The SHORE Score: A Novel Predictive Tool for Improvement After Decompression Surgery in Adult Chiari Malformation Type I.

BACKGROUND: A practical scoring system predicting significant improvement after surgical decompression in adult Chiari malformation type I (CM-1) based on validated outcome measures is lacking. We aimed to develop a simple score and improvement calculator to facilitate the decision making process in symptomatic CM-1 patients. METHODS: We evaluated adult CM-1 patients who presented to our institution between September 2006 and September 2018 and underwent surgical decompression. Previously treated patients were excluded. Univariable analysis and multivariable logistic regression were conducted to derive an optimal model predictive of improvement on last follow-up as measured by the Chicago Chiari Outcome Scale. A score was derived using the beta coefficients of the model, and predictive performance was assessed using receiver operating curves with bootstrap validation. Finally, a web-based improvement calculator was deployed. RESULTS: The surgical cohort consisted of 149 adult CM-1 patients, of which 100 (67%) experienced significant clinical improvement (Chicago Chiari Outcome Scale ≥14) after a mean follow-up of 1.9 years. The final model predictive of significant clinical improvement consisted of headache with Valsalva (odds ratio [OR] = 2.39; P = 0.030), nonwhite race (OR = 2.57; P = 0.041), absence of visual symptoms (OR = 2.59; P = 0.015), syrinx absence (OR = 1.59; P = 0.315), and increased odontoid retroflexion (OR = 2.82; P = 0.009). The score was termed SHORE, which summarizes the model's predictive factors, each assigned 1 point. The model had an area under the curve of 0.754 with an optimism-correct value of 0.721. A calculator was deployed under: https://jhuspine2.shinyapps.io/SHORE_score/. CONCLUSIONS: The score and calculator can serve as supplements to clinical decision making by providing realistic and personalized expectations of postoperative outcome.

[Forensic value of the odontoid process of the second cervical vertebra as the initial object for DNA identification]. / Sudebno-meditsinskoe znachenie zuba II sheinogo pozvonka kak iskhodnogo ob"ekta dlya identifikatsionnykh DNK-issledovanii.

Aim of this study is to evaluate the suitability of the fragments of the skeleton obtained from the burials from more than 50 years ago for identificational DNA-analysis. Anatomical and structural features of the odontoid process of the second cervical vertebra are presented, as well as the data of histological examination of the odontoid process and the body of the second cervical vertebra. We conclude that odontoid process of the second cervical vertebra have practical significance as starting material for obtaining high-molecular DNA in identification cases of skeletal human remains.

Anatomical evaluation of the craniovertebral junction on cone-beam computed tomography images.

INTRODUCTION: There are many craniometric measurements that are used in evaluating craniovertebral junction (CVJ) pathologies such as basilar invagination, atlantoaxial dislocation and platybasia. Therefore, it is important to determine the normal reference range of the craniometric measurements. This study aims to determine the morphometric reference values of the bony structures in the CVJ from cone-beam computed tomography (CBCT) images of a group of South Eastern Anatolian population. MATERIALS AND METHODS: The CBCT images of 300 individuals were retrospectively evaluated. 14 parameters on midsagittal and 2 parameters on the coronal plane were studied. The data were statistically evaluated. RESULTS: Measurement results were found as follows; the distances between odontoid process (OP) and McGregor line as 0.31 ± 3.22 mm, OP and Chamberlain line 1.06 ± 3.22 mm, OP and McRae line 5.30 ± 1.59 mm, OP and Fischgold digastric line 8.70 ± 4.12 mm, OP and Fischgold bimastoid line - 5.15 ± 4.86 mm, length of McRae line 35.58 ± 2.52 mm, atlantodental interval 1.28 ± 0.48 mm, posterior atlantodental interval 19.54 ± 2.24 mm, basion axial interval 4.01 ± 1.83 mm, basion dental interval 4.92 ± 1.77 mm, length of Modified Ranawat line 28.66 ± 2.38 mm, length of Redlund-Johnell line 35.11 ± 4.09 mm, clivus canal angle 157.62° ± 11.85°, Welcher basal angle 130.83° ± 6.29°, craniocervical tilt 126.98° ± 12.24° and Powers ratio as 0.72 ± 0.06. CONCLUSION: In this study, the morphometric values were evaluated according to age and gender in individuals who did not have any radiologic anomalies. The normal reference ranges may be useful for researchers who are researching pathology in this region. It is recommended to conduct further studies with different populations to determine the normal reference range.

