Atlas-Based Tongue Muscle Correlation Analysis From Tagged and High-Resolution Magnetic Resonance Imaging.

Purpose Intrinsic and extrinsic tongue muscles in healthy and diseased populations vary both in their intra- and intersubject behaviors during speech. Identifying coordination patterns among various tongue muscles can provide insights into speech motor control and help in developing new therapeutic and rehabilitative strategies. Method We present a method to analyze multisubject tongue muscle correlation using motion patterns in speech sound production. Motion of muscles is captured using tagged magnetic resonance imaging and computed using a phase-based deformation extraction algorithm. After being assembled in a common atlas space, motions from multiple subjects are extracted at each individual muscle location based on a manually labeled mask using high-resolution magnetic resonance imaging and a vocal tract atlas. Motion correlation between each muscle pair is computed within each labeled region. The analysis is performed on a population of 16 control subjects and 3 post-partial glossectomy patients. Results The floor-of-mouth (FOM) muscles show reduced correlation comparing to the internal tongue muscles. Patients present a higher amount of overall correlation between all muscles and exercise en bloc movements. Conclusions Correlation matrices in the atlas space show the coordination of tongue muscles in speech sound production. The FOM muscles are weakly correlated with the internal tongue muscles. Patients tend to use FOM muscles more than controls to compensate for their postsurgery function loss.

Abnormalities of the craniovertebral junction in the paediatric population: a novel biomechanical approach.

The craniovertebral junction (CVJ) is the bony transition between the cranium and cervical spine. It is a biomechanically complex articulation comprising the occipital condyles (Oc) the atlas (C1) and axis (C2). Pathologies affecting the CVJ in children are myriad with clinical features resulting from biomechanical instability, deformity, or neuraxial compression. Establishing the natural history and clinical burden of a condition is challenging in infants and young children, often complicated by co-existing neuromuscular and cognitive impairment. This makes investigation and treatment planning difficult. Each disease entity has a predilection for a particular biomechanical abnormality. Investigation using dynamic imaging is most appropriate in instability, computed tomography examination in abnormalities of deformity and magnetic resonance imaging examination in neuraxial compression. Treatment comprises reduction and immobilisation of instability, re-alignment of deformity, or decompression of the neuraxis. We present a review of disease entities affecting the CVJ in children categorised according to a simple mechanistic approach to aid investigation and treatment planning.

Assessment of Atlanto-Axial and Mandibular Rotation by Cone Beam Computed Tomography.

The cranial portion of the vertebral segment together with the atlanto-occipital joint represents a very complex area. Since this system could be influenced by different atlas and mandibular position, the aim of this work was to assess atlanto-axial and mandibular rotation. Scanora 3-dimensional cone bean computed tomography images from 205 patients without signs or symptoms of temporomandibular disorder were evaluated. Using a digitalized images analyzer, the axial rotations of atlas and mandible rotation were calculated, measuring the angle with respect to the frontal plane. The same direction for the axial rotation of the mandible and for the atlanto-axial rotation (consistent group) was observed in 80.98% of the patients; opposite directions (inconsistent group) were observed in 19.02%. Among the consistent group, the left rotation was observed in 71.08% of the patients and the right rotation in 28.92%. Absolute values showed a more marked rotation for atlas than mandible and higher values for the left rotation were reported for both.Taking together these data represents important starting points for the knowledge of atlas and mandible relationship and its functional and clinical implication.

Functional analyses of the primate upper cervical vertebral column.

