviation from the planned trajectory.

RESULTS

All pedicle screw placements were performed as planned without any technical problems. The reference array clamps remained in position at all the spinal levels at which they were employed with no loosening or displacement and no secondary damage to any of the spinous processes. Manual manipulation was performed but no displacement or slippage was observed. Image artefacts caused by the reference clamp were not significant as to obscure the area of interest. Both imaging modalities (Iso-C 3D and Vario 3D) generated sufficiently precise 3D images. There was no substantial difference in quality when those two systems were compared.

DISCUSSION

Insufficient fixation of the reference clamp can lead to failure and complications. To date, no reference clamp systems have been developed specifically for navigated spine surgery.

CONCLUSIONS

Stable reference array fixation is a critical step in navigated surgery. To date, the same reference clamps have been applied to the spinal anatomy as have been developed originally for the appendicular skeleton. The current investigators have developed a novel modular clamp and have demonstrated its efficacy in a cadaveric model.

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.

Extent of corpectomy determines primary stability following isolated anterior reconstruction in a thoracolumbar fracture model

BACKGROUND

Based on the development of minimal-invasive techniques and introduction of new implants enabling secure reconstruction an increasing number of patients are treated by isolated anterior column surgery. Most biomechanical studies dealing with thoracolumbar fracture models use worst-case scenarios of complete corpectomies to simulate vertebral body defects neglecting the influence of remaining cortical bone in partial corpus instability. Using a standardized partial and total corpectomy model we investigated the effect of the extent of corpectomy on stiffness in an anterior reconstruction model.

METHODS

Twelve human thoracolumbar specimens (Th11-L3) were loaded in a spine simulator with pure moments in the three motion planes. Following intact testing partial corp- and discectomy and later complete corpectomy of L1 were performed. Defects were instrumented by vertebral body replacements and additional anterior plating systems bridging the defect from Th12 to L2. Intersegmental rotations were measured between Th12 and L2.

FINDINGS

Significantly (P<0.05) increased range of motion was found in reconstructions of total compared to partial corpectomy. Total corpectomy reconstructions showed solely in lateral bending a significant reduction of range of motion compared to the intact state, while in axial rotation and flexion/extension it was significantly increased. Partial corpectomy reconstructions resulted in significantly reduced range of motion for lateral bending and flexion/extension compared to the intact specimen.

INTERPRETATION

Isolated anterior reconstructions of the thoracolumbar spine revealed sufficient stiffness in the partial vertebral corpus defect. In contrast, total corpectomy did not show an adequate stiffness. Especially in regard to rotational stiffness additional posterior fixation has to be recommended.

Biomechanics and materials of reconstruction after tumor resection in the spinal column

We initially review the general biomechanical principles that should be considered in surgical reconstruction of spinal tumors. This will be further clarified by more detailed descriptions for individual spinal regions in the subsequent part of the article. In the case of patients with spinal metastases, especially in patients with a median survival time less than a few months, a thorough review of the risks and benefits regarding surgical intervention must be discussed with the patient. However, once the decision for surgery has been made, a biomechanically sound reconstruction should be performed to help restore or maintain the patient's mobility.

Single-stage posterior corpectomy and expandable cage placement for treatment of thoracic or lumbar burst fractures

STUDY DESIGN

A prospective study was performed.

OBJECTIVE

To assess an unusual technique for corpectomy and expandable cage placement via single-stage posterior approach in acute thoracic or lumbar burst fractures.

SUMMARY AND BACKGROUND DATA

Burst fractures represent 10% to 20% of all spine injuries at or near the thoracolumbar junction, and can cause neurologic complications and kyphotic deformity. The goal of surgical intervention is to decompress the neural elements, restore vertebral body height, correct angular deformity, and stabilize the columns of the spine.

METHODS

The study comprised 14 patients (8 women and 6 men aged 40.3 years) who had 1 spinal burst fracture between T8 and L4 and who underwent single-stage posterior corpectomy, circumferential reconstruction with expandable-cage placement, and transpedicle screwing between January 2003 and May 2005. Neurologic status was classified using the American Spinal Injury Association (ASIA) impairment scale and functional outcomes were analyzed using a visual analogue scale (VAS) for pain. The kyphotic angle (alpha) and lordotic angle (beta) were measured in the thoracic or thoracolumbar and lumbar regions, respectively. RESULTS.: The mean follow-up time was 24 months (range, 12-48 months). Neurologic status was in 7 patients (preop: ASIA-E, postop: unchanged), 2 patients (preop: ASIA-D, postop: 1 unchanged, 1 improved to ASIA-E), 3 patients (preop: ASIA-C, postop: 2 improved to ASIA-D, 1 improved to ASIA-E), 2 patients (preop: ASIA-B, postop: 1 improved to ASIA-C, 1 unchanged). The mean operative time was 187.8 minutes. The mean blood loss was 596.4 mL. Regarding postoperative complications, 1 patient experienced transient worsening of neurologic deficits and 1 patient developed pseudarthrosis. The mean preoperative VAS score was 8.21 and the mean postoperative VAS score was 2.66 (P < 0.05). The mean preoperative kyphotic angle for the 11 individuals with the thoracic or thoracolumbar burst fractures was 24.6 degrees and the mean preoperative lordotic angle for the 3 individuals with lumbar burst fractures was 10.6 degrees. The corresponding values at 12 months postsurgery were 17.1 degrees and 13.6 degrees.

