Atlantoaxial Research Articles

3D-printed upper cervical models: accuracy validation and feasibility study into anterior occiput-to-axis screw fixation on them

Objective To validate the accuracy of 3D-printed upper cervical models and investigate the feasibility of use of the models in anterior occiput-to-axis screw fixation, in an attempt to provide a protocol of pre-operative plan for surgeons. Methods Forty-five adult atlantoaxial CT scans were obtained, imported into Mimics software for 3D reconstruction, successively imported into 3D printer to print the 3D models. Fourteen parameters were measured on both imaging system and 3D-printed models to validate the accuracy of 3D-printed models. Thirty upper cervical CT data were obtained and imported into Mimics software for 3D reconstruction. Cylinders in 1.75 mm radius were drawn to simulate the trajectory of anterior occiput-to-axis screw fixation. Anteroposterior view of the minimum lateral angle (α1) and maximum lateral angle (α2) and lateral view of the minimum posterior angle (β1) and maximum posterior angle (β2) were measured. Mean value of α1 and α2 was calculated as α3 and mean value of β1 and β2 as β3. Meanwhile, the 3D models were printed, and an angle guide device was used to introduce the anterior occiput-to-axis screws into the 3D models in reference to the angles of α3 and β3. Anteroposterior view of lateral angle (α4) and lateral view of posterior angle (β4) were measured. Differences in α3 vs. α4 and β3 vs. β4 were compared. Results All above 14 parameters did not differ significantly between radiographic images and 3D-printed models (P>0.05). Intraclass correlation coefficient (ICC) values of 13 parameters were >0.800. On the 3D digital models, the α3 was (12.6±3.7)° (left) and (12.0±4.2)° (right), and the β3 was (23.9±4.8)° (left) and (23.4±4.9)° (right). On the 3D-printed models, the α4 was (12.0±4.1)° (left) and (12.3±4.1)° (right), and β4 was (23.4±4.2)° (left) and (22.8±4.4)° (right). There were no significant differences in both comparisons of α3 vs. α4 and β3 vs. β4 (P>0.05). Conclusions The 3D printing technique enables accurate fabrication of upper cervical spine. Aided by the 3D reconstruction with screw trajectory simulation and angle guide device, the anterior occiput-to-axis screws are introduced on the 3D-printed models successfully. Key words: Imaging, three-dimensional; Spine; Computer-assisted design

Clinical and Anatomical Features as well as Pathological Conditions of Surgically Treated Adult Patients with Occipitalization of the Atlas.

This paper intends to clarify clinical and anatomical features as well as pathological conditions of surgically treated adult patients with occipitalization of the atlas. The authors reviewed 12 consecutive adult patients with occipitalization of the atlas who underwent surgery for myleopathy in our hospital. Mainly using preoperative computed tomography and three-dimensional computed tomography angiography, we investigated their anomalies of the osseous structures and vertebral artery at the cervical spine including the craniovertebral junction (CVJ). We also developed a new classification system for occipitalization of the atlas. Atlantoaxial subluxation (AAS) was detected in 9 patients (75%). The condition of AAS was irreducible in 7 patients. Among these 7 patients, deformity at the lateral atlantoaxial joints was detected in 2 patients. C2-3 fusion was detected in 6 patients (67%) among 9 patients with AAS. Anomalies of the VA were detected in 11 patients (92%). Occipitalization of the atlas was classified into three types according to their pathological conditions. In type 1 (2 patients) the medial atlantoaxial joint is semi-dislocated and the lateral atlantoaxial joints are severely deformed. Type 2 (7 patients) exhibits AAS but the lateral atlantoaxial joints are not deformed. Type 3 (3 patients) is not associated with AAS and therefore does not exhibit osseous stenosis at the CVJ. In type 3 the myelopathy was caused by another coexisting condition. Occipitalization of the atlas is classified into three types. The main pathological condition in both types 1 and 2 is AAS. Reduction of AAS is essential in both; however, reduction of AAS in type 1 is more technically demanding than in type 2. The pathological conditions of type 3 are completely different from those of the others, so an accurate diagnosis must be made. The new classification system is a useful guide for surgeons when planning surgical strategies.

