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

Personalisation of musculoskeletal models using Magnetic Resonance Imaging

Musculoskeletal (MSK) disorders affecting locomotion represent one of the leading causes for disability in the developed countries, impacting on the patients’ lifestyle and social inclusion, as well as the national healthcare resources. Due to the different aetiologies and progression of such diseases, and to the individual needs of patients, personalised assessment is currently promoted as the gold standard for the diagnosis and treatment of MSK disorders. The introduction of MSK models has recently integrated more traditional measurements of gait-related parameters, enabling the simulation of clinical scenarios and rehabilitation plans within a computational environment, therefore limiting the invasiveness of the experiments. However, the lack of standardised and validated procedures currently limits the adoption of these techniques in the clinical practice and restricts their shareability across the research community. The aim of this PhD thesis was to develop an innovative, robust, and repeatable procedure for the definition of MRI-based subject-specific MSKMs of the lower limb. A fully documented procedure (and associated methodologies) for producing such models was proposed. The final scope of this project is to promote the adoption of personalised modelling in the clinical assessment of lower-limb MSK disorders. The versatility of the proposed modelling approach was successfully tested by applying it in cohorts featured by different age (juvenile and elderly), genders and health conditions (juvenile idiopathic arthritis and osteopenia). In particular the model was tested for its ability to: discriminate joint kinematics and joint loadings that are typical of different populations; identify informative biomechanical parameters to characterise disease and disease progression in juvenile idiopathic arthritis; quantify the effect of different physiological muscle features, such as volumes and geometry, on the estimate of joint loading. As a result of the work carried out as part of the above studies, a significant advance in the standardisation and automation of the procedures needed for building fully personalised MRI-based models of the MSK system has been achieved. The model outputs were proved to have good repeatability and reproducibility and to be informative in all above applications. The proposed approach also showed a clear potential toward complementing traditional clinical gait analysis approaches by providing information on the muscle and joint internal forces, otherwise not easily accessible in-vivo. Future work will aim at reducing the cost, operator time, and errors associated to MRI-based MSK modelling by further improving and automating the image processing techniques and even replacing the MRI with affordable and portable technologies, such as ultrasound-based systems

Automatic generation of personalised skeletal models of the lower limb from three-dimensional bone geometries

The generation of personalised and patient-specific musculoskeletal models is currently a cumbersome and time-consuming task that normally requires several processing hours and trained operators. We believe that this aspect discourages the use of computational models even when appropriate data are available and personalised biomechanical analysis would be beneficial. In this paper we present a computational tool that enables the fully automatic generation of skeletal models of the lower limb from three-dimensional bone geometries, normally obtained by segmentation of medical images. This tool was evaluated against four manually created lower limb models finding remarkable agreement in the computed joint parameters, well within human operator repeatability. The coordinate systems origins were identified with maximum differences between 0.5 mm (hip joint) and 5.9 mm (subtalar joint), while the joint axes presented discrepancies between 1° (knee joint) to 11° (subtalar joint). To prove the robustness of the methodology, the models were built from four datasets including both genders, anatomies ranging from juvenile to elderly and bone geometries reconstructed from high-quality computed tomography as well as lower-quality magnetic resonance imaging scans. The entire workflow, implemented in MATLAB scripting language, executed in seconds and required no operator intervention, creating lower extremity models ready to use for kinematic and kinetic analysis or as baselines for more advanced musculoskeletal modelling approaches, of which we provide some practical examples. We auspicate that this technical advancement, together with upcoming progress in medical image segmentation techniques, will promote the use of personalised models in larger-scale studies than those hitherto undertaken

The use of near infrared spectroscopy (NIRS) to measure vascular haemodynamics in human bone tissue in vivo

