Pedicle screw pull-out testing in polyurethane foam blocks: Effect of block orientation and density

Synthetic bone models such as polyurethane (PU) foam are a well-established substitute to cadaveric bone for screw pull-out testing; however, little attention has been given to the effect of PU foam anisotropy on orthopaedic implant testing. Compressive and screw pull-out performance in three PU foam densities; 0.16 g/cm3 (PCF 10), 0.32 g/cm3 (PCF 20) and 0.64 g/cm3 (PCF 40) were performed in each of the X, Y or Z orientations. The maximum compressive force, stiffness in the linear region, maximum stress and modulus were determined for all compression tests. Pedicle screws were inserted and pulled out axially to determine maximum pull-out force, energy to failure and stiffness. One-way ANOVA and post hoc tests were used to compare outcome variables between PU foam densities and orientations, respectively. Compression tests demonstrated the maximum force was significantly different between all orientations for PCF 20 (X, Y and Z) while stiffness and maximum stress were different between X versus Y and X versus Z. Maximum pull-out force was significantly different between all orientations for PCF 10 foam. No significant differences were noted for other foam densities. There is potential for screw pull-out testing results to be significantly affected by orientation in lower density PU foams. It is recommended that a single, known orientation of the PU foam block be used for experimental testing.

Assessment of the Length of the Pedicle of the Anterolateral Thigh Flap

Purpose To estimate the length of the pedicle of the anterolateral thigh flap (ALT) and to assess how this length corresponds with the distances between the anatomical landmarks. Methods The study group consisted of patients who underwent computed tomography angiograms ranging minimally from the anterior superior iliac spine (ASIS) superiorly and tibia inferiorly. In the study we included 44 patients. In the axial window we identified single scans with (1) ASIS, (2) the apex of the greater trochanter, (3) the origin of the descending branch of the lateral femoral circumflex artery (LFCA), (4) the superolateral corner of the patella, (5) knee joint gap. Knowing the slice thickness in every patient and the difference in scan number we measured (A)-the distance between the scan (1) and the scan (4). This distance (A) represented the length of the line connecting ASIS and the superolateral corner of the patella (AP line). Next, we identified (6) the midpoint of the distance (A). Next we measured (B)-the distance between the scan (2) and the scan (5) and (C)-the distance between the scan (3) and the midpoint of the AP line (6). Results Mean distances between the scans were: (A) 45.34 cm (SD=4.14), (B) 43.12 cm (SD=4.08), (C) 11.69 cm (SD=1.62). There was low positive correlation between the distance (A) and the distance (C) (rs=0.43) and moderate positive correlation between the distance (B) and the distance (C) (rs=0.53). Conclusion Our study suggests that the mean estimated length of the ALT flap pedicle is 11.69 cm and that it positively correlates with the length of the femur and the length of the AP line.

A radiological parametric comparison of low-grade lytic spondylolisthesis to degenerative spondylolisthesis - A retrospective approach to establish its dysplastic origin

Objectives

This study aims to compare low-grade lytic spondylolisthesis (LS) and degenerative spondylolisthesis (DS) radiologically. In addition, it seeks to identify underlying similarities between LS and DS.

Methods

This study included patients with low-grade single-level spondylolisthesis at L4-L5 or L5-S1. They were categorized into LS and DS. Radiological features, including pedicle height, width, transverse, and sagittal angle, as well as anterior vertebral heights (AVH) and posterior vertebral heights (PVH), were measured using T1-weighted magnetic resonance imaging.

Results

The study involved 88 patients: 46 in the DS group and 42 in the LS group. In the LS group, the AVH was significantly higher than the posterior height at L4 and L5 (L4 PVH/AVH ratio 0.93 in LS vs. 0.96 in DS; L5 PVH/AVH ratio 0.84 in LS vs. 0.92 in DS), and pedicles were more medially oriented (L4: 19.62° in LS vs. 17.7° in DS; L5: 28.92° in LS vs. 26.47° in DS). In addition, at L5, the pedicle height (10.67 mm in LS vs. 11.48 mm in DS) and width (13.56 mm in LS vs. 14.37 mm in DS) were smaller compared to the DS group.

Conclusions

Low-grade LS shows distinct radiological vertebral and pedicle anatomy compared to DS. Short and thin pedicles and wedge-shaped vertebrae in LS resemble DS, indicating its dysplastic origin.

The articular surface technique for lumbar pedicle screw placement: a 3D feasibility study

Background

Traditional pedicle screws (TPSs) and cortical based trajectory pedicle screws each apply stability with fusions of the lumbar spine and have shown good success. However, the technical considerations of each technique imply complications of loosening and failure that either technique is uniquely prone to having. The current study proposes a new pedicle screw technique through the articular surface of the vertebral superior facet. It is hypothesized that this path will allow utilization of a larger screw that rivals that of the TPS technique, while also maintaining the high-density bone encountered in the cortical based trajectory technique.

Methods

Retrospective review of 50 consecutive trauma patients that underwent lumbar computed tomography (CT) scans at a Level 1 Trauma Center in the age range 18-45. These scans were uploaded to Brainlab software for ideal starting point and trajectory mapping of pedicle screws coursing through each superior facet and pedicle of vertebral levels L1-S1 without cortical breach. Satisfactory pedicle screw variables consisted of a medial angle <10 degrees, screw length at least 30 mm, screw width at least 5.0 mm, and starting point measurements such as distance to the inferior articular surface and distance to the lateral articular surface.

Results

A total of 600 virtual pedicle screws were placed, in which 525 were satisfactory and measured with the above variables. The pedicle widths were shown to significantly widen with lower-level vertebra in the lumbar spine. Approximately 72% of unsuccessful pedicle screws were placed in levels L1 and L2 allowing wider pedicle screws to be placed more further down the vertebral column.

Conclusions

The articular surface technique (AST) for pedicle screw placement is a viable alternative in lumbar spinal fusions that offers decreased soft tissue dissection. However, the technique is likely better suited for lower lumbar fusions in L3 to S1.

Hemodynamics in Distally Based Sural Flaps for Lower Leg Reconstruction: A Literature Review

Coverage of posttraumatic and chronic wounds at the distal leg is a difficult problem due to limited soft tissue available for local flaps. The sural flap is a versatile and effective method for reconstruction in this area since it does not need a significant amount of time or assistance to complete. Improving the survival of these flaps is critically dependent on understanding the basics of flap circulation and why recent modifications were introduced. This review will serve as a much-needed comprehensive analysis of these topics for surgeons looking to increase the reliability of their sural flaps.

Clinical outcomes following intraoperative pedicle disruption in fibula free flaps

OBJECTIVES

Iatrogenic injury of the fibula free flap pedicle is rare. Postoperative flap survival and reconstructive outcomes following intraoperative pedicle severance are unknown. This study assesses free flap outcomes following accidental severance of the peroneal vessels.

METHODS

Multi-institutional retrospective chart review from 2000 to 2020.

RESULTS

Of 2975 harvested fibula free flaps, 26 had a history of pedicle severance during surgical reconstruction. Reasons for intraoperative pedicle severance included transection during muscular dissection 10/26 (39%), accidental severance with the bone saw 12/26 (46%), and other 4/26 (15.6%). The surgeon responsible for pedicle severance included residents 5/26 (19%), fellows 10/26 (39%), attendings 10/26 (39%), and unknown 1/26 (3.9%). The pedicle artery and vein were severed 10/26 (39%), artery 8/26 (31%), and vein 8/26 (31%). Truncated pedicle vessels were used 3/26 (11.7%), intraoperative anastomoses were performed 23/26 (89%). Postoperative revision in the OR within 7 days of surgery was required 6/26 (23%); 4 flaps were salvaged and 2 flaps failed, both arterial thrombosis. Flap failure was attributed to vascular thrombosis. Long-term flap survival and successful reconstructions were reported 24/26 (92%).

CONCLUSION

Accidental severance of fibula free flap pedicle vessels can be corrected with intraoperative repair, without affecting long-term flap survival or reconstructive outcomes. Protecting the flap vessels while using the bone saw and during intramuscular dissection prevents accidental severance.

