Adult Spine Deformity (ASD) is a degenerative condition of the adult spine leading to altered spine curvatures and mechanical balance. Computational approaches, like Finite Element (FE) Models have been proposed to explore the etiology or the treatment of ASD, through biomechanical simulations. However, while the personalization of the models is a cornerstone, personalized FE models are cumbersome to generate. To cover this need, we share a virtual cohort of 16807 thoracolumbar spine FE models with different spine morphologies, presented in an online user-interface platform (SpineView). To generate these models, EOS images are used, and 3D surface spine models are reconstructed. Then, a Statistical Shape Model (SSM), is built, to further adapt a FE structured mesh template for both the bone and the soft tissues of the spine, through mesh morphing. Eventually, the SSM deformation fields allow the personalization of the mean structured FE model, leading to generate FE meshes of thoracolumbar spines with different morphologies. Models can be selectively viewed and downloaded through SpineView, according to personalized user requests of specific morphologies characterized by the geometrical parameters: Pelvic Incidence; Pelvic Tilt; Sacral Slope; Lumbar Lordosis; Global Tilt; Cobb Angle; and GAP score. Data quality is assessed using visual aids, correlation analyses, heatmaps, network graphs, Anova and t-tests, and kernel density plots to compare spinopelvic parameter distributions and identify similarities and differences. Mesh quality and ranges of motion have been assessed to evaluate the quality of the FE models. This functional repository is unique to generate virtual patient cohorts in ASD. Acknowledgements: European Commission (MSCA-TN-ETN-2020-Disc4All-955735, ERC-2021-CoG-O-Health-101044828)

Abstract. Objectives. to evaluate the efficacy and safety of topically applied tranexamic acid (TXA) in thoracolumbar spinal tuberculosis surgery, posterior approach. Methods. Thoracolumbar spine tuberculosis patients who requiring debridement, pedicle screw fixation and fusion surgery were divided into two groups. In the TXA group (n=50), the wound surface was soaked with TXA (1 g in 100 mL saline solution) for 3 minutes after exposure, after decompression, and before wound closure, and in the control group (n=116) using only saline. Intraoperative blood loss, drain volume 48 hours after surgery, amount of blood transfusion, transfusion rate, the haemoglobin, haematocrit after the surgery, the difference between them before and after the surgery, incision infection and the incidence of deep vein thrombosis between the two groups. Results. EBL for the control group was 783.33±332.71 mL and for intervention group 410.57±189.72 mL (p<0.001). The operative time for control group was 3.24±0.38 hours and for intervention group 2.99±0.79 hours (p<0.695). Hemovac drainage on days1 and 2 for control group was 167.10±53.83mL and 99.33±37.5 mL, respectively, and for intervention group 107.03±44.37mL and 53.38±21.99mL, respectively (p<0.001). The length of stay was significantly shorter in the intervention group (4.8±1.1 days) compared to control group (7.0±2.3 days). There was bo different in incision side infection and DVT. Conclusions. Topical TXA is a viable, cost-effective method of decreasing perioperative blood loss in major spine surgery with fewer overall complications than other methods. Further studies are required to find the ideal dosage and timing

Introduction and Objective. Up to 30% of thoracolumbar (TL) fractures are missed in the emergency room. Failure to identify these fractures can result in neurological injuries up to 51% of the casesthis article aimed to clarify the incidence and risk factors of traumatic fractures in China. The China National Fracture Study (CNFS. Obtaining sagittal and anteroposterior radiographs of the TL spine are the first diagnostic step when suspecting a traumatic injury. In most cases, CT and/or MRI are needed to confirm the diagnosis. These are time and resource consuming. Thus, reliably detecting vertebral fractures in simple radiographic projections would have a significant impact. We aim to develop and validate a deep learning tool capable of detecting TL fractures on lateral radiographs of the spine. The clinical implementation of this tool is anticipated to reduce the rate of missed vertebral fractures in emergency rooms. Materials and Methods. We collected sagittal radiographs, CT and MRI scans of the TL spine of 362 patients exhibiting traumatic vertebral fractures. Cases were excluded when CT and/or MRI where not available. The reference standard was set by an expert group of three spine surgeons who conjointly annotated (fracture/no-fracture and AO Classification) the sagittal radiographs of 171 cases. CT and/or MRI were used confirm the presence and type of the fracture in all cases. 302 cropped vertebral images were labelled “fracture” and 328 “no fracture”. After augmentation, this dataset was then used to train, validate, and test deep learning classifiers based on the ResNet18 and VGG16 architectures. To ensure that the model's prediction was based on the correct identification of the fracture zone, an Activation Map analysis was conducted. Results. Vertebras T12 to L2 were the most frequently involved, accounting for 48% of the fractures. Accuracies of 88% and 84% were obtained with ResNet18 and VGG16 respectively. The sensitivity was 89% with both architectures but ResNet18 had a significantly higher specificity (88%) compared to VGG16 (79%). The fracture zone used was precisely identified in 81% of the heatmaps. Conclusions. Our AI model can accurately identify anomalies suggestive of TL vertebral fractures in sagittal radiographs precisely identifying the fracture zone within the vertebral body

