Computer-assisted thoracic pedicle screw placement: an in vitro feasibility study

Video-assisted thoracoscopic image-guided spine surgery: evolution of 19 years of experience, from endoscopy to fully integrated 3D navigation

OBJECTIVE

The purpose of this study was to describe the evolution of thoracoscopic spine surgery from basic endoscopic procedures using fluoroscopy and anatomical localization through developmental iterations to the current technology use in which endoscopy and image-guided surgery are merged with intraoperative CT scanning.

METHODS

The authors provided detailed explanations of their thoracoscopic spine surgery techniques, beginning with their early-generation endoscopy with fluoroscopic localization, which was followed with point surface matching techniques and early image guidance. The authors supplanted this with the modern era of image guidance, thoracoscopic spine surgery, and seamless integration that has reached its current level of refinement.

RESULTS

A retrospective review of single-institution thoracoscopic procedures performed by the senior author over the course of 19 years yielded a total of 160 patients, including 73 women and 87 men. The mean patient age was 55 years, and the range included patients 16-94 years of age. There were no patients with worsened neurological function. One hundred sixteen patients underwent surgery for thoracic disc herniation, 18 for underlying neoplasms with spinal cord compression, 14 for osteomyelitis and discitis, 12 for thoracic deformity with neurological changes, and 8 for traumatic etiologies.

CONCLUSIONS

More than 19 years of experience has revealed the benefits of integrating thoracoscopic spine surgery with intraoperative CT scanning and image-guided surgery, including direct decompression without manipulation of neural elements, superior 3D spatial orientation, and localization of complex spinal anatomy. With the exponential growth of machine learning, robotics, artificial intelligence, and advances in imaging techniques and endoscopic imaging, there may be further refinements of this technique on the horizon.

Accuracy and safety of three-dimensionally printed animal-specific drill guides for thoracolumbar vertebral column instrumentation in dogs: Bilateral and unilateral designs

OBJECTIVE

To evaluate the safety and accuracy of a unilateral three-dimensionally printed animal-specific drill guide (3DASDG) design for unilateral stabilization in the thoracolumbar vertebral column of dogs compared to a bilateral design.

STUDY DESIGN

Cadaveric study.

SAMPLE POPULATION

Fifty-two corridors in one canine cadaver.

METHODS

Two 3DASDG designs with 2 drilling tubes each were created from T8 to L7 vertebrae. Fifty-two corridors were drilled on the right and the left sides by using unilateral and bilateral designs, respectively. Planned and postoperative trajectories (entry point, exit point, angle) were compared to establish the accuracy. Statistical analysis was used for accuracy comparison between designs. Safety was evaluated by using Zdichavsky classification.

RESULTS

Unilateral and bilateral drill guide designs were not different for entry point and angle deviations; however, they were different for the exit point deviations. Two corridors breached outside the vertebra. For all guides, mean entry and exit point deviations were less than 1 and 2 mm, respectively. The maximum entry or exit point deviation in both groups was 4.7 mm. The mean angle deviation was <3.5°, and the maximum angle deviation was 9.3°.

CONCLUSION

No difference was detected in accuracy of entry points and angle deviations between drill guide designs tested in normal vertebrae. The technique was classified as highly safe.

CLINICAL SIGNIFICANCE

A unilateral drill guide design may be a safe alternative to bilateral guides for unilateral stabilization of the thoracolumbar vertebral column in dogs.

A Novel Intraoperative Technique to Determine Cranio-Caudal Angulation of Pedicle Screws in Thoracolumbar Spine: A Prospective Computerized Tomography-Based Analysis of 428 Screws

BACKGROUND

We report a novel technique of directing the sagittal profile of thoracic and lumbar pedicle screws using a freehand technique without the use of intraoperative monitoring.

METHODS

This is a prospective computerized tomography (CT)-based evaluation of pedicle screw insertion in the thoracic and lumbar spine of 64 patients operated upon for varied etiologies. All the patients were operated upon independently by 2 young surgeons with 1 year of spinal-fellowship experience. Intraoperatively, a right-angle retractor was positioned to determine the sagittal inclination of the pedicle screw. Postoperatively, sagittal CT scans were analyzed for the sagittal profile of the screw. The vertebral bodies were divided into 3 equidistant zones (A, B, and C) from the superior to inferior endplates, and the positions of the screw tips were noted.

RESULTS

There were 41 men and 23 women (mean age = 45.5 years). A total of 428 screws were inserted. There were 2 cases of superior pedicle wall violation in D1 and D5. The majority (96.97%) of the pedicle screws were inserted into zones A and B.

CONCLUSIONS

We introduced a simple, accurate, and safe method of directing the sagittal inclination of the pedicle screw in the thoracic and lumbar spine without intraoperative image guidance.

The effect of simulation training on resident proficiency in thoracolumbar pedicle screw placement using computer-assisted navigation

OBJECTIVE

Residency work-hour restrictions necessitate efficient, reproducible training. Simulation training for spinal instrumentation placement shows significant benefit to learners' subjective and objective proficiency. Cadaveric laboratories are most effective but have high cost and low availability. The authors' goal was to create a low-cost, efficient, reproducible spinal instrumentation placement simulation curriculum for neurosurgery and orthopedic surgery residents using synthetic models and 3D computer-assisted navigation, assessing subjective and objective proficiency with placement of thoracolumbar pedicle screws.

METHODS

Fifteen neurosurgery and orthopedic surgery residents participated in a standardized curriculum with lecture followed by two separate sessions of thoracolumbar pedicle screw placement in a synthetic spine model utilizing 3D computer-assisted navigation. Data were collected on premodule experience, time and accuracy of screw placement, and both subjective and objective ratings of proficiency.

RESULTS

Fifteen of 15 residents demonstrated improvement in subjective (Physician Performance Diagnostic Inventory Scale [PPDIS]) and 14 in objective (Objective Structured Assessment of Technical Skills [OSATS]) measures of proficiency in navigated screw placement with utilization of this curriculum (p < 0.001 for both), regardless of the number of cases of previous experience using thoracolumbar spinal instrumentation. Fourteen of 15 residents demonstrated decreased time per screw placement from session 1 to session 2 (p = 0.006). There was no significant difference in pedicle screw accuracy between session 1 and session 2.

CONCLUSIONS

A standardized curriculum using synthetic simulation training for navigated thoracolumbar pedicle screw placement results in significantly improved resident subjective and objective proficiency. Development of a nationwide competency curriculum using simulation training for spinal instrumentation placement should be considered for safe, efficient resident training.

Effectiveness of the Thoracic Pedicle Screw Placement Using the Virtual Surgical Training System: A Cadaver Study

BACKGROUND

The virtual simulation surgery has initially exhibited its promising potentials in neurosurgery training.

OBJECTIVE

To evaluate effectiveness of the Virtual Surgical Training System (VSTS) on novice residents placing thoracic pedicle screws in a cadaver study.

METHODS

A total of 10 inexperienced residents participated in this study and were randomly assigned to 2 groups. The group using VSTS to learn thoracic pedicle screw fixation was the simulation training (ST) group and the group receiving an introductory teaching session was the control group. Ten fresh adult spine specimens including 6 males and 4 females with a mean age of 58.5 yr (range: 33-72) were collected and randomly allocated to the 2 groups. After exposing anatomic structures of thoracic spine, the bilateral pedicle screw placement of T6-T12 was performed on each cadaver specimen. The postoperative computed tomography scan was performed on each spine specimen, and experienced observers independently reviewed the placement of the pedicle screws to assess the incidence of pedicle breach.

RESULTS

The screw penetration rates of the ST group (7.14%) was significantly lower in comparison to the control group (30%, P < .05). Statistically significant difference in acceptable rates of screws also occurred between the ST (100%) and control (92.86%) group (P < .05). In addition, the average screw penetration distance in control group (2.37 mm ± 0.23 mm) was significantly greater than ST group (1.23 mm ± 0.56 mm, P < .05).

