The Accuracy of Patient-Specific Spinal Drill Guides Is Non-Inferior to Computer-Assisted Surgery:The Results of a Split-Spine Randomized Controlled Trial

In recent years, patient-specific spinal drill guides (3DPGs) have gained widespread popularity. Several studies have shown that the accuracy of screw insertion with these guides is superior to that obtained using the freehand insertion technique, but there are no studies that make a comparison with computer-assisted surgery (CAS). The aim of this study was to determine whether the accuracy of insertion of spinal screws using 3DPGs is non-inferior to insertion via CAS. A randomized controlled split-spine study was performed in which 3DPG and CAS were randomly assigned to the left or right sides of the spines of patients undergoing fixation surgery. The 3D measured accuracy of screw insertion was the primary study outcome parameter. Sixty screws inserted in 10 patients who completed the study protocol were used for the non-inferiority analysis. The non-inferiority of 3DPG was demonstrated for entry-point accuracy, as the upper margin of the 95% CI (−1.01 mm–0.49 mm) for the difference between the means did not cross the predetermined non-inferiority margin of 1 mm (p < 0.05). We also demonstrated non-inferiority of 3D angular accuracy (p < 0.05), with a 95% CI for the true difference of −2.30◦–1.35◦, not crossing the predetermined non-inferiority margin of 3◦ (p < 0.05). The results of this randomized controlled trial (RCT) showed that 3DPGs provide a non-inferior alternative to CAS in terms of screw insertion accuracy and have considerable potential as a navigational technique in spinal fixation

Design and Development of a Novel Expanding Pedicle Screw for Use in the Osteoporotic Lumbar Spine

Pedicle screws are commonly utilized in spinal surgery; however, traditional designs often do not provide adequate fixation in osteoporotic spines. The objective of this thesis was to develop a novel expanding screw for use in osteoporotic lumbar pedicles. Helical screws capable of expanding post insertion were built on a rapid prototype machine. A materials testing machine performed axial load to failure tests in both Sawbones and cadaveric specimens comparing the new design to traditional screws (rate = 10mm/min to 20 mm). Output parameters included yield load, ultimate load, stiffness, energy to failure and total energy. The expanding screw showed a 36% increase in total energy (p=0.02), but no other differences were identified. Based on this initial design, the expandable pedicle screws failed to demonstrate improved screw pullout; however, differences may be observed in other loading modes (i.e., toggle) and further design modifications and improvements in post-build machining may provide beneficial enhancements

Augmented navigation

Spinal fixation procedures have the inherent risk of causing damage to vulnerable anatomical structures such as the spinal cord, nerve roots, and blood vessels. To prevent complications, several technological aids have been introduced. Surgical navigation is the most widely used, and guides the surgeon by providing the position of the surgical instruments and implants in relation to the patient anatomy based on radiographic images. Navigation can be extended by the addition of a robotic arm to replace the surgeon’s hand to increase accuracy. Another line of surgical aids is tissue sensing equipment, that recognizes different tissue types and provides a warning system built into surgical instruments. All these technologies are under continuous development and the optimal solution is yet to be found. The aim of this thesis was to study the use of Augmented Reality (AR), Virtual Reality (VR), Artificial Intelligence (AI), and tissue sensing technology in spinal navigation to improve precision and prevent surgical errors. The aim of Paper I was to develop and validate an algorithm for automatizing the intraoperative planning of pedicle screws. An AI algorithm for automatic segmentation of the spine, and screw path suggestion was developed and evaluated. In a clinical study of advanced deformity cases, the algorithm could provide correct suggestions for 86% of all pedicles—or 95%, when cases with extremely altered anatomy were excluded. Paper II evaluated the accuracy of pedicle screw placement using a novel augmented reality surgical navigation (ARSN) system, harboring the above-developed algorithm. Twenty consecutively enrolled patients, eligible for deformity correction surgery in the thoracolumbar region, were operated on using the ARSN system. In this cohort, we found a pedicle screw placement accuracy of 94%, as measured according to the Gertzbein grading scale. The primary goal of Paper III was to validate an extension of the ARSN system for placing pedicle screws using instrument tracking and VR. In a porcine cadaver model, it was demonstrated that VR instrument tracking could successfully be integrated with the ARSN system, resulting in pedicle devices placed within 1.7 ± 1.0 mm of the planed path. Paper IV examined the feasibility of a robot-guided system for semi-automated, minimally invasive, pedicle screw placement in a cadaveric model. Using the robotic arm, pedicle devices were placed within 0.94 ± 0.59 mm of the planned path. The use of a semi-automated surgical robot was feasible, providing a higher technical accuracy compared to non-robotic solutions. Paper V investigated the use of a tissue sensing technology, diffuse reflectance spectroscopy (DRS), for detecting the cortical bone boundary in vertebrae during pedicle screw insertions. The technology could accurately differentiate between cancellous and cortical bone and warn the surgeon before a cortical breach. Using machine learning models, the technology demonstrated a sensitivity of 98% [range: 94-100%] and a specificity of 98% [range: 91-100%]. In conclusion, several technological aids can be used to improve accuracy during spinal fixation procedures. In this thesis, the advantages of adding AR, VR, AI and tissue sensing technology to conventional navigation solutions were studied

