Kinematics Of Cervical Spine Research Articles

Sex-Specific Intubation Biomechanics: Intubation Forces Are Greater in Male Than in Female Patients, Independent of Body Weight.

BackgroundStudies of head, neck, and cervical spine morphology and tissue material properties indicate that cervical spine biomechanics differ between adult males and females. These differences result in sex-specific cervical spine kinematics and injury patterns in response to standardized loading conditions. Because direct laryngoscopy and endotracheal intubation require the application of a load to the cervical spine, intubation biomechanics should be sex-specific. The aim of this study was to determine if intubation forces during direct laryngoscopy differ between male and female patients and, if so, is the difference independent of body weight.MethodsWe pooled original data from three previously published adult clinical intubation studies that used methodologically reliable intubation force measurements (measured total laryngoscope force applied to the tongue, and force values were insensitive to or accounted for other laryngoscope blade forces). All patients had undergone direct laryngoscopy and orotracheal intubation with a Macintosh 3 blade under general anesthesia. Patient data included sex, age, height, weight, and maximum intubation force. Least squares multivariable linear regression was performed between the dependent variable (maximum intubation force) and two independent variables (patient sex and patient weight). A third term was added for the interaction between patient sex and weight.ResultsAmong all patients (males n=42, females n=59), the median intubation force was 42.2 N (25th to 75th percentiles: 31.5 to 57.4 N). While controlling for patient body weight, intubation force differed between the sexes; P=0.011, with greater intubation force in male patients. While controlling for patient sex, there was a positive association between patient body weight and intubation force; P=0.009. In addition, there was a significant interaction between patient sex and weight; P=0.002, with intubation force in male patients having greater dependence on body weight. The difference in intubation force between male and female patients who had the same body weight exceeded 5 N when body weight exceeded 75 kg, and intubation force differences between male and female patients increased as patient body weight increased. Additional analyses using robust regression and using body mass index instead of weight provided comparable results.ConclusionIn adult patients, the biomechanics of direct laryngoscopy and intubation are sex-specific. Our findings support the need to control for patient sex and weight in future clinical and laboratory studies of the human cervical spine and head and neck biomechanics.

Biomechanical comparison of noncontiguous cervical disc arthroplasty and noncontiguous cervical discectomy and fusion in the treatment of noncontinuous cervical degenerative disc disease: a finite element analysis

BackgroundBiomechanical characteristics of noncontinuous ACDF and noncontinuous CDA in the treatment of noncontinuous cervical degenerative disc disease were still unclear. The aim of this research is to compare the differences between these two kinds of treatment methods and to verify the effectiveness of Prodisc-C in noncontinuous CDA.MethodsEight FEMs of the cervical spine (C2–C7) were built based on CT images of 8 mild CDDD volunteers. In the arthroplasty group, we inserted Prodisc-C at C3/4 and C5/6. In the fusion group, CoRoent® Contour and NuVasive® Helix ACP were implanted at C3/4 and C5/6. Initial loads of 75 N were used to simulate the head weight and muscle forces. The application of 1.0 N m moment on the top on the C2 vertebra was used to create motion in all directions. Statistical analyses were performed using STATA version 14.0 (Stata Corp LP, College Station, Texas, USA). Statistical significance was set at P < 0.05.ResultsThe IDPs in C2/3 (P < 0.001, P = 0.005, P < 0.001, P < 0.001), C4/5 (P < 0.001), and C6/7 (P < 0.001) of the intact group were significantly less than that in the fusion group in flexion, extension, lateral bending, and axial rotation, respectively. In addition, the IDPs in C2/3 (P < 0.001, P = 0.001, P < 0.001, P < 0.001), C4/5 (P < 0.001), and C6/7 (P < 0.001) of the arthroplasty group were significantly less than that in the fusion group in flexion, extension, lateral bending, and axial rotation, respectively. Contact forces of facet joints in C2/3 (P = 0.010) in the arthroplasty group was significantly less than that in the intact group. Contact forces of facet joints in C2/3 (P < 0.001), C4/5 (P < 0.001), and C6/7 (P < 0.001) in the arthroplasty group was significantly less than that in the fusion group. Contact forces of facet joints in C2/3 (P < 0.001), C4/5 (P < 0.001), and C6/7 (P < 0.001) in the intact group were significantly less than that in the fusion group.ConclusionsNoncontinuous CDA could preserve IDP and facet joint forces at the adjacent and intermediate levels to maintain the kinematics of cervical spine near preoperative values. However, noncontinuous ACDF would increase degenerative risks at adjacent and intermediate levels. In addition, the application of Prodisc-C in noncontinuous CAD may have more advantages than that of Prestige LP.

