Atlantoaxial Joint Distraction and Fusion with DTRAX Intra-Articular Cages: A Cadaveric Feasibility Study and Review of the Pertinent Literature.

PURPOSE: Atlantoaxial joint distraction is a key procedure for the treatment of selected patients affected by basilar invagination (BI). In recent years, several authors have reported various techniques of distraction and fixation of the C1-C2 joint using different types of intra-articular spacers, with or without posterior fixation. We review the pertinent literature and propose a feasibility study on the use of a new device for the distraction of the C1-C2 joint aimed to the descent of the dens out of the foramen magnum suggesting its application on selected cases of BI. METHODS: The GL-DTRAX Cervical Cage-SE is a cage approved by the Food and Drug Administration for distraction and fixation of subaxial cervical spine. Five adult cadaveric specimens were dissected surgically to evaluate the feasibility of DTRAX insertion inside the C1-C2 joint through a posterior approach. RESULTS: The cages were uneventfully set into the C1-C2 intra-articular space of all samples without the need to sacrifice C2 nerve roots and ganglia. Postoperative cervical computed tomography scanning confirmed the correct fitting of the devices in every sample. CONCLUSIONS: This cadaveric study highlights the feasibility of the DTRAX cage as a C1-C2 intra-articular device producing a substantial distraction of atlantoaxial complex and suggesting a possible therapeutic role in selected cases of BI.

Does focus of attention alter craniocervical flexion test motor learning? A randomized controlled trial.

OBJECTIVE: To evaluate the effects of three different foci of attention (internal, external and mixed) on motor learning using craniocervical flexion test in inexperienced participants. METHODS: Ninety healthy young adults, with no experience in the task, practiced the craniocervical flexion test under three different focus of attention: a) Mixed Focus (internal plus external), b) Internal Focus, and c) External Focus. We assessed immediate, post-training, and retention (one week after the last training session) aspects of motor learning by quantifying (i) the activity of the superficial cervical flexors muscles, (ii) craniocervical range of motion, and (iii) the performance on the craniocervical flexion test. RESULTS: None of the groups showed any significant immediate, post-training, or retention effects on superficial neck flexors activity and craniocervical range of motion progression. At immediate assessment, mixed focus had greater craniocervical flexion performance than external (MD 0.9, 95%CI 0.2 to 1.5), and internal foci (MD 1.4, 95%CI 0.8 to 2.1). At post-training, mixed focus led to better craniocervical performance compared to external (MD 1.6, 95%CI 0.8 to 2.4) and internal foci (MD 2.7, 95%CI 1.9 to 3.5). External focus had better scores on the craniocervical flexion test performance than internal focus (MD 1.1, 95%CI 0.3 to 1.9). Results remained similar at retention, with mixed focus being superior to internal (MD 2.3, 95%CI 1.7 to 3) and external foci (MD 1.5, 95%CI 0.9 to 2.1) on craniocervical flexion test performance. Similarly, the performance on the craniocervical flexion test performance remained similar at retention between external and internal foci (MD 0.9, 95%CI 0.2 to 1.5). CONCLUSION: In inexperienced asymptomatic participants, different foci of attention were not able to change cervical muscle activity and craniocervical range of motion during the craniocervical flexion test. Mixed focus was better than external and internal focus on the craniocervical flexion test. These findings were retained after one week.

Combined Procedure Allowing Atlantoaxial and Atlanto-Occipital Joint Motion for Complex Injuries in the Upper Cervical Spine.

This study was performed to explore an ideal limited fixation method for the treatment of unstable atlantoaxial fractures that can preserve the range of motion of the occipital and atlantoaxial joints and restore the stability of the upper cervical spine. A 64-year-old man was diagnosed with a complicated injury of the upper cervical spine. The anterior and posterior approach was used to reconstruct the stability of the upper cervical spine while preserving the range of motion of the occipital and atlantoaxial joints. Preoperative imaging and neurologic examinations were performed. Follow-up lasted 24 months. The patient clinically improved after undergoing this novel procedure. Seven days postoperatively, the patient's visual analog scale score was 3. Follow-up contrast computed tomography showed good reduction and fixation in the upper cervical spine. Two weeks postoperatively, the patient displayed good cervical vertebral activity, with no restriction during flexion, extension, rotation, or other movements. No intraoperative or postoperative complications occurred. This modified procedure for restoration of cervical stability may be an improvement over traditional posterior fusion because atlantoaxial motion is preserved. [Orthopedics. 2020;43(4):e329-e333.].

