Patellofemoral joint geometry and osteoarthritis features 3-10 years after knee injury compared with uninjured knees.

In this cross-sectional study, we compared patellofemoral geometry in individuals with a youth-sport-related intra-articular knee injury to uninjured individuals, and the association between patellofemoral geometry and magnetic resonance imaging (MRI)-defined osteoarthritis (OA) features. In the Youth Prevention of Early OA (PrE-OA) cohort, we assessed 10 patellofemoral geometry measures in individuals 3-10 years following injury compared with uninjured individuals of similar age, sex, and sport, using mixed effects linear regression. We also dichotomized geometry to identify extreme (>1.96 standard deviations) features and assessed likelihood of having extreme values using Poisson regression. Finally, we evaluated the associations between patellofemoral geometry with MRI-defined OA features using restricted cubic spline regression. Mean patellofemoral geometry did not differ substantially between groups. However, compared with uninjured individuals, injured individuals were more likely to have extremely large sulcus angle (prevalence ratio [PR] 3.9 [95% confidence interval, CI: 2.3, 6.6]), and shallow lateral trochlear inclination (PR 4.3 (1.1, 17.9)) and trochlear depth (PR 5.3 (1.6, 17.4)). In both groups, high bisect offset (PR 1.7 [1.3, 2.1]) and sulcus angle (PR 4.0 [2.3, 7.0]) were associated with cartilage lesion, and most geometry measures were associated with at least one structural feature, especially cartilage lesions and osteophytes. We observed no interaction between geometry and injury. Certain patellofemoral geometry features are correlated with higher prevalence of structural lesions compared with injury alone, 3-10 years following knee injury. Hypotheses generated in this study, once further evaluated, could contribute to identifying higher-risk individuals who may benefit from targeted treatment aimed at preventing posttraumatic OA.

Self-supervised-RCNN for medical image segmentation with limited data annotation.

Many successful methods developed for medical image analysis based on machine learning use supervised learning approaches, which often require large datasets annotated by experts to achieve high accuracy. However, medical data annotation is time-consuming and expensive, especially for segmentation tasks. To overcome the problem of learning with limited labeled medical image data, an alternative deep learning training strategy based on self-supervised pretraining on unlabeled imaging data is proposed in this work. For the pretraining, different distortions are arbitrarily applied to random areas of unlabeled images. Next, a Mask-RCNN architecture is trained to localize the distortion location and recover the original image pixels. This pretrained model is assumed to gain knowledge of the relevant texture in the images from the self-supervised pretraining on unlabeled imaging data. This provides a good basis for fine-tuning the model to segment the structure of interest using a limited amount of labeled training data. The effectiveness of the proposed method in different pretraining and fine-tuning scenarios was evaluated based on the Osteoarthritis Initiative dataset with the aim of segmenting effusions in MRI datasets of the knee. Applying the proposed self-supervised pretraining method improved the Dice score by up to 18% compared to training the models using only the limited annotated data. The proposed self-supervised learning approach can be applied to many other medical image analysis tasks including anomaly detection, segmentation, and classification.

Comparison of Dynamic Knee Contact Mechanics with T2 Imaging in Different Ages of Healthy Participants.

Aging is a known risk factor for Osteoarthritis (OA), however, relations between cartilage composition and aging remain largely unknown in understanding human OA. T2 imaging provides an approach to assess cartilage composition. Whether these T2 relaxation times in the joint contact region change with time during gait remain unexplored. The study purpose was to demonstrate a methodology for linking dynamic joint contact mechanics to cartilage composition as measured by T2 relaxometry. T2 relaxation times for unloaded cartilage were measured in a 3T General Electric magnetic resonance (MR) scanner in this preliminary study. High-speed biplanar video-radiography (HSBV) was captured for five 20-30-year-old and five 50-60-year-old participants with asymptomatic knees. By mapping the T2 cartilages to the dynamic contact regions, T2 values were averaged over the contact area at each measurement within the gait cycle. T2 values demonstrated a functional relationship across the gait cycle. There were no statistically significant differences between 20- and 30-year-old and 50-60-year-old participant T2 values at first force peak of the gait cycle in the medial femur (p = 1.00, U = 12) or in the medial tibia (p = 0.31, U = 7). In the medial and lateral femur in swing phase, the joint moved from a region of high T2 values at 75% of gait to a minimum at 85-95% of swing. The lateral femur and tibia demonstrated similar patterns to the medial compartments but were less pronounced. This research advances understanding of the linkage between cartilage contact and cartilage composition. The change from a high T2 value at ~ 75% of gait to a lower value near the initiation of terminal swing (90% gait) indicates that there are changes to T2 averages corresponding to changes in the contact region across the gait cycle. No differences were found between age groups for healthy participants. These preliminary findings provide interesting insights into the cartilage composition corresponding to dynamic cyclic motion and inform mechanisms of osteoarthritis.