CONCLUSION

This single-stage posterior approach for acute thoracic and lumbar burst fractures offers some advantages over the classic combined anterior-posterior approach. The results from this small series suggest that a single-stage posterior approach should be considered in select cases.

The effect of cement augmentation and extension of posterior instrumentation on stabilization and adjacent level effects in the elderly spine

STUDY DESIGN

An in vitro cadaveric study comparing different implant fixation techniques using a repeated measures design.

OBJECTIVE

To compare the effects of cement augmentation of pedicle screws and extension of posterior fixation on (i) 3-dimensional stabilization, and (ii) adjacent level effects in the aging spine.

SUMMARY OF BACKGROUND DATA

Device loosening and adjacent level effects are concerns in implant fixation in the elderly spine. Extension of posterior fixation and cement augmentation of pedicle screws have not been previously compared with respect to stabilization and adjacent level effects.

METHODS

Twelve T9 to L3 cadaveric specimens were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) with applied pure moments of +/-5 Nm. A T11 corpectomy was reconstructed with a vertebral body replacement device and T10 to T12 posterior instrumentation. Further stabilization was provided by posterior rod extension to L1 (flexible or rigid rods) and/or cement augmentation of T12 and L1 screws. The effects of cement augmentation and posterior rod extension on intersegmental motion were compared using the hybrid flexibility-stiffness protocol. Two-way repeated measures ANOVA and SNK post hoc tests (99% significance level) were used.

RESULTS

Range of motion at the corpectomy T10 to T12 levels significantly decreased after cement augmentation (AR 43%, LB 71%, FE 68%), and posterior rod extension (rigid rods: AR 26%, LB 64%, FE 57%) (flexible rods: AR 16%, LB 53%, FE 39%). Posterior rod extension significantly reduced range of motion at the rod extension level. Motion at the distal noninstrumented L1 to L2 level was increased significantly by posterior rod extension and cement augmentation. There were however, smaller magnitudes of increase in motion across L1 to L2 level with flexible rod and cement augmentation (AR 12%, LB 45%, FE 31%).

CONCLUSION

Cement augmentation of pedicle screws resulted in the most stable vertebral reconstruction, whereas flexible rod extension minimized changes in range of motion at both adjacent rod extension and distal noninstrumented levels.

Angular stable anterior plating following thoracolumbar corpectomy reveals superior segmental stability compared to conventional polyaxial plate fixation

STUDY DESIGN

Biomechanical in vitro testing of primary and secondary stability in 12 human thoracolumbar spinal specimens using a spine simulator.

OBJECTIVE

In a corpectomy model anterior plate systems were investigated for their ability to restore spinal stability particularly focusing on the influence of angular stability, bone mineral density (BMD) and failure mode.

SUMMARY OF BACKGROUND DATA

The concept of isolated anterior column reconstruction following thoracolumbar fractures using newly developed minimally invasive spine surgical techniques has attracted major clinical interest. In analogy to angular stable plate systems in long bone fixation the application of locking plates to the spine is aimed to limit loss of reduction and to improve stability.

METHODS

Twelve human spinal specimens (Th11-L3) were tested in a 6-degree-of-freedom spine simulator under pure moments of 7.5 Nm to investigate primary and secondary stiffness of 2 different anterior reconstruction options: (1) Synex II cage and MACS TL polyaxial anterior plating system, (2) Synex II cage and ArcoFix angular stable anterior plating system. An increasing 4-step cyclic loading model was included.

RESULTS

The angular stable plate system showed superior stability compared to the nonangular system in axial rotation and lateral bending. Flexion/extension loading demonstrated no difference between the systems in range of motion. A positive correlation between BMD and the number of load cycles until failure for the nonangular stable system (R2 = 0.90) was found. Different failure modes were investigated for the plating systems. The MACS system showed loosening at the connection between screw and plate inducing tilting under flexural load and final failure. The ArcoFix system revealed increased stability under cyclic loading and failed by parallel sintering to the endplate.

CONCLUSION

Anterior angular stable fixation showed higher primary and secondary stability following thoracolumbar corpectomy. In specimens with lower BMD the use of angular stable systems substantially increased stability. Angular stable systems, however, differ in the way of construct failure.

Giant cell tumor of the lumbar spine: operative management via spondylectomy and short-segment, 3-column reconstruction with pedicle recreation

BACKGROUND

Giant cell tumors of the lumbar spine are uncommon lesions. Aggressive management of such lesions via spondylectomy to obtain local control and prevent recurrence is often necessary. Spinal reconstruction after total spondylectomy can be challenging. Traditional reconstructions typically require multisegment fixation with an association loss of segmental motion and limited 3-column reconstruction.