Morphometric and functional study of the canine atlantoaxial joint.

The atlantoaxial joint can be affected by instability, in most cases a congenital pathology in young small breed dogs. Causes of atlantoaxial instability (AAI) are variable but are usually attributed to a lack of ligamentous support. The purpose of the present study was to specify the role of the ligamentous structures in the stabilisation of the atlantoaxial joint and to find possible adaptations of the ligaments' internal structure to their specific function. Five Beagle cadavers were included in this study. Each dog was subjected to a computed tomography (CT) and a magnetic resonance imaging (MRI) examination of the upper cervical region. This region was then dissected and the ligamentous structures stabilising the atlantoaxial joint were measured and removed for histological analysis. A ligament to dens ratio (LDR) was established in order to provide a basis for comparison with the measurements taken in other dog breeds. MRI and gross anatomical measurements were very similar, confirming the validity of the results. MRI thus seems reliable for evaluating the ligamentous structures of the canine occipitoatlantoaxial region. The movement exerting the greatest stress on the atlantoaxial ligaments and inducing the greatest distension of the alar ligaments was a head flexion combined with a rotation. A clear adaptation of the ligamentous shape and internal structure to their specific function was observed. Histologically, alar ligaments consisted of wavy collagen fibres and a high proportion of elastic fibres, providing them with a remarkable elasticity compared to the transverse ligament structure which was much more rigid.

Atlantoaxial Instability: Evolving Understanding.

The atlantoaxial joint is the most mobile joint in the body. The physical architecture of the joint is characterized by a uniformly round and approximately flat surface, which allows a wide range of unobstructed movements. The standing human posture and lifelong heartbeat like uninterrupted activity of the atlantoaxial joint, and its ability to facilitate saying both 'yes' and 'no' necessarily requires smooth and 'fluid' movements that are supported by strong yet supple ligaments. The magnificent architectural structure that is 'magically' designed and carved by nature to provide both stability and mobility and to allow a smooth and safe transit passage for the most critical neural and vascular structures can only be admired in awe and appreciated.

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.

Anatomy of Alar Ligament Part III: Biomechanical Study.

OBJECTIVE: Four layers of ligamentous stabilizers comprise the craniocervical junction, and the second layer is composed of apical and paired alar ligaments. The purpose of this study is to establish the tensile strength of the alar ligaments for better understanding the implications that can arise from trauma and other pathologies in the craniocervical region. METHODS: Nineteen sides from 10 fresh frozen adult cadaveric Caucasian heads were used in this study. The specimens were derived from 6 males and 4 females, and the age of the cadavers at death ranged from 67-90 years old. To measure the tensile strength, a tensile testing machine (M2-200, Mark-10 Corporation, Copiague, New York, USA) was used in this study. RESULTS: The force (N) necessary until failure for all alar ligaments ranged from 87-346 N with a mean of 186.9 ± 69.7 N. There was a significant difference when comparing tensile strength between males and females. CONCLUSIONS: Further studies will be necessary to determine their importance as secondary stabilizers and measure their ability to support similar forces when subject to rotation and lateral bending forces, as well as with flexion-extension.

Dynamic in vivo 3D atlantoaxial spine kinematics during upright rotation.

