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Tendon-driven continuum robot kinematic models are frequently computationally expensive, inaccurate due to unmodeled effects, or both. In particular, unmodeled effects produce uncertainties that arise during the robot’s operation that lead to variability in the resulting geometry. We propose a novel solution to these issues through the development of a Gaussian mixture kinematic model. We train a mixture density network to output a Gaussian mixture model representation of the robot geometry given the current tendon displacements. This model computes a probability distribution that is more representative of the true distribution of geometries at a given configuration than a model that outputs a single geometry, while also reducing the computation time. We demonstrate uses of this model through both a trajectory optimization method that explicitly reasons about the workspace uncertainty to minimize the probability of collision and an inverse kinematics method that maximizes the likelihood of occupying a desired geometry.

Ulnocarpal impaction syndrome is believed to be caused by abutment between the ulna and the ulnar carpus. We measured radiocarpal and midcarpal ranges of motion in 40 patients with ulnocarpal impaction syndrome by radiographic motion studies. The results showed that the radiocarpal and midcarpal ranges of motion were equally restricted in the affected wrist compared with the unaffected wrist. Therefore, motion of the radiocarpal joint and midcarpal joint contributed equally to total wrist motion bilaterally. No correlation between ulnar variance and the contribution of radiocarpal motion to overall wrist motion was found. Restriction of wrist motion in ulnocarpal impaction syndrome is not caused directly by abutment between the ulna and ulnar carpus, but a satisfactory explanation for restricted motion is still lacking.

With advances in imaging and computing technology the greater capacity to diagnose, plan and deliver care to patients with hand and wrist disorder is being realised. Work in our laboratory, has been able to identify certain specific rules that control wrist motion, and is a step on the pathway to creating a unified theory of carpal mechanics which will incorporate a kinetic biomechanical model. This will allow more precise anatomically based as well as quantitative diagnoses, but also an ability to test a proposed intervention in a “what if” scenario.

Purpose: Component position is critical in knee arthroplasty. We propose using a navigated knee axis (NKA) that is kinematically determined using a navigation system as an alignment reference, instead of defining the transepicondylar axis (TEA) with bony landmarks. This paper investigates whether this NKA should be computed over small arc segments versus over a full range of motion. Methods: Twelve unembalmed cadaver knees were tested. A navigation system computed the NKA for segments and for the full arc of motion in multiple planes. Results: The NKA computed near extension was different from the plane perpendicular to the mechanical axis (P > 0.005), while the NKA computed in flexion matched the TEA. Conclusion: The NKA determined from the full arc of motion was more reproducible and more closely estimated important knee parameters.

Pain is routinely implicated as a factor when considering impaired movement in injured populations. Movement velocity is often considered during the rehabilitation process; unfortunately our understanding of pain's impact on shoulder movement velocity in rotator cuff tear patients is less understood. Therefore, the purpose of this study was to test the hypothesis that there would be an increase in peak and mean shoulder elevation velocities following the decrease of shoulder pain in rotator cuff tear patients, regardless of tear size. Fifteen subjects with full-thickness rotator cuff tears (RCT) performed humeral elevation and lowering in three planes before and after receiving a lidocaine injection to relieve pain. Pain was assessed using a visual analog scale. Humeral elevation velocity data were collected using an electromagnetic tracking system. A significant reduction in pain (pre-injection 3.53 ± 1.99; post-injection 1.23 ± 1.43) resulted in significant increases in maximum and mean humeral elevation velocities. Mean shoulder elevation and lowering velocities increased 15.10 ± 2.45% while maximum shoulder movement velocities increased 12.77 ± 3.93%. Furthermore, no significant relationships were noted between tear size and movement velocity. These significant increases in movement velocity provide evidence to further support the notion that human motion can be inhibited by injury-associated pain, and that by reducing that pain through clinical interventions, human movement can be impacted in a positive fashion.

Purpose: We investigated the distribution of three-axis rotational directions of the tibiotalar joint in intact feet under axial loading and categorized them according to the combinations of the three-axis rotational directions of the tibiotalar joint as three-dimensional (3D) rotational patterns. Methods: The differences in rotational orientation of the talus relative to the tibia under unloaded and axial-loaded conditions were calculated from the 3D models of the tibiotalar joint that were reconstructed from magnetic resonance (MR) images in 27 intact male feet. Results: In the sagittal plane, the talus rotated into plantarflexion in 63% of the feet and into dorsiflexion in 30%. In the coronal plane, the talus rotated into inversion in 37% of the feet and into eversion in 33%. In the transverse plane, the talus rotated into adduction in 85% of the feet and into abduction in 4%. A total of 10 3D tibiotalar joint rotational patterns were observed under axial loading. There were no significant differences in the frequencies of the 10 tibiotalar joint rotational patterns (p > 0.05). Conclusions: The 3D tibiotalar joint rotational patterns under axial loading were consolidated into 10 directions, which provides insight into the subject-specific kinematics of the tibiotalar joint.