Tricompartment offloader knee brace reduces sagittal plane knee moments, quadriceps muscle activity, and pain during chair rise and lower in individuals with knee osteoarthritis.

The Levitation tricompartment offloader (TCO) knee brace provides an assistive knee extension moment with the goal of unloading all three compartments of the knee and reducing pain for individuals with multicompartment knee osteoarthritis (OA). This study aimed to determine the effect of the TCO brace on sagittal plane knee moments, quadriceps muscle activity, and pain in individuals with multicompartment knee OA. Lower limb kinematics, kinetics, and electromyography data were collected during a chair rise and lower to determine differences between bracing conditions. TCO brace use significantly decreased the peak net knee external flexion moment in high power mode, providing extension assistance during chair rise [p<0.001; mean difference (MD) (98.75% CI) -0.8 (-1.0, -0.6)%BWxH] and bodyweight support during chair lower [p<0.001; -1.1 (-1.6, -0.7)%BWxH]. Quadriceps activation intensity was significantly reduced with brace use by up to 67% for the vastus medialis [Z = -2.55, p = 0.008] and up to 39% for the vastus lateralis [Z = -2.67, p = 0.004]. Participants reported significantly reduced knee pain with the TCO brace worn in high power mode compared to the no brace condition [p = 0.014; MD (97.5% CI) -18.8 (-32.22, -2.34) mm]. These results support the intended mechanism of joint unloading via extension assistance with the TCO brace. The observed biomechanical changes were accompanied by immediate reductions in user reported pain levels, and support the use of the TCO for conservative management to reduce knee pain in patients with multicompartment knee OA.

Tricompartment offloader knee brace reduces contact forces in adults with multicompartment knee osteoarthritis.

The levitation tricompartment offloader (TCO) brace is designed to unload all three knee compartments by reducing compressive forces caused by muscle contraction. This study aimed to determine the effect of the TCO on knee contact forces and quadriceps muscle activity in individuals with knee osteoarthritis. Lower limb kinematics, kinetics, and electromyography data were collected during a chair rise-and-lower task. A three-dimensional inverse dynamics model of the lower leg and foot was used with a sagittal plane knee model to compute knee joint forces. TCO brace use significantly decreased forces in the tibiofemoral [p = 0.001; mean difference, MD (97.5% confidence interval, CI) -0.62 (-0.91, -0.33) body weight (BW)] and patellofemoral [p = 0.001; MD (97.5% CI) -0.88 (-1.36, -0.39) BW] compartments in high-power mode. Significant reductions in quadriceps tendon force [p = 0.002; MD (97.5% CI) -0.53 (-0.83, -0.23) BW] and electromyography intensity of the vastus medialis [p = 0.018, MD (97.5% CI) -30.7 (-59.1, -2.3)] and vastus lateralis [p = 0.012, MD (97.5% CI) -26.2 (-48.5, -3.9)] were also observed. The TCO significantly reduced tibiofemoral and patellofemoral contact forces throughout chair lower, and when knee flexion was greater than 50° during chair rise in high power. These results demonstrate that the TCO reduces contact forces in the tibiofemoral and patellofemoral joint compartments and confirms that the TCO unloads the joint by reducing compressive forces caused by the quadriceps. Clinical significance: The magnitude of knee joint unloading provided by the TCO is similar to that achieved by clinically recommended levels of bodyweight loss and is therefore expected to result in clinical benefits for knee osteoarthritis patients.

Empirical joint contact mechanics: A comprehensive review.

