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Study Design: Single-center retrospective cohort study Objectives: Type II odontoid fractures occur disproportionately among elderly populations and cause significant morbidity and mortality. It is a matter of debate whether these injuries are best managed surgically or conservatively. Our goal was to identify how treatment modalities and patient characteristics correlated with functional outcome and mortality. Methods: We identified adult patients (>60 years) with traumatic type II odontoid fractures. We used multivariate regression controlling for patient demographics, Glasgow Coma Scale (GCS) score, Charlson Comorbidity Index (CCI), modified Rankin Scale (mRS) score, modified Frailty Index (mFI-5 and mFI-11), fracture displacement, and conservative vs operative treatment. Results: Of the 59 patients (mean age 77.9 years), 24 underwent surgical intervention and 35 underwent conservative management. Operatively managed patients were younger (73.4 vs 80.6 years, P <.001) and had higher degree of fracture displacement (3.5 vs 1.0 mm, P =.002) than conservatively managed patients but no other differences in baseline characteristics. Twenty-four patients (40.7%) died within the study period (median time to death: 376 days). There were no differences between treatment groups in functional outcomes (mRS or Frankel Grade) or mortality (33.3% in operative group vs 45.7%, P =.34). There was a statistically significant correlation between higher presentation mRS score and subsequent mortality on multivariate analysis (OR = 2.06, 95% CI 1.04-4.10, P =.039), whereas surgical intervention, age, GCS score, CCI, mFI-5, mFI-11, sex, and fracture displacement were not significantly correlated. Conclusions: Mortality after type II odontoid fractures in elderly patients is common. mRS score at presentation may help predict mortality more accurately than other patient factors. [ABSTRACT FROM AUTHOR]

Introduction: Atlas fractures often accompany traumatic dens fractures, but existing literature on the management of simultaneous atlantoaxial fractures is limited. Methods: We examined all patients with traumatic dens fractures at our institution between 2008 and 2018. We used multivariable logistic regression and ordinal logistic regression to identify factors independently associated with presentation with a simultaneous atlas fracture, as well myelopathy severity, fracture nonunion, and selection for surgery. Results: Two hundred and eighty-two patients with traumatic dens fractures without subaxial fractures were identified, including 65 (22.8%) with simultaneous atlas fractures. The distribution of injury mechanisms differed between groups (χ2 P = 0.0360). On multivariable logistic regression, dens nonunion was positively associated with type II fractures (odds ratio [OR] = 2.00, P = 0.038) and negatively associated with having surgery (OR = 0.52, P = 0.049), but not with having a C1 fracture (P = 0.3673). Worse myelopathy severity on presentation was associated with having a severe injury severity score (OR = 102.3, P < 0.001) and older age (OR = 1.28, P = 0.002), but not with having an atlas fracture (P = 0.2446). Having a simultaneous atlas fracture was associated with older age (OR = 1.29, P = 0.024) and dens fracture angulation (OR = 2.62, P = 0.004). Among patients who underwent surgery, C1/C2 posterior fusion was the most common procedure, and having a simultaneous atlas fracture was associated with selection for occipitocervical fusion (OCF) (OR = 14.35, P = 0.010). Conclusions: Among patients with traumatic dens, patients who have simultaneous atlas fractures are a distinct subpopulation with respect to age, mechanism of injury, fracture morphology, and management. Traumatic dens fractures with simultaneous atlas fractures are independently associated with selection for OCF rather than posterior cervical fusion alone.

Retro-ondontoid pseudotumors represent soft tissue proliferation surrounding the transverse ligament of the atlas, which most commonly results in cervical neck pain or myelopathy due to impingement upon the cervicomedullary junction. The causes of retro-odontoid pseudotumor formation are varied and include metabolic, inflammatory, degenerative, and post-traumatic etiologies. To the best of our knowledge, an abducens nerve palsy as a result of a complex retro-odontoid pseudotumor has never been reported. We discuss a case of a 90-year-old woman who presents with acute lateral gaze palsy with multimodality imaging demonstrating a retro-odontoid pseudotumor with an unusual protrusion which courses superolaterally to the level of the pons and compresses the abducens nerve root entry zone.

Introduction: Atlas fractures often accompany traumatic dens fractures, but existing literature on the management of simultaneous atlantoaxial fractures is limited. Methods: We examined all patients with traumatic dens fractures at our institution between 2008 and 2018. We used multivariable logistic regression and ordinal logistic regression to identify factors independently associated with presentation with a simultaneous atlas fracture, as well myelopathy severity, fracture nonunion, and selection for surgery. Results: Two hundred and eighty-two patients with traumatic dens fractures without subaxial fractures were identified, including 65 (22.8%) with simultaneous atlas fractures. The distribution of injury mechanisms differed between groups (χ2 P = 0.0360). On multivariable logistic regression, dens nonunion was positively associated with type II fractures (odds ratio [OR] = 2.00, P = 0.038) and negatively associated with having surgery (OR = 0.52, P = 0.049), but not with having a C1 fracture (P = 0.3673). Worse myelopathy severity on presentation was associated with having a severe injury severity score (OR = 102.3, P < 0.001) and older age (OR = 1.28, P = 0.002), but not with having an atlas fracture (P = 0.2446). Having a simultaneous atlas fracture was associated with older age (OR = 1.29, P = 0.024) and dens fracture angulation (OR = 2.62, P = 0.004). Among patients who underwent surgery, C1/C2 posterior fusion was the most common procedure, and having a simultaneous atlas fracture was associated with selection for occipitocervical fusion (OCF) (OR = 14.35, P = 0.010). Conclusions: Among patients with traumatic dens, patients who have simultaneous atlas fractures are a distinct subpopulation with respect to age, mechanism of injury, fracture morphology, and management. Traumatic dens fractures with simultaneous atlas fractures are independently associated with selection for OCF rather than posterior cervical fusion alone. [ABSTRACT FROM AUTHOR]

