Os odontoideum and craniovertebral junction instability secondary to dystonia: case series and review of the literature.

INTRODUCTION: Os odontoideum refers to a rounded ossicle detached from a hypoplastic odontoid process at the body of the axis. The aetiology has been debated and believed to be either congenital or acquired (resulting from trauma). Os odontoideum results in incompetence of the transverse ligament and thus predisposes to atlantoaxial instability and spinal cord injury. METHODS/RESULTS: Three cases of children with severe dystonic cerebral palsy presenting with myelopathic deterioration secondary to atlantoaxial instability due to os odontoideum are presented. This observation supports the hypothesis of os odontoideum being an acquired phenomenon, secondary to chronic excessive movement with damage to the developing odontoid process. CONCLUSION: In children with cerebral palsy and dystonia, pre-existing motor deficits may conceal an evolving myelopathy and result in delayed diagnosis of clinically significant atlantoaxial subluxation.

Augmented Reality in Spine Surgery: A Case Study of Atlantoaxial Instrumentation in Os Odontoideum.

Despite advancement in surgical innovation, C1-C2 fixation remains challenging due to risks of screw malposition and vertebral artery (VA) injuries. Traditional image-based navigation, while useful, often demands that surgeons frequently shift their attention to external monitors, potentially causing distractions. In this article, we introduce a microscope-based augmented reality (AR) navigation system that projects both anatomical information and real-time navigation images directly onto the surgical field. In the present case report, we discuss a 37-year-old female who suffered from os odontoideum with C1-C2 subluxation. Employing AR-assisted navigation, the patient underwent the successful posterior instrumentation of C1-C2. The integrated AR system offers direct visualization, potentially minimizing surgical distractions. In our opinion, as AR technology advances, its adoption in surgical practices and education is anticipated to expand.

Odontoid fracture in geriatric patients - analysis of complications and outcome following conservative treatment vs. ventral and dorsal surgery.

BACKGROUND: Different treatment options are discussed for geriatric odontoid fracture. The aim of this study was to compare the treatment options for geriatric odontoid fractures. METHODS: Included were patients with the following criteria: age ≥ 65 years, identification of seniors at risk (ISAR score ≥ 2), and odontoid fracture type A/B according to Eysel and Roosen. Three groups were compared: conservative treatment, surgical therapy with ventral screw osteosynthesis or dorsal instrumentation. At a follow-up examination, the range of motion and the trabecular bone fracture healing rate were evaluated. Furthermore, demographic patient data, neurological status, length of stay at the hospital and at the intensive care unit (ICU) as well as the duration of surgery and occurring complications were analyzed. RESULTS: A total of 72 patients were included and 43 patients could be re-examined (range: 2.7 ± 2.1 months). Patients with dorsal instrumentation had a better rotation. Other directions of motion were not significantly different. The trabecular bone fracture healing rate was 78.6%. The patients with dorsal instrumentation were hospitalized significantly longer; however, their duration at the ICU was shortest. There was no significant difference in complications. CONCLUSION: Geriatric patients with odontoid fracture require individual treatment planning. Dorsal instrumentation may offer some advantages.

MR documented craniocervical ligamentous injury at age 18 months: delayed formation of OS odontoideum. Complex management issues. Case-based review.

OBJECTIVE: There are two separate theories regarding the genesis of os odontoideum: congenital and post-traumatic. Trauma documentation in the past has been the presence of a normal odontoid process at the time of initial childhood injury and subsequent development of the os odontoideum. True MR documentation of craniocervical injury in early childhood and subsequent os odontoideum formation has been very rare. METHODS: An 18-month-old sustained craniocervical ligamentous injury documented on MRI with transient neurological deficit. Chiari I abnormality was also recorded. Subsequent serial imaging of craniocervical region showed the formation of os odontoideum and instability. He became symptomatic from the os odontoideum and the Chiari I abnormality. The patient underwent decompression and intradural procedure for Chiari I abnormality and occipitocervical fusion. Postoperative course was complicated by the failure of fusion and redo. He later required transoral ventral medullary decompression. He recovered. RESULTS: This is an MR documented craniocervical ligamentous injury with sequential formation of os odontoideum with accompanying changes in the atlas. Despite a subsequent successful dorsal occipitocervical fusion, he became symptomatic requiring transoral decompression. CONCLUSIONS: Os odontoideum here is recognized as a traumatic origin with the presence of congenital Chiari I abnormality as a separate entity. The changes of the anterior arch of C1 as well as the os formation were serially documented and give credence to blood supply changes in the os and atlas as a result of the trauma. The recognized treatment of dorsal occipitocervical fusion failed in this case requiring also a ventral decompression of the medulla.

