Pedicle Rib Unit Research Articles

Anatomic Relationship of Bony Structures in Pedicle-Rib Unit and its Significance

The pedicle-rib unit is regarded as an expanded pedicle and is a new approach to thoracic pedicle fixation. Previous studies were mostly focused on anatomic, radiographic, and biomechanical assessment. However, there is no study on anatomic relationship of bony structures in the pedicle-rib unit. This article investigates the anatomic relationships between transverse process, pedicle, rib, and corresponding vertebrae body in the pedicle-rib unit, so as to improve the clinical safety of pedicle-rib unit screw placement. Forty-five normal dry adult cadaver specimens were included. Anatomic parameters were measured. Anatomic parameters were 1) the anatomic relationship between the transverse process and the pedicle (the distance from the horizontal center line of the transverse process to the center and the superior and inferior border of the pedicle); 2) the anatomic relationship between the transverse process and the rib (the overlap portion between the costal neck and the transverse process); 3) the anatomic relationship between the transverse process and the vertebral body (the relative position of the horizontal midline of the transverse process and the vertebral body); and 4) the anatomic relationship between the pedicle and the rib (the overlap portion between the costal neck and the pedicle). The midline of the transverse process was located within the range of the superior and inferior borders of the pedicle in the thoracic spine. The distance between the midline of the transverse process and the center of the pedicle was the closest at T6 and T7, but the farthest at T11 and T12. The anterolateral part of the transverse process was mostly covered by rib from T1 to T8, but it was less covered from T9 to T12. The midline of the transverse process corresponded to the upper third or middle third of the vertebral body. The pedicle is completely or mostly overlapped by the rib from T1 to T9 on the anterolateral side, but from T10 to T12, the rib overlapped the pedicle partially. The pedicle-rib unit is a three-dimensional anatomic structure. The pedicle, transverse process, and rib are not completely in the same plane, and their positions vary in different segments. Pedicle-rib unit screw fixation is anatomically feasible. Setting the screw in the upper-middle thoracic spine is safer than setting it in the lower thoracic spine.

Cortical Bone Trajectory Screw Fixation in the Upper and Middle Thoracic Spine (T1-T8): An Anatomic and Radiographic Assessment

To assess an alternative method of cortical bone trajectory (CBT) screw placement in the thoracic spine from T1 to T8 and to investigate the proper entry point, screw insertion angle, screw length, and diameter. Computed tomography images of 80 patients were used to measure all related parameters. Ten cadaveric spines were studied and 4.5-mm screws were inserted into both sides of the vertebrae. Computed tomography of all vertebrae previously inserted with CBT screws was performed and lateral or medial pedicle wall violation was checked. Of the inserted 160 CBT screws, 41.25% (66/160) penetrated the lateral pedicle wall, and the proportion of medial pedicle wall violation accounted for 0.625% (1/160). Maximal screw length tended to gradually increase from T1 to T8 (from 24.54 mm at T1 to 29.53 mm at T8). Compared with T4 and T5, maximal screw diameters of other thoracic levels were wider, ranging from 4.63 mm at T4 to 5.53 mm at T8. The greatest lateral angle was 8.66° in men and 8.39° in women at T8, whereas the smallest lateral angle was 4.97° in men and 4.67° in women at T1. The cephalad angle ranged from 17.23° at T7 to 31.50° at T1 and it was significantly larger in men at T7 (P < 0.05), T6 and T8 (P < 0.01). Based on the results of this study, we suggest that patients could be placed with 4.5× 25.0-30.0 mm CBT screws from T1 to T8 through the pedicle or pedicle rib unit.

Cortical bone trajectory screws placement via pedicle or pedicle rib unit in the pediatric thoracic spine (T9-T12): A 2-dimensional multiplanar reconstruction study using computed tomography.