CONCLUSION

The virtual reality surgical training of thoracic pedicle screw instrumentation effectively improves surgical performance of novice residents compared to those with traditional teaching method, and can help new beginners to master the surgical technique within shortest period of time.

A concept for a 3D-printed patient-specific stereotaxy platform for brain biopsy -a canine cadaver study

The treatment of intracranial lesions requires a precise diagnosis with subsequent identification of an adequate therapeutic approach. Stereotactic tumor biopsy may be considered the safest neurosurgical procedure in terms of anticipated results and potential surgical complications. The aim of the present paper was to demonstrate a new method of stereotactic biopsy, based on a patient-specific 3D printed platform in dogs. The system was tested on two canine cadavers, a small (Shih Tzu) and a large (Labrador) breed. Imaginary biopsy targets were defined in a superficial (caudate nucleus) and a deep (piriform lobe) position. Based on 3 Tesla MRI, individualized stereotactic platforms were designed using a semi-automatic approach, and manufactured additively using ABS M30. A pre- and intra-operative CT was performed to compare the planned vs. the realized needle position for precision analyses of the procedure. The target points varied with a precision between 0.09 mm and 0.48 mm. Manufacturing time required 480 to 700 min per platform. The presented patient-specific stereotactic system seems a suitable instrument for application in small animal neurosurgery. In particular, the implementation of relevant stereotactic data may help performing the procedure in rapid sequence and with higher precision than currently-used systems. Required adjustments and adaptions to the respective anatomical conditions are omitted and make the procedure reliable and safe.

Clinical significance of superior articular process as a reference point for free-hand pedicle screw insertion in thoracic spine

The trajectory of the pedicle screw perpendicular to the SAP (superior articular process) is consistent with the universal trajectory presented in the previous study of the entry point using computed tomography. The ideal entry point and trajectory of pedicle screw insertion have been a matter of considerable debate. We attempted to find the relationship between SAP and entry point and trajectory of the pedicle screw.Thoracic spine CT (computed tomography) scans of 9 volunteers were studied. A safe zone for the trajectory of the screw in the axial (MarginAx) and sagittal (MarginSag) was defined as the zone between lines perpendicular to the SAP along the medial and lateral cortex of the pedicle in the axial section, and the superior and inferior cortex in the sagittal section without violation of the pedicle walls. The midline of MarginAx and MarginSag was defined as the safe entry point of the trajectory in the axial and sagittal planes (TrajectoryAx and TrajectorySag), respectively.MarginAx and MarginSag were 4.14 ± 0.99 and 9.03 ± 2.01 mm, respectively. There was a statistically significant difference in TrajectoryAx between the upper and middle, and between the upper and lower (P = .0076 in both cases), but not between the middle and lower thoracic spine (P = .066). TrajectorySag was within 1 mm at the levels of T4, T8, T11 vertebrae and at 0 mm at the other levels. Thus, the midpoint of MarginSag was within 1 mm from the SAP base.There was a constant angular relationship with the SAP and the pedicle axis; the line perpendicular to the SAP can act as a trajectory. Therefore, we suggest that the SAP might be the only accurate and safe reference for pedicle screw insertion in the thoracic spine perpendicular to the SAP using freehand technique.

Causes of the failure and the revision methods for congenital scoliosis due to hemivertebra

The purpose of this study was to retrospectively investigate the causes of failure in the first operation and the revision procedure for patients with congenital scoliosis due to hemivertebra. Nineteen patients who underwent the revision operations because of failure in the first operation were included in this study. All the malformations were identified as fully segmented hemivertebra, including 16 cases in thoracolumbar vertebra (T10: three patients; T12: seven patients; L1: six patients), and three cases in thoracic vertebra (T8). The causes of failure in the first operation and the outcome of revision procedure for patients were retrospectively analyzed. All patients were successfully performed the personalized revision surgeries. The failure reasons of the first operation included limitations of the first operation procedure, no or incomplete resection of the malformed hemivertebra, improper operation during surgery, improper internal fixation material, and improper internal fixation scope. The average postoperative scoliosis Cobb's angle and kyphosis Cobb's angle were corrected from 54.1° preoperatively to 23.1° postoperatively, and 59.3° preoperatively to 25.8° postoperatively, respectively. The average postoperative distance between the C7 plumb line and the center sacral vertical line was decreased from 2.5 cm preoperatively to 1.5 cm postoperatively. The average follow-up period was 2.2 years. No serious complication was observed. The cause of the failure of the first operations for the congenital scoliosis due to hemivertebra is verified. Our study may provide a basis for the treatment of congenital scoliosis due to hemivertebra.

Navigation of pedicle screws in the thoracic spine with a new electromagnetic navigation system: a human cadaver study

INTRODUCTION

Posterior stabilization of the spine is a standard procedure in spinal surgery. In addition to the standard techniques, several new techniques have been developed. The objective of this cadaveric study was to examine the accuracy of a new electromagnetic navigation system for instrumentation of pedicle screws in the spine.

MATERIAL AND METHOD

Forty-eight pedicle screws were inserted in the thoracic spine of human cadavers using EMF navigation and instruments developed especially for electromagnetic navigation. The screw position was assessed postoperatively by a CT scan.

RESULTS

The screws were classified into 3 groups: grade 1 = ideal position; grade 2 = cortical penetration <2 mm; grade 3 = cortical penetration ≥2 mm. The initial evaluation of the system showed satisfied positioning for the thoracic spine; 37 of 48 screws (77.1%, 95% confidence interval [62.7%, 88%]) were classified as group 1 or 2.

DISCUSSION

The screw placement was satisfactory. The initial results show that there is room for improvement with some changes needed. The ease of use and short setup times should be pointed out. Instrumentation is achieved without restricting the operator's mobility during navigation.

CONCLUSION

The results indicate a good placement technique for pedicle screws. Big advantages are the easy handling of the system.

Introduction: Intraoperative spinal imaging and navigation

Image-guided surgery (IGS) has been evolving since the early 1990s and is now used on a daily basis in the operating theater for spine surgery at many institutions. In the last 5 years, spinal IGS has greatly benefitted from important enhancements including portable intraoperative CT (iCT) coupled with high-speed computerized stereotactic navigation systems and optical-based camera tracking technology.

An Ultrasound Technique of Bone Thickness Estimation for Pedicle Screw Insertion

Information on bone thickness is useful to surgeons in fixing pedicle screws in place. The quality of pedicle screw insertion continues to increase with the introduction of such techniques as navigation based on computed tomography and fluoroscopy. These techniques reduce error in pedicle screw placement and injury. However, the information reported on the real time measurement of depths drilled through cancellous bone, also known as trabecular bone or sponge bone, by the pedicle screw is minimal. It currently depends on palpation by the physician for judging the boundary between cortical and cancellous bone – an inaccurate technique that may produce errors in screw placement and the risk of injury during surgical processes. Ultrasound is used to help overcome such problems. Bone thickness is estimated in this study using an ultrasound transducer attached to 20 mm of polymethyl methacrylate, a clear glass-like acrylic. The bone thickness of five specimens was measured using ultrasound echo signals. Error in estimating bone thickness was small, 8.121%, showing the accuracy in bone thickness to be more than 90.00% which is suitable for use in estimating bone thickness in pedicle screw insertion.

CT provides precise size assessment of implanted titanium alloy pedicle screws

BACKGROUND

After performing instrumented spinal fusion with pedicle screws, postoperative imaging using CT to assess screw position may be necessary. Stainless steel implants produce significant metal artifact on CT, and the degree of distortion is at least partially dependent on the cross-sectional area of the implanted device. If the same effect occurs with titanium alloy implants, ability to precisely measure proximity of screws to adjacent structures may be adversely affected as screw size increases.

QUESTIONS/PURPOSES

We therefore asked whether (1) CT provides precise measurements of true screw widths; and (2) precision degrades based on the size of the titanium implant imaged.