METHODS

The authors report a case of a GCT of the lumbar spine occurring in a 49-year-old woman. The authors describe the surgical management of such a lesion via a 1-stage posterior-anterior-posterior procedure that entails a lumbar spondylectomy and short-segment posterior fixation with 3-column reconstruction using a stackable carbon-fiber-reinforced cage device with direct posterior rod connection for pedicle reconstruction.

RESULTS

At 33 months postoperative follow-up, neither tumor recurrence nor instrumentation-related complications were noted, bone fusion was prevalent, and sagittal alignment was well maintained. The patient reported no loss of functions, was neurologically intact, and remained active.

CONCLUSIONS

Aggressive operative management via spondylectomy of a lumbar GCT provides local tumor control. In select patients, spinal reconstruction after a spondylectomy via a 1-stage posterior-anterior-posterior approach to establish short-segment, 3-column reconstruction with recreation of the pedicles is a promising procedure that provides immediate spinal stabilization without evidence of early instrumentation-related complications, maintains spinal alignment, promotes a quick return to daily activities, and avoids sacrificing excessive motion segments and biomechanical function associated with more traditional procedures.

En bloc spondylectomy reconstructions in a biomechanical in-vitro study

Wide surgical margins make en bloc spondylectomy and stabilization a referred treatment for certain tumoral lesions. With a total resection of a vertebra, the removal of the segment's stabilizing structures is complete and the instrumentation guidelines derived from a thoracolumbar corpectomy may not apply. The influence of one or two adjacent segment instrumentation, adjunct anterior plate stabilization and vertebral body replacement (VBR) designs on post-implantational stability was investigated in an in-vitro en bloc spondylectomy model. Biomechanical in-vitro testing was performed in a six degrees of freedom spine simulator using six human thoracolumbar spinal specimens with an age at death of 64 (+/- 20) years. Following en bloc spondylectomy eight stabilization techniques were performed using long and short posterior instrumentation, two VBR systems [(1) an expandable titanium cage; (2) a connected long carbon fiber reinforced composite VBR pedicle screw system)] and an adjunct anterior plate. Test-sequences were loaded with pure moments (+/- 7.5 Nm) in the three planes of motion. Intersegmental motion was measured between Th12 and L2, using an ultrasound based analysis system. In flexion/extension, long posterior fixations showed significantly less range of motion (ROM) than the short posterior fixations. In axial rotation and extension, the ROM of short posterior fixation was equivalent or higher when compared to the intact state. There were only small, nonsignificant ROM differences between the long carbon fiber VBR and the expandable system. Antero-lateral plating stabilized short posterior fixations, but did not markedly effect long construct stability. Following thoracolumbar en bloc spondylectomy, it is the posterior fixation of more than one adjacent segment that determines stability. In contrast, short posterior fixation does not sufficiently restore stability, even with an antero-lateral plate. Expandable verses nonexpandable VBR system design does not markedly affect stability.

Three-dimensional stiffness in a thoracolumbar en-bloc spondylectomy model: a biomechanical in vitro study

BACKGROUND

In selected cases, en-bloc spondylectomy is the only option to reach wide resection margins for patients with malignant tumours of the thoracolumbar spine. These patients must be also provided a secure initial stabilization of the spine and this is the role of vertebral body replacements employed with posterior fixation systems. The aim of this study was to determine the postimplantation stiffness of a connected vertebral body replacement pedicle screw system in different implantation scenarios following an en-bloc spondylectomy. Reconstruction was varied by posterior fixation lengths and axial compression forces during implantation.

METHODS

Three-dimensional stiffness was assessed in 6 fresh frozen human spinal specimens (Th11-L3) using a six degree of freedom spine simulator. Following en-bloc spondylectomy reconstruction was performed using a carbon composite fibre vertebral body replacement connected to a posterior fixation system by two artificial pedicles. The spines were loaded with pure moments (7.5Nm) in the three main motion planes. The intersegmental rotations were measured between Th12 and L2.

FINDINGS

Reconstructions using long posterior fixation modes demonstrated significant (P<0.05) higher stiffness compared to short posterior fixations in all motion planes. In axial rotation short posterior fixation modes failed to reach the values of the intact state. Neither high nor low axial compression force during implantation showed a significant impact on postfusional stiffness.

INTERPRETATION

In this biomechanical model, the employed system should be implanted with a posterior fixation of two adjacent segments to the lesion in order to achieve a secure stabilization of the treated segment.

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.

