Laminar Screws Research Articles

Philosophies And Surgical Techniques on Os Odontoideum Treatment with Literature Review.

Os-odontoideum is a rare condition described radiographically and clinically as a congenital anomaly of the second cervical vertebra (axis). It is a smooth, independent ossicle of variable size and shape separated from the base of a shortened odontoid process by an obvious gap, with no osseous connection to the body of C2. This study reviewed the literature on OO to evaluate its etiology, clinical presentations, differential diagnosis, imaging modalities, and outcomes in the management of asymptomatic and symptomatic cases of Os Odontoideum. Key articles from PubMed, EMBASE, Google Scholar, and Cochrane were searched. Considering etiology, the traumatic hypothesis is favoured over the congenital hypothesis as per recent literature on OO. Clinical presentation varies from asymptomatic to mild neck pain to severe myelopathy and neurodeficit. Various C1-C2 instrumentation and fusion techniques like wiring, trans articular screw and laminar screws have been described with success rates. Os odontoideum is a rare condition with limited existing literature. Considering the significant risks involved if conservative management opts, like severe neuro deficit to sudden death on trivial trauma and the recent improvement of imaging tools helping to understand the pathology of the disease, surgery can be indicated even in an incidentally detected os odontoideum. However, a case-by-case approach can be considered for stable asymptomatic patients depending on factors such as age, activity level, comorbidities, syndromic association, and radiographic findings.

Evaluation of the Bone Union Occurring Subsequent to C1-2 Fusion Combined With C1 Laminectomy for the Surgical Treatment of Retro-Odontoid Pseudotumor.

Introduction Surgical treatments for retro-odontoid pseudotumors (ROPs) include C1 laminectomies and C1-2 and occipitocervical (OC) fusions. When a C1 laminectomy is combined with a C1-2 fusion, concerns arise regarding an increased risk of pseudarthrosis due to decreased bone grafting space. Extension of the fusion area to the OC region may be considered to ensure an adequate bone graft bed. However, this procedure is associated with a risk of complications. Thus, in this study, we investigated the bone fusion and clinical outcomes of C1-2 fusion combined with a C1 laminectomy. Methods Between January 2017 and December 2022, seven patients with ROPs who had undergone C1-2 fusion combined with a C1 laminectomy were included in the study. All patients were followed up for >1 year. Bone fusion was evaluated by computed tomography (CT) at one year postoperatively, while implant failure was assessed by radiography at the final follow-up. Clinical evaluations included preoperative and one-year postoperative Japanese Orthopaedic Association (JOA) scores and recovery rates. Results This study included five male and two female patients, with an average age of 71.9 years. The average follow-up duration was 3.3 years. The primary anchor choices included the C1 lateral mass screw and the C2 pedicle screw. In one case, the transarticular screw was utilized unilaterally, and in another case, a lamina screw was utilized unilaterally. One year postoperatively, CT revealed bone fusion in three of the seven patients. Fusion occurred at the lateral and median atlantoaxial joints in two cases and one case, respectively. Screw loosening was observed in one case. None of the patients required reoperations. The average JOA recovery rate was 34.6%. Conclusion This surgical technique is useful for stabilizing and decompressing the C1-2 region while preserving mobility at the OC joint. However, further long-term follow-up studies are required.

Feasibility of C2 Lamina Screw Placement in a New Zealand Cohort: Computed Tomography Analysis According to Ethnicity and Gender.