Lumbar-sacral pedicle screw insertion with preoperative CT-based navigation

Objectif: Nous avons effectué une étude chez 135 patients ayant subis une chirurgie lombo-sacrée avec vissage pédiculaire sous navigation par tomographie axiale. Nous avons évalué la précision des vis pédiculaires et les résultats cliniques. Méthodes: Cette étude comporte 44 hommes et 91 femmes (âge moyen=61, intervalle 24-90 ans). Les diamètres, longueurs et trajectoires des 836 vis ont été planifiés en préopératoire avec un système de navigation (SNN, Surgical Navigation Network, Mississauga). Les patients ont subi une fusion lombaire (55), lombo-sacrée (73) et thoraco-lombo-sacrée (7). La perforation pédiculaire, la longueur des vis et les spondylolisthesis sont évalués par tomographies axiales postopératoires. Le niveau de douleur est mesuré par autoévaluations, échelles visuelles analogues et questionnaires (Oswestry et SF-36). La fusion osseuse a été évaluée par l’examen des radiographies postopératoires. Résultats: Une perforation des pédicules est présente pour 49/836 (5.9%) des vis (2.4% latéral, 1.7% inférieur, 1.1% supérieur, 0.7% médial). Les erreurs ont été mineures (0.1-2mm, 46/49) ou intermédiaires (2.1 - 4mm, 3/49 en latéral). Il y a aucune erreur majeure (≥ 4.1mm). Certaines vis ont été jugées trop longues (66/836, 8%). Le temps moyen pour insérer une vis en navigation a été de 19.1 minutes de l΄application au retrait du cadre de référence. Un an postopératoire on note une amélioration de la douleur des jambes et lombaire de 72% et 48% en moyenne respectivement. L’amélioration reste stable après 2 ans. La dégénérescence radiologique au dessus et sous la fusion a été retrouvée chez 44 patients (33%) and 3 patients respectivement (2%). Elle est survenue en moyenne 22.2 ± 2.6 mois après la chirurgie. Les fusions se terminant à L2 ont été associées à plus de dégénération (14/25, 56%). Conclusion: La navigation spinale basée sur des images tomographiques préopératoires est une technique sécuritaire et précise. Elle donne de bons résultats à court terme justifiant l’investissement de temps chirurgical. La dégénérescence segmentaire peut avoir un impact négatif sur les résultats radiologique et cliniques.Objective: The authors studied 135 consecutive patients following a lumbo-sacral fixation using pedicle screws and CT-based navigation to evaluate pedicle screw accuracy and clinical outcomes. Methods: The series included 44 men and 91 women (mean age 61 years, range 24-90 years). All 836 screws were planned with pre-operative CT-Scans in a navigation system (SNN, Surgical Navigation Network, Mississauga, Ontario, Canada) for diameter, length and direction. Fixation included the lumbar spines only (55), the lumbo-sacral spine (73) or the thoraco-lumbo-sacral spine (7). Pedicle perforation, screw length and spondylolisthesis were assessed on post-operative CT-Scan. Pain was surveyed using self-rated scales, visual analogue scales, Oswestry and SF-36 questionnaires. Bony union was assessed on post-operative follow-up radiographs. Results: Pedicle perforation was found in 49/836 (5.9%) screws (2.4% laterally, 1.7% inferiorly, 1.1% superiorly, 0.7% medially). The errors were minor (0.1-2mm, 46/49) or intermediate (2.1 – 4 mm, 3/49). All intermediate errors were lateral. There were no major errors (≥ 4.1mm). Some screws were judged too long (66/836, 8%). The average time to insert one screw with navigation was 19.1 minutes from application to removal of the reference frame. The amount of improvement at one year post-operation for self-rated leg and back pain were 72% and 48% respectively. The improvement was stable over 2 years. Above-level and below-level radiological degenerations were found in 44 patients (33%) and 3 patients respectively (2%) and occurred on average 22.2 ± 2.6 months after the surgery. Fusions ending at L2 had the most degenerations (14/25, 56%). Conclusion: CT-based preoperative navigation for lumbo-sacral pedicle screw insertion is accurate and associated with a good short term outcome, making it worth the investment of the additional time required. Segmental degeneration may have a negative effect on radiological and clinical outcomes

