Pedicle Screw-rod Research Articles

Biomechanical Analysis of a Pedicle Screw-Rod System with a Novel Cross-Link Configuration.

Study DesignThe strength effects of a pedicle screw-rod system supplemented with a novel cross-link configuration were biomechanically evaluated in porcine spines.PurposeTo assess the biomechanical differences between a conventional cross-link pedicle screw-rod system versus a novel cross-link instrumentation, and to determine the effect of the cross-links.Overview of LiteratureTransverse cross-link systems affect torsional rigidity, but are thought to have little impact on the sagittal motion of spinal constructs. We tested the strength effects in pullout and flexion-compression tests of novel cross-link pedicle screw constructs using porcine thoracic and lumbar vertebrae.MethodsFive matched thoracic and lumbar vertebral segments from 15 porcine spines were instrumented with 5.0-mm pedicle screws, which were then connected with 6.0-mm rods after partial corpectomy in the middle vertebral body. The forces required for construct failure in pullout and flexion-compression tests were examined in a randomized manner for three different cross-link configurations: un-cross-link control, conventional cross-link, and cross-link passing through the base of the spinous process. Statistical comparisons of strength data were analyzed using Student's t-tests.ResultsThe spinous process group required a significantly greater pullout force for construct failure than the control group (p=0.036). No difference was found between the control and cross-link groups, or the cross-link and spinous process groups in pullout testing. In flexion-compression testing, the spinous processes group required significantly greater forces for construct failure than the control and cross-link groups (p<0.001 and p=0.003, respectively). However, there was no difference between the control and cross-link groups.ConclusionsA novel cross-link configuration that features cross-link devices passing through the base of the spinous processes increased the mechanical resistance in pullout and flexion-compression testing compared to un-cross-link constructs. This configuration provided more resistance to middle-column damage under flexion-compression testing than conventional cross-link configuration.

Addressing Stretch Myelopathy in Multilevel Cervical Kyphosis with Posterior Surgery Using Cervical Pedicle Screws.

Study DesignTechnique description and retrospective data analysis.PurposeTo describe the technique of cervical kyphosis correction with partial facetectomies and evaluate the outcome of single-stage posterior decompression and kyphosis correction in multilevel cervical myelopathy.Overview of LiteratureKyphosis correction in multilevel cervical myelopathy involves anterior and posterior surgery. With the advent of cervical pedicle screw-rod instrumentation, single-stage posterior kyphosis correction is feasible and can address stretch myelopathy by posterior shortening.MethodsNine patients underwent single-stage posterior decompression and kyphosis correction for multilevel cervical myelopathy using cervical pedicle screw instrumentation from March 2011 to February 2014 and were evaluated preoperatively and postoperatively with modified Japanese Orthopaedic Association (mJOA) scoring and computed tomography scans for radiological measurements. Kyphosis assessment was made with Ishihara curvature index and C2–C7 Cobb's angle. The linear length of the spinal canal and the actual spinal canal length were also evaluated. The average follow-up was 40.56 months (range, 20 to 53 months).ResultsThe average preoperative C2–7 Cobb's angle of 6.3° (1° to 12°) improved to 2° (10° to −9°). Ishihara index improved from −15.8% (−30.5% to −4.7%) to −3.66% (−14.5% to +12.6%). The actual spinal canal length decreased from 83.64 mm (range, 76.8 to 91.82 mm) to 82.68 mm (range, 75.85 to 90.78 mm). The preoperative mJOA score of 7.8 (range, 3 to 11) improved to 15.0 (range, 13 to 17).ConclusionsSingle-stage posterior decompression and kyphosis correction using cervical pedicle screws for multilevel cervical myelopathy may address stretch myelopathy, in addition to decompression in the transverse plane. However, cervical lordosis was not achieved with this method as predictably as by the anterior approach. The present study shows evidence of mild shortening of cervical spinal canal and a positive correlation between canal shortening and clinical improvement.

Biomechanical Stability of Transverse Connectors in the Setting of a Thoracic Pedicle Subtraction Osteotomy

Introduction The biomechanical effect of augmentation of a longitudinal constructs with one or two transverse connectors (TC) after a thoracic pedicle subtraction osteotomy (PSO) has not been evaluated previously. Previous investigations have suggested the role of transverse connectors for long segment thoracic constructs in enhancing torsional rigidity. We set out to evaluate the biomechanical contribution of TC to the stability of a long-segment pedicle screw–rod construct after a thoracic PSO. Methods Seven human cadaveric thoracic spines were prepared and instrumented from T4 to T10 with bilateral pedicle screws/rods and a PSO was performed at T7. Intact range of motion (ROM) testing was performed with nondestructive loading and analyzed by loading modality (axial rotation, flexion/extension, and lateral bending). ROM analysis was performed in the unaugmented construct, the construct augmented with one TC, and the construct augmented with two TC. No outside funding sources were utilized for this study. The authors have no potential conflicts of interest to report. Results Following PSO and an unaugmented longitudinal pedicle screw–rod construct, T4–T10 (overall construct) and T6–T8 (PSO site). ROM was significantly reduced in all planes of motion compared with intact condition ( p &lt; 0.05). Augmentation of longitudinal construct with either one or two TC did not significantly increase construct stability in flexion-extension or lateral bending compared with the unaugmented construct ( p &gt; 0.05). In contrast, during axial rotation, global ROM was significantly reduced by 43% and by 48% at T6–T8 following addition of two TC ( p &lt; 0.05). One TC did not significantly reduce torsional ROM. Conclusions Two transverse connectors significantly improved torsional rigidity of the entire construct and at the PSO site, with no differences in stability for flexion-extension and lateral bending, or with the addition of only one transverse connector. In the setting of a PSO and long segment pedicle screw–rod construct, augmentation with at least two transverse connectors should be considered to improve torsional rigidity.