Previous analyses have suggested variations in cervical spine canal morphology according to ethnicity, possibly in part due to variations in the posterior elements. The potential for these variations to affect the placement of instrumentation is uncertain. The aim of this study was to report on the feasibility of C2 lamina screw insertion in a New Zealand cohort including analysis of Māori, the indigenous people of New Zealand. A trauma computed tomography database was accessed to identify suitable images. On axial images, where the isthmus was at its widest, the outer diameter (OD) and inner diameter (ID) of the lamina were measured. Screw length was measured from a proposed entry point to the contralateral junction of the lamina and lateral mass. The spinolaminar angle was measured as the angle subtended by the screw trajectory and midsagittal plane. A 5.5-mm OD was accepted as a threshold for the feasibility of lamina screw placement. One hundred eighty-seven images were assessed: 115 New Zealand European and 72 Māori. The mean age of the cohort was 41.9 years (SD 19.6), and most patients (64%) were men. For the entire cohort, mean OD was 6.6 and 6.8 mm on the right and left, respectively; the mean inner diameter was 3.5 and 3.8 mm; mean screw length was 31.5 and 31.5 mm; and mean spinolaminar angle was 46.0° and 46.1°. C2 lamina screw placement was feasible in a majority of patients. Considering only Māori patients, placement was feasible in 96% of right and 94% of left laminae in men but 72% of right and 72% of left laminae in women. In a majority of patients, C2 lamina screw placement is feasible. However, advanced imaging must be carefully assessed preoperatively because data suggest that Māori women may not necessarily have optimal anatomy.Clinical RelevanceCare needs to be taken when assessing and planning surgery inpatients of different ethnicities because variations may exist in the morphology of the posterior elements of C2, leading to variation in optimal fixation strategy.Level of Evidence3.

C2 Vertebra: An Enigma for Young Spine/Neurosurgeons

Abstract Background Instrumentation of C2 vertebra is considered the most difficult for young neurosurgeons and trainees due to its complex anatomical structures, variety of surgical approaches and techniques, and proximity to important neurovascular structures. Key points from a surgical perspective for midline posterior approach is described in the era of neuroradiological advancements. Method Computed tomography angiographies (CTAs) of a total of 92 patients were evaluated with special attention to the key findings for insertion of screws for craniovertebral junction (CVJ) fixations. All these patients were operated though midline posterior approach in past 4 years. Results CTAs included various CVJ disorders, which included traumatic (n = 14), congenital (n = 55), and rheumatoid arthritis (n = 2) patients. Established landmarks for screw insertion sites do not prove safe for congenital anomalous CVJ conditions. Instead of highlighting screw insertion entry points, part of the corridor, which is relevant, should be stressed up on. Conclusion Midpoint of portion of bone segment medial to vertebral artery foramen should be the focus, which is important for pars interarticularis (and transarticular) and pedicle screws. A laminar screw should cross the midpoint of the lamina on each side.

Radiologic Examination of High Riding Vertebral Artery and Analysis of Secure Areas

ObjectiveTo radiologically examine the pedicle, lamina, and vertebral artery foraminal anatomies at the C2 vertebra for pedicular and laminar screw instrumentation at the axis in a Turkish population. Materials and MethodsFrom 2018 to 2019, we evaluated 100 patients who underwent cervical computed tomography (CT) for various reasons (excluding cervical pathologies) at Marmara University Hospital. The C2 pedicles were measured on CT images using measurement tools. In addition, axial computed tomography was performed at 0.1-mm intervals. Bilateral measurements were performed for each case. ResultsThe median right and left pedicle axial diameters were respectively 5.01 and 5.09 mm for the male patients and 4.31 and 4.38 mm for the female patients, showing a statistically significant difference between the sexes (p < 0.01). Of the patients, 15% had narrow pedicles. The pedicle sagittal diameters were smaller than 5 mm in 30% of the computed tomographic series. The internal height was <2 mm in 4% of the cases. ConclusionOur findings suggest significant individual and sex-related differences. Vertebral artery groove anomalies are commonly observed. Before performing a posterior craniocervical instrumentation surgery, a CT examination is beneficial because high-riding vertebral arteries must be kept in mind in determining the appropriate screw diameter and screw trajectory.

The Feasibility of Multiple Fixation Points in C2.

Analysis using three-dimensional simulation software for spinal screw placement and computed tomographic scan images. To assess the feasibility of achieving multiple (three or four) screw fixation points in C2 vertebra by using a combination of pedicle and laminar screws. Secure C2 fixation using multiple screws is required or beneficial in some unique cases. However, to the best of our knowledge, there have been no reports analyzing the feasibility of multiple screw fixation in C2. We used 1.0-mm interval computed tomographic scan images of 100 patients (50 men and 50 women) and screw trajectory simulation software. The diameter of all screws was set at 3.5 mm, considering its common usage in real surgery. The anatomical feasibility of placing both pedicle and laminar screws on the same side was evaluated. For all feasible sides, the three-dimensional distance between the screw entry points was measured. In 85% of cases, both pedicle and laminar screws could be placed on both sides, allowing for the insertion of 4 screws. In 11% of cases, 2 screws could be placed on one side, while only 1 screw was feasible on the other side, resulting in the placement of 3 screws. In all 181 sides where both types of screws could be inserted, the distance between their entry points exceeded 16.1 mm, which was sufficient to prevent the collision between the screw heads. C2 vertebra can accommodate three (11%) or four (85%) screws in 96% of cases.