Anterior vertebral body replacement with a titanium implant of adjustable height: a prospective clinical study

In the operative treatment of spinal injuries, the reconstruction of the anterior column of the thoracolumbar spine is still controversial. We conducted a prospective clinical study to investigate the clinical and radiological outcome of 50 patients treated with a vertebral body replacement of adjustable height (Synex). Fifty consecutive patients were evaluated during in-patient treatment and at 12 and 20 months post-operatively in clinical notes and radiographs. 38/50 patients were operated for traumatic fractures. Out of 50 patients 45 attended the follow-up clinic 1 year post-operatively and 39 of these patients were examined after 20 months. Twenty-five patients returned to pre-injury activities within 1 year. This number increased to 29/39 patients at 20 months. Seventy-three percent of the patients returned to their job. After 1 year 25/45 patients complained of little or no back pain and 6 months later six patients were limited in their back function. At 1 year only three patients complained of surgical site pain which was improved at their final follow-up at 20 months. Individual satisfaction was determined using a score on a visual analog scale containing 19 questions on back pain, and functional limitation of the spine that has to be filled in by the patients at three different points of time. The score decreased from 87/100 pre-operatively to 65/100 at 1 year follow-up (P<0.001). The average permanent correction of the injured vertebra was 16.8 degrees (88%) including 2.3 degrees (12%) loss of correction at 12 months after operation. Bony integration was obtained in 83%. Early and intermediate outcome with the Synex vertebral replacement device for reconstruction of the anterior column appears promising. The loss of correction or reduction was only minimal. On the basis of our results we recommend the Synex implant as an alternative for the fixation and stabilisation of thoracolumbar fractures. However, long-term results and a clinically random control study are still required.

Wirbelkörperersatz mit höhenvariablem Titanimplantat

OBJECTIVE

The reconstruction of the anterior column of the thoracolumbar spine is still controversial.

METHODS

The clinical notes and radiographs of 50 consecutive patients (29 M, 21 F, 43 years) treated with the Synex implant were reviewed at operation and at 12 and 20 months postoperatively.

RESULTS

Of 45 patients, 25 returned to pre-injury activities within 1 year and 29 of 39 within 20 months. Two-thirds of the patients who were followed up returned to their job. After 1 year 25 of 45 patients had no or mild limitations in their back function. Six months later this group decreased to 6 of 39 patients. Visual analog scale (VAS) decreased from 87/100 preoperatively to 65/100 at the 1-year follow-up. The average permanent reduction of the injured vertebrae was 16.9 degrees including 2.3 degrees loss of correction.

CONCLUSION

After reconstruction of the anterior column with the Synex implant only a minimal loss of correction or reduction was observed. The clinical outcome after use of the Synex implant appears promising. We recommend this implant as a valuable alternative for reconstruction of the anterior column of the thoracolumbar spine. However, long-term results are still required.

Current treatment strategies and outcomes in the management of symptomatic vertebral hemangiomas

OBJECTIVE

We analyzed the outcome of patients with symptomatic vertebral hemangiomas treated at University of California, San Francisco, over a 20 year period. Treatment included transarterial embolization, embolization followed by surgical decompression or vertebral reconstruction with arthrodesis, and percutaneous vertebroplasty alone.

METHODS

All medical, surgical, and radiological records were reviewed retrospectively. All patients underwent follow-up neurological examination and evaluation of back pain.

RESULTS

Sixteen patients diagnosed with symptomatic vertebral hemangiomas causing pain or neurological deficit were treated at University of California, San Francisco, between 1984 and 2004. Mean follow-up was 81 months. Seven of nine patients undergoing surgical decompression and tumor resection reported pain relief and demonstrated improvement in neurological deficit when present. Two patients had recurrent myelopathy: one was successfully treated with a second decompressive surgery, whereas the second underwent a staged vertebrectomy. All three patients undergoing vertebrectomy had cord compression from extraosseous tumor growth. Preoperative embolization reduced expected intraoperative blood loss in four patients. Three of four patients who underwent transarterial embolization alone experienced resolution of back pain. Two of four patients treated with vertebroplasty had long-term pain relief.

CONCLUSION

Transarterial embolization followed by laminectomy is a safe and effective procedure for the treatment of cord compression by vertebral hemangioma causing stenosis without instability or deformity. Vertebrectomy preceded by embolization and followed by reconstruction can be used to treat cord compression from extraosseous tumor extension. Transarterial embolization without decompression is an effective treatment for painful intraosseous hemangiomas. Vertebroplasty is useful for improving pain symptoms, especially when vertebral body compression fracture has occurred in patients without neurological deficit, but is less effective in providing long-term pain relief.

Single-stage thoracolumbar vertebrectomy with circumferential reconstruction and arthrodesis: surgical technique and results in 15 patients

OBJECTIVE

Circumferential reconstruction and arthrodesis can be necessary after thoracolumbar vertebrectomy. The authors describe a technique for single-stage thoracolumbar vertebrectomy with circumferential reconstruction and arthrodesis. The surgical results using this technique are reviewed.

METHODS

Fifteen patients ranging from 14 to 75 years of age underwent single-stage thoracolumbar vertebrectomy with circumferential reconstruction and arthrodesis. The vertebrectomy was performed through a posterior midline approach. Anterior column reconstruction was performed with expandable or nonexpandable cages. Anterior and posterolateral arthrodeses used autograft. Posterior segmental instrumentation was used in all cases.