Introduction. Senile kyphosis arises from anterior ‘wedge’ deformity of thoracolumbar vertebrae, often in the absence of trauma. It is difficult to reproduce these deformities in cadaveric spines, because a vertebral endplate usually fails first. We hypothesise that endplate fracture concentrates sufficient loading on to the anterior cortex that a wedge deformity develops subsequently under physiological repetitive loading. Methods. Thirty-four cadaveric thoracolumbar “motion segments,” aged 70–97 yrs, were overloaded in combined bending and compression. Physiologically-reasonable cyclic loading was then applied, at progressively higher loads, for up to 2 hrs. Before and after fracture, and again after cyclic loading the distribution of compressive loading on the vertebral body was assessed from recordings of compressive stress along the sagittal mid-plane of the adjacent intervertebral disc. Vertebral deformity was assessed from radiographs at the beginning and end of testing. Results. Initial overload usually fractured a vertebral endplate, at 2.31 kN (STD 0.85). There was minimal anterior wedging, but pressure in the nucleus of the adjacent disc was reduced by 65.2% on average, and relatively elevated in the annulus and neural arch. Subsequent cyclic loading then caused anterior wedge deformity of the vertebral body, with the height of the anterior and posterior cortex decreasing by 34.3% (13.2) and 12.7% (7.5) respectively, and wedge angle increasing from 5.0° (3.76) to 11.4° (3.93) (all p<0.001). Discussion and Conclusion. Our hypothesis is supported: initial minor damage facilitates progressive anterior wedge deformity by transferring compressive loading on to the anterior cortex. Detecting initial endplate damage is important to minimise subsequent vertebral deformity in patients with osteoporosis. No conflicts of interest. Sources of funding: Funding was provided by a Royal College of Surgeons of England Research Fellowship and by the Gloucestershire Arthritis Trust. This work was presented at the British Orthopaedic Research Society Meeting

Background. While the biomechanical properties of trans-pedicular screws have proven to be superior in the lumbar spine, little is known concerning pullout strength of trans-pedicle screws in comparison to different distal terminal constructs like sublaminar hooks alone, trans pedicular screws with sublaminar hooks and clow hooks alone in the thoracolumbar spine surgery. In vitro biomechanical pullout testing was performed to evaluate the axial pullout strength of four different distal terminal constructs in thoracolumbar spine surgery. Methods. 32 fresh-frozen lamb spines were used. The lamb spines were divided into four groups, each group is composed of eight lamb spine cadavers with a different distal fixation pattern was used to terminate the construct at L1. (Group 1) trans-pedicular screws alone, (Group 2) sublaminar hooks alone, (Group 3) trans-pedicular screws augmented with a sublaminar hooks via a domino connector and (Group 4) clow hooks alone. Results. The average pullout strength of group 1 was 927N, group2 was 626N, group 3 was 988N and group 4 was 972N. Group 3 and 4 showed the most significant pullout forces when compared to group 1 and group 2. However Group 3 and group 4 didn't show any significant statistical difference when compared to each others. Conclusion. Our study thus suggests that the strongest construct that may reduce the pullout phenomina in the distal fixation constructs are the trans-pedicular screw with laminar hooks. It is strongly advised to be used in osteoporotic bones and in conditions where pullout strength is required to be enhanced. But farther prospective clinical studies are needed to clearly demonstrate the beneficial effect of a trans-pedicular screw augmented with a laminar hooks in reducing the risk of distal instrumentation pullout. Level of Evidence. Level 5. Disclosure. The authors declare that no conflict of interests were associated with the present study

Introduction. Senile kyphosis arises from anterior ‘wedge’ deformity of thoracolumbar vertebrae, often in the absence of trauma. It is difficult to reproduce these deformities in cadaveric spines, because a vertebral endplate usually fails first. We hypothesise that endplate fracture concentrates sufficient loading on to the anterior cortex that a wedge deformity develops subsequently under physiological repetitive loading. Methods. Thirty-four cadaveric thoracolumbar “motion segments,” aged 70–97 yrs, were overloaded in combined bending and compression. Physiologically-reasonable cyclic loading was then applied, at progressively higher loads, for up to 2 hrs. Before and after fracture, and again after cyclic loading the distribution of compressive loading on the vertebral body was assessed from recordings of compressive stress along the sagittal mid-plane of the adjacent intervertebral disc. Vertebral deformity was assessed from radiographs at the beginning and end of testing. Results. Initial overload usually fractured a vertebral endplate, at 2.31 kN (STD 0.85). There was minimal anterior wedging, but pressure in the nucleus of the adjacent disc was reduced by 65.2% on average, and relatively elevated in the annulus and neural arch. Subsequent cyclic loading then caused anterior wedge deformity of the vertebral body, with the height of the anterior and posterior cortex decreasing by 34.3% (13.2) and 12.7% (7.5) respectively, and wedge angle increasing from 5.0° (3.76) to 11.4° (3.93) (all p<0.001). Discussion and Conclusion. Our hypothesis is supported: initial minor damage facilitates progressive anterior wedge deformity by transferring compressive loading on to the anterior cortex. Detecting initial endplate damage is important to minimise subsequent vertebral deformity in patients with osteoporosis. 256 words (250 excluding section headings) Acknowledgements Funding was provided by a Royal College of Surgeons of England Research Fellowship and by the Gloucestershire Arthritis Trust

