Foot Biomechanics 

Foot modelling for gait analysis

Julie Stebbins, Adward Paik, Tim Theologis, Mikhael Boukraa

The foot and ankle jointly provide the interface between the body and the supporting surface during locomotion. In addition to supporting body weight, they must accommodate a variety of internal and external forces reliably over the course of a lifetime. Clinical problems with the foot and ankle range from those present at birth (e.g. clubfoot), to those due to injury (e.g. metatarsal fracture), to those related to aging (e.g. adult acquired flatfoot). Detailed study of the dynamic behaviour of the foot and ankle complex is complicated by the large number of bones and joints involved and the difficulty in measuring the individual joint motions. Tracking the motion of multiple foot segments with skin-mounted markers has been possible in recent years, but the number of segments tracked is inevitably small (~3) compared to the number of bones involved (24+).  We now have several years of research and clinical experience working with our own multi-segment foot model (the Oxford Foot Model, as implemented in Vicon Nexus software).

The objective of our current research in this area is to improve the Oxford Foot Model and assessment of foot biomechanics generally through integration of motion capture, pressure measurement under the foot, and imaging techniques. Each of these methods is currently used in isolation, but the integration of these techniques should provide a more detailed and accurate assessment by simultaneously recording both abnormal motion as well as loading of the foot. The expected outcome of our work is a clinically relevant, accurate and detailed method for routine assessment of foot deformity in a dynamic context. This will allow comprehensive information regarding the foot to be accessible to clinicians, improving treatment planning and optimising outcomes. We have also started to look into in-shoe foot motion tracking.

Flatfoot

Catriona Kerr, Alpesh Kothari, Julie Stebbins, Tim Theologis, Julia Schnabel

Of the many clinical problems affecting the foot and ankle, flatfoot is one of the more subtle and challenging. It is characterised by partial or complete collapse of the medial longitudinal arch of the foot. The arch can either be flattened at all times, or only when the foot supports weight (known as 'flexible flatfoot'). All children are born with flat feet, and most, but not all, develop an arch by about age five. Treatment of feet which are clearly flat because they are deformed or injured is not controversial, but there is major uncertainty about whether a flat foot showing no clinical signs should be treated, just in case it should lead to pain, dysfunction, or arthritis somewhere in the lower limb later in life due to abnormal motion and loading over the course of several decades.

Flexible flatfeet are typically assessed and monitored clinically using basic observational tests, such as heel lifts/standing-on-toes to induce dorsiflexion of the hallux and to raise the arch, along with scoring systems for standing foot posture, such as the Foot Posture Index. Footprints and plantar pressure maps, quantified by various arch indices, are also used. Gait or video analysis, where available, may be undertaken. Our projects in this area are focussed on the condition flexible flatfoot in children and how a foot diagnosed as flat in a static condition behaves in a dynamic situation such as walking. We use kinematic, force, plantar pressure, and muscle activity measurements.

Morphology of the bones of the foot

Jessica Leitch, Emily O’Toole

The talus bone in the foot has a very complex shape, mainly because it articulates with several other bones: with the tibia and fibula to form the talocrural joint, with the calcaneus to form the subtalar joint, and with the navicular to form talonavicular joint. It is hypothesized that, in the adult, the shape of the talus (its morphology) is a result of the loads applied to it during growth and to the need for the talus to be mobile and also to accommodate the growth of the bones around it. One study has shown that in children the shape and orientation of three talar articular facets change over time and that certain principal components related to their shape significantly increased with body weight. This project is appling the canonical sampling methods used in the study of juvenile talus shape to analyse the shapes of talus bones in CT scans of adult feet. The principal moments of inertia of the talus and the bones surrounding it are also of interest.

Lower-limb Biomechanics

Patellofemoral pain syndrome in runners

Jessica Leitch, Julie Stebbins, Kathleen Reilly

Patellofemoral pain syndrome (PFPS) is the most common injury in runners. This project investigated the theory that prolonged eversion at the rear-foot causes prolonged tibial internal rotation and excessive femoral internal rotation, and predisposes female, distance runners to PFPS. The study was a case-control investigation between female runners with a history of PFPS (n = 9) and normal controls (n = 10). Gait analysis was used to measure lower-limb joint angles during barefoot, treadmill running. It was hypothesised that runners with PFPS would demonstrate prolonged rearfoot eversion and tibial internal rotation, and increased hip internal rotation compared to normal controls. The results did not support the theory that prolonged eversion and rear-foot structure predispose to PFPS during running, and attributing PFPS to these factors should be done with discretion. However, runners with a history of PFPS exhibited increased rear-foot eversion, reduced rear-foot dorsiflexion and increased knee internal rotation compared to normal controls during running, walking and squatting. Subjects with PFPS also demonstrated increased dorsiflexion at the mid-foot. It was proposed that increased eversion was secondary to reduced rear-foot dorsiflexion as this enabled compensatory dorsiflexion at the mid-tarsal complex. Due to the tight articulation of the ankle mortise, increased knee internal rotation corresponds well with excessive rear-foot eversion. A prospective study is required to establish whether these kinematic alterations are a cause or an effect of PFPS. 

Characterization of barefoot and shod walking and running using non-linear analysis techniques

 Richard Franzese, Julie Stebbins

This project aims to characterize shod and barefoot human walking and running gait by applying linear and nonlinear analyses to physiologically relevant gait variables. Footwear appears to alter kinematics, kinetics and muscle activity. In an attempt to understand how footwear alters kinematics, centre of mass acceleration and muscle activity, we simultaneously measure gastrocnemius and tibialis anterior muscle activity, the approximate centre of mass acceleration and three-dimensional motion of the lower limbs during treadmill walking and running. Nonlinear measures of the stride to stride variation of gait have potential for clinical use. By investigating this, we hope to understand how different conditions affect these variations and whether, for example, the behaviour is consistently correlated with specific conditions. Furthermore, compiling a database of barefoot and shod treadmill walking and running gait will provide a reference for future studies of normal and pathological subjects. 

Lower-limb dynamics during non-linear walking tasks in children with cerebral palsy

Philippe Dixon, Tim Theologis, Julie Stebbins

Current clinical gait analysis assesses only level walking in a straight line. We propose that the addition of non-linear walking tasks, such as turning round a corner, will add extra, vital information to the data currently available for clinical decision making. We are using a database of turning-gait kinematics in children with no gait impairments to define essential temporal and kinematic parameters (for example, step length, width, and frequency, ankle range of motion, and so on). These will then be used in a study of non-linear walking tasks in children with cerebral palsy. Specific clinical protocols will be designed, and methods for analysing and presenting the data in a clinically understandable form will be investigated.

Knee Biomechanics 

Cartilage loading and osteoarthritis of the knee

Jennifer Boyd, H.S. Gill

This project investigates the theory of a predominantly biomechanical trigger of osteoarthritis (OA) of the knee, as opposed to a primarily genetic or chemical trigger. Subject-specific finite element (FE) models of the knee have been created from normal subjects’ magnetic resonance imaging (MRI) scans. Motion data are collected for walking and other activities of daily living and used to calculate load cases to apply to the models. The flexion angles captured in the images and activities performed during motion analysis have been specifcally selected to investigate the medial and lateral contact points during both high and low flexion activities. When the resulting FE models are solved, data on both medial and lateral cartilage contact force, pressure distribution, and location will be available. Tibiofemoral contact locations will then be compared to cartilage lesion locations commonly cited in literature about OA.