Dawie van den Heever

Contact stresses in a patient-specific unicompartmental knee replacement

BACKGROUND Unicompartmental knee replacement has gained popularity in recent times, showing improved success rates. The main reasons for the failure of unicompartmental knee replacement are the wear of the polyethylene bearing, aseptic loosening and wear in the opposite compartment. The contact stresses involved are significant contributing factors to these causes of failure. METHODS In this study, a patient-specific unicompartmental knee replacement is proposed using a methodology based on neural network modeling of a database of healthy knee geometries. This custom implant was then compared to two conventional implant designs in terms of contact stress in a validated finite element model. FINDINGS The custom implant experienced lower contact stresses at the tibio-femoral joint compared to a fixed-bearing design and also displayed more uniform stress distribution at the bone-implant interface than any of the other implant designs. INTERPRETATION Custom unicompartmental knee replacements therefore have the potential of providing good contact stress distribution, preserve bone stock and could be more anatomically accurate.

A descriptive study of step alignment and foot positioning relative to the tee by professional rugby union goal-kickers

Abstract This study describes foot positioning during the final two steps of the approach to the ball amongst professional rugby goal-kickers. A 3D optical motion capture system was used to test 15 goal-kickers performing 10 goal-kicks. The distance and direction of each step, as well as individual foot contact positions relative to the tee, were measured. The intra- and inter-subject variability was calculated as well as the correlation (Pearson) between the measurements and participant anthropometrics. Inter-subject variability for the final foot position was lowest (placed 0.03 ± 0.07 m behind and 0.33 ± 0.03 m lateral to the tee) and highest for the penultimate step distance (0.666 ± 0.149 m), performed at an angle of 36.1 ± 8.5° external to the final step. The final step length was 1.523 ± 0.124 m, executed at an external angle of 35.5 ± 7.4° to the target line. The intra-subject variability was very low; distances and angles for the 10 kicks varied per participant by 1.6–3.1 cm and 0.7–1.6°, respectively. The results show that even though the participants had variability in their run-up to the tee, final foot position next to the tee was very similar and consistent. Furthermore, the inter- and intra-subject variability could not be attributed to differences in anthropometry. These findings may be useful as normative reference data for coaching, although further work is required to understand the role of other factors such as approach speed and body alignment.

Method for selection of femoral component in total knee arthroplasty (tka).

A method is proposed enabling a surgeon to preoperatively determine the preeminent type and size of prosthesis, from those available, to be used in a particular patient undergoing knee replacement surgery. Parameters of healthy knee geometry were estimated by employing an unsupervised neural network. These estimated parameters were then applied in a χ2 goodness of fit (GoF) test to determine which femoral prosthesis type and size delivers the most appropriate fit. This approach was used to determine the most suitable match of three implants for 34 different cases. Implant C performed the best and was the optimal fit in 59% of the cases, Implant A was the best fit in 38% of the cases and Implant B the best fit in 3% of the cases. This method shows promise in aiding a surgeon to select the optimal prosthesis type and size from an array of different conventional total knee replacements.

Development and testing of patient-specific knee replacements

This study presents a design methodology for designing and manufacturing patient-specific unicompartmental knee replacements. The design methodology uses mathematical modeling and an artificial neural network to predict the original and healthy articulating surfaces of a patients knee. The models are combined with medical images from the patient to create a knee prosthesis that is patient-specific. These patient-specific implants are then compared to conventional implants with respect to contact stresses and kinematics. The patient-specific implant experienced lower contact stresses at the tibiofemoral joint compared to a fixed-bearing design. Both the UKRs showed similar kinematic patterns to the normal knee using two different test rigs. The patient-specific UKR showed good results and with the other benefits it shows potential to dramatically improve clinical outcomes of knee replacement surgery.

Mathematical reconstruction of human femoral condyles

There is a direct correlation between ligament function and the articulating surface of the normal knee, and changes to any of these structures can affect the other. This is also true for knee replacements, where the articulating surface is greatly changed compared to the natural knee. This study investigated the morphometry of healthy knees and proposes a method to predict original normal knee profiles. A variety of mathematical techniques are compared in terms of the accuracy with which they can represent the original knee joint geometry. Additionally, a method of predicting the irregular femoral condyle geometry for an individual knee is described by making use of the mathematical techniques presented, and the accuracy of this method is also investigated. The mathematical approach using B-splines provides flexibility and can accurately describe the complex geometry of the femoral condyles in both the sagittal and transverse planes. It was further found that the condyles are highly asymmetrical; therefore simpler methods cannot portray the condyles sufficiently and are especially inaccurate in representing the lateral condyle. The study proposes a method for predicting the geometry of the femoral condyles with good accuracy. The B-spline model showed best results.

