Quantification of Soft Tissue Artefacts Using Motion Capture Data and Ultrasound Depth Measurements

The centre of rotation of the hip joint is needed for an accurate simulation of the joint performance in many applications such as pre-operative planning simulation, human gait analysis, and hip joint disorders. In human movement analysis, the hip joint center can be estimated using a functional method based on the relative motion of the femur to pelvis measured using reflective markers attached to the skin surface. The principal source of errors in estimation of hip joint centre location using functional methods is soft tissue artefacts due to the relative motion between the markers and bone. One of the main objectives in human movement analysis is the assessment of soft tissue artefact as the accuracy of functional methods depends upon it. Various studies have described the movement of soft tissue artefact invasively, such as intra-cortical pins, external fixators, percutaneous skeletal trackers, and Roentgen photogrammetry. The goal of this study is to present a non-invasive method to assess the displacements of the markers relative to the underlying bone using optical motion capture data and tissue thickness from ultrasound measurements during flexion, extension, and abduction (all with knee extended) of the hip joint. Results show that the artefact skin marker displacements are non-linear and larger in areas closer to the hip joint. Also marker displacements are dependent on the movement type and relatively larger in abduction movement. The quantification of soft tissue artefacts can be used as a basis for a correction procedure for hip joint kinematics

Soft tissue displacement over pelvic anatomical landmarks during 3-D hip movements

The position, in a pelvis-embedded anatomical coordinate system, of skin points located over the following anatomical landmarks (AL) was determined while the hip assumed different spatial postures: right and left anterior superior and posterior superior iliac spines, and the sacrum. Postures were selected as occurring during walking and during a flexion-extension and circumduction movement, as used to determine the hip joint centre position (star-arc movement). Five volunteers, characterised by a wide range of body mass indices (22-37), were investigated. Subject-specific MRI pelvis digital bone models were obtained. For each posture, the pose of the pelvis-embedded anatomical coordinate system was determined by registering this bone model with points digitised over bony prominences of the pelvis, using a wand carrying a marker-cluster and stereophotogrammetry. The knowledge of how the position of the skin points varies as a function of the hip posture provided information regarding the soft tissue artefact (STA) that would affect skin markers located over those points during stereophotogrammetric movement analysis. The STA was described in terms of amplitude (relative to the position of the AL during an orthostatic posture), diameter (distance between the positions of the AL which were farthest away from each other), and pelvis orientation. The STA amplitude, exhibited, over all postures, a median [inter-quartile] value of 9[6] and 16[11]. mm, for normal and overweight volunteers, respectively. STA diameters were larger for the star-arc than for the walking postures, and the direction was predominantly upwards. Consequent errors in pelvic orientation were in the range 1-9 and 4-11 degrees, for the two groups respectively

Quantification of Soft Tissue Artefacts Using Motion Capture Data and Ultrasound Depth Measurements

The centre of rotation of the hip joint is needed for an accurate simulation of the joint performance in many applications such as pre-operative planning simulation, human gait analysis, and hip joint disorders. In human movement analysis, the hip joint center can be estimated using a functional method based on the relative motion of the femur to pelvis measured using reflective markers attached to the skin surface. The principal source of errors in estimation of hip joint centre location using functional methods is soft tissue artefacts due to the relative motion between the markers and bone. One of the main objectives in human movement analysis is the assessment of soft tissue artefact as the accuracy of functional methods depends upon it. Various studies have described the movement of soft tissue artefact invasively, such as intra-cortical pins, external fixators, percutaneous skeletal trackers, and Roentgen photogrammetry. The goal of this study is to present a non-invasive method to assess the displacements of the markers relative to the underlying bone using optical motion capture data and tissue thickness from ultrasound measurements during flexion, extension, and abduction (all with knee extended) of the hip joint. Results show that the artefact skin marker displacements are non-linear and larger in areas closer to the hip joint. Also marker displacements are dependent on the movement type and relatively larger in abduction movement. The quantification of soft tissue artefacts can be used as a basis for a correction procedure for hip joint kinematics

Ultrasound and motion capture analysis for pre-operative planning in lower limb joint replacement surgeries