Recent work has highlighted functional correlations between direct measures of head and neck posture and primate cervical bony morphology. Primates with more horizontal necks exhibit middle and lower cervical vertebral features that indicate increased mechanical advantage for deep nuchal musculature and mechanisms for column curvature formation and maintenance. How features of the C1 and C2 reflect quantified measures of posture have yet to be examined. This study incorporates bony morphology from the upper cervical levels from 20 extant primate species in order to investigate further how posture correlates with cervical vertebrae morphology. Results from phylogenetic generalized least-squares analyses indicate that few vertebral features exhibit a significant relationship with posture when accounting for differences in size. When size-adjusted traits were correlated with posture, vertebral variation had a stronger relationship with neck posture than head posture variables. Two C1 traits-relative posterior arch length and superior facet curvature-were correlated with neck posture variables. Relative posterior arch length exhibits a positive relationship with neck posture, while superior articular facet curvature demonstrates a negative relationship, such that as the neck becomes more horizontal, the greater the facet curvature. Four C2 features were also correlated with neck posture: relative pedicle and lamina lengths, relative superior facet orientation, and dens orientation. Relative pedicle and lamina lengths become craniocaudally longer as the neck becomes more horizontal. Relative C2 superior facet orientation and dens orientation exhibit negative correlations with posture, such that as the neck becomes more horizontal, the superior facet becomes more caudally inclined and the dens more dorsally inclined. These results produce a similar functional signal observed in the middle and lower cervical spine. Modeling the cervical vertebrae of more pronograde taxa within a sigmoidal spinal column model is further discussed and may prove useful in refining and testing future hypotheses of primate cervical mechanics.

Morphometric study of the neural ossification centers of the atlas and axis in the human fetus.

PURPOSES: The knowledge of the developing cervical spine and its individual vertebrae, including their neural processes may be useful in the diagnostics of congenital vertebral malformations. This study was performed to quantitatively examine the neural ossification centers of the atlas and axis with respect to their linear, planar and volumetric parameters. METHODS: Using the methods of CT, digital-image analysis and statistics, the size of neural ossification centers in the atlas and axis in 55 spontaneously aborted human fetuses aged 17-30 weeks was studied. RESULTS: Without any male-female and right-left significant differences, the best fit growth dynamics for the neural ossification centers of the atlas and axis were, respectively, modelled by the following functions: for length: y = -13.461 + 6.140 × ln(age) ± 0.570 and y = -15.683 + 6.882 × ln(age) ± 0.503, for width: y = -4.006 + 1.930 × ln(age) ± 0.178 and y = -3.054 + 1.648 × ln(age) ± 0.178, for cross-sectional area: y = -7.362 + 0.780 × age ± 1.700 and y = -9.930 + 0.869 × age ± 1.911, and for volume: y = -6.417 + 0.836 × age ± 1.924 and y = -11.592 + 1.087 × age ± 2.509. CONCLUSIONS: The size of neural ossification centers of the atlas and axis shows neither sexual nor bilateral differences. The neural ossification centers of the atlas and axis grow logarithmically in both length and width and linearly in both cross-sectional area and volume. The numerical data relating to the size of neural ossification centers of the atlas and axis derived from the CT and digital-image analysis are considered specific-age reference values of potential relevance in both the ultrasound monitoring and the early detection of spinal abnormalities relating to the neural processes of the first two cervical vertebrae in the fetus.

[The biomechanical analysis of craniovertebral junction finite element model in atlas assimilation].

OBJECTIVE: To study the biomechanical change of the craniovertebral junction in conditions of atlas assimilation. METHODS: Mimics software was used to process CT data of the craniovertebral junction in a health adult to obtain the three-dimensional reconstruction and the cloudy points of C1, C2 and part of the occipital bone. Then the cloudy points were imported into the Abaqus 6. 8 software to establish the occipito-atlantoaxial finite element model in normal structure. According to the established model in normal structure, the model in conditions of atlas assimilation was set by changing the model parameters. Both models of normal structure and atlas assimilation were loaded with 1. 5 N . m static moment to simulate four motions of flexion, extension, lateral bending and axial rotation respectively. The movement characteristics,joint stress force and ligament deformation was analyzed. RESULTS: Under 1. 5 N . m moment, in model of atlas assimilation the C1-C2 range of movement decreased from 13. 55° to 11.88° in flexion,increased from 13. 22° to 15. 24° in extension and from 4. 05° to 4. 23° in lateral bending and remained unchanged in axial rotation when compared with the normal model. In flexion movement, the contact force of the atlanto-dental joint increased from 1. 59 MPa to 3. 28 MPa and the deflection of apical ligament, tectorial membrane and alar ligament increased 129. 1%, 157. 6% and 75. 1% respectively when compared with the normal model. CONCLUSIONS: The normal C1-C2 motion mode is destructed in conditions of atlas assimilation, leading to the changes of the range of movement,joint stress force and the ligament deformation at C1 C2 junction. The atlantoaxial instability will likely occur in flexion motion.