Rare Cause of Nuchal Pain: Calcification of the Alar Ligament

Calcification of the alar ligament is a rare condition, which usually develops in the elderly and tends to occur following traumatic injury or as a consequence of inflammatory disease. In crowned dens syndrome, calcium pyrophosphate dehydrate crystals deposit on the atlantoaxial joint. A 38-year-old woman with no history of traumatic injury presented with acute-onset neck pain. The patient was diagnosed with rheumatoid arthritis (RA) and …

Craniovertebral junction 360°: A combined microscopic and endoscopic anatomical study.

Objectives:Craniovertebral junction (CVJ) can be approached from various corridors depending on the location and extent of disease. A three-dimensional understanding of anatomy of CVJ is paramount for safe surgery in this region. Aim of this cadaveric study is to elucidate combined microscopic and endoscopic anatomy of critical neurovascular structures in this area in relation to bony and muscular landmarks.Materials and Methods:Eight fresh-frozen cadaveric heads injected with color silicon were used for this study. A stepwise dissection was done from anterior, posterior, and lateral sides with reference to bony and muscular landmarks. Anterior approach was done endonasal endoscopically. Posterior and lateral approaches were done with a microscope. In two specimens, both anterior and posterior approaches were done to delineate the course of vertebral artery and lower cranial nerves from ventral and dorsal aspects.Results:CVJ can be accessed through three corridors, namely, anterior, posterior, and lateral. Access to clivus, foreman magnum, occipital cervical joint, odontoid, and atlantoaxial joint was studied anteriorly with an endoscope. Superior and inferior clival lines, supracondylar groove, hypoglossal canal, arch of atlas and body of axis, and occipitocervical joint act as useful bony landmarks whereas longus capitis and rectus capitis anterior are related muscles to this approach. In posterior approach, spinous process of axis, arch of atlas, C2 ganglion, and transverse process of atlas and axis are bony landmarks. Rectus capitis posterior major, superior oblique, inferior oblique, and rectus capitis lateralis (RCLa) are muscles related to this approach. Occipital condyles, transverse process of atlas, and jugular tubercle are main bony landmarks in lateral corridor whereas RCLa and posterior belly of digastric muscle are the main muscular landmarks.Conclusion:With advances in endoscopic and microscopic techniques, access to lesions and bony anomalies around CVJ is becoming easier and straightforward. A combination of microscopic and endoscopic techniques is more useful to understand this anatomy and may aid in the development of future combined approaches.

Morphometric Characteristics of C1-C2 Vertebrae to Perform Anterior Transarticular Crossing Screw Fixation.

In unique clinical situations where C1-C2 posterior fixation is not available or has previously failed, an anterior transarticular screw (ATAS) may be a viable alternative. However, there are no previous reports that investigate possible screw angles, screw entry points, and screw length based on computed tomography (CT) multiplanar reconstruction images in Turkish patients. The aim of this study was to determine the morphometric characteristics C1-C2 vertebrae in order to perform anterior transarticular crossing screw fixation. Patients who underwent a complete CT scan of the cervical spine for causes other than an investigation of cervical spine malformation or congenital anomaly between the years 2013 and 2015 were included in this study. The anterior transarticular C1-C2 screw angles, screw entry point, and screw length were measured on coronal and sagittal CT multiplanar reconstruction images. Twenty-five male and 14 female patients were included in the study. The mean maximum screw angle for ATAS was found to be 41.18°±4.49°. The minimum and maximum screw lengths were 27.46±3.39 mm and 28.46±3.60 mm, respectively. Preoperatively, performing a calculation of the possible screw angles, screw entry point, and screw length based on CT multiplanar reconstruction images for ATAS is a safe and applicable method. In cases in which ATAS fixation across the atlantoaxial joint procedure should be performed without performing a measurement, a screw angle not more than 41.18°±4.49° on the coronal plane does not damage the vertebral artery. Furthermore, using screws shorter than 28.46±3.60 mm doesn"t purchase the atlantoaxial joint.