Neuronavigated Retropharyngeal Anterior Screw Fixation of the Odontoid for the Treatment of C2 Type II Fractures: Case Report.

Odontoid fractures, frequently observed in patients over the age of 70, often involve the base of the axis (Anderson-D'Alonzo type 2). For surgical treatment, posterior C1-C2 fixation is the traditional method, whose fusion rates range between 93 and 100%. However, morbidity and mortality rates are high. In addition, cervical motion, especially axial rotation, is postoperatively reduced. Nakanishi and Bohler introduced the anterior screw fixation approach for the surgical treatment of odontoid fracture type II. This procedure preserves the atlantoaxial complex motion, provides immediate stability and high fracture healing rates, and, most importantly, has a low incidence of complications with good fusion rates. The surgical strategy must take into account the patient's anatomy, the morphological characteristics of the fracture, the quality of the bone, and any concomitant injuries. In this chapter, we describe a C2 type II fracture treated via a neuronavigated anterior retropharyngeal approach.

Development of a Retro-Odontoid pseudotumor in the absence of atlantoaxial instability or rheumatoid arthritis Post-Laminoplasty: case report.

A retro-odontoid pseudotumor (ROP) is commonly associated with atlantoaxial instability (AAI) or rheumatoid arthritis (RA). However, we describe a patient with ROP in the absence of AAI or RA. An 81-year-old man who did not have a history of trauma to the head and neck admitted with neck pain, right upper extremity numbness, lower limb weakness, and walking disturbance. He had a history of C2 dome and C3-7 laminoplasty 10 years ago. Magnetic resonance imaging revealed a retro-odontoid mass with cervical cord compression. Dynamic radiography did not show signs of AAI. He underwent C1 laminectomy without fixation for the ROP. We speculated that the load on C1 and C2 increased because of the progression of kyphosis from C2 to C7 with increases in range of motion, which in turn caused change in the biomechanics of the cervical spine, leading to recurrent partial tear and degradation of the transverse ligament that induced formation of the ROP. Spinal surgeons should keep this complication in mind and inform patients about this potential postoperative complication.

Craniocervical junction involvement in inflammatory arthritis: a single-center radiologic study.

Background/aim: Craniocervical junction (CCJ) can be involved in inflammatory arthritis. We aimed to define types of CCJ involvement in rheumatoid arthritis (RA), spondyloarthritis (SpA), and psoriatic arthritis (PsA) and compare them with patients without inflammatory arthritides. Materials and methods: In this retrospective analysis, cervical CT or MRIs of patients with RA, SpA, or PsA, taken for any reason between 2010 and 2020, according to ICD-10 codes, were scanned. Demographic data of the patients were recorded. CCJ involvements (atlantoaxial, vertical, or subaxial subluxation, odontoid process involvement) were reevaluated by an experienced radiologist. The control group consisted of consecutive patients without inflammatory arthritis. Results: Exactly 459 patients (204 RA, 200 SpA, and 55 PsA) and 78 patients in the control group were included in the study. CCJ involvement was detected in 101 (49.5%) RA, 53 (26.5%) SpA, 10 (18.2%) PsA, and 4 patients (5.1%) in the control group (p < 0.001). The odontoid process was one of the main targets, especially in RA patients (69 (33.8%)), which was significantly higher than in the SpA, PsA, and control groups. Although vertical subluxation (VS) was numerically higher in the RA and SpA groups compared to the control group, VS-related brainstem compression was relatively uncommon: 6 (2.9%) in RA, 1 (0.5%) in AS, and none in the PsA and control groups. Conclusion: CCJ involvement can often be detected in patients with inflammatory arthritis, especially in RA and SpA patients. The odontoid process is the main target of inflammation.

[Minimally invasive surgery for invaginated CII odontoid process]. / Miniinvazivnaya khirurgiya invaginirovannogo zubovidnogo otrostka CII pozvonka.