Biomechanical stability of transverse connectors in the setting of a thoracic pedicle subtraction osteotomy

Background contextTransverse connectors (TCs) are often used to improve the rigidity of posterior spinal instrumentation as previous investigations have suggested that TCs enhance torsional rigidity in long-segment thoracic constructs. Posterior osteotomies, such as pedicle subtraction osteotomy (PSO), are used in severe thoracic deformities and provide a significant amount of correction; as a consequence, however, PSOs also induce three-column spinal instability. In theory, augmentation of longitudinal constructs with TC after a thoracic PSO may provide additional rigidity, but the concept has not been previously evaluated. PurposeTo evaluate the biomechanical contribution of TC to the rigidity of a long-segment pedicle screw-rod construct after a thoracic PSO. Study designAn in vitro fresh-frozen human cadaveric biomechanical analysis. MethodsSeven human cadaveric thoracic spines were prepared and instrumented from T4–T10 with bilateral pedicle screws/rods and a PSO was performed at T7. Intact range of motion (ROM) testing was performed with nondestructive loading and analyzed by loading modality (axial rotation [AR], flexion/extension [FE], and lateral bending [LB]). Range of motion analysis was performed in the unaugmented construct, the construct augmented with one TC, and the construct augmented with two TCs. ResultsAfter PSO and an unaugmented longitudinal pedicle screw-rod construct, T4–T10 (overall construct) and T6–T8 (PSO site) ROMs were significantly reduced in all planes of motion compared with intact condition (AR: 11.8° vs. 31.7°; FE: 2.4° vs. 12.3°; 3.4° vs. 17.9°, respectively, p<.05). Augmentation of longitudinal construct with either one or two TCs did not significantly increase construct rigidity in FE or LB compared with the unaugmented construct (p>.05). In contrast, during AR, global ROM was significantly reduced by 43% and 48% at T6–T8 (1.7° and 1.2° vs. 2.38°, respectively) after addition of one and two TCs (p<.05), respectively. One TC did not significantly reduce torsional ROM from the intact state. ConclusionsTwo TCs significantly improved torsional rigidity of the entire construct and at the PSO site, with no differences in rigidity for FE and LB or with the addition of only one TC. In the setting of a PSO and long-segment pedicle screw-rod construct, augmentation with at least two TCs should be considered to improve torsional rigidity.

In vitro biomechanical evaluation of four fixation techniques for distractive–flexion injury stage 3 of the cervical spine

Purpose. Anterior plate fixation has been reported to provide satisfactory results in cervical spine distractive flexion (DF) injuries stages 1 and 2, but will result in a substantial failure rate in more unstable stage 3 and above. The aim of this investigation was to determine the biomechanical properties of different fixation techniques in a DF-3 injury model where all structures responsible for the posterior tension band mechanism are torn.Methods. The multidirectional three-dimensional stiffness of the subaxial cervical spine was measured in eight cadaveric specimens with a simulated DF-3 injury at C5–C6, stabilized with four different fixation techniques: anterior plate alone, anterior plate combined with posterior wire, transarticular facet screws, and a pedicle screw–rod construct, respectively.Results. The anterior plate alone did not improve stability compared to the intact spine condition, thus allowing considerable range of motion around all three cardinal axes (p > 0.05). The anterior plate combined with posterior wire technique improved flexion–extension stiffness (p = 0.023), but not in axial rotation and lateral bending. When the anterior plate was combined with transarticular facet screws or with a pedicle screws–rod instrumentation, the stability improved in flexion–extension, lateral bending, and in axial rotation (p < 0.05).Conclusions. These findings imply that the use of anterior fixation alone is insufficient for fixation of the highly unstable DF-3 injury. In these situations, the use of anterior fixation combined with a competent posterior tension band reconstruction (e.g. transarticular screws or a posterior pedicle screws–rod device) improves segmental stability.