Injury to Cone Synapses by Retinal Detachment: Differences from Rod Synapses and Protection by ROCK Inhibition

Attachment of a detached retina does not always restore vision to pre-injury levels, even if the attachment is anatomically successful. The problem is due in part to long-term damage to photoreceptor synapses. Previously, we reported on damage to rod synapses and synaptic protection using a Rho kinase (ROCK) inhibitor (AR13503) after retinal detachment (RD). This report documents the effects of detachment, reattachment, and protection by ROCK inhibition on cone synapses. Conventional confocal and stimulated emission depletion (STED) microscopy were used for morphological assessment and electroretinograms for functional analysis of an adult pig model of RD. RDs were examined 2 and 4 h after injury or two days later when spontaneous reattachment had occurred. Cone pedicles respond differently than rod spherules. They lose their synaptic ribbons, reduce invaginations, and change their shape. ROCK inhibition protects against these structural abnormalities whether the inhibitor is applied immediately or 2 h after the RD. Functional restoration of the photopic b-wave, indicating cone-bipolar neurotransmission, is also improved with ROCK inhibition. Successful protection of both rod and cone synapses with AR13503 suggests this drug will (1) be a useful adjunct to subretinal administration of gene or stem cell therapies and (2) improve recovery of the injured retina when treatment is delayed.

Proximal Tibiofibular Joint Ganglion Cyst: A Rare Cause of Calf Pain

Intramuscular cysts are rare at the proximal calf. However, their etiology is varied, making accurate diagnosis and treatment really difficult. Ganglion cyst (GC) of the proximal tibiofibular (PTF) joint is a very rare entity with an estimated prevalence of 0.76%. Intramuscular extension of the GC arising from the PTF joint is an even rarer lesion, and only a few cases have been published in the literature. Hereby, we report an infrequent case of a GC arising from the PTF joint with a sizable pedicle and intramuscular (lateral head of gastrocnemius) extension to the posterolateral aspect of the right calf.

Lumbar Pedicle Morphometry of Dry Vertebral Columns in Relation to Transpedicular Fixation: A Cross-Sectional Study From Central India

INTRODUCTION

 The lumbar vertebrae are the largest vertebrae of the vertebral column, which support the maximum body weight. There has been an increased focus on transpedicular spinal fixation for addressing various lumbar spine pathology. However, its safety and efficacy require precise knowledge of the lumbar pedicle anatomy. Mismatched size of screw and pedicle may lead to failure of instrumentation. It may result in cortex perforation or pedicle fracture and loosening of the pedicle screw. The oversizing of the pedicle screw can result in dural tears, leakage of the cerebrospinal fluid, and injuries to the nerve root. As the racial variations in the anatomy of a pedicle are well known, this study was performed to assess the morphological parameters of the lumbar vertebrae pedicles in the Central Indian population so that the appropriate sizes of pedicular implants can be selected.

MATERIAL AND METHODS

The present study was conducted at a tertiary-level hospital and medical college on dry lumbar vertebrae specimens available in the department of anatomy. The measurement of morphometric parameters of the lumbar vertebrae pedicles was performed in 20 dry lumbar specimens using vernier calipers and a standard goniometer. The morphometric parameters included in the study are pedicle transverse external diameter (pedicle width), pedicle sagittal external diameter (pedicle height), transverse angle of the pedicle, and sagittal angle of the pedicle. Statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) system version 25 (Chicago, IL: SPSS Inc.).

RESULTS

 The broadest external transverse diameter was at the L5 level, with a mean of (17.54±1.6 mm) in the lumbar vertebrae. The broadest external sagittal pedicle diameter was at the L1 level (13.7±0.88 mm). The maximum transverse angle of the pedicle was at L5 with a mean of 25.39±3.10°. The maximum sagittal angle was at L1 with a mean of 5.44±0.71°.

CONCLUSION

 The increased concern regarding the internal fixation of the spine with pedicle screw systems created the need to have almost accurate anatomical knowledge of lumbar pedicles. Due to the dynamic nature of the lumbar spine and the body's load, maximum degeneration occurs at this spine segment, making it the most commonly operated region of the vertebral column. In our study, pedicle dimensions are comparable to populations of other Asian countries. However, the pedicle dimension of our population is lower than the White American population. This morphological variation of pedicle anatomy will help surgeons choose appropriate size screws and optimum angulations to insert the implant, decreasing complications.

Morphometric Study for C1 Pedicle Screw Placement in Thai Patients

Background  Traumatic atlantoaxial (upper cervical spine) leads to instability in weightbearing movement and neurological deficit. Presently, C1 (axial) lateral mass or pedicle screws for fixation are the most popular because of excellent mechanical performance for internal fixation. C1 pedicle screw fixation can reduce intraoperative blood loss and postoperative occipital neuralgia more than C1 lateral mass screws. However, screws cannot be inserted completely through the pedicle in some patients due to C1 size.

Objective  We aimed to determine the ideal pedicle screw entry point, angle of screw projection, and pedicle height in the Thai population.

Methods  Patient data were collected and measured using the INFINITT program at Mukdahan Hospital from September 2020 to June 2021. The C1 measurements, i.e., distance from the midline to the medial edge of the posterior arch (DPA) and medial edge transverse foramen (DTF), angle of screw projection, and length and height of the pedicle were recorded. Descriptive statistics and t -test were used to analyze the data.

Results  The mean Thai pedicle dimensions were DPA = 14.17 mm (range: 11.19–19.70 mm), DTF = 22.09 mm (range: 18.13–26.44 mm), ideal screw entry point = 18.13 mm (range: 15.19–22.00 mm), ideal angle of screw projection medial angulation = 2.67 degrees (range: 0–7 degrees), and height of posterior arch (pedicle) = 4.77 mm (range: 2.68–7.22 mm). Forty of 167 patients (24.0%) had a pedicle height less than 4.0 mm (bilateral 11 patients and unilateral 29 patients).

Conclusions  The ideal C1 pedicle screw entry point is approximately 18.13 mm from the midline. In the Thai samples with C1 pedicle height less than 4.0 mm, the screws cannot be inserted completely through the pedicle. Therefore, screw insertion should be partially through the pedicle (notching technique).

Traumatic Floating Neural Arch of the Subaxial Cervical Spine: Case Report

Bilateral traumatic pedicle fracture in the lower cervical spine is a very unusual lesion. Its association with bilateral facet dislocation has been reported once in the literature. We report a unique traumatic lesion considered as subaxial cervical floating neural arch with special emphasize on reduction maneuvers and surgical management. It was a case of bilateral C7 pedicle fracture with bilateral C6/C7 facet dislocation in a neurologically intact 70-year-old patient. Open posterior reduction with fixation followed by anterior fusion was performed with good functional and radiological outcomes at last follow up. The floating neural arch lesion is the combination of bilateral pedicle fracture and facet dislocation. The detection of such lesions imposes a two-stage surgery with open posterior reduction and anterior fusion.

Comparison of L5 pedicle morphology in patients with and without L5 spondylolysis

Only a small number of studies have reported on L5 pedicle morphology in the presence of spondylolisthesis let alone isolated spondylolysis and findings are therefore variable. The aim of this radiographic study was to analyze L5 pedicle morphology in the presence and absence of L5 spondylolysis. The was a retrospective cross-sectional analysis of computed tomographic (CT) imaging. Assessment of the L5 pedicle morphology (height, width, length, transverse angle and screw length) were measured in patients with and without L5 spondylolysis. Pelvic measures including pelvic incidence, sacral anatomic orientation and sacral table angle were recorded. Patients were matched for age and gender. Twenty-three patients with spondylolysis were matched to 46 patients without. The presence of spondylolysis alone did not have a significant influence on either pelvic or pedicle morphologic parameters. Only with the presence of associated spondylolisthesis was there a difference noted with an increase in pedicle length observed. Correlation analysis suggested further morphologic changes may result with increased remodeling. Isolated spondylolysis at L5 appears to have little influence on pedicle morphology in this CT-based analysis. Morphologic changes appear likely to become significant only with associated spondylolisthesis and associated remodeling.

Novel use of percutaneous cervical pedicle inlet screws for supplemental posterior fixation after anterior cervical deformity correction

Introduction

Correction of cervical deformity can be achieved using anterior cervical fixation and fusion techniques. However, supplemental posterior fixation is a critical component for ensuring biomechanical longevity and favorable patient outcomes. We present a novel percutaneous technique for posterior cervical fixation in patients where cervical pedicle (CP) screws may not be feasible and midline muscle dissection is not needed.