Rationale: Poor cardiovascular health is associated with reduced bone strength and increased risk of fragility fracture. However, direct measurement of intraosseous vascular health is difficult due to the density and mineral content of bone. The aim of this PhD project was to investigate the feasibility of near infrared spectroscopy (NIRS) for the investigation of vascular haemodynamics in human bone in vivo. NIRS provides inexpensive, non-invasive, safe, and real time data on changes in oxygenated and deoxygenated haemoglobin concentration at superficial anatomical sites. NIRS utilises a source optode of near infrared (NIR) light and detector optode that obtains representative data of the interactions of NIR photons with tissue. Method: A systematic review was performed identifying the current existing applications of NIRS (and similar technologies) for measuring human bone tissue in vivo. This review informed the development of an arterial occlusion protocol for obtaining haemodynamic measurements of the proximal tibia and lateral calf, including assessment of the protocol’s reliability. For thirty-six participants, NIRS results were also compared to alternative tests of bone haemodynamics involving dynamic contrast enhanced MRI (DCE-MRI), and measures of general bone health based on dual x-ray absorptiometry testing and blood markers of bone metabolism. Results: This thesis presents novel data demonstrating NIRS can obtain acceptably reliable markers of haemodynamics at the proximal tibia in vivo, comparable with reliability assessments of alternative modalities measuring intraosseous haemodynamics, and the use of NIRS for measuring muscle. Novel associations have been demonstrated between haemodynamic markers measured with NIRS and DCE-MRI, giving confidence NIRS truly represents bone haemodynamics. Increased NIRS markers of oxygen extraction during occlusion, and greater post-ischaemic vascular response to occlusion, were both associated with greater bone mineral density. Conclusion: As a feasibility study, this PhD project has demonstrated the potential for NIRS to contribute to research around the potential pathophysiological role of vascular dysfunction within bone tissue, but also the limitations and need for further development of NIRS technology.The Royal College of Radiologist

Biomechanical risk factors and reduced bone health in lower limb amputees

Bone constantly adapts to its surroundings through the formation and resorption of material, controlled by bone modelling and remodelling. Strains produced by mechanical loading are one factor that drive these processes and thus determine bone health. Lower limb amputees (LLA) adopt an asymmetrical movement pattern to compensate for the loss of a limb, resulting in a change in mechanical loading and subsequently a degradation in bone health. The aetiology of the majority of amputations is vascular diseases, which affect bone health. Therefore, it is not clear whether the asymmetrical loading, or comorbidities cause the degradation in bone health in LLA. Finite element models (FEM) are used to generate strain plots and predict the bone's response to mechanical loading. To understand the relationship between the degradation in bone health and asymmetrical loads in LLAs the asymmetrical loads can be applied to a healthy bone using FEMs, or simulated within a healthy population using restrictive devices. Therefore, the overall aim was to investigate the relationship between asymmetrical loading, as observed in LLA’s, and bone health, through the use of semi-subject specific FEMs and restrictive lower limb devices. Study one established a novel image processing method to convert peripheral quantative computed tomography (pQCT) scan images into binary and segment the tibia. The outer perimeter of the tibia was identified and sectioned to produce landmarks. The outer geometry landmarks were used to morph a base FEM, constructed from open source scan images to create semi-subject tibia FEM. Study two applied subject-specific joint reaction and muscle forces to the semi-subject tibia FEM. The strain plots output from Study two were validated against longitudinal geometrical changes from Study three. Study three, used 3D motion capture, pQCT and dual energy x-ray absorptiometry (DXA) to investigate gait and tibial geometry within a lower limb amputee and able-bodied population across twelve months. The coefficient of variation (CV) for able bodied subjects was less than 10% for ground reaction force (GRF) in level walking and less than 4% for bone total area. Study four, used a rigid foot orthosis and a trans-femoral prosthesis, to restrict able-bodied gait. Results showed participants walked significantly slower (p<0.01) in the restricted conditions, with a longer non-restricted step length (p<0.001). The loading rate and maximum GRF were higher in the non-restricted limb (p<0.05). Larger knee adductor moments were shown in the un-restricted leg in the trans-tibial condition (p<0.05). This thesis presents a novel method of constructing semi-subject specific FEMs from pQCT scans. This can be used to further investigate the link between asymmetrical loading and bone health in LLA's and other populations with asymmetrical gait. The use of restrictive devices allow investigation into LLA's specifically, without the interference of prosthetic variability, or comorbidities

Investigation of in-vivo hindfoot and orthotic interactions using bi-planar x-ray fluoroscopy