The Retroverted Dens: A Review of its Anatomy, Terminology, and Clinical Significance.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Micro-architecture study of the normal odontoid with micro-computed tomography.

Introduction: Odontoid fractures easily lead to instability, causing spinal cord injury. The aim of this study was to measure and analyze the micro-architecture and morphometric parameters of the normal odontoid with high-resolution three-dimensional (3D) micro-computed tomography (micro-CT).Methods: Micro-CT scans were obtained from five normal odontoid processes. The scanned data were reconstructed with micro-CT software, and the nutrient foramina and the ossification center of the base of the odontoid were revealed. The trabeculae of the odontoid were measured and divided into four parts to obtain the volume fraction of regions of interest.Results: High-resolution 3D images of the micro-structures' parameters were obtained from the odontoid using micro-CT software. The images demonstrated sponge-like trabecular bone, with the trabeculae showing a complex, net-like micro-construction. The subchondral bone plate was of lamella-like, compact construction and extended and transformed into a net-like structure with rod-shaped trabeculae arranged radially in all directions. There was a statistically significant difference in the volume fraction compared with the region of interest in the fourth part of the trabeculae and the first part of the odontoid (P < 0.05). The nutrient foramina and the ossification center of the odontoid were also observed.Conclusions: It is feasible to use high-resolution 3D micro-CT to evaluate the micro-architecture of the normal odontoid. Other studies can benefit from use of the micro-CT images, such as finite element evaluations.

Internal Morphology of the Odontoid Process: Anatomic and Imaging Study with Application to C2 Fractures.

OBJECTIVE: Fracture of the odontoid process is a critical injury to diagnose and often treat. The aim of this anatomic study was to present a comprehensive understanding of this part of the C2 vertebra. METHODS: We used 20 C2 vertebrae. Samples underwent imaging (computed tomography [CT] with and without three-dimensional reconstruction, micro-CT, 1.5T magnetic resonance imaging) and sagittal and coronal sectioning using a bone saw. Sectioned specimens were imaged under a digital handheld microscope, and transillumination of the bone was used to highlight its internal trabecular pattern. Three samples underwent infusion of the odontoid process with a hardening substance and were then decalcified. RESULTS: Internal trabecular patterns of the odontoid process of all specimens were discernible. In sagittal and coronal sections, trabecular patterns were highlighted with transillumination, but the patterns were much clearer using the digital microscope. Magnetic resonance imaging and CT provided the least detail of the imaging methods, but the trabecular patterns could be identified. Three-dimensional reconstruction of CT data was the preferred imaging method over magnetic resonance imaging and CT without three-dimensional reconstruction. The most distinct trabecular and cortical patterns were seen using micro-CT. Osteoporosis was seen in 2 specimens (10%). Five specimens (25%) were found to have a subdental synchondrosis. For most specimens, the trabeculae were found throughout the odontoid process. CONCLUSIONS: Improved knowledge of the anatomy, structural composition, and variations within the C2 vertebra may allow for better treatment options and patient care.

Anatomy of the dens and its implications for fracture treatment: an anatomical and radiological study.

PURPOSE: The most common injuries to the upper cervical spine are fractures of the dens axis. Therefore, the purpose of our study was to answer three questions, namely (1) whether the size of the dens is adequate at all levels to accommodate two screws, (2) what the angle of the posterior tilt of the dens is in a healthy individual and (3) compare the measured variables between the sexes. METHODS: The cohort comprised 50 males and 50 females CT examination of the craniocervical junction. We measured the five diameters of the dens and posterior dens angulation angle (PDAA) and screw insertion angle (SIA). The same dimensions were measured in a control group, consisting of 40 non-pathological second cervical vertebrae specimens. RESULTS: On CT scans, the mean PDAA was 162.7 degrees in males and 160.26 degrees in females; the mean SIA was 62.0 degrees in males and 60.2 degrees in females. On specimens, the mean PDAA was 169.47 degrees in males and 166.95 degrees in females; the mean SIA was 65.42 degrees in males and 64.47 degrees in females. All obtained values were higher in males; regardless of their measuring on either CT scans or specimens, differences between males and females were statistically significant (p < 0.05) in a, c, d and e values. CONCLUSIONS: The values of our measurements correlate with the dimensions identified previously in other studies. Based on our clinical experience and measurements, we presume that two 3.5-mm screws can be inserted into the dens of all adult patients, except for those with pronounced anatomical anomalies. Posterior dens angulation angle is slightly larger than we expected. The dens is significantly larger in males almost in all measurement. These slides can be retrieved under Electronic Supplementary Material.

