Screw Path Research Articles

Combination of sacral-alar-iliac screw and cortical bone trajectory screw techniques for lumbosacral fixation: technical note.

Lumbosacral fixation plays an important role in the management of devastating spinal pathologies, including osteoporosis, fracture, infection, tumor resection, and spinal deformities, which require long-segment fusion constructs to the sacrum. The sacral-alar-iliac (SAI) screw technique has been developed as a promising solution to facilitate both minimal invasiveness and strong fixation. The rationale for SAI screw insertion is a medialized entry point away from the ilium and in line with cranial screws. The divergent screw path of the cortical bone trajectory (CBT) provides a higher amount of cortical bone purchase and strong screw fixation and has the potential to harmoniously align with SAI screws due to its medial starting point. However, there has been no report on the combination of these two techniques. The objective of this study was to assess the feasibility of this combination technique. The subjects consisted of 17 consecutive patients with a mean age of 74.2 ± 4.7 years who underwent posterior lumbosacral fixation for degenerative spinal pathologies using the combination of SAI and CBT fixation techniques. There were 8 patients with degenerative scoliosis, 7 with degenerative kyphosis, 1 with an osteoporotic vertebral fracture at L5, and 1 with vertebral metastasis at L5. Fusion zones included T10-sacrum in 13 patients, L2-sacrum in 2, and L4-sacrum in 2. No patients required complicated rod bending or the use of a connector for rod assembly in the lumbosacral region. Postoperative CT performed within a week after surgery showed that all lumbosacral screws were in correct positions and there was no incidence of neurovascular injuries. The lumbosacral bone fusion was confirmed in 81.8% of patients at 1-year follow-up based on fine-cut CT scanning. No patient showed a significant loss of spinal alignment or rod fracture in the lumbosacral transitional region. This is the first paper on the feasibility of a combination technique using SAI and CBT screws. This technique could be a valid option for lumbosacral fixation due to the ease of rod placement with potential reductions in operative time and blood loss.

Morphological Parameters of the Thoracic Pedicle in an Asian Population: A Magnetic Resonance Imaging-Based Study of 3324 Pedicles.

Study Design:A cross-sectional magnetic resonance imaging (MRI)–based anatomical study.Objectives:Instrumentation of the thoracic spine may be challenging due to the unique pedicle morphology and the proximity of vital structures. As prior morphological studies have mostly been done in Caucasians, our study aims to determine the optimal pedicle screw size for transpedicular fixation in an Asian population.Methods:A retrospective analysis of 400 patients who had undergone MRI of the thoracic spine was performed. A total of 3324 pedicles were included. Pedicle morphology was graded qualitatively based on the size of its cancellous channel, and quantitatively with the following parameters: pedicle transverse diameter, pedicle screw path length, and pedicle angle. Subgroup analysis based on gender was performed.Results:Mean pedicle transverse diameter was the narrowest at the T4 (2.9 ± 1 mm) and T5 (3.1 ± 1.1 mm) level. The mean pedicle screw path length progressively increased from T1 (34 ± 4.6 mm) to T12 (47 ± 4.6 mm). The mean pedicle angle was the largest at T1 (34° ± 7.9°) and decreased caudally, to 9.4° ± 3.8° at the T12 level. Females had significantly lower mean pedicle diameter and screw path length than males at every vertebral level; however, they had a larger pedicle angle at T8 to T10. The most common size of the pedicle cancellous channel was more than 4 mm.Conclusion:Morphological differences in the Asian pedicle suggest that caution needs to be taken during thoracic spine instrumentation, particularly in Asian females who have significantly smaller pedicles. In such cases, the use of alternative techniques or intraoperative navigation may be useful.

Correlation between the Computed Tomography Values of the Screw Path and Pedicle Screw Pullout Strength: An Experimental Study in Porcine Vertebrae.