METHODS

CT scans performed on 20 patients after instrumented spinal fusion for scoliosis were reviewed. The sizes of 151 titanium alloy pedicle screws were measured and compared with known screw size. The amount of metal bloom artifact was determined for each of the four screw sizes. ANOVA with Tukey's post hoc test were performed to evaluate differences in scatter, and Spearman's rho coefficient was used to measure relationship between screw size and scatter.

RESULTS

All screws measured larger than their known size, but even with larger 7-mm screws the size differential was less than 1 mm. The four different screw sizes produced scatter amounts that were different from each other (p < 0.001).The amount of metal bloom artifact produced does increase as the size of the screw increases (rho = 0.962, p < 0.001).

CONCLUSIONS

CT of titanium alloy pedicle screws produces minimal artifact, thus making this the preferred imaging modality to assess screw position after surgery. Although the amount of artifact increases with the volume of titanium present, the degree of distortion is minimal and is usually less than 1 mm.

Image-guided navigation and video-assisted thoracoscopic spine surgery: the second generation

Object

Video-assisted thoracoscopic surgery (VATS) has evolved for treatment of a variety of spinal disorders. Early incorporation with image-guided surgery (IGS) was challenged due to reproducibility and adaptability, limiting the procedure's acceptance. In the present study, the authors report their experience with second-generation IGS and VATS technologies for anterior thoracic minimally invasive spinal (MIS) procedures.

Methods

The surgical procedure is described in detail including operating room set-up, patient positioning (a lateral decubitus position), placement of the spinal reference frame and portal, radiographic localization, registration, surgical instruments, and the image-guided thoracoscopic discectomy.

Results

Combined IGS and VATS procedures were successfully performed and assisted in anatomical localization in 14 patients. The mean patient age was 59 years (range 32–73 years). Disc herniation pathology represented the most common indication for surgery (n = 8 patients); intrathoracic spinal tumors were present in 4 patients and the remaining patients had infection and ossification of the posterior longitudinal ligament. All patients required chest tube drainage postoperatively, and all but 1 patient had drainage discontinued the following day. The only complication was a seroma that was presumed to be due to steroid therapy for postoperative weakness. At the final follow-up, 11 of the patients were improved neurologically, 2 patients had baseline neurological status, and the 1 patient with postoperative weakness was able to ambulate, albeit with an assistive device.

The evolution of thoracoscopic surgical procedures occurring over 20 years is presented, including their limitations. The combination of VATS and IGS technologies is discussed including their safety and the importance of 3D imaging. In cases of large open thoracotomy procedures, surgeries require difficult, extensive, and invasive access through the chest cavity; using a MIS procedure can potentially eliminate many of the complications and morbidities associated with large open procedures. The authors report their experience with thoracic spinal surgeries that involved MIS procedures and the new technologies.

Conclusions

The most significant advance in IGS procedures has resulted from intraoperative CT scanning and automatic registration with the IGS workstation. Image guidance can be used in conjunction with VATS techniques for thoracic discectomy, spinal tumors, infection, and ossification of the posterior longitudinal ligament. The authors' initial experience has revealed this technique to be useful and potentially applicable to other MIS procedures.

The ventral lamina and superior facet rule: a morphometric analysis for an ideal thoracic pedicle screw starting point

BACKGROUND CONTEXT

With the increasing popularity of thoracic pedicle screws, the freehand technique has been espoused to be safe and effective. However, there is currently no objective, definable landmark to assist with freehand insertion of pedicle screws in the thoracic spine. With our own increasing surgical experience, we have noted a reproducible and unique anatomic structure known as the ventral lamina.

PURPOSE

We set out to define the morphologic relationship of the ventral lamina to the superior articular facet (SAF) and pedicle, and describe an optimal medial-lateral pedicle screw starting point in the thoracic spine.

STUDY DESIGN

We conducted an in vitro fresh-frozen human cadaveric study.

METHODS

One hundred fifteen thoracic spine vertebral levels were evaluated. After the vertebral body was removed, Kirschner wires were inserted retrograde along the four boundaries of the pedicle. Using digital calipers, we measured width of the SAF and pedicle at the isthmus, and from the borders of the SAF to the boundaries of the pedicle. We calculated the morphologic relationship of the ventral lamina and the center of the pedicle (COP) to the SAF.

RESULTS

Two hundred twenty-nine pedicles were measured, with one pedicle excluded because of fracture of the SAF during disarticulation. The ventral lamina was clearly identifiable at all levels, forming the roof of the spinal canal and confluent with the medial pedicle wall (MPW). The mean distance from the SAF midline to the MPW was 1.36±1.23 mm medial. The MPW was lateral to SAF midline in 34 pedicles (14.85%) and, on average, was a distance of 0.52±0.51 mm lateral. The mean distance from the SAF midline to the COP was 2.17±1.38 mm lateral. The COP was medial to SAF midline in only 11 pedicles (4.80%).

CONCLUSIONS

The ventral lamina is an anatomically reproducible structure located consistently medial to the SAF midline (85%). We also found the COP consistently lateral to the SAF midline (95%). Based on these morphologic findings, the medial-lateral starting point for thoracic pedicle screws should be 2 to 3 mm lateral to the SAF midline (superior facet rule), allowing screw placement in the COP and avoiding penetration into the spinal canal.

Accuracy and efficacy of thoracic pedicle screws in scoliosis with patient-specific drill template

With the rapid increase in the use of thoracic pedicle screws in scoliosis, accurate and safe placement of screw within the pedicle is a crucial step during the scoliosis surgery. To make thoracic pedicle screw placement safer various techniques are used, Patient-specific drill template with pre-planned trajectory has been thought as a promising solution, it is critical to assess the efficacy, safety profile with this technique. In this paper, we develop and validate the accuracy and safety of thoracic transpedicular screw placement with patient-specific drill template technique in scoliosis. Patients with scoliosis requiring instrumentation were recruited. Volumetric CT scan was performed on each desired thoracic vertebra and a 3-D reconstruction model was generated from the CT scan data. The optimal screw size and orientation were determined and a drill template was designed with a surface that is the inverse of the posterior vertebral surface. The drill template and its corresponding vertebra were manufactured using rapid prototyping technique and tested for violations. The navigational template was sterilized and used intraoperatively to assist with the placement of thoracic screws. After surgery, the positions of the pedicle screws were evaluated using CT scan and graded for validation. This method showed its ability to customize the placement and the size of each pedicle screw based on the unique morphology of the thoracic vertebra. In all the cases, it was relatively very easy to manually place the drill template on the lamina of the vertebral body during the surgery. This method significantly reduces the operation time and radiation exposure for the members of the surgical team, making it a practical, simple and safe method. The potential use of such a navigational template to insert thoracic pedicle screws in scoliosis is promising. The use of surgical navigation system successfully reduced the perforation rate and insertion angle errors, demonstrating the clear advantage in safe and accurate pedicle screw placement of scoliosis surgery.

Learning retention of thoracic pedicle screw placement using a high-resolution augmented reality simulator with haptic feedback

BACKGROUND

We evaluated the use of a part-task simulator with 3D and haptic feedback as a training tool for a common neurosurgical procedure--placement of thoracic pedicle screws.

OBJECTIVE

To evaluate the learning retention of thoracic pedicle screw placement on a high-performance augmented reality and haptic technology workstation.

METHODS

Fifty-one fellows and residents performed thoracic pedicle screw placement on the simulator. The virtual screws were drilled into a virtual patient's thoracic spine derived from a computed tomography data set of a real patient.

RESULTS

With a 12.5% failure rate, a 2-proportion z test yielded P = .08. For performance accuracy, an aggregate Euclidean distance deviation from entry landmark on the pedicle and a similar deviation from the target landmark in the vertebral body yielded P = .04 from a 2-sample t test in which the rejected null hypothesis assumes no improvement in performance accuracy from the practice to the test sessions, and the alternative hypothesis assumes an improvement.

CONCLUSION

The performance accuracy on the simulator was comparable to the accuracy reported in literature on recent retrospective evaluation of such placements. The failure rates indicated a minor drop from practice to test sessions, and also indicated a trend (P = .08) toward learning retention resulting in improvement from practice to test sessions. The performance accuracy showed a 15% mean score improvement and more than a 50% reduction in standard deviation from practice to test. It showed evidence (P = .04) of performance accuracy improvement from practice to test session.

