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PurposeTo define the longitudinal rotation axis around which individual vertebrae rotate, and to establish the various extra- and intravertebral rotation patterns in thoracic adolescent idiopathic scoliosis (AIS) patients, for better understanding of the 3D development of the rotational deformity.MethodsSeventy high-resolution CT scans from an existing database of thoracic AIS patients (Cobb angle: 46°–109°) were included to determine the vertebral axial rotation, rotation radius, intravertebral axial rotation, and local mechanical torsion for each spinal level, using previously validated image processing techniques.ResultsFor all levels, the longitudinal rotation axis, from which the vertebrae rotate away from the midline, was localized posterior to the spine. The axis became closer to the spine at the apex: apex, r = 11.5 ± 5.1 cm versus two levels above (radius = 15.8 ± 8.5 cm; p < 0.001) and beneath (radius = 14.2 ± 8.2 cm; p < 0.001). The vertebral axial rotation, intravertebral axial rotation, and local mechanical torsion of the vertebral bodies were largest at the apex (21.9° ± 7.4°, 8.7° ± 13.5° and 3.0° ± 2.5°) and decreased toward the neutral, junctional zones (p < 0.001).ConclusionIn AIS, the vertebrae rotate away around an axis that is localized posterior to the spine. The distance between this axis and the spine is minimal at the apex and increases gradually to the neutral zones. The vertebral axial rotation is accompanied by smaller amounts of intravertebral rotation and local mechanical torsion, which increases toward the apical region. The altered morphology and alignment are important for a better understanding of the 3D pathoanatomical development of AIS and better therapeutic planning for bracing and surgical intervention.Graphic abstractThese slides can be retrieved under Electronic Supplementary Material.

Knowledge of spinal kinematics is essential for the diagnosis and management of spinal diseases. Distinguishing between physiological and pathological motion patterns can help diagnose these diseases, plan surgical interventions and improve relevant tools and software. During the last decades, numerous studies based on diverse methodologies attempted to elucidate spinal mobility in different planes of motion. The authors aimed to summarize and compare the evidence about cervical spine kinematics under healthy and degenerative conditions. This includes an illustrated description of the spectrum of physiological cervical spine kinematics, followed by a comparable presentation of kinematics of the degenerative cervical spine. Data was obtained through a systematic MEDLINE search including studies on angular/translational segmental motion contribution, range of motion, coupling and center of rotation. As far as the degenerative conditions are concerned, kinematic data regarding disc degeneration and spondylolisthesis were available. Although the majority of the studies identified repeating motion patterns for most motion planes, discrepancies associated with limited sample sizes and different imaging techniques and/or spine configurations, were noted. Among healthy/asymptomatic individuals, flexion extension (FE) and lateral bending (LB) are mainly facilitated by the subaxial cervical spine. C4–C5 and C5–C6 were the major FE contributors in the reported studies, exceeding the motion contribution of sub-adjacent segments. Axial rotation (AR) greatly depends on C1–C2. FE range of motion (ROM) is distributed between the atlantoaxial and subaxial segments, while AR ROM stems mainly from the former and LB ROM from the latter. In coupled motion rotation is quantitatively predominant over translation. Motion migrates caudally from C1–C2 and the center of rotation (COR) translocates anteriorly and superiorly for each successive subaxial segment. In degenerative settings, concurrent or subsequent lesions render the association between diseases and mobility alterations challenging. The affected segments seem to maintain translational and angular motion in early and moderate degeneration. However, the progression of degeneration restrains mobility, which seems to be maintained or compensated by adjacent non-affected segments. While the kinematics of the healthy cervical spine have been addressed by multiple studies, the entire nosological and kinematic spectrum of cervical spine degeneration is partially addressed. Large—scale in vivo studies can complement the existing evidence, cover the gaps and pave the way to technological and clinical breakthroughs.

Purpose The relationship between axial surface rotation (ASR) measured by surface topography (ST) and axial vertebral rotation (AVR) measured by radiography in the transverse plane is not well defined. This study aimed to: (1) quantify ASR and AVR patterns and their magnitudes from T1 to L5; (2) determine the correlation or agreement between the ASR and AVR; and (3) investigate the relationship between axial rotation differences (ASR–AVR) and major Cobb angle. Methods This is a retrospective study evaluating patients (age 8–18) with IS or spinal asymmetry with both radiographic and ST measurements. Demographics, descriptive analysis, and correlations and agreements between ASR and AVR were evaluated. A piecewise linear regression model was further created to relate rotational differences to Cobb angle. Results Fifty-two subjects met inclusion criteria. Mean age was 14.1 ± 1.7 and 39 (75%) were female. Looking at patterns, AVR had maximal rotation at T8, while ASR had maximal rotation at T11 ( r  = 0.35, P  = .006). Cobb angle was 24.1° ± 13.3° with AVR of − 1° ± 4.6° and scoliotic angle was 20.9° ± 11.5° with ASR of − 2.3° ± 6.6°. (ASR–AVR) vs Cobb angle was found to be very weakly correlated with a curve of less than 38.8° ( r  = 0.15, P  = .001). Conclusion Our preliminary findings support that ASR measured by ST has a weak correlation with estimation of AVR by 3D radiographic reconstruction. This correlation may further help us to understand the application of transverse rotation in some clinical scenarios such as specific casting manipulation, padding mechanism in brace, and surgical correction of rib deformity.