An estimated 3 million youth participate in youth baseball. The purpose of this review is to highlight musculoskeletal development and specific throwing-related injuries in youth baseball players, as well as the current knowledge of pitching biomechanics, which are closely intertwined with the both arm development and injuries. Methods: A systematic literature review was conducted to highlight musculoskeletal development, throwing-related injuries and pitching mechanics. Results: Youth athletes are actively going through skeletal maturation which includes the formation of new bone at the epiphyseal plate, increasing muscle mass and/or strength, and morphological changes in tendons and ligaments. These processes setup youth pitchers to sustain throwing injuries at their shoulder and elbow in ways that differ from their adult counterparts. Faulty pitching biomechanics may also cause throwing injuries. Deviation from proper mechanics at any point can cause injuries in the shoulder and elbow. Conclusion: Many musculoskeletal changes occur during the development of a youth baseball player. Some of these changes are beneficial for improving throwing performance, but also predispose the athlete to injury. Improper biomechanics may be related to the throwing-related injuries that are seen in youth baseball players.

Background: With cell phone use and ownership on the rise, daily circumstances often require individuals to divide attentional resources between walking and a cell phone-related task. This division of attention has been found to detrimentally effect task performance, making pedestrian cell phone usage an increasing safety concern. However, most studies have investigated the impact of dual-tasks on situational awareness and few have focused on tasks other than texting. Therefore, this study aimed to investigate the effect of various cell phone-related tasks on lower limb kinematics during walking.

Methods: Fourteen healthy, college-aged subjects completed gait analysis trials in five walking conditions, one single-task walking condition and four dual task conditions: Walk+Converse, Walk+Read (Simple), Walk+Read (Difficult), and Walk+Text. Subjects’ movements were recorded with a motion capture system and peak sagittal plane lower extremity joint angles, gait velocity, and stride length were calculated.

Results: Of the eight kinematic outcome measures analyzed, all but one revealed some significant (p < 0.05) differences between dual-task walking conditions. Gait velocity and stride length both decreased due to the addition of the dual tasking, with the magnitude of the reduction becoming more apparent with the increased difficulty of the cell phone-based task.

Conclusion: This study supports a fundamental change to gait kinematics in response to cell phone use while walking, with the magnitude of impact being directly related to the complexity of the secondary task. The significant changes to gait kinematics in complex dual-task situations could present a threat to balance.

Purpose: Most shoulder pathologies are associated with altered scapular kinematics which is mentioned as scapular dyskinesis. Scapular mobility, especially in upward rotation, measurement is essential for diagnosis and treatment. Easy-to-use, clinically applicable 2-dimensional (2-D) measurements would show excellent intra-tester reliability. To quantify intra-tester reliability for measuring scapular upward rotation in individuals with scapular dyskinesias, the landmark palpation with a video annotation tool was used.

Methods: Ten participants with scapular dyskinesis were recruited. Scapular upward rotation was measured at rest, 30°, 60°, 90°, and 120° of humeral elevation in the coronal plane both raising and lowering phases. Two trials were conducted for each arm position randomly, and an assessor took the pictures throughout. The video annotation tool (2-D Kinovia program) was used for measuring scapular upward rotation angles between days. The intra-tester reliability of scapular upward rotation was calculated.

Results: This measurement technique demonstrated excellent intra-tester reliability (ICC${}_{3,1}$ = 0.98), range 0.96–0.99, and standard error of measurement was less than 1°.

Conclusions: The findings demonstrated that using this technique to measure scapular upward rotation was reliable in subjects with scapular dyskinesis.

The purpose of this paper was to investigate the anatomical location of the main axes of rotation of the knee, that is the axes of flexion-extension and longitudinal rotation. We compared 4 hypotheses on the correlation between the axis of flexion-extension and the femoral anatomy and 4 hypotheses on the correlation between the axis of longitudinal rotation and the tibial anatomy in 6 normal human knees. The methods used for the study were:. digitization by an electrogoniometer; computer reconstruction of motion and bone geometry, and an original geometrical interpolation to identify axes location. Our results suggest that: (a) the axis of flexion-extension lies in a cone spanned by the transepicondylar line and the so called FFc line;¹⁹ (b) the axis of longitudinal rotation can be represented by a line parallel to the tibial anatomical axis intersecting the flexion axis in a fixed point of the medial compartment.