Empirical joint contact mechanics measurement (EJCM; e.g. contact area or force, surface velocities) enables critical investigations of the relationship between changing joint mechanics and the impact on surface-to-surface interactions. In orthopedic biomechanics, understanding the changes to cartilage contact mechanics following joint pathology or aging is critical due to its suggested role in the increased risk of osteoarthritis (OA), which might be due to changed kinematics and kinetics that alter the contact patterns within a joint. This article reviews and discusses EJCM approaches that have been applied to articulating joints such that readers across different disciplines will be informed of the various measurement and analysis techniques used in this field. The approaches reviewed include classical measurement approaches (radiographic and sectioning, dye staining, casting, surface proximity, and pressure measurement), stereophotogrammetry/motion analysis, computed tomography (CT), magnetic resonance imaging (MRI), and high-speed videoradiography. Perspectives on approaches to advance this field of EJCM are provided, including the value of considering relative velocity in joints, tractional stress, quantification of joint contact area shape, consideration of normalization techniques, net response (superposition) of multiple input variables, and establishing linkages to regional cartilage health status. EJCM measures continue to provide insights to advance our understanding of cartilage health and degeneration and provide avenues to assess the efficacy and guide future directions of developing interventions (e.g. surgical, biological, rehabilitative) to optimize joint's health and function long term.

Kinematics of the head and associated vertebral artery length changes during high-velocity, low-amplitude cervical spine manipulation.

BACKGROUND: Cervical spine manipulation (CSM) is a frequently used treatment for neck pain. Despite its demonstrated efficacy, concerns regarding the potential of stretch damage to vertebral arteries (VA) during CSM remain. The purpose of this study was to quantify the angular displacements of the head relative to the sternum and the associated VA length changes during the thrust phase of CSM. METHODS: Rotation and lateral flexion CSM procedures were delivered bilaterally from C1 to C7 to three male cadaveric donors (Jan 2016-Dec 2019). For each CSM the force-time profile was recorded using a thin, flexible pressure pad (100-200 Hz), to determine the timing of the thrust. Three dimensional displacements of the head relative to the sternum were recorded using an eight-camera motion analysis system (120-240 Hz) and angular displacements of the head relative to the sternum were computed in Matlab. Positive kinematic values indicate flexion, left lateral flexion, and left rotation. Ipsilateral refers to the same side as the clinician's contact and contralateral, the opposite. Length changes of the VA were recorded using eight piezoelectric ultrasound crystals (260-557 Hz), inserted along the entire vessel. VA length changes were calculated as D = (L1 - L0)/L0, where L0 = length of the whole VA (sum of segmental lengths) or the V3 segment at CSM thrust onset; L1 = whole VA or V3 length at peak force during the CSM thrust. RESULTS: Irrespective of the type of CSM, the side or level of CSM application, angular displacements of the head and associated VA length changes during the thrust phase of CSM were small. VA length changes during the thrust phase were largest with ipsilateral rotation CSM (producing contralateral head rotation): [mean ± SD (range)] whole artery [1.3 ± 1.0 (- 0.4 to 3.3%)]; and V3 segment [2.6 ± 3.6 (- 0.4 to 11.6%)]. CONCLUSIONS: Mean head angular displacements and VA length changes were small during CSM thrusts. Of the four different CSM measured, mean VA length changes were largest during rotation procedures. This suggests that if clinicians wish to limit VA length changes during the thrust phase of CSM, consideration should be given to the type of CSM used.

Concurrent validity and reliability of a semi-automated approach to measuring the magnetic resonance imaging morphology of the knee joint in active youth.