Statistical shape modelling of the thoracic spine for the development of pedicle screw insertion guides

Spinal fixation and fusion are surgical procedures undertaken to restore stability in the spine and restrict painful or degenerative motion. Malpositioning of pedicle screws during these procedures can result in major neurological and vascular damage. Patient-specific surgical guides offer clear benefits, reducing malposition rates by up to 25%. However, they suffer from long lead times and the manufacturing process is dependent on third-party specialists. The development of a standard set of surgical guides may eliminate the issues with the manufacturing process. To evaluate the feasibility of this option, a statistical shape model (SSM) was created and used to analyse the morphological variations of the T4–T6 vertebrae in a population of 90 specimens from the Visible Korean Human dataset (50 females and 40 males). The first three principal components, representing 39.7% of the variance within the population, were analysed. The model showed high variability in the transverse process (~ 4 mm) and spinous process (~ 4 mm) and relatively low variation (< 1 mm) in the vertebral lamina. For a Korean population, a standardised set of surgical guides would likely need to align with the lamina where the variance in the population is lower. It is recommended that this standard set of surgical guides should accommodate pedicle screw diameters of 3.5–6 mm and transverse pedicle screw angles of 3.5°–12.4°

Biomechanical investigation of the factors related to pedicle screw fixation strength

Spinal pathologies or injuries can severely compromise the quality of life for the patients. The surgical intervention is often performed using internal fixation devices. Fixation with pedicle screws is a well-established method providing spinal stability and deformity correction. However, reported rates of fixation failure because of screw loosening have become a major concern, especially with the appearance of new and more powerful surgical techniques. Numerous experimental studies have been devoted to pedicle screw fixation strength evaluation. The evaluation methods are commonly including preoperative measurements of bone mineral density, screw insertional torque measurement and pullout tests. Bone mineral density measurement gives only to some extent an estimation of the pedicle screw fixation strength. Several studies indicated that the screw insertional torque measurement can provide predictive information on the fixation strength. However, the latter was not confirmed by other studies. This controversy illustrates the need for improving the understanding of factors related to pedicle screw fixation strength. In addition, there is a need for better understanding the mechanisms of pedicle screw loosening leading to failure and their effects on the fixation strength. The main objective of this doctoral thesis was to improve the understanding on the mechanisms of pedicle screw loosening and the factors related to pedicle screw fixation strength. This objective is related to two hypotheses: 1) the indentation force measured while performing the pilot hole and the torque observed during screw insertion are related to the screw pullout force and stiffness; 2) cyclic bending load (toggling) on pedicle screw in craniocaudal (CC) and mediolateral (ML) directions loosens the screw and affects the pullout force and stiffness. Three specific objectives were defined to verify the hypotheses using two experimental protocols. The first specific objective was to develop and validate tools measuring the indentation force while performing the pilot hole and the insertional torque during pedicle screw insertion. The second objective was to compare the screw loosening mechanisms through toggling in different modes and evaluate their effects on pedicle screw pullout force and stiffness. Finally, the third objective was to establish the relationships between the indentation force, the insertional torque and the screw pullout force and stiffness. The first protocol was performed on synthetic bone surrogates mainly to explore the first specific objective. Furthermore, to account for the effect of various bone densities and toggling modes on pullout force and stiffness, pedicle screw were pulled out with and without toggling from synthetic bone surrogates of three different densities. With five repetitions, a total of 36 trials have been completed. Finally, potential relationships between the indentation force and the insertional torque with the pullout force and stiffness were explored. The second protocol was performed on porcine vertebrae to investigate the second and the third specific objectives. As the second specific objective, three toggling modes (CC, ML and no toggling (NT)) were performed on porcine lumbar vertebrae ranging from L1 to L3. The screws were then submitted to axial pullout test. A complete design of experiment with two factors and three levels (32 = 9 trials) was used to investigate on the main effect of toggling mode and vertebral level on screw pullout force and stiffness, as well as their quadratic interactions. With five repetitions, a total of 54 trials were performed on 27 isolated vertebrae, using both pedicles. Finally, potential relationships were investigated between the indentation force while performing a pilot hole, the insertional torque during screw insertion, and the pullout force and stiffness with and without toggling. The results of the first protocol suggest that screw toggling significantly affects the pullout force (P = 0.01) and stiffness (P < 0.0001). A higher pullout force and stiffness was demonstrated for higher density without toggling. The effect of density was higher than the effect of toggling on pullout force. The indentation force while performing the pilot hole was significantly correlated to pullout force and stiffness (r = 0.99, P < 0.0001 and r = 0.92, P < 0.0001 respectively). Strong correlations were also shown between the insertional torque during screw insertion and the pedicle screw pullout force and stiffness (r = 0.98, P < 0.0001 and r = 0.91, P < 0.0001 respectively). The study on porcine vertebrae showed that screw toggling significantly affects the pullout force (P = 0.0004) and stiffness (P 0.85, P < 0.0001). For pullout force without toggling BMD and pedicle area were the main contributing factors to the regression model. For the stiffness with and without toggling, the indentation force was the single best factor with highest contribution to the regression model. In conclusion, pedicle screw toggling significantly affects the pedicle screw pullout force and stiffness. Screw toggling, in particular CC toggling, should be considered in the biomechanical evaluation of pedicle screw fixation strength. Furthermore, the contribution of toggling was more important on the stiffness than the pullout force. The effect of vertebral level should be considered in determining the fixation strength. The developed instruments and methods for indentation force measurement during pilot hole creation and insertional torque measurement during screw insertion were reproducible, and provide valuable data to estimate pedicle screw pullout force and stiffness. The relationship between the pilot hole indentation force and screw insertional torque, and the screw pullout force and stiffness are a affected by the toggling mode. Indentation force and insertional torque measurements, together with BMD measurement, are recommended for a better estimation of pedicle screw fixation strength after CC toggling

Effects of Biologics on Pedicle Screw Fixation in a Sheep Model: Histological and Biomechanical Analysis