Dens fractures are an increasingly common injury, yet their epidemiology and its implications remain underexamined. We retrospectively analyzed all traumatic dens fracture patients managed at our institution over a 10-year period, examining demographic, clinical, and outcomes data. Patient subsets were compared across these parameters. Among 303 traumatic dens fracture patients, we observed a bimodal age distribution with a strong goodness of fit centered at age 22.3 ± 5.7 (R = 0.8781) and at 77.7 ± 13.9 (R = 0.9686). A population pyramid demonstrated a bimodal distribution among male patients, but not female patients, which was confirmed with a strong goodness of fit for male patient subpopulations age <35 (R = 0.9791) and age ≥35 (R = 0.8843), but a weaker fit for a second female subpopulation age <35. Both age groups were equally likely to undergo surgery. Patients younger than age 35 were more likely to be male (82.4% vs. 46.9%, odds ratio [OR] = 5.29 [1.54, 17.57], P = 0.0052), have motor vehicle collision as their mechanism of injury (64.7% vs. 14.1%, OR = 11.18 [3.77, 31.77], P < 0.0001), and to have a severe trauma injury severity score (17.6% vs. 2.9%, OR = 7.23 [1.88, 28.88], P = 0.0198). Nevertheless, patients age <35 were less likely to have fracture nonunion at follow (18.2% vs. 53.7%, OR = 0.19 [0.041, 0.76], P = 0.0288). The dens fracture patient population comprises 2 subpopulations, distinguished by differences in age, sex, injury mechanism and severity, and outcome, with male dens fracture patients demonstrating a bimodal age distribution. Young, male patients were more likely to have high-energy injury mechanisms leading to severe trauma, yet were less likely to have fracture nonunion at follow-up. [ABSTRACT FROM AUTHOR]

Background: Patients with simultaneous fractures of the atlas and dens have traditionally been managed according to the dens fracture's morphology, but data supporting this practice are limited. Methods: We retrospectively examined all patients with traumatic atlas fractures at our institution between 2008 and 2016. We used multivariable regression and propensity score matching to compare the presentation, management, and outcomes of patients with isolated atlas fractures to patients with simultaneous atlas-dens fractures. Results: Ninety-nine patients were identified. Patients with isolated atlas fractures were younger (61 ± 22 vs. 77 ± 14, P = 0.0003), had lower median Charlson Comorbidity Index (3 vs. 5, P = 0.0005), had better presenting Nurick myelopathy scores (0 vs. 3, P < 0.0001), and had different mechanisms of injury (P = 0.0011). Multivariable regression showed that having a simultaneous atlas-dens fracture was independently associated with older age (odds ratio [OR] =1.59 [1.22, 2.07], P = 0.001), worse presenting myelopathy (OR = 3.10 [2.04, 4.16], P < 0.001), and selection for surgery (OR = 4.91 [1.10, 21.97], P = 0.037). Propensity score matching yielded balanced populations (Rubin's B = 23.3, Rubin's R = 1.96) and showed that the risk of atlas fracture nonunion was no different among isolated atlas fractures compared to simultaneous atlas-dens fractures (P = 0.304). Age was the only variable independently associated with atlas fracture nonunion (OR = 2.39 [1.15, 5.00], P = 0.020), having a simultaneous atlas-dens fracture was not significant (P = 0.2829). Conclusions: Among patients with atlas fractures, simultaneous fractures of the dens occur in older patients and confer an increased risk of myelopathy and requiring surgical stabilization. Controlling for confounders, the risk of atlas fracture nonunion is equivalent for isolated atlas fractures versus simultaneous atlas-dens fractures. [ABSTRACT FROM AUTHOR]

Purpose: Motor-evoked potentials (MEPs) evaluated with transcranial magnetic stimulation (TMS) allow functional evaluation of corticospinal conduction. The aim of this study is to evaluate the value of MEPs for the assessment of spinal cord transmission in clinically minimally symptomatic or asymptomatic patients with acute-subacute odontoid pathologies. Material and Methods: The MEPs were measured from five cases with acute-subacute odontoid dislocations by using TMS. Demographic features, neurological examinations, and neuroimaging findings of the patients have also been recorded. Results: The central motor conduction times (CMCTs) and MEP latencies were prolonged bilaterally in all patients with acute-subacute odontoid dislocation. Additionally, MEP amplitudes were also found to be decreased in all cases. Conclusions: MEP is quite valuable to show involvement in clinically and radiologically silent cases. Our findings in acute-subacute cases without myelopathy showed us that the CMCTs were prolonged especially in the cases who had motor deficits but also in asymptomatic cases. [ABSTRACT FROM AUTHOR]

Objective Chronic ‘displaced’ displaced type II fractures, though uncommon, are difficult to manage. They usually require a transoral procedure followed by a posterior instrumented fusion. We describe here, a new method to reduce the fractured displaced odontoid using a posterior cervical approach only. Methods Prospective and observational, n=14 had a ‘displaced and irreducible’ old fracture dens causing cord compression (type I, 1; type II, 13). They underwent a novel technique to reduce the fracture. The C1 arch was first drilled and removed. The C1 lateral masses on both sides were then drilled completely and a spacer was placed between the occiput and C2 facet. Following this, an intraoperative reducing maneuver was performed, utilizing the spacer as a fulcrum, and then achieving complete reduction and realignment. Results All patients improved clinically (mean Nurick preoperative score: 4.07±0.8; the postoperative score was 1.3±0.4). The mean correction in effective canal diameter was 74.3%±9.5% and the mean correction in actual canal diameter was 77%±8.7%. Solid bone fusion was demonstrated in 12 patients with at least 1-year follow-up (follow-up range, 12–35 months; mean, 21.8±9.8 months). Conclusion The new described modification of distraction, compression extension, and reduction seems to be effective for ‘displaced’ chronic fracture dens with cord compression. It avoids additional transoral surgery in these patients.

