Joint Axes Research Articles

A new Bricard-like mechanism with anti-parallelogram units

This paper proposes a new Bricard-like mechanism composed of three anti-parallelogram units. First, the configuration and connection of the Bricard-like mechanism are given. Second, the mechanism is simplified as a spatial single-loop overconstrained 6R mechanism with variable links’ lengths and its Denavit-Hartenberg (D-H) parameters are obtained by identifying the six revolute joints axes. Third, the degree of freedom of the mechanism is calculated through the closure equations, and kinematic paths of output variables are plotted with respect to the input variable. Then, a serial of Bricard-like mechanisms are connected to construct the deployable mechanism. Finally, three prototypes of the Bricard-like mechanism and the triangular prism deployable mechanism composed of four Bricard-like mechanisms are designed and fabricated to verify the feasibility of the proposed method and analysis.

Sliding Mode Control with Model-Based Switching Functions applied on a 7-DOF Exoskeleton Arm

This article features a novel sliding mode controller for robotic arms using nonlinear model-based switching functions. The new controller is experimentally validated on a 7-DOF exoskeleton arm used for upper-limb rehabilitation applications. The proposed approach features a novel concept using model-based switching functions in the sliding mode controller, which leads to considerable simplifications on the torque control inputs. Compared to conventional linear switching functions, model-based switching functions show substantial control performance improvements on the torque inputs, such as transient constraints reduction and enhanced robustness, while maintaining a very good tracking performance. Moreover, model-based switching functions design ensures a complete decoupling of chattering effect between joint axes. Furthermore, this approach can be combined with existing chattering reduction techniques to ensure proper control of chattering levels on the torque inputs. These advantages make the practical implementation of the model-based switching functions approach particularly desirable for wearable robotics, where smooth movements and high accuracy are important requirements for patients’ comfort and security.

Sparse Magnetometer-free Inertial Motion Tracking – A Condition for Observability in Double Hinge Joint Systems

Inertial measurement units are commonly used in a growing number of application fields to track or capture motions of kinematic chains, such as human limbs, exoskeletons or robotic actuators. A major challenge is the presence of magnetic disturbances that results in unreliable magnetometer readings. Recent research revealed that this problem can be overcome by exploitation of kinematic constraints. While typically each segment of the kinematic chain is equipped with an IMU, a novel approach called sparse inertial motion tracking aims at inferring the complete motion states from measurements of a reduced set of sensors. In the present contribution, we combine the magnetometer-free and the sparse approach for real-time motion tracking of double-hinge joint systems with non-parallel joint axes. Analyzing the observability of the system, we find a condition which assures that the relative orientations between all segments are uniquely determined by a kinematic constraint, which contains only the gyroscope readings. Furthermore, we propose a moving-horizon estimator and validate it in a simulation study of four movements, which differ by their degrees of excitation. The results of this study confirm the theoretical conjectures and demonstrate that magnetometer-free sparse inertial real-time motion tracking is feasible under precise and simple excitation conditions.

Development of internal sound sensor using stethoscope and its applications for machine monitoring

With the development of Internet of Things (IoT), predictive maintenance (PdM) for smart manufacturing receives attentions recently. For the monitoring of machines with rotary components, sound and vibration emitted from the machines have been utilized as the meaningful information. However, sound sensors are susceptible to external noise and the costs for signal conditioning should be considered. In this paper, a stethoscope is utilized as an internal sound sensor which are capable of noise reduction and affordable as IoT solutions. After the stethoscope was assembled with a microphone, a frequency range for measurement was identified as 0~255Hz using the swept-sine technique. Two stethoscope sensors were attached to an industrial robot, and the capability of noise reduction is verified by similarity of Short-Time Fourier Transform (STFT) spectrograms from sounds with and without existence of factory noise. Next, impact tests were performed to detect collision when the robot was stationary, and collisions by human hand during robot operation were detected from STFT spectrogram analysis. Finally, the Convolutional Neural Network (CNN) model from the spectrograms was established to estimate a rotating joint axis during operation, showing 91% and 90.83% accuracy for each stethoscope, respectively.