Study DesignBiomechanical study.PurposeTo assess the correlation between the computed tomography (CT) values of the pedicle screw path and screw pull-out strength.Overview of LiteratureThe correlation between pedicle screw pull-out strength and bone mineral density has been well established. In addition, several reports have demonstrated a correlation between bone mineral density and CT values. However, no previous biomechanical studies investigated the correlation between CT values and pedicle screw pull-out strength.MethodsSixty fresh-frozen lumbar vertebrae from 6-month-old pigs were used. Before screw insertion, the CT values of the screw path were obtained for each sample. Specimens were then randomly divided into three equal groups. Each group had one of three pedicle screws inserted: 4.0-mm LEGACY (4.0-LEG), 4.5-mm LEGACY (4.5-LEG), or 4.5-mm SOLERA (4.5-SOL) (all from Medtronic Sofamor Danek Inc., Memphis, TN, USA). Each screw had a consistent 30-mm thread length. Axial pull-out testing was performed at a rate of 1.0 mm/min. Correlations between the CT values and pedicle screw pull-out strength were evaluated using Pearson’s correlation coefficient analysis.ResultsThe correlation coefficients between the CT values of the screw path and pedicle screw pull-out strength for the 4.0-LEG, 4.5-LEG, and 4.5-SOL groups were 0.836 (p<0.001), 0.780 (p<0.001), and 0.873 (p<0.001), respectively. Greater CT values were associated with greater screw pull-out strength.ConclusionsThe CT values of the screw path were strongly positively correlated with pedicle screw pull-out strength, regardless of the screw type and diameter, suggesting that the CT values could be clinically useful for predicting pedicle screw pull-out strength.

Establishing validity of the fundamentals of spinal surgery (FOSS) simulator as a teaching tool for orthopedic and neurosurgical trainees

BACKGROUND CONTEXTPedicle screw placement is a demanding surgical skill as a spine surgeon can face challenges including variations in pedicle morphology and spinal deformities. Available CT simulators for spine pedicle placement can be very costly and hands-on cadaver courses are limited by specimen availability and are not readily accessible. PURPOSETo conduct validation of a simulated training device for essential spine surgery skills. DESIGNCross-sectional, empirical study of physician performance on a surgical simulator model. SAMPLESpine attending physicians and residents from four different academic institutions across the United States. OUTCOME MEASURESPerformance metrics on two surgical simulator tasks. METHODSAfter IRB approval, an inexpensive ($30) simulator was developed to test two main psychomotor tasks (1) creation of the pedicle screw path with a standard gearshift probe without cortical breaks and (2) the ability to palpate for the presence or absence of cortical breaches as well as determine the location of wall defects. Orthopedic and neurosurgery residents (N=72) as well as spine attending surgeons (N=26) participated from four different institutions. To test construct validity, performance metrics were compared between participants of different training status through one-way analysis of variance and linear regression analysis, with significance set at p<.05. RESULTSSpine attending surgeons consistently scored higher than the residents, in the screw trajectory task with triangular base (p=.0027) and defect probing task (p=.0035). In defect probing, performance improved with linear trend by number of residency training years with approaching significance (p=.0721). In that task, independent of institutional affiliation, PGY-2 residents correctly identified an average of 1.25±0.43 fewer locations compared with attending physicians (p=.0049). More than 80% of the spine attendings reported they would use the simulator for training purposes. CONCLUSIONSThis low-cost fundamentals of spine surgery simulator detected differences in performances between spine attending surgeons and surgical residents. Programs should consider implementing a simulator such as fundamentals of spine surgery to assess and develop pedicle screw placement ability outside of the operating room.

Novel design for the adjustable knock-out mechanism with a Roberts linkage

This article presents a new adjustable knock-out mechanism of a bolt former with a Roberts linkage and an adjustable crank-rocker linkage. The design requirements of the new mechanism are based on the analysis of an existing adjustable knock-out mechanism. The new adjustable knock-out mechanism mainly consisting of a Roberts linkage, and an adjustable crank-rocker linkage is proposed to meet the specified requirements. The path of the knock-out screw is approximately a straight line and the method presented is illustrated by an example.