Objective: Osteoinductive recombinant human bone morphogenetic protein (rhBMP–2) was delivered on an absorbable collagen sponge (ACS) within a novel titanium screw implant in an IACUC approved non–osteoporotic ovine spine model. Biomechanical pull–out strength, undecalcified histology, microradiography, and quantitative histomorphometry were used to assess effects of augmentation with rhBMP–2 on the holding power and peri–implant bone formation. Methodology: rhBMP–2 (0.43 mg/ml) soaked ACS was placed within and around cannulated and fenestrated titanium pedicle screw implants. Sixty–four implants were randomly divided into 4 treatment groups (n=16 each). Biomechanical pull–out testing was done on half of the screws (n=32) to determine the pull–out strength, stiffness, and energy to failure. For histology, half of the implants were sectioned perpendicular to the long axis (axial), and the other half were sectioned parallel to long axis (longitudinal). Differential staining, microradiography and histomorphometry were performed. Data were statistically analyzed by ANOVA (p=0.05) and Bonferroni/Dunn pair–wise comparisons (p=0.0083). Findings: Pull–out test: Empty 6 weeks group demonstrated the highest pull–out strength (3718N) compared to rhBMP–2/ACS 12 weeks (2330N, pde novoosteopenic bone as far as 8–10 mm away from the screw. Conclusions: rhBMP–2 did not significantly improve the biomechanical pull–out properties (stiffness, strength, and energy) of the titanium implant. 12 weeks rhBMP–/ACS specimens had improved biomechanical pull–out strength and stiffness compared to 6 weeks rhBMP–2/ACS specimens. rhBMP–2 application was associated with early transient bone resorption, de novo florid osteopenic bone, and statistically significant bone density differences at the 6 weeks period. These were replaced by remodeled bone at the 12 weeks time period

Factors affecting accuracy and fusion rate in lumbosacral fusion surgery - a preclinical and clinical study

Lumbosacral fusion surgery is indicated in symptomatic degenerative lumbosacral disorder, when the origin of pain is demonstrated to lie within the restricted number of functional spinal units and when the pain is refractory to the conservative treatment, to eliminate painful motion of the spinal units. Inaccurate placement of pedicle screws may cause neurological symptoms, and result in early hardware failure and return of spinal instability symptoms. All spinal instrumentation eventually fails without solid bony fusion, and the presence of symptomatic bony non-union at least a year after fusion surgery is defined as pseudoarthrosis. Bioactive glasses (BAGs) are synthetic, biocompatible, osteoconductive and osteostimulative materials with angiogenic and antibacterial properties, able to bond to bone. In a study of 147 patients and 837 pedicle screws placed due to degenerative lumbosacral spine disorder, 14.3 % breached the pedicle. New neurological symptoms