Methods

Three patients presented to our hospital with cervical pathology amendable to circumferential cervical fusion. After adequate deformity correction was performed through an anterior cervical decompression and fusion, staged posterior supplemental fixation was achieved using percutaneous CP inlet (CPI) screws using a percutaneous muscle-sparing approach.

Results

All three patients underwent CPI screw placement without postoperative neurovascular complications. Postoperative radiographic follow-up showed the desired, proper screw placement, with continued maintained cervical alignment.

Conclusions

CPI screw placement may be alternative hybrid screw that achieves a advantageous safety profile while also avoiding an open midline exposure.

Comparison of the maximum possible lengths of insertable screws in the Subaxial Cervical Spine

BACKGROUND

Lateral mass screws are the most commonly used fixation technique in the Subaxial Cervical Spine (SCS), their main advantages being that they are easy to insert and safe in their application. Pedicle screws are significantly longer, are quite challenging to insert in most settings and are accompanied by the risk of serious complications such as vascular and neural injuries. We have therefore developed a new technique, which permits safe insertion of long screws in the SCS.

METHODS

A radiological evaluation was carried out to determine the maximum possible insertable screw length in the SCS when using the following techniques: pedicle, lateral mass (Magerl's) and "Attallah" screws. Scans of 66 cervical spines were analyzed to determine the maximum possible screw lengths of all three screw insertion techniques, based on the standard description through the vertebrae from C3 to C7.

RESULTS

The maximum possible length of the Attallah screw of 20.7 ± 2.5 mm (mean value ± SD) is only 2.4 mm shorter than the pedicle screw (23.1 ± 1.8 mm) along the SCS. The lateral mass screw is with 10.2 ± 1.3 mm full 12.9 mm shorter than the pedicle screw.

CONCLUSIONS

The maximum possible length of the Attallah screw is close to that of the pedicle screw and significantly greater than that of the lateral mass screw. We provide a fixation method comparable to the pedicle screw in its strength and to the lateral mass screw in its safety.

Proposal of Treatment Strategy for Pedicle Fractures of the C2: An Analysis of 49 Cases

Spine surgeons often confuse C2 pedicle fractures (PFs) with pars interarticularis fractures. In addition, little information is available about the characteristics and treatment strategies for C2 PFs. We sought to investigate the characteristics of C2 PFs and to propose an appropriate treatment strategy. A total of forty-nine patients with C2 PFs were included in this study. We divided these patients into unilateral and bilateral C2 PF groups. The incidence rates and characteristics of other associated C2 and C2-3 injuries, and other cervical injuries, were evaluated. In addition, treatment methods and outcomes were analyzed. Twenty-two patients had unilateral C2 PFs and twenty-seven patients had bilateral C2 PFs. Among the cases of unilateral C2 PFs, all patients had one or more other C2 fractures, and twenty patients (90.9%) had one or two C2 body fractures. Meanwhile, among the cases of bilateral C2 PF, all patients had two or more other C2 fractures and one or two C2 body fractures. In unilateral C2 PFs, three patients with C2-3 anterior slip or adjacent cervical spine (C1-3) injury underwent surgery and nineteen patients (86.4%) were treated with conservative methods. In bilateral C2 PFs, three patients with C2-3 anterior slip or SCI at C2-3 underwent surgery and twenty-four patients (88.9%) were treated with conservative methods. Our results showed that C2 PFs do not occur alone and are always accompanied by other associated C2 injuries. C2 PFs should, generally, be thought of as a more complex fracture type than hangman's fracture or dens fracture. Despite the complex fracture characteristics, most C2 PFs can be managed with conservative treatment. However, surgical treatments should be considered if the C2 PFs are accompanied by the C2-3 anterior slip and adjacent cervical spine injury.

Anterolateral thigh free flaps with T-shaped pedicles and multiple venous anastomosis for extremity reconstruction

The anterolateral thigh free flap is one of the most preferred options for reconstructing soft tissues of the extremities and vascular anastomosis is one of the most important factors for flaps survival. T-anastomosis and double venous anastomosis have been widely used for increasing flap survival. This report shows both application of T-shape pedicle and multiple venous anastomosis to each 43 cases for extremity reconstruction that have not been described so far in the literature and it showed the necessity of multiple anastomosis. The locations of the lesions were 8 upper extremities (4 hands, 3 forearms, and 1 upper arm) and 35 lower extremities (5 forefeet, 6 dorsal feet, 4 plantar feet, 11 ankles, and 9 lower legs). We applied T-shaped arterial pedicle to limited anatomical area that had 2 or more major arterial communication sites to overcome the obstruction by reverse flow from communication vessels when 1 of the 2 anastomosis was obstructed. We classified multiple venous anastomosis according to flow direction and the vascular connections between the superficial and deep veins. In result, 37 cases survived completely but 2 flaps developed severe necrosis (>50%) because of infection and hematoma and 4 flaps developed partial necrosis due to wound infection. In conclusion, T-shaped pedicle and multiple venous anastomosis is a method to improve free flap survival and useful in cases where sacrificing a dominant vessel is inevitable or those in which only 1 vessel remains.

Infarcted wandering spleen: A case report from Saudi Arabia

Spleen is normally positioned in the left upper quadrant. Abnormal location where it is not found in its normal anatomical position is called wandering spleen (WS). Wandering spleen is a rare medical condition that occurs due to developmental abnormality or acquired laxity of the ligaments that hold the spleen in its normal anatomical position. It affects children and young adults, especially childbearing age women. Patients affected with this condition may present with nonspecific symptoms requiring a high index of suspicion. Here, we are presenting a 20-year-old female known to have WS ended up with infarcted WS requiring emergency splenectomy.

Computer-Assisted Navigation Is Associated With Decreased Rates of Hardware-Related Revision After Instrumented Posterior Lumbar Fusion

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To (1) define utilization trends for navigated instrumented posterior lumbar fusion (PLF), (2) compare reasons and rates of revision at 30-day, 60-day, 90-day, and 1-year follow-up, and (3) compare 90-day perioperative complications between navigated versus conventional instrumented PLF.

METHODS

Patients who underwent navigated or conventional instrumented PLF were identified from the Humana insurance database using the PearlDiver Patient Records between 2007-2017. Usage of navigation was characterized. Patient demographics and operative characteristics (number of levels fused, interbody usage) were compared between the 2 treatment groups. Propensity score matching was done and comparisons were made for revision rates at different follow-up periods (categorized by reasons) and other 90-day perioperative complications.

RESULTS

This study included 1,648 navigated and 23 429 conventional instrumented PLF. Navigated cases increased over the years studied to approximately 10% in 2017. Statistical analysis after propensity score matching revealed significantly lower rates of hardware-related revision at 90-day follow-up in the navigated cohort (0.49% versus 1.15%, P = .033). At 1-year follow-up, the navigated cohort continued to have significantly lower rates of hardware-related revision (1.70% versus 2.73%, P = .044) as well as all cause revision (2.67% versus 4.00%, P = .032). There were no statistical differences between the 2 cohorts in any of the 90-day perioperative complications studied, such as cellulitis and blood transfusion (P > .05 for all).

CONCLUSIONS

These findings suggest that navigation is associated with reductions in hardware-related revisions after instrumented PLF. However, these results should be interpreted cautiously in the setting of potential confounding by other unmeasured variables.

Evaluation of K-wireless robotic and navigation assisted pedicle screw placement in adult degenerative spinal surgery: learning curve and technical notes

Background

K-wireless robotic pedicle screw instrumentation with navigation is a new technology with large potential. Barriers to adoption are added registration time with robotic-navigated system and reliable screw positioning. Understanding the learning curve and limitations is crucial for successful implementation. The purpose of this study was to describe a learning curve of k-wireless robotic assisted pedicle screw placement with navigation and compare to conventional techniques.

Methods

A retrospective review of prospectively collected data of 65 consecutive adult patients underwent robotic-navigated posterior spinal fusion by a single spine surgeon. Registration, screw placement, and positioning times were recorded. All patients underwent intra-operative 3D fluoroscopy and screw trajectory was compared to pre-operative CT.