Reduction of high-grade lumbosacral spondylolisthesis by minimally invasive transforaminal lumbar interbody fusion: A technical note

Abstract Objective To demonstrate the feasibility and efficacy of reduction of high-grade lumbosacral spondylolisthesis via a minimally invasive approach. Summary of background data Reduction of high-grade spondylolisthesis remains controversial and technically challenging. Although minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) has gained wide acceptance in recent years, it still has not been reported to achieve complete reduction of high grade slips. Methods In this technical note, the authors present a case of L5/S1 Meyerding Grade III fixed spondylolisthesis managed by MI-TLIF with percutaneous screws. Surgical techniques and key steps for reduction are described in detail. Results A 50-year-old woman had low back pain for 8 years. She also presented with radiculopathy of lower limbs and frequency/urgency of urination. The radiographs and computed tomography (CT) of the lumbar spine demonstrated degenerative spondylolisthesis, Meyerding grade III, at the level of L5/S1. The slippage was fixed on dynamic radiographs and there was neuroforaminal stenosis on the magnetic resonance image. The patient underwent MI-TLIF with percutaneous pedicle screw-rod fixation for arthrodesis at L5/S1. Her symptoms subsided after the operation. The one-and-half year follow-up radiographs, including CT, demonstrated complete reduction of the high-grade slippage and fusion of the lumbosacral spondylolisthesis. Conclusion Minimally invasive TLIF is a viable option for reduction of high-grade spondylolisthesis at L5/S1.

Biomechanical Analysis for Low Lumbar Spine Segment Fusion with Different Cage Locations

Aims: This paper aims to investigate the influence of cage location on the biomechanical behavior of lumbar spine with Transforaminal Lumbar Interbody Fusion (TLIF). Methodology: Firstly, a three-dimensional finite element (FE) model for L4-L5 low lumbar spine segment is established based on computed tomography scan images of a 30-year-old healthy male volunteer. Flexion, extension, lateral bending and torsion motions are simulated and compared with in-vitro cadaveric test data in the literature to validate the lumbar spine FE model. The intact spine model is then modified to TLIF model with one cage insertion under three different implant angles (30°, 45° and 60°). Results: Numerical results show that after fusion treatment the stress increases dramatically, and mainly distributes on cage and pedicle screw-rod system. Though 45° fusion does not have the lowest von Mises stress at the pedicle screw-rod system and the cage, it is still within an allowable Original Research Article Jiang et al.; BJAST, 6(5): 508-519, 2015; Article no.BJAST.2015.106 509 strength limit. Besides, 45° fusion has the best balanced stability in four basic physiological motions. So if only one cage uses, the 45° posterior location may be more suitable for L4-L5 interbody fusion than 30° and 60° location. Conclusion: If only one cage uses, the 45° posterior location may be more suitable for L4-L5 interbody fusion than 30° and 60° location.

Evaluation of the Effect of Fixation Angle between Polyaxial Pedicle Screw Head and Rod on the Failure of Screw-Rod Connection.

Introduction. Polyaxial screws had been only tested according to the ASTM standards (when they were perpendicularly positioned to the rod). In this study, effects of the pedicle screws angled fixation to the rod on the mechanical properties of fixation were investigated. Materials and Method. 30 vertically fixed screws and 30 screws fixed with angle were used in the study. Screws were used in three different diameters which were 6.5 mm, 7.0 mm, and 7.5 mm, in equal numbers. Axial pull-out and flexion moment tests were performed. Test results compared with each other using appropriate statistical methods. Results. In pull-out test, vertically fixed screws, in 6.5 mm and 7.0 mm diameter, had significantly higher maximum load values than angled fixed screws with the same diameters (P < 0.01). Additionally, vertically fixed screws, in all diameters, had significantly greater stiffness according to corresponding size fixed with angle (P < 0.005). Conclusion. Fixing the pedicle screw to the rod with angle significantly decreased the pull-out stiffness in all diameters. Similarly, pedicle screw instrumentation fixed with angle decreased the minimum sagittal angle between the rod and the screw in all diameters for flexion moment test but the differences were not significant.

The Surgical Treatment Principles of Atlantoaxial Instability Focusing on Rheumatoid Arthritis.

Object. This retrospective review was conducted to determine the surgical treatment principle for rheumatoid arthritis (RA) patients with atlantoaxial instability (AAI). Methods. Thirteen patients with AAI, including 5 RA patients, received preoperative computed tomography- (CT-) based image-guided navigation system (IGS) in C1 lateral mass-C2 pedicle screw-rod system fixation (LC1-PC2 fixation). These 13 patients were analyzed for 52 screws inserted into C1 and C2. We defined these patients as non-RA group (8 patients, 32 screws) and RA group (5 patients, 20 screws). The neurological status for RA group was evaluated using the Ranawat classification. The causes of AAI, surgical indications, complications, surgical method revolution, and CT-based navigation application are discussed. Results. None of the 13 patients expressed neurological function deterioration. The non-RA group screw accuracy was 100%. In the RA group, 1 RA patient developed left C2 screw loosening at 1+ months after operation due to screw malposition. The screw accuracy for this group was 95%. Conclusions. Higher intraoperative surgical complication rate was described in RA patients. Preoperative CT-based IGS in LC1-PC2 fixation can provide good neurological function and screw accuracy results. However, for higher screw accuracy in RA patients, intraoperative CT-based IGS application may be considered.