Post-traumatic knee osteoarthritis is attributed to alterations in joint morphology, alignment, and biomechanics triggered by injury. While magnetic resonance (MR) imaging-based measures of joint morphology and alignment are relevant to understanding osteoarthritis risk, time consuming manual data extraction and measurement limit the number of outcomes that can be considered and deter widespread use. This paper describes the development and evaluation of a semi-automated software for measuring tibiofemoral and patellofemoral joint architecture using MR images from youth with and without a previous sport-related knee injury. After prompting users to identify and select key anatomical landmarks, the software can calculate 37 (14 tibiofemoral, 23 patellofemoral) relevant geometric features (morphology and alignment) based on established methods. To assess validity and reliability, 11 common geometric features were calculated from the knee MR images (proton density and proton density fat saturation sequences; 1.5 T) of 76 individuals with a 3-10-year history of youth sport-related knee injury and 76 uninjured controls. Spearman's or Pearson's correlation coefficients (95% CI) and Bland-Altman plots were used to assess the concurrent validity of the semi-automated software (novice rater) versus expert manual measurements, while intra-class correlation coefficients (ICC2,1; 95%CI), standard error of measurement (95%CI), 95% minimal detectable change, and Bland-Altman plots were used to assess the inter-rater reliability of the semi-automated software (novice vs resident radiologist rater). Correlation coefficients ranged between 0.89 (0.84, 0.92; Lateral Trochlear Inclination) and 0.97 (0.96, 0.98; Patellar Tilt Angle). ICC estimates ranged between 0.79 (0.63, 0.88; Lateral Patellar Tilt Angle) and 0.98 (0.95, 0.99; Bisect Offset). Bland-Altman plots did not reveal systematic bias. These measurement properties estimates are equal, if not better than previously reported methods suggesting that this novel semi-automated software is an accurate, reliable, and efficient alternative method for measuring large numbers of geometric features of the tibiofemoral and patellofemoral joints from MR studies.

Improved-Mask R-CNN: Towards an accurate generic MSK MRI instance segmentation platform (data from the Osteoarthritis Initiative).

INTRODUCTION: Objective assessment of osteoarthritis (OA) Magnetic Resonance Imaging (MRI) scans can address the limitations of the current OA assessment approaches. Detecting and extracting bone, cartilage, and joint fluid is a necessary component for the objective assessment of OA, which helps to quantify tissue characteristics such as volume and thickness. Many algorithms, based on Artificial Intelligence (AI), have been proposed over recent years for segmenting bone and soft tissues. Most of these segmentation methods suffer from the class imbalance problem, can't differentiate between the same anatomic structure, or do not support segmenting different rang of tissue sizes. Mask R-CNN is an instance segmentation framework, meaning it segments and distinct each object of interest like different anatomical structures (e.g. bone and cartilage) using a single model. In this study, the Mask R-CNN architecture was deployed to address the need for a segmentation method that is applicable to use for different tissue scales, pathologies, and MRI sequences associated with OA, without having a problem with imbalanced classes. In addition, we modified the Mask R-CNN to improve segmentation accuracy around instance edges. METHODS: A total of 500 adult knee MRI scans from the publicly available Osteoarthritis Initiative (OAI), and 97 hip MRI scans from adults with symptomatic hip OA, evaluated by two readers, were used for training and validating the network. Three specific modifications to Mask R-CNN yielded the improved-Mask R-CNN (iMaskRCNN): an additional ROIAligned block, an extra decoder block in the segmentation header, and connecting them using a skip connection. The results were evaluated using Hausdorff distance, dice score for bone and cartilage segmentation, and differences in detected volume, dice score, and coefficients of variation (CoV) for effusion segmentation. RESULTS: The iMaskRCNN led to improved bone and cartilage segmentation compared to Mask RCNN as indicated with the increase in dice score from 95% to 98% for the femur, 95-97% for the tibia, 71-80% for the femoral cartilage, and 81-82% for the tibial cartilage. For the effusion detection, the dice score improved with iMaskRCNN 72% versus Mask R-CNN 71%. The CoV values for effusion detection between Reader1 and Mask R-CNN (0.33), Reader1 and iMaskRCNN (0.34), Reader2 and Mask R-CNN (0.22), Reader2 and iMaskRCNN (0.29) are close to CoV between two readers (0.21), indicating a high agreement between the human readers and both Mask R-CNN and iMaskRCNN. CONCLUSION: Mask R-CNN and iMaskRCNN can reliably and simultaneously extract different scale articular tissues involved in OA, forming the foundation for automated assessment of OA. The iMaskRCNN results show that the modification improved the network performance around the edges.

Validation of a magnetic resonance imaging based method to study passive knee laxity: An in-situ study.