Results

A total of 364 instrumented pedicles were planned robotically, 311 (85.4%) were placed robotically; 17 screws (4.7%) converted to k-wire, 21 (5.8%) converted to freehand, and 15 (4.1%) planned freehand. Of the 311 robotically placed pedicle screws, three dimensional fluoroscopic imaging showed 291 (93.5%) to be GRS Grade A in the axial plane (fully contained within the pedicle) and 281 (90.4%) were GRS Grade A in the sagittal plane. All breached screw deviations from plan were identified on 3D fluoroscopy during surgery and repositioned and confirmed by additional 3d fluoroscopy scan. Reasons for conversion included morphology of starting point (n=18), soft tissue pressure (n=9), hypoplastic pedicles (n=6), obstructive reference pin placement (n=2), and robotic arm issues (n=1). Seventeen (5.5%) critical breaches (≥2-4 mm) were recorded in 11 patients, 9 (2.9%) critical breaches were due to soft tissue pressure causing skive. Two patients experienced 6 (1.9%) critical breaches from hypoplastic pedicles, and 3 (0.9%) unplanned lateral breaches were found in another patient. One patient (0.3%) experienced skive due to morphology and spinal instability from isthmic spondylolisthesis. Imaging showed 143 screws placed medially to plan (1.2±0.9 mm), 170 lateral (1.2±1.1 mm), 193 screws caudal (1.0±0.6 mm) and 117 cranial (0.6±0.5 mm). No adverse clinical sequelae occurred from implantation of any screw.

Conclusions

The learning curve showed improvement in screw times for the first several cases. Understanding the learning curve and situations where the robotic technique may be suboptimal can help guide the surgeon safe and effectively for adoption, as well as further refine these technologies.

Residual antler periosteum holds the potential to partially regenerate lost antler tissue

Deer antlers are the only mammalian organs that can fully regenerate, which relies on pedicle periosteum (PP). Interestingly during the growing phase, antlers themselves can regenerate partially lost antler tissue. However, what tissue type in the growing antlers fulfills this role is not known. Following antler removal during the growing phase, a "second" antler regenerates from the stump. In this study, the "second" antler growing from the cut antler base (AB) was examined in both red and sika deer. The results showed that all regenerating antlers were formed from the peripheral edge of the AB, where the antler periosteum (AnP) is located. The growth center showed a clear demarcation from the AB bone in red deer. Therefore, it is highly likely that AnP is the tissue that possesses the potential. Factors that might affect this potential were explored and the main factor was found to be AB calcification, which was controlled by rising androgens. Thus, the ultimate antler regeneration potential of the AnP was assessed through castration and repeated antler removal. The results demonstrated that the regeneration potential of AnP was somewhat limited and inferior to that of the PP. The ability of AnP to achieve partial regeneration may be evolutionarily conserved, as the regeneration of partially lost antlers within the season is secured; whereas, with PP, a new set of antlers in the next season is guaranteed. This two-level mechanism may signify how evolutionarily important it is for deer to possess reasonably intact antlers.

Lumbar Pedicle Morphology and Vertebral Dimensions in Isthmic and Degenerative Spondylolisthesis-A Comparative Study

BACKGROUND

The pedicle screw is the most common device used to achieve fixation in fusion of spondylolistheses. Safe and accurate placement with this technique relies on a thorough understanding of the bony anatomy. There is a paucity of literature comparing the surgically relevant osseous anatomy in patients with a degenerative spondylolisthesis (DS) and an isthmic spondylolisthesis (IS). The goal of this study was to determine the differences in the osseous anatomy in patients with a DS and those with an IS.

METHODS

A retrospective comparative cohort study was conducted on patients with a single-level, symptomatic L4-L5 DS or a single-level, symptomatic L5-S1 IS. Magnetic resonance imaging for these patients was reviewed. Morphometries of the pedicle and vertebral body were analyzed by 2 independent observers for the levels from L3 to S1, and radiographic parameters were compared between groups.

RESULTS

A total of 572 levels in 143 patients were studied, including 103 patients with a DS and 40 with an IS. After accounting for confounders, IS and DS had an independent effect on transverse vertebral body width, pedicle height and width, and sagittal pedicle angle. Patients with an IS had a smaller pedicle height (P < .001) and pedicle width (P = .001) than patients with DS. In addition, the angulation of the pedicles varied on the basis of the diagnosis.

CONCLUSIONS

The osseous anatomy is significantly different in patients with a DS than with an IS. Patients with an IS have smaller pedicles in the lumbar spine. Also, the L4 and L5 pedicles are more caudally angulated and the S1 pedicle is less medialized.

LEVEL OF EVIDENCE

3.

CLINICAL RELEVANCE

Understanding the differences in pedicle anatomy is important for the safe placement of pedicle screws.

Case Report: Multimodal Imaging Features of Pedunculated Liver Masses in Seven Dogs

This study describes the multimodal imaging characteristics of pedunculated liver masses in seven dogs [Cocker Spaniel (n = 2), Maltese (n = 1), Shih-Tzu (n = 2), and Schnauzer (n = 2)]. These masses are anatomic variants of hepatic masses in which the center of the mass lies outside the liver contour. Prior to referral, only one dog had been diagnosed with a hepatic mass, four had been diagnosed with mid-abdominal masses of unknown origin, and two had been misdiagnosed with splenic head and pancreatic masses. Using radiographs, the mass locations were classified as cranioventral (n = 3), mid-abdominal (n = 2), or craniodorsal (n = 2). The gastric axis was deviated in various directions in four cases. Based on computed tomography (CT) findings, the masses were noted to originate from every liver lobe (two from the left lateral lobe) and to possess parenchymal (n = 6) or vascular (n = 1) pedicles. The histopathological results showed that three masses were benign [hepatic adenoma (n = 1) and nodular hyperplasia (n = 2)] and four were malignant [hepatocellular carcinoma (n = 3) and cholangiocarcinoma (n = 1)]. For three dogs, triple-phase CT maximum intensity projection images in the arterial phase clearly showed that the masses were connected to the hepatic artery. We propose that a pedunculated liver mass should be considered as a differential diagnosis when a mass is located in the mid-abdomen, even if it is separated from the liver and with the gastric axis deviated in various directions. We consider CT imaging to be a useful tool for diagnosis, evaluation, and surgical planning in dogs with a pedunculated liver mass.

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.

Outcomes of Venous End-to-Side Microvascular Anastomoses of the Head and Neck

Objectives/Hypothesis

The literature on outcomes of end‐to‐side (ETS) anastomoses for microvascular reconstruction of the head and neck is limited. This series reviews ETS in free tissue transfer (FTT) across multiple institutions to better understand their usage and associated outcomes.

Study Design

Retrospective review of 2482 consecutive patients across three tertiary institutions.

Methods

Adult patients (> 18) who received a FTT from 2006 to 2019 were included.

Results

Two hundred and twenty‐one FTT were identified as requiring at least one ETS anastomosis. These ETS cases had a failure rate of 11.2% in comparison to 3.8% in a cohort of end‐to‐end (ETE) cases (P < .001). ETS cases were significantly more likely to have a prior neck dissection (P < .001), suggesting the ETS method was utilized in select circumstances. A second ETS anastomosis improved survival of the FTT (P = .006), as did utilization of a coupler over suture (P = .002). Failure due to venous thrombosis was significantly more common with one ETS anastomosis instead of two ETS anastomoses (P = .042).

Conclusions

ETS is effective but is often used as a secondary technique when ETE is not feasible; as such, in this series, ETS was associated with higher failure. A second anastomosis and the use of the coupler for completing the anastomoses were associated with lower rates of failure.

Level of Evidence

3 Laryngoscope, 131:1286–1290, 2021

Anastomotic Revision in Head and Neck Free Flaps

OBJECTIVES/HYPOTHESIS

Predictors of free tissue transfer (FTT) failure and the need for postoperative revision (POR) have been extensively studied; however, there are little data evaluating outcomes when intraoperative revision (IOR) at initial surgery is required. This study seeks to better understand the impact IOR of the pedicle has on FTT outcomes.

STUDY DESIGN

Retrospective review of 2482 consecutive patients across three tertiary institutions.