Artificial atlanto-axial joints: On the “move”

The current management of atlantoaxial dislocation emphasizes on C1-2 reduction and fusion. The fusion of C1-2, however, hampers the neck movements significantly. The author has designed and developed artificial C1-2 joints that can mimic the natural joints to some extent. The concept and nuances of the design has been described. The joints have been fixed in dry cadaveric bones to demonstrate the possible movements.

A Case of Atlanto-Axial Joint Subluxation Following Tonsillectomy in Patient of Tonsillar Cancer with Preoperative Radiotherapy: Grisel's Syndrome

A Case of Atlanto-Axial Joint Subluxation Following Tonsillectomy in Patient of Tonsillar Cancer with Preoperative Radiotherapy: Grisel's Syndrome

Is atlantoaxial instability the cause of "high" cervical ossified posterior longitudinal ligament? Analysis on the basis of surgical treatment of seven patients.

Background:Multilevel ossified posterior longitudinal ligaments (OPLLs), particularly those that extend into the high cervical region, are formidable and challenging surgical problems. The aim of the presentation is to analyze the results of surgical treatment of seven consecutive patients having high cervical OPLL with atlantoaxial and subaxial facetal fixations.Objectives:We analyze the role of atlantoaxial instability in the management of OPLL that extended into the high cervical region, above the lower border of C3 vertebra.Materials and Methods:All patients in the series were males. The age of the patients ranged 48-65 years. Clinical evaluation was done by a 5-point clinical grading scale described by us, Japanese Orthopedic Association (JOA) score, and visual analog scale (VAS). All patients were identified to have relatively “subtle” but definite atlantoaxial facetal instability on sagittal imaging and the instability was confirmed by direct handling of the facets during surgery. All patients were treated by multilevel facetal fixation that included fixation of atlantoaxial facets. The aim of surgery was stabilization and arthrodesis of the involved spinal segments, as instability was considered to be the prime pathogenetic factor of OPLL. Spinal canal decompression, either by anterior corpectomy or discoidectomy or by posterior laminectomy or laminoplasty was not done and no attempts were made to remove the OPLL. At an average follow-up of 8 months, all patients showed progressive symptomatic recovery.Conclusion:Atlantoaxial facetal instability can be a cause or an association of high cervical OPLL. Stabilization of the atlantoaxial joint forms a remarkably effective method of treatment.

Non-traumatic Atlanto-axial Rotatory Subluxation- Grisel’s Syndrome Case Report and Literature Review

Study design: Case report of conservatively treated non-traumatic Atlanto-axial rotatory sublaxation. Objective: To report our case with this rare condition (non-traumatic Atlanto-axial rotatory subluxation-Grisel Syndrome) in a 9-year old girl presenting with torticollis and neck pain and literature review. Summary of background data: Atlanto-axial rotatory fixation or non-traumatic atlanto-axial subluxation which is usually secondary to an infection or an inflammation at the head and neck region is a rare subtype of subluxation in which a pathologic fixation of the atlas on the axis is present. It is most common in paediatric patients and it can be managed conservatively in the acute stage. In contrast, cases of chronic non-traumatic atlanto-axial rotatory subluxation are usually treated with operative reduction, according to literature data. Although high success rates have been achieved with operative reduction in chronic cases, a significant reduction in neck motion occurs due to the atlanto-axial fusion. Methods: A 9-year-old girl developed torticollis established longer than 10 weeks as a result of an upper respiratory tract infection. Computed tomography showed a type 1 rotatory subluxation of the Atlanto-axial joint according to the classification of Fielding and Hawkins. The patient was treated by manual reduction according to Jeszenszky (Jeszenszky transoral Citation Nr 22) under general anaesthesia and fluoroscopy control, and then a halo vest had been applied for 6 weeks. Results: We successfully treated this patient with chronic non-traumatic Atlanto-axial rotatory subluxation with manual reduction and immobilisation by applying a halo-body-jacket. She showed full recovery of neck motion and normal Atlanto-axial angle on clinical and radiological follow-up after 1 month and 3 months respectively. Conclusion: Chronic non-traumatic Atlanto-axial rotatory subluxation is a rare condition which can easily escape the attention of physicians especially in children. Conservative treatment with complete reduction under anaesthesia and subsequent immobilisation via halo-body-jacket for at least 6 weeks is a viable option as presented in this case report. Surgical treatment should be reserved only for cases of failure of conservative management (recurrence or irreducible subluxation).