Background: Patients with simultaneous fractures of the atlas and dens have traditionally been managed according to the dens fracture's morphology, but data supporting this practice are limited. Methods: We retrospectively examined all patients with traumatic atlas fractures at our institution between 2008 and 2016. We used multivariable regression and propensity score matching to compare the presentation, management, and outcomes of patients with isolated atlas fractures to patients with simultaneous atlas-dens fractures. Results: Ninety-nine patients were identified. Patients with isolated atlas fractures were younger (61 ± 22 vs. 77 ± 14, P = 0.0003), had lower median Charlson Comorbidity Index (3 vs. 5, P = 0.0005), had better presenting Nurick myelopathy scores (0 vs. 3, P < 0.0001), and had different mechanisms of injury (P = 0.0011). Multivariable regression showed that having a simultaneous atlas-dens fracture was independently associated with older age (odds ratio [OR] =1.59 [1.22, 2.07], P = 0.001), worse presenting myelopathy (OR = 3.10 [2.04, 4.16], P < 0.001), and selection for surgery (OR = 4.91 [1.10, 21.97], P = 0.037). Propensity score matching yielded balanced populations (Rubin's B = 23.3, Rubin's R = 1.96) and showed that the risk of atlas fracture nonunion was no different among isolated atlas fractures compared to simultaneous atlas-dens fractures (P = 0.304). Age was the only variable independently associated with atlas fracture nonunion (OR = 2.39 [1.15, 5.00], P = 0.020), having a simultaneous atlas-dens fracture was not significant (P = 0.2829). Conclusions: Among patients with atlas fractures, simultaneous fractures of the dens occur in older patients and confer an increased risk of myelopathy and requiring surgical stabilization. Controlling for confounders, the risk of atlas fracture nonunion is equivalent for isolated atlas fractures versus simultaneous atlas-dens fractures.

A new species of Dunkleosteus, D. tuderensis sp. nov., is named based on an infragnathal from the Famennian of the Tver Region, Russia. CT scanning of the holotype revealed two high-density bony constituents comparable in position and interrelations to components described for coccosteomorph arthrodires, supported by the presence of at least two clusters of large vascular canals marking separate arterial supplies. Coccosteomorph and dunkleosteid pachyosteomorphs exhibit similar growth patterns including labio-basal depositions of vascularized bone in the infragnathals and basally in the supragnathals. In contrast to coccosteomorphs, dunkleosteid reinforcement of the occlusal margins occurred via the formation of dense osteonal bone, in parallel with resorption forming extensive lingual fossae. Active bone remodeling proceeded without a complete reworking of the primary osteonal bone structure and the original arrangement of vascular canals. Due to inconsistent anatomical terminology in gnathal elements of dunkleosteid arthrodires, a revised terminology is suggested and new terms are introduced. [ABSTRACT FROM AUTHOR]

Over the last few decades, the importance of the sagittal plane and its contour has gained significant recognition. Through full-body stereoradiography, the understanding of compensatory mechanisms, and the concept of global balance and reciprocal change has expanded. There have been a few reports describing how cervical realignment surgery affects global spinal alignment (GSA) and global balance. Despite the research efforts, the concept of reciprocal change and global balance is still perplexing. Understanding the compensatory status and main drivers of deformity in a patient is vital because the compensatory mechanisms may resolve reciprocally following cervical realignment surgery. A meticulous preoperative evaluation of the whole-body alignment, including the pelvis and lower extremities, is paramount to appreciate optimal GSA in the correction of spinal malalignment. This study aims to summarize relevant literature on the reciprocal changes in the whole body caused by cervical realignment surgery and review recent perspectives regarding cervical compensatory mechanisms.

Objective C2 slope (C2S), a cervical parameter mathematically approximated as T1 slope minus cervical lordosis (T1S–CL), predicts functional improvement in cervical deformity patients. Nonetheless, C2S is a positional parameter based only on the horizontal axis. The current study aims to introduce novel odontoid parameters and establish their relationships with patient-reported health-related quality of life (HRQoL). Methods Lateral plain radiographs of 32 adults who underwent multilevel posterior cervical fusion were analyzed. The odontoid parameters included odontoid incidence (OI), C2S, odontoid tilt (OT), and gravity line-C2 distance (GL-C2), while the cervical parameters were the Cobb angle at C0–1, C1–2, C0–2, C2–7, C2–7 sagittal vertical axis (cSVA), T1 slope, and T1S–CL. The range of motion (ROM) of the occipito-atlantoaxial complex was measured in flexion and extension plain radiographs. Scores on the Neck Disability Index (NDI) and visual analogue scale (VAS) for axial neck (VASn) and arm pain were measured. Results Compared to asymptomatic subjects, patients had larger C2S, cSVA, and T1S–CL, and smaller OT. Preoperatively, OI was significantly correlated with the ROM of C1–2 (r = 0.37, p < 0.05) and C0–2 (r = 0.46, p < 0.01). OT and C2S had significant correlations with the C0–1, C1–2, and C0–2 angles, GL-C2, and T1S–CL. Postoperative NDI scores were significantly correlated with OI (r = -0.40, p < 0.05) and OT (ρ = -0.37, p < 0.05). VASn was significantly correlated with GL-C2 (r = -0.35, p < 0.05). Conclusion The odontoid parameters were significantly correlated with established cervical parameters and HRQoL measures. OI is a constant parameter representing the individual's compensatory reservoir at the upper cervical spine.

Objective: Chronic 'displaced' displaced type II fractures, though uncommon, are difficult to manage. They usually require a transoral procedure followed by a posterior instrumented fusion. We describe here, a new method to reduce the fractured displaced odontoid using a posterior cervical approach only. Methods: Prospective and observational, n = 14 had a 'displaced and irreducible' old fracture dens causing cord compression (type I, 1; type II, 13). They underwent a novel technique to reduce the fracture. The C1 arch was first drilled and removed. The C1 lateral masses on both sides were then drilled completely and a spacer was placed between the occiput and C2 facet. Following this, an intraoperative reducing maneuver was performed, utilizing the spacer as a fulcrum, and then achieving complete reduction and realignment. Results: All patients improved clinically (mean Nurick preoperative score: 4.07 ± 0.8; the postoperative score was 1.3 ± 0.4). The mean correction in effective canal diameter was 74.3% ± 9.5% and the mean correction in actual canal diameter was 77% ± 8.7%. Solid bone fusion was demonstrated in 12 patients with at least 1-year follow-up (follow-up range, 12-35 months; mean, 21.8 ± 9.8 months). Conclusion: The new described modification of distraction, compression extension, and reduction seems to be effective for 'displaced' chronic fracture dens with cord compression. It avoids additional transoral surgery in these patients. [ABSTRACT FROM AUTHOR]