Knee laxity can be described as an increased anterior tibial translation (ATT) or decreased stiffness of the tibiofemoral joint under an applied force. Küpper et al. (2013, 2016) and Westover et al. (2016) previously developed and reported on a magnetic resonance (MR)-based in vivo measure of knee laxity. In this study, the application of an in situ knee loading apparatus (ISKLA) is presented as a step toward validating the MR-based methodology for measuring ATT and stiffness. The ISKLA is designed to measure these outcome variables using MR imaging and is validated against a gold-standard ElectroForce mechanical test instrument (TA Instruments 3550). Accuracy was assessed through an in situ experimental setup by testing four cadaveric specimens with both the MR-based methodology and in the ElectroForce system. The outcome of the current study showed that the MR-based ATTs and stiffness measurements using the ISKLA were within 1.44-2.10 mm and 0.16-6.14 N/mm, respectively, of the corresponding values measured by the gold standard system. An excellent ICC was observed for ATT (0.97) and good ICC for stiffness (0.87) between the MR and ElectroForce-based systems across all target force levels. These findings suggest that the MR-based approach can be used with satisfactory accuracy and correlation to the gold standard measure.

Vertical Drop Jump Biomechanics of Patients With a 3- to 10-Year History of Youth Sport-Related Anterior Cruciate Ligament Reconstruction.

BACKGROUND: A better understanding of movement biomechanics after anterior cruciate ligament reconstruction (ACLR) could inform injury prevention, knee injury rehabilitation, and osteoarthritis prevention strategies. PURPOSE: To investigate differences in vertical drop jump (VDJ) biomechanics between patients with a 3- to 10-year history of youth sport-related ACLR and uninjured peers of a similar age, sex, and sport. STUDY DESIGN: Cross-sectional study. Level of evidence III. METHODS: Lower limb kinematics and bilateral ground-reaction forces (GRFs) were recorded for participants performing 10 VDJs. Joint angles and GRF data were analyzed, and statistical analysis was performed using 2 multivariate models. Dependent variables included sagittal (ankle, knee, and hip) and coronal (knee and hip) angles at initial contact and maximum knee flexion, the rate of change of coronal knee angles (35%-90% of the support phase; ie, slopes of linear regression lines), and vertical and mediolateral GRFs (normalized to body weight [BW]). Fixed effects included group, sex, and time since injury. Participant clusters, defined by sex and sport, were considered as random effects. RESULTS: Participants included 48 patients with a history of ACLR and 48 uninjured age-, sex-, and sport-matched controls (median age, 22 years [range, 18-26 years]; 67% female). Patients with ACLR demonstrated steeper negative coronal knee angle slopes (ß = -0.04 deg/% [95% CI, -0.07 to -0.00 deg/%]; P = .025). A longer time since injury was associated with reduced knee flexion (ß = -0.2° [95% CI, -0.3° to -0.0°]; P = .014) and hip flexion (ß = -0.1° [95% CI, -0.2° to -0.0°]; P = .018). Regardless of ACLR history, women displayed greater knee valgus at initial contact (ß = 2.1° [95% CI, 0.4° to 3.8°]; P = .017), greater coronal knee angle slopes (ß = 0.05 deg/% [95% CI, 0.02 to 0.09 deg/%]; P = .004), and larger vertical GRFs (landing: ß = -0.34 BW [95% CI, -0.61 to -0.07 BW]; P = .014) (pushoff: ß = -0.20 BW [95% CI, -0.32 to -0.08 BW]; P = .001). CONCLUSION: Women and patients with a 3- to 10-year history of ACLR demonstrated VDJ biomechanics that may be associated with knee motion control challenges. CLINICAL RELEVANCE: It is important to consider knee motion control during activities such as VDJs when developing injury prevention and rehabilitation interventions aimed at improving joint health after youth sport-related ACLR.

Volumetric quantitative measurement of hip effusions by manual versus automated artificial intelligence techniques: An OMERACT preliminary validation study.

OBJECTIVE: Preliminary assessment, via OMERACT filter, of manual and automated MRI hip effusion Volumetric Quantitative Measurement (VQM). METHODS: For 358 hips (93 osteoarthritis subjects, bilateral, 2 time points), 2 radiologists performed manual VQM using custom Matlab software. A Mask R-CNN artificial-intelligence (AI) tool was trained to automatically compute joint fluid volumes. RESULTS: Manual VQM had excellent inter-observer reliability (ICC 0.96). AI predicted hip fluid volumes with ICC 0.86 (status), 0.58 (change) vs. 2 human readers. CONCLUSION: Hip joint fluid volumes are reliably assessed by VQM. It is feasible to automate this approach using AI, with promising initial reliability.