Thoracic cortical bone trajectory (CBT) screw fixation can maximize the thread contact with cortical bone, and it is 53.8% higher than that of the traditional pedicle screws. Moreover, it can also enable less tissue dissection and retraction for reduced muscle disruption.Eighty pediatric patients are divided into 4 age groups and their thoracic vertebrae are analyzed on computed tomography (CT) images. The maximal screw length, maximal screw diameter, screw diameter, and the cephalad angle are measured. The statistical analysis is performed using the Student's t-test and Pearson's correlation analysis.Maximal screw length increases from T9 to T12 and there are significant differences between girls and boys at T9, T10, T11, and T12 in majority of groups (P < 0.05). The maximal screw diameter and screw diameter increase from T9 to T12. The maximal screw diameter ranges from 6.27 mm to 10.20 mm, whereas the screw diameter ranges from 3.87 mm to 6.75 mm. Meanwhile, the maximum cephalad angle is 23.06° and the minimum is 13.11°. No statistically significant differences in the cephalad angle are found at all levels.Our study establishes the feasibility of 4.5 to 5.5 mm CBT screws fixation via pedicle or pedicle rib unit in the pediatric thoracic spine. The entry point of the pediatric thoracic CBT screws is 6 o’clock orientation of the pedicle. Findings of our study also provide insights into the screw insertion angle and screw size decision.

Digital measurement of anatomical parameters associated with vertebral units fixed by ribs and pedicle fixation of T4-T10

Objective To perform digital 3D measurement of anatomic parameters associated with vertebral units fixed by ribs and pedicle fixation of T4-T10, providing evidence for clinical application. Methods Spiral CT scan of T4-T10 vertebrae was conducted in 15 normal adults without spinal disorder. The data were imported into computer to establish units and disc models of thoracic and rib vertebrae T4-T10 using Mimics 16.0 software and Ansys 11.0 finite element software. The following data were measured in the vertebral pedicle-rib unit fixation group (group A) by software: transverse diameter of vertebral pedicle-rib unit, length of the outside pedicle screw, inclination angle of pedicle screw, and maximum and minimum inclination angles of pedicle screw; the following data were also measured in the pedicle fixation group (group B) by software: pedicle transverse diameter, length of pedicle screw, inclination angle of pedicle screw, and maximum and minimum inclination angles of pedicle screw. The corresponding parameters were compared between groups A and B. Results In both groups, the transverse diameters and screw lengths gradually increased with the increase in the vertebral sequence while the inclination angle of pedicle screw, and maxi-mum and minimum inclination angles of pedicle screw decreased with the increase in the vertebral sequence. All the parameters in groups A were significantly larger than the corresponding ones in group B (P<0.05). Conclusions Of the spinal segment of T4-T10, the rib vertebral unit fixation can provide greater safe screw angles and screw diameters for clinical surgery. This is of vital significance for reducing the surgical complexity and improving screw prehension. Key words: Thoracic vertebrae; Computer, digital; Imaging, three-dimensional; Vertebral unit fixed by ribs

Minimally invasive cortical bone trajectory screws placement via pedicle or pedicle rib unit in the lower thoracic spine: a cadaveric and radiographic study.

To evaluate the feasibility of cortical bone trajectory (CBT) screws fixation via pedicle or pedicle rib unit in the cadaveric thoracic spine (T9-T12). Computed tomography (CT) images of 100 patients are analyzed by multiplanar reconstruction. Ten cadaveric thoracic spines are used to insert 4.5×35.0mm CBT screws at all levels from T9 to T12. Maximal screw length obtained by CT has a tendency to gradually increase from T9 (29.64mm) to T12 (32.84mm), and the difference reaches significant level at all levels except T9 versus T10 (P<0.01). Maximal screw diameter increases from T9 (4.92mm) to T12 (7.47mm) and the difference reaches significant level among all levels (P<0.01). Lateral angle increases from T9 (7.37°) to T12 (10.47°), and the difference reaches significant level among all levels except T11 versus T12. Cephalad angle from T9 to T12 are 19.03°, 22.10°, 25.62° and 27.50° (P<0.01), respectively. The percentage of the inner and outer pedicle breakage are 2.5 and 22.5%, respectively. The violation of lateral pedicle wall occurs at T9 and T10, especially for women at T9. Both radiographic and cadaveric studies establish the feasibility of CBT screws placement via pedicle or pedicle rib unit in the lower thoracic spine (T9-T12). Furthermore, our measurements are also useful for application of this technique.