Estudo de acurácia em cirurgia assistida por navegação na revisão cirúrgica de deformidade vertebral

OBJETIVO: Avaliar as vantagens da cirurgia com navegação na revisão cirúrgica de deformidades vertebrais, verificando a acurácia deste método. MÉTODO: Foram revisados cincos pacientes com deformidades vertebrais que tiveram intercorrências na primeira cirurgia. Esses pacientes foram submetidos a um estudo de tomografia computadorizada (TC) com cortes de 2mm da coluna vertebral antes da segunda cirurgia. Nos cinco pacientes submetidos a reabordagem cirúrgica procedeu-se a instrumentação posterior com auxílio da navegação. Foram 84 parafusos pediculares implantados, sendo que 33 destes parafusos foram assistidos por computação. A navegação foi empregada nos níveis da deformidade vertebral onde a anatomia apresentava-se alterada inviabilizando o correto uso dos parâmetros anatômicos para inserção de parafusos pediculares. Nos demais níveis onde era possível a correta identificação desses parâmetros anatômicos foi utilizada a técnica padrão. A TC pós-operatória foi realizada para aferição do posicionamento dos parafusos pediculares. Avaliamos os resultados obtidos no posicionamento com e sem o uso da navegação. O tempo de fluoroscopia e o tempo da cirurgia também foram comparados com o padrão ouro da literatura. RESULTADOS: Dos 33 parafusos implantados com navegação observou-se uma acurácia de 94%, com uma taxa de violação pedicular de 6%. CONCLUSÕES: O uso da navegação é importante nas revisões cirúrgicas das deformidades vertebrais com anatomia alterada, influenciando no bom resultado final da cirurgia.

Auxílio da tomografia computadorizada no planejamento pré-operatório de pacientes portadores de escoliose idiopática do adolescente

A escoliose idiopática do adolescente (EIA) é uma doença diagnosticada no início da puberdade. Ela apresenta etiologia indefinida e caracteriza-se pelo desvio lateral da coluna vertebral maior que 10°, associado à rotação do corpo vertebral. O uso de instrumentação de terceira geração produziu um melhor resultado na correção da curva do que as técnicas anteriores. Porém, ainda existem dificuldades técnicas no momento da passagem e da escolha dos parafusos pediculares, devido à angulação e ao diâmetro dos pedículos vertebrais. Apesar de apresentar vantagens, essa técnica não é isenta de riscos e complicações, necessitando de uma maior curva de aprendizado pelo médico-cirurgião, bem como de um adequado planejamento pré-operatório. Até o momento, não há na literatura relato sobre a utilização da tomografia computadorizada no auxílio do planejamento cirúrgico de pacientes com escoliose. Diante do exposto, objetivamos, no presente estudo, descrever uma técnica de planejamento pré-operatório, com o auxílio da tomografia computadorizada para a fixação da coluna em pacientes com escoliose idiopática do adolescente, especificando a angulação e o diâmetro dos pedículos vertebrais, o que poderá auxiliar o médico-cirurgião no momento da fixação.

Universal Clamp system in thoracolumbar spinal fixation: technical note

BACKGROUND

The Universal Clamp is a polyester band passed under the lamina and connected to a rod by a titanium clamp that has been recently reported as an alternative for replacing screws and hooks for thoracolumbar spinal diseases. To date, there is no report of an evaluation of the effectiveness and safety of posterior fixation and fusion using this technique.

METHODS

This study was a prospective evaluation of a cohort of 18 patients with thoracolumbar disorders that were surgically treated between November 2006 and June 2007 with Universal Clamps for spinal fixation. Fifteen cases were traumatic fractures with others two with degenerative severe stenosis and one kyphotic stenosis. Levels treated were thoracolumbar in 15 cases, thoracic in two cases, and lumbar in one case. Seventeen patients underwent correction and instrumentation using a hybrid construct of screws and clamps, while one patient underwent fixation using Universal Clamps only. Intraoperative evoked potentials were monitored in all cases. One patient had infection that resolved after antibiotic therapy without implant removal. No neurological adverse event was seen. There was no rod breakage or clamp loosening during a follow-up of 12 months.

CONCLUSIONS

The polyester band is soft and flexible, and the anterior-posterior spinal canal space occupied by the band is less than by sublaminar wire steel cable, thus avoiding direct spinal cord trauma during sublaminar passage. The flat configuration of the cable distributes the load over a larger contact area under the lamina compared to metal wires without producing imaging artefacts in postoperative imaging. This preliminary report demonstrates the efficacy and safety of this technique for the stabilization of thoracolumbar spinal disorders.

Image-guided pedicle screw insertion accuracy: a meta-analysis

Improved pedicle screw insertion accuracy has been reported with the assistance of computer tomography-based navigation. Studies also indicated that fluoroscopy-based navigation offers high accuracy and is comparable to CT-based assistance. However, different population characteristics and assessment methods resulted in inconsistent conclusions. We searched OVID, Springer, and MEDLINE databases to conduct a meta-analysis of the published literature specifically looking at accuracy of pedicle screw placement with different navigation methods. Subgroups and descriptive statistics were determined based on the subject type (in vivo or cadaveric), navigational method, and spinal level. A total number of 7,533 pedicle screws were summarised in our database with 6,721 screws accurately inserted into the pedicles (89.22%). Overall, the median placement accuracy for the in vivo CT-based navigation subgroup (90.76%) was higher than that with the use of two-dimensional (2D) fluoroscopy-based navigation (85.48%). We concluded that CT-based navigation could provide a higher accuracy in the placement of pedicle screws for all subgroups presented. In the lumbar level, 2D fluoroscopy-based navigation was comparable with CT-based navigation. Discrepancy between the two navigation types increased in the thoracic level for the in vivo populations, where there was less potential in the use of 2D fluoroscopy-based navigation than CT-based navigation.

Single-staged anterior and posterior spinal fusion: a safe and effective alternative for severe and rigid adolescent idiopathic scoliosis in China

AIM

Delayed treatment of adolescent idiopathic scoliosis (AIS) is common in Mainland China because of the lack of public education about health care resulting in the reluctance to undergo surgery. This leads to a high incidence of complex cases where surgeons may not be trained in advanced procedures. We report the efficacy of single-staged anterior and posterior spinal fusion for correction of severe AIS in China.

METHODS

A retrospective review was performed of 31 consecutive cases in which patients were treated at the Orthopaedic Department of Changhai Hospital in Shanghai between 2001 and 2004 with a combined anterior and posterior spinal fusion with screws, hooks, sublaminar wires or cables.

RESULTS

Thirty-one patients with AIS with Lenke type 1, 2, 3 and 4 curves were included for analysis. At least one of the curves was >or=90 degrees in each patient. The mean coronal and sagittal Cobb angles of the main thoracic curve were 98 degrees and 22 degrees before surgery, 50.5 degrees and 21 degrees after surgery, and 53.7 degrees and 24 degrees at follow-up, respectively. No neurological deficits or deaths occurred. Solid arthrodesis with coronal and sagittal balance was achieved in all patients.

CONCLUSIONS

A single-stage anterior release and fusion and posterior fusion for treatment of severe AIS is good alternative to pedicle screws/vertebrectomy on the basis of risk-benefit balance, and can be performed by surgeons not experienced in more complex procedures. The risk of pulmonary complications may be preferable to the risk of severe neurological complications when thoracic pedicle screws are applied, especially when surgeons are not adequately trained in their use.