METHODS

Adult patients (>18) who received a FTT and underwent anastomotic revision from 2006 to 2019 were included. Logistic regression was performed to predict revision, and recursive partitioning was performed to classify risk of failure based on type of revision and vessels revised.

RESULTS

Failure rates for IOR (19%) and POR (27%) were higher compared to a nonrevised failure rate of 2% (P < .01 and P < .01, respectively). Intraoperative venous revision (IORv, n = 13), arterial (IORa, n = 114), and both (IORb, n = 11) were associated with failure rates of 8% (odds ratio [OR] 3.5, P = .23), 18% (OR = 9.0, P < .01), 45% (OR = 35.3, P = <.01), respectively. Arterial revision was most common among IOR (83%, P < .01). Postoperative venous revision (PORv, n = 35), arterial (PORa, n = 36), and both (PORb, n = 11) were associated with failure rates of 20% (OR = 15.7, P < .01), 27% (OR = 10.6, P < .01), and 39% (OR = 27.0, P < .01), respectively. Failure rate for flaps that had POR after IOR (PORi, n = 11) was 45% (OR = 18.2, P < .01). Diabetes predicted IOR (P = .006); tobacco use, heavy alcohol use, and prior radiation predicted POR (P = .01, P = .05, and P = .01, respectively).

CONCLUSION

Both IOR and POR were associated with increased failure compared to nonrevised flaps. The risk of failure increases sequentially with intraoperative or POR of the vein, artery, or both vessels. Revision of both vessels and POR after IOR are strongly predictive of failure.

LEVEL OF EVIDENCE

3 Laryngoscope, 131:1035-1041, 2021.

Morphometry of the C2 Pedicle and Lamina in Thai Patients

Background

Traumatic upper cervical spine leads to instability and neurological deficit. At present, C2 (axis) pedicle or lamina screws for fixation are popular because further external immobilization is not needed. However, these techniques demand experience inserting the screws and carry the risk of vertebral artery or spinal cord injury. In some patients, the C2 screws cannot be inserted because of limited C2 size.

Objective

To determine the width, length, height, and angle in the C2 pedicle and lamina in the Thai population.

Materials and Methods

Patient data were collected from the Picture Archiving and Communication System at the Faculty of Medicine, Prince of Songkla University from January 2016 to December 2017. The C2 parameters, i.e., width, length, height, and angle of the pedicle and lamina were recorded.

Results

The CT C-spine scans of 270 patients were enrolled. The mean Thai C2 pedicle dimensions were width 5.51 mm, length 23.78 mm, angle 39.04°, and height 8.64 mm. The mean C2 lamina dimensions were width 5.88 mm, length 32.17 mm, angle 49.46°, and height 12.27 mm. Twenty-four patients from the 270 patients (8.8%) had a pedicle width <3.5 mm but all patients had a lamina width ≥3.5 mm.

Conclusion

In the Thai samples, 8.8% had a C2 pedicle width <3.5 mm which would not allow insertion of screws; however, they could be replaced with lamina screws since the lamina width was ≥3.5 mm. In this study, all of the patients who could not be inserted pedicle can be replaced with lamina screws inserted.

Posterior screw fixation in the subaxial cervical spine: a technique and literature review

Posterior cervical spine fixation is a key component in achieving spinal arthrodesis for treating various cervical spine pathologies including neoplastic, inflammatory, traumatic and degenerative diseases. Historically, various wiring techniques had played major roles in posterior cervical spine fixation. Today, posterior cervical screw fixation is utilized by most spine surgeons instead of wiring for its superior biomechanical strength. A review of lateral mass, pedicle, intralaminar and transfacet screw fixation techniques in the subaxial cervical spine is presented in a detailed fashion. A comparison among different posterior cervical subaxial fixation techniques is also included. Although the safety of freehand techniques was demonstrated in the majority of the existing studies, real-time navigation is becoming increasingly utilized for cervical screw insertion, especially for cervical pedicle screws, where the freehand technique is technically demanding and may carry a higher risk of neurovascular injury. Several different posterior screw fixation techniques exist for the subaxial cervical spine with generally low complication rate. Spine surgeons should be familiar with these techniques and choose the optimal technique based on each patient's individual anatomy and surgical needs.

Triggered EMG (T-EMG) Values of Pedicle Screws with a Powered Screwdriver vs A Standard Probe in Adolescent Idiopathic Scoliosis Do Not Agree: A Prospective Validation Study

Triggered electromyography (t-EMG) is a common technique used during spinal instrumentation in surgery for adolescent idiopathic scoliosis. This study tests the validity of t-EMG values obtained with a standard ball-tipped probe after completion of screw placement versus t-EMG values obtained during screw insertion with a powered screwdriver. t-EMG values were collected for screws spanning T7-L5 using both a standard probe and a powered screwdriver. A power analysis determined that a sample size of 300 screws would provide enough precision to estimate limits of agreement within ±2 mA. A monopolar constant current stimulation technique (0.2 ms duration and 3.11 Hz stimulation rate) was used at each level. EMG was acquired with placement of bipolar pairs of subdermal needle electrodes. A Bland-Altman plot was used to assess agreement between threshold readings from the two techniques. Twenty-nine patients were enrolled in this study with 305 screws. t-EMG values measured using a powered screwdriver were on average 1 mA lower than values from a standard probe. When readings less than or equal to 20 mA were considered, the limits of agreement were approximately 4 and 7 mA overall. In total, 28/305 (9%) screws were removed and reinserted, 9/305 (3%) screws were redirected, and 3/305 (1%) screws were aborted based on t-EMG readings. Despite a small overall difference in t-EMG value between the standard probe and screwdriver, there was still large variability in agreement between the two techniques. t-EMG values obtained with a powered screwdriver during screw insertion are not interchangeable with values measured by a probe.

Percutaneous Pedicle Screws in the Obese: Should the Skin Incision Be More Lateral?

Objective: To determine if the skin incision for lumbar percutaneous pedicle screws should be more lateral in the obese patient.

Methods: This was a retrospective radiographic analysis of 30 obese and non-obese lumbar spine computed tomography (CT) radiographs comparing the depth of soft tissue along the anatomic axis of the pedicle at L4 and L5.

Results: The average distance from the pedicle trajectory on the skin to the lateral border of the pedicle at L4 was 1.4 cm and 3.8 cm in the non-obese and obese groups, respectively. The average distance from the pedicle trajectory on the skin to the lateral border of the pedicle at L5 was 2.1 cm and 4.3 cm in the non-obese and obese groups, respectively; both these differences reached statistical significance, p <0.05.

Conclusions: This radiographic study supports a more lateral start point for percutaneous pedicle screws in obese patients to maintain an anatomic trajectory when inserting percutaneous pedicle screws into the lumbar spine at L4 and L5. If a skin incision is made at only 1 cm lateral to the pedicle in the obese patient, the surgeon often has to place significant traction on the skin edge to lateralize their instrumentation to achieve an appropriate angle of insertion. By making a more lateral skin incision, less manipulation of the skin and soft tissues is needed to maintain an anatomic trajectory of the pedicle screw. Decreasing soft tissue manipulation may decrease wound and instrumentation complications in this at-risk population.

Pedicle stress shielding following growing rod implantation: case report

Growing rod surgery for skeletally immature patients helps correct severe scoliosis while allowing continued spinal column growth. Previous reports have studied vertebral body changes following growing rod surgery, but there are currently no published reports on alterations in pedicle morphology. Given the potential need for definitive spinal fusion with pedicle screw instrumentation, an awareness of changes in pedicle morphology is critical. A morphometric analysis of pedicles was performed using 3D reconstructions of 3 CT scans (preoperative and at 3 and 6 years) obtained in a young girl with infantile idiopathic scoliosis (T7 apex) who underwent unilateral rib-to-spine growing rod (2nd-4th ribs to L1) implantation with lengthening every 6 months for 6 years. The pedicle widths on the growing rod side from T5 to T9 (apex ± 2) were all smaller at 6 years postoperatively than preoperatively, while the same-level pedicles opposite the device significantly increased in width. These findings support anecdotal intraoperative reports by surgeons and provide evidence of pedicle stress shielding due to growing rod distraction and force deprivation.