Morphology study of thoracic transverse processes and its significance in pedicle-rib unit screw fixation.

Thoracic transverse process is an important anatomic structure of the spine. Several anatomic studies have investigated the adjacent structures of the thoracic transverse process. But there is still a blank on the morphology of the thoracic transverse processes. The purpose of the cadaveric study is to investigate the morphology of thoracic transverse processes and to provide morphology basis for the pedicle-rib unit (extrapedicular) screw fixation method. Forty-five adult dehydrated skeletons (T1-T10) were included in this study. The length, width, thickness, and the tilt angle (upward and backward) of the thoracic transverse process were measured. The data were then analyzed statistically. On the basis of the morphometric study, 5 fresh cadavers were used to place screws from transverse processes to the vertebral body in the thoracic spine, and then observed by the naked eye and on computed tomography scans. The lengths of thoracic transverse processes were between 16.63±1.59 and 18.10±1.95 mm; the longest was at T7, and the shortest was at T10. The widths of thoracic transverse processes were between 11.68±0.80 and 12.87±1.48 mm; the widest was at T3, and the narrowest was at T7. The thicknesses of thoracic transverse processes were between 7.86±1.24 and 10.78±1.35 mm; the thickest was at T1, and the thinnest was at T7. The upward tilt angles of thoracic transverse processes were between 24.9±3.1 and 3.0±1.56 degrees; the maximal upward tilt angle was at T1, and the minimal upward tilt angle was at T7. The upward tilt angles of T1 and T2 were obviously different from the other thoracic transverse processes (P<0.01). The backward tilt angles of thoracic transverse processes gradually increased from 24.5±2.91 degrees at T1 to 64.5±5.12 degrees at T10. The backward tilt angles were significantly different between each other, except between T5 and T6. In the validation study, screws were all placed successfully from transverse processes to the vertebrae of thoracic spine. The length, width, and thickness of the thoracic transverse processes are suitable for screw placement. And the obvious upward and backward tilt angles provide an excellent screw passage from transverse process to the vertebral body. Screw placement from the transverse processes to the vertebral body is feasible in the thoracic spine. However, there is still some place for improvement of the pedicle-rib unit screw fixation method.

Clinical anatomy of vertebrae in scoliosis: global analysis in four different diseases by multiplanar reconstructive computed tomography

Background contextFew accurate analyses of clinically useful vertebral anatomy have been conducted, and most have focused on thoracic idiopathic scoliosis. PurposeTo evaluate the different anatomic characteristics in scoliosis by disease type and level. Study designObservational cohort study. Patient sampleForty-eight patients with scoliosis were included in this study. Outcome measuresSubjects underwent computed tomography (CT) of the whole spine. MethodsForty-eight patients with scoliosis were included in this study: 15 adolescent idiopathic, 11 cerebral palsy (CP), 10 muscular dystrophy (MD), and 12 congenital (CG) scoliosis patients with similar demographics. Subjects underwent CT of the whole spine, preoperatively. Eight anatomic parameters were measured in multiplanar reconstructive CT images, and statistical analysis was performed to investigate differences. ResultsIn general, values in the anatomic parameters were similar for the four diseases. Each parameter showed the unique change pattern according to the spinal level regardless of curvature shape, direction, or magnitude. In particular, chord length (CL) in MD and CG scoliosis was lower than in adolescent idiopathic scoliosis (AIS) and CP, and pedicle rib unit length was lower in CG scoliosis than in the other diseases (p<.05). Comparisons of convex and concave anatomies in AIS showed that inner pedicle width (PWI) and outer pedicle width (PWO) were wider for convex side, CL, pedicle width, and transverse pedicle angle were greater for concave side (p<.05), and differences were more significant at apices. However, in CP, PWI and PWO were similar between convex and concaves sides (p>.05). Although PWI and PWO were wider for convex sides and CL and pedicle length were greater for concave sides in MD (p<.05), differences were less significant at apices. Particularly, CG scoliosis showed severely deformed anatomy, with differences of seven parameters at apical vertebrae (p<.05). ConclusionClinical anatomies of vertebrae in scoliosis were found to differ significantly at different levels and in terms of convexity and disease type.