Intended and non-intended kinematic effects of atlanto-axial rotational high-velocity, low-amplitude techniques.

INTRODUCTION: The study of neck kinematics during high-velocity, low-amplitude manipulations of the atlanto-axial segment is essential to understanding cervical motion mechanisms and their impact and possible risk for soft-tissue injuries during treatment of spine disorders. METHODS: Twenty fresh-frozen specimens were tested during manual application of an axial rotation technique. FINDINGS: The kinematics indicate the thrust induced motion components of approximately 1° at the treated segment around all three axes of the local embedded reference frame. Moreover, an equal amount of axial rotation motion took place at the adjacent atlanto-occipital joint. INTERPRETATION: Overall atlanto-axial motion remained below the level of slow regional mobilization of the cervical spine. These findings can be correlated to literature data concerning the limited increase in vertebral artery strain during high-velocity, low-amplitude manipulation.

The atlas-axis complex in chamaeleonids (Squamata: Chamaeleonidae), with description of a new anatomical structure of the skull.

The comparative vertebral morphology of different chamaeleonid genera has been generally neglected and some aspects such as the comparative anatomy of the neck region remain poorly known. The atlas and axis of all chamaeleonid genera (Brookesia, Rieppeleon, Archaius, Rhampholeon, Nadzikambia, Bradypodion, Chamaeleo, Calumma, Furcifer, Kinyongia, and Trioceros) are studied here. Considerable morphological differences are revealed. Additionally, some taxa exhibit sexual dimorphism in the atlas and axis. An extremely long, divided posterodorsal process is present in males of the Trioceros johnstoni + Trioceros jacksonii clade. The solid and well-developed morphology of the posterodorsal process in males of this taxon could reflect its competitive behavior-males fight with their horns and attempt to dislodge one another from branches during encounters. An additional area of insertion for the cervical musculature may indicate an incremental cervical musculature mass and cross sectional area that can add extra support and stability to the head and assist during combat involving lateral pushing. This character is not present in females. Heterochronic processes have played a role in the evolution of chamaeleonids, as evidenced in many characters of the atlas-axis complex. A new hypothesis of an anterior shifting of synapophyses of the axis is erected and a new derived anatomical structure of the parietal of Chamaeleo calyptratus is described (the processus parietalis inferior). The presence of the processus parietalis inferior is associated with the evolution of the dorsally elevated parietal crest.

Reliability of the craniocervical posture assessment: visual and angular measurements using photographs and radiographs.

OBJECTIVE: The purposes of this study were to determine the intrarater and interrater reliability of the craniocervical posture in a sagittal view using quantitative measurements on photographs and radiographs and to determine the agreement of the visual assessment of posture between raters. METHODS: One photograph and 1 radiograph of the sagittal craniocervical posture were simultaneously taken from 39 healthy female subjects. Three angles were measured on the photographs and 10 angles on the radiographs of 22 subjects using Alcimage software (Alcimage; Uberlândia, MG, Brazil). Two repeated measurements were performed by 2 raters. The measurements were compared within and between raters to test the intrarater and interrater reliability, respectively. Intraclass correlation coefficient and SEM were used. κ Agreement was calculated for the visual assessment of 39 subjects using photographs and radiographs between 2 raters. RESULTS: Good to excellent intrarater and interrater intraclass correlation coefficient values were found on both photographs and radiographs. Interrater SEM was large and clinically significant for cervical lordosis photogrammetry and for 1 angle measuring cervical lordosis on radiographs. Interrater κ agreement for the visual assessment using photographs was poor (κ = 0.37). CONCLUSION: The raters were reliable to measure angles in photographs and radiographs to quantify craniocervical posture with exception of 2 angles measuring lordosis of the cervical spine when compared between raters. The visual assessment of posture between raters was not reliable.

