Minimally invasive pedicle screw placement with image-guided navigation in cervical spine injuries.

BackgroundC1 posterior arch screw placement is one of the most effective treatments for atlantoaxial instability (AAI), which can be performed by either pedicle or lateral mass screw fixation. This study attempted to compare the feasibility and clinical outcomes of C1 pedicle with lateral mass screw fixations for treatment of AAI with C1 posterior arches >4 mm.MethodsA total of 140 patients with AAI (C1 posterior arches measuring >4 mm) was enrolled in this single-center, randomized, double-blind trial. The subjects were randomly assigned into two treatments: C1 pedicle (group A) or lateral mass (group B) screw fixation. The patients, independent evaluating physicians and radiologists were blinded throughout the entire study. Patients were assessed before operation and in a series of follow-ups at 6 weeks, 6 months, 1 year, and 3 years post-surgery. The operation time, volume of blood loss, intraoperative complications, bone fusion rates, Japanese Orthopaedic Association (JOA) and visual analog scale (VAS) scores were monitored.ResultsAll 140 patients showed overall improvements in clinical symptoms after surgery. The mean follow-up time was 24.5 ± 13.0 months. In both groups, the mean JOA scores improved significantly at the time of final follow-up as compared to prior surgery (group A: 7.1 ± 1.4 vs 13.7 ± 1.9; group B:7.3 ± 1.8 vs 13.1 ± 1.4; improvement rates: 87.2 % (group A) and 86.5 % (group B)). The VAS scores also decreased significantly in both groups at the time of final follow-up as compared to prior surgery (group A: 6.0 ± 1.3 vs 1.7 ± 0.8, and group B: 5.7 ± 1.1 vs 2.1 ± 1.2). Bone fusion was achieved within 12 months postoperatively in the patients from both groups. The operation time was significantly shorter and volume of blood loss was significantly less in the patients from group A as compared to group B (p < 0.01). Furthermore, thirteen patients had burst bleeding from the C1-2 venous plexus and nine patients had immediate pain and numbness in the occipitocervical region due to C2 nerve roots irritation during lateral mass screw replacement, which were not observed in the patients with C1 pedicle screw insertion. No complications such as screw loosening, shifting, breakage, or AAI were observed in both groups.ConclusionsC1 pedicle screw fixation is less invasive and simpler, and has fewer complications. It renders better clinical outcomes than lateral mass screw fixation for treatment of AAI.Trial registrationCurrent Controlled Trials ChiCTR-IOR-15006748.

Anatomical and biomechanical analysis of sacral pedicle and lateral mass

To the Editor

A biomechanical study. To compare, in cervical vertebrae (C3-C6), the pullout strengths of pedicle screws and lateral mass screws after both types of screw had been subjected to a period of cyclic loading in 2 planes. In posterior subaxial cervical fixation systems, screws are usually inserted into the lateral mass. As an alternative to lateral mass fixation, pedicle screw fixation became popular in the 1990s and was first used for lower cervical spine trauma cases. However, it is controversial as to whether lateral mass screw fixation in the upper-middle cervical spine offers as much biomechanical security as compared with pedicle screw fixation. For each of the 32 vertebrae, 1 side was randomly chosen to receive a pedicle screw and the other side a lateral mass screw. The pedicle or lateral mass screws inserted into the first 16 vertebrae were cyclically loaded to simulate torsion and the remaining 16 vertebrae were cyclically loaded to simulate flexion/extension of the spine. At the end of the cyclic loading each screw was pulled out along its long axis. For the torsion group, the mean pullout strength of the pedicle screws was nearly 4 times greater than the mean pullout strength of the lateral mass screws (cf 762 N with 191 N). In contrast, the mean pullout strength of the pedicle screws in the flexion/extension group was only twice the mean pullout strength of the lateral mass screws (cf 571 N with 289 N). Not forgetting the potential risks of inserting pedicle screws in cervical vertebrae, pedicle screws are a better biomechanical choice than lateral mass screws for cervical fixation at the levels C3 through to C6.