A new superficial landmark for the odontoid process: a cadaveric study.

When image guidance is not available or when there is a need to confirm the findings of such technology, superficial landmarks can still play a role in providing surgeons with estimations of the position of deeper anatomical structures. To our knowledge, surface landmarks for the position of the odontoid process have not been investigated. We have therefore performed an anatomical study to investigate such a landmark. One-centimeter metallic rods were placed on the philtrum of the upper lip of 20 cadaveric head specimens. To assess the position relative to the odontoid process, we took lateral and anteroposterior radiographs and recorded the measurements. Descriptive findings from radiographic observations indicated a reasonable approximation between the philtrum and the midpoint of the odontoid process. Based on our results, we suggest that the philtrum of the upper lip can serve as a first line estimation of the position of the odontoid process and can assist in verifying this bony structure following the use of image guidance.

Evaluation of the dens-to-axis length ratio and dens angle in toy-breed dogs with and without atlantoaxial instability and in healthy Beagles.

OBJECTIVE To evaluate and compare morphological characteristics of the dens in atlantoaxial instability (AAI)-predisposed toy-breed dogs (TBDs) with and without AAI and non-AAI-predisposed healthy Beagles. ANIMALS 80 AAI-affected and 40 nonaffected TBDs and 40 Beagles. PROCEDURES Each dog underwent CT examination of the cervical vertebral column. On median 3-D multiplanar reconstruction images, the dens angle (DA) was measured as were the lengths of the dens and the body of the axis; the dens-to-axis length ratio (ratio of the dens length to the axis body length [DALR]) was calculated. Data were compared among dog groups. RESULTS The DALR in nonaffected TBDs and Beagles did not differ significantly. The mean DALR for AAI-affected TBDs was significantly lower than that for nonaffected TBDs. The mean DA of AAI-affected TBDs was significantly greater than that of Beagles and nonaffected TBDs. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that a low DALR might be associated with a high probability of dens abnormalities in TBDs. Additionally, dens length in AAI-affected TBDs appeared to be smaller than that in non-AAI-affected TBDs, given the low DALR in AAI-affected TBDs. Further investigations to determine reference ranges of the DA and DALR and the potential usefulness of those variables as diagnostic markers for AAI in TBDs are warranted.

Construction of Finite Element Model for an Artificial Atlanto-Odontoid Joint Replacement and Analysis of Its Biomechanical Properties.

AIM: To investigate the stress distribution on artificial atlantoaxial-odontoid joint (AAOJ) components during flexion, extension, lateral bending and rotation of AAOJ model constructed with the finite element (FE) method. MATERIAL AND METHODS: Human cadaver specimens of normal AAOJ were CT scanned with 1 mm -thickness and transferred into Mimics software to reconstruct the three-dimensional models of AAOJ. These data were imported into Freeform software to place a AAOJ into a atlantoaxial model. With Ansys software, a geometric model of AAOJ was built. Perpendicular downward pressure of 40 N was applied to simulate gravity of a skull, then 1.53 N• m torque was exerted separately to simulate the range of motion of the model. RESULTS: An FE model of atlantoaxial joint after AAOJ replacement was constructed with a total of 103 053 units and 26 324 nodes. In flexion, extension, right lateral bending and right rotation, the AAOJ displacement was 1.109 mm, 3.31 mm, 0.528 mm, and 9.678 mm, respectively, and the range of motion was 1.6°, 5.1°, 4.6° and 22°. CONCLUSION: During all ROM, stress distribution of atlas-axis changed after AAOJ replacement indicating that AAOJ can offload stress. The stress distribution in the AAOJ can be successfully analyzed with the FE method.

Morphometric analysis of the odontoid process: using computed tomography--in the Greek population.