Posterior spinal surgery is associated with a significant amount of blood loss. The factors predisposing the patient to excessive bleeding-and therefore transfusion- are not well established nor is the effect of transfusion on the outcomes following spinal surgery. We had two goals in this study. First, we were to investigate any suspected risk factors of transfusion in posterior thoraco-lumbar fusion patients. Second, we wanted to observe the negative impact-if one existed- of transfusion on the outcomes of surgery

All adults undergoing posterior thoraco-lumbar spine fusion in our institution from May 2015 to May 2018 were included. Data collected included demographic data as well as BMI, preoperative hemoglobin, American Society of Anesthesiologists classification (ASA), delta Hemoglobin, estimated blood loss, incidence of transfusion, number of units transfused, number of levels fused, length of stay and re-admission within 30 days. The data was analyzed to correlate these variables with the frequency of transfusion and then to assess the association of adverse outcomes with transfusion.

125 patients were included in the study. Only 6 patients (4.8%) required re-admission within the first 30 days after discharge. Length of stay averaged 8.4 days (3–74). 18 patients (14.4%) required transfusion peri-operatively. When multiple variables were analyzed for any correlation, the number of levels fused, age and BMI had statistically significant correlation with the need for transfusion (P <0.005)

Patients undergoing posterior thoraco-lumbar fusion are more likely to require blood transfusion if they were older, over-weight & obese or had a multi-level fusion. Receiving blood transfusion is associated with increased complication rates.

Introduction. Pedicle screw loosening in posterior instrumentation of thoracolumbar spine occurs up to 60% in osteoporotic patients. These complications may be alleviated using more flexible implant materials and novel designs that could be optimized with reliable computational modeling. This study aimed to develop and validate non-linear homogenized finite element (hFE) simulations to predict pedicle screw toggling. Method. Ten cadaveric vertebral bodies (L1-L5) from two female and three male elderly donors were scanned with high-resolution peripheral quantitative computed tomography (HR-pQCT, Scanco Medical) and instrumented with pedicle screws made of carbon fiber-reinforced polyether-etherketone (CF/PEEK). Sample-specific 3D-printed guides ensured standardized instrumentation, embedding, and loading procedures. The samples were biomechanically tested to failure in a toggling setup using an electrodynamic testing machine (Acumen, MTS) applying a quasi-static cyclic testing protocol of three ramps with exponentially increasing peak (1, 2 and 4 mm) and constant valley displacements. Implant-bone kinematics were assessed with a stereographic 3D motion tracking camera system (Aramis SRX, GOM). hFE models with non-linear, homogenized bone material properties including a strain-based damage criterion were developed based on intact HR-pQCT and instrumented 3D C-arm scans. The experimental loading conditions were imposed, the maximum load per cycle was calculated and compared to the experimental results. HR-pQCT-based bone volume fraction (BV/TV) around the screws was correlated with the experimental peak forces at each displacement level. Result. The nonlinear hFE models accurately (slope = 1.07, intercept = 0.2 N) and precisely (R. 2. = 0.84) predicted the experimental peak forces at each displacement level. BV/TV alone was a weak predictor (R. 2. <0.31). Conclusion. The hFE models enable fast design iterations aiming to reduce the risk of screw loosening in low-density vertebrae. Improved flexible implant designs are expected to contribute to reduced complication rates in osteoporotic patients