Anatomical study of the technique of the axis laminar screws and development of guide

PurposeTo develop a bidirectional slide guide to assist screw placement in the axial lamina and to preliminarily discuss the accuracy and feasibility of auxiliary screw placement.MethodsCT data from 40 randomly selected patients were imported into the software for modelling, and cross-pinning was used to simulate pinning. According to the different crossing methods of the upper and lower laminar screws, they are divided into two groups. In the software, the position of the needlepoint of each screw is accurately measured, and the needle point is kept unchanged to simulate the movable range of the screw tail under the condition that the body does not penetrate the cortical bone. The data were compared by grouping and gender. Finally, the guide was designed by combining the screw exit point and fine adjustment angle data of all patients with the centripetal principle of the slide rail.ResultsThe needle exit data L1/L2/L3/L4 were 6.44 ± 0.52 mm, 7.05 ± 0.48 mm, 3.55 ± 0.75 mm and 5.09 ± 0.74 mm, respectively, and the fine adjustment angle of the slide rail was 10.51° ± 0.87°. There was no significant difference between the two groups or between men and women (p > 0.05).ConclusionIn this experiment, using the data obtained from the simulation of screw insertion, a two-way slide guide was designed to assist the insertion of axial laminar screws. The guide locks the screw outlet point to position and guides the screw inlet point, which improves the accuracy and safety of screw placement.

A Novel Trajectory of C7 Laminar Screws Determined Using Three-Dimensional Computed Tomography and Surgical Simulation Software: Comparison with a Pre-existing Trajectory.

Examination using three-dimensional screw trajectory software and computed tomographic scans. To evaluate the feasibility of a novel trajectory for C7 laminar screws and to compare it with an old trajectory. The previously reported trajectory of C7 laminar screws has a horizontal direction without a fixed target point. Our new trajectory has a cephalad direction with a fixed target point. Computed tomographic scans of a total of 50 male and 50 female patients were utilized. The placement of C7 laminar screws was activated employing the new and old trajectories. The success rate, the causes of failure, and the maximum allowable length of each trajectory were compared. Employing the new trajectory, the success rates of the unilaminar and bilaminar screws were 93% and 83%, respectively, which were significantly better than the old trajectory (80%, p<0.0001 and 70%, p=0.0003). The most prevalent cause of failure was laminar cortical breach followed by facet joint violation. The new trajectory also offered significantly longer maximum allowable screw length in unilaminar (32.5±4.3 mm vs. 26.5±2.6 mm, p<0.001), bilaminar cephalic (29.5±3.8 mm vs. 25.9±2.6 mm, p<0.0001) and bilaminar caudal (33.1±2.6 mm vs. 25.8±3.1 mm, p<0.001) screws than the old trajectory. With the new and old trajectories, 70% vs. 6% of unilaminar, 60% vs. 2% of bilaminar caudal, and 32% vs. 4% of bilaminar cephalic screws could be protracted perfectly into the corresponding lateral mass without any laminar cortical or facet joint violation (p<0.0001). The novel trajectory possesses a substantially higher success rate, longer maximum allowable screw length, and higher chance to be extended into the lateral mass (a condition known as a lamino-lateral mass screw) than the old trajectory.

Biomechanical Comparison of Facet Versus Laminar C2 Screws.

