Application of a new percutaneous multi-function pedicle locator in minimally invasive spine surgery.

In this study, a new percutaneous multi-function pedicle locator was designed for personalized three-dimensional positioning of a pedicle in minimally invasive spine surgery (MISS) without computer-assisted navigation technology. The proposed locator was used in a number of patients during MISS, and its advantages were analyzed. Based on the position of a pedicle determined by computed tomography (CT) and fluoroscopic images of a patient, 6 lines and 2 distances were used to determine the puncture point of a pedicle screw on skin, while 2 angles were used to indicate the direction of insertion of a pedicle guide needle from the patient's body surface. The results of the proposed locator were compared with those of the conventional freehand technique in MISS. The potential benefits of using the locator included enhanced surgical accuracy, reduced operation time, alleviation of the harmful intra-operative radiation exposure, lower costs, and shortened learning curve for young orthopedists.

Conventional versus stereotactic image guided pedicle screw placement during spinal deformity correction: a retrospective propensity score-matched study of a national longitudinal database.

PURPOSE/AIM: To compare complications, readmissions, revisions, and payments between navigated and conventional pedicle screw fixation for treatment of spine deformity. METHODS: The Thomson Reuters MarketScan national longitudinal database was used to identify patients undergoing osteotomy, posterior instrumentation, and fusion for treatment of spinal deformity with or without image-guided navigation between 2007-2016. Conventional and navigated groups were propensity-matched (1:1) to normalize differences between demographics, comorbidities, and surgical characteristics. Clinical outcomes and charges were compared between matched groups using bivariate analyses. RESULTS: A total of 4,604 patients were identified as having undergone deformity correction, of which 286 (6.2%) were navigated. Propensity-matching resulted in a total of 572 well-matched patients for subsequent analyses, of which half were navigated. Rate of mechanical instrumentation-related complications was found to be significantly lower for navigated procedures (p = 0.0371). Navigation was also associated with lower rates of 90-day unplanned readmissions (p = 0.0295), as well as 30- and 90-day postoperative revisions (30-day: p = 0.0304, 90-day: p = 0.0059). Hospital, physician, and total payments favored the conventional group for initial admission (p = 0.0481, 0.0001, 0.0019, respectively); however, when taking into account costs of readmissions, hospital payments became insignificantly different between the two groups. CONCLUSIONS: Procedures involving image-guided navigation resulted in decreased instrumentation-related complications, unplanned readmissions, and postoperative revisions, highlighting its potential utility for the treatment of spine deformity. Future advances in navigation technologies and methodologies can continue to improve clinical outcomes, decrease costs, and facilitate widespread adoption of navigation for deformity correction.

Intraoperative CT Scan Verification of Pedicle Screw Placement in AIS to Prevent Malpositioned Screws: Safety Benefit and Cost.

STUDY DESIGN: Prospective database review. OBJECTIVES: Determine if use of intraoperative 3D imaging of pedicle screw position provides clinical and cost benefit. SUMMARY OF BACKGROUND: Injury or reoperation from malpositioned pedicle screws in adolescent idiopathic scoliosis (AIS) surgery occurs but is increasingly considered to be a never-event. To avoid complications, intraoperative 3D imaging of screw position may be obtained. METHODS: A prospective, consecutive AIS database at a high-volume pediatric spine center was examined three years before and after implementation of an intraoperative low-dose computed tomographic (CT) scan protocol. All screws were placed via freehand technique and corrected if found to be outside optimal trajectory on the postplacement CT scan. Demographic and outcome data were compared between cohorts, along with number, location, and reason for screw change. Cost analysis was based on the average cost of revision surgery for screw malposition versus intraoperative CT use. RESULTS: There were 153 patients in the pre-CT and 153 in the post-CT cohorts with a minimum 2-year follow-up. Two reoperations were needed for revision of improper screw placement in the pre-CT group and none in the post-CT group. Number of patients needed to harm was 76 (absolute risk increase = 1.31% [-0.49%, 3.11%]). Of those who had intraoperative CT scans, 80 (52.3%) needed on average 1.75 screw trajectories/lengths changed. Forty-three percent were medial breaches; of these, 39% were in the concavity. There were no differences between patients who did and did not need screw repositioning with regard to body mass index (BMI), age, curve size, surgeon/trainee side, screw density, or preoperative and one-year postoperative Scoliosis Research Society-22 patient questionnaire (SRS-22) scores. The average cost of reoperation for malposition was $4,900, whereas the cost of a single intraoperative CT was $232. CONCLUSION: Intraoperative CT is an effective tool to prevent reoperation in AIS surgery for incorrect screw placement. Despite high volume, experience, and specialty training, incorrect trajectories occur and systems should be in place for preventable error. LEVEL OF EVIDENCE: Level II.

How Many Screws Are Necessary to Be Considered an Experienced Surgeon for Freehand Placement of Thoracolumbar Pedicle Screws?: Analysis Using the Cumulative Summation Test for Learning Curve.

