Pedicle Cortex Research Articles

Posterior endpoint determination of the lumbar pedicle central axis on the anterior–posterior fluoroscopic image for pedicle screw insertion

The transpedicular procedure has been widely used in spinal surgery. The determination of the best entry point is the key to perform a successful transpedicular procedure. Various techniques have been used to determine this point, but the results are variable. This study was carried out to determine the posterior endpoint of the lumbar pedicle central axis on the standard anterior–posterior (AP) fluoroscopic images. Computer-aided design technology was used to determine the pedicle central axis and the posterior endpoint of the pedicle central axis on the posterior aspect of the vertebra. The standard AP fluoroscopic image of the lumbar vertebral models by three-dimensional printing was achieved. The endpoint projection on the AP fluoroscopic image was determined in reference to the pedicle cortex projection by the measurements of the angle and distance on the established X–Y coordinate system of the radiologic image. The projection of posterior endpoint of the lumbar pedicle central axis were found to be superior to the X-axis of the established X–Y coordinate system and was located on the pedicle cortex projection on the standard AP fluoroscopic image of the vertebra. The projection point was distributed in different sectors in the coordinate system. It was located superior to the X-axis by 18° to 26° at L1, while they were located superior to the X-axis by 12° to 14° at L2 to L5. The projections of posterior endpoints of the lumbar pedicle central axis were located in different positions on the standard AP fluoroscopic image of the vertebra. The determination method of the projection point was helpful for selecting an entry point for a transpedicular procedure with a fluoroscopic technique.

Impact of intraoperative imaging on decision-making during spine surgery: a survey among spine surgeons using simulated intraoperative images

PurposeTo assess whether the intention to intraoperatively reposition pedicle screws differs when spine surgeons evaluate the same screws with 2D imaging or 3D imaging.MethodsIn this online survey study, 21 spine surgeons evaluated eight pedicle screws from patients who had undergone posterior spinal fixation. In a simulated intraoperative setting, surgeons had to decide if they would reposition a marked pedicle screw based on its position in the provided radiologic imaging. The eight assessed pedicle screws varied in radiologic position, including two screws positioned within the pedicle, two breaching the pedicle cortex < 2 mm, two breaching the pedicle cortex 2–4 mm, and two positioned completely outside the pedicle. Surgeons assessed each pedicle screw twice without knowing and in random order: once with a scrollable three-dimensional (3D) image and once with two oblique fluoroscopic two-dimensional (2D) images.ResultsAlmost all surgeons (19/21) intended to reposition more pedicle screws based on 3D imaging than on 2D imaging, with a mean number of pedicle screws to be repositioned of, respectively, 4.1 (± 1.3) and 2.0 (± 1.3; p < 0.001). Surgeons intended to reposition two screws placed completely outside the pedicle, one breaching 2-4mm, and one breaching < 2 mm more often based on 3D imaging.ConclusionWhen provided with 3D imaging, spine surgeons not only intend to intraoperatively reposition pedicle screws at risk of causing postoperative complications more often but also screws with acceptable positions. This study highlights the potential of intraoperative 3D imaging as well as the need for consensus on how to act on intraoperative 3D information.

Pedicle screw path planning for multi-level vertebral fixation.

For the spinal internal fixation procedures, connecting rods to the pedicle screws are commonly used in all spinal segments from the cervical to sacral spine. So far, we have only seen single vertebral screw trajectory planning methods in literatures. Joint screw placements in multi-level vertebrae with the constraint of an ipsilateral connecting rod are not considered. In this paper, a screw trajectory planning method that considers screw-rod joint system with both multi-level vertebral constraints and individual vertebral safety tolerance areproposed. The proposed method addresses three challenging constraints jointly for multi-level vertebral fixation with pedicle screws. First, a cylindrical screw safe passage model is suggested instead of a unique mathematical optimal trajectory for a single pedicle. Second, the flexible screw cap accessibility model is also included. Third, the connecting rod is modeled to accommodate the spine contour and support the needed gripping capacity. The retrospective clinical data of relative normal shape spines from Beijing Jishuitan hospital were used in the testing. The screw trajectories from the existing methods based on single vertebra and the proposed method based on multi-level vertebrae optimization are calculated andcompared. The results showed that the calculated screw placements by the proposed method can achieve 88% success rate without breaking the pedicle cortex and 100% in clinical class A quality (allow less than 2mm out of the pedicle cortex) compared to 86.1% and 99.1%, respectively, with the existing methods. Expert evaluation showed that the screw path trajectories and the connecting rod calculated by the new method satisfied the clinical implantationrequirements. The new screw planning approach that seeks an overall optimization for multi-level vertebral fixation is feasible and more advantageous for clinical use than the single vertebral approaches.