咽後膿瘍と鑑別を要した石灰沈着性頸長筋腱炎の3例

Acute calcific retropharyngeal tendinitis is an inflammation of the longus coli muscle characterized by the acute onset of neck pain, swallowing pain, and limitations of neck movement. Although symptoms subside spontaneously within one to two weeks, many cases are treated with antibiotics because clinical outcomes are similar to a severe infection of the retropharyngeal area such as a retropharyngeal abscess. We report herein on 3 cases of acute calcific retropharyngeal tendinitis. The first and second cases were hospitalized, had many examinations and were diagnosed retrospectively. The third patient was treated as an outpatient after a CT scan. Typical CT imaging shows prevertebral soft-tissue swelling without ring enhancement, and amorphous calcification just anterior to the atlanto-axial joint, allowing us early diagnosis.

Une cause rare de cervicalgie fébrile

Une cervicalgie fébrile est souvent secondaire à une méningite ou à une spondylodiscite, exceptionnellement à une arthropathie microcristalline. Nous en rapportons un cas. Un homme de 81 ans sans antécédents particuliers est hospitalisé pour cervicalgie fébrile. Les diagnostics initialement évoqués étaient ceux de méningite et de spondylodiscite. L'examen a montré une raideur globale du rachis cervical. L'IRM rachidienne a montré une anomalie de signal de l'articulation atloïdo-axoïdienne se réhaussant après injection de gadolinium avec une hypertrophie synoviale associée à un aspect irrégulier et hétérogène de la dent de l'axis. Les coupes tomodensitométriques atlo-axoïdiennes montraient des calcifications péri-odontoïdales confirmant le diagnostic de syndrome de dent couronnée (SDC). L'évolution était favorable sous AINS. Le SDC mérite d'être mieux connu ; il peut mimer de nombreux diagnostics et être responsable de fièvre au long cours.

A study of indications and assessment of fusion rates for atlantoaxial subluxation

Background: Stabilization of the atlantoaxial articulation presents special problems due to the unique anatomical and functional characteristics of the upper cervical vertebra. The majority of rational movements occur at C1-C2; the cervical stabilization limits rational movement of the neck. The objective of the study was to assess the fusion rates using different techniques of atlantoaxial arthrodesis. Methods: All the patients who were operated for atlantoaxial stabilization in the department of neurosurgery, between December 2012 and March 2015 formed the study group. Demographic data, detailed history of symptoms and other morbidities were recorded. Routine hematological and biochemical parameters were assessed. Imaging features like X-ray c spine {neutral, flexion & extension view}, CT scans C-spine, and MRI C-spine was used. The anatomic characteristics of cervicovertebral junction, presence of ventral or dorsal compression and atlantoaxial stability were noted. Operative details like types of approach, whether dorsal wiring or screw fixation or both were noted. Results: Twelve patients had anterior displacement of the atlas on the axis averaging 9.6 mm. Five had posterior displacement averaging 9.2 mm. More than 2/3 of patients had preserved motor function, grade D according to Frankel Classification. More than 60% patients had difficulty in walking and required support to walk. Most of the patients presented with long tract signs and objective weakness. Most common procedure done was C1 lateral mass and C2 pedicle screw fixation. The next common procedure performed was C1-C2 fusion with Sub laminar wiring using titanium wires. There was no mortality. Conclusions: There is no best method for OCF, and the method of surgery should be bases on the type of instability, the integrity of posterior cervical elements, the extension of decompression, co morbidities, individual anatomic variation, and the surgeon’s familiarity with the techniques.