OBJECTIVE: To determine the amount of screws needed to achieve an adequate skill level for pedicle screw placement (PSP) via the freehand technique in the nondeformed thoracolumbar spine using the cumulative summation test for learning curve (LC-CUSUM) analysis. METHODS: This study includes the first 85 patients who underwent pedicle screw installation in the thoracic and lumbar spine by a single orthopedic surgeon. The surgeon had 1 years' experience of fellowship training in a tertiary teaching hospital. The learning curve of freehand PSP was investigated using the LC-CUSUM analysis. Procedure success was defined as acceptable accuracy of PSP, which was divided into group 1 (the screw breaches the pedicle's cortex by less than 2 mm) and group 2 (the screw is completely within the pedicle). RESULTS: A total of 52 cases and 313 pedicle screws were included and analyzed in this study. The LC-CUSUM analysis signaled competency for freehand PSP at the 115th pedicle screw (17th case) in group 1 and at the 312th pedicle screw (52nd case) in group 2. This means that a trainee with no experience with freehand PSP reached an adequate accuracy level of PSP with less than 2 mm pedicle breaches at the 115th screw and completely within the pedicle at the 312th screw. There were no major complications, such as neurovascular injury, and life-threatening complications. CONCLUSIONS: In this study, the learning curve analysis demonstrated that a substantial learning period may be necessary before an adequate level of performance is achieved for freehand PSP in the nondeformed thoracolumbar spine.

Implant density is not related to patient-reported outcome in the surgical treatment of patients with idiopathic scoliosis.

Aims: There is little information about the optimum number of implants to be used in the surgical treatment of idiopathic scoliosis. Retrospective analysis of prospectively collected data from the Swedish spine register was undertaken to discover whether more implants per operated vertebra (implant density) leads to a better outcome in the treatment of idiopathic scoliosis. The hypothesis was that implant density is not associated with patient-reported outcomes, the correction of the curve or the rate of reoperation. Patients and Methods: A total of 328 patients with idiopathic scoliosis, aged between ten and 20 years at the time of surgery, were identified in the Swedish spine register (Swespine) and had patient reported outcomes including the Scoliosis Research Society 22r instrument (SRS-22r) score, EuroQol 5 dimensions quality of life, 3 level (EQ-5D-3L) score and a Viual Analogue Score (VAS) for back pain, at a mean follow-up of 3.1 years and reoperation data at a mean follow-up of 5.5 years. Implant data and the correction of the curve were assessed from radiographs, preoperatively and a mean of 1.9 years postoperatively. The patients were divided into tertiles based on implant density. Data were analyzed with analysis of variance, logistic regression or log-rank test. Some analyses were adjusted for gender, age at the time of surgery, the flexibility of the major curve and follow-up. Results: The mean number of implants per operated vertebra in the low, medium and high-density groups were 1.36 (1.00 to 1.54), 1.65 (1.55 to 1.75) and 1.91 (1.77 to 2.00), respectively. There were no statistically significant differences in the correction of the curve, the SRS-22r total score, EQ-5D-3L index or number of reoperations between the groups (all p > 0.34). In the SRS-22r domains, self-image was marginally higher in the medium implant density group (p = 0.029) and satisfaction marginally higher in the high implant density group (p = 0.034). Conclusion: These findings suggest that there is no clear advantage in using a high number of implants per operated vertebra in the surgical treatment of patients with idiopathic scoliosis. Cite this article: Bone Joint J 2018;100-B:1080-6.

Posterior paraspinal muscle versus post-middle approach for the treatment of thoracolumbar burst fractures: A randomized controlled trial.

BACKGROUND: This randomized controlled trial (RCT) aimed to compare the clinical outcomes of thoracolumbar burst fractures (TLBFs) treated with open reduction and internal fixation via the posterior paraspinal muscle approach (PPMA) and the post-middle approach (PA). METHODS: Patients with a traumatic single-level TLBFs (T10-L2), treated at our hospital between December 2009 and December 2014, were randomly allocated to Group A (PPMA) and Group B (PA). Sex, age, time from injury to surgery, the American Spinal Injury Association Impairment Scale score (ASIAIS), comorbidities, vertebral level, pre- and postoperative kyphotic angle (KA), visual analog scale (VAS) pain score, and the Oswestry Disability Index (ODI) scores were included in the analysis. Operative time, intraoperative blood loss, x-ray exposure time, postoperative drainage volume, superficial infection, and occurrence of deep infection were documented. The patients were followed up at 2 weeks; 1, 3, and 6 months; 1 and 2 years; and every 6 months thereafter. Radiological assessments were performed to assess fracture union and detect potential loosening and breakage of the pedicle screws and rods at each follow-up. Postoperative VAS and ODI scores were used to evaluate the clinical outcomes. RESULTS: A total of 62 patients were enrolled (30 in Group A and 32 in Group B, respectively). The operative time (P < .001) and x-ray exposure time (P < .001) in Group A were significantly longer than those in Group B. However, compared to Group B, there were less intraoperative blood loss (P < .001), lower postoperative drainage volume (P < .001), lower VAS scores (2-week (P = .029), 1-month (P = .023), 3-month (P = .047), and 6-month follow-up (P = .010)), and lower ODI scores (2-week, P = .010; 1-month, P < .001; 3-month, P = .028; and 6-month follow-up, P = .033) in Group A. CONCLUSIONS: Although PPMA required a longer operative time and x-ray exposure time, PPMA provided several advantages over PA, including less intra-operative blood loss and lower postoperative drainage volume, and greater satisfaction with postoperative pain relief and functional improvement, than PA, especially at the 6-month follow-up after surgery. Further high-quality multicenter studies are warranted to validate our findings.