RESULTS

Fifteen procedures have been performed to date, 4 for tumor and 11 for fracture. The range of treated levels was T4 to L2 (7 thoracic spine and 8 lumbar spine levels). One patient was incomplete preoperatively (Frankel Grade C) and improved to being intact postoperatively (Frankel Grade E), another improved from Frankel Grade C to Frankel Grade D. All other patients were neurologically unchanged postoperatively. Mean operative time was 4.0 hours. Average blood loss was 1100 ml. Average number of levels fused was 5.8 (range 4-9). There were four complications: one delayed transient neurological deficit after deformity correction, one infection, one postoperative myocardial infarction, and one hardware failure. All patients were treated and had a good recovery.

CONCLUSION

The authors present a method for thoracolumbar vertebrectomy, circumferential reconstruction, and arthrodesis performed in a single stage, solely via a posterior approach. This is an alternative to anterior (i.e., thoracoabdominal and retroperitoneal) and lateral (i.e., lateral extracavitary) approaches that can be used for circumferential reconstruction and arthrodesis. Potential advantages and pitfalls are discussed.

Effect of bilateral facetectomy of thoracolumbar spine T11–L1 on spinal stability

Spinal stenosis can be found in any part of the spine, though it is most commonly located on the lumbar and cervical areas. It has been documented in the literature that bilateral facetectomy in a lumbar motion segment to increase the space induces an increase in flexibility at the level at which the surgery was performed. However, the result of bilateral facetectomy on the stability of the thoracolumbar spine has not been studied. A nonlinear three-dimensional finite element (FE) model of thoracolumbar T11-L1 was built to explore the influence of bilateral facetectomy. The FE model of T11-L1 was validated against published experimental results under various physiological loadings. The FE model with bilateral facetectomy was evaluated under flexion, extension, lateral bending and axial rotation to determine alterations in kinematics. Results show that bilateral facetectomy causes increase in motion, considerable increase in axial rotation and least increase in lateral bending. Removal of facets did not result in significant change in the sagittal motion in flexion and extension.

Effects of fusion-bone stiffness on the mechanical behavior of the lumbar spine after vertebral body replacement

BACKGROUND

Implants for vertebral body replacement are often inserted together with an additional stabilizing implant, e.g. an internal fixation device. During implantation bone grafts or milled bone is normally added to the anterior implant. Little is known about the stiffening effect of this fusion-bone mass on the mechanical behavior of the corresponding bone region, including the load distribution between the different parts.

METHODS

A three-dimensional finite element model of the lumbar spine was created with a vertebral body replacement at L3, a paired internal fixation device between L2 and L4, and left anterolateral fusion bone. The elastic modulus of fusion bone was varied in discrete steps between 0 MPa and 10,000 MPa. The model was loaded to simulate standing, 20 degrees flexion, 15 degrees extension and 6 degrees axial rotation in the lumbar spine.

FINDINGS

The elastic modulus of fusion bone has a considerable effect on the compressive force on vertebral body replacement and fusion bone for all loading cases studied. For extension, it also affects intersegmental rotation, the force in the erector spinae muscle, the compressive force on the internal fixator and intradiscal pressure in the adjacent discs. The elastic modulus most strongly affects the different parameters at values between 0 MPa and 500 MPa.

INTERPRETATION

Adding bone mass during vertebral body replacement reduces the loads on the ventral implant for all loading cases studied but extension when the fusion-bone stiffens. This protects the implant from fatigue. The load on the fusion bone increases with increasing elastic modulus. Thus bone grafts should be used whenever possible.

Effects of tensioning the lumbar fasciae on segmental stiffness during flexion and extension: Young Investigator Award winner

STUDY DESIGN

Biomechanical study of unembalmed human lumbar segments.

OBJECTIVE

To investigate the effects of tensioning the lumbar fasciae (transversus abdominis [TrA]) aponeurosis) on segment stiffness during flexion and extension.

SUMMARY OF BACKGROUND DATA

Animal and human studies suggest that TrA may influence intersegmental movement via tension in the middle and posterior layers of lumbar fasciae (MLF, PLF).

METHODS

Compressive flexion and extension moments were applied to 17 lumbar segments from 9 unembalmed cadavers with 20 N lateral tension of the TrA aponeurosis during: 1) "static" tests: load was compared when fascial tension was applied during static compressive loads into flexion-extension; 2) "cyclic loading" tests: load, axial displacement, and stiffness were compared during repeated compressive loading cycles into flexion-extension. After testing, the PLF was incised to determine the tension transmitted by each layer.

RESULTS

At all segments and loads (<200 N), fascial tension increased resistance to flexion loads by approximately 9.5 N. In 15 of 17, fascial tension decreased resistance to extension by approximately 6.6 N. Fascial tension during cyclic flexion loading decreased axial displacement by 26% at the onset of loading (0-2 N) and 2% at 450 N (13 of 17). During extension loading, fascial tension increased displacement at the onset of loading (10 of 17) by approximately 23% and slightly (1%) decreased displacement at 450 N. Segment stiffness was increased by 6 N/mm in flexion (44% at 25 N) and decreased by 2 N/mm (8% at 25 N) in extension. More than 85% of tension was transmitted through the MLF.