Atlantoaxial rotatory fixation--a cause of torticollis.

BACKGROUND: A rare, but important cause of torticollis in children is atlantoaxial rotatory fixation. If the patient remains undiagnosed for more than three months, surgery is generally the only therapeutic alternative. In this article we present our experiences of surgical treatment of late-diagnosed atlantoaxial rotatory fixation in children. MATERIAL AND METHOD: This article is based on a review of the case notes of patients who underwent surgery for atlantoaxial rotatory fixation in the Department for Neurosurgery at Oslo University Hospital, Rikshospitalet, during the period 2004-10. RESULTS: The material sample consists of six children aged from seven to 14 years. Five had suffered minor trauma to the upper neck region, while one had had an upper respiratory tract infection. The diagnosis was made 5-36 months after the onset of symptoms. In three of the patients, an attempt was made at closed reduction without success. A CT scan one year postoperatively showed a normal position of the atlantoaxial joint in two patients and partial reduction in three. In the sixth patient there was bone fusion at the time of the operation, and open reduction was unsuccessful. All six patients had reduced rotational movement of the neck at the one-year check-up. INTERPRETATION: All our patients were diagnosed more than five months after the onset of symptoms. Full or partial reduction was achieved in five of the six.

Ligaments of the craniocervical junction.

The specialized ligaments of the craniocervical junction must allow for stability yet functional movement. Because injury to these important structures usually results in death or morbidity, the neurosurgeon should possess a thorough understanding of the anatomy and function of these ligaments. To the authors' knowledge, a comprehensive review of these structures is not available in the medical literature. The aim of the current study was to distill the available literature on each of these structures into one offering.

In vitro characterization of the anterior to posterior curvature of the superior articular facets of the atlas as a function of age.

BACKGROUND CONTEXT: Reference is made in the literature to the inherent instability of the atlantooccipital joint in infants and young children because of pliant ligaments, undeveloped musculature, smaller condyles, and the relative lack of anteroposterior curvature of the superior articular facet surfaces of the atlas. The combination of these morphologic factors is purported to make this population particularly vulnerable to whiplash-type injuries. Although a significant difference in the magnitude of the anteroposterior curvature of the superior articular facet surfaces of the atlas between young children and adults has been observed, quantitative analysis of the curvature of these surfaces has not been documented. PURPOSE: To quantify the anterior to posterior curvature of the superior articular facet surfaces of the atlas as a function of age. STUDY DESIGN: This study is a retrospective analysis of the anterior to posterior curvature of the superior articular facet surfaces of the atlas as a function of age in 15 pediatric cadaver specimens from the Hamann-Todd Osteology Collection in Cleveland, Ohio, and 18 adult cadaver specimens from the Department of Experimental Anatomy in Brussels, Belgium. METHODS: A stylus, connected to a three-dimensional digitizer, was used to manually define a series of points on the perimeter of the superior articular facet surfaces of the atlas of each specimen. The digitized data points were then used to generate two planes that approximated the anterior and posterior aspects of the articular surfaces in three-dimensional space. A line through a point on each plane and perpendicular to that plane was defined for each of the two planes. The angle between the two perpendicular lines was calculated and used to quantify the curvature of the facet surface. RESULTS: The anteroposterior curvature of the superior articular facet surfaces of the atlas increases from an average angle of 11.5 (±4.7) degrees at 1 year of age and asymptotically approaches an average angle of 43.5 (±13.4) degrees at 80 years of age. There is a direct relationship between age and the anterior to posterior curvature of the superior articular surfaces of the atlas that can be approximated (r(2)=0.94) with a sigmoid function. Ninety percent of the final curvature is achieved at approximately 8 years of age.

The transverse occipital ligament: anatomy and potential functional significance.