SEGMENTAL SPINAL INSTRUMENTATION IN THE MANAGEMENT OF SCOLIOSIS

SPINAL INSTRUMENTATION FOR the correction of spinal deformity began with Harrington and his rod system. The use of the Harrington rods was limited, however, because of the need for long-segment instrumentation, distraction, and the potential for hood dislodgment and construct failure. Luque subsequently introduced the next generation of spinal fixation techniques via the concept of segmental instrumentation; his use of sublaminar wires allowed the construct to be fixated to the spine at every level. This arrangement allowed greater control over correction of spinal deformities and significantly lessened the incidence of hardware dislodgment. Modern instrumentation systems, including the use of pedicle screws, permit even greater control of the spine in multiple planes during deformity correction. Newer strategies have decreased the incidence of neurological injury during implant application and provide greater stability. A review of segmental fixation, including surgical techniques, is provided in this article.

Electromagnetic navigation in minimally invasive spine surgery: results of a cadaveric study to evaluate percutaneous pedicle screw insertion

Background

This cadaveric study compared efficacy and safety of an electromagnetic (EM) guidance system versus conventional fluoroscopy for percutaneous pedicle screw fixation. As percutaneous pedicle screw fixation becomes increasingly common in spinal surgery, intraoperative imaging systems that maximize efficiency while minimizing radiation exposure and inaccurate trajectories will be progressively more important. Published studies have validated the safety of percutaneous screw fixation using conventional fluoroscopic guidance and frameless optical stereotaxy, though EM guidance systems have not been evaluated for percutaneous placement in the lumbosacral spine. The aim of the study was to evaluate the clinical applicability of an EM system for minimally invasive spine fusion in the lumbosacral spine.

Methods

Five human cadaveric specimens underwent bilateral lumbosacral percutaneous screw fixation from L1 to S1 using conventional anteroposterior (AP) and lateral fluoroscopic techniques on one side and 2-dimesional (2D) EM guidance on each matching side. Intraoperative efficiency was evaluated, and pedicle, vertebral, and critical breach rates were assessed on postoperative computed tomography (CT).

Results

Overall mean fluoroscopy time per screw was 58.9 ± 44.7 seconds for conventional fluoroscopy compared to 27.4 ± 13.5 seconds for electromagnetic guidance (P = .0003). Pedicle, vertebral, and critical breach rates for the L1-S1 were 32.1%, 10.7%, and 25.0% for conventional fluoroscopy and 42.8%, 10.7%, and 14.1% for electromagnetic guidance (difference not statistically significant [ns]). In comparing critical breaches in the lumbar spine (L1-L5), there was a significant difference between 2-D EM guidance (0) and CF guidance (6) (P = .02).

Conclusions

Two-dimensional EM navigation provides a modality for lumbosacral percutaneous pedicle screw fixation that is more efficient and safer than conventional fluoroscopy. This data provides a foundation for further clinical trials of this technology.

Level of Evidence

Level 5 – Bench Research

Computer-assisted pedicle screw placement for thoracolumbar spine fracture with separate spinal reference clamp placement and registration

BACKGROUND

The objective of the study was to improve the accuracy of computer-assisted pedicle screw installation in the spine. This study evaluates the accuracy of computer-assisted pedicle screw placement with separate spinal reference clamp placement and registration on each instrumented vertebra for thoracolumbar spine fractures.

METHODS

Postoperative radiographs and CT scans assessed the accuracy of pedicle screw placement in 21 adult patients on each instrumented vertebra. Screw placements were graded as good if the screws were placed in the central core of the pedicle and the cancellous portion of the body. Screw placements were graded as fair if the screws were placed slightly eccentrically, causing erosion of the pedicular cortex, and with less than a 2-mm perforation of the pedicular cortex. Screw placements were graded as poor if screws were placed eccentrically with a large portion of the screw extending outside the cortical margin of the pedicle and with more than a 2-mm perforation of the pedicular cortex.

RESULTS

A total of 140 image-guided pedicle screws were placed in 21 patients: 78 in the thoracic and 62 in the lumbar spine. Of the 140 pedicle screw placements, 96.4% (135/140) were categorized as good; 3.6% (5/140), fair; and 0% were poor. All 5 fair placement screws were placed in the thoracic spine without any mobility.

CONCLUSION

Separate registration increases accuracy of screw placement in thoracolumbar pedicle instrumentation. Separate spinal reference clamp placement in the instrumented vertebra provides real-time virtual imaging that decreases the possibility of downward displacement during manual installation of the screw.

Double pedicle screw instrumentation in the osteoporotic spine: a biomechanical feasibility study

STUDY DESIGN

A biomechanical feasibility test.

OBJECTIVE

To assess the overall feasibility, safety, and mechanical effectiveness of an intrapedicular double-screw construct in the thoracolumbar spine.

SUMMARY OF BACKGROUND DATA

The bony purchase of the pedicle screw fixation is often not strong enough in elderly patients with osteoporosis. Our hypothesis was that the elliptical cross-section of the pedicle would allow the insertion of 2 smaller diameter pedicle screws resulting in a bony purchase superior to the standard single-screw technique.

METHODS

Thirty-six double-screw constructs (5mm diameter AOUSS and 5 mm Schanz screw) and 36 standard single pedicle screws (6mm diameter AOUSS screw) were placed. Screw pullout, multiaxial flexibility, and axial failure load testing was performed.

RESULTS

Visual inspection, palpation, and radiograph confirmed that there were no pedicle breaches. In the double-screw group, all but 2 constructs had ideal direction. Pullout strength of the double-screw construct was no different than that of the single-screw construct. However, stiffness increased considerably in all testing modes. Axial load to failure, adjusted for bone mineral density, and dimensional variation, also increased. All differences were statistically significant except for axial rotation that was only marginally significant.

CONCLUSIONS

The double-screw construct appears feasible and safe in the thoracolumbar spine. In this study, the new technique demonstrates a mechanical advantage over the standard single-screw technique. Further in vitro cadaveric safety studies with better adapted instrumentation are needed before the technique can be widely recommended.

A comparison of two techniques in image-guided thoracic pedicle screw placement: a retrospective study of 37 patients and 277 pedicle screws

Object

The goal of this study was to compare the accuracy of thoracic pedicle screw placement aided by two different image-guidance modalities.

Methods

The charts of 40 consecutive patients who had undergone stabilization of the thoracic spine between January 2003 and January 2005 were retrospectively reviewed. Three patients were excluded from the study because, on the basis of preoperative findings, small pedicle diameter precluded the use of pedicle screws. Thus, a total of 37 patients had 277 screws placed with the aid of either virtual fluoroscopy or isocentric C-arm 3D navigation. The indications for surgery included trauma, degenerative disease, and tumor, and were similar in both groups. All 37 patients underwent postoperative computed tomography scanning, and an independent reviewer graded all screws based on axial, sagittal, and coronal projections for a full determination of the placement of the screw in the pedicle.

Results

The rate of unintended perforations was found to depend on pedicle diameter (p < 0.0001). There were no statistical differences between groups with regard to rate or grade of cortical perforations. Overall, the rate and grade of perforations was low, and there were no neurological or vascular complications.

Conclusions

The authors have shown that either image-guidance system may be used with a high degree of accuracy and safety. Because both systems were found to be comparably safe and accurate, the choice of image-guidance modality may be determined by the level of surgeon comfort and/or availability of the system.

Thoracic pedicle screw placement: analysis using anatomical landmarks without image guidance

STUDY DESIGN

Prospective laboratory study analyzing the technique of pedicle screw placement in a cadaveric model.

OBJECTIVES

To determine whether a freehand technique without image guidance can be used to safely place pedicle screws in the thoracic spine.

SUMMARY OF BACKGROUND DATA

The use of thoracic pedicle screws for the treatment of spinal deformity has been gaining increased acceptance among surgeons. Although these implants improve deformity correction, there is still concern regarding the risks to neurological and vascular structures and regarding the experience level needed to use this implant. This study was designed to determine whether these implants could be placed safely without imaging modalities.

METHODS

Six fresh cadaveric specimens were instrumented from vertebral segments T4-T11. Ninety-six screws were placed along the anatomical axis of the pedicle. Pedicles were dissected to determine the wall violations, the position of neural structures, and the lateral coverage of the pedicle by the rib head.