The current study aims to compare the clinico radiological outcomes between Non-Fusion Anterior Scoliosis (NFASC) Correction and Posterior Spinal Fusion (PSF) for Lenke 5 curves at 2 years follow up. Methods:38 consecutive Lenke 5 AIS patients treated by a single surgeon with NFASC (group A) or PSF (group B) were matched by age, Cobb's angle, and skeletal maturity. Intraoperative blood loss, operative time, LOS, coronal Cobbs, and SRS22 scores at 2 years were compared. Flexibility was assessed by modified Schober's test. Continuous variables were compared using student t-tests and categorical variables were compared using chi-square. The cohort included 19 patients each in group A and B . Group A had M:F distribution of 1:18 while group B had 2:17. The mean age in group A and group B were 14.8±2.9 and 15.3±3.1 years respectively. The mean follow-up of patients in groups A and B were 24.5±1.8 months and 27.4±2.1 months respectively. Mean pre-op thoracolumbar/lumbar (TL/L) cobbs for group A and group B were 55°±7° and 57.5°±8° respectively. At two years follow up, the cobbs for group A and B were 18.2°±3.6° and 17.6°±3.5° respectively (p=0.09). The average operating time for groups A and B were 169±14.2 mins and 219±20.5 mins respectively (p<0.05). The average blood loss of groups A and B were 105.3±15.4 and 325.3±120.4 respectively (p<0.05). The average number of instrumented vertebra between groups A and B were 6.2 and 8.5 respectively (p<0.05). The average LOS for NFASC and PSF was 3.3±0.9 days and 4.3±1.1 days respectively (p<0.05). No statistically significant difference in SRS 22 score was noted between the two groups. No complications were recorded. Our study shows no significant difference in PSF and NFASC in terms of Cobbs correction and SRS scores, but the NFASC group had significantly reduced blood loss, operative time, and fewer instrumented levels. NFASC is an effective alternative technique to fusion to correct and stabilize Lenke 5 AIS curves with preservation of spinal motion

The current study aims to find the role of Enhance Recovery Pathway (ERP) as a multidisciplinary approach aimed to expedite rapid recovery, reduce LOS, and minimize morbidity associated with Non Fusion Anterior Scoliosis Correction (NFASC) surgery. A retrospective analysis of 35 AIS patients who underwent NFASC with Lenke 1 and Lenke 5 curves with a minimum of 1 year of follow-up was done. Patient demographics, surgical details, postoperative analgesia, mobilization, length of stay (LOS), patient satisfaction survey score with respect to information and care, and 90 days complications were collected. The cohort included 34 females and 1 male with a mean age of 15.2 years at the time of surgery. There were 16 Lenke 1 and 19 Lenke 5 in the study. Mean preoperative major thoracic and thoracolumbar/lumbar Cobb's angle were 52˚±7.6˚ and 51˚±4.5˚ respectively. Average blood loss and surgical time were 102 ±6.4 ml and 168 ± 10.2 mins respectively. Average time to commencing solid food was 6.5±1.5 hrs. Average time to mobilization following surgery was 15.5± 4.3 hrs. The average duration to the stopping of the epidural was 42.5±3.5 hrs. The average dose of opioid consumption intraoperatively was 600.5±100.5 mcg of fentanyl i.v. and 12.5±4.5 mg morphine i.v. Postoperatively opioids were administered via an epidural catheter at a dose of 2 mg of morphine every 24 hours up to 2 days and an infusion of 2mcg/hr of fentanyl along with 0.12-0.15% ropivacaine. The average duration to transition to oral analgesia was 55.5±8.5 hrs .20 patients had urinary catheter and the average time to removal of the catheter was 17.5±1.4 hrs. 25 patients had a chest tube and the average time to remove of chest tube was 25.5±3.2 hrs. The average length of hospital stay was 3.1±0.5 days. No patient had postoperative ileus or requirement of blood transfusion or any other complications. No correlation was found between LOS and initial cobb angle. The application of ERP in AIS patients undergoing NFASC results in reduced LOS and indirectly the cost, reduced post-operative opioid use, and overall improve patient satisfaction score

Introduction:. Most of the published papers on AI based diagnosis have focused on the algorithm's diagnostic performance in a ‘binary’ setting (i.e. disease vs no disease). However, no study evaluated the actual value for the clinicians of an AI based approach in diagnostic. Detection of Traumatic thoracolumbar (TL) fractures is challenging on planar radiographs, resulting in significant rates of missed diagnoses (30-60%), thus constituting a field in which a performance improvement is needed. Aim of this study is therefore to evaluate the value provided by AI generated saliency maps (SM), i.e. the maps that highlight the AI identified region of interests. Methods:. An AI model aimed at identifying TL fractures on plain radiographs was trained and tested on 567 single vertebrae images. Three expert spine surgeons established the Ground Truth (GT) using CT and MRI to confirm the presence of the fracture. From the test set, 12 cases (6 with a GT of fracture and 6 with a GT of no fracture, associated with varying levels of algorithm confidence) were selected and the corresponding SMs were generated and shown to 7 independent evaluators with different grade of experience; the evaluators were requested to: (1) identify the presence or absence of a fracture before and after the saliency map was shown; (2) grade, with a score from 1 (low) to 6 (high) the pertinency (correlation between the map and the human diagnosis), and the utility (the perceived utility in confirming or not the initial diagnosis) of the SM. Furthermore, the usefulness of the SM was evaluated through the rate of correct change in diagnosis after the maps had been shown. Finally, the obtained scores were correlated with the algorithm confidence for the specific case. Results:. Of the selected maps, 8 had an agreement between the AI diagnosis and the GT, while in 4 the diagnosis was discordant (67% accuracy). The pertinency of the map was found higher when the AI diagnosis was the same as the GT and the human diagnosis (respectively p-value = .021 and <.000). A positive and significant correlation between the AI confidence score and the perceived utility (Spearman: 27%, p-value=.0-27) was found. Furthermore, evaluator with experience < 5 year found the maps more useful than the experts (z-score=2.004; p-value=.0455). Among the 84 evaluation we found 12 diagnostic errors in respect to the GT, 6 (50%) of which were reverted after the saliency map evaluation (z statistic = 1.25 and p-value = .21). Discussion:. The perceived utility of AI generated SM correlate with the model confidence in the diagnosis. This highlights the fact that to be considered helpful, the AI must provide not only the diagnosis but also the case specific confidence. Furthermore, the perceived utility was higher among less experienced users, but overall, the SM were useful in improving the human diagnostic accuracy. Therefore, in this setting, the AI enhanced approach provides value in improving the human performance