Evidence level of the placement of screws outside pedicle in thoracic and lumbar spine / Nível de evidência sobre a colocação de parafusos fora do pedículo na coluna torácica e lombar / Nivel de evidencia de la colocación de tornillos fuera del pedículo en columna torácica y lumbar

ABSTRACT International recommendations in spine surgery require reproducible, safe and effective procedures. The placement of pedicle screws is technically demanding and relies on different methods of support, which result a high rate of complications related to suboptimal screw placement, with reports ranging from 15.7% to 40% according to Hansen-Algenstaedt N and Koktekir E in separate studies. This study carried out a systematic review of existing literature to identify the level of evidence of the placement of pedicle screws outside the pedicle in thoracic and lumbar spine. For the systematic review, a search of the existing literature, based on the use of MeSH terms in PubMed-Medline, Ovid, The Cochrane Library, MedicLatina, Elsevier, and EBSCO databases. According to the literature found, most authors agree that the placement of screws outside the pedicle itself does not represent a serious complication or that requires repositioning in a second surgery even when they are found to have a violation up to 50% of the medial wall of the pedicle. However, they agree that repositioning should be immediate if it is shown with imaging studies such as MRI and CT that endangers vascular and/or neurological structures, or are associated with biomechanical alterations of the spine. Level of Evidence II; Systematic Review of studies level II.

RESUMO As recomendações internacionais em cirurgia da coluna vertebral, forçam a execução de procedimentos reprodutíveis, seguros e eficazes. A colocação de Parafusos transpediculares é tecnicamente exigente e se baseia em métodos diferentes de apoio, dando como resultado uma alta taxa de complicações relacionadas com a colocação sub-optima de parafusos, apresentando relatórios variando de 15,7% para 40%, de acordo com Hansen-Algenstaedt N e Koktekir E em estudos independentes. Este estudo é uma revisão sistemática da literatura existente, identificando o nível de evidência sobre a colocação de parafusos transpediculares fora do pedículo em coluna torácica e lombar. Para a revisão sistemática, foi conduzida uma pesquisa da literatura, baseada no uso de termos MeSH, nos bancos de dados: PubMed-Medline, Ovid, The Cochrane Library, MedicLatina, Elsevier e EBSCO. De acordo com o encontrado, a maioria dos autores concordam que a colocação dos parafusos fora pedículo em si não representem uma complicação grave e não obriga a realocação deles em um segundo tempo cirúrgico, mesmo que eles apresentam uma violação de até 50% da parede medial do pedículo. No entanto, concordam que o posicionamento deve ser imediato se pôr em perigo as estruturas vasculares ou neurológicas ou estarem associados a alterações na biomecânica vertebral. Nível de Evidência II; Revisão Sistemática do nível de estudos II

RESUMEN Las recomendaciones internacionales en cirugía de columna obligan a realizar procedimientos reproducibles, seguros y eficaces. La colocación de tornillos trans-pediculares es demandante técnicamente y se apoya en diversos métodos de asistencia, que dan como resultado un alto índice de complicaciones relacionadas con la colocación subóptima de los tornillos, con reportes que van desde el 15,7% al 40% según Hansen-Algenstaedt N y Koktekir E en estudios independientes. Este estudio realiza una revisión sistemática de la literatura existente, donde se identifica el nivel de evidencia de la colocación de tornillos transpediculares fuera del pedículo en la columna torácica y lumbar. Para la revisión sistemática se realizó una búsqueda de la bibliografía existente, basada en la utilización de términos MeSH, en la base de datos: PubMed-Medline, Ovid, The Cochrane Library, MedicLatina, Elsevier y EBSCO. De acuerdo con la literatura encontrada, la mayoría de los autores concuerdan en que la colocación de tornillos fuera de pedículo en sí misma no representa una complicación grave o que requiera recolocación en un segundo tiempo quirúrgico, aun cuando se encuentren con una violación de hasta el 50% de la pared medial del pedículo; sin embargo concuerdan en que la recolocación debe ser inmediata si se demuestra con estudios de imagen como IRM y TAC que pone en riesgo estructuras vasculares y/o neurológicas, o se asocian a alteraciones biomecánicas de la columna vertebral.Nivel de Evidencia II; Revisión sistemática de Estudios de Nivel II.