Defining the anatomic axis joint center distance and anatomic axis joint center ratio of the distal femur in the coronal plane

Background: The aim of this radiographic study was to define the anatomic axis joint center distance (aJCD) and anatomic axis joint center ratio (aJCR) of the distal femur in the coronal plane for skeletally mature individuals. Methods: A cross-sectional radiographic study was conducted to calculate the horizontal distances between the anatomical axis and the center of the knee at the level of the intercondylar notch and the joint line. Ratios relating these points to the width of the femur were then calculated. Results: A total of 164 radiographs were included: 91 male (55.5%) and 73 female patients (44.5%) with a mean age of 44.9 ± 18.1 years, with 79 right (48.2%) and 85 left (51.8%). The mean intercondylar width was 75.6 ± 6.6 mm, the mean aJCD at the notch was 3.6 ± 1.8 mm, the mean aJCD at the joint line was 4.9 ± 1.8 mm, the mean aJCR at the notch was 45.2 ± 2.4, and the mean aJCR at the joint line was 43.5 ± 2.4. The intercondylar width was significantly different (P < 0.001) between males (79.5 ± 4.8 mm) and females (70.6 ± 5.0 mm). A significant difference between the aJCR at the notch (P = 0.004) and the aJCR at the joint line (P = 0.003) was observed in males and females. No differences between the aJCD at the notch and/or aJCD at the joint line were observed between males versus females, left versus right, and those younger versus those older than 65 years. Conclusion: This is the first objective description of the aJCR of the distal femur in the coronal plane. This ratio can be used to aid the planning and execution of distal femoral deformity correction, retrograde femoral nailing, and total knee arthroplasty. Level of Evidence: IV

Accuracy and kinematics consistency of marker-based scaling approaches on a lower limb model: a comparative study with imagery data

Medical images are not typically included in protocol of motion laboratories. Thus, accurate scaling of musculoskeletal models from optoelectronic data are important for any biomechanical analysis. The aim of the current study was to identify a scaling method based on optoelectronic data, inspired from literature, which could offer the best trade-off between accurate geometrical parameters (segment lengths, orientation of joint axes, marker coordinates) and consistent inverse kinematics outputs (kinematic error, joint angles). The methods were applied on 26 subjects and assessed with medical imagery building EOS-based models, considered as a reference. The main contribution of this paper is to show that the marker-based scaling followed by an optimisation of orientation joint axes and markers local coordinates, gives the most consistent scaling and joint angles with EOS-based models. Thus, when a non-invasive mean with an optoelectronic system is considered, a marker-based scaling is preliminary needed to get accurate segment lengths and to optimise joint axes and marker local coordinates to reduce kinematic errors.AbbrevationsAJCAnkle joint centreCKEcumulative kinematic errorDoFdegree of freedomEBEOS-basedHBheight-basedHJChip joint centreKJCknee joint centreMBmarker-basedMSMmusculoskeletal modelsSPMstatistical parametric mappingSTAsoft tissue artifactEBa.m∗EOS-based with optimised joint axes, and all model markers coordinatesMBa.m∗marker-based with optimised joint axes, and all model markers coordinatesMBl.a.mmarker-based with optimised segment lengths, joint axes, and selected model markers coordinatesASISanterior superior illiac spinePSISposterior superior illiac spine

Plane kinematic calibration method for industrial robot based on dynamic measurement of double ball bar