Three-dimensional digitizing and anatomic study of lumbar vertebral canal and pedicle in children

Introduction

Spinal pedicle screw internal fixation has been widely used in adult spine injury fixation. Due to being in a period of continuous growth and development, the spine of children at different ages shows different characteristics from adults in terms of anatomy, physiological function, and biomechanics. Furthermore, because the pedicle of children is small, has large anatomic variation, and has complex adjacent relationships, the surgical risk is extremely high. How to improve the screwing accuracy is the key to the success of children's pedicle internal fixation. Therefore, applying the concept of digitized and individualized screwing will be of great significance to children's pedicle screwing.

Aim

To investigate the morphologies, development patterns, and aging characteristics of the lumbar vertebral pedicle (LVP) in children aged 6-11 years, and to provide a theoretical basis for screw implantation and related biomechanical studies.

Material and methods

A total of 60 children aged 6-11 years were selected for the intergroup measurement and statistical analysis of their lumbar diameter, pedicle diameter, screw canal length (SCL), etc.

Results

Generally, the vertebral foramen diameter (ID), sagittal diameter (SD), pedicle width (PW), and SCL as well as the pedicle height (PH) exhibited an increasing trend with age and increasing vertebral sequence among children aged 6-11 years.

Conclusions

By observing the LVP in children using 3D digital reconstruction technology, the morphology of the spinal canal and pedicles at different lumbar segments showed obvious development patterns, and the best treatment protocol should be selected according to the LVP characteristics in clinical applications.

Posterior Subaxial Cervical Spine Screw Fixation: A Review of Techniques

STUDY DESIGN

A narrative literature review.

OBJECTIVES

To review the surgical techniques of posterior screw fixation in the subaxial cervical spine.

METHODS

A broad literature review on the most common screw fixation techniques including lateral mass, pedicle, intralaminar and transfacet screws was performed on PubMed. The techniques and surgical nuances are summarized.

RESULTS

The following techniques were described in detail and presented with illustrative figures, including (1) lateral mass screw insertion: by Roy-Camille, Louis, Magerl, Anderson, An, Riew techniques and also a modified technique for C7 lateral mass fixation; (2) pedicle screw fixation technique as described by Abumi and also a freehand technique description; (3) intralaminar screw fixation; and finally, (4) transfacet screw fixation, as described by Takayasu, DalCanto, Klekamp, and Miyanji.

CONCLUSIONS

Many different techniques of subaxial screw fixation were described and are available. To know the nuances of each one allows surgeons to choose the best option for each patient, improving the success of the fixation and decrease complications.

Hyoliths with pedicles illuminate the origin of the brachiopod body plan

Hyoliths are a taxonomically problematic group of Palaeozoic lophotrochozoans that are among the first shelly fossils to appear in the Cambrian period. On the basis of their distinctive exoskeleton, hyoliths have historically been classified as a separate phylum with possible affinities to the molluscs, sipunculans or lophophorates-but their precise phylogenetic position remains uncertain. Here, we describe a new orthothecide hyolith from the Chengjiang Lagerstätte (Cambrian Series 2 Stage 3), Pedunculotheca diania Sun, Zhao et Zhu gen. et sp. nov., which exhibits a non-mineralized attachment structure that strikingly resembles the brachiopod pedicle-the first report of a peduncular organ in hyoliths. This organ establishes a sessile, suspension feeding ecology for these orthothecides and-together with other characteristics (e.g. bilaterally symmetrical bivalve shell enclosing a filtration chamber and the differentiation of cardinal areas)-identifies hyoliths as stem-group brachiopods. Our phylogenetic analysis indicates that both hyoliths and crown brachiopods derived from a tommotiid grade, and that the pedicle has a single origin within the brachiopod total group.

Fracture generation in human vertebrae under compression loading: The influence of pedicle preservation and bone mineral density on in vitro fracture behavior

BACKGROUND

Fractured vertebral bodies are a common and wide spread health issue.

OBJECTIVE

The purpose of this study was to develop a standardized method to experimentally generate compression fractures in vertebral bodies. The influence of the pedicles has been investigated with regards to the fracture behavior. The correlation between bone mineral density (BMD), the cause of fractures and the fracture behavior was investigated.

METHODS

Twenty-one fresh frozen human lumbar spines were examined for bone mineral density (BMD) by means of quantitative computed tomography (qCT). All soft tissue was removed, vertebrae were carefully separated from each other and the exposed cranial and caudal endplates were covered with a thin layer of resin to generate a plane and homogeneous surface. A total of 80 vertebral bodies were tested until fracture.

RESULTS

A good positive correlation was found between BMD, fracture compression force and stiffness of the vertebral body. No significant differences were found between the fractures generated in vertebral bodies with and without pedicles, respectively.

CONCLUSIONS

Our model represents a consolidation of already existing testing devices. The comparative measurement of the BMD and the fracture behavior shows validity. In contrast to other authors, the force was applied to the whole vertebral body. Furthermore the upper and lower plates were not parallelized and therefore the natural anatomic shape was imitated. Fracture behavior was not altered by removing the pedicles.

Quantitative Assessment of the Anatomical Footprint of the C1 Pedicle Relative to the Lateral Mass: A Guide for C1 Lateral Mass Fixation

STUDY DESIGN

Anatomic study.

OBJECTIVES

To determine the relationship of the anatomical footprint of the C1 pedicle relative to the lateral mass (LM).

METHODS

Anatomic measurements were made on fresh frozen human cadaveric C1 specimens: pedicle width/height, LM width/height (minimum/maximum), LM depth, distance between LM's medial aspect and pedicle's medial border, distance between LM's lateral aspect to pedicle's lateral border, distance between pedicle's inferior aspect and LM's inferior border, distance between arch's midline and pedicle's medial border. The percentage of LM medial to the pedicle and the distance from the center of the LM to the pedicle's medial wall were calculated.

RESULTS

A total of 42 LM were analyzed. The C1 pedicle's lateral aspect was nearly confluent with the LM's lateral border. Average pedicle width was 9.0 ± 1.1 mm, and average pedicle height was 5.0 ± 1.1 mm. Average LM width and depth were 17.0 ± 1.6 and 17.2 ± 1.6 mm, respectively. There was 6.9 ± 1.5 mm of bone medial to the medial C1 pedicle, which constituted 41% ± 9% of the LM's width. The distance from C1 arch's midline to the medial pedicle was 13.5 ± 2.0 mm. The LM's center was 1.6 ± 1 mm lateral to the medial pedicle wall. There was on average 3.5 ± 0.6 mm of the LM inferior to the pedicle inferior border.

CONCLUSIONS

The center of the lateral mass is 1.6 ± 1 mm lateral to the medial wall of the C1 pedicle and approximately 15 mm from the midline. There is 6.9 ± 1.5 mm of bone medial to the medial C1 pedicle. Thus, the medial aspect of C1 pedicle may be used as an anatomic reference for locating the center of the C1 LM for screw fixation.

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.

C7 intra-laminar screws for complex cervicothoracic spine surgery-a case series

Background

C7 has relatively unique anatomy compared to the remainder of the subaxial cervical spine (C3-C6) and upper thoracic spine. The C7 laminar has been previously reported in feasibility and biomechanical studies as an adequate fixation point in contrast to the lateral mass or pedicles, with few reports of its use in clinical practice. The purpose of this study was to review the safety and efficacy of using the C7 laminar as a fixation point in constructs involving the cervical spine and cervicothoracic junction.

Methods

Between February 2013 and July 2016, 10 patients (6 males, 4 females) had 19 C7 intra-laminar screws sited (bilateral in 9 patients, unilateral in 1 patient). Six patients had trauma as an underlying etiology, 2 of which had pseudoarthrosis from prior surgery. Three patients had cervical myelopathy from degenerative disease, 2 of which required anterior and posterior instrumentation for correction of deformity and 1 which had stand-alone posterior fixation. One patient had stabilization for an underlying malignancy.

Results

One patient died 2 weeks following their high cervical injury secondary to complications of respiratory failure. None of the remaining 9 patients were noted to have construct failure at a median follow up of 1 year (range, 6 months to 4 years) and all were noted to have satisfactory positioning of the instrumentation on post-operative imaging. The patient with malignancy died 6 months later from extra-spinal disease, there was one wound breakdown requiring debridement without infection in a revision case, and one patient required laminectomy for post-traumatic syrinx formation.