Pedicle Screw Fixation and Posterolateral Fusion in Lumbar Spondylolisthesis-A Prospective Analysis

Introduction: Spondylolisthesis is defined as the anterior slippage of one vertebra on another. The commonest level involved is L5 – S1 (89%). The displacement is a result of loose posterior locking mechanism which in turn leads to instability with symptomatic thecal sac and nerve root compression. Surgical stabilization helps in preventing further neurological insult and to enhance the recovery. Materials and Methods: This is a prospective study comprising of 20 patients with spondylolisthesis who were treated with pedicle screw-rod fixation and postero-lateral fusion with iliac bone graft during the period of Jan 2013 to Mar 2014. These patients were reviewed periodically both clinically and radiologically for a period of 6 months following operative fixation. For determining the outcome, the Japanese orthopaedic association (JOA) Scoring system was used. Results: Patient’s perception of their quality of life improved markedly after surgery. Overall clinical result was categorized into excellent, good, fair and poor by determining final correction of slip, maintenance of correction, and the functional outcome. 10 patients (50%) had an excellent outcome. 6 patients (30%) had good result and 4 patients (20%) had fair results. Conclusion: From our study, we conclude that pedicle screw fixation and postero-lateral fusion is an effective treatment modality in patients with spondylolisthesis and the results obtained in our study are in par with the other studies that have been conducted elsewhere. Key-Words: Spondylolisthesis, Postero-lateral fusion, Pedicle screw fixation.

Lumbar spine superior-level facet joint violations: percutaneous versus open pedicle screw insertion using intraoperative 3-dimensional computer-assisted navigation

Background Percutaneous pedicle screw use has a high rate of cranial facet joint violations (FVs) because of the facet joint being indirectly visualized. Computer-assisted navigation shows the anatomic structures clearly, and may help to lower the rate of FVs during pedicle screw insertion. This study used computed tomography (CT) to evaluate and compare the incidence of FVs between percutaneous and open surgeries employing computer-assisted navigation for the implantation of pedicle screw instrumentation during lumbar fusions. Methods A prospective study, including 142 patients having lumbar and lumbosacral fusion, was conducted between January 2013 and April 2014. All patients had bilateral posterior pedicle screw-rod instrumentation (top-loading screws) implanted by the same group of surgeons; intraoperative 3-dimensional computer navigation was used during the procedures. All patients underwent CT examinations within 6 months postoperation. The CT scans were independently reviewed by three reviewers blinded to the technique used. Results The cohort comprised 68 percutaneous and 74 open cases (136 and 148 superior-level pedicle screw placements, respectively). Overall, superior-level FVs occurred in 20 patients (20/142, 14.1%), involving 27 top screws (27/284, 9.5%). The percutaneous technique (7.4% of patients, 3.7% of top screws) had a significantly lower violation rate than the open procedure (20.3% of patients, 14.9% of top screws). The open group also had significantly more serious violations than did the percutaneous group. Both groups had a higher violation rate when the cranial fixation involved the L5. A 1-level open procedure had a higher violation rate than did the 2- and 3-level surgeries. Conclusions With computer-assisted navigation, the placement of top-loading percutaneous screws carries a lower risk of adjacent-FVs than does the open technique; when FVs occur, they tend to be less serious. Performing a single-level open lumbar fusion, or the fusion of the L5-S1 segment, requires caution to avoid cranial adjacent FVs.

Total sacrectomy via posterior approach for malignant sacral tumors

Objective To investigate the surgical indication,approach,resection methods and complications of total sacrectomy via posterior approach for primary malignant sacral tumors involving high level (S1,S2).Methods 5 cases of primary malignant sacral tumors treated by total sacrectomy via posterior approach and iliolumbar reconstruction from March 2010 to March 2011 were analyzed retrospectively.There were 3 males and 2 females.The mean age was 41,ranging from 32 to 55.The imageology examination showed osteolytic destruction,among which there were 4 cases of obvious soft tissue mass,1 case of obvious sacral foramina expansion with bone damage.MRI showed 1 case of the tumors in S1-S5,1 case of the tumors in S1 、S2,1 case of the tumors in S1-S3.The smallest tumor was 9.2 cm×7.6 cm×4.1 cm,while the largest was 22.0 cm× 19.0 cm× 16.0 cm.Preoperative TTNB were done on the 5 patients.Pathological diagnosis:2 cases of chordoma,1 case of malignant neurilemmoma,1 case of chondrosarcoma and 1 case of malignant hemangioendothelioma.5 patients had sacrococcygeal pain or lumbocrural pain before the surgery.Visual analogue scale (VAS):2 cases of 2,2 cases of 6 and 1 case of 8.Ilium stability reconstructions were all performed on 5 patients with spine pedicle screw-rod system.Results The mean operation time was 6.5 hours (range,4.5-11 hours),with the mean intraoperative blood loss of 3 700 ml (range,2 000-7 200 ml).There was no perioperative death.The mean follow-up time was 17 months (range,9-23 months).There were 2 cases of wound complications 2 weeks after surgery and healed by second intention with washing and drainage after debridement.There was no deep infection.1 case of rectal injury,which was performed with colostomy during the operation,and stoma returned 12 weeks after surgery.4 cases of sciatic nerve symptom of lower limbs and plantar flexion dyskinesia after bilateral S1 nerve roots resection.The patients walked with ankle brace fixed after the surgery.There was 1 case of implant breakage and no obvious spine down.5 patients had functional disability in sphincter after surgery.1 case of hemangioendothelioma recurred locally 9 months later.Local radiotherapy was performed since there was no reoperation indication.The patient is currently on the 13th month follow-up and survives with tumors.Compared with combined approach,the selection of posterior approach alone has relatively strict surgery indications.Conclusion Total sacrectomy via posterior approach is an effective way to treat the primary high-level malignant sacral tumors.The good surgical resection boundary is important to achieve the good oncology prognosis.The occurrence rate of postoperative complication is high,which has great influence on patients' postoperative neurological function. Key words: Sacrum; Bone neoplasms; Surgical procedures, operative