A new calibration method is proposed to improve the circular plane kinematic accuracy of industrial robot by using dynamic measurement of double ball bar (DBB). The kinematic model of robot is established by the MDH (Modified Denavit-Hartenberg) method. The error mapping relationship between the motion error of end-effector and the kinematic parameter error of each axis is calculated through the Jacobian iterative method. In order to identify the validity of the MDH parameter errors, distance errors and angle errors of each joint axis were simulated by three orders of magnitude respectively. After multiple iterations, the average value of kinematic error modulus of end-effector was reduced to nanometer range. Experiments were conducted on an industrial robot (EPSON C4 A901) in the working space of 180 mm × 490 mm. Due to the measuring radius of DBB, the working space was divided into 30 sub-planes to measure the roundness error before and after compensation. The average roundness error calibrated by the proposed method at multi-planes decreased about 21.4%, from 0.4637 mm to 0.3644 mm, while the standard deviation of roundness error was reduced from 0.0720 mm to 0.0656 mm. In addition, by comparing the results of positioning error measured by the laser interferometer before and after calibration, the range values of motion errors of end-effector were decreasing by 0.1033 mm and 0.0730 mm on the X and Y axes, respectively.

A New Approach to Expandable Structures: Crossed Expandable Frames (X-Frames)

The use of expandable structures in the field of building began in the 1960s, based on the pioneering work of Emilio Pérez Piñero. They underwent significant developments at the end of the 20th century, with typologies based on scissors or bundle modules. Until now, this typology has not been further enhanced, despite some very interesting contributions.&lt;br/&gt; These studies are usually based on straight bar expandable structures, although there are some interesting proposals based on the deployability of parallel arc systems, even in real buildings. However, other possible types of expandable structures have not been explored to date.&lt;br/&gt; In this paper, a new system for expandable structures is proposed, which opens new and interesting design possibilities based on the same folding principle. The system consists of deploying elements such as arches or frames with multiple intersections. Solutions for cylindrical vaults with horizontal axis joints and more complex geometries such as conoids are proposed, as well as domes with vertical and horizontal axis joints. Finally, other structures with special kinematic compatibility difficulties, such as concentric domes or toroids, are also studied.

Lie Group Based Type Synthesis Using Transformation Configuration Space for Reconfigurable Parallel Mechanisms With Bifurcation Between Spherical Motion and Planar Motion

Abstract This paper investigates novel reconfigurable parallel mechanisms with bifurcation between planar subgroup SE(2) and rotation subgroup SO(3) based on a transformation configuration space. Having recollected necessary theoretical fundamentals with regard to compositional submanifolds and kinematic bonds, the motion representation of the platform of reconfigurable parallel mechanisms are investigated. The transformation configuration space of a reconfigurable parallel mechanism with motion branches is proposed with respect to the fact that the intersection of Lie subgroups or submanifolds is the identity element or a non-identity element. The switch conditions of the transformation configuration space are discussed, leading to establishment of a theoretical foundation for realizing a switch of motion branches. The switch principle of reconfigurable parallel mechanisms is further investigated with respect to the common motion between SE(2) parallel-mechanism motion generators and SO(3) parallel-mechanism motion generators. Under this principle, the subchains with common motion generators are synthesized and divided into two types of generators. The first type of generators generates kinematic chains with a common intersection of three joint axes, and the second type of generators generates a common intersection of two joint axes. Following this, two types of reconfigurable parallel mechanisms with three identical subchains are synthesized, resulting in 11 varieties in which platforms can be switched between SE(2) and SO(3) after passing through the singularity configuration space.

Mobile assembly of two Bennett linkages and its application to transformation between cuboctahedron and octahedron

The Bennett linkage has been proposed as a building block of deployable structures as it can generate desirable spatial motions with the least number of links. However, these deployable structures are based on the tiling of Bennett linkages. No spatial assembly of Bennett linkages has been developed to form any transformation between regular and semi-regular polyhedrons. In this paper, we propose a new type of mobile assembly consisting of a pair of Bennett linkages connected by four spherical joints. We show that this particular assembly can be used to construct transformable polyhedrons. Using an alternative form of such assembly, a polyhedral transformation between cuboctahedron and octahedron with one degree of freedom is realised. The axes of the revolute joints within the Bennett linkages are determined by the geometrical relationship between the deployed geometry and the folded one. The transformation between two polyhedral shapes has no bifurcation which is proven through kinematic analysis and demonstrated by a physical model. This transformable polyhedron has great potential for the aerospace applications where transportability and protection of payload are critical design features.