Objective By using angulation of the axis itself, this study aims to define and analyze odontoid incidence (OI) and odontoid tilt (OT) as novel cervical alignment parameters and investigate their correlations with cervical alignment. Methods Novel and existing parameters were measured with whole-spine lateral plain radiographs and EOS images of 42 adults without cervical symptoms. The correlations of OI, OT, C2 slope (C2S), and T1 slope (T1S) were calculated. Results The OI, OT, and C2S showed significant correlations with C2–7 angle (r = 0.43, r = -0.42, r = 0.62, respectively) and C0–2 angle (r = -0.33, r = 0.48, r = -0.61, respectively). OI, OT, T1S were independent predictors of the C2–7 angle in univariate regression analysis (adjusted-R2 = 0.17, R2 = 0.15, R2 = 0.28, respectively). OI, OT, and T1S were independent predictors in the multivariable regression analysis with estimated standardized coefficients of 0.36, -0.67, -0.69, respectively (adjusted- R2 = 0.80, p < 0.001). Regarding the C0–2 angle, OI and OT were independent predictors in the univariate regression analysis (adjusted-R2 = 0.08, R2 = 0.21, respectively). Conclusion OI, OT, and C2S had significant correlations with cervical alignment. As the pelvic incidence, the OI is the only anatomical and constant parameter that could be used as a reference point related to the cervical spine from the rostral end. The study results may serve as baseline data for further studies on the alignment and balance of the cervical spine.

Purpose: Anterior trans-articular C1–C2 screw placement can be considered as a surgical alternative in different conditions affecting the atlantoaxial region. While its rigidity is similar to posterior Magerl and Harms techniques, it also provides some surgical advantages. However, the literature lacks papers exhaustively describing indication criteria, surgical steps, and pitfalls. Methods: This is a radiological study on 100 healthy subjects. Thin-layer CT scans of the craniovertebral junction were retrieved from the institutional database. The coronal inclination of the C1–C2 joint rim and the depth of the entry point of the screw with respect to the anterior profile of C2 were measured. The antero-posterior and the medio-lateral surgical corridors for the screw placement, and the wideness of the target area on the upper surface of C1 were also measured. Results: The multivariate analysis showed that the coronal inclination of the C1–C2 articular joint rim strongly influences the surface extension of the C1 target area; the depth of the entry point and the C1–C2 articular rim inclination seem to be independent factors in influencing both the medio-lateral and the antero-posterior surgical corridors wideness. A decisional algorithm on whether to perform an anterior or posterior approach to the atlantoaxial region was also proposed. Conclusions: We can conclude that, as much as the C1–C2 articular rim is tending to the horizontal line, and as deeper is the entry point of the screw on the anterior profile of C2, as easier the anterior C1–C2 trans-articular screw placement will result. [ABSTRACT FROM AUTHOR]

Case: Two patients with delayed presentations of neck pain and fixed kyphotic deformity after trauma were found to have atlantoaxial spondyloptosis (AAS) with type II dens fractures. Owing to the rarity of AAS, outcomes and optimal treatment are not well understood. In both cases, closed reduction was achieved with a dynamic overhead traction setup, followed by posterior surgical stabilization with C1-2 screw fixation. Conclusion: Closed reduction remains a challenge because of the marked deformity of interlocking C1-C2 joints. However, patients with chronic fixed atlantoaxial dislocation due to odontoid fractures can be safely managed with closed reduction and fusion of C1-C2. Level of Evidence: Level V. [ABSTRACT FROM AUTHOR]

Osteoid osteoma (OO) is a primary benign tumor that accounts for up to 3% of all bone tumors. The cervical spine is less affected by OOs, and very few cases of C2 OOs have been reported in the literature, both in adults and children. Surgery may be required in case of functional torticollis, stiffness, and reduced range of motion (ROM) due to cervical OOs refractory to medical therapy. Several posterior and anterior surgical techniques have been described to remove C2 OOs. In particular, anterior approaches to the cervical spine represent the most used surgical route for treating C2 OOs. We describe the first case of OO of the odontoid process removed through a transnasal endoscopic approach with the aid of neuronavigation in a 6-year-old child. No intraoperative complications occurred, and the post-operative course was uneventful. The patient had immediate relief of neck pain and remained pain-free throughout the follow-up period, with complete functional recovery of the neck range of motion (ROM). In this case, based on the favorable anatomy, the transnasal endoscopic approach represented a valuable strategy for the complete removal of an anterior C2 OO without the need for further vertebral fixation since the preservation of ligaments and paravertebral soft tissue. [ABSTRACT FROM AUTHOR]

A new species of Dunkleosteus, D. tuderensis sp. nov., is named based on an infragnathal from the Famennian of the Tver Region, Russia. CT scanning of the holotype revealed two high-density bony constituents comparable in position and interrelations to components described for coccosteomorph arthrodires, supported by the presence of at least two clusters of large vascular canals marking separate arterial supplies. Coccosteomorph and dunkleosteid pachyosteomorphs exhibit similar growth patterns including labio-basal depositions of vascularized bone in the infragnathals and basally in the supragnathals. In contrast to coccosteomorphs, dunkleosteid reinforcement of the occlusal margins occurred via the formation of dense osteonal bone, in parallel with resorption forming extensive lingual fossae. Active bone remodeling proceeded without a complete reworking of the primary osteonal bone structure and the original arrangement of vascular canals. Due to inconsistent anatomical terminology in gnathal elements of dunkleosteid arthrodires, a revised terminology is suggested and new terms are introduced.