RESULTS

Ninety-seven percent of screws had less than 1 mm of wall violation, with 84 screws (87.5%) fully contained within the pedicle. Four screws (4.16%) violated the medial cortex. No violations occurred superiorly, inferiorly, or anteriorly. Nerve roots were in contact with the inferior pedicle wall at all levels. The average distance from nerve to the superior pedicle ranged from 3.85 to 5.04 mm.

CONCLUSIONS

Placing pedicle screws along the anatomical axis without image guidance produced a low level of pedicle wall disruption. This technique uses a reproducible start point at each level, and the results are equal to or better than those of other cadaveric studies that have used guidance systems.

Image guidance in spine surgery

Computer image guidance is one of the most significant recent technologic advancements in the field of spine surgery, because preoperative or intraoperative images can be used for multiplanar, three-dimensional intraoperative navigation. Laboratory and clinical studies have demonstrated that image guidance increases the safety and accuracy of a variety of spinal procedures. This article describes the application of intraoperative image guidance to spinal surgery, with a particular focus on minimal access procedures. Although commonly performed separately, these techniques can work in a complementary fashion. The apparent benefits and limitations of the various image-guided modalities are described.

Image-guided spinal surgery

BACKGROUND

The purpose of this review is to present a comprehensive summary of commonly used methods of spinal image guidance, including the benefits and limitations of this novel technology.

METHODS

The relevant medical literature was examined, supplemented by the author's laboratory and clinical experience with image-guided spinal surgery.

RESULTS

Spinal image guidance has undergone significant evolution and rapid technological advancement in recent years. Image guidance provides three-dimensional visualization of the spine that can be used for preoperative planning and intraoperative navigation. There are three commonly used methods of spinal image guidance: preoperative CT-based, fluoroscopy-based, and 3D fluoroscopy. Each of these methods demonstrates lower rates of spinal implant misplacement than non-image-guided techniques.

CONCLUSIONS

Image guidance provides highly accurate intraoperative navigation and the medical literature suggests that this technology increases the safety of a variety of routine and complex spinal procedures.

Ideal entry point for the thoracic pedicle screw during the free hand technique

We have attempted to determine the spatial orientation of the base of the superior articular process in relation to the centre of the pedicle and then measure the transverse and sagittal screw angles using this ideal pedicle screw entry point - the base of the superior articular process at the junction of the lateral one-third and medial two-thirds. The proposed advantages of this technique are the easily identifiable entry point, the well-defined transverse and sagittal screw angles and a very low incidence of medial and inferior pedicle violation.

Pedicle screw placement accuracy: a meta-analysis

STUDY DESIGN

A meta-analysis of the published literature was conducted specifically looking at accuracy and the postoperative methods used for the assessment of pedicle screw placement in the human spine.

OBJECTIVES

This study specifically aimed to identify postoperative methods used for pedicle screw placement assessment, including the most common method, and to report cumulative pedicle screw placement study statistics from synthesis of the published literature.

SUMMARY OF BACKGROUND DATA

Safety concerns have driven specific interests in the accuracy and precision of pedicle screw placement. A large variation in reported accuracy may exist partly due to the lack of a standardized evaluation method and/or the lack of consensus to what, or in which range, is pedicle screw placement accuracy considered satisfactory.

METHODS

A MEDLINE search was executed covering the span from 1966 until 2006, and references from identified papers were reviewed. An extensive database was constructed for synthesis of the identified studies. Subgroups and descriptive statistics were determined based on the type of population, in vivo or cadaveric, and separated based on whether the assistance of navigation was employed.

RESULTS

In total, we report on 130 studies resulting in 37,337 total pedicle screws implanted, of which 34,107 (91.3%) were identified as accurately placed for the combined in vivo and cadaveric populations. The most common assessment method identified pedicle screw violations simply as either present or absent. Overall, the median placement accuracy for the in vivo assisted navigation subgroup (95.2%) was higher than that of the subgroup without the use of navigation (90.3%).

CONCLUSIONS

Navigation does indeed provide a higher accuracy in the placement of pedicle screws for most of the subgroups presented. However, an exception is found at the thoracic levels for both the in vivo and cadaveric populations, where no advantage in the use of navigation was found.

Thoracic Pedicle Screw Insertion in Scoliosis Using Posteroanterior C-arm Rotation Method

OBJECTIVE

Previous researches have emphasized the importance and difficulties in accurate thoracic pedicle screw insertion in scoliosis patients. However, there has been no report on accuracy of the insertion using posteroanterior C-arm fluoroscopy rotated to allow en face visualization of the pedicle in humans. This study aimed to evaluate the accuracy of the thoracic pedicle screw insertion technique using a C-arm fluoroscopy rotation method for the treatment of scoliosis.

METHODS

Between October 1997 and September 2005, 33 scoliosis patients who underwent surgical treatment with a total of 410 screws were analyzed. Eleven were male, 22 female and the mean age was 13.4 years. The mean preoperative Cobb angle was 59.7 degrees. Screws were inserted using the C-arm rotation method; screw positions were evaluated with postoperative computed tomography scans.

RESULTS

The mean preoperative Cobb angle of 59.7 degrees was corrected to 18.9 degrees (range, 3 to 45 degrees) in the coronal plane (mean correction rate 68%). Postoperative computed tomography scans demonstrated 48 screws penetrated the medial (9 screws) or lateral (39 screws) pedicle cortex with a mean distance of 3.1 and 3.6 mm, respectively. No screws penetrated the inferior or superior cortex in the sagittal plane.

CONCLUSIONS

Thoracic pedicle screw insertion in scoliosis patients using the posteroanterior C-arm rotation method allows en face visualization of both pedicles by rotating the C-arm to compensate for the rotational deformity, making it a practical, simple and safe method.

Clinical Accuracy of Cervicothoracic Pedicle Screw Placement

OBJECTIVE

Posterior transpedicular fixation at the cervicothoracic junction (CTJ) is increasing in popularity. However, the clinical accuracy of pedicle screw placement at the CTJ has not been specifically assessed.

METHODS

Between January 2000 and July 2004, 60 consecutive patients underwent a variety of posterior spinal procedures necessitating pedicle screw placement at C7, T1, and T2. Thirty-two patients had cervicothoracic screws (3.5 to 4.5 mm) placed by an "open" technique (laminectomies or lamino-foraminotomies) and 28 patients with either a closed (before any decompression) 2-dimensional (n=19, fluoroscopy) or 3-dimensional (n=9, CT) computer-assisted technique. Screws were independently assessed for pedicle breach on postoperative CT and scored using a points-based classification system.

RESULTS

The total number of screws placed was 86, 63 and 45 in the open, closed-2-dimensional and closed-3-dimensional groups, respectively. Overall, 61(70.9%), 51(81%), and 40(89%) screws were completely within the pedicle. In the open group, the majority of pedicle breaches were more than 2 mm [n=3 (<2 mm), n=20 (2-4 mm), n=2 (>4 mm)]. Screw violation occurred laterally 11/25(44%), medially 3/25(12%), inferiorly 7/25(28%), and superiorly 4/25(16%). In the closed technique, all breaches were lateral. Seventeen screws (n=11-2-dimensional, n=5-3-dimensional) breached the pedicle by a margin of less than 2 mm and 1 screw (2-dimensional) by 2 to 4 mm. Pedicle screw accuracy was significantly improved with computer-assisted techniques. However, there was no significant difference between the 2-dimensional and 3-dimensional techniques. For all patients, there were no clinically significant screw misplacements, nor any need for screw revision.

CONCLUSIONS

Computer-assisted surgery allows for more accurate placement of pedicle screws at the CTJ. Although a higher proportion of major pedicular breaches occurred in the "open lamina/lamino-foraminotomy" group, no screws required revision in either group.

Randomized clinical study to compare the accuracy of navigated and non-navigated thoracic pedicle screws in deformity correction surgeries

STUDY DESIGN

Randomized clinical trial (level I evidence).

OBJECTIVE

To compare the accuracy of non-navigation and Iso-C based navigation in pedicle screw fixation in thoracic spine deformities.