BACKGROUND: Knowledge of the anatomy of ligaments that bind the craniocervical junction is important for treating patients with lesions of this region. Although the anatomy and function of these ligaments have been well described, those of the transverse occipital ligament (TOL) have remained enigmatic. OBJECTIVE: To describe the anatomy and functions of the transverse occipital ligament. METHODS: Via a posterior approach, 9 cadaveric specimens underwent dissection of the craniocervical junction with special attention to the presence and anatomy of the TOL. RESULTS: The TOL was identified in 77.8% of the specimens. The ligament was found to be rectangular with fibers running horizontally between the lateral aspects of the foramen magnum. The attachment of each ligament near the occipital condyle was consistent, and each ligament was found superior to the transverse portion of the cruciform ligament and inserted just posterior to the lateral attachment sites of the alar ligaments. The average width, length, and thickness of the TOL was 0.34, 1.94, and 0.13 cm, respectively. The TOL in some specimens also had connections to the alar and transverse ligaments. CONCLUSION: The TOL was found in the majority of our specimens. The possible functions of this ligament when attached to the alar ligaments include providing additional support to these structures in stabilizing lateral bending, flexion, and axial rotation of the head. Knowledge of this ligament may aid in further understanding craniocervical stability and help in differentiating normal from pathology via imaging modalities.

C1 lateral mass fixation: a comparison of constructs.

OBJECTIVE: We review our experience and technique for C1 lateral mass screw fixation. We compare the results of 3 different constructs incorporating C1 lateral mass screws: occipitocervical (OC) constructs, C1-C2 constructs, and C1 to mid/low cervical constructs. METHODS: We performed a retrospective chart review of 42 consecutive patients who underwent C1 lateral mass fixation by 2 of the authors (PVM and DC). The patient population consisted of 24 men and 18 women with a mean age of 64 years. Twenty-two patients had C1-C2 constructs. Twelve patients had constructs that started at C1 and extended to the mid/low cervical spine (one extended to T1). Eight patients underwent OC fusions incorporating C1 screws (2 of which were OC-thoracic constructs). All constructs were combined either with a C2 pars screw (38 patients), C2 translaminar screw (1 patient), or C3 lateral mass screw (3 patients). No C2 pedicle screws were used. Fusion was assessed using flexion-extension x-rays in all patients and computed tomographic scans in selected cases. Clinical outcomes were assessed with preoperative and postoperative visual analog scale neck pain scores and Nurick grading. The nuances of the surgical technique are reviewed, and a surgical video is included. RESULTS: Two patients (5%) were lost to follow-up. The mean follow-up for the remaining patients was 2 years. During the follow-up period, there were 4 deaths (none of which were related to the surgery). For patients with follow-up, the visual analog scale neck pain score improved a mean of 3 points after surgery (P < .001). For patients with myelopathy, the Nurick score improved by a mean of 1 grade after surgery (P < .001). The postoperative complication rate was 12%. The complication rate was 38% in OC constructs, 17% in C1 to mid/low cervical constructs, and 0% for C1-C2 construct cases. Patients with OC constructs had the statistically highest rate of complications (P < .001). Patients with C1 to mid/low cervical constructs had more complications than those with C1-C2 constructs (P < .001). Of the 42 cases, there were 3 pseudoarthroses (1 in an OC case, 1 in a C1 to midcervical construct, and 1 in a C1-C2 construct). OC constructs had the highest risk of pseudoarthrosis (13%) (P < .001). CONCLUSION: Patients treated with C1 lateral mass fixation constructs have a high fusion rate, reduced neck pain, and improved neurologic function. Constructs using C1 lateral mass screws do not need to incorporate C2 pedicle screws. Constructs incorporating C1 lateral mass screws are effective when combined with C2 pars screws, C2 translaminar screws, and C3 lateral mass screws. Constructs using C1 screws are associated with a higher complication rate and a higher pseudoarthrosis rate if extended cranially to the occiput or if extended caudally below C2.

Atlantoaxial rotatory fixation.