The Relationship of the Lapidus Intramedullary Nail to Neurologic and Tendinous Structures in the Foot: An Anatomic Study

Category:Bunion, Midfoot/ForefootIntroduction/Purpose:The lapidus procedure is a longstanding operation performed for the treatment of hallux valgus deformity with a concomitant hypermobile first ray. Orthopaedic surgeons have a myriad of options to choose from in performing the lapidus procedure. The implantation of orthopaedic implants comes with the risk of iatrogenic injury to surrounding anatomy. Several cadaveric studies in the humerus and femur have described potential neurovascular structures at risk during placement of intramedullary nail systems. The purpose of this study was to determine the proximity of nail insertion and interlocking mechanisms in the Lapidus Phantom Intramedullary Nail System (Paragon 28, Inc.) to neurologic and tendinous structures in the foot.Methods:A titanium intramedullary nail was inserted from the first metatarsal to the medial cuneiform spanning the first tarsometatarsal joint in 10 fresh-frozen cadaver feet. K-wires were inserted in the proximal lateral, proximal medial, and distal medial-to-lateral interlock screw paths. The tibialis anterior tendon, extensor hallucis longus tendon, and superficial peroneal nerve were carefully dissected and exposed, and the distance from each of these anatomic landmarks were then measured and recorded from four different aspects of the nail: Proximal lateral interlocking screw path, proximal medial interlocking screw path, nail insertion, distal interlocking screw path. Distances were averaged, ranges were determined.Results:The tibialis anterior tendon was in closest proximity to the proximal medial interlock K-wire with an average distance of 0.4 mm. The proximal medial interlock bisected the tibialis anterior tendon in three of the specimens. The extensor hallucis longus tendon was in closest proximity to the nail insertion with an average distance of 1.2 mm. A branch of the superficial peroneal nerve was in closest proximity to the distal interlock K-wire with an average distance of 7.5 mm, however, the nerve came in direct contact with the proximal medial interlock K-wire in two of the specimens.Conclusion:The Lapidus intramedullary nail’s proximal medial interlock screw poses the greatest threat to the tibialis anterior tendon, with the distance from the tendon to the interlock K-wire being 3 mm or less in all specimens tested. The extensor hallucis longus tendon is at risk of injury with insertion of the nail. Medial to lateral interlocking poses the greatest danger to a branch of the superficial peroneal nerve. Blunt dissection should be performed using this system with a path to bone before instrumentation to reduce the risk of nerve and tendon injury in the foot.

Anatomic study of the lumbar lamina for safe and effective placement of lumbar translaminar facet screws.

ObjectiveTo evaluate the anatomic characteristics of the lumbar lamina and suggest a safe and effective strategy for setting lumbar translaminar facet screws.MethodsThe width and length of the lumbar lamina, screw path, lateral angle of the lamina, and maximum and minimum caudal angles of the lamina from L3 to L5 were measured with Mimics software using 32 patients’ computed tomographic data.ResultsThe optimal screw entry point was located at the median of the spinous process base or slightly lower. The ideal screw trajectory was from the entry point to the base of the transverse process and across the center of the facet joint. A length of 35 to 45 mm was suitable for L3 to L4 in most cases, and a length of 45 to 50 mm was safe for L5 in most cases. The screw should be inserted at an angle of 49.4° to 59.29° laterally and 43.68° to 57.58° caudally at L3 to L5. For the ideal caudal angle, error of <3° was considered safe.ConclusionThe optimal entry point, ideal screw trajectory, ideal screw-setting angles, and safest range of the angle and length of the lumbar lamina were identified in this anatomical study.

Machine learning for automated 3-dimensional segmentation of the spine and suggested placement of pedicle screws based on intraoperative cone-beam computer tomography.

The goal of this study was to develop and validate a system for automatic segmentation of the spine, pedicle identification, and screw path suggestion for use with an intraoperative 3D surgical navigation system. Cone-beam CT (CBCT) images of the spines of 21 cadavers were obtained. An automated model-based approach was used for segmentation. Using machine learning methodology, the algorithm was trained and validated on the image data sets. For measuring accuracy, surface area errors of the automatic segmentation were compared to the manually outlined reference surface on CBCT. To further test both technical and clinical accuracy, the algorithm was applied to a set of 20 clinical cases. The authors evaluated the system's accuracy in pedicle identification by measuring the distance between the user-defined midpoint of each pedicle and the automatically segmented midpoint. Finally, 2 independent surgeons performed a qualitative evaluation of the segmentation to judge whether it was adequate to guide surgical navigation and whether it would have resulted in a clinically acceptable pedicle screw placement. The clinically relevant pedicle identification and automatic pedicle screw planning accuracy was 86.1%. By excluding patients with severe spinal deformities (i.e., Cobb angle > 75° and severe spinal degeneration) and previous surgeries, a success rate of 95.4% was achieved. The mean time (± SD) for automatic segmentation and screw planning in 5 vertebrae was 11 ± 4 seconds. The technology investigated has the potential to aid surgeons in navigational planning and improve surgical navigation workflow while maintaining patient safety.

