Angular measurements of knee joint are a key factor in orthoses design, actually is very important for human gait analysis in order to obtain a deep knowledge of the musculoskeletal system performance. Video-based motion analysis systems have been used as measurement tools to quantify the angle and movement of knee joint. Though this technique is good, it requires special equipment and high computational cost. This work introduces a novel method of knee joint measurement. The design is mainly based on the contactless magnetic absolute encoder AS5040 (Austria Microsystems ^® , USA), and the microprocessor type PIC16F877A. The developed device has a resolution of 0.35 degrees, quite enough for an orthosis that requires knee position measurements. The reliability of the system was evaluated by making: 1) Static measurements by using a mechanical goniometer as reference, in which a correlation up to 0.999 was obtained. 2) Dynamical measurements by performing flexion-extension movements by a healthy subject and comparing the records with a commercial motion analysis system (APAS ^® , USA). A correlation of 0.9943 was obtained. Besides, trials were performed by three subjects under natural gait.

Pressure ulcers are skin injuries caused by long term exposition to high pressures on support points that interrupt blood circulation reducing the transport of oxygen and nutrients to the cells. They mainly affect people with poor mobility that stay in seating position for long periods of time. In spite of the diversity of commercial prototypes of cushions, ulcers caused by pressure are still a problem for wheelchair users. This work describes the design of a measurement system of pressure distribution in sedentary position. The aim of the system is to record the pressure concentration in order to obtain specific information about the supporting areas, and with these data used as feedback, eventually to determine an efficient random stimulation sequence to provide, in the future, a system to prevent these referred injuries. The proposed system consists of a 12 air-cell division cushion. Each cell has a pressure sensor and an input for electro valves to inflate and deflate. The recording and control of the valves is carried out through a graphical interface designed in LabVIEW®. A calibration procedure for the designed cushion was made by comparing the greatest load values pressure with a commercial platform, similar results were obtained.

The distribution and release of pressure on ischial regions are two important parameters for evaluating the effectiveness of a cushion; especially the release of pressure over time on ischial tuberosities, which is significant for preventing pressure ulcers. The aim of this work is to evaluate the effect on interface pressure through the application of a proposed alternating pressure sequence for an air-cell cushion. Six healthy volunteers were asked to sit on the air cell cushion, in static and alternating modes, as well as on a typical foam cushion for 12 minutes. Interface pressure was monitored with a matrix sensor system. Interface pressure values on ischial tuberosities, user contact area and pressure distribution were analyzed. Results showed that IP on IT tends to increase in both foam and static cushions, while in alternating cushion IP on IT tends to decrease. User contact area was significantly larger in alternating cushion than in static or foam cushions. Moreover, there is a better pressure re-distribution with alternating cushion than with the other cushions. The goal of the alternating sequence is to redistribute pressure and stimulate the ischial regions in order to promote blood flow and prevent pressure occurring in wheelchair users.