A markerless RSA method was used to determine the effect of orthotics on the normal, pes planus and pes cavus populations. Computed tomography (CT) was used to create bone models that were imported into the virtual environment. Joint coordinate systems were developed to measure kinematic changes in the hindfoot during weight-bearing gait and quiet standing. The objectives of this thesis were to (1) implement a fluoroscopy-based markerless RSA system on the foot, (2) determine the effect of various orthotics at midstance of fully weight-bearing dynamic gait, and (3) determine the effect of orthotics as measured using three different techniques. Every individual in this study reacted differently depending on the footwear condition tested. Despite the change in alignment caused by orthotics lacking statistical significance it appears the change may be significant with more subjects. Fluoroscopy should enable substantial improvements in orthotic design for optimal results in the future

Individualised Modelling for Preoperative Planning of Total Knee Replacement Surgery

Total knee replacement (TKR) surgery is routinely prescribed for patients with severe knee osteoarthritis to alleviate the pain and restore the kinematics. Although this procedure was proven to be successful in reducing the joint pain, the number of failures and the low patients’ satisfaction suggest that while the number of reoperations is small, the surgery frequently fail to restore the function in full. The main cause are surgical techniques which inadequately address the problem of balancing the knee soft tissues. The preoperative planning technique allows to manufacture subject-specific cutting guides that improves the placement of the prosthesis, however the knee soft tissue is ignored. The objective of this dissertation was to create an optimized preplanning procedure to compute the soft tissue balance along with the placement of the prosthesis to ensure mechanical stability. The dissertation comprises the development of CT based static and quasi-static knee models able to estimate the postoperative length of the collateral lateral ligaments using a dataset of seven TKR patients; In addition, a subject-specific dynamic musculoskeletal model of the lower limb was created using in vivo knee contact forces to perform the same analysis during walking. The models were evaluated by their ability to predict the postoperative elongation using a threshold based on the 10 % of the preoperative length, through which the model detected whether an elongation was acceptable. The results showed that the subject-specific static model is the best solution to be included in the optimized, subject-specific, preoperative planning framework; full order musculoskeletal model allowed to estimate the postoperative length of the ligaments during walking, and at least in principle while performing any other activity. Unlike the current methodology used in clinic this optimized preoperative planning framework might help the surgeon to understand how the position of the TKR affects the knee soft tissue

Femoral neck anteversion: measurement, predictors, and effects on musculoskeletal function

Total femoral torsion and other lower limb geometry parameters show substantial inter-individual variation and contribute to clinical outcomes such as hip dysplasia, hip and knee osteoarthritis, atypical fractures, and disadvantageous kinematics. This thesis aimed to identify appropriate methods to assess femoral torsion. Thereafter, to investigate its determinants and relationship to other aspects of lower limb geometry and muscle function. The literature review identified the clinical importance of femoral torsion, a lack of standardisation in femoral torsion measurement, and the strength and weaknesses of current methods whilst highlighting the need for quick and accurate techniques employable in children. The first study proved the concept of a new three-dimensional biomedical imaging device using a standard ultrasound device, with a linear array probe, coupled with a coordinate-measuring system. This achieved only poor-to-moderate test-retest reliability for femoral torsion (ICC=0.329; CI -0.542-0.843) and femoral length (ICC=0.615; CI -0.071-0.919) respectively but identified a number of potential avenues for improvement of the technique. The second study characterised lower limb geometry in individuals with X-linked hypophosphatemia (XLH) and controls and found large differences in several parameters of lower limb geometry between the two groups. The identification of ~ 18° smaller intertrochanteric rather than shaft torsion in these individuals can inform surgical guidelines. The third study explored the associations of long-term power exercise with lower limb geometry in young and older adults. Only small associations were observed with training and age as effects on femoral bowing in the order of magnitude of ~2°. The ability to alter skeletal geometry through exercise throughout adulthood seems limited, reinforcing the importance of childhood physical activity for lifelong skeletal health. This thesis presented novel insights and methodologies regarding the characterisation of lower limb geometry on three planes and the relationship between the different shape parameters, informing future surgical procedures. It also added new evidence of skeletal shape adaptations to chronic exercise in adulthood and impaired phosphate metabolism

Mathematical modelling and simulation of the foot with specific application to the Achilles tendon