TL 18209 - Relationship between the knee and hindfoot axes among patients with advanced gonarthrosis

Introduction: The relationship between knee and hindfoot alignment is intuitive, but the number of studies on associated deformities remains limited. The objective of this study is to assess the correlation between the femorotibial joint axis and the hindfoot axis in patients with advanced gonarthrosis. Methods: The knee and hindfoot axes were assessed in 72 patients with indications for total knee replacement. Knee radiographs and long axial view radiographs of the hindfoot were acquired from all patients. The hindfoot/ankle function of the patients was assessed using the American Orthopedic Foot and Ankle Society (AOFAS) scale. Statistical analysis was performed at a maximum significance level of 5%. Results: The sample included 24 (33.3%) men and 48 (66.7%) women with a mean age of 58.7 years. The results showed that 79.2% subjects had genu varum (mean: 15º±7.69), and 20.8% had genu valgum (mean: 15.9º) (p&gt;0.05); 46 (63.89%) patients had hindfoot varus (mean: 8.5º±6.07), and 26 (36.11%) had hindfoot valgus (mean: 3.9º±3.92). We observed a significant association between the knee and hindfoot axes (p&lt;0.05). There was no significant correlation only between genu valgum–hindfoot varus (p&lt;0.05). The mean AOFAS score was 74.26 points, with significantly higher scores among patients with hindfoot varus. The AOFAS score was correlated with the hindfoot and knee axes (P&lt;0.05). Conclusion: The knee and hindfoot axes were associated in patients with advanced gonarthrosis. In addition, the patients with hindfoot varus showed better ankle function according to the AOFAS score.

Kinematics Analysis of Manipulator using Soft Computing Technique

In this paper, the analysis and modeling of six joint axes of a robotic arm having three DOF spherical arm and three DOF spherical wrist have been done to solve the kinematics and inverse kinematics. Kinematics provides the rational explication of a robotic manipulator. For the analysis of industrial robotics manipulator a particular type of kinematics model is required. The Denavit Hartenberg criterion has been used to solve the kinematics equations. MATLAB, Firefly Algorithm (FFA) and Roboanalyzer have been used to get the home position and differences in error at different values of six-DOF manipulator. Error can be optimized to as low as 10-17with the firefly algorithm.

MiR-17-5p Regulates Heterotopic Ossification by Targeting ANKH in Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized with heterotopic ossification of the axis joints ligaments, resulting in joint disability. MicroRNAs (miRNAs) are regulators of mRNAs that play a crucial role in the AS pathological process. Here, we showed that the level of miR-17-5p was significantly higher in fibroblasts and ligament tissues from AS patients as compared to the non-AS individuals. Knockdown of the miR-17-5p from the fibroblasts derived from AS patients exhibited decreased osteogenic differentiation and ossification. On the other hand, AS patient-derived fibroblasts overexpressing miR-17-5p displayed the increased osteogenesis. Furthermore, inhibition of miR-17-5p ameliorated osteophyte formation, and the sacroiliitis phenotype in AS rats received emulsified collagen. Mechanistically, miR-17-5p regulated osteogenic differentiation by targeting the 3ʹ UTR of ankylosis protein homolog (ANKH). Also, downregulation of miR-17-5p slowed AS progression through regulation of cytokines, such as dickkopf-1 (DKK1) and vascular endothelial growth factor (VEGF). In conclusion, our findings reveal a role of the miR-17-5p-ANKH axis in the regulation of heterotopic ossification, which is essential for therapeutic intervention in heterotopic ossification in AS.