Pre-operative planning in total knee and hip arthroplasty is important for surgical outcome and patient satisfaction. Current clinical gold standards for pre-operative planning include imaging methods which are invasive to the patient and limited to one position of analysis. Lower limb and pelvic alignment are assessed in planning for total knee and hip arthroplasty respectively and have shown to vary in their measurements between standing and supine. B-mode ultrasound has shown to be a promising method for gaining superficial structures like muscles and bones. B-mode ultrasound can be performed rapidly and is relatively cheap and measurements can be conducted with the patient in various positions. The aim of this thesis is to establish non-invasive protocols for pre-operative planning in knee and hip surgeries. Several approaches were developed to non-invasively measure lower limb and pelvic alignment. These consisted of using integrated motion capture and ultrasound system (OrthoPilot, Aesculap). A smart system (Aesculap) which consisted of a smart phone, smart tablet and ultrasound device was used to measure pelvic tilt from the anterior pelvic plane. A motion capture system on its own was used to measure the pelvic tilt in alternative manners. And finally, a synchronised ultrasound and motion capture setup was used for three-dimensional reconstructions of bone geometries. Supine and standing measurements were conducted which showed the flexibility of the measurements unlike common alternatives (X-Ray, MRI, CT). Several operators performed precise measurements of key lower limb parameters. For example, varus-valgus was shown to be measured within 1 degree across operators. Femur and tibia segment lengths were also consistent (<5mm maximum variation between operators). Femur and tibia torsion measurements were less reliable (up to 10-15 degrees of variation between operators). Pelvic tilt measurements were also found to be unreliable regardless of the measurement technique. Initial promise and feasibility of three-dimensional reconstructions of all lower limb joint axis for implementation into musculoskeletal models was also shown. Joint contact forces differences between the implementation of MRI and ultrasound parameters into the models were less than 1 body weight. Overall, ultrasound has shown to be useful in the assessment of lower limb parameters and bone geometries. This work has built upon previous findings to continue its development in the field of pre-operative planning and musculoskeletal modelling. Further work will include a large validation of subject-specific musculoskeletal modelling from ultrasound reconstructions. Improvements to the lower limb assessment with OrthoPilot will also be investigated

A Method to Track 3D Knee Kinematics by Multi-Channel 3D-Tracked A-Mode Ultrasound

This paper introduces a method for measuring 3D tibiofemoral kinematics using a multi-channel A-mode ultrasound system under dynamic conditions. The proposed system consists of a multi-channel A-mode ultrasound system integrated with a conventional motion capture system (i.e., optical tracking system). This approach allows for the non-invasive and non-radiative quantification of the tibiofemoral joint’s six degrees of freedom (DOF). We demonstrated the feasibility and accuracy of this method in the cadaveric experiment. The knee joint’s motions were mimicked by manually manipulating the leg through multiple motion cycles from flexion to extension. To measure it, six custom ultrasound holders, equipped with a total of 30 A-mode ultrasound transducers and 18 optical markers, were mounted on various anatomical regions of the lower extremity of the specimen. During experiments, 3D-tracked intra-cortical bone pins were inserted into the femur and tibia to measure the ground truth of tibiofemoral kinematics. The results were compared with the tibiofemoral kinematics derived from the proposed ultrasound system. The results showed an average rotational error of 1.51 ± 1.13° and a translational error of 3.14 ± 1.72 mm for the ultrasound-derived kinematics, compared to the ground truth. In conclusion, this multi-channel A-mode ultrasound system demonstrated a great potential of effectively measuring tibiofemoral kinematics during dynamic motions. Its improved accuracy, nature of non-invasiveness, and lack of radiation exposure make this method a promising alternative to incorporate into gait analysis and prosthetic kinematic measurements later.</p

Quantification of knee extensor muscle forces: a multimodality approach

Given the growing interest of using musculoskeletal (MSK) models in a large number of clinical applications for quantifying the internal loading of the human MSK system, verification and validation of the model’s predictions, especially at the knee joint, have remained as one of the biggest challenges in the use of the models as clinical tools. This thesis proposes a methodology for more accurate quantification of knee extensor forces by exploring different experimental and modelling techniques that can be used to enhance the process of verification and validation of the knee joint model within the MSK models for transforming the models to a viable clinical tool. In this methodology, an experimental protocol was developed for simultaneous measurement of the knee joint motion, torques, external forces and muscular activation during an isolated knee extension exercise. This experimental protocol was tested on a cohort of 11 male subjects and the measurements were used to quantify knee extensor forces using two different MSK models representing a simplified model of the knee extensor mechanism and a previously-developed three-dimensional MSK model of the lower limb. The quantified knee extensor forces from the MSK models were then compared to evaluate the performance of the models for quantifying knee extensor forces. The MSK models were also used to investigate the sensitivity of the calculated knee extensor forces to key modelling parameters of the knee including the method of quantifying the knee centre of rotation and the effect of joint translation during motion. In addition, the feasibility of an emerging ultrasound-based imaging technique (shear wave elastography) for direct quantification of the physiologically-relevant musculotendon forces was investigated. The results in this thesis showed that a simplified model of the knee can be reliably used during a controlled planar activity as a computationally-fast and effective tool for hierarchical verification of the knee joint model in optimisation-based large-scale MSK models to provide more confidence in the outputs of the models. Furthermore, the calculation of knee extensor muscle forces has been found to be sensitive to knee joint translation (moving centre of rotation of the knee), highlighting the importance of this modelling parameter for quantifying physiologically-realistic knee muscle forces in the MSK models. It was also demonstrated how the movement of the knee axis of rotation during motion can be used as an intuitive tool for understanding the functional anatomy of the knee joint. Moreover, the findings in this thesis indicated that the shear wave elastography technique can be potentially used as a novel method for direct quantification of the physiologically-relevant musculotendon forces for independent validation of the predictions of musculotendon forces from the MSK models.Open Acces