OBJECTIVE: Atlantoaxial rotatory fixation (AARF) remains a recondite entity. Our normative study using CT motion analysis shows that there is a high degree of concordance for rotational behavior of C1 and C2 in children 0 to 18 years. C1 always crosses C2 at or near 0 degree. The predictable relationship between C1 and C2 is depicted by 3 distinct regions on the motion curve: when C1 rotates from 0 to 23 degrees, it moves alone while C2 remains stationary at 0 (the single-motion phase). When C1 rotates from 24 to 65 degrees, C1 and C2 move together (the double-motion phase), but C1 always moves faster as C2 is being pulled by yoking ligaments. From 65 degrees onward, C1 and C2 move in unison (the unison-motion phase) with a fixed, maximal separation angle of approximately 43 degrees, the head rotation being carried exclusively by the subaxial segments. Because of this high concordance among patients and a relatively narrow variance from the mean, the physiological composite motion curve can be used as a normal template for the diagnosis and classification of AARF. METHODS: Using a 3-position CT protocol to obtain the diagnostic motion curve, we identified 3 distinct types of AARF. Type I AARF patients show essentially unaltered ("locked") C1-C2 coupling regardless of corrective counterrotation, with curves that are horizontal lines in the upper 2 quadrants of the template. Type II AARF patients show reduction of the C1-C2 separation angle with forced correction, but C1 cannot be made to cross C2. Their curves slope downward from the right to left upper quadrants but never traverse the x axis. Type III AARF patients show C1-C2 crossover but only when the head is cranked far to the opposite side. Their motion curves traverse the x axis far left of 0 degree (C1 < -20). Thus, type I, II, and III AARF are in descending degrees of pathological stickiness. A fourth group of patients showing motion curve features between normal and type III AARF are designated as belonging to a diagnostic gray zone (DGZ). The AARF patients are further classified as acute if treatment is started less than 1 month from the onset of symptoms, as subacute if the delay in treatment is 1 to 3 months, and chronic if treatment delay exceeds 3 months. The treatment protocol for AARF consists of reduction using either halter or caliper traction and then immobilization with brace or halo, depending on the AARF type and chronicity. Recurrent slippage and irreducibility are treated with C1-C2 fusion. RESULTS: The treatment course and outcome of AARF are analyzed according to the AARF type and chronicity. The difficulty and duration of treatment, the number of recurrent slippage, the rate of irreducibility, the need for halo and fusion, and the percentage ultimately losing normal C1-C2 rotation are significantly greater in type I patients than type III patients, with type II patients somewhere in between. Likewise, all parameters are much worse in patients with any type of chronic AARF than acute AARF. The worse subgroup is chronic type I versus the best subgroup of acute type III. Recurrent AARF patients do much worse than nonrecurrent AARF patients. Recurrence is, in turn, adversely influenced by both the severity (type) and chronicity of AARF. The symptoms of most DGZ patients will resolve with analgesics, but a few remain symptomatic or deteriorate to true AARF requiring the full treatment. CONCLUSION: Thus, children with painful torticollis should undergo the 3-position CT protocol not only to confirm the diagnosis of AARF but also to grade its severity. Closed reduction with traction should be instituted immediately to avoid the serious consequences of chronicity. Proper typing and reckoning of the pretreatment delay are requisites for selecting treatment modalities. Recurrent dislocation and incomplete reduction should be treated with posterior C1-C2 fusion in the best achievable alignment.

Anatomic and biomechanical considerations of the craniovertebral junction.

An understanding of the regional anatomy and specific biomechanics of the craniovertebral junction is relevant to the specific diseases that affect the region as well as instrumentation of the occiput, atlas, and axis. This article reviews the bony, ligamentous, and vascular anatomy of the region, in relation to the posterior surgical approach to this anatomically unique segment of the cervical spine. Anatomic variations of the area are also discussed. Basic principles of instrumentation of the region are also reviewed. The kinematics of the region as they pertain to the anatomic discussion are reviewed and discussed.