Conclusions

The C7 laminar provides an alternative fixation point for constructs involving the subaxial cervical spine and cervicothoracic junction, with excellent safety and efficacy in this small series. Larger series are required to more clarify the risk profile of this technique.

Evaluation of Multi-Slice Spiral Computed Tomography in In vivo Simulation of Individualized Cervical Pedicle Screw Placement at C3-C7 in Chinese Healthy Population

BACKGROUND

Cervical pedicle screw fixation through posterior approach has shown greater cervical stability advantage. The cervical pedicle screw fixation technique through posterior approach is demanding. The key to the technique is the choice of point and angle of screw entrance. The angle of screw placement is variable. Morphometric measurements of the cervical pedicle are a prerequisite for individualized screw. CT imaging has become the most reliable and important means to obtain cervical pedicle's measurement data and morphology in vivo. This study explores the feasibility and application of precise in vivo measurements by multi-slice computed tomography (MSCT) for individualized cervical transpedicular screw placement at C3-C7 in Chinese healthy population.

MATERIALS AND METHODS

80 adults who underwent cervical examination by enhanced and nonenhanced computed tomography angiography, respectively, were selected and submitted to bone algorithm reconstruction for slice thickness and interval of 0.75 mm to acquire clear images and detailed bone structures. Simulation of individualized screw placement was performed with a 4.0 mm diameter screw with the help of postprocessing workstation. Pedicle transverse angle (PTA) and sagittal angle (PSA) were measured using the single- and double-line methods (analog nailing, 4.0 mm in diameter) in 160 pairs of C3-C7 pedicles, setting positive and negative values for cranial direction and foot side PSAs, respectively. Comparison of the measured change scope in PTA and PSA between the two methods was carried out; the range was defined as the error range.

RESULTS

Significantly, different results (P < 0.05) were obtained between the single- and double-line methods in the error ranges of PTA and PSA in C3-C7 pedicles. Interestingly, the double-line method was better in simulating the actual needs of individualized nailing. The mean values of PTA and PSA were 42.9°, 45.5°, 42.4°, 37.1°, 29.0° and 8.4°, 5.0°, -4.0°, and -7.8°, -8.1°, respectively, with the double-line method.

CONCLUSION

MSCT reconstruction techniques can determine the direction and required parameters for individualized screw placement. In addition, accurate in vivo measurements of PTA and PSA, particularly PSA, provide the orthopedic surgeon with theoretical guidance and reliable basis in screw placement.

Retrospective Review on Accuracy: A Pilot Study of Robotically Guided Thoracolumbar/Sacral Pedicle Screws Versus Fluoroscopy-Guided and Computerized Tomography Stealth-Guided Screws

Introduction Pedicle screw insertion is the mainstay of thora-cic and lumbosacral posterior spinal instrumentation. However, it may be associated with complications such as screw mal-positioning. The purpose of this study was to develop a pilot study to compare the accuracy of robot-guided screw insertion versus hand-guided screw placement for spinal instrumentation. The hand-guided screws were placed with assistance from computerized tomography (CT) stealth guidance or fluoroscopy. Materials and methods A retrospective analysis of medical records was done for all patients that had pedicle screw insertion for instrumentation between the dates of December 2013 and January 2016 with post-screw placement CT imaging. The analysis was conducted on screw accuracy between the two categories based on the Gertzbein-Robbins classification. Results A total of 49 screws were analyzed for accuracy in six patients. There was no statistically significant difference between the accuracy of hand-placed pedicle screws versus the robotically placed screws (p = 0.311). There was no statistically significant difference in blood loss (p = 0.616), length of procedure (p = 0.192), or post-operative length of stay (p = 0.587). Conclusion The findings of our pilot study agree with most prior studies that there was no statistically significant difference in the accuracy of pedicle screw placement between the two methods of screw placement. Therefore, the techniques are equivocal in accuracy. The new technology (robotic-guidance) is as safe as conventional techniques for screw placement. Just like in any surgery, the technique preference should remain surgeon dependent. The results are only from a small sample size in the development of a pilot study so a strong reliance on the data would not be suggested. The study was a preliminary study that will be used as a template and learning process to create a future prospective study to investigate CT stealth and robotically guided screw placement versus "free hand" guided screws.

Reliability analysis of Cobb measurement in degenerative lumbar scoliosis using endplate versus pedicle as bony landmarks

OBJECTIVES

Degenerative changes of endplates in older patients and tilting of vertebral body in lumbosacral lordosis could make an accurate identification of endplates for the Cobb measurement difficult. Pedicles have been proposed as alternative landmarks because they are usually better visualized, and offer similar clinical validity to the endplates. The objective of this study was to investigate the reliability of the pedicle method of Cobb measurement in degenerative lumbar scoliosis and compare it with the traditional endplate method.

METHODS

Two hundred and eighty-four radiographs of degenerative lumbar scoliosis were evaluated. The radiographs were classified into groups based on the patient's age (< 60 years, 60 to 80 years, and > 80 years), level of lower end vertebra (LEV) (LEV at L5, and LEV at or above L4), and curve severity (< 20°, 20° to 40°, and > 40°). Three observers independently measured the radiographs using the endplate and pedicle methods twice with an interval of 1 week. The intra- and interobserver reliabilities were calculated using intraclass correlation coefficients (ICC).

RESULTS

The intra- and interobserver ICC values were better for all observers in the > 80 years age group using the pedicle method. The intraobserver ICC values of pedicle method were also better in the LEV at L5 group, and the interobserver ICC values showed a slightly better consistency with the pedicle method. For patients with > 40° curves, the intraobserver ICC values for all observers as well as interobserver ICC values were better using the endplate method.

CONCLUSION

The reliabilities of the endplate and pedicle methods for degenerative lumbar scoliosis were both excellent. The pedicle method might be better in older patients (> 80 years) and those with LEV at L5; while the endplate method could have some strength in severe cases (> 40°).

Radiographic anatomical relationship between spinous process and pedicle in thoracolumbar and lumbar spine

Pedicle screws are widely used in spinal surgeries, but it remains technically demanding to place. There are numerous studies on the anatomy of pedicle; however, there is very little insight on the relationship between the pedicle and the spinous process, which is an important part of the spinal posterior column.The aim of the study was to investigate the radiographic anatomical relationship between spinous processes and pedicles in the thoracolumbar and lumbar spine, in order to reveal a novel entrance point for pedicle screw insertion.Sixty candidates were enrolled in this study; cases were excluded with degenerative disorders and other disorders as osteoporosis, deformity, and tumor. Radiographs and computer tomography scans between T10 and L5 were obtained on each case. The distance was measured that between the superior margin of spinous process root and the superior border, the inferior border and the axis of pedicle. In laboratory, 5 fresh cadavers were used to imitate the pedicle screw insertion.The basic reference point was supposed as the intersection between the horizontal line of superior margin of spinous process root and the central vertical line of the superior facet. For T10 to T12, the pedicle axis was 5 mm beyond the reference point. For L1 to L4, the pedicle axis was at the reference point. At L5, the pedicle axis was 5 mm beneath the reference point. In laboratory, 80 screws were all inserted into pedicles successfully according to the newly referred entrance point.The study reveals the radiographic anatomical relationship between the pedicle and the spinous process. The pedicle axis is around the horizontal line of the superior margin of spinous process root. It provides a new anatomic mark of pedicle screw entrance point.

Resectable primary pleural myxoid liposarcoma with a pedicle: report of a rare case and literature review

Primary pleural myxoid liposarcoma is a rare tumor. Here, we report a primary myxoid liposarcoma occupying the majority of the left thoracic cavity with features suggesting invasion. Computed tomography (CT) at medical check-up incidentally revealed a bulky inhomogeneous fatty mass. The tumor's large size made a prediction of its resectability by preoperative CT difficult. The patient underwent an operation, which revealed that the tumor was attached to the pleura with a thin pedicle; the tumor was resected completely. Few therapies for pleural liposarcoma other than resection are available; hence, surgery should be considered even if the tumor's size implies invasion on radiological imaging. In this case report, we discuss the imaging findings of this case with a review of the related literature.