Odontoidectomy is indicated for anterior compression of the brainstem by invaginated odontoid process. This procedure can currently be performed via transoral microsurgical and transnasal endoscopic access. OBJECTIVE: To analyze the results of endoscopic transnasal odontoidectomy. MATERIAL AND METHODS: We assessed treatment outcomes in 10 patients with anterior compression of the brainstem by invaginated odontoid process. All patients underwent endoscopic transnasal odontoidectomy. RESULTS: Brainstem decompression was achieved in all cases. CONCLUSION: Currently, endoscopic transnasal approach is gradually replacing the transoral one in some patients requiring anterior odontoidectomy. Analysis of literature data reflects the development of this technique taking into account various features of surgical treatment including optimization of dimensions of surgical field, attempts to perform C1-sparing surgeries and analysis of sufficient size of trepanation. Nasopalatine and nasoclival lines are used to select optimal access. Nevertheless, the choice of access depends on equipment of the hospital and surgical experience in most cases.

Odontoid Type II fractures in elderly: what are the real management goals and how to best achieve them? A multicenter European study on functional outcome.

Odontoid fractures constitute the most common cervical fractures in elderly. External immobilization is the treatment of choice for Type I and III; there is still no wide consensus about the best management of Type II fractures. Observational multicenter study was conducted on a prospectively built database on elderly patients (> 75 years) with Type II odontoid fracture managed conservatively during the last 10 years. All patients underwent CT scan on admission and at 3 months; if indicated, selected patient had CT scan at 6 and 12 months. All patients were clinically evaluated by Neck Disability Index (NDI), Charlson Comorbidity Index (CCI), and American Society of Anaesthesiologists classification (ASA) on admission; NDI was assessed also at 6 weeks, 3, 6, 12, and 24 months; furthermore, a quality of life (QoL) assessment with the SF-12 form was performed at 3 and 12 months. Among the 260 patients enrolled, 177 (68%) were women and 83 (32%) men, with a median age of 83 years. Patients were followed up for a minimum of 24 months: 247 (95%) showed an excellent functional outcome within 6 weeks, among them 117 (45%) showed a good bony healing, whereas 130 (50%) healed in pseudo-arthrosis. The residual 5% were still variably symptomatic at 12 weeks; however, only 5 out of 13 (2% of the total cohort) required delayed surgery. This study showed that a conservative approach to odontoid Type II fracture in elderly is an effective and valid option, resulting in an excellent functional outcome (regardless of bony fusion) in the majority of cases. Failure of conservative treatment can be safely addressed with surgical fixation at a later stage.

Endoscopic endonasal odontoidectomy: a long-term follow-up results for a cohort of 21 patients.

BACKGROUND: Endoscopic endonasal odontoidectomy (EEO) has been described as a potential approach for craniovertebral junction (CVJ) disease which could cause anterior bulbomedullary compression and encroaching. Due to the atlantoaxial junction's uniqueness and complex biomechanics, treating CVJ pathologies uncovers the challenge of preventing C1-C2 instability. A large series of patients treated with endonasal odontoidectomy is reported, analyzing the feasibility and necessity of whether or not to perform posterior stabilization. Furthermore, the focus is on the long-term follow-up, especially those whom only underwent partial C1 arch preservation without posterior fixation. METHODS: This study is a retrospective analysis of patients with ventral spinal cord compression for non-reducible CVJ malformation, consecutively treated with EEO from July 2011 to March 2019. Postoperative dynamic X-ray and CT scans were obtained in each case in order to document CVJ decompression as well as to exclude instability. The anterior atlas-dens interval, posterior atlas-dens interval and C1-C2 total lateral overhang were measured as a morphological criteria to determine upper cervical spine stability. RESULTS: Twenty-one patients (11:10 F:M) with a mean age of 60.6 years old at the time of surgery (range 34-84 years) encountered the inclusion criteria. For all 21 patients, a successful decompression was achieved at the first surgery. In 11 patients, the partial C1 arch integrity did not require a posterior cervical instrumentation on the bases of postoperative and constant follow-up radiological examination. In 13 cases, an improvement of motor function was recorded at the time of discharge. Only one patient had further motor function improvement at follow-up. Among the patients that did not show any significant motor change at discharge, 4 patients showed an improvement at the last follow-up. CONCLUSIONS: The outcomes, even in C1 arch preservation without posterior fixation, are promising, and it could be said that the endonasal route potentially represents a valid option to treat lesions above the nasopalatine line.