AIM: A morphometric analysis of the odontoid process of the A2 vertebra, in the Greek population, was conducted using CT scan. We aimed to determine the feasibility to use one or two screws when treating fractures of this anatomic element. PATIENTS AND METHODS: One hundred and fifteen patients (57 men) of a mean age of 48 years (16-95 years) underwent a cervical spine CT scan examination. The anterior-posterior and transverse diameters of the odontoid process were measured from the base, at 1-mm interval upward on axial CT images. The length from the tip of the odontoid process to the anterior-inferior angle of the body of the axis was calculated. Data concerning the height and weight of the examined patients were collected. RESULTS: The mean transverse and anterior-posterior distances were found to be 11.46 and 10.45 mm, respectively, for the upper end of the odontoid process. At the neck level of the odontoid process, the equivalent mean values were 11.12 and 8.73 mm, respectively, while at the base, these distances were found to be 13.84 and 12.3 mm, respectively. The mean distance from the tip of the odontoid to its base was 17.25 and 17.28 mm, respectively, while the mean distance from the tip of the dens to the anterior-inferior corner of the axis' body was 39.2 mm. Men showed greater values than women. CONCLUSIONS: In this study, it was shown that in the Greek population there is enough room for one 4.5-mm or one 3.5-mm cannulated screw to be used. The application of two 3.5-mm screws is feasible in 58.6 % of the male and 26.3 % of the female population. This confirms that the knowledge of the true dimensions of the odontoid process is of paramount importance before the proper management of fractured dens using the anterior screw technique.

The odontoid process: a comprehensive review of its anatomy, embryology, and variations.

BACKGROUND: The odontoid process is a critical component of the cranio-cervical junction. Therefore, clinicians who diagnose, treat, or operate this region need a strong background in regard to the embryology, anatomy, and anatomical variations that may be seen for the odontoid process. METHODS: A literature review was performed, using standard search engines, to explore the morphology, embryology, and anatomical variants of the odontoid process. CONCLUSIONS: A sound understanding of the development of the odontoid process, both in normal and in variant forms, as well as its phenotypical morphology is a prerequisite for the diagnosis and treatment of patients presenting with disorders affecting the cranio-cervical spine.

The selective odontoidectomy: endoscopic endonasal approach to the craniocervical junction.

OBJECTIVE: The resection of the odontoid process via an extended endoscopic endonasal approach has been recently proposed as an alternative to the microscopic transoral method. We aimed to delineate a minimally invasive endoscopic transnasal odontoidectomy and to describe the endoscopic anatomy of the anterior craniovertebral junction (CVJ). MATERIALS AND METHODS: The anterior CVJ of 14 fresh adult cadavers were selectively accessed via a binostril endoscopic endonasal approach using 0- and 30-degree endoscopes. RESULTS: The nasopharynx was widely exposed without removing any of the turbinates and without performing a sphenoidotomy. Occipital condyles and lateral masses of the C1 vertebra have been exposed inferiorly at lateral margins of the exposure, in addition to the foramen lacerum, which came into view at the superolateral corner of the operative field. The anterior arch of C1 and the upper 1.5 cm of the odontoid process of C2 have been removed via a minimally invasive endoscopic transnasal approach in all dissections. CONCLUSIONS: We propose the selective odontoidectomy as a minimally invasive method for the endoscopic endonasal removal of the odontoid process. By using this approach, turbinates and the sphenoid sinus remain unharmed. In addition, this approach may be used in exposing pathologies situated laterally at the anterior CVJ, such as the lateral masses of atlas and occipital condyles.

The odontoid process: various configuration types in MR examinations.

PURPOSE: Several developmental anomalies have been described with respect to the odontoid process. The purpose of the study was to describe the MR appearance of the odontoid process and to calculate the prevalence of its morphological variants. METHODS AND MATERIALS: We retrospectively reviewed 133 patients (85 males and 48 females, age range of 19-81 years, mean 39.5), examined within a 7-year period. Patients were divided into two age groups: ≤30 and >30-year-old. The morphology of the odontoid process was classified into type I: pyramidal tip and type II: ovoid or convex tip. The incidence of os odontoideum and os terminale and the presence of longitudinal cleft were also recorded. Fischer's exact test was used for statistical analysis (p < 0.05). RESULTS: Type I was identified in 54 cases (40.6 %) and type II in 79 cases (59.4 %). Os odontoideum was recorded in one case (0.7 %), os terminale in 24 cases (18 %) and the presence of a longitudinal cleft (partial or complete) in 86 cases (64.7 %). Type I showed a higher prevalence in the ≤30 age group (p < 0.05). No differences were shown between sexes. CONCLUSION: The configuration types of odontoid process are reported herein. The clinical relevance of this morphological variation needs to be elucidated with further studies.

A new guide tube for odontoid screw fixation for unstable odontoid fractures: report of 6 case series.