Transpedicular or transisthmic screws for C2 instrumentation represent the gold standard; however, the anatomy is not always compatible (hypoplastic pedicles, procidentia of the vertebral artery). Laminar screws (LS) have been proposed as a rescue technique and recently, bicortical facet screws (FS). To date, the biomechanical property of FS remains unknown. To compare the pull-out resistance of bicortical facet (FS) vs laminar (LS) C2 screws. Thirty-two human cadaveric C2 vertebrae were screened by CT scan imaging and dual x-ray absorptiometry before receiving both techniques and were randomized according to side and sequence (FS or LS first). Screw positioning was validated using 2-dimensional x-rays. Sixty-four mechanical tests were performed using pure tensile loading along the axis of the screws until pull-out. Mean pull-out strengths were compared using paired tests, multivariate and survival analysis (Kaplan-Meier curves). The morphometric data were consistent with previous studies. Over 64 tests, the mean pull-out strength of LS (707 ± 467 N) was significantly higher than that of FS (390 ± 230 N) ( P = .0004). Bone mineral density was weakly correlated with pull-out strength (r = 0.42 for FS and r = 0.3 for LS). Both techniques were mechanically equivalent for vertebrae in which intralaminar cortical grip was not achievable for LS. The mean pull-out strength for LS with laminar cortical grip (1071 ± 395 N) was significantly higher than that of LS without (423 ± 291 N) ( P < .0001). Our results suggest that bicortical FS of C2 offer less mechanical resistance than LS.

Posterior Atlantoaxial Screw Placement in a Portuguese Population: A Morphometric Analysis Based on Computed Tomography Scan Measurements.

Objective The present study aims to evaluate the screw length and trajectory angles for posterior atlantoaxial fixation in a Portuguese population, through the study of cervical computed tomography (CT) scans. Methods Cervical CT scans of 50 adults were measured according to predefined screw trajectories of C1-C2 transarticular (C1C2TA), C1 lateral mass (C1LM), C2 pedicle (C2P), C2 pars and C2 laminar (C2L) screws. For each of these trajectories, screw length and angles were measured and compared between males and females. Results For the C1C2TA screw trajectory, the mean length, medial, and cranial angles were 34.12 ± 3.19 mm, 6.24° ± 3.06, and 59.25° ± 5.68, respectively, and for the C1LM screw trajectory, they were 27.12 ± 2.15 mm, 15.82° ± 5.07, and 13.53° ± 4.80, respectively. The mean length, medial, and cranial angles for the C2P screw trajectory were 23.44 ± 2.49 mm, 27.40° ± 4.88, and 30.41° ± 7.27, respectively; and for the C2 pars screw trajectory, they were 16.84 ± 2.08 mm, 20.09° ± 6.83, and 47.53° ± 6,97. The mean length, lateral, and cranial angles for the C2L screw trajectory were 29.10 ± 2.48 mm, 49.80° ± 4.71, and 21.56° ± 7.76, respectively. There were no gender differences except for the lengths of the C1C2TA ( p = 0,020) and C2L ( p = 0,001) screws, which were greater in males than in females. Conclusion The present study provides anatomical references for the posterior atlantoaxial fixation in a Portuguese population. These detailed data are essential to aid spine surgeons to achieve safe and effective screw placement.

Accuracy of Patient-Specific Drill Guide Template for Bilateral C1-C2 Laminar Screw Placement: A Cadaveric Study

We sought to evaluate the accuracy of using patient-specific drill guides to place bilateral laminar screws in C1 and C2. Nine cervical specimens (8 males; mean age: 66.6 [56-73]) with the occiput attached (C0-C3) were used in this study. Preoperative computed tomography (CT) scans were used to create digital anatomic models for templating and guide creation. A total of 36 screws were placed with the aid of 3-dimensional printed, patient-specific guides (2 screws at C1 and C2). Postoperative CT scans were performed following screw insertion. The planned and actual trajectories were compared using preoperative and postoperative imaging based on the angular and entry point deviation. After screw placement and postoperative imaging, each specimen was dissected and performed a visual inspection for breaches. No breaches or violations were observed on postprocedural CT and visual inspection. The average variation of the entry point in the X, Y, and Z axes was 0.3 ± 0.28, 0.41 ± 0.38, and 0.29 ± 0.24, respectively. No statistically significant difference (P > 0.05) was observed between the planned and obtained entry points. There was no significant difference (P > 0.05) in the deviation analysis between the planned and obtained angles in the axial and coronal planes. The study demonstrates that patient-specific drill guides allow for accurate C1 and C2 bilateral laminar screw placement, with a low risk of cortical breach.