Effectiveness analysis of three-dimensional printing assisted surgery for unstable pelvic fracture

To evaluate the effectiveness of three-dimensional (3D) printing assisted internal fixation for unstable pelvic fractures. The clinical data of 28 patients with unstable pelvic fractures admitted between March 2015 and December 2017 were retrospectively analyzed. The patients were divided into two groups according to different surgical methods. Eighteen cases in the control group were treated with traditional anterior and posterior open reduction and internal fixation with plate; 10 cases in the observation group were treated with 3D printing technology to make pelvic models and assist in shaping the subcutaneous steel plates of the anterior ring. Sacroiliac screw navigation template was designed and printed to assist posterior ring sacroiliac screw fixation. There was no significant difference between the two groups in gender composition, age, cause of injury, fracture type, and time interval from injury to surgery ( P>0.05). The operation time, intraoperative blood loss, intraoperative fluoroscopy times, incision length, waiting time for weight-bearing exercise, and fracture healing time were recorded and compared between the two groups. Majeed score was used to evaluate the function at last follow-up. At immediate after operation, the reduction was evaluated according to Matta imaging scoring criteria, and the success of sacroiliac joint screw implantation in the observation group was evaluated. The deviation of screw entry point and direction between postoperative screws and preoperative simulated screws were compared in the observation group. All the operation was successfully completed, and all patients were followed up 6-18 months (mean, 14.4 months). In the control group, 1 case had wound infection and 2 cases had deep vein thrombosis. No serious complication such as important blood vessels, and nerve injury and pulmonary embolism occurred in other patients in the two groups. No screw pulling out or steel plate breaking occurred. The operation time, intraoperative blood loss, fluoroscopy times, incision length, and waiting time for weight-bearing exercise of the control group were significantly more than those of the observation group ( P<0.05); there was no significant difference in fracture healing time between the two groups ( t=0.12, P=0.90). There was no significant difference in reduction quality between the two groups at immediate after operation ( Z=-1.05, P=0.30); Majeed score of the observation group was significantly better than that of the control group at last follow-up ( Z=-2.42, P=0.02). The success rate of sacroiliac joint screw implantation in the observation group reached category Ⅰ. In the observation group, the deviation angle of the direction of the screw path between the postoperative screw and the preoperative simulated screw implant was (0.09±0.22)°, and the deviation values of the entry points on the X, Y, and Z axes were (0.13±0.63), (0.14±0.58), (0.15±0.53) mm, respectively. There was no significant difference when compared with those before the operation (all values were 0) ( P>0.05). Computer design combined with 3D printing technology to make personalized pelvic model and navigation template applied to unstable pelvic fractures, is helpful to accurately place sacroiliac screw, reduce the operation time, intraoperative blood loss, and the fluoroscopy times, has good waiting time for weight-bearing exercise and function, and it is an optional surgical treatment for unstable fractures.

Feasibility of Transosseous Nonarticular Fixation of Lisfranc Injuries.

The optimal techniques for Lisfranc open reduction and internal fixation techniques remain debated. The purpose of the current study was to describe the joints involved in Lisfranc fixation and to determine if nonarticular transosseous internal fixation would be possible. Twenty cadaver Lisfranc joints were dissected and the articular cartilage was quantified by calibrated digital imaging software. Utilizing CT data, a computational model of the foot was developed and the mean joint surface was mapped and nonarticular screw paths between bones was determined. For the medial-middle cuneiform (C1-C2) connection, 27.3% of the lateral face of C1 and 43.7% of the medial face of C2 was articular cartilage. Three variations of articular morphology were observed on C1 and 2 on C2. From the 3D models, it was determined that a joint-sparing, transosseous screw trajectory was possible between C1 and the second metatarsal and between C1 and C2. These screw paths were large enough to accommodate clinically useful screw diameters (>5 mm). The screw trajectories were roughly perpendicular to the long axis of the foot and take a plantar-medial to dorsal-lateral orientation. The articular surface of the Lisfranc joint was quantified for the first time and may be smaller than some surgeons realize. This study demonstrated the orientation required to minimize articular damage. The clinical significance of the current study was that a nonarticular screw trajectory was possible, and this information may help guide the placement of these screws.