Long Thoracic and Lumbar Spinal Stabilization with a Minimally Invasive Spine Surgery Technique

Objectives: The purpose of the current case presentation was to indicate the usefulness of long thoracic and lumbar (TL) spinal stabilization by percutaneous minimally invasive instrumentation. Materials and methods: From August 2012 to May 2013, we performed long TL spinal stabilization with VIPER 2 system (Depuy Spine, Inc., MA, US) by using a minimally invasive surgery (MIS) posterior approach in 4 patients. The first case was a 54 year old male who suffered from burst fracture of T12 (Frankel A) with brain contusion by a fall. The second case was a 68 year old male who developed incomplete paraplegia by metastatic renal cell carcinoma of T11 (Frankel C). The third case was a 79 year old male who affected Chance fracture of T12 (Frankel E) with an ankylosing spinal hyperostosis. And the fourth case was a 75 year old male who sustained pathological fracture of T8 (Frankel A) due to metastasis of prostatic carcinoma accompanied by an ankylosing spinal hyperostosis. The assessment included the clinical outcome of the patients and implant imaging evaluation. Results: Physical function was improved in all cases with quick pain relief. Mean operative time was 204 minutes. Mean estimated blood loss was 62.5 ml. In radiographic evaluation, spinal alignment was successfully maintained. One pedicle screw in case 3 cut out laterally in a pedicle-rib unit, but other pedicle screws in all cases were correctly inserted. No implant related complication was observed. And there were no conversions to open surgery. Discussion: In comparison with conventional open surgery, intraoperative blood loss, operative time, and postoperative pain were remarkably decreased in a MIS technique. Long TL spinal stabilization with a MIS technique is useful method for the patients who are desirable to avoid major surgical procedure.

A Novel Method of Screw Placement for Extremely Small Thoracic Pedicles in Scoliosis

A retrospective clinical study. To introduce a novel method of pedicle screw placement for extremely small thoracic pedicles in scoliosis and evaluate the safety and accuracy of the method. Few studies have provided technical guidelines for screw placement in patients with extremely small thoracic pedicles in scoliosis. In a severely rotated scoliotic spine, thoracic pedicle screw placement is challenging, and particularly more so for extremely small pedicles with a diameter less than 2 mm. The authors introduced a novel method of screw placement for these small pedicles: "medial margin targeting method."The C-arm fluoroscope is rotated until a true PA image of the rotated vertebral body is acquired and both pedicle shadows are symmetrically visualized en face. In extremely small pedicles, pedicle shadows appear as long, slender ellipses or lines. An imaginary pedicle outline is presumed with the elliptical or linear shadows being the medial margin of the pedicle. The entry point of a screw can be made at the 10-o'clock or 2-o'clock position on the presumed pedicle outline, and the screw can be safely inserted targeting the presumed medial margin with caution not to penetrate the medial cortex using the guidance of a true PA image. This is a kind of extrapedicular screw placement method.The safety and accuracy of this method were evaluated in 97 patients with scoliosis who had undergone posterior correction and instrumentation using postoperative computed tomography scans. A total of 1634 pedicle screws were inserted into thoracic pedicles, 128 of them (7.8%) being extremely small pedicles with a diameter less than 2 mm. Among 128 extremely small thoracic pedicles with a diameter less than 2 mm, one screw (0.8%) violated the medial cortex and 22 screws (17.6%) violated the anterior cortex of the vertebral body. No screws violated the lateral cortex of the pedicle-rib unit. There were no complications associated with screw misplacement. In scoliosis patients with extremely small thoracic pedicles, our pedicle screw placement method targeting the presumed medial margin in a true PA C-arm image allows easy application with accuracy and safety, which would not possible by any other method described so far.