Vertical Drop Jump Performance in Youth With Juvenile Idiopathic Arthritis.

OBJECTIVE: Juvenile idiopathic arthritis (JIA) is associated with altered body structure and function outcomes that may expose youth with JIA to a greater risk of secondary joint injury. This study aimed to examine differences in vertical drop jump (VDJ) biomechanics for youth with JIA and healthy youth (control group). METHODS: The present study was a matched pair cohort study. Youth with JIA (n = 30) and their age- and sex-matched control peers participated in this ethics-approved study. Lower-extremity biomechanics information was obtained using a motion analysis system (Motion Analysis) and 2 force plates (AMTI). Biomechanics outcomes included hip, knee, and ankle joint angles, ground reaction forces (GRF), and VDJ phase durations. Other outcomes included disease activity, physical disability, and sports participation. Matched pairs data (JIA-control) were analyzed using a multivariate random coefficient model (version 3.5.0, R Core Team; joint angles, potential confounders) and paired samples t-tests with Bonferroni correction (α = 0.0125; GRF, VDJ phase durations). RESULTS: Youth with JIA had low disease activity, pain, and disability scores. Youth with JIA maintained a more erect posture at the hip (ß = -4.0°, P = 0.004), knee (ß = 7.5°, P = 0.004) and ankle (ß = -2.6°, P = 0.001). GRF and phase durations outcomes did not meet criteria for significant differences. Knee extension increased with participant age (ß = -1.0°, P = 0.002), while female participants displayed greater hip flexion (ß = -6.6°, P = 0.001) and less ankle dorsiflexion (ß = 2.3°, P = 0.006). CONCLUSION: This study provides evidence for a stiff knee landing strategy by youth with JIA. These findings inform targets for physical therapy management to mitigate the risks of a secondary joint injury in sports participation.

Consequences of Juvenile Idiopathic Arthritis on Single Leg Squat Performance in Youth.

OBJECTIVE: Juvenile idiopathic arthritis (JIA) affects body structure and function outcomes that may increase the risk of acute joint injury. The purpose of this study was to examine single leg squat (SLS) biomechanics for youth with JIA and their healthy peers. The study design was a matched pair cohort study. METHODS: Sixty-five youth (JIA n = 30; control n = 35) participated in this ethics-approved study. Participants performed 3 sets of 5 consecutive SLS tasks. Disease activity and functional status were assessed using the Juvenile Arthritis Disease Activity Score and Child Health Assessment Questionnaire. Indexed (most-affected leg [JIA]; dominant leg [control]) and contralateral extremity biomechanics were obtained using a 12-camera system. Outcomes included hip flexion/extension (FE), adduction/abduction (AA), and internal/external (IE) rotation range of motion (ROM). Data were analyzed using a multivariate random coefficient model in R (α⍺ = 0.05). RESULTS: A total of 29 matched pairs were analyzed. Youth with JIA had low disease activity and performed the SLS with a more internally rotated hip (indexed leg P = 0.023, ß = -1.9°). Female participants displayed greater hip FE (indexed leg P = 0.015, ß = -4.3°; contralateral leg P = 0.005, ß = -4.8°) and IE ROM (indexed leg P = 0.021, ß = -2.1°) than male participants. Associations were observed for body mass index and hip IE ROM (contralateral leg P = 0.001, ß = -0.4°), knee flexion angle, and hip FE ROM (indexed leg P = 0.001, ß = 0.4°; contralateral leg P = 0.001, ß = 0.5°) and AA (indexed leg P = 0.010, ß = 0.1°; contralateral leg P = 0.002, ß = 0.2°). CONCLUSION: This study identified functional alterations for an SLS in youth with JIA. These findings support the use of physical therapy as part of a multidisciplinary management approach, to restore normal hip posture and movement.

Characterizing healthy knee symmetry using the finite helical axis and muscle power during open and closed chain tasks.

