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The human foot is a biomechanical marvel which forms the distal link in the lower limb kinematic chain. With its small polyarticular construct and flexibility, it supports the body and provides balance during walking. The first metatarsophalangeal joint (MTPJ) is a vital joint in the forefoot for normal load transmission and energy efficient locomotion. Albeit a lot in literature about this joint, paucity still exists in the biomechanical aspects. Also, there is a speculation in the biomechanical world that the time integral component of pressure recorded from the plantar pressure measuring devices maybe representative of the shear force recorded from force platforms. The aim of the current study was to quantify the kinematics of the first MTPJ in three dimensions and the pedobarographic data under the first MTPJ during each sub-phase of stance in the gait cycle of normal subjects and to assess the correlation between the shear force from the force plate of the motion capture system with the variables from the barefoot plantar pressure measuring device. Similar quantification will be undertaken for the patients with isolated hallux rigidus. After obtaining ethical approval, 40 normal subjects (80 feet) and 6 patients with varying grades of hallux rigidus were recruited for the study. The equipment used to collect data included the Vicon® motion analysis system, AMTI® force plate and the emed® plantar pressure measuring device. Various checks were performed to establish the reliability of the system setup. Four trials from each foot were taken. Of the 320 total trials from the normal subjects, the trial numbers varied for specific tasks as some trials which were suitable for testing one objective might not be suitable for testing the other. One of the patients’ data could not be used as the data quality was below par due to issues with marker tracking. The correlation between the shear force from the force plate and the anthropometric measurements/parameters from the plantar pressure measuring device was performed using the statistical regression model. The Vicon® data of the whole stance phase revealed that the first MTPJ’s sagittal plane motion ranged from 9° of plantarflexion to 53° of dorsiflexion. In the coronal plane, the maximum pronation was 34° and supination was 31°. In the transverse plane, the maximum varus was 11° and the valgus was 24°. There were two dorsiflexion peaks; one at the Initial contact and the other at Pre-swing. The joint moved from supination to pronation and varus to valgus during the progression of stance phase from Initial contact to Pre-swing. Considering the emed®-m, there were four basic parameters namely the force, area, peak pressure and maximum mean pressure from which the other parameters were derived. Only the basic parameters accounted for the sub-phases of stance and it came to light that the force under the first MTPJ was maximum in the terminal stance (22.1%). For the whole stance phase, the first MTPJ contributed about 11% of the contact area, 14.5% of the mean area, 24% of the maximum force, 56% of the peak pressure, 63% of maximum mean pressure, 44% of Pressure-time integral, 14% of Force-time integral and 14% of mean force. The correlation equation with reasonable number of dependent variables obtained by the statistical regression model could account for only 46% of the shear force. Among the paired correlation equations with single dependent variable, the one with the mean force was the best and even this could only account for 31.1% of the shear force. Albeit 3 patients were having similar radiological grading of the pathology and 2 others falling into another grade, their objective data were diverse and couldn’t be grouped together. The normal kinematics of the first MTPJ and the pedobarographic data under the first MTPJ were quantified during each subphase of stance. Attempt to use one system alone instead of two to calculate the shear force did not provide satisfactory results. The patients’ data questions the use of radiology alone in deciding the management plan which is a common scenario in the current clinical setting.

Ankle sprains are one of the most common type of sports injury. They occur most frequently when the foot is in a supine or inverted position. Recovery from an ankle sprain can take from one and up to 26 weeks depending on the severity of the injury. During that period the individual will be unable to participate in any meaningful sports activity and as such it is important to be able to prevent the occurrence of such injuries. Prevention of ankle sprain injuries would require a better understanding of the risk factors of this injury. Several studies attempted to assess such risk actors by inducing foot inversion or supination however the platforms used in these studies were shown to be limited. Hence the main aim of this project is to develop a system that can be used to assess the effect of sudden foot and ankle inversion/supination on the musculoskeletal system of dynamic subjects (e.g. walking, running, jumping, etc.). For this purpose a three degrees of freedom (DOF) rotating platform has been designed, manufactured and installed in the Institute of Motion Analysis and Research (IMAR) Sports Laboratory. The platform rotates around 3 different axes allowing inversion or supination of the foot and ankle of dynamic subjects. The degree of rotation around each axis can easily be set by the researcher/operator. A strain gauge was used to detect foot strike to the platform. As a safety measure laser emitter/receivers check that the entire foot is on the footplate before the platform rotates. Optical encoders provide essential feedback of rotation angles, speed and acceleration. The necessary software and user interface for controlling the platform were also written and tested. The platform was synchronised with a bilateral four-channel EMG (electromyography) system and a 12 camera Vicon® MX-13 system thus allowing measurement of muscle activity and kinematic data during the supination of the foot. A set of software modules were written to allow automated management and processing of the data generated by the new system. The new system was then implemented in a study to validate it and to assess the role of shoes in ankle sprains. In this study, subjects would walk in three different foot conditions: barefoot, and with two different types of sports shoes, along the walkway of the Sports Laboratory where the platform was fitted. When a subject steps on the embedded platform, it rotates causing the subject's foot to supinate. At the same time, the EMG data from the peroneus longus, tibialis anterior, and lateral gastrocnemius muscles are recorded, along with the kinematics of the subject's whole body. The obtained results demonstrated the validity of the newly developed system. Data from the validation study also revealed increased muscle activity following induced foot supination in shod conditions compared to barefoot. Muscle activity of the rotating platform step was found to be significantly higher than the steps before and after. The platform rotation was also found to have an observable effect on body kinematics. The newly developed system is hoped to help provide a better understanding of the risk factors of ankle sprain injury and how to prevent this injury. The system can be used to help improve the design of current footwear and identify which footwear provides better protection against ankle sprain injury. The system can also be used to assess the effectiveness of different ankle injury rehabilitation schemes and different training programs that aim to reduce ankle sprain injuries. The new system can be utilised to identify individuals who are at risk of sustaining an ankle sprain injury. The system can also be utilised in studies outside the scope of ankle sprain injuries.