Objective The conventional criteria for defining the basilar invagination (BI) focus on the relationship of odontoid tip to basion and opisthion, landmarks that are intrinsically variable especially in presence of occipitalised atlas. A universal single reference line is proposed that helps in unequivocally establishing the diagnosis of BI, may be relevant in establishing both Goel types A and B BI, as well as in differentiating a ‘very high’ from ‘regular’ BI. Methods Study design – case-control study. In 268 patients (group I with BI [n = 89] including Goel type A BI [n = 66], Goel type B BI [n = 23], and group II controls [n = 179]), the perpendicular distance between odontoid tip and line subtended between posterior tip of hard palate-internal occipital protuberance (P-IOP line) was measured. Logistic regression analysis determined factors influencing the proposed parameter (p < 0.05). Results In patients with a ‘very high’ BI (n = 5), the odontoid tip intersected/or was above the P-IOP line. In patients with a ‘regular’ BI (n = 84), the odontoid tip was 6.56 ± 3.9mm below the P-IOP line; while in controls, this distance was 12.53 ± 4.28 mm (p < 0.01). In Goel type A BI, the distance was 7.01 ± 3.78 mm and in type B BI, it was 5.07 ± 4.19 mm (p = 0.004). Receiver-operating characteristic curve analysis identified 9.0 mm (8.92–9.15 mm) as the cut-point for diagnosing BI using the odontoid tip-P-IOP line distance as reference. Conclusion The odontoid tip either intersecting the P-IOP line (very high BI) or being < 9 mm below the P-IOP line (Goel types A and B BI) is recommended as highly applicable criteria to establish the diagnosis of BI. This parameter may be useful in establishing the diagnosis in all varieties of BI.

Retro-odontoid pseudotumor formation consists of an abnormal growth of granulation tissue typically posterior to the odontoid process, resulting as a manifestation of atlantoaxial instability. This instability can occur as a result of conditions ranging from severe mechanical trauma to metabolic disease or autoimmune conditions such as rheumatoid arthritis. A pseudotumor may impinge on the spinal nerves or even the spinal cord and brainstem, manifesting symptoms from severe neck pain to cervicomedullary compression or myelopathy, and in some cases even sudden death. The objective of this review is to consolidate the findings in published case reports and relevant prior literature reviews regarding the formation of retro-odontoid pseudotumor. We address the pathophysiology involved in acquired and congenital pseudotumor formation, including those associated with rheumatoid arthritis (panni). Additionally, we discuss past and current operative techniques designed to curtail and ultimately regress a retro-odontoid pseudotumor and pannus. Surgical techniques that are addressed include ventral decompression (both transoral and transnasal), dorsal decompression, and indications for posterior instrumentation in pannus formation, particularly in cases that may be sufficiently treated in lieu of an anterior approach. Finally, we will examine the role of external orthoses as both a method of conservative treatment as well as a potential adjunct to the aforementioned surgical procedures.

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. [ABSTRACT FROM AUTHOR]

Objective We aimed to report the treatment approaches we administered to the patients admitted to our clinic for odontoid fracture, accompanied by literature. Material and Methods Eighteen patients with odontoid fracture who admitted to our clinic were evaluated retrospectively. Six patients were female, twelve patients were male and the mean age was 45,5 (16-87). Type 1 fracture in 7 patients, Type 2 fracture in 4 patients and Type 3 fractures in 7 patients were determined. As 86% of the patients with type 1 fracture, and 57% of the patients with type 3 fracture were treated conservatively, all patients with type 2 fracture treated with anterior odontoid screw and in 1 patient with type 3 fracture posterior arthrodesis was performed. Six of the conservatively treated patients used Halo-Vest, 3 of them used Philadelphia cervical collar, and 2 of them used sterno-occipito-mandibular immobilizer (SOMI). Results Fusion was occurred in 7 patients (64%) of 11 patients, who treated conservatively, and in the 4 patients (36%) surgery was planned as non-fusion was occurred. Two of these patients with no symptoms did not accept surgery. In one patient, with anterior surgery, posterior occipitocervical fusion was done as screw malposition was seen. Conclusion In decision making of the odontoid fractures, type of the fracture and age of the patient should be considered. As deciding the surgical technique beside clinical improvement, fusion rate is also important. In the elder patients anterior screwing should be preferred to conserve mobility; in the older patients posterior fusion should be preferred not to have mechanical deficiency and to minimize the other complications. However appropriate treatment strategy is still not clear. [ABSTRACT FROM AUTHOR]

Background: Cervical spine injury is the most common vertebral injury after major trauma, 20% of all cervical fractures happen to be odontoid fractures. In young adults, odontoid fracture usually happens as a result of high-energy trauma after a motor vehicle accident (MVA). MVA in Riyadh represents 38.4% of all trauma cases, in which the head-and-neck are the most injured body parts. This research aims to provide information about the incidence of odontoid process fracture post-MVA in Riyadh, Saudi Arabia. Methods: The design of this study was retrospective. A single level one trauma center database (trauma registry) was used to identify odontoid fractures post-MVA. All trauma cases from 2008 to the most recent were included, a total of 17,047 patients, to identify cervical spine fractures and further identify odontoid fracture incidence. The patients' radiographs were reviewed retrospectively, and odontoid fractures were classified by a board-certified spine surgeon. A descriptive analysis was carried out to report basic data distribution. Pearson's correlation was carried out to assess associations. Results: A total number of cervical spine fracture was 1195 patients (6.6% of the total sample). The incidence of odontoid fractures during the entire study period from 2008 to 2018 was 42 of 480 patients with C2 cervical trauma, constituting 8.75% C2 fractures, and 3.5% of cervical spine fractures. The mean age was 41.75 ± 18 years. There were three patients (onemale, two females) with type I odontoid fracture, 26 (all males) with type II, and 13 (11 males, 2 females) with type III. Most patients were managed conservatively (83.33%), whereas 16.67% underwent surgical management. Conclusion: The incidence of posttraumatic odontoid fractures is low, given the younger population of this study. This does not predict future incidence rates with the continued improvement of road traffic laws and awareness in the population.

Abstract Background Treatment of odontoid fractures with odontoid screws is an established method for fusion. However, it is facilitated by using advanced equipment in the operating theatre not always available as in developing countries. Objectives In this study we aim to outline the important key points for successful placement of odontoid screw in the absence of advanced tools, e.g. navigation or O-arm. Materials and methods Fifteen patients suffering from type II odontoid fractures were managed with single odontoid screw. Reduction of the fractures was achieved. A simple instrument set was used with the help of a single plane image intensifier. Longitudinal incision was used in 4 cases, and transverse incision was used in the remaining eleven cases. Anatomical identification of the midline helped to mark the entry point. The entry point used was millimetres below the anteroinferior edge of the axis vertebra. A short-headed screw was used. Results Road traffic accident was the only mechanism of trauma reported in our study. All of the patients were neurologically intact. All of the patients remained neurologically intact after the procedure. There were no instances of wrong trajectory of the screw in our study. During follow-up, we found good union of all the fractures. Only 2 cases suffered from mild dysphagia. Conclusion Fixation of odontoid fractures by anterior odontoid screws appears to be a safe and feasible procedure even in underequipped theatres. Anatomical knowledge helps in determining midline. Various modifications can help in overcoming shortcomings.