Imaging Characterization of Non-Rheumatoid Retro-Odontoid Pseudotumors: Comparison with Atlantoaxial Manifestation of Rheumatoid Arthritis.

Backgroundand Objectives: To date, imaging characterization of non-rheumatic retro-odontoid pseudotumors (NRROPs) has been lacking; therefore, NRROPs have been confused with atlantoaxial joint involvement of rheumatoid arthritis (RA). It is important to differentiate these two disease because the treatment strategies may differ. The purpose of this study is to characterize imaging findings of NRROPs and compare them with those of RA. Material and Methods: From January 2015 to December 2019, 27 patients (14 women and 13 men) with NRROPs and 19 patients (15 women and 4 men) with RA were enrolled in this study. We evaluated various imaging findings, including atlantoaxial instability (AAI), and measured the maximum diameter of preodontoid and retro-odontoid spaces with magnetic resonance imaging (MRI) and computed tomography (CT). Results: Statistical significance was considered for p < 0.05. AAI was detected in eight patients with NRROPs and in all patients with RA (p < 0.0001). Seventeen patients with NRROPs and six patients with RA showed spinal cord compression (p = 0.047). Compressive myelopathy was observed in 14 patients with NRROPs and in 4 patients with RA (p = 0.048). Subaxial degeneration was observed in 25 patients with NRROPs and in 9 patients with RA (p = 0.001). Moreover, C2-3 disc abnormalities were observed in 11 patients with NRROPs and in 2 patients with RA (p = 0.02). Axial and longitudinal diameter of retro-odontoid soft tissue and preodontoid and retro-odontoid spaces showed significant differences between NRROP and RA patients (p < 0.0001). Furthermore, CT AAI measurements were differed significantly between NRROP and RA patients (p < 0.05). Conclusions: NRROPs showed prominent retro-odontoid soft tissue thickening, causing compressive myelopathy and a high frequency of subaxial and C2-3 degeneration without AAI.

Displaced odontoid synchondrosis fracture with C1-2 dysjunction in an 18-month-old child: challenges and solutions.

BACKGROUND: Odontoid synchondral fractures in very young children with displacement/angulation are highly unstable and require surgical intervention. Soft and small bones with poor pull-out strengths make instrumentation and manipulation difficult. CASE REPORT: We report an 18-month-old child with such a fracture where minimal traction made C1-2 dysjunction apparent with neurological worsening. The C1-2 facets were fixed with a short plate and facetal screws. The child had a good outcome. CONCLUSION: Traction should be applied cautiously to avoid distraction injuries. Careful intraoperative manipulation should be planned to avoid any pull outs/fractures while realigning the spine and fixing it.

Global alignment taking into account the cervical spine with odontoid hip axis angle (OD-HA).

INTRODUCTION: Global alignment analysis is of upmost importance in adult spinal deformity patients (ASD). Numerous parameters exist in the literature to measure global alignment based upon C7 or T1. One common limitation of these parameters is that they neglect the cervical segment which is essential in spinal compensatory mechanisms and in horizontal gaze preservation. A recent stereoradiography analysis of asymptomatic subjects introduced a new 3D parameter (ODHA), defined as the angle between the vertical reference line and the line joining the odontoid tip (OD) to hip axis center (HA). Thus, the goal of this study was to analyze 3D global alignment of ASD patients using the new parameter odontoid hip axis angle and its relationship to other spinal parameters. METHODS: In this prospective study, 90 adult patients with lumbar scoliosis (Cobb > 20°) were included. All subjects underwent low dose biplanar X-rays with 3D spinal reconstructions. Based on published normative values of ODHA, we defined abnormally high value as mean ODHA of asymptomatic subject + 2SD (i.e., ODHA > 6.1°). Values of 3D radiographic parameters and ODI were compared between patients with ODHA > 6.1° and < 6.1°. RESULTS: Mean ODHA was 5+/- 3.6° (0.4° to 18.6°). 22 patients had abnormally high ODHA. They were older than the 68 other patients (68+/- 9y vs 53+/- 14y, p = 0.001), without any significant difference in terms of sex, BMI and rate of rotatory subluxation (54% vs 62%, p = 0.06). However, coronal and sagittal deformity was more important in patients with abnormal ODHA (larger Cobb angle, coronal malalignment, pelvic tilt and lower lumbar lordosis). Patients with abnormal ODHA had significantly worst ODI (50+/- 23 vs 30+/- 18, p = 0.0005). CONCLUSION: Extreme values of ODHA are observed in significantly older patients with significant functional impairment. In addition, in these patients with sagittal malalignment with loss of lumbar lordosis, who recruit compensatory mechanisms such as pelvic retroversion, the cervical area is also involved with a posture in cervical hyperlordosis to maintain the head over the pelvis. Thus, ODHA is an interesting parameter allowing a more comprehensive alignment measurement taking into account the mechanisms of compensation of the cervical spine to the pelvis.