The intralaminar screw (ILS) fixation technique offers an alternative to pedicle screw (PS) and lateral mass screw (LMS) fixation in the C7 spine. Although cadaveric studies have described the anatomy of the pedicles, laminae, and lateral masses at C7, 3-dimensional computed tomography (CT) imaging is the modality of choice for pre-surgical planning. In this study, the goal was to determine the anatomical parameter and optimal screw trajectory for ILS placement at C7, and to compare this information to PS and LMS placement in the C7 spine as determined by CT evaluation. A total of 120 patients (60 men and 60 women) with an average age of 51.7±13.6 years were selected by retrospective review of a trauma registry database over a 2-year period. Patients were included in the study if they were older than 15 years of age, had standardized axial bone-window CT imaging at C7, and had no evidence of spinal trauma. For each lamina and pedicle, width (outer cortical and inner cancellous), maximal screw length, and optimal screw trajectory were measured, and the maximal screw length of the lateral mass were measured using m-view 5.4 software. Statistical analysis was performed using Student's t-test. At C7, the maximal PS length was significantly greater than the ILS and LMS length (PS, 33.9±3.1 mm; ILS, 30.8±3.1 mm; LMS, 10.6±1.3; p<0.01). When the outer cortical and inner cancellous width was compared between the pedicle and lamina, the mean pedicle outer cortical width at C7 was wider than the lamina by an average of 0.6 mm (pedicle, 6.8±1.2 mm; lamina, 6.2±1.2 mm; p<0.01). At C7, 95.8% of the laminae measured accepted a 4.0-mm screw with a 1.0 mm of clearance, compared with 99.2% of pedicle. Of the laminae measured, 99.2% accepted a 3.5-mm screw with a 1.0 mm clearance, compared with 100% of the pedicle. When the outer cortical and inner cancellous height was compared between pedicle and lamina, the mean lamina outer cortical height at C7 was wider than the pedicle by an average of 9.9 mm (lamina, 18.6±2.0 mm; pedicle, 8.7±1.3 mm; p<0.01). The ideal screw trajectory at C7 was also measured (47.8±4.8° for ILS and 35.1±8.1° for PS). Although pedicle screw fixation is the most ideal instrumentation method for C7 fixation with respect to length and cortical diameter, anatomical aspect of C7 lamina is affordable to place screw. Therefore, the C7 intralaminar screw could be an alternative fixation technique with few anatomic limitations in the cases when C7 pedicle screw fixation is not favorable. However, anatomical variations in the length and width must be considered when placing an intralaminar or pedicle screw at C7.

Biomechanical comparison of five different posterior cervicothoracic junction (C7-T1) fixation constructs in a cadaveric model. To determine whether augmenting C7 lateral mass screws with spinous process wires or additional fixation in the C6 lateral mass can create constructs of similar normalized stiffness to that of C7 pedicle screws. Cervical pedicle screws are known to provide excellent fixation but are potentially dangerous and technically demanding to insert. Lateral mass screws are safer and easier to insert but have less pullout strength and must often be short at C7. Twelve cadaveric cervicothoracic specimens (C5-T2) were randomly assigned to one of three experiments: Experiment A (Part 1 and Part 2), Experiment B, and Experiment C (Part 1 and Part 2) (n = 4 each for each experiment). First, the intact specimens were biomechanically tested according to a seven-part loading protocol. The specimens were then destabilized, and then restabilized with the following constructs in conjunction with bilateral T1 pedicle screws and biomechanically tested again using the same seven-part biomechanical protocol as was applied to the intact specimens. Experiment A: Part 1: lateral mass screw fixation at C7 (C7LM); then Part 2: retested after augmentation with triple wiring (C7LM+W). Experiment B: pedicle screw fixation at C7 (C7PS). Experiment C: Part 1: C6 and C7 lateral mass screws (C6C7LM); then Part 2: retested after augmentation with triple wiring (C6C7LM+W). Thus, five different constructs were biomechanically compared in these three experiments. None of the lateral mass constructs demonstrated a significant increase in normalized stiffness when augmented with wiring in any mode of testing. In axial compression, the C7PS construct showed significantly higher (P < 0.001) normalized stiffness than any of the other four constructs. In extension, there were no significant differences among any of the five constructs. Inflexion, right/left lateral bending and right/left axial torsion, the C7PS construct again showed significantly higher normalized stiffness (P < 0.05) than lateral mass fixation at C7 alone. However, in these five modes of testing, the addition of a secondary point of lateral mass fixation at C6 (C6C7LM) produced a construct with a normalized stiffness similar to that of C7PS with no significant difference (P > 0.05). C7 pedicle screw fixation provides the construct with the highest normalized stiffness for stabilizing the cervicothoracic junction. If C7 pedicle fixation is not possible, then performing two-level lateral mass fixation at C6 and C7 will achieve a construct with similar normalized stiffness except in axial compression. The addition of triple wiring to the spinous processes does not significantly increase lateral mass construct normalized stiffness.