Diagnosing dysfunctional atlantoaxial motion is challenging given limitations of current diagnostic imaging techniques. Three-dimensional imaging during upright functional motion may be useful in identifying dynamic instability not apparent on static imaging. Abnormal atlantoaxial motion has been linked to numerous pathologies including whiplash, cervicogenic headaches, C2 fractures, and rheumatoid arthritis. However, normal C1/C2 rotational kinematics under dynamic physiologic loading have not been previously reported owing to imaging difficulties. The objective of this study was to determine dynamic three-dimensional in vivo C1/C2 kinematics during upright axial rotation. Twenty young healthy adults performed full head rotation while seated within a biplane X-ray system while radiographs were collected at 30 images per second. Six degree-of-freedom kinematics were determined for C1 and C2 via a validated volumetric model-based tracking process. The maximum global head rotation (to one side) was 73.6±8.3°, whereas maximum C1 rotation relative to C2 was 36.8±6.7°. The relationship between C1/C2 rotation and head rotation was linear through midrange motion (±20° head rotation from neutral) in a nearly 1:1 ratio. Coupled rotation between C1 and C2 included 4.5±3.1° of flexion and 6.4±8.2° of extension, and 9.8±3.8° of contralateral bending. Translational motion of C1 relative to C2 was 7.8±1.5mm ipsilaterally, 2.2±1.2mm inferiorly, and 3.3±1.0mm posteriorly. We believe this is the first study describing 3D dynamic atlantoaxial kinematics under true physiologic conditions in healthy subjects. C1/C2 rotation accounts for approximately half of total head axial rotation. Additionally, C1 undergoes coupled flexion/extension and contralateral bending, in addition to inferior, lateral and posterior translation.

Comparison of Atlantoaxial Rotation and Functional Outcomes of Two Nonfusion Techniques in the Treatment of Anderson-D'Alonzo Type II Odontoid Fractures.

STUDY DESIGN: A retrospective comparative study. OBJECTIVE: The aim of this study was to compare the outcomes of anterior screw fixation and posterior temporary-fixation in the treatment of Anderson-D'Alonzo type II odontoid fractures. SUMMARY OF BACKGROUND DATA: Posterior C1-C2 temporary-fixation can spare the motion of C1-C2 in the treatment of odontoid fractures. However, it is unknown whether it can achieve the same outcomes as anterior screw fixation. METHODS: Data of 20 patients who underwent posterior temporary-fixation due to Anderson-D'Alonzo type II odontoid fractures with intact transverse ligament were retrospectively reviewed. Another 20 patients undergoing anterior screw fixation were randomly selected as the control group. The range of motion (ROM) in rotation of C1-C2 measured on functional computed tomography (CT) scan and outcomes evaluated by the visual analog scale (VAS) for neck pain, neck stiffness, patient satisfaction, and neck disability index (NDI) were compared between two groups at the final follow-up. RESULTS: At the final follow-up, 19 cases in each groups achieved facture healing. Total C1-C2 ROM in rotation on both sides in the posterior temporary-fixation group was 32.4 ±â€Š12.5°, smaller than 40.0 ±â€Š13.0 in the anterior fixation group. However, there was no statistical difference between two groups. And there was no significant difference between two groups in functional outcomes evaluated by VAS for neck pain, neck stiffness, patient satisfaction, and NDI. CONCLUSION: Posterior temporary-fixation can spare the motion of C1-C2 and achieve same good clinical outcomes as anterior screw fixation in the treatment of Anderson-D'Alonzo type II odontoid fractures. It was an ideal alternative strategy to anterior screw fixation. LEVEL OF EVIDENCE: 3.

The Effect of Target Position on the Accuracy of Cervical-Spine-Rotation Active Joint-Position Sense.

CONTEXT: The cervical spine can be divided into upper and lower units, each making a different contribution to the magnitude of rotation and proprioception. However, few studies have examined the effect of the cervical-rotation positions on proprioception. OBJECTIVE: To compare cervical-spine rotation active joint-position sense (AJPS) near midrange of motion (mid-ROM; 30°) and near end-ROM (60°). DESIGN: Cross-sectional study. SETTING: Human performance research laboratory. PARTICIPANTS: 53 military helicopter pilots (age 28.4 ± 6.2 y, height 175.3 ± 9.3 cm, weight 80.1 ± 11.8 kg). MAIN OUTCOME MEASURES: A motion-analysis system was used to record cervical-rotation kinematics. Subjects sat in a chair wearing a headband and blindfold. First, they actively rotated the head right or left to a target position (30°/60°), with real-time verbal cues provided by the tester. Subjects held the target position for 5 s and then returned to the start position. After this, they replicated the target position as closely as possible. Five trials were performed in both directions to both target positions (R30/R60/L30/L60). Order of direction/position was randomized. The difference between target and replicated positions was calculated and defined as absolute error (AE), and the mean of 5 trials was used for analyses. Wilcoxon signed-ranks tests were used to compare AJPS at the different target positions (P < .0125 with Bonferroni adjustments). RESULTS: End-ROM AEs were significantly more accurate than mid-ROM AEs (P = .001). CONCLUSION: Cervical-spine-rotation AJPS is more accurate near end-ROM than mid-ROM. Both target positions should be used to examine cervical-spine-rotation AJPS of both the upper and lower units.