Fluoroscopic Detection of Ventral Wall Violation during C2 Intralaminar Screw Insertion: A Descriptive Study

Introduction: The C2 (second cervical) laminar screws were considered for rigid fixation of the axis because the use of pars or pedicle screws posed a risk to the vertebral artery with C2. Though considered to be a relatively safe method, ventral spinal canal violations have been reported in laminar screws fixations. Fluoroscopy-based image guidance may increase the accuracy and safety of the technique. Aim: To report the use of fluoroscopy technique in the detection of ventral wall violation during C2 intralaminar screw insertion. Materials and Methods: This descriptive study reports seven dry axis vertebrae from the adult south Indian population for which fluoroscopic analysis was done from January 2013 to December 2013. True lateral views were taken before and after applying a vertical line of barium paint on the ventral surface of the lamina at two points: at the centre of the lamina and close to the facet joints at the face to-laminar junction. Results: In the total seven dry axis vertebrae analysed, the mean ratio of the distance from the spinolaminar junction to the barium line (drawn on the ventral surface of the lamina just next to face to laminar junction) to the distance between the spinolaminar junction and uppermost part of inferior articular facet of C2 vertebrae was 0.465±0.0389 mm. Conclusion: Even though considered a relatively safer technique, laminar cortical violations have been reported in C2 translaminar screw fixations. Fluoroscopy-based imaging guidance can improve the accuracy of C2 translaminar screw insertion, as this technology provides real-time imaging during the process of screw insertion and helps in accurate screw sizing.

Surgical management of os odontoideum: An Algerian center experience.

ABSTRACTBackground:Os odontoideum (OO) is a craniovertebral junction malformation of unknown origin. In most times, this lesion is highly unstable demanding surgical management. We present our series of OO surgical management and we discuss clinical, radiological, and management aspects of this pathology via our experience and literature opinions.Methods:This is a retrospective study of patients operated on at our department between May 2014 and May 2021 for OO. All patients were explored with plane X-rays and computed tomography (CT). In some cases, magnetic resonance imaging (MRI) was necessary. Posterior C1–C2 or C1-C3 fixation with polyaxial screws and rod fixation was used. In postoperative, the patient is asked to put Philadelphia collar for 3 months. Hospitalization periods vary between 3 and 7 days. After discharge, all our patients are followed up regularly in consultation. Control radiographs of the occipito cervical region were performed. After 3 months postoperatively, the CT scan is performed on all our patients to assess the quality of fusion. Patient's follow-up ranges from 4 months to 6 years.Results:Fifteen patients were included in this study; nine males (60%) and six females (40%); with mean age of 32.5 years old. Ten patients (67%) presented motor weakness, three patients (20%) with neck pain, one patient (6.5%) with torticollis, and one patient (6.5%) presented vertigo. No notable cervical trauma was present in six patients (40%) and in nine patients (60%), a remote history of traumatism was noted. All cases of our series presented mobile OO. Normal thickness of the C2 pedicle was noted in nine patients (60%). In two patients (13%), there was hypoplasia of one pedicle and in four patients (27%) both pedicles. MRI showed direct signs of spinal cord aggression: simple compression, myelomalacia, strangulation, or hypotrophy. C1 lateral mass screw fixation was performed in all patients; and according to C2 morphology: nine patients underwent C1-C2 pedicular fixation, in one patient, bilateral crossing C2 laminar screws technique, in three patients, we skipped C2 to perform a C1-C3 articular fixation, and in two patients, C1-C2-C3 fixations were performed. All patients improved clinically. In one patient, we noted an infection resulting in bad wound healing this infection was successfully treated with no complications. In the patient with bilateral crossing C2 laminar screws technique, CT control objectified 4 mm exceeding of one screw; the patient was reoperated and the screw was slightly pulled back. No other complications were noted.Conclusion:Congenital origin of OO is always evoked. C1-C2 fixation according to Goel and Harms technique with grafting proved its safety, providing high fixation quality with the acceptable biodynamic outcome. Once treated, the prognostic of OO is in general good, and improvement is observed in most patients with few complications.