P15. Power-assisted pedicle screw placement decreases screw wobble

BackgroundIn atlantoaxial instabilities, posterior C1/C2 fusion using lateral mass screws (LMS) or pedicle screws (PS) in a mono- or bicortical position in the atlas is a typical treatment. The bone microstructure and positioning of the screw trajectories appear to be of significant relevance for stability.PurposeThe aim of this study was a comparative analysis of the mechanical durability of screw fixation concerning microstructural characteristics of the trajectories of LMS and PS in mono- and bicortical position.MethodsHuman C1 from geriatric body donors (n = 28; 50% female, age 80.8 ± 13.9 years) were collected and characterized based on their bone microstructure. Additionally, the mechanical stability of LMS and PS fixation in mono- and bicortical positioning was tested by mechanical loading. High-resolution quantitative computed tomography was used to analyze the bone microstructure of cylinders corresponding to the trajectories of PS and LMS in mono- and bicortical locations in each C1. After instrumentation with both screw types and types of fixation, the mechanical stability was tested by increased cyclic loading in cranio-caudal direction.ResultsTrajectories of PS presented with more bone volume and a higher contact length to cortical bone. Simultaneously, a higher number of cycles and a higher maximum force was needed to loosen PS compared to LMS, while the loose by torque at the experiment end was still greater in PS. Differences between mono- and bicortical positioning of PS and LMS have only been observed in the initial stiffness of screws. When comparing microstructural and mechanical properties, the cortical contact length and bone volume in screw trajectories were strongest associated with a high loose and cycle count.ConclusionsThis study suggests that mono- and bicortical positioning of PS is similarly efficient in creating a stable basis for screw fixation in the atlas. While PS are superior to LMS, the contact with cortical bone is of major relevance for a stable foundation.

Accuracy of freehand pedicle screws versus lateral mass screws in the subaxial cervical spine.

Pre- and postoperative MRI analysis of central decompression in MIS fusion with lumbar stenosis