Currently, between 17% of patients undergoing surgery for adult spinal deformity experience severe instrumentation related problems such as screw pullout or proximal junctional failure necessitating revision surgery. Cables may be used to reinforce pedicle screw fixation as an additive measure or may provide less rigid fixation at the construct end levels in order to prevent junctional level problems. The purpose of this study is to provide insight into the maximum expected load during flexion in UHMWPE cable in constructs intended for correction of adult spine deformity (degenerative scoliosis) in the PoSTuRe first-in-man clinical trial. Following the concept of toppinoff, a new construct is proposed with screw/cable fixation of rods at the lower levels and standalone UHMWPE cables at the upper level (T11). A parametric FE model of the instrumented thoracolumbar spine, which has been previously validated, was used to represent the construct. Pedicle screws are modeled by assigning a rigid tie constraint between the rod and the lamina of the corresponding spinal level. Cables are modeled using linear elastic line elements, fixing the rod to the lamina medially at the cranial laminar end and laterally at the caudal laminar end. A Youngs modulus was assigned such that the stiffness of the line element was the same as that of the cable. An 8 Nm flexion moment was applied to the cranial endplate. The maximum value of the force in the wire (80 N) is found at the T11 (upper) level. At the other levels, forces in the cable are very small because most of the force is carried by the screw (T12) or because the wires are force shielded by the contralateral and adjacent level pedicle screws (L2, L3). The model provides first estimates of the forces that can be expected in the UHMWPE cables in constructs for kyphosis correction during movement. It is expected that this approach can help in defining the number of wires for optimal treatment

Summary Statement. Bilaretal epiphysiodesis of he neurocentral cartilages causes shortening of the sagittal length of the pedicles and a subsequent spinal stenosis at the operated segments, resembling that found in patients with achrondroplasia. Introduction. The introduction of pedicle screws in the immature spine may have implications for the growth of the vertebra. The effect of blocking the growth of neurocentral cartilage (NC) is not yet fully defined. Block hypothetically leads to a bilateral symmetrical alteration of the vertebral growth. Using an experimental animal model, our goal is to analyze if a bilateral epiphysiodesis of the NC using pedicle screws is able to induce narrowing of the spinal canal in the thoracolumbar spine. Experimental animals and Methods. A total of 24 domestic pigs were operated on by bilateral blocking of the NC using pedicle screws. The animals were divided into 4 groups depending on the level of blockage: A, low thoracic levels; B, thoracolumbar transitional hinge; C, upper lumbar spine; and D, blocking of the caudal lumbar level below L5 segment. Different morphological, morphometric and standard radiological parameters were analyzed at the thoracic and lumbar vertebrae of the animals. The deviation from the physiological parameters was established by comparing all parameters obtained in the NC-blocked animals with those acquired in 14 pigs without NC blocking. These animals were considered as the control group. Results. None of the animals that underwent NC epiphysiodesis showed asymmetrical spinal growth inducing deformities in the coronal plane. There was neither rotation nor wedging of the vertebral bodies. Whatever the level involved, NC epiphysiodesis caused shortening of the sagittal length of the pedicles and a subsequent decreasing of the antero-posterior diameter of the spinal canal. These features resulted in a frank spinal stenosis at the operated levels. However, the transverse diameter of the spinal canal was conserved in the coronal plane. In the sagittal plane, blocking of the neurocentral cartilage conditioned a lumbar hyperlordosis with compensatory kyphosis of the upper level to the operated vertebra. Conclusions. Symmetrical growth arresting of neurocentral cartilages induces a narrow spinal canal by decreasing the sagittal diameter similar to that observed in patients with achondroplasia. The most affected structure was the development of the vertebral pedicles