Hybrid constructs pedicle screw with apical sublaminar bands versus pedicle screws only for surgical correction of adolescent idiopathic scoliosis.

PURPOSE: To compare the 2-year minimum postoperative results of posterior correction and spinal arthrodesis using translational correction with hybrid (sublaminar bands on concave side and pedicle screw) constructs versus correction with intermediate density pedicle screw-only constructs in the treatment of AIS (Lenke 1). METHODS: A total of 37 patients with AIS at single institutions who underwent posterior spinal arthrodesis pedicle screw with sublaminar bands at the apex (19 patients) (Group A) or pedicle screw-only (18) constructs (Group B) were selected and matched according to similar age at surgery 13.8 years (Group A) and 14.3 years (Group B), similar arthrodesis area 12.3 (Group A) and 11.5 (Group B), all curves Lenke type 1 with similar pre-op curve 54° (Group A) and 57° (Group B). Patients were evaluated pre-op, immediately post-op, and at min 2-year follow-up according to radiographic curve correction, operating time, intraoperative blood loss, and f.u. loss of correction. RESULTS: The average curve correction was 65.6% in sublaminar group and 68% in pedicle screw group. At 2-year follow-up, loss of the major curve correction was 2% in sublaminar group compared to 3% in pedicle screw group. Postoperative coronal and sagittal balance was similar in both groups. Operating time averaged 200 min (Group A) and 180 min (Group B). Intraoperative blood loss was significantly different in both groups 700 ± 160 cc in sublaminar group and 630 ± 150 cc in pedicle screw group. There were no neurologic complications in both groups. CONCLUSION: The two groups offer similar curve correction without neurologic complications in the surgical treatment of AIS (Lenke 1). The use of sublaminar bands on the apex (concave side) can be a valid fixation in the presence of hypoplastic pedicle, can reduce the thoracic hypokyphosis and derotate the vertebra but had more blood loss comparing to pedicle screws alone. These slides can be retrieved under Electronic Supplementary Material.

Management of Pediatric Posttraumatic Thoracolumbar Vertebral Body Burst Fractures by Use of Single-Stage Posterior Transpedicular Approach.

PURPOSE: The posterior transpedicular approach (PTA) is a posterior approach that has the advantage of achieving circumferential arthrodesis by a single posterior-only approach. The purpose of this study was to analyze our experience with PTA in the management of pediatric traumatic thoracolumbar burst fractures (TTLBFs). METHODS: Consecutive pediatric patients (age ≤18 years) with TTLBFs treated with PTA for 6 years were included in this retrospective study. Correction of kyphotic deformity and change in neurologic status were analyzed to assess outcome. The Cobb angle and American Spinal Injury Association (ASIA) grade were used for this purpose. RESULTS: There were 6 male and 8 female patients. Five patients had complete injury (ASIA-A), and 9 had incomplete injury. The mean Thoracolumbar Injury Classification and Severity score was 6.71. The mean preoperative Cobb angle was 14.71° and improved to -3.35° postoperatively (mean kyphosis correction -18.05°). Two of the patients experienced iatrogenic nerve root injury. There was 1 postoperative mortality due to complications unrelated to the surgery. The mean Cobb angle was -0.07° at the 32.2-month follow-up visit. Six patients experienced cage subsidence, but none required revision surgery. Postoperatively, 11 (78.5%) patients showed neurologic improvement, and none experienced deterioration. The average ASIA score improved from 2.5 to 3.78. A fusion rate of 100% (n = 12) was observed at the last follow-up visit. CONCLUSIONS: The present study demonstrates that PTA is a feasible approach in selected pediatric patients with unstable traumatic thoracolumbar burst fractures, with results comparable with those in the adult population. This study demonstrates in detail the procedure, along with the neurologic and radiologic outcomes of this approach in the pediatric population.

Spinal navigation for minimally invasive thoracic and lumbosacral spine fixation: implications for radiation exposure, operative time, and accuracy of pedicle screw placement.

PURPOSE: Navigation is emerging as a useful adjunct in percutaneous, minimally invasive spinal surgery (MIS). The aim of this study was to compare C-Arm navigated, O-Arm navigated and conventional 2D-fluoroscopy assisted MIS thoracic and lumbosacral spine fixation techniques in terms of operating time, radiation exposure and accuracy of pedicle screw (PS) placement. METHODS: Retrospective observational study of 152 consecutive adults who underwent MIS fixations for spinal instability: 96 2D-fluoroscopy assisted, 39 3D-C-Arm navigated and 27 using O-Arm navigated. RESULTS: O-Arm navigation significantly reduced PS misplacement (1.23%, p) compared to 3D-C-Arm navigation (7.29%, p = 0.0082) and 2D-fluoro guided placement (5.16%, p = 0379). 3D-C-Arm navigation was associated with lower procedural radiation exposure of the patient (0.4 mSv) than O-Arm navigation (3.24 mSv) or 2D-fluoro guidance (1.5 mSv). Operative time was comparable between three modalities. CONCLUSIONS: O-Arm navigation provides greater accuracy of percutaneous instrumentation placement with an acceptable procedural radiation dose delivered to the patients and comparable operative times. These slides can be retrieved under Electronic Supplementary material.