The impact of odontoid screw fixation techniques on screw-related complications and fusion rates: a systematic review and meta-analysis.

PURPOSE: The primary goal of this study was to conduct a systematic review and meta-analysis of articles focused on odontoid screw fixation (OSF) and screw-related complications or non-union rates. METHODS: We conducted a systematic review of the PubMed and Crossref databases between January 1982 and December 2019. Inclusion criteria comprised detailed descriptions of the surgical technique and screw-related complications (screw cut-out, loosening, breakage, malposition) or fusion rates. RESULTS: The initial selection consisted of 683 abstracts. A total of 150 full texts were chosen for detailed study, and 83 articles were included in the analysis. The point estimates for screw-related complications were as follows: 1. screw malposition frequency-4.8%; 2. screw cut-out rate-5.0%; 3. screw loosening/pull-out-3.8%; and 4. screw fracture rate-3.1%. The point estimate for the non-union rate was 9.7%. Statistical analysis of the screw-related complications rate based on surgical technique details was also performed CONCLUSIONS: Double-screw OSF performance in elder patients resulted in a higher risk of post-operative screw cut-out. In other cases, the development of screw-related complications did not depend on the method of intraoperative head fixation, selection of the implant entry point for OSF, type of the used screws, or cannulated instruments application. The outcomes of single-screw fixation through the anterior lip of the C2 vertebra were comparable to other techniques of OSF. Further, statistically reliable studies should be carried out to identify the optimal technique of OSF.

The odontoid-CSVL distance in a global population of asymptomatic volunteers: normative values and implications for spinal coronal alignment.

PURPOSE: In a population of asymptomatic volunteers across 5 countries, we sought to: (a) establish normative values of the Odontoid-Central Sacral Vertical Line (OD-CSVL) across patient factors, and (b) assess correlations of OD-CSVL with other radiographic parameters. METHODS: A prospective, cross-sectional study of asymptomatic adult volunteers, ages 18-80 years, were enrolled across 5 countries (France, Japan, Singapore, Tunisia, United States) forming the Multi-Ethnic Alignment Normative Study (MEANS) cohort. Included volunteers had no known spinal disorder(s), no significant neck/back pain (VAS ≤ 2; ODI ≤ 20), and no significant scoliosis (Cobb ≤ 20°). Radiographic measurements included commonly used coronal alignment parameters (mm) and angles (°). OD-CSVL was defined as the difference between the odontoid plumb line (line from the tip of the odontoid vertically down) and the CSVL (vertical line from the center of the sacrum). Chi-square, student's t tests, Kruskal-Wallis, Wilcoxon rank-sum, linear regression, and Pearson's correlation were used with significance at p < 0.05. RESULTS: 467 volunteers were included with normative OD-CSVL values by age decade, gender, BMI, and country. Mean ± SD OD-CSVL was 8.3 mm ± 6.5 mm and 31 (6.6%) volunteers were almost perfectly aligned (OD-CSVL < 1 mm). A linear relationship was seen between OD-CSVL with both age (p < 0.001) and BMI (p = 0.015). Significant variation was seen between OD-CSVL and 5 different ethnicities (p = 0.004). OD-CSVL correlated best with other coronal radiographic parameters, C7-CSVL (r = 0.743, p < 0.001), OD-knee (r = 0.230, p < 0.001), CAM-knee (r = 0.612, p < 0.001), and regional TL cobb angle (r = 0.4214, p = 0.005). CONCLUSION: Among asymptomatic volunteers, increased OD-CSVL was significantly associated with increased age, increased BMI, and ethnicity, but not gender. OD-CSVL correlated strongest with C7-CSVL, TL cobb angle, OD-knee, and CAM-knee. OD-CSVL. These results support further study of OD-CSVL in symptomatic adult spine deformity patients.