Analysis of adjacent-segment cervical kinematics: the role of construct length and the dorsal ligamentous complex.

Lateral mass fixation stabilizes the cervical spine while causing minimal morbidity and resulting in high fusion rates. Still, with 2 years of follow-up, approximately 6% of patients who have undergone posterior cervical fusion have worsening kyphosis or symptomatic adjacent-segment disease. Based on the length of the construct, the question of whether to extend the fixation system to undisrupted levels has not been answered for the cervical spine. The authors conducted a study to quantify the role of construct length and the terminal dorsal ligamentous complex in the adjacent-segment kinematics of the subaxial cervical spine. In vitro flexibility testing was performed using 6 human cadaveric specimens (C2-T8), with the upper thoracic rib cage and osseous and ligamentous integrity intact. An industrial robot was used to apply pure moments and to measure segmental motion at each level. The authors tested the intact state, followed by 9 postsurgical permutations of laminectomy and lateral mass fixation spanning C2 to C7. Constructs spanning a single level exerted no significant effects on immediate adjacent-segment motion. The addition of a second immobilized segment, however, created significant changes in flexion-extension range of motion at the supradjacent level (+164%). Regardless of construct length, resection of the terminal dorsal ligaments did not greatly affect adjacent-level motion except at C2-3 and C7-T1 (increasing by +794% and +607%, respectively). Dorsal ligamentous support was found to contribute significant stability to the C2-3 and C7-T1 segments only. Construct length was found to play a significant role when fixating two or more segments. The addition of a fused segment to support an undisrupted cervical level is not suggested by the present data, except potentially at C2-3 and C7-T1. The study findings emphasize the importance of the C2-3 segment and its dorsal support.

Clinical Relevance of Cervical Kinematic Quality Parameters in Planar Movement.

Comprehending cervical spinal motion underlies the understanding of the mechanisms of cervical disorders. We aimed to better define the clinical relevance of cervical spine kinematics, focusing on quality parameters describing cervical spine planar motion. The most common study focuses were kinematic quality parameters after cervical arthroplasty and in normal subjects, patients with cervical degeneration, and patients with cervical deformities. Kinematic quality parameters are important for cervical degeneration prevention, being detected sooner than differences on imaging examinations and being significantly related to the degree of cervical degeneration. Kinematic quality parameters are effective for evaluating the changes of cervical motion pattern after cervical fusion and non‐fusion, assessing operative and adjacent segments in the early stages, and predicting adjacent segment degeneration. However, owing to current research limitations, and controversy about the changes of kinematic quality parameters after different surgical procedures, current assessments are limited to cervical spine flexion and extension. Different osteotomy methods of cervical deformity have different effects on cervical motion patterns and quality parameters. Choosing the most effective surgical method remains a challenge and kinematic quality parameters in cervical deformity are important future research topics. This review highlights the instantaneous center of rotation, the center of rotation, and the instantaneous axis of rotation as being important kinematic quality parameters of cervical spinal motion. These can be used to detect abnormal cervical mobility, to diagnose cervical degeneration, to design disc protheses, and to evaluate surgical effects earlier than other methods. Owing to limitations of research methods there is variation in the way parameters are defined by various researchers. No uniform standard exists for defining degenerative motion quality parameters in normal asymptomatic, degenerative, and postoperative patients. Therefore, further study is required. New study techniques and defining kinematic quality parameters in normal subjects will clarify the definitions of these parameters, enhancing their future clinical usefulness.