CONCLUSIONS

Tension on the lumbar fasciae simulating moderate contraction of TrA affects segmental stiffness, particularly toward the neutral zone.

Primary stability of anterior lumbar stabilization: interdependence of implant type and endplate retention or removal

This is a comparative in vitro biomechanical study of the primary stability of an anterior lumbar interbody stabilization. The objective was to compare the stability of a interbody stabilizing titanium cage with and without the retention of the bordering vertebral endplates, as well as to compare the titanium cage with a tricalcium phosphate block when the endplates are removed. An adequate blood supply is critical for interbody fusion, which suggests surgical treatment of the bordering endplates. On the other hand, primary stability is improved by the retention of the endplates. Furthermore, bone substitute materials are finding more frequent use due to complications associated with autologous bone grafts. Ten bovine lumbar spine motion segments (average age 6 months) were investigated. Pure bending loadings as well as eccentric axial compression loadings were applied. A titanium cage and tricalcium phosphate block, were tested in conjunction with an anterior augmentation (MACS). Range of motion, neutral zone (NZ) and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1,500 N. Range of motion of both implants in flexion-extension was significantly smaller than physiologic (cage without endplates 4.3 degrees , cage with 2.8 degrees , block without 3.4 degrees , and physiologic 6.6 degrees , all p<0.001). The cage with endplates and the block without endplates were both significantly stiffer than physiologic in all directions except left lateral bending. The block without endplates and the cage with endplates were both stiffer than the cage without endplates. The results suggest that the use of the bone substitute block provides better stability than the cage when the endplates are removed.

Comparative biomechanical testing of anterior and posterior stabilization procedures

STUDY DESIGN

This is a comparative in vitro biomechanical study in a calf lumbar spine model.

OBJECTIVES

The objective was to compare the primary stability of an anterior instrumentation, an intercorporal cage in combination with an anterior instrumentation, and a posterior instrumentation for monosegmental spondylodesis.

SUMMARY OF BACKGROUND DATA

Spondylodesis can be achieved through a posterior lumbar fusion, posterior lumbar intercorporal fusion, or an anterior lumbar intercorporal fusion. The posterior lumbar fusion is the gold standard, although the anterior approach offers some potential advantages to the transpedicular posterior techniques.

METHODS

Stability testing was performed on 30 calf lumbar spine motion segments in a physiologic state (n = 30), with either an isolated anterior (MACS) or posterior instrumentation (SOCON), and with an anterior instrumentation augmented with an intercorporal cage (MACS-Cage, n = 10, respectively). Range of motion, neutral zone, and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1500 N.

RESULTS

The isolated posterior instrumentation was found to be more stable than the isolated or augmented anterior instrumentation in flexion/extension, although no significant differences were observed in lateral bending or axial rotation. The results of this biomechanical study suggest that an augmented anterior instrumentation provides similar stability for bony fusion as does the golden standard posterior instrumentation, with the exception of flexion/extension.

CONCLUSION

An augmented anterior instrumentation may provide similar stability for bony fusion as does the posterior instrumentation.

Range of motion in reconstruction situations following corpectomy in the lumbar spine: a question of bone mineral density?

STUDY DESIGN

In vitro biomechanical study to evaluate the stability of different types of instrumentation in the lumbar spine following corpectomy in relation to bone mineral density (BMD).

OBJECTIVES

To investigate the relation between the stability of a spinal instrumentation and BMD. To determine a threshold value of BMD allowing a single ventral instrumentation following corpectomy in the lumbar spine.

SUMMARY OF BACKGROUND DATA

Some in vitro studies determined the biomechanical properties of different spinal instrumentations in various spinal injury models. To the authors' knowledge, there are no published data available concerning stabilization in relation to BMD. A guideline for the treatment of a corpectomy depending on BMD would be helpful in order to choose the appropriate surgical method.

METHODS

Twenty-four fresh frozen human lumbar cadaveric spine specimens L1-L3 were used for testing of biomechanical properties. Plain radiographs were taken. BMD was determined using quantitative computed tomography (QCT). Testing in a 6 df loading device included native specimens and specimens after corpectomy of L2, restoration of the defect with a titanium cage, and two reconstruction situations: single ventral and additional dorsal instrumentation. Load-displacement curves and range of motion parameters were recorded and correlated with BMD.

RESULTS

A significant (P < 0.05) influence of BMD on range of motion was found. Single ventral instrumentation was critical concerning axial rotation. Combined dorsoventral instrumentation offered sufficient stability. The threshold value for use of single ventral instrumentation is a BMD > or = 0.22 g/cm.

CONCLUSIONS

Single ventral instrumentation can provide sufficient stability following corpectomy in the lumbar spine under the condition of a high BMD. Determination of BMD and the use of this guideline provides a valid tool for surgical planning.