Modelling and in vivo evaluation of tendon forces and strain in dynamic rehabilitation exercises: a scoping review

Objectives Although exercise is considered the preferred approach for tendinopathies, the actual load that acts on the tendon in loading programmes is usually unknown. The objective of this study was to review the techniques that have been applied in vivo to estimate the forces and strain that act on the human tendon in dynamic exercises used during rehabilitation. Design Scoping review. Data sources Embase, PubMed, Web of Science and Google Scholar were searched from database inception to February 2021. Eligibility criteria Cross-sectional studies available in English or Spanish language were included if they focused on evaluating the forces or strain of human tendons in vivo during dynamic exercises. Studies were excluded if they did not evaluate tendon forces or strain; if they evaluated running, walking, jumping, landing or no dynamic exercise at all; and if they were conference proceedings or book chapters. Data extraction and synthesis Data extracted included year of publication, study setting, study population characteristics, technique used and exercises evaluated. The studies were grouped by the types of techniques and the tendon location. Results Twenty-one studies were included. Fourteen studies used an indirect methodology based on inverse dynamics, nine of them in the Achilles and five in the patellar tendon. Six studies implemented force transducers for measuring tendon forces in open carpal tunnel release surgery patients. One study applied an optic fibre technique to detect forces in the patellar tendon. Four studies measured strain using ultrasound-based techniques. Conclusions There is a predominant use of inverse dynamics, but force transducers, optic fibre and estimations from strain data are also used. Although these tools may be used to make general estimates of tendon forces and strains, the invasiveness of some methods and the loss of immediacy of others make it difficult to provide immediate feedback to the individuals.This work is part of a government-funded project supported by the University Teaching Training Programme (FPU) of the Ministry of Science, Innovation and Universities of Spain. Grant number: FPU17/00161. The University of Malaga has supported this study with the contribution of funds to support its publication in open access

The conventional gait model - success and limitations

The Conventional Gait Model (CGM) is a generic name for a family of closely related and very widely used biomechanical models for gait analysis. After describing its history, the core attributes of the model are described followed by evaluation of its strengths and weaknesses. An analysis of the current and future requirements for practical biomechanical models for clinical and other gait analysis purposes which have been rigorously calibrated suggests that the CGM is better suited for this purpose than any other currently available model. Modifications are required, however, and a number are proposed

Development and Application of the Pelvic Tracker

Backpacks are commonly used by students of all ages and there has been a growing concern in many countries in relation to the backpack loads carried by school children and its association with the rise in complaints of neck, shoulder and back pain. Of further concern is the work of Hestbaek et al. (2006) which has shown a correlation between experiencing back pain as an adolescent and experiencing low back pain as an adult. In recent years, a number of studies have investigated physiological and movement kinematic responses to load carriage, such as oxygen consumption, heart rate, gait pattern and trunk posture (Hong et al., 2000; Pascoe et al., 1997). However, most of the studies that focused on children carrying loads looked only at gait patterns and trunk and neck postures. None of the previous studies investigated the compensatory pelvic motions of school children due to increased loads. Also, it was reported that one of the major limitations of measuring pelvic kinematics whilst carrying a backpack was occlusion of retro-reflective markers, and consequently this limits the type of activity and subject to be measured using an optical motion tracking system. Despite the presence of a variety of models, there are still debates on their reliability and repeatability, and consequently there is no clearly defined standard or consensus. In this thesis, a novel methodology was developed to measure pelvic kinematics. Its repeatability and reliability was validated experimentally by comparing it to the most relevant previous method. The result of this experiment showed that the new method improved the repeatability, reliability and reproducibility of kinematics data of the pelvis and overcomes a number of theoretical and experimental limitations, such as marker occlusion. The validated method was used to develop a protocol to measure the pelvic kinematics in adolescents whilst carrying loaded backpacks of 17% and 25% of their body weight during different activities of daily living on the basis of a survey which was conducted to explore the average daily weight that children carry to school in the UK. The result of this experiment revealed that as the load increased to 25% of the body weight, the instability in postural control increased and significant changes in pelvic tilt and rotation were noted in almost all activities. It was revealed in this study that female and male subjects used different mechanism to compensate for the effect of a heavy backpack. It was evident that carriage of loaded backpack will result in alteration of the movement of the pelvis and may in future promote postural deviation and increase lower back pain.Open Acces