[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.

Biomechanical properties of the atlantoaxial joint with naturally-occurring instability in a toy breed dog. A comparative descriptive cadaveric study.

The biomechanical properties of the atlanto-axial joint in a young Yorkshire Terrier dog with spontaneous atlantoaxial instability were compared to those of another young toy breed dog with a healthy atlantoaxial joint. The range-of-motion was increased in flexion and lateral bending in the unstable joint. In addition, lateral bending led to torsion and dorsal dislocation of the axis within the atlas. On gross examination, the dens ligaments were absent and a longitudinal tear of the tectorial membrane was observed. These findings suggest that both ventral and lateral flexion may lead to severe spinal cord compression, and that the tectorial membrane may play a protective role in some cases of atlantoaxial instability.

Atlanto-axial facet displacement during rotational high-velocity low-amplitude thrust: An in vitro 3D kinematic analysis.

BACKGROUND: Very little is known about the kinematics of the upper cervical spine in particular during Manual Therapy techniques. In fact no data about displacement of the atlanto-axial joint during High-Velocity Low-Amplitude (HVLA) thrust are available. Knowing the precise kinematics of these vertebrae might allow a better comprehension of such important technique and possible vital structures involvement. METHODS: A Zebris CMS20 ultrasound-based motion tracking system was adopted. Twenty fresh human cervical specimens were used in this study. Facet joint displacements of C1 relative to C2 were analysed during three consecutive HVLA thrusts into rotation. Displacement during the thrust and the maximum displacement reached with the manoeuvre were analysed. RESULTS: Descriptive statistics showed a mean Norm displacement during the thrust of 0.5 mm (SD ± 0.5). The maximum displacement, representing the overall facet movement from neutral to end-range position, indicated a Norm value of 6.0 mm (SD ± 3.4). Heterogeneous displacement directions were found during the thrust. Intra and inter-rater reliability reached an insufficient reproducibility level. Considering the amount of displacement induced, no statistical significant differences between the registrations were shown. CONCLUSION: Displacement during the execution of HVLA thrust is unintentional, unpredictable and not reproducible. On the other hand and in accordance with other studies, the displacement induced with the present technique seems not to be able to endanger vital structure on the Spinal Cord and the Vertebral Artery. This study also adds to a better comprehension of the kinematic of the atlanto-axial segment during the performance of HVLA manipulation.

Anatomy and biomechanics of the craniovertebral junction.

The craniovertebral junction (CVJ) has unique anatomical structures that separate it from the subaxial cervical spine. In addition to housing vital neural and vascular structures, the majority of cranial flexion, extension, and axial rotation is accomplished at the CVJ. A complex combination of osseous and ligamentous supports allow for stability despite a large degree of motion. An understanding of anatomy and biomechanics is essential to effectively evaluate and address the various pathological processes that may affect this region. Therefore, the authors present an up-to-date narrative review of CVJ anatomy, normal and pathological biomechanics, and fixation techniques.

In vitro biomechanics of the craniocervical junction-a sequential sectioning of its stabilizing structures.