Improving pedicle screw path planning by vertebral posture estimation

Objective. Robot-assisted pedicle screw placement in spinal surgery can reduce the complications associated with the screw placement and reduce the hospital return counts due to malfunctions. However, it requires accurate planning for a high-quality procedure. The state-of-the-art technologies reported in the literature either ignore the anatomical variations across vertebrae or require substantial human interactions. We present an improved approach that achieves pedicle screw path planning through multiple projections of a numerically re-oriented vertebra with the estimated posture. Approach. We proposed an improved YOLO-type neural network model (YOLOPOSE3D) to estimate the posture of a vertebra before pedicle path planning. In YOLOPOSE3D, the vertebral posture is given as a rotation quaternion and 3D location coordinates by optimizing the intersection over union of the vertebra with the predicted posture and the actual posture. Then, a new local coordinate system is established for the vertebra based on the estimated posture. Finally, the optimal pedicle screw path trajectory is determined from the multiple projections of the vertebra in the local coordinates. Main results. The experimental results in difficult cases of scoliosis showed that the new YOLOPOSE3D network could accurately detect the location and posture of the vertebra with average translation and orientation errors as small as 1.55 mm and 2.55°. The screw path planning achieved 83.1% success rate without breaking the pedicle cortex for the lumbar vertebral L1–L5, which is better than that of a doctor’s manual planning, 82.4%. With the clinical class A requirement to allow less than 2 mm out of the pedicle cortex, the success rate achieved nearly 100%. Significance. The proposed YOLOPOSED3D method can accurately determine the vertebral postures. With the improved posture prior, better clinical outcomes can be achieved for pedicle screw placement in spine internal fixation procedures.

Feasibility of C2 Pedicle Screw Fixation With the "in-out-in" Technique for Patients With Basilar Invagination.

Retrospective study. To evaluate the feasibility of C2 pedicle screw fixation with the "in-out-in" technique in patients with basilar invagination (BI). The "in-out-in" technique is a fixation technique in which the screw enters the vertebrae through the parapedicle. The technique has been used in upper cervical spine fixation. However, anatomic parameters associated with the application of this technique in patients with BI are unclear. We measured the C2 pedicle width (PW), the distance between the vertebral artery (VA) and the transverse foramen (VATF), the safe zone, and the limit zone. The lateral safe zone is the distance from the medial/lateral cortex of the C2 pedicle to the VA (LPVA/MPVA), and the medial safe zone is the distance from the medial/lateral cortex of the C2 pedicle to the dura (MPD/LPD). The lateral limit zone is the sum of LPVA/MPVA and VATF (LPTF/MPTF), and the medial limit zone is the distance from the medial/lateral cortex of the C2 pedicle to the spinal cord (MPSC/LPSC). PW, LPVA, MPVA, and VATF were measured on the reconstructed CT angiography. PW, MPD, LPD, MPSC, and LPSC were measured on MRI. We define a width greater than 4mm as safe for screw. The t -test was used to compare the parameters between male and female, left and right sides in all patients, and PW in CTA and MRI data in the same patient. For intrarater reliabilities, interclass correlation coefficients were calculated. A total of 154 patients (49 CTA, 143 MRI) were included. The average PW, LPVA, MPVA, LPTF, MPTF, MPD, LPD, MPSC, and LPSC were 5.30mm, 1.28mm, 6.60mm, 2.45mm, 8.94mm, 2.09mm, 7.07mm, 5.51mm, and 10.48mm, respectively. Furthermore, in patients with PW <4mm, 53.6% of MPVA, 86.2% of LPTF, and all limit zones were larger than 4mm. In patients with BI, there is sufficient space medially and laterally to the C2 pedicle for partial screw encroachment to achieve "in-out-in" fixation, even if the pedicle is small. Level-4.

Comparison of the accuracy of intraoperative lateral fluoroscopy versus postoperative computed tomography in spinal fusions.