Summary Statement. Incorrect pedicle screw placement can lead to neurological complications. Practice outside the operating room on realistic bone models, with force feedback, could improve safety. Pedicle forces in cadaveric specimens are reported, to support development of a training tool for residents. Introduction. Inserting screws into the vertebral pedicles is a challenging step in spinal fusion and scoliosis surgeries. Errors in placement can lead to neurological complications and poor mechanical fixation. The more experienced the surgeon, the better the accuracy of the screw placement. A physical training system would provide orthopaedic residents with the feel of performing pedicle cannulation before operating on a patient. The proposed system consists of realistic bone models mimicking the geometry and material properties of typical patients, coupled with a force feedback probe. The purpose of the present study was to determine the forces encountered during pedicle probing to aid in the development of this training system. Methods. We performed two separate investigations. In the first study, 15 participants (9 expert surgeons, 3 fellows, 3 residents) were asked to press a standard pedicle awl three times onto a mechanical scale, blinded to the force, demonstrating what force they would apply during safe pedicle cannulation and during unsafe cortical breach. In the second study, three experienced surgeons used a standard pedicle awl fitted with a one-degree of freedom load cell to probe selected thoracolumbar vertebrae of eight cadaveric specimens to measure the forces required during pedicle cannulation and deliberate breaching, in randomised order. A total of 42 pedicles were tested. Results. Both studies had wide variations in the results, but were in general agreement. Cannulation (safe) forces averaged approximately 90 N (20 lb) whereas breach (unsafe) forces averaged approximately 135–155 N (30–35 lb). The lowest average forces in the cadaveric study were for pedicle cannulation, averaging 86 N (range, 23–125 N), which was significantly lower (p<0.001) than for anterior breach (135 N; range, 80–195 N); medial breach (149 N; range, 98–186 N) and lateral breach (157 N; range, 114–228 N). There were no significant differences among the breach forces (p>0.1). Cannulation forces were on average 59% of the breach forces (range, 19–84%) or conversely, breach forces were 70% higher than cannulation forces. Discussion. To our knowledge, axial force data have not previously been reported for pedicle cannulation and breaching. A large range of forces was measured, as is experienced clinically. Additional testing is planned with a six-degree-of-freedom load cell to determine all of the forces and moments involved in cannulation and breaching throughout the thoracolumbar spine. These results will inform the development of a realistic bone model as well as a breach prediction algorithm for a physical training system for spine surgery. The opportunity to learn and practice outside of the operating room, including learning from deliberate mistakes, should increase the confidence and comprehension of residents performing the procedure, enhance patient safety, reduce surgical time, and allow faster progression of learning inside the operating room

INTRODUCTION. Growth-guidance constructs are an alternative to growing rods for the surgical treatment of early onset scoliosis (EOS). In growth-guidance systems, free-sliding anchors preserve longitudinal spinal growth, thereby eliminating the need for surgical lengthening procedures. Non-segmental constructs containing ultra-high molecular weight polyethylene (UHMWPE) sublaminar wires have been proposed as an improvement to the traditional Luque trolley. In such a construct, UHMWPE sublaminar wires, secured by means of a knot, serve as sliding anchors at the proximal and distal ends of a construct, while pedicle screws at the apex prevent rod migration and enable curve derotation. Ideally, a construct with the optimal UHMWPE sublaminar wire density, offering the best balance between providing adequate spinal fixation and minimizing surgical exposure, is designed preoperatively for each individual patient. In a previous study, we developed a parametric finite element (FE) model that potentially enables preoperative patient-specific planning of this type of spinal surgery. The objective of this study is to investigate if this model can capture the decrease in range of motion (ROM) after spinal fixation as measured in an experimental study. MATERIALS AND METHODS. In a previous in vitro study, the ROM of an 8-segment porcine spine was measured before and after instrumentation, using different instrumentation constructs with a sequentally decreasing number of wire fixation points. In the current study, the parametric FE model of the thoracolumbar spine was first validated relative to ROM values reported in the literature. The rods, screws, and sublaminar wires were implemented, and the model was subsequently used to replicate the in vitro tests. The experimental and simulated ROM”s for the different instrumentation conditions were compared. RESULTS. Good agreement between in vitro biomechanical tests and FE simulations was observed in terms of the decrease in ROM for the complete construct with wires at each level. The stepwise increase in total ROM with decreasing number of wires at the construct ends was less prominent in silico in comparison to in vitro. CONCLUSION. Important first steps in the implementation and validation of a growth-guidance construct for EOS patients in a patient-specific FE model of the spine have been made in this study. The parametric nature of the FE model allows for rapid personalization. Although further improvements to the model will be necessary to better distinguish between different spinal instrumentation constructs, we conclude that the model can well capture essential aspects of spinal motion and the overall effect of instrumentation