Optimization of compressive loading parameters to mimic in vivo cervical spine kinematics in vitro

The human cervical spine supports substantial compressive load in vivo. However, the traditional in vitro testing methods rarely include compressive loads, especially in investigations of multi-segment cervical spine constructs. Previously, a systematic comparison was performed between the standard pure moment with no compressive loading and published compressive loading techniques (follower load – FL, axial load – AL, and combined load – CL). The systematic comparison was structured a priori using a statistical design of experiments and the desirability function approach, which was chosen based on the goal of determining the optimal compressive loading parameters necessary to mimic the segmental contribution patterns exhibited in vivo. The optimized set of compressive loading parameters resulted in in vitro segmental rotations that were within one standard deviation and 10% of average percent error of the in vivo mean throughout the entire motion path. As hypothesized, the values for the optimized independent variables of FL and AL varied dynamically throughout the motion path. FL was not necessary at the extremes of the flexion–extension (FE) motion path but peaked through the neutral position, whereas, a large negative value of AL was necessary in extension and increased linearly to a large positive value in flexion. Although further validation is required, the long-term goal is to develop a “physiologic” in vitro testing method, which will be valuable for evaluating adjacent segment effect following spinal fusion surgery, disc arthroplasty instrumentation testing and design, as well as mechanobiology experiments where correct kinematics and arthrokinematics are critical.

Cervical spine kinematics during machine-based and live scrummaging

ABSTRACTThe aim of this study was to compare cervical spine kinematics in rugby union front row players during machine-based and “live” scrummaging. Cervical spine kinematics was measured via electromagnetic tracking of sensors attached to the head and thorax. Joint angles were extracted from each trial at two time points (“bind” prior to engagement and instant of impact) for comparison between scrummaging conditions. The effect of scrummaging condition on kinematics was evaluated using a mixed effects model and estimations were based on a Bayesian framework. With differences ranging from 38° to 50°, the results show that the cervical spine is consistently more flexed when scrummaging against opponents than against a scrum machine. In contrast, there are little differences in the excursion of lateral-flexion (range 5–8°) and axial rotation (7°) between the two conditions. The findings from this study provide clear information on motion patterns in different scrum formations, and suggest that the current design of scrum machines may not promote the same pattern of movement that occurs in live scrums. The results highlight that findings from previous studies that have investigated kinematics during machine-based scrummaging may not be generalisable to a competitive scrummaging context.

Characteristics of Cervical Spine Motion in Different Types of Cervical Alignment: Kinematic MRI Study.

Retrospective study. To evaluate how each type of sagittal cervical alignment affects the motion of the upper and subaxial cervical spine using kinematic magnetic resonance imaging. The sagittal malalignment of the cervical spine from degeneration in the subaxial cervical spine reflects a disruption in the kinematic properties of the cervical spine and affects the motion of adjacent segments. Changes in the sagittal parameters and kinematics of the upper cervical spine and upper thoracic spine due to the kyphosis are unknown. Kinematic magnetic resonance imaging of the cervical spine in neutral position from 311 patients, including 90 lordotic, 90 straight, 90 global kyphotic, and 41 segmental kyphotic were analyzed. The lordotic angle at the upper and lower cervical spine, and T1 slope were measured in the neutral position and again in flexion and extension for dynamic analysis. The number of levels with significant disk degeneration was higher in the global kyphosis group. In the global kyphosis group, neutral sagittal parameters showed some characteristics of compensation to the malalignment. Compared with the lordotic group, patients with global kyphosis demonstrated significantly higher lordotic angle of the upper cervical spine and more horizontal T1 slope. The dynamic evaluation showed greater range of motion of the entire cervical spine and subaxial cervical spine in younger patients. However, we still found greater range of motion of the occipito-atlanto-axial complex in global kyphosis, even when controlling for age and number of levels with significant disk degeneration. Sagittal malalignment of the cervical spine affects all parts of the cervical motion complex. The global kyphotic alignment of subaxial cervical spine affects the kinematic properties of the occipito-atlanto-axial complex and upper thoracic spine to compensate for the alteration of cervical alignment. These differences are not seen in straight and segmental kyphosis. Level 3.

