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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2020)

Over the past several decades, there have been advances in the development of complex robotic devices for daily assistance or rehabilitation. The use of such devices, however, has largely remained limited to a research setting due to the prohibitive cost and required operational engineering expertise. Likewise, dedicated biomechanics facilities perform quantitative motion analysis, contrasting the qualitative and static imaging methods which are standard in clinical care. The aim of this dissertation is to develop and validate affordable methods and devices for assessing and assisting human motion.

We first present a framework for improved estimation of whole-body human kinematics with data from a single depth-camera. The algorithm incorporates biomechanical and dynamic constraints for near-real time analysis of human motion. The approach is validated against data from a ground-truth motion capture system on sit-to-stand (STS), an activity of daily living which requires significant torque generation and coordinated movement of multiple joints. We additionally present two methods for modeling the torso: a generalized relationship for the lower-lumbar angle and an optimization-based method for estimating a subject-specific model. Building on these modeling methods, we introduce a passive elastic knee orthotic device which provides bilateral knee assistance during STS. The device design and analysis integrate models of the human and device dynamics. Preliminary human subjects tests demonstrate a decrease in the human knee torque as well as positive changes in whole-body biomechanics. Finally, we introduce an affordable planar robotic manipulandum for upper limb assessment and assistance. The mechanical, electrical, and control architectures are presented, along with preliminary human subjects tests of reaching and elliptical trajectories with force field assistance under an admittance controller. A protocol for the assessment of strength and coordination is introduced and integrated with a biomechanical model of the arm. With a total material cost of less than $800, this device provides an accessible platform for clinical robotic assessment and rehabilitation.

    • Article
    • Peer Reviewed
    UC San Francisco Previously Published Works (2019)
    The study of joint kinematics and dynamics has broad clinical applications, including the identification of pathological motions or compensation strategies and the analysis of dynamic stability. High-end motion capture systems, however, are expensive and require dedicated camera spaces with lengthy setup and data processing commitments. Depth cameras, such as the Microsoft Kinect, provide an inexpensive, marker-free alternative at the sacrifice of joint-position accuracy. In this work, we present a fast framework for adding biomechanical constraints to the joint estimates provided by a depth camera system. We also present a new model for the lower lumbar joint angle. We validate key joint position, angle, and velocity measurements against a gold standard active motion-capture system on ten healthy subjects performing sit to stand (STS). Our method showed significant improvement in mean absolute error and intraclass correlation coefficients for the recovered joint angles and position-based metrics. These improvements suggest that depth cameras can provide an accurate and clinically viable method of rapidly assessing the kinematics and kinetics of the STS action, providing data for further analysis using biomechanical or machine learning methods.
      Cover page: Kinematic and Kinetic Validation of an Improved Depth Camera Motion Assessment System Using Rigid Bodies
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2020)
      There are a lack of quantitative measures for clinically assessing upper limb function. Conventional biomechanical performance measures are restricted to specialist labs due to hardware cost and complexity, while the resulting measurements require specialists for analysis. Depth cameras are low cost and portable systems that can track surrogate joint positions. However, these motions may not be biologically consistent, which can result in noisy, inaccurate movements. This paper introduces a rigid body modelling method to enforce biological feasibility of the recovered motions. This method is evaluated on an existing depth camera assessment: the reachable workspace (RW) measure for assessing gross shoulder function. As a rigid body model is used, position estimates of new proximal targets can be added, resulting in a proximal function (PF) measure for assessing a subject's ability to touch specific body landmarks. The accuracy, and repeatability of these measures is assessed on ten asymptomatic subjects, with and without rigid body constraints. This analysis is performed both on a low-cost depth camera system and a gold-standard active motion capture system. The addition of rigid body constraints was found to improve accuracy and concordance of the depth camera system, particularly in lateral reaching movements. Both RW and PF measures were found to be feasible candidates for clinical assessment, with future analysis needed to determine their ability to detect changes within specific patient populations.
        Cover page: Reachable Workspace and Proximal Function Measures for Quantifying Upper Limb Motion
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2019)
        Kinetic and dynamic motion analysis provides quantitative, functional assessments of human ability that are unobtainable through static imaging methods or subjective surveys. While biomechanics facilities are equipped to perform this measurement and analysis, the clinical translation of these methods is limited by the specialized skills and equipment needed. This paper presents and validates a method for estimating dynamic effects such as joint torques and body momenta using a single depth camera. An allometrically scaled, sagittal plane dynamic model is used to estimate the joint torques at the ankles, knees, hips, and low back, as well as the torso momenta, and shear and normal loads at the L5-S1 disk. These dynamic metrics are applied to the sit-to-stand motion and validated against a gold-standard biomechanical system consisting of full-body active motion-capture and force-sensing systems. The metrics obtained from the proposed method were found to have excellent concordance with peak metrics that are consistent with prior biomechanical studies. This suggests the feasibility of using this system for rapid clinical assessment, with applications in diagnostics, longitudinal tracking, and quantifying patient recovery.
          Cover page: Estimating Sit-to-Stand Dynamics Using a Single Depth Camera
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2019)

          Study design

          A longitudinal cohort study.

          Objective

          To define a set of objective biomechanical metrics that are representative of adult spinal deformity (ASD) post-surgical outcomes and that may forecast post-surgical mechanical complications. Current outcomes for ASD surgical planning and post-surgical assessment are limited to static radiographic alignment and patient-reported questionnaires. Little is known about the compensatory biomechanical strategies for stabilizing sagittal balance during functional movements in ASD patients.

          Methods

          We collected in-clinic motion data from 15 ASD patients and 10 controls during an unassisted sit-to-stand (STS) functional maneuver. Joint motions were measured using noninvasive 3D depth mapping sensor technology. Mathematical methods were used to attain high-fidelity joint-position tracking for biomechanical modeling. This approach provided reliable measurements for biomechanical behaviors at the spine, hip, and knee. These included peak sagittal vertical axis (SVA) over the course of the STS, as well as forces and muscular moments at various joints. We compared changes in dynamic sagittal balance (DSB) metrics between pre- and post-surgery and then separately compared pre- and post-surgical data to controls.

          Results

          Standard radiographic and patient-reported outcomes significantly improved following realignment surgery. From the DSB biomechanical metrics, peak SVA and biomechanical loads and muscular forces on the lower lumbar spine significantly reduced following surgery (- 19 to - 30%, all p < 0.05). In addition, as SVA improved, hip moments decreased (- 28 to - 65%, all p < 0.05) and knee moments increased (+ 7 to + 28%, p < 0.05), indicating changes in lower limb compensatory strategies. After surgery, DSB data approached values from the controls, with some post-surgical metrics becoming statistically equivalent to controls.

          Conclusions

          Longitudinal changes in DSB following successful multi-level spinal realignment indicate reduced forces on the lower lumbar spine along with altered lower limb dynamics matching that of controls. Inadequate improvement in DSB may indicate increased risk of post-surgical mechanical failure. These slides can be retrieved under Electronic Supplementary Material.
            Cover page: ISSLS PRIZE IN BIOENGINEERING SCIENCE 2019: biomechanical changes in dynamic sagittal balance and lower limb compensatory strategies following realignment surgery in adult spinal deformity patients
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