With progress of modern technology, manually-propelled wheelchairs are still of importance for individuals with mobility impairments. The repeated wheelchair propulsion and strenuous daily activities cause high loads and thus injuries on the upper extremity joints. Over the past few years, a considerable number of studies have been made on biomechanical analysis of wheelchair propulsion and wheelchair-related activities. Thorough investigation of biomechanics during wheelchair propulsion enhances comprehension of mechanism of injuries and provides information to improve wheelchair design and fitting. Numerous investigations have been made to demonstrate factors which cause low effectiveness of force application and inefficiency of movements. Emphasis was also placed on developing analytical models to simulate wheelchair propulsion.

The reliable knowledge that model-based three-dimensional (3D) fluoroscopy can provide about in vivo joints kinematics is essential to diagnose orthopedic pathologies, develop new prosthesis, and evaluate clinical procedures. To exploit 3D fluoroscopy for the analysis of elbow kinematics, its use was evaluated considering a single model for the forearm or two different models for the ulna and radius. Active elbow flexion-extension and prono-supination motor tasks of a healthy male subject were acquired by means of fluoroscopy. The 3D bone models were automatically aligned to the relevant projections. The pose estimation algorithm sought the tangency condition of the projection rays with the model surface, minimizing a cost function and exploiting an adaptive distance map. Five iterative guided alignments were performed to avoid the final convergence to a local minimum. The results highlighted the critical alignment of the ulna/radius model, particularly when prono-supination is performed. From the physiological motion patterns and given the values of the cost function, 3D fluoroscopy was proven to be applicable to the analysis of the elbow kinematics when single bone models for the ulna and radius are used.

This study investigates upper limb movement and electromyography (EMG) signals during snatch under various loading conditions and discusses results from six lifting phases. Qualisys motion analysis and Noraxon EMG systems were used to record upper limb movement and muscle activity. When lifting heavy weights, the maximum shoulder flexion angle exceeded 180° in the rise phase and thus, was higher than when lifting lower weight categories. The deltoid and biceps muscles exhibited higher activity during this phase when lifting heavy weights. It can be inferred that the deltoid muscle is activated in this phase in order to maintain the shoulder in an abducted position, and to maintain hyperflexion of the biceps. Muscle activity of the deltoid and biceps in the second pull phase also increased significantly during heavy weight lifting. We infer that the effective use of these two muscles in the second pull phase would produce higher peak barbell vertical velocity, increasing the amount of weight can be lifted. Muscle activity for the latissimus dorsi during first pull showed a statistically significant increase when lifting heavy weights. This ability by the latissimus dorsi to generate higher velocities early in the concentric phase (downswing) possibly contributed to the improved final performance during heavy weight lifting.

Walking is daily physical activity and a common way of exercise during pregnancy, but morphological changes can modify the gait pattern. Biomechanical models can help in evaluating joint mechanical loads and kinetics and kinematics during gait, and provide patterns. This study aimed to describe the gait pattern during the second trimester of pregnancy and give an orientation for biomechanical modeling for pregnant women. The ankle and hip joints seem to be more overloaded, mainly in the sagittal and frontal planes, respectively. Results show that pregnant women have a similar walking pattern to the normal gait. This model construction was revealed to be appropriate for describing gait during the second trimester of pregnancy.

The motion of the skeletal estimated from skin attached marker-based motion capture(MOCAP) systems is known to be affected by significant bias caused by anatomical landmarks mislocation but especially by soft tissue artifacts (such as skin deformation and sliding, inertial effects and muscle contraction). As a consequence, the error associated with this bias can propagate to joint kinematics and kinetics data, particularly in small rodents. The purpose of this study was to perform a segmental kinematic analysis of the rat hindlimb during locomotion, using both global optimization as well as segmental optimization methods. Eight rats were evaluated for natural overground walking and motion of the right hindlimb was captured with an optoeletronic system while the animals walked in the track. Three-dimensional (3D) biomechanical analyses were carried out and hip, knee and ankle joint angular displacements and velocities were calculated. Comparison between both methods demonstrated that the magnitude of the kinematic error due to skin movement increases in the segmental optimization when compared with the global optimization method. The kinematic results assessed with the global optimization method matches more closely to the joint angles and ranges of motion calculated from bone-derived kinematics, being the knee and hip joints with more significant differences.

This study examined chronic, isolated posterior cruciate ligament (PCL) rupture patients, dividing them into symptomatic and asymptomatic groups according to whether they displayed obvious symptoms in daily activities. Each group comprised 10 patients while 10 healthy, young individuals were adopted as the control group. Using a three-dimensional motion analysis system and force plates, the gait patterns of the PCL-deficient patients were analyzed from both kinematics and kinetics perspectives to identify whether they differed from the control group and to compare symmetry between the injured and uninjured sides. The results showed that the symptomatic PCL-deficient group was closer to "normal", and the asymptomatic PCL-deficient group showed less knee extension moment and lower power absorption in the terminal stance than the control group. Additionally, the symptomatic PCL-deficient group appeared to have a relatively symmetric gait while the asymptomatic PCL-deficient group primarily showed an asymmetric gait also occurring in the terminal stance, including less joint moment and lower power absorption of the hip and knee, and lower vertical ground reaction force (GRF). Regarding the gait adaptations of the asymptomatic PCL-deficient group these compensation mechanisms are most likely to have been produced in order to assist in joint stabilization and reduce symptoms in joints.