The Role of Posterior Screw Fixation in Single-Level Transforaminal Lumbar Interbody Fusion During Whole Body Vibration: A Finite Element Study.

OBJECTIVE: Few studies have evaluated the need for supplementary instrumentation after lumbar interbody fusion under the condition of whole body vibration (WBV) that is typically present in vehicles. This study aimed to determine the effect of posterior pedicle screw fixation on dynamic response of the whole lumbar spine to vertical WBV after transforaminal lumbar interbody fusion (TLIF). METHODS: A previously validated nonlinear, osteoligamentous finite element (FE) model of the intact L1-sacrum human lumbar spine was modified to simulate single-level (L4-L5) TLIF without and with bilateral pedicle screw fixation (BPSF). Transit dynamic analysis was performed on the 2 developed models under a sinusoidal vertical vibration load of ±40 N and a compressive follower preload of 400 N. The resulting dynamic response results for the 2 models in terms of stresses and deformations were recorded and compared. RESULTS: When compared with no fixation, BPSF decreased dynamic responses of the spinal levels to the vertical vibration after TLIF. At the fused level (L4-L5), vibration amplitudes of the von-Mises stresses in L4 inferior endplate and L5 superior endplate decreased after BPSF by 48.0% and 46.4%, respectively. At other disc levels (L1-L2, L2-L3, L3-L4, and L5-S1), vibration amplitudes of the disc bulge, von-Mises stress in annulus ground substance and intradiscal pressure also produced 4.2%-9.0%, 2.3%-8.9%, and 3.4%-8.8% deceases, respectively, after BPSF. CONCLUSIONS: After TLIF, application of BPSF can be helpful in the prevention of spine injury during vertical WBV.

Pedicle screw anchorage of carbon fiber-reinforced PEEK screws under cyclic loading.

PURPOSE: Pedicle screw loosening is a common and significant complication after posterior spinal instrumentation, particularly in osteoporosis. Radiolucent carbon fiber-reinforced polyetheretherketone (CF/PEEK) pedicle screws have been developed recently to overcome drawbacks of conventional metallic screws, such as metal-induced imaging artifacts and interference with postoperative radiotherapy. Beyond radiolucency, CF/PEEK may also be advantageous over standard titanium in terms of pedicle screw loosening due to its unique material properties. However, screw anchorage and loosening of CF/PEEK pedicle screws have not been evaluated yet. The aim of this biomechanical study therefore was to evaluate whether the use of this alternative nonmetallic pedicle screw material affects screw loosening. The hypotheses tested were that (1) nonmetallic CF/PEEK pedicle screws resist an equal or higher number of load cycles until loosening than standard titanium screws and that (2) PMMA cement augmentation further increases the number of load cycles until loosening of CF/PEEK screws. METHODS: In the first part of the study, left and right pedicles of ten cadaveric lumbar vertebrae (BMD 70.8 mg/cm3 ± 14.5) were randomly instrumented with either CF/PEEK or standard titanium pedicle screws. In the second part, left and right pedicles of ten vertebrae (BMD 56.3 mg/cm3 ± 15.8) were randomly instrumented with either PMMA-augmented or nonaugmented CF/PEEK pedicle screws. Each pedicle screw was subjected to cyclic cranio-caudal loading (initial load ranging from - 50 N to + 50 N) with stepwise increasing compressive loads (5 N every 100 cycles) until loosening or a maximum of 10,000 cycles. Angular screw motion ("screw toggling") within the vertebra was measured with a 3D motion analysis system every 100 cycles and by stress fluoroscopy every 500 cycles. RESULTS: The nonmetallic CF/PEEK pedicle screws resisted a similar number of load cycles until loosening as the contralateral standard titanium screws (3701 ± 1228 vs. 3751 ± 1614 load cycles, p = 0.89). PMMA cement augmentation of CF/PEEK pedicle screws furthermore significantly increased the mean number of load cycles until loosening by 1.63-fold (5100 ± 1933 in augmented vs. 3130 ± 2132 in nonaugmented CF/PEEK screws, p = 0.015). In addition, angular screw motion assessed by stress fluoroscopy was significantly smaller in augmented than in nonaugmented CF/PEEK screws before as well as after failure. CONCLUSIONS: Using nonmetallic CF/PEEK instead of standard titanium as pedicle screw material did not affect screw loosening in the chosen test setup, whereas cement augmentation enhanced screw anchorage of CF/PEEK screws. While comparable to titanium screws in terms of screw loosening, radiolucent CF/PEEK pedicle screws offer the significant advantage of not interfering with postoperative imaging and radiotherapy. These slides can be retrieved under Electronic Supplementary Material.

