Friction of Teflon-S-coated Ti-6Al-4V under conditions of oscillatory relative motion

An extendable prosthesis for implantation in a human leg has been developed. The friction forces during extension of the prosthesis must be low, so a coating of Teflon-S was applied to the sliding surfaces. During walking, damage can occur as a result of oscillatory relative motion. Therefore experiments were performed with an apparatus which simulated this type of motion. It was found that the coefficient of friction reached a maximum value within one million movement cycles. This maximum value of the coefficient of friction increased with decreasing coating thickness. Even at an initial coating thickness of less than 1 μm, coating with Teflon-S was found to be very effective in reducing friction

Temperature changes in serial casting in the treatment of clubfoot

INTRODUCTION: Idiopathic clubfoot (talipes equinovarus) is a congenital deformity of the foot. The common treatment consists of serial manipulation and casting, known as the Ponseti method, which is started in the first week after birth. After an average of five cast changes and often a percutaneous Achilles tenotomy the deformity is corrected [1]. An abduction orthosis is worn for several years to prevent relapse. The application of plaster cast includes soaking the roll in lukewarm water which starts the exothermic curing reaction. After the plaster has cured the surplus water evaporates, which is an endothermic process. Heat is drawn from the surrounding but also from the patient. One case study describes observed hypothermia after the application of a plaster jacket for immobilization of the cervical spine [2]. In a survey among parents (unreported, 49 respondents) a number of parents mentioned that their child seemed to feel cold the first hours after a new cast had been applied. The aim of current study is to investigate the temperature changes underneath the cast in the treatment of clubfoot with the Ponseti method. METHODS: A 1-wire DS1825 digital thermometer (Maxim Integrated, San Jose, CA, USA) was used to measure the temperature underneath the cast. The sensor was placed underneath the sole of the foot and attached to a custom made data logger which stored time and temperature data every 10 minutes for a full week. Dip duration was calculated as the time from the moment the first maximum was reached until the temperature reached the mean value of the last 6 days. T-Tests were used to test the temperature difference for statistical significance.According to the Medical ethical evaluation committee of the UMCG the study does not fall under the Medical Research Involving Human Subjects act. RESULTS AND DISCUSSION: Preliminary results of the first seven measurements in four subjects (age 2-30d, all boys, 2 bilateral) are presented in Figure 1. Figure 1: Typical measurement of the temperature underneath the cast during the first 24 hours after casting.After an initial temperature increase after the application of the plaster cast, a decrease was visible in all measurements (p < 0.000). This dip reached a minimum of 23-33°C and lasted 5.9-16h before reaching a relatively stable 34-37°C. During the ISB2017 the additional results of the remaining scheduled measurements will be presented. CONCLUSIONSA considerable decrease in skin temperature was observed after the application of long leg casts in the treatment of clubfoot. Especially in bilateral cases this might cause discomfort or even hypothermia. ACKNOWLEDGEMENTS: This study has been supported by the Dutch Technology Foundation

An extendable modular endoprosthetic system for bone tumour management in the leg

A modular endoprosthetic system has been developed at the Groningen University Hospital and the University of Twente. The system can bridge a defect resulting from the resection of a malignant bone tumour which has developed around the knee joint of a child. Since the other healthy leg continues to grow, the system includes an element whose length can be adjusted non-invasively by using an external magnetic field. In addition to this lengthening element, there are one hip and two knee components, connectors of various lengths, and fixation elements. The paper describes the elements of the modular endoprosthetic system. Tables are created by means of which the elemental composition of such an endoprosthesis can be determined for each individual patient

A trap motion in validating muscle activity prediction from musculoskeletal model using EMG

Musculoskeletal modeling nowadays is becoming the most common tool for studying and analyzing human motion. Besides its potential in predicting muscle activity and muscle force during active motion, musculoskeletal modeling can also calculate many important kinetic data that are difficult to measure in vivo, such as joint force or ligament force. This paper will validate muscle activity predicted by the model during a static motion like knee flexion motion (squat motion). In this experiment, knee flexion motion was performed by 5 healthy subjects and modeled by using Gait Lower Extremity model from AnyBody Modeling System (AMS). Eight lower limb muscle activity prediction from the model will be validated by 8 EMG electrodes that measured the same muscles during squat motion. Muscle activity pattern and the position of onset would be used as a key factor in this validation study. Pearson correlation coefficient will be used to compare the pattern of both graphs. Knee joint force prediction from the model will also be compared with the literature studies. The result showed that 3 muscles showed high correlation coefficient, while the other 4 muscles showed slightly medium and one showed low correlation. Time delay of muscle activation between the model and EMG was recorded from Vastus Medialis muscle (18.38 ms) and Vastus Lateralis (22.8 ms), with muscle activation from the model was late compared to EMG. In conclusion, this statistical study has shown some detail differences between EMG and muscle activity prediction from the model. Knee flexion motion can be used as a trap motion when validating muscle activity of a musculoskeletal model, because the model will activate muscle activity based on motion data of markers, while in knee-flexed position, there was no marker’s movement, but the EMG was highly active due to the posture of the subjects in maintaining the knee-flexed position. However, the knee compressive force prediction from the model has showed positive confirmation from the literatures