Accurate measurement of internal/external rotation joint angle is critical in assessing the shoulder function, especially in the clinical practice as it plays a key role in evaluating activities of daily living and monitoring the rehabilitation progress. This study analyzed the effectiveness of using a marker cluster placed over the proximal epiphysis of the ulna to measure humeral axial rotation with respect to the thorax, comparing it with the traditional method that uses a cluster placed on the upper arm. Data were collected simultaneously using the proposed indirect approach and a conventional marker cluster to analyze three internal/external rotations performed in the Ski-Pose, frontal, and sagittal plane. Linear regressions for time series comparison reported a coefficient of determination R2 > 0.9919 in all tasks.The linear coefficients (a1) were as follows: Ski-Pose (a1 = 0.64 ± 0.10), frontal plane (a1 = 0.74 ± 0.05), and sagittal plane (a1 = 0.73 ± 0.04). Three additional planar tasks were recorded for concurrent validity and RMSE was reported for the main joint angle, obtaining a maximum of 3.87° for the pure flexion/extension task and 1.94° for the abduction/adduction task. A forearm pronation/supination task without axial rotation yielded a maximum error standard deviation of 2.64°. Proximal ulna tracking showed a statistically higher maximum range of motion than humeral tracking in pure axial rotation tasks. This indirect tracking approach is a promising alternative to the traditional cluster technique due to its reduced sensitivity to soft tissue artifacts.

Currently, the relationship between axial rotation of the vertebrae and bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) remains controversial. The aim of this study is to quantitatively assess the effect of vertebral rotation on volumetric bone mineral density (v-BMD) and areal bone mineral density (a-BMD), further to propose the corrected strategies. To achieve this, a phantom, which was rotated from 0° to 25° in 5° increments, was utilized. Bone mineral content (BMC), a-BMD, v-BMD, and projected area (p-AREA) were measured. The Kruskal–Wallis non-parametric test or one-way ANOVA was used to examine the differences in variables between the different groups. The Pearson and Spearman correlation was used to test the relationships between quantitative parameters and rotated angles. Linear regression analysis was used to evaluate the relationship between angles and quantitative parameters. The findings indicate that, as the angle increased, a-BMD and v-BMD decreased ( P  < 0.001) , and the p-AREA increased ( P  < 0.001), but the BMC stays constant. The rotated angle was negative correlated (r = − 0.925, P  < 0.001) with a-BMD and v-BMD (r = − 0.880, P  < 0.001), positive (r = 0.930, P  =  < 0.001) correlated with p-AREA. The linear regression analysis showed that a-BMD = 0.808–0.01 × Angle and v-BMD = 151.808–1.588 × Angle. This study showed that, axial rotation might lead to a lower measured for a-BMD and v-BMD, it should be modified. This gives clinicians some insights into how to deal with osteoporosis in scoliosis patients. It's essential for clinicians to incorporate these findings into their diagnostic processes to prevent potential misdiagnosis and over-treatment of osteoporosis.

Glenohumeral and scapulothoracic motion combine to generate humerothoracic motion, but their discrete contributions towards humerothoracic axial rotation have not been investigated. Understanding their contributions to axial rotation is important to judge the effects of pathology, surgical intervention, and physiotherapy. Therefore, the purpose of this study was to investigate the kinematic coupling between glenohumeral and scapulothoracic motion and determine their relative contributions towards axial rotation. Twenty healthy subjects (10 M/10F, ages 22–66) were previously recorded using biplane fluoroscopy while performing arm elevation in the coronal, scapular, and sagittal planes, and external rotation in 0° and 90° of abduction. Glenohumeral and scapulothoracic contributions towards axial rotation were computed by integrating the projection of glenohumeral and scapulothoracic angular velocity onto the humeral longitudinal axis, and analyzed using one dimensional statistical parametric mapping and linear regression. During arm elevation, scapulothoracic motion supplied 13–20° (76–94%) of axial rotation, mainly via scapulothoracic upward rotation. The contribution of scapulothoracic motion towards axial rotation was strongly correlated with glenohumeral plane of elevation during arm elevation. During external rotation, scapulothoracic motion contributed 10° (8%) towards axial rotation in 0° of abduction and 15° (15%) in 90° of abduction. The contribution of scapulothoracic motion towards humerothoracic axial rotation could explain the simultaneous changes in glenohumeral plane of elevation and axial rotation associated with some pathologies and surgeries. Understanding how humerothoracic motion results from the functional coupling of scapulothoracic and glenohumeral motions may inform diagnostic and treatment strategies by targeting the source of movement impairments in clinical populations.