Summary Statement. Novel radiopaque UHMWPE sublaminar cables may be a promising alternative to gliding pedicle screws or titanium sublaminar cables within a growth-guidance system for the surgical treatment of early onset scoliosis. Introduction. Growth-guidance or self-lengthening rod systems are an alternative to subcutaneous growing rods and the vertical expandable prosthetic titanium rib for the treatment of early onset scoliosis. Their main perceived advantage over growing rods is the marked decrease in subsequent operative procedures. The Shilla growth-guidance system and a modern Luque trolley are examples of such systems; both depend on gliding pedicle screws and/or sliding titanium sublaminar wires. However, the unknown consequences of metal-on-metal wear debris are reason for concern especially in young patients. In this study, instrumentation stability, residual growth in the operated segment after surgery and biocompatibility of the novel radiopaque UHMWPE cables as an alternative to gliding pedicles screws or titanium sublaminar wires were assessed in an immature sheep model. Materials and methods. Twelve immature sheep were treated with segmental sublaminar spinal instrumentation: dual CoCr rods were held in place by pedicle screws at the most caudal instrumented level (L5) and novel radiopaque UHMWPE (Bi. 2. O. 3. additive) woven cables were placed at 5 thoracolumbar levels. Lateral radiographs were taken at 4-week intervals to evaluate growth of the instrumented segment. Four age-matched, unoperated animals served as radiographic control. After 24 weeks follow-up, the animals were sacrificed and the spines were harvested for histological evaluation and CT analysis. Results. No neurological deficits and no complications occurred during the initial postoperative period. One animal died during follow-up due to unknown cause. At sacrifice, none of the cables had loosened and the instrumentation remained stable. Substantial growth occurred in the instrumented segment (L5-T13) in the intervention group. No significant difference in growth of the operated segment was found between the intervention and control groups. Histological analysis showed fibrous encapsulation of the novel radiopaque UHMWPE sublaminar cable in the epidural space, with no evidence of chronic inflammation. Discussion. Novel radiopaque UHMWPE cables may be a promising alternative to gliding pedicle screws or titanium sublaminar cables within a growth-guidance system. UHMWPE cables may improve growth results due to the smooth surface properties of the UHMWPE cable and address concerns regarding the consequences of metal-on-metal wear debris

Introduction. Delamination of the annulus fibrosus is an early feature of disc degeneration, and it allows individual lamellae to collapse into the nucleus, or to bulge radially outwards. We . hypothesise. that delamination is driven by high gradients of compressive stress in the annulus. Methods. 102 thoracolumbar motion segments (T8-9 to L5-S1) were dissected from 42 cadavers aged 19–92 yrs. Each specimen was subjected to 1 kN compression, while intradiscal compressive stresses were measured by pulling a pressure transducer along the disc's mid-sagittal diameter. Stress gradients were measured, in the anterior and posterior annulus, as the average rate of increase in compressive stress (MPa/mm) between the nucleus and the region of maximum stress in the annulus. Average nucleus pressure was also recorded. Disc degeneration was assessed macroscopically on a scale of 1–4. Results. Compared to grade 2 discs, moderately degenerated grade 3 discs showed increased stress gradients in the annulus, especially in the posterior annulus where they increased by an average 106%. Nucleus pressure showed minimal changes. However, comparing grade 3 discs with severely degenerated grade 4 discs showed that nucleus pressure fell by 47%, while stress gradients showed little or no further change. Discussion. The results support our hypothesis. In early disc degeneration, a minor reduction in nucleus pressure is sufficient to generate high stress gradients in the annulus. These shear adjacent lamellae, causing delamination and allowing internal displacement of nucleus. As disc degeneration progresses, nucleus migration causes severe decompression, and compressive loading is transferred increasingly to the neural arch. Conflicts of Interest. None. Source of Funding. None. This abstract has not been previously published in whole or in part; nor has it been presented previously at a national meeting

Introduction. Osteoporotic vertebral fractures can cause severe vertebral wedging and kyphotic deformity. This study tested the hypothesis that kyphoplasty restores vertebral height, shape and mechanical function to a greater extent than vertebroplasty following severe wedge fractures. Methods. Pairs of thoracolumbar “motion segments” from seventeen cadavers (70–97 yrs) were compressed to failure in moderate flexion and then cyclically loaded to create severe wedge deformity. One of each pair underwent vertebroplasty and the other kyphoplasty. Specimens were then creep loaded at 1.0kN for 1 hour. At each stage of the experiment the following parameters were measured: vertebral height and wedge angle from radiographs, motion segment compressive stiffness, and stress distributions within the intervertebral discs. The latter indicated intra-discal pressure (IDP) and neural arch load-bearing (F. N. ). Results. Fracture and cyclic loading reduced anterior vertebral height by 34%, increased wedge angle from 5.0° to 11.4°, increased F. N. by 58% and reduced IDP and compressive stiffness by 96% and 44% respectively. Kyphoplasty restored anterior height to a greater extent than vertebroplasty (p<0.001), by 96% versus 59% immediately after augmentation, and by 79% versus 47% after subsequent creep loading. Wedge angle was also reduced to a greater extent following kyphoplasty than vertebroplasty (p<0.02) by 7.2° vs 4.2° after augmentation and 6.6° vs 4.0° after creep loading. IDP, F. N. and compressive stiffness were restored to a similar extent by both procedures. Conclusion. Kyphoplasty and vertebroplasty were equally effective in restoring mechanical function following severe wedge fractures, but kyphoplasty was better able to correct deformity by restoring vertebral height and reducing wedging. No conflicts of interest. Sources of funding: Funding was provided by a Royal College of Surgeons of England Research Fellowship and the Gloucestershire Arthritis Trust. Materials were provided by Medtronic and Depuy. This abstract has not been previously published in whole or substantial part nor has been presented previously at a national meeting