This study compared the accuracy of intraoperative lateral fluoroscopic images versus postoperative computed tomography (CT) 3D studies in the treatment of thoracolumbar spinal fusions. In a tertiary care hospital (study duration 6 months), we compared the use of lateral fluoroscopic images with the postoperative CT scans in 64 patients with thoracic or lumbar fractures undergoing spinal fusions. Out of the 64 patients, 61% were lumbar followed by 39% thoracic fractures. In the lumbar spine, the accuracy of screw placement utilizing lateral fluoroscopy versus postoperative CT 3D was 97.4%, while in thoracic spine, accuracy was reduced to 84.4%. Of the 64 patients, just 4 (6.2%) patients demonstrated lateral pedicle cortex penetration, 1 (1.5%) patient had a medial pedicle cortex breach, while none exhibited anterior vertebral body cortex penetration. This study documented the efficacy of lateral fluoroscopy in intraoperative thoracic and lumbar spinal fixation as confirmed by postoperative CT 3D studies. These findings support the continued use of fluoroscopy rather than CT intraoperatively to lower the risk of radiation exposure to both patients and surgeons.

The role of counter-torque holders in tightening of pedicle screw-rod constructs: a biomechanical study in a porcine model

BACKGROUND CONTEXTPedicle screw-rod assembly procedures following pedicle screw insertion include contouring and placing rods into screw tulips, introducing set screws into the tulip along the screw thread, applying a counter-torque holder and tightening all the set screws clockwise. Even if an appropriate pedicle screw is implanted, screw dislodgement after tightening of the tulip and set screw is not uncommon. Pedicle wall violation resulting from excessive rotational force due to inadequate use of a counter-torque holder might be the reason. However, the strain change in the pedicle during tulip-set screw tightening and the role of counter-torque have never been investigated. PURPOSEThis study determined differences in the strain change in the outer and inner pedicle walls during tulip-set screw tightening; additionally, the influence of counter-torque on pedicle wall violation was elucidated. STUDY DESIGNA controlled biomechanical study; the strain values of outer and inner pedicle walls in cadaveric porcine L4-L5 vertebrae during tulip-set screw tightening with or without a counter-torque holder were measured. METHODSTwelve L4-L5 fresh-frozen porcine lumbar vertebrae were implanted with screw-rod constructs; the set screw was randomly locked into the tulip in the right L5, right L4, left L5 and left L4 testing groups. The maximal values from eight strain gauges (P-R-O: outer cortex of right pedicle in proximal vertebra; P-R-I: inner cortex of right pedicle in proximal vertebra; D-R-O: outer cortex of right pedicle in distal vertebra; D-R-I: inner cortex of right pedicle in distal vertebra; P-L-O: outer cortex of left pedicle in proximal vertebra; P-L-I: inner cortex of left pedicle in proximal vertebra; D-L-O: outer cortex of left pedicle in distal vertebra; D-L-I: outer cortex of left pedicle in proximal vertebra) for each specimen during tightening to 12 Nm were measured. RESULTSThe maximal strain values of the ipsilateral strain gauges in all testing groups were almost significantly higher when a counter-torque holder was not used than when one was used. The strain values in the adjacent pedicle of specimens without a counter-torque holder were significantly increased: P-R-O and P-R-I in the right L5 group; D-R-I in the right L4 group; P-L-I and P-L-O in the left L5 group; D-L-O and D-L-I in the left L4 group. CONCLUSIONSThe constraint effect of counter-torque during tulip-set screw tightening is necessary. Clockwise rotational force with a fragile lateral pedicle wall suggests that caution is required when using a counter-torque holder to tighten the right L5 and left L4 constructs. CLINICAL SIGNIFICANCEA counter-torque holder is important during tulip-set screw tightening; improper use may lead to adjacent pedicle wall violation, sequentially resulting in pedicle screw loosening.

Accuracy of Inserting a Pedicle Screw Percutaneously to Fix Thoracic and Lumbar Spinal Fractures by Minimally Invasive Procedures: A Prospective Observational Study

Aim: To assess the accuracy of inserting a pedicle screw percutaneously to fix thoracic and lumbar spinal fractures by minimally invasive procedures. Study design: Prospective observational study. Place and duration: This study was conducted at , Pakistan Institute of Medical Sciences Islamabad, Pakistan from March 2020 to March 2021. Methodology: A total of 50 patients were evaluated, who had suffered from spinal injuries in the form of thoracic and lumbar spine fractures and were admitted for spinal surgery. Extensive CT scans were ordered for these patients and on the basis of these scans, the clinicians authorized and assessed the positioning for the percutaneous pedicle screw. However, in cases where the scans were not enough to visualize the exact placement of the pedicle cortex, an approach known as the cortical encroachment was applied. In cases where the need for the screw to be inserted laid outside the boundaries of the pedicle cortex the clinicians utilized a method known as the frank penetration. If placement for this screw was located outside the boundaries of the pedicle these boundaries were categorized in three types. Minor: if the displacement was less than 3 millimeters, moderate: where the placement lay between 3 to 6 millimeters and severe: where the placement was greater than 6 millimeters. Results: At total of 380 screws were fitted percutaneously in 50 patients. A total of 281(74%) of these screws were fitted inside the pedicle, 53 screws (14%) were placed in such a way that they encroached the pedicle and 46 (12%) of the cases showed that the screws penetrated the pedicle. Minor screw penetration was in 32 (8.47%) cases, moderate penetration in 10 (2.58 %) and severe penetration in 3 (0.7%) cases. Among one of severe screw penetration post-operative neurological symptoms were noted. Conclusion: Our study concludes that most of the pedicle positioning of screws were ideally placed, while in few cases there were Encroachment and perforation Keywords: Thoracic spine, lumber spine, spinal injury, pedicel screw