Assessment of two measurement techniques of cervical spine and C1-C2 rotation in the outcome research of axis fractures: a morphometrical analysis using dynamic computed tomography scanning.

STUDY DESIGN: In vivo study on cervical spine motion. OBJECTIVE: To estimate the accuracy of clinical measurements, using a handheld goniometer for the assessment of total cervical neck rotation in outcome research of patients with C2 fractures and particularly odontoid fractures. Investigation on whether functional computed tomography (CT)-scanning is decisive in the investigation of functional outcome after C2 fractures. SUMMARY OF BACKGROUND DATA: Pertinent literature exists concerning indications, techniques, complications of treatment, and risk factors for nonunion in C2 fractures; however, there are scarce data regarding the functional outcome in C2 fractures. Only a few studies assess functional outcome in terms of clinical outcome vehicles and clinical investigation of axial neck rotation, using a handheld goniometer. Measurements of axial neck rotation using a handheld goniometer are assumed not sufficient to compare the results of treatment strategies for C2-fractures or elucidate the ability for posttreatment rotation of C1-C2. METHODS: The authors selected a homogenous group of 35 patients treated for C2 fractures using nonsurgical and surgical techniques. 69% of patients had odontoid fractures. Mean age of patients was 52 years. Patients were subjected to clinical assessment of axial cervical range of motion for rotation, using a handheld goniometer. Patients were also subjected to functional CT-scanning and measurements of total neck and atlantoaxial rotation were performed according to an established protocol. RESULTS: With clinical measurements mean range of motion for left and right axial neck rotation was both 56 degrees. According to the functional CT scans, the mean left-sided and right-sided axial neck rotation was 48.6 degrees and 52.0 degrees. The mean for left- and right-sided atlantoaxial rotation was 20.2 degrees and 20.6 degrees. Total axial atlantoaxial rotation on CT scans was 40.3 degrees and total axial neck rotation was 103.3 degrees. In comparison to age and gender matched normal individuals total cervical neck rotation was reduced to a mean of 69.5%. The differences between total axial neck rotation assessed using a handheld goniometer and with functional CT-scanning were strongly significant (P < 0.0001). In addition, there was no statistically significant correlation between the clinically assessed total neck rotation to either the left or the right side and the ipsilateral percentage atlantoaxial rotation of total head neck rotation. CONCLUSION: The current study demonstrated that for the comparison of functional outcome after different therapies of C2 fractures clinical measurements do not serve for reliable data on total neck rotation and particularly atlantoaxial rotation and the percentage of C1-C2 rotation of total neck rotation. The use of dynamic CT-scans in the analysis of functional outcome after C2 fractures is strongly recommended.

The kinematic relationships of the upper cervical spine.

STUDY DESIGN: A retrospective radiographic study. OBJECTIVE: To elucidate the kinematic relationships of the upper cervical spine. SUMMARY OF BACKGROUND DATA: To our knowledge, few reports have described the kinematic relationships of the upper cervical spine in patients with general age-related cervical spondylosis. METHODS: We performed Kinetic magnetic resonance imaging for 295 consecutive patients experiencing neck pain without neurologic symptoms. Subjects with rheumatoid arthritis, traumatic history, and severe degenerative changes in the upper cervical spine were excluded. Anterior atlantodens interval (AADI) and the cervicomedullary angle in 3 different postures were measured, and the variations in each value between flexion and neutral (F-N), neutral and extension (N-E), and flexion and extension (F-E) were calculated. The subjects were classified into 3 groups according to the space available for the cord values (A: or=15 mm). RESULTS: AADI significantly increased from extension to flexion posture, however, no significant differences were observed in every posture among the groups. F-N variation in AADI showed no significant differences among the groups; however, N-E variation between Groups A and C and between Groups B and C and F-E variation between Groups A and C showed significant differences. The cervicomedullary angle significantly increased from flexion to extension posture, however, no significant differences were observed in every posture among the groups. Angle variations among the groups showed no significant differences, except for F-N angle variation between Groups B and C. None of the variations in AADI and the cervicomedullary angle were significantly correlated. CONCLUSION: Our results suggest that only the kinematics of the atlantoaxial movement, especially the posterior movement, was greatly affected by the narrowing of space available for the cord. The central atlantoaxial joint may be closely related to the mechanisms for protecting the spinal cord by restriction of the atlantoaxial movement.