3-Dimensional Cervical Movement Characteristics and the Influence of Thoracic Treatment on a Subgroup of Acute Neck Pain Patients

ObjectiveThe purpose of this study was to investigate the influence of thoracic high-velocity low-amplitude thrust (HVLAT) manipulation on quantitative and qualitative 3-dimensional cervical spine kinematic patterns in a subgroup of patients with acute neck pain. MethodsThirty patients with acute neck pain, aged 20 to 59, received a thoracic HVLAT manipulation. Three-dimensional kinematics of the cervical spine were registered pretreatment and posttreatment using an electromagnetic tracking system. Quantitative and qualitative parameters were calculated for axial rotation, lateral bending, and flexion-extension movement. Subjective pain ratings were measured with the visual analogue scale and the Neck Disability Index and were collected pretreatment and posttreatment. ResultsAfter treatment, the range of motion of the main motion improved significantly for axial rotation (P = .034), lateral bending (P < .001), and flexion-extension (P = .031). Although for axial rotation as the main motion, the smoothness of the flexion-extension movement improved significantly after treatment (P = .036), the reverse was true for flexion-extension as the main motion. Visual analogue scale scores exhibited a statistically (P < .001) and clinically significant reduction of pain sensation. The mean change in Neck Disability Index scores only exhibited a statistically significant improvement 1 week after treatment. ConclusionThoracic HVLAT manipulation led to positive changes in quantitative and qualitative aspects of 3-dimensional cervical spine kinematics. Because of the 1-intervention group design, external factors influencing the healing process could not be eliminated.

A radiographic investigation of cervical spine kinematics when reading a tablet in a reclined trunk position

The purpose of this study was to use radiographic measurements to compare cervical spine kinematics in various tablet computer reading postures. Radiographs were taken of twenty-two participants reading a tablet computer in five different postures. The lower cervical spine was more flexed in the semi-reclined (-8.2 ± 3.8°) and the reclined (-14.9 ± 4.0°) tablet positions compared to an upright (-4.43 ± 4.8°) tablet posture. Of the tablet reading positions, the reclined position had the lowest gravitational moment arm (5.2 ± 2.3 cm) and a skull angle closest to neutral (-9.4 ± 11.4°), while exhibiting the largest extension in the C1-C2 joint (34.4 ± 9.1°). Altering trunk position when reading a tablet could reduce the load required to support the head, but could put the head in a more forward head posture, stretch the cervical extensor muscles, and potentially result in pain.

Effect of pediatric growth on cervical spine kinematics and deformations in automotive crashes

Finite element (FE) models are a powerful tool that can be used to understand injury mechanisms and develop better safety systems. This study aims to extend the understanding of pediatric spine biomechanics, where there is a paucity of studies available. A newly developed and continuously scalable FE model was validated and scaled to 1.5-, 3-, 6-, 10-, 14- and 18-year-old using a non-linear scaling technique, accounting for local topological changes. The oldest and youngest ages were also scaled using homogeneous geometric scaling. To study the effect of pediatric spinal growth on head kinematics and intervertebral disc strain, the models were exerted to 3.5 g acceleration pulse at the T1 vertebra to simulate frontal, rear and side impacts. It was shown that the head rotation increases with age, but is over predicted when geometrically scaling down from 18- to 1.5-year-old and under predicted when geometrically scaling up from 1.5- to 18-year-old. The strain in the disc, however, showed a clear decrease with age in side impact and for the upper cervical spine in rear impact, indicating a higher susceptibility for neck injury at younger ages. In the frontal impact, no clear age dependence could be seen, suggesting a large contribution from changed facet joint angles, and lower levels of strain, suggesting a lower risk of injury. The results also highlight the benefit of rearward facing children in a seat limiting head lateral motion.

Cervical spine kinematics measured during rugby union scrums: Reliability of optoelectronic and electromagnetic tracking systems

Measuring cervical spine kinematics in rugby scrummaging is important from an injury prevention perspective. However, choosing an appropriate measurement system is challenging. Since reliability of...

A Comparison of Cervical Spine Motion After Immobilization With a Traditional Spine Board and Full-Body Vacuum-Mattress Splint.