The safety of TiRobot-guided percutaneous transpedicular screw implantation

To evaluate the safety of TiRobot-guided percutaneous transpedicular screw implantation. The medical records of 158 patients with thoracolumbar fractures and lumbar degenerative diseases who underwent percutaneous transpedicular screw implantation were retrospectively analyzed between January 2018 and December 2020. The patients were divided into trial group (TiRobot-guided screw implantation, 86 cases) and control group (fluoroscopy-guided screw implantation, 72 cases). There was no significant difference in gender, age, pathology, lesion segment, and the average number of screw implantation per case ( P>0.05). The operation time, fluoroscopic dose, fluoroscopic time, and fluoroscopic frequency were compared between the two groups. One day postoperatively, the convergence angle was measured and the penetration of the pedicle cortex was evaluated according to Gertzbein-Robbins classification standard. The operation time, fluoroscopic dose, fluoroscopic time, and fluoroscopic frequency of the trial group were significantly lesser than those of control group ( P<0.05). One day postoperatively, the convergence angle of trial group was (21.10±4.08)°, which was significantly larger than control group (19.17±3.48)° ( t=6.810, P=0.000). According to the Gertzbein-Robbins classification standard, 446 pedicle screws were implanted in trial group, trajectories were grade A in 377 screws, grade B in 46 screws, grade C in 23 screws, and the accuracy of screw implantation was 94.8%; 380 pedicle screws were implanted in control group, trajectories were grade A in 283 screws, grade B in 45 screws, grade C in 44 screws, grade D in 6 screws, grade E in 2 screws, and the accuracy of screw implantation was 86.3%. There was significant difference in the accuracy of screw implantation between the two groups ( χ 2=25.950, P=0.000). Compared with traditional percutaneous transpedicular screw implantation, TiRobot-guided percutaneous transpedicular screw implantation can improve the accuracy of screw implantation, reduce radiation exposure, and improve surgical safety, which has a good application prospect.

Surgical Outcome of Spinal Fusion for Osteogenesis Imperfecta With Scoliosis: Is the Hybrid System With Pedicle Screws Applicable to Weak, Tiny, and Fragile Vertebrae?

Corrective surgery for spinal deformity associated with osteogenesis imperfecta (OI) is challenging due to the severe and rigid deformity combined with extreme bone fragility. However, surgical outcomes still remain unclear. In addition, the applicability of pedicle screws (PSs) to the tiny and fragile vertebrae in patients with OI is poorly understood. This study evaluated the surgical outcome, and the accuracy and safety of PS placement in patients with OI. Twenty-five patients with OI were included in this study. Mean age was 21.0±9.3 (10 to 49) years. Mean follow-up was 5.8±2.0 years. The Sillence classification showed 16 patients had the mildest type I, 1 patient had moderate type IV, and 8 patients had the most severe type III. Fifteen patients underwent anterior release followed by posterior fusion, and 10 patients underwent only posterior fusion. The accuracy of PS placement was evaluated with postoperative computed tomography. Scoliosis was corrected from 95.6 to 65.8 degrees after surgery (correction rate 32.5%) and 68.1 degrees at final follow-up (both, P<0.01). Space available for the lung was improved from 76.3% to 84.9% (P<0.05). No implant dislodgement occurred after surgery. A total of 290 screws were placed, of which 213 screws (73.4%) were placed completely. However, 30 screws (10.3%) penetrated >2 mm. In particular, rates of >2 mm penetration was much higher in type III than type I and IV (27.8% vs. 3.0%; P<0.01). Complications related to spinal surgery included 2 transient neurological disturbances. PSs were applicable to spinal fusion surgery in patients with OI. However special care should be taken in placing PSs because of the weakness of the pedicle cortex, which was easily penetrated especially in Sillence type III. Level IV.