Predictive value of pedicle involvement with MRI in spine metastases

OBJECTIVES

The study aimed to retrospectively evaluate the accuracy and value of magnetic resonance imaging (MRI) in predicting pedicle involvement for patients with spine metastases.

METHODS

Forty-five patients with a vertebral metastasis encroaching at least one pedicle were studied using MRI before surgery and regularly after surgery. Patients were categorized on the basis of their numbers of pedicle involvement (Group 1: one pedicle was involved, n = 23; Group 2: two pedicles were involved, n = 22). The diagnostic accuracy was calculated, and comparisons of intraoperative blood loss and recurrence rate between the two groups were performed.

RESULTS

The overall performance of MRI in predicting the pedicle involvement was as follows: accuracy, 94.4%; sensitivity, 95.5%; and specificity, 91.3%. Less intraoperative blood loss was observed for Group 1 compared with Group 2 (1,661 ± 672 ml and 2,173 ± 790 ml, respectively, P = 0.024). Tumor relapse occurred in 8.7% (2/23) of Group 1 and in 22.7% (5/22) of Group 2 with median recurrence free survival time 14 and 9 months, respectively.

CONCLUSIONS

MRI is a reliable approach to assess pedicle involvement. It has potential for use in the evaluation of the clinical characteristics of patients with spine metastases.

Morphometric measurement of the cervical spine for minimally invasive pedicle screw fixation using reverse engineering and three-dimensional reconstruction

BACKGROUND

Percutaneous cervical pedicle screw fixation has been proven to be an effective method of cervical screw instrumentation, which has the advantages of less invasiveness and low blood loss. Emerging evidence has indicated that the cervical spinous process plays an important role in percutaneous spine surgery. However, there is a limited amount of information on the fundamental research of pedicle and its associated imaging parameter measurement. The purpose of this study was to measure the anatomic data of the pedicle screw channel (PSC) using reverse engineering and three-dimensional reconstruction, and also to discuss the three-dimensional relationship between the cervical spinous process and the pedicle screw channel.

METHODS

Twenty adult subjects (10 males, 10 females, age range 19-46 years) were studied using the method of three-dimensional CT reconstruction and reverse engineering. The centrum was divided into 10 equal parts from front to back. The bisectors were defined as borderline depths of the centrum, from front to back, 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 0% of borderline depths were presented. Then, a 3D coordinate system was constructed to measure all the data, including the radius of the inscribed circle, the length of the PSC, the insertion angle, the distances from entry point to cervical spinous process and skin depth. All the indexes were measured from 70% to 90% borderline depth.

RESULTS

The radius of the inscribed circles from C₃ to C₇ at 90% borderline depth were 2.94 ± 0.55 mm, 3.04 ± 0.40 mm, 3.15 ± 0.36 mm, 3.28 ± 0.47 mm, 3.89 ± 0.54 mm, respectively. The lengths of the PSC were between 25 and 32 mm. The insertion angles for 70% to 90% borderline depth were 28.33°, 34.28°, 37.92°, respectively. The relationship between the PSC and spinous process was measured as the distance from the entry point to the end of the spinous process, which were, respectively, 26.91 mm, 28.18 mm, 30.03 mm, 35.67 mm, 41.99 mm from C₃ to C₇ .The distance from the skin to the entry point of C_3-7 increased gradually.

CONCLUSIONS

The measurements of this study could provide detailed information for percutaneous cervical screw fixation. The data of the relationship between the cervical spinous process and the pedicle screw channel present valuable technical information for the design, optimization and clinical application of the aiming device for percutaneous cervical pedicle screw fixation. Copyright © 2016 John Wiley & Sons, Ltd.

Cervical pedicle morphometry in a Latin American population: A Brazilian study

The goal of this study was to conduct a detailed computed tomography (CT) assessment in the Brazilian population of the screw starting point, trajectory, and dimensions of pedicle in the cervical spine.Two hundred consecutive patients were retrospectively evaluated using cervical spine CT, with imaging reconstruction of each cervical vertebrae in the axial plane with 2 mm, and in sagittal reconstructions with 3 mm. Parameters in axial plane included the pedicle width (PW), pedicle axis length (PAL), pedicle transverse angle (PTA), and the distance from the entry point to the point between the lamina and spinous process (DEP). Measurements in the sagittal plane involved the pedicle height (PH) and the pedicle sagittal angle (PSA).The mean PW and PH were smaller in females than in males in all cervical vertebrae, but there were no significant differences of PTA among genders. PSA ranged from 15.2° to 23.7°. Mean values of PAL and DEP had a tendency to decrease from the proximal to distal cervical vertebrae. PW was <4 mm in 7.5% of men (C3) and 25% of women (C3), and <4.5 mm in 20% (C3 male) and 66% (C3 female). The intra- and inter-observer reliability were very good for the tomographic measurement of PW, and good for PH. For PAL, the intraobserver reliability was good, but the interobserver reliability varied from moderate to good. Considering PTA and PSA, the intraobserver reliability was good, but the interobserver reliability moderate for PTA and poor or fair for PSA. DEP measurements showed poor intraobserver reliability, and poor or moderate interobserver reliability.Our results presented similar trend of previous studies, but the frequency of patients with PW <4.5 mm in our population is higher, suggesting an increased risk during the attempting of transpedicular screw technique.

Pedicle screw placement in patients with variant atlas pedicle

Objective

To investigate how the anatomy of variant atlas vertebra impacts on the strategy used to place pedicle screws used to treat atlantoaxial instability.

Methods

The study enrolled patients with cervical instability who had a posterior arch pedicle height <3.5 mm at the anchor point, a vertebral artery groove height <3.5 mm, or both. Pedicle screws were fitted according to the anatomy of the variant atlas vertebra. Patients were followed-up to evaluate accuracy of the screw placement and maintenance of cervical stability.

Results

A total of 28 patients were enrolled. The mean height of the atlas pedicle proximal section was >5.0 mm. For the vertebral artery groove, the height of the lateral region was significantly greater than that of the medial region. Approximately 60% of atlas vertebrae had lateral heights >3.5 mm (34 of 56). The majority of the posterior arch heights were <3.0 mm. There were no perioperative or postoperative complications observed.

Conclusions

Pedicle screw placement in the lateral pedicle region is the safest and most reliable strategy to treat variant atlas pedicles.

Pedicle streaking: A novel and simple aid in pedicle positioning in free tissue transfer

Introduction:

The pedicle positioning in free tissue transfer is critical to its success. Long thin pedicles are especially prone to this complication where even a slight twist in the perforator can result in flap loss. Pedicles passing through the long tunnels are similarly at risk. Streaking the pedicle with methylene blue is a simple and safe method which increases the safety of free tissue transfer.

Materials and Methods:

Once the flap is islanded on the pedicle and the vascularity of the flap is confirmed, the pedicle is streaked with methylene blue dye at a distance of 6-7 mm. The streaking starts from the origin of the vessels and continued distally on to the under surface of flap to mark the complete course of the pedicle in alignment. The presence of streaking in some parts and not in rest indicates twist in the pedicle.

Observation and Results:

Four hundred and sixty five free flaps have been done at our centre in the last 5 years. The overall success rate of free flaps is 95.3% (22 free flap failures). There has not been a single case of pedicle twist leading to flap congestion and failure.

Conclusion:

This simple and novel method is very reliable for pedicle positioning avoiding any twist necessary for successful free tissue transfer.

A Rare Presentation of Cervical Spine Osteochondroma

INTRODUCTION

Cervical spine osteochondromas are rare tumors that usually involve the posterior spinal elements. Osteochondromas of the cervical spine presenting anteriorly as a mass over the supraclavicular region has not been reported in the literature.

CASE REPORT

A 12-year-old boy presented with right sided supraclavicular swelling. Plain radiographs revealed a bony mass. Computerized tomography (CT) and magnetic resonance imaging scans of the cervical region showed a bony mass arising from pedicle and encroaching onto lamina of C6 vertebra. He underwent excision biopsy of the mass through an anterior approach. The histopathological diagnosis was osteochondroma. At 4-year follow-up, he was asymptomatic and CT scan revealed no recurrence.

CONCLUSION

Tumors arising from the posterior elements are difficult to diagnose by plain radiographs alone and require special imaging modalities to show their exact location, nature, and extent.