Introduction Robotic spine surgery has been developed to improve spine surgery, especially the placement of pedicle screws recently. There have been no basic studies regarding the changes in joint angles and kinematics of surgeons during pedicle screw fixation. Understanding kinematics and joint movements of the surgeon during the placement of pedicle screws is essential to create an effective robot suitable for spinal surgery. The objective of this study is to assess the joint kinematics of the surgeon during the insertion of lumbar pedicle screws. Materials and Methods This is a cross-sectional study. We enrolled 18 experienced spine surgeons in this study, who each performed lumbar pedicle screw placement using a spine surgery simulator at the spinal level L3/4. To assess the movements of the surgeons, we used an optoelectronic motion analysis system with 16 cameras. A total of 20 markers were placed from the cervical spine to the pelvis (12 markers; C2, C4, C7, T6, L1, L3, PSIS x 2, ASIS x 2, Sacrum × 2), on both shoulders (2 markers; acromion), the right elbow (1 marker; olecranon), the right wrist (2 markers; ulna and radius styloid process), and the screw driver (3 markers; proximal handle × 1 and distal handle × 2). Using 3-dimentional motion images, distance changes in 5 joints (αB, body; αS, shoulder; αE, elbow; αW, wrist; and αI, instrument), and angle changes in 6 joints (αB, body; αS, shoulder; αE, elbow; αW, wrist; αI, instrument; and αP, pedicle) regarding X-, Y-, and Z-axes were calculated during pedicle screw placement. The distance and angle changes were measured at 8 setting points (L3/4 x Right/Left x Start/End) during pedicle screw placement and compared between joints. Results Whole joint distances and angles differed significantly according to setting points during pedicle screw placement. Fluctuations in distance increased gradually from the proximal joint (αB) to distal joint (αI; instrument) and the largest change was noted along the X-axis. Angle fluctuations were largest at the distal point (αP, pedicle) but did not gradually increase and the αE (elbow) showed the second largest fluctuation. Changes along the X-axis change were larger than those of the Y- and Z-axes. Conclusion The distances moved by whole joints gradually increased from proximal portions of the body to the hand, but in terms of angle changes, the elbow joint was the most dynamic during lumbar pedicle screw placement. Whole joints of surgeons carry out harmonic role during lumbar pedicle screw placement. Disclosure of Interest J. Y. Park: Conflict with Technology Innovation Program (10040097) funded by the Ministry of Trade, Industry and Energy, Republic of Korea (MOTIE, Korea) S. U. Kuh: None declared Y. E. Cho: Conflict with Technology Innovation Program (10040097) funded by the Ministry of Trade, Industry and Energy, Republic of Korea (MOTIE, Korea) References Kosmopoulos V, Schizas C. Pedicle screw placement accuracy: a meta-analysis. Spine 2007;32(3):E111-E120 Marcus HJ, Cundy TP, Nandi D, Yang GZ, Darzi A. Robot-assisted and fluoroscopy-guided pedicle screw placement: a systematic review. Eur Spine J 2014;23(2):291–297 Lieberman IH, Togawa D, Kayanja MM, et al. Bone-mounted miniature robotic guidance for pedicle screw and translaminar facet screw placement: Part I—Technical development and a test case result. Neurosurgery 2006;59(3):641-650, discussion 641–650 Devito DP, Kaplan L, Dietl R, et al. Clinical acceptance and accuracy assessment of spinal implants guided with SpineAssist surgical robot: retrospective study. Spine 2010;35(24):2109–2115 Kantelhardt SR, Martinez R, Baerwinkel S, Burger R, Giese A, Rohde V. Perioperative course and accuracy of screw positioning in conventional, open robotic-guided and percutaneous robotic-guided, pedicle screw placement. Eur Spine J 2011;20(6):860–868 Oppenheimer JH, DeCastro I, McDonnell DE. Minimally invasive spine technology and minimally invasive spine surgery: a historical review. Neurosurg Focus 2009;27(3):E9 Preuss RA, Popovic MR. Three-dimensional spine kinematics during multidirectional, target-directed trunk movement in sitting. J Electromyogr Kinesiol 2010;20(5):823–832 Park JY, Kim KH, Kuh SU, Chin DK, Kim KS, Cho YE. Spine surgeon's kinematics during discectomy according to operating table height and the methods to visualize the surgical field. Eur Spine J 2012;21(12):2704–2712 Rao SS, Bontrager EL, Gronley JK, Newsam CJ, Perry J. Three-dimensional kinematics of wheelchair propulsion. IEEE Trans Rehabil Eng 1996;4(3):152–160 Gronley JK, Newsam CJ, Mulroy SJ, Rao SS, Perry J, Helm M. Electromyographic and kinematic analysis of the shoulder during four activities of daily living in men with C6 tetraplegia. J Rehabil Res Dev 2PO.130;37(4):423–432 Wagner H, Tilp M, von Duvillard SP, Mueller E. Kinematic analysis of volleyball spike jump. Int J Sports Med 2009;30(10):760–765 Vickers DR, Palk C, McIntosh AS, Beatty KT. Elderly unilateral transtibial amputee gait on an inclined walkway: a biomechanical analysis. Gait Posture 2008;27(3):518–529 Abu-Faraj ZO, Harris GF, Smith PA. Surgical rehabilitation of the planovalgus foot in cerebral palsy. IEEE Trans Neural Syst Rehabil Eng 2001;9(2):202-214 PubMed Perry J. Anatomy and biomechanics of the shoulder in throwing, swimming, gymnastics, and tennis. Clin Sports Med 1983;2(2):247–270