Robot assisted sacroiliac screw placement with a modified method of screw path planning

Objective: To introduce a robot-assisted modified method of sacroiliac screw path planning in order to reduce the incidence of screw misplacement. Methods: The study involved 13 patients suffering from posterior pelvic injuries treated by percutaneous sacroiliac screw in Yantai Shan Hospital from August 2016 to May 2018. The patients included 9 males and 4 females, aged from 18 to 70 years (mean age 46.2 years). Causes of injury were traffic accidents (n=7), crushing injury (n=4) and fall from height (n=2). According to AO classification, 8 cases were classified with type B fractures (3 with type B1 and 5 with type B2), and 5 cases with type C fractures (2 with type C1, 1 with type C2, 2 with type C3). All the patients were treated by robot-assisted percutaneous sacroiliac screws (AO cannulated screws with a diameter of 7.3 mm) with an improved method of screw path planning. The screw placement time, blood loss, postoperative neurological, vascular and visceral function etc were observed. X-ray and CT were checked in the follow-up after the operation. Visual analogue scale (VAS) score was used to assess the pain degree of patients one week after the surgery. Results: All the sacroiliac screws were successfully implanted once with the robot-assisted improved method of screw path planning. The mean placement time of single screw was 15.9 min and the mean blood loss for single screw placement was less than 1 ml. No clinical manifestations of injuries of blood vessels, internal organs and lumbosacral nerve was found after the operation. The postoperative X-ray films and CT showed that none of the sacroiliac screws wore out the sacral body or the sacral wing's frontal cortex. Also, it was found that none of the sacroiliac screws strayed into the sacral canal and the intervertebral space. The mean VAS score decreased from preoperative 6.9 (4-10) to postoperative 1.8(0-3). Conclusion: The robot-assisted improved method of screw path planning contributes to safe and accurate sacroiliac screw placement.

The Relationship of Multiplanar Distal and Uniplanar Proximal Interlocking Screws to Neurovascular Structures with the Depuy Synthes Humeral Nail-EX: An Anatomic Study.

To determine the proximity of neurovascular structures to multiplanar distal interlocking screws and proximal interlocking devices for an antegrade inserted humeral nail. Humeral nails (Depuy Synthes Humeral Nail-EX, Paoli, PA) were inserted into 10 matched cadavers with 3 distal interlocking trajectories: anterior to posterior (A-P), anterolateral to posteromedial, and anteromedial to posterolateral (AM-PL). The distance of the screw path and screw head to the radial, lateral antebrachial cutaneous nerve (LACN), and median nerves and the brachial artery was measured. Proximally, the distance of spiral blades and/or interlocking screws to the axillary nerve was measured. The median distance of the screw path/screw head inserted (A-P) to the LACN was 0 mm/0 mm in the left arm and 3.5 mm/1.6 mm in the right arm. The median distance of the screw path/screw head inserted AM-PL to the median nerve was 7.08 mm/0 mm in the left arm and 0 mm/0.12 mm in the right arm. The median distance of the screw path/screw head inserted AM-PL to the brachial artery was 4.05 mm/3.83 mm in the left arm and 2.19 mm/2.84 mm in the right arm. The humeral head was radiographically divided into 3 zones. The average distances of the axillary nerve to interlocking devices placed into zone 2 and zone 3 of the humeral head are 14.65 mm and 1.07 mm, respectively. When using the DePuy Synthes Humeral Nail-EX, AM-PL screws may risk the median nerve and brachial artery; thus, this trajectory is not recommended. The LACN may be at risk with A-P and to a lesser degree, anterolateral to posteromedial screws. Proximally, interlocking devices in zone 3 of the humeral head may risk the axillary nerve.