The significance of removing ruptured intervertebral discs for interbody fusion in treating thoracic or lumbar type B and C spinal injuries through a one-stage posterior approach.

ObjectivesTo identify the negative effect on treatment results of reserving damaged intervertebral discs when treating type B and type C spinal fracture-dislocations through a one-stage posterior approach.MethodsThis is a retrospective review of 53 consecutive patients who were treated in our spine surgery center from January 2005 to May 2012 due to severe thoracolumbar spinal fracture-dislocation. The patients in Group A (24 patients) underwent long-segment instrumentation laminectomy with pedicle screw-rod fixators for neural decompression. In Group B (29 patients), the patients underwent long-segment instrumentation laminectomy with pedicle screw-rod fixators for neural decompression evacuating of the ruptured disc and inserting of a bone graft into the evacuated disc space for interbody fusion. The mean time between injury and operation was 4.1 days (range 2–15 days). The clinical, radiologic and complication outcomes were analyzed retrospectively.ResultsPeriodic follow-ups were carried out until an affirmative union or treatment failure took place. A progressive kyphosis angle larger than 10°, loss of disc height, pseudoarthrosis, recurrence of dislocation or subluxation, or instrument failure before fusion were considered treatment failures. Treatment failures were detected in 13 cases in Group A (failure rate was 54.2%). In Group B, there were 28 cases in which definitive bone fusion was demonstrated on CT scans, and CT scans of the other cases demonstrated undefined pseudoarthrosis without hardware failure. There were statistically significant differences between the two groups (p<0.001 chi-square test). The neurologic recoveries, assessed by the ASIA scoring system, were not satisfactory for the neural deficit patients in either group, indicating there was no significant difference with regard to neurologic recovery between the two groups (p>0.05 Fisher's exact test).ConclusionIntervertebral disc damage is a common characteristic in type B and C spinal fracture-dislocation injuries. The damaged intervertebral disc should be removed and substituted with a bone graft because reserving the damaged disc in situ increases the risk of treatment failure.

Direct Repair for Treatment of Lumbar Symptomatic Spondylolysis without Spondylolisthesis in Young Patients Using Gillet Technique (V-Shaped Rod)

Introduction Spondylolysis developed during individual growth. In this article, direct repair of the pars defect was used to treat lumbar symptomatic spondylolysis without spondylolisthesis in young patients. Indication and postoperative outcomes of this operation were analyzed, to investigate the method of early treatment of spondylolysis, which can avoid the complication of spinal fusion for delayed isthmic spondylolisthesis caused by spondylolysis. Materials and Methods Twelve cases of lumbar symptomatic spondylolysis were retrospectively reviewed; all the cases received direct repair for the pars defect during 2005 to 2011, and was followed up for at least 2 years. Among them, there are eight cases of male and four cases of female, average 24.5 years old; there are 10 L5 spondylolysis and 4 L4 spondylolysis. They have low back pain and X-ray-confirmed bilateral spondylolysis without spondylolisthesis. There was no disc degeneration on MRI. The operation includes pars debridement, pedicle screw insertion, V-shaped rod connection, and bone autograft. VAS score was used to evaluate the pain status of the patient. Results All the patients got symptoms relieved, VAS score was reduced from 4.8 preoperation to 2.3 postoperation, and they all resumed to original work. During follow-up, the pars defect attained bony union in X-ray and 3D CT scan. Conclusion For the developmental spondylolysis with severe local symptom, but no disc degeneration, direct repair for the pars defect with pedicle screw and V-shaped rod and bone autograft can be used to heal the pars defect. This treatment, which is safe and effective, can reduce occurrence of disc degeneration caused by lumbar instability and delayed spondylolisthesis, avoid complications caused by spinal fusion. Disclosure of Interest None declared