Reconfiguration of a 3-(rR)PS Metamorphic Parallel Mechanism Based on Complete Workspace and Operation Mode Analysis

Abstract This paper focuses on the reconfiguration of a 3-(rR)PS metamorphic parallel mechanism based on complete workspace and operation mode analysis. The mechanism consists of three (rR)PS legs, and each (rR) joint is composed of two perpendicular revolute joints. One of the (rR) joint axes can be reconfigured continuously, which allows the mechanism to exhibit three distinct configurations. Initially, the constraint equations are derived by using algebraic geometry approach, and the primary decomposition is computed for the three configurations. It reveals that the 3-(rR)PS metamorphic parallel mechanism can exhibit one up to two operation modes among three configurations. When the second axes of the three (rR) joints intersect at a finite point and not coplanar, the 3-(rR)PS metamorphic parallel mechanism has only one operation mode. If the second axes of the three (rR) joints are coplanar, the 3-(rR)PS metamorphic parallel mechanism has two operation modes. It is shown that both operation modes have the same motion type, namely, 1T2R motion. However, to realize the same trajectories in both operation modes, the moving platform will have different orientations. Hence, the orientation workspaces of both operation modes are characterized and the axodes are used to compare the instantaneous motion of the moving platform when passing through the same trajectories. Based on these results, an identification approach is introduced to identify which operation mode a given mechanism pose belongs to and this provides a useful method for trajectory planning.

The Role of Dietary Fiber in Rheumatoid Arthritis Patients: A Feasibility Study.

Short-chain fatty acids are microbial metabolites that have been shown to be key regulators of the gut–joint axis in animal models. In humans, microbial dysbiosis was observed in rheumatoid arthritis (RA) patients as well as in those at-risk to develop RA, and is thought to be an environmental trigger for the development of clinical disease. At the same time, diet has a proven impact on maintaining intestinal microbial homeostasis. Given this association, we performed a feasibility study in RA patients using high-fiber dietary supplementation with the objective to restore microbial homeostasis and promote the secretion of beneficial immunomodulatory microbial metabolites. RA patients (n = 36) under routine care received daily high-fiber bars or cereals for 28 days. Clinical assessments and laboratory analysis of immune parameters in blood and stool samples from RA patients were done before and after the high-fiber dietary supplementation. We observed an increase in circulating regulatory T cell numbers, favorable Th1/Th17 ratios, as well as decreased markers of bone erosion in RA patients after 28 days of dietary intervention. Furthermore, patient-related outcomes of RA improved. Based on these results, we conclude that controlled clinical studies of high-fiber dietary interventions could be a viable approach to supplement or complement current pharmacological treatment strategies.

Changes in the Mechanical Axis and Weight-Bearing Line of the Ankle After Varus Knee Correction

Category:Ankle, HindfootIntroduction/Purpose:Varus limb malalignment results in an imbalance of force transmission to the knee joint, resulting in a concentrated load in the medial compartment. A varus knee correction may affect the ankle and subtalar joint, because the weight-bearing load on the lower extremity extends from the hip to the foot. A previous study suggested that the true mechanical axis of the lower limb should be calculated with a line from the center of the femoral head to the lowest point of the calcaneus, not to the center of the tibial plafond. Therefore, we performed this study to evaluate changes in the mechanical axis and weight- bearing line of the ankle after varus knee correction.Methods:Patients with a varus knee who were followed-up after they had undergone high tibial osteotomy (HTO) or total knee replacement arthroplasty (TKA) at an age of >20 years, and who had undergone preoperative and postoperative scanogram were included in this study. The hip-knee-ankle (HKA) angle, mechanical axis, and weight-bearing line (line from the center of the femoral head to the lowest point of the calcaneus) were measured on the radiographs. The point at which the mechanical axis and weight-bearing line passed through the tibial plafond was the ankle joint axis point. The postoperative change in the ankle joint axis point on the mechanical axis and weight-bearing line according to the HKA angle correction was adjusted by multiple factors using a linear mixed model.Results:A total of 257 limbs from 198 patients were included in this study. The preoperative HKA was 7.3 ± 4.7° and corrected to 0.4 ± 3.8°. Although the ankle axis points on both axes moved laterally after HTO and TKA, the ankle joint axis of the weight- bearing line showed a significant larger lateral movement (22.5±35.7%) (Fig.) than that of the mechanical axis (15.7±16.0%) in terms of rate of change (p = 0.006). The ankle joint axis point on the weight-bearing line moved laterally by 0.9% per degree of postoperative HKA angle decrease (p < 0.001). The change in the ankle joint axis point on the mechanical axis was not statistically significant after HTO and TKA (p = 0.223).Conclusion:The mechanical axis and weight-bearing line of the ankle moved laterally after the varus knee correction. The ankle joint axis on the weight-bearing line moved laterally as the HKA angle decreased after the surgery, whereas the varus knee correction did not significantly affect the ankle joint axis on the mechanical axis. The varus knee correction might affect the subtalar joint as well as the ankle joint. Therefore, we believe that our findings warrant consideration in pre- and postoperative evaluations using the weight-bearing line of patients undergoing varus knee correction.