Effect of two-level pedicle-screw fixation with different rod materials on lumbar spine: A finite element study.

BACKGROUND: Pedicle-screw-rod fixation system is very popular surgical remedy for degenerative disc disease. It is important to observe load vs. spinal motion characteristic for better understanding of clinical problems and treatment of spinal instability associated with low-back pain. OBJECTIVE: The objective of this study is to understand the effect [range of motion (ROM) and intervertebral foramen height] of pedicle-screw fixation with three rod materials on lumbar spine under three physiological loading conditions. METHOD: A three-dimensional finite element (FE) model of lumbar to sacrum (L1-S) vertebrae with pedicle-screw-rod fixation at L3-L5 level is developed. Three rod materials [titanium alloy (Ti6Al4V), ultra-high molecular weight poly ethylene (UHMWPE) and poly-ether-ether-ketone (PEEK)] are used for two-level fixation and the FE models are simulated for axial rotation, lateral bending and flexion-extension under ±10 Nm moment and 500 N compressive load and compared with the intact (natural) model. RESULT & DISCUSSION: For axial rotation, lateral bending and flexion, ROM increased 2.8, 4.5 and 1.83 times respectively for UHMWPE, and 3.7, 7.2 and 2.15 times respectively for PEEK in comparison to Ti6Al4V. As ROM is 49, 29 and 31% of the intact model during axial rotation, lateral bending and flexion respectively, PEEK rod produced better motion flexibility than Ti6Al4V and UHMWPE rod. Foramen height increased insignificantly by 2.21% for the PEEK rod with respect to the intact spine during flexion. For the PEEK rod, maximum stress of 40 MPa during axial rotation is much below the yield stress of 98 MPa. CONCLUSION: Ti6Al4V pedicle-screw-rod fixation system highly restricted the ROM of the spine, which is improved by using UHMWPE and PEEK, having lower stiffness. The foramen height did not vary significantly for any implant materials. In terms of ROM and maximum stress, PEEK rod may be considered for a better implant design to get better ROM and thus mobility.

Radiographic and Functional Outcome in Adolescent Idiopathic Scoliosis Operated With Hook/Hybrid Versus All-Pedicle Screw Instrumentation-A Retrospective Study in 149 Patients.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: To compare radiographic outcome and health-related quality of life in patients with adolescent idiopathic scoliosis (AIS) treated with hook/hybrid (H/H) or all-pedicle screw (PS) instrumentation. SUMMARY OF BACKGROUND DATA: PS instrumentation has largely replaced H/H in the surgical treatment of AIS but whether a normalized sagittal profile can be obtained with the PS construct is still debated. Additionally, comparative studies assessing HRQL and surgical complications are needed. METHODS: Two consecutive series of surgically treated AIS patients were included. Surgical treatment consisted of H/H or low-profile all-PS instrumentation. Radiographic and clinical follow-up, including SRS-22r questionnaires, was performed a minimum of two years postoperatively. RESULTS: There were 85 and 64 patients in the H/H and PS group, respectively. The groups did not differ on baseline parameters apart from a lower flexibility in the H/H group (34% ± 14% vs. 39% ± 14% in the PS group, p = .026). Mean curve correction at final follow-up was 31% ± 13% versus 49% ± 12% in the H/H and PS group, respectively (p < .001), and mean loss of correction was 7° versus 4° (p < .001). The Cincinnati correction index was significantly higher in the PS group at final follow-up (p < .001). Postoperative thoracic kyphosis was significantly higher in the H/H group (27° ± 11° vs. 22° ± 11° in the PS group) with a mean change in kyphosis of 3° ± 9° versus -3° ± 12° in the H/H and PS group, respectively. SRS-22 scores did not differ between the two groups (p > .090), and the reoperation rate at final follow-up was 9% in the H/H group and 6% in the PS group (p = .556). CONCLUSIONS: In a large consecutive cohort of AIS patients followed for a minimum of two years, we found a significantly better curve correction and less loss of correction with PS instrumentation compared to H/H. There was no significant difference in SRS-22r scores at final follow-up. LEVEL OF EVIDENCE: Level III.

Full fusion of proximal thoracic curve helps to prevent postoperative cervical tilt in Lenke type 2 adolescent idiopathic scoliosis patients with right-elevated shoulder.