Clinical analysis of acute limited neck motion in 420 children

Objective To study the clinical features of acute limited neck motion in children and its differen-tial diagnosis, and to improve doctors' awareness and the early diagnosis of the disease. Methods A total of 420 patients with acute limited neck motion as the chief complaint and atlantoaxial rotary subluxation as the first diagnosis between January 2005 and January 2014 in Nanjing Children's Hospital Affiliated to Nanjing Medical University were enrolled.The clinical manifestations, imaging and consultation data of the 420 patients were retrospectively analyzed. Results There were totally 248 male patients and 172 female patients.The ages ranged from 2 to 14 years old(the mean age was 7.2 years old), the course ranged from 2 hours to 2 days.Among 420 patients, 353 patients were diagnosed as atlantoaxial rotatory subluxation.Forty-two patients were diagnosed as cervical intervertebral disc calcification.Seven patients were diagnosed as Tourette syndrome.Four patients were diagnosed as intracranial tumors.Three patients were diagnosed as cervical eosinophilic granuloma.Two patients were diagnosed as cervical spinal tuberculosis.Two patients were diagnosed as viral encephalitis.Two patients were diagnosed as benign paroxysmal torticollis.Two patients were diagnosed as Kawasaki disease.One patient was diagnosed as neuroblastoma.One patient was diagnosed as hemophilia A. One patient was diagnosed as drug adverse reaction of metoclopramide.According to Fielding clinical classification, 204 patients were type Ⅰ, 122 patients were type Ⅱ, 21 patients were type Ⅲ, and 6 patients were type Ⅳ. Conclusions Based on disease distribution of acute limited neck motion in children, atlantoaxial rotatory subluxation seems to be the predominant while non-atlantoaxial rotatory subluxation is not uncommon.Differential diagnoses should be considered to avoid misdiagnosis.For atlantoaxial rotatory subluxation, conservative treatment including continuous mandible occipital belt traction and brace has been proved to be very effective methods. Key words: Atlantoaxial rotatory subluxation; Acute limited neck motion; Differential diagnosis; Child

New Posterior Atlantoaxial Restricted Non-Fusion Fixation for Atlantoaxial Instability: A Biomechanical Study.

Loss of axial rotation and lateral bending after atlantoaxial fusion reduces a patient's quality of life. Therefore, effective, nonfusion fixation alternatives are needed for atlantoaxial instability. To evaluate the initial stability and function of posterior atlantoaxial restricted nonfusion fixation (PAARNF), a new protocol, using cadaveric cervical spines compared with the intact state, destabilization, and posterior C1-C2 rod fixation. Cervical areas C0 through C3 were used from 6 cadaveric spines to test flexion-extension, lateral bending, and axial rotation range of motion (ROM). With the use of a machine, 1.5-Nm torque at a rate of 0.1 Nm/s was used and held for 10 seconds. The specimens were loaded 3 times, and data were collected in the third cycle and tested in the following sequence: (1) intact, (2) destabilization (using a type II odontoid fracture model), (3) destabilization with PAARNF (PAARNF group), and (4) rod implantation (rod group). The order of tests for the PAARNF and rod groups was randomly assigned. The average flexion-extension ROM in the PAARNF group was 7.44 ± 2.05°, which was significantly less than in the intact (P = .00) and destabilization (P = .00) groups but not significantly different from that of the rod group (P = .07). The average lateral bending ROM (10.59 ± 2.33°; P = .00) and axial rotation ROM (38.79 ± 13.41°; P = .00) of the PAARNF group were significantly greater than in the rod group. However, the values of the PAARNF group showed no significant differences compared with those of the intact group. PAARNF restricted atlantoaxial flexion-extension but preserved axial rotation and lateral bending at the atlantoaxial joint in a type II odontoid fracture model. However, it should not be used clinically until further studies have been performed to test the long-term effects of this procedure.