CT scan study of atlantoaxial rotatory mobility in asymptomatic adult subjects: a basis for better understanding C1-C2 rotatory fixation and subluxation.

STUDY DESIGN: Normal rotation was evaluated in a group of 40 asymptomatic adults. OBJECTIVE: To determine the normal rotational limits of C1-C2 in adults and define when a rotatory fixation occurs in the limits of normality or in subluxation. The term subluxation should be used only when C1-C2 is rotated beyond normal limits. SUMMARY OF BACKGROUND DATA: Concepts about rotatory fixation were established by accepting that it may occur within the limits of normal range of motion. Although nowadays CT is the current image method used to evaluate any case of torticollis, no study has been performed in adult population on what really normal rotation look like in CT scans. METHODS: The study included the measurement of the rotational movement of the neck and a CT scan study of the articular processes of C1-C2 in maximal, left and right, active rotation. A superposition of 6 consecutive slices was carried out, obtaining a linear contour of the axial view of C1-C2. Rotation angle and contact surface loss were measured. RESULTS: The average neck rotation angle was 79 degrees (range: 74 degrees to 81 degrees ). The superposition of the images taken in every rotational direction showed a wide contact loss between the correspondent C1-C2 articular surfaces (42.4%-85.7%; average: 70%). The report of these images, carried out by 3 independent radiologists, concluded that there was a rotatory subluxation in all these cases. CONCLUSION: Our results coincide with our previous published ones conducted in children, and lead us to conclude that a CT scan showing wide-but incomplete-rotational facet displacement is not sufficient to define subluxation. We perceive that there is a risk of overdiagnosis and overtreatment (C1-C2 arthrodesis) when evaluating upper cervical spine rotational problems. The concept of both rotatory fixation and subluxation should be revised, and quantifying the rotational angle and contact surface loss between C1-C2 can be very useful.

Artificial atlanto-odontoid joint replacement through a transoral approach.

Resection of the odontoid process and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurological complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior C1-C2 fusion. However, this results in considerable loss of rotation function of the atlantoaxial complex. From the viewpoint of retaining the rotation function and providing stability, we designed an artificial atlanto-odontoid joint based on anatomical measurements of 50 pairs of dry atlantoaxial specimens by digital calipers and 10 fresh cadaveric specimens by microsurgical techniques. The metal-on-metal titanium alloy joint has an arc-shaped atlas component, and a hollow cylindrical bushing into which fits a rotation axle of an inverted v-shaped axis component and is implanted through a transoral approach. After the joint was implanted onto specimens with anterior decompression, biomechanical tests were performed to compare the stability parameters in the intact state, after decompression, after artificial joint replacement, and after fatigue test. Compared to the intact state, artificial joint replacement resulted in a significant decrease in the range of motion (ROM) and neutral zone (NZ) during flexion, extension, and lateral bending (P < 0.001); however, with regard to axial rotation, there was no significant difference in ROM (P = 0.405), a significant increase in NZ (P = 0.008), and a significant decrease in stiffness (P = 0.003). Compared to the decompressed state, artificial joint replacement resulted in a significantly decreased ROM (P B 0.021) and NZ (P B 0.002) and a significantly increased stiffness (P \ 0.001) in all directions. Following artificial joint replacement, there was no significant difference in ROM (P C 0.719), NZ (P C 0.580), and stiffness (P C 0.602) in all directions before and after the fatigue test. The artificial joint showed no signs of wear and tear after the fatigue test. This artificial atlanto-odontoid joint may be useful in cases of odontoid resection due to malunion or nonunion of odontoid fracture, atraumatic odontoid fracture, irreducible atlas dislocation, posterior atlantoaxial subluxation, or congenital skull base abnormalities.