The lack of awareness of the exact number of instantaneous centers of knee flexion/extension rotation leads to the presence in the market of total knee arthroplasty (TKA) femoral components designed under different hypotheses. Although single radius (SR) designs are thought to replicate the physiological behavior in a more realistic way, surgeons do not always agree about the veracity of their theoretical advantages with respect to the multiple radii components (J-curve (JC) design). Apart from clinical studies, up to now, any literature study biomechanically and exhaustively compares these two TKA solutions, thus a finite element analysis (FEA) has been carried out. In particular, two models were defined to analyze the performance of a SR design and a JC design with the same tibial component during gait cycle and squat motor task. Tibio-femoral kinematics and kinetics have been investigated comparing the resulting contact area between components, internal–external (IE) rotation, position and magnitude of the center of total forces due to contact pressure and polyethylene von Misses stresses. Results demonstrate that, for low demanding tasks, there are no significant differences between the two designs, however, during the squat motor task, some changes in contact force and increases in polyethylene stress were identified for the SR solution.

The objective of this study was to evaluate the effects of a semi-constrained artificial disc with upward instantaneous center of rotation (ICR) on the biomechanics of the cervical spine. A three-dimensional nonlinear finite element model of the lower cervical spine (C4–C7) was developed using computed tomography (CT) data. The FE model was validated by comparing it to previously published experimental results for flexion-extension, lateral bending and axial rotation movements. The validated model was then altered to include prosthesis at the C5–C6 level. A hybrid test protocol was used to investigate the effects of total disc replacement. The results of this study showed that this artificial disc can help maintain the same range of motion (ROM) and intradiscal pressure as the intact model for most loading conditions. We also found that loads on the facet joints increased dramatically at index level. The capsular ligaments were also found to transmit more tension during flexion at implanted level. Although the artificial disc with upward ICR was found to restore normal kinematics, and prevented increases in intradiscal pressure, it was also associated with an overloading of the facet joints and capsular ligaments leading to potentially undesirable outcomes in the long term.

The purpose of this study was to create a kinematic model of the knee joint with six degrees of freedom (DOF) and evaluate the effect of medial collateral ligament (MCL) and lateral collateral ligament (LCL) rupture on cartilage contact point distribution on the tibia during flexion. We hypothesized that collateral ligament contributions vary over six DOF of knee joint articulation and affect the cartilage contact point distribution during joint articulation. The ligament contributions and distribution of joint cartilage contact points cannot be fully assessed with simplified joint models or invasive experiments. Therefore, we developed a new model in which the tibia and femur centers of mass were determined from their surface geometry, and the displacement of the moving tibia was determined from the displacements of the attached ligaments. Compared to the intact knee, the tibia with the LCL removed had higher medial translation and lower valgus rotation. The tibia with the MCL removed had higher lateral translation and higher valgus rotation than the intact knee. At 0${}^{\circ }$, 30${}^{\circ }$, and 60${}^{\circ }$, the tibia with the LCL removed had more internal rotation than the intact knee. Understanding six DOF knee joint kinematics with integration of ligament contributions and cartilage contact positions is useful for the diagnosis of ligament injuries and the design of articulating surfaces for total arthroplasty.

Morphological changes are associated to pregnancy, such as weight gain and increased volume of the trunk. The soft tissue artifact can also increase with these characteristics and affect the real joint kinematics. The main objective of this study was to understand the effect of using three different constraining sets in the lower limb joints, in the amount of soft tissue artifact (STA) of pregnant women, in order to obtain the most appropriated joint set to be used in gait and in this population. The ankle, knee and hip joints were modeled respectively with the following characteristics: (1) Universal–revolute–spherical (URS), (2) spherical–revolute–spherical (SRS) and (3) spherical–spherical–spherical (SSS). The six degrees of freedom (6DOF) model was used as the basis for comparison and considered the one with the highest error associated to the STA. In pregnant women, the URS model seems to affect more the kinematic variables when compared with the 6DOF model. Assuming that the kinematic error associated with pregnant women is increased due to the STA, the URS model may be affecting more the angular kinematics of the knee joint. SSS model seems to be more appropriated to analyze gait in second trimester pregnant women.