Study on the application of a new type of vertebral plate nail guide

To explore safety and accuracy of novel C2 laminar staple guide through in vitro experiments. From January 2018 to June 2018, 40 patients who underwent three-dimensional CT of cervical spine were selected, including 21 males and 19 females, heighted from 165 to 180 cm with an average of (172.9±9.5) cm, aged from 38 to 55 years old (51.1±12.8) years old, excluding patients with axis lamina defect and hypoplasia. Two sets of 3D printed specimens were made from the three-dimensional CT data of cervical spine of each patient, and both of than were used for the in vitro nailing experiment. According to different nail placement methods, in vitro experimental part of this experiment was divided into guide nail placement group and hand nail placement group, 40 pieces in each group. At the same time, the three-dimensionalmodel of cervical spine of 40 patients was reconstructed on computer, and the ideal needle point data and inclination angle were obtained by computer simulation of the nail placement. This is 3D simulation nail placement group, 40 pieces. With vitro experiment, the risk level of screw placement, the position of needle exit point and inclination angle were measured in guide nail group and hand nail group. Based on the accuracy of needle point and inclination angle of nail path, the data of guide nail group, the hand nail group and 3D simulation nail group were compared, and the data of each group were statistically analyzed to determine the accuracy. In guide nail group, 75 screws were acceptable and 5 were dangerous. The acceptable rate was 94%, and the double cortical rate was 93%. There were 62 position-acceptable screws in hand nail group, and 18 positions were dangerous, with an acceptable rate of 78% and a double cortical rate of 33%. The difference between two groups was statistically significant (P<0.05). There was no significant difference in accuracy of needle exit point and inclination angle of nail path between guide nail group and 3D simulation nail group (P>0.05), but there was significant difference in the accuracy of needle exit point and inclination angle of nail path between hand nail group and 3D simulation nail group (P<0.05). The guide is universal, with stable structure, accurate guidance, and easy operation. It could be placed with bilateral lamina screws at the same time, shortening the time of nail placement, avoiding collision of two way cross screws, increase the rate of double cortex. Ultimately, efficiency and security can be improved.

Modification of Wright’s Technique for C2 Translaminar Screws Based on Medical Imaging Analysis

Background: To describe and explain the improvement of Wright C2 transforaminal screw fixation technique. Methods: 23 male patients and 10 female patients (a total of 33 patients, average age of 55 years) were implanted with lamina screws on one side or both sides by improved technique. Adopt improved technology, there is a simple hole in the middle of the lateral brain plate, and the screw can be seen directly to prevent the spine from being invaded. Results: With the improved technique, 169 minutes (90–210 minutes) is the average operation time, and 136 ml (80–420 minutes) is the estimated average blood loss. Average length of 26.5 mm (range 24–30) plate screws. After an average follow-up of 12.4 (1.5–30) months, all patients achieved good clinical outcomes. Conclusions: To modify the Wright’s technique, an additional unicortical “hole” was in the middle of the backplane. Through this improved technique, the screw can be directly seen to be inserted into the dorsal cortex of the lamina, thereby reducing the risk of invading the spinal canal and shortening the operation time.

2021 Canadian Spine Society Abstracts.

# Abstract 45. Determining clinically important improvement following surgery for degenerative conditions of the spine: analysis of the Canadian Spine Outcomes and Research Network (CSORN) Registry {#article-title-2} There is significant variability in clinically important improvement (CII)

Occipitocervical instrumented fixation utilising patient-specific C2 3D-printed spinal screw trajectory guides in complex paediatric skeletal dysplasia.