Understanding healthy joint movement and muscle control, and injurious alterations, is important to determine musculoskeletal contributions to post-injury joint instabilities or altered dynamic joint function. The contralateral limb is often used as a point of reference to determine the effects of knee joint injury. However, it is currently difficult to interpret within subject variability between limbs as this is not well established in the healthy population. There is a continuing need to characterize healthy knee joint mechanics and neuromuscular control to determine the degree of symmetry within healthy individuals. The current study quantified limb symmetry in healthy individuals using the finite helical axis with a unique reference position (rFHA) and electromyography (EMG) approaches, for a closed-chain single leg squat (SLS) and an open-chain seated leg swing. Muscle power and FHA translation, orientation and dispersion were similar between limbs. However, the FHA was located significantly more anterior in the dominant limb relative to the contralateral during both tasks. These between-limb differences in FHA location could be attributed to differences in joint geometry and strength between limbs. This finding provides evidence that healthy knees have asymmetries which have implications for selection of control limbs in studies comparing conditions within and between individuals. Differences identified in dynamic joint function between tasks suggest that the SLS is useful for revealing joint asymmetries due to altered muscular control strategies, while the swing task is expected to highlight asymmetries in joint motion due to altered knee structures following injury.

Robust Self-Supervised Learning of Deterministic Errors in Single-Plane (Monoplanar) and Dual-Plane (Biplanar) X-Ray Fluoroscopy.

Fluoroscopic imaging that captures X-ray images at video framerates is advantageous for guiding catheter insertions by vascular surgeons and interventional radiologists. Visualizing the dynamical movements non-invasively allows complex surgical procedures to be performed with less trauma to the patient. To improve surgical precision, endovascular procedures can benefit from more accurate fluoroscopy data via calibration. This paper presents a robust self-calibration algorithm suitable for single-plane and dual-plane fluoroscopy. A three-dimensional (3D) target field was imaged by the fluoroscope in a strong geometric network configuration. The unknown 3D positions of targets and the fluoroscope pose were estimated simultaneously by maximizing the likelihood of the Student-t probability distribution function. A smoothed k-nearest-neighbour (kNN) regression is then used to model the deterministic component of the image reprojection error of the robust bundle adjustment. The Maximum Likelihood Estimation step and the kNN regression step are then repeated iteratively until convergence. Four different error modeling schemes were compared while varying the quantity of training images. It was found that using a smoothed kNN regression can automatically model the systematic errors in fluoroscopy with similar accuracy as a human expert using a small training dataset. When all training images were used, the 3D mapping error was reduced from 0.61-0.83 mm to 0.04 mm post-calibration (94.2-95.7% improvement), and the 2D reprojection error was reduced from 1.17-1.31 to 0.20-0.21 pixels (83.2-83.8% improvement). When using biplanar fluoroscopy, the 3D measurement accuracy of the system improved from 0.60 mm to 0.32 mm (47.2% improvement).

Gait Adaptations in Youth With Juvenile Idiopathic Arthritis.

OBJECTIVE: Juvenile idiopathic arthritis (JIA) affects body structure and function and physical activity outcomes. The present study was undertaken to examine differences in gait kinematics during fixed-speed treadmill walking for youth with JIA and typically developing (TD) youth. METHODS: Sagittal plane gait kinematics were obtained using a 12-camera system (Motion Analysis) for youth with JIA (n = 30) and their age and sex-matched TD peers (n = 30). Outcomes included disease activity, pain, well-being, and peak sagittal hip, knee, and ankle joint angles. Kinematics were analyzed for the indexed leg (IL) (i.e., the affected leg of participants with JIA) compared to the dominant leg of TD participants and for the contralateral leg (CL) (i.e., the less/not affected leg of participants with JIA) compared to the nondominant leg of TD participants. Kinematics differences were investigated using multivariate Hotelling's T2 statistic (paired samples; α = 0.05) and simultaneous 95% confidence intervals (95% CIs). Potential confounders (age, sex, body mass index) were assessed using linear mixed-effects models with random effect for pairs. RESULTS: Youth with JIA had low disease activity, pain, and disability scores. Deviations in bilateral joint angles were observed (IL P = 0.015, CL P = 0.009). Youth with JIA walked with greater initial hip flexion (mean difference IL 2.8° [95% CI -0.6, 6.2]; CL 3.0° [-0.9, 6.9]) and lower knee extension (mean difference IL -2.2° [95% CI -4.4, 0.1]; CL -3.3° [-7.4, 0.8]), and lower hip extension during terminal stance (mean difference IL 3.4° [95% CI -0.3, 7.0]; CL 4.0° [1.0, 7.0]). CONCLUSION: Despite low disease activity, youth with JIA avoided the close-packed knee position, commonly associated with joint inflammation and pain. These findings highlight secondary consequences of JIA and inform targets for physical therapy management for youth with JIA.