Controllers using Discrete Sliding Mode Control for 1 &amp; 2-link FMs with Output Samples

The main highlight of this paper being, the design &amp; development of Controllers using Discrete Sliding Mode Control for 1 &amp; 2-link FMs with output samples is being presented for controlling a 2-link FRM considering 2 DOF in 3 Dimensional Euclidean space along with the simulation results. A 2-link FRM with 2-DOF is being considered and the base motor is attached to the single flexible link &amp; the other link is fixed to the extreme end of the 1st link to which the shoulder motor is connected and the entire set-up is a single structure one and 2 motors are being used for actuation purposes &amp; is being controlled / regulated using the developed sliding mode controller, i.e., the dual links are rotating with respect to the base, further the link-2 is rotating with respect to the shoulder axes &amp; the joint axes of the two are parallel and perpendicular w.r.t. the robot work surface. Hence, the entire system can be called as a planar mechanism, i.e., the 2 links are moving parallel to the plane of the work surface (x – y plane). There are 2 joints, viz., base joint &amp; the shoulder joint along with the end-effector being the tip of the 2-link manipulator. The small errors that occurs in the control signal u is due to the changes during the set-point. Simulink model is being developed in the Simulink-Matlab environment &amp; after running the model, the simulation results observed, the obtained results shows the efficacy of the methodology developed.

MAG.I.C.AL.–A Unified Methodology for Magnetic and Inertial Sensors Calibration and Alignment

This paper introduces the MAGnetometer-Inertial sensors Calibration and ALignment (MAG.I.C.AL.) methodology for unified calibration and joint axes alignment of three-axis magnetometer, three-axis accelerometer, and three-axis gyroscope. MAG.I.C.AL. compensates for all linear time-invariant distortions such as scale-factor, cross-coupling, and offset, including the soft-iron and hard-iron distortions of the magnetometer. It introduces a new, computationally efficient, least-squares-based iterative algorithm for the calibration of the magnetometer and the accelerometer. It aligns their axes and introduces a new way to calibrate the gyroscope based on their joint data. MAG.I.C.AL. is implemented in a 15-step sequence achieving fast convergence and high accuracy without using any external piece of equipment and without requiring external attitude references. Simulation and experimental results using low-cost sensors are presented to support the accuracy, efficiency, and the applications of the algorithm.

Early typing diagnostic and predictive value of AKA, APF and ACPA in juvenile idiopathic arthritis