Is a single anterolateral screw-plate fixation sufficient for the treatment of spinal fractures in the thoracolumbar junction? A biomechanical in vitro investigation

Controversy exists about the indications, advantages and disadvantages of various surgical techniques used for anterior interbody fusion of spinal fractures in the thoracolumbar junction. The purpose of this study was to evaluate the stabilizing effect of an anterolateral and thoracoscopically implantable screw-plate system. Six human bisegmental spinal units (T12-L2) were used for the biomechanical in vitro testing procedure. Each specimen was tested in three different scenarios: (1) intact spinal segments vs (2) monosegmental (T12/L1) anterolateral fixation (macsTL, Aesculap, Germany) with an interbody bone strut graft from the iliac crest after both partial corpectomy (L1) and discectomy (T12/L1) vs (3) bisegmental anterolateral instrumentation after extended partial corpectomy (L1), and bisegmental discectomy (T12/L1 and L1/L2). Specimens were loaded with an alternating, nondestructive maximum bending moment of +/-7.5 Nm in six directions: flexion/extension, right and left lateral bending, and right and left axial rotation. Motion analysis was performed by a contact-less three-dimensional optical measuring system. Segmental stiffness of the three different scenarios was evaluated by the relative alteration of the intervertebral angles in the three main anatomical planes. With each stabilization technique, the specimens were more rigid, compared with the intact spine, for flexion/extension (sagittal plane) as well as in left and right lateral bending (frontal plane). In these planes the bisegmental instrumentation compared to the monosegmental case had an even larger stiffening effect on the specimens. In contrast to these findings, axial rotation showed a modest increase of motion after bisegmental instrumentation. To conclude, the immobilization of monosegmental fractures in the thoracolumbar junction can be secured by means of bone grafting and the implant used in this study for all three anatomical planes. After bisegmental anterolateral stabilization a sufficient reduction of the movements was registered for flexion/extension and lateral bending. However, the observed slight increase of the range of motion in the transversal plane may lead to loosening of the implant before union. Therefore, the use of an additional dorsal fixation device should be considered.

Biomechanical analysis of anterior poly-methyl-methacrylate reconstruction following total spondylectomy for metastatic disease

STUDY DESIGN

Three reconstruction options were evaluated biomechanically following total spondylectomy using human cadaveric spine specimens. OBJECTIVES.: To evaluate and compare the stability of combined anterior and posterior fixation incorporating poly-methyl-methacrylate with alternative accepted reconstruction techniques.

SUMMARY OF BACKGROUND DATA

Total spondylectomy represents the most radical option for decompression in metastatic spinal cord compression. Poly-methyl-methacrylate is considered a useful adjunct in spinal column stabilization and arthrodesis; however, there is little published biomechanical data to support its use in this setting.

METHODS

Ten fresh-frozen human cadaveric spines (T9-L3) were used. After intact analysis, a total spondylectomy was performed at T12. Three potential reconstruction techniques were tested for their ability to restore stiffness to the specimen: 1) multilevel posterior pedicle screw instrumentation from T10-L2; 2) anterior instrumentation (ATL Z plate II) and rib graft at T11-L1 with multilevel posterior pedicle screw instrumentation from T10-L2; and 3) anterior cement (Simplex P) and pins construct (T12) with multilevel posterior pedicle screw instrumentation from T10-L2. Each of the three potential reconstruction techniques was tested on each specimen in random order using nondestructive testing under load control.

RESULTS

Only combined stabilization techniques (e.g., anterior instrumentation and rib graft with multilevel posterior pedicle screw instrumentation and anterior cement-and-pins construct with multilevel posterior pedicle screw instrumentation) restored stiffness to a level equivalent to or higher than that of the intact spine in all loading modes (P < 0.05). Anterior cement-and-pins construct with multilevel posterior pedicle screw instrumentation provided more stability to the specimen than anterior instrumentation and rib graft with multilevel posterior pedicle screw instrumentation in compression and flexion testing (P < 0.05). Posterior instrumentation alone did not restore stiffness to the intact level in compression and flexion testing (P < 0.005).

CONCLUSIONS

Combined anterior and posterior reconstruction using a cement construct provides equal to or more stability than the intact spine in all testing modes. Posterior stabilization alone is an inferior method of reconstruction following total spondylectomy. Poly-methyl-methacrylate has the advantage over traditional anterior reconstruction techniques in that it can be inserted using a posterior approach.

Biomechanical effects of the body augmenter for reconstruction of the vertebral body

STUDY DESIGN

An in vitro biomechanical study of the stabilizing effects of the body augmenter and posterior instrumentation on experimental thoracolumbar fractures with vertebral defects.

OBJECTIVE

To evaluate the effects of the body augmenter and instrumentation on the stability of the spine-device construct.