Accuracy and technical limits of percutaneous pedicle screw placement in the thoracolumbar spine.

The two-dimensional fluoroscopic method of percutaneous pedicle screw instrumentation has been clinically described as reliable method in the caudal thoracic and lumbosacral spine. Its accuracy has not been clearly reported in the cranial thoracic spine. The aim of this in vitro study was to investigate percutaneous pedicle screw placement accuracy according to pedicle dimensions and vertebral levels. Six fresh-frozen human specimens were instrumented with 216 screws from T1 to S1. Pedicle isthmus widths, heights, transversal pedicles and screws were measured on computed tomography. Pedicle cortex violation ≥ 2mm was defined as screw malposition. The narrowest pedicles were at T3-T5. A large variability between transversal pedicle axes and percutaneous pedicle screw was present, depending on the spinal level. Screw malposition rates were 36.1% in the cranial thoracic spine (T1-T6), 16.7% in the caudal thoracic spine (T7-T12), and 6.9% in the lumbosacral spine (L1-S1). The risk for screw malposition was significantly higher at cranial thoracic levels compared to caudal thoracic (p = 0.006) and lumbosacral (p < 0.0001) levels. Cortex violation ≥ 2mm was constantly present if the pedicle width was < 4.8mm. Percutaneous pedicle screw placement appears safe in the caudal thoracic and lumbosacral spine. The two-dimensional fluoroscopic method has a limited reliability above T7 because of smaller pedicle dimensions, difficulties in visualizing radiographic pedicle landmarks and kyphosis.

Intraoperative Neuromonitoring and Lumbar Spinal Instrumentation: Indications and Utility

ABSTRACT Multimodal intraoperative neurophysiologic monitoring (IONM) can be utilized as an adjunct to lumbar spinal instrumentation in order to aid with avoidance of neurologic complications. The most commonly utilized modalities include somatosensory-evoked potentials, motor-evoked potentials, and electromyography. Somatosensory-evoked potentials (SSEPs) allow for continuous assessment of the dorsal columns of the spinal cord and are therefore most useful during procedures with a posterior approach to the cervical and thoracic spine. Motor-evoked potentials (MEPs) and electromyography (EMG) can be applied intermittently to assess motor nerve function. The utility of each individual modality can be largely dependent on the surgical approach. Approaches to lumbar spinal instrumentation can be generally categorized as anterior, lateral, and posterior. For lateral approaches, electromyography can be helpful in identifying neural structures crossing the surgical field to prevent injury. In posterior and anterior approaches, somatosensory-evoked potentials and motor-evoked potentials can be used to assess nerve injury during and after maneuvers for decompression and instrumentation. Additionally, during the placement of pedicle screws, direct stimulation with triggered electromyography can be used to detect the pedicle cortex’s breach. The efficacy of intraoperative neuromonitoring is dependent on prompt and accurate recognition of changes in signals. This is then followed by accurate recognition of the cause for these changes and appropriate responses by the surgeon, anesthesiologist, and monitoring personnel to correct the change.

Accuracy of cervical pedicle screw placement with four different designs of rapid prototyping navigation templates: a human cadaveric study

Purpose Due to the high perforation rate of cervical pedicle screw placement, we have designed four different types of rapid prototyping navigation templates to enhance the accuracy of cervical pedicle screw placement. Methods Fifteen human cadaveric cervical spines from C2 to C7 were randomly divided into five groups, with three specimens in each group. The diameter of pedicle screw used in this study was 3.5 mm. Groups 1–4 were assisted by the two-level template, one-level bilateral template, one-level unilateral template and one-level point-contact template, respectively. Group 5 was without any navigation template. After the surgery, the accuracy of screw placement in the five groups was evaluated using postoperative computed tomographic scans to observe whether the screw breached the pedicle cortex. Results A total of 180 pedicle screws were inserted without any accidents. The accuracy rate was 75%, 100%, 100%, 91.7%, and 63.9%, respectively, from Groups 1 to 5. All the template groups were significantly higher than Group 5, though the two-level navigation template group was significantly lower than the other three template groups. The operation time was 4.72 ± 0.28, 4.81 ± 0.29, 5.03 ± 0.35, 8.42 ± 0.36, and 10.05 ± 0.52 min, respectively, from Groups 1 to 5. The no template and point-contact procedures were significantly more time-consuming than the template procedures. Conclusion This study demonstrated that four different design types of navigation templates achieved a higher accuracy in assisting cervical pedicle screw placement than no template insertion. However, the two-level template’s accuracy was the lowest compared to the other three templates. Meanwhile, these templates avoided fluoroscopy during the surgery and decreased the operation time. It is always very challenging to translate cadaveric studies to clinical practice. Hence, the one-level bilateral, unilateral, and point-contact navigation templates designed by us need to be meticulously tested to verify their accuracy and safety.