corresponding to the breach were observed in 25.9 % of patients with pedicle breach, and 89.2 % of the symptomatic breaches were either medially or inferiorly. A preclinical controlled study of novel BAG S53P4 putty showed good biocompatibility, slightly higher intramedullary ossification of putty group compared to the control group, and that the binder agent did not disturb formation of new bone in vivo. The interbody fusion rate was 95.8 % with BAG S53P4 putty as bone graft expander with autograft in clinical lumbosacral interbody fusion, indicating at least as good interbody fusion results as the presently used materials. One early operative subsidence remaining unchanged over the study period was observed with putty.Lannerangan luudutusleikkausten tarkkuuteen ja luutumiseen vaikuttavat tekijät Lannerangan luudutusleikkaus voidaan tehdä oireisessa lannerangan rappeumasairaudessa, kun kivun syyn on osoitettu sijaitsevan rajallisessa määrässä selkärangan toiminnallisia yksikköjä ja kun kipu ei vähene leikkauksettomilla hoidoilla. Leikkauksella voidaan poistaa kipua tuottava selkärangan toiminnallisten yksikköjen liike. Epätarkka pedikkeliruuvien asettaminen voi aiheuttaa neurologisia oireita ja johtaa nopeaan kiinnitysosien irtoamiseen ja rangan epätukevuusoireiden palaamiseen. Suuri osa selkärangan kiinnityslaitteista irtoaa lopulta, jollei luutumista kiinnitettyjen kohtien välillä tapahdu. Vuoden kuluttua luudutusleikkauksesta oireista luutumatonta kiinnityskohtaa nimitetään pseudoartroosiksi. Bioaktiiviset lasit ovat synteettisiä, bioyhteensopivia, osteokonduktiivisia ja osteostimulatiivisia materiaaleja, joilla on angiogeenisiä ja antibakteerisia ominaisuuksia, ja ne voivat sitoutua suoraan luuhun. 147 potilaalle lannerangan rappeumasairauden vuoksi asetetut 837 pedikkeliruuvia käsittävän tutkimuksen mukaan 14.3 % ruuveista rikkoi luisen pedikkelin seinämän. 25.9 %:lla potilaista, joilla ruuvi läpäisi pedikkelin seinämän, ilmeni uusia neurologisia oireita, ja 89.2 %:lla oireisista potilaista pedikkeliruuvi läpäisi pedikkelin seinämän mediaalisesti tai inferiorisesti. Prekliinisessä kontrolloidussa tutkimuksessa uudenlainen bioaktiivisesta lasista valmistettu S53P4 luunkorviketahna todettiin bioyhteensopivaksi, ja sen avulla saavutettiin hieman vertailuryhmää parempi luutuminen luuydinontelossa. Tahnan sidosaineen ei eläinkokeessa todettu häiritsevän luun muodostumista. Kliinisessä tutkimuksessa saavutettiin 95.8 %:n luutuminen käytettäessä S53P4 biolasitahnaa yhdessä oman luun kanssa lannerangan nikamasolmujen välisessä luudutuksessa. Siten yhdessä oman luun kanssa käytettäessä S53P4 biolasitahnalla saadaan aikaan vähintään yhtä hyvä nikamasolmujen välinen luutuminen kuin nykyisin käytettävillä synteettisillä luunkorvikkeilla. Tutkimuksessa todettiin yksi leikkauksen yhteydessä tapahtunut nikamasolmujen välisen implantin päätelevyyn painuminen, jonka suuruus ei muuttunut seurantakuvantamisissa