Understanding spinal kinematics is essential, not only for the comprehension and diagnosis of spinal diseases, but also for improving modern tools and software. The sheer volume and complexity of now available information can be overwhelming. We aimed to distil it into a form that facilitates comparison among diverse studies addressing spinal kinematics under healthy and degenerative conditions. We specifically aimed to define a baseline definition of the spectrum of normal spinal kinematics that in turn allows a comparable definition of kinematics of the degenerative lumbar spine. The considered data was obtained by a systematic MEDLINE search including studies on angular/translational segmental motion contribution, range of motion, coupling and center of rotation. As for degenerative conditions, we collected publications on disc degeneration, facet joint osteoarthritis, facet joint tropism, spondylolisthesis, ligament degeneration and paraspinal muscle degeneration. While we could demonstrate repeating motion patterns for some topics, agreement in other fields is limited due to methodological variances and small sample sizes, particularly in publications with highly accurate but complex techniques. Besides, the high frequency of concurrent degenerative processes complicates the association between diseases and subsequent kinematical changes. Despite several substantial gaps, we stand at the precipice of technological breakthroughs that can power future large-scale studies.

Musculoskeletal risk is mediated by body posture, especially for static tasks. Workstations that require non-neutral postures can lead to increased load, muscular fatigue and injury risk. However, demands during simple axial rotation tasks are not well-defined. The purpose of this study is to quantify the muscular activity of during static axial rotation in a range of postures. Eighteen participants performed 76 axial rotation exertions in varying combinations of humeral elevation angles (30°-60°-90°-120°-150°), plane of elevation (30°-60°-90°-120°) and exertion intensity (20–40%). Six unilateral (right) muscles (pectoralis major (clavicular and sternal), posterior deltoid, teres major, infraspinatus, latissiumus dorsi) were monitored using surface electromyography (EMG). EMG was normalized and integrated over 2 s. The influences of elevation, plane, and intensity on activity levels were then tested with a 3-way ANOVAs (p < .05). During internal rotation, activity was highest at low elevation/high plane combinations for the internal rotators, but at high elevation/low plane combinations for the external rotators. During the 40% intensity exertions, activity levels were highest at lower elevations for internal rotator but at high elevations for the external rotators. During external rotation, as the degree of elevation increased, the activity of the external rotator muscles also increased while internal rotators were unaffected. Humeral muscles responsible for axial rotation are influenced by arm posture during axial rotation exertions. High elevation and plane combinations resulted in high demands for external rotator muscles and this should be considered for job design and injury risk.

Tracking hip and thigh axial rotation has limited accuracy due to the large soft tissue artifact. We proposed a tracking-markers cluster anchored to the prominent distal part of the iliotibial band (ITB) to improve thigh tracking. We investigated if the ITB cluster improves accuracy compared with a traditionally used thigh cluster. We also compared the hip kinematics obtained with these clusters during walking and step-down. Hip and thigh kinematics were assessed during a task of active internal-external rotation with the knee extended, in which the shank rotation is a reference due to smaller soft-tissue artifact. Errors of the hip and thigh axial rotations obtained with the thigh clusters compared to the shank cluster were computed as root-mean-square errors, which were compared by paired t-tests. The angular waveforms of this task were compared using the statistical parametric mapping (SPM). Additionally, the hip waveforms in all planes obtained with the thigh clusters were compared during walking and step-down, using Coefficients of Multiple Correlation (CMC) and SPM (α = 0.05 for all analyses). The ITB cluster errors were approximately 25 % smaller than the traditional cluster error (p < 0.001). ITB cluster errors were smaller at external rotation angles while the traditional cluster error was smaller at internal rotation angles (p < 0.001), although the clusters’ waveforms were not significantly different (p ≥ 0.005). During walking and step-down, both clusters provided similar hip kinematics (CMC ≥ 0.75), but differences were observed in parts of the cycles (p ≤ 0.04). The findings suggest that the ITB cluster may be used in studies focused on hip axial rotation.

Femoral condyle motion of the knee is generally reported using a morphological trans-epicondyle axis (TEA) or geometric center axis (GCA) in the investigation of the knee kinematics. Axial rotation of the femur is recognized as a characteristic motion of the knee during flexion, but is controversial in the literature. This study investigated the biomechanical factors that could be associated to the axial rotations of the femur using both physiological and morphological measurement methods. Twenty healthy knees were investigated during a weightbearing flexion from 0° to 120° at a 15° increment using an imaging technique. A 3D model was constructed for each knee using MR images. Tibiofemoral cartilage contact points were determined at each flexion position to represent physiological knee motion. The contact distance on each condyle was measured between consecutive contact points. The TEA and GCA were used to measure morphological anteroposterior translations of the femoral condyles. The differences between the medial and lateral condyle motions were used to calculate the physiological and morphological axial rotations of the femur. Both the physiological and morphological methods measured external rotations of the femur at low flexion range (0°-45°) and minimal rotations at higher flexion angles. However, the morphological method measured larger posterior translations of the lateral femoral condyle than the medial condyle (p < 0.05), implying a medial pivoting rotation; in contrast, the physiological method measured larger contact distances on the medial condyle than on the lateral condyle (p < 0.05), implying a lateral pivoting rotation. These data could provide useful references for future investigation of kinematics of the knee before and after surgical repair, such as using total knee arthroplasty.