Transpedicular Screw Placement Accuracy Using the O-Arm Versus Freehand Technique at a Single Institution.

Study Design:Retrospective cohort.Objective:The objective of this study was to assess the effectiveness of the O-arm as an intraoperative imaging tool by comparing accuracy of pedicle screw placement to freehand technique.Methods:The study comprised a total of 1161 screws placed within the cervical (n = 187) thoracic (n = 657), or lumbar (n = 317) spinal level. A pedicle breach was determined by any measurable displacement of the screw outside of the pedicle cortex in any plane on postoperative images. Each pedicle screw was subsequently classified by its placement relative to the targeted pedicle. Statistical analysis was then performed to determine the frequency and type of pedicle screw mispositioning that occurred using the O-arm versus freehand technique.Results:A total of 155 cases (O-arm 84, freehand 71) involved the placement of 454 pedicle screws in the O-arm group and 707 pedicle screws in the freehand group. A pedicle breach occurred in 89 (12.6%) screws in the freehand group and 55 (12.1%) in the O-arm group (P = .811). Spinal level operated upon did not influence pedicle screw accuracy between groups (P > .05). Three screws required revision surgery between the 2 groups (O-arm 1, freehand 2, P > .05). The most frequent breach type was a lateral pedicle breach (O-arm 22/454, 4.8%; freehand 54/707, 7.6%), without a significant difference between groups (P > .05).Conclusions:The use of the O-arm coupled with navigation does not assure improved transpedicular screw placement accuracy when compared with the freehand technique.

Design, application, and evaluation of a novel method for determining optimal trajectory of thoracic pedicle screws

BackgroundThis is an experimental study performed on 15 adult cadavers. In this cadaveric study, we designed and evaluated a novel methodology for determining the optimal trajectory for the placement of thoracic pedicle screws. The accuracy of thoracic pedicle screw placement is critical to the spinal surgery. The concept, implement method, and significance of the optimal thoracic pedicle trajectory have not been reported.MethodsThe experimental study was performed on 15 adult cadavers. The Mimics software was used to design optimal trajectory through the pedicle central axis. Using three-dimensional (3D) printing, a navigation module with a locating facet and a stabilizing facet was developed. The thoracic pedicle screws were inserted with the help of the navigation module. The three-dimensional coordinates for the entry and the exit points of the screws were compared between the planned trajectories and the postoperative trajectories. The differences in coordinates were analyzed to evaluate the precision of the screw placement.ResultsThe trajectories through the pedicle central axis showed an excellent symmetry between the single segments and for all thoracic vertebrae. Out of a total of 358 screws that were inserted, 15 (4.2%) screws breached the pedicle cortex with a breach distance of <2 mm. The qualifying rate was 98.6% (353/358) for the entry point precision of ≥3.2 mm, and 98.9% (354/358) for the exit point precision of ≥6.4 mm. In comparison to the designed qualified rate of 100% (358/358), the χ2 was 3.22 and 2.26, respectively (P>0.05).ConclusionsThe optimal trajectory was obtained through the pedicle central axis, which significantly reduced the risk of cortex breach. A high degree of precision was obtained for the entry and the exit points of the screws when the postoperative trajectory was compared with the designed trajectory.

Individualized artificial titanium alloy spinal lamina with 3D printing technology