BACKGROUND: To date, no study had reported the phenomenon of deteriorated postoperative cervical tilt in Lenke type 2 adolescent idiopathic scoliosis patients. The purpose of this study is to evaluate the cervical tilt in Lenke type 2 adolescent idiopathic scoliosis patients with right-elevated shoulder treated by either full fusion or partial/non fusion of the proximal thoracic curve. METHODS: A total of 30 Lenke type 2 AIS patients with preoperative right-elevated shoulder underwent posterior spinal instrumentation from 2009 to 2011 were included in this study. All the subjects were divided into 2 groups according to the selection of upper instrumented vertebra. There were 14 cases proximally fused to T1 or T2 (Group A) and 16 cases proximally fused to T3 or below (Group B). Both standing anteroposterior and sagittal X-ray films of the spine obtained preoperatively, one week after the operation, and at a minimum of two-year follow-up were analyzed with respect to the following parameters: cervical tilt, T1 tilt, proximal thoracic Cobb angle, main thoracic Cobb angle, apical vertebral translation of proximal thoracic curve, apical vertebral translation of main thoracic curve, radiographic shoulder height, cervical lordosis, proximal thoracic kyphosis and main thoracic kyphosis. RESULTS: Most (83.3%) of the patients in these two groups gained satisfactory shoulder balance after surgery. However, the cervical tilt significantly improved in group A (p < 0.001) but deteriorated in group B (p < 0.001). In group A, the decrease of cervical tilt significantly positively correlated with that of T1 tilt (p < 0.001). In group B, the increase of cervical tilt significantly positively correlated with both the increase of T1 tilt (p < 0.001) and the increase of apical vertebral translation of proximal thoracic curve (p < 0.05). CONCLUSIONS: Lenke type 2 AIS patients with right-elevated shoulder gain improved shoulder but deteriorated cervical tilt after partial/non fusion of proximal thoracic curve. Full fusion of proximal thoracic curve helps to prevent the residual cervical tilt in these patients.

Progressive Kyphosis Associated with Tethered Cord Syndrome Treated by Posterior Vertebral Column Resection in a Pediatric Patient.

Posterior vertebral column resection is a novel surgical approach for the treatment of progressive kyphosis associated with tethered cord syndrome that was first treated with untethering surgery. A patient with tethered cord syndrome associated with kyphosis first underwent untethering surgery, resulting in progressive kyphosis. Posterior vertebral column resection was performed to correct the kyphosis while shortening the spinal column to prevent the spinal cord from stretch injury. Good correction of kyphosis and reduction of tension on the neural elements were achieved without any neurological deficits. In progressive kyphosis associated with tethered cord syndrome, posterior vertebral column resection after untethering surgery represents a safe and efficacious but technically challenging option.

Minimally invasive guidewireless, navigated pedicle screw placement: a technical report and case series.

OBJECTIVE Percutaneous pedicle screw insertion (PPSI) is a mainstay of minimally invasive spinal surgery. Traditionally, PPSI is a fluoroscopy-guided, multistep process involving traversing the pedicle with a Jamshidi needle, placement of a Kirschner wire (K-wire), placement of a soft-tissue dilator, pedicle tract tapping, and screw insertion over the K-wire. This study evaluates the accuracy and safety of PPSI with a simplified 2-step process using a navigated awl-tap followed by navigated screw insertion without use of a K-wire or fluoroscopy. METHODS Patients undergoing PPSI utilizing the K-wire-less technique were identified. Data were extracted from the electronic medical record. Complications associated with screw placement were recorded. Postoperative radiographs as well as CT were evaluated for accuracy of pedicle screw placement. RESULTS Thirty-six patients (18 male and 18 female) were included. The patients' mean age was 60.4 years (range 23.8-78.4 years), and their mean body mass index was 28.5 kg/m2 (range 20.8-40.1 kg/m2). A total of 238 pedicle screws were placed. A mean of 6.6 pedicle screws (range 4-14) were placed over a mean of 2.61 levels (range 1-7). No pedicle breaches were identified on review of postoperative radiographs. In a subgroup analysis of the 25 cases (69%) in which CT scans were performed, 173 screws were assessed; 170 (98.3%) were found to be completely within the pedicle, and 3 (1.7%) demonstrated medial breaches of less than 2 mm (Grade B). There were no complications related to PPSI in this cohort. CONCLUSIONS This streamlined 2-step K-wire-less, navigated PPSI appears safe and accurate and avoids the need for radiation exposure to surgeon and staff.

Accuracy of cannulated pedicle screw versus conventional pedicle screw for extra-pedicular screw placement in dysplastic pedicles without cancellous channel in adolescent idiopathic scoliosis: a computerized tomography (CT) analysis.