AIM: We describe a modified form of traditional open surgery with a new guide tube. This guide tube permits anterior screwing of odontoid in a shorter time with a more simple technique as compared to traditional open surgery, endoscopic and percutaneous surgeries. MATERIAL AND METHODS: Our series includes 6 patients who were operated for unstable odontoid fracture. We used a new guide tube for anterior odontoid screw fixation. This guide tube was designed by the first author to facilitate the insertion of the K-wire for placement of a cannulated lag screw. RESULTS: Successful placement of the odontoid screws and immediate spinal stabilization were achieved in all patients. Solid fusion was observed during follow-up time in all patients. CONCLUSION: This screw insertion technique for odontoid screw fixation provides a minimally invasive, safe and easy surgery in contrast to other surgical approaches.

Whole-spine magnetic resonance imaging study in healthy Chinese adolescents.

OBJECTIVE: To establish a preliminary magnetic resonance imaging (MRI) database of whole spine of healthy Chinese adolescents. METHODS: MRI examination of whole spine and hindbrain was performed in 41 enrolled students aged 11-17 years (mean age 13.95; 18 males, 23 females) using a 1.5-T MR Scanner. Measurements of the ratio of anteroposterior (AP) and transverse (TS) diameters of the cord, cerebellar tonsillar level related to the basion-opsithion (BO) line, location of conus medullaris, total cord length, total vertebral length, cord/vertebral length ratio, thoracic cord area, thoracic vertebral area, thoracic cord/vertebral area ratio were obtained. RESULTS: Mean values of cervical AP and TS were 6.63 mm and 12.21 mm, respectively. The mean level of cerebellar tonsillar related to BO line was 3.97 mm. Mean level of conus medullaris located in L1 lower 1/3. Total cord length was 399.34 mm, total vertebral length was 529.49 mm, Cord/vertebral length ratio was 0.75 and thoracic cord/vertebral area ratio was 0.17 on average. Vertebral length was correlated with age (r = 0.352, P = 0.024) whereas cord length and their ratio were not (P > 0.05). Compared with female, male had significantly larger cervical AP and TS, longer cervical cord (P < 0.01), higher position of conus medullaris (P < 0.05). CONCLUSION: MRI is a useful tool for assessment of the whole spine. The longitudinal and cross-sectional morphology of spinal cord in healthy Chinese adolescents may benefit further study of spine cord in adolescent idiopathic scoliosis as well as in other spine diseases.

Occurrence and significance of odontoid lateral mass interspace asymmetry in trauma patients.

BACKGROUND: The odontoid lateral mass interspace (OLMI) is the space between the lateral aspect of the dens axis and the medial circumference of the massa lateralis atlantis. The position of OLMI asymmetry as a normal variant or pathologic finding is an area of debate and clinical interest in trauma patients. We designed this prospective study to lay a framework for proposing strategies for the appropriate use of OLMI. METHODS: A total of 301 adult patients admitted for trauma were included. Computed tomography (CT) and magnetic resonance imaging (MRI) of the cervical spine were performed and examined for the presence OLMI asymmetry and bony/ligamentous lesions of the occipitoatlantoaxial complex. RESULTS: Head rotation is linked to the occurrence of OLMI asymmetry. Reliable OLMI asymmetry evaluation is limited by observer agreement under a threshold value of 1.0 mm. In all, 86 patients (28.6 %) were found to have OLMI asymmetry on CT after trauma. Among these patients, 17.4 % had a bony/ligamentous lesion of the occipitoatlantoaxial complex. Among the patients without OLMI asymmetry, 8.8 % were found to have such lesions. CONCLUSIONS: OLMI asymmetry should only be investigated by CT scans of the head in optimal position and with the threshold value of 1.0 mm. OLMI asymmetry should not be used alone as a sign of a cervical spine lesion. MRI should be performed if: (1) the physician has a high degree of suspicion of a cervical spine lesion; (2) OLMI asymmetry was demonstrated on a technically adequate CT scan; (3) clinical symptoms persist in patients with OLMI asymmetry when no acute MRI was performed.

Acute non-ambulatory tetraparesis with absence of the dens in two large breed dogs: case reports with a radiographic study of relatives.