Imaging analysis of morphological changes to vertebrae in adolescent idiopathic scoliosis

This thesis employs imaging analysis using CT and MRI scans to comprehensively document the changing three-dimensional pedicle anatomy that occurs in the growing spine of adolescent idiopathic scoliosis patients and compare this to healthy control subjects. This study aims to not only provide information regarding the pathophysiology of adolescent idiopathic scoliosis but also to provide critical information to spinal surgeons operating on these spines to reduce the risk of serious complications

A Learning-based Method for Online Adjustment of C-arm Cone-Beam CT Source Trajectories for Artifact Avoidance

During spinal fusion surgery, screws are placed close to critical nerves suggesting the need for highly accurate screw placement. Verifying screw placement on high-quality tomographic imaging is essential. C-arm Cone-beam CT (CBCT) provides intraoperative 3D tomographic imaging which would allow for immediate verification and, if needed, revision. However, the reconstruction quality attainable with commercial CBCT devices is insufficient, predominantly due to severe metal artifacts in the presence of pedicle screws. These artifacts arise from a mismatch between the true physics of image formation and an idealized model thereof assumed during reconstruction. Prospectively acquiring views onto anatomy that are least affected by this mismatch can, therefore, improve reconstruction quality. We propose to adjust the C-arm CBCT source trajectory during the scan to optimize reconstruction quality with respect to a certain task, i.e. verification of screw placement. Adjustments are performed on-the-fly using a convolutional neural network that regresses a quality index for possible next views given the current x-ray image. Adjusting the CBCT trajectory to acquire the recommended views results in non-circular source orbits that avoid poor images, and thus, data inconsistencies. We demonstrate that convolutional neural networks trained on realistically simulated data are capable of predicting quality metrics that enable scene-specific adjustments of the CBCT source trajectory. Using both realistically simulated data and real CBCT acquisitions of a semi-anthropomorphic phantom, we show that tomographic reconstructions of the resulting scene-specific CBCT acquisitions exhibit improved image quality particularly in terms of metal artifacts. Since the optimization objective is implicitly encoded in a neural network, the proposed approach overcomes the need for 3D information at run-time.Comment: 12 page