Background:The National Athletic Trainers’ Association (NATA) advocates for cervical spine immobilization on a rigid board or vacuum splint and for removal of athletic equipment before transfer to an emergency medical facility.Purpose:To (1) compare triplanar cervical spine motion using motion capture between a traditional rigid spine board and a full-body vacuum splint in equipped and unequipped athletes, (2) assess cervical spine motion during the removal of a football helmet and shoulder pads, and (3) evaluate the effect of body mass on cervical spine motion.Study Design:Controlled laboratory study.Methods:Twenty healthy male participants volunteered for this study to examine the influence of immobilization type and presence of equipment on triplanar angular cervical spine motion. Three-dimensional cervical spine kinematics was measured using an electromagnetic motion analysis system. Independent variables included testing condition (static lift and hold, 30° tilt, transfer, equipment removal), immobilization type (rigid, vacuum-mattress), and equipment (on, off). Peak sagittal-, frontal-, and transverse-plane angular motions were the primary outcome measures of interest.Results:Subjective ratings of comfort and security did not differ between immobilization types (P > .05). Motion between the rigid board and vacuum splint did not differ by more than 2° under any testing condition, either with or without equipment. In removing equipment, the mean peak motion ranged from 12.5° to 14.0° for the rigid spine board and from 11.4° to 15.4° for the vacuum-mattress splint, and more transverse-plane motion occurred when using the vacuum-mattress splint compared with the rigid spine board (mean difference, 0.14 deg/s [95% CI, 0.05-0.23 deg/s]; P = .002). In patients weighing more than 250 lb, the rigid board provided less motion in the frontal plane (P = .027) and sagittal plane (P = .030) during the tilt condition and transfer condition, respectively.Conclusion:The current study confirms similar motion in the vacuum-mattress splint compared with the rigid backboard in varying sized equipped or nonequipped athletes. Cervical spine motion occurs when removing a football helmet and shoulder pads, at an unknown risk to the injured athlete. In athletes who weighed more than 250 lb, immobilization with the rigid board helped to reduce cervical spine motion.Clinical Relevance:Athletic trainers and team physicians should consider immobilization of athletes who weigh more than 250 lb with a rigid board.

Reliability and validity of an electromagnetic tracking system to measure cervical spine kinematics during Rugby Union scrums

Background: Cervical spine injuries in Rugby Union as a result of scrummaging are common. However, precise injury mechanisms remain unclear, in part due to the challenges of measuring cervical spine kinematics in-vivo and in ecologically valid environments. For example, in live scrums, the cervical spine is hidden by other players and thus traditional visual-based measurement systems, such as optoelectronic motion capture systems, cannot be used. Therefore, the aim of this study was to investigate the reliability and validity of a portable electromagnetic tracking (EMT) system as an alternative method for measuring cervical spine kinematics, first during a simple scrummaging task.

Space Available for Cord, Motion, and disc degeneration at the adjacent segments level of degenerative cervical spondylolisthesis using kinematic MRI

The objective was to evaluate motion, disc degeneration and Space Available for Cord (SAC) at the adjacent segments of degenerative cervical spondylolisthesis (DCS) using kinematic Magnetic Resonance Imaging (kMRI). The cervical spine kMRI of sixty-one DCS spinal levels (38 anterolisthesis and 23 retrolisthesis) were analyzed at the listhesis level and its adjacent segments in three position using kMRI. MRAnalyzer3 was used to analyze translation, angular motion and SAC. The caudad level had significantly less translation motion than the listhesis level in overall DCS or grade 2 anterolisthesis group (P<0.05). The cephalad level had significant more translational motion than the caudad level in overall DCS or grade 1 retrolisthesis group (P<0.05). For disc degeneration, the cephalad level had the least disc degeneration and showed significant difference with the listhesis level in overall DCS or overall anterolisthesis or overall retrolisthesis or grade 2 anterolisthesis or grade 1 or 2 retrolisthesis (P<0.05). For SAC, the listhesis level had the narrowest space in overall DCS groups. In neutral position, grade 1 anterolisthesis had significantly larger SAC at the listhesis and the cephalad level than grade 1 retrolisthesis (P<0.05). In conclusion, DCS affected cervical spine motion and kinematics. Grade 1 retrolisthesis showed tendency of narrower SAC at the cephalad level more than the same grade anterolisthesis. The likelihood of the adjacent segment disease and spinal cord compression are higher in both grade 2 anterolisthesis and retrolisthesis.

Effects of cervical arthroplasty on neck response during a simulated rotary-wing aircraft impact

ABSTRACTA computational finite element analysis was performed to evaluate the effects of C5-6 cervical total disc replacement (CTDR) on cross-sectional neck loading and cervical spine kinematics during a simulated rotary-wing aircraft ground impact. The neck of a human body finite element model was modified to include a C5-6 interbody arthroplasty with either a Prestige ST or ProDisc-C CTDR. The adjacent-level, cross-sectional loading for the C5-6 segment was not greatly altered by the CTDRs, as indicated by CORrelation and Analysis (CORA) ratings of 0.988 for the Prestige ST and 0.909 for the ProDisc-C. The CTDRs increased the interbody range of motion, altering both the interbody and cervical facet loading. While the facet capsules experienced increased tension in both CTDR simulations, established injury threshold levels were not reached. Overall, cervical arthroplasty at the C5-6 level did not appear to have a deleterious effect on the dynamic neck response during a simulated rotary-wing aircraft impact.