Objective To investigate the early typing diagnostic and predictive value of anti-keratin antibodies(AKA), anti-perinuclear factor(APF) and anti-citrullinated protein antibodies(ACPA) in patients of juvenile idiopathic arthritis (JIA). Methods A retrospective study was conducted to collect 144 cases of JIA who were hospitalized in Capital Institute of Pediatrics from December 2013 to June 2016 and followed up for at least one year.Among them,66 were males (46%) and 78 were females (54%).The age at diagnosis was between 1 year 5 months to 15 years 9 months.144 patients were tested for AKA,ACPA,APF and TNFα upon admission. Chi-square test or Fisher exact test were used to compare the positive rates of three antibodies among different subtypes. Mann-Whitney nonparametric test and Chi-square test or Fisher exact test were used to analyze the data of prognosis between antibody-positive group and antibody-negative group in the course of disease. Results In 144 patients, 49(34%) were classified as systemic arthritis, 28 (19.4%) as polyarthritis, 61(42.3%) as oligoarthritis, and 6(4.2%) as enthesitis-associated arthritis. 52 cases (36.1%) were positive for one antibody or more antibodies of AKA/APF/ACPA at the early stage, 14(9.7%) were AKA positive, 44(30.6%) were ACPA positive and 12(8.3%) were APF positive. The positive rates of ACPA/AKA/APF antibodies were significantly different among different subtypes(χ2=33.863,26.860,14.395; P<0.01,<0.01,<0.05).The rates in polyarthritis were higher than those in systemic arthritis and oligoarthritis; In 95 children with non-systemic form, the level of TNFα in antibody-positive group (43 cases) was higher than that in antibody-negative group (52 cases) at the early stage(Z=4.785, P<0.01);144 patients were followed up for at least one year,the rates of patients who accepted biologic therapies were significantly different between antibody-positive group and antibody-negative group (50% vs 25%). So do the rates of patients with joint deformities (17.3% vs 2.2%) and with important joints involvement (hip and axis joints) (59.6% vs 14.1%) (χ2=9.249,10.875,32.392; P<0.01,<0.01,<0.01). Further more, the number of joints involved in the antibody-positive group (7.07±3.85) was significantly more than that in the antibody-negative group (2.31±1.64) (F=63.822, P<0.01). Conclusions AKA,APF and ACPA are important in the early typing diagnosis of JIA,and may be closely related to the prognosis of patients with JIA. Key words: Arthritis, juvenile; Keratins; Autoantibodies; Antibodies, Antinuclear; Anti-citrullinated protein antibodies; Early diagnosis; Prognosis

Clinical and radiological outcomes of conservative treatment for unilateral sagittal split fractures of C1 lateral mass

ObjectiveThe aim of this study was to assess the effect of transverse atlantal ligament (TAL) integrity on clinical and radiological outcomes in patients with unilateral sagittal split fracture (USSF) of the C1 lateral mass (LM). MethodsTwenty-six consecutive patients (16 men and 10 women; mean age: 52 years (range: 32–69)) with C1 LM USSF were included in this study. Sixteen were TAL injury group (nine of type I injuries and seven of type II injuries according to Dickman's classification) and ten were TAL intact group. All cases were conservatively treated with a rigid brace for TAL intact or by halo-vest stabilization for TAL injury for three months. The mean follow-up was 16 months (range, 12–47 months). The results were compared with radiological assessment of fracture healing, LM displacement and Neck visual analog scale. ResultsAt the last follow-up, for TAL intact group, total LM displacement (LMD), unilateral LMD of fracture side, atlanto-dental interval, basion-dental interval, clivus canal angle, and atlanto-occipital joint axis angle were maintained compared to initial presentation. However, for TAL injury group, all radiological parameters were worsened. The worsening of radiological parameters was more severe in type I injury than type II injury except for total LMD and unilateral LMD. Neck visual analog scale significantly decreased and patient's satisfaction was higher in TAL intact group compared to TAL injury group. ConclusionConservative treatment for USSF of C1 LM with TAL injury failed to achieve healing of the fracture, which resulted in lateral displacement of C1 LM. This caused coronal and sagittal malalignment of occipitocervical junction, resulting in unsatisfactory clinical outcomes. Our results suggest that early surgical stabilization should be considered in USSF of C1 LM with TAL injury, especially type I injury. However, conservative treatment may be sufficient for a USSF of the C1 LM with TAL intact. Level of EvidenceLevel III, Therapeutic Study.