In this thesis, the development of an anatomically meaningful musculoskeletal model of the human foot with specific application to the Achilles tendon is presented. An in vivo experimental method of obtaining parameter values for the mechanical characteristics of the Achilles tendon and the gastrocnemius muscle is presented incorporating a Hill-type muscle model. The incentive for this work has been to enable the prediction of movement with regard to Achilles tendon motion of healthy volunteers, in order to then compare it with the movement of a pathologic gait and help in preventing Achilles tendon injuries. There are relatively few mathematical models that focus on the characterisation of the human Achilles tendon as part of a muscle-tendon unit in the literature. The mechanical properties of the Achilles tendon and the muscles connected to the tendon are usually calculated or predicted from muscle-tendon models such as the Hill-type muscle models. A significant issue in model based movement studies is that the parameter values in Hill-type muscle models are not determined by data obtained from in vivo experiments, but from data obtained from cadaveric specimens. This results in a complication when those predictive models are used to generate realistic predictions of human movement dynamics. In this study, a model of the Achilles tendon-gastrocnemius muscle is developed, incorporating assumptions regarding the mechanical properties of the muscle fibres and the tendinous tissue in series. Ultrasound images of volunteers, direct measurements and additional mathematical calculations are used to determine the initial lengths of the muscle-tendon complex as well as the final lengths during specific movements of the foot and the leg to parameterise the model. Ground reaction forces, forces on specific joints and moments and angles for the ankle are obtained from a 3D motion capture system. A novel experimental marker placement for the Achilles tendon is developed and generated in the 3D motion capture system. Movement dynamics of the foot are described using Newton’s laws, the principle of superposition and a technique known as the method of sections. Structural identifiability analyses of the muscle model ensured that values for the model parameters could be uniquely determined from perfect noise free data. Simulated model dynamics are fitted to measured movements of the foot. Model values are obtained on an individual subject basis. Model validation is performed from the experimental data captured for each volunteer and from reconstruction of the movements of specific trajectories of the joints, muscles and tendons involved in those movements. The major output of this thesis is a validated model of the Achilles tendon-gastrocnemius muscle that gives specific parameters for any individual studied and provides an integral component in the ultimate creation of a dynamic model of the human body. A new approach that was introduced in this thesis was the coupling of the Achilles tendon force from the musculoskeletal model to the muscle-tendon model and the non-linearity approach studied through a motion capture system. This approach and the new Achilles tendon marker placement is to the best of the author's knowledge, novel in the field of muscle-tendon research

ULTRA CLOSE-RANGE DIGITAL PHOTOGRAMMETRY AS A TOOL TO PRESERVE, STUDY, AND SHARE SKELETAL REMAINS

Skeletal collections around the world hold valuable and intriguing knowledge about humanity. Their potential value could be fully exploited by overcoming current limitations in documenting and sharing them. Virtual anthropology provides effective ways to study and value skeletal collections using three-dimensional (3D) data, e.g. allowing powerful comparative and evolutionary studies, along with specimen preservation and dissemination. CT- and laser scanning are the most used techniques for three-dimensional reconstruction. However, they are resource-intensive and, therefore, difficult to be applied to large samples or skeletal collections. Ultra close-range digital photogrammetry (UCR-DP) enables photorealistic 3D reconstructions from simple photographs of the specimen. However, it is the least used method in skeletal anthropology and the lack of appropriate protocols often limit the quality of its outcomes. This Ph.D. thesis explored UCR-DP application in skeletal anthropology. The state-of-the-art of this technique was studied, and a new approach based on cloud computing was proposed and validated against current gold standards. This approach relies on the processing capabilities of remote servers and a free-for-academic use software environment; it proved to produce measurements equivalent to those of osteometry and, in many cases, they were more precise than those of CT-scanning. Cloud-based UCR-DP allowed the processing of multiple 3D models at once, leading to a low-cost, quick, and effective 3D production. The technique was successfully used to digitally preserve an initial sample of 534 crania from the skeletal collections of the Museo Sardo di Antropologia ed Etnografia (MuSAE, Università degli Studi di Cagliari). Best practices in using the technique for skeletal collection dissemination were studied and several applications were developed including MuSAE online virtual tours, virtual physical anthropology labs and distance learning, durable online dissemination, and values-led participatorily designed interactive and immersive exhibitions at the MuSAE. The sample will be used in a future population study of Sardinian skeletal characteristics from the Neolithic to modern times. In conclusion, cloud-based UCR-DP offers many significant advantages over other 3D scanning techniques: greater versatility in terms of application range and technical implementation, scalability, photorealistic restitution, reduced requirements relating to hardware, labour, time, and cost, and is, therefore, the best choice to document and value effectively large skeletal samples and collections