Imaging of Atlanto-Occipital and Atlantoaxial Traumatic Injuries: What the Radiologist Needs to Know.

Approximately one-third of all cervical spine injuries involve the craniocervical junction (CCJ). Composed of the occiput and the first two cervical vertebrae, this important anatomic landmark, in conjunction with an intricate ligamentous complex, is essential to maintaining the stability of the cervical spine. The atlantoaxial joint is the most mobile portion of the spine, predominantly relying on the ligamentous framework for stability at that level. As acute onsite management of trauma patients continues to improve, CCJ injuries, which often lead to death onsite where the injury occurred, are increasingly being encountered in the emergency department. Understanding the anatomy of the CCJ is crucial in properly evaluating the cervical spine, allowing the radiologist to assess its stability in the trauma setting. The imaging findings of important CCJ injuries, such as atlanto-occipital dissociation, occipital condyle fractures, atlas fractures with transverse ligament rupture, atlantoaxial distraction, and traumatic rotatory subluxation, are important to recognize in the acute setting, often dictating patient management. Thin-section multidetector computed tomography with sagittal and coronal reformats is the study of choice in evaluating the extent of injury, allowing the radiologist to thoroughly evaluate the stability of the cervical spine. Furthermore, magnetic resonance (MR) imaging is increasingly being used to evaluate the spinal soft tissues and ligaments, and to identify associated spinal cord injury, if present. MR imaging is also indicated in patients whose neurologic status cannot be evaluated within 48 hours of injury. .

Técnicas de redução e estabilização da subluxação atlantoaxial em cães – revisão de literatura

Atlantoaxial subluxation is a neurological condition caused by a congenital and/or development abnormality that affects young small-breed dogs. It can also have a traumatic origin; in this case, it can affect any breed or dog at any age. In this condition, the cranial surface of the axis is dorsally dislodged towards the spinal canal, resulting in compression of the spinal cord and its nerve roots. Clinical signs vary from mild cervical pain to neurological deficits such as ataxia, tetraparesis or tetraplegia. The diagnosis is based on anamnesis, clinical signs and neurological examination, and it is confirmed by imaging. Surgical treatment encompasses dorsal and ventral approaches to reduce and stabilize the atlantoaxial joint. The aim of this work is to present a literature review on the techniques for reduction and stabilization of the atlantoaxial joint in cases of subluxation.

The importance of atlantoaxial fixation after odontoidectomy.