BACKGROUND CONTEXT: Occipitocervical dislocations involve translations of the craniocervical joints. The relative contributions of each ligament to overall stability and the effects of the occipitoatlantal joint capsules on the pathologic translation are unknown. Although incidences of occipitocervical dislocations are rare after blunt trauma, they are usually fatal. When patients do survive these dislocations, the proper diagnosis is difficult, which in turn may increase the fatality rate. A biomechanical model may provide a greater pathologic understanding of craniocervical subluxation. PURPOSE: The purpose of the study is to build an in vitro biomechanical model to determine which stabilizing ligament(s) of the craniocervical junction are most important in restraining rotation and translations during these rotations. This may guide clinical diagnosis, which could assist in treatment options. STUDY DESIGN/SETTING: The study design includes a biomechanical cadaveric test. METHODS: Seven cadaveric specimens were tested using a 6-degree-of-freedom spine simulator under the following conditions: intact, clivus/alar removal (CR), transverse ligament destruction (TLD), occipitoatlantal (OA) joint capsulotomyoccipitoatlantal (OA) joint capsulotomy (C0-C1 JC), and C1-C2 joint capsulotomy (C1-C2 JC). Flexion-extension (FE), lateral bending (LB), and axial rotation (AR) were applied (2.5 Nm) to a C0-C2 segment, whereas anterior-posterior (AP) and cranial-caudal (CC) translations were recorded. Average motions were normalized to intact (100%) for each joint. RESULTS: Increases in C0-C1 angular and translational motions occurred after TLD and C0-C1 JC. At the atlantoaxial joint, there were significant (p<.05) increases from intact in FE (TLD=154%, C0-C1 JC=174%) and in AR (TLD=178%, C0-C1 JC=224%). Anterior-posterior translation during applied LB increased significantly after TLD (248% intact). Cranial-caudal translation during applied FE increased significantly after TLD (188%) and C0-C1 JC (361%). Increases in C1-C2 angular motion occurred after TLD and C1-C2 JC and in translation after CR and TLD. At the C1-C2 joint, there were significant increases from intact in FE (TLD=172%, C1-C2 JC=160%) and in LB (TLD=286%, C1-C2 JC=332%); in AR, there were no statistical differences. Anterior-posterior translation increased significantly after CR (280%). Cranial-caudal translation also increased significantly after CR (205%) and TLD (298%) during LB. CONCLUSIONS: Transverse and alar ligaments appear to be the main stabilizers of the craniocervical junction. The vertical structures attached to the clivus and OA joint capsules function as secondary stabilizers. Craniocervical dislocations seem to affect FE and lateral bending the most, whereas increased translation seems to occur primarily in the AP and CC directions. Models of craniocervical trauma should section all three restraining structures for the future studies.

Biomechanical analysis of the longitudinal ligament of upper cervical spine in maintaining atlantoaxial stability.

STUDY DESIGN: In vitro human cadaveric biomechanical study. OBJECTIVES: To investigate the roles of transverse atlantal ligament (TAL) and longitudinal ligament (LL) of the upper cervical spine (UCS) in maintaining atlantoaxial stability. SETTING: China. METHODS: Six intact UCS specimens were harvested and embedded in polymethylmethacrylate. Three-dimensional movements including flexion, extension, right and left lateral bending, and axial rotation, as well as the C1-C2 displacement in flexion (atlantodental interval, ADI), were tested on specimens with the following state sequentially: (1) intact (intact group), (2) TAL transected (TAL group) and (3) TAL and LL disrupted (TAL+LL group) using an electromechanical testing machine. RESULTS: Compared with intact group, the flexion/extension motion range and ADI were significantly higher in TAL group when the loading was 10 N or >100 N. However, no significant differences were detected between the two groups within a range of physiological loading (10-100 N). Similarly, significant differences in right-left lateral bending and axial rotation between TAL and intact groups occurred only when the loading was 150 N. However, when both of the TAL and LL were resected, the atlantoaxial joint showed obvious instability compared with TAL or intact group, which were further demonstrated in the analyses of the three-dimensional movements (significant differences at any loading). CONCLUSION: Within physiological loading range, the LLs have sufficient capacities to maintain the stability of atlantoaxial joint even if there are TAL injuries in atlas fractures.

Biomechanical evaluation of the stabilizing function of the atlantoaxial ligaments under shear loading: a canine cadaveric study.