Background: Laminectomy and decompression is a common procedure for treating spine diseases. However, due to the lack of a posterior, bony braced structure, the dural sac and nerve roots can adhere to the surrounding tissues, and scar formation can occur in muscle and soft tissues. This can cause new compression post surgery, and failure of the operation. Objective: This study aimed to produce an individualized titanium alloy spine lamina using 3D printing technology, and to evaluate its effectiveness by implantation in human cadaveric spines. Methods: Six adult lumbar cadaver specimens were used, and computed tomography (CT) was used to obtain DICOM medical digital image standard data. The lumbar vertebrae structure was reconstructed by three-dimensional (3D) modeling software, and then simulated lumbar laminectomy was performed. Based on the characteristics of the original lamina, an artificial spine lamina was designed, including suture holes at the posterior ligament attachment point and a locking screw hole for fixation. A titanium alloy spine lamina was fabricated by 3D printing, and a guide plate to assist artificial lamina implantation was designed. Using the guide plated, L4 lumbar vertebrae segment laminectomy was performed on the 6 lumbar spine specimens, titanium alloy spine lamina were implanted and fixed with cortical bone trajectory screws. After implantation, CT was performed to record the length of the screw, the trajectory of the screw in the pedicle, and changes of bony spinal canal volume and anteroposterior diameter of the spinal canal. Results: The morphology of artificial spine lamina matched that of the original lamina. The artificial lamina was easy to implant, and matched the original lamina. The laminas were fixed by 12 cortical screws (diameter, 4.5 mm; median length, 34.67 ± 1.97 mm). CT scan indicated that all screws passed through the pedicle cortex by &lt; 2 mm (2 screws penetrated the inner wall). The bony canal volume of the L4 vertebral pedicle was 311.23 ± 38.17 mm2 before operation and 356.17 ± 43.11 mm2 after operation, and there was statistical difference (P &lt; 0.001). The anteroposterior diameter of spinal canal was 17.82 ± 2.03 mm before surgery and 20.67 ± 2.38 mm after surgery, and they were statistically different (P &lt; 0.001). Conclusion: An individualized artificial titanium alloy spine lamina designed and produced with 3D printing technology can be used to reconstruct the structure of the posterior spine complex after lumbar laminectomy. The artificial lamina can increase the volume of the spinal canal and provide a posterior ligament reconstruction attachment point.

Application of three-level navigation template in surgery for hemivertebrae in adolescents

Objective . To assess efficacy and safety of using a three-level navigation template in the surgical treatment of congenital spinal deformities. Material and Methods . Three-level navigation templates were used in surgical treatment of four consecutively operated 10–17-year-old patients with congenital scoliosis associated with thoracic hemivertebrae. The correctness of screw position was evaluated according to CT data using a 2-mm increment method: class 0 – intraosseous screw position; class 1 – the screw extends beyond the pedicle cortex by less than 2 mm; class 2 – by 2–4 mm; and class 3 – by more than 4 mm. Preoperative DICOM data were processed with free software. The model of target zone and navigation template were 3D printed and used in surgery. Results . Four of 16 (25 %) pedicles were narrower than 4.35 mm and were estimated as difficult for implantation with a planned violation of the integrity of the endplate. Perforation of the outer cortical layer took place in all these cases, and screw position corresponded to class 2 only in pedicle width of 1.9 mm. In pedicles wider than 4.35 mm, 11 of 12 (91.7 %) screws were implanted intraosseously. One screw extended beyond the pedicle cortex by 0.8 mm (class 1). Conclusion . Three-level navigation template can be considered as an effective means of positioning transpedicular screws in secondarily changed segments adjacent to anomalous one and confounding implantation. Free software is sufficient for preparing 3D-model of target zone and navigation template, and such a model is a highly informative reference object that is convenient to use during the operation. A navigation template made using 3D printing does not require the use of expensive equipment, which can make surgery for congenital scoliosis more accessible.

Computed tomography measurement of the bone matrix of vertebral pedicle and its clinical significance

To provide the anatomic basis for the clinical application of the transpedicular screw fixation. Thirty spine (C2-L5) specimens were used. The width of the pedicle cortex and width of the pedicle medullary cavity (WPC and WPMC), and the height of the pedicle cortex and height of the pedicle medullary cavity (HPC and HPMC) were measured at the isthmus of the pedicle using computed tomography (CT) scanning. Width of the pedicle medullary cavity changed in a three-dovetailed-saddle shape with four peaks and three valleys, namely C2 (high), C4`5 (low), T2 (high), T4 (the lowest), T12 (high), L1 (low) and L5 (the highest). HPMC of the cervical pedicle changed in a saddle shape, gradually increasing from C5-L5. WPC, WPMC, HPC and HPMC showed a regular change, respectively. In each segment, the superior border of the pedicle cortex had a nearly consistent thickness to the interior border within an identical pedicle, while the pedicle cortex thickness radio of the medial and lateral border was nearly 3:1 among the cervical pedicles, 2:1 among thoracic pedicles, and 1:1 among lumbar pedicles. Both HPMC and WPMC are the dominant factors for the choice of screw diameter, but HPMC should also be considered in C2-T1 pedicles, especially C6 and C7. Additionally, the screw for C3-6 or T4-6 pedicles should be about 3.0 mm in diameter.