OBJECT Although anterior odontoidectomy has been widely accepted as a procedure for decompression of the craniovertebral junction (CVJ), postoperative biomechanical instability has not been well addressed. There is a paucity of data on the necessity for and choice of fixation. METHODS The authors conducted a retrospective review of consecutively treated patients with basilar invagination who underwent anterior odontoidectomy and various types of posterior fixation. Posterior fixation included 1 of 3 kinds of constructs: occipitocervical (OC) fusion with atlantoaxial (AA) fixation, OC fusion without AA fixation, or AA-only (without OC) fixation. On the basis of the use or nonuse of AA fixation, these patients were assigned to either the AA group, in which the posterior fixation surgery involved both the atlas and axis simultaneously, regardless of whether the patient underwent OC fusion, or the non-AA group, in which the OC fusion construct spared the atlas, axis, or both. Clinical outcomes and neurological function were compared. Radiological results at each time point (i.e., before and after odontoidectomy and after fixation) were assessed by calculating the triangular area causing ventral indentation of the brainstem in the CVJ. RESULTS Data obtained in 14 consecutively treated patients with basilar invagination were analyzed in this series; the mean follow-up time was 5.75 years. The mean age was 53.58 years; there were 7 males and 7 females. The AA and non-AA groups consisted of 7 patients each. The demographic data of both groups were similar. Overall, there was significant improvement in neurological function after the operation (p = 0.03), and there were no differences in the postoperative Nurick grades between the 2 groups (p = 1.00). According to radiological measurements, significant decompression of the ventral brainstem was achieved stepwise in both groups by anterior odontoidectomy and posterior fixation; the mean ventral triangular area improved from 3.00 ± 0.86 cm2 to 2.08 ± 0.51 cm2 to 1.68 ± 0.59 cm2 (before and after odontoidectomy and after fixation, respectively; p < 0.05). The decompression gained by odontoidectomy (i.e., reduction of the ventral triangular area) was similar in the AA and non-AA groups (0.66 ± 0.42 cm2 vs 1.17 ± 1.42 cm2, respectively; p = 0.38). However, the decompression achieved by posterior fixation was significantly greater in the AA group than in the non-AA group (0.64 ± 0.39 cm2 vs 0.17 ± 0.16 cm2, respectively; p = 0.01). CONCLUSIONS Anterior odontoidectomy alone provides significant decompression at the CVJ. Adjuvant posterior fixation further enhances the extent of decompression after the odontoidectomy. Moreover, posterior fixation that involves AA fixation yields significantly more decompression of the ventral brainstem than OC fusion that spares AA fixation.

Long-term growth and alignment after occipitocervical and atlantoaxial fusion with rigid internal fixation in young children.

OBJECT The long-term consequences of atlantoaxial (AA) and occipitocervical (OC) fusion and instrumentation in young children are unknown. Anecdotal reports have raised concerns regarding altered growth and alignment of the cervical spine after surgical intervention. The purpose of this study was to determine the long-term effects of these surgeries on the growth and alignment of the maturing spine. METHODS A multiinstitutional retrospective chart review was conducted for patients less than or equal to 6 years of age who underwent OC or AA fusion with rigid instrumentation at 9 participating centers. All patients had at least 3 years of clinical and radiographic follow-up data and radiographically confirmed fusion. Preoperative, immediate postoperative, and most recent follow-up radiographs and/or CT scans were evaluated to assess changes in spinal growth and alignment. RESULTS Forty children (9 who underwent AA fusion and 31 who underwent OC fusion) were included in the study (mean follow-up duration 56 months). The mean vertical growth over the fused levels in the AA fusion patients represented 30% of the growth of the cervical spine (range 10%-50%). Three different vertical growth patterns of the fusion construct developed among the 31 OC fusion patients during the follow-up period: 1) 16 patients had substantial growth (13%-46% of the total growth of the cervical spine); 2) 9 patients had no meaningful growth; and 3) 6 patients, most of whom presented with a distracted atlantooccipital dislocation, had a decrease in the height of the fused levels (range 7-23 mm). Regarding spinal alignment, 85% (34/40) of the patients had good alignment at follow-up, with straight or mildly lordotic cervical curvatures. In 1 AA fusion patient (11%) and 5 OC fusion patients (16%), we observed new hyperlordosis (range 43°-62°). There were no cases of new kyphosis or swan-neck deformity, evidence of subaxial instability, or unintended subaxial fusion. No preoperative predictors of these growth patterns or alignment were evident. CONCLUSIONS These results demonstrate that most young children undergoing AA and OC fusion with rigid internal fixation continue to have good cervical alignment and continued growth within the fused levels during a prolonged follow-up period. However, some variability in vertical growth and alignment exists, highlighting the need to continue close long-term follow-up.