Odontoid pannus is an abnormal collection of degenerative or inflammatory tissue on the C1-dens joint that can result in severe spinal cord compression myelopathy. Treatment options vary depending on severity and etiology. In cases of severe cord compression, surgical management could be either through a purely posterior approach or in combination with an anterior decompression via endoscopic endonasal approach (EEA). This case presents a 77-year-old female who underwent posterior cervical fixation for odontoid pannus causing dramatic cervical myelopathy who failed to improve over a 6-month period and required anterior transodontoid pannus resection and decompression via EEA. The video can be found here: https://stream.cadmore.media/r10.3171/2024.1.FOCVID23176., Competing Interests: Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this publication.The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this publication., (© 2024, The Authors.)

Osteoid osteoma (OO) is a primary benign tumor that accounts for up to 3% of all bone tumors. The cervical spine is less affected by OOs, and very few cases of C2 OOs have been reported in the literature, both in adults and children. Surgery may be required in case of functional torticollis, stiffness, and reduced range of motion (ROM) due to cervical OOs refractory to medical therapy. Several posterior and anterior surgical techniques have been described to remove C2 OOs. In particular, anterior approaches to the cervical spine represent the most used surgical route for treating C2 OOs. We describe the first case of OO of the odontoid process removed through a transnasal endoscopic approach with the aid of neuronavigation in a 6-year-old child. No intraoperative complications occurred, and the post-operative course was uneventful. The patient had immediate relief of neck pain and remained pain-free throughout the follow-up period, with complete functional recovery of the neck range of motion (ROM). In this case, based on the favorable anatomy, the transnasal endoscopic approach represented a valuable strategy for the complete removal of an anterior C2 OO without the need for further vertebral fixation since the preservation of ligaments and paravertebral soft tissue.

Background: Fractures can occur in various locations within the odontoid process with differing orientations. However, little is known about what factors contribute to the anterior versus posterior angles/orientation of these fractures. Methods: We evaluated 74 patients with odontoid fractures (2013-2018) from a single-institution. Patients' fracture angles/orientations were measured on computed tomography studies, and were grouped into oblique posterior (OP) or oblique anterior (OA) groups. We also took into account cervical sagittal balance utilizing upright x-rays. Other variables studied included patients' ages, sagittal balance measurements, and the mechanisms of injury. Results: Fracture angles were significantly steeper in the OP group. OP fractures had larger C2-C7 sagittal vertical axis, occiput-C2 angles, and occiput-C7 angles versus anteriorly oriented fractures. In our linear regression model, advanced age and large occiput-C2 angles were predictive of the odontoid fracture angle. Patients who sustained ground-level falls also had significantly steeper fracture angles versus those involved in motor vehicle accidents. Conclusion: The odontoid tends to fracture at a steep, posterior angle in elderly patients who demonstrate a large positive sagittal balance when the head is extended following a ground-level falls. [ABSTRACT FROM AUTHOR]

Case: We report a case of self-inflicted transoral gunshot injury in a 24-year-old man resulting in mechanical block to cervical rotation. Anterior surgical removal of the pellet was successful with the patient experiencing no early or long-term functional deficits. Conclusion: Given the rarity of a cervical spine injury from gunshot wound without long-term complications, this unique case supports the role of early operative management in such injuries. [ABSTRACT FROM AUTHOR]

The fixation of type 2 odontoid fractures poses significant challenges in the elderly population due to coexistent osteoporosis and communition resulting in a high failure rate with conventional anterior screw fixation. Two elderly patients with unstable odontoid peg fractures and coexistent osteoporosis were treated with stentoplasty and anterior odontoid screw fixation. Additional anterior transarticular C1–2 screws were placed to address C1–2 instability. Both patients made an uneventful clinical recovery. One of the anterior C1–2 screws loosened due to the poor purchase in the osteoporotic bone in one patient. This did not affect the final outcome, and both the patients demonstrated maintained reduction and good alignment of odontoid peg after 2 years of follow-up. There was no intraoperative cement leak, pseudoarthrosis, or loss of reduction. Stentoplasty coupled with the anterior odontoid screw is a safe technique that can provide a biomechanically sound fixation of type 2 odontoid fractures in the presence of osteoporosis and significant communition.

Objective: The conventional criteria for defining the basilar invagination (BI) focus on the relationship of odontoid tip to basion and opisthion, landmarks that are intrinsically variable especially in presence of occipitalised atlas. A universal single reference line is proposed that helps in unequivocally establishing the diagnosis of BI, may be relevant in establishing both Goel types A and B BI, as well as in differentiating a 'very high' from 'regular' BI. Methods: Study design - case-control study. In 268 patients (group I with BI [n = 89] including Goel type A BI [n = 66], Goel type B BI [n = 23], and group II controls [n = 179]), the perpendicular distance between odontoid tip and line subtended between posterior tip of hard palate-internal occipital protuberance (P-IOP line) was measured. Logistic regression analysis determined factors influencing the proposed parameter (p < 0.05). Results: In patients with a 'very high' BI (n = 5), the odontoid tip intersected/or was above the P-IOP line. In patients with a 'regular' BI (n = 84), the odontoid tip was 6.56 ± 3.9mm below the P-IOP line; while in controls, this distance was 12.53 ± 4.28 mm (p < 0.01). In Goel type A BI, the distance was 7.01 ± 3.78 mm and in type B BI, it was 5.07 ± 4.19 mm (p = 0.004). Receiver-operating characteristic curve analysis identified 9.0 mm (8.92-9.15 mm) as the cut-point for diagnosing BI using the odontoid tip-P-IOP line distance as reference. Conclusion: The odontoid tip either intersecting the P-IOP line (very high BI) or being < 9 mm below the P-IOP line (Goel types A and B BI) is recommended as highly applicable criteria to establish the diagnosis of BI. This parameter may be useful in establishing the diagnosis in all varieties of BI. [ABSTRACT FROM AUTHOR]