Biomechanical Testing of a Lumbar Motion Normalization Device

Introduction Two specific scenarios that may benefit from dynamic lumbar stabilization are single-level moderate instability, where the stabilizing tissues are relatively incompetent, and juxta-level to fusion, where the last instrumented level requires intermediate stiffness (“topping off”) to prevent transfer of high stresses from the stiffer fusion construct to the intact adjacent levels. Both scenarios were evaluated in vitro to determine the biomechanical response of a new pedicle screw-based dynamic stabilizer. Materials and Methods Seven human cadaveric L2-S1 segments were tested (1) intact, (2) after moderate destabilization, (3) after 2-level hybrid posterior fixation, consisting of bilateral dynamic pedicle screws at L4 interconnected with rigid rods to standard pedicle screws at L5 and S1, (4) after 2-level rigid fixation, (5) after 1-level (L4-L5) dynamic fixation, and (6) after 1-level rigid fixation. In each condition, flexion, extension, lateral bending, and axial rotation were induced with pure moments of 7.5 Nm, while angular motion was tracked optoelectronically. Range of motion (ROM) and sagittal instantaneous axis of rotation (IAR) were calculated. Results In 1-level constructs, dynamic hardware allowed 104% of intact ROM, whereas rigid hardware allowed 49% of intact ROM. Relative to the intact IAR location at L4-L5, the IAR was shifted significantly farther posterior by rigid 1-level instrumentation than dynamic 1-level instrumentation. In 2-level constructs, the dynamic level (L4-L5) allowed significantly greater ROM than the rigid level (L5-S1) in all directions but allowed significantly less ROM than the intact level (L3-L4) in all directions except axial rotation. Conclusion Dynamic instrumentation shifted the IAR less than rigid instrumentation, providing more favorable kinematics. This dynamic stabilizer provided 1-level ROM that was close to intact ROM during all loading modes in vitro. In the “topping off” construct, the dynamic segment allowed intermediate ROM to give balanced transitional flexibility. Disclosure of Interest J. Zucherman: Conflict with Spartek Medical, Inc. K. Hsu: Conflict with Spartek Medical, Inc. N. Crawford: Conflict with Spartek Medical, Inc. L. Perez-Orribo: None declared P. Reyes: None declared N. Rodriguez-Martinez: None declared References Bono CM, Kadaba M, Vaccaro AR. Posterior pedicle fixation-based dynamic stabilization devices for the treatment of degenerative diseases of the lumbar spine. J Spinal Disord Tech 2009;22(5):376–383 Bozkuş H, Senoğlu M, Baek S, et al. Dynamic lumbar pedicle screw-rod stabilization: in vitro biomechanical comparison with standard rigid pedicle screw-rod stabilization. J Neurosurg Spine 2010;12(2):183–189 Crawford NR, Brantley AGU, Dickman CA, Koeneman EJ. An apparatus for applying pure nonconstraining moments to spine segments in vitro. Spine 1995;20(19):2097–2100 Crawford NR, Peles JD, Dickman CA. The spinal lax zone and neutral zone: measurement techniques and parameter comparisons. J Spinal Disord 1998;11(5):416–429 Schulte TL, Hurschler C, Haversath M, et al. The effect of dynamic, semi-rigid implants on the range of motion of lumbar motion segments after decompression. Eur Spine J 2008;17(8):1057–1065

Expandable PEEK Spacers for Interbody Distraction in the Lumbar Spine

Introduction StaXx XD is an expandable PEEK wafer implant that has been used in the treatment of lumbar degenerative disease. PEEK implants have been successfully used as interbody devices. There have been little studies evaluating the outcome of expandable PEEK devices. The aim of the current study was to determine the clinical effectiveness and radiographic outcome of expandable PEEK cages for interbody fusion. Materials and Methods This was a retrospective study of 49 consecutive patients who underwent lumbar interbody fusion with implantation of expandable PEEK cages in combination with posterior instrumentation using pedicle screw-rod constructs primarily for degenerative disorders. The patient's clinical outcomes were evaluated using the visual analog scale (VAS) and the Oswestry disability index (ODI). In addition, disc height, foraminal height, listhesis, local disc angle, lumbar lordosis, and graft subsidence were evaluated on pre-op, post-op, and on latest follow-op imaging. Results A total of 16 patients (32.6%) had undergone previous surgery at the index level. From pre-op to an average follow-up of 19.3 months, there was significant improvement in VAS back (6.42 vs. 3.11, p &lt; 0.001), VAS buttock (4.66 vs. 1.97, p = 0.002), VAS leg (4.55 vs. 1.96, p &lt; 0.001), and ODI (21.7 vs. 12.1, p &lt; 0.001) scores. In addition, there was significant increase in the average disc height (6.49 vs. 8.18 mm, p = 0.037) and foraminal height (15.6 vs. 18.53, p = 0.0001), and there was a significant reduction in the amount of listhesis (5.13 vs. 3.15, p = 0.005). The increase in average local disc angle and overall lumbar lordosis was not significant. Subsidence of 0.66 mm (7.4%) was observed at the latest follow-up ( p = 0.35). Conclusion Our mid-term results indicate that in situ expandable PEEK spacers for lumbar interbody distraction can effectively and durably restore the disc height and foraminal height and are associated with significant improvement in the clinical outcome. Disclosure of Interest None declared