Establishing outcome measures in early knee osteoarthritis.

The classification and monitoring of individuals with early knee osteoarthritis (OA) are important considerations for the design and evaluation of therapeutic interventions and require the identification of appropriate outcome measures. Potential outcome domains to assess for early OA include patient-reported outcomes (such as pain, function and quality of life), features of clinical examination (such as joint line tenderness and crepitus), objective measures of physical function, levels of physical activity, features of imaging modalities (such as of magnetic resonance imaging) and biochemical markers in body fluid. Patient characteristics such as adiposity and biomechanics of the knee could also have relevance to the assessment of early OA. Importantly, research is needed to enable the selection of outcome measures that are feasible, reliable and validated in individuals at risk of knee OA or with early knee OA. In this Perspectives article, potential outcome measures for early symptomatic knee OA are discussed, including those measures that could be of use in clinical practice and/or the research setting.

Effect of stochastic resonance on proprioception and kinesthesia in anterior cruciate ligament reconstructed patients.

Low amplitude mechanical noise vibration has been shown to improve somatosensory acuity in various clinical groups with comparable deficiencies through a phenomenon known as Stochastic Resonance (SR). This technology showed promising outcomes in improving somatosensory acuity in other clinical patients (e.g., Parkinson's disease and osteoarthritis). Some degree of chronic somatosensory deficiency in the knee has been reported following anterior cruciate ligament (ACL) reconstruction surgery. In this study, the effect of the SR phenomenon on improving knee somatosensory acuity (proprioception and kinesthesia) in female ACL reconstructed (ACLR) participants (n = 19) was tested at three months post-surgery, and the results were compared to healthy controls (n = 28). Proprioception was quantified by the measure of joint position sense (JPS) and kinesthesia with the threshold to detection of passive movement (TDPM). The results based on the statistical analysis demonstrated an overall difference between the somatosensory acuity in the ACLR limb compared to healthy controls (p = 0.007). A larger TDPM was observed in the ACLR limb compared to the healthy controls (p = 0.002). However, the JPS between the ACLR and healthy limbs were not statistically significantly different (p = 0.365). SR significantly improved JPS (p = 0.006) while the effect was more pronounced in the ACLR cohort. The effect on the TDPM did not reach statistical significance (p = 0.681) in either group. In conclusion, deficient kinesthesia in the ACLR limb was observed at three months post-surgery. Also, the positive effects of SR on somatosensory acuity in the ACL reconstructed group warrant further investigation into the use of this phenomenon to improve proprioception in ACLR and healthy groups.

Advancing quantitative techniques to improve understanding of the skeletal structure-function relationship.

Although all functional movement arises from the interplay between the neurological, skeletal, and muscular systems, it is the skeletal system that forms the basic framework for functional movement. Central to understanding human neuromuscular development, along with the genesis of musculoskeletal pathologies, is quantifying how the human skeletal system adapts and mal-adapts to its mechanical environment. Advancing this understanding is hampered by an inability to directly and non-invasively measure in vivo strains, stresses, and forces on bone. Thus, we traditionally have turned to animal models to garner such information. These models enable direct in vivo measures that are not available for human subjects, providing information in regards to both skeletal adaptation and the interplay between the skeletal and muscular systems. Recently, there has been an explosion of new imaging and modeling techniques providing non-invasive, in vivo measures and estimates of skeletal form and function that have long been missing. Combining multiple modalities and techniques has proven to be one of our most valuable resources in enhancing our understanding of the form-function relationship of the human skeletal, muscular, and neurological systems. Thus, to continue advancing our knowledge of the structural-functional relationship, validation of current tools is needed, while development is required to limit the deficiencies in these tools and develop new ones.