Retro-odontoid pseudotumor formation consists of an abnormal growth of granulation tissue typically posterior to the odontoid process, resulting as a manifestation of atlantoaxial instability. This instability can occur as a result of conditions ranging from severe mechanical trauma to metabolic disease or autoimmune conditions such as rheumatoid arthritis. A pseudotumor may impinge on the spinal nerves or even the spinal cord and brainstem, manifesting symptoms from severe neck pain to cervicomedullary compression or myelopathy, and in some cases even sudden death. The objective of this review is to consolidate the findings in published case reports and relevant prior literature reviews regarding the formation of retro-odontoid pseudotumor. We address the pathophysiology involved in acquired and congenital pseudotumor formation, including those associated with rheumatoid arthritis (panni). Additionally, we discuss past and current operative techniques designed to curtail and ultimately regress a retro-odontoid pseudotumor and pannus. Surgical techniques that are addressed include ventral decompression (both transoral and transnasal), dorsal decompression, and indications for posterior instrumentation in pannus formation, particularly in cases that may be sufficiently treated in lieu of an anterior approach. Finally, we will examine the role of external orthoses as both a method of conservative treatment as well as a potential adjunct to the aforementioned surgical procedures. [ABSTRACT FROM AUTHOR]

Retroclival hemorrhages in adults are very rare and are mostly associated with trauma. Prompt diagnosis is usually very important to avoid neurological deficits and even death. We present a case of retroclival hemorrhage identified at autopsy in a 37 year old man who had a history of trauma.

A five-month-old female Boerboel puppy presented with a rapidly expanding fibrous growth around the canine tooth of the right maxilla was diagnosed as having acanthomatous ameloblastoma based on findings from skull radiography, cytology of fine needle aspiration, biopsy and histopathology of resected growth. Lateral radiograph of the skull revealed moderate osteolysis of the maxilla with presence of un-erupted maxillary canine teeth. Cytology of fine needle aspirate from the growth showed clusters of epithelial cells that were hyperchromatic and showing palisade arrangement. The mass was surgically resected using diathermy instrument following general anaesthesia using combination of intramuscular injection of xylazine (0.5mg/kg), and intravenous injection of propofol (4mg/kg). Post-operative management included Ibuprofen suspension (100mg) administered for 3-days, intravenous vincristine (0.5mg/m2) once weekly and oral cyclophosphamide (50mg) was administered twice weekly for six weeks. Histopathology of the growth showed odontogenic epithelium embedded in pulp ectomesenchyme. Features of odontogenic epithelium include palisading epithelium with anti-basilar nuclei and centrally located cells having features of stellate reticulum. This is probably the first reported case of acanthomatous ameloblastoma in a Boerboel puppy that was successfully managed. [ABSTRACT FROM AUTHOR]

Background Data: Traumatic Odontoid Epiphysiolysis fractures, although rare in the overall incidence of spinal trauma, these fractures are one of the common fractures in young children. The appropriate treatment of this type of odontoid fractures remains controversial. The rarity of literature reports on these fractures and limited number of cases prevented the consensus on the optimal line of treatment. Purpose: To clarify the role of non-operative treatment in this type of fracture and ascertain its beneficial role in reaching sound fusion. Study Design: Prospective assessment of Traumatic Odontoid Epiphysiolysis in young child with literature review. Patients and Methods: A 4 years female child developed Traumatic Odontoid Epiphysiolysis after falling downstairs. The child was neurologically intact with severe neck pain and spasm. On examination apparent neck spasm and limitation of movement was noticed. The patient was managed by non-operative treatment. External immobilization using Minerva orthosis for 12 weeks was conducted under fluoroscopy to ascertain optimum position. The patient was followed up clinically and radiologically for 3 months. Literature review of series reporting children with Traumatic Odontoid Epiphysiolysis fractures was also conducted. Results: Realignment and sound fusion was obtained after 12 weeks. The patient remained neurologically intact. Neck pain and limitation of movement improved after removal of the external fixation. As regard literature review, 105 cases were reported with Traumatic Odontoid Epiphysiolysis fractures, external immobilization was done successfully in 87%, and surgical intervention using wiring or screws was done only in 13% of cases. Conclusion: Closed reduction and external fixation can be the primary treatment option for Traumati Odontoid Epiphysiolysis with high rate of fusion. (2018ESJ154)

Study Design: Retrospective cohort study. Objective: Type III odontoid fractures are classically treated nonoperatively, yet, the current literature on Type III odontoid fractures includes fractures of multiple etiologies and fracture morphologies. We hypothesize that a subgroup of complex, Type III fractures caused by high-energy mechanisms are more likely to fail nonoperative treatment. Materials and Methods: Acute Type III odontoid fractures were identified at a single institution from 2008 to 2015. Fractures were categorized as high- or low-energy fracture with high-energy fractures defined as those with lateral mass comminution (>50%) or secondary fracture lines into the pars interarticularis or vertebral body. Patients were treated in either a hard collar orthosis or halo vest and were followed for fracture union and stability. Results: One hundred and twenty-five Type III odontoid fractures were identified with 51% classified as complex fractures. Thirty-three patients met the inclusion and exclusion criteria including 15 patients treated in a halo vest and 18 in a hard collar orthosis. Mean follow-up was 32 (±44) weeks. Seven patients demonstrated progressive displacement of either 2 mm of translation or 5° of angulation and underwent delayed surgical stabilization. Two additional patients required delayed surgery for nonunion and myelopathy. Initial fracture displacement and angulation were not correlative with final outcome. No statistical advantage of halo vest versus hard collar orthosis was observed. Conclusions: Complex Type III odontoid fractures are distinctly different from low-energy injuries. In the current study, 21% of patients were unsuccessfully treated nonoperatively with external immobilization and required surgery. For complex Type III fractures, we recommend initial conservative treatment, while maintaining close monitoring throughout patient recovery and fracture union.