BACKGROUND: Non-ambulatory tetraparesis with an absence of the dens of C2 (axis) has not previously been reported in large breed dogs. An absence or hypoplasia of the dens has been reported in both small, medium and large breed dogs, but not in closely related animals. METHODS: Two young large-breed dogs (a German shepherd and a Standard poodle) both with an acute onset of non-ambulatory tetraparesis were subjected to physical, neurological and radiographic examinations. Both dogs were euthanased and submitted for postmortem examination within one week of onset of clinical signs. To investigate possible heritability of dens abnormalities, oblique radiographs of the cranial cervical vertebrae were taken of nine and eighteen dogs related to the German shepherd and the Standard poodle, respectively. RESULTS: Absence of the dens, atlantoaxial instability and extensive spinal cord injury was found in both case dogs. Radiographs revealed a normal dens in both parents and in the seven littermates of the German shepherd. An absence or hypoplasia of the dens was diagnosed in six relatives of the Standard poodle. CONCLUSIONS: Atlantoaxial subluxation with cervical spinal cord injury should be considered as a differential diagnosis in non-ambulatory tetraparetic young large breed dogs. Absence of the dens and no history of external trauma increase the likelihood for this diagnosis. This study provides evidence to suggest that absence or hypoplasia of the dens is inherited in an autosomal way in Standard poodle dogs.

Does the third cervical vertebra need to be rimmed for odontoid screwing? A hypothetical study of anatomic landmarks.

BACKGROUND: The superoanterior portion of the third cervical vertebra may need to be rimmed during anterior odontoid screw fixation procedures. We, therefore, retrospectively evaluated radiological data to analyze the anatomical relation between the second and third cervical vertebra of the patients who were operated by an anterior cervical approach with respect to the question if odontoid screw fixation would have been possible without rimming or not. PATIENTS AND METHODS: Patients in whom the anterior approach for cervical disc prolapse and/or cervical stenosis was used between 2008 and 2010 were included in this study. The odontoid screw angle, and the angle between the lower second and the upper third cervical vertebral endplate were measured on intraoperative cervical lateral radiographs. If the screw line passed through the superior anterior portion of the third vertebral body, it was determined that the third cervical vertebra would have been needed to be rimmed if odontoid screwing would have been planned. RESULTS: 100 patients were included. There were 50 males and 50 females with a mean age of 47.9 years (mean ± SD: 47.9 ± 12.6 years). The mean odontoid screw angle, and the angle between the lower second and the upper third cervical vertebral endplate were 65.61° ± 3.75° and 15.24° ± 4.85° (nonparallel vertebral endplates only), respectively. The odontoid screw angle, in which the third cervical vertebra would not have been needed to be rimmed, was 63.87° ± 2.84°. In addition, the odontoid screw angle in which the third cervical vertebra would have been needed to be rimmed was 67.28° ± 3.77°. CONCLUSION: The odontoid screw angle may be easily measured on lateral radiographs. In cases in which the odontoid screw angle is 67.28° ± 3.77° or higher, the superoanterior portion of the third cervical vertebra would be needed to be rimmed for proper screw fixation of odontoid fractures.

A novel technique of odontoidoplasty and C1 arch reconstruction: anatomical and biomechanical basis.

BACKGROUND: Transoral odontoidectomy and resection of the anterior C1 arch destabilize the atlantoaxial joint and risk its stability. OBJECTIVE: To preserve stability in such cases we devised and evaluated a proof-of-concept study. The arch and dens were dissected and decompression was performed on cadavers. The dens was replaced with an odontoid screw, and the C1 arch was replaced with a rib-graft substitute using miniplates. We assessed the biomechanical strength of the C1 ring and 3D occipitoatlantoaxial flexibility before and after the repair. METHODS: Five silicon-injected fixed cadaver heads were dissected. The arch of C1 and dens were preserved and reconstructed using odontoid screws and miniplates. Once the feasibility of the technique was established, we biomechanically tested 6 cadaveric occiput-C2 specimens in 3 phases: (1) intact/normal range of motion (ROM), (2) after transection of dens and C1 arch, and (3) with odontoidoplasty using odontoid screws and C1 arch reconstruction. RESULTS: After odontoidectomy and arch removal, angular ROM increased significantly in all directions of loading. Resection increased flexion-extension at the occiput-C1 and at C1-C2 by 21% and 129%, respectively. Reconstruction slightly increased flexion-extension stability (16% and 107%, respectively) relative to normal.With 70 N applied compression, the C1 ring separation was 1145% greater than normal. After reconstruction, the separation was only 89% greater than normal (statistically significant, P = .002). CONCLUSION: C1 arch reconstruction with or without odontoidoplasty restores only partial angular stability of the atlantoaxial joint but provides restoration of the ability of the C1 lateral masses to resist splaying, often observed as postodontoidectomy cranial settling.