Does fracture-extension into the pars interarticularis alter outcomes in odontoid failure? a technical note on pars interarticularis osteotomy and atlantoaxial distraction arthrodesis.

PURPOSE: Odontoid process fractures can extend rostral into the C2 arch. We investigated the clinical impact of a concurrent fracture of the pars interarticularis on odontoid failure. To overcome the surgical challenges related to the morphology of these fractures, we describe a novel surgical strategy using atlantoaxial joint distraction arthrodesis. METHODS: We conducted a single centre cohort study of 13 consecutive patients with odontoid fractures extending into the pars treated between June 2016 and June 2018. Criteria for a stable fibrous non-union were: Atlanto-Dens Interval (ADI) < 3 mm, Posterior Atlanto-Dens Interval (PADI) > 14 mm and lack of symptomatic motion at the fracture site. Atlantoaxial instability was defined as greater than 50% subluxation across the C1-C2 joint. Return to pre-injury performance status was considered a satisfactory clinical outcome. RESULTS: The mean age of the patient population was 77.2 years (SD 11.9). The mean follow-up time was 15 months (SD 5.2). 69% had an associated atlantoaxial instability (P-value 0.0005). Cervical orthosis treatment was associated with a high non-union rate (70%) (P-value 0.04) although it did not affect the overall clinical outcome. 2 cases presented with cord compression were treated surgically with pars interarticularis osteotomy and atlantoaxial distraction arthrodesis. CONCLUSIONS: Odontoid fracture with extension into the pars interarticularis often present with atlantoaxial instability and may result in stable fibrous non-union if treated non-operatively. The C1-C2 segment can be stabilised with atlantoaxial distraction arthrodesis achieved through an osteotomy of the pars interarticularis.

Comparative study of 3D printed navigation template-assisted atlantoaxial pedicle screws versus free-hand screws for type II odontoid fractures.

OBJECTIVE: The objective of the study was to compare the safety, efficacy, and accuracy of the pedicle screws with the three-dimensional (3D) printed navigation template to the free-hand screws for type II odontoid fractures. PATIENTS AND METHODS: A total of 60 patients with type II odontoid fractures, treated with either template guiding pedicle screws or free-hand screws, were retrospectively assessed. The guiding group was treated with pedicle screws with the assistance of a virtual reality (VR) software-designed, 3D printed navigation template with two guide tubes. The safety rate and treatment efficacy of the screw placement, as well as the trajectory accuracy, were evaluated by respective measures and compared between two surgical groups. RESULTS: There were reduced surgical time (P < 0.05), blood loss (P < 0.01), and C-arm shots (P < 0.01) with 3D printed template guiding screws. The rates of safe pedicle screws in both C1 and C2 were significantly higher in 3D guiding group (P < 0.01) compared to the free-hand group, and the scores of visual analogue scale (VAS) and impairment scale (ASIA) were improved in guiding group at 1 week post-surgery (P < 0.01 and P < 0.05, respectively). Postoperative CT and image reconstruction showed the 3D guiding group had better horizontal screw accuracy on both sides of C1 (L: P < 0.001, R: P < 0.01) and C2 (L: P < 0.001, R: P < 0.01) than free-hand group. CONCLUSION: The herein screw technique using 3D printed navigation template leads to greater improvement in the screw safety, efficacy, and accuracy, which may be a promising alternative to free-hand surgery for the treatment of odontoid fractures.

Pediatric dens anatomy and its implications for fracture treatment: an anatomical and radiological study.