The evaluation of cervical spine mobility without significant spondylosis by kMRI.

Retrospective analysis of kinetic magnetic resonance images (kMRI). To analyse the kinematics of cervical spine inpatients without significant spondylosis and to understand the normal movement of the cervical spine as reference for future comparison. Although some studies have been conducted to describe the normal mobility of the cervical spine, prior studies did not establish a relationship between the kinematics of cervical spine and disc degeneration. Only a few studies of the kinematics of the non-degenerated cervical spine have been reported; however, they focused on single level and not all the levels of cervical spine. 468 symptomatic patients underwent upright cervical kMRI, and cervical disc degeneration was evaluated with a new grading system. This grading system consists of four grades (0-III), and the cervical spines with grade 0 and grade I discs were included in this study. Finally, 61 symptomatic patients were studied 34 male and 27 female with an average age of 41.9 years. kMRI was used to define the normal mobility of the cervical spine by calculating the translation motion, angular variation and percentage angular contribution to the total cervical spine. The translation motion of the cervical spine at each level was 0.85 ± 1.22 mm at C2/3, 1.05 ± 1.19 mm at C3/4, 0.63 ± 1.19 mm at C4/5, 0.57 ± 0.91 mm at C5/6, 0.16 ± 0.86 mm at C6/7 and -0.11 ± 0.81 at C7/T1. In general, the translation motion decreased from proximal segment to distal segment. The angular variation of the cervical spine at each level was 5.58 ± 3.86° at C2/3, 8.26 ± 4.81° at C3/4, 9.11 ± 4.87° at C4/5, 10.05 ± 5.26° at C5/6, 8.31 ± 4.30° at C6/7 and 4.87 ± 3.28° at C7/T1. The angular variation at C2/3 and C7/T1 was significantly lower compared to other levels (P < 0.05). The contribution of each cervical level to the total angular mobility of cervical spine was the greatest at C5/6 (21.68 ± 10.31%) and least at C7/T1 (11.11 ± 7.60%) (P < 0.05). This study demonstrates the normal cervical segmental mobility for the entire cervical spine using kMRI. These results will be helpful to understand the normal mobility of the cervical spine and for understanding the relationship between kinematics of the cervical spine and disc degeneration for future comparisons.

Out-of-Position Rear Impact Tissue-Level Investigation Using Detailed Finite Element Neck Model

Objective: Whiplash injuries can occur in automotive crashes and may cause long-term health issues such as neck pain, headache, and visual and auditory disturbance. Evidence suggests that nonneutral head posture can significantly increase the potential for injury in a given impact scenario, but epidemiological and experimental data are limited and do not provide a quantitative assessment of the increased potential for injury. Although there have been some attempts to evaluate this important issue using finite element models, none to date have successfully addressed this complex problem.Methods: An existing detailed finite element neck model was evaluated in nonneutral positions and limitations were identified, including musculature implementation and attachment, upper cervical spine kinematics in axial rotation, prediction of ligament failure, and the need for repositioning the model while incorporating initial tissue strains. The model was enhanced to address these issues and an iterative procedure was used to determine the upper cervical spine ligament laxities. The neck model was revalidated using neutral position impacts and compared to an out-of-position cadaver experiment in the literature. The effects of nonneutral position (axial head rotation) coupled with muscle activation were studied at varying impact levels.Results: The laxities for the ligaments of the upper cervical spine were determined using 4 load cases and resulted in improved response and predicted failure loads relative to experimental data. The predicted head response from the model was similar to an experimental head-turned bench-top rear impact experiment. The parametric study identified specific ligaments with increased distractions due to an initial head-turned posture and the effect of active musculature leading to reduced ligament distractions.Conclusions: The incorporation of ligament laxity in the upper cervical spine was essential to predict range of motion and traumatic response, particularly for repositioning of the neck model prior to impact. The results of this study identify a higher potential for injury in out-of-position rear collisions and identified at-risk locations based on ligament distractions. The model predicted higher potential for injury by as much as 50% based on ligament distraction for the out-of-position posture and reduced potential for injury with muscle activation. Importantly, this study demonstrated that the location of injury or pain depends on the initial occupant posture, so that both the location of injury and kinematic threshold may vary when considering common head positions while driving.