The anatomic and radiographic morphometry of thoracic pedicle rib unit

To investigate the spatial structure of pedicle rib units in normal thoracic human spines and to compare the dimensions of the pedicle rib unit with corresponding dimensions. Thoracic spine specimens in four fresh adult cadaveric were used. Computerized tomographic (CT) images (including two-dimensional, three-dimensional reconstruction) of the thoracic spines were obtained. Measurement parameters include:the width, the height, the chord length and the sagittal angles of the pedicle rib unit compared with pedicle, especially for the pedicle-rib overlapping height. The pedicle rib unit was not a simple two-dimensional structure but a three-dimensional structure. The shortest height of pedicle rib unit was (12.6 ± 0.8) mm (T(1)), while the longest was (16.9 ± 1.1) mm (T(11)). The shortest height of pedicle-rib overlap was (7.2 ± 0.3) mm (T(1)), while the longest was (11.8 ± 1.0) mm (T(10)). The height of pedicle rib unit and the height of pedicle were significantly larger than that of the pedicle-rib overlap (P < 0.05), while there was no significantly difference between the height of pedicle rib unit and the height of pedicle (P > 0.05). The pedicle rib unit is a complicated spatial structure, and the longitudinal height of pedicle-rib overlap should be taken as the real height of the unit.

Morphometric Comparisons Between the Pedicle and the Pedicle Rib Unit in the Immature Chinese Thoracic Spine

Morphology comparisons between the pedicle and pedicle rib unit in the immature spine were conducted through computed tomographic scans. To establish reference data concerning the dimensions of the pedicle rib unit for normal children. Until recently, studies on extrapedicular fixation were mostly based on adults. No published study has assessed the morphology of the pedicle rib unit in the normal immature population. Establishment of the basic morphometric characteristics may be beneficial in treating immature patients with spinal disorders. Measurements were carried out on the chest computed tomography scans of the immature Chinese patients without any spinal disorder findings. The width, chord length, and transverse angle of the pedicle rib unit were obtained and compared with the corresponding pedicle index. Difference between sex groups was measured, and significant statistical correlations were carefully studied to determine potentially important clinical relationships. The mean values and the standard deviations obtained for each thoracic segment were determined. The width, chord length, and transverse angle of the pedicle rib unit were significantly larger than corresponding pedicle measurements at all levels. Significant difference for measurements between sexes was found at some segments. Compared with the sex, age seemed to have a more significant effect on the measurements. Linear pedicle and pedicle rib unit dimensions had good correlations with age, whereas the transverse angle seemed to change little with age. Compared with the dimensions of the immature pedicle, the significantly larger size of the corresponding pedicle rib unit provides a more ample space, which accommodates screws with larger diameters. Extrapedicular vertebral body fixation was anatomically feasible for the immature spine. The new procedure should be cautiously applied to avoid potential implant failures or a new deformity because of the growth of the immature spine.

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

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. 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. 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.

An extrapedicular approach to the placement of screws in the thoracic spine: an anatomic and radiographic assessment.

A radiographic and anatomic study of an extrapedicular method of screw placement in cadaveric thoracic spines. To evaluate an alternative method of thoracic vertebral body screw fixation using an extrapedicular screw technique. To evaluate the anatomic safe zones and proper starting point for this alternative approach to the placement of screw fixation in the thoracic spine. Despite the clinical successes reported with thoracic pedicle screw-rod constructs, controversy exists about the safety of this technique in pedicles that are anatomically too small for transpedicular fixation. An alternative method of extrapedicular screw fixation was evaluated in this present study. Two fresh, unfixed, adult cadavers were obtained randomly; 6.0-mm AO Synthes pedicle screws were placed using an extrapedicular approach bilaterally from T3 to T10. The screws were placed according to one defined method described later. Computerized tomographic (CT) images were obtained. The position of each screw was analyzed. The cadavers were then dissected with the screw pathway exposed and the relation of the screw to surrounding anatomy documented. All screws did not penetrate the spinal canal. All screws were within the pedicle rib unit and did not penetrate the neural foramen or pleura. This study, although only introductory, indicates the potential for extrapedicular vertebral body fixation in the thoracic spine. Biomechanical evaluations are presently being conducted to evaluate the use of extrapedicular thoracic screw fixation.