Background: Type 2 odontoid fractures are the most common type of fracture of the axis. In rare cases, nonunion of a type 2 odontoid fracture can be hypertrophic resulting in myelopathy due to cervical cord compression. Case Description: A 48-year-old male presented with hypertrophic nonunion of a chronic type 2 odontoid fracture resulting in cord compression/myelopathy. This was adequately treated utilizing a C1 decompression and C1-3 instrumented fusion; no anterior procedure was necessary. Conclusion: Here, we successfully treated a patient with a hypertrophic nonunion of a chronic type 2 odontoid fracture utilizing a posterior only approach consisting of a C1 laminectomy with C1-C3 fusion. [ABSTRACT FROM AUTHOR]

Purpose: Os odontoideum is a rare anatomical and morphological variation of the odontoid process and associated with a range of symptoms such as spinal cord and vertebral artery injuries. This study aimed to evaluate the frequency of os odontoideum in Turkish cases by sagittal/coronal cervical magnetic resonance imaging (MRI) and computed tomography (CT) and analyze the relationship with age, gender and related symptoms. Methods: The incidence of os odontoideum was retrospectively diagnosed by sagittal/coronal cervical CT and MRI out of 16,122 subjects aged 20–70 years (mean 46) in the period between 2014 and 2018. The relationship of os odontoideum with age, gender, and symptoms was recorded. Results: The statistical analysis of the study was performed by the χ² test and two-way mixed ANOVA. Os odontoideum was detected in 18 (0.11%) (11 males; 7 females) out of 16,122 patients. The mean age was 47.5 ± 1.4 years in the females and 43.5 ± 2.5 years in the males (p < 0.05). 6 odontoideum were detected out of 6467 (3756 males, mean 48 ± 0.7, 2711 females, mean 46 ± 1.2) subjects by CT and 12 odontoideum were detected out of 9655 patients (5607 males and 4048 females) by MRI. Conclusion: Neck pain was the most frequent symptom. The prevalence of os odontoideum especially round type is more frequent in older male patients over 40 years old with head and neck pain or atlantoaxial instability, and is less common in Turkish subjects when compared to various ethnic groups. [ABSTRACT FROM AUTHOR]

Background: Type 2 odontoid fractures are the most common type of fracture of the axis. In rare cases, nonunion of a type 2 odontoid fracture can be hypertrophic resulting in myelopathy due to cervical cord compression. Case Description: A 48-year-old male presented with hypertrophic nonunion of a chronic type 2 odontoid fracture resulting in cord compression/myelopathy. This was adequately treated utilizing a C1 decompression and C1-3 instrumented fusion; no anterior procedure was necessary. Conclusion: Here, we successfully treated a patient with a hypertrophic nonunion of a chronic type 2 odontoid fracture utilizing a posterior only approach consisting of a C1 laminectomy with C1-C3 fusion. [ABSTRACT FROM AUTHOR]

Little attention has been given to the retroverted dens within the existing medical literature. However, this finding can have a clinical impact, especially in patients with Chiari malformation type I (CM1), as it can have consequences for further treatment. Using standard search engines, we performed a literature review of anatomical, radiologic, and clinical studies as well as pathologic and surgical considerations related to the retroverted dens. Key words for our search included retroverted dens; retroflexed dens; odontoid retroflexion; posterior inclination; and tilted dens. A retroverted dens is most commonly found in the pediatric population in relation to CM1. Research has demonstrated that high degree of dens angulation can result in significant anterior brain stem compression with the need for both anterior and posterior decompression in patients with symptomatic CM1. A greater degree of dens angulation can lead to neurologic symptoms secondary to spinomedullary compression. Therefore, correct measurements are essential as such findings can influence presurgical planning. [ABSTRACT FROM AUTHOR]

Purpose: The cement augmentation of a conventional anterior screw fixation in type II odontoid process fractures for elderly patients significantly increased stiffness and load to failure under anterior-posterior load in comparison with non-augmented fixation. The amount and quality of bone cement are usually taken ad hoc in clinical practise. In this study, we wanted to clarify the role of bone cement amount and its quality to the stiffness of odontoid and vertebrae body junction.Methods: Finite-element method was used to achieve different scenarios of cement augmentation. For all models, an initial stiffness was calculated. Model (1) the intact vertebrae were virtually potted into a polymethylmethacrylate base via the posterior vertebral arches. A V-shaped punch was used for loading the odontoid in an anterior-posterior direction. (2) The odontoid fracture type IIa (Anderson-D'Alonzo classification) was achieved by virtual transverse osteotomy. Anterior screw fixation was virtually performed by putting self-drilling titanium alloy 3.5 mm diameter anterior cannulated lag screw with a 12 mm thread into the inspected vertebrae. A V-shaped punch was used for loading the odontoid in an anterior-posterior direction. The vertebrae body was assumed to be non-cemented and cemented with different volume.Results: The mean cement volume was lowest for body base filling with 0.47 ± 0.03 ml. The standard body filling corresponds to 0.95 ± 0.15 ml. The largest volume corresponds to 1.62 ± 0.12 ml in the presence of cement leakage. The initial stiffness of the intact C2 vertebrae was taken as the reference value. The mean initial stiffness for non-porous cement (E = 3000 MPa) increased linearly (R2 = 0.98). The lowest stiffness (123.3 ± 5.8 N/mm) was measured in the intact C2 vertebrae. However, the highest stiffness (165.2 ± 5.2 N/mm) was measured when cement leakage out of the odontoid peg occurred. The mean initial stiffness of the base-only cemented group was 147.2 ± 8.4 N/mm compared with 157.9 ± 6.6 N/mm for the base and body cemented group. This difference was statistically significant (p < 0.0061). The mean initial stiffness for porous cement (E = 500 MPa) remains constant. Therefore, there is no difference between cemented and non-cemented junction. This difference was not statistically significant (p < 0.18).Conclusion: The present study showed that the low porous cement was able to significantly influence the stiffness of the augmented odontoid screw fixation in vitro, although further in vivo clinical studies should be undertaken. Our results suggest that only a small amount of non-porous cement is needed to restore stiffness at least to its pre-fracture level and this can be achieved with the injection of 0.7-1.2 ml of cement. These slides can be retrieved under Electronic Supplementary Material. [ABSTRACT FROM AUTHOR]