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

BackgroundVery 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. MethodsA 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. ResultsDescriptive 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. ConclusionDisplacement 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.

Three-dimensional intervertebral kinematics in the healthy young adult cervical spine during dynamic functional loading

The objective of this study was to determine the intervertebral kinematics of the young, healthy cervical spine during dynamic, three-dimensional, functional loading. Intervertebral motion was characterized by the range of motion (ROM) and the helical axis of motion (HAM). Biplane radiographs of the cervical spine were collected at 30 images/s as 29 participants (20–35yr) performed dynamic flexion\\extension, axial rotation, and lateral bending. Vertebral motion (C1–T1 in flexion\\extension, C3–T1 in lateral bending and axial rotation) was tracked with sub-millimeter accuracy using a validated volumetric model-based tracking process that matched subject-specific CT-based bone models to the radiographs. Flexion\\extension ROM was smallest at the C2–C3 motion segment (12.7±2.6°) and largest at the C5–C6 motion segment (19.7±3.7°). During head lateral bending and axial rotation, the intervertebral bending ROM was greater than the rotation ROM at every motion segment. The HAM demonstrated differences among motion segments and among movements. During flexion\\extension, the helical axis of motion was directed nearly perpendicular to the sagittal plane for the C2–C3 through C7–T1 motion segments. During lateral bending, the angle between the HAM and the transverse plane progressively increased from the C6–C7 motion segment (approximately ±22°) to the C3–C4 motion segment (approximately ±40°). During axial rotation, the angle between the transverse plane and the HAM was approximately ±42° at the C3–C4 through C5–C6 motion segments, and approximately ±32° at the C6–C7 motion segment. This study provides valuable reference data for evaluating the effects of age, degeneration, and surgical procedures on cervical spine kinematics during three-dimensional dynamic functional loading.

Cervical spine kinematics after anterior cervical discectomy with or without implantation of a mobile cervical disc prosthesis; an RCT.

BackgroundWhen surgically treating cervical degenerative disc disease, the most commonly performed procedure is anterior cervical discectomy. This procedure is performed with, or without fusion promoting methods. For both options the rate of fusion is high and there is much debate whether fusion of the treated segment is a contributing factor to accelerated degeneration of adjacent motion segments. In an effort to prevent degeneration of adjacent segments (ASDeg) due to loss of mobility at the operated level, cervical disc arthroplasty (CDA) was introduced. To evaluate the effectiveness of CDA in preventing ASDeg long term studies are necessary. However, prevention of ASDeg is based on the premise that mobile disc prostheses preserve cervical spine motion in a physiological way. In this article the authors describe a short term protocol for a study that aims to investigate whether CDA reaches the intended goal: restoration or preservation of physiological cervical spine motion. To this end, a technique is used to establish the sequence of contributions of cervical motion segments to flexion/extension of the spine.Methods24 subjects between 18 and 55 years old, with radicular symptoms due to a herniated disc between C5 and C7, refractory to conservative therapy are randomized to simple discectomy, or CDA. These groups are preceded by a pilot group of three subjects receiving CDA. Fluoroscopic flexion-extension recordings are acquired preoperatively, and at three and 12 months postoperative. At these same time points, patient reported outcomes are collected, and a neurological examination is performed by and independent physician.DiscussionStudies investigating arthroplasty determine mobility by measuring segmental range of motion (sROM), which gives no information other than presence, and quantity, of mobility. SROM suffer from high variability. The authors therefore chose to use a method previously used in healthy controls, to describe the dynamic process of cervical spine motion in more detail. Determining cervical spine motion patterns has been reported to be more consistent than sROM. If a physiological motion pattern is absent after surgery in the CDA group, prevention of future ASDeg is less likely. Radiological outcomes will be correlated to clinical outcomes.Trial RegistrationNCT00868335Electronic supplementary materialThe online version of this article (doi:10.1186/s12891-015-0479-4) contains supplementary material, which is available to authorized users.