Robotic prosthetic challenges for clinical applications

This paper presents the challenges currently being encountered for the accelerated application of robotic prosthetics in clinical applications. The main goal is to evaluate technological challenges and methods that have been utilized to foster development of the intelligent artificial robotic prosthetics. Success that have been achieved during in vitro researches were evaluated based on clinical application and ultimately commercialization of the designs. Emphasis is on cost of researches, designs, commercialization and accessibility to the general populace. Although the use of robotic prosthetic limbs has been largely accepted by the scientific world, the amputees have been encountering several disadvantages such as weight increase, intricate and frequent maintenance and noisy actuation coupled with unreliable control system as a result of poor signal acquisition and processing. Novel techniques proposed such as pattern recognition for feature extraction and machine learning for robustness, adaptability and stability were either based on simulations in softwares such as Autodesk, OpenSim or Matlab resulting in limited prototypes and hardware developments thereby reducing the clinical applicability of the technologies. Even up to this period of time permanent assistive devices are viewed by the physically challenged as separate, lifeless mechanisms and not intimate extension of the human body structurally, neurologically and dynamically.

Development of a gesture and voice controlled system for burn injury prevention in individuals with disabilities

Burn injury is a major public health issue in developing countries, with most injuries being largely associated with the use of kitchen stoves. This study details the development of a cost-effective gesture and voice recognition controlled (GVC) system to be used by individuals with disabilities to reduce the likelihood of burn injury and improve their quality of life. The device replaces conventional dial controls with voice and hand gesture recognition sensors and software which are designed to be easily implemented into a household kitchen. Preliminary evaluation of the GVC systems performance in gesture and voice recognition, gas leak detection and ignition control tests were conducted using a Bunsen burner as a stove top surrogate. The voice and gesture recognition tests yielded sensitivities of 88% and 100%, respectively. These results suggest that the GVC system may be a promising solution for burn injury prevention pending further work to improve its reliability and robustness.

INVESTIGATING THE EFFECTS OF PASSIVE MECHANICAL ANKLE ON UNILATERAL OSTEOMYOPLASTIC TRANSTIBIAL AMPUTEES

Purpose The study presents an investigation of the asymmetries in normal gait associated with the use of prosthetic mechanical passive ankle devices when performing ambulatory-related activities fo...

Development of a diagnostic feedback device to assess neonatal cardiopulmonary resuscitation chest compression performance

Neonatal cardiopulmonary resuscitation (NCPR) is an important intervention to save the lives of newborns who suffer from cardiac and respiratory arrest. Despite its importance there is a dearth of NCPR research and no commercially available feedback device suitable for use during NCPR. The aim of this study is to develop a diagnostic feedback device in the form of a patch placed on the infants chest. The diagnostic feedback patch measures both the compression depth and force during NCPR, while giving audio-visual feedback according to current NCPR guidelines. The patch was systematically evaluated by conducting a series of hardware validation tests to assess the depth, force and feedback performance. The average errors in the depth and force were found to be 10.8% and 12.4%, respectively, with maximal errors below 20.7% and 24.1%. These results along with positive outcome of the feedback test suggest that the device is reliable on a hardware level and is suitable for further evaluation in a clinical setting.Neonatal cardiopulmonary resuscitation (NCPR) is an important intervention to save the lives of newborns who suffer from cardiac and respiratory arrest. Despite its importance there is a dearth of NCPR research and no commercially available feedback device suitable for use during NCPR. The aim of this study is to develop a diagnostic feedback device in the form of a patch placed on the infants chest. The diagnostic feedback patch measures both the compression depth and force during NCPR, while giving audio-visual feedback according to current NCPR guidelines. The patch was systematically evaluated by conducting a series of hardware validation tests to assess the depth, force and feedback performance. The average errors in the depth and force were found to be 10.8% and 12.4%, respectively, with maximal errors below 20.7% and 24.1%. These results along with positive outcome of the feedback test suggest that the device is reliable on a hardware level and is suitable for further evaluation in a clinical setting.

Portable video-oculography device for implementation in sideline concussion assessments: A prototype

Concussion is currently a serious health problem and can lead to severe brain dysfunction. There is a definite need for sensitive and reliable tests to detect and evaluate the subtle changes in brain function caused by concussion. This study details the development of a low cost portable eye tracking device that can aid in the detection of concussions. The device evaluates ocular motor function and can be used on the sidelines of sporting events to give a quick indication of the severity of head trauma. It can further be used to evaluate and monitor mild Traumatic Brain Injuries and aid in the return to play decision making process. Preliminary results show good accuracy and a fact test administration time. The device shows promise and will be tested in a large scale clinical trial.