OBJECTIVES: To evaluate the stabilizing function of atlanto-axial ligaments in dogs. STUDY DESIGN: Cadaveric biomechanical study. ANIMALS: Beagle dog cadavers (n = 10). METHODS: The craniocervical region was collected from 10 Beagle cadavers, and the occipito-atlanto-axial region was prepared and freed from the surrounding muscles. Care was taken to preserve integrity of the atlantoaxial ligaments and atlantoaxial joint capsule. The atlanto-occipital joints were blocked with 2 diverging transarticular 1.8 mm positive threaded K-wires. Specimen extremities were embedded in polymethylmethacrylate (PMMA) and mounted on a simulator testing shear load at the atlantoaxial joint. Range of motion (ROM) and neutral zone (NZ) were determined with all ligaments intact, after cutting the apical ligament, both alar ligaments, the transverse ligaments and finally after cutting the dorsal atlantoaxial ligament. RESULTS: ROM increased similarly and stepwise during testing. The most significant increase was observed after transection of the alar ligaments. CONCLUSION: The alar ligaments seem to be the most important ligamentous structures for stabilization of the atlantoaxial joint under shear load.

The influence of age, sex, and posture on the measurement of atlantodental interval in a normal population.

OBJECTIVE: The atlantodental interval (ADI) is used in assessing atlantoaxial stability. This measurement may potentially be affected by several features encountered during patient examination. This study examined the influence of 3 features: age, sex, and posture, on the measurement of ADI in a normal population. METHODS: The ADI was measured sequentially on 269 lateral cervical radiographs of adults with no demonstrated bony injury. Images were stratified by age and sex with equal representation in each age group. A further 25 asymptomatic adults were assessed for posture using craniovertebral angle measured from digital lateral photographs. The ADI was then measured from a lateral radiograph. The data were examined for correlation between age, craniovertebral angle, and ADI using Spearman rank correlation. The ADI of age groups was compared by Kruskal-Wallis test. The relationship between ADI and sex was examined using Wilcoxon rank sum test. Interaction between age and sex was explored using an interaction term in regression analysis. RESULTS: The ADI decreased with age, median measurements reducing from 2.07 to 0.85 mm across age groups (P < .01). No significant relationship was demonstrated between ADI and sex. No significant interaction was demonstrated between age and sex. Measurements of craniovertebral angle did not correlate with ADI (ρ = 0.03, P = .90). CONCLUSION: The magnitude of ADI decreases with advancing age. Age should be considered a modifying factor when interpreting measurement of ADI, particularly in consideration of potential minor instabilities. Patient sex does not appear to influence ADI, either independently or in interaction with age. Craniocervical posture variation does not influence ADI in an asymptomatic adult population.

Toward understanding normal craniocervical rotation occurring during the rotation stress test for the alar ligaments.

BACKGROUND: The rotation stress test is recommended for assessing alar ligament integrity. Although some authors, in the literature regarding the rotation stress test, accept that rotation will occur during testing, estimates of range occurring with a normal test response vary between 20 and 40 degrees. None of these estimates are based on formal examination of the test. OBJECTIVE: The purposes of this study were: (1) to examine the range of craniocervical rotation occurring during rotation stress testing for the alar ligaments in individuals who are healthy and (2) to investigate a measurement protocol for quantifying rotation. DESIGN: A within-subject experimental study was conducted. METHODS: Sixteen participants underwent magnetic resonance imaging in neutral and end-range rotation stress test positions. Measurements followed a standardized protocol relative to the position of the axis. A line connecting the transverse foramena of the axis created a reference plane. The position of the occiput in the head-neutral position was calculated as the angle formed between a line joining the foramena lacerum and the reference plane. Measurements were repeated at the end-range test position. Total rotation of the occiput was calculated as the difference in angles measured in neutral and test positions. Measurement was performed on 4 occasions, and reliability of measurements was assessed using the standard error of measurement (SEM) and the intraclass correlation coefficient (ICC). RESULTS: Measurement of rotation of the occiput relative to a stabilized axis ranged between 1.7 and 21.5 degrees (X=10.6, SD=5.1, SEM=1.14, ICC=.96, 95% confidence interval=.90-.98). LIMITATIONS: Sustaining the test position for imaging increased the potential for loss of end-range position and image quality. Testing could be performed only in the neutral position, not in 3 planes as commonly described. CONCLUSIONS: The range of craniocervical rotation during rotation stress testing of intact alar ligaments should typically be 21 degrees or less. Rotation may be quantified using the method protocol outlined.