Background. In the annulus fibrosus of degenerated intervertebral discs, disruption to inter-lamellar cross-ties appears to lead to delamination, and the development of anulus fissures. We hypothesise that such internal disruption is likely to be driven by high gradients of compressive stress (i.e. large differences in stress from the nucleus to the mid anulus). Methods. Eighty-nine thoracolumbar motion segements, from T7/8 to L4/5, were dissected from 38 cadavers aged 42-96 yrs. Each was subjected to 1 kN compressive loading, while intradiscal compressive stresses were measured by pulling a pressure transducer along the disc's mid-sagittal diameter. Measurements were repeated in flexed and extended postures. Stress gradients were measured, in the anterior and posterior anulus of each disc, as the average rate of increase in stress (MPa/mm) between the nucleus and the region of maximum compressive stress in the anulus. Average nucleus pressure (IDP) was also recorded. Results. Stress gradients increased with grade of disc degeneration, especially in the posterior anulus (p<0.04 or better). Age had little additional influence, despite an inverse correlation with IDP (p<0.04). Stress gradients increased in the anterior anulus in flexion, and were greatest of all in the posterior anulus in extension, sometimes exceeding 0.5 MPa/mm. In the most severely degenerated discs, stress gradients remained high, even though peak anulus stresses and IDP were reduced as a result of load-bearing being transferred to the neural arch. Discussion. Stress gradients are highest in the region of the disc (the middle posterior anulus) that is most disrupted by the degenerative process. Unlike the overall peak stresses, or IDP, stress gradients remain high in severely degenerated discs, and are not reduced when load-bearing is transferred to the neural arch. These results suggest that stress gradients play a major role in the internal disruption of degenerated human discs. Acknowledgements. M Stefanakis would like to thank the Greek Institute of Scholarships (I.K.Y) for financial support

Summary. At the clinical CT image resolution level, there is no influence of the image voxel size on the derived finite element human cancellous bone models. Introduction. Computed tomography (CT)-based finite element (FE) models have been proved to provide a better prediction of vertebral strength than dual-energy x-ray absorptiometry [1]. FE models based on µCTs are able to provide the golden standard results [2], but due to the sample size restriction of the µCT and the XtremeCT machines, the clinical CT-based FE models is still the most promising tool for the in vivo prediction of vertebrae's strength. It has been found [3] that FE predicted Young's modulus of human cancellous bone increases as the image voxel size increases at the µCT resolution level [3]. However, it is still not clear whether the image voxel size in the clinical range has an impact on the predicted mechanical behavior of cancellous bone. This study is designed to answer this question. Methods. For this study, 6 thoracolumbar vertebrae (Th12) obtained from the female donors were scanned in the non-dissected cadavers under 2 different resolutions – group A: 120 kVp, 100 mAs, with a resolution of 0.29×0.29×1.3 mm. 3. ; group B: 120 kVp, 360 mAs, with a resolution of 0.18×0.18×0.6 mm. 3. A solid calibration phantom (QRM-BDC) was placed beneath the cadavers during the scans. Cuboids with the size of 12.3×12.3×14.3 mm. 3. were cropped from the center of each vertebral body. The FE model was created by converting each image voxel into hexahedron (C3D8). Inhomogeneous material property was defined for the cuboid [4], i.e. the image greyscale value were firstly calibrated into the bone mineral density (BMD), then the Young's modulus and yield stress were calculated from the BMD [5] for each element. Statistical analysis was performed to compare the FE predicted mechanical properties between the groups and the significance level was set to 95% (α=0.05). Results. The trabecular structure is more clearly mimicked in the models from group B than those from group A. The modulus (mean ± SE) in group A is 5.9% higher than that in group B (193.33 ± 31.67 MPa vs. 182.50 ± 27.07 MPa). The yield strength (mean ± SE) in group A is 6.4% higher than that in group B (0.99 ± 0.21MPa vs. 0.93 ± 0.17MPa). However, the paired t-test shows there is no significant difference of the mechanical properties in the two groups (p=0.109 for the modulus and p=0.234 for the yield strength). Discussion. This study shows that there is no influence of the voxel size on the clinical CT derived FE cancellous bone models. This finding can help choose a better, less invasive CT protocol for the patient when creating a clinical CT image based FE model. Acknowledgements. This study is financially supported by the Federal Ministry of Education and Research and the state of Hamburg, Germany