Wednesday, September 26, 2018 2:00 PM – 3:00 PM Integrating Technology into Practice: 58. Validity of the Fundamental of Spinal Surgery (FOSS) simulator as a teaching tool for orthopedic and neurosurgical trainees

BACKGROUND CONTEXT While all surgical disciplines require years of study to acquire knowledge and experience, surgical trainees must also develop the necessary psychomotor skills to perform surgical procedures. To date, there are limited validated tools to objectively assess trainees as they progress through their education. Pedicle screw placement is a demanding surgical skill set to learn and teach as challenges such as variations in pedicle morphology and spinal deformities can be encountered. Available CT simulators for pedicle placement can be costly and hands on cadaver courses are limited by specimen availability. PURPOSE We sought to develop a cost-effective training tool that could be used by all orthopedic and neurosurgical residencies. STUDY DESIGN/SETTING Multicenter study (four academic institutions). PATIENT SAMPLE Orthopedic and neurosurgery residents and spine attending surgeons are recruited. OUTCOME MEASURES Outcomes measures include the scores for all three tasks and the time taken to complete the tasks. METHODS After IRB approval, a low cost spine simulator ($30.00) was created to test three main skill sets all pertaining to the task of placing a pedicle screw: ability to find appropriate trajectory, ability to navigate down the isthmus of a pedicle, and ability to recognize wall penetrations. Residents as well as spine attending surgeons were recruited to participate from four different institutions. Each participant was given three tasks to complete. Task 1 entails creation of the pedicle screw path with a standard gearshift probe, with the number of “cortical breaks” being recorded. Task 2 entails testing the ability to palpate for the presence or absence of wall defects. Task 3 is the ability to determine the location of wall defects. The number of correct answers for task 2 and 3 are recorded. RESULTS The ability to differentiate between surgical residents and master spine surgeons was obtained. In all tasks, spine attending surgeons scored higher than residents. Attending surgeons reported that FOSS simulator is a good tool which can be beneficial for training surgical residents in terms of tactile feedback and directionality of probe and pedicle placement. Moreover, the FOSS stimulator also allowed participants the ability to feel the difference between young cortical bone versus osteoporotic bone. Eighty-one percent of the spine attending surgeons reported that they would use this educational technology in the future for training purposes. Eighty-four percent of all residents, and 100% of PGY1 residents reported that they would use FOSS simulator for training. CONCLUSIONS Recent published work has demonstrated the role of low cost tools for teaching and testing psychomotor skills in orthopedic surgery. Here, we developed the next tool to be used for spine surgery. FOSS is an invaluable asset as it will allow surgical trainees to engage and enhance their visual, auditory and proprioceptive feedback safely during pedicle screw placement outside of the operating room. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Accuracy of robot-assisted pedicle screw insertion in adolescent idiopathic scoliosis: is triggered electromyographic pedicle screw stimulation necessary?

Screw malpositioning is an identifiable cause of intraoperative neurophysiologic changes. Although triggered screw electromyography (t-EMG) has been found to exhibit high sensitivity for identifying malpositioned screws, no previous study has assessed the utility of combining t-EMG with robotic-assisted pedicle screw placement for identifying malpositioned screws. We sought to evaluate the utility of t-EMG used in combination with robotic-assisted pedicle screw placement for identifying malpositioned screws in patients with adolescent idiopathic scoliosis (AIS). Patients undergoing robotic-assisted posterior spinal fusion with pedicle screw fixation for AIS underwent retrospective review from a single surgeons prospectively collected database. Preoperative demographic data and curve characteristics were recorded. Computed tomography (CT) scans were reviewed, measuring pedicle width and classifying pedicle morphology using the channel classification system. Pedicle data was compared against intra-operative t-EMG data, with a minimal threshold of 8 mA used for screw removal and screw path examination and the rate of screw re-direction recorded. All pedicle screws were verified using image intensification. Forty-nine patients (11 males, 38 females, average age 14.49 years) with an average curve magnitude of 51 degrees and placement of 844 pedicle screws to attain an average curve correction of 67.7%. The incidence of an absent pedicle (type C or D morphology) was 2%. Overall, 24 screws (2.8%) were identified with an abnormal t-EMG threshold. All screws were found to have an intact medial wall upon probing and were reinserted without re-direction. No patient or curve characteristic was predictive of abnormal t-EMG amplitude but smaller pedicles correlated with smaller amplitudes. With precise pre-operative planning, robotic-assisted pedicle screw placement has shown to be a safe and effective method in treating AIS patients as shown by the lack of medial pedicle breach and malpositioned screws. We found no evidence to support combined use of t-EMG for identifying medially malpositioned screws.