Instability of the craniocervical junction in paediatric patients with skeletal dysplasia poses a unique set of challenges including anatomical abnormalities, poor bone quality, skeletal immaturity and associated general anaesthetic risks. Instrumented fixation provides optimal stabilisation and fusion rates. The small vertebrae make the placement of C2 pedicle screws technically demanding with low margins of error between the spinal canal and the vertebral artery. We describe a novel clinical strategy utilising 3D-printed spinal screw trajectory guides (3D-SSTG) for individually planned C2 pedicle and laminar screws. The technique is based on a pre-operative CT scan and does not require intraoperative CT imaging. This reduces the radiation burden to the patient and forgoes the associated time and cost. The time for model generation and sterilisation was < 24h. We describe two patients (3 and 6years old) requiring occipitocervical instrumented fixation for cervical myelopathy secondary to Morquio syndrome with 3D-SSTGs. In the second case, bilateral laminar screw trajectories were also incorporated into the same guide due to the presence of high-riding vertebral arteries. Registration of the postoperative CT to the pre-operative imaging revealed that screws were optimally placed and accurately followed the predefined trajectory. To our knowledge, we present the first clinical report of 3D-printed spinal screw trajectory guides at the craniocervical junction in paediatric patients with skeletal dysplasia. The novel combination of multiple trajectories within the same guide provides the intraoperative flexibility of potential bailout options. Future studies will better define the potential of this technology to optimise personalised non-standard screw trajectories.

Treatment strategy and curative effect analysis of os odontoideum complicated with atlantoaxial joint dislocation

To explore the treatment strategy and clinical efficacy for os odontoideum complicated with atlantoaxial dislocation. The clinical data of 17 patients with os odontoideum complicated with atlantoaxial dislocation surgically treated from January 2006 to January 2015 were retrospectively analyzed, including 7 males and 10 females, aged 17 to 53 (43.1±11.3) years old;course of disease was 3 to 27(10.2±6.9) months. All patients received cranial traction before operation, 12 of 14 patients with reducible dislocation were treated by posterior atlantoaxial fixation and fusion, and 2 patients with atlantooccipital deformity were treated by posterior occipitocervical fixation and fusion;3 patients with irreducible alantoaxial dislocation were treated by transoral approach decompression combined with posterior atlantoaxial fixation and fusion. The operation time, intraoperative blood loss and perioperative complications were recorded. Visual analogue scale (VAS) and Japanese Orthopaedic Association (JOA) score were used to evaluate the change of neck pain and neurological function. Atlantoaxial joint fusion rate was evaluated by CT scan. The operation time of posterior fixation and fusion ranged from 86 to 170 (92.2±27.5) min, and the intraoperative blood loss was 200-350 (250.7±65.2) ml. No vertebral artery injury and spinal cord injury were recorded. Among the patients underwent atlantoaxial fixation and fusion, 1 patient with reducible dislocation fixed by C2 laminar screw lost reduction after primary operation, and received anterior release again and finally occipitocervical fusion. All patients were followed up for 15 to 58 (32.0±12.2) months. VAS score was decreased from preoperative 4.2±0.9 to 1.3±0.7 at final follow up and the JOA score was improved from preoperative 11.2±1.2 to 16.9±0.8 at final follow-up. CT scan confirmed that the atlantoaxial or occipitocervical fusion wasgood, and the fusion time was 5 to 9 (6.7±0.6) months. Surgical treatment of os odontoideum complicated with atlantoaxial dislocation can achieve satisfactory results, improve the patient's neurological function and improve the quality of life, however the surgical options needs to be individualized.

Suitability of the Subaxial Cervical Laminae for Laminar Screws in the Pediatric Population: A Radiologic Anatomical Study