SUMMARY OF BACKGROUND DATA

Thoracic pedicle screw insertion for spinal deformity correction can be associated with increased pedicle breaches. Iso-C based navigation has been reported to improve the accuracy of pedicle screw placement, but its use in the presence of deformity has not been reported.

METHODS

Twenty-seven patients with scoliosis and 6 patients with kyphosis had a total of 478 thoracic pedicle screws. The average Cobb angle was 58.4 degrees +/- 8 degrees (range 50 degrees -80 degrees), and the mean kyphotic angle was 54.6 degrees +/- 4 degrees (range 51 degrees -76 degrees). By random allocation, 17 patients had screw insertion under navigation (242 screws) and 16 under fluoroscopic control (236 screws). The 2 groups were compared for accuracy of screw placement, time for screw insertion, and the number of times the C-arm had to be brought into the field. Two independent blinded observers determined accuracy using postoperative computed tomography assessments.

RESULTS

There were 54 (23%) pedicle breaches in the non-navigation group as compared to only 5 (2%) in the navigation group (P < 0.001). Thirty-eight screws (16%) in the non-navigation group had penetrated the anterior or lateral cortex compared to 2 screws (0.8%) in the navigation group. Average screw insertion time in the non-navigation group was 4.61 +/- 1.05 minutes (range 1.8-6.5) compared to 2.37 +/- 0.72 minutes (range 1.16-4.5) in navigation group (P < 0.01). The C-arm had to be moved into the operation field on an average of 1.5 +/- 0.25 times (range 1-3) per screw. With single screening data, an average of 11.4 pedicles (range 9-14) could be visualized without necessity to bring the C-arm into operating field again.

CONCLUSIONS

Iso-C navigation increases accuracy, and reduces surgical time and radiation in thoracic deformity correction surgeries.

Inserting pedicle screws in the upper thoracic spine without the use of fluoroscopy or image guidance. Is it safe?

Several studies have looked at accuracy of thoracic pedicle screw placement using fluoroscopy, image guidance, and anatomical landmarks. To our knowledge the upper thoracic spine (T1-T6) has not been specifically studied in the context of screw insertion and placement accuracy without the use of either image guidance or fluoroscopy. Our objective was to study the accuracy of upper thoracic screw placement without the use of fluoroscopy or image guidance, and report on implant related complications. A single surgeon inserted 60 screws in 13 consecutive non-scoliotic spine patients. These were the first 60 screws placed in the high thoracic spine in our institution. The most common diagnosis in our patient population was trauma. All screws were inserted using a modified Roy-Camille technique. Post-operative axial computed tomography (CT) images were obtained for each patient and analyzed by an independent senior radiologist for placement accuracy. Implant related complications were prospectively noted. No pedicle screw misplacement was found in 61.5% of the patients. In the remaining 38.5% of patients some misplacements were noted. Fifty-three screws out of the total 60 implanted were placed correctly within all the pedicle margins. The overall pedicle screw placement accuracy was 88.3% using our modified Roy-Camille technique. Five medial and two lateral violations were noted in the seven misplaced screws. One of the seven misplaced screws was considered to be questionable in terms of pedicle perforation. No implant related complications were noted. We found that inserting pedicle screws in the upper thoracic spine based solely on anatomical landmarks was safe with an accuracy comparable to that of published studies using image-guided navigation at the thoracic level.

Does computer-assisted spine surgery reduce intraoperative radiation doses?

STUDY DESIGN

Prospective clinical study.

OBJECTIVE

Computer-assisted surgery (CAS) means improved accuracy in inserting screws. Usually the required time of the intraoperative use of a C-arm device is reduced. The aim of the study was to quantify the radiation doses during spine surgery in different types of computer-assisted surgical procedures (i.e., computerized tomography [CT] based and C-arm) compared to standard methods and, as a new technique, the Iso-C3D C-arm (Siemens, GER).

SUMMARY OF BACKGROUND DATA

A total of 38 individuals were enrolled in the study, including 8 who underwent standard spine surgery, 10 with CT-based, 9 with C-arm based, and 11 with Iso-C3D C-arm based. The thermoluminescence dosimetry measurements were 2 at the radiation source, 2 at the patient, and 2 at the receiver.

METHODS

This study is based on the thermoluminescence method. A total of 38 individuals were enrolled in the study. Despite the small number of patients, the existing results up until now showed a clear reduction of the duration of radiation time using CAS compared to standard methods in spine surgery. Much more important is the fact that the radiation doses were clearly reduced from a median of 1091 mGy using the standard procedure versus 432 mGy in CT-based and 664 mGy in C-arm based guided surgery. The Iso-C3D C-arm showed a median of 152 mGy.

RESULTS

The duration of radiation was reduced from 177 seconds in the standard spine procedure to 75 seconds in CT-based CAS spine intervention. Comparing the different types of CAS application at the spine, the Iso-C3D C-arm based surgery is the method with the lowest duration of radiation. The radiation doses at the C-arm tube (source) are reduced from a median of 1091 mGy in the standard procedure versus 432 mGy in CT-based and 664 mGy in C-arm based guided surgery. In this study, the median dose of an Iso-C3D C-arm was 152 mGy.

CONCLUSION

These findings are important for the operating room personnel, which is exposed daily to radiation intraoperatively, as well as the patients, when using CAS procedures.

Three-dimensional rotational X-ray navigation for needle guidance in percutaneous vertebroplasty: an accuracy study

STUDY DESIGN

The position of a needle tip displayed on a navigation system after transpedicular introduction into a vertebral body is compared with the real position of the needle tip when using a direct navigation coupling between a three-dimensional rotational X-ray (3DRX) system and a navigation system.

OBJECTIVES

To assess whether the needle tip position displayed by the navigation system corresponds to the real needle position and to quantitatively determine needle navigation accuracy in a clinically relevant setting.

SUMMARY OF BACKGROUND DATA

Image-guided navigation has reportedly increased the accuracy and safety of pedicle screw insertion and decreased complication rates. In former studies, the result of image-guided navigation was mainly compared qualitatively with the result of conventional fluoroscopy-guided procedures. Previously, a direct navigation coupling between a 3DRX system and a standard navigation system was introduced that bypasses the need for explicit patient-to-image registration necessary for image-guided orthopedic surgery. In a phantom experiment, the reported accuracy of navigation with the coupling to a 3DRX system was approximately 1 mm. However, in a clinical setting, additional errors can be introduced.

METHODS

Twenty-three needles were placed transpedicularly into vertebral bodies of embalmed human trunks using 3DRX-guided navigation. The navigated needle tip positions were compared with the real needle tip positions manually extracted from 3DRX volumes acquired after completion of the introduction.

RESULTS

The average distance between the navigated needle tip and the real position of the needle tip extracted from a postprocedure 3DRX volume was 2.5 +/- 1.5 mm.

CONCLUSIONS

Accuracy of 3DRX-guided navigation is 2.5 +/- 1.5 mm in a clinically relevant setting, which is less than the accuracy determined in phantom experiments.

Accuracy evaluation of direct navigation with an isocentric 3D rotational X-ray system

Minimally invasive interventions are often performed under fluoroscopic guidance. Drawbacks of fluoroscopic guidance are the fact that the presented images are 2D projections and that both the patient and the clinician are exposed to radiation. Image-guided navigation using pre-interventionally acquired 3D MR or CT data is an alternative. However, this often requires invasive anatomical landmark-based, marker-based or surface-based image-to-patient registration. In this paper, a coupling between an image-guided navigation system and an intraoperative C-arm X-ray device with 3D imaging capabilities (3D rotational X-ray (3DRX) system) that enables direct navigation without invasive image-to-patient registration on 3DRX volumes, is described and evaluated. The coupling is established in a one-time preoperative calibration procedure. The individual steps in the registration procedure are explained and evaluated. The acquired navigation accuracy using this coupling is approximately one millimeter.