Morphometry of the lower thoracic and lumbar pedicles and its relevance in pedicle fixation.

To assess the pedicle morphology in the lower thoracic and lumbar spine in an Indian population and to determine the causes of pedicle wall violation by pedicle screws. Computerised tomographic scans of 135 consecutive patients with thoracolumbar and lumbar spine fractures were prospectively analysed to determine the pedicle morphology. The transverse pedicle angle, pedicle diameter and screw path length at 527 uninjured levels were measured. Post-operative CT scans of 117 patients were analysed to determine the accuracy of 468 pedicle screws at 234 vertebrae. The lowest (mean±SD) transverse pedicle width in the lower thoracic spine was 5.4±0.70mm, whereas in the lumbar spine it was 7.2±0.87mm. The shortest (mean±SD) screw path length in lower thoracic pedicles was 35.8±2.10 and 41.9±2.18mm in the lumbar spine. The mean transverse pedicle angle in the lower thoracic spine was consistently less than 5°, whereas it gradually increased from L1 through L5 from 8.5° to 30°. Forty-one screws violated the pedicle wall, due to erroneous angle of screw insertion. In the current study, pedicle dimensions were smaller compared to the Western population. In Indian patients, pedicle screws of 5mm diameter and 30mm length, and 6mm diameter and 35mm length can safely be used in the lower thoracic and lumbar spine, respectively. However, it is important to assess the pedicle morphology on imaging prior to pedicle fixation.

Anatomical Consideration for Posterior Atlantoaxial Transarticular Screw Fixation from Reformatted Two-Dimensional CT Images

Background: Posterior transarticular C1-C2 fixation by screw is a widely used technique to correct atlantoaxial instability. However, the screw trajectory must be precise because the adjacent vital organs include the spinal cord and vertebral artery in the transverse foramen. Due to the lack of an objective measuring method, clarifying the range of the safe zone of screw trajectory in both the sagittal and coronal planes is important. Objective: To clarify the safe zone and ideal trajectory for screw fixation ensuring safety and without violating the transverse foramen and spinal canal. Methods: Radiographs of the normal upper cervical spine and coronal reconstruction CT scans from the entry point of the screw on C2 was performed and the safe zone for the screw path was drawn. The points of screw intersection on the superior articular surface of C2 were measured from the posterior rim of the superior articular surface of C2 then the safe zone of the screw in the coronal plane was drawn in the coronal oblique plane along the screw direction. Results: Average safe zone in the sagittal plane was 51.6 – 61.2 relative to the superior articular of C2 and the safe zone in the coronal view was medially 9.5 and laterally 4.2 relative to the midline of the spinous process. The safe zone and ideal screw trajectory should intersect C2 at 8.03 and 4.5 mm from the posterior rim of the superior articular surface on C2. Conclusion: The result of this study showed the range of the safe zone of the posterior atlantoaxial screw trajectory that guides to minimize the risk of misdirection and violating the transverse foramen by the screw. The areas on the superior articular of C2 intersected by the trajectories making the longest paths are guides to purchase the longest path of bone to achieve more stability and pullout strength

Anatomic parameters of the sacral lamina for osteosynthesis in transverse sacral fractures.

To analyze the morphometric parameters of the dorsal sacral lamina and pedicles to determine if there is adequate bony architecture to support plate osteosynthesis. Two reviewers performed measurements on 98 randomly selected high-resolution CT scans of the pelvis to quantify the bony anatomy ofthe sacral lamina. Measurements included the depths of the lamina at each sacrallevel, the trajectory and depth of the sacral pedicles from the sacral lamina, and the width of the sacral canal. A bone mineral density analysis was performed on the sacral lamina using Hounsfield units (HU) and compared to the L1 and S1 vertebral bodies. The sacral lamina were found to form peaks and troughs which we refered to as major and minor sections.Onaverage, thethicknesswas > 4mm at all major screw starting points, indicating adequate geometry for screw fixation. The sacral pedicle depths were 27, 18, 16, and 14mm at S2-S5, respectively. The average angulation from midline of this screw path directed laterally to avoid the sacral canal was 20°, 17°, 8°, and - 8° for the S2-5 pedicles, respectively. Average sacral canal diameter was 11mm for S2 and 8mm for S3-5. The sacral lamina had an average bone mineral density of 635 HU, which was significantly different from the density of the L5 (220 HU) and S1 (165 HU) vertebral bodies (p < 0.005).This morphometric data was used to pilot a new plating technique. The sacral lamina offers a novel target for screw fixation and meets the basic geometric and compositional criteria for screw purchase. To our knowledge, this study represents the first morphometric analysis performed on the sacral lamina and pedicles for plate application.