Introduction: The laminar screw method was popularized during recent years. Since no data exist in the literature on its suitability for subaxial levels in the pediatric population, a radiologic anatomical study was planned to evaluate the suitability of the laminae for laminar screws in children. Methods: The laminar thicknesses from C3 to C7 were measured in axial sections in 120 pediatric patients using computed tomography. The patients were divided into 3 age-groups: ages 4–6, 7–9, and 10–12. Each age-group consisted of 20 boys and 20 girls. The suitability of the laminae was evaluated for 3.5-mm-thick commercially available screws and also for the 3-mm screws that could be produced in the future. If the height of the base of the spinous process is ≥ 9 mm, the segment was accepted as suitable for the bilateral screw, and ≥5 mm is for the unilateral screw. Additionally, laminar thickness and length were measured for possible short screws longer than 15 mm in the laminae that were distally thin but proximally thick. Results: The C4 and C5 levels had the thinnest (2.77 ± 0.6 mm and 2.81 ± 0.6 mm, respectively) and C7 had the thickest laminae (4.66 ± 0.6 mm) in all age-groups. No significant differences were found between boys and girls and right and left laminae. According to the age-groups, an increase in laminar thickness was possible by growing, but only C7 laminae thickness was statistically different between 10–12 and 4–6 age-groups (p < 0.001). The last rate of the suitability was 9.1% for the 3.5-mm-thick screws and 13.75% for the 3-mm-thick screws after deletion of the bilateral insertion due to the short base of the spinous process and adding the possible short screws in the distally thin but proximally thick laminae. The rates increased with age, but the only statistically significant difference was found between 4–6- and 10–12-year-old age-groups (p < 0.001). Conclusions: Laminar screws may be suitable for some levels of C7, C6, and C3 even in the young pediatric population. The use of thinner screws (3 mm) may increase the suitability rate. Therefore, laminar screw choice may be considered as a salvage method in pediatric patients, and all laminae may be evaluated individually for suitability. This study did not evaluate the safety and efficacy of the method in children, and these issues must be studied further.

Letter: C2 Pedicle Screws Combined With C1 Laminar Hooks for Reducible Atlantoaxial Dislocation: An Ideal Salvage Technique for C1-C2 Pedicle Screws.

To the Editor: We read the article by Han et al1 with great interest in which the authors describe an innovative option to salvage C1-C2 fusion using laminar hooks instead of pars screws. We take this opportunity to share a similar experience and agree that it is not always possible to place screws in C1 or C2. C1-C2 fusion using C1 lateral mass and C2 pars or pedicle screws is a safe modality for the reduction and fusion of abnormal C1-C2 alignment and instability, including cases of post-traumatic C1-C2 subluxation.2-4 We managed a case of a 4-yr-old child who suffered odontoid tip fracture with rotatory atlantoaxial dislocation (Figure 1) following a fall from a height and presenting with torticollis and quadriparesis. The patient presented to us 2 wk after the fall. A 3-dimensional (3D) computed tomography (CT) reconstruction revealed a thin C2 pars and lamina. Based on CT measurements, a high chance of cortical breach of C2 while placing 3.5-mm pars or pedicle screws was anticipated during preoperative planning. Hence, that laminar screws over C2 could be an option during surgery was kept as an alternative salvaging procedure. The subluxation reduced under traction as soon as bilateral C1-C2 joints were opened and further distracted using dissectors. Then C1-C2 joint surfaces were curetted, and bone chips from iliac crest were inserted. The placement of C2 pedicle, pars, or laminar screws is considered to be more technically demanding than C1 lateral screw placement.5 Often, it is the C2 screw placement that more commonly leads to vascular or neural injury.6 This is particularly true in the case of children in which the small dimension of C2 makes it even more difficult to place screws of diameter 3.5 mm, which is the commonly available size.FIGURE 1.: Preoperative imaging of the patient showing the odontoid fracture and atlantoaxial dislocation A in the sagittal view. In the 3D CT angiogram, the right lateral mass of C1 is not visible B from the posterior view, which is seen subluxated anteriorly in the anterior view C.C1 lateral mass screws were placed according to the technique described by Goel et al.7 Because C2 dimensions were very thin for 3.5-mm screws, laminar hooks were placed bilaterally over C2 and minirods placed between C1 lateral mass screws and C2 laminar hooks. Finally, the C1 and C2 laminae were decorticated and iliac crest graft placed to achieve posterior bony fusion as well. A repeat scan at 3 mo showed good decompression of the craniovertebral junction and cord along with the implant in Situ (Figure 2). The patient's myelopathy has improved and is now mobilized independently. Therefore, in cases in which certain factors preclude the use of C2 pars/pedicle or lamina screws, C2 laminar hooks can be a useful rescue adjunct.FIGURE 2.: Postoperative CT showing a good reduction achieved with restoration of canal space in the sagittal view A. The 3D color rendering on maximum intensity projection B shows the C1 lateral mass screws and C2 laminar hooks in Situ.Funding This study did not receive any funding or financial support. Disclosures The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.