Pedicle Screw-Rod Fixation for Treatment of Lumbosacral Intervertebral Disc Degeneration in Dogs with Low Back Pain

Introduction Low back pain in nonchondrodystrophic large breed dogs is a common problem and the most common cause is degenerative lumbosacral stenosis (DLSS). DLSS is characterized by intervertebral disc (IVD) degeneration of L7-S1, disc bulging, disc herniation, spinal canal stenosis, compression of neuronal tissue (cauda equina), thickened nerve roots (neuritis), soft tissue and bony proliferations, and foraminal stenosis. This ultimately results in discogenic and neurogenic pain. DLSS in dogs maybe treated conservatively or surgically. The most common surgical treatment is decompressive dorsal laminectomy and partial discectomy but in severe degenerated IVDs or in cases with foraminal stenosis and neuritis this may not be sufficient to treat low back pain. In these cases, pedicle screw-rod fixation (PSRF) can be performed. The aim of PSRF was to increase the intervertebral foraminal space for the exiting nerves and to promote spinal fusion. Distraction of the peripheral joints is one of the most promising new techniques in allowing chondrocytes to initiate repair of damaged cartilage in osteoarthritis. IVD degeneration, such as osteoarthritis, is also characterized by a decreasing number of nucleus pulposus cells and disc matrix. PSRF allows distraction of the IVD and may initiate, in a similar fashion as in joints, repair of the disc matrix. This was investigated in a pilot study in a dog that underwent temporary distraction and follow-up with magnetic resonance imaging (MRI). The aim of the present study was to investigate the effectiveness of PSRF in dogs with severe lumbosacral disc degeneration, to assess the effect of PSRF on the intervertebral foramina and on spinal fusion and, in a pilot study, to investigate the regenerative role of temporary distraction on the degenerated lumbosacral disc. Materials and Methods Eleven dogs with confirmed diagnosis of DLSS and IVD degeneration underwent PSRF of the lumbosacral junction ( Fig. 1 ). In 10 (out of the 11) dogs, PSRF was combined with dorsal laminectomy, disc fenestration, and various techniques to promote spinal fusion. In a subset of these patients (4 of 10 dogs), permanent distraction of the lumbosacral joint before PSRF was applied. In order to investigate the effect of temporary distraction of the degenerated lumbosacral joint, the PSRF was applied on the distracted joint for 3 months and removed thereafter. During follow-up, the dogs were monitored using questionnaires to owners and by clinical evaluation, diagnostic imaging with computed tomography and MRI, and measurement of ground reaction forces by force plate analysis. In the 4 dogs in which permanent distraction was applied, the increase in the intervertebral foramen was measured and in 1 dog the effect of temporary distraction on the disc matrix was evaluated on MRI. Results Clinical evaluation, responses of questionnaires to owners, and force plate data showed improvement or complete resolution of clinical signs after pedicle screw-rod fixation in 11 dogs during follow-up periods ranging from 5 months to 4 years. Diagnostic imaging showed no implant failures. In none of the 10 dogs was intervertebral body bone fusion of the lumbosacral joint achieved. In the dogs in which permanent distraction was applied, postoperative imaging showed significant enlargement of the intervertebral foramen between L7 and S1 ( Fig. 1 ). In the dog with temporary distraction, MRI indicated no changes in the IVD signal 3 months after removal of the PSRF device. [Figure: see text] Conclusion Pedicle screw-rod fixation offers a surgical treatment option for large dogs with severe degenerative lumbosacral stenosis. However, PSRF alone does not result in intervertebral body fusion between L7 and S1 and for that additional methods are necessary. Distraction and PSRF is effective in enlarging the intervertebral foramina and alleviating clinical signs. Temporary distraction alone, to initiate regeneration of the intervertebral disc matrix, did not have adverse effects and is an interesting concept for further investigation. Disclosure of Interest None declared

Lumbar spine stability after combined application of interspinous fastener and modified posterior lumbar interbody fusion: a biomechanical study