PURPOSE: Separation of C2 growth plates and dens fractures are the most common types of injuries to the axis (C2) in children. Operative treatment of these injuries with the use of direct osteosynthesis requires a profound knowledge of detailed anatomy and dimensions of the axis. The main issue addressed by the study was the age at which the size of the dens is adequate at all levels to accommodate two screws, and the size of the posterior dens angulation angle (PDAA) in a healthy child in individual age periods. METHODS: Dimensions and angles of the dens and C2 in individual age categories in both boys and girls were measured in a series of 203 CT scans of individuals 0-18 years old and on anatomical specimens (42 samples). In addition, 5 histological series of this region from the fetal period were reviewed. RESULTS: Dimensions of the dens gradually increase with age, with a considerable acceleration during growth spurt periods that are different in boys and girls. PDAA is markedly changing with age; in the fetal period, the dens shows a slight anterior angulation which gradually transforms into posterior angulation, as early as between 4 and 6 years of age. The screw insertion angle changes accordingly. CONCLUSION: During growth, there occur changes in PDAA that should be respected in evaluation of transformation of anterior into posterior angulation, as shown by imaging methods. Dens dimensions theoretically allow insertion of two 3.5 mm screws as early as from the age of 1 year.

Clinical features and early post-operative complications of isolated C2 odontoid fractures: a retrospective analysis using a national inpatient database in Japan.

PURPOSE: To examine the clinical features and post-treatment complications in patients with isolated C2 odontoid fractures. METHODS: We extracted data for all patients who were admitted with C2 odontoid fractures from the Japanese Diagnosis Procedure Combination database between July 2010 and March 2017. We then compared the post-treatment complications during hospitalization according to treatment types: conservative treatment (with or without use of halo-vest) and surgery (anterior or posterior spinal fixation). RESULTS: A total of 3167 patients (1533 men, 1634 women; mean age, 70 years) with isolated C2 odontoid fractures were identified, including 1124 patients (35%) aged ≥ 80 years. Among the total patients, 2476 (78%) received conservative treatment (with halo-vest, 728; without halo-vest, 1748). The remaining 691 patients (22%) underwent surgery (anterior surgery, 129; posterior surgery, 556; combined surgery, 6). There were no differences between the conservative treatment and surgery groups in baseline characteristics and preexisting comorbid conditions except for age (71 vs. 69 years, p = 0.042). In-hospital death occurred in 136 patients (4.3%). There was no significant difference in in-hospital mortality between the two groups (overall, conservative treatment 4.6% vs. surgery 3.0%, p = 0.066; age ≥ 80 years, conservative treatment 7.2% vs. surgery 5.4%, p = 0.34). Use of halo-vest was not associated with increased mortality (with halo-vest 3.7% vs. without halo-vest 5.0%, p = 0.15). CONCLUSION: The great majority of isolated odontoid fractures occurred in elderly patients. Conservative treatment and surgery had similarly low in-hospital mortality. Use of halo-vest was not associated with an increase in mortality.

A biomechanical comparison of a cement-augmented odontoid screw with a posterior-instrumented fusion in geriatric patients with an odontoid fracture type IIb.

PURPOSE: Possible surgical therapies for odontoid fracture type IIb include odontoid screw osteosynthesis (OG) with preservation of mobility or dorsal C1/2 fusion with restriction of cervical rotation. In order to reduce material loosening in odontoid screw osteosynthesis in patients with low bone density, augmentation at the base of the axis using bone cement has been established as a suitable alternative. In this study, we compared cement-augmented OG and C1/2 fusion according to Harms (HG). METHODS: Body donor preparations of the 1st and 2nd cervical vertebrae were randomized in 2 groups (OG vs. HG). The range of motion (ROM) was determined in 3 principle motion plains. Subsequently, a cyclic loading test was performed. The decrease in height of the specimen and the double amplitude height were determined as absolute values as an indication of screw loosening. Afterward, the ROM was determined again and loosening of the screws was measured in a computed tomography. RESULTS: A total of 16 were included. Two groups of 8 specimens (OG vs. HG) from patients with a median age of 80 (interquartile range (IQ) 73.5-85) years and a reduced bone density of 87.2 (IQ 71.2-104.5) mg/cc dipotassium hydrogen phosphate were examined for their biomechanical properties. Before and after exposure, the OG preparations were significantly more mobile. At the time of loading, the OG had similar loading properties to HG decrease in height of the specimen and the double amplitude height. Computed tomography revealed similar outcomes with regard to the screw loosening rate (62.5 vs. 87.5%, p = 0.586). CONCLUSION: In patients with an odontoid fracture type IIb and reduced bone density, cement-augmented odontoid screw yielded similar properties in the loading tests compared to the HG. It may, therefore, be considered as a primary alternative to preserve cervical mobility in these patients.