Achieving interfragmentary compression without special drilling technique or screw design.

this study demonstrates that compression is generated using fully threaded screws without using a predrilled glide hole. The insertional torque required to generate compression with fully threaded screws is increased but is clinically applicable. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1099-1105, 2018.

The effect of the parameters of posterior occipital condylar screws on the safety of screw placement

Objective To investigate the safety of the occipital condylar screw with vertical position and evaluate the selection strategy of the posterior approach of the posterior occipital condylar screw in Chinese people. Methods The clinical imaging data of 60 outpatients from September 2013 to September 2015 were retrospectively analyzed, 36 male and 24 female, the average age was 41.6±9.2 (range from 25-58), Excluded occipitocervical injury, tumor and deformity patients. We built a three-dimensional digital model and simulated placing screw by utilizing CT data on Mimics software, after that we took the occipital condyle posterior medial and lateral midpoint as the entry point, then made 2 points equidistantly to the midpoint in vertical direction. We put 3.5 mm diameter virtual screws in 4 different conditions: largest cranial angle, smallest cranial angle, longest screw path and shortest screw path. Then we assessed the anatomical relationship between the screw and the hypoglossal canal or the atlanto-occipital joint by a three-dimensional window and measured the cranial angle, medial angle and length of screw path, then calculated the safety angle of the cranial angle, the successful rate of setting screw, and compared the safety of different screw points by 3-Matic software. Results 120 occipital condyles were obtained from the CT data of 60 patients by Mimics software. There was no significant difference in the data of the cranial angle, medial angle, safety range and length between both left and right sides. The obtained safe cranial angle of each point respectively was 20.9°±6.0° (lowest point), 17.0°±6.2° (middle point), and 11.6°±7.1°(top point), obviously the largest angle was in the lower point and the smallest was in the top point. The difference was statistically significant. We then acquired the successful rates of different cranial angle of each point, the highest successful rate was 99.17%, 96.67%, 74.17% in lowest, middle and top point when cranial angle were 3°or 4°, 3°and 0°respectively. The successful rates of lower point and middle point were significantly higher than the top point, and the difference was statistically significant. The medial angle parameters obtained were 34.41°±2.59° on left and 34.06°±2.44° on right, and there was no significant difference. The length parameters of the longest screw path acquired were 23.09±1.47 mm, 22.84±1.40 mm and 23.15±1.45 mm at top, middle and lowest entry point. The average value of shortest screw path of each point was 21 mm, and there was no significant difference among every entry point. Conclusion Among the occipital condyle posterior screw entering points, selecting the lower point can improve the success rate and safety; the change of nail enter point in the vertical direction has little effect on the length of the nail. We can increase the safety and reduce the risk of occipital condylar screw placement as far as possible through the three-dimensional digital technology. Key words: Internal fixators; Cervical vertebrae; Image processing, computer-assisted; Treatment outcome

Spontaneous Core Rotation in Ferrofluid Pipe Flow.

Ferrofluid flow along a tube of radius R in a constant axial magnetic field is revisited. Our analytical solution and numerical simulations predict a transition from an initially axial flow to a steady swirling one. The swirl dynamo arises above some critical pressure drop and magnetic field strength. The new flow pattern consists of two phases of different symmetry: The flow in the core resembles Poiseuille flow in a rotating tube of the radius r_{*}<R, where each fluid element moves along a screw path, and the annular layer of the thickness R-r_{*}, where the flow remains purely axial. These phases are separated by a thin domain wall. The swirl appearance is accompanied with a sharp increase in the flow rate that might serve for the detection of the swirling instability.