Posterior lumbar interbody fusion (PLIF) and internal fixation are commonly performed for the treatment of lower back pain due to lumbar spinal degeneration. We have developed a novel interspinous fixation device, the interspinous fastener (ISF) for potential use in the surgical management of degenerative spinal disease. The aim of this study was to assess the in vitro biomechanical characteristics of calf lumbar spine specimens after ISF fixation with modified PLIF. Ten lumbar spine (L3-L6) specimens from ten fresh calf cadavers (8-10weeks of age) were used. Each specimen underwent sequential testing for each of the following four groups: no instrumentation (INTACT); interspinous fusion device fixation+PLIF (ISF); unilateral pedicle screw and titanium rod fixation+PLIF (UPS); bilateral pedicle screw and titanium rod fixation+PLIF (BPS). Outcome measures included angular range of motion (ROM) during unloaded and loaded (8Nm) flexion, extension, left bending, right bending, left torsion and right torsion. For all unloaded and loaded assessments, ROM was significantly higher in the INTACT group compared with all other groups (P<0.05). Similarly, ROM was significantly higher in the UPS group (indicating decreased stability) compared with the ISF and BPS groups (P<0.05). The only significant difference between the ISF and BPS groups was in the ROM with unloaded extension (higher in the BPS group, P=0.006). We found that ISF fixation with PLIF of the lower lumbar spine provided biomechanical stability that was equivalent to that associated with bilateral pedicle screw/rod fixation with PLIF. The ISF shows potential as an alternative means of fixation in the surgical management of degenerative spinal disease.

Comparison of minimally invasive self-dilating pedicle screw-rod system and conventional pedicle screw-rod system for treatment of thoracolumbar fractures

Objective To compare the midterm clinical outcomes of minimally invasive percutaneous self-dilating pedicle screw-rod system and conventional open pedicle screw-rod system in the treatment of thoracolumbar fractures.Methods Enrolled in this research were 46 patients who had received surgery in our department from January 2012 to March 2013 for thoracolumbar fracture without neurological symptoms.Of them,24 were treated with minimally invasive percutaneous fixation by self-dilating pedicle screw-rod system and 22 with open fixation by conventional pedicle screw-rod system.There were no significant differences between the 2 groups in general data preoperation (P ＞ 0.05).The 2 groups were compared in terms of perioperative indexes,follow-up radiographic indexes and Oswestry disability index (ODI).Results All patients were followed up for 10 to 14 months (average,12 months).Compared with the open group,the minimally invasive group had smaller incisions,less intraoperative blood loss,less postoperative drainage,lower visual analogue scale (VAS) scores for incision one day postoperative,but longer operation time and intraoperative radiation exposure,with statistical significances in all the above differences (P ＜ 0.05).Compared with preoperation,significant improvements were observed at the last follow-up in all the patients regarding cobb angle,sagittal index and anterior height of the fractured vertebral body (P ＜ 0.05),but there were no significant differences between the 2 groups regarding cobb angle,sagittal index and anterior height of the fractured vertebral body at the last follow-up (P ＞ 0.05).There was no significant difference between the 2 groups either regarding ODI at the last follow-up (P ＞ 0.05).Conclusion Minimally invasive percutaneous self-dilating pedicle screw-rod system is an effective and safe treatment of thoracolumbar fractures,because it may lead to more limited invasion,less bleeding,and quicker recovery than the conventional pedicle screw-rod system. Key words: Thoracic vertebrae; Lumbar vertebrae; Fracture, bone; Surgical procedures,minimally invasive

Biomechanical comparison of reconstruction plate versus pedicle screw-rod system in fixation of the models of Tile B1 pelvic injury

Objective To compare the biomechanical properties of reconstruction plate and pedicle screw-rod system in fixation of the models of Tile B1 pelvic injury.Methods We used 7 cadaveric specimens of normal adult pelvis from 2 males and 5 females with an average death age of 42.1 years.The cadaveric pelvis preserved an intact spine from the fifth lumbar vertebra to 20 centimeters above the proximal ends of both femurs,intact pubic symphysis,bilateral hip joints,bilateral sacroiliac joints,and major pelvic ligaments.After the pelvic specimens were put in an AGS-X biomechanical testing machine at a simulated standing neutral posture,they were subjected to a vertical load of up to 500 N downward from the L5 vertebral body.The displacements of the symphysis pubis were recorded sequentially in the following 4 conditions:1.intact pelvis (the intact group); 2.models of Tile B1 pelvic injury simulating rotatory unstable injury of the pelvis in which the symphysis pubis was cut apart in combination with ruptures of ipsilateral sacrospinous and sacrotuberous ligaments (the injury group); 3.Tile B1 pelvic injury fixated with a reconstruction plate (the plate group).4.Tile B1 pelvic injury fixated with the pedicle screw-rod system (the screw-rod group).Results Under the vertical load of 500 N,the displacements of the symphysis pubis in the intact,injury,plate and screw-rod groups were respectively 0.121 ±0.025 mm,4.512 ±0.391 mm,0.358 ±0.051 mm,and 0.656 ±0.103 mm.There were significant differences between the 4 groups (F =725.707,P =0.000).The displacement increased from the intact group,the plate group,the screw-rod group to the injury group.The differences between any 2 groups were significant (P ＜ 0.05).Conclusions In fixation of the models of Tile B1 pelvic injury,the reconstruction plate and the pedicle screw-rod system can both effectively restore the biomechanical stability of the injured pelvis.However,internal fixation with the reconstruction plate may yield better biomechanical stability than that with the pedicle screw-rod system. Key words: Pelvis; Fracture fixation, internal; Bone plates; Bone nails; Biomechanics