35. How many screws are necessary to be considered an experienced surgeon for freehand placement of thoracolumbar pedicle screws? Analysis of the learning curve using the cumulative summation test for learning curve (LC-CUSUM)

BACKGROUND CONTEXT Several studies have demonstrated the learning curve for freehand pedicle screw placement (PSP) in residents, spinal fellows, and young surgeons. Also, the authors have suggested the numbers of required screws for PSP. Despite advances in statistical analysis for the learning curve, there is no study investigating how many screws are required to reach an adequate performance level in freehand PSP. PURPOSE The purpose of this study was to determine the amount of screws needed to achieve an adequate skill level for PSP via the freehand technique in the nondeformed thoracolumbar spine using the cumulative summation for learning curve (LC-CUSUM) analysis. STUDY DESIGN/SETTING A retrospective case series. PATIENT SAMPLE The first 85 patients who underwent thoracolumbar PSP using the freehand technique with postoperative computed tomography (CT) were included in the analysis. OUTCOME MEASURES The accuracy of PSP was evaluated using postoperative CT by an independent observer who was unaware of the purpose of this study. The accuracy of pedicle screw position was determined using a 5-grade system: Grade A, the screw was completely within the pedicle; Grade B, the screw breaches the pedicle's cortex by less than 2 mm; Grade C, pedicle cortical breach was less than 4 mm; Grade D, pedicle cortical breach was less than 6 mm; and Grade E, pedicle cortical breach of 6 mm or more. METHODS The surgeon had one year's experience of fellowship training in the tertiary teaching hospital. The learning curve of freehand PSP was investigated using LC-CUSUM analysis. Procedure success was defined as an acceptable accuracy of pedicle screw, which is divided into two groups (group 1: the screw breaches the pedicle's cortex by less than 2 mm, group 2: the screw is completely within the pedicle). RESULTS Total 52 cases and 313 pedicle screws were included and analyzed in this study. In group 1 accuracy, the LC-CUSUM signaled competency for freehand PSP at the 115th pedicle screw (17th case). In group 2 accuracy, the LC-CUSUM signaled competency for freehand PSP at the 312th pedicle screw (52nd case). This means that a trainee with no experience with freehand PSP reached adequate accuracy level of pedicle screw with less than 2 mm pedicle breaches at 115th screw, and with completely within the pedicle at 312th screw. The rate of pedicle screw breached the pedicle less than 2 mm (group 1) was 88.5% and the rate of accuracy of pedicle screw completely within the pedicle (group 2) was 70%. There were no major complications, such as neurovascular injury, and life-threatening complications. CONCLUSIONS In this study, the learning curve analysis demonstrated that a substantial learning period may be necessary before an adequate level of performance is achieved for freehand PSP in the non-deformed thoracolumbar spine. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Increased Axial Facet Angle Correlates With Poor Percutaneous Pedicle Screw Placement

Abstract INTRODUCTION To test the hypothesis that axial facet angle correlates with poor pedicle screw placement (and especially facet violation) in percutaneous fluoroscopy-guided pedicle screw placement. METHODS A total of 95 consecutive patients who underwent minimally invasive fluoroscopic instrumented fusion of the lumbar or lumbosacral spine were included. Postoperative computed tomography (CT) was used to categorize pedicle screw placement as follows: good (no breach), acceptable (breach within safe zone and/or any amount of tip breach), poor (outside safe zone, and/or violation of unfused facet, and/or unfused endplate violation). Safe zone was defined as 4 mm lateral or 2 mm inferomedial breach of pedicle cortex. Axial facet angle was measured against a midsagittal line. Global mean axial facet angles at L4, L5, and S1 were calculated. RESULTS Of the total 349 screws, 38 (10.7%) were categorized as poor placement, and of these 31 (82%) were due to unfused facet violation. Global axial facet angle means were 36.8 degrees for L4, 45.8 for L5, and 50.5 for S1. Mean axial facet angles associated with poorly placed screws were 42.7 degrees for L4 and 51.4 degrees for L5 these angles are higher than the global means at L4 (P = .063) and L5 (P = .028). Subgroup analysis demonstrated that the mean axial facet angles associated with unfused facet violation was 44.0 degrees for L4 and 53.2 degrees for L5. These means were significantly higher than the global means at L4 (P = .027) and L5 (P = .009). No poor screw placement was found at the S1 level. CONCLUSION Increased axial facet angle significantly correlates with poor screw placement and especially with facet violation in percutaneous fluoroscopy-guided pedicle screw placement at L4 and L5. Care should be taken to evaluate for high axial facet angles in preoperative planning.