The diagnosis and management for the combination fractures of atlas and axis

Objective To investigate the treatment strategies and clinical effect of the combination fractures of atlas and axis. Methods Data of 56 cases with combination fractures of the atlas and axis treated from July 2006 to March 2014 were retrospectively analyzed. There were 36 males and 20 females with mean age of 38.6 years old (range, 21 to 63 years old). Dickman Atlantoaxial compound fracture classification: C1-II type dens fracture 21 cases, C1 fracture-atlantoaxial stability fracture 8 cases; C1 fracture-III type dens fracture 9 cases; C1 fracture-Hangman fracture 18 cases. 8 cases of C1-atlantoaxial stability fracture, 2 cases of C1-III type dens fracture and 7 cases of C1-Hangman fracture had conservative treatment and the other 39 cases were taken surgery. There were 13 patients who suffered from nerve injury such as limbs numbness, movement and the reflecting barrier before surgery: 2 Frankel B, 4 Frankel C, and 7 Frankel D. The mean preoperative JOA score was 8.6 ranging from 5.5 to 12.8. Results All patients were followed-up for a mean period of 32 months (range, 6-58 months). All the operated segments of atlas and axis showed stability and X ray showed fusion achieved within six months (average 4.5 months). Postoperative pain, upper limb numbness and neck pain were improved. 13 cases who had neurological symptoms before surgery achieved an average of 1-2 degrees of Frankel grade recovery after 6 months. The average JOA scores 6 months after operation were 14.1 ranging from 11.5 to 15.8 and the rate of improvement was 82.7% ranging from 71.5% to 95.3%. At the latest follow-up, 39 cases with surgical treatment had no complications such as fracture fixation, spinal cord injury, vertebral artery injury and cerebrospinal fluid leakage; 1 case occurred wound infection which healed after a month by debridement and dressing. Conclusion C1 fracture-III type dens fracture and stable axis fracture and stable Hangman stability fracture should be undertaken with conservative treatment. C1 fracture-II type dens fracture with atlantoodontoid interval >5 mm and unstable Hangman fracture should be treated with posterior cervical pedicle screw fixation. Occipitocervical fixation could be taken with the atlas anatomical abnormalities, severe comminuted fractures and atlas pedicle screw fixation loosening. Key words: Cervical atlas; Axis; Fractures, bone; Fracture fixation, internal

Biomechanical Evaluation of the Stabilizing Function of Three Atlantoaxial Implants Under Shear Loading: A Canine Cadaveric Study.

To compare the biomechanical properties of a ventral transarticular lag screw fixation technique, a new dorsal atlantoaxial instability (AAI) clamp, and a new ventral AAI hook plate under sagittal shear loading after transection of the ligaments of the atlantoaxial joint. Cadaveric biomechanical study. Canine cadavers (n = 10). The occipitoatlantoaxial region of Beagles euthanatized for reasons unrelated to the study was prepared leaving only ligamentous structures and the joint capsules between the first 2 cervical vertebrae (C1 and C2). The atlanto-occipital joints were stabilized with 2 transarticular diverging positive threaded K-wires. The occipital bone and the caudal end of C2 were embedded in polymethylmethacrylate and loaded in shear to a force of 50 Newtons. The range of motion (ROM) and neutral zone (NZ) of the atlantoaxial joint were determined after 3 loading cycles with atlantoaxial ligaments intact, after ligament transection, and after fixation with each implant. The testing order of implants was randomly assigned. The implants tested last were subjected to failure testing. All stabilization procedures decreased the ROM and NZ of the atlantoaxial joint compared to transected ligament specimens. Only stabilization with transarticular lag screws and ventral plates produced a significant reduction of ROM compare to intact specimens. Fixation with transarticular lag screws and a ventral hook plate was biomechanically similar and provided more rigidity compared to dorsal clamp fixation. Further load cycling to failure tests and clinical studies are required before making clinical recommendations.