PURPOSE: This study aimed at studying the accuracy and safety of extra-pedicular screw insertion for dysplastic pedicles in AIS comparing cannulated screw system versus conventional screw system. METHODS: 104 AIS patients with 1524 pedicle screws were evaluated using CT scan. 302 screws were inserted in dysplastic pedicles using fluoroscopic guidance technique. 155 screws were inserted using a cannulated system (Group 1), whereas 147 screws were inserted using standard screws (Group 2). The pedicle perforations were assessed using a classification by Rao et al.; G0: no violation; G1: <2 mm perforation; G2: 2-4 mm perforation; and G3: >4 mm perforation). For anterior perforations, the pedicle perforations were assessed using a modified grading system (Grade 0: no violation, Grade 1: less than 4 mm perforation; Grade 2: 4 mm to 6 mm perforation; and Grade 3: more than 6 mm perforation). RESULTS: The perforation rate in Group 1 was 4.5% and in Group 2 was 15.6% (p = 0.001). Most of the perforations were anterior perforations (53.3%). The anterior perforation rate in Group 1 was 1.9% compared to 8.8% in Group 2 (p = 0.009). Group 1 has a medial perforation rate of 1.3% compared to Group 2, 6.1% (p = 0.031). The rate of critical pedicle perforation in Group 1 was 2.6% and in Group 2 was 6.8% (p = 0.102). In Group 1, there were no critical medial perforation but there was one G2 lateral perforation, one G2 superior perforation and two G3 anterior perforations. In Group 2, there were three G2 medial perforations, one G2 lateral perforation, one G2 anterior perforation and five G3 anterior perforations. CONCLUSION: Usage of cannulated screw system significantly increases the accuracy of pedicle screw insertion in dysplastic pedicles in AIS.

Pedicle screw insertion accuracy in terms of breach and reposition using a new intraoperative cone beam computed tomography imaging technique and evaluation of the factors associated with these parameters of accuracy: a series of 695 screws.

PURPOSE: The goals of this study were to assess the accuracy of pedicle screw insertion using an intraoperative cone beam computed tomography (CBCT) system, and to analyze the factors potentially influencing this accuracy. METHODS: Six hundred and ninety-five pedicle screws were inserted in 118 patients between October 2013 and March 2016. Screw insertion was performed using 2D-fluoroscopy or CBCT-based navigation. Accuracy was assessed in terms of breach and reposition. All the intraoperative CBCT scans, done after screw insertion, were reviewed to assess the accuracy of screw placement using two established classification systems: Gertzbein and Heary. Generalized linear mixed models were used to model the odds (95% CI) for a screw to lead to a breach according to the independent variables. RESULTS: The breach rate was 11.7% using the Gertzbein classification and 15.4% using the Heary classification. Seventeen screws (2.4%) were repositioned intraoperatively. The only factor affecting statistically the odds to have a breach was the indication of surgery. The patients with non-degenerative disease had a significantly higher risk of breach than those with degenerative disease. CONCLUSION: Use of intraoperative CBCT as 2D-fluoroscopy or coupled with a navigation system for pedicle screw insertion is accurate in terms of breach occurrence and reposition. However, these rates depend on the classification or grading system used. Use of a navigation system does not decrease the risk of breach significantly. And the risk of breach is higher in non-degenerative conditions (trauma, scoliosis, infection, and malignancy disease) than in degenerative diseases.

Treatment of thoracolumbar burst fractures by short-segment pedicle screw fixation using a combination of two additional pedicle screws and vertebroplasty at the level of the fracture: a finite element analysis.

BACKGROUND: Traditional one-above and one-below four-screw posterior short-segment instrumentation is used for unstable thoracolumbar burst fractures. However, this method has a high rate of implant failure and early loss of reduction. The purpose of this study was to use finite element (FE) analysis to determine the effect of treating thoracolumbar burst fractures by short-segment pedicle screw fixation using a combination of two additional pedicle screws and vertebroplasty at the level of the fracture. METHODS: An intact T11-L1 spine FE model was created from the computed tomography images of a male subject. Four fixation models with posterior fusion devices (pedicle screws, rods, cross-link) were established to simulate an unstable thoracolumbar fracture with different fusion surgeries: short-segment fixation with: 1) a link (S-L); 2) intermediate bilateral screws (S-I); 3) a link and calcium sulfate cement (S-L-C); 4) intermediate bilateral screws and calcium sulfate cement (S-I-C). Different loading conditions (flexion, extension, lateral bending, and axial rotation) were applied on the models and analyzed with a FE package. The range of motion (ROM), and the maximum value and distribution of the implant stress, and the stress in the facet joint, were compared between the intact and fixation models. RESULTS: The ROM in flexion, extension, axial rotation, and lateral bending was the smallest in the S-I-C model, followed by the S-I, S-L-C, and S-L models. Maximum von Mises stress values were larger under lateral bending and axial rotation loadings than under flexion and extension loading. High stress was concentrated at the crosslink and rod junctions. Maximal von Mises stress on the superior vertebral body for all loading conditions was larger than that on the inferior vertebral body. The maximal von Mises stress of the pedicle screws during all states of motion were 265.3 MPa in S-L fixation, 192.9 MPa in S-I fixation, 258.4 MPa in S-L-C fixation, and 162.3 MPa in S-I-C fixation. CONCLUSIONS: Short-segment fixation with two intermediate pedicle screws together with calcium sulfate cement at the fractured vertebrae may provide a stiffer construct and less von Mises stress of the pedicle screws and rods as compared to other types of short-segment fixation.