Evaluation of registration techniques for spinal image guidance

Object

Paired point matching alone and paired point matching combined with surface matching are the two techniques used for the registration step in preoperative computerized tomography–based spinal image guidance. In the present study the authors sought to compare paired point–matching registration alone with paired point matching supplemented with surface matching to determine if the addition of surface matching improves navigational accuracy.

Methods

Pedicle screws were placed in three embalmed human cervicothoracic spinal specimens during image guidance to serve as a reference points. The specimens were then rescanned, and each level was registered using paired point matching alone and then by paired point supplemented with surface matching. Navigational accuracy was assessed by placing the stereotactic probe in the center of the screw head, and measuring the apparent distance between the screw head and probe on the computer monitor. Statistical analysis was used to compare the registration error and navigational error between the two techniques.

Seventy-five screws were placed at 46 vertebral levels. The mean registration error for the paired point matching/surface matching technique (0.5 mm) was significantly lower (p < 0.001) than that of the paired point matching alone technique (1.2 mm); however, the intertechnique difference in navigational error was nearly equivalent (1.3 mm compared with 1.4 mm) and statistically insignificant (p > 0.05).

Conclusions

Although the addition of surface matching to paired point registration significantly decreased the mean registration error, the actual navigational accuracy between the two techniques was equivalent when easily distinguishable points were meticulously selected. The use of paired point matching alone did not compromise the accuracy of navigation and is likely to result in decreased operating time.

Miniature robotic guidance for spine surgery — introduction of a novel system and analysis of challenges encountered during the clinical development phase at two spine centres

BACKGROUND

Instrumented spinal fusion surgery is increasingly performed. Breaching of the pedicle occurs in 3-55% of screws; clinically significant screw misplacements occur in 0-7% of all transpedicular screw placements. Several techniques have reduced this incidence but none gained popularity due to cost as well as staff issues. Surgical robots offer distinct added value in accuracy and minimal invasiveness. The aim of this study is to introduce the SpineAssist--a novel spine surgery miniature robot, to discuss the various reasons that had prevented full success with its use, to identify patients related, technical related, and surgeon related issues, and to offer ways to avoid them.

METHODS

The SpineAssist miniature robotic system is presented, including a short description of the system, its mode of action and a short summary of the surgical procedure.15 patients had undergone lumbar fusion procedures using the robotic system as part of clinical trials in two Israeli spine centres. A group of 9 procedures was identified within this prospective cohort. This group represents a wide array of technical challenges and human errors which were encountered during the clinical development phase of the SpineAssist. These 9 cases were conducted in two different sites by different surgical teams, over a period of 9 months, with an average interval of 7 weeks between consecutive cases. The cases were analysed for patient, system, surgeon and technical issues causing the difficulty. Conclusions were drawn as to how to avoid these hurdles in the future.

RESULTS

In six cases the system operated smoothly, resulting in accurate screws placement according to the pre-operative plan, this was confirmed by a post-operative CT scan. Technical and surgical challenges which are associated with the system early development stage were encountered during 9 procedures. On the technical side, the following phenomena were evident: 1) failure of the software to automatically achieve satisfying CT-to-fluoro image registration and 2) failure of the hospital's peripheral equipment/logistics preventing registration. On the clinical side of things, the following issues were encountered: 1) failure to avoid excessive pressure on the guiding arm caused by surrounding soft tissues, leading to a shift in the entry point and trajectory of the tool guide. 2) a surgeon applying too much force on the tool guide at the tip of the robotic arm, causing deviation from plan. 3) pre-operative plan out of the reach of the robot arm and 4) attachment of the clamp to the spinous process in a suboptimal orientation.

CONCLUSIONS

It is expected that following a steep learning curve in the range of 5-10 cases, recommended to take place within 2-3 weeks time, the surgical team will gain sufficient experience in operating the SpineAssist miniature robotic device in order to achieve excellent surgical results. The system may be used for wide range of applications including but not limited to pedicle screws, trans-facet and trans-laminar screws, biopsy needles, vertebroplasty or kyphoplasty tools and more. The preoperative plan has to be logical, intraoperative fluoro images taken with care, gentle surgical technique must be kept - maintaining the integrity of the posterior elements, and avoiding pressure between the robot arms and the soft tissues. During the clinical development phase discussed in this study, both teams used an early version of the system. Based on the results of this study several significant software and hardware improvements have already been implemented. It is our hope that describing and analysing our findings will help in planning and preparing for the clinical utilization of the SpineAssist system in future sites and will shorten their learning curve. By the time this article is published wider clinical experience will have been gathered and we expect to soon follow up with an analysis of clinical utilization of this system in a larger study group.

Accuracy and Safety of Thoracic Pedicle Screw Placement in Spinal Deformities

OBJECTIVES

To determine the safety of pedicle screw fixation in thoracic spine deformity correction.

METHODS

One hundred twelve pedicle screws were surgically placed in 25 patients with degenerative, posttraumatic, and Scheuermann kyphosis and idiopathic and neuromuscular scoliosis. Screw position was evaluated using intraoperative and postoperative radiographs and thin-slice computed tomography.

RESULTS

Of the total 112 thoracic pedicle screws that were inserted, 98 screws (87.5%) were fully contained within the cortical boundaries of the pedicle. When comparing proximal screws (T1-T8) with distal screws (T9-T12) and convex placed screws with concave ones, a statistically significant difference in screw placement was evident (P < 0.05). More misplaced screws were seen proximally and on the concave side. Of the 14 malpositioned screws, 2 (1.8%) demonstrated aortic abutment. There were no neurologic deficits, vascular injuries, or mechanical failures recorded.

CONCLUSIONS

Placement of thoracic pedicle screws is both feasible and safe.

Clinical and radiological results after parapedicular screw fixation of the thoracic spine

OBJECT

The proximity of thoracic pedicles to the spinal cord and neurovascular structures has prompted numerous efforts to obtain proper screw placement. The aim of this study was to evaluate the feasibility and efficacy of thoracic parapedicular (intercostovertebral) screw fixation by following anatomical landmarks and using fluoroscopy.

METHODS

Thoracic parapedicular screw fixation was performed in 41 patients (328 screws). Postoperative computerized tomography scans were obtained in all cases to analyze the position of each screw with respect to the pedicle rib unit, the spinal canal, and the vertebral body (VB) according to a proposed novel grading system. Additionally, screw convergence angles were calculated for each instrumented level. There was no additional morbidity associated with parapedicular screw insertion. In a single case a screw suspected of entering the spinal canal was revised without causing neurological damage. The remaining screws were placed entirely within the pedicle rib unit and VB without breaching the neural foramina, pleura, or vascular structures.

CONCLUSIONS

Thoracic and thoracolumbar instability can be treated adequately and safely by using parapedicular screw fixation guided by anatomical landmarks and fluoroscopic imaging. The use of computer-aided navigation may be beneficial but does not appear to be mandatory.

Image-guided thoracoscopic spinal surgery: a merging of 2 technologies

STUDY DESIGN

Retrospective clinical and intraoperative navigational data review.

OBJECTIVE

To evaluate quantitatively the application of frameless stereotactic image guidance in thoracoscopic discectomy procedures.

SUMMARY OF BACKGROUND DATA

Thoracoscopic spinal surgery has technical and anatomic challenges that result in difficult orientation with a 2-dimensional imaging procedure in a complex 3-dimensional structure.

METHODS

There were 16 patients who underwent image-guided thoracoscopic discectomy procedures that combine these 2 technologies. Accuracy was determined by the registration (calculated) error and actual navigation (intraoperative) error. The clinical outcomes and complications were reviewed.

RESULTS

Accuracy determined by registration (calculated) and navigation (intraoperative) was 1.7 and 1.2 mm, respectively. The additional time required for the image guidance portion of the procedure was countered by the efficiency of the remaining procedure. Clinical outcomes and complication were comparable with previous experience.

CONCLUSIONS

Image-guided thoracoscopic spinal surgery can provide 3-dimensional orientation to a 2-dimensional imaging procedure that ultimately improves accuracy, efficiency, and safety. Future developments in combining guidance technology with standard surgical procedures will likely continue.