SUMMARY OF BACKGROUND DATA

Posterior instrumentations alone are widely used to accomplish spinal reduction and provide stability for an injured spine; however, implant failure rates have been reported to be approximately 20%. Transpedicular discectomy and bone graft has reported only 33% fusion rates. Combined anterior bony strut and posterior instrumentation was a challenge to geriatric patients with vulnerable medical conditions and possible vascular and pulmonary complications. Therefore, a new design, the body augmenter, tries to reconstruct the vertebral body through internal mechanical support and also encourage bony fusion. This study is to evaluate its initial mechanical effects.

METHODS

Twenty fresh porcine T11-L3 vertebrae were harvested. The L1 vertebra with one third or one half corpectomy was performed to simulate a fracture injury with vertebral defects. Posterior instrumentation alone (PI group), posterior instrumentation with body augmenters (BA group), and anterior instrumentation with tricortical bony strut and DCP 1 level above and 1 level below the fracture site (DCP group) were applied as treatment strategies. Load-displacement and torque-angle plots were generated and used to calculate axial stiffness and torsional rigidity for these constructs with vertebral fracture at the L1 vertebrae. Axial compression, extension, and flexion tests were performed at intact and spine-device constructs to document spinal stability.

RESULTS

The construct stability had a complex association to the device applied. In the one third corpectomy group, the BA group had significantly higher compression stiffness than the PI group. In the one half corpectomy group, the flexion and compression stiffness of the BA group became significantly greater than the PI group, and the extension stiffness is significantly higher than the DCP group.

CONCLUSIONS

The body augmenters combined with posterior instrumentation increased the spinal construct stability during compression, flexion, and extension. According to results in this study, the body augmenter could provide a better initial stability of construct and prevent the implant failure of posterior instrumentation and may be a feasible substitute for the anterior role in the future.

[Vertebral body replacement in spine surgery]

Autografts and allogeneous bone grafts as well as cages are used for the reconstruction of the anterior column after corpectomy. Recently, expandable cages for vertebral body replacement have been developed. Based on our own experience, the purpose of this study was to summarize the available biomechanical and clinical data of expandable corpectomy cages and to compare it with established fixation techniques. If used correctly, expandable cages offer several surgical advantages in comparison to non-expandable cages. However there were no significant differences between the biomechanical properties of expandable and non-expandable cages. Additionally, design variations of expandable corpectomy cages did not show any significant impact on the biomechanical stability. Currently available mid-term clinical and radiological data on the treatment of fractures, metastasis and infection of the cervical, thoracic and lumbar spine demonstrated no significant difference between expandable and non-expandable cages. However, the increased stress-shielding effect of expandable cages compared to non-expandable cages might result in a deterioration of the long-term clinical outcome.

Biomechanical comparison of expandable cages for vertebral body replacement in the thoracolumbar spine

STUDY DESIGN

An in vitro biomechanical study of expandable cages for vertebral body replacement in the human thoracolumbar spine.

OBJECTIVES

The purpose of this study was to compare the in vitro biomechanical properties of 3 different expandable cages with a nonexpandable cage.

SUMMARY AND BACKGROUND DATA

Recently, there has been a rapid increase in the use and the commercial availability of expandable cages for vertebral body replacement in the thoracolumbar spine. Although all 3 expandable cages, evaluated in this study, are approved for clinical use in Europe, little information is available concerning the biomechanical properties of these implants.

MATERIAL AND METHODS

Thirty-two human thoracolumbar spines (T11 to L3) were tested in flexion, extension, axial rotation, and lateral bending with a nondestructive loading technique using an unconstrained testing apparatus. Three-dimensional displacement was measured using an optical measurement system. First, all motion segments were tested intact. After complete corporectomy of L1, cages were implanted according to producer's information. The following implants (n = 8/group) were tested: 1) meshed titanium cage (nonexpandable cage, DePuy AcroMed); 2) X-tenz (expandable cage, DePuy AcroMed); 3) Synex (expandable Cage; Synthes); and 4) VBR (expandable cage, Ulrich). Finally, posterior stabilization using the Universal Spine System (Synthes), posterior-anterior stabilization using the Universal Spine System (Synthes), and anterior plating (Locking Compression Plate, Synthes) was applied to each test specimen. The mean apparent stiffness values, range of motion, and neutral and elastic zone were calculated from the corresponding load-displacement curves.

RESULTS

No significant differences could be determined between the in vitro biomechanical properties of expandable and nonexpandable cages. In comparison to the intact motion segment, isolated anterior stabilization using cages and anterior plating significantly decreased stiffness and increased range of motion in all directions. In contrast, additional posterior stabilization significantly increased stiffness and decreased range of motion in all directions compared to the intact motion segment. The combined anterior-posterior stabilization demonstrated greatest stiffness results.

CONCLUSION

Biomechanical results indicate that design variations of expandable cages for vertebral body replacement are of little importance. Additionally, no significant difference could be determined between the biomechanical properties of expandable and nonexpandable cages. After corporectomy, isolated implantation of expandable cages plus anterior plating was not able to restore normal stability of the motion segment. Therefore, isolated anterior stabilization using cages plus Locking Compression Plate should not be used for vertebral body replacement in the thoracolumbar spine.