Pedicle or lateral mass screws in Goel-Harms construct? A biomechanical analysis

Retrospective comparative study. The aim of this study was to compare cervical sagittal alignment after posterior fusion surgery with lateral mass screw (LMS) and cervical pedicle screw (CPS) fixation. LMS fixation in the subaxial cervical spine has become the preferred method of posterior cervical fusion. Although CPS has biomechanical benefits, it also has neurovascular risks. Few studies to date have compared sagittal alignment changes after posterior cervical fusion using CPS and LMS fixation. From 2006 to 2017, 71 consecutive patients underwent posterior cervical fusion using CPS (n = 51) or LMS (n = 20) fixation. Patients who underwent fusion with both types of screws and those who planned to undergo additional anterior fusion surgery were excluded. The minimum follow-up period was 12 months. C2-C7 Cobb angle for cervical lordosis (CL), fusion segmental angle (SA), C2-C7 sagittal vertical axis (SVA), and T1 slope (T1S) were measured. Immediate postoperative SA and SVA differed significantly in patients who underwent CPS and LMS fixation. SA changes were more substantial after CPS fixation, with a significant difference maintained until final follow-up. Over time, CL, SVA, and T1S tended to return to their preoperative states regardless of screw type. Two patients who underwent LMS fixation, but none who underwent CPS fixation, required unplanned or additional anterior fusion surgery for revision. The present study is the first radiologic comparison of LMS and CPS fixation after posterior-only fusion surgery. CPS resulted in more reliable and well-preserved SA correction, whereas CL and SVA did not differ between the two groups over time due to loss of correction.Level of Evidence: 4.

Object The aim of this study was to conduct the first in vitro biomechanical comparison of immediate and postcyclical rigidities of C-7 lateral mass versus C-7 pedicle screws in posterior C4–7 constructs. Methods Ten human cadaveric spines were treated with C4–6 lateral mass screw and C-7 lateral mass (5 specimens) versus pedicle (5 specimens) screw fixation. Spines were potted in polymethylmethacrylate bone cement and placed on a materials testing machine. Rotation about the axis of bending was measured using passive retroreflective markers and infrared motion capture cameras. The motion of C-4 relative to C-7 in flexion-extension and lateral bending was assessed uninstrumented, immediately after instrumentation, and following 40,000 cycles of 4 Nm of flexion-extension and lateral bending moments at 1 Hz. The effect of instrumentation and cyclical loading on rotational motion across C4–7 was analyzed for significance. Results Preinstrumented spines for the 2 cohorts were comparable in bone mineral density and range of motion in both flexion-extension (p = 0.33) and lateral bending (p = 0.16). Lateral mass and pedicle screw constructs significantly reduced motion during flexion-extension (11.3°–0.26° for lateral mass screws, p = 0.002; 10.51°–0.30° for pedicle screws, p = 0.008) and lateral bending (7.38°–0.27° for lateral mass screws, p = 0.003; 11.65°–0.49° for pedicle screws, p = 0.03). After cyclical loading in both cohorts, rotational motion over C4–7 was increased during flexion-extension (0.26°–0.68° for lateral mass screws; 0.30°–1.31° for pedicle screws) and lateral bending (0.27°–0.39° and 0.49°–0.80°, respectively), although the increase was not statistically significant (p &gt; 0.05). There was no statistical difference in postcyclical flexion-extension (p = 0.20) and lateral bending (0.10) between lateral mass and pedicle screws. Conclusions Both C-7 lateral mass and C-7 pedicle screws allow equally rigid fixation of subaxial lateral mass constructs ending at C-7. Immediately and within a simulated 6-week postfixation period, C-7 lateral mass screws may be as effective as C-7 pedicle screws in biomechanically stabilizing long subaxial lateral mass constructs.

Objective To compare the cervical biomechanical stability of lateral fixation piece and pedicle screws of screw fixation.Methods The 12 cervical vertebras as experimental sample,and from C4 to C5 were cut off and caused cervical instability model.Three ways of non fixation,lateral mass screw fixation and pedicle screw fixation were implemented.Then flexibility and rotation torque and stiffness were tested.Stability of two kinds of internal fixation was evaluated.Results In the 3-D range of movement,lateral mass screw fixation was notably smaller than that of pedicle screws fixation (P ＜ 0.05).The lateral mass screw fixation had more strength than pedicle screws fixation (P ＜ 0.05).Conclusion The instability of lower cervical spine patients may use lateral mass screw fixation,and its biomechanical stability is better. Key words: Cervical; Screw fixation; Biomechanical stability